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 and a positive electrode for a lithium ion secondary battery capable of obtaining a lithium ion secondary battery with excellent cycle characteristics, and to provide a lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery.SOLUTION: For a positive electrode material for a lithium ion secondary battery, a high-energy side peak intensity in quadrupole splitting of iron ions is higher than a low-energy side peak intensity in quadrupole splitting of iron ions, in Mossbauer spectra obtained by the Mossbauer spectroscopy.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] Olivine-based positive electrode active materials allow lithium ions within the crystal to diffuse in only one dimension. Therefore, lithium-ion secondary batteries equipped with positive electrodes containing olivine-based positive electrode active materials have the problem that when a large current is passed through them instantaneously, the lithium ions cannot diffuse quickly enough, resulting in high overvoltage (voltage drop).

[0003] Conventionally, lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiMn 1-x Fe x It is known that by synthesizing an olivine-based positive electrode active material made of olivine-based PO4, it is possible to increase the capacity of a lithium-ion secondary battery equipped with a positive electrode containing the olivine-based positive electrode active material. Patent Document 1 discloses that by specifying the isomer shift value in a Mössbauer spectrum obtained by Mössbauer spectroscopy, a small amount of trivalent Fe is intentionally dissolved in the crystal to generate defects in the crystal, allowing lithium ions to diffuse in two or three dimensions within the crystal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6477948 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when using lithium ion secondary batteries, further improvements in performance have been required with respect to cycle characteristics, which are an indicator of durability.

[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, a positive electrode for a lithium ion secondary battery, which can provide a lithium ion secondary battery having excellent cycle characteristics, and a lithium ion secondary battery including this positive electrode for a lithium ion secondary battery. [Means for solving the problem]

[0007] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a positive electrode material for a lithium ion secondary battery capable of producing a lithium ion secondary battery with excellent cycle characteristics can be obtained by preparing a positive electrode material for a lithium ion secondary battery such that, in a Mössbauer spectrum obtained by analyzing the positive electrode material for a lithium ion secondary battery by Mössbauer spectroscopy, the intensity of the peak on the high-energy side of the quadrupole splitting of iron ions is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of iron ions, and have thus completed the present invention.

[0008] The present invention has the following aspects. [1] A positive electrode material for lithium-ion secondary batteries, in which the intensity of the peak on the high-energy side of the quadrupole splitting of iron ions is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of iron ions in a Mössbauer spectrum obtained by Mössbauer spectroscopy. [2] The positive electrode material for a lithium ion secondary battery according to [1], comprising primary particles in which a carbonaceous coating is formed on the surface of electrode active material particles, and aggregate particles in which a plurality of the primary particles are aggregated, and having an average particle diameter of 0.3 μm or more and 5.0 μm or less as measured with a laser diffraction particle size distribution analyzer. [3] The positive electrode material for a lithium ion secondary battery according to [2], wherein the primary particles have an olivine structure with an average particle diameter of 50 nm or more and 500 nm or less. [4] The positive electrode material for a lithium ion secondary battery according to [2] or [3], wherein the carbonaceous coating has a thickness of 0.5 nm or more and 10 nm or less. [5] 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, wherein the positive electrode mixture layer contains the positive electrode material for a lithium ion secondary battery according to any one of [1] to [4]. [6] A lithium ion secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, the lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to [5] as the positive electrode. [Effects of the Invention]

[0009] According to the positive electrode material for a lithium ion secondary battery of 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 can provide a lithium ion secondary battery with excellent cycle characteristics, as well as a lithium ion secondary battery including this positive electrode for a lithium ion secondary battery. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a state in which a Mössbauer spectrum is split into two spectra. [Figure 2] FIG. 2 is a diagram showing a Mössbauer spectrum of the positive electrode material of Example 1. [Figure 3] FIG. 1 is a diagram showing a Mössbauer spectrum of the positive electrode material of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] [Cathode materials for lithium-ion secondary batteries] In the positive electrode material for a lithium ion secondary battery of this embodiment, in a Mössbauer spectrum obtained by Mössbauer spectroscopy, the intensity of the peak on the high-energy side of the quadrupole splitting of the iron ions is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of the iron ions.

[0013] In the positive electrode material for a lithium ion secondary battery of this embodiment, in a Mössbauer spectrum obtained by Mössbauer spectroscopy, the ratio (peak intensity B / peak intensity A) of the peak intensity (hereinafter sometimes referred to as "peak intensity B") on the high-energy side of the quadrupole splitting of iron ions to the peak intensity (hereinafter sometimes referred to as "peak intensity A") on the low-energy side of the quadrupole splitting of iron ions is preferably 1.02 or more, more preferably 1.04 or more. The upper limit of the ratio (peak intensity B / peak intensity A) may be 1.1 or less, or may be 1.08 or less. When the ratio (peak intensity B / peak intensity A) is 1 / 02 or more, the decrease in capacity during charging and discharging is suppressed.

[0014] Mössbauer spectroscopy is the analysis of Mössbauer nuclei ( 57 Co→ 57 The decay process of Fe is in the excited state 57 When gamma rays emitted from Fe are resonantly absorbed without recoil by the same kind of Mössbauer nucleus in the ground state in another solid (sample), the amount of absorption or the amount of scattering emitted after absorption is examined as a function of energy (Mössbauer spectrum).

[0015] In this embodiment, it is assumed that the spectrum obtained by this Mössbauer spectroscopy analysis can be approximated by a Lorentzian theoretical linear equation, and that the peak half-widths of the peaks for each component are all equal, that the peak heights at symmetrical positions are equal, and that the spectrum is a sum of theoretical linear equations. Based on this assumption, curve fitting is performed to determine the peak positions and calculate the integrated intensity of each component. The theoretical linear equation is expressed by the following equation (1):

[0016]

number

[0017] In the above equation (1), f(E) is the count at Doppler velocity E, E is the Doppler velocity (linearly proportional to energy), B is the baseline count, and I i is the absorption intensity of the i-th peak, Γ i is the half-width of the i-th peak, x 0i is the center of the i-th peak, δ is the isomer shift, Δ is the quadrupole splitting, and H is the internal magnetic field. The relative area ratio of each component when the sum of squares of the residuals is minimized by the least squares method is defined as the spectral area intensity.

[0018] In this embodiment, in the spectrum obtained by Mössbauer spectroscopy, if the Fe is paramagnetic (internal magnetic field H=0), a two-split peak is observed, and if the Fe is ferromagnetic or antiferromagnetic (internal magnetic field H≠0), a six-split peak is observed, and no peaks other than two or six are observed.

[0019] In a Mössbauer spectrum, the spectrum being split into two refers to the state shown in Figure 1.

[0020] The quadrupole splitting in a Mössbauer spectrum is the distance between two split peaks. It is generally believed that splitting occurs when a structure is isotropic but has ligands with different electronegativities, when the structure is distorted, or when these are mixed.

[0021] The positive electrode material for a lithium ion secondary battery of this embodiment preferably contains primary particles in which a carbonaceous coating is formed on the surface of electrode active material particles, and agglomerated particles (secondary particles) in which a plurality of the primary particles are aggregated together.

[0022] In the positive electrode material for lithium ion secondary batteries of this embodiment, the average particle size measured with a laser diffraction particle size analyzer is preferably 0.3 μm to 5.0 μm, more preferably 0.4 μm to 4.0 μm, and even more preferably 0.45 μm to 3.5 μm. When the average particle size is equal to or greater than the lower limit, the structure of the positive electrode mixture layer can be made uniform when the positive electrode material paste for lithium ion secondary batteries is applied to an aluminum current collector and dried, thereby 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 electrode active material particles, and of aggregated particles in which a plurality of such primary particles are aggregated.

[0023] The average particle size of the primary particles is calculated by randomly selecting 100 particles observed under a scanning electron microscope (SEM) and averaging the particle size of the primary particles.

[0024] 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. The reason why the average primary particle diameter of the primary particles, including the electrode active material particles having an olivine structure coated with a carbonaceous coating, is set within the above range is as follows: If the average primary particle diameter is less than 50 nm, the specific surface area of ​​the primary particles increases, increasing the mass of carbon required and reducing the charge / discharge capacity. Furthermore, carbon coating becomes difficult, making it impossible to obtain primary particles with a sufficient coverage rate, and a good mass energy density cannot be obtained, particularly at low temperatures or during high-speed charge / discharge. On the other hand, if the average primary particle diameter exceeds 500 nm, it takes a long time for lithium ions or electrons to move within the primary particles, thereby increasing internal resistance and deteriorating output characteristics, which is undesirable.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 / m 2 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.

[0029] 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 6.0m2 / 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 carbonaceous electrode active material composite particles exceeds 1 / g, the mass of carbon required increases due to the increase in the specific surface area of ​​the carbonaceous electrode active material composite particles, 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 or at high-speed charge / discharge.

[0030] "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 A y 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).

[0031] 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.

[0032] Li xFe 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.

[0033] 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.

[0034] Li in this embodiment x Fe 1-y-z A y M z PO4 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.

[0035] "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.

[0036] 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)

[0037] According to the positive electrode material for a lithium ion secondary battery of the present embodiment, in a Mössbauer spectrum obtained by Mössbauer spectroscopy, the intensity of the peak on the high-energy side of the quadrupole splitting of the iron ion is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of the iron ion, and therefore, a lithium ion secondary battery with excellent cycle characteristics can be obtained.

[0038] [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 zand coating the surface of the PO4 particles with a carbonaceous coating.

[0039] The method for adjusting the positive electrode material for lithium ion secondary batteries of this embodiment so that the intensity of the peak on the high-energy side of the quadrupole splitting of iron ions is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of iron ions in a Mössbauer spectrum obtained by Mössbauer spectroscopy is not particularly limited. For example, in hydrothermal synthesis, a first step is performed to synthesize precursor particles that will become core particles, and the precursor particles obtained in the first step are used as materials to perform hydrothermal synthesis again, thereby promoting particle growth and forming target particles.

[0040] 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 A y M z A raw material slurry α containing a precursor of PO4 is prepared.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 to obtain the positive electrode material for a lithium-ion secondary battery of this embodiment. Heating at temperatures below 500°C is not preferred because the carbonization of the carbonaceous film is insufficient, resulting in a significant decrease in electrical conductivity. Heating at temperatures above 1000°C is also not preferred because some of the lithium volatilizes, resulting in a decrease in battery capacity.

[0065] "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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] [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.

[0070] 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.

[0071] "Binder" As the binder, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, etc. are preferably used.

[0072] 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.

[0073] "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.

[0074] 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.

[0075] "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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] [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.

[0081] 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.

[0082] 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.

[0083] 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]

[0084] EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the embodiments described in the Examples.

[0085] [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 2 hours. After this reaction, the mixture was cooled to room temperature (25°C) to obtain a precipitated cake-like reaction product. This reaction product was thoroughly washed multiple times with distilled water, and the water content was kept at 30% to prevent it from drying out, to obtain a precursor. Furthermore, 200 mL of a slurry mixture was prepared again in the same manner as above. 2 g of precursor material was added to the slurry mixture, which was then placed in a 500 mL pressure-resistant sealed container and subjected to a second 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 reaction product was thoroughly washed multiple times with distilled water, and the moisture content was maintained at 30% to prevent drying, resulting in a cake-like substance. A small amount of the cake-like substance was collected and vacuum-dried 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 resulting cake-like LiFePO4 (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 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"). The obtained carbonaceous-coated granules were pulverized using a jet mill (product name: SJ-100, manufactured by Nisshin Engineering Inc.) at a feed rate of 180 g / hour to obtain a positive electrode material containing a carbonaceous-coated electrode active material (hereinafter referred to as "carbonaceous-coated electrode active material").

[0086] [Example 2] A positive electrode material containing a carbonaceous coated electrode active material was obtained in the same manner as in Example 1, except that the amount of the precursor added during the second hydrothermal synthesis was 1 g.

[0087] [Example 3] A positive electrode material containing a carbonaceous coated electrode active material was obtained in the same manner as in Example 1, except that the amount of the precursor added during the second hydrothermal synthesis was changed to 4 g.

[0088] [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 reaction product was thoroughly washed with distilled water multiple times and the moisture content was maintained at 30% to prevent drying, resulting in a cake-like substance. A small amount of the cake-like substance was collected and vacuum-dried 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 resulting cake-like LiFePO4 (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 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 800°C for 1 hour using a rotary kiln in a nitrogen atmosphere to obtain carbonaceous coated granules. The obtained carbonaceous-coated granules were pulverized using a jet mill (product name: SJ-100, manufactured by Nisshin Engineering) at a feed rate of 180 g / hour to obtain a positive electrode material containing a carbonaceous-coated electrode active material.

[0089] Comparative Example 2 A positive electrode material containing a carbonaceous coated electrode active material was obtained in the same manner as in Comparative Example 1, except that the heat treatment temperature was set to 700° C. and crushing with a jet mill was not performed.

[0090] Comparative Example 3 A positive electrode material containing a carbonaceous coated electrode active material was obtained in the same manner as in Comparative Example 2, except that the amount of carbon source added was 2.5 g.

[0091] "evaluation" The following evaluations were carried out on the positive electrode materials obtained in Examples 1 to 3 and Comparative Examples 1 to 3. The results are shown in Table 1.

[0092] [Evaluation of cathode materials for lithium-ion secondary batteries] (1) Particle size distribution of the positive electrode material The positive electrode material was dispersed in water, and the particle size distribution of the positive electrode material contained in the 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."

[0093] (2) Measurement of the average particle size of primary particles The average particle size of primary particles including electrode active material particles and carbonaceous coatings formed on the surfaces of the electrode active material particles was determined by averaging the particle sizes of 200 or more primary particles measured by scanning electron microscope (SEM) observation.

[0094] (3) Measurement of carbonaceous coating thickness The thickness of the carbonaceous coating was determined by averaging the thickness of each coated carbon layer in 30 fields of view using a transmission electron microscope (TEM).

[0095] (4) Mössbauer spectrum measurement The positive electrode materials of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to Mössbauer spectroscopic analysis by Mössbauer spectroscopy. The Mössbauer spectra were measured by a transmission method. The details are shown below. Measurement method: Constant acceleration mode, room temperature, normal pressure Source: 57 Co / Rh matrix, 1.85 [GBq] Velocity axis calibration method: Of the six magnetic split peaks in the spectrum of pure iron foil at room temperature, the center positions of the four inner peaks were taken as X2, X3, X4, and X5 [channels] and calculated using the following formula. X0[channel]=(X2+X3+X4+X5) / 4 Γ[channel]=20.422 / {0.0835(X5-X2)+0.8385(X4-X3)} The spectrum obtained by this Mössbauer spectroscopy analysis was assumed to be approximated by a theoretical Lorentzian linear equation, and the intensity of each peak was calculated by fitting using numerical calculation software. The intensity ratio was calculated as the peak intensity on the high-energy side / the peak intensity on the low-energy side. 2 shows the Mössbauer spectrum of the positive electrode material of Example 1. FIG. 3 shows the Mössbauer spectrum of the positive electrode material of Comparative Example 1.

[0096] [Fabrication of Lithium-ion Secondary Battery] Using the positive electrode materials of Examples 1 to 3 and Comparative Examples 1 to 3, lithium ion secondary batteries were fabricated. The positive electrode material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidinone (NMP) as a solvent so that the mass ratio in the paste was positive electrode material:AB:PVdF = 90:5:5, and these were mixed to prepare a positive electrode material paste. Next, this positive electrode material paste was applied to the surface of an aluminum foil (electrode current collector) having a thickness of 30 μm to form a coating film, and the coating film was dried and pressed to have a predetermined density to form a positive electrode mixture layer on the surface of the aluminum foil, thereby obtaining a positive electrode plate having the aluminum foil and the positive electrode mixture layer. Then, the positive electrode plate is molded into a molded piece with a positive electrode area of ​​9 cm 2 The square was punched out into a plate having a tab margin around the periphery. A tab was then welded to the tab margin to prepare a test electrode (positive electrode).

[0097] Next, natural graphite as the negative electrode active material, styrene butadiene latex (SBR) as a binder, and carboxymethyl cellulose (CMC) as a viscosity adjuster were added to pure water as a solvent so that the mass ratio of the paste was natural graphite:SBR:CMC = 98:1:1, and these were mixed to prepare a negative electrode material paste (for negative electrode). The prepared negative electrode material paste (for negative electrode) was applied to the surface of a 10 μm thick copper foil (current collector) to form a coating film, and the coating film was dried to form a negative electrode mixture layer on the copper foil surface, thereby obtaining a negative electrode plate having the copper foil and the negative electrode mixture layer. Then, the negative electrode plate was molded into a negative electrode with an area of ​​9 cm 2 The sheet was punched out into a plate having a tab margin around the square. A tab was then welded to the tab margin to prepare a negative electrode.

[0098] The positive and negative electrodes were placed opposite each other with a 25 μm thick porous polypropylene separator in between, and immersed in 500 mL of a 1 mol / L lithium hexafluorophosphate (LiPF6) solution as a non-aqueous electrolyte solution (non-aqueous electrolyte solution), followed by sealing with a laminate film to prepare a lithium ion secondary battery. The LiPF6 solution was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1.

[0099] [Evaluation of Lithium-ion Secondary Batteries] (1) Capacity retention measurement At an ambient temperature of 25°C, the discharge capacity was measured by constant current charging and discharging with a charge current of 2C and a discharge current of 2C, and the measured value was taken as the initial discharge capacity. Thereafter, the ambient temperature was set to 45°C, and constant current charging and discharging was performed 600 times with a charging current of 2C and a discharging current of 2C. Thereafter, the ambient temperature was set to 25°C, and the charging current was set to 2C and a discharging current was set to 2C, and the discharge capacity was measured by constant current charging and discharging to obtain the discharge capacity after cycling. The capacity retention rate after the cycle test was calculated according to the following formula (3). Cycle test capacity retention rate = discharge capacity after cycling / initial discharge capacity (3)

[0100] [Table 1]

[0101] From the results shown in Table 1, the lithium ion secondary batteries using the lithium ion secondary battery positive electrode materials of Examples 1 to 3 have a higher peak intensity on the high-energy side of the quadrupole splitting of iron ions than the peak intensity on the low-energy side of the quadrupole splitting of iron ions, and therefore have a high capacity retention rate in the cycle test and excellent cycle characteristics. On the other hand, the lithium-ion secondary batteries using the lithium-ion secondary battery positive electrode materials of Comparative Examples 1 to 3 have a low cycle test capacity retention rate and poor cycle characteristics because the peak intensity on the high-energy side of the quadrupole splitting of iron ions is equal to the peak intensity on the low-energy side of the quadrupole splitting of iron ions. Note that the lithium-ion secondary battery using the lithium-ion secondary battery positive electrode material of Comparative Example 3 and the lithium-ion secondary battery using the lithium-ion secondary battery positive electrode material of Example 2 have the same cycle test capacity retention rate, but the lithium-ion secondary battery using the lithium-ion secondary battery positive electrode material of Comparative Example 3 has a low first-cycle capacity and, in this respect, is inferior in performance to the lithium-ion secondary battery using the lithium-ion secondary battery positive electrode material of Example 2. [Industrial Applicability]

[0102] 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. It has an olivine structure and contains Li ｘ Fe １－ｙ－ｚ A ｙ M ｚ P.O. ４ (wherein A is at least one element selected from the group consisting of Mn, Co, and Ni; M is at least one element 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), and the electrode active material comprises primary particles having a carbonaceous coating formed on the surface thereof, and aggregate particles formed by aggregation of a plurality of the primary particles, In the Mössbauer spectrum obtained by Mössbauer spectroscopy, The intensity of the peak on the high-energy side of the quadrupole splitting of the iron ion is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of the iron ion, The average particle size measured using a laser diffraction particle size distribution analyzer in accordance with JIS Z8825 "Particle size analysis - laser diffraction and scattering method" is 0.3 μm or more and 5.0 μm or less, A positive electrode material for a lithium ion secondary battery, wherein the ratio of the intensity B of the peak on the high energy side to the intensity A of the peak on the low energy side (peak intensity B / peak intensity A) is 1.04 or more.

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

3. 3. 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.

4. 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 3.

5. 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 4 as a positive electrode.

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