Method for producing positive electrode active material nanoparticles for lithium-ion secondary battery

Abstract

The present invention relates to a method which is for producing positive electrode active material nanoparticles for a lithium-ion secondary battery and with which it is possible to effectively support carbon and micronize particles.　That is, the present invention is a method for producing positive electrode active material nanoparticles which are for a lithium-ion secondary battery and are represented by formula (A) of LiaMnbFecMxPO4 and in which carbon is supported, the method comprising the following steps (I)-(III): (I) a step for mixing a lithium compound, a metal compound including at least a manganese compound and / or an iron compound, a phosphate compound, and water to obtain slurry water i; (II) a step for adding conductive carbon material and ammonia nitrogen together to the obtained slurry water i at a mass ratio of an addition amount of the conductive carbon material to an addition amount of the ammonia nitrogen (conductive carbon material: ammonia nitrogen) of 1:1 / 25 to 1:1 / 2 to obtain slurry water ii; and (III) a step for hydrothermally reacting the obtained slurry water ii, and then calcining the resultant to obtain nanoparticles.

Description

Method for producing nanoparticles of positive electrode active material for lithium-ion secondary batteries

[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.

[0002] In order to enhance the usefulness of positive electrode active material particles made of compounds such as Li(Fe,Mn)PO4 having an olivine structure as a positive electrode material for lithium ion secondary batteries, it is desirable to reinforce the electronic conductivity and reduce the particle size, and various manufacturing methods have been developed.

[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.

[0004] JP 2020-102321 A JP 2023-47467 A

[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 nanoparticles of a positive electrode active material for lithium ion secondary batteries, which can achieve both effective carbon loading and particle size reduction.

[0007] Therefore, the present inventors conducted extensive research to solve the above-mentioned problems, and as a result, discovered a method for producing nanoparticles of positive electrode active material for lithium ion secondary batteries that can achieve both effective carbon loading and particle size reduction by using a conductive carbon material and ammoniacal nitrogen and going through specific steps.

[0008] That is, the present invention provides a compound represented by the following formula (A): a Mn b Fec 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 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 method for producing carbon-supported positive electrode active material nanoparticles for lithium ion secondary batteries, the method 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 slurry water i; (II) adding a conductive carbon material and ammoniacal nitrogen to the obtained slurry water i all 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; and (III) subjecting the obtained slurry water ii to a hydrothermal reaction, followed by calcining the reaction to obtain nanoparticles.

[0009] According to the manufacturing method of the present invention, it is possible to obtain nanoparticles of a positive electrode active material for a lithium ion secondary battery, which are effectively supported with carbon and have effectively fine particles. Therefore, a lithium ion secondary battery constructed with a positive electrode using such nanoparticles of a positive electrode active material for a lithium ion secondary battery can effectively reduce unnecessary elution of metals constituting the nanoparticles of a positive electrode active material for a lithium ion secondary battery, even after exposure to a harsh operating environment.

[0010] FIG. 1 is a pattern diagram showing the analysis results of an XRD pattern.

[0011] The present invention will be described in detail below. The method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery of the present invention is a method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery (hereinafter also referred to as "nanoparticles (A)") that are represented by the following formula (A) and that are supported by carbon: Li a Mnb 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 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.)

[0012] In the above formula (A), a is preferably 0.6≦a≦1.2, more preferably 0.65≦a≦1.15, and even more preferably 0.7≦a≦1.1. b is preferably 0.4≦b≦0.8. c is preferably 0.2≦c≦0.6. x may be 0≦x≦0.2, or may be 0≦x≦0.15, or may be 0≦x≦0.1. Furthermore, from the viewpoint of further increasing the discharge capacity, M may be Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd.

[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 Fe0.36 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 Fe 0.27 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, even more preferably 20 nm or more and less than 50 nm, and particularly preferably 40 nm or more and less than 50 nm. Note that the "average particle size" of the nanoparticles (A) refers to the value obtained by calculating the crystallite size from the X-ray diffraction pattern using the XRD / Lebert method.

[0015] The amount of carbon supported in the total amount (100% by mass) 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 even more preferably 1.0% by mass to 1.3% by mass.

[0016] The carbon supported on the nanoparticles (A) corresponds to the carbon obtained by carbonizing the carbon material used in producing the nanoparticles (A), i.e., the carbon content of the carbon material in terms of carbon atoms. Therefore, the amount of carbon supported in 100% by mass of the total amount of nanoparticles (A) may be calculated from the carbon content 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 comprises the steps of: a Mn b Fe c M xPO4...(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 method for producing carbon-supported positive electrode active material nanoparticles for lithium ion secondary batteries, the method 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 slurry water i; (II) adding a conductive carbon material and ammoniacal nitrogen to the obtained slurry water i all 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; and (III) subjecting the obtained slurry water ii to a hydrothermal reaction to obtain nanoparticles.

[0018] It is presumed that the manufacturing method of the present invention allows the conductive carbon material and ammonia nitrogen added together to simultaneously promote each other without inhibiting each other, and instead effectively support and refine the particles. Therefore, the resulting nanoparticles (A) are extremely fine particles in which particle coarsening is effectively suppressed, and carbon is effectively supported on the particles while being well coated. Therefore, a lithium ion secondary battery obtained using the nanoparticles (A) can effectively suppress the unnecessary elution of the metals constituting the nanoparticles (A) even after repeated use or exposure to harsh environments.

[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 a slurry water i.

[0020] Usable lithium compounds include hydroxides (e.g., LiOH.H2O, LiOH), carbonates, sulfates, and acetates, with hydroxides being 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. Among 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 so as to achieve such amounts.

[0025] Nitrogen may be purged from the slurry water i after the addition of the raw materials. 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 compound. This allows trilithium phosphate (LiPO) to be formed as a precursor of the nanoparticles (A) in the slurry water i after the addition of the raw materials, 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 hours to 1 hour, more preferably 0.25 hours to 0.5 hours.

[0027] Step (II) is a step of simultaneously adding a conductive carbon material and ammoniacal nitrogen 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 to obtain slurry water ii. In this way, by using ammoniacal nitrogen together with the conductive carbon material that will later become the supported carbon and adding them simultaneously at a specific mass ratio, it becomes possible to effectively and efficiently support carbon on the nanoparticles (A) while effectively miniaturizing the nanoparticles themselves, 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 a positive electrode active material for a lithium ion secondary battery. By undergoing the production method of the present invention, the conductive carbon material is carbonized to form carbon, which is then supported on the nanoparticles (A).

[0029] Specific examples of conductive carbon materials that can be used include 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 to effectively function 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] Ammoniacal nitrogen is a nitrogen compound containing an NHx- structure in its molecule. Specific examples of ammoniacal 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 aqueous slurry 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 solids content of the slurry water i. 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 solids 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 solids 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 solids content of the slurry water i.

[0033] After adding the conductive carbon material and ammoniacal nitrogen to the aqueous slurry (i) all at once, the resulting mixture is preferably stirred and mixed to obtain aqueous slurry (ii) from the viewpoints of effectively achieving both effective carbon loading and particle size reduction, and 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, ultrasonic stirring is preferably used for the stirring and mixing in order to more effectively dissolve the conductive carbon material and ammoniacal nitrogen.

[0034] Step (III) is a step in which the slurry water (ii) obtained in step (II) is subjected to a hydrothermal reaction followed by calcination 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. When the reaction is carried out at 130°C to 180°C, the pressure is preferably 0.3 MPa to 0.9 MPa. When the reaction is carried out at 140°C to 160°C, the pressure is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 hours to 48 hours, more preferably 0.2 hours to 24 hours. After the hydrothermal reaction, the nanoparticles (A) are preferably isolated as preliminary particles by filtering, washing with water, and drying before calcination. Freeze drying or vacuum drying can be used as a drying method.

[0035] The isolated preliminary particles of nanoparticles (A) are then calcined to obtain nanoparticles (A). The calcination is preferably performed in a reducing atmosphere or an inert atmosphere, at a calcination temperature of preferably 500°C to 1000°C, more preferably 550°C to 900°C, for a calcination time of preferably 0.5 to 12 hours, more preferably 1 to 6 hours.

[0036] The nanoparticles (A) may be used as they are as a positive electrode material, or granules formed by appropriate granulation may be used. In particular, it is desirable to form and use granules from the viewpoint that the particle size is appropriately adjusted and handling is easy when coating as a positive electrode material. To granulate the nanoparticles (A), a commonly used method can be used. For example, spray drying may 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 the D obtained by the volume-based particle size distribution based on the laser diffraction / scattering method. 50 For example, a laser diffraction apparatus (Microtrac MT3000II, manufactured by MicrotracBEL, particle transmittance: transparent, particle shape: non-spherical, particle refractive index: 1.52, solvent: ethanol, solvent refractive index: 1.36) is used to determine the particle size distribution, 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] Here, the negative electrode is not particularly limited in terms of its material composition, and any known material composition 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 formed 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 an inorganic salt selected from LiPF, LiBF, LiClO, and LiAsF, a derivative of the inorganic salt, an organic salt selected from LiSOCF, LiC(SOCF), and LiN(SOCF), LiN(SOCF) and LiN(SOCF)(SOCF), and a derivative of the organic salt.

[0042] The separator serves to electrically insulate the positive and negative electrodes and retain the electrolyte, 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 P.O. 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 S4 can be used.

[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.

[0045] The present invention will be described in detail 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 Average Particle Size of Nanoparticles (A)>> Measurement was carried out using an X-ray diffractometer (D8 ADVANCE A-25, manufactured by Bruker AXS). The measurement conditions were: target CuKα, tube voltage 40 kV, tube current 40 mA, scan range 10 to 70° (2θ), step width 0.023°, and scan speed 0.13° / step. The XRD pattern was analyzed using the XRD / Lebert method to calculate the crystallite size, and this value was used as the average particle size of the nanoparticles as a positive electrode active material for lithium ion secondary batteries.

[0047] <<Carbon Loading Amount of Nanoparticles (A)>> The carbon content of the resulting positive electrode active material particles 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 resulting 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 solids content of slurry water i) and 0.13 g of ethylenediamine (0.3 parts by mass per part by mass of the solids content of slurry water i) were added all at once to slurry water i-1, and the mixture was stirred for 0.25 hours to obtain slurry water ii-1. The resulting mixture was then subjected to a hydrothermal reaction at 170°C for 1 hour, followed by freeze-drying 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 supported amount: 1.3% by mass was obtained.

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

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

[0051] [Example 4] Nanoparticles (A)-4 (LiMn 0.7 Fe 0.3 PO4, carbon supported amount: 1.1% by mass was obtained.

[0052] [Example 5] Nanoparticles (A)-5 (LiMn 0.7 Fe 0.3 PO4, carbon supported amount: 1.2% by mass was obtained.

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

[0054] [Example 7] Nanoparticles (A)-7 (LiMn 0.7 Fe 0.3 PO4, carbon supported amount: 1.1% by mass was obtained.

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

[0056] [Example 9] Nanoparticles (A)-9 (LiMn 0.7 Fe 0.3 PO4, carbon supported amount: 1.0% by mass was obtained.

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

[0058]

[0059] Evaluation of Metal Leaching Reduction Effect 1) Preparation of Battery Physical Properties A positive electrode for a lithium-ion secondary battery was prepared using each nanoparticle (A) obtained in the Examples and Comparative Examples. Specifically, the obtained nanoparticle (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. The resulting material was then punched into a 2 cm x 2 cm square and pressed using a gap 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 graphite negative electrode (manufactured by Hosen Co., Ltd.) punched to 2.2 cm x 2.2 cm was used as the negative electrode. The electrolyte solution 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 full-cell secondary battery.

[0060] 2) Analysis of Metal Leaching Amount Using the obtained full-cell secondary battery, a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation) was used to charge at a constant current of 0.2 C and a cut-off voltage of 4.5 V in a 30 ° C environment, and discharge at a constant current of 0.2 C and a cut-off voltage of 2.0 V. This was repeated 500 times. Thereafter, the full-cell secondary battery was disassembled, and the removed positive electrode was decomposed with aqua regia and filtered, and then 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 based on the Mn and Fe constituting the nanoparticles (A) used in the production of each full-cell secondary battery (100 mol%), respectively. The results are shown in Table 2.

[0061] In addition, the closer the value of the remaining amount (mol %) is to 100 mol %, the more effectively it can be evaluated that the effect of suppressing metal elution from the nanoparticles (A) constituting the positive electrode of the full-cell type secondary battery is exerted.

[0062]

[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 for measuring the average particle size of the nanoparticles (A). The obtained XRD pattern diagram is shown in Figure 1. The bottom row of Figure 1 shows the LiMn 0.67 Fe 0.23 1 shows an XRD pattern of the crystal structure of PO (LMFP) (cited from standard data for the crystal structure of LMFP: LMFP ICSD 54820, published by the Japan Chemical Information Association). 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 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 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 method for producing carbon-supported positive electrode active material nanoparticles for lithium ion secondary batteries, the method 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 slurry water i; (II) adding a conductive carbon material and ammoniacal nitrogen to the obtained slurry water i all 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; and (III) subjecting the obtained slurry water ii to a hydrothermal reaction, followed by calcining the reaction to obtain nanoparticles.

2. A 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 ethylenediamine, ammonium nitrate, and ammonium phosphate.

3. A method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery 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. A method for producing nanoparticles of a positive electrode active material for lithium ion secondary batteries, according to any one of claims 1 to 3, 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. A method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the mixing in step (I) is performed by stirring and mixing using ultrasonic waves.

6. A method for producing nanoparticles of a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, 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. A method for producing nanoparticles of positive electrode active material for lithium ion secondary batteries according to any one of claims 1 to 6, wherein the amount of carbon supported is 0.5 mass% to 3 mass% based on a total amount (100 mass%) of the nanoparticles of positive electrode active material for lithium ion secondary batteries.

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