WO2023112876A1 - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

The present invention provides a positive electrode active material for lithium secondary batteries, said positive electrode active material comprising a lithium metal composite oxide and a Li-X compound containing Li and element X. The Li-X compound is an oxide having lithium ion conductivity, the element X is at least one element selected from the group consisting of Nb, W, and Mo, and expressions (A) and (B) are satisfied. (A): 0.09 ≤ X(XPS)/X(ICP) ≤ 0.22 (B): 0.5 ≤ Li(XPS)/Li(ICP) ≤ 1.5

Description

Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery and lithium secondary battery

The present invention relates to a positive electrode active material for lithium secondary batteries, a positive electrode for lithium secondary batteries, and a lithium secondary battery.
This application claims priority based on Japanese Patent Application No. 2021-203448 filed in Japan on December 15, 2021, the contents of which are incorporated herein.

A positive electrode active material for lithium secondary batteries is used for the positive electrode that constitutes the lithium secondary battery. A positive electrode active material for a lithium secondary battery contains a lithium metal composite oxide.

For example, Patent Document 1 describes a lithium transition metal compound powder containing an oxide containing at least one or more elements selected from a main component raw material corresponding to a lithium metal composite oxide and Mo, W, Nb, Ta and Re. revealing the body

Such a lithium transition metal-based compound powder is expected to improve rate characteristics and output characteristics when used as a positive electrode material for lithium secondary batteries, thereby achieving cost reduction, high voltage resistance, and high safety. It is described in Patent Document 1.

JP-A-2008-305777

As the application of lithium secondary batteries progresses, positive electrode active materials for lithium secondary batteries that can provide lithium secondary batteries with longer life as well as battery characteristics and safety are in demand.
A phenomenon that a lithium secondary battery swells during charging is known as a phenomenon that shortens the life of a lithium secondary battery. It is known that this phenomenon is caused by gas generated by a side reaction that occurs when the lithium secondary battery is in a charged state. Therefore, it is important to suppress gas generation in lithium secondary batteries that are expected to be stored in a charged state.

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a secondary battery.

One aspect of the present invention includes [1] to [8].
[1] A positive electrode active material for a lithium secondary battery comprising a lithium metal composite oxide and a Li—X compound containing Li and an element X, wherein the Li—X compound is an oxide having lithium ion conductivity A positive electrode active material for a lithium secondary battery, wherein the element X is one or more elements selected from the group consisting of Nb, W and Mo, and satisfies the following (A) and (B).
0.09≦X(XPS)/X(ICP)≦0.22 (A)
0.5≦Li(XPS)/Li(ICP)≦1.5 (B)
(In (A), X (XPS) is the abundance (%) of the element X on the surface of the particles of the positive electrode active material for a lithium secondary battery, measured by X-ray photoelectron spectroscopy. X ( ICP) is the abundance ratio (%) of the element X in the particles of the positive electrode active material for a lithium secondary battery, measured by ICP emission spectroscopy.
In (B), Li (XPS) is the abundance (%) of Li on the surface of the particles of the positive electrode active material for a lithium secondary battery, measured by X-ray photoelectron spectroscopy. Li (ICP) is the abundance ratio (%) of Li in the particles of the positive electrode active material for a lithium secondary battery, measured by ICP emission spectroscopy. )
[2] The positive electrode active material for a lithium secondary battery according to [1], wherein the X(XPS) satisfies the following (C).
0.01≦X(XPS)≦0.30 (C)
[3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the Li(XPS) satisfies the following (D).
0.4≦Li (XPS)≦1.2 (D)
[4] The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], represented by the following compositional formula (I).
Li[Li _a (Ni _(1-yzw) Co _y M _z X _w ) _1-a ]O ₂ (I)
(In formula (I), M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Ga, B, Si, S and P. , X is one or more elements selected from the group consisting of Nb, W and Mo, and formula (I) is −0.1≦a≦0.2, 0≦y≦0.5, 0≦ satisfy z≦0.7, 0<w≦0.1, and y+z+w<1.)
[5] The positive electrode active material for lithium secondary batteries according to any one of [1] to [4], wherein D ₁₀ , D ₉₀ and D ₅₀ satisfy the following (E).
( _D90 - _D50 )/( _D50 - _D10 ) ≤ 3.0 (E)
(In (E), _D10 is the 10% cumulative volume particle size of the positive electrode active material for lithium secondary batteries, _D50 is the 50% cumulative volume particle size, and _D90 is the 90% cumulative volume particle size.)
[6] The positive electrode active material for lithium secondary batteries according to any one of [1] to [5], which has a BET specific surface area of 1.0 m ² /g or more.
[7] A positive electrode for lithium secondary batteries comprising the positive electrode active material for lithium secondary batteries according to any one of [1] to [6].
[8] A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to [7].

According to the present invention, it is possible to provide a positive electrode active material for a lithium secondary battery that hardly generates gas even when stored in a charged state, a positive electrode for a lithium secondary battery using the same, and a lithium secondary battery.

According to the present invention, it is possible to provide a longer-life lithium secondary battery.

1 is a schematic diagram showing an example of a lithium secondary battery; FIG. 1 is a schematic diagram showing an example of an all-solid lithium secondary battery; FIG.

<Positive electrode active material for lithium secondary battery>
The positive electrode active material for a lithium secondary battery of this embodiment includes a lithium metal composite oxide and a Li—X compound containing Li and the element X. The positive electrode active material for lithium secondary batteries satisfies (A) and (B) described later.

In this specification, a metal composite compound (Metal Composite Compound) is hereinafter referred to as "MCC".
A lithium metal composite oxide (Lithium Metal Composite Compound) is hereinafter referred to as “LiMO”.
A cathode active material for lithium secondary batteries is hereinafter referred to as "CAM".
The notation "Li" indicates that it is an Li element, not an elemental Li metal, unless otherwise specified. The notation of other elements such as Ni, Co, and Mn is the same.

When the numerical range is described as, for example, "1-10 μm" or "1-10 μm", it means the range from 1 μm to 10 μm, including the lower limit of 1 μm and the upper limit of 10 μm.

CAMs are particles, and particles include primary particles and secondary particles.
As used herein, the term "primary particles" refers to particles that do not appear to have grain boundaries and that constitute secondary particles. More specifically, the term “primary particles” means particles that do not show clear grain boundaries on the particle surface when observed with a scanning electron microscope or the like in a field of view of 5,000 to 20,000 times.
As used herein, the term "secondary particle" means a particle in which a plurality of the primary particles are three-dimensionally bonded with gaps therebetween. The secondary particles have a spherical or substantially spherical shape.
Generally, the secondary particles are formed by agglomeration of 10 or more primary particles.

In this embodiment, the primary particles provided in the CAM are primary particles of LiMO.
In this embodiment, at least some of the primary particles provided by the CAM are provided with a Li—X compound on their surface.
The secondary particles contained in the CAM are aggregates of primary particles and have gaps between the primary particles.

Li-X compounds exist, for example, on the surfaces and gaps of secondary particles. A Li—X compound present on the surface of the LiMO can act as a film that protects the LiMO from the electrolyte. Therefore, the decomposition reaction of the electrolyte caused by the contact of the electrolyte with LiMO can be suppressed. A Li—X compound containing the element X is highly chemically stable, so it is difficult to be incorporated into the crystal structure of LiMO, and is likely to exist on the surface and in the gaps of LiMO, so that such an effect is exhibited.

<<Lithium Metal Composite Oxide>>
LiMO is a compound containing Li, Ni, Co, and the element M, which are optional metal elements. The element M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Ga, B, Si, S and P.

<<Li-X compound>>
A Li—X compound is a compound containing Li and the element X. Element X is one or more elements selected from the group consisting of Nb, W and Mo.
Specific examples of Li—X compounds include lithium niobate, lithium tungstate, and lithium molybdate. These Li—X compounds have lithium ion conductivity.

Examples of lithium niobate include Li ₃ NbO ₄ , LiNbO ₃ , LiNb ₃ O ₈ , Li ₈ Nb ₂ O ₉ and the like.

Lithium tungstates include LiWO ₄ , Li ₂ WO ₄ or Li ₄ WO ₅ .

Lithium molybdate includes Li ₂ MoO ₄ .

From the viewpoint of exhibiting high lithium ion conductivity, the Li—X compound is preferably lithium niobate or lithium tungstate, and particularly preferably lithium niobate.

[Confirmation method of Li-X compound]
Whether the CAM contains a compound containing the element X can be confirmed by confirming the element X in the CAM by the method described in [Composition analysis] below. Next, whether the compound containing the element X is a Li—X compound containing Li can be confirmed by performing X-ray absorption fine structure (XAFS) analysis and X-ray photoelectron spectroscopy (XPS) analysis of the CAM. can.

According to the XAFS analysis, information on the local structure of the atom of interest can be obtained. The local structure of an atom includes, for example, the valence of the atom, adjacent atomic species, connectivity, and the like.
In the XAFS analysis, the ratio (I/I ₀ ) of the X-ray intensity (I ₀ ) before irradiating the CAM and the X-ray intensity (I) after passing through the CAM to be measured is measured and analyzed.

In XPS analysis, the CAM's constituent elements and their electronic states can be analyzed by irradiating the surface of the CAM with X-rays and measuring the energy of the generated photoelectrons. By performing the XPS analysis, it is possible to analyze the composition of the compound containing the element X included in the CAM.

In this embodiment, the composition analysis of the compound containing element X utilizes XAFS analysis.
Specifically, the fabricated CAM containing the element X is introduced into an XAFS beamline, which is a measurement apparatus, and the XAFS measurement and analysis of the element X are performed under the following conditions. At this time, an XAFS measurement of a standard sample of the assumed Li—X compound is also carried out.
Measuring device: Inter-University Research Institute Corporation High Energy Accelerator Research Organization BL-12C
Measurement absorption edge: Nb-K absorption edge, WL absorption edge, Mo-K absorption edge

By subtracting the baseline value from the peak value of the obtained XAFS spectrum and comparing the peak shapes of the CAM and the standard sample, the composition analysis of the compound containing element X is performed.

<<(A) and (B)>>
CAM satisfies the following (A) and (B).
0.09≦X(XPS)/X(ICP)≦0.22 (A)
0.5≦Li(XPS)/Li(ICP)≦1.5 (B)
(In (A), X (XPS) is the abundance (%) of the element X on the surface of the CAM particle measured by X-ray photoelectron spectroscopy. X (ICP) is ICP emission spectroscopy It is the abundance ratio (%) of the element X in the particles of the CAM measured by the method.
In (B), Li (XPS) is the abundance (%) of Li on the surface of the CAM particles measured by X-ray photoelectron spectroscopy. Li (ICP) is the abundance ratio (%) of Li in the CAM particles measured by ICP emission spectroscopy. )

[Measurement of X (XPS) and Li (XPS)]
In this embodiment, "X-ray photoelectron spectroscopy" is described as "XPS".
According to XPS, the constituent elements of the surface of the CAM particle can be analyzed by measuring the energy of photoelectrons generated when the surface of the CAM particle is irradiated with X-rays.

The "surface of the CAM particle" where the constituent elements are analyzed by XPS is the outermost surface of the CAM particle and the depth region where photoelectrons generated from the outermost surface toward the center of the particle can escape. This depth region refers to a region up to a depth of approximately 10 nm.

In this embodiment, the binding energy of photoelectrons emitted from the surface of CAM particles when irradiated with AlKα rays as excitation X-rays is analyzed. XPS can analyze X (XPS) and Li (XPS) on the surface of CAM particles.

When measuring XPS, AlKα rays are used as the X-ray source, and a neutralization gun (acceleration voltage of 0.3 V, current of 100 μA) is used for charge neutralization during measurement.

The measurement conditions are spot size = 100 µm, PassEnergy = 112 eV, Step = 0.1 eV, and Dwelltime = 50 ms. For the obtained XPS spectrum, analysis software (MultiPak (Version 9.9.0.8)) is used to calculate the number of elements of each metal element from the peak area of each metal element existing on the surface of the particles in the CAM. A few mg of CAM powder is used for the measurement.

Next, from the calculated number of elements of each metal element, the ratio of the number of elements of element X to 100% of the total number of metal elements excluding Li, that is, X (XPS) (unit: %) is obtained.

Also, from the calculated number of elements of each metal element, the ratio of the number of elements of Li to 100% of the total number of metal elements excluding Li, that is, Li (XPS) (unit: %) is obtained.

As an X-ray photoelectron spectrometer used for XPS measurement, for example, PHI5000 VersaProbe III manufactured by ULVAC-Phi, Inc. can be used.

[Measurement of X (ICP) and Li (ICP)]
In the present embodiment, "measurement by ICP emission spectroscopy" is described as "ICP measurement".
By ICP measurement, the amount of elements X and Li contained in the CAM particles can be analyzed.

First, several tens of mg of CAM powder are dissolved in acid or alkali. At this time, the element is dissolved at a rate such that the element concentration in the solution is on the order of ppm. After that, analysis is performed using an ICP emission spectrometer.

As an ICP emission spectrometer, for example, SPS3000 manufactured by SII Nanotechnology Co., Ltd. can be used.

The number of elements of each metal element is calculated from the amount of each metal element contained in the particles in the CAM obtained by ICP measurement. Then, the ratio of the number of elements of the element X to 100% of the total number of metal elements excluding Li, that is, X (ICP) (unit: %) is obtained.

Also, from the calculated number of elements of each metal element, the ratio of the number of Li elements to 100% of the total number of metal elements excluding Li, that is, Li (ICP) (unit: %) is obtained.

(A)
CAM satisfies the above (A).

The CAM preferably satisfies any one of the following (A)-1 to (A)-4.
0.10≦X(XPS)/X(ICP)≦0.21 (A)−1
0.11≦X(XPS)/X(ICP)≦0.20 (A)-2
0.12≦X(XPS)/X(ICP)≦0.19 (A)-3
0.12≦X(XPS)/X(ICP)≦0.18 (A)-4

X(XPS)/X(ICP) is the ratio of X(ICP), which is the abundance of element X contained in the secondary particles of the CAM, to X(XPS), which is the abundance of element X on the surface of the secondary particles. Show the ratio. The value of X(XPS)/X(ICP) is an index of how unevenly distributed the element X is between the surface and gaps of the secondary particles. "Secondary particle gap" means a gap that exists inside the secondary particles.

The Li—X compound has the property of being less likely to be unevenly distributed inside the secondary particles, and when the presence of the element X is confirmed from the value of X (ICP), the surface of the secondary particles, or the gaps between the secondary particles, Alternatively, element X may be present in both. In the CAM that satisfies (A), the element X is considered to be unevenly distributed in the gaps between the secondary particles.

When the value of X(XPS)/X(ICP) is equal to 1, the abundance of the element X between the surface and the gap of the secondary particles is small. It is considered that X exists uniformly.
When the value of X(XPS)/X(ICP) exceeds 1, it is considered that the element X is unevenly distributed on the surface of the secondary particles.
When the value of X(XPS)/X(ICP) is smaller than 1, it is considered that the element X is unevenly distributed in the gaps of the secondary particles.

Secondary particles are aggregates of primary particles, and there are spaces (gaps and pores) inside the secondary particles. Secondary particles having such a structure are considered to have a larger inner surface area than the outer surface area of the secondary particles. A decomposition reaction of the electrolytic solution can also occur on the outer and inner surfaces of the secondary particles. Here, the outer surface of the secondary particles means the interface between the space outside the secondary particles and the primary particles that make up the secondary particles, and the inner surface of the secondary particles means the space inside the secondary particles. It means an interface with a primary particle that constitutes a secondary particle.

In the secondary particles that satisfy (A) above, it is believed that the inner surface of the secondary particles is protected by the Li-X compound at a higher rate than the outer surface of the secondary particles. It is considered that the inner surface of the secondary particles has a greater influence on the decomposition reaction of the electrolytic solution of the entire secondary particles than the outer surface of the secondary particles. Therefore, if the inner surfaces of the secondary particles are protected, the decomposition reaction of the electrolytic solution is effectively suppressed, and it is thought that the amount of gas generated when stored in a charged state can be suppressed.

(B)
CAM satisfies the above (B).

The CAM preferably satisfies any one of the following (B)-1 to (B)-3.
0.55 ≤ Li (XPS) / Li (ICP) ≤ 1.4 (B) -1
0.6≦Li (XPS)/Li (ICP)≦1.3 (B)-2
0.7≦Li (XPS)/Li (ICP)≦1.2 (B)-3

Li (XPS) / Li (ICP) is the ratio of Li (ICP), which is the abundance of Li contained in the secondary particles of the CAM, to Li (XPS), which is the abundance of Li on the surface of the secondary particles. show. The value of Li(XPS)/Li(ICP) is an index of how unevenly distributed Li is on the surface and in the gaps of the secondary particles.

The uneven distribution of Li according to the value of Li(XPS)/Li(ICP) is the same as the above description of X(XPS)/X(ICP). In a CAM that satisfies (B), the existence ratio of Li on the surface and the gaps of the secondary particles is small, in other words, it is considered that Li is uniformly present on the surface and the gaps of the secondary particles. . When the value of Li (XPS) / Li (ICP) exceeds 1, the residual Li component is unevenly distributed on the surface of the secondary particles, and when it is less than 1, the residual Li component is unevenly distributed inside the secondary particles. Become.

The residual Li component is a lithium compound that remains unreacted during the production of CAM, or a lithium compound (for example, lithium carbonate) that is produced by a side reaction with components in the atmosphere. The residual Li component causes generation of gas during charging of the lithium secondary battery.

The following two are typical examples of causes for gas generation inside a lithium secondary battery.
The first is a reductive decomposition reaction of the electrolytic solution that occurs on the surface of the CAM particles. The surfaces of the CAM particles on which the reductive decomposition reaction occurs are the surfaces of the secondary particles of the CAM and the surfaces of the primary particles constituting the secondary particles.

The second is a reaction caused by an acid (for example, hydrogen fluoride) generated when the electrolyte that constitutes the lithium secondary battery is decomposed during charging. When the resulting acid reacts with the residual Li component, a gassing side reaction occurs. When the residual Li component is unevenly distributed on the surface of the secondary particles, gas is likely to be generated.

In the CAM that satisfies (A), the Li—X compound is unevenly distributed in the interstices of the secondary particles rather than on the surfaces of the secondary particles. When the battery operates, the electrolyte diffuses inside from the surface of the secondary particles. At this time, since the Li—X compound unevenly distributed in the gaps between the secondary particles acts as a protective film, reductive decomposition of the electrolytic solution is less likely to occur. Therefore, generation of gas can be suppressed.
Furthermore, the CAM that satisfies (B) has a small uneven distribution of Li on the surface and inside of the secondary particles, so the residual Li component is less unevenly distributed, and Li is uniformly present on the surface and in the gaps of the secondary particles. it seems to do. Such a CAM is less likely to cause a side reaction with the electrolyte. Therefore, generation of gas can be suppressed.

A CAM that satisfies (A) and (B) can provide a lithium secondary battery that hardly generates gas when stored in a charged state for the above reasons.

(C)
X(XPS) preferably satisfies the following (C).
0.01≦X(XPS)≦0.30 (C)

X(XPS) preferably satisfies (C)-1 to (C)-3 below.
0.02≦X(XPS)≦0.25 (C)−1
0.03≦X(XPS)≦0.2 (C)-2
0.04≦X(XPS)≦0.18 (C)-3

In a CAM that satisfies (C) in addition to (A) and (B), the element X is also present on the surface of the secondary particles, and the element X is unevenly distributed in the gaps between the secondary particles. Such a CAM can provide a lithium secondary battery that generates less gas when stored in a charged state.

(D)
Li(XPS) preferably satisfies (D) below.
0.4≦Li (XPS)≦1.2 (D)

Li(XPS) preferably satisfies (D)-1 to (D)-3 below.
0.45≦Li (XPS)≦1.15 (D)−1
0.50≦Li (XPS)≦1.1 (D)-2
0.55≦Li (XPS)≦1.05 (D)-3

In addition to (A) and (B), the CAM that satisfies (D) has a small bias in the Li abundance ratio between the surface and the gaps of the secondary particles, and excessive Li exists on the surface of the secondary particles. That is, the residual Li component present on the surfaces of the secondary particles is small, and side reactions with the electrolytic solution are less likely to occur. Such a CAM can provide a lithium secondary battery that generates less gas when stored in a charged state.

In addition to (A), (B), and (C), the CAM that satisfies (D) has an uneven distribution of the element X in the gaps between the secondary particles, and the existence ratio of Li between the surface and the gaps of the secondary particles The bias is small, Li is not excessively present on the surface of the secondary particles, that is, the residual Li component present on the surface of the secondary particles is small, and the gaps between the secondary particles are effectively protected by the Li—X compound. This makes it more difficult for side reactions with the electrolyte to occur. Such a CAM can provide a lithium secondary battery that generates less gas when stored in a charged state.

[Composition formula]
CAM preferably contains Li, Ni, and element X, and is preferably represented by the following compositional formula (I). More preferably, CAM contains Li, Ni, element X, and one or more elements selected from the group consisting of Co, Mn and Al.
Li[Li _a (Ni _(1-yzw) Co _y M _z X _w ) _1-a ]O ₂ (I)
(In formula (I), M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Ga, B, Si, S and P. , X is one or more elements selected from the group consisting of Nb, W and Mo, and formula (I) is −0.1≦a≦0.2, 0≦y≦0.5, 0≦ satisfy z≦0.7, 0<w≦0.1, and y+z+w<1.)

In the composition formula (I), a is preferably -0.03 or more, more preferably 0 or more, and particularly preferably 0.002 or more, from the viewpoint of improving cycle characteristics. From the viewpoint of obtaining a lithium secondary battery with high initial efficiency, a is preferably 0.1 or less, more preferably 0.09 or less, and particularly preferably 0.07 or less.

The above upper limit and lower limit of a can be combined arbitrarily.
a preferably satisfies −0.03≦a≦0.1, more preferably satisfies 0≦a≦0.09, and particularly preferably satisfies 0.002≦a≦0.07.

In the composition formula (I), from the viewpoint of obtaining a lithium secondary battery with high discharge efficiency, it is preferable to satisfy 0 < y + z + w < 0.6, more preferably 0 < y + z + w ≤ 0.5, and 0 < y + z + w It is particularly preferable to satisfy ≦0.25, and more preferably to satisfy 0<y+z+w≦0.2.

In composition formula (I), y is preferably 0.05 or more, more preferably 0.08 or more, from the viewpoint of obtaining a lithium secondary battery with low battery internal resistance. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, it is preferably 0.4 or less, more preferably 0.3 or less.
The upper limit and lower limit of y can be combined arbitrarily. Examples of combinations include 0.05≦y≦0.4 and 0.08≦y≦0.3.

In composition formula (I), z is preferably 0.0002 or more, more preferably 0.0005 or more, from the viewpoint of improving cycle characteristics. Moreover, it is preferably 0.15 or less, more preferably 0.13 or less, and particularly preferably 0.10 or less.
The upper limit and lower limit of z can be combined arbitrarily. Examples of combinations include 0.0002≦z≦0.15, 0.0005≦z≦0.13, and 0.0005≦z≦0.10.
z preferably satisfies 0.0002≦z≦0.15.

In composition formula (I), w is preferably 0.001 or more, more preferably 0.002 or more, from the viewpoint of improving cycle characteristics. Moreover, it is preferably 0.09 or less, more preferably 0.08 or less, and particularly preferably 0.07 or less.
The upper limit and lower limit of w can be combined arbitrarily. Examples of combinations include 0.001≦w≦0.09, 0.002≦w≦0.08, and 0.002≦w≦0.07.
w preferably satisfies 0.001≦w≦0.09.

M is preferably at least one element selected from the group consisting of Mn, Ti, Mg, Al, W, Nb, Zr, and B, and from the group consisting of Mn, Al, W, Nb, Zr, and B At least one selected element is more preferred.

Composition formula (I) satisfies 0.002≦a≦0.07, 0.08≦y≦0.3, 0.0002≦z≦0.15 and 0.001≦w≦0.09. preferable.

[Composition analysis]
The composition analysis of CAM can be measured using an ICP emission spectrometer after dissolving the obtained CAM powder in hydrochloric acid.
As the ICP emission spectrometer, for example, SPS3000 manufactured by SII Nanotechnology Co., Ltd. can be used.

(Layered structure)
The crystal structure of CAM is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.

The hexagonal crystal structure is: P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63, P-6, P6/m, P63/m, P622, From P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6/mmm, P6/mcc, P63/mcm and P63/mmc belong to any one space group selected from the group consisting of

The monoclinic crystal structure consists of P2, P21, C2, Pm, Pc, Cm, Cc, P2/m, P21/m, C2/m, P2/c, P21/c and C2/c. It belongs to any one space group selected from the group.

Among these, in order to obtain a lithium secondary battery with a high initial discharge capacity, the crystal structure is a hexagonal crystal structure assigned to the space group R-3m, or a monoclinic crystal structure assigned to C2/m. A crystalline structure is particularly preferred.

The crystal structure of CAM can be calculated by powder X-ray diffraction measurement using CuKα as a radiation source and a diffraction angle 2θ measurement range of 10-90°. Specifically, it can be confirmed by observation using a powder X-ray diffraction measurement device (for example, Ultima IV manufactured by Rigaku Corporation).

<< _D10 , _D90 and _D50 >>
D ₁₀ , D ₉₀ and D ₅₀ of the CAM preferably satisfy the following (E).
( _D90 - _D50 )/( _D50 - _D10 ) ≤ 3.0 (E)
(In (E), _D10 is the 10% cumulative volume particle size of CAM. _D50 is the 50% cumulative volume particle size of CAM. _D90 is the 90% cumulative volume particle size of CAM.)

Preferred examples of (E) are described below.
(D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ )≦2.9 (E)−1
(D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ )≦2.85 (E)−2
(D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ )≦2.7 (E)−3

Preferred examples of (E) are further described below.
1.0≦(D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ )≦3.0 (E)−10
1.1≦(D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ )≦2.9 (E)−11 1.3≦(D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ ) ≦2.85 (E)-12
1.5≤( _D90 - _D50 )/( _D50 - _D10 )≤2.7 (E)-13

A CAM that satisfies (E) is easy to fill when manufacturing a positive electrode, and tends to be in good contact with a conductive aid. Therefore, a positive electrode with low resistance can be manufactured. In addition, the CAM that satisfies (E) suppresses the presence of coarse particles, makes it less likely that particle cracking will occur during the production of the positive electrode, and will less likely cause side reactions on the surface of the CAM. Therefore, generation of gas can be suppressed.

[Measurement of _D10 , _D90 and _D50 ]
D ₁₀ , D ₅₀ and D ₉₀ can be measured by the following dry method.

Specifically, first, dry particle size distribution is measured with a laser diffraction particle size distribution meter using CAM 2g to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the value of the particle diameter at 10% accumulation from the microparticle side is D ₁₀ (μm), the particle diameter value at 50% accumulation from the microparticle side is D ₅₀ (μm), and the microparticles D ₉₀ (μm) is the value of the particle diameter at 90% accumulation from the particle side.
As a laser diffraction particle size distribution analyzer, MS2000 manufactured by Malvern, for example, can be used.
The _D50 of compound X described below can be measured in the same manner as above, except that compound X is used instead of CAM.

<<BET specific surface area>>
The CAM preferably has a BET specific surface area of 1.0 m ² /g or more. Also, the CAM preferably has a BET specific surface area of 2.5 m ² /g or less. The CAM preferably has a BET specific surface area of 1.2-2.5 m ² /g, more preferably 1.4-2.5 m ² /g.

Using a CAM having a BET specific surface area equal to or higher than the above lower limit facilitates enhancing the output characteristics of the lithium secondary battery.
When a CAM having a BET specific surface area equal to or less than the above upper limit value is used, the contact area between the CAM and the electrolytic solution is less likely to increase, and gas due to decomposition of the electrolytic solution is less likely to be generated.

[Measurement of BET specific surface area]
The BET specific surface area of CAM can be measured with a BET specific surface area measuring device. As the BET specific surface area measuring device, for example, Macsorb (registered trademark) manufactured by Mountech Co., Ltd. can be used. When powdery CAM is measured, it is preferable to dry it at 105° C. for 30 minutes in a nitrogen atmosphere as a pretreatment.

In this embodiment, it is confirmed by the following method whether or not gas is unlikely to be generated when stored in a charged state.
Specifically, after the lithium secondary battery is charged and stored under predetermined conditions, the amount of gas generated is measured.

[Measurement of gas generation amount]
(Preparation of positive electrode for lithium secondary battery)
The CAM of the present embodiment, the conductive material, and the binder are kneaded at a ratio of CAM:conductive material:binder=92:5:3 (mass ratio) to prepare a pasty positive electrode mixture. N-methyl-2-pyrrolidone is used as an organic solvent when preparing the positive electrode mixture. Acetylene black is used as the conductive material. Polyvinylidene fluoride is used as the binder.

The obtained positive electrode mixture is applied to an Al foil having a thickness of 40 μm as a current collector, dried at 60° C. for 1 hour, and vacuum-dried at 150° C. for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of this positive electrode for a lithium secondary battery is 34.96 cm ² .

(Preparation of negative electrode for lithium secondary battery)
By adding and kneading artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) at a composition ratio of artificial graphite: SBR: CMC = 96.5: 2: 1.5 (mass ratio) , to prepare a paste-like negative electrode mixture. Pure water is used as a solvent when preparing the negative electrode mixture.

The resulting negative electrode mixture was applied to a Cu foil having a thickness of 10 μm as a current collector, dried at 60° C. for 1 hour, and vacuum-dried at 120° C. for 8 hours to obtain a negative electrode for a lithium secondary battery. rice field. The electrode area of this negative electrode for lithium secondary battery was 37.44 cm ² .

(Production of lithium secondary battery)
A separator (polyethylene porous film) is placed on the negative electrode produced in (Preparation of negative electrode for lithium secondary battery), and the lithium secondary battery prepared in (Preparation of positive electrode for lithium secondary battery) is placed thereon. After placing the positive electrode, wrap it with an aluminum laminate film. 1000 .mu.l of electrolyte solution is poured thereinto, and the aluminum laminate is sealed by a vacuum packaging machine to produce a lithium secondary battery (pouch type). As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a ratio of 1.3 mol/l in a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (16:10:74 (volume ratio)) is used.

Using the lithium secondary battery produced by the above method, the amount of gas generated is measured by the following method.

(Measuring method)
Using CAM as a positive electrode, a pouch-type lithium secondary battery is produced.

The pouch-type lithium secondary battery is formed under the following conditions.
Formation conditions: Charge to 10% SOC at 0.05 CA at a test temperature of 25 ° C., leave for 10 hours at a test temperature of 60 ° C., then CC-CV charge to 4.3 V at 0.1 CA at a test temperature of 25 ° C. Current is charged to 0.05 CA. Further, after discharging to 2.5 V at 0.2 CA, two cycles of charging and discharging at 0.2 CA are performed.

After that, the volume of the lithium secondary battery is measured by the Archimedes method to obtain the volume before storage.
The Archimedes method is a method of measuring the actual volume of the entire lithium secondary battery from the difference between the weight of the lithium secondary battery in air and the weight in water using an automatic hydrometer.

Then, it is charged to 4.3V and stored in a constant temperature bath at 60°C for 7 days. After that, the volume of the pouch-type lithium secondary battery discharged to 2.5 V at a current value of 0.2 CA is measured by the Archimedes method. The amount of gas generated (unit: cc/g) is determined from the difference between the volume after storage at 60°C for 7 days and the volume before storage. The mass (g) in the unit of the amount of generated gas is the standard for the weight of the CAM.

It should be noted that, in a test in which a lithium secondary battery in a charged state is stored in a constant temperature bath at 60°C for 7 days, side reactions are more likely to occur than at room temperature, and gas is easily generated. That is, the above test is an accelerated test assuming storage of the lithium secondary battery in a charged state at room temperature for a long period of time, and is a test condition generally used in this technical field. If the amount of gas generated in the above test is small, it can be evaluated that gas is hardly generated even when the battery is stored in a charged state at room temperature for a long period of time.

If the amount of gas generated measured by the above method is 0.13 cc/g or less, it is evaluated as "difficult to generate gas even when stored at room temperature for a long period of time in a charged state."

<CAM manufacturing method 1>
CAM production method 1 is a method in which the steps of producing MCC, mixing MCC, a lithium compound and compound X to obtain a mixture, and obtaining CAM are performed in this order. MCC is a metal composite oxide or metal composite hydroxide. Compound X will be described later.

[Manufacturing process of MCC]
First, MCC containing Ni and optional elements Co and element M is prepared.
MCC can be produced by a batch co-precipitation method or a continuous co-precipitation method. The manufacturing method will be described in detail below, taking a metal composite hydroxide containing Ni, Co and Al as an example.

First, a nickel salt solution, a cobalt salt solution, an aluminum salt solution, and a complexing agent are reacted by a co-precipitation method, particularly the continuous method described in JP-A-2002-201028, to form Ni _(1-yz) Co A metal composite hydroxide represented by _yAlz (OH) ₂ (wherein y+z< ₁ ) is produced.

The nickel salt that is the solute of the nickel salt solution is not particularly limited, but for example, one or more of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate can be used.

As the cobalt salt that is the solute of the cobalt salt solution, for example, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used.

As the aluminum salt that is the solute of the aluminum salt solution, for example, aluminum sulfate, sodium aluminate, or the like can be used.

The above metal salts are used in proportions corresponding to the composition ratio of Ni _(1-yz) Co _y Al _z (OH) ₂ . Also, water is used as a solvent.

A complexing agent is a compound capable of forming a complex with Ni, Co, and Al ions in an aqueous solution. Examples include ammonium ion donors, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

Ammonium ion donors include ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride.

The complexing agent may not be contained, and when the complexing agent is contained, the amount of the complexing agent contained in the mixed solution containing the nickel salt solution, the cobalt salt solution, the aluminum salt solution and the complexing agent is, for example, The mol ratio to the total number of mols of the metal salt is greater than 0 and 2.0 or less.

In the coprecipitation method, in order to adjust the pH value of the mixed solution containing the nickel salt solution, the cobalt salt solution, the aluminum salt solution and the complexing agent, before the pH of the mixed solution changes from alkaline to neutral, Add an alkaline aqueous solution. Sodium hydroxide and potassium hydroxide can be used as the alkaline aqueous solution.

It should be noted that the pH value in this specification is defined as the value measured when the temperature of the mixed liquid is 40°C. If the temperature of the mixed liquid sampled from the reaction tank is not 40°C, the mixed liquid is heated or cooled to 40°C and the pH is measured.

When the nickel salt solution, cobalt salt solution, and aluminum salt solution as well as the complexing agent are continuously supplied to the reactor, Ni, Co, and Al react to form Ni _(1-yz) Co _y Al. _z (OH) ₂ is produced.

During the reaction, the temperature of the reaction vessel is controlled, for example, within the range of 20-80°C, preferably 30-70°C.

Also, during the reaction, the pH value of the mixed solution in the reaction vessel is controlled within the range of pH 9-13, preferably pH 11-13.

The materials in the reaction vessel are appropriately agitated to mix.
The reactor used in the continuous co-precipitation process is an overflow-type reactor in which the formed reaction precipitate is overflowed and separated from the top of the reactor.

The inside of the reaction tank may be an inert atmosphere. An inert atmosphere suppresses the aggregation of elements that are more easily oxidized than Ni, and a uniform MCC can be obtained.

Also, oxygen may be introduced into the reaction tank. A method of introducing oxygen into the reactor includes a method of bubbling an oxygen-containing gas. At this time, it is preferable to introduce oxygen gas while maintaining an inert atmosphere without introducing a large amount of oxygen.

After the above reaction, the reaction product obtained is washed with water and then dried to obtain a metal composite hydroxide. In addition, if contaminants derived from the mixed solution remain only by washing the reaction product with water, the reaction product may optionally be washed with weak acid water, sodium hydroxide, or potassium hydroxide. It may be washed with an alkaline solution.

When manufacturing a metal composite oxide as MCC, the metal composite oxide can be prepared by oxidizing the metal composite hydroxide (oxidation step). In the oxidation step, it is preferable that the total time from the start of temperature rise to the end of temperature retention is 1 hour or more and 30 hours or less. The heating rate until reaching the maximum holding temperature is preferably 180° C./hour or more, more preferably 200° C./hour or more, and particularly preferably 250° C./hour or more.

The maximum holding temperature in this specification is the maximum temperature of the holding temperature of the furnace atmosphere in the oxidation step or the firing step described later, and when the oxidation step or firing step has a plurality of steps, the maximum holding temperature It means the temperature of the process of oxidation or calcination at the highest temperature among the processes.

The heating rate in this specification refers to the time from the start of temperature rise to the maximum holding temperature in the apparatus used in the oxidation process or the firing process, and the time from the temperature at the start of heating in the furnace to the maximum holding temperature. It is calculated from the temperature difference between

At the time of oxidation, various gases, for example, inert gases such as nitrogen, argon and carbon dioxide, oxidizing gases such as air and oxygen, or mixed gases thereof may be supplied into the reaction vessel.

An oxidizing agent may also be used. As the oxidizing agent, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, ozone, and the like can be used.

Drying conditions for MCC are not particularly limited. When MCC is a metal composite oxide or metal composite hydroxide, the drying conditions may be, for example, any of the following conditions 1) to 3).
1) Conditions under which the metal composite oxide or metal composite hydroxide is not oxidized or reduced. Specifically, the drying conditions are such that the metal composite oxide is maintained as a metal composite oxide, and the metal composite hydroxide is maintained as a metal composite hydroxide.
2) Conditions under which the metal composite hydroxide is oxidized. Specifically, the drying conditions are such that the metal composite hydroxide is oxidized to the metal composite oxide.
3) Conditions under which the metal composite oxide is reduced. Specifically, the drying conditions are such that the metal composite oxide is reduced to the metal composite hydroxide.

An inert gas such as nitrogen, helium or argon may be used in the atmosphere during drying in order to create a condition in which the metal composite oxide or metal composite hydroxide is not oxidized or reduced.
Oxygen or air may be used in the drying atmosphere to create conditions for oxidizing the metal composite hydroxide.

Also, in order to create conditions for reducing the metal composite oxide, a reducing agent such as hydrazine or sodium sulfite may be used in an inert gas atmosphere during drying.

After drying the MCC, it may be appropriately classified.

[Step of obtaining a mixture]
After drying the MCC as necessary, the lithium compound and the compound X are mixed.

As the lithium compound, one or more of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, and lithium oxide may be used in combination.
Among these lithium compounds, lithium hydroxide and lithium acetate can react with carbon dioxide in the air and contain several percent of lithium carbonate.

A compound X is a compound containing the element X described above.

Compound X containing Nb includes niobium oxide (Nb ₂ O ₅ , NbO).

Compound X containing W includes tungsten oxide (WO ₃ , WO ₂ ), tungstic acid, and tungsten chloride.

Compound X containing Mo includes molybdenum oxide (MoO ₃ ).

By firing a mixture containing MCC, a lithium compound, and compound X, a CAM comprising LiMO and a Li-X compound and satisfying (A) and (B) is obtained. In the following description, a mixture containing MCC, a lithium compound, and compound X may be referred to as mixture 1.

By firing the mixture 1, the MCC reacts with the lithium compound to grow primary particles, which are aggregated and sintered to form secondary particles having gaps. Furthermore, Li contained in the lithium compound reacts with element X contained in compound X to form a Li—X compound. The Li—X compound exists in the interstices of the secondary particles.

As a result of studies by the present inventors, it has been found that when using compound X in which the particle diameter and the circularity obtained by the method described below (Method for measuring circularity) are adjusted to an appropriate range, element X It was found that a large amount of X is unevenly distributed, and a CAM having a larger amount of element X present in the interstices than in the surface of the secondary particles is easily obtained. The dispersibility of compound X in MCC can be enhanced by adjusting the particle size and circularity of compound X within appropriate ranges.

The amount of compound X added varies depending on the type of element X. The amount of the compound X to be added is appropriately adjusted according to the ratio of the substance amount of the element X to the total substance amount of the metal elements contained in MCC.

For example, the ratio of the substance amount of the element X is preferably 0.1-2.5 mol%.

(Method for measuring circularity)
The circularity of compound X is measured by the following method.
First, an image of compound X is photographed with an optical microscope to obtain a particle image, which is a projected image of compound X. Next, the circularity calculated by the following formula (X) is measured for each particle that constitutes the compound X. A circularity distribution curve of the compound X is obtained by plotting the obtained circularity on the horizontal axis and the cumulative volume on the vertical axis.
The circularity shown in the following formula (X) means that the closer the numerical value is to 1, the better the circularity.
Circularity=4πS/L ² (X)
(S is the projected area of the projected image of compound X, and L is the perimeter of the particle of compound X.)

In the obtained circularity distribution curve, the circularity value at the time of 50% accumulation from the low circularity particle side is the 50% cumulative volume circularity _C50 . Similarly, in the obtained cumulative circularity distribution curve, the circularity values at 10% and 90% cumulative from the low circularity particle side are 10% cumulative volume circularity C ₁₀ and 90% cumulative volume circularity, respectively. degree C ₉₀ .

For example, Malvern's Morphologi series (apparatus name: Morphologi G3SE) can be used to measure circularity.

The _C50 of the compound X containing Nb is preferably 0.6 or more, more preferably 0.7 or more, and particularly preferably 0.8 or more.

(C ₉₀ -C ₁₀ )/C ₅₀ of compound X containing Nb is preferably 0.9 or less, more preferably 0.8 or less, and particularly preferably 0.7 or less. In addition, (C ₉₀ -C ₁₀ )/C ₅₀ of compound X containing Nb is preferably 0.30 or more, more preferably 0.35 or more, and particularly preferably 0.40 or more.
(C ₉₀ -C ₁₀ )/C ₅₀ of compound X containing Nb is, for example, 0.30-0.9, 0.35-0.8, 0.40-0.7.

The _C50 of the compound X containing W or Mo is preferably 0.6 or more, more preferably 0.7 or more, and particularly preferably 0.8 or more.

(C ₉₀ -C ₁₀ )/C ₅₀ of compound X containing W or Mo is preferably 0.8 or less, more preferably 0.7 or less, particularly 0.6 or less. preferable. In addition, (C ₉₀ -C ₁₀ )/C ₅₀ of compound X containing W or Mo is preferably 0.1 or more, more preferably 0.15 or more, and particularly preferably 0.25 or more.
(C ₉₀ -C ₁₀ )/C ₅₀ of compound X containing W or Mo is, for example, 0.1-0.8, 0.15-0.7, 0.25-0.6.

When _C50 is within the above range, it means that compound X has a high degree of circularity. By adding such a compound X, the contact between MCC and the compound X is facilitated, and the dispersibility of the Li—X compound is improved.

When (C ₉₀ -C ₁₀ )/C ₅₀ is within the above range, it means that compound X has a certain variation in circularity. When (C ₉₀ -C ₁₀ )/C ₅₀ is equal to or less than the above upper limit, the compound X having a low degree of circularity contributes to an increase in the specific surface area, thereby making it easier for the compound X to come into contact with MCC. The element X becomes easier to diffuse on the surface of the MCC. As a result, the secondary particles of the resulting CAM tend to contain Li—X compounds. When (C ₉₀ -C ₁₀ )/C ₅₀ is equal to or higher than the lower limit, the compound X with low circularity is not too much and easily comes into contact with the MCC, facilitating surface diffusion into the interstices of the secondary particles of the CAM.

In order to efficiently unevenly distribute the Li—X compound in the gaps between the secondary particles of the CAM, D ₅₀ (μm) of the compound X is preferably 0.02-20 μm, more preferably 0.05-14 μm. more preferred.

The _D50 of the Nb-containing compound X is preferably 10 μm or less, more preferably 5.0 μm or less, and even more preferably 3.0 μm or less. The _D50 of the Nb-containing compound X is preferably 0.02 μm or more, particularly preferably 0.05 μm or more.
The D ₅₀ of compound X containing Nb is for example 0.02-10 μm, 0.05-3.0 μm.

The _D50 of compound X containing W or Mo is preferably 1.29 μm or less, more preferably 1.28 μm or less. The _D50 of the compound X containing W or Mo is preferably 0.02 μm or more, particularly preferably 0.05 μm or more.
The D ₅₀ of compound X containing W or Mo is, for example, 0.02-1.29 μm, 0.05-1.28 μm.

When a compound X having D ₅₀ , C ₅₀ and (C ₉₀ -C ₁₀ )/C ₅₀ within the above ranges is used, a large amount of the element X is unevenly distributed in the gaps of the secondary particles, and the gaps of the secondary particles are more concentrated than the surfaces. It becomes easier to obtain a CAM with a large amount of element X present, and it becomes easier to manufacture a CAM that satisfies (A), (B), (C) and (D).

It is preferable to uniformly mix MCC, lithium compound, and compound X until there are no aggregates of each. Although the mixing device is not limited as long as MCC, the lithium compound, and the compound X can be uniformly mixed, it is preferable to use, for example, a Loedige mixer for mixing.

The lithium compound, MCC and compound X are used in consideration of the composition ratio of the final product. The lithium compound, MCC, and compound X are used in proportions corresponding to the compositional ratio of the above compositional formula (I).

Further, in the CAM, which is the final product, the CAM obtained is obtained by mixing the Li contained in the lithium compound and the total metal elements contained in the MCC at a molar ratio of 0.98 or more and 1.1 or less. (B) and (D) of (B) and (D) are easily controlled within the preferred range of the present embodiment.

[Step of obtaining CAM]
By firing a mixture of MCC, a lithium compound and compound X, a CAM with LiMO and a Li—X compound in the interstices can be obtained. For firing, dry air, atmospheric air, an oxygen atmosphere, an inert atmosphere (nitrogen, argon), a mixed gas of these, or the like is used depending on the desired composition. In this embodiment, it is preferable to bake in an oxygen atmosphere.

The firing process may be a single firing or may have multiple firing stages.
When there are multiple firing steps, the step of firing at the highest temperature is referred to as main firing. Temporary sintering may be performed before main sintering at a temperature lower than that of main sintering. Further, after the main firing, post-baking may be performed in which the material is fired at a temperature lower than that of the main firing.

The firing temperature (maximum holding temperature) of the main firing is preferably 600° C. or higher, more preferably 650° C. or higher, and particularly preferably 700° C. or higher, from the viewpoint of promoting the growth of LiMO particles. From the viewpoint of preventing cracks from being formed in the LiMO particles and maintaining the particle strength, the temperature is preferably 1200° C. or lower, more preferably 1100° C. or lower, and particularly preferably 1000° C. or lower.
In addition, when the firing process is performed only once, it is preferable to carry out at the firing temperature of the main firing.

The upper limit and lower limit of the maximum holding temperature for main firing can be combined arbitrarily.
Examples of combinations include 600-1200°C, 650-1100°C and 700-1000°C.
When the main firing is carried out at 600° C. or higher, a CAM that satisfies (A), (B), (C) and (D) is likely to be obtained.

The firing temperature for pre-firing or post-firing should be lower than the firing temperature for main firing, and may be in the range of 350-800°C, for example.

The firing temperature may be appropriately adjusted according to the type of transition metal element used, the type and amount of precipitant and inert melting agent.

Also, the holding time at the maximum holding temperature is 0.1 to 20 hours, preferably 0.5 to 10 hours. The rate of temperature increase to the maximum holding temperature is preferably 50-400° C./hour, and the rate of temperature decrease from the maximum holding temperature to room temperature is preferably 10-400° C./hour.

[Optional process]
- Washing step In the present embodiment, it is preferable to wash the fired product after firing with a cleaning liquid such as pure water or an alkaline cleaning liquid.
Examples of alkaline cleaning solutions include LiOH (lithium hydroxide), NaOH ( _sodium hydroxide), KOH (potassium hydroxide), _Li2CO3 (lithium carbonate), _{Na2CO3 (} sodium carbonate), and _{K2CO3 .} An aqueous solution of one or more anhydrides selected from the group consisting of (potassium carbonate) and (NH ₄ ) ₂ CO ₃ (ammonium carbonate) and an aqueous solution of the hydrate of said anhydride can be mentioned. Ammonia can also be used as the alkali.

In the washing process, the method of contacting the cleaning liquid and the fired product includes a method of putting the fired product into each cleaning solution and stirring it, a method of showering each cleaning solution as shower water on the fired product, and a method of pouring the fired product into the cleaning solution. is added and stirred, the fired product is separated from each cleaning solution, and then each cleaning solution is used as shower water to be applied to the separated fired product.

The temperature of the cleaning liquid used for cleaning is preferably 15°C or lower, more preferably 10°C or lower, and particularly preferably 8°C or lower. By controlling the temperature of the cleaning liquid within the above range and at a temperature at which the cleaning liquid does not freeze, excessive elution of lithium ions from the crystal structure of the baked product into the cleaning liquid during cleaning can be suppressed.

The baked product after washing may be dried as appropriate.

A CAM is obtained through the above steps.

<CAM manufacturing method 2>
CAM production method 2 is a method in which a step of producing MCC, a step of mixing MCC and a lithium compound to obtain LiMO, and a step of mixing LiMO and compound X and firing to obtain CAM are performed in this order. is.

[Manufacturing process of MCC]
The description of the MCC manufacturing process in the CAM manufacturing method 2 is the same as the description of the MCC manufacturing process in the CAM manufacturing method 1 above.

[Step of obtaining LiMO]
The obtained MCC and a lithium compound are mixed. LiMO is obtained by firing a mixture containing MCC and a lithium compound.

As the lithium compound used in this step, the same compound as the lithium compound described in CAM production method 1 can be used.

The above lithium compound and MCC are used in consideration of the composition ratio of the final product. For example, when a metal composite hydroxide containing Ni, Co, and Al is used as MCC, the lithium compound and MCC are Li[Li _a (Ni _(1-yz) Co _y Al _z ) _1-a ]O ₂ It is used at a ratio corresponding to the composition ratio (in the formula, y+z<1). In addition, in the CAM, which is the final product, when the Li contained in the lithium compound and the total metal elements contained in the MCC are mixed at a ratio such that the molar ratio is 0.98 to 1.1, the resulting CAM ( It is easy to control B) and (D) within the preferred ranges of the present embodiment.

For the primary firing described later, dry air, oxygen atmosphere, inert atmosphere, etc. are used depending on the desired composition.

The firing process for firing the mixture containing MCC and the lithium compound is preferably performed only once. In the following, firing of a mixture containing MCC and a lithium compound is referred to as primary firing.

The primary firing should be lower than the firing temperature of the secondary firing described later, for example, the range of 350°C or higher and 800°C or lower.

[Step of obtaining CAM]
The CAM is obtained by mixing the fired product obtained after the primary firing with the compound X and firing the mixture. A step of firing a mixture of the fired product obtained after the primary firing and the compound X is referred to as secondary firing.

Due to the primary firing, the MCC reacts with the lithium compound to grow the primary particles, and the primary particles are aggregated and sintered to form secondary particles with gaps. By mixing the fired product obtained after the primary firing with the compound X and performing the secondary firing, the element X is likely to exist in the gaps between the secondary particles. Since the sintering of the primary particles and the diffusion of the element X into the gaps between the primary particles are likely to occur in the secondary firing process, it is considered that the element X is likely to exist in the gaps of the secondary particles.

The explanation of compound X used in CAM production method 2 is the same as the explanation of compound X in CAM production method 1.

The firing temperature (maximum holding temperature) of the secondary firing is preferably 600° C. or higher, more preferably 650° C. or higher, and more preferably 700° C. or higher, from the viewpoint of allowing the Li—X compound to exist uniformly in the gaps between the secondary particles of the CAM. Especially preferred. From the viewpoint of preventing crack formation in the CAM particles and maintaining particle strength, the temperature is preferably 1200° C. or lower, more preferably 1100° C. or lower, and particularly preferably 1000° C. or lower.

The upper limit and lower limit of the highest holding temperature for secondary firing can be combined arbitrarily.
Examples of combinations include 600-1200°C, 650-1100°C and 700-1000°C.
If the secondary firing is carried out at 600° C. or higher, (A), (B), (C) and (D) can be easily controlled within the preferred ranges of the present embodiment.

The firing temperature of the secondary firing may be appropriately adjusted according to the type of transition metal element used, the type and amount of precipitant and inert melting agent.

Also, in the secondary firing, the holding time at the maximum holding temperature is 0.1 to 20 hours, preferably 0.5 to 10 hours. The rate of temperature increase to the maximum holding temperature is preferably 50-400° C./hour, and the rate of temperature decrease from the maximum holding temperature to room temperature is preferably 10-400° C./hour. Air, oxygen, nitrogen, argon, or a mixed gas of these can be used as the atmosphere for the secondary firing.

The amount of compound X to be added is adjusted according to the type of element X so that the ratio of the substance amount of element X to the total substance amount of metal elements other than Li contained in LiMO is within a preferable range.

For example, the ratio of the substance amount of the element X is preferably 0.1-2.5 mol%.

Compound X and LiMO are uniformly mixed until there are no compound X aggregates or LiMO aggregates. Although the mixing device is not limited as long as the compound X and LiMO can be uniformly mixed, it is preferable to use, for example, a Loedige mixer for mixing.

After the secondary firing, the above [optional step] may be carried out.
A CAM is obtained by the above steps.

<Lithium secondary battery>
Next, the configuration of a lithium secondary battery suitable for using the CAM of this embodiment will be described.
Furthermore, a positive electrode for a lithium secondary battery (hereinafter sometimes referred to as a positive electrode) suitable for using the CAM of the present embodiment will be described.
Furthermore, a lithium secondary battery suitable for use as a positive electrode will be described.

An example of a lithium secondary battery suitable for using the CAM of the present embodiment has a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolytic solution placed between the positive electrode and the negative electrode.

FIG. 1 is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

First, as shown in the partial enlarged view of FIG. An electrode group 4 is formed by laminating a positive electrode 2, a separator 1, and a negative electrode 3 in this order and winding them.

The positive electrode 2 has, for example, a positive electrode active material layer containing CAM, and a positive electrode current collector having the positive electrode active material layer formed on one surface. Such a positive electrode 2 can be manufactured by first preparing a positive electrode mixture containing CAM, a conductive material, and a binder, and supporting the positive electrode mixture on one surface of a positive electrode current collector to form a positive electrode active material layer.

Examples of the negative electrode 3 include an electrode in which a negative electrode mixture containing a negative electrode active material (not shown) is supported on a negative electrode current collector, and an electrode composed solely of a negative electrode active material. can be manufactured in

Next, after housing the electrode group 4 and an insulator (not shown) in the battery can 5, the can bottom is sealed, the electrode group 4 is impregnated with the electrolytic solution 6, and the electrolyte is arranged between the positive electrode 2 and the negative electrode 3. . Further, by sealing the upper portion of the battery can 5 with the top insulator 7 and the sealing member 8, the lithium secondary battery 10 can be manufactured.

The shape of the electrode group 4 is, for example, a columnar shape such that the cross-sectional shape of the electrode group 4 cut in the direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners. can be mentioned.

In addition, as the shape of the lithium secondary battery having such an electrode group 4, a shape defined by IEC60086, which is a standard for batteries defined by the International Electrotechnical Commission (IEC), or JIS C 8500 can be adopted. . For example, a shape such as a cylindrical shape or a rectangular shape can be mentioned.

Further, the lithium secondary battery is not limited to the wound type configuration described above, and may have a layered configuration in which a layered structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of laminated lithium secondary batteries include so-called coin-type batteries, button-type batteries, and paper-type (or sheet-type) batteries.

For the positive electrode, separator, negative electrode and electrolyte that constitute the lithium secondary battery, for example, the configurations, materials and manufacturing methods described in [0113] to [0140] of WO2022/113904A1 can be used.

<All-solid lithium secondary battery>
The CAM of this embodiment can be used as a CAM for an all-solid lithium secondary battery.

FIG. 2 is a schematic diagram showing an example of an all-solid lithium secondary battery. The all-solid lithium secondary battery 1000 shown in FIG. 2 has a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer package 200 that accommodates the laminate 100. Moreover, the all-solid lithium secondary battery 1000 may have a bipolar structure in which a CAM and a negative electrode active material are arranged on both sides of a current collector. Specific examples of bipolar structures include structures described in JP-A-2004-95400.

The positive electrode 110 has a positive electrode active material layer 111 and a positive electrode current collector 112 . The positive electrode active material layer 111 contains the above-described CAM and solid electrolyte. Moreover, the positive electrode active material layer 111 may contain a conductive material and a binder.

The negative electrode 120 has a negative electrode active material layer 121 and a negative electrode current collector 122 . The negative electrode active material layer 121 contains a negative electrode active material. Further, the negative electrode active material layer 121 may contain a solid electrolyte and a conductive material.

The laminate 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122 . In addition, all-solid lithium secondary battery 1000 may have a separator between positive electrode 110 and negative electrode 120 .

The all-solid lithium secondary battery 1000 further has an insulator (not shown) for insulating the laminate 100 and the exterior body 200 and a sealing body (not shown) for sealing the opening 200 a of the exterior body 200 .

For the exterior body 200, a container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel can be used. Moreover, as the exterior body 200, a container in which a laminated film having at least one surface subjected to corrosion-resistant processing is processed into a bag shape can also be used.

Examples of the shape of the all-solid lithium secondary battery 1000 include coin-shaped, button-shaped, paper-shaped (or sheet-shaped), cylindrical, rectangular, and laminated (pouch-shaped).

The all-solid-state lithium secondary battery 1000 is illustrated as having one laminate 100 as an example, but the present embodiment is not limited to this. The all-solid-state lithium secondary battery 1000 may have a configuration in which the laminate 100 is used as a unit cell and a plurality of unit cells (laminate 100 ) are sealed inside the exterior body 200 .

For all-solid-state lithium secondary batteries, for example, the configurations, materials and manufacturing methods described in [0151] to [0181] of WO2022/113904A1 can be used.

Since the CAM of the present embodiment is used in the lithium secondary battery configured as described above, it is possible to provide a lithium secondary battery that generates a small amount of gas when stored in a charged state.

In addition, since the positive electrode having the configuration described above has the CAM having the configuration described above, the amount of gas generated can be reduced even if the lithium secondary battery is stored in a charged state.

Furthermore, since the lithium secondary battery configured as described above has the positive electrode described above, it becomes a secondary battery that generates a small amount of gas even when stored in a charged state.

One aspect of the present invention includes [11] to [22].
[11] A CAM comprising LiMO and the Li—X compound, wherein the Li—X compound is an oxide having lithium ion conductivity, and satisfies (A)-3 and (B) above. , CAM.
[12] The CAM according to [11], wherein the X(XPS) satisfies (C)-2 above.
[13] The CAM according to [11] or [12], wherein the Li(XPS) satisfies (D)-2 above.
[14] The CAM according to any one of [11] to [13], which satisfies the following compositional formula (I)-1.
Li[Li _a (Ni _(1-yzw) Co _y M _z X _w ) _1-a ]O ₂ (I)-1
(In formula (I)-1, M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Ga, B, Si, S and P. and X is one or more elements selected from the group consisting of Nb, W and Mo, and formula (I)-1 is 0.002 ≤ a ≤ 0.07, 0.08 ≤ y ≤ 0 .3, 0.0002≦z≦0.15, 0.001≦w≦0.09, and 0<y+z+w≦0.5.)
[15] The CAM according to any one of [11] to [14], wherein D ₁₀ , D ₉₀ and D ₅₀ satisfy (E)-13 above.
[16] The CAM according to any one of [11] to [15], having a BET specific surface area of 1.4-2.5 m ² /g.
[17] The CAM according to any one of [11] to [16], which satisfies (A)-4 above.
[18] The CAM according to any one of [11] to [17], which satisfies (B)-3 above.
[19] The CAM according to any one of [11] to [18], wherein the X(XPS) satisfies (C)-3 above.
[20] The CAM according to any one of [11] to [19], wherein the Li(XPS) satisfies (D)-3 above.
[21] A positive electrode for a lithium secondary battery, comprising the CAM according to any one of [11] to [20].
[22] A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to [21].

[Measurement of X (XPS) and Li (XPS)]
X (XPS) and Li (XPS) were measured by the method described in [Measurement of X (XPS) and Li (XPS)] above.

[Measurement of X (ICP) and Li (ICP)]
X(ICP) and Li(ICP) were measured by the method described in [Measurement of X(ICP) and Li(ICP)] above.

[Composition analysis]
The composition analysis of CAM was performed by the method described in [Composition analysis] above.

[Measurement of _D10 , _D90 and _D50 ]
D ₁₀ , D ₉₀ and D ₅₀ of CAM and D ₅₀ of Nb ₂ O ₅ and WO ₃ were measured by the method described in [Measurement of D ₁₀ , D ₉₀ and D ₅₀ ] above.

[Measurement of BET specific surface area]
The BET specific surface area was measured by the method described in [Measurement of BET specific surface area] above.

[Measurement of gas generation amount]
The amount of generated gas was measured by the method described in [Measurement of amount of generated gas].

C ₁₀ , C ₁₀ , and C ₉₀ were measured by the above (method for measuring circularity).

<<Example 1>>
1. Production of CAM-1 After water was put into a reactor equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added and the liquid temperature was maintained at 50°C.

A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and an aluminum sulfate aqueous solution were mixed at a ratio of 88:9:3 for the atomic ratio of Ni, Co, and Al to prepare a mixed raw material solution.

Next, this mixed raw material liquid and an aqueous solution of ammonium sulfate were continuously added as a complexing agent into the reactor while stirring. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the mixed liquid in the reaction tank was 11.6 (when measured at a liquid temperature of 40° C.), to obtain particles of metal composite hydroxide.
After washing the metal composite hydroxide particles, they were dehydrated with a centrifuge, isolated, and dried at 105° C. to obtain MCC1, which is a metal composite hydroxide.

MCC1 and lithium hydroxide monohydrate powder were weighed and mixed at a molar ratio of Li/(Ni+Co+Al)=1.10.
Furthermore, Nb ₂ O ₅ was weighed and mixed at a ratio of Nb/(Ni+Co+Al)=1.0 mol %.

The Nb ₂ O ₅ used in Example 1 had a D ₅₀ of 1.26 μm, a C ₅₀ of 0.82, and a (C ₉₀ -C ₁₀ )/C ₅₀ of 0.41.

After that, it was baked at 650° C. for 5 hours in an oxygen atmosphere.
After that, it was further fired at 790° C. for 6 hours in an oxygen atmosphere.

After that, it was washed with water and dried at 210°C for 10 hours in a nitrogen atmosphere to obtain CAM-1.

2. Evaluation of CAM-1 Composition analysis of CAM-1 was performed, and when it corresponded to the composition formula (I), a = 0.01, y = 0.09, z = 0.03, and w = 0.01. , element X was Nb and element M was Al. XAFS measurement of CAM-1 confirmed the formation of a Li—X compound.

<<Example 2>>
1. Production of CAM-2 The same experiment as in Example 1 was conducted except that the firing temperature of 790°C in Example 1 was changed to 760°C to obtain CAM-2.

2. Evaluation of CAM-2 A composition analysis of CAM-2 was performed, and when it corresponded to the composition formula (I), a = 0.06, y = 0.09, z = 0.02, and w = 0.01. , element X was Nb and element M was Al. XAFS measurement of CAM-2 confirmed the formation of a Li—X compound.

<<Example 3>>
1. Production of CAM-3 MCC1 and lithium hydroxide monohydrate powder were weighed and mixed at a molar ratio of Li/(Ni+Co+Al)=1.10.
The resulting mixture was fired at 650° C. for 5 hours in an oxygen atmosphere to obtain a fired product.

The fired product and WO ₃ were weighed and mixed at a ratio of W/(Ni+Co+Al)=0.75 mol %.

WO ₃ used in Example 3 had a D ₅₀ of 0.25 μm, a C ₅₀ of 0.86, and a (C ₉₀ −C ₁₀ )/C ₅₀ of 0.29.

After that, it was fired at 790°C for 6 hours in an oxygen atmosphere.

After that, it was washed with water and dried under reduced pressure at 150°C for 10 hours to obtain CAM-3.

2. Evaluation of CAM-3 When the composition analysis of CAM-3 was performed and it corresponded to the composition formula (I), a = -0.02, y = 0.09, z = 0.03, and w = 0.002. , element X was W and element M was Al. XAFS measurement of CAM-3 confirmed the formation of a Li—X compound.

<<Comparative Example 1>>
1. Preparation of CAM-11 Same as Example 1, except that Nb ₂ O ₅ with a D ₅₀ of 34.0 μm, a C ₅₀ of 0.69, and a (C ₉₀ -C ₁₀ )/C ₅₀ of 0.50 was used. A similar experiment was performed to obtain CAM-11.

2. Evaluation of CAM-11 Composition analysis of CAM-11 was performed, and when it corresponded to the composition formula (I), a = 0.016, y = 0.090, z = 0.021, and w = 0.005. , element X was Nb and element M was Al. XAFS measurement of CAM-11 confirmed the formation of a Li—X compound.

<<Comparative Example 2>>
1. Preparation of CAM-12 Same as Example 1, except using Nb ₂ O ₅ with a D ₅₀ of 1.30 μm, a C ₅₀ of 0.82, and a (C ₉₀ -C ₁₀ )/C ₅₀ of 0.27. A similar experiment was performed to obtain CAM-12.

2. Evaluation of CAM-12 Composition analysis of CAM-12 was performed, and when it corresponded to the composition formula (I), a = 0.033, y = 0.087, z = 0.029, and w = 0.012. , element X was Nb and element M was Al. XAFS measurement of CAM-12 confirmed the formation of a Li—X compound.

<<Comparative Example 3>>
1. Production of CAM-13 MCC1 and lithium hydroxide monohydrate powder were weighed and mixed at a molar ratio of Li/(Ni+Co+Al)=1.10.
The resulting mixture was fired at 650° C. for 5 hours in an oxygen atmosphere to obtain a fired product.

The calcined product and Nb ₂ O ₅ described in Comparative Example 2 were weighed and mixed at a ratio of Nb/(Ni+Co+Al)=1.0 mol %.

After that, it was fired at 760°C for 6 hours in an oxygen atmosphere.

After that, it was washed with water and dried at 210°C for 10 hours in a nitrogen atmosphere to obtain CAM-13.

2. Evaluation of CAM-13 A composition analysis of CAM-13 was performed, and when it corresponded to the composition formula (I), a = 0.02, y = 0.09, z = 0.03, and w = 0.01. , element X was Nb and element M was Al. XAFS measurement of CAM-13 confirmed the formation of a Li—X compound.

<<Comparative Example 4>>
1. Production of CAM-14 MCC1 and lithium hydroxide monohydrate powder were weighed and mixed at a molar ratio of Li/(Ni+Co+Al)=1.03.
Further, Nb ₂ O ₅ described in Comparative Example 1 was weighed and mixed at a ratio of Nb/(Ni+Co+Al)=1.0 mol %.
After that, it was baked at 650° C. for 5 hours in an oxygen atmosphere.
After that, it was further fired at 790° C. for 6 hours in an oxygen atmosphere to obtain CAM-14.

2. Evaluation of CAM-14 When the composition analysis of CAM-14 was performed and it corresponded to the composition formula (I), a = -0.01, y = 0.09, z = 0.03, and w = 0.01. , the element X was Nb, and the element M was Al. XAFS measurement of CAM-14 confirmed the formation of a Li—X compound.

X (XPS), X (ICP), X (XPS)/X (ICP), Li (XPS), Li (ICP), Li (XPS) of CAM-1 to CAM-3 and CAM-11 to CAM-14 /Li(ICP), D ₁₀ , D ₅₀ , D ₉₀ , (D ₉₀ −D ₅₀ )/(D ₅₀ −D ₁₀ ), BET specific surface area and gas generation rate are shown in Table 1.

As shown in Table 1, when a CAM that satisfies (A) and (B) was used, it was possible to manufacture a lithium secondary battery that generated a small amount of gas in the high-temperature storage test in a charged state.

DESCRIPTION OF SYMBOLS 1... Separator, 2... Positive electrode, 3... Negative electrode, 4... Electrode group, 5... Battery can, 6... Electrolytic solution, 7... Top insulator, 8... Sealing body, 10... Lithium secondary battery, 21... Positive electrode lead, 31 Negative electrode lead 100 Laminated body 110 Positive electrode 111 Positive electrode active material layer 112 Positive electrode current collector 113 External terminal 120 Negative electrode 121 Negative electrode active material layer 122 Negative electrode current collector DESCRIPTION OF SYMBOLS 123... External terminal 130... Solid electrolyte layer 200... Exterior body 200a... Opening part 1000... All-solid-state lithium secondary battery

Claims (8)

1. A positive electrode active material for a lithium secondary battery comprising a lithium metal composite oxide and a Li—X compound containing Li and an element X, wherein the Li—X compound is an oxide having lithium ion conductivity. , wherein the element X is one or more elements selected from the group consisting of Nb, W and Mo, and satisfies the following (A) and (B), a positive electrode active material for a lithium secondary battery.
   0.09≦X(XPS)/X(ICP)≦0.22 (A)
   0.5≦Li(XPS)/Li(ICP)≦1.5 (B)
   (In (A), X (XPS) is the abundance (%) of the element X on the surface of the particles of the positive electrode active material for a lithium secondary battery, measured by X-ray photoelectron spectroscopy. X ( ICP) is the abundance ratio (%) of the element X in the particles of the positive electrode active material for a lithium secondary battery, measured by ICP emission spectroscopy.
   In (B), Li (XPS) is the abundance (%) of Li on the surface of the particles of the positive electrode active material for a lithium secondary battery, measured by X-ray photoelectron spectroscopy. Li (ICP) is the abundance ratio (%) of Li in the particles of the positive electrode active material for a lithium secondary battery, measured by ICP emission spectroscopy. )
2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein said X(XPS) satisfies the following (C).
   0.01≦X(XPS)≦0.30 (C)
3. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein said Li(XPS) satisfies (D) below.
   0.4≦Li (XPS)≦1.2 (D)
4. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3, represented by the following compositional formula (I).
   Li[Li _a (Ni _(1-yzw) Co _y M _z X _w ) _1-a ]O ₂ (I)
   (In formula (I), M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Ga, B, Si, S and P. , X is one or more elements selected from the group consisting of Nb, W and Mo, and formula (I) is −0.1≦a≦0.2, 0≦y≦0.5, 0≦ satisfy z≦0.7, 0<w≦0.1, and y+z+w<1.)
5. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein D ₁₀ , D ₉₀ and D ₅₀ satisfy the following (E).
   ( _D90 - _D50 )/( _D50 - _D10 ) ≤ 3.0 (E)
   (In (E), _D10 is the 10% cumulative volume particle size of the positive electrode active material for lithium secondary batteries, _D50 is the 50% cumulative volume particle size, and _D90 is the 90% cumulative volume particle size.)
6. The positive electrode active material for lithium secondary batteries according to any one of claims 1 to 5, having a BET specific surface area of 1.0 m ² /g or more.
7. A positive electrode for lithium secondary batteries comprising the positive electrode active material for lithium secondary batteries according to any one of claims 1 to 6.
8. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 7.

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