JP2015118892A - Positive electrode active material for lithium secondary batteries, precursor of positive electrode active material for lithium secondary batteries, lithium secondary battery electrode, lithium secondary battery, and battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material for lithium secondary batteries large in discharge capacity, and superior in input and output characteristics; and a lithium secondary battery arranged by such a positive electrode active material.SOLUTION: A positive electrode active material for lithium secondary batteries comprises: a lithium transition metal complex oxide having α-NaFeOstructure. In the lithium transition metal complex oxide, the transition metal(Me) includes Co, Ni and Mn; and the mole ratio Li/Me of lithium (Li) to the transition metal is larger than one. The lithium transition metal complex oxide includes Na and K; the content of Na and K is 1000-20000 ppm in total.

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery, a precursor of the positive electrode active material, an electrode for a lithium secondary battery containing the positive electrode active material, a lithium secondary battery including the electrode, and a battery module.

  Nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries, in particular lithium secondary batteries, have been used as power sources for mobile devices such as notebook computers and mobile phones, but in recent years, electric vehicles (EV) and hybrids have been used. It is also used as a power source for automobiles such as automobiles (HEV) and plug-in hybrid automobiles (PHEV).

In conventional nonaqueous electrolyte secondary batteries, LiCoO ₂ has been mainly used as a positive electrode active material. However, the discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g. As a positive electrode active material for a lithium secondary battery, a solid solution of LiCoO ₂ and another compound is known. Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 <x ≦ 1/2) having a α-NaFeO ₂ type crystal structure and being a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ Was announced in 2001. LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , which are examples of the solid solution, have a discharge capacity of 150 to 180 mAh / g, and are charged and discharged. Excellent cycle performance.

For the so-called “LiMeO ₂ type” active material as described above, the composition ratio Li / Me of lithium (Li) with respect to the ratio of transition metal (Me) is larger than 1, for example, Li / Me is 1.25 to 1.6. There are known so-called “lithium-rich” active materials (see, for example, Patent Documents 1 and 2). Such a material can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). Here, when the composition ratio Li / Me of lithium (Li) with respect to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), and thus, for example, Li / Me is 1.5. In this case, α = 0.2.

Patent Documents 1 and 2 describe active materials as described above. Further, in these patent documents, a positive electrode potential range of 4.3 V (vs. Li ^/ Li ⁺ ) and 4.8 V or less (vs. Li ^/ Li ⁺ ) is described as a battery manufacturing method using the active material. In this case, the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less. Or even if it is a case where the charge method which is less than 4.4V (vs.Li/Li <^+> ) is employ | adopted, it describes that the battery which can obtain the discharge capacity of 200 mAh / g or more can be manufactured.

Thus, unlike the so-called “LiMeO ₂ type” positive electrode active material, the so-called “lithium-excess type” positive electrode active material has a relatively high potential exceeding 4.3 V, particularly 4.4 V or more, at least in the first charge. A characteristic is that a high discharge capacity can be obtained by carrying out the process to a potential of.

  On the other hand, it is also known that a positive electrode active material for a lithium secondary battery including a lithium transition metal composite oxide composed of Li and a transition metal element (Co, Ni, Mn, etc.) contains an alkali component (Patent Document) 3-6).

In Patent Document 3, “the following general formula (1):
Li _(x) Ni _(1-ab) Co _(a) Mn _(b) O ₂ (1)
(Wherein x is 0.98 ≦ x ≦ 1.20, a is 0 <a ≦ 0.5, and b is 0 <b ≦ 0.5.)
The residual alkali amount present in the surface layer portion of the primary particles is 4000 ppm or less, and the amount of sulfate radicals present in the surface layer portion of the primary particles is 500 to 11000 ppm. A positive electrode active material for a lithium secondary battery. (Claim 1),
“A firing raw material mixture containing a lithium compound, a nickel compound, a cobalt compound, and a manganese compound is fired at 950 ° C. or less, and the following general formula (1):
Li _(x) Ni _(1-ab) Co _(a) Mn _(b) O ₂ (1)
(Wherein x is 0.98 ≦ x ≦ 1.20, a is 0 <a ≦ 0.5, and b is 0 <b ≦ 0.5.)
A first firing step for obtaining a lithium composite oxide represented by:
A sulfate aqueous solution treatment step of washing the lithium composite oxide represented by the general formula (1) obtained in the first firing step and contacting with a sulfate aqueous solution to obtain a sulfate aqueous solution treated product;
A second firing step of firing the sulfate aqueous solution treated product at 400 to 800 ° C. to obtain a positive electrode active material for a lithium secondary battery;
A positive electrode active material for a lithium secondary battery, characterized in that (Claim 4) is described. An object of the present invention is to provide a lithium nickel cobalt manganese based composite oxide having a small amount of residual alkali present in the surface layer portion of primary particles and having excellent cycle characteristics (paragraph [0011]). Is.

  Patent Document 3 states that “the remaining alkali amount present in the surface layer portion of the primary particles of the positive electrode active material is 5 g of a sample and 100 g of ultrapure water is measured in a beaker at 25 ° C. using a magnetic stirrer. The dispersion was then filtered, and 30 ml of the filtrate was titrated with 0.1N HCl with an automatic titrator (model COMMITITE-2500), and the remaining alkali amount present in the sample (A value obtained by converting the amount of lithium into lithium carbonate) was calculated. "(Paragraph [0103]).

In Patent Document 4, “in a positive electrode active material used for a non-aqueous electrolyte secondary battery,
The positive electrode active material is a lithium-nickel-cobalt-manganese composite oxide,
The lithium-nickel-cobalt-manganese composite oxide contains tungsten and niobium. (Claim 1), "The water-soluble alkali component contained in the lithium-nickel-cobalt-manganese composite oxide is 0.2 wt% or less. The positive electrode active material according to claim 4 "(claim 4) is described. The present invention is intended to provide a positive electrode active material having excellent output characteristics and low gas generation and a battery using the same (paragraph [0009]).

Patent Document 4 states that “50 ml of pure water is added to 10 g of the positive electrode active material, stirred for 1 hour, and then filtered. After the filtrate is diluted to an appropriate concentration, phenolphthalein is added as an indicator, and H ₂ SO ₄ solution performs titrated with .H ₂ SO ₄ solution alkali content neutralized with assumes that all lithium hydroxide, from the titration results, obtains the weight ratio of the lithium hydroxide for the positive electrode active material. this value Is water-soluble alkali ”(paragraph [0056]).

Patent Document 5 discloses “an active material for a lithium secondary battery including a solid solution of a sodium-containing lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the chemical composition formula of the solid solution is Li _{1 + x−. y} Na _y Co _a Ni _b Mn _c O _{2 + d} (0 <y ≦ 0.1, 0.4 ≦ c ≦ 0.7, x + a + b + c = 1, 0.1 ≦ x ≦ 0.25, −0.2 ≦ d ≦ 0.2) and an X-ray diffraction pattern that can be assigned to a hexagonal crystal (space group P3 ₁ 12), and the half width of the diffraction peak on the (003) plane at the Miller index hkl is 0.30 °. And a half-width of the diffraction peak of the (114) plane is 0.50 ° or less. ”(Invention 1) According to the invention, “the initial efficiency is high and the discharge capacity is large. Among them we can provide a lithium secondary battery active material the discharge capacity is larger at low temperature "(paragraph [0038]) that has been shown. Moreover, as an Example, it is shown by the method using a coprecipitation hydroxide precursor that content (value of said y) of Na shall be 0.01-0.1 mol (refer Table 1). .

  Patent Document 6 states that “a lithium compound, a Ni metal or a compound thereof, and a metal or a compound thereof composed of one or more transition metal elements selected from the group consisting of Mn, Co, Ti, Cr and Fe are mixed. A method for producing a lithium composite metal oxide, characterized in that the obtained raw material mixture is fired at 630 ° C. or higher in an atmosphere having a carbon dioxide concentration of 1% by volume to 15% by volume. ”(Claim 1) The raw material mixture is one or more selected from the group consisting of carbonates, sulfates and chlorides of one or more elements selected from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba. 7. A method for producing a lithium composite metal oxide according to any one of claims 1 to 6, further comprising a reaction accelerator composed of a compound.

Patent Document 6 states that “in the firing, the raw material mixture may contain a reaction accelerator. Specific examples of the reaction accelerator include NaCl, KCl, RbCl, CsCl, and CaCl _2. , MgCl ₂ , SrCl ₂ , BaCl _2, NH ₄ Cl and other chlorides, Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , MgCO ₃ , SrCO ₃ and BaCO ₃ Carbonates, sulfates such as K ₂ SO ₄ and Na ₂ SO ₄ and fluorides such as NaF, KF and NH ₄ F. Among these, Na, K, Rb, Cs, Ca, Mg are preferable. The chloride, carbonate or sulfate of at least one element selected from the group consisting of Sr and Ba can be mentioned, and is more preferably carbonate or sulfate, and is also included in the raw material mixture. Other Transition metal element moves metal compound, in the case of Mn and Fe, as particularly preferable examples of the reaction accelerator can be preferred. Accelerant _{carbonates, NaCl, KCl, Na 2 CO} 3, K ₂ CO ₃ , Na ₂ SO ₄ , K ₂ SO ₄ , Na ₂ CO ₃ , K ₂ CO ₃ , Na ₂ SO ₄ , K ₂ SO ₄ are more preferable, and K ₂ CO ₃ is particularly preferable. Two or more kinds of reaction accelerators can be used in combination.The raw material mixture contains a reaction accelerator, thereby improving the reactivity during firing of the raw material mixture and adjusting the BET specific surface area of the resulting lithium composite metal oxide. The method of adding the reaction accelerator to the raw material mixture is not particularly limited, but when producing the raw material mixture, the composite transition metal compound is synthesized by liquid phase mixing as described above. In case, dry matter and Richi In addition, when by-product salts (for example, KCl, K ₂ SO ₄ ) generated during liquid phase mixing remain in the composite transition metal compound, these by-products are mixed. A raw salt may be used as a reaction accelerator, and in this case, a deficiency of the reaction accelerator may be added at the time of mixing the dried product and the lithium compound. It may remain in the oxide, or may be removed by washing, evaporation, etc. The mixing ratio of the raw material mixture and the reaction accelerator is 0.1 parts by weight with respect to 100 parts by weight of the raw material mixture. The amount is preferably 100 parts by weight or less and more preferably 1.0 part by weight or more and 40 parts by weight or less. (Paragraph [0038]).

WO2012 / 091015 WO2013 / 084923 JP 2011-1224086 A JP 2009-140787 A International Publication WO2012 / 039413 Japanese Unexamined Patent Publication No. 2012-126631

The discharge capacity of the so-called “lithium-rich” active material described above is generally greater than the so-called “LiMeO ₂ type” active material. However, in recent years, lithium secondary batteries used in the automobile field such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles have been required to have active materials having a large discharge capacity and excellent input / output characteristics. An excellent output characteristic leads to an excellent acceleration performance of the automobile, and an excellent input characteristic leads to an excellent ability to accept regenerative electric power during deceleration of the automobile. Patent Documents 1 to 6 do not disclose an active material having a large discharge capacity and excellent input / output characteristics. The present invention has been made in view of the above problems, and provides a positive electrode active material for a lithium secondary battery having a large discharge capacity and excellent input / output characteristics, and a lithium secondary battery using the positive electrode active material. This is the issue.

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

In the present invention, in order to solve the above problems, the following means are adopted.
(1) A positive electrode active material for a lithium secondary battery containing a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the lithium transition metal composite oxide has Co, Ni and transition metals (Me) A positive electrode active material for a lithium secondary battery, comprising Mn, wherein the molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1, and Na and K are contained.
(2) The positive electrode active material for a lithium secondary battery according to (1), wherein a molar ratio Li / Me of lithium (Li) to the transition metal is larger than 1.2 and smaller than 1.6.
(3) The positive electrode active material for a lithium secondary battery according to (1) or (2), wherein the contents of Na and K are 1000 ppm or more and 20000 ppm or less in total.
(4) A carbonate precursor of a positive electrode active material for a lithium secondary battery, represented by MeCO ₃ (Me is a transition metal containing Co, Ni, and Mn) and containing Na and K.
(5) The electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries in any one of said (1)-(3).
(6) A lithium secondary battery comprising the lithium secondary battery electrode of (5).
(7) A battery module configured by assembling a plurality of the lithium secondary batteries of (6).

  According to the present invention, it is possible to provide a lithium secondary battery having a large discharge capacity and an excellent input / output characteristic including a positive electrode active material containing a novel lithium transition metal composite oxide.

Schematic showing a battery module constructed by assembling a plurality of lithium secondary batteries of the present invention Schematic showing a car equipped with a battery module

The composition of the lithium transition metal composite oxide contained in the active material for a lithium secondary battery according to the present invention is that the transition metal (Me) contains Co, Ni and Mn from the viewpoint that a high discharge capacity can be obtained. The lithium / Li molar ratio Li / Me is greater than 1, typically as Li _{1 + α} Me _1-α O ₂ (α> 0), so-called “lithium-rich” type .

In the present invention, in order to obtain a lithium secondary battery having a large discharge capacity, the molar ratio Li / Me of Li to the transition metal element Me is set to be larger than 1.2 and smaller than 1.6. In the formula Li _{1 + α} Me _1-α O ₂ , it is preferable to satisfy 1.2 <(1 + α) / (1-α) <1.6. Among these, from the viewpoint of obtaining a lithium secondary battery having a particularly large discharge capacity and excellent initial efficiency and high-rate discharge performance, the one having the Li / Me of 1.25 to 1.45 should be selected. Is more preferable.

  Further, the molar ratio Co / Me of Co to the transition metal element Me is preferably 0.05 to 0.40 in that a lithium secondary battery having a large discharge capacity and excellent initial charge / discharge efficiency can be obtained. 0.10 to 0.30 is more preferable.

In order to improve the initial efficiency and high rate discharge performance of the lithium secondary battery, the molar ratio Mn / Mn of the transition metal element Me is preferably 0.5 or more. In a so-called “LiMeO ₂ type” active material, when the molar ratio Mn / Me is 0.5 or more, the structure changes to a spinel type when charged and does not have a structure attributed to the α-NaFeO ₂ structure. In contrast, there was a problem as an active material for a lithium secondary battery, whereas the “lithium-excess type” active material had α-NaFeO ₂ even when charged with a molar ratio Mn / Me of 0.5 or more. Since the structure can be maintained, the structure having a molar ratio Mn / Me of 0.5 or more characterizes a so-called “lithium-rich” active material. The molar ratio Mn / Me is more preferably 0.5 to 0.75.

In the present invention, the transition metal (Me) contains Co, Ni and Mn, and the lithium (Li) molar ratio Li / Me to the transition metal is greater than 1, that is, the lithium transition metal composite oxide, that is, the above composition formula A lithium transition metal composite oxide represented by Li _{1 + α} Me _1-α O ₂ (Me is a transition metal containing Co, Ni and Mn, α> 0) includes Na and K. The present inventor has found that the direct current internal resistance (SOC 30% DCR) in a state where the charging depth is shallow (30%) is significantly reduced by using Na and K together. A smaller performance value means better input / output characteristics. This is an important characteristic required for batteries for electric vehicles. When only Na and only K are included, the discharge capacity is improved as in the comparative example described later, but the improvement of the input / output characteristics is small.

  The total content of Na and K in the lithium transition metal composite oxide is preferably 1000 ppm or more and 20000 ppm or less, and more preferably 2000 ppm or more and 17000 ppm or less. When the contents of Na and K are less than 1000 ppm, the discharge capacity is not increased and the input / output characteristics are not sufficiently improved, and the initial efficiency is also lowered. When it exceeds 20000 ppm, the increase in discharge capacity and the improvement of input / output characteristics are saturated.

  In order to contain Na and K in the lithium transition metal composite oxide, a sodium compound such as sodium carbonate and / or a potassium compound such as potassium carbonate is used as a neutralizing agent in the step of preparing a carbonate precursor described later. Then, it is possible to adopt a method in which Na and / or K is left in the washing step, and a sodium compound such as sodium carbonate and / or a potassium compound such as potassium carbonate is added in the subsequent baking step.

In the present invention, the carbonate precursor of the positive electrode active material for a lithium secondary battery is represented by MeCO ₃ (Me is a transition metal containing Co, Ni, and Mn), and contains Na and K. it can.
It is presumed that residual Na and K in the neutralization / washing process during the preparation of the precursor act as a primary particle growth inhibitor in the so-called “lithium-excess type” lithium transition metal composite oxide firing process, It is considered that the electrode characteristics of a lithium secondary battery containing this lithium transition metal composite oxide as a positive electrode active material are improved.

  In order to adjust the Na and K contents to 3000 ppm or more, Na and K are left in the carbonate precursor as described above, and sodium compounds such as sodium carbonate and / or potassium carbonate are used in the subsequent firing step. It is preferable to employ a method of adding a potassium compound such as. A method of adding a sodium compound such as sodium carbonate and a potassium compound such as potassium carbonate in the subsequent firing step without leaving Na and K in the carbonate precursor can also be employed.

  The lithium transition metal composite oxide according to the present invention is represented by the above general formula, and is essentially a composite oxide composed of Li, Co, Ni and Mn, and contains a small amount of Na and K. However, as long as the effects of the present invention are not impaired, alkali metals other than Na and K, alkaline earth metals such as Mg and Ca, transition metals typified by 3d transition metals such as Fe and Zn, etc. It is not excluded to contain other metals.

The lithium transition metal composite oxide according to the present invention has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charging and discharging) is attributed to the space group P3 ₁ 12 or R3-m. Among these, those belonging to the space group P3 ₁ 12 are superlattice peaks (Li [Li _1/3 Mn _2/3 ] O ₂ near 2θ = 21 ° on the X-ray diffraction diagram using the CuKα tube. The peak observed in the monoclinic type) is confirmed. However, when charging is performed once and Li in the crystal is desorbed, the symmetry of the crystal changes, whereby the superlattice peak disappears and the lithium transition metal composite oxide belongs to the space group R3-m. Will come to be. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” should be represented by adding a bar “-” on “3” of “R3m”.

The lithium transition metal composite oxide according to the present invention is assigned to either the hexagonal space group P3 ₁ 12 or R3-m, and 2θ = 18.6 ° ± 1 on an X-ray diffraction diagram using a CuKα tube. The half-value width of the diffraction peak at 0 ° is 0.20 ° to 0.27 ° or / and the half-value width of the diffraction peak at 2θ = 44.1 ° ± 1 ° is 0.26 ° to 0.39 °. preferable. By doing so, it becomes possible to increase the discharge capacity of the positive electrode active material. The diffraction peak of 2θ = 18.6 ° ± 1 ° is a (003) plane in space group _P3 1 12 and R3-m in Miller indices hkl, the diffraction peak of 2θ = 44.1 ° ± 1 °, the The space group P3 ₁ 12 is indexed on the (114) plane, and the space group R3-m is indexed on the (104) plane.

Moreover, it is preferable that a lithium transition metal complex oxide does not change a structure during overcharge. This can be confirmed by being observed as a single phase belonging to the space group R3-m on the X-ray diffraction diagram when electrochemically oxidized to a potential of 5.0 V (vs. Li ^/ Li ⁺ ). Thereby, the lithium secondary battery excellent in charge / discharge cycle performance can be obtained.

Further, the lithium transition metal composite oxide has an oxygen positional parameter obtained from a crystal structure analysis by the Rietveld method based on the X-ray diffraction pattern, which is 0.262 or less at the end of the discharge of 2 V (vs. Li ^/ Li ⁺ ). It is preferable that it is 0.267 or more at the end of charge of 4.3 V (vs. Li ^/ Li ⁺ ) after the charge conversion. Thereby, a lithium secondary battery excellent in high rate discharge performance can be obtained. Note that the oxygen positional parameter is Me (transition metal) spatial coordinates (0, 0, 0) for the α-NaFeO ₂ type crystal structure of the lithium transition metal composite oxide belonging to the space group R3-m, This is the value of z when the spatial coordinates of Li (lithium) are defined as (0, 0, 1/2) and the spatial coordinates of O (oxygen) are defined as (0, 0, z). In other words, the oxygen position parameter is a relative index indicating how far the O (oxygen) position is from the Me (transition metal) position (see Patent Documents 1 and 2).

  In the present invention, the positive electrode active material for a lithium secondary battery and the carbonate precursor thereof preferably have a 50% particle size (D50) of 8 to 10 μm in the particle size distribution measurement. When producing a lithium transition metal composite oxide from a hydroxide precursor, excellent performance cannot be obtained unless the particle size is controlled to be smaller, but by producing from a carbonate precursor, 50% in the particle size distribution measurement. Even if the particle diameter (D50) is 8 to 10 μm, an active material having a discharge capacity (0.1 C capa) of 200 mAh / g or more can be obtained.

BET specific surface area of the positive electrode active material according to the present invention, the initial efficiency, in order to obtain a lithium secondary battery having excellent high rate discharge performance, preferably at least ^{1m 2 / g, 2~7m 2 /} g is more preferable.
Further, the tap density is preferably 1.25 g / cc or more, more preferably 1.7 g / cc or more, in order to obtain a lithium secondary battery excellent in high rate discharge performance.

In addition, the active material via the carbonate precursor has a peak differential pore volume of 0.85 mm ³ / (g · nm) or more in the pore region of ^{30 to} 50 nm, whereas the hydroxide precursor The active material that has passed through has a peak differential pore volume of about 0.50 mm ³ / (g · nm) in the pore region of ^{30 to} 50 nm, and the differential peak becomes a pore region of about 60 nm.

The lithium transition metal composite oxide according to the present invention has a pore diameter in the range of 30 to 40 nm where the differential pore volume obtained by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method shows a maximum value. The pore volume is 0.85 mm ³ / (g · nm) or more. When the peak differential pore volume is 0.85 mm ³ / (g · nm) or more, a lithium secondary battery having excellent initial efficiency can be obtained. Further, by setting the peak differential pore volume to 1.76 mm ³ / (g · nm) or less, it is possible to obtain a lithium secondary battery having particularly excellent discharge capacity in addition to the initial efficiency. The volume is preferably 0.85 to 1.76 mm ³ / (g · nm).

Next, a method for producing the active material for a lithium secondary battery of the present invention will be described.
The active material for a lithium secondary battery of the present invention basically includes a raw material containing a metal element (Li, Mn, Co, Ni) constituting the active material according to the composition of the active material (oxide). It can be obtained by adjusting and baking this. However, with respect to the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li raw material during firing.
In producing an oxide having a desired composition, a so-called “solid phase method” in which salts of Li, Co, Ni, and Mn are mixed and fired, or Co, Ni, and Mn were previously present in one particle. A “coprecipitation method” is known in which a coprecipitation precursor is prepared, and a Li salt is mixed and fired therein. In the synthesis process by the “solid phase method”, especially Mn is difficult to uniformly dissolve in Co and Ni, so it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In literatures and the like, many attempts have been made to dissolve Mn in a part of Ni or Co (LiNi _1-x Mn _x O ₂ etc.) by solid phase method, but the “coprecipitation method” is selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the “coprecipitation method” is employed in the examples described later.

When preparing a coprecipitation precursor, Mn is easily oxidized among Co, Ni and Mn, and it is not easy to prepare a coprecipitation precursor in which Co, Ni and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Co, Ni and Mn tends to be insufficient. In particular, in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is particularly important to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used. Among these, when preparing a coprecipitated carbonate precursor as in the examples described later, it is preferable to employ carbon dioxide as a gas not containing oxygen because an environment in which carbonate is more easily generated is provided. .

Although the pH in the step of producing a precursor by co-precipitation of a compound containing Co, Ni and Mn in a solution is not limited, an attempt is made to prepare the co-precipitation precursor as a co-precipitation carbonate precursor. When it does, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cm ³ or more, and high-rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by setting the pH to 8.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

  The coprecipitation precursor is preferably a compound in which Mn, Ni, and Co are uniformly mixed. In the present invention, in order to obtain an active material for a lithium secondary battery having a large discharge capacity, the coprecipitation precursor is preferably a carbonate. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, a higher density active material can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

  The raw materials for the coprecipitation precursor include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate as the Ni compound. As examples of the Co compound, cobalt sulfate, cobalt nitrate, cobalt acetate, and the like can be given as examples.

  In the present invention, a reaction crystallization method is employed in which a raw material aqueous solution of the coprecipitation precursor is supplied dropwise to a reaction tank maintaining alkalinity to obtain a coprecipitation carbonate precursor. Here, in order to produce a coprecipitated carbonate precursor containing Na, a sodium compound such as sodium carbonate is used as a neutralizing agent, but sodium carbonate or a mixture of sodium carbonate and lithium carbonate is used. Is preferred. Further, in order to produce a coprecipitated carbonate precursor containing K, a potassium compound such as potassium carbonate is used as a neutralizing agent. In order to produce a coprecipitated carbonate precursor containing Na and K, it is preferable to use a mixture of sodium carbonate and potassium carbonate or a mixture of sodium carbonate, potassium carbonate and lithium carbonate as a neutralizing agent. To produce a coprecipitated carbonate precursor that does not contain Na and K, lithium carbonate can be used as a neutralizing agent.

  The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution in one particle of the coprecipitation precursor to be generated. In particular, Mn is difficult to form a uniform element distribution with Co and Ni, so care must be taken. The preferred dropping rate is influenced by the reaction vessel size, stirring conditions, pH, reaction temperature, etc., but is preferably 30 ml / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 ml / min or less, and most preferably 5 ml / min or less.

  In addition, when a complexing agent is present in the reaction tank and a certain convection condition is applied, the particle rotation and revolution in the stirring tank are promoted by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, the particles grow concentrically in stages while colliding with each other. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

  The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, it is preferably 15 h or less, more preferably 10 h or less, and most preferably 5 h or less.

  Moreover, the preferable stirring duration time for setting D50, which is a particle diameter at which the cumulative volume in the particle size distribution of the secondary particles of the carbonate precursor and the lithium transition metal composite oxide is 50%, to 8 to 10 μm is controlled by the pH. It depends on. For example, when the pH is controlled to 8.3 to 8.9, the stirring duration is preferably 5 to 7 h, and when the pH is controlled to 7.5 to 8.0, the stirring duration is 3 to 3 hours. 5h is preferred.

When the carbonate precursor particles are prepared using a sodium compound such as sodium carbonate and / or a potassium compound such as potassium carbonate as a neutralizing agent, sodium ions attached to the particles in the subsequent washing step and / or Alternatively, potassium ions are removed by washing, but in the present invention, it is preferable to remove by washing under conditions such that Na remains at 1000 ppm or more and / or K remains at 1000 ppm or more. For example, when the produced carbonate precursor is removed by suction filtration, a condition that the number of washings with 200 ml of ion-exchanged water is 5 times can be employed.

The carbonate precursor is preferably dried at 80 ° C. to less than 100 ° C. in an air atmosphere under normal pressure. By drying at 100 ° C. or higher, more water can be removed in a short time, but by drying at 80 ° C. for a long time, an active material having more excellent electrode characteristics can be obtained. Although the reason is not necessarily clear, since the carbonate precursor is a porous body having a specific surface area of 50 to 100 m ² / g, it has a structure that easily adsorbs moisture. Therefore, by drying at a low temperature, a state in which a certain amount of adsorbed water remains in the pores in the state of the precursor is removed from the pores in the firing step of mixing with the Li salt and firing. The invention may be because molten Li can enter the pores so as to replace the adsorbed water, and thereby, an active material having a more uniform composition can be obtained compared with the case of drying at 100 ° C. Have guessed. In addition, although the carbonate precursor obtained by drying at 100 ° C. exhibits a black brown color, the carbonate precursor obtained by drying at 80 ° C. has a skin color, so the precursor Can be distinguished by the color.

Therefore, in order to quantitatively evaluate the difference in the precursors found above, the hues of the respective precursors are measured, and standard colors for paints (JPMA Standard Paint Colors) issued by the Japan Paint Manufacturers Association in accordance with JIS Z 8721. ) Compared with the 2011 F version. For measuring the hue, a color reader CR10 manufactured by Konica Minolta Co., Ltd. was used. According to this measuring method, the value of dL * representing lightness is larger in white and smaller in black. Further, the value of da * representing the hue is larger when red is stronger and smaller when green is stronger (red is weaker). In addition, the value of db * representing the hue becomes larger when yellow is stronger and larger when blue is stronger (yellow is weaker).
The hue of the 100 ° C. dried product (Comparative Example) is in the range reaching the standard color F05-40D in the red direction compared to the standard color F05-20B, and in the white direction compared to the standard color FN-10. It was found to be within the range leading to the standard color FN-25. Among these, it was recognized that the color difference from the hue exhibited by the standard color F05-20B was the smallest.
On the other hand, the hue of the 80 ° C. dried product (Example) is in the range reaching the standard color F19-70F in the white direction as compared with the standard color F19-50F, and is black compared with the standard color F09-80D. It was found that it was in the range reaching the standard color F09-60H in the direction. Especially, it was recognized that the color difference with the hue which standard color F19-50F exhibits is the smallest.
From the above knowledge, the hue of the carbonate precursor is preferably positive in all of dL, da and db as compared with the standard color F05-20B, dL is +5 or more, da is +2 or more, and db is It can be said that +5 or more is more preferable.

  The active material for a lithium secondary battery of the present invention can be suitably prepared by mixing the carbonate precursor and the Li compound and then heat-treating them. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc. However, with respect to the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

  In the present invention, in order to contain Na and K in the lithium transition metal composite oxide, it is preferable that the Na compound and / or K compound is mixed with the carbonate precursor together with the Li compound in the firing step. As the Na compound, sodium carbonate is preferable. As the K compound, potassium carbonate is preferred. The content of Na and K in the carbonate precursor is 3000 ppm or less, but the content of Na and K can be 3000 ppm or more by mixing Na compound and / or K compound.

The firing temperature affects the reversible capacity of the active material.
When the firing temperature is too high, the obtained active material collapses with an oxygen releasing reaction, and in addition to the hexagonal crystal of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is obtained. The defined phase tends to be observed as a phase separation rather than as a solid solution phase. If too many such phase separations are contained, it is not preferable because it leads to a reduction in the reversible capacity of the active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably less than the temperature at which the oxygen release reaction of the active material affects. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range according to the present invention. However, there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to keep it. In particular, it is confirmed that the oxygen release temperature of the precursor shifts to the lower temperature side as the amount of Co contained in the sample increases. As a method for confirming the oxygen release temperature of the active material, a mixture of a coprecipitation precursor and a lithium compound may be subjected to thermogravimetric analysis (DTA-TG measurement) in order to simulate the firing reaction process. In this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the Li component volatilized, and the instrument may be damaged. Therefore, a composition in which crystallization is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance. Goods should be subjected to thermogravimetric analysis.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present invention, the firing temperature is preferably at least 700 ° C. or higher. By sufficiently crystallizing, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
In addition, the inventors have analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the sample synthesized at a temperature up to 750 ° C., strain remains in the lattice, and at a temperature higher than that, It was confirmed that almost all strains could be removed by synthesis. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it is preferable to employ a synthesis temperature (firing temperature) and a Li / Me ratio composition in which the strain amount affecting the lattice constant is 2% or less and the crystallite size is grown to 50 nm or more. all right. Although changes due to expansion and contraction are observed by charging and discharging by molding these as electrodes, it is preferable as an effect that the crystallite size is maintained at 30 nm or more in the charging and discharging process. That is, an active material having a remarkably large reversible capacity can be obtained only by selecting the firing temperature as close as possible to the oxygen release temperature of the active material.

As described above, since the preferable firing temperature varies depending on the oxygen release temperature of the active material, it is generally difficult to set a preferable range of the firing temperature, but the molar ratio Li / Me is 1.2 to 1.6. In this case, the firing temperature is preferably more than 700 to 950 ° C., and more preferably around 800 to 900 ° C. when Li / Me is 1.25 to 1.45.
As described above, the positive electrode active material for a lithium secondary battery according to the present invention is produced.

The negative electrode material is not limited, and any negative electrode material that can deposit or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

  It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained mixed solution is applied on a current collector such as an aluminum foil or a copper foil, or is pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. Is done. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  The nonaqueous electrolyte used for the lithium secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the nonaqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C _{4 H 9) 4 NI, (} C 2 H 5) 4 N-mal _{ate, (C 2 H 5)} 4 N-benzoate, (C 2 H 5) 4 N-phtalate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts of lithium dodecyl benzene sulfonate, and the like. These These ionic compounds can be used alone or in admixture of two or more.

Furthermore, by mixing and using LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The configuration of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, and a flat battery. When the lithium secondary battery of the present invention is used as a power source for an automobile such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV), a battery module (set) having a plurality of lithium secondary batteries is used. Battery).

  As shown in FIG. 1, the battery module 10 includes a plurality (four in the figure) of rectangular power storage units 200. The battery module 10 may further include a charge / discharge control device 100. The figure shows the inside of the housing case 220 through the housing case 220 of the power storage unit 200. The battery module 10 also includes a case for housing the discharge control device 100 and the plurality of power storage units 200, but is omitted from the drawing. The plurality of power storage units 200 are arranged in parallel so that their long side faces each other, and the respective power storage units 200 are connected in parallel. Here, four power storage units 200 are provided, but any number of power storage units 200 may be provided. Further, the shape of the power storage unit 200 is not particularly limited.

  Each power storage unit 200 includes a plurality (six in the figure) of rectangular lithium secondary batteries 210 and a housing case 220 that houses the plurality of lithium secondary batteries 210. The plurality of lithium secondary batteries 210 are arranged in parallel so that their long sides face each other, and each lithium secondary battery 210 is connected in series. Note that the number of lithium secondary batteries 210 is not limited to six, and may be other plural numbers or one. Further, the shape of the lithium secondary battery 210 is not particularly limited.

  FIG. 2 is a conceptual diagram of an automobile 1000 on which the battery module 10 is mounted. Here, the automobile 1000 includes a battery module 10 and a vehicle body 20 that houses the battery module 10. That is, the automobile 1000 is an automobile such as an electric vehicle (EV), a hybrid vehicle (HEV), or a plug-in hybrid vehicle (PHEV) that runs using the battery module 10 as a power source. It has.

Both the conventional positive electrode active material and the active material of the present invention can be charged / discharged when the positive electrode potential reaches around 4.5 V (vs. Li ^/ Li ⁺ ). However, depending on the type of nonaqueous electrolyte used, if the positive electrode potential during charging is too high, the nonaqueous electrolyte may be oxidized and decomposed, resulting in a decrease in battery performance. Therefore, in use, a lithium secondary battery capable of obtaining a sufficient discharge capacity even when a charging method is adopted in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less. May be required. When the active material of the present invention is used, for example, 4.4 V (vs. Li ^/ Li) such that the maximum potential of the positive electrode during charging is lower than 4.5 V (vs. Li ^/ Li ⁺ ) during use. ⁺ ) Or less and 4.3 V (vs. Li ^/ Li ⁺ ) or less, even if a charging method is adopted, it is possible to take out a discharge electric quantity exceeding the capacity of the conventional positive electrode active material of about 200 mAh / g or more. Is possible.

In order for the positive electrode active material according to the present invention to have a high discharge capacity, the transition metal element constituting the lithium transition metal composite oxide is present in a portion other than the transition metal site of the layered rock salt type crystal structure. It is preferable that the ratio is small. This is because, in the precursor to be subjected to the firing step, the transition metal elements such as Co, Ni, and Mn in the precursor core particles are sufficiently uniformly distributed, and appropriate for promoting the crystallization of the active material sample. This can be achieved by selecting the conditions for the firing process. If the distribution of the transition metal in the precursor core particles subjected to the firing step is not uniform, a sufficient discharge capacity cannot be obtained. Although the reason for this is not necessarily clear, when the distribution of the transition metal in the precursor core particles to be subjected to the firing step is not uniform, the resulting lithium transition metal composite oxide has a layered rock salt type crystal structure other than the transition metal site. The present inventors speculate that this is due to the occurrence of so-called cation mixing, in which a part of the transition metal element is present at the lithium site. The same inference can be applied to the crystallization process in the firing step. If the crystallization of the active material sample is insufficient, cation mixing in the layered rock salt type crystal structure is likely to occur. When the distribution uniformity of the transition metal element is high, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane when the X-ray diffraction measurement result belongs to the space group R3-m is large. Tend. In the present invention, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is preferably I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.0. Further, it is preferable that I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 in the state after the discharge after charging and discharging. If the precursor synthesis conditions and procedure are inadequate, the peak intensity ratio will be smaller and often less than 1.

By adopting the synthesis conditions and synthesis procedures described in the present specification, a high-performance positive electrode active material as described above can be obtained. In particular, when the charging upper limit potential is set lower than 4.5 V (vs. Li ^/ Li ⁺ ), for example, it is set lower than 4.4 V (vs. Li ^/ Li ⁺ ) or 4.3 V (vs. Li ^/ Li ⁺ ). In this case, a positive electrode active material for a lithium secondary battery capable of obtaining a high discharge capacity can be obtained.

Example 1
Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00 g) and manganese sulfate pentahydrate (65.27 g) were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 2.0 M aqueous sulfate solution having a molar ratio of 12.50: 19.94: 67.56 was prepared. On the other hand, 750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in the} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropping, an aqueous solution containing 1.0 M sodium carbonate, 1.0 M potassium carbonate and 0.4 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 7. .9 (± 0.05). After completion of the dropping, stirring in the reaction vessel was continued for 3 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.
Next, using a suction filtration device, the coprecipitated carbonate particles generated in the reaction vessel are separated, and further, washing is performed 5 times when 200 ml is washed once with ion-exchanged water. Sodium ions and potassium ions adhering to the particles were washed and removed under the conditions, and were dried in an air atmosphere at 80 ° C. for 20 hours in an air atmosphere using an electric furnace. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

Then, the process of baking the coprecipitated carbonate precursor was performed. Add 0.970 g of lithium carbonate to 2.278 g of the coprecipitated carbonate precursor, mix well using a smoked automatic mortar, and the molar ratio of Li: (Co, Ni, Mn) is 130: 100. A powder was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), heated in air at atmospheric pressure and normal temperature to 900 ° C. over 10 hours, Firing was performed at 900 ° C. for 4 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, lithium transition metal complex oxide Li _1.13 Co _0.11 Ni _0.17 Mn _0.59 O ₂ containing Na and K according to Example 1 was produced. It was confirmed by X-ray diffraction measurement that this lithium transition metal composite oxide had an α-NaFeO ₂ structure.

(Example 2)
In the firing step of Example 1, lithium lithium according to Example 2 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate and 0.007 g of potassium carbonate in addition to 0.970 g of lithium carbonate. A transition metal composite oxide was produced.

(Example 3)
In the firing step of Example 1, the lithium according to Example 3 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.009 g of sodium carbonate and 0.014 g of potassium carbonate in addition to 0.970 g of lithium carbonate. A transition metal composite oxide was produced.

Example 4
In the firing step of Example 1, the lithium carbonate is changed to 1.021 g to be added to 2.228 g of the coprecipitated carbonate precursor, and mixed well using a smoked automatic mortar, and Li: (Co, Ni, Mn ) Was prepared in a molar ratio of 140: 100. Thus, a lithium transition metal composite oxide Li _1.17 Co _0.10 Ni _0.17 Mn _0.56 O _{2 according} to Example 4 was produced.

(Example 5)
In the calcination step of Example 4, lithium carbonate according to Example 5 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate and 0.007 g of potassium carbonate in addition to 1.021 g of lithium carbonate. A transition metal composite oxide was produced.

(Example 6)
In the calcination step of Example 4, the lithium according to Example 6 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.009 g of sodium carbonate and 0.014 g of potassium carbonate in addition to 1.021 g of lithium carbonate. A transition metal composite oxide was produced.

(Example 7)
In the precursor preparation step of Example 1, instead of an aqueous solution containing 1.0 M sodium carbonate, 1.0 M potassium carbonate and 0.4 M ammonia as neutralizing agents, 1.0 M lithium carbonate and 0 M A coprecipitated carbonate precursor was prepared by using an aqueous solution containing 4M ammonia. In addition, in the baking step, lithium transition metal according to Example 7 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.002 g of sodium carbonate and 0.004 g of potassium carbonate in addition to 0.970 g of lithium carbonate. A composite oxide was produced.

(Example 8)
In the firing step of Example 7, lithium lithium according to Example 8 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate and 0.004 g of potassium carbonate in addition to 0.970 g of lithium carbonate. A transition metal composite oxide was produced.

Example 9
In the baking step of Example 7, lithium lithium according to Example 9 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.002 g of sodium carbonate and 0.007 g of potassium carbonate in addition to 0.970 g of lithium carbonate. A transition metal composite oxide was produced.

(Example 10)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 10 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 11)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 11 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.009 g of sodium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 12)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 12 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.014 g of sodium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 13)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 13 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.007 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 14)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 14 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.014 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 15)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 15 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.021 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 16)
In the precursor preparation step of Example 1, instead of an aqueous solution containing 1.0 M sodium carbonate, 1.0 M potassium carbonate and 0.4 M ammonia as neutralizing agents, 1.0 M lithium carbonate and 0 M A coprecipitated carbonate precursor was prepared by using an aqueous solution containing 4M ammonia. In addition, in the baking step, lithium transition metal according to Example 16 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.002 g of sodium carbonate and 0.004 g of potassium carbonate in addition to 1.021 g of lithium carbonate. A composite oxide Li _1.17 Co _0.10 Ni _0.17 Mn _0.56 O ₂ was produced.

(Example 17)
In the firing step of Example 16, lithium lithium according to Example 17 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate and 0.004 g of potassium carbonate in addition to 1.021 g of lithium carbonate. A transition metal composite oxide was produced.

(Example 18)
In the calcination step of Example 16, the lithium according to Example 18 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.002 g of sodium carbonate and 0.007 g of potassium carbonate in addition to 1.021 g of lithium carbonate. A transition metal composite oxide was produced.

(Example 19)
In the firing step of Example 1, lithium transition metal composite oxide Li according to Example 19 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate in addition to 1.021 g of lithium carbonate. _1.17 Co _0.10 Ni _0.17 Mn _0.56 O ₂ was produced.

(Example 20)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 20 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.009 g of sodium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 21)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 21 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.014 g of sodium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 22)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 22 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.007 g of potassium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 23)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 23 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.014 g of potassium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 24)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 24 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.021 g of potassium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 25)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 25 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.032 g of sodium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 26)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 26 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.050 g of sodium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 27)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 27 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.068 g of sodium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 28)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 28 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.049 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 29)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 29 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.077 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 30)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 30 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.105 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Example 31)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 31 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.032 g of sodium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 32)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 32 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.050 g of sodium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 33)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 33 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.068 g of sodium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 34)
In the baking step of Example 1, the lithium transition metal composite oxide according to Example 34 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.049 g of potassium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 35)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 35 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.077 g of potassium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Example 36)
In the firing step of Example 1, the lithium transition metal composite oxide according to Example 36 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.105 g of potassium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Comparative Example 1)
In the precursor preparation step of Example 1, instead of an aqueous solution containing 1.0 M sodium carbonate, 1.0 M potassium carbonate and 0.4 M ammonia as neutralizing agents, 2.0 M sodium carbonate and 0 M A coprecipitated carbonate precursor was prepared by using an aqueous solution containing 4M ammonia. In addition, in the firing step, lithium transition metal composite oxide Li _{1 according} to Comparative Example 1 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.018 g of sodium carbonate in addition to 1.021 g of lithium carbonate _{. 17} Co _0.10 Ni _0.17 Mn _0.56 O ₂ was produced.

(Comparative Example 2)
In the firing step of Comparative Example 1, the lithium transition metal composite oxide according to Comparative Example 2 was added to 2.228 g of the coprecipitated carbonate precursor by adding 0.005 g of sodium carbonate in addition to 1.021 g of lithium carbonate. Produced.

(Comparative Example 3)
In the firing step of Comparative Example 1, 1.021 g of lithium carbonate was added to 2.228 g of the coprecipitated carbonate precursor to produce a lithium transition metal composite oxide according to Comparative Example 3.

(Comparative Example 4)
In the step of preparing the precursor of Comparative Example 3, instead of an aqueous solution containing 2.0 M sodium carbonate and 0.4 M ammonia as a neutralizing agent, 1.0 M sodium carbonate, 1.0 M lithium carbonate, and 0 A lithium transition metal composite oxide according to Comparative Example 4 was prepared by using an aqueous solution containing 4 M ammonia.

(Comparative Examples 5 to 8)
In the step of preparing the precursor of Comparative Example 4, instead of setting the ratio of sodium carbonate and lithium carbonate (molar ratio of Na / Li) of the neutralizing agent to 1/1 [M], Comparative Examples 5 to 8 in Table 1 A lithium transition metal composite oxide according to Comparative Examples 5 to 8 was produced in the same manner as in Comparative Example 4 except that the changes were made as described in.

(Comparative Example 9)
In the precursor preparation step of Example 1, instead of an aqueous solution containing 1.0 M sodium carbonate, 1.0 M potassium carbonate and 0.4 M ammonia as neutralizing agents, 2.0 M potassium carbonate and 0 M A coprecipitated carbonate precursor was prepared by using an aqueous solution containing 4M ammonia. In addition, in the firing step, lithium transition metal composite oxide Li _{1. according} to Comparative Example 9 is added to 2.278 g of the coprecipitated carbonate precursor by adding 0.018 g of potassium carbonate in addition to 0.970 g of lithium carbonate _{. 13} Co _0.11 Ni _0.17 Mn _0.59 O ₂ was produced.

(Comparative Example 10)
In the firing step of Comparative Example 9, the lithium transition metal composite oxide according to Comparative Example 10 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.011 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Comparative Example 11)
In the firing step of Comparative Example 9, the lithium transition metal composite oxide according to Comparative Example 11 was added to 2.278 g of the coprecipitated carbonate precursor by adding 0.004 g of potassium carbonate in addition to 0.970 g of lithium carbonate. Produced.

(Comparative Example 12)
In the firing step of Comparative Example 9, lithium transition metal composite oxide according to Comparative Example 12 was prepared by adding 0.970 g of lithium carbonate to 2.278 g of the coprecipitated carbonate precursor.

(Comparative Example 13)
In the precursor preparation step of Comparative Example 12, instead of an aqueous solution containing 2.0 M potassium carbonate and 0.4 M ammonia as a neutralizing agent, 1.0 M potassium carbonate, 1.0 M lithium carbonate and 0 M A lithium transition metal composite oxide according to Comparative Example 13 was prepared by using an aqueous solution containing 4 M ammonia.

(Comparative Example 14)
In the step of preparing the precursor of Comparative Example 12, instead of an aqueous solution containing 2.0 M potassium carbonate and 0.4 M ammonia as a neutralizing agent, 0.5 M potassium carbonate, 1.5 M lithium carbonate and 0 M A lithium transition metal composite oxide according to Comparative Example 14 was prepared by using an aqueous solution containing 4 M ammonia.

(Measurement of Na amount and / or K amount contained in lithium transition metal composite oxide)
The amount of Na and / or K contained in the obtained lithium transition metal composite oxide was determined as follows.
50 mg of the active material was weighed and put into 10 ml of a 10 wt% aqueous hydrochloric acid solution. This aqueous solution was heated on a hot plate at 150 ° C. to sufficiently dissolve the active material. Then, it filtered using the suction filtration apparatus and removed the microparticles | fine-particles contained in aqueous solution. 90 ml of ion exchange water was added to the filtered aqueous solution and stirred to prepare a 100 ml sample solution. Moreover, in order to prepare a calibration curve for determining the content of Na and / or K, three types of reference solutions with known Na and K concentrations were prepared. This reference solution was prepared by diluting Na and K standard solutions (manufactured by Nacalai Tesque, 1000 ppm) with ion-exchanged water to a target concentration.
The content of Na and / or K was measured by performing analysis with an ICP emission spectroscopic analyzer (SHIMADZU, ICPS-8100) using about 20 to 40 ml of each of the sample solution and the reference solution.
Further, the amount of Na and / or K contained in the lithium transition metal composite oxide can be measured by atomic absorption spectrometry in addition to the above-described ICP emission spectral analysis.

(Measurement of particle diameter)
The lithium transition metal composite oxides according to Examples 1 to 36 and Comparative Examples 1 to 14 were subjected to particle size distribution measurement according to the following conditions and procedures. Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as the measuring device. The measurement apparatus includes an optical bench, a sample supply unit, and a computer equipped with control software. A wet cell having a laser light transmission window is installed on the optical bench. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a sample to be measured is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in a sample supply unit and circulated and supplied to a wet cell by a pump. The sample supply unit is always subjected to ultrasonic vibration. In this measurement, water was used as a dispersion solvent. Moreover, Microtrac DHS for Win98 (MT3000) was used for the measurement control software. For the “substance information” to be set and input to the measuring apparatus, 1.33 is set as the “refractive index” of the solvent, “TRANSPARENT” is selected as the “transparency”, and “non-spherical” is selected as the “spherical particle”. Was selected. Prior to sample measurement, perform “Set Zero” operation. The “Set zero” operation is an operation to subtract the influence of disturbance elements other than the scattered light from the particles (glass, dirt on the glass wall, glass irregularities, etc.) on subsequent measurements. A background operation is performed in a state where only certain water is added and only water as a dispersion solvent is circulating in the wet cell, and the background data is stored in the computer. Next, perform the “Sample LD (Sample Loading)” operation. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion that is circulated and supplied to the wet cell during measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instructions of the measurement control software. It is an operation to throw up. Subsequently, the measurement operation is performed by pressing the “Measure” button. The measurement operation is repeated twice, and the measurement result is output from the computer as the average value. The measurement results are as a particle size distribution histogram and values of D10, D50, and D90 (D10, D50, and D90 are particle sizes at which the cumulative volume in the particle size distribution of the secondary particles is 10%, 50%, and 90%, respectively) To be acquired. The measured D50 value was 8 μm. Further, in the step of preparing the coprecipitated carbonate precursor, when the time for further stirring in the reaction vessel was changed from 3h to 4h after completion of the dropping, the value of D50 was 10 μm.
The cumulative volume in the particle size distribution of the secondary particles of the carbonate precursor was almost the same as that of the lithium transition metal composite oxide.

(Production and evaluation of lithium secondary battery)
Using the lithium transition metal composite oxides according to Examples 1 to 36 and Comparative Examples 1 to 14 as positive electrode active materials for lithium secondary batteries, lithium secondary batteries were prepared according to the following procedure, and battery characteristics were evaluated. .

  Using N-methylpyrrolidone as a dispersion medium, an active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate. In addition, the mass and coating thickness of the active material applied per fixed area were standardized so that the test conditions were the same among the lithium secondary batteries according to all the examples and comparative examples.

  For the purpose of accurately observing the single behavior of the positive electrode, metallic lithium was used in close contact with the nickel foil current collector for the counter electrode, that is, the negative electrode. Here, a sufficient amount of metallic lithium was disposed on the negative electrode so that the capacity of the lithium secondary battery was not limited by the negative electrode.

As an electrolytic solution, LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) had a volume ratio of 6: 7: 7 so that the concentration was 1 mol / l. The solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the electrodes are exposed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. The metal resin composite film was hermetically sealed with the fusion allowance where the inner surfaces of the metal resin composite films faced each other except for the portion serving as the injection hole, and the injection hole was sealed after the electrolyte solution was injected.

  The lithium secondary battery produced by the above procedure was subjected to an initial charge / discharge process at 25 ° C. Charging was performed at a constant current and a constant voltage with a current of 0.1 CA and a voltage of 4.6 V, and the charge termination condition was when the current value attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 CA and a final voltage of 2.0 V. This charge / discharge was performed for two cycles. Here, a pause process of 30 minutes was provided after charging and after discharging, respectively. The percentage indicated by “(discharged electric quantity) / (charged electric quantity) × 100” in the first cycle in the initial charge / discharge process was recorded as “initial efficiency (%)”.

(Charge / discharge test)
Next, the charge voltage was changed and the 1-cycle charging / discharging test was done. All voltage control was performed on the positive electrode potential. The conditions for this charge / discharge test are the same as the conditions for the initial charge / discharge step, except that the charge voltage is 4.3V. The amount of electricity discharged at this time was recorded as “discharge capacity (mAh / g)” (indicated as “0.1 C capa” in the table).

(Measurement of DC internal resistance)
The direct current internal resistance (SOC 30% DCR) in a state where the charging depth is shallow (30%) was determined as follows. Constant current and constant voltage charging with a current of 0.1 CmA and a voltage of 4.3 V was performed, and the amount of electricity charged was measured. After a 30-minute pause, a constant current discharge with a current of 0.1 CmA was performed, and the discharge was paused when 70% of the amount of electricity was applied to the amount of charge. A test was performed in which discharge was performed for 1 second at each rate discharge current 30 minutes after the discharge was stopped. Specifically, first, discharging was performed at a current of 0.1 CmA for 1 second, and after a pause of 2 minutes, supplementary charging was performed at a current of 0.1 CmA for 1 second. Further, after a rest of 2 minutes, the battery was discharged for 1 second at a current of 1 CmA, and after a rest of 2 minutes, supplementary charging was performed for 10 seconds at a current of 0.1 CmA. Further, after a rest of 2 minutes, the battery was discharged at a current of 2 CmA for 1 second, and after a rest of 2 minutes, a supplementary charge was performed at a current of 0.1 CmA for 20 seconds. The voltage of 1 second after each rate discharge was plotted with respect to the current value, and the slope of the graph subjected to fitting by the least square method was calculated and recorded as “SOC 30% DCR (Ω)”.

  Table 1 shows the test results of lithium secondary batteries using the lithium transition metal composite oxides according to Examples 1 to 36 and Comparative Examples 1 to 14 as positive electrode active materials.

From Table 1, the lithium secondary battery using the positive electrode active material of Examples 1-36 in which Li / Me of the lithium transition metal composite oxide is larger than 1 and Na and K are included is shown in the discharge capacity (0.1 C capa ) Is as large as 200 mAh / g or more, the SOC 30% DCR is 5Ω or less, the input / output characteristics are excellent, and the initial efficiency is 90% or more, which is high.
On the other hand, in the lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 to 14 containing only Na and only K, when the content of Na or K is a certain level or more, the discharge capacity is improved and the initial Although the efficiency is increased, the SOC 30% DCR is large, and the input / output characteristics cannot be improved sufficiently.
In order to obtain a positive electrode active material having a particularly large (0.1 C capa) discharge capacity (210 mAh / g or more) and a particularly small SOC 30% DCR (4.8 Ω or less), Na in the lithium transition metal composite oxide is used. The K content is preferably 1000 ppm to 20000 ppm.

  In said Example, content of Na and K of lithium transition metal complex oxide of this invention is based on the result of having measured about lithium transition metal complex oxide (positive electrode active material) before producing an electrode. Described. However, with respect to a lithium secondary battery having a charge / discharge history, the contents of Na and K can be obtained by performing the treatment according to the following procedure.

  First, a lithium secondary battery having a charge / discharge history (in the case of the present invention, a lithium secondary battery whose “discharge capacity (mAh / g)” was measured in the example) was discharged at a low rate of about 0.1 CmA. The battery is sufficiently discharged, the lithium secondary battery is disassembled in an atmosphere with a dew point of −20 ° C. or lower, and the positive electrode is taken out. The taken-out positive electrode is put into an 80 degreeC thermostat, and it dries until the attached electrolyte solution (solvent) volatilizes sufficiently. 55 mg of the mixture is collected from the mixture layer containing the positive electrode active material from this positive electrode, and ICP emission spectroscopic analysis is performed according to the procedure described in the examples. The obtained value is converted into the concentration per mass of the positive electrode active material.

In the positive electrode using the positive electrode active material of the example, no significant change was observed in the contents of Na and K even after charge and discharge. Therefore, according to the above measurement method, it can be said that the contents of Na and K in the positive electrode active material can be measured even in a lithium secondary battery after charge and discharge.
In addition, in the lithium secondary battery using the positive electrode containing the positive electrode active material of the present invention, Na and K in the positive electrode active material may leak from the positive electrode depending on use conditions. In this case, since Na and K are also contained in the electrolytic solution and the negative electrode, not only the contents of Na and K in the positive electrode but also the amounts of Na and K contained in the electrolytic solution and / or the negative electrode. By measuring, it becomes possible to know the amount of Na and K contained in the positive electrode active material more accurately.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 10 Battery module 20 Car body main body 100 Charging / discharging control apparatus 200 Power storage unit 210 Rectangular lithium secondary battery 220 Housing case 1000 Car

  By using a positive electrode active material containing the novel lithium transition metal composite oxide of the present invention, a lithium secondary battery having a large discharge capacity and excellent input / output characteristics can be provided. It is useful as a lithium secondary battery for electric vehicles, hybrid vehicles, plug-in hybrid vehicles and the like.

Claims (7)

A positive electrode active material for a lithium secondary battery comprising a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the lithium transition metal composite oxide contains Co, Ni and Mn as a transition metal (Me) A positive electrode active material for a lithium secondary battery, wherein a molar ratio Li / Me of lithium (Li) to the transition metal is greater than 1, and Na and K are contained.   2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein a molar ratio Li / Me of lithium (Li) to the transition metal is larger than 1.2 and smaller than 1.6.   3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the total content of Na and K is 1000 ppm or more and 20000 ppm or less. A carbonate precursor of a positive electrode active material for a lithium secondary battery, which is represented by MeCO ₃ (Me is a transition metal containing Co, Ni and Mn) and contains Na and K.   The electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries of any one of Claims 1-3.   A lithium secondary battery comprising the electrode for a lithium secondary battery according to claim 5.   A battery module configured by assembling a plurality of lithium secondary batteries according to claim 6.

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