Method for manufacturing positive electrode active material nanoparticles for lithium ion secondary battery

Abstract

To provide a method for manufacturing positive electrode active material nanoparticles for a lithium ion secondary battery that can achieve both effective carbon support and particle size reduction.SOLUTION: A method for manufacturing positive electrode active material nanoparticles for a lithium ion secondary battery is represented by the formula (A): LiaMnbFecMxPO4, and is configured such that carbon is supported, and includes the following steps of (I) mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i, (II) adding conductive carbon material and ammonia nitrogen to the obtained slurry water i all at once at a mass ratio of the amount of conductive carbon material added to the amount of ammonia nitrogen added (conductive carbon material: ammonia nitrogen) of 1:1 / 25 to 1:1 / 2 to obtain slurry water ii, and (III) subjecting the obtained slurry water ii to a hydrothermal reaction and then firing it to obtain nanoparticles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing nanoparticles of a positive electrode active material for lithium ion secondary batteries, which are fine particles and can reduce unnecessary elution of metals constituting the particles. [Background technology]

[0002] Positive electrode active material particles made of compounds such as Li(Fe,Mn)PO4 with an olivine structure are desirable for use as positive electrode materials in lithium-ion secondary batteries, as they are required to have improved electronic conductivity and finer particles. Various manufacturing methods have been developed to date.

[0003] For example, Patent Document 1 discloses a manufacturing method using vegetable protein as a carbon material. Patent Document 2 discloses composite particles using particles made of an olivine-type transition metal lithium compound with a size of 50 nm to 200 nm, and attempts are made to support carbon derived from cellulose nanofibers, etc. Both of these efforts aim to improve the cycle characteristics of lithium-ion secondary batteries. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-102321 [Patent Document 2] Japanese Patent Application Publication No. 2023-47467 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even with the techniques described in any of the above patent documents, it is difficult to effectively achieve both effective carbon loading and particle size reduction, and there is still room for improvement.

[0006] Therefore, the present invention relates to a method for producing positive electrode active material nanoparticles for a lithium ion secondary battery that can achieve both effective carbon loading and particle refinement. **Means for Solving the Problems**

[0007] As a result of intensive studies to solve the above problems, the present inventors have found a method for producing positive electrode active material nanoparticles for a lithium ion secondary battery that can achieve both effective carbon loading and particle refinement by passing through specific steps while using a conductive carbon material and ammonia nitrogen.

[0008] That is, the present invention provides the following formula (A): Li a Mn b Fe c M x PO4···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. ) A method for producing positive electrode active material nanoparticles for a lithium ion secondary battery, which is represented by the formula and has carbon supported thereon, comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water i (II) A step of adding a conductive carbon material and ammonia nitrogen to the obtained slurry water i in a lump at a mass ratio (conductive carbon material: ammonia nitrogen) of 1:1 / 25 to 1:1 / 2 to obtain slurry water ii (III) A step of subjecting the obtained slurry water ii to a hydrothermal reaction and then firing to obtain nanoparticles The present invention provides a method for producing positive electrode active material nanoparticles for a lithium ion secondary battery, which comprises the above steps.

Advantages of the Invention

[0009] According to the manufacturing method of the present invention, it is possible to obtain cathode active material nanoparticles for a lithium-ion secondary battery that effectively carry carbon and effectively refine particles. Therefore, in the case of a lithium-ion secondary battery constructed with a cathode using such cathode active material nanoparticles for a lithium-ion secondary battery, even after being exposed to a harsh usage environment, unnecessary elution of the metal constituting the cathode active material nanoparticles for a lithium-ion secondary battery can be effectively reduced.

Brief Description of the Drawings

[0013] Specifically, for example, LiMnPO4, LiFePO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.9 Fe 0.1 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.75 Fe 0.19 Zr 0.03 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4, Li 0.6 Mn 0.84 Fe 0.36 PO4, etc. Among them, LiMn 0.8 Fe 0.2 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, Li 1.2 Mn 0.63 Fe0.27 PO4 is preferred.

[0014] The average particle size of the nanoparticles (A) obtained by the present invention is preferably 1 nm or more and less than 50 nm, more preferably 5 nm or more and less than 50 nm, still more preferably 20 nm or more and less than 50 nm, and even more preferably 40 nm or more and less than 50 nm. In addition, the "average particle size" in the nanoparticles (A) means a value obtained by calculating the crystallite size using the XRD / Ruland method for the X-ray diffraction pattern.

[0015] The carbon loading amount in 100% by mass of the total amount of the nanoparticles (A) obtained by the present invention is preferably 0.5% by mass to 3% by mass, more preferably 0.9% by mass to 2% by mass, and still more preferably 1.0% by mass to 1.3% by mass.

[0016] In addition, the carbon supported on the nanoparticles (A) is carbon formed by carbonizing the carbon material used in the production of the nanoparticles (A), that is, it corresponds to the amount of carbon atoms of the carbon material. Therefore, the carbon loading amount in 100% by mass of the total amount of the nanoparticles (A) may be determined by calculation from the amount of carbon atoms of the total amount of the carbon material used, or may be determined by measurement using a carbon-sulfur analyzer.

[0017] The method for producing the positive electrode active material nanoparticles (nanoparticles (A)) for a lithium ion secondary battery of the present invention is represented by the following formula (A): Li a Mn b Fe c M x PO4···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd; a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3.) and carbon is supported on the nanoparticles of a positive electrode active material for a lithium ion secondary battery, the nanoparticles comprising the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain a slurry water i. (II) A step of adding a conductive carbon material and ammoniacal nitrogen to the obtained slurry water i at a mass ratio of the conductive carbon material to the ammoniacal nitrogen (conductive carbon material:ammoniacal nitrogen) of 1:1 / 25 to 1:1 / 2 to obtain slurry water ii. (III) A step of subjecting the obtained slurry water ii to a hydrothermal reaction to obtain nanoparticles. The manufacturing method includes the steps of:

[0018] In the manufacturing method of the present invention, it is presumed that the conductive carbon material and ammonia nitrogen added together do not have an inhibitory effect on each other, but rather have some kind of promoting effect on each other, making it possible to simultaneously promote effective carbon loading and particle refinement. Therefore, the obtained nanoparticles (A) are ultrafine particles in which particle coarsening is effectively suppressed, and carbon is effectively loaded on the particles while being well coated. Therefore, in the case of a lithium ion secondary battery obtained using the nanoparticles (A), even after repeated use or exposure to a harsh usage environment, it is possible to effectively prevent the metals constituting the nanoparticles (A) from being unnecessarily eluted.

[0019] Step (I) is a step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain slurry water i.

[0020] Usable lithium compounds include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, sulfates, and acetates. Of these, hydroxides are preferred.

[0021] Usable manganese compounds include one or more of metal oxalates, metal sulfates, metal chlorides, and hydrates thereof, with metal sulfates and hydrates thereof being preferred.

[0022] Examples of iron compounds that can be used include one or more of metal oxalates, metal sulfates, metal chlorides, and hydrates thereof. Of these, metal sulfates and hydrates thereof are preferred. Metal compounds (M: M has the same meaning as M in formula (A)) other than these manganese compounds and iron compounds may also be used.

[0023] 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.

[0024] The slurry water i obtained by mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphoric acid compound, and water preferably contains 2.0 to 4.0 moles, and more preferably 2.0 to 3.1 moles, of lithium per mole of phosphoric acid, and each raw material may be added appropriately to achieve such amounts.

[0025] Nitrogen may be purged from the slurry water i after the raw materials have been added. Purging with nitrogen allows the reaction to proceed with a reduced dissolved oxygen concentration in the slurry water i, thereby suppressing oxidation of the metal compounds. This allows trilithium phosphate (Li3PO4) to be formed as a precursor of the nanoparticles (A) in the slurry water i after the raw materials have been added, thereby promoting the miniaturization of the nanoparticles (A).

[0026] Furthermore, when adding and mixing the above raw materials, it is preferable to carry out ultrasonic stirring and mixing from the viewpoint of improving dispersibility or solubility and obtaining a highly uniform slurry water i. In this case, the time for ultrasonic stirring and mixing is preferably 0.25 to 1 hour, more preferably 0.25 to 0.5 hours.

[0027] Step (II) is a step of obtaining slurry water ii by adding a conductive carbon material and ammoniacal nitrogen all at once to the slurry water i obtained in step (I) at a mass ratio (conductive carbon material:ammoniacal nitrogen) of 1:1 / 25 to 1:1 / 2 of the amount of conductive carbon material added to the amount of ammoniacal nitrogen added (conductive carbon material:ammoniacal nitrogen). By using ammoniacal nitrogen together with the conductive carbon material that will later become the supported carbon and adding them all at once at a specific mass ratio, it is possible to effectively reduce the size of the nanoparticles (A) themselves while also effectively and efficiently supporting carbon on them, and therefore it is possible to effectively reduce the elution of unnecessary metals in the resulting lithium-ion secondary battery.

[0028] The conductive carbon material is a material used to effectively enhance the electronic conductivity of the resulting nanoparticles of positive electrode active material for lithium ion secondary batteries, and is carbonized to carbon by the production method of the present invention, and is supported on the nanoparticles (A).

[0029] Specific examples of conductive carbon materials that can be used include one or more selected from monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch, dextrin, and cellulose; polysaccharide nanofibers such as cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, and chitosan nanofibers; polyols and polyethers such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among these, from the viewpoint of improving solubility and dispersibility in solvents, allowing the material to function effectively as a carbon material, and effectively suppressing metal elution from the nanoparticles (A), one or more selected from monosaccharides, polysaccharides, and polysaccharide nanofibers are preferred, and one or more selected from glucose, cellulose, and cellulose nanofibers are more preferred.

[0030] Ammonia nitrogen is a nitrogen compound containing an NHx- structure in its molecule. Specific examples of ammonia nitrogen that can be used in the present invention include one or more compounds selected from ethylenediamine, ammonium nitrate, and ammonium phosphate. Among these, ethylenediamine is preferred from the viewpoint of effectively achieving both effective carbon loading and particle size reduction.

[0031] The mass ratio of the amount of conductive carbon material to the amount of ammoniacal nitrogen (conductive carbon material:ammoniacal nitrogen) added all at once to the slurry water i obtained in step (I) is 1:1 / 25 to 1:1 / 2, preferably 1:1 / 20 to 1:1 / 5, more preferably 1:1 / 15 to 1:1 / 10, and even more preferably 1:1 / 13.5 to 1:1 / 11.5.

[0032] More specifically, the amount of the conductive carbon material added is preferably 1 to 8 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 3 to 6 parts by mass, per part by mass of the solid content of the slurry water i. Even more specifically, for example, when sucrose is used as the conductive carbon material, the amount added is preferably 4 to 8 parts by mass, more preferably 4 to 7 parts by mass, and even more preferably 4 to 6 parts by mass, per part by mass of the solid content of the slurry water i. Furthermore, for example, when cellulose is used as the conductive carbon material, the amount added is preferably 3 to 7 parts by mass, more preferably 3 to 6 parts by mass, and even more preferably 3 to 5 parts by mass, per part by mass of the solid content of the slurry water i. The amount of ammonia nitrogen added is preferably 0.1 to 1.2 parts by mass, more preferably 0.13 to 0.5 parts by mass, and even more preferably 0.2 to 0.34 parts by mass per part by mass of the solid content of the slurry water i.

[0033] After adding the conductive carbon material and ammoniacal nitrogen to the slurry water (i) all at once, it is preferable to obtain the slurry water (ii) by stirring and mixing the mixture from the viewpoint of effectively achieving both effective carbon loading and particle size reduction, and from the viewpoint of the solubility of the conductive carbon material and ammoniacal nitrogen. The stirring and mixing time is preferably 0.25 to 24 hours, more preferably 0.5 to 15 hours. Furthermore, in order to more effectively dissolve the conductive carbon material and ammoniacal nitrogen, it is preferable to use ultrasonic stirring for the stirring and mixing.

[0034] Step (III) is a step in which the slurry water ii obtained in step (II) is subjected to a hydrothermal reaction and then calcined to obtain nanoparticles. 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. After the hydrothermal reaction and before calcination, the nanoparticles (A) are preferably isolated as preliminary particles by filtering, washing with water, and drying. The drying method may be freeze drying or vacuum drying.

[0035] The isolated preliminary particles of nanoparticles (A) are then calcined to obtain nanoparticles (A). The firing conditions 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 12 hours, more preferably 1 hour to 6 hours.

[0036] The nanoparticles (A) may be used as they are as a positive electrode material, or may be appropriately granulated to form granules. It is particularly preferable to use the nanoparticles in the form of granules, as this allows for an appropriate particle size adjustment and facilitates handling when applied as a positive electrode material. A commonly used method can be used to granulate the nanoparticles (A). For example, spray drying can be performed using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.). The average particle size of the granules is preferably 1 μm to 20 μm. The average particle size of the granules is determined by the volume-based particle size distribution based on the laser diffraction / scattering method. 50 For example, the particle size distribution is determined using a laser diffraction device (Microtrac MT3000II, manufactured by MicrotracBEL, particle transmittance: transparent, particle shape: non-spherical, particle refractive index: 1.52, solvent: ethanol, solvent refractive index: 1.36), and the D 50 The value (μm) can be obtained.

[0037] Thereafter, a lithium ion secondary battery can be constructed according to a conventional method. Specifically, for example, the nanoparticles (A) are mixed 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] 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]

[0045] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. The physical properties of the obtained particles were determined by the following methods. The results are shown in Table 1.

[0046] <<Measurement of the average particle size of nanoparticles (A)>> Measurements were carried out using an X-ray diffractometer (D8 ADVANCE A-25, manufactured by BrukerAXS). The measurement conditions were CuKα target, 40 kV tube voltage, 40 mA tube current, 10-70° (2θ) scan range, 0.023° step width, and 0.13° / step scan speed. The XRD pattern was analyzed using the XRD / Lebert method to calculate the crystallite diameter, which was used as the average particle diameter of the nanoparticles of the positive electrode active material for lithium-ion secondary batteries.

[0047] <<Carbon loading amount of nanoparticles (A)>> The carbon content of the obtained particles of positive electrode active material for lithium ion secondary batteries was measured using a carbon / sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.).

[0048] [Example 1] 16 g of pre-prepared trilithium phosphate was added to 38.4 g of water, followed by ultrasonic stirring and mixing for 0.5 hours to obtain a trilithium phosphate aqueous solution. Next, while stirring the obtained trilithium phosphate aqueous solution, 4.1 g of iron sulfate monohydrate, 0.1 g of sodium sulfite, and 9.2 g of manganese sulfate monohydrate were added, and the mixture was stirred for 0.25 hours to obtain slurry water i-1. The molar ratio of manganese to iron (Mn:Fe) in slurry water i-1 was 7:3. Next, 13 g of sucrose (4 parts by mass per part by mass of the solid content of the slurry water i) and 0.13 g of ethylenediamine (0.3 parts by mass per part by mass of the solid content of the slurry water i) were added to the slurry water i-1 all at once, and the mixture was stirred for 0.25 hours to obtain slurry water ii-1. The mixture was then subjected to a hydrothermal reaction at 170°C for 1 hour, and then freeze-dried at -50°C for 12 hours to obtain the precursor of nanoparticles (A). The obtained precursor of nanoparticles (A) was calcined at 700°C for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain nanoparticles (A)-1 (LiMn 0.7 Fe 0.3 PO4, carbon loading: 1.3% by mass was obtained.

[0049] [Example 2] Nanoparticles (A)-2 (LiMn 0.7 Fe 0.3 PO4, carbon loading: 2.4% by mass was obtained.

[0050] [Example 3] Nanoparticles (A)-3 (LiMn 0.7 Fe 0.3 PO4, carbon loading: 2.5% by mass was obtained.

[0051] [Example 4] Nanoparticles (A)-4 (LiMn) were prepared in the same manner as in Example 1, except that 13 g of sucrose and 0.65 g of ethylenediamine were added to the slurry water i-1 at once. 0.7 Fe 0.3 PO4, carbon loading: 1.1% by mass was obtained.

[0052] [Example 5] Nanoparticles (A)-5 (LiMn) were prepared in the same manner as in Example 1, except that 13 g of sucrose and 0.26 g of ethylenediamine were added to the slurry water i-1 at once. 0.7 Fe 0.3 PO4, carbon loading: 1.2% by mass was obtained.

[0053] [Example 6] Nanoparticles (A)-6 (LiMn 0.7 Fe 0.3 PO4, carbon loading: 1.2% by mass was obtained.

[0054] [Example 7] Nanoparticles (A)-7 (LiMn) were prepared in the same manner as in Example 1, except that 0.13 g of ammonium phosphate was used instead of ethylenediamine, and this and 13 g of sucrose were added to the slurry water i-1 all at once. 0.7 Fe 0.3 PO4, carbon loading: 1.1% by mass was obtained.

[0055] [Example 8] Nanoparticles (A)-8 (LiMn 0.7 Fe 0.3 PO4, carbon loading: 1.0% by mass was obtained.

[0056] [Example 9] Nanoparticles (A)-9 (LiMn) were prepared in the same manner as in Example 1, except that 26 g of cellulose was used instead of sucrose, and this and 0.13 g of ethylenediamine were added to the slurry water i-1 all at once. 0.7 Fe 0.3 PO4, carbon loading: 1.0% by mass was obtained.

[0057] [Comparative Example 1] Nanoparticles (A)-z (LiMn 0.7 Fe 0.3 PO4, carbon loading: 4% by mass was obtained.

[0058] [Table 1]

[0059] <Evaluation of the effect of reducing metal elution> 1) Preparation of battery properties The nanoparticles (A) obtained in the examples and comparative examples were used to prepare positive electrodes for lithium-ion secondary batteries. Specifically, the nanoparticles (A), 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 a positive electrode slurry. The positive electrode slurry was applied to a current collector made of 20 μm thick aluminum foil using a coating machine and vacuum dried at 80°C for 12 hours. Then, a 2 cm x 2 cm square was punched out and pressed using a gap-type press (manufactured by Ikawa Manufacturing Co., Ltd.) to form a positive electrode. Next, a full-cell secondary battery was constructed using the above positive electrode. A 2.2 cm × 2.2 cm punched graphite negative electrode (manufactured by Hosen Co., Ltd.) was used as the negative electrode. The electrolyte used was a 1 mol / L LiPF6 solution in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7. A polymer porous 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 full-cell secondary battery.

[0060] 2) Analysis of metal elution amount The obtained full-cell secondary battery was used in a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation) under conditions of 30°C, constant current charging at 0.2 C and a cut-off voltage of 4.5 V, and constant current discharging at 0.2 C and a cut-off voltage of 2.0 V, and this cycle was repeated 500 times. Thereafter, the full-cell secondary battery was disassembled, and the removed positive electrode was decomposed in aqua regia and filtered, after which the remaining amounts of Mn and Fe were quantified by ICP-OES optical emission spectrometry. Next, based on the obtained quantitative values, the remaining amounts (mol%) of Mn and Fe were calculated when the Mn and Fe constituting the nanoparticles (A) used in the production of each full-cell secondary battery were set as the standard (100 mol%). The results are shown in Table 2.

[0061] Furthermore, the closer this residual amount (mol%) is to 100 mol%, the more effectively it can be evaluated that the effect of suppressing metal elution from the nanoparticles (A) that constitute the positive electrode of the full-cell secondary battery is being exhibited.

[0062] [Table 2]

[0063] <XRD pattern analysis> For the particles obtained in Example 1 and Comparative Example 1, XRD patterns were obtained using an X-ray diffractometer (D8 ADVANCE A-25, manufactured by Bruker AXS) under the same measurement conditions as those used to measure the average particle size of the nanoparticles (A). The resulting XRD pattern is shown in FIG. In addition, the bottom row of Figure 1 shows LiMn 0.67 Fe 0.23 The XRD pattern of the crystal structure of PO4(LMFP) (standard data for the crystal structure of LMFP: cited from the Japan Chemical Information Association, LMFP ICSD 54820) is shown. From FIG. 1, it was confirmed that the particles obtained in Example 1 and Comparative Example 1 had the desired crystal structure.

Claims

1. The following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ 2O ４ ・・・(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0≦b≦1.2, 0≦c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.) and a carbon-supported positive electrode active material nanoparticle for a lithium ion secondary battery, the positive electrode active material nanoparticle being represented by the following steps (I) to (III): (I) A step of mixing a lithium compound, a metal compound containing at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain a slurry water i. (II) A step of adding a conductive carbon material and ammoniacal nitrogen to the obtained slurry water i at once in a mass ratio of the amount of the conductive carbon material to the amount of the ammoniacal nitrogen (conductive carbon material:ammoniacal nitrogen) of 1:1 / 25 to 1:1 / 2 to obtain slurry water ii. (III) A step of subjecting the obtained slurry water ii to a hydrothermal reaction and then calcining it to obtain nanoparticles. The method for producing positive electrode active material nanoparticles for lithium ion secondary batteries comprises:

2. 2. The method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the ammonia nitrogen used in step (II) is one or more selected from the group consisting of ethylenediamine, ammonium nitrate, and ammonium phosphate.

3. 3. The method for producing positive electrode active material nanoparticles for lithium ion secondary batteries according to claim 1 or 2, wherein the conductive carbon material used in step (II) is one or more selected from the group consisting of monosaccharides, polysaccharides, polysaccharide nanofibers, polyols, polyethers, and organic acids.

4. 3. The method for producing positive electrode active material nanoparticles for lithium ion secondary batteries according to claim 1, wherein the amount of ammonia nitrogen added in step (II) is 0.1 to 1.2 parts by mass per 1 part by mass of the solid content of the slurry water i.

5. 3. The method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the mixing in step (I) is performed by stirring and mixing using ultrasonic waves.

6. 3. The method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the average particle size of the nanoparticles of a positive electrode active material for a lithium ion secondary battery is 1 nm or more and less than 50 nm.

7. 3. The method for producing positive electrode active material nanoparticles for lithium ion secondary batteries according to claim 1, wherein the amount of carbon supported is 0.5% by mass to 3% by mass in 100% by mass of the total amount of the positive electrode active material nanoparticles for lithium ion secondary batteries.

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