Positive electrode active material composite particles for lithium ion secondary batteries and method for manufacturing the same

Abstract

To provide positive electrode active material composite particles for lithium ion secondary batteries capable of constructing lithium ion secondary batteries with excellent high-temperature life characteristics while using a lithium phosphate compound with an olivine structure as a material, and a method for manufacturing the same.SOLUTION: Positive electrode active material composite particles for lithium ion secondary batteries have an average composition represented by formula (X): LiFeaMnbMxcPO4 and exhibit a core-shell structure, and a core portion is formed from particles having an average composition represented by formula (A): LiFedMneM1fPO4, and a shell portion is formed from a material having an average composition represented by formula (B): LigFehM2iPO4.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to positive electrode active material composite particles for lithium ion secondary batteries, which have excellent high-temperature life characteristics, and a method for producing the same. [Background technology]

[0002] Positive electrode active materials made of compounds such as Li(Fe,Mn)PO4 with an olivine structure are highly safe in high-temperature environments and are therefore highly useful as positive electrode materials for lithium-ion secondary batteries. Therefore, various development efforts have been made to further improve battery performance. For example, Patent Document 1 discloses LiMn 1-x-y Fe x M y A positive electrode active material containing positive electrode active material particles represented by PO4 and having a difference in Fe ratio between the composition of the particle surface and the composition of the particle center has been disclosed, and attempts have been made to improve cycle characteristics, float charge resistance, and discharge rate performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-209463 Summary of the Invention [Problem to be solved by the invention]

[0004] However, while high-temperature durability is required as one of the important performance characteristics of lithium-ion secondary batteries, the positive electrode material described in Patent Document 1 above is still unable to sufficiently avoid deterioration over time, and there is a risk that a lithium-ion secondary battery constructed using this material will not be able to exhibit excellent high-temperature durability.

[0005] Therefore, the present invention relates to a positive electrode active material composite particle for a lithium ion secondary battery capable of constructing a lithium ion secondary battery having excellent high-temperature life characteristics while using a lithium phosphate compound having an olivine-type structure as a material, and a method for producing the same.

Means for Solving the Problems

[0006] Thus, as a result of intensive studies to solve the above problems, the present inventors have found that positive electrode active material composite particles for a lithium ion secondary battery having a core-shell structure, in which the core part and the shell part are each formed of a lithium phosphate compound having a specific olivine-type structure, can exhibit excellent high-temperature life characteristics in the obtained lithium ion secondary battery.

[0007] That is, the present invention provides the following formula (X): LiFe a Mn b M x c PO4···(X) (In formula (X), M x represents Na, Mg, Ti, Al, Zn, Cu, Sn, Ni, V, Nb, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, and c satisfy 0.5 < a ≤ 1, 0 < b < 0.5, and 0 < c ≤ 0.3, and 2a + 2b + (valence of M x ) × c = 2. ) A positive electrode active material composite particle for a lithium ion secondary battery having an average composition represented by the following formula and exhibiting a core-shell structure, wherein the core part has the following formula (A): LiFe d Mn e M 1 f PO4···(A) (In formula (A), M 1 represents Mg, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. d, e, and f satisfy 0 ≤ d ≤ 1, 0 < e ≤ 1, and 0 ≤ f ≤ 0.3, and 2d + 2e + (valence of M 1 ) × f = 2. ) The shell portion is formed of particles having an average composition represented by the following formula (B): Li g Fe h M 2 i PO4···(B) (In formula (B), M 2 represents Na, Mg, Ti, Al, Zn, Cu, Sn, Ni, Co, Zr, V, or Nb. g, h, and i are in the range of 0.8≦g≦1.2, 0.5≦h≦0.99, 0.01≦i≦0.5, and g+2h+(M 2 (valence of i) × i = 3. The present invention provides positive electrode active material composite particles for lithium ion secondary batteries, which are formed from a material having an average composition represented by the following formula:

[0008] The present invention also provides a method for producing a pharmaceutical composition comprising the following steps (I) to (V): (I) A step of obtaining a slurry water by mixing a lithium compound, a metal compound including at least a manganese compound, a phosphate compound, and water, and then subjecting the resulting mixture to a hydrothermal reaction to obtain a slurry water A containing preliminary particles of the particles (A). (II) Lithium compounds, at least iron compounds and metals (M 2 ) A step of mixing a metal compound containing a compound, a phosphate compound, and water to obtain slurry water B. (III) A step of adding the slurry water A obtained in the step (I) dropwise to the slurry water B obtained in the step (II) to obtain a mixed solution X1. (IV) A step of removing water from the obtained mixed liquid X and then firing the mixture to obtain a fired body X2. (V) A step of subjecting the obtained fired body X2 to a wet grinding treatment The present invention provides a method for producing the above positive electrode active material composite particles for a lithium ion secondary battery, comprising: [Effects of the Invention]

[0009] According to the present invention, a lithium ion secondary battery having excellent high-temperature life characteristics can be realized. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the present invention will be described in detail. The positive electrode active material composite particles for a lithium ion secondary battery of the present invention have a core-shell structure and are represented by the following formula (X): LiFe a Mn b M x c PO4···(X) (In formula (X), M x represents Na, Mg, Ti, Al, Zn, Cu, Sn, Ni, V, Nb, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, and c satisfy 0.5 < a ≤ 1, 0 < b < 0.5, and 0 < c ≤ 0.3, and 2a + 2b + (valence of M x ) × c = 2. ) It is a so-called olivine-type lithium phosphate compound having an average composition represented by (hereinafter, the positive electrode active material composite particles for a lithium ion secondary battery of the present invention are also referred to as "composite particles (X)").

[0011] In the above formula (X), for a, preferably 0.6 < a < 1, more preferably 0.6 < a < 0.9. For b, preferably 0.1 < b < 0.5, more preferably 0.2 < b < 0.5. For c, preferably 0 < c ≤ 0.2. And for M x , preferably Ti, V, Mg, Nb, Mg, Nb or Zr, more preferably Ti, Mg or Nb.

[0012] More specifically, examples of the positive electrode active material composite particles for a lithium ion secondary battery represented by the above formula (X) include, for example, LiFe 0.66 Mn 0.33 V 0.01 PO4, LiFe 0.635 Mn 0.36 V 0.005 PO4, LiFe 0.618 Mn 0.38 Mg 0.001 Ti 0.001 PO4, LiFe 0.672 Mn 0.32 Mg 0.004Ti 0.004 PO4, LiFe 0.74 Mn 0.24 Mg 0.01 Ti 0.01 PO4, LiFe 0.744 Mn 0.24 Mg 0.008 Ti 0.008 PO4, Li 0.994 Nb 0.006 Fe 0.72 Mn 0.21 Mg 0.07 PO4, Li 0.996 Nb 0.004 Fe 0.68 Mn 0.32 PO4, Li 0.996 Nb 0.004 Fe 0.68 Mn 0.32 PO4, etc. Among them, LiFe 0.618 Mn 0.38 Mg 0.001 Ti 0.001 PO4, LiFe 0.672 Mn 0.32 Mg 0.004 Ti 0.004 PO4, LiFe 0.74 Mn 0.24 Mg 0.01 Ti 0.01 PO4, LiFe 0.744 Mn 0.24 Mg 0.008 Ti 0.008 PO4, Li 0.994 Nb 0.006 Fe 0.72 Mn 0.21 Mg 0.07 PO4 and the like are preferred. The average composition of the composite particles (X) is a composition determined by subjecting the composite particles (X) to ICP analysis.

[0013] The average particle size of the composite particles (X) is preferably 51 nm to 350 nm, more preferably 56 nm to 300 nm, and even more preferably 61 nm to 250 nm. The average particle size of the composite particles (X) means the average value of the measured particle sizes (length of the longest axis) of 100 particles randomly selected in observation with a TEM electron microscope.

[0014] In the composite particle (X) having a core-shell structure, the mass ratio of the core part to the shell part (core: shell) is preferably 1:1 to 20:1, more preferably 1.2:1 to 19.5:1, and still more preferably 1.4:1 to 19:1. Note that the mass ratio of the core part to the shell part (core: shell) corresponds to the mass ratio of the content of the particle (A) to the content of the material (B) (particle (A): material (B)) in the composite particle (X).

[0015] In the positive electrode active material composite particle for a lithium ion secondary battery of the present invention, the core part has the following formula (A): LiFe d Mn e M 1 f PO4···(A) (In formula (A), M 1 represents Mg, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. d, e, and f satisfy 0 ≦ d ≦ 1, 0 < e ≦ 1, and 0 ≦ f ≦ 0.3, and 2d + 2e + (valence of M 1 ) × f = 2. ) It is formed of particles (hereinafter, also referred to as "particle (A)") which are so-called olivine-type lithium phosphate compounds containing at least manganese (Mn) and having an average composition represented by

[0016] In the above formula (A), for d, it is preferably 0.2 < d < 0.5, more preferably 0.2 < d < 0.4. For e, it is preferably 0.5 < e < 1, more preferably 0.7 < e < 0.9. For f, it is preferably 0.05 ≦ f ≦ 0.25. For M 1 , it is preferably Mg or Zr. [[ID=३३]] More specifically, as the particles represented by the above formula (A), for example, LiMnPO4, LiFe 0.2 Mn 0.8 PO4, LiFe 0.59 Mn 0.41 PO4, LiFe [[ID=४३]] 0.6 Mn0.4 PO4, LiFe 0.6 Mn 0.3 Mg 0.1 PO4, LiFe 0.7 Mn 0.2 Zr 0.1 PO4, etc. Among them, LiFe 0.2 Mn 0.8 PO4, LiFe 0.59 Mn 0.41 PO4, LiFe 0.6 Mn 0.4 PO4, LiFe 0.6 Mn 0.3 Mg 0.1 PO4 and the like are preferred. The average composition of the particles (A) is a composition determined by performing ICP analysis on the particles (A).

[0017] The average particle size of the particles (A) (core portion) is preferably 50 nm to 300 nm, more preferably 55 nm to 250 nm, and even more preferably 60 nm to 200 nm. The average particle size of the particles (A) means the average value of the measured particle sizes (length of the longest axis) of 100 particles randomly selected in observation with a TEM electron microscope.

[0018] In the positive electrode active material composite particle for a lithium ion secondary battery of the present invention, the shell portion is represented by the following formula (B): Li g Fe h M 2 i PO4···(B) (In formula (B), M2 represents Na, Mg, Ti, Al, Zn, Cu, Sn, Ni, Co, Zr, V, or Nb. g, h, and i represent numbers that satisfy the following conditions: 0.8≦g≦1.2, 0.5≦h≦0.99, 0.01≦i≦0.5, and g+2h+(valence of M2)×i=3.) The material (hereinafter also referred to as "material (B)") is a so-called olivine-type lithium phosphate compound having an average composition represented by the following formula and containing at least iron (Fe).

[0019] In formula (B), for g, it is preferably 0.8 ≦ g ≦ 1.1, more preferably 0.9 ≦ g ≦ 1.1. For h, it is preferably 0.6 < h ≦ 0.99, more preferably 0.7 < h ≦ 0.99. For i, it is preferably 0.01 ≦ i < 0.4, more preferably 0.01 ≦ i < 0.3. And these g, h, and i are numbers that satisfy g + 2h + (valence of M) × i = 3. M 2 For M, it is preferably Mg, Ti, Zr, V, or Nb. More specifically, examples of the material represented by the above formula (B) include, for example, LiFe 0.95 V 0.05 PO4, LiFe 0.985 Mg 0.005 Ti 0.01 PO4, LiFe 0.96 Mg 0.02 Ti 0.02 PO4, Li 0.98 FeNb 0.02 PO4, Li 0.97 FeAl 0.01 PO4, LiFe 0.99 Cu 0.01 PO4, Li 0.95 FeNa 0.05 PO4 and the like. Among them, LiFe 0.95 V 0.05 PO4, LiFe 0.985 Mg 0.005 Ti 0.01 PO4, LiFe 0.96 Mg 0.02 Ti 0.02 PO4, Li 0.98 FeNb 0.02 PO4 and the like are preferred. In addition, the average composition of the material (B) is the composition estimated by the difference between the average composition of the above composite particles (X) specified by ICP analysis and the average composition of the above particles (A) specified by ICP analysis.

[0020] In the composite particles (X) of the present invention, the average thickness of the shell portion formed by the material (B) is preferably 1 nm to 30 nm, more preferably 2 nm to 25 nm, and even more preferably 3 nm to 2 nm. The average thickness of the shell portion is the difference between the average particle size of the composite particles (X) and the average particle size of the particles (A), as determined by TEM electron microscope observation.

[0021] In the composite particles (X) of the present invention, the ratio of the average particle diameter of the core portion to the average thickness of the shell portion (core diameter / shell thickness) is preferably 2.5 to 35, more preferably 3 to 30, and even more preferably 3.5 to 25, from the viewpoint of exhibiting excellent high-temperature life characteristics.

[0022] The positive electrode active material composite particles for a lithium ion secondary battery (composite particles (X)) of the present invention can be produced by the following steps (I) to (V): (I) A step of obtaining a slurry water by mixing a lithium compound, a metal compound including at least a manganese compound, a phosphate compound, and water, and then subjecting the resulting mixture to a hydrothermal reaction to obtain a slurry water A containing preliminary particles of the particles (A). (II) Lithium compounds, at least iron compounds and metals (M 2 ) A step of mixing a metal compound containing a compound, a phosphate compound, and water to obtain slurry water B. (III) A step of adding the slurry water A obtained in the step (I) dropwise to the slurry water B obtained in the step (II) to obtain a mixed solution X1. (IV) A step of removing water from the obtained mixed liquid X and then firing the mixture to obtain a fired body X2. (V) A step of subjecting the obtained fired body X2 to a wet grinding treatment The manufacturing method can be obtained by the following steps.

[0023] Step (I) is a step of obtaining a slurry water by mixing a lithium compound, a metal compound containing at least a manganese compound, a phosphate compound, and water, and then subjecting the mixture to a hydrothermal reaction to obtain a slurry water A containing preliminary particles of the particles (A). By using the slurry water A containing preliminary particles of the particles (A) obtained in step (I), the core portion of the composite particle (X) can be formed from the particles (A).

[0024] Usable lithium compounds include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Of these, hydroxides are preferred.

[0025] The metal compound that can be used is one that contains at least a manganese compound. The manganese compound may be one or more of metal oxalates, metal sulfates, metal chlorides, and hydrates thereof, with metal sulfates and hydrates thereof being preferred.

[0026] Furthermore, an iron compound may be used as appropriate. Examples of such iron compounds include one or more of metal oxalates, metal sulfates, metal chlorides, and hydrates thereof. Among these, metal sulfates and hydrates thereof are preferred. In addition to these manganese compounds, metals other than manganese compounds and iron compounds (M 1 :M 1 has the same meaning as M in formula (A) may be used.

[0027] Examples of phosphoric acid compounds that can be used include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, etc. Among these, phosphoric acid is preferably used.

[0028] The lithium compound, the metal compound containing at least a manganese compound, and the phosphate compound are mixed with water to obtain a slurry water. The contents of the lithium compound, the metal compound, and the phosphate compound in the slurry water can be adjusted, for example, by mixing the particles (A) with lithium manganese iron phosphate (LiFe 0.2 Mn 0.8PO4), the molar ratio of the total content of the manganese compound and the iron compound to the content of the lithium compound is preferably 1:1 to 1:2.5 in terms of the conversion ratio of metal ions (total of manganese ions and iron ions) to lithium ions (metal ions:lithium ions).Furthermore, the molar ratio of the content of the lithium compound to the content of the phosphate compound is preferably 1:1 to 2.5:1 in terms of the conversion ratio of lithium ions to phosphate ions (lithium ions:phosphate ions).

[0029] The content of water in the slurry water is preferably 10 to 50 moles, more preferably 13 to 30 moles, per mole of phosphorus ion of the phosphate compound, from the viewpoints of solubility of the raw material compounds, ease of stirring, synthesis efficiency, etc.

[0030] When preparing the aqueous slurry, the order of addition of the above components is not particularly limited. However, from the viewpoint of preventing side reactions and facilitating the reaction, it is preferable to first mix at least the phosphate compound, the lithium compound, and water, and then add the metal compound to prepare the aqueous slurry. The phosphate compound is preferably added dropwise while stirring. The rate of addition of the phosphate compound is preferably 15 mL / min to 50 mL / min, more preferably 20 mL / min to 45 mL / min, and even more preferably 28 mL / min to 40 mL / min. The stirring time after addition of the phosphate compound is preferably 1 hour to 24 hours, more preferably 5 hours to 15 hours. In addition, it is preferable to reduce the dissolved oxygen content of the stirred slurry water by nitrogen bubbling, which can effectively prevent oxidation of the metal compound added in the subsequent step. Next, the metal compounds are added to the prepared slurry water, and the order of adding the metal compounds is not particularly limited.

[0031] Next, the slurry water obtained by mixing a lithium compound, a metal compound containing at least a manganese compound, a phosphate compound, and water is subjected to a hydrothermal reaction. The hydrothermal reaction may be carried out at a temperature of 100°C or higher, preferably 130°C to 180°C. The hydrothermal reaction is preferably carried out in a pressure-resistant vessel, and when the reaction is carried out at 130°C to 180°C, the pressure is preferably 0.3MPa to 0.9MPa, and when the reaction is carried out at 140°C to 160°C, the pressure is preferably 0.3MPa to 0.6MPa. The hydrothermal reaction time is preferably 0.1 hours to 48 hours, more preferably 0.2 hours to 24 hours. The slurry water subjected to the hydrothermal reaction is filtered, washed with water, and dried to isolate the preliminary particles of the particles (A). The drying method may be freeze drying or vacuum drying.

[0032] Water is added to the resulting preliminary particles of particles (A) to obtain slurry water A. At this time, a conductive carbon material such as glucose or cellulose nanofiber, a dispersant such as a polycarboxylic acid-based dispersant such as ammonium polycarboxylate, and the like may be added together with the water as needed. When a dispersant is used, the amount of the dispersant added is preferably 0.05 to 5 parts by mass per 100 parts by mass of the preliminary particles of particles (A). Furthermore, when preparing the slurry water A, it is preferable to stir the water, and the stirring time is preferably 0.5 to 24 hours, more preferably 1 to 6 hours.

[0033] From the viewpoint of favorably forming a core-shell structure together with material (B), the solid content of the slurry water A is preferably 1% by mass to 40% by mass, more preferably 3% by mass to 35% by mass, and even more preferably 5% by mass to 30% by mass. In addition, when the raw material compound contains water, such as when a hydrate or the like is used as the raw material compound, the solid content of the slurry water A is the amount excluding the water content, and can be calculated from the amount of the raw material compound added.

[0034] Step (II) is a step of preparing a lithium compound, at least an iron compound, and a metal (M 2This is a step of mixing a metal compound containing a phosphate compound, a phosphate compound, and water to obtain slurry water B. By using the slurry water B obtained in step (II), the shell portion of the composite particle (X) can be formed from material (B).

[0035] The order of steps (I) and (II) is not particularly limited, and step (I) may be performed after step (II), or steps (I) and (II) may be performed simultaneously. That is, steps (I) and (II) are steps for preparing slurry water A and slurry water B, respectively, to be used in the subsequent step (III).

[0036] The lithium compound, iron compound, and optionally phosphate compound that can be used in step (II) are the same as those that can be used in step (I). Usable metals other than iron compounds (M 2 :M 2 (has the same meaning as M in formula (B)) Examples of the compound include halides, sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, and ammonium salts. Among these, halides, nitrates, acetates, and ammonium salts are preferred.

[0037] In preparing the slurry water B in the step (II), the above compounds and the like may be mixed in a conventional manner while appropriately using a pH adjuster.

[0038] From the viewpoint of favorably forming a core-shell structure together with the particles (A), the solid content of the slurry water B is preferably 0.01% by mass to 40% by mass, more preferably 0.1% by mass to 35% by mass, and even more preferably 1% by mass to 30% by mass. The solid content of the slurry water B is the amount excluding the amount of water when the raw material compound used contains water, such as when a hydrate or the like is used as the raw material compound, and is the amount excluding the amount of volatile matter (the amount of "nitric acid" in the case of a nitrate) when the raw material compound used is a raw material compound that is partially volatilized by undergoing step (IV) described later, such as when a nitrate or the like is used as the raw material compound, and can be calculated from the amount of the raw material compound added.

[0039] Step (III) is a step of adding dropwise the slurry water A obtained in step (I) to the slurry water B obtained in step (II) to obtain a mixed liquid X1, which allows preliminary particles of the particles (A) that will become the core part to be well embedded in the material (B) that will become the shell part, thereby facilitating the formation of a core-shell structure. The rate at which the slurry water A is dropped into the slurry water B is preferably 0.1 mL / min to 100 mL / min, more preferably 1 mL / min to 80 mL / min, and even more preferably 5 mL / min to 60 mL / min. It is preferable to dropwise add the slurry water A while stirring the slurry water B. The stirring time for the slurry water B is preferably 0.5 to 24 hours, more preferably 1 to 6 hours.

[0040] The solid content X of the resulting mixed solution X1 is preferably 10% by mass to 70% by mass, more preferably 15% by mass to 65% by mass, and even more preferably 20% by mass to 60% by mass, from the viewpoint of efficiently and effectively forming a core-shell structure. As with the solid content of the slurry water A and the solid content of the slurry water B, the solid content of the mixed solution X1 is calculated by excluding the amount of water when the raw material compounds used contain water, and excluding the amount of volatile matter when the raw material compounds used are partially volatilized by the step (IV) described below. The solid content can be calculated from the total amount of the raw material compounds added. Alternatively, the solid content can be calculated as the sum of the solid content of the slurry water A and the solid content of the slurry water B.

[0041] Step (IV) is a step of removing water from the mixed liquid X obtained in step (III) and then calcining the mixture to obtain a calcined body X2, which is a preliminary body of the composite particles (X) having a core-shell structure. The method for removing water from the mixed liquid X is not particularly limited, and a method of heating to 70°C to 250°C may be used as appropriate, and a method of subsequently exposing to an environment of 90°C to 200°C to remove water may be further combined. When the water is removed, a gel h is obtained in which a plurality of fine droplets of slurry A are present in slurry B. The obtained gel h may be transferred to a heat-resistant container, but this is not essential. After the operation of removing water from the mixed liquid X, the baking conditions may be changed directly and the mixture may proceed to the baking step. From the viewpoint of yield, it is preferable to change the baking conditions directly and bake the mixed liquid X after the operation of removing water from the mixed liquid X. To remove moisture, a suitable heating means may be used, such as an electric furnace or an externally heated kiln.

[0042] The firing conditions in step (IV) are preferably a reducing atmosphere or an inert atmosphere, the firing temperature is preferably 500°C to 1000°C, more preferably 550°C to 900°C, and the firing time is preferably 0.5 hours to 24 hours, more preferably 1 hour to 6 hours. For firing, a conventional heating means may be appropriately selected. Indirect heating or direct heating may be appropriately selected. Specific examples of such heating means include an electric furnace, an internally heated kiln, and an externally heated kiln.

[0043] Step (V) is a step of subjecting the fired body X2 obtained in step (IV) to a wet grinding treatment, thereby obtaining composite particles (X) with a core-shell structure in which the core is formed of particles (A) and the shell is formed of material (B).

[0044] When subjecting the fired body X2 to the wet grinding treatment, it is preferable to add a solvent to the fired body X2 to form a slurry. Examples of the solvent include water, ethanol, or a mixture thereof. The solid content of the slurry is preferably 10% by mass to 70% by mass, more preferably 15% by mass to 65% by mass, and even more preferably 20% by mass to 60% by mass. In this case, a conductive carbon material such as glucose or cellulose nanofiber, or a dispersant such as a polycarboxylic acid-based dispersant such as ammonium polycarboxylate may be added together with water as needed. When a dispersant is used, the amount of the dispersant added is preferably 0.05 parts by mass to 5 parts by mass per 100 parts by mass of the fired body X2.

[0045] As the apparatus used for the wet grinding treatment, a planetary ball mill or a bead mill is preferably used. The materials for the balls or beads in such an apparatus include ZrO2, Al2O3, steel, tungsten carbide, etc. Among these, ZrO2 is preferred. The diameter of the balls or beads is preferably 0.5 mm to 10 mm, and more preferably 0.5 mm to 3 mm.

[0046] The time for wet grinding treatment (grinding time) is preferably 0.5 to 48 hours, more preferably 1 to 24 hours, and the grinding speed is preferably 50 to 1800 rpm, more preferably 100 to 1600 rpm.

[0047] To obtain core-shell structured composite particles (X) with an appropriate particle size, it is preferable to carry out the wet-milling treatment in multiple stages, i.e., by decreasing the diameter of the balls or beads in each stage. Specifically, for example, when wet-pulverization is carried out in two stages, in the first stage of wet-pulverization, the diameter of the balls or beads is preferably 2 mm to 10 mm, more preferably 2 mm to 5 mm, the pulverization time is preferably 0.5 hours to 24 hours, more preferably 1 hour to 12 hours, and the pulverization speed is preferably 50 rpm to 400 rpm, more preferably 100 rpm to 300 rpm. Next, in the second stage wet grinding treatment, the diameter of the balls or beads is preferably 0.5 mm to 1 mm, more preferably 0.5 mm to 0.8 mm, the grinding time is preferably 0.5 hours to 48 hours, more preferably 1 hour to 24 hours, and the grinding speed is preferably 50 rpm to 1800 rpm, more preferably 100 rpm to 1600 rpm.

[0048] After the wet grinding treatment, the composite particles (X) are preferably obtained by drying. Before the drying treatment, it is advisable to remove unnecessary coarse particles and fine particles using a wet classifier or a centrifuge. As for the drying conditions, the drying temperature is preferably 70 to 200° C., more preferably 80 to 150° C. The drying time is preferably 3 to 48 hours, more preferably 6 to 24 hours.

[0049] The composite particles (X) can be used as a positive electrode material as it is, and a lithium ion secondary battery can be constructed according to a conventional method. Specifically, for example, the composite particles (X) are kneaded with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, or the like to prepare a positive electrode slurry, which is then applied to a current collector and press-molded to form a positive electrode.

[0050] The lithium ion secondary battery to which such a positive electrode can be applied is not particularly limited as long as it essentially comprises a positive electrode, a negative electrode, an electrolyte solution, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte.

[0051] The negative electrode is not particularly limited in terms of its material composition, and any known material can be used as long as it can absorb lithium ions during charging and release them during discharging. For example, lithium metal, graphite, silicon-based materials (Si, SiOx), lithium titanate, or carbon materials such as amorphous carbon can be used. It is preferable to use an electrode made of an intercalating material capable of electrochemically absorbing and releasing lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, such as a combination of graphite and silicon-based materials.

[0052] The electrolyte solution is prepared by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent typically used in electrolyte solutions for lithium ion secondary batteries, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, and oxolane compounds.

[0053] The supporting salt is not particularly limited in type, but is preferably at least one of inorganic salts selected from LiPF6, LiBF4, LiClO4, and LiAsF6, derivatives of these inorganic salts, organic salts selected from LiSO3CF3, LiC(SO3CF3)2, LiN(SO3CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9), and derivatives of these organic salts.

[0054] The separator serves to electrically insulate the positive and negative electrodes and retain the electrolyte solution, and may be, for example, a porous synthetic resin film, particularly a porous film made of a polyolefin polymer (polyethylene, polypropylene).

[0055] The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. 0.51 Li 0.34 TiO 2.94 , Li 1.3 Al 0.3 Ti 1.7(PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 , Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, 30Li2S 26B2S3 44LiI, 63Li2S 36SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 70Li2S 30P2S5, 50Li2S 50GeS2, Li7P3S 11 , Li 3.25 P 0.95 Just use S4.

[0056] The shape of the lithium ion secondary battery having the above-described configuration is not particularly limited, and may be various shapes such as a coin shape, a cylindrical shape, a square shape, or an irregular shape enclosed in a laminate outer casing. [Example]

[0057] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. The average particle size of the particles was measured by the following method.

[0058] <<Measurement of average particle size>> Using a TEM electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.), the average particle size (length of the longest axis) of 100 randomly selected particles was measured. The sample was prepared by dispersion processing, and the accelerating voltage during measurement was set to 200 kV.

[0059] [Example 1] Slurry water a1 was obtained by mixing 1272 g of LiOH·H2O and 4 L of water. Next, while maintaining the temperature at 25°C, 1153 g of 85% aqueous phosphoric acid solution was added dropwise at 35 mL / min to the resulting slurry a1 while stirring for 3 minutes. The mixture was then stirred at 400 rpm for 12 hours to obtain slurry water a2 containing Li3PO4. Nitrogen was purged into the resulting slurry water a2 to reduce the dissolved oxygen concentration of the slurry water a2 to 0.5 mg / L or less. Then, 964 g of MnSO4·5H2O and 1668 g of FeSO4·7H2O were added to the total amount of slurry water a2 to obtain slurry water a3. The molar ratio of the added MnSO4·5H2O to FeSO4·7H2O (manganese compound:iron compound) was 40:60.

[0060] The resulting slurry water a3 was then placed in an autoclave and subjected to a hydrothermal reaction at 170°C for 1 hour. The pressure inside the autoclave was 0.8 MPa. After the hydrothermal reaction, the resulting crystals were filtered and then washed with 12 parts by mass of water per part by mass of the crystals. The washed cake d1 (water content: 32%) was freeze-dried at -50°C for 12 hours to obtain preliminary particles of particles (A). 185 g of the resulting cake d1, 6.3 g of glucose, 12.5 g of an ammonium polycarboxylate dispersant (SN Dispersant 5027, manufactured by San Nopco), and 500 mL of water were added, and the mixture was dispersed using an ultrasonic agitator (T25, manufactured by IKA) for 30 minutes to uniformly color the entire mixture, yielding slurry water A1 (solid content: 24% by mass).

[0061] Next, 8.4 g of LiOH·H2O, 34.5 g of FeC2O4·2H2O, 23.0 g of NH4H2PO4·2H2O, 0.9 g of Mg(CH3COO)2·4H2O, 0.8 g of TiCl4, 126 g of citric acid monohydrate, and 500 ml of water were mixed to obtain slurry water B1 (solid content: 6 mass%). Next, while stirring the slurry water B1, the slurry water A1 was added dropwise to the slurry water B1 at a rate of 50 mL / min to obtain a mixed liquid X1-1 (solid content: 16% by mass). Thereafter, the mixed liquid X1-1 was heated to 80°C to remove water, and a gel h1 was obtained. The obtained gel h1 was cured at 200° C. for 2 hours, and then fired at 750° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain a fired body X2-1.

[0062] 3 g of the fired body X2-1 was ground with 20 ml of ethanol and φ3 mm ZrO2 balls at 400 rpm for 1 hour to obtain slurry water X3-1. Then, the φ3 mm ZrO2 balls were replaced with φ0.5 mm ZrO2 balls, and the ground material was ground at 400 rpm for 4 hours to obtain slurry water X3-2. Next, coarse particles were removed from the obtained slurry water X3-2 using a wet classifier, and then fine particles were removed using an ultracentrifuge. The mixture was then dried at 80°C to obtain composite particles X-1 (LiFe 0.672 Mn 0.32 Mg 0.004 Ti 0.004 PO4) was obtained.

[0063] [Example 2] Composite particles X-2 (LiFe) were prepared in the same manner as in Example 1, except that slurry water B2 (solid content: 6 mass%) obtained by mixing 8.4 g of LiOH·H2O, 34.5 g of FeC2O4·2H2O, 23.0 g of NH4H2PO4·2H2O, 31.2 g of NH4VO, 126 g of citric acid monohydrate, and 500 ml of water was used instead of slurry water B1. 0.66 Mn 0.33 V 0.01 PO4) was obtained.

[0064] [Example 3] Composite particles X-3 (Li) were prepared in the same manner as in Example 1, except that slurry water B3 (solid content: 6 mass%) obtained by mixing 8.2 g of LiOH·H2O, 34.5 g of FeC2O4·2H2O, 23.0 g of NH4H2PO4·2H2O, 51.1 g of NbCl, 126 g of citric acid monohydrate, and 500 ml of water was used instead of slurry water B1. 0.996 Nb 0.004 Fe 0.68 Mn 0.32 PO4) was obtained.

[0065] [Example 4] 220 g of cake d1 obtained in Example 1, 6.3 g of glucose, 15 g of the above polycarboxylate ammonium dispersant, and 500 mL of water were added, and the mixture was dispersed using an ultrasonic agitator for 30 minutes to uniformly color the entire mixture, thereby obtaining slurry water A4 (solid content: 28% by mass). Next, 2.1 g of LiOH·H2O, 8.6 g of FeC2O4·2H2O, 5.8 g of NH4H2PO4·2H2O, 0.2 g of Mg(CH3COO)2·4H2O, 0.2 g of TiCl4, 31 g of citric acid monohydrate, and 500 ml of water were mixed to obtain slurry water B4 (solid content: 2 mass%). Next, composite particles X-4 (LiFe 0.618 Mn 0.38 Mg 0.001 Ti 0.001 PO4) was obtained.

[0066] [Example 5] 139 g of cake d1 obtained in Example 1, 6.3 g of glucose, 9.4 g of the above polycarboxylate ammonium dispersant, and 500 mL of water were added, and the mixture was dispersed using an ultrasonic agitator for 30 minutes to uniformly color the entire mixture, thereby obtaining slurry water A5 (solid content: 19% by mass). Next, 16.8 g of LiOH·H2O, 69.1 g of FeC2O4·2H2O, 46.0 g of NH4H2PO4·2H2O, 1.7 g of Mg(CH3COO)2·4H2O, 1.5 g of TiCl4, 252 g of citric acid monohydrate, and 500 ml of water were mixed to obtain slurry water B5 (solid content: 13% by mass). Next, composite particles X-5 (LiFe 0.74 Mn 0.24 Mg 0.01 Ti 0.01 PO4) was obtained.

[0067] [Example 6] The composite particles X-6 (LiFe 0.672 Mn 0.32 Mg 0.004 Ti 0.004 PO4) was obtained.

[0068] [Example 7] Composite particles X-7 (Li) were prepared in the same manner as in Example 1, except that preliminary particles of particles (A) obtained by subjecting the slurry water a3 obtained in Example 1 to a hydrothermal reaction at 110°C for 0.5 hours were used, and slurry water B7 (solid content: 6 mass%) obtained by mixing 8.2 g of LiOH·H2O, 34.5 g of FeC2O4·2H2O, 23.0 g of NH4H2PO4·2H2O, 51.1 g of NbCl, 126 g of citric acid monohydrate, and 500 ml of water was used instead of slurry water B1. 0.996 Nb 0.004 Fe 0.68 Mn 0.32 PO4) was obtained.

[0069] [Example 8] The same procedure as in Example 1 was repeated except that instead of the slurry water X3-2, the slurry water X3-1 obtained in Example 1 was further pulverized with ZrO2 balls of 0.5 mm diameter at 200 rpm for 12 hours to obtain slurry water X8-2. 0.618 Mn 0.38 Mg 0.001 Ti 0.001 PO4) was obtained.

[0070] [Example 9] The same procedure as in Example 1 was repeated, except that instead of the slurry water X3-2, the slurry water X3-1 obtained in Example 1 was further pulverized at 1200 rpm for 1 hour using ZrO2 balls with a diameter of 0.5 mm, and the slurry water X9-2 was obtained. 0.744 Mn 0.24 Mg 0.008 Ti 0.008 PO4) was obtained.

[0071] [Comparative Example 1] The slurry water A1 obtained in Example 1 was heated to 80°C to remove water, and a mixture Z was obtained. Next, the obtained mixture Z was fired at 750°C for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain particles Z (LiFe 0.6 Mn 0.4 PO4) was obtained.

[0072] <Battery property evaluation 1> Positive electrodes for lithium ion secondary batteries were fabricated using composite particles X-1 to X-9 obtained in the examples and particle Z obtained in the comparative example. Specifically, these composite particles X-1 to X-9 or particle Z obtained, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 85:10:5, and N-methyl-2-pyrrolidone was added to the mixture and thoroughly kneaded to prepare positive electrode slurry. The positive electrode slurry was applied to a current collector made of aluminum foil with a thickness of 20 μm using a coater and vacuum dried at 80°C for 12 hours. The resulting mixture was then punched into a φ14 mm disk and pressed using a hand press at 16 MPa for 2 minutes to form a positive electrode. Next, a coin-type secondary battery was constructed using the above positive electrode. A graphite negative electrode (HS-LIB-N-Gr-001) punched to a diameter of 15 mm was used as the negative electrode. The electrolyte was a 1 mol / L solution of LiPF6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7. A porous polymer film was used as the separator. These battery components were assembled and housed in an atmosphere with a dew point of −50°C or lower using standard methods to obtain a coin-type secondary battery (CR-2032). The resulting coin-type secondary battery was subjected to 500 cycles of constant current charging at 1C with a cutoff voltage of 4.3V at 45°C using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation) to determine the lifespan (%) calculated using the following formula (z): Life characteristics (%) = {(discharge capacity after 500 cycles) / (discharge capacity at the first cycle)} × 100 (z) The results are shown in Table 1.

[0073] <Battery property evaluation 2> Using each coin-type secondary battery obtained in Evaluation 1 of Battery Properties, the value of life characteristics (%) was determined using the above formula (z) in the same manner as in Evaluation 1, by repeating 100 cycles of charging at a constant current of 1 C with an end voltage of 4.3 V in an environment of 60°C using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation) and discharging at a constant current of 1 C with an end voltage of 2 V. The results are shown in Table 1.

[0074] [Table 1]

Claims

1. The following formula (X): LiFe ａ Mn ｂ M ｘ ｃ PO ４ ・・・(X) (In formula (X), M ｘ represents Na, Mg, Ti, Al, Zn, Cu, Sn, Ni, V, Nb, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, and c satisfy 0.5<a≦1, 0<b<0.5, and 0<c≦0.3, and 2a+2b+(M ｘ (valence of x) × c = 2. and a core-shell structure, wherein the core portion is represented by the following formula (A): LiFe ｄ Mn ｅ M １ ｆ PO ４ ・・・(A) (In formula (A), M １ represents Mg, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. d, e, and f satisfy 0≦d≦1, 0<e≦1, and 0≦f≦0.3, and 2d+2e+(M １ (valence of x) × f = 2. The shell portion is formed of particles having an average composition represented by the following formula (B): Li ｇ Fe ｈ M ２ ｉ 2O ４ ・・・(B) (In formula (B), M ２ represents Na, Mg, Ti, Al, Zn, Cu, Sn, Ni, Co, Zr, V, or Nb. g, h, and i are in the range of 0.8≦g≦1.2, 0.5≦h≦0.99, 0.01≦i≦0.5, and g+2h+(M ２ (valence of i) × i = 3. The positive electrode active material composite particles for a lithium ion secondary battery are formed from a material having an average composition represented by the formula:

2. 2. The positive electrode active material composite particle for a lithium ion secondary battery according to claim 1, wherein the mass ratio of the core portion to the shell portion (core:shell) is 1:1 to 20:

1.

3. 3. The positive electrode active material composite particle for a lithium ion secondary battery according to claim 1, wherein the ratio of the average particle diameter of the core portion to the average thickness of the shell portion (core diameter / shell thickness) is 2.5 to 35.

4. 3. The positive electrode active material composite particle for a lithium ion secondary battery according to claim 1, wherein the average particle diameter of the core portion is 50 nm to 300 nm.

5. The following steps (I) to (V): (I) A step of obtaining a slurry water by mixing a lithium compound, a metal compound including at least a manganese compound, a phosphate compound, and water, and then subjecting the resulting mixture to a hydrothermal reaction to obtain a slurry water A containing preliminary particles of the particles (A). (II) A lithium compound, at least an iron compound, and a metal (M ２ a step of mixing a metal compound containing a phosphate compound, a phosphate compound, and water to obtain a slurry water B; (III) A step of adding the slurry water A obtained in the step (I) dropwise to the slurry water B obtained in the step (II) to obtain a mixed liquid X1. (IV) A step of removing water from the obtained mixed liquid X and then firing the mixture to obtain a fired body X2. (V) A step of subjecting the obtained fired body X2 to a wet grinding treatment The method for producing positive electrode active material composite particles for a lithium ion secondary battery according to claim 1 , comprising:

6. 6. The method for producing positive electrode active material composite particles for a lithium ion secondary battery according to claim 5, wherein the wet pulverization treatment in step (V) is treatment using a planetary ball mill or a bead mill.

7. 7. The method for producing positive electrode active material composite particles for a lithium ion secondary battery according to claim 6, wherein the processing speed of the wet grinding treatment in step (V) is 50 rpm to 1800 rpm.

8. 7. The method for producing positive electrode active material composite particles for a lithium ion secondary battery according to claim 5 or 6, wherein the solid content of the slurry water A obtained in step (I) is 1% by mass to 40% by mass, and the solid content of the slurry water B obtained in step (II) is 0.01% by mass to 40% by mass.

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