WO2023106336A1 - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

This positive electrode active material for a lithium secondary battery includes a plurality of particles having a layered structure and including a lithium metal complex oxide, wherein the lithium metal complex oxide includes at least Li, Ni, Al, and an element M, and satisfies the following conditions (1) and (2).　(1) Regarding the proportion R1 of the number of atoms of Al to the total number of atoms of Ni, Al, and the element M, as obtained for each particle by measuring the surfaces of the plurality of particles by SEM-EDX, the relative standard deviation of the proportion R1 among the plurality of particles is greater than 28.5% and less than or equal to 70%.　(2) Regarding the proportion R2 of the number of atoms of Al to the total number of atoms of Ni, Al, and the element M, as obtained for each particle by measuring cross-sections of the plurality of particles by SEM-EDX, the relative standard deviation of the proportion R2 among the plurality of particles is greater than 13% and less than or equal to 50%.

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 to Japanese Patent Application No. 2021-199660 filed in Japan on December 8, 2021, the content of which is incorporated herein.

The positive electrode active material for lithium secondary batteries contains a lithium metal composite oxide. As lithium metal composite oxides, composite metal oxides containing metal elements such as Ni, Co and Al and Li are widely used. When the lithium secondary battery is charged and discharged, lithium ions are desorbed and intercalated on the particle surfaces of the positive electrode active material for lithium secondary batteries. Therefore, attempts have been made to improve the performance of lithium secondary batteries by controlling the surface state and structure of particles of positive electrode active materials for lithium secondary batteries.

For example, Patent Document 1 discloses a positive electrode active material composed of particles of a lithium-nickel composite oxide, comprising a core composed of the lithium-nickel composite oxide, and a coating layer formed on the surface of the core and composed of a compound containing aluminum. discloses a positive electrode active material having It is disclosed that the coating layer has an Al concentration of 2% by mass or more as measured by a scanning electron microscope-energy dispersive X-ray analysis method.

JP-A-2017-188211

The purpose of the positive electrode active material for lithium secondary batteries in Patent Document 1 is to achieve a lithium secondary battery with high capacity and good initial charge/discharge efficiency. However, positive electrode active materials for lithium secondary batteries have room for further improvement in terms of initial discharge capacity and repeated charge/discharge performance of lithium secondary batteries.

The present invention has been made in view of the above circumstances, and a positive electrode for a lithium secondary battery that can obtain a lithium secondary battery that has a high initial discharge capacity and does not easily decrease in discharge capacity even after repeated charging and discharging. An object of the present invention is to provide an active material, a positive electrode for a lithium secondary battery and a lithium secondary battery using the same.

The present invention has the following aspects.
[1] A positive electrode active material for a lithium secondary battery containing a plurality of particles containing a lithium metal composite oxide having a layered structure,
The lithium metal composite oxide contains at least Li, Ni, Al and element M,
The element M is one or more selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P is an element of
A positive electrode active material for a lithium secondary battery that satisfies the following conditions (1) and (2).
(1) The number of Al atoms relative to the total number of Ni, Al, and element M atoms obtained for each particle by measuring the surfaces of the plurality of particles with a scanning electron microscope-energy dispersive X-ray spectroscopy. Regarding the ratio R1, the relative standard deviation of the ratio R1 in the plurality of particles is greater than 28.5% and no greater than 70%.
(2) The number of Al atoms with respect to the total number of Ni, Al, and element M atoms obtained for each particle by measuring the cross section of the plurality of particles with the scanning electron microscope-energy dispersive X-ray spectroscopy. , the relative standard deviation of the ratio R2 in the plurality of particles is greater than 13% and less than or equal to 50%.
[2] The positive electrode active material for a lithium secondary battery according to [1], wherein the ratio of the number of particles having a ratio R1 of 10 atomic % or less to the total number of the plurality of particles is 99% or more.
[3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the ratio of the number of particles having a ratio R2 of 10 atomic % or less to the total number of the plurality of particles is 88% or more.
[4] The positive electrode active material for lithium secondary batteries according to any one of [1] to [3], wherein the positive electrode active material for lithium secondary batteries has a 50% cumulative volume particle size of 5 μm or more and 20 μm or less.
[5] The lithium secondary according to any one of [1] to [4], wherein the ratio of the 90% cumulative volume particle size to the 10% cumulative volume particle size of the positive electrode active material for lithium secondary batteries is 3 or less. Positive electrode active material for batteries.
[6] The positive electrode active material for lithium secondary batteries according to any one of [1] to [5], wherein the positive electrode active material for lithium secondary batteries has a compositional formula represented by formula (A).
Li[Li _m (Ni _(1-xy) Al _x M _y ) _1-m ]O ₂ (A)
(In formula A, M is selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P It is one or more elements and satisfies −0.1≦m≦0.2, 0<x≦0.5 and 0<y<0.5.)
[7] In the powder X-ray diffraction measurement using CuKα rays of the positive electrode active material for a lithium secondary battery, the diffraction peak intensity height within the range of 2θ = 44.1 ± 1° is 2θ = 18.0 for H2. The lithium according to any one of [1] to [6], wherein the ratio H1/H2 of H1, which is the diffraction peak intensity height within the range of 5 ± 1 °, is 1.5 or more and 1.6 or less. Positive electrode active material for secondary batteries.
[8] A positive electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries according to any one of [1] to [7].
[9] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [8].

INDUSTRIAL APPLICABILITY According to the present invention, a positive electrode active material for a lithium secondary battery and a lithium secondary battery using the same can obtain a lithium secondary battery that has a high initial discharge capacity and does not easily decrease in discharge capacity even after repeated charging and discharging. A positive electrode for a secondary battery and a lithium secondary battery can be provided.

1 is a schematic configuration diagram showing an example of a lithium secondary battery; FIG. 1 is a schematic diagram showing the overall configuration of an all-solid lithium secondary battery of the present embodiment; FIG.

A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described below. Preferred examples and conditions may be shared among the following embodiments. Moreover, in this specification, each term is defined below.

In the specification of the present application, a metal composite compound is hereinafter referred to as "MCC", a lithium metal composite oxide is hereinafter referred to as "LiMO", and a positive electrode active material for a lithium secondary battery (Cathode Active Material for lithium secondary batteries) is hereinafter referred to as "CAM".

"Ni" refers to nickel atoms, not nickel metal. “Li” and “Al” and the like similarly refer to lithium atoms and aluminum atoms and the like, respectively.

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.

"Cumulative volume particle size" is a value measured by a laser diffraction scattering method. Specifically, 0.1 g of CAM powder is added to 50 ml of a 0.2% by mass sodium hexametaphosphate aqueous solution to obtain a dispersion in which the powder is dispersed. Next, the particle size distribution of the resulting dispersion is measured using a laser diffraction/scattering particle size distribution analyzer (eg Mastersizer 2000 manufactured by Malvern) to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the value of the particle diameter when 10% is accumulated from the fine particle side is the 10% cumulative volume particle size (hereinafter sometimes referred to as D ₁₀ ) (μm), and from the fine particle side The value of the particle size at 50% accumulation is the 50% cumulative volume particle size (hereinafter sometimes referred to as D ₅₀ ) (μm), and the value of the particle size at 90% accumulation from the microparticle side is 90% accumulation. Volume particle size (hereinafter sometimes referred to as _D90 ) (μm).

"CAM composition analysis" is analyzed by the following method. For example, after dissolving CAM powder in hydrochloric acid, it is measured using an ICP emission spectrometer. As an ICP emission spectrometer, for example, Optima7300 manufactured by PerkinElmer Co., Ltd. can be used.

In this embodiment, scanning electron microscope-energy dispersive X-ray spectroscopy is referred to as "SEM-EDX". As a scanning electron microscope-energy dispersive X-ray spectrometer, for example, a Schottky field emission scanning electron microscope equipped with Oxford Instruments X-Max 150 as an EDX detector (JSM-7900F manufactured by JEOL Ltd. ) can be used.

[Crystal structure]
The crystal structure of LiMO can be calculated by performing CAM powder X-ray diffraction measurement using CuKα as a radiation source and measuring the diffraction angle 2θ in the range of 10 to 90°. Specifically, it can be confirmed by observation using a powder X-ray diffraction measurement device (for example, Ultima IV manufactured by Rigaku Corporation). The ratio H1/H2 of the diffraction peak intensity height (H1) within the range of 2θ = 18.5 ± 1 ° to the diffraction peak intensity height (H2) within the range of 2θ = 44.4 ± 1 ° is the above powder It can be obtained by performing powder X-ray diffraction measurement of CAM using an X-ray diffractometer and analyzing corresponding diffraction peaks with analysis software (for example, integrated powder X-ray analysis software JADE).

"Initial discharge capacity and 50th discharge capacity retention rate" were measured under the following conditions after producing a lithium secondary battery by the following method.

<Preparation of positive electrode for lithium secondary battery>
CAM, a conductive material (acetylene black), and a binder (PVdF) were added and kneaded so as to have a composition of CAM: conductive material: binder = 92:5:3 (mass ratio), thereby producing a pasty positive electrode mixture. Prepare the agent. NMP is used as an organic solvent when preparing the positive electrode mixture.

The obtained positive electrode mixture is applied to an Al foil having a thickness of 40 μm as a current collector 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 1.65 cm ² .

<Production of lithium secondary battery (coin-type half cell)>
The following operations are performed in an argon atmosphere glove box.
<Preparation of positive electrode for lithium secondary battery> Place the positive electrode for lithium secondary battery prepared in the part for coin battery R2032 (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down on the lower cover. A laminated film separator (16 μm-thick laminated body obtained by laminating a heat-resistant porous layer on a polyethylene porous film) is placed thereon. 300 μl of electrolytic solution is injected here. The electrolytic solution used is obtained by dissolving LiPF ₆ in a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate at a volume ratio of 30:35:35 (volume ratio) to 1 mol/l.
Next, metallic lithium is used as the negative electrode, the negative electrode is placed on the upper side of the laminated film separator, the upper lid is placed via a gasket, and the lid is crimped with a crimping machine to produce a lithium secondary battery (coin type half cell R2032).

"Initial discharge capacity" means a value measured by charging and discharging under the following conditions. The prepared lithium secondary battery was subjected to constant current charging at 0.2 CA up to 4.3 V at 25 ° C. and then constant voltage charging at 4.3 V for 5 hours. A constant current discharge at 2 CA is performed. The discharge capacity is measured, and the obtained value is defined as "initial discharge capacity" (mAh/g).

"The 50th discharge capacity retention rate" means a value measured by conducting a test in which charge-discharge cycles are repeated 50 times under the conditions shown below.

The lithium secondary battery produced is initially charged and discharged under the above conditions. After the initial charge/discharge, the charge/discharge is repeated at 1 CA under the same temperature and voltage conditions as the initial charge/discharge. After that, the discharge capacity (mAh/g) at the 50th cycle is measured. The ratio of the discharge capacity at the 50th cycle to the initial discharge capacity is defined as the 50th discharge capacity retention rate (%), that is, the cycle efficiency.

In this specification, a lithium secondary battery with a high 50th discharge capacity retention rate is sometimes described as having good cycle characteristics, meaning that the discharge capacity is less likely to decrease even after repeated charging and discharging.

<Positive electrode active material for lithium secondary battery>
The CAM of the present embodiment contains a plurality of particles containing LiMO having a layered structure, LiMO contains at least Li, Ni, Al and an element M, and the element M is Co, Mn, Fe, Cu, Ti , Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P are one or more elements selected from the group consisting of the following (1) and (2) meet the conditions.
(1) Regarding the ratio R1 of the number of Al atoms to the total number of atoms of Ni, Al, and the element M obtained for each particle by measuring the surface of a plurality of particles with SEM-EDX, the ratio in a plurality of particles The relative standard deviation of R1 is greater than 28.5% and less than or equal to 70%.
(2) Regarding the ratio R2 of the number of Al atoms to the total number of atoms of Ni, Al, and the element M obtained for each particle by measuring the cross section of a plurality of particles with SEM-EDX, the ratio in a plurality of particles The relative standard deviation of R2 is greater than 13% and less than or equal to 50%.

The CAM in this embodiment contains a plurality of particles. In other words, the CAM in this embodiment is powdery. In this embodiment, the CAM may contain only secondary particles, or may contain a mixture of primary particles and secondary particles.

In the present embodiment, "primary particles" are particles that do not appear to have grain boundaries when observed in a field of view of 10,000 times using a scanning electron microscope or the like. "Secondary particles" are particles in which the primary particles are agglomerated. That is, secondary particles are aggregates of primary particles.

The CAM of this embodiment satisfies the above (1) and (2).
Whether the CAM satisfies (1) and (2) can be confirmed by analyzing the surface and cross section of the CAM with SEM-EDX.

In this specification, the measurement range of the particle surface for calculating the ratio R1 is defined as the range from the outermost surface of the particle to the depth measurable by SEM-EDX at an acceleration voltage of 15 kV. Similarly, the measurement range of the particle cross section for calculating the ratio R2 is defined as the range from the outermost surface of the particle cross section produced by the method described below to the depth that can be measured by SEM-EDX at an acceleration voltage of 15 kV.

<SEM-EDX measurement>
The particle surface is measured by SEM-EDX at an acceleration voltage of 15 kV and a resolution of 119 nm. The particles to be measured may be 100 or more particles, for example, 150 particles having an equivalent circle diameter of 5 μm or more. A ratio R1 is calculated for each particle to be measured, and a relative standard deviation (unit: %) of the ratio R1 of all particles to be measured is calculated.

Prepare the cross section of the particles by the following method. First, particles are dispersed in a particle-fixing resin. Thereafter, vacuum degassing is performed, and the resulting product is sandwiched between aluminum plates and cured. Thereby, a cured product of the resin containing the particles is obtained.

The cured product is fixed on a sample table and set in a cross-sectional sample preparation device (also called a cross-section polisher, for example, IB-19520CCP manufactured by JEOL). Argon ion beam processing is performed at an ion acceleration voltage of 6.0 kV to produce a cross section of the particle.

The particle cross section is analyzed with SEM-EDX at an acceleration voltage of 15 kV and a resolution of 60 nm. The particle cross section to be measured may be a cross section of 100 or more, for example, 150 particles having an equivalent circle diameter of 5 μm or more. A ratio R2 is calculated for each particle to be measured, and a relative standard deviation (unit: %) of the ratio R2 of all particles to be measured is calculated.

When LiMO contains Al, the particle structure tends to be stabilized, and the CAM performance tends to improve. Therefore, LiMO preferably contains Al. However, in LiMO containing Al to such an extent that the performance of CAM is improved, Al tends to segregate in the manufacturing process, specifically the main firing process described later. Excessive segregation of Al tends to impede the diffusion of lithium ions and reduce the initial discharge capacity. In addition, if the Al content of LiMO is too low to suppress Al segregation, or if the fired product after main firing is washed excessively, the cycle characteristics tend to deteriorate.

In the present embodiment, both the initial discharge capacity and cycle characteristics of the lithium secondary battery can be improved by appropriately controlling the segregation amount of Al contained in the CAM. When the Al segregation amount is controlled by the manufacturing method described later, the variation in the Al ratio on the particle surface between the CAM particles and the variation in the Al ratio in the inside of the particle, that is, in the cross section of the particle are controlled. That is, a CAM that satisfies (1) and (2) can improve both the initial discharge capacity and cycle characteristics of a lithium secondary battery.

The relative standard deviation of the ratio R1 is greater than 28.5% and 70% or less, preferably 28.6-60.0%, more preferably 30.0-50.0%, 35 .0-50.0% is more preferred. When the relative standard deviation of the ratio R1 is more than 28.5%, Al is sufficiently contained in the CAM, and the cycle characteristics of the lithium secondary battery are improved. When the relative standard deviation of the ratio R1 is 70% or less, the diffusion inhibition of lithium ions due to Al segregation is suppressed, and the initial discharge capacity is improved.

The relative standard deviation of the ratio R2 is greater than 13% and 50% or less, preferably greater than 13.0% and 50.0% or less, more preferably 15.0-40.0%, 17 0-35.0% is more preferred, and 18.0-30.0% is particularly preferred. When the relative standard deviation of the ratio R2 is more than 13%, Al is sufficiently contained in the CAM, and the cycle characteristics of the lithium secondary battery are improved. When the relative standard deviation of the ratio R2 is 50% or less, the diffusion inhibition of lithium ions due to Al segregation is suppressed, and the initial discharge capacity is improved.

When the relative standard deviations of the ratios R1 and R2 are within the above range, it can be said that many particles in which the Al segregation parts exist are dispersed. The “Al segregation portion” is a portion of the particles X where Al is segregated. In the above-described SEM-EDX measurement, the particle surface and particle cross-section to be measured (hereinafter referred to as "surface to be measured") are arbitrarily selected. Therefore, when there are many particles in which the Al segregation parts are dispersed, the Al ratio (ratio R1 and ratio R2) for each surface to be measured tends to have little variation. On the other hand, if there is a bias in the presence of Al segregation parts, there may be a surface to be measured that contains many Al segregation parts and a surface to be measured that contains almost no Al segregation parts. Therefore, the ratio of Al (the ratio R1 and the ratio R2) tends to vary for each surface to be measured.

The ratio of the number of particles with a ratio R1 of 10 atomic% or less to the total number of a plurality of particles (hereinafter sometimes referred to as ratio a) is preferably 99% or more, and 99.5 to 100% More preferably, 99.9-100% is even more preferable. When the ratio a is within the above range, the variation in composition on the particle surface between particles is small, so the initial discharge capacity tends to be higher.

The ratio of the number of particles having a ratio R2 of 10 atomic% or less to the total number of a plurality of particles (hereinafter sometimes referred to as ratio b) is preferably 88% or more, more preferably 90 to 100%. , 99-100% is more preferred. When the ratio b is within the above range, the variation in the composition inside the particles between particles is small, so the initial discharge capacity tends to be higher.

The D ₅₀ of CAM is preferably 5-20 μm, more preferably 5.0-20 μm, even more preferably 5.0-17 μm, particularly preferably 5.0-15 μm. When the _D50 of CAM is within the above range, the cycle characteristics are likely to be improved.

The D ₉₀ /D ₁₀ of CAM is preferably 3 or less, more preferably 2-3, even more preferably 2.55-2.98, even more preferably 2.6-2.98. When the D ₉₀ /D ₁₀ of CAM is within the above range, the discharge capacity is higher and the cycle characteristics are better.

LiMO contained in the CAM contains at least Li, Ni, Al and element M, and is preferably represented by formula (A).
Li[Li _m (Ni _(1-xy) Al _x M _y ) _1-m ]O ₂ (A)
(In formula A, M is selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P It is one or more elements and satisfies −0.1≦m≦0.2, 0<x≦0.5 and 0<y<0.5.)

From the viewpoint of obtaining a lithium secondary battery with excellent cycle characteristics, m in the formula (A) is more preferably -0.05 or more, and more preferably more than 0. From the viewpoint of obtaining a lithium secondary battery with a higher initial coulombic efficiency, m in the formula (A) is preferably 0.08 or less, more preferably 0.06 or less.

The upper limit and lower limit of m can be arbitrarily combined. Combinations include, for example, m greater than 0 and 0.2 or less, -0.05 to 0.08, greater than 0 and 0.06 or less, and the like.

From the viewpoint of obtaining a lithium secondary battery with low battery internal resistance, x in the formula (A) is preferably 0.01 or more, more preferably 0.02 or more. x in the formula (A) is preferably 0.3 or less, more preferably 0.1 or less.

The upper and lower limits of x can be arbitrarily combined. Examples of combinations include 0.01 to 0.3, 0.02 to 0.3, 0.02 to 0.1, and the like.

From the viewpoint of obtaining a lithium secondary battery with low battery internal resistance, y in the formula (A) is preferably 0.01 or more, more preferably 0.03 or more, and even more preferably 0.05 or more. y in the formula (A) is preferably 0.3 or less, more preferably 0.1 or less.

The upper limit and lower limit of y can be combined arbitrarily. Combinations include, for example, 0.01 to less than 0.5, 0.03 to less than 0.5, 0.03 to 0.3, 0.05 to 0.1, and the like.

Further, from the viewpoint of obtaining a lithium secondary battery with a large initial discharge capacity, in the present embodiment, x + y in the formula (A) is preferably more than 0 and 0.50 or less, more preferably more than 0 and 0.48 or less. It is preferably more than 0 and more preferably 0.46 or less.

From the viewpoint of obtaining a lithium secondary battery with excellent cycle characteristics, M is preferably one or more metals selected from the group consisting of Co, Mn, W, B, Nb, and Zr. M is at least one element M1 selected from the group consisting of Co and Mn, and Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, and one or more elements M2 selected from the group consisting of S and P.

The CAM ratio H1/H2 is preferably 1.5-1.6, more preferably 1.51-1.59. When the ratio H1/H2 is within the above range, the initial discharge capacity and cycle characteristics tend to be high.

The crystal structure of LiMO is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.

The hexagonal crystal structure is composed of P3, P3 ₁ , P3 ₂ , R3, P-3, R-3, P312, P321, P3 ₁ 12, P3 ₁ 21, P3 ₂ 12, P3 ₂ 21, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P6 ₁ , P6 ₅ , P6 ₂ , P6 ₄ , P6 ₃ , P-6, P6/m, P6 ₃ /m, P622, P6 ₁ 22, P6 ₅ 22, P6 ₂ 22, P6 ₄ 22, P6 ₃ 22, P6mm, P6cc, P6 ₃ cm, P6 ₃ mc, P- It belongs to any one space group selected from the group consisting of 6m2, P-6c2, P-62m, P-62c, P6/mmm, P6/mcc, P6 ₃ /mcm, and P6 ₃ /mmc.

The monoclinic crystal structures are P2, P2 ₁ , C2, Pm, Pc, Cm, Cc, P2/m, P2 ₁ /m, C2/m, P2/c, P2 ₁ /c, and C2 It belongs to any one space group selected from the group consisting of /c.

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.

<Method for manufacturing CAM>
A method of manufacturing a CAM will be described. The CAM production method includes at least production of MCC, mixing of MCC and a lithium compound, calcination of the mixture of MCC and the lithium compound, main calcination of the reactant obtained by the calcination, and washing.

(1) Production of MCC MCC may be a metal composite hydroxide, a metal composite oxide, or a mixture thereof. Metal composite hydroxides and metal composite oxides, for example, contain Ni, Al, and element M in molar ratios represented by formula (A′) below, and are represented by formula (A″) below. The preferred ranges of x and y in formula (A') or (A'') are the same as the preferred ranges of x and y in formula (A) above.
Ni:Al:M=(1-xy):x:y (A')
Ni _{( 1-xy) AlxMyOα (} OH) _2-β (A'')
(In formula (A′) and formula (A″), M is Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, One or more elements selected from the group consisting of S and P, satisfying 0 < x ≤ 0.5 and 0 < y < 0.5.Formula (A'') is 0 ≤ α ≤ 3, −0.5≦β≦2 and β-α<2.)

A method for producing MCC containing Ni, Al and Co will be described below as an example. First, a metal composite hydroxide containing Ni, Al and Co is prepared. A metal composite hydroxide can be produced by a batch coprecipitation method or a continuous coprecipitation method.

Specifically, by the continuous coprecipitation method described in JP-A-2002-201028, a nickel salt solution, a cobalt salt solution, an aluminum salt solution and a complexing agent are reacted to obtain Ni _(1-xy) A metal composite hydroxide represented by Al _{x My} (OH) ₂ is produced.

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

As the aluminum salt that is the solute of the aluminum salt solution, for example, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride and aluminum acetate can be used.

At least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used as the cobalt salt that is the solute of the cobalt salt solution.

The above metal salts are used in proportions corresponding to the composition ratio of Ni _(1-xy) Al _x M _y (OH) ₂ . That is, the amount of each metal salt is defined so that the molar ratio of Ni, Al and Co in the mixed solution containing the metal salt corresponds to (1-xy):x:y in formula (A'). do. Also, water is used as a solvent.

The complexing agent is one capable of forming complexes with nickel ions, aluminum ions and cobalt ions in an aqueous solution. etc.), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid and uracil diacetic acid and glycine.

A complexing agent may or may not be used in the manufacturing process of the metal composite hydroxide. When a complexing agent is used, the amount of the complexing agent contained in the mixture containing the nickel salt solution, aluminum salt solution, cobalt salt solution and complexing agent is, for example, metal salts (nickel salts, aluminum salts and cobalt salts). 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 aluminum salt solution, the cobalt salt solution and the complexing agent, before the pH of the mixed solution changes from alkaline to neutral, Add the alkali metal hydroxide. Alkali metal hydroxides are, for example, sodium hydroxide or potassium hydroxide.

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. When 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 of the mixed liquid is measured.

When the nickel salt solution, aluminum salt solution, and cobalt salt solution as well as the complexing agent are continuously supplied to the reactor, Ni, Co and Al react to form Ni _(1-xy) Al _x Co _y (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 set within the range of 9-13, preferably 10-12.5, and the pH is controlled within ±0.5.

For the reaction tank used in the continuous coprecipitation method, an overflow type reaction tank can be used to separate the formed reaction precipitate.

When producing a metal composite hydroxide by a batch coprecipitation method, the reaction tank includes a reaction tank without an overflow pipe and a thickening tank connected to the overflow pipe, and the overflowed reaction precipitate is removed in the thickening tank. Apparatus having a mechanism for concentrating and recirculating to the reaction vessel, etc., may be mentioned.

Various gases, for example, inert gases such as nitrogen, argon or carbon dioxide, oxidizing gases such as air or oxygen, or mixed gases thereof may be supplied into the reaction vessel.

By appropriately controlling the concentration of the metal salt supplied to the reaction tank, the temperature of the reaction tank, the pH of the mixed solution, and the like, _D50 and _D90 / _D10 of the CAM can be controlled within the range of the present embodiment.

After the above reaction, isolate the neutralized reaction precipitate. For isolation, for example, a method of dehydrating a slurry containing a reaction precipitate (that is, a coprecipitate slurry) by centrifugation, suction filtration, or the like is used.

The isolated reaction precipitate is washed, dehydrated, dried and sieved to obtain a metal composite hydroxide containing Ni, Al and Co.

It is preferable to wash the reaction precipitate with water or an alkaline washing solution. In the present embodiment, the reaction precipitate is preferably washed with an alkaline washing liquid, more preferably washed with an aqueous sodium hydroxide solution. Also, the reaction precipitate may be washed with a washing liquid containing elemental sulfur. Examples of the cleaning solution containing elemental sulfur include an aqueous potassium or sodium sulfate solution.

When MCC is a metal composite oxide, the metal composite hydroxide is heated to produce the metal composite oxide. Multiple heating steps may be performed if desired. The heating temperature in this specification means the set temperature of the heating device. When a plurality of heating steps are performed, the heating temperature means the temperature of the step heated at the highest temperature among the respective heating steps.

The heating temperature is preferably 400-700°C, more preferably 450-680°C. When the heating temperature is 400 to 700° C., the metal composite hydroxide is sufficiently oxidized and a metal composite oxide having a BET specific surface area within an appropriate range is obtained.

The time for holding at the heating temperature is 0.1 to 20 hours, preferably 0.5 to 10 hours. The heating rate to the heating temperature is, for example, 50-400° C./hour.

The atmosphere in the heating device may be a moderate oxygen-containing atmosphere (oxygen, atmospheric air, etc.). The oxygen-containing atmosphere may be a mixed gas atmosphere of an inert gas (nitrogen, argon, etc.) and an oxidizing gas (oxygen, air, etc.). good too. When the atmosphere in the heating device is an oxygen-containing atmosphere, the transition metal contained in the metal composite hydroxide is moderately oxidized, making it easier to control the form of MCC.

The oxygen or oxidizing agent in the oxygen-containing atmosphere should contain sufficient oxygen atoms to oxidize the transition metal.

When the oxygen-containing atmosphere is a mixed gas atmosphere of an inert gas and an oxidizing gas, the atmosphere in the heating device is changed by a method such as passing an oxidizing gas into the heating device or bubbling the oxidizing gas into the mixed liquid. can be controlled by

As an oxidizing agent, a peroxide such as hydrogen peroxide, a peroxide salt such as permanganate, a perchlorate, a hypochlorite, nitric acid, a halogen, ozone, or the like can be used.

(2) Mixing of MCC and Lithium Compound This step is a step of mixing a lithium compound and MCC to obtain a mixture.

After drying the MCC as necessary, it is mixed with a lithium compound. After drying the MCC, it may be appropriately classified.

In this embodiment, at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride, and lithium fluoride can be used as the lithium compound. Among these, either one of lithium hydroxide and lithium carbonate or a mixture thereof is preferred.

A mixture is obtained by mixing the lithium compound and MCC in consideration of the composition ratio of the final object. Specifically, the lithium compound and MCC are mixed at a ratio corresponding to the composition ratio of formula (A) above. The amount (molar ratio) of Li to the total amount of 1 of metal atoms contained in MCC is preferably 1.00 or more, more preferably 1.02 or more, and even more preferably 1.05 or more. A fired product is obtained by firing a mixture of a lithium compound and MCC as described later.

(3) Temporary Firing of Mixture The mixture of MCC and lithium compound is calcined to form a reaction product of MCC and lithium compound. In the present embodiment, calcination means firing at a temperature lower than the firing temperature in the main firing described later (when the firing process described later has a plurality of firing stages, the firing temperature in the firing stage performed at the lowest temperature). It is to be. The calcination may be performed multiple times.

The calcination temperature is, for example, preferably 400°C or higher and lower than 700°C, more preferably 500-695°C, and even more preferably 600-690°C. When the firing temperature is 400° C. or higher, the reaction between MCC and the lithium compound is promoted. Further, when the firing temperature is less than 700° C., even when using MCC with a large Ni content, a lithium secondary battery with excellent cycle characteristics can be achieved.

The firing temperature in this specification means the temperature of the atmosphere in the firing furnace, and is the maximum temperature held in the firing process (hereinafter sometimes referred to as the maximum held temperature). In the case of a firing process having a plurality of firing steps, the firing temperature means the temperature of the step of firing at the highest holding temperature among the firing steps.

The retention time in calcination is preferably 1-8 hours, more preferably 1.0-6 hours, and particularly preferably 1.2-5 hours. When the holding time in the calcination is 1 hour or longer, the reaction between MCC and the lithium compound can be sufficiently enhanced. When the retention time in the firing is 8 hours or less, volatilization of lithium ions is less likely to occur, resulting in improved battery performance.

The atmosphere during preliminary firing and main firing described later is preferably an oxygen-containing atmosphere, more preferably an oxygen atmosphere. When the atmosphere at the time of preliminary firing and the main firing described later is an oxygen-containing atmosphere, oxygen defects are suppressed, and the battery performance is improved by stabilizing the structure.

The mixture of MCC and lithium compound may be fired in the presence of an inert melting agent. The inert melting agent may remain in the fired product, or may be removed after firing by washing with a cleaning liquid as described later. As an inert melting agent, for example, those described in WO2019/177032A1 can be used.

(4) Main Firing of Reactant The main calcination of the reaction product may have a plurality of calcination stages with different calcination temperatures. For example, a first firing step and a second firing step in which firing is performed at a higher temperature than the first firing step may be performed independently. Furthermore, it may have firing stages with different firing temperatures and firing times.

Al contained in LiMO tends to segregate during main firing. Also, the Al segregation part may move to the particle surface during the main firing. Al segregation that has migrated to the surface tends to flow out during subsequent cleaning. The presence of an appropriate amount of Al segregation can mitigate the expansion and contraction of LiMO caused by charging and discharging of the lithium secondary battery.

The firing temperature of the main firing is preferably 700°C or higher, more preferably 700-1100°C, even more preferably 700-750°C. When the firing temperature is 700° C. or higher, a CAM having a strong crystal structure can be obtained. Further, when the firing temperature is 1100° C. or less, volatilization of lithium ions on the particle surface can be reduced. Moreover, when the firing temperature is 750° C. or lower, it becomes easier to control the relative standard deviation of the ratio R1 and the ratio R2 within the range of the present embodiment.

The holding time in main firing is preferably 1 to 50 hours. When the holding time in the main firing is 1 hour or longer, the reaction between unreacted MCC and the lithium compound in the reactants can be sufficiently enhanced. When the retention time in the main firing is 50 hours or less, volatilization of lithium ions is less likely to occur, and battery performance is improved.

By firing the reaction product of MCC and the lithium compound as described above, a fired product is obtained.

(5) Washing of fired product After the firing step, the fired product is washed to remove the remaining unreacted lithium compound and inert melting agent, thereby obtaining a CAM. Pure water or an alkaline cleaning liquid can be used for cleaning. Examples of the alkaline cleaning solution include aqueous solutions of one or more anhydrides selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate and ammonium carbonate, and hydrates thereof. can be mentioned. Ammonia water can also be used as the alkaline cleaning liquid.

The temperature of the cleaning liquid is preferably 15°C or lower, more preferably 10°C or lower, and even more preferably 8°C or lower. The lower limit of the temperature of the cleaning liquid is, for example, 5°C. By controlling the temperature of the cleaning liquid within the range above which the cleaning liquid does not freeze, excessive elution of lithium ions from the crystal structure of LiMO into the cleaning liquid during cleaning can be suppressed.

As a method of bringing the cleaning solution and the fired product into contact, there is a method in which the fired product is put into each cleaning solution and stirred. Moreover, the method of pouring each washing|cleaning liquid as shower water on a baking product may be used. Furthermore, a method may also be employed in which the fired product is put into the cleaning solution and stirred, then the fired product is separated from each cleaning solution, and then each cleaning solution is used as shower water to be poured over the separated fired product.

In the cleaning, it is preferable to bring the cleaning liquid and the fired product into contact within the appropriate time range. The "appropriate time" in washing refers to a time sufficient to disperse the particles of the fired product while removing the unreacted lithium compound and inert melting agent remaining on the surface of the fired product. It is preferable to adjust the washing time according to the aggregation state of the baked product. Washing times in the range of, for example, 5 minutes to 1 hour are particularly preferred.

The ratio of the fired product to the mixture of the cleaning liquid and the fired product (hereinafter sometimes referred to as slurry) is preferably 5-60% by mass, more preferably 20-50% by mass, and 30% by mass. % and 50% by mass or less is more preferable. When the proportion of the fired product is 5-60% by mass, the unreacted lithium compound and any inert melting agent can be removed, and the relative standard deviation of the proportion R1 and the proportion R2 is controlled within the range of the present embodiment. easier to do.

After washing the baked product, it is preferable to dehydrate and filter the baked product. As a method for dehydration filtration, pressure filtration, pressure filtration, vacuum filtration, or the like can be used. The weight of the baked product per filtration area in dehydration filtration is preferably 5-30 kg/m ² , more preferably 20-30 kg/m ² . When the weight of the baked product per filtration area is 5 kg/m ² or more, excessive outflow of Al is suppressed, and the relative standard deviation of the ratio R1 and the ratio R2 can be easily controlled within the range of the present embodiment. From the viewpoint of filterability, the weight of the baked product per filtration area is preferably 30 kg/m ² or less.

After the dehydration of the fired product, the fired product is preferably heat-treated. The temperature and method for heat-treating the baked product are not particularly limited, but from the viewpoint of preventing a decrease in charge capacity, the temperature is preferably 100 ° C. or higher, more preferably 130 ° C. or higher, and 150 ° C. or higher. More preferred. The upper limit temperature is not particularly limited, but it is preferably 700° C. or lower, more preferably 600° C. or lower, and 400° C. or lower as long as it does not affect the crystallite size distribution of the fired product. is more preferred. The volatilization amount of lithium ions can be controlled by the heat treatment temperature.

The upper limit and lower limit of the heat treatment temperature can be combined arbitrarily. For example, the heat treatment temperature is preferably 100-700°C, more preferably 130-600°C, even more preferably 150-400°C.

The atmosphere during the heat treatment includes an oxygen atmosphere, an inert atmosphere (nitrogen atmosphere, etc.), a reduced pressure atmosphere, or a vacuum atmosphere. By performing the heat treatment after cleaning in the above atmosphere, reaction between the CAM and moisture or carbon dioxide in the atmosphere is suppressed during the heat treatment, and a CAM with few impurities can be obtained. Moreover, after the heat treatment of the fired product, it is preferable to subject the fired product to sieving treatment.

By washing the fired material under the above conditions, at least part of the segregated Al can be removed appropriately. By washing the baked product under the above conditions, the segregated Al flows out, the diffusion of lithium ions is less likely to be inhibited by the Al segregation, and the initial discharge capacity of the lithium secondary battery can be improved. In addition, by washing the fired product under the above conditions, excessive outflow of Al can be prevented, so that the expansion and contraction of LiMO caused by charging and discharging of the lithium secondary battery can be alleviated by the generated voids. , the cycle characteristics are improved.

By performing the heating conditions of the metal composite hydroxide, the firing conditions of the mixture and the reaction product, the cleaning conditions of the fired product, and the heat treatment conditions within the above ranges, the relative standard deviation of the CAM ratio R1 and the ratio R2, the ratio a , the ratio b, D ₅₀ , D ₉₀ /D ₁₀ , H1/H2 can be adjusted within the above ranges.

<Lithium secondary battery>
A configuration of a lithium secondary battery suitable for using the CAM of the present embodiment will be described. Also, 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.

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.

An example of a lithium secondary battery 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. 2 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 FIG. 2, a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are arranged as follows: 1 and the negative electrode 3 are stacked in this order and wound to form an electrode group 4 .

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>
Next, while explaining the configuration of the all-solid lithium secondary battery, the positive electrode using the CAM according to one embodiment of the present invention as the CAM of the all-solid lithium secondary battery and the all-solid lithium secondary battery having this positive electrode will be explained. do.

FIG. 3 is a schematic diagram showing an example of the all-solid lithium secondary battery of this embodiment. The all-solid lithium secondary battery 1000 shown in FIG. 3 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 houses 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 material forming each member will be described later.

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 positive electrode having the above configuration has the CAM described above, it is possible to provide a lithium secondary battery with high initial discharge capacity and good cycle characteristics.

Furthermore, since the lithium secondary battery with the above configuration has the positive electrode described above, it has a high initial discharge capacity and good cycle characteristics.

Another aspect of the present invention includes the following aspects.
[11] A CAM containing a plurality of particles containing LiMO having a layered structure,
The LiMO contains at least Li, Ni, Al and the element M,
The CAM, wherein the relative standard deviation of said ratio R1 is 28.6-60.0% and the relative standard deviation of said ratio R2 is 17.0-35.0%.
[12] The CAM according to [11], wherein the ratio a is 99.9-100%.
[13] The CAM according to [11] or [12], wherein the ratio b is 99-100%.
[14] The CAM of any one of [11] to [13], wherein the CAM has a _D50 of 5.0-15 μm.
[15] The CAM according to any one of [11] to [14], wherein D ₉₀ /D ₁₀ of the CAM is 2-3.
[16] The CAM according to any one of [11] to [15], wherein the composition formula of the CAM is represented by Formula (A)-1.
Li[Li _m (Ni _(1-xy) Al _x M _y ) _1-m ]O ₂ (A)-1
(In formula A, M is selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P It is one or more elements and satisfies 0<m≦0.2, 0.02≦x≦0.1, and 0.05≦y≦0.1.)
[17] The CAM according to any one of [11] to [16], wherein the ratio H1/H2 of the CAM is 1.5-1.6.
[18] The CAM according to any one of [11] to [17], wherein the relative standard deviation of the ratio R1 is 35.0-50.0%.
[19] The CAM according to any one of [11] to [18], wherein the relative standard deviation of the ratio R2 is 18.0-35.0%.
[20] A positive electrode for a lithium secondary battery, containing the CAM according to any one of [11] to [19].
[21] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [20].

The present invention will be described in detail below with reference to examples, but the present invention is not limited by the following description.

<Composition analysis>
The composition analysis of the CAM produced by the below-described method was performed by the above-described "CAM composition analysis" method.

<Cumulative volume particle size>
The D ₁₀ , D ₅₀ and D ₉₀ of the CAM produced by the method described below were measured by the "cumulative volume particle size" measurement method described above.

<SEM-EDX analysis>
The relative standard deviation of the ratio R1, the relative standard deviation of the ratio R2, the ratio a and the ratio b were calculated by the method described in "SEM-EDX analysis" above. The particles to be measured when calculating the ratio R1 are 150 particles having an equivalent circle diameter of 5 μm or more, and the cross section of the particles to be measured when calculating the ratio R2 are 100 particles having an equivalent circle diameter of 5 μm or more. It was a cross section of a certain particle.

<Measurement of crystal structure and diffraction peak intensity height>
The crystal structure of LiMO and the CAM ratio H1/H2 were measured and calculated by the method described in [Crystal structure] above.

<Initial discharge capacity and 50th discharge capacity retention rate>
A lithium secondary battery was produced by the method described in "Initial discharge capacity and 50th discharge capacity retention rate", and the initial discharge capacity and the 50th discharge capacity were measured.

(Example 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 so that the molar ratio of Ni, Co, and Al was 0.88:0.09:0.03 to prepare a mixed raw material solution.

Next, this mixed raw material solution and an aqueous solution of ammonium sulfate as a complexing agent were continuously added into the reaction tank while stirring. A sodium hydroxide aqueous solution was added dropwise at appropriate times so that the pH of the mixed liquid in the reaction tank was 11.6 (measurement temperature: 40° C.), and a reaction precipitate 1 was obtained.

After washing the reaction precipitate 1, it was dehydrated and dried to obtain a metal composite hydroxide 1 containing Ni, Co and Al.

The metal composite hydroxide 1 was held at 650°C in an air atmosphere for 5 hours, heated, and cooled to room temperature to obtain MCC1, which is a metal composite oxide.

Lithium hydroxide was weighed so that the amount (molar ratio) of Li to the total amount of Ni, Co and Al contained in MCC1 was 1.10. Mixture 1 was obtained by mixing MCC1 and lithium hydroxide.

This mixture 1 was calcined at 650°C for 5 hours in an oxygen atmosphere to obtain a reactant 1. The reactant 1 was calcined at 720° C. for 5 hours in an oxygen atmosphere to obtain a calcined product 1 .

The baked product 1 and pure water are mixed so that the ratio of the baked product 1 to the total amount is 30% by mass, and the slurry is stirred for 20 minutes and washed. CAM-1 was obtained by heat-treating at ° C. for 10 hours, drying the water remaining after dehydration and filtration, and sieving. The weight of the baked product 1 per filtration area was 26.9 kg/m ² .

A composition analysis of CAM-1 revealed that m = 0.03, x = 0.03, y = 0.09 in formula (A), and element M was Co. LiMO contained in CAM-1 had a layered structure.

(Example 2)
CAM-2 was obtained in the same manner as in Example 1, except that the fired product 2 was obtained by changing the temperature during the main firing of the reaction product 1 to 700°C. The weight of the baked product 2 per filtration area was 25.0 kg/m ² .

A composition analysis of CAM-2 revealed that m = 0.04, x = 0.03, y = 0.09 in formula (A), and element M was Co. LiMO contained in CAM-2 had a layered structure.

(Example 3)
Except that the temperature at the time of main firing of reaction product 1 was changed to 700 ° C. to obtain fired product 3, and that the ratio of fired product 3 to the total amount was set to 40% by mass in the washing step, CAM-3 was obtained in the same manner as in Example 1. The weight of the baked product 3 per filtration area was 25.0 kg/m ² .

A composition analysis of CAM-3 revealed that m = 0.04, x = 0.03, y = 0.09 in formula (A), and element M was Co. LiMO contained in CAM-3 had a layered structure.

(Comparative example 1)
CAM-C1 was obtained in the same manner as in Example 1, except that the fired product 1 was used as the CAM without being washed.

A composition analysis of CAM-C1 revealed that m = 0.1, x = 0.03, y = 0.09 in formula (A), and element M was Co. LiMO contained in CAM-C1 had a layered structure.

(Comparative example 2)
Lithium hydroxide was weighed so that the amount (molar ratio) of Li to 1 of the total amount of Ni, Co and Al contained in MCC1 was 1.00. Mixture 2 was obtained by mixing MCC1 and lithium hydroxide. This mixture 2 was calcined at 650° C. for 5 hours in an oxygen atmosphere to obtain a reactant 2 .
A calcined product 5 was obtained in the same manner as in Example 1, except that the reactant 2 was calcined at 740° C. for 15 hours in an oxygen atmosphere. The obtained calcined product 5 and pure water are mixed so that the ratio of the calcined product 5 to the total amount is 5% by mass, and the prepared slurry is stirred for 5 minutes and washed. It was heat-treated in an atmosphere at 120° C. for 10 hours, and the water remaining after dehydration was dried to obtain CAM-C2. The weight of the fired product 5 per filtration area was 1.1 kg/m ² .

A composition analysis of CAM-C2 revealed that m = 0.96, x = 0.03, y = 0.07 in formula (A), and element M was Co. LiMO contained in CAM-C2 had a layered structure.

(Comparative Example 3)
The reactant 2 was calcined at 780° C. for 5 hours in an oxygen atmosphere to obtain a calcined product 6 . The obtained baked product 6 and pure water are mixed so that the ratio of the baked product 6 to the total amount is 5% by mass, and the prepared slurry is stirred for 5 minutes and washed. It was heat-treated at 120° C. for 10 hours in an atmosphere, and the water remaining after dehydration and filtration was dried to obtain CAM-C3. The weight of the fired product 6 per filtration area was 1.1 kg/m ² .

A composition analysis of CAM-C3 revealed that m = 0.96, x = 0.03, y = 0.09 in formula (A), and element M was Co. LiMO contained in CAM-C3 had a layered structure.

CAM-1 to CAM-3 of Examples 1 to 3 and CAM-C1 to CAM-C3 of Comparative Examples 1 to 3 with or without washing process, CAM D ₅₀ , CAM D ₉₀ /D ₁₀ , ratio R1 relative Table 1 shows the standard deviation, the relative standard deviation of the ratio R2, the ratio a, the ratio b, the diffraction peak intensity height ratio H1/H2, and the initial discharge capacity and cycle efficiency of the lithium secondary battery using each CAM.

In CAM-1 to CAM-3 of Examples 1 to 3, the relative standard deviation of the ratio R1 was 28.7-48.1% and the relative standard deviation of the ratio R2 was 15.2-22.7%. rice field. Furthermore, the initial discharge capacity of the lithium secondary batteries using CAM-1 to CAM-3 was 197-202 mAh/g, and the cycle efficiency was 83.8-90.4%.

On the other hand, in Comparative Example 1 in which the baked product was not washed, the relative standard deviation of the ratio R1 was 93.1% and the relative standard deviation of the ratio R2 was 78.9%. It is considered that since washing was not performed after firing, the segregated Al did not flow out and diffusion of lithium ions was inhibited by Al segregation. In Comparative Example 2, the relative standard deviation of the ratio R1 was 31.5% and the relative standard deviation of the ratio R2 was 11.0%. It is considered that the expansion and contraction of LiMO due to charging and discharging could not be buffered because the CAM-C2 did not contain a sufficient amount of Al due to excessive outflow of Al without dehydration filtration under predetermined conditions. In Comparative Example 3, the relative standard deviation of the ratio R1 was 28.2% and the relative standard deviation of the ratio R2 was 17.7%. This is probably because Al segregated on the particle surface after firing due to the high firing temperature, and a large amount of Al segregation flowed out from the surface of CAM-C3 because dehydration and filtration were not performed under the prescribed conditions. The initial discharge capacity of the coin half-cells using CAM-C1 to CAM-C3 was 184-198 mAh/g, and the cycle efficiency was 67.7-93.4%.

INDUSTRIAL APPLICABILITY According to the present invention, a CAM capable of obtaining a lithium secondary battery that has a high initial discharge capacity and whose discharge capacity does not easily decrease even after repeated charging and discharging, and a positive electrode for a lithium secondary battery and a lithium secondary battery using the same. We can provide the following batteries.

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 (9)

A positive electrode active material for a lithium secondary battery containing a plurality of particles containing a lithium metal composite oxide having a layered structure,
The lithium metal composite oxide contains at least Li, Ni, Al and element M,
The element M is one or more selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P is an element of
A positive electrode active material for a lithium secondary battery that satisfies the following conditions (1) and (2).
(1) The number of Al atoms relative to the total number of Ni, Al, and element M atoms obtained for each particle by measuring the surfaces of the plurality of particles with a scanning electron microscope-energy dispersive X-ray spectroscopy. Regarding the ratio R1, the relative standard deviation of the ratio R1 in the plurality of particles is greater than 28.5% and no greater than 70%.
(2) The number of Al atoms with respect to the total number of Ni, Al, and element M atoms obtained for each particle by measuring the cross section of the plurality of particles with the scanning electron microscope-energy dispersive X-ray spectroscopy. , the relative standard deviation of the ratio R2 in the plurality of particles is greater than 13% and less than or equal to 50%. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the ratio of the number of particles having a ratio R1 of 10 atomic% or less to the total number of the plurality of particles is 99% or more. The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the ratio of the number of particles having a ratio R2 of 10 atomic% or less to the total number of the plurality of particles is 88% or more. The positive electrode active material for lithium secondary batteries according to any one of claims 1 to 3, wherein the positive electrode active material for lithium secondary batteries has a 50% cumulative volume particle size of 5 µm or more and 20 µm or less. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein the ratio of the 90% cumulative volume particle size to the 10% cumulative volume particle size of the positive electrode active material for a lithium secondary battery is 3 or less. . The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5, wherein the compositional formula of the positive electrode active material for a lithium secondary battery is represented by formula (A).
Li[Li _m (Ni _(1-xy) Al _x M _y ) _1-m ]O ₂ (A)
(In formula A, M is selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S and P It is one or more elements and satisfies −0.1≦m≦0.2, 0<x≦0.5 and 0<y<0.5.) In powder X-ray diffraction measurement using CuKα rays of the positive electrode active material for lithium secondary batteries, 2θ = 18.5 ± 1 for H2, which is a diffraction peak intensity height within the range of 2θ = 44.1 ± 1 ° The positive electrode for a lithium secondary battery according to any one of claims 1 to 6, wherein the ratio H1/H2 of H1, which is the diffraction peak intensity height within the range of °, is 1.5 or more and 1.6 or less. active material. A positive electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries according to any one of claims 1 to 7. A lithium secondary battery having the positive electrode for a lithium secondary battery according to claim 8.

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