JP2014056722A - Phosphate compound, positive electrode material for secondary battery, and method for producing secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an olivine-based phosphate compound having enhanced electron conductivity and ion conductivity, and a positive-electrode material that exhibits a high discharge capacity and that is excellent in the rate maintenance rate and the discharge capacity maintenance rate.SOLUTION: A phosphate compound has a composition represented by the formula Li(MnFeM)PXO, where M is at least one selected from the group consisting of Co and Ni; X is at least one selected from the group consisting of V, Si, B, and Al; q, r, a, b, and x satisfy the following conditions, 0≤q<0.20, 0≤r<0.20, 0≤(q+r)<0.20, -0.1≤a≤0.1, -0.1≤b≤0.1, and 0.0005<x≤0.10; and d is dependent on the valence of Mn, Fe, M, and X, and q, r, a, b, and x, and is the number that achieves electroneutrality.

Description

  The present invention relates to a phosphoric acid compound, a positive electrode material for a secondary battery, and a method for producing a secondary battery.

  In recent years, in the development of electric vehicles, hybrid vehicles, and the like, lithium ion secondary batteries are required to have a significantly higher capacity, higher energy, and larger size while maintaining safety. Further, from the viewpoint of energy problems, development of medium-sized or large-sized stationary storage batteries having high safety and reliability is progressing in order to smooth power supply and demand and to stably supply power in an emergency. Some of these have been put to practical use.

As a positive electrode material used for these batteries, an olivine-type lithium phosphate compound (LiMPO ₄ / M) typified by olivine-type lithium iron phosphate (LiFePO ₄ ) from the viewpoint of resources, safety, cost, stability, and the like. Is a transition metal element), and some have been put into practical use. However, since the olivine type lithium phosphate compound (LiMPO ₄ ) has a higher electrical resistance than the conventional material, the lithium insertion / extraction reaction is slow during the charging / discharging of the lithium ion secondary battery using it as the positive electrode material. As a result, there is a problem that the charge / discharge capacity and energy density of the secondary battery are likely to be lower than theoretical values.

Lithium iron phosphate (LiFePO ₄ ) and lithium manganese phosphate (LiMnPO ₄ ), which are one of the olivine-type lithium phosphate compounds, each have a discharge capacity of 170 mAh / g. The release occurs at around 3.4V and 4.0V, respectively. Therefore, the energy density of LiMnPO ₄ (multiplier of discharge capacity and operating voltage) is larger than that of LiFePO ₄ . In addition, these solid solutions of lithium iron manganese phosphate (LiFe _1-x Mn _x PO ₄ , 0 <x <1) also have a higher average operating voltage and higher energy density as the value of x increases. There is expected. However, the larger the value of x, the more difficult it is to express the theoretical capacity and the theoretical working voltage (for example, Non-Patent Document 1). Note that lithium cobalt phosphate (LiCoPO ₄ ) and lithium manganese phosphate (LiNiPO ₄ ) are difficult to use from the viewpoint of resources, safety, cost, and the like.

  Thus, as a method for improving such characteristics, substitution or doping of cations (Li and M) and anions (P) (for example, Non-Patent Document 2) is known. However, there are few known examples regarding the latter.

Patent Document 1 discloses a compound represented by the composition formula LiMP _1-x A _x O ₄ (M is a transition metal, A is an element having an oxidation number of +4 or less, and 0 <x <1). Is described. Examples of M include Ti (4+), Al (3+), B (3+), Zr (4+), Sn (4+), V (4+), Pb (4+), and Ge (4+) and charge It is also shown that the gap between the discharge profiles is narrowed and the charge / discharge capacity is increased.

  Patent Document 2 discloses a lithium-transition metal-phosphorus composite compound having an olivine structure (the transition metal is one or more selected from Fe, Mn, Ni, and Co, and a part of phosphorus is selected from B or Al). The active material represented by 1) is described, and it is shown that the cycle characteristics are improved.

Patent Document 3 discloses a composition formula Li _x A _y O ₄ (A is one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, and Cu, and 0 <x ≦ 2, 0 < A substance obtained by substituting a part of phosphate ions of a substance having an olivine structure with y ≦ 1.5) with an oxo acid other than phosphate ions, such as silicate ions and borate ions, is described as an electrode. It is shown that the rate characteristic is improved when used as.

Patent Document 4, by mol%, 20-50% of Li ₂ O, the _Fe 2 _{O 3} 5 to 40%, and the _P 2 _{O 5} 20 to 50%, also, to this MnO ₂ 0 In addition, it contains 0.1 to 25% of (Nb ₂ O ₅ + V ₂ O ₅ + SiO ₂ + B ₂ O ₃ + GeO ₂ + Al ₂ O ₃ + Ga ₂ O ₃ + Sb ₂ O ₃ + Bi ₂ O ₃ ) The precursor glass for lithium ion secondary battery positive electrode materials and crystallized glass powder are described. Furthermore, a lithium ion secondary battery positive electrode material containing crystallized glass powder and a conductive active material is described, which indicates that the electrical conductivity of the material is improved.

Japan Special Table 2008-506243 Japanese Unexamined Patent Publication No. 2010-123339 Japanese Unexamined Patent Publication No. 2011-216201 Japanese Unexamined Patent Publication No. 2009-087933

Atsuo. Yamada et al., Chemistry of Materials, 18, 804-813 (2006) Sung-Yoon Chung et al., Nature Materials, 1, 123-128 (2002)

  In Non-Patent Document 1, it is considered that the reason why the theoretical discharge capacity and the theoretical operating voltage are difficult to express is that the electron conductivity and the ionic conductivity are low. Furthermore, after the continuous charge / discharge history, good rate characteristics and cycle characteristics have not been obtained, but it is thought to be due to irreversible structural changes.

In the compound described in Patent Document 1, in order to make the oxidation state of the transition metal M into a multivalent state (average valence is not an integer), an ion lower than the valence (P + 5) of the anion which is a counter ion is used. It replaces P ions. In the examples, there is shown a method for producing a substance in which M is Co or Fe and 2 mol% of P is substituted with Ti by a solid phase reaction using a Ti source of Li ₄ TiO ₄ . However, the reaction is complicated, and it is necessary to perform the grinding step and the heating step twice. Further, there is no description or suggestion of an example in which M contains Mn.

  The method for producing a substance described in Patent Document 2 is also a production method by a solid phase reaction method, and the reaction is complicated, and it is necessary to perform the pulverization step and the heating step twice. Moreover, in the Examples, there is only an example when the transition metal is Fe, and there is no example when the transition metal contains Mn.

  The method for producing a substance described in Patent Document 3 is a hydrothermal synthesis method, and has a problem of high production cost. In addition, the examples include only an example when M is Fe, and there is no example when M includes Mn.

Patent Document 4 shows examples (Table 1 and Table 2) in which Nb ₂ O ₅ is added, but does not describe examples of adding other elements (particularly, substitution examples of P) and actions in that case. . The addition of an oxide such as Nb ₂ O ₅ is included for the purpose of improving the glass forming ability (paragraphs [0043] and [0044] in the specification). Moreover, although the Example which added MnO is shown (Table 3), the addition example of another element and the effect | action in that case are not described.

  An object of the present invention is to provide an olivine-type phosphoric acid compound and a method for producing the same, in which electronic conductivity and ionic conductivity are enhanced. In addition, the present invention provides a positive electrode material for a secondary battery and a secondary battery that exhibit high discharge capacity, are excellent in rate maintenance ratio and discharge capacity maintenance ratio (cycle characteristics), and have improved reliability. Objective.

  The present invention is the following [1] to [11].

[1] A phosphoric acid compound having a composition represented by the following formula (1).
_{Li 1 + a (Mn 1- (} q + r) Fe q M r) 1 + b P 1-x X x O 4 + c (1)
(Wherein M is at least one selected from the group consisting of Co and Ni, X is at least one selected from the group consisting of V, Si, B and Al, and q, r, a, b and x are 0 ≦ q <0.20, 0 ≦ r <0.20, 0 ≦ (q + r) <0.20, −0.1 ≦ a ≦ 0.1, −0.1, respectively. ≦ b ≦ 0.1, and 0.0005 <x ≦ 0.10, d depends on the valence of Mn, Fe, M, and X, and on q, r, a, b, and x, Number that satisfies electrical neutrality.)

[2] The phosphate compound according to [1], wherein in the formula (1), X is V.

[3] The phosphoric acid compound according to [1] or [2], wherein r is 0 in the formula (1).

[4] A positive electrode material for a secondary battery containing the phosphate compound according to any one of [1] to [3].

[5] A secondary battery comprising the secondary battery positive electrode material according to [4].

[6] In terms of oxide-based mol%, Li ₂ O is 20% to 35%, P ₂ O ₅ is 20% to 35%, MnO ₂ is 35% to 55%, and Fe ₂ O ₃ is used. 0% or more and less than 5%, and at least one selected from the group consisting of V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ is 0.01% or more and 2.5% or less, Co ₃ O Heating the raw material formulation containing ₄ to 0% to less than 3% and NiO from 0% to less than 10% to obtain a melt by melting the raw material formulation;
Cooling the melt to obtain a solidified product;
Pulverizing the solidified product to obtain a pulverized product;
Heating the pulverized product to obtain particles containing crystals containing an olivine structure;
The manufacturing method of the phosphoric acid compound characterized by implementing in this order.

[7] The production method according to claim 6, wherein the raw material formulation is melted at 1,000 ° C. to 1,400 ° C. in an inert gas or a reducing gas.

[8] The production method according to [6] or [7], wherein the melt is cooled at a cooling rate of 10 ³ to 10 ¹⁰ ° C / second.

[9] The production method according to any one of [6] to [8], wherein the melt is cooled in an inert gas or a reducing gas.

[10] The pulverized product includes the solidified product and at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material, and a carbon equivalent amount (mass) in the carbon source is The production according to any one of [6] to [9], which is 0.1 to 20% by mass with respect to the total mass of the mass of the solidified product and the carbon equivalent amount (mass) in the carbon source. Method.

[11] The production method according to any one of [6] to [10], wherein the pulverized product is heated at 300 ° C to 900 ° C in an inert gas or a reducing gas.

  According to the present invention, it is possible to provide an olivine-type phosphate compound having improved electron conductivity and ionic conductivity and a method for producing the same. ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material and secondary battery which were excellent in the rate maintenance factor and the discharge capacity maintenance factor, and having improved the reliability while expressing high discharge capacity can be provided.

It is a figure which shows the X-ray-diffraction pattern of the phosphoric acid compound obtained by Example 8, 9, 10, and 11 of the Example.

In the present specification, the olivine-type phosphate compound is a basic formula LiM′PO ₄ (M ′ may include Mn as an essential component and may include at least one selected from the group consisting of Fe, Co, and Ni). This refers to the substance represented. The olivine structure is a crystal structure in which the crystal system is orthorhombic and the space group is represented by Pnma.

  In addition, a crystal including an olivine structure is also referred to as an olivine crystal, and a particle including an olivine crystal is also referred to as an olivine crystal particle. The olivine type crystal particle may partially include a crystal structure other than the olivine type crystal, or may partially include an amorphous structure. It is preferable that substantially all of the olivine type crystal particles are made of olivine type crystals.

[Phosphate compound]
The phosphoric acid compound of the present invention has a composition represented by the following formula (1).

_{Li 1 + a (Mn 1- (} q + r) Fe q M r) 1 + b P 1-x X x O 4 + c (1)
(Wherein M is at least one selected from the group consisting of Co and Ni, X is at least one selected from the group consisting of V, Si, B and Al, and q, r, a, b and x are 0 ≦ q <0.20, 0 ≦ r <0.20, 0 ≦ (q + r) <0.20, −0.1 ≦ a ≦ 0.1, −0.1, respectively. ≦ b ≦ 0.1, and 0.0005 <x ≦ 0.10, d depends on the valence of Mn, Fe, M, and X, and on q, r, a, b, and x, Number that satisfies electrical neutrality.)
The phosphate compound having the composition represented by the formula (1) is an olivine-type phosphate compound, and when used as a positive electrode material for a secondary battery, exhibits a high discharge capacity while maintaining a rate maintenance rate and a discharge capacity. The rate is high, the reliability is high, and the manufacturing cost is low.

  q and r are 0 ≦ q <0.20, 0 ≦ r <0.20, and 0 ≦ (q + r) <0.20. When q ≧ 0.20, it is difficult to obtain a phosphoric acid compound having a high operating voltage when a positive electrode material is used, and when r ≧ 0.20, the manufacturing cost increases, and (q + r) ≧ 0.20. Then, the rate maintenance rate and the discharge capacity maintenance rate are lowered. Further, as the olivine-type phosphoric acid compound, Co and Ni are elements that can increase the voltage but are expensive, and therefore r = 0 is preferable.

  The atom X is considered to exist mainly by substituting the P position. The atom X is preferably V because it has a great effect of increasing electrochemical properties.

  When x is 0.0005 <x ≦ 0.10, particularly 0.001 ≦ x ≦ 0.05, the structure of the phosphate compound is stabilized, and the rate maintenance rate, discharge capacity maintenance rate, and energy density (discharge) This is preferable because the product of the capacity and the operating voltage is considered to be improved. When x <0.0005, the effect of increasing the electrochemical properties is not sufficient, and when x> 0.10, the discharge capacity of the phosphoric acid compound is reduced and the manufacturing cost is increased.

  a and b are −0.1 ≦ a ≦ 0.1 and −0.1 ≦ b ≦ 0.1. If a and b are each less than −0.1 or greater than 0.1, it is difficult to obtain a phosphate compound. It is more preferable that −0.05 ≦ a ≦ 0.05 and −0.05 ≦ b ≦ 0.05 to increase the discharge capacity retention rate.

  c is a number that depends on the valences of Mn, Fe, and M, and a, b, q, r, and x, and satisfies the electrical neutrality. The valence of Mn, Fe, Co, and Ni in the phosphoric acid compound is preferably +2.

  When the phosphoric acid compound of the present invention is used as a positive electrode material for a secondary battery, the positive electrode material for a secondary battery preferably contains a conductive material. The conductive material is derived from at least one carbon source selected from the group consisting of organic compounds and carbon-based conductive materials. The conductive material is preferably present on the surface of the phosphoric acid compound particles or the interparticle interface. The content of the conductive material is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, and more preferably 2 to 10% by mass with respect to the total mass of the phosphoric acid compound and the conductive material. Is particularly preferred.

  It is particularly preferable that the phosphoric acid compound particles include olivine type crystal particles and consist only of olivine type crystal particles. The crystal particles include both primary particles and secondary particles. When secondary particles are present in the obtained phosphoric acid compound, they may be crushed and pulverized in such a range that the primary particles are not destroyed.

  The average particle diameter of the phosphoric acid compound particles is preferably 10 nm to 10 μm, particularly preferably 10 nm to 1 μm, in terms of volume median diameter. By making the average particle diameter within this range, the conductivity of the phosphoric acid compound becomes higher. The average particle size can be measured with a laser diffraction / scattering particle size measuring device.

The specific surface area of the phosphate compound particles is preferably 0.2~200m ² / g, more preferably 1~200m ² / g, more preferably 3 to 50 m ² / g. By making a specific surface area into this range, the electroconductivity of a phosphoric acid compound becomes high. The specific surface area can be measured with a specific surface area measuring apparatus using a nitrogen adsorption method. The average particle size and specific surface area of the phosphoric acid compound are the average particle size and specific surface area when the phosphoric acid compound does not contain a conductive material.

The average particle diameter of the phosphoric acid compound particles coated with the conductive material is preferably 10 nm to 10 μm, particularly preferably 10 nm to 2 μm, in terms of volume median diameter. By making the average particle diameter within this range, the conductivity of the phosphoric acid compound becomes higher. The specific surface area of the phosphoric acid compound is preferably 0.2~200m ² / g, more preferably ^{1~200m 2 / g, 5~50m 2 /} g is particularly preferred. By making a specific surface area into this range, the electroconductivity of a phosphoric acid compound becomes high.

[Method for producing phosphate compound]
The manufacturing method of the phosphoric acid compound of this invention implements each process of the following melting processes (I)-heating process (IV) in this order. Other steps may be performed before, between and after the melting step (I) to the heating step (IV) as long as each step is not affected.

Melting step (I): Oxide-based mol%, oxide-based mol%, Li ₂ O 20% to 35%, P ₂ O ₅ 20% to 35%, MnO ₂ 35% or more and 55% or less, Fe ₂ O ₃ of 0% or more and less than 5%, and at least one selected from the group consisting of V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ is 0.00. Heating a raw material formulation containing 01% or more and 2.5% or less, Co ₃ O ₄ 0% or more and less than 3%, and NiO 0% or more and less than 10% to obtain a melt by melting;
Cooling step (II): a step of cooling the melt to obtain a solidified product,
Pulverization step (III): a step of pulverizing the solidified product to obtain a pulverized product;
Heating step (IV): A step of heating the pulverized product to obtain particles containing crystals containing an olivine structure.

(Melting step (I))
In the melting step (I), the raw material containing each atomic source (Li, Mn, P, or / and Fe, Co, Ni, V, Si, B, Al) was adjusted to have a composition in the above range. Prepare the raw material formulation.

  The raw material formulation having the composition in the above range can be completely melted and the melt has an appropriate viscosity, and can be easily processed in the subsequent cooling step.

Li ₂ O is a main component of the phosphoric acid compound, and the Li ₂ O content is 20% to 35%, preferably 23% to 30%. When it is less than 20% or more than 35%, it is difficult to obtain a uniform melt, and it becomes difficult to obtain a phosphoric acid compound even if the obtained pulverized product is heated.

P ₂ O ₅ is a main component of the phosphoric acid compound, and the P ₂ O ₅ content is 20% to 35%, preferably 23% to 30%. When it is less than 20% or more than 35%, it becomes difficult to obtain a phosphoric acid compound even when the obtained pulverized product is heated.

MnO ₂ is the main component of the phosphoric acid compound, and the MnO ₂ content is 35% to 55%, preferably 40% to 52%. This range is preferable because a material having a high operating voltage is easily obtained when the positive electrode material is used. If it is less than 35%, it is difficult to obtain a material having a high operating voltage. On the other hand, when the content is more than 55%, it becomes difficult to obtain a phosphoric acid compound even if the obtained pulverized product is heated.

At least one selected from the group consisting of V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ is an essential component, and improves the electronic conductivity and ionic conductivity of the phosphate compound of the present invention. Works. It also has the effect of expanding the melting range of the melt. The content of at least one selected from the group consisting of V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ is 0.01% to 2.5%, preferably 0.025% It is 1.5% or less and more preferably 0.025% or more and 1.25% or less. Within this range, good electrochemical properties can be expressed. Moreover, the melt which has moderate viscosity can be obtained. If it exceeds 2.5%, the discharge capacity tends to decrease. If the content is less than 0.01%, the above-described action is difficult to occur. V ₂ O ₅ is preferable because of its great effect of increasing electrochemical properties.

Fe ₂ O ₃ is an optional component. The Fe ₂ O ₃ content is 0% or more and less than 5%. This range is preferable because a melt having an appropriate viscosity can be obtained. If it is 5% or more, it is difficult to obtain a material having a high operating voltage. Further, if it exceeds 0%, the discharge capacity can be further increased, which is more preferable.

Co ₃ O ₄ and NiO are optional components. When the Co ₃ O ₄ content and the NiO content are 0% or more and less than 3% and 0% or more and less than 10%, respectively, a material having a high operating voltage is easily obtained when the positive electrode material is used. When the Co ₃ O ₄ content is 3% or more, or the NiO content is 10% or more, it is difficult to obtain a uniform melt.

Co ₃ O ₄ and NiO are each 0%, and Fe ₂ O ₃ is preferably less than 5%.

  The valence of Mn, Fe, Co, and Ni in the melt is preferably in the range of +2 to +5. +2, +8/3, or +3 for Fe, +2, +3, or +4 for Mn, +2, +3, +4, or +5 for Nb, +2, +8/3, or +3 for Co, In the case of Ni, +2 or +4 is preferable. The valence of these elements in the obtained crystal grains is preferably +2.0 to +2.5, more preferably +2.0 to +2.2, and particularly preferably +2.

As the compound containing Li in the raw material preparation, lithium carbonate (Li ₂ CO ₃ ), lithium hydrogen carbonate (LiHCO ₃ ), lithium hydroxide (LiOH), and lithium phosphate (Li ₃ PO ₄ , (LiPO ₃ ) _n It is preferable to use at least one selected from the group consisting of These make it easier to obtain the desired phosphate compound. In addition, lithium chloride (LiCl), lithium nitrate (LiNO ₃ ), lithium sulfate (Li ₂ SO ₄ ), and organic acid salts such as lithium acetate (CH ₃ COOLi) and lithium oxalate ((COOLi) ₂ ) are used. (However, a part or all of the at least one kind may each form a hydrated salt.) Of these, Li ₂ CO ₃ , LiHCO ₃ , and (LiPO ₃ ) _n are particularly preferable because they are inexpensive and easy to handle.

As the compound containing P in the raw material preparation, phosphorus oxide (P ₂ O ₅ ), ammonium phosphate (hydrogen) ((NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ ) It is preferable to use at least one selected from the group consisting of lithium phosphate (Li ₃ PO ₄ , (LiPO ₃ ) _n ), and phosphates of Mn, Fe, Co, and Ni. These make it easier to obtain the desired phosphate compound. In addition, phosphoric acid (H ₃ PO ₄ ), metaphosphoric acid ((HPO ₃ ) _n ), polyphosphoric acid (H _{n + 2} P _n O _{3n + 1} ), phosphorous acid (H ₃ PO ₃ ), and hypophosphorous acid (H ₃ PO ₂ ) may be used. When each of the above compounds contains water of crystallization, the water-containing compound is included. Of these, ammonium dihydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), lithium phosphate (Li ₃ PO ₄ , LiPO ₄ ), and (LiPO ₃ ) _n are preferable because of ease of handling and availability.

As a compound containing Mn in the raw material preparation, manganese oxide (MnO, Mn ₂ O ₃ , Mn ₃ O ₄ ), manganese hydroxide (Mn (OH) _2, etc.), manganese oxyhydroxide (MnO (OH) ₂ ) And at least one selected from the group consisting of manganese phosphate (Mn ₃ (PO ₄ ) ₂ , Mn ₂ P ₂ O _7, etc.). These make it easier to obtain the desired phosphate compound. Further, manganese chloride (MnCl ₂ etc.), manganese nitrate (Mn (NO ₃ ) ₂ etc.), manganese sulfate (MnSO ₄ etc.), Mn alkoxide (Mn (OCH ₃ ) ₂ , Mn (OC ₂ H ₅ ) ₂ etc. ), And organic acid salts such as manganese acetate (Mn (CH ₃ COO) ₂ ) and manganese oxalate (Mn (COO) ₂ ). When each of the above compounds contains water of crystallization, the water-containing compound is included. Among these, MnO ₂ and MnO are particularly preferable from the viewpoint of availability and cost.

Examples of the compound containing V in the raw material preparation include vanadium oxide (VO, V ₂ O ₃ , VO ₂ , V ₂ O ₅ ), lithium vanadate, vanadate of Mn, Fe, Ni, and Co, and ammonium vanadate. (NH ₄ VO ₃ ), vanadium silicate, vanadium aluminate, a compound with phosphoric acid (VPO ₄ etc.), vanadium chloride (VCl ₃ etc.), and at least selected from the group consisting of vanadium oxysulfate (VOSO ₄ etc.) One is preferred. Among these, V ₂ O ₅ is particularly preferable because it is inexpensive and easy to handle.

As the compound containing Si in the raw material formulation, silicon oxide (SiO ₂ ), lithium silicate (Li ₂ SiO ₃ , Li ₄ SiO _4, etc.), Mn, Fe, Ni, and Co silicate (MnSiO ₃ , Mn ₂ SiO ₄ etc.), phosphate silicate, vanadate silicate, borate silicate, and at least one selected from the group consisting of aluminosilicates are preferred. Note that the compound containing Si may be crystalline or amorphous. Of these, SiO ₂ is particularly preferable from the viewpoint of cost and availability.

Compounds containing B in the raw material formulation include boron oxide (B ₂ O ₃ ), boric acid (H ₃ BO ₃ ), lithium borate (such as Li ₃ BO ₃ ), Mn, Fe, Ni, and Co boron At least one selected from the group consisting of acid salts, boron phosphates, borate silicates, and aluminum borates is preferred. Among these, B ₂ O ₃ and H ₃ BO ₃ are particularly preferable from the viewpoints of cost and availability.

As the compound containing Al in the raw material preparation, aluminum oxide (Al ₂ O ₃ ), aluminum oxyhydroxide (including AlO (OH), aluminum oxyhydroxide salt), lithium aluminate, Mn, Fe, Ni, and Co aluminate, aluminosilicate, aluminum phosphate (AlPO ₄ ), aluminum borate (AlBO ₃ ), aluminum chloride (AlCl ₃ ), aluminum nitrate (Al (NO ₃ ) ₃ ), and aluminum sulfate (Al ₂ (SO ₄ ) ₃ etc.) is preferably at least one selected from the group consisting of ₃ ). Among these, Al ₂ O ₃ and AlO (OH) are particularly preferable from the viewpoints of cost and availability.

As the compound containing Fe, Co, and Ni in the raw material preparation, oxides (FeO, Fe ₃ O ₄ , Fe ₂ O ₃ , CoO, Co ₃ O ₄ , Co ₂ O ₃ , NiO), oxyhydroxides (FeO (OH) etc.), phosphate (Fe ₃ (PO ₄ ) ₃ , Fe ₃ PO ₄ etc.), chloride (FeCl ₂ , FeCl ₃ etc.), nitrate (Fe (NO ₃ ) ₂ etc.), sulfuric acid Salt (FeSO ₄ , Fe ₂ (SO ₄ ) ₃ etc.), Fe alkoxide (Fe (OCH ₃ ) ₂ , Fe (OC ₂ H ₅ ) ₂ etc.), and Fe acetate salt (Fe (CH ₃ COO) ₂ Etc.) and at least one selected from the group consisting of organic acid salts such as iron oxalate (Fe (COO) ₂ etc.). Among these, at least one compound selected from the group consisting of Fe ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ and NiO is more preferable from the viewpoint of availability and cost.

  In principle, the composition of the raw material formulation corresponds theoretically to the composition of the melt obtained from the raw material formulation. However, since there are components that are easily lost due to volatilization during the melting process in the raw material formulation, such as P, the composition of the obtained melt is based on the oxide calculated from the amount of each raw material charged. It may be slightly different from the mol%.

  The purity of each raw material is not particularly limited as long as it does not deteriorate the desired characteristics, but the purity excluding hydration water is preferably 99% or more, more preferably 99.9% or more. .

  The particle size of each raw material is not particularly limited as long as it is within a range in which a uniform melt can be obtained by melting. Each raw material is preferably melted after being mixed dry or wet using a mixing / pulverizing means such as a mixer, ball mill, planetary mill or the like.

  In the melting step (I), the raw material mixture obtained by the above method is then heated to melt. It is preferable to put the raw material preparation in a container or the like, and heat and melt it using a heating furnace. Examples of the container include alumina, carbon, silicon carbide, zirconium boride, titanium boride, boron nitride, carbon, platinum, platinum alloy containing rhodium, refractory bricks, and reduction. A container made of a material such as a material (for example, graphite) can be used. In order to prevent volatilization and evaporation in the heating furnace, the container is preferably fitted with a lid. The heating furnace is preferably a resistance heating furnace, a high frequency induction furnace, or a plasma arc furnace. The resistance heating furnace is preferably an electric furnace provided with a heating element made of an alloy such as a nichrome alloy, silicon carbide, or molybdenum silicide.

The melting step (I) can be carried out in air, in an inert gas, or in a reducing gas. When carried out in an inert gas or a reducing gas, the valences of Mn, Fe, Co, and Ni can be maintained in a state close to +2 or +2, and a desired phosphate compound can be easily obtained, which is preferable. When melted in the air, it is preferable to perform reduction (for example, change from M ³⁺ to M ²⁺ ) in the subsequent heating step (IV).

Here, the inert gas refers to a gas containing 99% by volume or more of at least one gas selected from rare gases such as helium (He) and argon (Ar) and nitrogen (N ₂ ) gas. The reducing gas is a gas having a reducing property such as hydrogen (H ₂ ), carbon monoxide (CO), or ammonia (NH ₃ ) in the above-described inert gas, and the content is 0.1% by volume or more. More preferably, the gas is present at 1 to 10% by volume, and the oxygen (O ₂ ) content is 1% by volume or less, and more preferably 0.1% by volume or less. However, when gas is generated during decomposition or melting of the raw material, the atmosphere does not have to be satisfied during the period. Furthermore, the raw material preparation may be melted in an atmosphere (0.8 × 10 ⁵ Pa or less) in which an inert atmosphere or a reducing atmosphere is decompressed.

  The heating temperature for melting is preferably 1,000 to 1,400 ° C, particularly preferably 1,200 to 1,350 ° C. Here, melting means that each raw material is melted and is in a transparent state visually. When the heating temperature is not less than the lower limit of the above range, melting becomes easy, and when it is not more than the upper limit, the raw material is hardly volatilized. The heating time is preferably 0.2 to 2 hours, particularly preferably 0.5 to 2 hours. When the heating time is not less than the lower limit of the above range, the uniformity of the melt is sufficient, and when it is not more than the upper limit, the raw material is hardly volatilized. Moreover, you may stir in order to raise the uniformity of a melt. Further, the melt may be clarified at a temperature lower than the melting temperature until the next cooling step (II) is performed.

(Cooling step (II))
The cooling step (II) is a step of cooling the melt obtained in the melting step (I) to near room temperature (20 to 25 ° C.) to obtain a solidified product. The solidified product is preferably an amorphous material, but a part of the solidified product may be a crystallized product. The amount of the crystallized product in the solidified product is preferably 0 to 30% by mass with respect to the total mass of the solidified product. When a large amount of crystallized material is contained, it becomes difficult to obtain a granular or flaky solidified material. Moreover, the wear of the cooling device is accelerated, and the burden of the subsequent pulverization step (III) is increased. When the solidified product contains an amorphous material, the next pulverization step (III) can be easily performed, and the composition and particle size of the phosphoric acid compound can be easily controlled. When an olivine-type phosphate compound is produced by crystallizing an amorphous substance, the reaction time can be shortened compared to the case of synthesizing a compound from a plurality of powders by a solid-phase reaction. Uniformity of composition, structure, etc. can be improved.

  The cooling of the melt can be carried out in air, in an inert gas or in a reducing gas. When carried out in an inert gas or a reducing gas, the facilities are simple and oxidation of Mn, Fe, Co, and Ni can be prevented or suppressed. In the case of rapid cooling in an open system, it is preferable that the atmosphere around the contact portion between the material to be cooled (melt) and the cooling medium (for example, a twin roller) is an inert atmosphere or a reducing atmosphere.

The cooling rate of the melt is preferably 1 × 10 ³ ° C./second or more, and more preferably 1 × 10 ⁴ ° C./second or more. When the cooling rate is higher than this value, an amorphous material is easily obtained. The upper limit of the cooling rate is preferably about 1 × 10 ¹⁰ ° C./second from the viewpoint of manufacturing equipment and mass productivity, and is particularly preferably 1 × 10 ⁸ ° C./second from the viewpoint of practicality. The cooling rate of the melt is particularly preferably 1 × 10 ³ ° C./sec to 1 × 10 ¹⁰ ° C./sec.

  As a method for cooling the melt, a method in which the melt is dropped between twin rollers rotating at a high speed, a method in which the melt is dropped on a rotating single roller to cool, a carbon plate that has cooled the melt, A method of cooling by pressing on a metal plate is preferred. Among these, a cooling method using twin rollers is particularly preferable because the cooling rate is high and a large amount of processing can be performed. As the double roller, it is preferable to use one made of metal such as stainless steel, carbon or ceramic.

  The solidified product obtained in the cooling step (II) is preferably flaky or fibrous. In the case of flakes, the average thickness is preferably 200 μm or less, particularly preferably 100 μm or less. The average diameter of the plane perpendicular to the flaky average thickness is not particularly limited. In the case of a fibrous form, the average diameter is preferably 50 μm or less, particularly preferably 30 μm or less. When the average thickness or average diameter is not more than the upper limit of the above range, the burden on the pulverization step (III) can be reduced, and the crystallization efficiency in the heating step (IV) can be increased. The average thickness and average diameter can be measured with a caliper or a micrometer. The average diameter can also be measured by microscopic observation.

(Crushing step (III))
The pulverization step (III) is a step of pulverizing the solidified product obtained in the cooling step (II) to obtain a pulverized product. Since the solidified product usually contains a large amount of amorphous material or consists of an amorphous material, there is an advantage that it can be easily pulverized. Further, there is an advantage that pulverization can be performed without imposing a burden on an apparatus used for pulverization and the particle size can be easily controlled. On the other hand, in the conventional solid phase reaction, pulverization is performed after the heating step, but there is a problem that residual stress is generated by pulverization and battery characteristics and the like are deteriorated. In the production method of the present invention, since the pulverization step (III) is performed before the heating step (IV), the residual stress generated in the pulverization step (III) can be reduced or removed in the heating step (IV).

  The pulverization is preferably performed using a cutter mill, jaw crusher, hammer mill, ball mill, jet mill, planetary mill or the like. Moreover, pulverization can be efficiently advanced by using each method stepwise depending on the particle diameter. For example, it is preferable to preliminarily make it fine with a hand massage or a hammer because the burden of the pulverization process is reduced. Further, after preliminary pulverization with a cutter mill, pulverization with a planetary mill or ball mill is preferable because the time required for pulverization can be shortened. From the viewpoint of productivity, it is particularly preferable to use a ball mill.

  As the grinding media, it is preferable to use zirconia balls, alumina balls, silicon nitride balls, silicon carbide balls, glass balls, or the like. In particular, zirconia balls are preferable because they have a low wear rate and can suppress the mixing of impurities. The diameter of the grinding media is preferably 0.1 to 30 mm. After pulverization is performed in multiple stages and pulverization is performed with a large pulverization medium, the pulverization medium and the pulverized product may be separated and pulverized using a smaller pulverization medium. With this method, the remaining of unground particles can be suppressed.

  The pulverization container is not particularly limited, but the pulverization efficiency is good when the pulverization medium and the solidified material are placed in the container up to 30 to 80% of the container capacity. When using a ball mill, the grinding time is preferably 6 to 360 hours, more preferably 6 to 120 hours, and particularly preferably 12 to 96 hours. If the pulverization time is not less than the lower limit of the above range, the pulverization can be sufficiently advanced, and if it is not more than the upper limit, excessive pulverization can be suppressed.

  The pulverization may be performed either dry or wet, but is preferably performed wet from the viewpoint of pulverization particle size. As a solvent used for pulverization (hereinafter also referred to as pulverization solvent), water or an organic solvent such as ethanol, isopropyl alcohol, acetone, hexane, or toluene can be used. Water is preferable from the viewpoint of cost and safety. On the other hand, when a problem such as elution of the solidified product occurs in the polar solvent, the organic solvent is preferable. When the pulverization solvent is filled up to 30 to 80% by volume of the container capacity in a state where the solidified product and the pulverization medium are contained, the pulverization efficiency is improved. When the pulverization is performed by a wet process, it is preferable to carry out the heating step (IV) after removing the pulverization solvent by sedimentation, filtration, drying under reduced pressure, drying by heating, or the like. However, when the pulverizing solvent is small, particularly when the ratio of the mass of the solid content to the mass of the pulverized product is 30% or more, the pulverized product containing the pulverizing solvent may be used for the heating step (IV). .

  The average particle diameter of the pulverized product is preferably 10 nm to 10 μm, more preferably 10 nm to 5 μm, in terms of volume-based median diameter. It is preferable for the average particle size to be equal to or greater than the lower limit of the above range because the pulverized products do not sinter and become too large in the heating step (IV). It is preferable for it to be not more than the upper limit of the above range because the heating temperature and time in the heating step (IV) can be reduced, and the particle size of the resulting phosphoric acid compound can be reduced. The average particle size is measured with a laser diffraction / scattering particle size measuring device.

  Since the phosphoric acid compound of the present invention is an insulating material, when used as a positive electrode material for a secondary battery, it is preferable to coat at least a part of the surface of the phosphoric acid compound with a conductive material. In the pulverization step (III), it is preferable to include at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material. As the carbon source, it is particularly preferable to use an organic compound and a carbon-based conductive material in combination. By using in combination, the distribution of the carbon-based conductive material in the phosphoric acid compound becomes uniform, and the contact area with the organic compound and its thermal decomposition product (carbide) increases. By these, the electroconductivity of the positive electrode material for secondary batteries using a phosphoric acid compound can be improved.

  The pulverization step (III) is preferably a step of obtaining a pulverized product of a solidified product and a carbon source. The pulverization step (III) includes a step of pulverizing after mixing the solidified product and the carbon source, a step of mixing after pulverizing the solidified product and the carbon source, and a step of adding the carbon source after pulverizing the solidified product. It is more preferable that

  The ratio of the mass of the carbon source is such that the carbon conversion amount (mass) in the carbon source is 0.1 to 20 with respect to the total mass of the mass of the solidified product and the carbon conversion amount (mass) in the carbon source. An amount of mass% is preferred, an amount of 0.1-10 mass% is more preferred, and an amount of 2-10 mass% is particularly preferred. By setting the amount of the carbon source to be equal to or higher than the lower limit of the above range, the electrical conductivity can be sufficiently increased when the phosphoric acid compound is used as a positive electrode material for a secondary battery. When the thickness of the conductive material covering the phosphoric acid compound does not become too thick by setting it to the upper limit value or less of the above range, a positive electrode for a secondary battery is produced using a phosphoric acid compound. The electrolyte can be sufficiently distributed to the material.

  When the organic compound is included in the solidified product, the pulverization step (III) is preferably performed by a wet method in order to uniformly disperse the pulverized product surface. The pulverization step (III) when the solidified material contains only the carbon-based conductive material may be dry.

  Organic compounds as carbon sources include glucose, sucrose, glucose-fructose invert sugar, caramel, paraffin, starch, pregelatinized starch, carboxymethylcellulose, ethylcellulose, camphor, melamine, stearic acid, oleic acid, linoleic acid, ascorbic acid More preferably, at least one selected from the group consisting of polyethylene glycol, polyvinyl alcohol, polyacrylic acid, and phenolic resin, glucose, sucrose, ethyl cellulose, camphor, melamine, stearic acid, ascorbic acid, polyethylene glycol, polyvinyl alcohol, and Particularly preferred is at least one selected from the group consisting of polyacrylic acid.

  The carbon-based conductive material as the carbon source is preferably at least one selected from the group consisting of carbon black, graphite, acetylene black, carbon fiber, and amorphous carbon. As the amorphous carbon, those in which a C—O bond peak or a C—H bond peak causing a decrease in conductivity of the positive electrode material is not substantially detected in the FT-IR analysis are preferable.

(Heating step (IV))
The heating step (IV) is a step in which the pulverized product obtained in the pulverization step (III) is heated to obtain a phosphate compound containing crystals containing an olivine structure. The obtained phosphoric acid compound is preferably particulate. Moreover, it is preferable that a phosphoric acid compound does not contain an amorphous substance. The fact that the phosphoric acid compound does not contain an amorphous substance can be confirmed by the fact that no halo pattern is detected by X-ray diffraction.

  In the heating step (IV), since the pulverized product is heated, the relaxation of the residual stress generated by the pulverization is promoted. Further, since crystal nuclei are generated and grains are grown by heating, it is easy to control the composition, grain size and distribution of the phosphate compound.

  The heating temperature is preferably 300 to 900 ° C, more preferably 500 to 900 ° C, and particularly preferably 550 to 800 ° C. When the heating temperature is 300 ° C. or higher, a carbonization reaction is likely to occur, and a phosphoric acid compound crystal is likely to be generated. When the heating temperature is 900 ° C. or lower, the pulverized product is hardly melted, and the crystal system and the particle diameter are easily controlled. In the case of the heating temperature, phosphoric acid compound particles having olivine type crystals having appropriate crystallinity, particle diameter, particle size distribution and the like are easily obtained. Moreover, it is easy to obtain phosphate compound particles in which the conductive material is uniformly bonded to the surface of the particles.

  The heating is not limited to being held at a constant temperature, and may be performed by setting the holding temperature in multiple stages. When the heating temperature is increased, the particle diameter of the generated particles tends to increase. Therefore, it is preferable to set the heating temperature according to the desired particle diameter. The heating time (holding time depending on the heating temperature) is preferably 1 to 72 hours in consideration of a desired particle size. Heating is preferably performed in a box furnace, tunnel kiln furnace, roller hearth furnace, rotary kiln furnace or the like.

Heating is preferably performed in air, an inert gas, or a reducing gas, and particularly preferably performed in an inert gas or a reducing gas. The conditions of the inert gas and the reducing gas are the same as those in the melting step (I). In addition, the gas atmosphere can be adjusted by introducing methane gas or acetylene gas into the furnace. The pressure may be any of normal pressure, pressurization (1.1 × 10 ⁵ Pa or more), and reduced pressure (0.9 × 10 ⁵ Pa or less). In addition, when a container containing a reducing agent (for example, graphite) and pulverized material is loaded in a heating furnace, reduction of M in the pulverized material (for example, change from M ³⁺ to M ²⁺ ) is promoted. can do. Thereby, a phosphoric acid compound can be obtained with good reproducibility.

  After the heating step (IV), it is usually cooled to room temperature. The cooling rate is preferably 30 to 300 ° C./hour. By setting the cooling rate within this range, distortion due to heating can be removed. Further, the cooling may be left to cool to room temperature. The cooling is preferably allowed to cool to room temperature. Cooling is preferably performed in an inert gas or a reducing gas. The cooling is preferably performed from 300 to 900 ° C. in the heating step (IV) to room temperature at a cooling rate of 30 to 300 ° C./hour.

  After obtaining the phosphoric acid compound in the heating step (IV), a pulverized product of the phosphoric acid compound and a carbon source may be obtained, and then the pulverized product may be heated in an inert gas or a reducing gas. .

  In the production method of the present invention, when at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material is included, a conductive material derived from the carbon source is uniformly formed on the surface of the phosphate compound particles. And can be firmly bonded. The phosphoric acid compound particles to which the conductive material is bonded can be used as a positive electrode material for a secondary battery as it is. When an organic compound is used as the carbon source, the organic compound is carbonized in the heating step (IV), and the carbide covers at least a part of the surface of the phosphate compound as a conductive material. When a carbon-based conductive material is used as the carbon source, the material covers at least a part of the surface of the phosphate compound as a conductive material. Further, when both are used as the carbon source, the carbide derived from the organic compound and the carbon-based conductive material cover at least a part of the surface of the phosphate compound to form a conductive material network.

[Positive electrode for secondary battery and secondary battery]
A positive electrode for a secondary battery and a secondary battery can be produced using the phosphoric acid compound obtained by the production method of the present invention as a positive electrode material for a secondary battery. Examples of the secondary battery include a metal lithium secondary battery, a lithium ion secondary battery, and a lithium polymer secondary battery, and a lithium ion secondary battery is preferable. The battery shape is not limited, and various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be appropriately employed.

  The positive electrode for a secondary battery of the present invention can be manufactured according to a known electrode manufacturing method except that the phosphoric acid compound of the present invention is used. For example, if necessary, the phosphoric acid compound of the present invention may be a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, (Polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc.) and further mixed with a known conductive material (acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, etc.) if necessary, and further known Organic solvents (N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropyl alcohol) Emissions, ethylene oxide, was slurried with tetrahydrofuran), by a method such as coating the known current collector (aluminum or stainless steel metal foil and the like), can be produced.

  As the structure of the secondary battery, a structure in a known secondary battery can be adopted except that the positive electrode for a secondary battery obtained by the production method of the present invention is used as an electrode. The same applies to separators, battery cases, and the like. As the negative electrode, a known negative electrode active material can be used as the active material, and at least one selected from the group consisting of carbon materials, alkali metal materials, and alkaline earth metal materials is preferably used. As the electrolytic solution, a non-aqueous electrolytic solution is preferable. That is, as the secondary battery obtained by the production method of the present invention, a nonaqueous electrolyte lithium ion secondary battery is preferable. The secondary battery obtained by the production method of the present invention is useful as a secondary battery mounted in a plug-in hybrid vehicle or an electric vehicle, or as a storage battery for storing power.

  Although an example is given and explained concretely, the present invention is not limited to the following explanation. Examples 1 to 16 and Examples 31 to 46 are examples, and Examples 21 and 51 are comparative examples.

[Examples 1 to 16, 21]
(Melting step (I))
The composition of the melt is Li ₂ O, P ₂ O ₅ , MnO ₂ , Fe ₂ O ₃ , Co ₃ O ₄ , V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ equivalent (unit: Mol%) so that the proportions shown in Table 1 are obtained, respectively, lithium carbonate (Li ₂ CO ₃ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ), manganese dioxide (MnO ₂ ), triiron tetroxide ( Fe ₃ O _4), tricobalt tetraoxide _{(Co 3 O} 4), vanadium pentoxide _{(V 2 O} 5), silicon dioxide _(SiO 2), boron oxide _{(B 2 O} 3), and aluminum oxide (Al ₂ O ₃ ) was weighed, mixed and pulverized by a dry method to obtain a raw material formulation.

The obtained raw material mixture was filled in a platinum alloy crucible containing 20% by mass of rhodium. Next, the crucible was placed in an electric furnace (manufactured by Motoyama Co., Ltd., apparatus name: NH-3035) having a heating element made of molybdenum silicide. The electric furnace was heated at a rate of 300 ° C./hour and heated at 1,280 to 1,320 ° C. for 0.5 hours while flowing N ₂ gas at a flow rate of ₂ L / min. After confirming that it became transparent visually, a melt was obtained.

(Cooling step (II))
The melt in the crucible obtained in the melting step (I) is passed through a stainless steel double roller having a diameter of about 15 cm rotating at 400 revolutions per minute to cool the melt to room temperature at 1 × 10 ⁵ ° C./sec. A solidified product was obtained. The obtained solidified product was a glassy substance.

(Crushing step (III))
The flaky solidified product obtained in the cooling step (II) was lightly kneaded and finely ground, and then coarsely pulverized using a cutter mill. Furthermore, this was pulverized wet with a ball mill using zirconia balls as a pulverizing medium and dried to obtain a finely pulverized product. The pulverization was performed stepwise using a ball having a diameter of 5 mm and then a ball having a diameter of 2 mm. Ethanol was used as a grinding solvent.

  Glucose, sucrose, and carbon black are added to the finely pulverized product, and the mass ratio of the finely pulverized product, the carbon equivalent of glucose, the carbon equivalent of sucrose, and the carbon equivalent of carbon black is 89: 3: 5: 3. Then, a small amount of pure water was added and mixed. The pulverized material mixed with the carbon source was dried and then subjected to the subsequent heating step (IV).

(Heating step (IV))
The pulverized material obtained by mixing a carbon source, an electric furnace (manufactured Motoyama Co., device name: SKM-3035) using a _{H 2} gas at 3 _vol% H 2 -N ₂ gas, heated for 8 hours at 600 ° C. Then, the mixture was cooled to room temperature to precipitate phosphoric acid compound particles.

(Measurement of X-ray diffraction)
The mineral phase of the obtained phosphoric acid compound particles was examined using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, apparatus name: RINT TTRIII). The particles of Examples 1 to 16 and Example 21 were all confirmed to be olivine-type crystal particles in which the crystal system is orthorhombic and the space group is considered to be Pnma. The X-ray diffraction patterns of the phosphoric acid compound particles obtained in Examples 8, 9, 10, and 11 are shown in FIGS. 1 (a), (b), (c), and (d), respectively.

(Measurement of particle size distribution and specific surface area)
The particle size distribution of the phosphoric acid compound of the obtained phosphoric acid compound particles was measured with a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, Ltd., apparatus name: LA-920). The volume-converted median diameters of all examples and all comparative examples were 0.29 to 0.36 μm.

Furthermore, the specific surface area was measured with a specific surface area measuring device (manufactured by Shimadzu Corporation, device name: ASAP2020). The specific surface areas of all Examples and all Comparative Examples were 26 to 36 m ² / g.

(Composition analysis)
The chemical composition of the obtained phosphoric acid compound particles was measured. First, organic substances on the particle surface were removed by oxidation with 4 mol / L H ₂ O ₂ , and then a 6.0 mol / L HCl solution was added and decomposed at 80 ° C. Li in the decomposition solution was quantified using an atomic absorption photometer (manufactured by Hitachi High-Technologies Corporation, apparatus name: Z-2310). Moreover, P, Mn, Fe, and Nb in the decomposition solution were quantified using an inductively coupled emission spectroscopic analyzer (manufactured by Seiko Instruments Inc., apparatus name: SPS3100). From the quantitative values of Li, P, Mn, Fe, Co, Ni, V, Si, B and Al, Li ₂ O, P ₂ O ₅ , MnO, FeO, CoO, NiO, V ₂ O ₅ , SiO ₂ , B ₂ O _3, and _Al 2 _{O 3} amounts were calculated. Table 2 shows quantitative values of the chemical compositions of the phosphoric acid compound particles obtained in Examples 1 to 16 and Example 21.

(Measurement of carbon content)
The carbon content of the obtained phosphoric acid compound particles was measured with a carbon analyzer (manufactured by Horiba, Ltd., apparatus name: EMIA-920V). The carbon content of all examples and all comparative examples was 7.3 to 8.3 mass%.

[Examples 31 to 46, Example 51: Production Examples of Positive Electrode for Li-ion Secondary Battery and Evaluation Battery]
The phosphoric acid compound particles (active material), the polyvinylidene fluoride resin (binder) and acetylene black (conductive material) obtained in Examples 1 to 16 and Example 21 are in a mass ratio of 80: 8: 12 The slurry was weighed and mixed in N-methylpyrrolidone (solvent) until uniform to prepare a slurry. Next, the slurry was applied to an aluminum foil having a thickness of 20 μm with a doctor blade. The solvent was removed by drying at 120 ° C. in the air, and then the coating layer was consolidated by a roll press and cut into strips having a width of 10 mm and a length of 40 mm.

  The coating layer was peeled off leaving a 10 × 10 mm tip of strip-shaped aluminum foil, which was used as an electrode. The coating thickness of the obtained electrode after roll pressing was 20 μm. The obtained electrode was vacuum-dried at 150 ° C. and then carried into a glove box filled with purified argon gas. The electrode was opposed to a counter electrode obtained by pressure bonding a lithium foil to a nickel mesh through a separator made of porous polyethylene film, and both sides were sandwiched and fixed by a polyethylene plate to obtain a counter electrode.

  The counter electrode was put in a polyethylene beaker, and a nonaqueous electrolyte solution in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (1: 1 volume ratio) at a concentration of 1 mol / L was injected. Fully impregnated. The counter electrode after impregnation with the electrolytic solution was taken out from the beaker, placed in an aluminum laminate film bag, the lead wire portion was taken out and sealed to form a half-cell. The characteristics of this half-cell were measured as follows.

(Evaluation of electrochemical properties of positive electrode for Li-ion secondary battery)
The obtained half-cell was placed in a constant temperature bath at 25 ° C. and connected to a constant current charge / discharge tester (manufactured by Hokuto Denko Co., Ltd., device name: HJ201B) to perform an initial charge / discharge test. The current density was charged / discharged with the current value per mass of the electrode active material (the mass excluding the conductive material and the binder) being 15 mA / g (equivalent to 0.088 C). The end-of-charge voltage was 4.5 V based on the Li counter electrode, and discharge was started immediately after reaching the end-of-voltage. The end-of-discharge voltage was 1.5 V with respect to the Li counter electrode. Table 3 shows the initial discharge capacity values obtained in Examples 31 to 46 and Example 51.

  Next, the rate maintenance rate was measured. The current density during charging was 15 mA / g, and the current density during discharging was 15 mA / g, 37.5 mA / g, 150 mA / g, 300 mA / g, 600 mA / g, and 1200 mA / g. Moreover, the charge end voltage was set to 4.5 V with respect to the Li counter electrode, and discharge was started immediately after reaching the end voltage. The end-of-discharge voltage was set to 2.0 V based on the Li counter electrode. A value obtained by dividing the discharge capacity value at 600 mA / g by the discharge capacity value at 15 mA / g was defined as a rate maintenance rate. Table 3 shows the rate maintenance ratios obtained in Examples 31 to 46 and Example 51.

  Furthermore, the discharge capacity retention rate was measured. The current densities during charging and charging were 150 mA / g and 37.5 mA / g, respectively, and the charge end potential and discharge end voltage were 4.5 V and 1.5 V, respectively, based on the Li counter electrode. This charging / discharging was repeated 20 times. The ratio of the 20th discharge capacity value to the 1st discharge capacity value was defined as the discharge capacity retention rate. Table 3 shows the discharge capacity retention rates obtained in Examples 31 to 46 and Example 51.

It has been found that the phosphoric acid compound of the present invention exhibits excellent electrochemical properties, particularly rate maintenance rate and discharge capacity maintenance rate. That is, it was confirmed that the phosphoric acid compound of the present invention can be used as a positive electrode material for a secondary battery, and a positive electrode for a secondary battery having good electrochemical properties can be obtained efficiently.

  The phosphoric acid compound of the present invention is useful when applied to a positive electrode material for a secondary battery and further to a secondary battery. The method for producing a phosphate compound of the present invention is useful because a phosphate compound having excellent electrochemical properties can be produced inexpensively and efficiently.

Claims (11)

A phosphoric acid compound having a composition represented by the following formula (1).
_{Li 1 + a (Mn 1- (} q + r) Fe q M r) 1 + b P 1-x X x O 4 + c (1)
(Wherein M is at least one selected from the group consisting of Co and Ni, X is at least one selected from the group consisting of V, Si, B and Al, and q, r, a, b and x are 0 ≦ q <0.20, 0 ≦ r <0.20, 0 ≦ (q + r) <0.20, −0.1 ≦ a ≦ 0.1, −0.1, respectively. ≦ b ≦ 0.1, and 0.0005 <x ≦ 0.10, d depends on the valence of Mn, Fe, M, and X, and on q, r, a, b, and x, Number that satisfies electrical neutrality.)   The phosphoric acid compound according to claim 1, wherein X is V in the formula (1).   The phosphoric acid compound according to claim 1 or 2, wherein in the formula (1), r is 0.   The positive electrode material for secondary batteries containing the phosphoric acid compound as described in any one of Claims 1-3.   The secondary battery containing the positive electrode material for secondary batteries of Claim 4. In terms of oxide-based mol%, Li ₂ O is 20% to 35%, P ₂ O ₅ is 20% to 35%, MnO ₂ is 35% to 55%, and Fe ₂ O ₃ is 0% or more. Less than 5%, and at least one selected from the group consisting of V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ is 0.01% or more and 2.5% or less, and Co ₃ O ₄ is 0 Heating a raw material formulation containing at least 3% and less than 3% and NiO at 0% to less than 10% to obtain a melt by melting,
Cooling the melt to obtain a solidified product;
Pulverizing the solidified product to obtain a pulverized product;
Heating the pulverized product to obtain particles containing crystals containing an olivine structure;
The manufacturing method of the phosphoric acid compound characterized by implementing in this order.   The manufacturing method according to claim 6, wherein the raw material preparation is melted at 1,000 ° C. to 1,400 ° C. in an inert gas or a reducing gas. The manufacturing method according to claim 6 or 7, wherein the melt is cooled at a cooling rate of 10 ³ to 10 ¹⁰ ° C / second.   The manufacturing method according to any one of claims 6 to 8, wherein the melt is cooled in an inert gas or a reducing gas.   The pulverized product includes the solidified product and at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material, and a carbon equivalent amount (mass) in the carbon source is the amount of the solidified product. The manufacturing method as described in any one of Claims 6-9 which is 0.1-20 mass% with respect to the total mass of mass and the carbon conversion amount (mass) in this carbon source.   The manufacturing method according to any one of claims 6 to 10, wherein the pulverized product is heated at 300 ° C to 900 ° C in an inert gas or a reducing gas.

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