JP2020050562A - Metal composite hydroxide and method for producing the same, positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material having a high tap density and a composite hydroxide which is a precursor, which constitutes a high output secondary battery. A method for producing a metal composite hydroxide 10 containing nickel, manganese, tungsten, optionally cobalt, and an element M, wherein a reaction vessel is provided with a first raw material aqueous solution containing a metal element and an ammonium ion supplier. The first crystallization step of supplying and adjusting the pH of the reaction solution to obtain the first metal composite hydroxide particles, the reaction solution containing the first metal composite hydroxide particles, A second raw material aqueous solution containing more tungsten than the first raw material aqueous solution and an ammonium ion supplier are supplied to adjust the pH of the reaction solution to form a tungsten concentrated layer 3 on the surface of the first metal composite hydroxide particles. Then, a second crystallization step of obtaining second metal composite hydroxide particles is provided, and the obtained metal composite hydroxide has a tap density of 1.7 g / cm 3 or more and 2.3 g / cm 3 or less, Solid structure with primary particles agglomerated Including the secondary particles. [Selection diagram] Fig. 1

Description

  The present invention relates to a metal composite hydroxide and a method for producing the same, a positive electrode active material for a lithium ion secondary battery and a method for producing the same, and a lithium ion secondary battery using the same.

  2. Description of the Related Art In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, development of small and lightweight lithium ion secondary batteries having high energy density has been strongly desired. Further, there is a strong demand for the development of a high-output secondary battery as a power source for driving vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

  As a secondary battery satisfying such a demand, there is a lithium ion secondary battery which is a kind of lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of removing and inserting lithium is used as an active material used as a material of the negative electrode and the positive electrode.

  Among the lithium ion secondary batteries, lithium ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode active material can achieve a voltage of 4V class, and are currently regarded as batteries having a high energy density. Research and development are being actively conducted, and some of them are being put to practical use.

As a positive electrode active material of such a lithium ion secondary battery, a lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, a lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _{0. 5} Mn _0.5 O ₂ ) has been proposed.

  By the way, in order to further improve the output characteristics of the lithium ion secondary battery, a method of increasing the specific surface area of the positive electrode active material is generally known. When the specific surface area of the positive electrode active material is increased, a sufficient reaction area with the electrolytic solution can be secured when the positive electrode active material is incorporated in a secondary battery. Therefore, several techniques have been proposed for improving the output characteristics by controlling the particle structure of the positive electrode active material.

  For example, Patent Documents 1 to 3 propose a method for producing a positive electrode active material using a composite hydroxide obtained by a crystallization step performed in two stages as a precursor. The positive electrode active materials described in these patent documents have a small particle size, a narrow particle size distribution, a hollow structure or a space inside the particles, thereby having a high specific surface area and excellent output characteristics. . However, for example, a positive electrode active material having higher output characteristics is required as a power source for driving a vehicle such as a hybrid vehicle.

  On the other hand, as a means for realizing a positive electrode active material having higher output characteristics by further reducing the reaction resistance, the addition of a different element to a lithium metal composite oxide constituting the positive electrode active material is being studied. As such dissimilar elements, for example, transition metals such as Mo, Nb, W, and Ta which can take expensive numbers have been proposed.

  For example, in Patent Literature 4, a lithium transition metal-based compound having a function capable of inserting and removing lithium ions is used as a main component, and an additive that suppresses grain growth and sintering during firing is added to the main component material. Lithium transition metal compound powder obtained by adding at least one or more at a ratio of 0.01 mol% or more and less than 2 mol% with respect to the total molar amount of transition metal elements in the main component raw material, and then firing. The body has been described. Further, the additive is an oxide containing at least one element selected from Mo, W, Nb, Ta, and Re, and the total of Li and metal elements other than the additive element on the surface portion of the primary particles. It is described that the total atomic ratio of the additional element to the total particle is at least 5 times the atomic ratio of the whole particles.

In Patent Document 5, a step of dispersing W on the surfaces of primary particles of a lithium metal composite oxide powder by adding and mixing an alkaline aqueous solution in which a specific proportion of a tungsten compound is dissolved, By heat-treating the mixed aqueous alkali solution and the lithium metal composite oxide powder in which the tungsten compound is dissolved in the range of 100 to 700 ° C., it can be represented by any of Li ₂ WO ₄ , Li ₄ WO ₅ , and Li ₆ W ₂ O _9. A production method has been proposed in which fine particles containing lithium tungstate are formed on the surface of the lithium metal composite oxide powder or the surface of primary particles of the powder.

  Patent Literature 6 discloses a positive electrode active material including a lithium metal composite oxide, which includes primary particles and secondary particles formed by agglomeration of primary particles, and forms secondary particles through which a liquid electrolyte can penetrate. A positive electrode active material having a compound layer having a thickness of 20 nm or less containing lithium in which tungsten is concentrated is provided on the surface or at the grain boundary of the lithium metal composite oxide in the vicinity or inside of the surface of the lithium metal composite oxide. As a preferable method for obtaining the powder, a lithium metal composite oxide can be obtained by mixing and mixing the tungsten compound when mixing the composite hydroxide or the composite oxide and the lithium compound, and firing the mixture. However, in this method, it is said that the particle diameter of the tungsten compound is preferably 1/5 or less of the manganese composite hydroxide or the average particle diameter of the manganese composite hydroxide.

  Further, in Patent Document 7, in a crystallization reaction, a nucleation step and a particle growth step are separated by pH control to produce composite hydroxide particles, and tungsten is added to the surface of the obtained composite hydroxide particles. And a method for producing a transition metal composite hydroxide having a coating step of forming a coating containing: and a positive electrode active material using the hydroxide as a precursor.

In Patent Document 8, a layer of a first positive electrode active material represented by Li _x1 Ni _{a1 Mnb1} Co _c1 O ₂ is provided on the surface of the current collector, and the surface of the first positive electrode active material is provided on the surface of the first positive electrode active material. _{li x2 Ni a2 Mn b2 Co c2} M d O 2 (M is Mo, W, and Nb) second cathode active layer positive electrode attached to the lithium secondary battery of the substance represented by have been proposed.

  Patent Document 9 discloses a method for producing a nickel-cobalt composite hydroxide, in which a solution containing nickel, cobalt and manganese, a complex ion-forming agent and a basic solution are separately and simultaneously placed in one reaction vessel. By supplying to the first crystallization step to obtain nickel-cobalt composite hydroxide particles, after the first crystallization step, further, a solution containing nickel, cobalt and manganese, a complex ion forming agent, a basic solution And a solution containing the element M are separately and simultaneously supplied, so that nickel, cobalt, manganese and the element M (Al, Mg, Ca, Ti, Zr, Nb, Ta) are added to the nickel-cobalt composite hydroxide particles. , Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, Lu, at least one selected from the group consisting of A second crystallization step of crystallizing the composite hydroxide particles containing the upper element), wherein the total mol of nickel, cobalt and manganese supplied in the first crystallization step is represented by MOL (1), the second crystal Where the total mole of nickel, cobalt and manganese supplied in the precipitation step is MOL (2), 0.30 ≦ MOL (1) / {MOL (1) + MOL (2)} <0.95 Has been proposed.

JP 2012-246199 A JP 2013-147416 A JP-A-2006-094307 JP 2008-305777 A JP 2013-125732 A JP 2014-197556 A JP 2012-252844 A JP 2012-079608 A JP 2016-210675 A

  However, in the method described in Patent Literature 4, some of the added elements such as Mo, Ta, and W substitute for Ni arranged in a layer in the crystal, and the battery capacity, cycle characteristics, and the like are reduced. There was a problem that the battery characteristics deteriorated.

  In addition, although the lithium metal composite oxide produced by the production method described in Patent Document 5 has improved output characteristics, when the thickness of the tungsten fine particles formed on the particle surface is not uniform, the cycle characteristics are not sufficient. was there.

  Further, the method described in Patent Document 6 is not industrially suitable because it is necessary to grind the tungsten compound once in order to obtain a nano-order tungsten compound, and is not easy to handle. In addition, since the thickness of the compound layer can be varied due to the non-uniformity of the particle size of the obtained fine particles, the reduction of the reaction resistance is insufficient and the effect of improving the output characteristics is limited. It is also described that tungsten is contained as an additional element in a manganese composite hydroxide in order to obtain the powder, but it is difficult to form a tungsten-enriched compound layer on a nano-order by this method.

  In addition, the method described in Patent Document 7 is not industrially preferable because the number of steps is increased because a step of coating tungsten is added. In addition, tungsten is deposited by controlling the pH in the coating step, but it is difficult to coat uniformly because the thickness of the coating layer is not uniform due to fluctuations in the pH to be controlled. In addition, in the case of using a lithium metal composite oxide obtained by mixing lithium and a metal composite hydroxide that is unevenly coated with tungsten, the coating layer becomes a resistance and the output is rather reduced. there were.

  In addition, the positive electrode active material formed by the method described in Patent Literature 8 is charged and discharged when used in a secondary battery because the first positive electrode active material and the second positive electrode active material are in different phases. There is a problem in that there is a deviation in the structural change during the reaction, and cracks occur during repeated charge / discharge, thus deteriorating the cycle characteristics.

  In addition, the composite hydroxide and the positive electrode active material obtained by the method described in Patent Document 9 have SEM-EDX of SEM-EDX in the second layer in which the ratio of the depth in the radial direction is 5% or more and less than 50%. It is described that the element has a peak of the element M in the spectrum, and in the positive electrode active material, the element M containing tungsten is contained inside the surface layer of the secondary particles, so that the crystallinity is reduced and the element is used in a secondary battery. When this is done, the battery characteristics may be degraded.

  In view of the above problems, the present invention is a positive electrode active material having a high crystallinity, and a high tap density when used for a positive electrode of a secondary battery, and has a positive electrode resistance when used for a positive electrode of a secondary battery. It is an object of the present invention to provide a positive electrode active material that can reduce (reaction resistance) and obtain a high output, and a metal composite hydroxide that is a precursor thereof.

In the first embodiment of the present invention, nickel, manganese, and tungsten, and optionally cobalt and the element M are included, and the atomic ratio of each metal element is Ni: Mn: Co: W: M = x: y: z: a: b (x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is at least one element selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) A method of producing a metal composite hydroxide, comprising: supplying a first raw material aqueous solution containing a metal element and an ammonium ion supplier to a reaction vessel, adjusting the pH of the reaction aqueous solution in the reaction vessel, A first crystallization step of obtaining first metal composite hydroxide particles by performing a crystallization reaction, and a first metal composite hydroxide A second aqueous solution containing a metal element and containing more tungsten than the first aqueous solution and an ammonium ion donor are supplied to the reaction aqueous solution containing the product particles, and the pH of the reaction aqueous solution is adjusted. Performing a crystallization reaction to form a tungsten-enriched layer on the surfaces of the first metal composite hydroxide particles, thereby obtaining second metal composite hydroxide particles. The metal composite hydroxide obtained after the second crystallization step has a tap density of 1.7 g / cm ³ or more and 2.3 g / cm ³ or less and a plurality of primary particles aggregated. A method for producing a metal composite hydroxide, including secondary particles having an actual structure, is provided.

  Further, the first crystallization step includes a nucleation step of performing nucleation and a particle growth step of performing particle growth, and the second crystallization step includes performing the particle growth following the particle growth step. The first crystallization step and the second crystallization step are performed in a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less, and the first crystallization step and the second crystallization step It is preferable to adjust the pH of the reaction aqueous solution to be lower than the pH value of the reaction aqueous solution in the nucleation step.

  Further, the metal element in the first raw material aqueous solution is added to the reaction tank in a range of 50% by mass or more and 95% by mass or less based on the total amount of metal added in the first crystallization step and the second crystallization step. After the supply, the second raw material aqueous solution in the second crystallization step is preferably supplied. Preferably, the second crystallization step includes forming the tungsten-enriched layer to have a thickness of 100 nm or less in a direction from the surface of the second metal composite hydroxide toward the center. . Further, the addition of the second raw material aqueous solution in the second crystallization step is performed at a time point when 50% or more and 95% or less with respect to the entire time during which the particle growth is performed in the first and second crystallization steps. It is preferred to do so. Further, it is preferable that the supply of the second raw material aqueous solution is performed by separately supplying the first raw material aqueous solution and the aqueous solution containing tungsten to the reaction aqueous solution. The concentration of tungsten in the aqueous solution containing tungsten is preferably 18% by mass or more based on the whole aqueous solution containing tungsten.

In the second embodiment of the present invention, nickel, manganese, and tungsten, and optionally, cobalt and the element M are contained, and the atomic ratio of each metal element is Ni: Mn: Co: W. : M = x: y: z: a: b (x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0 .1, 0 ≦ b ≦ 0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) A metal composite hydroxide having a tungsten concentration layer on a surface layer, a tap density of 1.7 g / cm ³ or less and 2.3 g / cm ³ or more, and a plurality of primary particles aggregated. The present invention provides a metal composite hydroxide containing secondary particles having a solid structure.

  The average thickness of the tungsten concentration layer is preferably 100 nm or less. Further, the average particle size of the composite hydroxide is 4.0 μm or more and 9.0 μm or less, and [(d90−d10) / MV], which is an index indicating the spread of the particle size distribution, is 0.65 or less. Is preferred.

  In the third embodiment of the present invention, a lithium compound is mixed with at least one of a metal composite hydroxide obtained by the above manufacturing method and a metal composite oxide obtained by heat-treating the metal composite hydroxide. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising the steps of: obtaining a lithium mixture by firing the mixture; and firing the lithium mixture to obtain a lithium metal composite oxide.

  Also, the value of (d50 of the positive electrode active material / d50 of the metal composite hydroxide), which is an index indicating the degree of aggregation of the particles of the lithium metal composite oxide, is 0.95 or more and 1.05 or less. Adjustment is preferred.

In the fourth embodiment of the present invention, lithium, nickel, manganese, and tungsten, and optionally cobalt and the element M are included, and the atomic ratio of each metal element is Li: Ni: Co: Mn: W: M = 1 + u: x: y: z: a: b (x + y + z = 1, −0.05 ≦ u ≦ 0.50, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0 .55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, And at least one element selected from Ta), wherein the lithium metal composite oxide is a secondary particle having a solid structure in which a plurality of primary particles are aggregated. Containing, the surface layer of the primary particles present on the surface or inside of the secondary particles, and at the grain boundaries between the primary particles, tungsten Exist compounds containing finely lithium is concentrated, and the tap density of 1.8 g / cm ³ or less 2.4 g / cm ³ or more and, BET specific surface area of 0.6 m ² / g or more 1.2 m ² / g or less of the positive electrode active material for a lithium ion secondary battery.

  Further, it is preferable that the crystallite diameter of the (003) plane obtained by powder X-ray diffraction measurement is 120 nm or more.

  In a fifth embodiment of the present invention, a lithium ion secondary battery comprising the above-mentioned positive electrode active material for a lithium ion secondary battery, comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, A secondary battery is provided.

  Advantageous Effects of Invention According to the present invention, when a positive electrode active material having high crystallinity and a high tap density is used for a positive electrode of a secondary battery, the positive electrode resistance (reaction resistance) is reduced and a high output is obtained. And a metal composite hydroxide that is a precursor thereof. Further, according to the present invention, a secondary battery including such a positive electrode active material can be provided. Further, according to the present invention, it is possible to provide a method capable of easily producing such a positive electrode active material and a metal composite hydroxide on an industrial scale. Therefore, the industrial significance of the present invention is extremely large.

1A and 1B are schematic diagrams showing an example of a metal composite hydroxide, and FIG. 1C is a cross-sectional SEM image showing a metal composite hydroxide having a solid structure. This is an example. FIG. 2 is a diagram illustrating an example of a method for producing a metal composite hydroxide. FIG. 3 is a diagram showing an example of a method for producing a metal composite hydroxide. FIGS. 4A and 4B are diagrams illustrating the time of disclosure of addition of an aqueous solution containing tungsten. FIGS. 5A and 5B are schematic diagrams illustrating an example of a lithium metal composite oxide. FIG. 6 is a diagram illustrating an example of a method for producing a lithium metal composite oxide. FIG. 7 is a schematic diagram showing a coin cell battery for evaluation used in the examples. FIGS. 8A and 8B are a drawing-substitute photograph (upper figure) showing the distribution of W by surface analysis using EDX of a metal composite hydroxide, and the tungsten-concentrated layer in the drawing-substitute photograph. FIG.

  Hereinafter, a metal composite hydroxide and a method for manufacturing the same, a positive electrode active material for a lithium ion secondary battery and a method for manufacturing the same, and a lithium ion secondary battery according to the embodiment will be described with reference to the drawings. The present invention is not limited to the embodiments described below. In the drawings, some components are emphasized or some components are simplified for easy understanding, and actual structures, shapes, scales, and the like may be different.

1. Metal composite hydroxide FIGS. 1A and 1B are schematic diagrams showing an example of a metal composite hydroxide according to the present embodiment, and FIG. 1C shows a metal having a solid structure. It is an example of a cross-sectional SEM image showing a composite hydroxide. As shown in FIG. 1A, the metal composite hydroxide 10 includes secondary particles 2 formed by aggregating a plurality of primary particles 1. The shape of the primary particles 1 constituting the secondary particles 2 is not particularly limited, but may be, for example, a plate-like or needle-like shape, or may be fine primary particles smaller than these. Further, the particle structure of the secondary particles 2 is not particularly limited, and includes a solid structure in which almost no voids are found inside the secondary particles 2, a hollow structure having a hollow portion in the center of the secondary particles 2, and a secondary structure. The particles 2 may have a void structure having a plurality of voids inside the particles 2, a multilayer structure having a layered void inside the secondary particles 2, and among them, the obtained positive electrode active material has a higher particle strength. And a high tap density, a solid structure is preferable.

  In the present specification, the phrase “the secondary particles 2 have a solid structure” means that the plurality of primary particles 1 are relatively uniformly and densely distributed throughout the inside of the secondary particles 2, It means having a structure in which one or a plurality of clear hollow portions (eg, occupying 10% or more of the cross-sectional area of the secondary particles 2) does not exist (see FIG. 1C). When the metal composite hydroxide 10 has a solid structure, the porosity of the metal composite hydroxide 10 (the void area inside the secondary particles 2 with respect to the cross-sectional area of the secondary particles 2) is, for example, 20% or less. And preferably 10% or less.

  The metal composite hydroxide 10 may be composed of only the secondary particles 2 or may be composed of the secondary particles 2 and the single primary particles 1.

(Tungsten concentrated layer)
As shown in FIG. 1B, the metal composite hydroxide 10 (secondary particles 2) has a tungsten-enriched layer 3 in which tungsten is concentrated on its surface. The tungsten concentration layer 3 is a layered region formed on the surface of the metal composite hydroxide 10 and in which tungsten is more concentrated than the inside of the secondary particles 2 and exists. The positive electrode active material using the metal composite hydroxide 10 on which the tungsten enriched layer 3 is formed as a precursor has high crystallinity and reduced positive electrode resistance (reaction resistance). The secondary battery can obtain high output. For example, as shown in FIG. 8, the tungsten concentration layer 3 can be confirmed by detecting the W distribution by surface analysis using an energy dispersive X-ray analyzer (EDX). In FIG. 1B, the primary particles 1 are not shown.

  As will be described later, the tungsten-enriched layer 3 is formed by mixing the metal composite hydroxide 10 (precursor) and a lithium compound and firing the mixture (see FIG. 6) to form a compound 23 containing tungsten and lithium (for example, tungsten). (Eg, lithium oxide) (see FIG. 5).

  For example, as shown in FIGS. 5A and 5B, in the lithium metal composite oxide 20 (positive electrode active material), the compound 23 containing tungsten and lithium is formed on the surface of the primary particles 21 or the primary particles. 21 are formed at the grain boundaries. Since the compound 23 containing tungsten and lithium has high ionic conductivity, when the lithium metal composite oxide 20 (the positive electrode active material) is used for the positive electrode of the secondary battery, the surface layer of the primary particles 21 that comes into contact with the electrolyte, Alternatively, the presence of the compound 23 containing tungsten and lithium at the grain boundaries between the primary particles 21 can reduce the positive electrode resistance of the positive electrode active material and greatly contribute to improving the output characteristics of the secondary battery.

  In addition, when the conventional method for producing a metal composite hydroxide is used, tungsten contained in the metal composite hydroxide 10 (precursor) can suppress sintering inside the secondary particles 2 during firing. there were. Therefore, the conventional tungsten-containing precursor contradicts that while the tungsten in the obtained positive electrode active material contributes to the reduction of the positive electrode resistance, the crystallinity of the lithium metal composite oxide constituting the positive electrode active material decreases. Had a problem. Therefore, it has been difficult to achieve high output characteristics and high crystallinity in a secondary battery in a positive electrode active material containing tungsten obtained by using a conventional manufacturing method. However, since the metal composite hydroxide 10 according to the present embodiment forms the tungsten enriched layer 3 on the surface layer, almost no influence occurs on the sintering of the tungsten inside the secondary particles 2 during firing. In addition, the positive electrode resistance can be reduced, and the crystallinity of the obtained lithium metal composite oxide 20 can be increased.

  The average thickness of the tungsten concentrated layer 3 can be, for example, 200 nm or less, preferably 100 nm or less, more preferably 10 nm or more and 100 nm or less in the direction from the surface of the metal composite hydroxide 10 toward the center. And more preferably 20 nm or more and 50 nm or less. When the thickness of the tungsten concentration layer 3 is 100 nm or less, the crystallinity of the lithium metal composite oxide 20 can be made higher, and when the lithium metal composite oxide 20 is used for a positive electrode of a secondary battery, Positive electrode resistance can be further reduced, and output characteristics can be improved.

  The average thickness of the tungsten enriched layer 3 is determined by cutting a sample in which the metal composite hydroxide 10 is embedded in a resin or the like to prepare a sample of the cross section of the secondary particles 2, and measuring the distribution of W using EDX. Perform analysis and measure. Specifically, in the sample of the secondary particle 2 cross section, the secondary particle 2 cross section that is 80% or more of the volume average particle diameter (MV) measured using a laser beam diffraction scattering particle size analyzer is randomly generated. In each of the selected 20 secondary particles 2, the thickness of the portion (tungsten-enriched layer 3) where W is detected to be dense in the direction from the surface of the metal composite hydroxide 10 toward the center C is selected. Width) is measured at five or more locations, and the average of the thickness of the tungsten concentrated layer 3 in each of the secondary particles 2 is determined. Then, by calculating the average value of the thickness of each of the selected 20 secondary particles 2, the average thickness of the tungsten-enriched layer 3 can be obtained.

  If the average thickness of the tungsten-concentrated layer 3 exceeds 100 nm, the effect of suppressing sintering by tungsten during firing is increased, and the growth of the primary particles 21 may be hindered. Therefore, in the obtained lithium metal composite oxide 20, a large number of primary particles having a small crystallite diameter are formed, and many crystal grain boundaries are generated, so that the reaction resistance in the positive electrode may increase. Further, as the growth of the primary particles 21 is suppressed, the crystallinity of the lithium metal composite oxide 20 may decrease.

  On the other hand, when the average thickness of the tungsten concentration layer 3 is less than 10 nm, the specific surface area increases, and the metal composite hydroxides 10 easily aggregate during firing, so that the packing density of the obtained positive electrode active material decreases. As a result, the battery capacity per volume may decrease. Further, the compound 23 containing tungsten and lithium may not be sufficiently formed in the lithium metal composite oxide 20, and the lithium ion conductivity may not be sufficient.

  The average thickness of the tungsten concentrated layer 3 is, for example, in the direction from the surface of the secondary particles 2 to the center C of the secondary particles 2 with respect to the volume average particle diameter (MV) of the metal composite hydroxide 10. , 3% or less. The average thickness of the tungsten concentration layer 3 is preferably 2% or less, more preferably 0.1% or less, from the viewpoint of further improving the crystallinity of the lithium metal composite oxide 20 and further reducing the reaction resistance. % To 2%, more preferably 0.1% to 1%, and still more preferably 0.1% to 0.5%.

(Volume average particle size)
The volume average particle size (MV) of the metal composite hydroxide 10 is not particularly limited, but is preferably 4.0 μm or more, more preferably 4 μm or more and 9.0 μm or less, and preferably 4.0 μm or more and 7 μm or less. It is. The volume average particle diameter (MV) of the metal composite hydroxide 10 correlates with the volume average particle diameter (MV) of the lithium metal composite oxide 20 (positive electrode active material) using the metal composite hydroxide 10 as a precursor. For this reason, by controlling the volume average particle size (MV) of the metal composite hydroxide 10 to the above range, the lithium metal composite oxide 20 (see FIG. 5) having the metal composite hydroxide 10 as a precursor can be obtained. The volume average particle size (MV) can also be controlled within the above range.

  When the volume average particle size (MV) of the metal composite hydroxide 10 is less than 4 μm, the specific surface area increases, and the metal composite hydroxide 10 is used in the firing step (step S40, see FIG. 6) when producing the positive electrode active material. The particles of the oxide 10 are easily aggregated, the packing density of the obtained positive electrode active material is reduced, and the battery capacity per volume (volume) may be reduced. The volume average particle size (MV) can be determined, for example, from a volume integrated value measured by a laser light diffraction / scattering particle size analyzer.

(Expansion of particle size distribution)
[(D90-d10) / MV] of the metal composite hydroxide 10, which is an index indicating the spread of the particle size distribution, is 0.65 or less. The particle size distribution of the lithium metal composite oxide 20 (positive electrode active material) is strongly affected by the metal composite hydroxide 10 as its precursor. For this reason, when the metal composite hydroxide 10 containing many fine particles and coarse particles is used as a precursor, the lithium metal composite oxide 20 also contains many fine particles and coarse particles. In a secondary battery using such a lithium metal composite oxide 20 as a positive electrode active material, battery characteristics such as thermal stability, cycle characteristics, and output characteristics may be reduced. Therefore, when [(d90-d10) / MV] of the metal composite hydroxide 10 is adjusted to the above range, the particle size distribution of the lithium metal composite oxide 20 obtained by using this as a precursor is narrowed to obtain fine particles or Mixing of coarse particles can be suppressed.

  The lower limit of [(d90−d10) / MV] of the metal composite hydroxide 10 is not particularly limited, but is preferably about 0.25 or more from the viewpoint of cost and productivity. Assuming production on an industrial scale, it is not realistic to use the metal composite hydroxide 10 with [(d90-d10) / MV] being too small.

  Note that d10 is the particle size at which the particles of each particle size are accumulated from the smaller particle size side, and the accumulated volume is 10% of the total volume of all the particles, and d90 is the same. It means the particle size whose cumulative volume is 90% of the total volume of all particles. In addition, d10 and d90 can be determined from the integrated value of the volume measured by the laser light diffraction / scattering particle size analyzer, similarly to the volume average particle size (MV).

(Tap density)
The tap density of the metal composite hydroxide 10 is preferably 1.7 g / cm ³ or more and 2.3 g / cm ³ or less, more preferably 1.8 g / cm ³ or more and 2.2 g / cm ³ or less. More preferably, it is 1.9 g / cm ³ or more and 2.1 g / cm ³ or less.

  The tap density of the metal composite hydroxide 10 is correlated with the tap density of the lithium metal composite oxide 20 (positive active material) using the metal composite hydroxide 10 as a precursor, and the metal composite hydroxide 10 has a solid structure. , The tap density of the obtained lithium metal composite oxide 20 tends to be slightly higher than the tap density of the metal composite hydroxide 10. Therefore, by controlling the tap density of the metal composite hydroxide 10 within the above range, the tap density of the lithium metal composite oxide 20 (see FIG. 5) using the metal composite hydroxide 10 as a precursor can be increased. It is possible to control the range to be described later. When the tap density of the metal composite hydroxide 10 is in the above range, the obtained lithium metal composite oxide 20 also has a high tap density. Therefore, when the lithium metal composite oxide 20 is used for the positive electrode, a secondary battery having a high volume energy density can be obtained.

  The positive electrode active material obtained by using the metal composite hydroxide 10 as a precursor has the tungsten concentrated layer 3 and has a preferable range of the above-mentioned [(d90−d10) / MV]. , Thermal stability, cycle characteristics, and output characteristics can be further improved, and a higher energy density can be achieved by setting the tap density within the above range. In addition, when the metal composite hydroxide 10 has a solid structure, the obtained positive electrode active material has high particle strength, so that the energy density per volume can be increased, and at the time of a charge / discharge cycle. Generation of cracks and the like in the positive electrode active material can be suppressed, and cycle characteristics can be improved.

(composition)
Although the composition of the metal composite hydroxide 10 is not particularly limited, for example, the metal composite hydroxide 10 contains Ni, Co and W, and optionally Mn and M, and has the number of atoms of each metal element. When the ratio (A) is Ni: Co: Mn: W: M = x: y: z: a: b (x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta At least one metal element selected from the group consisting of

  Since the ratio (A) of the number of atoms of each metal element in the metal composite hydroxide 10 is maintained even in the lithium metal composite oxide 20, the metal composite represented by the above-mentioned metal element ratio (A) is maintained. In the hydroxide 10, the composition ranges of nickel, manganese, cobalt, tungsten and the element M constituting the hydroxide 10 and the critical significance thereof are the same as those of the positive electrode active material represented by the ratio (B) described later. Therefore, a description of these matters is omitted here.

The metal complex hydroxide 10 is represented by the general formula _{(A1): Ni x Mn y} Co z W a M b (OH) 2 + α (x + y + z = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, 0 ≦ α ≦ 0.5, M is Mg, Ca, Al, Ti, V, (Cr, Zr, Nb, Mo, Hf, and one or more metal elements selected from Ta).

In the general formula (A1), from the viewpoint of achieving further improvements in capacity characteristics of the secondary battery using the positive electrode active material obtained, its composition formula _{(A2): Ni x Mn y} Co z W a M _b (OH) 2 + α (x + y + z = 1, 0.7 <x ≦ 0.95, 0.05 ≦ y ≦ 0.1, 0 ≦ z ≦ 0.2, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, 0 ≦ α ≦ 0.5, and M is preferably one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, and Mo). Further, from the viewpoint of achieving both thermal stability and battery capacity, the value of x in the above general formula (A2) is more preferably 0.7 <x ≦ 0.9, and 0.7 <x ≦ 0.9. More preferably, x ≦ 0.85.

In the general formula (A1), from the viewpoint of achieving further improvement of the thermal stability of the secondary battery using the resulting positive electrode active material, its composition, the general formula _{(A3): Ni x Mn y} Co z W a M _b (OH) _{2 + α} (x + y + z = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, 0 ≦ α ≦ 0.5, and M is preferably one or more elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta). .

2. 2 to 3 are diagrams illustrating an example of a method for manufacturing a metal composite hydroxide according to the present embodiment. The manufacturing method according to the present embodiment includes nickel, manganese, and tungsten, optionally cobalt, and the element M by a crystallization reaction, and the atomic ratio of each metal element is Ni: Mn: Co: W: M = x: y: z: a: b (x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) Is a method for producing a metal composite hydroxide represented by the formula: By the manufacturing method according to the present embodiment, the metal composite hydroxide 10 having the above characteristics can be easily manufactured on an industrial scale.

[Crystallization reaction]
As shown in FIG. 2, in the method for producing the metal composite hydroxide 10, nickel (Ni) and manganese (Mn) and optionally cobalt (Co) and / or a metal element A first crystallization step of supplying a first raw material aqueous solution containing (M) and an ammonium ion supplier and performing a crystallization reaction to obtain first metal composite hydroxide particles (step S10); And supplying a second raw material aqueous solution containing more tungsten than the first raw material aqueous solution and an ammonium ion supplier to the reaction aqueous solution containing the first metal composite hydroxide particles to carry out a crystallization reaction. Performing a second crystallization step (Step S20) of forming a tungsten-enriched layer on the surface of the first metal composite hydroxide particles to obtain second metal composite hydroxide particles.

  In the method for producing a metal composite hydroxide according to this embodiment, in the second crystallization step (Step S20), the surface of the first composite hydroxide particles obtained in the first crystallization step (Step S10) Then, by forming the tungsten concentration layer 3, the second metal composite hydroxide particles can be obtained. Since the inside of the second metal composite hydroxide particles does not contain tungsten or is composed of the first metal composite hydroxide particles having a low tungsten content, the lithium metal obtained by using this as a precursor The composite oxide 20 (positive electrode active material) has a high crystallinity inside the particles, and the compound 23 containing tungsten and lithium derived from the tungsten enriched layer 3 forms the surface of the primary particles 21 or a grain boundary between the primary particles 21. , The secondary battery has excellent output characteristics.

  As shown in FIG. 3, the first crystallization step (Step S10) further includes a nucleation step (Step S11) for mainly performing nucleation and a particle growth step (Step S12) for mainly performing particle growth. Is preferred. The nucleation step (step S11) and the particle growth step (step S12) can be separated clearly, for example, by controlling the pH of the reaction aqueous solution, and have a narrow particle size distribution and a uniform metal particle size. The hydroxide 10 can be obtained. The second crystallization step (Step S20) is a step of mainly performing grain growth following the grain growth step (Step S12).

  A method for producing a nickel composite hydroxide including such a two-stage crystallization process is disclosed in, for example, Patent Documents 2 and 3, and refer to these documents for detailed conditions. Then, the conditions can be appropriately adjusted. In addition, the method for producing a metal composite hydroxide according to the present embodiment can form the tungsten-enriched layer 3 having a desired film thickness using the conditions of a known crystallization method, as described later. , Can be easily applied to industrial scale production.

  Hereinafter, each step of the manufacturing method including the nucleation step (step S11) and the particle growth step (step S12) will be described with reference to FIG. Note that the following description is an example of a method for producing the metal composite hydroxide 10, and is not limited to this method.

(1) First crystallization step (Step S10)
(Nucleation process)
First, the first raw material aqueous solution and the ammonium ion supplier are supplied, and the pH of the reaction aqueous solution (nucleation aqueous solution) in the reaction tank is controlled within a predetermined range to perform nucleation (step S11). The first raw material aqueous solution is prepared, for example, by dissolving a compound containing a transition metal as a raw material in water. In the method for producing a metal composite hydroxide described below, the composition ratio of the metal composite hydroxide formed by crystallization in each step is the same as the composition ratio of each metal in the raw material aqueous solution, The composition ratio of each metal in the raw material aqueous solution can be the composition ratio of the transition metal of the target metal composite hydroxide. The first raw material aqueous solution may contain a small amount of tungsten or may not contain tungsten.

  First, an alkaline aqueous solution and an aqueous solution containing an ammonium ion supplier are supplied and mixed into a reaction tank, and the pH value measured at a liquid temperature of 25 ° C. is 12.0 to 14.0, and the ammonium ion concentration is A pre-reaction aqueous solution of 3 g / L or more and 25 g / L or less is prepared.

In the case of mainly obtaining particles of a metal composite hydroxide having a solid structure having a tap density of 1.7 g / cm ³ or more and 2.3 g / cm ³ or less, for example, the oxygen concentration in the reaction atmosphere in the reaction vessel is The atmosphere is preferably a non-oxidizing atmosphere of 5% by volume or less, more preferably an atmosphere having an oxygen concentration of 1% by volume or less. The atmosphere is controlled by, for example, introducing nitrogen gas. The pH value of the aqueous solution before the reaction can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

  Next, the first raw material aqueous solution is supplied into the reaction tank while stirring the pre-reaction aqueous solution in the reaction tank to form a reaction aqueous solution (nucleus forming aqueous solution). In the nucleation step (step S11), the pH value of the aqueous solution for nucleation and the concentration of ammonium ions change with the nucleation in the reaction aqueous solution. It is preferable to control so that the pH value of the solution is maintained in the range of pH 12.0 to 14.0 based on the solution temperature of 25 ° C., and the concentration of ammonium ion is maintained in the range of 3 g / L to 25 g / L. When the pH value of the reaction aqueous solution (the aqueous solution for nucleation) is in the above range, nuclei hardly grow and nucleation occurs preferentially.

  The pH value of the reaction aqueous solution (aqueous solution for nucleation) measured at a liquid temperature of 25 ° C. is preferably 12.0 or more and 14.0 or less, more preferably 12.3 or more and 13.5 or less, and further preferably 12. The range is 5 or more and 13.3 or less. When the pH is in the above range, nucleus growth can be suppressed, nucleation can be prioritized, and nuclei generated in the nucleation step can be uniform and have a narrow particle size distribution. On the other hand, when the pH value is less than 12.0, the growth of nuclei (particles) proceeds along with the nucleation, so that the particle diameter of the obtained metal composite hydroxide particles becomes non-uniform, and the particle size distribution deteriorates. When the pH value exceeds 14.0, the nuclei generated are too fine, and the reaction aqueous solution (nucleus generation aqueous solution) may gel.

  In addition, it is preferable that the fluctuation range of the pH value in the reaction aqueous solution (the aqueous solution for nucleation) be within ± 0.2. When the fluctuation range of the pH value is large, the nucleation amount and the ratio of the particle growth are not constant, and it is difficult to obtain metal composite hydroxide particles having a narrow particle size distribution.

  The ammonium ion concentration of the aqueous reaction solution (the aqueous solution for nucleation) is preferably adjusted to 3 g / L or more and 25 g / L or less, more preferably 5 g / L or more and 20 g / L or less. Since ammonium ions function as a complexing agent in the reaction aqueous solution, if the ammonium ion concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, or the reaction aqueous solution tends to gel. As a result, it is difficult to obtain metal composite hydroxide particles having a uniform shape and particle size. On the other hand, when the ammonium ion concentration exceeds 25 g / L, the solubility of metal ions becomes too large, so that the amount of metal ions remaining in the reaction aqueous solution increases, which may cause a composition deviation or the like.

  If the concentration of ammonium ions fluctuates during the crystallization reaction, the solubility of metal ions fluctuates, and uniform metal composite hydroxide particles cannot be formed. For this reason, it is preferable to control the fluctuation range of the ammonium ion concentration to a certain range through the nucleation step (step S11) and the particle growth step (step S12), and specifically, to the fluctuation range of ± 5 g / L. It is preferable to control.

  In the nucleation step (step S11), the generation of new nuclei is continuously continued by supplying the aqueous solution containing the first raw material aqueous solution, the aqueous alkali solution and the ammonium ion donor to the aqueous reaction solution (the aqueous solution for generating nuclei). Is done. Then, when a predetermined amount of nuclei are generated in the aqueous solution for nucleation, the nucleation step is ended. At this time, the amount of nuclei generated can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the nucleation aqueous solution.

  The amount of nuclei generated in the nucleation step (step S11) is not particularly limited. However, from the viewpoint of obtaining metal composite hydroxide particles having a narrow particle size distribution, the crystallization step (the first crystallization step and the second crystallization step) is performed. (Including a precipitation step), preferably 0.1 atomic% or more and 2 atomic% or less, and more preferably 0.1 atomic% or more and 1.5 atomic% with respect to the metal element in the metal compound contained in the raw material aqueous solution supplied through It is more preferable to set the following.

  In the nucleation step, the upper limit of the temperature of the reaction aqueous solution (nucleation forming aqueous solution) is not particularly limited, but is preferably, for example, 60 ° C or lower, and more preferably 50 ° C or lower. If the temperature of the reaction aqueous solution (nucleus forming aqueous solution) exceeds 60 ° C., primary crystals may be distorted and the tap density may start to decrease. Note that the lower limit of the temperature of the reaction aqueous solution (nucleus forming aqueous solution) is, for example, 20 ° C. or higher.

(Grain growth process)
Next, particles are grown in a reaction aqueous solution (aqueous solution for particle growth) whose pH has been adjusted to a specific range (step S12). A reaction aqueous solution (aqueous solution for particle growth) is formed by supplying a first raw material aqueous solution, an alkaline aqueous solution, and an aqueous solution containing an ammonium ion donor to a generated reaction aqueous solution containing nuclei. The reaction aqueous solution (aqueous solution for particle growth) is preferably adjusted to have a pH value of 10.5 or more and 12.0 or less and a ammonium ion concentration of 3 g / L or more and 25 g / L or less measured at a liquid temperature of 25 ° C. Thereby, in the reaction aqueous solution (particle growth aqueous solution), the particle growth is performed more predominantly than the nucleation.

In the case of mainly obtaining particles of a metal composite hydroxide having a solid structure having a tap density of 1.7 g / cm ³ or more and 2.3 g / cm ³ or less, for example, the oxygen concentration in the reaction atmosphere in the reaction vessel is The atmosphere is preferably a non-oxidizing atmosphere of 5% by volume or less, more preferably an atmosphere having an oxygen concentration of 1% by volume or less. When the oxygen concentration of the reaction atmosphere in the reaction tank is 1% by volume or less, the secondary particles 2 having a solid structure in which the primary particles 1 are densely arranged can be easily obtained. Can be further improved in crystallinity. The atmosphere is controlled by, for example, introducing nitrogen gas.

  Specifically, after the nucleation step is completed, the pH value of the aqueous solution for nucleation in the reaction tank is adjusted to 10.5 or more and 12.0 or less based on a liquid temperature of 25 ° C., and the reaction aqueous solution is used in the particle growth step. An aqueous solution for particle growth is formed. Adjustment of the pH value can be performed by stopping the supply of only the alkaline aqueous solution. From the viewpoint of improving the uniformity of the particle diameter, it is possible to temporarily stop the supply of all the aqueous solutions and adjust the pH value. preferable. In addition, the pH value is adjusted when the reaction aqueous solution (aqueous solution for nucleation) uses the same kind of inorganic acid as the acid constituting the compound containing a transition metal as a raw material, for example, when a transition metal sulfate is used as a raw material. May be performed by supplying sulfuric acid.

  Next, the supply of the first raw material aqueous solution is restarted while stirring the reaction aqueous solution (aqueous solution for particle growth). At this time, since the pH value of the aqueous solution for particle growth is in the above-described range, new nuclei are hardly generated, nucleus (particle) growth proceeds, and the first metal composite hydroxide having a predetermined particle size is obtained. Particles can be formed. Also in the particle growth step (step S12), the pH value and the ammonium ion concentration of the aqueous solution for particle growth change with the particle growth, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied at appropriate times to adjust the pH value and the ammonium ion concentration. It is necessary to maintain the above range.

  The pH value of the reaction aqueous solution (particle growth aqueous solution) is 10.5 to 12.0, preferably 11.0 to 12.0, more preferably 11.5 to 11.9, based on a liquid temperature of 25 ° C. Control within the range. When the pH is within the above range, the generation of new nuclei is suppressed, the particle growth can be prioritized, and the obtained metal composite hydroxide can be uniform and have a narrow particle size distribution. On the other hand, when the pH value is less than 10.5, the ammonium ion concentration increases, and the solubility of the metal ions increases, so that not only the crystallization reaction speed decreases, but also the amount of metal ions remaining in the reaction aqueous solution. May increase and productivity may deteriorate. When the pH value exceeds 12.0, the amount of nuclei generated during the particle growth step increases, and the particle size of the obtained metal composite hydroxide particles becomes non-uniform, which may deteriorate the particle size distribution.

  It is preferable that the fluctuation range of the pH value in the reaction aqueous solution (particle growth aqueous solution) be within ± 0.2. When the fluctuation range of the pH value is large, the nucleation amount and the ratio of the particle growth are not constant, and it is difficult to obtain a metal composite hydroxide having a narrow particle size distribution.

  Further, it is preferable that the pH value in the particle growth step (step S12) is adjusted to a value lower than the pH value in the nucleation step (step S11). The pH value of the step (Step S12) is preferably lower than the pH value of the nucleation step (Step S11) by 0.5 or more, more preferably 0.8 or more.

  For example, when the pH value of the reaction aqueous solution (nucleus generation step and / or particle growth step) is 12.0, it is a boundary condition between nucleation and nucleus growth. Any of the conditions of the generation step or the particle growth step can be set. That is, when the pH value in the nucleation step is higher than 12.0 and a large amount of nuclei are generated, and when the pH value in the particle growth step is 12.0, a large amount of nuclei are present in the reaction aqueous solution, Particle growth occurs preferentially, and metal composite hydroxide particles having a narrow particle size distribution can be obtained. On the other hand, when the pH value in the nucleation step is 12.0, since there is no nucleus to grow in the reaction aqueous solution, nucleation occurs preferentially, and the pH value in the particle growth step should be lower than 12.0. Then, the generated nuclei grow and good metal composite hydroxide particles can be obtained.

  The ammonium ion concentration of the reaction aqueous solution (aqueous solution for particle growth) can be the same as the preferable range of the ammonium ion concentration in the reaction aqueous solution (the aqueous solution for nucleation). Further, the fluctuation range of the ammonium ion concentration can be the same as the preferable range in the reaction aqueous solution (aqueous solution for nucleation).

(2) Second crystallization step (Step S20)
Next, a second raw material aqueous solution containing a metal element and containing more tungsten than the first raw material aqueous solution and an ammonium ion supplier are supplied to the reaction aqueous solution containing the first metal composite hydroxide particles. A crystallization reaction is performed (step S20). Thereby, the second metal composite hydroxide particles having the tungsten concentrated layer formed on the surfaces of the first metal composite hydroxide particles are obtained.

  In the second crystallization step, the first raw material aqueous solution is continuously formed in the second crystallization step because the particle growth is performed with secondary particles in which a plurality of primary particles are aggregated as nuclei. A second crystallization step (Step S20) in which the second raw material aqueous solution containing more tungsten and the ammonium ion donor are supplied to the reaction aqueous solution containing the first metal composite hydroxide particles. It can be performed. Thereby, a tungsten-enriched layer is formed on the outer peripheral portion of the secondary particles constituting the first composite oxide particles.

  In the method for producing a metal composite hydroxide according to the present embodiment, for example, the timing of starting the addition of the second raw material aqueous solution (that is, the timing of disclosing the second crystallization step) is adjusted. The thickness of the tungsten concentration layer formed on the outer periphery of the composite hydroxide particles can be easily controlled.

  In the second crystallization reaction (step S20), the metal element in the first raw material aqueous solution is added to the total amount of metal added in the first crystallization step and the second crystallization step by, for example, 10%. The supply can be started by supplying the second raw material aqueous solution at the time of supply to the reaction tank of not less than mass%. Thereby, a tungsten concentration layer can be easily formed on the surface of the first metal composite hydroxide particles.

  Further, from the viewpoint of obtaining a positive electrode active material having higher crystallinity and being used for a positive electrode of a secondary battery and further reducing the reaction resistance, the metal element in the first raw material aqueous solution is subjected to the first crystallization. Supply to the reaction tank preferably in the range of 50% by mass to 95% by mass, more preferably in the range of 75% by mass to 90% by mass, based on the total amount of metal added in the step and the second crystallization step. At this point, the second raw material aqueous solution is supplied, and the second crystallization step (Step S20) can be started.

  Since the second crystallization step (step S20) is a step in which the particles are grown, similarly to the particle growth step (step S12), the pH, the temperature, the ammonium ion concentration of the reaction aqueous solution, the atmosphere in the reaction tank, and the like are set. And the like can be the same conditions as in the particle growth step (step S12). By continuously performing the second crystallization step (Step S20) under the same conditions as the particle growth step (Step S12), the productivity is easily increased, and the surface of the first metal composite hydroxide particles is coated with tungsten. The formation of a concentrated layer can be performed.

  In addition, the supply of the second raw material aqueous solution may be performed by separately preparing a raw material aqueous solution containing a metal element other than tungsten and an aqueous solution containing tungsten and supplying each of them to the reaction tank. By separately supplying an aqueous solution containing tungsten, a tungsten-concentrated layer can be formed more easily and uniformly. Further, as shown in FIG. 2, the second raw material aqueous solution may include the first raw material aqueous solution and an aqueous solution containing tungsten (W), and each aqueous solution may be separately supplied to the reaction aqueous solution. Thus, by changing the concentration of the aqueous solution containing tungsten and the flow rate when supplying the aqueous solution containing tungsten to the reaction tank, a concentrated layer of tungsten can be formed uniformly, and the tungsten can be easily concentrated. It is possible to adjust the thickness of the layer.

  The aqueous solution containing tungsten can be adjusted, for example, by dissolving a tungsten compound in water. The tungsten compound to be used is not particularly limited, and a compound containing tungsten without using lithium can be used. Preferably, sodium tungstate can be used.

  The tungsten (W) concentration of the aqueous solution containing tungsten is not particularly limited, but is, for example, 0.1 mol / l or more and 0.5 mol / l or less, preferably 0.2 mol / l or more and 0.4 mol / l or less. The flow rate of the aqueous solution containing tungsten is not particularly limited, but is, for example, 5 L / min or more and 20 L / min or less, and preferably 10 L / min or more and 15 L / min or less.

  The thickness of the tungsten concentration layer can also be controlled by adjusting the concentration of an aqueous solution containing tungsten or adjusting the flow rate of the aqueous solution. For example, when the concentration of the aqueous solution containing tungsten and the addition flow rate are fixed, the thickness and concentration of the formed tungsten concentrated layer can be adjusted more accurately and easily by adjusting the start time of the addition of the aqueous solution containing tungsten. be able to.

  FIG. 4 is a diagram illustrating a preferred example of the manufacturing method according to the present embodiment. In FIG. 4, the first crystallization step (step S10) includes a nucleation step (step S11) and a particle growth step (step S12) separately, and the particle growth step (step S12) When the second crystallization step (step S20) is performed by supplying the aqueous solution containing tungsten together with the first raw material aqueous solution, the addition of the aqueous solution containing tungsten is disclosed (the second crystallization step). (At the time of disclosure).

  FIG. 4 (A) shows that the tungsten compound is changed from 75% of the total time during which the grain growth is performed from the start of the grain growth to the end of the grain growth (the end of the crystallization step). It is a figure showing an example at the time of adding an aqueous solution. In this case, as shown in the lower part of FIG. 4A, the tungsten concentration layer 3 can be formed on the surface layer (outer periphery) of the secondary particles (first metal composite hydroxide particles). In addition, when an aqueous solution of a tungsten compound is added in the entire process from the start point to the end point of the particle growth, a tungsten concentrated layer is not formed.

  FIG. 4B shows the tungsten compound starting from the point when 87.5% has elapsed with respect to the entire time during which the grain growth is performed from the start of the grain growth to the end of the grain growth (end of the crystallization step). FIG. 4 is a diagram showing an example of a case where an aqueous solution of the above is added. In this case, as shown in the lower part of FIG. 4B, compared to the case where the addition was started to the surface layer (outer periphery) of the secondary particles (first metal composite hydroxide particles) from the time when the above 75% elapsed. Thus, a more concentrated tungsten concentration layer can be formed.

As described above, when the second crystallization step (Step S20) is performed by supplying the aqueous solution containing tungsten together with the first raw material aqueous solution, the supply of the aqueous solution containing tungsten (second raw material aqueous solution) is performed in the first and second steps. For example, at the time when 10% or more elapses, preferably at the time when 50% or more and 95% or less elapse, more preferably at 75% or more 90% with respect to the entire time from the start to the end of the particle growth in the second crystallization step % Or less. When the time for which the supply is disclosed is within the above range, a tungsten-enriched layer can be obtained easily and with good productivity. Further, when the time point at which the addition of the aqueous solution containing tungsten is disclosed is later within the above range, the crystallite size of the obtained positive electrode active material tends to be able to be increased. The addition of the aqueous solution containing tungsten is continued until the crystallization reaction ends.
Hereinafter, each raw material and conditions preferably used in the crystallization step will be described.

(First and second raw material aqueous solutions)
The first raw material aqueous solution and the second raw material aqueous solution contain nickel and manganese, and optionally cobalt, the element M, and tungsten. Further, the first raw material aqueous solution may not contain tungsten. In the second crystallization step, when the first raw material aqueous solution and the aqueous solution containing tungsten are used as the second raw material aqueous solution, the ratio of the metal element in the first raw material aqueous solution is determined by the metal complex finally obtained. It becomes the composition ratio of hydroxide (excluding tungsten). For this reason, in the first raw material aqueous solution, the content of each metal element can be appropriately adjusted according to the target composition of the metal composite hydroxide. For example, when trying to obtain the metal composite hydroxide particles represented by the above ratio (A), the ratio of the metal element in the raw material aqueous solution is set to Ni: Mn: Co: M = x: y: z: b. (However, adjust so that x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ b ≦ 0.1) Can be. In addition, the composition of the first raw material aqueous solution and the second raw material aqueous solution used in the first crystallization step and the second crystallization step may be different. In this case, the total content of each metal element in the raw material aqueous solution used in each crystallization step can be the composition ratio of the obtained metal composite hydroxide.

  The compound of the metal element (transition metal) used for preparing the first raw material aqueous solution and the second raw material aqueous solution is not particularly limited, but water-soluble nitrates, sulfates, hydrochlorides, and the like are used for ease of handling. It is preferable to use sulfate, and it is particularly preferable to use a sulfate from the viewpoint of preventing cost and halogen contamination.

  Further, an element M (M is at least one element selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) in the metal composite hydroxide. In the case of containing, the compound for supplying the element M is also preferably a water-soluble compound, for example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, sulfuric acid Vanadium, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate, ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate, ammonium tungstate, and the like can be preferably used.

  The concentration of the first raw material aqueous solution and the second raw material aqueous solution is preferably 1 mol / L or more and 2.6 mol / L or less, more preferably 1.5 mol / L or more and 2.2 mol / L in total of the metal compounds. The following is assumed. If the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized substances per reaction vessel is reduced, so that the productivity is reduced. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol / L, the concentration of the metal compound exceeds the saturation concentration at room temperature, so that the crystals of the respective metal compounds may re-precipitate and clog pipes and the like.

  In addition, the metal compound described above does not necessarily need to be supplied to the reaction tank as one type of raw material aqueous solution. For example, when a crystallization reaction is performed using a metal compound that produces a compound other than the target compound by reacting when mixed, the crystallization reaction is performed individually so that the total concentration of the aqueous solutions of all the metal compounds is in the above range. An aqueous solution of a metal compound may be prepared and supplied as an aqueous solution of an individual metal compound into the reaction vessel at a predetermined ratio.

  Further, the supply amounts of the first raw material aqueous solution and the second raw material aqueous solution are determined based on the product (second metal composite hydroxide particles) in the reaction solution (particle growth aqueous solution) at the end of the crystallization step. Is preferably 30 g / L or more and 200 g / L or less, more preferably 80 g / L or more and 150 g / L or less. When the concentration of the product is less than 30 g / L, the aggregation of the primary particles may be insufficient. On the other hand, if the concentration of the product exceeds 200 g / L, the aqueous solution for nucleation or the aqueous solution for particle growth may not be sufficiently diffused in the reaction tank, and the particle growth may be biased.

(Alkaline aqueous solution)
The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkaline metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the reaction aqueous solution, but is preferably added as an aqueous solution because of easy pH control. In this case, the concentration of the alkali metal hydroxide aqueous solution is preferably 20% by mass to 50% by mass, and more preferably 20% by mass to 30% by mass. By regulating the concentration of the aqueous alkali metal solution to such a range, it is possible to prevent the pH value from locally increasing at the addition position while suppressing the amount of the solvent (the amount of water) supplied to the reaction system. And metal composite hydroxide particles having a narrow particle size distribution can be efficiently obtained.

  The method of supplying the aqueous alkali solution is not particularly limited as long as the pH value of the aqueous reaction solution does not locally increase and is maintained within a predetermined range. For example, the reaction aqueous solution may be supplied by a pump capable of controlling the flow rate such as a constant-rate pump while sufficiently stirring.

(Aqueous solution containing ammonium ion donor)
The aqueous solution containing the ammonium ion donor is not particularly limited, either. For example, aqueous ammonia or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate or ammonium fluoride can be used.

When ammonia water is used as the ammonium ion supplier, the concentration is preferably 20% by mass to 30% by mass, more preferably 22% by mass to 28% by mass. By regulating the concentration of the ammonia water in such a range, the loss of ammonia due to volatilization or the like can be suppressed to a minimum, so that the production efficiency can be improved.
In addition, the supply method of the aqueous solution containing the ammonium ion supply body can also be supplied by a pump whose flow rate can be controlled, similarly to the alkaline aqueous solution.

(Reaction atmosphere)
By controlling the atmosphere in the reaction tank to an oxidizing atmosphere or a non-oxidizing atmosphere, the particle structure and the tap density of the metal composite hydroxide are controlled. When mainly obtaining particles of a metal composite hydroxide having a solid structure with a tap density of 1.7 g / cm ³ or more and 2.3 g / cm ³ or less, a nucleation step (step S11) and a particle growth step ( In steps S12 and S20), for example, it is preferable to set a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less, and more preferable to set an atmosphere having an oxygen concentration of 1% by volume or less. For example, when the oxygen concentration in the reaction atmosphere is set to 1% by volume or less, it is preferable to control the mixed atmosphere of oxygen and an inert gas.

(Reaction temperature)
The temperature (reaction temperature) of the reaction aqueous solution is preferably 20 ° C. or higher, more preferably 20 ° C. or higher and 60 ° C. or lower throughout the crystallization step (nucleation step, particle growth step, and second crystallization step). Control. When the reaction temperature is lower than 20 ° C., nucleation is likely to occur due to the low solubility of the reaction aqueous solution, and it becomes difficult to control the average particle size and particle size distribution of the obtained metal composite hydroxide. There is. The upper limit of the reaction temperature is not particularly limited. However, when the temperature exceeds 60 ° C., the volatilization of ammonia is promoted, and an ammonium ion supplier supplied to control the ammonium ion in the reaction aqueous solution within a certain range. And the production cost increases. If the reaction temperature exceeds 60 ° C., in the nucleation step (step S11), the primary crystal may be distorted and the tap density may be reduced.

(Manufacturing equipment)
In the method for producing a metal composite hydroxide according to the present embodiment, it is preferable to use an apparatus that does not collect products until the reaction is completed, for example, a batch reaction tank. With such an apparatus, unlike the continuous crystallization apparatus that recovers the product by the overflow method, the growing particles are not collected at the same time as the overflow liquid, so the metal composite hydroxide having a narrow particle size distribution. Particles can be easily obtained.

  In the method for producing a metal composite hydroxide according to the present embodiment, it is preferable to control the reaction atmosphere during the crystallization reaction. Therefore, it is preferable to use a device capable of controlling the atmosphere, such as a closed device. With such an apparatus, since the reaction atmosphere in the nucleation step and the particle growth step can be appropriately controlled, the metal composite hydroxide particles having the above-described particle structure and having a narrow particle size distribution can be easily obtained. Can be obtained.

  The composition of the metal composite hydroxide 10 obtained by the production method of the present embodiment is not particularly limited as long as the above-described particle structure, average particle size, and particle size distribution can be realized. ) Can be suitably applied to the metal composite hydroxide represented by the formula (1).

3. Positive electrode active material for lithium ion secondary battery The positive electrode active material according to the present embodiment includes lithium, nickel, manganese, and tungsten, and optionally cobalt and the element M, and the number of atoms of each metal element. The ratio is Li: Ni: Mn: Co: W: M = (1 + u): x: y: z: a: b (x + y + z = 1, -0.05 ≦ u ≦ 0.50, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is Mg, Ca, Al, Ti, V , Cr, Zr, Nb, Mo, Hf, and Ta) (hereinafter, referred to as “lithium metal composite oxide”). The lithium metal composite oxide has a hexagonal layered crystal structure.

  5A and 5B are schematic diagrams illustrating an example of the lithium metal composite oxide according to the present embodiment. As shown in FIG. 5A, the lithium metal composite oxide 20 includes secondary particles 22 formed by aggregating a plurality of primary particles 21. Note that the lithium metal composite oxide 20 may be composed of only the secondary particles 22 or may be composed of the secondary particles 22 and the single primary particles 21. Hereinafter, the details of the lithium metal composite oxide 20 will be described with reference to FIGS. 5A and 5B.

(Compound containing tungsten and lithium)
As shown in FIG. 5A, the lithium metal composite oxide 20 contains tungsten and lithium on the surface layer of the primary particles 21 existing on the surface or inside the secondary particles 22 and on the grain boundaries between the primary particles 21. Compound 23 is present in a concentrated form. The existence site of the compound 23 containing tungsten and lithium can be confirmed, for example, by detecting a W distribution by surface analysis using an energy dispersive X-ray analyzer (EDX) as shown in FIG. Further, it is preferable that the compound 23 containing tungsten and lithium is present more on the surface (surface layer) than inside the secondary particles 22.

  In the case where the surface layer of the positive electrode active material is coated with a heterogeneous compound, the movement (intercalation) of lithium ions is greatly restricted, and as a result, the advantage of the high capacity of the lithium metal composite oxide cannot be sufficiently exhibited. is there. On the other hand, the compound 23 containing tungsten and lithium (for example, lithium tungstate) has a high lithium ion conductivity and thus has an effect of promoting the movement of lithium ions. The compound 20 forms a conductive path of Li at the interface with the electrolytic solution by forming a compound 23 containing tungsten and lithium on the surface layer of the primary particles 21 near the surface and on the grain boundary between the primary particles 21. By doing so, it is possible to reduce the reaction resistance of the positive electrode active material and improve the output characteristics. The compound 23 containing tungsten and lithium can be present in the form of fine particles near the surface of the lithium metal composite oxide 20, for example.

The compound 23 containing tungsten and lithium is not particularly limited, and examples thereof include lithium tungstate such as Li ₂ WO ₄ , Li ₄ WO ₅ , and Li ₂ W ₂ O ₇ . These lithium tungstates are concentrated and formed on the surface layer of the primary particles 21 existing on the surface or inside of the secondary particles 22, and on the grain boundaries between the primary particles 21, thereby forming the lithium metal composite oxide 20. When the lithium ion conductivity is further increased and used for a positive electrode of a secondary battery, the reduction in reaction resistance becomes greater.

(Particle structure)
The structure of the secondary particles 22 of the lithium metal composite oxide 20 is not particularly limited, and may be, for example, a solid structure in which primary particles are formed by relatively agglomeration without gaps. Alternatively, a hollow structure having a plurality of voids 24 or a hollow structure having a hollow portion 25 may be used. The structure of the secondary particles 22 of the lithium metal composite oxide 20 is preferably a solid structure from the viewpoint of higher particle strength and higher tap density.

  In the present specification, the phrase “the secondary particles 22 have a solid structure” means that the plurality of primary particles 1 are uniformly and densely distributed throughout the inside of the secondary particles 2, and that the primary particles 1 Or, it has a structure in which a plurality of hollow portions (eg, occupying 10% or more of the cross-sectional area of the secondary particles 2) does not exist. When the metal composite hydroxide 10 has a solid structure, the porosity of the metal composite hydroxide 10 (the void area inside the secondary particles 2 with respect to the cross-sectional area of the secondary particles 22) is, for example, 20% or less. And preferably 10% or less.

  When the lithium metal composite oxide 20 has a solid structure by inheriting the solid structure characteristic of the above-described metal composite hydroxide, the voids inside the secondary particles 22 are small, so that the lithium metal composite oxide 20 is compared with other structures. And the most excellent particle strength. In addition, when the lithium metal composite oxide 20 has a high particle strength, the energy density per volume can be further increased, and the occurrence of cracks or the like in the positive electrode active material during a charge / discharge cycle is suppressed, and the cycle is reduced. The characteristics can be improved.

  The positive electrode active material according to the present embodiment, in the production of the secondary particles 22 (metal composite hydroxide) having a multilayer structure including the hollow portion 25 and the space portion 26, is continuously connected to a conventionally known particle growth step, By adding the second crystallization step of adding the aqueous solution containing tungsten as described above, the metal composite hydroxide 10 having the tungsten-enriched layer 3 formed on the surface layer, and the lithium using this as a precursor The metal composite oxide 20 can be obtained. The lithium metal composite oxide 20 has a multilayer structure including the hollow portion 25 and the space portion 26 due to the presence of the compound 23 containing lithium and tungsten at the surface layer of the primary particles 21 and the grain boundary between the primary particles 21. The output characteristics can be further improved while maintaining the crystallinity of the positive electrode active material including the secondary particles 22.

(Volume average particle size)
The volume average particle size (MV) of the positive electrode active material is not particularly limited, but can be, for example, 3 μm or more and 9 μm or less. When the volume average particle size (MV) is in the above range, the battery capacity per unit volume of the secondary battery using the positive electrode active material can be increased, and the thermal stability and output characteristics can be improved. it can. On the other hand, when the volume average particle diameter (MV) of the positive electrode active material is less than 4 μm, the filling property of the positive electrode active material decreases, and it is difficult to increase the battery capacity per unit volume (volume). When the volume average particle size (MV) of the positive electrode active material exceeds 9 μm, the reaction area of the positive electrode active material starts to decrease, so that the output characteristics may not be sufficient.

  In addition, the volume average particle size (MV) of the positive electrode active material can be determined from, for example, a volume integrated value measured by a laser light diffraction / scattering particle size analyzer, as in the case of the metal composite hydroxide 10 described above.

(Particle size distribution)
The positive electrode active material has an index [(d90−d10) / MV] indicating the spread of the particle size distribution, and is preferably 0.65 or less. When [(d90−d10) / MV] is within the above range, the positive electrode active material is composed of the lithium metal composite oxide 20 having a very narrow particle size distribution. Such a positive electrode active material has a small proportion of fine particles and coarse particles, and a secondary battery using this positive electrode active material for a positive electrode is excellent in thermal stability, cycle characteristics, and output characteristics.

  On the other hand, when [(d90-d10) / MV] exceeds 0.65, the ratio of fine particles and coarse particles in the positive electrode active material increases. A secondary battery using a positive electrode active material having a large particle size distribution, for example, generates heat due to a local reaction of fine particles, reduces heat stability, and selectively deteriorates fine particles. Cycle characteristics may be degraded. In addition, a secondary battery using a positive electrode active material having a wide particle size distribution has a large proportion of coarse particles, so that a sufficient reaction area between the electrolytic solution and the positive electrode active material cannot be secured, and output characteristics deteriorate. May be.

  In addition, on the premise of production on an industrial scale, it is not realistic to use a material whose [(d90−d10) / MV] is excessively small as the positive electrode active material. Therefore, in consideration of cost and productivity, the lower limit of [(d90−d10) / MV] in the positive electrode active material is preferably 0.25 or more. The meaning of d10 and d90 in [(d90-d10) / MV] and the method of measuring these are the same as those of the metal composite hydroxide described above.

(Sinter aggregation)
The positive electrode active material has an index of sintering aggregation [lithium metal composite oxide d50 / metal composite hydroxide d50] (hereinafter referred to as “d50 ratio”) of 0.95 or more and 1.05 or less. Preferably, there is. When the d50 ratio is within the above range, the positive electrode active material can be composed of the lithium metal composite oxide 20 in which aggregation of the secondary particles due to sintering aggregation is suppressed. Such a positive electrode active material has a high filling property in the positive electrode of a secondary battery, and when used in a positive electrode of a secondary battery, has a high capacity, a small variation in characteristics, and excellent uniformity. Can be obtained.

  On the other hand, when the d50 ratio exceeds 1.05, the specific surface area may decrease or the filling property may decrease due to aggregation of sintering. A secondary battery using such a positive electrode active material may have reduced reactivity due to reduced reactivity, and may also have a reduced battery capacity. In addition, in a secondary battery using such a positive electrode active material, when repeatedly charged and discharged, the secondary particles in the positive electrode selectively collapse from a weak portion where the secondary particles are aggregated, so that the cycle characteristics May be a factor that greatly impairs the performance.

  Further, when the d50 ratio is less than 1.0, by crushing the lithium metal composite oxide 20, a part of the primary particles 21 was missing from the secondary particles 22 and the particle diameter was reduced. In particular, when the d50 ratio is less than 0.95, a large number of fine particles are generated due to the large number of the missing primary particles 21 and the particle size distribution may be widened.

  The metal composite hydroxide d50 means d50 of the metal composite hydroxide 10 used as a precursor when producing the lithium metal composite oxide 20. The d50 of each particle can be measured by a laser diffraction / scattering particle size analyzer, and the particles at each particle size are accumulated from the smaller particle size side, and the accumulated volume is 50% of the total volume of all the particles. % Means the particle size.

(Crystallite diameter)
The positive electrode active material according to the present embodiment is, as in a conventional manufacturing method, compared with a positive electrode active material using a metal composite hydroxide obtained by uniformly adding tungsten throughout the crystallization step as a precursor. The crystallite diameter of the (003) plane obtained by powder X-ray diffraction measurement can be further increased. The crystallite diameter of the (003) plane of the positive electrode active material can be, for example, 110 nm or more, may be 115 nm or more, and is preferably 120 nm or more. When the crystallite diameter of the (003) plane of the positive electrode active material is 120 nm or more, the secondary battery using the positive electrode active material for the positive electrode has high crystallinity, and the positive electrode resistance is reduced. And thermal stability also improves. On the other hand, when the crystallite diameter of the (003) plane of the positive electrode active material is less than 120 nm, the crystallinity may not be sufficient, or the thermal stability of the secondary battery may decrease.

  The upper limit of the crystallite diameter of the (003) plane of the positive electrode active material is not particularly limited, but can be, for example, 200 nm or less, and preferably 120 nm or more and 150 nm or less. In the positive electrode active material of the present embodiment, since the high crystallinity can be maintained by using the metal composite hydroxide 10 having the tungsten concentrated layer 3 on the surface as a precursor as described above, the crystallite of the (003) plane can be maintained. The diameter can be in the above range.

(Tap density)
The tap density of the positive electrode active material is preferably 1.8 g / cm ³ or more and 2.4 g / cm ³ or less, and more preferably 2.0 g / cm ³ or more and 2.2 g / cm ³ or less. When the tap density of the positive electrode active material is in the above range, a secondary battery having a higher volume energy density can be obtained. On the other hand, when the tap density is less than 1.8 g / cm ³ , there are many voids in the particle structure and the particle strength is reduced, so that the cycle characteristics may be reduced. In addition, the filling property of the positive electrode active material is reduced, and it is difficult to increase the battery capacity per unit volume.

When the particle size distribution of the positive electrode active material is large, the tap density tends to increase. In this case, fine particles may be selectively deteriorated and cycle characteristics may be deteriorated. Therefore, [(d90−d10) / MV] which is an index indicating the spread of the particle size distribution of the positive electrode active material is within the above range (eg, 0.65 or less), and the tap density is within the above range (eg, (1.8 g / cm ³ or more and 2.4 g / cm ³ or less), it has high volume energy density and excellent cycle characteristics.

(Specific surface area)
The BET specific surface area of the positive electrode active material is preferably from 0.6 m ² / g to 1.2 m ² / g, more preferably from 0.7 m ² / g to 1.1 m ² / g, further preferably 0.8 m ² / g or more and 1.0 m ² / g or less. When the BET specific surface area is in the above range, the contact area with the electrolyte can be made sufficient when the positive electrode of the secondary battery is used, so that the positive electrode resistance can be reduced and sufficient output characteristics can be obtained. it can.

(composition)
Positive electrode active material of the present embodiment, as long as it has characteristics as described above, the composition is not particularly limited, for example, the general formula _{(B): Li 1 + u} Ni x Mn y Co z W a M b O 2 (-0 0.05 ≦ u ≦ 0.50, x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta).

  In the general formula (B), the value of u indicating the amount of lithium (Li) is preferably -0.05 to 0.50, more preferably 0 to 0.50, and further preferably 0 to 0.35. It is as follows. When the value of u is in the above range, the output characteristics and capacity characteristics of a secondary battery using this positive electrode active material as a positive electrode material can be improved. On the other hand, when the value of u is less than -0.05, the positive electrode resistance of the secondary battery increases, and the output characteristics cannot be improved. On the other hand, when the value of u exceeds 0.50, the initial discharge capacity may decrease or the positive electrode resistance may increase.

  In the general formula (B), the value of x indicating the content of nickel (Ni) is preferably from 0.3 to 0.95, more preferably from 0.3 to 0.9. Nickel is an element that contributes to higher potential and higher capacity of the secondary battery. If the value of x is less than 0.3, the capacity characteristics of a secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of x exceeds 0.95, the content of the other element decreases, and the effect of the other element cannot be obtained.

  In the general formula (B), the value of y indicating the content of manganese (Mn) is preferably 0.05 or more and 0.55 or less, and more preferably 0.10 or more and 0.40 or less. Manganese is an element that contributes to improvement in thermal stability. When the value of y is less than 0.05, the thermal stability of a secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of y exceeds 0.55, Mn is eluted from the positive electrode active material during high-temperature operation, and the charge / discharge cycle characteristics may be degraded.

  In the general formula (B), the value of z indicating the content of cobalt (Co) is preferably from 0 to 0.4, more preferably from 0.10 to 0.35. Cobalt is an element that contributes to improvement of charge / discharge cycle characteristics. When the value of z exceeds 0.4, the initial discharge capacity of a secondary battery using this positive electrode active material may be significantly reduced.

  In the general formula (B), the value of a indicating the content of tungsten (W) is more than 0 and 0.1 or less when the total number of moles of Ni, Co, and Mn is 1, and is preferably 0.1 or less. It is 0.001 or more and 0.01 or less, more preferably 0.0045 or more and 0.006 or less. When the value of a is within the above range, the positive electrode active material has more excellent output characteristics and cycle characteristics while maintaining high crystallinity. In addition, as described above, W is mainly contained in the surface layer of the primary particles 21 near the surface of the secondary particles 22 or in the grain boundary between the primary particles 21 in the positive electrode active material.

  In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material of the present embodiment may contain the element M in addition to the above-described metal elements. Examples of the element M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum ( Mo), hafnium (Hf), and tantalum (Ta) can be used.

  In the general formula (B), the value of b indicating the content of the element M is preferably 0 or more and 0.1 or less, more preferably 0.1 or less, when the total number of moles of Ni, Co and Mn is 1. It is 001 or more and 0.05 or less. When the value of b exceeds 0.1, the metal element contributing to the Redox reaction decreases, so that the battery capacity may decrease.

In the positive electrode active material represented by the general formula (B), from the viewpoint of achieving further improvements in capacity characteristics of the secondary battery, its composition formula _{(B1): Li 1 + u} Ni x Mn y Co z W a _{M b O 2 (-0.05 ≦ u} ≦ 0.20, x + y + z = 1,0.7 <x ≦ 0.95,0.05 ≦ y ≦ 0.1,0 ≦ z ≦ 0.2,0 < a ≦ 0.1, 0 ≦ b ≦ 0.1, M is one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, and Mo, Hf, and Ta. Element). Above all, from the viewpoint of achieving both thermal stability and battery capacity, the value of x in the above general formula (B1) is more preferably set to 0.7 <x ≦ 0.9, and 0.7 <x ≦ 0.9. It is more preferred that ≦ 0.85.

From the viewpoint of achieving further improvement of the thermal stability, the composition, the general formula _{(B2): Li 1 + u} Ni x Mn y Co z W a M b O 2 (-0.05 ≦ u ≦ 0.50, x + y + z = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is , Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta).

4. Method for Producing Positive Electrode Active Material for Lithium-Ion Secondary Battery FIG. 6 is a diagram illustrating an example of a method for producing a positive electrode active material according to the present embodiment. According to the manufacturing method of the present embodiment, the positive electrode active material containing the above-described lithium metal composite oxide 20 can be easily manufactured on an industrial scale. The positive electrode active material containing the lithium metal composite oxide 20 is not particularly limited as long as it has the specific structure, average particle size, and particle size distribution described above, and can be obtained by a known manufacturing method.

  As shown in FIG. 6, in the method for manufacturing a positive electrode active material according to the present embodiment, a step of mixing a metal composite hydroxide 10 obtained by the above-described manufacturing method and a lithium compound to obtain a lithium mixture (step) S30), and a step of firing the lithium mixture to obtain a lithium metal composite oxide (Step S40). If necessary, a step such as a heat treatment step or a calcining step may be added in addition to the steps described above.

  Tungsten in the tungsten concentrated layer 3 formed on the surface layer of the metal composite hydroxide 10 reacts with the lithium compound in the mixing step (step S30) with the lithium compound and the firing step (step S40) to form the lithium metal composite. A compound 23 containing tungsten and lithium is formed on the surface of the primary particles in the oxide 20 and on the grain boundaries between the primary particles. Hereinafter, a method for manufacturing the positive electrode active material according to the present embodiment will be described with reference to FIG.

(Mixing process)
First, a lithium compound is mixed with at least one of a metal composite hydroxide and a metal composite oxide obtained by heat-treating the metal composite hydroxide (hereinafter, these are also collectively referred to as a “precursor”). Thus, a lithium mixture is obtained (step S30).

  In step S30, the ratio (Li) of the sum (Me) of the number of atoms of metal atoms other than lithium in the lithium mixture, specifically, nickel, cobalt, manganese, and the element M, to the number of atoms of lithium (Li) / Me) is 0.95 or more and 1.5 or less, preferably 1.0 or more and 1.5 or less, more preferably 1.0 or more and 1.35 or less, and still more preferably 1.0 or more and 1.2 or less. Thus, the precursor and the lithium compound are mixed. That is, since Li / Me does not change before and after the firing step, the precursor and the lithium compound are mixed such that Li / Me in the mixing step becomes Li / Me of the target positive electrode active material. Note that Li / Me may exceed 1 or may exceed 1.1 from the viewpoint of sufficiently forming the compound 23 containing tungsten and lithium.

  The lithium compound used for mixing is not particularly limited, but from the viewpoint of availability, it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof. Particularly, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate.

  It is preferable that the precursor and the lithium compound are sufficiently mixed so that fine powder is not generated. Insufficient mixing may cause variations in Li / Me between the individual particles, making it impossible to obtain sufficient battery characteristics. Note that a general mixer can be used for mixing. For example, a shaker mixer, a redige mixer, a julia mixer, a V blender, and the like can be used.

(Heat treatment process)
Before the mixing step (step S30), a step of heat-treating the metal composite hydroxide (heat treatment step) may be arbitrarily provided. The precursor obtained by the heat treatment may be mixed with a lithium compound (not shown). Here, as the precursor obtained after the heat treatment, a metal composite hydroxide in which at least a part of excess water is removed in the heat treatment step, a precursor in which the metal composite hydroxide is converted to an oxide by the heat treatment step ( Metal composite oxide) or a mixture thereof.

  The heat treatment step is a step of heating and heat-treating the metal composite hydroxide to remove at least a part of the water contained in the metal composite hydroxide. This makes it possible to reduce the amount of water remaining until after the firing step (step S40) to a certain amount, and to suppress a variation in the composition of the obtained positive electrode active material.

  The heat treatment temperature is, for example, 105 ° C. or more and 750 ° C. or less. When the heat treatment temperature is lower than 105 ° C., the excess water in the metal composite hydroxide cannot be sufficiently removed, and the variation may not be sufficiently suppressed. On the other hand, when the heat treatment temperature exceeds 700 ° C., not only no further effect can be expected, but also the production cost increases.

In the heat treatment step, it is only necessary to remove water to such an extent that the number of atoms of each metal component in the positive electrode active material or the ratio of the number of Li atoms does not vary. There is no need to convert things. However, from the viewpoint of reducing the variation in the number of atoms of each metal component and the ratio of the number of atoms of Li, heat treatment is performed at 400 ° C. or more to convert all metal composite hydroxides to composite oxides. Is preferred. The above-described variation can be further suppressed by determining the number of atoms of the metal component contained in the metal composite hydroxide under the heat treatment conditions in advance by analysis and determining the mixing ratio with the lithium compound. .
The atmosphere in which the heat treatment is performed is not particularly limited, and may be a non-reducing atmosphere, but is preferably in an air stream from the viewpoint that it can be easily performed.

  The heat treatment time is not particularly limited, but is preferably 1 hour or more, and more preferably 5 hours or more and 15 hours or less, from the viewpoint of sufficiently removing moisture in the metal composite hydroxide.

(Firing process)
Next, the lithium mixture is fired to obtain the lithium metal composite oxide 20 (Step S40). This step is a step of obtaining lithium metal composite oxide 20 by sintering under a predetermined condition to diffuse lithium into the precursor. The obtained lithium metal composite oxide 20 may be used as it is as a positive electrode active material, or may be used as a positive electrode active material after a particle size distribution is adjusted by a crushing step, as described later.

[Firing temperature]
The firing temperature is preferably from 650 ° C to 980 ° C. When the firing temperature is lower than 650 ° C., lithium does not sufficiently diffuse into the precursor, and surplus lithium (including unreacted lithium compound) and unreacted metal composite hydroxide or metal composite oxide remain. Or the crystallinity of the obtained lithium metal composite oxide may be insufficient. On the other hand, when the firing temperature exceeds 980 ° C., sintering between lithium composite oxide particles is severe, abnormal grain growth may be caused, and the ratio of irregularly shaped coarse particles may increase.

  In the case of producing the positive electrode active material represented by the general formula (B1), the firing temperature is preferably 650 ° C or more and 900 ° C or less. In the case of manufacturing the positive electrode active material represented by the general formula (B2), the firing temperature is preferably 800 ° C or higher and 980 ° C or lower.

[Heating rate]
The heating rate up to the firing temperature is preferably 2 ° C./min to 10 ° C./min, and may be 5 ° C./min to 9 ° C./min. Further, in the firing step (step S40), the temperature may be maintained at a temperature near the melting point of the lithium compound used, preferably for 1 hour to 5 hours, more preferably 2 hours to 5 hours. This allows the precursor and the lithium compound to react more uniformly.

[Firing time]
The holding time (firing time) at the above firing temperature is preferably at least 2 hours, more preferably 4 hours to 24 hours. The holding time (sintering time) of the sintering temperature may be 2 hours or more and 15 hours or less, or may be 2 hours or more and 10 hours or less. When the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the precursor, and excess lithium, unreacted metal composite hydroxide or metal composite oxide remains, or the obtained lithium The crystallinity of the metal composite oxide may not be sufficient.

[Cooling rate]
After the calcination time (holding time), the cooling rate from the calcination temperature to at least 200 ° C is preferably 2 ° C / min to 10 ° C / min, and more preferably 3 ° C / min to 7 ° C / min. Is more preferred. By controlling the cooling rate within the above range, it is possible to prevent the equipment such as the sagger from being damaged by rapid cooling while securing the productivity.

[Firing atmosphere]
The atmosphere during the firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume or more and 100% by volume or less, particularly preferably an oxygen gas having an oxygen concentration in the above range and an inert gas. It is a mixed atmosphere. That is, firing is preferably performed in the air or in an oxygen stream. If the oxygen concentration in the atmosphere is less than 18% by volume, the crystallinity of the lithium metal composite oxide may not be sufficient.

[Firing furnace]
The furnace used in the firing step (Step S40) is not particularly limited, and may be any furnace that can heat the lithium mixture in the air or in an oxygen stream. Further, from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas is preferable, and a batch-type or continuous-type electric furnace may be used. In addition, the same furnace can be selected for the furnace used in the heat treatment step and the calcining step from the viewpoint of keeping the atmosphere in the furnace uniform.

(Calcination process)
When lithium hydroxide or lithium carbonate is used as the lithium compound, calcination may be performed after the mixing step (Step S30) and before the firing step (Step S40). The calcination is a step of calcining the lithium mixture at a temperature lower than the calcination temperature described below and at a temperature of 350 ° C to 800 ° C, preferably 450 ° C to 780 ° C. Thereby, lithium can be sufficiently diffused in the precursor, and more uniform lithium composite oxide particles can be obtained.

  The holding time at the above temperature is preferably from 1 hour to 10 hours, and more preferably from 3 hours to 6 hours. Also, the atmosphere in the calcining step is preferably an oxidizing atmosphere, as in the above-mentioned baking step (Step S40), and more preferably an atmosphere having an oxygen concentration of 18% by volume or more and 100% by volume or less.

(Crushing process)
The lithium metal composite oxide 20 obtained in the firing step (step S40) may have agglomeration or slight sintering. In such a case, it is preferable to crush the aggregates or sintered bodies of the secondary particles 22 of the lithium metal composite oxide 20. Thereby, the volume average particle size (MV) and the particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range. In addition, crushing means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles 22 generated by sintering necking between the secondary particles 22 during firing, and the secondary particles 22 themselves are almost destroyed. Means to separate the aggregates without dissolving the aggregates.

  Known methods can be used for the crushing method. For example, a pin mill, a hammer mill, or the like can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

5. Lithium ion secondary battery The lithium ion secondary battery (hereinafter, also referred to as “secondary battery”) according to this embodiment includes a positive electrode including a positive electrode active material, a negative electrode, and an electrolyte. The lithium ion secondary battery can be configured by the same components as the conventionally known lithium ion secondary battery, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. The secondary battery may be, for example, an all-solid secondary battery including a positive electrode, a negative electrode, and a solid electrolyte. Hereinafter, each component other than the positive electrode will be described.

  It should be noted that the embodiments described below are merely examples, and the lithium ion secondary battery of the present invention is applied to embodiments with various changes and improvements based on the embodiments described in this specification. It is also possible.

(Positive electrode)
A positive electrode of a secondary battery is manufactured using the above positive electrode active material. Hereinafter, an example of a method for manufacturing a positive electrode will be described. First, the above-described positive electrode active material (powder), a conductive agent and a binder (binder) are mixed, and if necessary, activated carbon and a target solvent such as viscosity adjustment are added, and the mixture is kneaded. A positive electrode mixture paste is prepared.

  Since the mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium secondary battery, it can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass. The content of the conductive agent may be set to 1 part by mass to 20 parts by mass, and the content of the binder may be set to 1 part by mass to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil, and dried to disperse the solvent, thereby producing a sheet-shaped positive electrode. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the intended battery, and used for battery production. However, the method for manufacturing the positive electrode is not limited to the above-described method, but may be another method.

  As the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, or the like), or a carbon black-based material such as acetylene black or Ketjen black can be used.

  The binder plays a role of binding the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin And polyacrylic acid.

  If necessary, a positive electrode active material, a conductive agent and activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(Negative electrode)
For the negative electrode, metallic lithium, a lithium alloy, or the like can be used. The negative electrode is prepared by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions and adding an appropriate solvent to form a paste into a negative electrode mixture on the surface of a metal foil current collector such as copper. A material formed by coating, drying, and, if necessary, compressing to increase the electrode density may be used.

  As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite and a phenol resin, and a powdered carbon material such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder similarly to the positive electrode, and an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material and the binder. Solvents can be used.

(Separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode, and holds the electrolyte.A known separator can be used.For example, a thin film such as polyethylene or polypropylene may be used, and a film having many fine pores may be used. it can.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, a non-aqueous electrolyte can be used. As the non-aqueous electrolyte, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent may be used. Further, as the non-aqueous electrolyte, an ionic liquid in which a lithium salt is dissolved may be used. In addition, the ionic liquid refers to a salt composed of cations and anions other than lithium ions, and which is liquid even at normal temperature.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, and chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, and further, tetrahydrofuran and 2-hydrogen carbonate. One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more kinds may be mixed. Can be used.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  When the lithium ion secondary battery is an all-solid secondary battery, a solid electrolyte may be used as the non-aqueous electrolyte. The solid electrolyte has a property that can withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

  As the inorganic solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, or the like is used.

The oxide solid electrolyte is not particularly limited, and any oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, for example, lithium phosphate _{(Li 3 PO 4), Li} 3 PO 4 N X, LiBO 2 N X, LiNbO 3, LiTaO 3, Li 2 SiO 3, Li 4 SiO 4 -Li 3 PO ₄ , Li ₄ SiO ₄ —Li ₃ VO ₄ , Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ —ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≦ X ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ etc. I can do it.

The sulfide-based solid electrolyte is not particularly limited, and any electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 _{S-B 2 S 3, Li} 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O _{5, LiI-Li 3 PO 4} -P 2 S 5 , and the like.

In addition, as the inorganic solid electrolyte, one other than the above may be used. For example, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, or the like may be used.

  The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and for example, polyethylene oxide, polypropylene oxide, a copolymer thereof, or the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Shape and configuration of secondary battery)
The positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above, the positive electrode, the negative electrode, and the lithium ion secondary battery according to the present embodiment including the solid electrolyte include a cylindrical shape and a stacked shape. Various shapes are possible.

  When a non-aqueous electrolyte is used as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated via a separator to form an electrode body.The obtained electrode body is impregnated with the non-aqueous electrolyte, and the positive electrode current collector and the outside are impregnated. Connect between the positive electrode terminal and the negative electrode current collector and the negative electrode terminal which communicates with the outside using a current collecting lead or the like, and seal the battery case to complete the lithium ion secondary battery. .

[Characteristics of lithium ion secondary battery]
As described above, the lithium ion secondary battery according to the present invention uses the positive electrode active material obtained by using the above-described metal composite hydroxide 10 as a precursor, and thus has excellent capacity characteristics, output characteristics, and cycle characteristics. Moreover, as compared with a conventional secondary battery using a positive electrode active material made of lithium nickel-based oxide particles, the thermal stability is excellent.

  As described above, the lithium ion secondary battery according to the present invention has excellent capacity characteristics, output characteristics, and cycle characteristics, and small portable electronic devices (notebook personal computers and local Phone terminal). Further, the lithium ion secondary battery of the present invention is excellent in thermal stability, not only can be miniaturized and high output, but also can simplify an expensive protection circuit, so that the mounting space can be reduced. It can also be suitably used as a power source for transportation equipment subject to restrictions.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In addition, in the following Examples and Comparative Examples, unless otherwise specified, each sample of a special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used for producing the metal composite hydroxide and the positive electrode active material. Further, through the nucleation step and the particle growth step, the pH value of the reaction aqueous solution is measured with a pH controller (Nippon Chemical Co., Ltd., NPH-690D), and the supply amount of the sodium hydroxide aqueous solution is adjusted based on the measured values. Thus, the fluctuation range of the pH value of the reaction aqueous solution in each step was controlled within a range of ± 0.2.

(Example 1)
(A) Production of metal composite hydroxide [nucleation step]
First, 1.2 L of water was put into the reaction tank, and the temperature in the tank was set to 40 ° C. while stirring at 790 rpm. At this time, nitrogen gas was introduced into the reaction tank, and the reaction atmosphere was a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less. Subsequently, an appropriate amount of a 25% by mass aqueous sodium hydroxide solution and 25% by mass aqueous ammonia are supplied into the reaction tank so that the pH value becomes 12.5 based on a liquid temperature of 25 ° C. and the ammonium ion concentration becomes 10 g / L. By adjusting to, an aqueous solution before the reaction was formed.

  At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate are dissolved in water so that the molar ratio of each metal element is Ni: Mn: Co: Zr = 38: 30: 32: 0.2, and 2 mol / mol A first raw material aqueous solution of L was prepared.

  Next, an aqueous solution for the nucleation step was formed by supplying the first raw material aqueous solution to the aqueous solution before the reaction at 13 ml / min, and nucleation was performed for 2.5 minutes. At this time, a 25% by mass aqueous solution of sodium hydroxide and 25% by mass of aqueous ammonia were appropriately supplied to maintain the pH value and ammonium ion concentration of the aqueous solution for nucleation in the above ranges.

[Grain growth step]
After the nucleation is completed, supply of all the aqueous solutions is temporarily stopped, sulfuric acid is added to the reaction tank, and the pH value is adjusted to 11.6 based on a liquid temperature of 25 ° C., whereby the particle growth is completed. An aqueous solution was formed. After confirming that the pH value reached a predetermined value, the first raw material aqueous solution was supplied to the reaction tank, and nuclei (particles) generated in the nucleation step were grown. As a reaction atmosphere, a nitrogen gas was introduced, and a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less was continuously maintained.

[Second crystallization step]
As the second raw material aqueous solution, the first raw material aqueous solution and an aqueous solution containing tungsten were used. As an aqueous solution containing tungsten, sodium tungstate dihydrate was prepared by mixing the obtained hydroxides with a molar ratio of each metal element of Ni: Co: Mn: Zr: W = 38: 30: 32: 0.2: 0. The resulting solution was dissolved in water to give an aqueous solution of sodium tungstate.

  At the time point when 19/20 hours (95%) had elapsed with respect to the entire time for performing the particle growth, the first aqueous solution was supplied, and the supply of the aqueous sodium tungstate solution to the reaction tank was started (addition range: 5%). By stopping the supply of all the aqueous solutions, the particle growth step was completed. Thereafter, the obtained product was washed with water, filtered and dried to obtain a powdery metal composite hydroxide.

  In addition, in the particle growth step in the first crystallization step and the second crystallization step, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution are supplied in a timely manner through these steps to form the particle growth step. The pH value of the working aqueous solution and the ammonium ion concentration were maintained in the above ranges. The reaction atmosphere was adjusted to a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less by introducing nitrogen gas, and switching between the non-oxidizing atmosphere and the oxidizing atmosphere was performed four times. The supply rate of the first raw material aqueous solution was constant (13 ml / min) throughout the crystallization step.

(B) Evaluation of Metal Complex Hydroxide According to analysis using an ICP emission spectrometer (ICPE-9000, manufactured by Shimadzu Corporation, ICPE-9000), this metal complex hydroxide has a general formula: Ni _{0. 38} Mn _0.30 Co _0.32 Zr _0.002 W _0.005 (OH) ₂

  The average particle size of the metal composite hydroxide was measured using a laser light diffraction / scattering type particle size analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.), and d10 and d90 were measured. [(D90-d10) / MV], which is an index shown, was calculated. As a result, it was confirmed that the average particle size of the metal composite hydroxide was 5.4 μm and [(d90−d10) / MV] was 0.43.

  In addition, in order to confirm the presence or absence of the tungsten enriched layer in the metal composite hydroxide and its thickness, the energy loaded on a scanning transmission electron microscope (HD-2300A, manufactured by Hitachi High-Technologies Corporation) was used. Using a dispersive X-ray analyzer (EDX), a surface analysis of the cross section of the metal composite hydroxide was performed. As a result, it was confirmed that a portion (tungsten concentrated layer) where tungsten was concentrated and present was formed on the surface layer of the metal composite hydroxide, and that the thickness was 3 to 8 m.

  The tap density was measured using a shaking specific gravity measuring device (KRS-409, manufactured by Kuramochi Kagaku Seisakusho Co., Ltd.) after filling the obtained metal composite hydroxide into a 20 ml graduated cylinder. The measurement was performed after densely filling by a method in which free fall from a height of 2 cm was repeated 500 times. Table 1 shows the evaluation results.

(C) Preparation of Positive Electrode Active Material The metal composite hydroxide obtained as described above was shaken with a shaker mixer (TURBULA Type T2C manufactured by Willy & Bakkofen (WAB) Co., Ltd.) so that Li / Me became 1.14. ) Was thoroughly mixed with lithium carbonate to obtain a lithium mixture.

  The lithium mixture is heated to 900 ° C. in a stream of air (oxygen concentration: 21% by volume) at a rate of 2.52.5 ° C./min and held at this temperature for 4 hours for firing and cooling. Cooled to room temperature at a rate of about 4 ° C / min. The positive electrode active material thus obtained had agglomeration or slight sintering. For this reason, this positive electrode active material was crushed, and the average particle size and the particle size distribution were adjusted.

(D) Evaluation of Positive Electrode Active Material According to an analysis using an ICP emission spectrometer, this positive electrode active material was represented by the general formula: Li _1.14 Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 W ₀ It was confirmed that the compound was represented by _0.005 O ₂ . In addition, the average particle size of the lithium metal composite oxide is measured using a laser light diffraction / scattering particle size analyzer, and d10 and d90 are measured, which is an index indicating the spread of the particle size distribution [(d90-d10). / MV] was calculated. As a result, it was confirmed that the lithium metal composite oxide had an average particle size of 5.3 μm, [(d90−d10) / MV] was 0.43, and the d50 ratio was 1.04.

  The crystallite diameter of the (003) plane was measured using an X-ray diffractometer (X @ Pert PRO, manufactured by Spectris Co., Ltd.) and found to be 1,433 (143.3 nm).

  In addition, in order to confirm the distribution of tungsten in the lithium metal composite oxide using a scanning transmission electron microscope, a surface analysis of the cross section of the lithium metal composite oxide was performed using an energy dispersive X-ray analyzer (EDX). . As a result, it was confirmed that in the lithium metal composite oxide, tungsten was largely contained in the surface layer of the primary particles near the surface of the secondary particles and in the grain boundary between the primary particles.

  The tap density was evaluated under the same conditions as for the metal composite hydroxide, and the BET specific surface area was evaluated using a specific surface area measuring device (Mount Co., Ltd., Maxsorb 1200 series) employing a flow method-nitrogen gas adsorption method. did. The evaluation results are shown in Table 2.

(E) Production of Secondary Battery FIG. 7 is a diagram showing a 2032 type coin battery CBA used for evaluation of battery characteristics. Hereinafter, a method for manufacturing a secondary battery will be described with reference to FIGS.

  The obtained positive electrode active material: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg were mixed and press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. By drying at 12 ° C. for 12 hours, a positive electrode PE was produced.

Next, using this positive electrode PE, a 2032 type coin battery CBA was produced in a glove box in an Ar atmosphere where the dew point was controlled at -80 ° C. For the negative electrode NE of this 2032 type coin battery, lithium metal having a diameter of 17 mm and a thickness of 1 mm is used, and an electrolyte such as ethylene carbonate (EC) and diethyl carbonate (DEC) using 1 M LiClO ₄ as a supporting electrolyte is used. A mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. A 25 μm-thick polyethylene porous film was used as the separator SE. Note that the 2032 type coin battery CBA has a gasket GA and is assembled into a coin-shaped battery with the positive electrode can PC and the negative electrode can NC.

(F) Battery evaluation [resistance]
Using the coin battery CBA assembled above, the resistance value was measured by the AC impedance method at an SOC of 20%, and the relative value based on Comparative Example 1 was calculated as Ref. Was calculated as the resistance value. Table 2 shows the results.

(Examples 2 to 8)
As shown in Table 1, a metal composite hydroxide was obtained under the same conditions as in Example 1 except that the timing (addition time) of the aqueous solution containing tungsten during grain growth was changed. Table 1 shows the evaluation results of the obtained metal composite hydroxides.

  Further, the metal composite hydroxide obtained in Examples 2 to 8 using an energy dispersive X-ray analyzer (EDX) mounted on a scanning transmission electron microscope (HD-2300A, manufactured by Hitachi High-Technologies Corporation). Was analyzed, and the obtained distribution of W was analyzed. As a result, in the metal composite hydroxides obtained in Examples 2 to 8, a portion (tungsten-enriched layer) where tungsten is concentrated and present on the surface layer of the secondary particles is detected, and the thickness is 20 nm or more and 160 nm. It was confirmed that:

  Next, a positive electrode active material and a secondary battery were obtained under the same conditions as in Example 1 except that the obtained metal composite hydroxide was used as a precursor. Table 2 shows the evaluation results of the obtained metal composite hydroxide and the positive electrode active material. Further, the lithium metal composite oxide obtained in Examples 2 to 8 was obtained by using an energy dispersive X-ray analyzer (EDX) mounted on a scanning transmission electron microscope (HD-2300A, manufactured by Hitachi High-Technologies Corporation). Was analyzed, and the obtained distribution of W was analyzed. As a result, it was confirmed that the lithium metal composite oxides obtained in Examples 2 to 8 had a large amount of tungsten in the surface layer of the primary particles near the surface of the secondary particles and in the grain boundaries between the primary particles. Was done.

(Comparative Example 1)
A metal composite hydroxide was obtained under the same conditions as in Example 1 except that the tungsten compound was added from the start of the particle growth step (the addition range was 100%). Table 1 shows the evaluation results of the obtained metal composite hydroxides. Next, a cathode active material and a secondary battery were manufactured under the same conditions as in Example 1 except that the obtained metal composite hydroxide was used as a precursor. Tables 1 and 2 show the evaluation results of the obtained positive electrode active material and the secondary battery.

(Comparative Example 2)
The use of a metal composite hydroxide containing no tungsten (Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 (OH) ₂ ) and the mixing of the metal composite hydroxide with lithium carbonate And lithium oxide was added and mixed to obtain a lithium mixture (external addition). The following procedure was performed under the same conditions as in Example 1 under the same conditions as in the positive electrode active material (Li _1.14 Ni _0.38 Mn). _0.30 Co _0.32 Zr _0.002 W _0.005 O ₂ ) and a secondary battery. Tables 1 and 2 show the evaluation results of the obtained positive electrode active material and the secondary battery.

(Comparative Example 3)
In the crystallization step, a metal composite hydroxide, a positive electrode active material, and a secondary battery were produced under the same conditions as in Example 1 except that the aqueous solution of sodium tungstate was not supplied in the second crystallization step. Tables 1 and 2 show the evaluation results of the obtained metal composite hydroxide, positive electrode active material, and secondary battery.

(Evaluation results)
It was confirmed that the metal composite hydroxide obtained in the example formed a tungsten concentrated layer on the surface. Further, the positive electrode active material obtained in the example has a larger crystallite diameter as compared with Comparative Example 1 in which tungsten was added in the entire crystallization step, and when used as a positive electrode of a secondary battery. , Low positive electrode resistance (resistance value).

  In addition, the metal composite hydroxides obtained in Examples 1 to 6 were formed with a tungsten-enriched layer having a thickness of 100 nm or less, and the positive electrode active materials obtained using these metal composite hydroxides as precursors were: Compared to Comparative Example 2 in which a tungsten compound was externally added, the compound had a larger crystallite diameter and exhibited a lower resistance value when used as a positive electrode of a secondary battery.

  On the other hand, the positive electrode active material obtained in Comparative Example 3 without addition of tungsten has a relatively large crystallite diameter as compared with the other Examples and Comparative Examples in which tungsten is added, but is used as a positive electrode of a secondary battery. The results showed that the resistance was large and the output characteristics were inferior.

DESCRIPTION OF SYMBOLS 10 ... Metal composite hydroxide 1 ... Primary particle 2 ... Secondary particle 3 ... Tungsten concentrated layer 20 ... Lithium metal composite oxide 21 ... Primary particle 22 ... Secondary particle 23 ... Compound containing tungsten and lithium 24 ... Void 25 ... Hollow portion 26 Space portion CBA Coin battery CA Case PC Positive electrode can NC Negative electrode can GA Gasket PE Positive electrode NE Negative electrode SE Separator

Claims (15)

It contains nickel, manganese, and tungsten, optionally cobalt, and the element M, and the atomic ratio of each metal element is Ni: Mn: Co: W: M = x: y: z: a: b (x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0. 1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta). So,
A first raw material aqueous solution containing the metal element and an ammonium ion supplier are supplied to the reaction tank, the pH of the reaction aqueous solution in the reaction tank is adjusted, and the crystallization reaction is performed, whereby the first metal A first crystallization step of obtaining composite hydroxide particles;
A reaction solution containing the first metal composite hydroxide particles is supplied with a second raw material aqueous solution containing the metal element and containing more tungsten than the first raw material aqueous solution, and an ammonium ion donor. Then, by adjusting the pH of the reaction aqueous solution and performing a crystallization reaction, a tungsten-concentrated layer is formed on the surface of the first metal composite hydroxide particle, and the second metal composite hydroxide particle is formed. And a second crystallization step,
The metal composite hydroxide obtained after the second crystallization step has a tap density of 1.7 g / cm ³ or more and 2.3 g / cm ³ or less and is a solid formed by aggregating a plurality of primary particles. Including secondary particles having a structure,
A method for producing a metal composite hydroxide. The first crystallization step includes a nucleation step of performing nucleation and a particle growth step of performing particle growth, and the second crystallization step performs particle growth following the particle growth step. Including
The first crystallization step and the second crystallization step are performed in a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less,
The particle growth in the first crystallization step and the second crystallization step adjusts the pH of the reaction aqueous solution to be lower than the pH value of the reaction aqueous solution in the nucleation step. 2. The method for producing a metal composite hydroxide according to 1.   The metal element in the first raw material aqueous solution is in a range of 50% by mass or more and 95% by mass or less based on the total amount of metals added in the first crystallization step and the second crystallization step. 3. The method for producing a metal composite hydroxide according to claim 1, wherein the second raw material aqueous solution is supplied in the second crystallization step after the supply to the reaction tank. 4.   The second crystallization step includes forming the tungsten-enriched layer so as to have a thickness of 100 nm or less in a direction from the surface of the second metal composite hydroxide particle toward the center. A method for producing a metal composite hydroxide according to any one of claims 1 to 3.   The addition of the second aqueous solution of the raw material in the second crystallization step is performed at a point in time when 50% or more and 95% or less have elapsed in the first and second crystallization steps with respect to the entire time during which the particle growth is performed. The method for producing a metal composite hydroxide according to any one of claims 1 to 4, which is performed.   The method according to any one of claims 1 to 5, wherein the supply of the second raw material aqueous solution is performed by separately supplying the first raw material aqueous solution and an aqueous solution containing tungsten to the reaction aqueous solution. A method for producing a metal composite hydroxide.   The method for producing a metal composite hydroxide according to claim 6, wherein the concentration of tungsten in the aqueous solution containing tungsten is 18% by mass or more based on the whole aqueous solution containing tungsten. Nickel, manganese, and tungsten, and optionally cobalt and the element M, and the atomic ratio of each metal element is Ni: Mn: Co: W: M = x: y: z: a : B (x + y + z = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1 , M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta),
Having a tungsten concentration layer on the surface, and
Including a secondary particle having a tap density of 1.7 g / cm ³ or less and 2.3 g / cm ³ or more, and having a solid structure in which a plurality of primary particles are aggregated;
Metal composite hydroxide.   The metal composite hydroxide according to claim 8, wherein the average thickness of the tungsten concentration layer is 100 nm or less.   The volume average particle diameter (MV) is 4.0 μm or more and 9.0 μm or less, and [(d90−d10) / MV], which is an index indicating the spread of the particle size distribution, is 0.65 or less. Or the metal composite hydroxide according to claim 9. A metal composite hydroxide obtained by the production method according to any one of claims 1 to 7, and at least one of a metal composite oxide obtained by heat-treating the metal composite hydroxide, and a lithium compound. Mixing to obtain a lithium mixture;
Baking the lithium mixture to obtain a lithium metal composite oxide, comprising: a step of producing a positive electrode active material for a lithium ion secondary battery.   The value of d50 of the positive electrode active material / d50 of the metal composite hydroxide, which is an index indicating the degree of aggregation of the lithium metal composite oxide particles, is 0.95 or more and 1.05 or less. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 11, which is adjusted. It contains lithium, nickel, manganese, and tungsten, and optionally cobalt and the element M, and the atomic ratio of each metal element is Li: Ni: Co: Mn: W: M = 1 + u: x: y: z: a: b (x + y + z = 1, -0.05≤u≤0.50, 0.3≤x≤0.95, 0.05≤y≤0.55, 0≤z≤0.4 , 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1, M is at least one selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta Element) contains a lithium metal composite oxide represented by
The lithium metal composite oxide includes secondary particles having a solid structure in which a plurality of primary particles are aggregated,
The surface layer of the primary particles present on the surface or inside of the secondary particles, and, on the grain boundaries between the primary particles, a compound containing tungsten and lithium is concentrated and present,
The tap density is 1.8 g / cm ³ or less, 2.4 g / cm ³ or more, and
A BET specific surface area of 0.6 m ² / g or more and 1.2 m ² / g or less;
A positive electrode active material for lithium ion secondary batteries.   14. The positive electrode active material for a lithium ion secondary battery according to claim 13, wherein the (003) plane crystallite diameter obtained by powder X-ray diffraction measurement is 120 nm or more.   A positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode active material for a lithium ion secondary battery according to claim 13 or 14 is used as a positive electrode material of the positive electrode. battery.