Positive electrode materials for lithium-ion secondary batteries, positive electrodes for lithium-ion secondary batteries, lithium-ion secondary batteries

Abstract

To provide a positive electrode material for a lithium ion secondary battery that can remove water adsorbed in pores of a carbon material, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery including the positive electrode for the lithium ion secondary battery.SOLUTION: A positive electrode material for a lithium ion secondary battery includes at least one of a primary particle in which a carbonaceous coating is formed on a surface of a positive electrode active material particle and an aggregated particle in which the plurality of primary particles are aggregated, and an organic solvent adhered to the primary particle. In measurement at 200°C by headspace gas chromatography-mass spectrometry, a content of the organic solvent is within a range of 50 ppm or more and 500 ppm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery. [Background technology]

[0002] To form a positive electrode mixture layer for a positive electrode of a lithium-ion secondary battery, a positive electrode material paste containing a positive electrode active material coated with a carbon material, a conductive additive, a binder, and an organic solvent is used. The positive electrode material paste is required to have reduced viscosity and improved durability. The carbon material contained in the positive electrode material paste adsorbs water in its pores. Therefore, simply drying the paste makes it difficult to remove water from the carbon material, which causes an increase in viscosity when the paste is kneaded. Therefore, a method for removing the water adsorbed in the pores of the carbon material has been sought to reduce the viscosity of the positive electrode material paste.

[0003] Patent Document 1 describes that a drying treatment of a composite slurry containing layered lithium composite oxide secondary particles, lithium-based polyanion particles having carbon supported on the surface, lithium-based polyanion particles, and an organic solvent is carried out at 50°C to 150°C. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-136206 Summary of the Invention [Problem to be solved by the invention]

[0005] The method described in Patent Document 1 can remove water adhering to the surface of the carbon material, but cannot remove water adsorbed in the pores of the carbon material.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a positive electrode material for a lithium ion secondary battery, which is capable of removing water adsorbed in the pores of a carbon material, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery including the positive electrode for a lithium ion secondary battery. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A cathode active material comprising at least one of primary particles having a carbonaceous coating formed on the surface thereof and aggregated particles formed by aggregation of a plurality of the primary particles, and an organic solvent adhered to the primary particles, A positive electrode material for lithium-ion secondary batteries, in which the organic solvent content is detected to be between 50 ppm and 500 ppm when measured at 200°C using headspace gas chromatography mass spectrometry. [2] The positive electrode material for a lithium ion secondary battery according to [1], wherein the organic solvent is at least one selected from methanol, ethanol, propanol, isobutyl alcohol, acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, hexane, kerosene, N-methyl-2-pyrrolidone, and polyvinylidene fluoride. [3] The positive electrode material for a lithium ion secondary battery according to [1] or [2], wherein the water content determined by the Karl Fischer moisture evaporation method is 1500 ppm or less. [4] The positive electrode material for a lithium ion secondary battery according to any one of [1] to [3], which has an average particle size of 0.3 μm or more and 10.0 μm or less as measured by a laser diffraction particle size distribution analyzer. [5] The positive electrode material for a lithium ion secondary battery according to any one of [1] to [4], wherein the primary particles have an olivine structure with an average particle diameter of 50 nm or more and 500 nm or less. [6] The positive electrode material for a lithium ion secondary battery according to any one of [1] to [5], wherein the carbonaceous coating has a thickness of 0.5 nm or more and 10 nm or less. [7] A positive electrode for a lithium ion secondary battery comprising an electrode current collector and a positive electrode mixture layer formed on the electrode current collector, The positive electrode mixture layer contains the positive electrode material for a lithium ion secondary battery according to any one of [1] to [6]. [8] A lithium ion secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, A lithium ion secondary battery comprising, as a positive electrode, the positive electrode for a lithium ion secondary battery according to [7]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a positive electrode material for a lithium ion secondary battery and a positive electrode for a lithium ion secondary battery that are capable of removing water adsorbed in the pores of a carbon material, as well as a lithium ion secondary battery including this positive electrode for a lithium ion secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiments of the positive electrode material for a lithium ion secondary battery, the positive electrode for a lithium ion secondary battery, and the lithium ion secondary battery of the present invention will be described below. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0010] [Cathode materials for lithium-ion secondary batteries] The positive electrode material for a lithium-ion secondary battery of this embodiment includes at least one of primary particles in which a carbonaceous coating is formed on the surface of positive electrode active material particles and aggregated particles in which a plurality of the primary particles are aggregated, and an organic solvent adhered to the primary particles, and when measured at 200°C by headspace gas chromatography-mass spectrometry, the content of the organic solvent is detected to be in the range of 50 ppm or more and 500 ppm or less.

[0011] In the positive electrode material for lithium ion secondary batteries of this embodiment, the organic solvent content is detected in the range of 50 ppm to 500 ppm when measured at 200°C by headspace gas chromatography-mass spectrometry (GC-MS). The organic solvent content detected by the headspace gas chromatography-mass spectrometry is preferably 70 ppm to 400 ppm, more preferably 80 ppm to 300 ppm. If the organic solvent content is less than the lower limit, adsorbed moisture is not removed, resulting in poor cycle characteristics. If the organic solvent content exceeds the upper limit, the applied paste evaporates during drying, which makes voids more likely to form in the electrode and reduces the energy density.

[0012] The content of the organic solvent is measured using a gas chromatograph mass spectrometer (model: 6890N / 5975, manufactured by Agilent) and a headspace device (model: TurboMatrix40, manufactured by Perkin Elmer).

[0013] The positive electrode material for lithium ion secondary batteries of this embodiment preferably has a water content of 1500 ppm or less, more preferably 1300 ppm or less, and even more preferably 1100 ppm or less, as determined by Karl Fischer moisture evaporation method. When the water content of the positive electrode material for lithium ion secondary batteries is equal to or less than the upper limit, adhesion to the current collector during electrode fabrication is improved, and the coating film is less likely to peel off from the current collector.

[0014] The water content of the positive electrode material for a lithium ion secondary battery can be measured as follows. The positive electrode material for lithium ion secondary batteries is dried in a vacuum atmosphere at 100° C. for 24 hours to thoroughly remove moisture adsorbed on the surface of the positive electrode material for lithium ion secondary batteries. Next, the dried positive electrode material for lithium-ion secondary batteries is heated to 100°C to 250°C using a Karl Fischer moisture meter (product name: CA-200 / VA-200, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) to measure the amount of moisture detected.

[0015] The positive electrode material for a lithium ion secondary battery of this embodiment preferably includes primary particles having an organic solvent attached thereto and a carbonaceous coating formed on the surface of the positive electrode active material particles, and agglomerated particles (secondary particles) formed by aggregation of a plurality of the primary particles.

[0016] The organic solvent attached to the primary particles is preferably at least one selected from methanol, ethanol, propanol, isobutyl alcohol, acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, hexane, kerosene, N-methyl-2-pyrrolidone, and polyvinylidene fluoride. The attachment of such an organic solvent to the primary particles inhibits re-adsorption of water, improving the stability of the particle surface.

[0017] The positive electrode material for lithium ion secondary batteries according to this embodiment preferably has an average particle size, as measured by a laser diffraction particle size distribution analyzer, of 0.3 μm to 10.0 μm, more preferably 0.4 μm to 9.5 μm, and even more preferably 0.5 μm to 9.0 μm. When the average particle size is equal to or greater than the lower limit, the structure of the positive electrode mixture layer obtained by coating and drying the positive electrode material paste for lithium ion secondary batteries on an aluminum current collector can be made uniform, suppressing local overvoltages associated with charge / discharge reactions and reducing the amount of metal elution. When the average particle size is equal to or less than the upper limit, the positive electrode material can be densely packed, improving the energy density per unit volume of the positive electrode. The average particle size referred to here is the average particle size of primary particles in which a carbonaceous coating is formed on the surface of positive electrode active material particles, and of aggregated particles in which a plurality of such primary particles are aggregated.

[0018] The average particle size of the primary particles is calculated from the average particle size of 100 randomly selected particles observed under a scanning electron microscope (SEM).

[0019] The primary particles preferably have an olivine structure with an average particle diameter of 50 nm or more and 500 nm or less. That is, the electrode active material particles constituting the primary particles preferably have an olivine structure, and the primary particles preferably have an average particle diameter of 50 nm or more and 500 nm or less. The average particle size of the primary particles is more preferably 60 nm or more and 400 nm or less, and even more preferably 80 nm or more and 250 nm or less.

[0020] The reason why the average primary particle size of the primary particles, including the electrode active material particles having an olivine structure and coated with a carbonaceous film, is set to the above range is as follows: If the average primary particle size is less than 50 nm, the specific surface area of ​​the primary particles increases, which increases the mass of carbon required and reduces the charge / discharge capacity. Furthermore, carbon coating becomes difficult, making it impossible to obtain primary particles with a sufficient coverage rate, and therefore, it is not possible to obtain a good mass energy density, particularly at low temperatures or during high-speed charge / discharge. On the other hand, if the average primary particle size exceeds 500 nm, it takes a long time for the lithium ions or electrons to move within the primary particles, which is undesirable because it increases the internal resistance and deteriorates the output characteristics.

[0021] The shape of the secondary particles is not particularly limited, but it is preferable that the shape is spherical, since this facilitates the production of a positive electrode material made of spherical particles, in particular, true spherical particles. The reason why a spherical shape is preferable is as follows: The amount of solvent can be reduced when preparing a positive electrode material paste for a lithium ion secondary battery by mixing the secondary particles coated with a carbonaceous coating, a binder, and a solvent. Furthermore, this positive electrode material paste for a lithium ion secondary battery can be easily applied to an electrode current collector. Furthermore, a spherical shape minimizes the surface area of ​​the secondary particles, which in turn minimizes the amount of binder added, thereby reducing the internal resistance of the resulting positive electrode. Furthermore, by making the secondary particles spherical, particularly true spherical, they can be easily packed closely together, which increases the amount of the positive electrode material for a lithium ion secondary battery packed per unit volume, thereby increasing the electrode density and the capacity of the lithium ion secondary battery, which is preferable.

[0022] The thickness of the carbonaceous coating on the primary particles is preferably 0.5 nm or more and 10 nm or less, and more preferably 0.5 nm or more and 5.5 nm or less. The reason for the thickness of the carbonaceous coating being set within the above range is as follows: If the thickness of the carbonaceous coating is less than 0.5 nm, the carbonaceous coating is too thin to form a film with the desired resistance value. As a result, the conductivity decreases, and it becomes impossible to ensure the conductivity required for the positive electrode material. On the other hand, if the thickness of the carbonaceous coating exceeds 10 nm, the battery activity, for example, the battery capacity per unit mass of the positive electrode material, decreases.

[0023] The coverage of the primary particles with the carbonaceous coating is preferably 60% or more, and more preferably 80% or more. When the coverage of the carbonaceous coating is 60% or more, the coating effect of the carbonaceous coating can be sufficiently obtained. The pore size in the carbonaceous coating is preferably 0.4 nm or more and 2.0 nm or less, and more preferably 0.5 nm or more and 1.0 nm or less. The reason for specifying the pore diameter in the carbonaceous coating within the above range is as follows: If the pore diameter is less than 0.4 nm, solvated lithium ions cannot pass through the pores, and the battery will not function. If the pore diameter exceeds 2.0 nm, the water adsorbed within the pores will form a stable cluster structure, making it difficult to remove.

[0024] The carbon loading amount relative to the specific surface area of ​​the positive electrode material for a lithium ion secondary battery of this embodiment ([carbon loading amount] / [specific surface area]) is 0.5 mg / m 2 ≥ 2.0 mg / m 2 Preferably, it is 0.7 mg / m or less. 2 ≥ 1.6 mg / m2 More preferably, it is: The reason why the amount of carbon supported relative to the specific surface area in the positive electrode material for a lithium ion secondary battery of this embodiment is limited to the above range is as follows: the amount of carbon supported relative to the specific surface area is 0.5 mg / m 2 If the carbon loading amount is less than 2.0 mg / m, when a lithium ion secondary battery is formed, the discharge capacity at a high rate of charge and discharge becomes low, making it difficult to achieve sufficient charge and discharge rate performance. 2 If the carbon content exceeds 100%, the amount of carbon is too large, and the battery capacity of the lithium ion secondary battery per unit mass of the primary particles decreases more than necessary.

[0025] The specific surface area of ​​the positive electrode material for a lithium ion secondary battery of this embodiment is 5.0 m 2 / g or more and 20m 2 / g or less, and 5.5m 2 / g or more and 18m 2 / g or less is more preferable, and 6.0m 2 / g or more and 16m 2 It is more preferable that the saturation coefficient is 1 / g or less. The reason why the specific surface area of ​​the positive electrode material for a lithium ion secondary battery of this embodiment is limited to the above range is as follows: 2 If the specific surface area is less than 20 m / g, it takes time for the lithium ions or electrons to move within the crystal, which is undesirable because the internal resistance increases and the output characteristics deteriorate. 2 If the specific surface area of ​​the electrode active material particles coated with the carbonaceous film exceeds 1 / g, the mass of carbon required increases due to the increase in the specific surface area of ​​the electrode active material particles coated with the carbonaceous film, resulting in a decrease in charge / discharge capacity. Furthermore, carbon coating becomes difficult, and primary particles with a sufficient coverage cannot be obtained. This is undesirable because a good mass energy density cannot be obtained, particularly at low temperatures and at high-speed charge / discharge.

[0026] "Electrode active material particles" The electrode active material particles having an olivine structure are not particularly limited, but for example, Li ions having a crystal structure suitable for Li diffusion are x Fe 1-y-z Ay M z It is preferable that the composition is made of PO4 (wherein A is at least one selected from the group consisting of Mn, Co, and Ni, M is at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, V, B, Al, Ga, In, Si, Ge, and rare earth elements, 0.85≦x≦1.1, 0≦y≦0.85, 0≦z≦0.2).

[0027] Li x Fe 1-y-z A y M z The reason why x in PO4 satisfies 0.85≦x≦1.1 is as follows. If x is less than 0.85, when an active material that does not contain lithium ions is used in the negative electrode, the amount of lithium ions in the battery decreases, resulting in a decrease in battery capacity, which is undesirable. On the other hand, if x exceeds 1.1, the olivine structure cannot be maintained, resulting in a decrease in crystal stability, which is undesirable.

[0028] Li x Fe 1-y-z A y M z The reason why y in PO4 satisfies 0≦y≦0.85 is as follows: If y exceeds 0.85, the ratio of Fe becomes too small, which undesirably reduces the lithium ion diffusion rate and electron conduction rate within the crystal, resulting in a deterioration in input / output characteristics.

[0029] Li x Fe 1-y-z A y M z The reason why z in PO4 satisfies 0≦z≦0.2 is as follows: if z exceeds 0.2, the ratio of electrochemically inactive metals increases, which is undesirable as it reduces the battery capacity per unit mass of the positive electrode material.

[0030] Li in this embodiment x Fe 1-y-z A y M zPO4 is preferably one in which y = 0 and z = 0. That is, in the positive electrode material for a lithium ion secondary battery of this embodiment, the electrode active material particles are preferably made of LiFePO4. By using LiFePO4 for the electrode active material particles, the lithium ion diffusion rate and electron conduction rate within the crystal are improved, improving input / output characteristics.

[0031] "Carbonaceous film" The carbonaceous coating is a pyrolytic carbonaceous coating obtained by carbonizing an organic compound as a raw material. The carbon source as a raw material for the carbonaceous coating is preferably derived from an organic compound with a carbon purity of 42.00% or more and 60.00% or less.

[0032] In the positive electrode material for a lithium-ion secondary battery of this embodiment, when a plurality of types of organic compounds are used, the "carbon purity" of the carbon source serving as the raw material for the carbonaceous coating is calculated as follows: the amount of carbon (% by mass) in the amount of each organic compound is calculated from the amount of each organic compound (% by mass) and the known carbon purity (%), and the total amount of carbon (% by mass) is added up; and the "carbon purity" is calculated from the total amount of the organic compounds (% by mass) and the total carbon amount (% by mass) according to the following formula (2). Carbon purity (%) = total carbon content (mass%) / total content (mass%) × 100 (2)

[0033] The positive electrode material for a lithium ion secondary battery of this embodiment contains at least one of primary particles in which a carbonaceous coating is formed on the surface of positive electrode active material particles and aggregate particles in which a plurality of the primary particles are aggregated, and an organic solvent adhered to the primary particles. When measured at 200°C by headspace gas chromatography-mass spectrometry, the organic solvent content is detected to be in the range of 50 ppm to 500 ppm, and therefore water adsorbed in the pores of the carbon material can be removed when a positive electrode for a lithium ion secondary battery is produced.

[0034] [Method of manufacturing positive electrode materials for lithium-ion secondary batteries] The method for producing the positive electrode material for a lithium ion secondary battery of this embodiment is not particularly limited. For example,x Fe 1-y-z A y M z In the case of PO4, a raw material slurry α is obtained by mixing a Li source, an Fe source, an A source, an M source, and a P source with a solvent containing water as a main component, and heating the obtained raw material slurry α to a temperature in the range of 100°C or more and 300°C or less, whereby Li x Fe 1-y-z A y M z A process for synthesizing PO4 particles and dissolving Li in an aqueous solvent containing a carbon source. x Fe 1-y-z A y M z The raw material slurry β in which PO4 particles are dispersed is dried and granulated, and then heated to a temperature in the range of 500°C or more and 1000°C or less to produce Li x Fe 1-y-z A y M z A step of coating the surface of PO4 particles with a carbonaceous coating, and a step of coating Li x Fe 1-y-z A y M z PO4 particles (hereinafter referred to as "carbonaceous coated Li x Fe 1-y-z A y M z PO4 particles) and stirring them with an organic solvent. x Fe 1-y-z A y M z and vacuum drying the PO4 particles.

[0035] Li x Fe 1-y-z A y M z The method for synthesizing PO particles is not particularly limited. For example, a Li source, an Fe source, an A (at least one selected from the group consisting of Mn, Co, and Ni) source, an M (at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) source, and a P source may be added to a solvent containing water as a main component, and the mixture may be stirred to form Li. x Fe 1-y-z Ay M z A raw material slurry α containing a precursor of PO4 is prepared.

[0036] These Li source, Fe source, A source, M source, and P source are added to a solvent containing water as the main component so that the molar ratio (Li source:Fe source:A source:M source:P source), i.e., the molar ratio of Li:Fe:A:M:P, is 0.85-5:0.1-2:0-2:0-2:1-2, and the mixture is stirred and mixed to prepare raw material slurry α. In order to mix these Li source, Fe source, A source, M source and P source uniformly, it is preferable to first prepare the Li source, Fe source, A source, M source and P source into an aqueous solution and then mix them. The molar concentrations of the Li source, Fe source, A source, M source, and P source in this raw material slurry α are high purity, and the Li source has high crystallinity and is very fine. x Fe 1-y-z A y M z Since it is necessary to obtain PO4 particles, the concentration is preferably 0.1 mol / L or more and 3 mol / L or less.

[0037] Examples of Li sources include hydroxides such as lithium hydroxide (LiOH), inorganic lithium salts such as lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium nitrate (LiNO3), lithium phosphate (Li3PO4), dilithium hydrogen phosphate (Li2HPO4), and lithium dihydrogen phosphate (LiH2PO4), and organic lithium salts such as lithium acetate (LiCH3COO) and lithium oxalate ((COOLi)2), and hydrates of these. At least one selected from this group is preferably used as the Li source. Lithium phosphate (Li3PO4) can also be used as a Li source and a P source.

[0038] As the Fe source, for example, divalent Fe compounds such as iron(II) chloride (FeCl), iron(II) sulfate (FeSO), and iron(II) acetate (Fe(CHCOO)) or their hydrates can be used, and trivalent Fe compounds such as lithium iron(III) phosphate (FePO), iron(III) nitrate (Fe(NO), iron(III) chloride (FeCl), and iron(III) citrate (FeCHO) or their hydrates can be used. Only a divalent Fe compound may be used as the Fe source, only a trivalent Fe compound may be used as the Fe source, or both a divalent Fe compound and a trivalent Fe compound may be used as the Fe source. Using both a divalent Fe compound and a trivalent Fe compound as the Fe source is preferred because it facilitates the formation of a solid solution of trivalent Fe in the crystal.

[0039] The Mn source is preferably a Mn salt, such as manganese(II) chloride (MnCl), manganese(II) sulfate (MnSO), manganese(II) nitrate (Mn(NO), manganese(II) acetate (Mn(CHCOO) and hydrates thereof. At least one selected from this group is preferably used as the Mn source.

[0040] The Co source is preferably a Co salt, such as cobalt(II) chloride (CoCl), cobalt(II) sulfate (CoSO), cobalt(II) nitrate (Co(NO), cobalt(II) acetate (Co(CHCOO) and hydrates thereof. At least one selected from this group is preferably used as the Co source.

[0041] The Ni source is preferably a Ni salt, such as nickel chloride (NiCl), nickel sulfate (NiSO), nickel nitrate (Ni(NO), nickel acetate (Ni(CHCOO) and hydrates thereof. At least one selected from this group is preferably used as the Ni source.

[0042] The Mg source is preferably a Mg salt, such as magnesium chloride (II) (MgCl), magnesium sulfate (II) (MgSO), magnesium nitrate (II) (Mg(NO)), magnesium acetate (II) (Mg(CHCOO)), and hydrates thereof. At least one selected from this group is preferably used as the Mg source.

[0043] The Ca source is preferably a Ca salt, such as calcium chloride (II) (CaCl), calcium sulfate (II) (CaSO), calcium nitrate (II) (Ca(NO)), calcium acetate (II) (Ca(CHCOO)), and hydrates thereof, and at least one selected from the group consisting of these is preferably used.

[0044] The Co source is preferably a Co salt, such as cobalt(II) chloride (CoCl), cobalt(II) sulfate (CoSO), cobalt(II) nitrate (Co(NO), cobalt(II) acetate (Co(CHCOO) and hydrates thereof. At least one selected from this group is preferably used as the Co source.

[0045] The Sr source is preferably a Sr salt, such as strontium carbonate (SrCo3), strontium sulfate (SrSO4), or strontium hydroxide (Sr(OH)2), and at least one selected from the group consisting of these is preferably used.

[0046] The Ba source is preferably a Ba salt, such as barium(II) chloride (BaCl), barium(II) sulfate (BaSO), barium(II) nitrate (Ba(NO)), barium(II) acetate (Ba(CHCOO)), and hydrates thereof, and at least one selected from the group consisting of these is preferably used.

[0047] The Ti source is preferably a Ti salt, and examples thereof include titanium chloride (TiCl4, TiCl3, TiCl2), titanium oxide (TiO), and hydrates thereof, and at least one selected from the group consisting of these is preferably used.

[0048] The Zn source is preferably a Zn salt, such as zinc chloride (II) (ZnCl), zinc sulfate (II) (ZnSO), zinc nitrate (II) (Zn(NO), zinc acetate (II) (Zn(CHCOO) and hydrates thereof. At least one selected from this group is preferably used as the Zn source.

[0049] Examples of the B source include boron compounds such as chlorides, sulfates, nitrates, acetates, hydroxides, and oxides, and at least one selected from the group consisting of these is preferably used.

[0050] Examples of the Al source include aluminum compounds such as chlorides, sulfates, nitrates, acetates, and hydroxides, and at least one selected from the group consisting of these is preferably used.

[0051] Examples of Ga sources include gallium compounds such as chlorides, sulfates, nitrates, acetates, and hydroxides, and at least one selected from the group consisting of these is preferably used.

[0052] Examples of the In source include indium compounds such as chlorides, sulfates, nitrates, acetates, and hydroxides, and at least one selected from the group consisting of these is preferably used.

[0053] Examples of the Si source include sodium silicate, potassium silicate, silicon tetrachloride (SiCl4), silicates, and organic silicon compounds, and at least one selected from the group consisting of these is preferably used.

[0054] Examples of the Ge source include germanium compounds such as chlorides, sulfates, nitrates, acetates, hydroxides, and oxides, and at least one selected from the group consisting of these is preferably used.

[0055] Examples of rare earth element sources include chlorides, sulfates, nitrates, acetates, hydroxides, and oxides of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and at least one selected from the group consisting of these is preferably used.

[0056] The P source is preferably at least one selected from phosphoric acids such as orthophosphoric acid (H3PO4) and metaphosphoric acid (HPO3), phosphates such as ammonium dihydrogen phosphate (NH4H2PO4), diammonium hydrogen phosphate ((NH4)2HPO4), ammonium phosphate ((NH4)3PO4), lithium phosphate (Li3PO4), dilithium hydrogen phosphate (Li2HPO4), and lithium dihydrogen phosphate (LiH2PO4), and hydrates thereof.

[0057] The solvent containing water as the main component is either water alone or an aqueous solvent containing water as the main component and, if necessary, an aqueous solvent such as alcohol. The aqueous solvent is not particularly limited as long as it is a solvent that can dissolve the Li source, Fe source, A source, M source, and P source. Examples of the solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, and diacetone alcohol; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether; ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone, and cyclohexanone; amides such as dimethylformamide, N,N-dimethylacetoacetamide, and N-methylpyrrolidone; and glycols such as ethylene glycol, diethylene glycol, and propylene glycol. These aqueous solvents may be used alone or in combination of two or more.

[0058] Next, the raw material slurry α is placed in a pressure vessel, heated to a temperature in the range of 100°C to 300°C, preferably 100°C to 250°C, and subjected to hydrothermal treatment for 1 hour to 72 hours. x Fe 1-y-z A y M z Obtain PO4 particles. In this case, by adjusting the temperature and time during the hydrothermal treatment, Li x Fe 1-y-z A y M z The particle size of the PO4 particles can be controlled to a desired size.

[0059] Next, Li was added to an aqueous solvent containing a carbon source. x Fe 1-y-z A y Mz The PO4 particles are dispersed to prepare raw slurry β. Next, the raw material slurry β is dried and granulated, and then heated at a temperature in the range of 500°C to 1000°C, preferably 500°C to 800°C, for 1 hour to 100 hours. x Fe 1-y-z A y M z The surface of the PO4 particles is coated with a carbonaceous film, and the carbonaceous-coated Li x Fe 1-y-z A y M z PO4 particles are obtained. Here, heating at temperatures below 500°C is not preferred because the carbonization of the carbonaceous coating is insufficient and the conductivity is significantly reduced. On the other hand, heating at temperatures above 1000°C is not preferred because some of the lithium volatilizes, reducing the battery capacity.

[0060] Next, carbonaceous coated Li x Fe 1-y-z A y M z An organic solvent is added to the PO4 particles and stirred. The organic solvent used is the same as the organic solvent attached to the primary particles.

[0061] Carbonaceous coated Li x Fe 1-y-z A y M z The amount of organic solvent added to the PO4 particles was x Fe 1-y-z A y M zThe amount of organic solvent is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 3 parts by mass or more and 25 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of PO4 particles. If the amount of organic solvent is less than the above lower limit, it becomes difficult to remove the organic solvent, and high temperatures are required to remove the excess organic solvent. When the temperature is raised to a high temperature, even the organic solvent adhering to the particle surface is removed, impairing the surface adsorption of the organic solvent. If the amount of organic solvent is less than the above upper limit, it becomes easy to remove the organic solvent without raising the temperature, and it becomes possible to dry the organic solvent while it remains adsorbed on the surface.

[0062] Next, the carbonaceous coating Li x Fe 1-y-z A y M z The PO4 particles are vacuum dried to obtain the positive electrode material for a lithium ion secondary battery of this embodiment.

[0063] "Carbon source" The carbon source is not particularly limited as long as it is an organic compound that can form a carbonaceous coating on the surface of the electrode active material particles. The organic compound is preferably a compound that is soluble or dispersible in water. Examples include salicylic acid, catechol, hydroquinone, resorcinol, pyrogallol, phloroglucinol, hexahydroxybenzene, benzoic acid, phthalic acid, terephthalic acid, phenylalanine, water-dispersible phenolic resins, sugars such as sucrose, glucose, and lactose, carboxylic acids such as malic acid and citric acid, unsaturated monohydric alcohols such as allyl alcohol and propargyl alcohol, ascorbic acid, and polyvinyl alcohol. One or more of these can be mixed to achieve a carbon purity of 42.00% or higher.

[0064] In the method for producing a positive electrode material for a lithium ion secondary battery of this embodiment, the amount of carbon source added (addition rate) is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, when the total mass of the electrode active material particles and the carbon source is 100% by mass.

[0065] If the amount of carbon source added is less than 0.5% by mass, the mixing stability of the positive electrode material for lithium ion secondary batteries will decrease, which is undesirable, whereas if the amount of carbon source added is more than 15% by mass, the content of the positive electrode active material will relatively decrease, which is undesirable because it will degrade the battery characteristics.

[0066] Furthermore, when multiple types of organic compounds are used as carbon sources, the amount of each organic compound is adjusted as described above so that the carbon purity of the organic compounds is 42.00% or more and 60.00% or less.

[0067] [Positive electrodes for lithium-ion secondary batteries] The positive electrode for a lithium ion secondary battery of this embodiment includes an electrode current collector and a positive electrode mixture layer (positive electrode) formed on the electrode current collector, and the positive electrode mixture layer contains the positive electrode material for a lithium ion secondary battery of this embodiment. That is, the positive electrode for a lithium ion secondary battery of this embodiment is formed by using the positive electrode material for a lithium ion secondary battery of this embodiment and forming a positive electrode mixture layer on one main surface of an electrode current collector.

[0068] The method for producing the positive electrode for a lithium ion secondary battery of this embodiment is not particularly limited as long as it is a method that can form a positive electrode on one main surface of an electrode current collector using the positive electrode material for a lithium ion secondary battery of this embodiment. Examples of the method for producing the positive electrode for a lithium ion secondary battery of this embodiment include the following methods. First, a positive electrode material paste for a lithium ion secondary battery is prepared by mixing the positive electrode material for a lithium ion secondary battery of this embodiment, a binder, a conductive additive, and a solvent.

[0069] "Binder" As the binder, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, etc. are preferably used.

[0070] The content of the binder in the positive electrode material paste for lithium ion secondary batteries is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 6% by mass or less, when the total mass of the positive electrode material for lithium ion secondary batteries according to this embodiment, the binder, and the conductive additive is taken as 100% by mass.

[0071] "Conductive additive" The conductive additive is not particularly limited, but for example, at least one selected from the group consisting of acetylene black, ketjen black, furnace black, vapor grown carbon fiber (VGCF), carbon nanotubes, and other fibrous carbons is used.

[0072] The content of the conductive additive in the positive electrode material paste for lithium ion secondary batteries is preferably 1% by mass or more and 15% by mass or less, and more preferably 3% by mass or more and 10% by mass or less, when the total mass of the positive electrode material for lithium ion secondary batteries according to this embodiment, the binder, and the conductive additive is taken as 100% by mass.

[0073] "solvent" A solvent may be added appropriately to the lithium ion secondary battery positive electrode material paste containing the lithium ion secondary battery positive electrode material according to this embodiment to facilitate application to an object to be applied, such as an electrode current collector. The solvent used in the electrode-forming paint or electrode-forming paste may be appropriately selected in accordance with the properties of the binder resin. Examples of the solvent include water, methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, diacetone alcohol, and other alcohols; ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, γ-butyrolactone, and other esters; diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and other ethers; acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone, cyclohexanone, and other ketones; dimethylformamide, N,N-dimethylacetoacetamide, N-methylpyrrolidone, and other amides; ethylene glycol, diethylene glycol, propylene glycol, and other glycols. These may be used alone or in combination of two or more.

[0074] The content of the solvent in the positive electrode material paste for lithium ion secondary batteries is preferably 60 parts by mass or more and 400 parts by mass or less, and more preferably 80 parts by mass or more and 300 parts by mass or less, where the total mass of the positive electrode material for lithium ion secondary batteries according to this embodiment, the binder, and the solvent is 100 parts by mass. By containing the solvent in the above range, it is possible to obtain a positive electrode material paste for a lithium ion secondary battery that has excellent electrode formability and excellent battery characteristics.

[0075] The method for mixing the positive electrode material for a lithium ion secondary battery of this embodiment, the binder, the conductive additive, and the solvent is not particularly limited as long as it is a method that can uniformly mix these components, and examples thereof include methods using a kneader such as a ball mill, a sand mill, a planetary mixer, a paint shaker, or a homogenizer.

[0076] Next, the positive electrode material paste for a lithium ion secondary battery is applied to one main surface of an electrode current collector to form a coating film, and this coating film is dried and then pressed and bonded to obtain a positive electrode for a lithium ion secondary battery in which a positive electrode mixture layer is formed on one main surface of the electrode current collector.

[0077] According to the positive electrode for a lithium ion secondary battery of this embodiment, since it contains the positive electrode material for a lithium ion secondary battery of this embodiment, a lithium ion secondary battery with excellent cycle characteristics can be obtained.

[0078] [Lithium-ion secondary battery] The lithium ion secondary battery of this embodiment includes the positive electrode for a lithium ion secondary battery of this embodiment, a negative electrode, a separator, and an electrolyte solution.

[0079] In the lithium ion secondary battery of this embodiment, the negative electrode, the electrolyte, the separator, and the like are not particularly limited. The negative electrode may be made of, for example, metallic Li, carbon material, Li alloy, or Li4Ti5O 12 The following negative electrode materials can be used. Moreover, a solid electrolyte may be used instead of the electrolytic solution and the separator.

[0080] The electrolyte solution is prepared by mixing, for example, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1, and adding lithium hexafluorophosphate (LiPF) to the resulting mixed solvent at a concentration of, for example, 1 mol / dm 3 It can be prepared by dissolving the material in such a manner that The separator may be made of, for example, porous propylene.

[0081] The lithium ion secondary battery of this embodiment has excellent cycle characteristics because it includes the positive electrode for a lithium ion secondary battery of this embodiment. [Example]

[0082] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0083] [Production of positive electrode material for lithium ion secondary batteries] [Example 1] LiOH was used as the Li source, NH4H2PO4 as the P source, and FeSO4·7H2O as the Fe source. These were mixed with pure water in a mass ratio of Li:Fe:P = 3:1:1 to prepare 200 mL of a uniform slurry mixture. Next, this mixture was placed in a 500 mL pressure-resistant sealed container and subjected to hydrothermal synthesis at 170°C for 12 hours. After this reaction, the mixture was cooled to room temperature (25°C) to obtain a precipitated cake-like reaction product. This precipitate was thoroughly washed multiple times with distilled water and kept at a moisture content of 30% to prevent it from drying out, resulting in a cake-like substance. A small amount of the cake-like substance was collected and dried in vacuum at 70°C for 2 hours. The resulting powder was analyzed by X-ray diffraction, confirming the formation of single-phase LiFePO4. 20 g of the obtained cake-like LiFePO4 (positive electrode active material) and 0.73 g of polyvinyl alcohol as a carbon source were mixed with water to a total amount of 100 g, and the mixture was milled together with 150 g of zirconia beads with a diameter of 0.1 mm to obtain a slurry (mixture) with a dispersed particle size (d50) of 100 nm. Thereafter, the mixture was dried and granulated using a spray dryer at a temperature such that the drying outlet temperature was 60°C, to obtain granulated powder. The obtained granulated powder was heat-treated at 700° C. for 1 hour using a rotary kiln in a nitrogen atmosphere to obtain granules coated with carbonaceous material (hereinafter referred to as "carbonaceous-coated granules"). 1 g of acetone was added to 10 g of the obtained carbonaceous-coated granules, and the mixture was stirred for 10 minutes using a planetary mixer. After stirring, the mixture was stored at 50°C for 1 hour and then vacuum-dried in a vacuum dryer at 25°C until the pressure reached -0.1 MPa to remove excess acetone, yielding a positive electrode material containing a carbonaceous-coated positive electrode active material with acetone attached (hereinafter referred to as "carbonaceous-coated positive electrode active material").

[0084] [Example 2] The granulated powder obtained by the spray dryer was crushed using a jet mill (product name: SJ-100, manufactured by Nisshin Engineering Inc.) at a feed rate of 180 g / hour, and a positive electrode material containing a carbonaceous-coated positive electrode active material having acetone attached thereto was obtained in the same manner as in Example 1, except that 1 g of acetone was added per 10 g of the crushed powder.

[0085] [Example 3] A positive electrode material containing a carbonaceous coated positive electrode active material having ethanol attached thereto was obtained in the same manner as in Example 1, except that 2 g of ethanol was added to 10 g of the granulated powder obtained by the spray dryer.

[0086] [Example 4] A positive electrode material containing a carbonaceous coated positive electrode active material having acetone attached thereto was obtained in the same manner as in Example 2, except that the amount of acetone added was set to 0.5 g.

[0087] [Example 5] A positive electrode material containing a carbonaceous coated positive electrode active material having methanol attached thereto was obtained in the same manner as in Example 1, except that the temperature of the hydrothermal synthesis was 190° C. and the organic solvent added was methanol.

[0088] [Example 6] A positive electrode material containing a carbonaceous-coated positive electrode active material having methyl ethyl ketone attached thereto was obtained in the same manner as in Example 1, except that the temperature of the hydrothermal synthesis was 160°C and the organic solvent added was methyl ethyl ketone.

[0089] [Example 7] A positive electrode material containing a carbonaceous coated positive electrode active material having acetone attached thereto was obtained in the same manner as in Example 1, except that the amount of polyvinyl alcohol as the carbon source was 2.5 g and the amount of acetone added was 2.5 g.

[0090] [Example 8] A positive electrode material containing a carbonaceous-coated positive electrode active material having N-methyl-2-pyrrolidone attached thereto was obtained in the same manner as in Example 1, except that the organic solvent added was N-methyl-2-pyrrolidone and the amount of N-methyl-2-pyrrolidone added was 2.5 g.

[0091] [Comparative Example 1] LiOH was used as the Li source, NH4H2PO4 as the P source, and FeSO4·7H2O as the Fe source. These were mixed with pure water in a mass ratio of Li:Fe:P = 3:1:1 to prepare 200 mL of a uniform slurry mixture. Next, this mixture was placed in a 500 mL pressure-resistant sealed container and subjected to hydrothermal synthesis at 170°C for 12 hours. After this reaction, the mixture was cooled to room temperature (25°C) to obtain a precipitated cake-like reaction product. This precipitate was thoroughly washed multiple times with distilled water and kept at a moisture content of 30% to prevent it from drying out, resulting in a cake-like substance. A small amount of the cake-like substance was collected and dried in vacuum at 70°C for 2 hours. The resulting powder was analyzed by X-ray diffraction, confirming the formation of single-phase LiFePO4. 20 g of the obtained cake-like LiFePO4 (positive electrode active material) and 0.73 g of polyvinyl alcohol as a carbon source were mixed with water to a total amount of 100 g, and the mixture was milled together with 150 g of zirconia beads with a diameter of 0.1 mm to obtain a slurry (mixture) with a dispersed particle size (d50) of 100 nm. Thereafter, the mixture was dried and granulated using a spray dryer at a temperature such that the drying outlet temperature was 60°C, to obtain granulated powder. The obtained granulated powder was subjected to a heat treatment in a tubular furnace at 700° C. for 1 hour under a nitrogen atmosphere to obtain a positive electrode material containing a carbonaceous-coated positive electrode active material.

[0092] Comparative Example 2 A positive electrode material containing a carbonaceous-coated positive electrode active material was obtained in the same manner as in Comparative Example 1, except that the granulated powder obtained by the spray dryer was crushed using a jet mill (product name: SJ-100, manufactured by Nisshin Engineering) at a feed rate of 180 g / hour.

[0093] Comparative Example 3 A positive electrode material containing a carbonaceous coated electrode active material to which ethanol was attached was obtained in the same manner as in Example 1, except that 0.1 g of ethanol was added to 10 g of the granulated powder obtained by the spray dryer.

[0094] Comparative Example 4 A positive electrode material containing a carbonaceous coated positive electrode active material having ethanol attached thereto was obtained in the same manner as in Example 1, except that 4 g of acetone was added to 10 g of the granulated powder obtained by the spray dryer.

[0095] [evaluation] The positive electrode materials obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated as follows.

[0096] "Average particle size of positive electrode active material" The positive electrode material was dispersed in water, and the particle size distribution of the positive electrode material contained in the resulting dispersion was measured using a particle size distribution analyzer (product name: LA-920, manufactured by Horiba, Ltd.) according to a method conforming to JIS Z8825 "Particle size analysis - laser diffraction and scattering method," and the obtained D50 value was taken as the average particle size. The results are shown in Table 1.

[0097] "Average particle size of primary particles" The average particle size of the primary particles of the electrode active material was determined by averaging the particle sizes of 200 or more primary particles measured by observation with a scanning electron microscope (product name: S-4800, manufactured by Hitachi High-Technologies Corporation). The results are shown in Table 1.

[0098] "Carbonaceous coating thickness" The thickness of the carbonaceous coating was determined by averaging the thickness of each carbonaceous coating in 30 fields of view using a transmission electron microscope (product name: HF-2000, manufactured by Hitachi High-Technologies Corporation). The results are shown in Table 1.

[0099] "Organic solvent content" The content of organic solvent in each positive electrode material was measured using a gas chromatograph mass spectrometer (model: 6890N / 5975, manufactured by Agilent) and a headspace analyzer (model: TurboMatrix40, manufactured by Perkin Elmer). The results are shown in Table 1.

[0100] "Karl Fischer moisture content measurement" The positive electrode material was dried in a vacuum atmosphere at 100° C. for 24 hours to thoroughly remove moisture adsorbed on the surface of the positive electrode material. Next, the amount of moisture detected when the dried cathode material was heated to 100°C to 250°C was measured using a Karl Fischer moisture meter (product name: CA-200 / VA-200, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The results are shown in Table 1.

[0101] "Fabrication of lithium-ion secondary batteries" The positive electrode materials obtained in Examples 1 to 8 and Comparative Examples 1 to 4, acetylene black (AB) as a conductive additive, polyvinylidene fluoride (PVdF) resin as a binder, and N-methyl-2-pyrrolidone were mixed to prepare a positive electrode material paste containing the positive electrode material, a mixture of AB and PVdF in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone. The obtained positive electrode material paste was applied onto an aluminum foil having a thickness of 30 μm, dried, and then pressed to a predetermined density to prepare an electrode plate. The resulting electrode plate was placed on a substrate with a coating surface area of ​​9 cm 2 Then, the electrode was punched out into a plate having a tab margin around the periphery, and a tab was welded to prepare a test electrode. On the other hand, a coated electrode coated with natural graphite was used as the counter electrode. A porous polypropylene film was used as the separator. A 1 mol / L lithium hexafluorophosphate (LiPF6) solution was used as the non-aqueous electrolyte (nonaqueous electrolyte solution). The solvent used for this LiPF6 solution was a 1:1 volumetric mixture of ethylene carbonate and diethyl carbonate, with 1 mass % vinylene carbonate added as an additive. Then, the test electrode, counter electrode, and non-aqueous electrolyte prepared as described above were used to prepare laminate-type cells, which were used as lithium ion secondary batteries of Examples and Comparative Examples.

[0102] "Capacity maintenance rate" The discharge capacity of the lithium-ion secondary battery was measured by constant current charging and discharging at an ambient temperature of 25°C, with a charge current of 2C and a discharge current of 2C, and the measured value was designated as the initial discharge capacity of the lithium-ion secondary battery. Thereafter, the ambient temperature was set to 60°C, and the lithium-ion secondary battery was subjected to constant current charging and discharging 600 times at a charge current of 2C and a discharge current of 2C. Thereafter, the discharge capacity of the lithium-ion secondary battery was measured again by constant current charging and discharging at an ambient temperature of 25°C, with a charge current of 2C and a discharge current of 2C, and the discharge capacity of the lithium-ion secondary battery after cycling was determined. The capacity retention rate of the lithium ion secondary battery after the cycle test was calculated using the following formula (1). The results are shown in Table 1. Cycle test capacity retention rate = discharge capacity after cycling / initial discharge capacity (1)

[0103] [Table 1]

[0104] The results shown in Table 1 show that the positive electrode materials of Examples 1 to 8 have an organic solvent content in the range of 50 ppm to 500 ppm, and therefore the moisture content of the positive electrode material can be reduced to 1400 ppm or less. On the other hand, the positive electrode material of Comparative Example 1 contained 0 ppm of organic solvent, and therefore the water content of the positive electrode material was 1700 ppm. In addition, the positive electrode material of Comparative Example 2 contained 0 ppm of organic solvent, and therefore the water content of the positive electrode material was 1800 ppm. In addition, the positive electrode material of Comparative Example 3 contained 40 ppm of organic solvent, and therefore the water content of the positive electrode material was 1500 ppm. In addition, the positive electrode material of Comparative Example 4 had an organic solvent content of 1000 ppm, and therefore the water content of the positive electrode material was 980 ppm. [Industrial Applicability]

[0105] The positive electrode material for lithium ion secondary batteries of the present invention is useful as a positive electrode for lithium ion secondary batteries.

Claims

1. The cathode active material includes at least one of primary particles having a carbonaceous coating formed on the surface thereof and aggregated particles formed by aggregation of a plurality of the primary particles, and an organic solvent adhered to the primary particles, A positive electrode material for a lithium ion secondary battery, having an organic solvent content in the range of 50 ppm to 500 ppm as measured at 200°C by headspace gas chromatography mass spectrometry.

2. 2. The positive electrode material for lithium ion secondary batteries according to claim 1, wherein the organic solvent is at least one selected from the group consisting of methanol, ethanol, propanol, isobutyl alcohol, acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, hexane, kerosene, N-methyl-2-pyrrolidone, and polyvinylidene fluoride.

3. 2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the water content determined by Karl Fischer moisture evaporation method is 1500 ppm or less.

4. 2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the average particle diameter measured with a laser diffraction particle size distribution analyzer is 0.3 μm or more and 10.0 μm or less.

5. 2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the primary particles have an olivine structure with an average particle diameter of 50 nm or more and 500 nm or less.

6. 2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the carbonaceous coating has a thickness of 0.5 nm or more and 10 nm or less.

7. A positive electrode for a lithium ion secondary battery comprising: an electrode current collector; and a positive electrode mixture layer formed on the electrode current collector, The positive electrode mixture layer contains the positive electrode material for lithium ion secondary batteries according to any one of claims 1 to 6.

8. A lithium ion secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, A lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to claim 7 as a positive electrode.

Images