JP7767726B2 - Positive electrode materials for lithium-ion secondary batteries, positive electrodes for lithium-ion secondary batteries, lithium-ion secondary batteries - Google Patents

Description

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.

In olivine-based positive electrode active materials, lithium ions within the crystals 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 applied instantaneously, the lithium ions cannot diffuse quickly enough, resulting in high overvoltage (voltage drop).

It has been known that synthesizing an olivine-based positive electrode active material made of lithium iron phosphate (LiFePO ₄ ) or lithium manganese iron phosphate (LiMn _1-x Fe _x PO ₄ ) so as to minimize the content of trivalent Fe makes it possible to increase the capacity of a lithium ion secondary battery equipped with a positive electrode containing an olivine-based positive electrode active material. Patent Document 1 discloses that specifying an isomer shift value in a Mössbauer spectrum obtained by Mössbauer spectroscopy intentionally causes a small amount of trivalent Fe to form a solid solution in the crystal, generating defects in the crystal and allowing lithium ions to diffuse in two or three dimensions within the crystal.

Patent No. 6477948

However, when using lithium-ion secondary batteries, further improvements in performance were required in terms of cycle characteristics, which are an indicator of durability.

The present invention was made in consideration of the above circumstances, and aims to provide a positive electrode material for a lithium-ion secondary battery and a positive electrode for a lithium-ion secondary battery that can produce a lithium-ion secondary battery with excellent cycle characteristics, as well as a lithium-ion secondary battery equipped with this positive electrode for a lithium-ion secondary battery.

As a result of intensive research aimed at solving the above-mentioned problems, the inventors discovered that by preparing a positive electrode material for a lithium ion secondary battery so 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 the iron ion is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of the iron ion, a positive electrode material for a lithium ion secondary battery with excellent cycle characteristics can be obtained, leading to the completion of the present invention.

The present invention has the following aspects.
[1] A positive electrode material for a lithium ion secondary battery, in which, in a Mössbauer spectrum obtained 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.
[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 thickness of the carbonaceous coating is 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.

The positive electrode material for lithium-ion secondary batteries of the present invention can provide a positive electrode material for lithium-ion secondary batteries and a positive electrode for lithium-ion secondary batteries that can produce lithium-ion secondary batteries with excellent cycle characteristics, as well as a lithium-ion secondary battery equipped with this positive electrode for lithium-ion secondary batteries.

FIG. 1 is a diagram showing a state in which a Mössbauer spectrum is split into two spectra. FIG. 2 is a diagram showing a Mössbauer spectrum of the positive electrode material of Example 1. FIG. 1 is a diagram showing a Mössbauer spectrum of the positive electrode material of Comparative Example 1.

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.

[Positive electrode material 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.

In the positive electrode material for a lithium ion secondary battery according to the present embodiment, in a Mössbauer spectrum obtained by Mössbauer spectroscopy, the ratio (peak intensity B/peak intensity A) of the intensity of the peak on the high-energy side of the quadrupole splitting of the iron ion (hereinafter also referred to as "peak intensity B") to the intensity of the peak on the low-energy side of the quadrupole splitting of the iron ion (hereinafter also referred to as "peak intensity A") 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 can be suppressed.

Mössbauer spectroscopy is performed by examining the energy dependence (Mössbauer spectrum) of the amount of gamma rays absorbed or the amount of scattering emitted after absorption when a gamma ray emitted from a Mössbauer nucleus ( ^57Fe in the excited standard during the decay process of ^57Co → ^57Fe ) incorporated as a radioactive isotope (radiation source) in a solid is resonantly absorbed without recoil by the same kind of Mössbauer nucleus in the ground state in another solid (sample).

In this embodiment, we assume that the spectrum obtained by this Mössbauer spectroscopy analysis can be approximated by a Lorentzian theoretical linear equation, and that the peak half-widths 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 used is the following equation (1).

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, _Ii is the absorption intensity of the i-th peak, _Γi is the half-width of the i-th peak, _x0i 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.

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 obtained, and if the Fe is ferromagnetic or antiferromagnetic (internal magnetic field H ≠ 0), a six-split peak is obtained, and no peaks other than two or six are observed.

In a Mössbauer spectrum, when a spectrum is split into two, it means a state as shown in Figure 1.

The quadrupole splitting value in a Mössbauer spectrum is the distance between two split peaks. It is generally believed that splitting into two occurs when a structure is structurally isotropic but ligands with different electronegativities are coordinated, when the structural arrangement is distorted, or when these are mixed.

The positive electrode material for lithium-ion secondary batteries of this embodiment preferably includes primary particles in which a carbonaceous coating is formed on the surface of electrode active material particles, and agglomerated particles (secondary particles) in which multiple primary particles are aggregated together.

In the positive electrode material for lithium ion secondary batteries of this embodiment, the average particle diameter measured with a laser diffraction particle size distribution analyzer is preferably 0.3 μm or more and 5.0 μm or less, more preferably 0.4 μm or more and 4.0 μm or less, and even more preferably 0.45 μm or more and 3.5 μm or less. When the average particle diameter 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 diameter 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.

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

The primary particles preferably have an olivine structure and an average particle diameter of 50 nm to 500 nm. That is, the electrode active material particles constituting the primary particles preferably have an olivine structure and an average particle diameter of 50 nm to 500 nm.
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 containing 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.

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.

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 specifying the thickness of the carbonaceous coating 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.

The coverage of the carbonaceous coating on the primary particles is preferably 60% or more, and more preferably 80% or more. A coverage of 60% or more ensures sufficient coverage of the carbonaceous coating.

Furthermore, 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 preferably 0.5 mg/ ^m2 or more and 2.0 mg/ ^m2 or less, and more preferably 0.7 mg/ ^m2 or more and 1.6 mg/m2 or ^less .
The reason why the carbon loading amount relative to the specific surface area in the positive electrode material for lithium ion secondary batteries of this embodiment is limited to the above range is as follows: If the carbon loading amount relative to the specific surface area is less than 0.5 mg/ ^m2 , when a lithium ion secondary battery is formed, the discharge capacity at a high-speed charge/discharge rate will be low, making it difficult to achieve sufficient charge/discharge rate performance. On the other hand, if the carbon loading amount relative to the specific surface area exceeds 2.0 mg/ ^m2 , the carbon amount will be too high, and the battery capacity of the lithium ion secondary battery per unit mass of the primary particles will be reduced more than necessary.

The specific surface area of the positive electrode material for a lithium ion secondary battery of this embodiment is preferably 5.0 m ² /g or more and 20 m ² /g or less, more preferably 5.5 m ² /g or more and 18 m ² /g or less, and even more preferably 6.0 m ² /g or more and 16 m ² /g or less.
The reason why the specific surface area of the positive electrode material for lithium-ion secondary batteries of this embodiment is limited to the above range is as follows: If the specific surface area is less than 5.0 m ² /g, it takes a long time for lithium ions or electrons to move within the crystal, which increases internal resistance and deteriorates output characteristics, which is undesirable. On the other hand, if the specific surface area exceeds 20 m ² /g, the specific surface area of the carbonaceous electrode active material composite particles increases, which increases the mass of carbon required and reduces charge/discharge capacity. Furthermore, carbon coating becomes difficult, making it impossible to obtain primary particles with a sufficient coverage rate, which is undesirable because a good mass energy density cannot be obtained, particularly at low temperatures and at high-speed charge/discharge.

"Electrode active material particles"
The electrode active material particles having an olivine structure are not particularly limited, but are preferably made of, for example, Li _x Fe _1-y-z A _y M _z PO ₄ (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) having a crystal structure suitable for Li diffusion.

The reason why x satisfies 0.85≦x≦1.1 in Li _x Fe _1-y-z A _y M _z PO ₄ is as follows. If x is less than 0.85, when an active material not containing 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 and crystal stability decreases, which is undesirable.

The reason why y satisfies 0≦y≦0.85 in Li _x Fe _1-y-z A _y M _z PO ₄ 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, thereby degrading input/output characteristics.

The reason why z satisfies 0≦z≦0.2 in Li _x Fe _1-y-z A _y M _z PO ₄ is as follows: if z exceeds 0.2, the ratio of electrochemically inactive metals increases, which is undesirable because it reduces the battery capacity per unit mass of the positive electrode material.

In this embodiment, Li _x Fe _1-y-z A _y M _z PO ₄ preferably satisfies 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 LiFePO ₄ .
When the electrode active material particles are made of _LiFePO4 , the lithium ion diffusion rate and electron conduction rate within the crystal are improved, and the input/output characteristics are improved.

"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 having a carbon purity of 42.00% or more and 60.00% or less.

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 amount (mass%) / total blend amount (mass%) × 100 (2)

The positive electrode material for lithium ion secondary batteries of this embodiment has a Mössbauer spectrum obtained by Mössbauer spectroscopy, 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, thereby enabling the production of a lithium ion secondary battery with excellent cycle characteristics.

[Method of manufacturing a positive electrode material for lithium ion secondary batteries]
The method for producing a positive electrode material for a lithium ion secondary battery according to this embodiment is not particularly limited. For example, when the electrode active material particles are composed of Li _x Fe _1-y-z A _y M _z PO ₄ , the method includes the steps of: mixing a Li source, an Fe source, an A source, an M source, and a P source with a solvent mainly composed of water to obtain a raw material slurry α; heating the obtained raw material slurry α to a temperature in the range of 100°C or higher and 300°C or lower to synthesize Li _x Fe _1-y-z A _y M _z PO ₄ particles under pressure; and drying and granulating raw material slurry β obtained by dispersing the Li _x Fe _1-y-z A _y M _z PO ₄ particles in an aqueous solvent containing a carbon source, followed by heating the resulting mixture to a temperature in the range of 500°C or higher and 1000°C or lower to synthesize Li _x Fe _1-y-z A _y M _z PO 4 particles. and a step of coating the surfaces of the _particles with a carbonaceous film.

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 in a Mössbauer spectrum obtained by Mössbauer spectroscopy is greater than the intensity of the peak on the low-energy side of the quadrupole splitting of iron ions is not particularly limited. For example, in hydrothermal synthesis, the desired particles can be formed by using a first step to synthesize precursor particles that will become nuclei particles, and the precursor particles obtained in the first step as materials, and then performing hydrothermal synthesis again to promote particle growth.

The method for synthesizing the Li _x Fe _1-y-z A _y M _z PO ₄ particles is not particularly limited, but 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 are added to a solvent containing water as a main component, and stirred to prepare raw material slurry α containing a precursor of Li _x Fe _1-y-z A _y M _z PO ₄ .

These Li source, Fe source, A source, M source, and P source are added to a solvent containing water as a 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 to 5:0.1 to 2:0 to 2:0 to 2:1 to 2, and the mixture is stirred and mixed to prepare raw material slurry α.
In consideration of uniform mixing of the Li source, Fe source, A source, M source, and P source, it is preferable that the Li source, Fe source, A source, M source, and P source are each first made into an aqueous solution and then mixed.
The molar concentrations of the Li source, Fe source, A source, M source, and P source in this raw material slurry α are preferably 0.1 mol/L or more and 3 mol/L or less, since it is necessary to obtain highly pure, highly crystalline, and very fine Li _x Fe _1-y-z A _y M _z PO ₄ particles.

Examples of Li sources include hydroxides such as lithium hydroxide (LiOH), lithium carbonate _{( Li2CO3} ), lithium chloride (LiCl) _, lithium nitrate (LiNO3) _, lithium phosphate ( _Li3PO4 ) _{, dilithium hydrogen phosphate (Li2HPO4), lithium dihydrogen phosphate (LiH2PO4 ) ,} and other lithium inorganic acid salts, lithium _{acetate (LiCH3COO )} , lithium oxalate ((COOLi) ₂ ), and other lithium organic acid salts, and hydrates thereof. At least one selected from these groups is preferably used as the Li source.
Lithium phosphate (Li ₃ PO ₄ ) can also be used as a Li source and a P source.

As the Fe source, for example, as a divalent Fe compound, iron compounds such as iron(II) chloride (FeCl ₂ ), iron(II) sulfate (FeSO ₄ ), iron(II) acetate (Fe(CH ₃ COO) ₂ ), or hydrates thereof, are used, and as a trivalent Fe compound, iron compounds such as lithium iron(III) phosphate (FePO ₄ ), iron(III) nitrate (Fe(NO ₃ ) ₃ ), iron(III) chloride (FeCl ₃ ), iron(III) citrate (FeC ₆ H ₅ O ₇ ), or hydrates thereof, are 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 preferable because it makes it easier to form a solid solution of trivalent Fe in the crystal.

The Mn source is preferably a Mn salt, such as manganese(II) chloride ( _MnCl2 ), manganese(II) sulfate ( _MnSO4 ), manganese(II) nitrate (Mn( _NO3 ) ₂ ), manganese(II) acetate (Mn( _CH3COO ) ₂ ), and hydrates thereof. At least one selected from this group is preferably used as the Mn source.

The Co source is preferably a Co salt, such as cobalt(II) chloride ( _CoCl2 ), cobalt(II) sulfate ( _CoSO4 ), cobalt(II) nitrate (Co( _NO3 ) ₂ ), cobalt(II) acetate (Co( _CH3COO ) ₂ ), or hydrates thereof. At least one selected from these groups is preferably used as the Co source.

The Ni source is preferably a Ni salt, such as nickel(II) chloride (NiCl ₂ ), nickel(II) sulfate (NiSO ₄ ), nickel(II) nitrate (Ni(NO ₃ ) ₂ ), nickel(II) acetate (Ni(CH ₃ COO) ₂ ), or hydrates thereof. At least one selected from these groups is preferably used as the Ni source.

The Mg source is preferably a Mg salt, such as magnesium chloride (II) (MgCl ₂ ), magnesium sulfate (II) (MgSO ₄ ), magnesium nitrate (II) (Mg(NO ₃ ) ₂ ), magnesium acetate (II) (Mg(CH ₃ COO) ₂ ), or hydrates thereof. At least one selected from this group is preferably used as the Mg source.

The Ca source is preferably a Ca salt, such as calcium chloride (II) (CaCl ₂ ), calcium sulfate (II) (CaSO ₄ ), calcium nitrate (II) (Ca(NO ₃ ) ₂ ), calcium acetate (II) (Ca(CH ₃ COO) ₂ ), or hydrates thereof, and at least one selected from the group consisting of these is preferably used.

The Co source is preferably a Co salt, such as cobalt(II) chloride ( _CoCl2 ), cobalt(II) sulfate ( _CoSO4 ), cobalt(II) nitrate (Co( _NO3 ) ₂ ), cobalt(II) acetate (Co( _CH3COO ) ₂ ), or hydrates thereof. At least one selected from these groups is preferably used as the Co source.

The Sr source is preferably a Sr salt, such as strontium carbonate (SrCo ₃ ), strontium sulfate (SrSO ₄ ), or strontium hydroxide (Sr(OH) ₂ ). At least one selected from the group consisting of these is preferably used.

The Ba source is preferably a Ba salt, such as barium(II) chloride (BaCl ₂ ), barium(II) sulfate (BaSO ₄ ), barium(II) nitrate (Ba(NO ₃ ) ₂ ), barium(II) acetate (Ba(CH ₃ COO) ₂ ), or hydrates thereof, and at least one selected from the group consisting of these is preferably used.

The Ti source is preferably a Ti salt, such as titanium chloride (TiCl ₄ , TiCl ₃ , TiCl ₂ ), titanium oxide (TiO), and hydrates thereof, and at least one selected from the group consisting of these is preferably used.

The Zn source is preferably a Zn salt, such as zinc chloride (ZnCl ₂ ), zinc sulfate (ZnSO ₄ ), zinc nitrate (Zn(NO ₃ ) ₂ ), zinc acetate (Zn(CH ₃ COO) ₂ ), or hydrates thereof. At least one selected from this group is preferably used as the Zn source.

Examples of B sources 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.

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.

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

Examples of In sources 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.

Examples of the Si source include sodium silicate, potassium silicate, silicon tetrachloride (SiCl ₄ ), silicates, and organic silicon compounds, and at least one selected from the group consisting of these is preferably used.

Examples of Ge sources 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.

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.

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.

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. For example, 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.

Next, the raw material slurry α is placed in a pressure vessel, heated to a temperature in the range of 100°C or higher and 300°C or lower, preferably 100°C or higher and 250°C or lower, and subjected to hydrothermal treatment for 1 hour or higher and 72 hours or lower, to obtain Li _x Fe _1-y-z A _y M _z PO ₄ particles.
In this case, by adjusting the temperature and time of the hydrothermal treatment, it is possible to control the particle size of the Li _x Fe _1-yz A _y M _z PO ₄ particles to a desired size.

Next, the Li _x Fe _1-yz A _y M _z PO ₄ particles are dispersed in an aqueous solvent containing a carbon source to prepare raw material slurry β.
Next, this raw material slurry β is dried and granulated, and then heated at a temperature in the range of 500°C or higher and 1000°C or lower, preferably 500°C or higher and 800°C or lower, for 1 hour or higher and 100 hours or lower, to coat the surfaces of _{the LixFe1 -y- zAyMzPO4 particles} with a carbonaceous coating, thereby obtaining the positive electrode material for lithium-ion secondary batteries of this embodiment. Here, heating at a temperature lower than 500°C is not preferred because the carbonaceous coating is insufficiently carbonized and the conductivity is significantly reduced. On the other hand, heating at a temperature higher than 1000°C is not preferred because some of the lithium volatilizes, reducing the battery capacity.

"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.

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, where the total mass of the electrode active material particles and the carbon source is 100% by mass.

Addition of less than 0.5% by mass of carbon source is undesirable because it reduces the mixing stability of the positive electrode material for lithium-ion secondary batteries. On the other hand, addition of more than 15% by mass of carbon source is undesirable because it reduces the relative content of positive electrode active material and reduces battery performance.

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

[Positive electrode for lithium ion secondary battery]
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.

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.

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

The binder content 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, where the total mass of the positive electrode material for lithium ion secondary batteries, binder, and conductive additive according to this embodiment is taken as 100% by mass.

"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.

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, where the total mass of the positive electrode material for lithium ion secondary batteries, binder, and conductive additive according to this embodiment is taken as 100% by mass.

"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 alcohols such as water, 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 may be used alone or in combination of two or more.

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, when the total mass of the positive electrode material for lithium ion secondary batteries according to the present embodiment, the binder, and the solvent is taken as 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.

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. Examples include methods using a kneading machine such as a ball mill, sand mill, planetary mixer, paint shaker, or homogenizer.

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

The positive electrode for a lithium ion secondary battery of this embodiment contains the positive electrode material for a lithium ion secondary battery of this embodiment, making it possible to obtain a lithium ion secondary battery with excellent cycle characteristics.

[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.

In the lithium ion secondary battery of this embodiment, the negative electrode, the electrolyte, the separator, and the like are not particularly limited.
As the negative electrode, for example, a negative electrode material such as metallic Li, a carbon material, a Li alloy, or Li ₄ Ti ₅ O ₁₂ can be used.
Moreover, a solid electrolyte may be used instead of the electrolytic solution and the separator.

The electrolyte solution can be prepared by, for example, mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1, and dissolving lithium hexafluorophosphate (LiPF ₆ ) in the resulting mixed solvent to a concentration of, for example, 1 mol/dm ³ .
The separator may be made of, for example, porous propylene.

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.

The present invention will be specifically explained below using examples and comparative examples. Note that the present invention is not limited to the embodiments described in the examples.

[Production of positive electrode material for lithium ion secondary batteries]
[Example 1]
LiOH was used as the Li source, NH ₄ H ₂ PO ₄ as the P source, and FeSO _{4.7H 2} O as the Fe source, and these were mixed with pure water in a substance 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, and used as 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 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 LiFePO ₄ .
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 having 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 a 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").

[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 in the second hydrothermal synthesis was 1 g.

[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 in the second hydrothermal synthesis was changed to 4 g.

[Comparative Example 1]
LiOH was used as the Li source, NH ₄ H ₂ PO ₄ as the P source, and FeSO _{4.7H 2} O as the Fe source, and these were mixed with pure water in a substance 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 having 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 a granulated powder.
The resulting 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 Co., Ltd.) at a feed rate of 180 g/hour to obtain a positive electrode material containing a carbonaceous-coated electrode active material.

[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.

[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.

"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.

[Evaluation of cathode materials for lithium-ion secondary batteries]
(1) Particle Size Distribution of 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 meter (product name: LA-920, manufactured by Horiba, Ltd.) according to a method conforming to JIS Z8825 "Particle Size Analysis - Laser Diffraction and Scattering Method."

(2) Measurement of Average Particle Diameter of Primary Particles The average particle diameter 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 diameters of 200 or more primary particles measured by scanning electron microscope (SEM) observation.

(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 through observation with a transmission electron microscope (TEM).

(4) Mössbauer Spectroscopic 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. Radiation 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 designated as X2, X3, X4, and X5 [channels], and the velocity axis was 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 fitting was performed using numerical calculation software to calculate the intensity of each peak. 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.

[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.
A positive electrode material paste was prepared by adding a positive electrode material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder 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 mixing them.
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 so that the coating film had a predetermined density, forming 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.
Thereafter, the positive electrode plate was punched using a molding machine into a plate shape having a tab margin around a square with a positive electrode area of 9 cm ^2. Furthermore, a tab was welded to the tab margin to prepare a test electrode (positive electrode).

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 copper foil (current collector) having a thickness of 10 μm to form a coating film, and the coating film was dried to form a negative electrode mixture layer on the surface of the copper foil, thereby obtaining a negative electrode plate having the copper foil and the negative electrode mixture layer.
Thereafter, the negative electrode plate was punched using a molding machine into a plate shape having a tab margin around a square having a negative electrode area of 9 cm ^2. Furthermore, a tab was welded to the tab margin to prepare a negative electrode.

The positive and negative electrodes were placed opposite each other with a 25 μm thick porous polypropylene separator interposed between them, and the resulting battery was immersed in 500 mL of a 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) solution as a non-aqueous electrolyte solution, followed by sealing with a laminate film to produce a lithium ion secondary battery. The LiPF ₆ solution was a 1:1 volumetric mixture of ethylene carbonate and diethyl carbonate.

[Evaluation of Lithium-ion Secondary Batteries]
(1) Measurement of Capacity Retention Rate The discharge capacity was measured by constant current charging and discharging at an ambient temperature of 25° C., with a charge current of 2 C and a discharge current of 2 C, 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 again, 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)

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.

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 (5)

the electrode active material has an olivine structure and comprises primary particles having a carbonaceous coating formed on the surface thereof, the primary particles being made of Li _x Fe _1-y-z A _y M _z PO ₄ (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), and agglomerated particles in which a plurality of the primary particles are aggregated together,
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. 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. 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. 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,
A positive electrode for a lithium ion secondary battery, wherein the positive electrode mixture layer contains the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 3 . 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.