JP7244615B1 - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

A positive electrode active material for a lithium secondary battery is provided, which enables obtaining a lithium secondary battery which has a high initial discharge capacity and whose discharge capacity does not easily decrease even after repeated charging and discharging. A lithium metal composite oxide and a plurality of particles X containing Al segregation parts are included, the particles X have voids, the lithium metal composite oxide contains at least Li, Ni and Al, A positive electrode active material for a lithium secondary battery, wherein a cross-sectional image of particles X obtained by SEM satisfies conditions (1) and (2). (1) In the binarized image, the ratio of the total area of the dark color portion existing in the area surrounded by the outer periphery of the bright color portion to the total area of the region surrounded by the outer periphery of the light color portion is 0. 05% and 0.4% or less. (2) In the binarized image, the ratio of the number of particles Y whose circularity represented by formula (i) is 0.33 or less to the total number of particles X is greater than 0% and less than or equal to 5.0%. is. [Selection figure] None

Description

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.

A positive electrode active material for a lithium secondary battery is composed of a plurality of particles containing 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. As the lithium secondary battery is charged and discharged, lithium ions are desorbed and inserted on the particle surface of the positive electrode active material for lithium secondary batteries.

For example, Patent Document 1 describes lithium metal composite oxide particles containing lithium, nickel, cobalt, and aluminum and mainly composed of secondary particles having a porosity of less than 20%, and lithium metal composite oxide particles. A positive electrode active material for a lithium secondary battery is described, which has a coating layer formed on its surface and which consists of an ion-conducting polymer containing electronically-conducting particles.

JP-A-2019-140093

The positive electrode active material for lithium secondary batteries of Patent Document 1 is excellent in weather resistance and long-term storage stability. 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. An object of the present invention is to provide a substance, 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 X containing a lithium metal composite oxide and an Al segregation part,
The particles X have voids,
The lithium metal composite oxide has a layered structure and contains at least Li, Ni, and Al,
A positive electrode active material for a lithium secondary battery, wherein a cross-sectional image of the particles X obtained by a scanning electron microscope satisfies the conditions (1) and (2).
(1) In an image obtained by binarizing the cross-sectional image so that the lithium metal composite oxide is bright and the voids and the Al segregation part are dark, the area of the region surrounded by the outer periphery of the bright-colored portion The ratio of the total area of the dark color portions existing in the region surrounded by the outer periphery of the bright color portion to the total sum is more than 0.05% and 0.4% or less.
(2) In the binarized image, the ratio of the number of particles Y whose circularity represented by formula (i) is 0.33 or less to the total number of particles X is greater than 0%. 0% or less.
Circularity = 4πS/L ² (i)
In formula (i), S is the area of the region surrounded by the perimeter of the light-colored portion, and L is the perimeter length of the light-colored portion.
[2] The lithium secondary according to [1], wherein the ratio of the number of particles Z having a circularity of 0.45 or more to the total number of particles X in the binarized image is 70% or more. Positive electrode active material for batteries.
[3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the positive electrode active material has a 50% cumulative volume particle size of 5 to 20 μm.
[4] The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], wherein the ratio of the 90% cumulative volume particle size to the 10% cumulative volume particle size of the positive electrode active material is 3 or less. .
[5] The positive electrode active material for a lithium secondary battery according to any one of [1] to [4], wherein the composition formula of the positive electrode active material 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.)
[6] In the powder X-ray diffraction measurement (XRD) using CuKα rays of the positive electrode active material, 2θ = 18.5 ± for the diffraction peak intensity height (H2) within the range of 2θ = 44.1 ± 1 ° The lithium according to any one of [1] to [5], wherein the ratio (H1/H2) of the diffraction peak intensity height (H1) within the range of 1° is 1.5 or more and 1.6 or less. Positive electrode active material for secondary batteries.
[7] A positive electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries according to any one of [1] to [6].
[8] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [7].

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.

FIG. 3 is a diagram showing the results of SEM analysis of a positive electrode active material for a lithium secondary battery in one embodiment of the present invention; FIG. 3 is a diagram showing the results of SEM analysis of a positive electrode active material for a lithium secondary battery in one embodiment of the present invention; FIG. 3 is a diagram showing the results of SEM analysis of a positive electrode active material for a lithium secondary battery in one embodiment of the present invention; 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 is 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 rather than nickel metal. “Li” and “Al” and the like similarly refer to lithium atoms and aluminum atoms and the like, respectively.

For example, when a numerical range is described as "1-10 μm" or "1-10 μm", it means a range from 1 μm to 10 μm, including a lower limit of 1 μm and an upper limit of 10 μm.

"Cumulative volume particle size" is a value measured by a laser diffraction scattering method. Specifically, 0.1 g of a measurement object, for example, CAM powder, is put into 50 ml of a 0.2% by mass sodium hexametaphosphate aqueous solution to obtain a dispersion liquid 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 Perkin Elmer Co., Ltd. can be used.

In this embodiment, a scanning electron microscope is described as "SEM". As the scanning electron microscope, for example, a Schottky field emission scanning electron microscope (manufactured by JEOL Ltd., product name JSM-7900F) can be used.

The crystal structure of LiMO can be calculated by CAM powder X-ray diffraction measurement using CuKα as a radiation source and measuring the diffraction angle 2θ in a 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° and the diffraction peak intensity height (H2) within the range of 2θ = 44.4 ± 1° is 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" means a value measured by charging and discharging under the following conditions. A lithium secondary battery is charged at 0.2 CA to 4.3 V at 25° C. and then charged at 4.3 V for 5 hours. A constant current discharge 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 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 (%).

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 includes a plurality of particles X containing LiMO and Al segregation parts, the particles X have voids, and the LiMO has a layered structure and contains at least Li, Ni and Al. , the cross-sectional image of the particle X obtained by SEM satisfies the conditions (1) and (2).
(1) In the image obtained by binarizing the cross-sectional image so that LiMO is bright and the voids inside the particle X and the Al segregation part are dark, the light color for the total area of the region surrounded by the outer periphery of the bright color part The ratio of the total area of the dark color portions present in the region surrounded by the outer perimeter of the portion is greater than 0.05% and less than or equal to 0.4%.
(2) In the binarized image, the ratio of the number of particles Y having a circularity represented by formula (i) of 0.33 or less to the total number of particles X is greater than 0% and less than or equal to 5.0%. be.
Circularity = 4πS/L ² (i)
In formula (i), S is the area of the region surrounded by the perimeter of the light-colored portion, and L is the perimeter length of the light-colored portion.

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

In the present embodiment, "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 (1) and (2).
(1) In the image obtained by binarizing the cross-sectional image so that LiMO is bright and the voids inside the particle X and the Al segregation part are dark, the light color for the total area of the region surrounded by the outer periphery of the bright color part The ratio of the total area of the dark color portions present in the region surrounded by the outer perimeter of the portion is greater than 0.05% and less than or equal to 0.4%.
(2) In the binarized image, the ratio of the number of particles Y having a circularity represented by formula (i) of 0.33 or less to the total number of particles X is greater than 0% and less than or equal to 5.0%. be.
Circularity = 4πS/L ² (i)
In formula (i), S is the area of the region surrounded by the perimeter of the light-colored portion, and L is the perimeter length of the light-colored portion.

<Cross-sectional SEM image analysis>
Whether the CAM satisfies (1) and (2) can be confirmed by the following method. First, CAM is dispersed in a particle-fixing resin. After that, vacuum degassing is performed, and the obtained product is sandwiched between aluminum plates and cured. Thereby, a cured product of a resin containing CAM is obtained.

The cured product is fixed on a sample stand and set in a cross-section 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 fabricate a cross section of the CAM.

A cross section of the CAM is observed with an SEM at an acceleration voltage of 15 kV. The number of particles X, which are particles to be analyzed, should be 200 or more.

The resulting image (backscattered electron image) is binarized and analyzed using quantitative analysis software TRI/3D-BON-FCS (manufactured by Ratoc System Engineering). The image resolution is x, y=0.023 μm, z=0.023 μm.

Specifically, Auto-LW, which is a function of the quantitative analysis software, converts the image into two gradations, and distinguishes LiMO displayed in bright colors and voids and Al segregation portions displayed in dark colors. The amount of backscattered electrons generated differs depending on the elements that make up the sample, and the larger the atomic number, the greater the amount of generated backscattered electrons. Therefore, in the image (backscattered electron image), LiMO containing mainly transition metal elements, which are heavy elements, is bright, and voids and Al segregation parts mainly containing C and Al elements, which are light elements, are dark.

In the obtained image, if some of the voids and Al segregation parts present on the CAM surface show intermediate contrast, only the intermediate contrast parts are extracted using the image calculation function, and the dark color inside the grain is displayed. A process to overlap with the gap is performed. By this treatment, the shape of the positive electrode active material from which the Al segregation part on the particle surface has been removed and the void part in the particle can be more accurately identified to perform two-gradation, that is, binarization.

From the binarized image, using the image calculation function, particles with an equivalent circle diameter of 6 μm or less, particles with missing analysis image edges, particles with cracks during preprocessing for analysis, and particles with unclear particle shapes ( A cross-section at the edge of the grain) is removed. From the binarized image thus obtained, the ratio of the total area of the dark-colored portions existing in the region surrounded by the outer periphery of the light-colored portion to the total area of the regions surrounded by the outer periphery of the light-colored portion is Calculated after labeling with TRI/2D-PRT, which is an optional function of the software. Also, the ratio of the number of particles Y having a circularity of 0.33 or less represented by the formula (i) to the total number of particles X is calculated.

1 to 3 are diagrams showing SEM analysis results of a positive electrode active material for a lithium secondary battery in one embodiment of the present invention, and are images binarized by the above-described method. FIG. 2 is an enlarged view of a region P surrounded by dashed lines in FIG. FIG. 3 is an enlarged view of a region Q surrounded by dashed lines in FIG. The intra-particle voids and Al segregation portions are defined as portions having an equivalent circle diameter of 0.5 μm or more, which exist within the regions surrounded by the outer periphery of the light-colored portions in the dark-colored portions in the binarized image. For example, the portion surrounded by reference numeral 42 in FIG. 2 is the intra-particle void and the Al segregation portion.

The area of the CAM is the area surrounded by the perimeter of the bright color portion 41 in the binarized image. In other words, the area of the CAM is the total area of LiMO, intra-particle voids present in the particles, and Al segregation portions present in the particles. As shown in FIG. 3, when the Al segregation portion 42 is exposed on the surface portion of the CAM, in other words, when the Al segregation portion exists outside the region surrounded by the outer periphery of the light-colored portion, the area of the CAM is Al segregation part is not included. That is, the area surrounded by the perimeter L of the light-colored portion is calculated as the area of the CAM.

The ratio of the total area of the dark-colored portions existing in the regions surrounded by the outer circumferences of the light-colored portions to the total area of the regions surrounded by the outer circumferences of the light-colored portions of the plurality of particles X (hereinafter, may be referred to as the ratio a) ) is calculated. If the ratio a is greater than 0.05% and less than or equal to 0.4%, the condition (1) is satisfied. The proportion a is preferably 0.1-0.35%, more preferably 0.15-0.3%, particularly preferably 0.15-0.27%. If the ratio a is more than 0.05% and 0.4% or less, it means that there are voids and Al segregation parts inside the particles, and LiMO expansion occurs when the lithium secondary battery is repeatedly charged and discharged. and shrinkage can be relaxed at the voids and Al segregation. As a result, cracking of the particles X is suppressed, and the cycle characteristics of the lithium secondary battery are improved. In addition, when the voids are appropriately present, the desorption and insertion reaction fields of Li ions are increased, so that the initial discharge capacity is improved.

The circularity of particle X is represented by formula (i).
Circularity = 4πS/L ² (i)
In formula (i), S is the area of the region surrounded by the perimeter of the bright portion. L is the perimeter length of the light-colored portion.

When the ratio of the number of particles Y having a circularity of 0.33 or less to the total number of particles X (hereinafter sometimes referred to as ratio b) is greater than 0% and 5.0% or less, It satisfies the condition (2). The proportion b is preferably 0.5-4.5%, more preferably 1.5-4%, even more preferably 2.0-3.5%, 2.5- 3.5% is particularly preferred.

When the proportion b is greater than 0%, CAM means containing particles with a circularity of 0.33 or less. In a CAM in which LiMO contains Al, Al segregation is likely to occur during the manufacturing process, specifically the main firing process described later. The Al segregation part is likely to move to the particle surface, and is likely to flow out in the washing process that follows the main firing process. When the Al segregation portion flows out, voids are formed in that portion. If the CAM is manufactured so that it contains voids and Al segregations, the proportion b will be greater than 0%. Manufacturing conditions for including voids and Al segregated parts in the CAM will be described in detail later.

When the ratio b is 5.0% or less, the ratio of particles having a large amount of Al segregation on the particle surface as shown in FIG. can be secured.

The ratio of the number of particles Z having a circularity of 0.45 or more to the total number of the plurality of particles X (hereinafter sometimes referred to as ratio c) is preferably 70-95%, and preferably 70-90%. %, more preferably 70-85%. When the ratio c is 70 to 95%, the initial discharge capacity is likely to be improved.

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

The _D90 / _D10 of CAM is preferably 3 or less, more preferably 2.98 or less, and even more preferably 2.96 or less. When the D ₉₀ /D ₁₀ of the CAM is 3 or less, the cycle characteristics are likely to be improved.

LiMO contained in CAM is a metal oxide containing at least Li, Ni and Al. CAM is preferably a metal oxide represented by the compositional 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 -0.1 or more, more preferably -0.05 or more, and more preferably more than 0. In addition, from the viewpoint of obtaining a lithium secondary battery with a higher initial coulombic efficiency, m in the formula (A) is 0.2 or less, preferably 0.08 or less, and 0.06 or less. is more preferred.

The upper limit and lower limit of m can be combined arbitrarily. Combinations include, for example, m being -0.1 to 0.2, more than 0 to 0.2 or less, -0.05 to 0.08, more than 0 to 0.06 or less.

From the viewpoint of obtaining a lithium secondary battery with low battery internal resistance, x in the formula (A) is greater than 0, preferably 0.01 or more, and more preferably 0.02 or more. x in the formula (A) is 0.5 or less, preferably 0.3 or less, and more preferably 0.1 or less.

The upper limit and lower limit of x can be combined arbitrarily. Examples of combinations include 0.01 to 0.5, 0.02 to 0.3, and 0.02 to 0.1.

From the viewpoint of obtaining a lithium secondary battery with low battery internal resistance, y in the formula (A) is 0 or more, preferably 0.03 or more, and more preferably 0.05 or more. y in the formula (A) is less than 0.5, 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, 0.03 to less than 0.5, 0.03 to 0.3, 0.05 to 0.1, and the like.

In the present embodiment, from the viewpoint of obtaining a lithium secondary battery with a large battery capacity, 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. , more preferably greater than 0 and less than or equal to 0.46.

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, M is preferably one or more metals selected from the group consisting of Mn, W, B, Nb, and Zr.

In the powder X-ray diffraction measurement (XRD) of CAM, the diffraction peak intensity height within the range of 2θ = 18.5 ± 1 ° with respect to the diffraction peak intensity height (H2) within the range of 2θ = 44.1 ± 1 ° The ratio (H1/H2) of (H1) is preferably 1.5 or more and 1.6 or less, more preferably 1.51 or more and 1.59 or less. When the ratio (H1/H2) is 1.5 or more and 1.6 or less, the initial discharge capacity tends to increase.

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 discharge capacity, the crystal structure is a hexagonal crystal structure assigned to the space group R-3m, or a monoclinic crystal assigned to C2 / m. A 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. The metal composite hydroxide and metal composite oxide contain Ni and X in a molar ratio represented by the following formula (A′), for example, and are represented by the following formula (A″).
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, is one or more elements selected from the group consisting of S and P, and satisfies 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 generally known batch coprecipitation method or 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 AlxCoy} (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.

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

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.

In addition, the value of pH in this specification is defined as the value measured when the temperature of the liquid mixture is 40 degreeC. The pH of the mixed solution is measured when the temperature of the mixed solution sampled from the reaction tank reaches 40°C. If the sampled mixture is below 40°C, the mixture is heated to 40°C and the pH is measured. If the sampled mixed liquid exceeds 40°C, the mixed liquid is cooled to 40°C and the pH 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.

Further, during the reaction, the pH value in the reaction tank is set within the range of 9-13, preferably 10-12.5 when the temperature of the aqueous solution is 40° C., and the pH is within ±0.5. Control.

The reactor used in the continuous coprecipitation method can be of the overflow type 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 fed into the reactor.

The _D50 and _D90 / _D10 of the MCC and the _D50 and _D90 / _D10 of the finally obtained CAM can be adjusted by appropriately controlling the concentration of the metal salt supplied to the reaction tank, the reaction temperature, the reaction pH, and the like. It can be controlled within the range of this embodiment.

After the above reaction, the neutralized reaction precipitate is isolated. 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.

Washing of the reaction precipitate is preferably carried out with water or an alkaline washing liquid. In the present embodiment, cleaning with an alkaline cleaning solution is preferred, and cleaning with an aqueous sodium hydroxide solution is more preferred. Alternatively, cleaning may be performed using a cleaning liquid containing elemental sulfur. Examples of the cleaning liquid containing elemental sulfur include an aqueous potassium or sodium sulfate solution.

When MCC is a metal composite oxide, the metal composite oxide is produced by heating the metal composite hydroxide. Specifically, the metal composite hydroxide is heated at 400-700°C. Multiple heating steps may be performed if desired. The heating temperature in this specification means the set temperature of the heating device. When there are a plurality of heating steps, it means the temperature when heated at the maximum holding temperature in each heating step.

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. If the heating temperature is less than 400°C, the metal composite hydroxide may not be sufficiently oxidized. If the heating temperature exceeds 700° C., the metal composite hydroxide may be excessively oxidized and the BET specific surface area of the metal composite oxide may become too small.

The holding time 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. Air, oxygen, nitrogen, argon, or a mixed gas thereof can be used as the heating atmosphere.

The inside of the heating device may have a moderately oxygen-containing atmosphere. The oxygen-containing atmosphere may be a mixed gas atmosphere of an inert gas and an oxidizing gas, or may be a state in which an oxidizing agent is present in an inert gas atmosphere. When the inside of the heating device is in a moderately oxygen-containing atmosphere, the transition metal contained in the metal composite hydroxide is moderately oxidized, making it easier to control the form of the metal composite oxide.

Oxygen and the oxidizing agent in the oxygen-containing atmosphere should have enough 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 controlled by passing the oxidizing gas through the heating device or bubbling the oxidizing gas into the mixed liquid. method.

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

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 used in this embodiment. Among these, either one of lithium hydroxide and lithium carbonate or a mixture thereof is preferred. Moreover, when the lithium hydroxide contains lithium carbonate, the content of lithium carbonate in the lithium hydroxide is preferably 5% by mass or less.

The lithium compound and MCC are mixed in consideration of the composition ratio of the final product to obtain a mixture. Specifically, the lithium compound and MCC are mixed at a ratio corresponding to the composition ratio of the above compositional formula (A). 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) Pre-Baking of Mixture A mixture of MCC and a lithium compound is calcined to form a reactant. 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 steps, the firing temperature in the firing step performed at the lowest temperature). It is to be. The firing temperature during temporary firing is, for example, in the range of 400°C or higher and lower than 700°C. 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 to 695°C, even more preferably 600 to 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 highest 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 stages, the firing temperature means the temperature when heating at the highest holding temperature among the firing stages. The above upper limit and lower limit of the firing temperature can be combined arbitrarily.

The holding time in calcination is preferably 1 to 8 hours, more preferably 1.0 to 4 hours, and particularly preferably 1.2 to 3 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 firing is 8 hours or less, volatilization of lithium is less likely to occur, and battery performance is improved.

The firing atmosphere for temporary firing is preferably an oxygen-containing atmosphere or an oxygen atmosphere. When the firing atmosphere of the preliminary firing is an oxidizing atmosphere, oxygen defects are reduced and the structure is stabilized, thereby improving the battery performance.

(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 700°C or higher, preferably 700-1100°C, more preferably 700-750°C. When the firing temperature is 700° C. or higher, LiMO 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, an Al segregation portion can be appropriately present.

The retention 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.

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 inert melting agents, those described in WO2019/177032A1, for example, can be used.

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 an aqueous solution 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. Excessive elution of lithium ions from the crystal structure of LiMO into the cleaning liquid during cleaning can be suppressed by controlling the temperature of the cleaning liquid within the above-described range so that the cleaning liquid does not freeze.

As a method of contacting the cleaning liquid and the baked product, there is a method in which the baked product is put into each cleaning liquid 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 used 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 cleaning, it is preferable to bring the cleaning liquid and the baked product into contact for an appropriate time. 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 ratio of the fired product is 5 to 60% by mass, the unreacted lithium compound and the inert melting agent can be removed, making it easier to control the Al segregation portion within a preferred range.

After washing the fired product, it is preferable to heat-treat the fired product. 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 is preferably 700° C. or lower, more preferably 600° C. or lower, as long as the crystallite size distribution obtained in the firing step is not affected.
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 heat treatment includes an oxygen atmosphere, an inert atmosphere, 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.

After the heat treatment of the fired product, it is preferable to carry out a sieving treatment. Although the method of sieving the baked product is not particularly limited, it is preferable to carry out the sieving treatment while continuously supplying air with a controlled moisture concentration. The concentration of moisture contained in air is preferably 3000 ppm or less, more preferably 2600 ppm or less, relative to the total mass of air and moisture. Although the lower limit of the water concentration is not particularly limited, for example, 2.55 ppm can be mentioned with respect to the total mass of air and water. By performing the sieving process while continuously supplying air with a controlled moisture concentration, it becomes easier to control the Al segregation parts and the voids within a preferable range. A turbo screener or the like can be used as such a sieving apparatus.

By firing and sieving under the above conditions, at least part of the segregated Al can be removed. As a result, voids are generated that serve as reaction sites for desorption and insertion of Li ions, and the initial discharge capacity of the lithium secondary battery can be improved. Moreover, the expansion and contraction of LiMO caused by charging and discharging of the lithium secondary battery can be mitigated by the generated voids.

<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 electrolyte disposed between the positive electrode and the negative electrode.

FIG. 4 is a schematic diagram showing an example of a lithium secondary battery. The cylindrical lithium secondary battery 10 of this embodiment is manufactured as follows.

First, as shown in FIG. 4, 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 .

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 structure described above, and may have a layered structure 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.

Hereinafter, each configuration will be described in order.
(positive electrode)
The positive electrode 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 a positive electrode current collector.

(Conductive material)
A carbon material can be used as the conductive material of the positive electrode. Examples of carbon materials include graphite powder, carbon black (eg, acetylene black), and fibrous carbon materials.

The proportion of the conductive material in the positive electrode mixture is preferably 5 to 20 parts by mass with respect to 100 parts by mass of CAM.

(binder)
A thermoplastic resin can be used as the binder of the positive electrode. Examples of thermoplastic resins include polyimide resins; fluorine resins such as polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) and polytetrafluoroethylene; polyolefin resins such as polyethylene and polypropylene; can be mentioned.

(Positive electrode current collector)
A strip-shaped member made of a metal material such as Al, Ni, or stainless steel can be used as the positive electrode current collector of the positive electrode.

As a method for supporting the positive electrode mixture on the positive electrode current collector, the positive electrode mixture is made into a paste using an organic solvent, the obtained positive electrode mixture paste is applied to at least one side of the positive electrode current collector and dried, A method of fixing by performing an electrode pressing process can be mentioned.

When the positive electrode mixture is made into a paste, an organic solvent that can be used includes N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

Examples of the method for applying the positive electrode mixture paste to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.
A positive electrode can be manufactured by the method mentioned above.

(negative electrode)
The negative electrode of the lithium secondary battery may be capable of doping and dedoping lithium ions at a potential lower than that of the positive electrode, and an electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector; An electrode consisting of a negative electrode active material alone can be mentioned.

(Negative electrode active material)
Examples of the negative electrode active material of the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, and alloys, which can be doped and undoped with lithium ions at a potential lower than that of the positive electrode. be done.

Examples of carbon materials that can be used as the negative electrode active material include graphite such as natural graphite or artificial graphite, cokes, carbon black, carbon fibers, and baked organic polymer compounds.

Examples of oxides that can be used as the negative electrode active material include oxides of silicon represented by _the formula SiO _x (where x is a positive real number _{) such as SiO 2 and} SiO; , x is a positive real number); metal composite oxides containing lithium and titanium, such as Li ₄ Ti ₅ O ₁₂ and LiVO ₂ ;

Metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal. As a material that can be used as a negative electrode active material, a material described in WO2019/098384A1 or US2020/0274158A1 may be used.

These metals and alloys are mainly used alone as electrodes after being processed into a foil shape, for example.

Among the above negative electrode active materials, the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (good potential flatness), the average discharge potential is low, and the capacity retention rate when repeatedly charged and discharged is low. A carbon material containing graphite as a main component, such as natural graphite or artificial graphite, is preferably used for reasons such as high (good cycle characteristics). The shape of the carbon material may be, for example, flaky such as natural graphite, spherical such as mesocarbon microbeads, fibrous such as graphitized carbon fiber, or aggregates of fine powder.

The negative electrode mixture may contain a binder, if necessary. Examples of binders include thermoplastic resins, and specific examples include PVdF, thermoplastic polyimide, carboxymethyl cellulose (hereinafter sometimes referred to as CMC), styrene-butadiene rubber (hereinafter sometimes referred to as SBR). some), polyethylene and polypropylene.

(Negative electrode current collector)
Examples of the negative electrode current collector that the negative electrode has include a belt-like member made of a metal material such as Cu, Ni, or stainless steel.

As a method for supporting the negative electrode mixture on such a negative electrode current collector, as in the case of the positive electrode, a method of pressure molding, a paste using a solvent etc. is applied or dried and then pressed on the negative electrode current collector. A method of crimping may be mentioned.

(separator)
As the separator of the lithium secondary battery, for example, a material having the form of a porous film, nonwoven fabric, or woven fabric made of a material such as a polyolefin resin such as polyethylene and polypropylene, a fluororesin, or a nitrogen-containing aromatic polymer is used. can be used. Moreover, the separator may be formed using two or more of these materials, or the separator may be formed by laminating these materials. Also, the separator described in JP-A-2000-030686 or US20090111025A1 may be used.

(Electrolyte)
An electrolytic solution that a lithium secondary battery has contains an electrolyte and an organic solvent.

Electrolytes contained in the electrolytic solution include lithium salts such as LiClO ₄ and LiPF ₆ , and mixtures of two or more of these may be used.

As the organic solvent contained in the electrolytic solution, carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate can be used.

As the organic solvent, it is preferable to use a mixture of two or more of these. Among them, a mixed solvent containing carbonates is preferable, and a mixed solvent of a cyclic carbonate and a non-cyclic carbonate and a mixed solvent of a cyclic carbonate and an ether are more preferable.

Further, as the electrolytic solution, it is preferable to use an electrolytic solution containing a fluorine-containing lithium salt such as LiPF ₆ and an organic solvent having a fluorine substituent, since the safety of the obtained lithium secondary battery is increased. As the electrolyte and organic solvent contained in the electrolytic solution, the electrolyte and organic solvent described in WO2019/098384A1 or US2020/0274158A1 may be used.

<All-solid lithium secondary battery>
Next, while explaining the configuration of the all-solid lithium secondary battery, the positive electrode using LiMO 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. 5 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. 5 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. Materials forming each member will be described later.

The laminate 100 may have an external terminal 113 connected to the positive current collector 112 and an external terminal 123 connected to the negative 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-state lithium secondary battery 1000 further includes 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 .

As 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-state lithium secondary battery 1000 include coin-shaped, button-shaped, paper-shaped (or sheet-shaped), cylindrical, rectangular, and laminated (pouch-shaped) shapes.

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 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 .

Hereinafter, each configuration will be described in order.

(positive electrode)
The positive electrode 110 of this embodiment has a positive electrode active material layer 111 and a positive electrode current collector 112 .

The positive electrode active material layer 111 includes the CAM and the solid electrolyte which are one embodiment of the present invention described above. Moreover, the positive electrode active material layer 111 may contain a conductive material and a binder.

(solid electrolyte)
As the solid electrolyte contained in the positive electrode active material layer 111 of the present embodiment, a solid electrolyte having lithium ion conductivity and used in known all-solid lithium secondary batteries can be employed. Examples of such solid electrolytes include inorganic electrolytes and organic electrolytes. Examples of inorganic electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hydride-based solid electrolytes. Examples of organic electrolytes include polymer-based solid electrolytes. Examples of each electrolyte include compounds described in WO2020/208872A1, US2016/0233510A1, US2012/0251871A1, and US2018/0159169A1, and examples thereof include the following compounds.

(Oxide solid electrolyte)
Examples of oxide-based solid electrolytes include perovskite-type oxides, NASICON-type oxides, LISICON-type oxides, and garnet-type oxides. Specific examples of each oxide include compounds described in WO2020/208872A1, US2016/0233510A1, and US2020/0259213A1, and examples thereof include the following compounds.

Perovskite oxides include Li—La—Ti-based oxides such as Li _a La _1-a TiO ₃ (0<a<1), Li _b La _1-b TaO ₃ (0<b<1) and the like. Examples thereof include Li—La—Ta-based oxides and Li—La—Nb-based oxides such as Li _c La _1-c NbO ₃ (0<c<1).

Examples of NASICON-type oxides include Li _1+d Al _d Ti _2-d (PO ₄ ) ₃ (0≦d≦1). The NASICON-type oxide is Li _m M ¹ _n M ² _o P _p O _q (where M ¹ is selected from the group consisting of B, Al, Ga, In, C, Si, Ge, Sn, Sb and Se). One or more selected elements ^M2 is one or more elements selected from the group consisting of Ti, Zr, Ge, In, Ga, Sn and Al m, n, o, p and q is an arbitrary positive number).

As the LISICON-type oxide, Li ₄ M ³ O ₄ —Li ₃ M ⁴ O ₄ (M ³ is one or more elements selected from the group consisting of Si, Ge, and Ti. M ⁴ is P is one or more elements selected from the group consisting of , As and V).

Garnet-type oxides include Li—La—Zr-based oxides such as Li ₇ La ₃ Zr ₂ O ₁₂ (also referred to as LLZ).

The oxide-based solid electrolyte may be a crystalline material or an amorphous material.

(Sulfide-based solid electrolyte)
Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ based compounds, Li ₂ S—SiS ₂ based compounds, Li ₂ S—GeS ₂ based compounds, Li ₂ S—B ₂ S ₃ based compounds, LiI- Si ₂ SP ₂ S ₅ based compounds, LiI-Li ₂ SP ₂ O ₅ based compounds, LiI-Li ₃ PO ₄ -P ₂ S ₅ based compounds and Li ₁₀ GeP ₂ S ₁₂ based compounds, etc. can be done.

In this specification, the expression "based compound" that refers to a sulfide-based solid electrolyte refers to a solid electrolyte that mainly contains raw materials such as "Li ₂ S" and "P ₂ S ₅ " described before "based compound". Used as a generic term for For example, Li ₂ SP ₂ S ₅ based compounds include solid electrolytes that mainly contain Li ₂ S and P ₂ S ₅ and further contain other raw materials. The ratio of Li ₂ S contained in the Li ₂ SP ₂ S ₅ based compound is, for example, 50 to 90% by mass with respect to the entire Li ₂ SP ₂ S ₅ based compound. The ratio of P ₂ S ₅ contained in the Li ₂ SP ₂ S ₅ based compound is, for example, 10 to 50% by mass with respect to the entire Li ₂ SP ₂ S ₅ based compound. In addition, the ratio of other raw materials contained in the Li ₂ SP ₂ S ₅ compound is, for example, 0 to 30% by mass with respect to the entire Li ₂ SP ₂ S ₅ compound. The Li ₂ SP ₂ S ₅ -based compound also includes solid electrolytes in which the mixing ratio of Li ₂ S and P ₂ S ₅ is varied.

Li ₂ SP ₂ S ₅ compounds include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -LiCl, Li ₂ SP _{2 S5 - LiBr} , _Li2SP2S5 - _{LiI - LiBr , Li2SP2S5} - _Li2O , _Li2SP2S5 - _Li2O -LiI and _Li2S- P ₂ S ₅ -Z _m S _n (m and n are positive numbers, Z is Ge, Zn or Ga).

Li ₂ S—SiS ₂ compounds include Li ₂ S—SiS ₂ , Li ₂ S—SiS ₂ —LiI, Li ₂ S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ —LiCl, and Li ₂ S—SiS. ₂ - _{B2S3 -} LiI, _Li2S - _{SiS2 - P2S5} -LiI, _Li2S - _{SiS2 - P2S5 -} LiCl, Li2S _{- SiS2} - _Li3PO4 , Li _2S —SiS ₂ —Li ₂ SO ₄ and Li ₂ S—SiS ₂ —Li _x MO _y (x, y are positive numbers; M is P, Si, Ge, B, Al, Ga, or In; There is.) and so on.

Examples of Li ₂ S—GeS ₂ based compounds include Li ₂ S—GeS ₂ and Li ₂ S—GeS ₂ —P ₂ S ₅ .

The sulfide-based solid electrolyte may be a crystalline material or an amorphous material.

(Hydride solid electrolyte)
Examples of hydride solid electrolyte materials include LiBH ₄ , LiBH ₄ -3KI, LiBH ₄ -PI ₂ , LiBH ₄ -P ₂ S ₅ , LiBH ₄ -LiNH ₂ , 3LiBH ₄ -LiI, LiNH ₂ , Li ₂ AlH ₆ , Li( _NH2 ) _2I , _Li2NH , LiGd( _BH4 ) _3Cl , _Li2 ( _BH4 )( _NH2 ), _Li3 ( _NH2 )I and _Li4 ( _BH4 )( _NH2 ) ₃ etc. can be mentioned.

(Polymer solid electrolyte)
Examples of polymer-based solid electrolytes include organic polymer electrolytes such as polyethylene oxide-based polymer compounds and polymer compounds containing one or more selected from the group consisting of polyorganosiloxane chains and polyoxyalkylene chains. . In addition, a so-called gel type in which a non-aqueous electrolyte is held in a polymer compound can also be used.

Two or more kinds of solid electrolytes can be used in combination as long as the effects of the invention are not impaired.

(Conductive material and binder)
As the conductive material included in the positive electrode active material layer 111, the materials described in (Conductive material) can be used. Also, the ratio described in the above (Conductive material) can be similarly applied to the ratio of the conductive material in the positive electrode mixture. Further, as the binder contained in the positive electrode, the materials described in the above (Binder) can be used.

(Positive electrode current collector)
As the positive electrode current collector 112 included in the positive electrode 110, the material described in the above (Positive electrode current collector) can be used.

As a method for supporting the positive electrode active material layer 111 on the positive electrode current collector 112 , there is a method of pressure-molding the positive electrode active material layer 111 on the positive electrode current collector 112 . Cold pressing or hot pressing can be used for pressure molding.

Alternatively, a mixture of CAM, a solid electrolyte, a conductive material, and a binder is pasted using an organic solvent to form a positive electrode mixture, and the obtained positive electrode mixture is applied to at least one surface of the positive electrode current collector 112, dried, and pressed. The positive electrode current collector 112 may carry the positive electrode active material layer 111 by pressing and fixing.

Alternatively, a mixture of the CAM, the solid electrolyte, and the conductive material is pasted using an organic solvent to form a positive electrode mixture, and the obtained positive electrode mixture is applied to at least one surface of the positive electrode current collector 112, dried, and sintered. Thus, the positive electrode current collector 112 may support the positive electrode active material layer 111 .

As the organic solvent that can be used for the positive electrode mixture, the same organic solvent that can be used when the positive electrode mixture described above (Positive electrode current collector) is made into a paste can be used.

Examples of the method for applying the positive electrode mixture to the positive electrode current collector 112 include the methods described above in (Positive electrode current collector).

The positive electrode 110 can be manufactured by the method described above. Specific combinations of materials used for the positive electrode 110 include the CAM described in this embodiment and the combinations described in Table 1.

(negative electrode)
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. As the negative electrode active material, the negative electrode current collector, the solid electrolyte, the conductive material and the binder, those described above can be used.

As a method for supporting the negative electrode active material layer 121 on the negative electrode current collector 122 , as in the case of the positive electrode 110 , there is a method of pressure molding, and a paste-like negative electrode mixture containing a negative electrode active material is applied onto the negative electrode current collector 122 . a method of applying a paste-like negative electrode mixture containing a negative electrode active material onto the negative electrode current collector 122, drying it, and then sintering it.

(Solid electrolyte layer)
The solid electrolyte layer 130 has the solid electrolyte described above.

The solid electrolyte layer 130 can be formed by depositing an inorganic solid electrolyte on the surface of the positive electrode active material layer 111 of the positive electrode 110 described above by sputtering.

Further, the solid electrolyte layer 130 can be formed by applying a paste mixture containing a solid electrolyte to the surface of the positive electrode active material layer 111 of the positive electrode 110 described above and drying the mixture. After drying, the solid electrolyte layer 130 may be formed by press molding and further pressing by cold isostatic pressing (CIP).

Laminate 100 is formed by stacking negative electrode 120 on solid electrolyte layer 130 provided on positive electrode 110 as described above, using a known method, such that negative electrode active material layer 121 is in contact with the surface of solid electrolyte layer 130 . It can be manufactured by

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

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

[EXAMPLES] Hereafter, although an Example is shown and this invention is demonstrated in detail, this 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 cumulative volume particle sizes D ₁₀ , D ₅₀ and D ₉₀ of the CAM produced by the below-described method were measured by the above-described "cumulative volume particle size" measurement method.

<Cross-sectional SEM image analysis>
Percentage of the total area of the dark color portion present in the region surrounded by the outer periphery of the light color portion to the total area of the region surrounded by the outer periphery of the light color portion by the method described in the above "Cross-sectional SEM image analysis" (ratio a), the ratio (ratio b) of the number of particles Y having a circularity of 0.33 or less, and the ratio (ratio c) of the number of particles Z having a circularity of 0.45 or more to the total number of particles X Calculated.

<Measurement of diffraction peak intensity height>
The diffraction peak intensity height (H1) within the range of 2θ = 18.5 ± 1 ° and the diffraction peak intensity height (H2) within the range of 2θ = 44.4 ± 1 ° are measured by the above-described measurement method. The diffraction peak intensity height ratio (H1/H2) was calculated.

<Preparation of positive electrode for lithium secondary battery>
CAM obtained by the manufacturing method described later, a conductive material (acetylene black), and a binder (PVdF) are added and kneaded so that the composition of CAM: conductive material: binder = 92:5:3 (mass ratio). A pasty positive electrode mixture was prepared by the above. NMP was used as an organic solvent when preparing the positive electrode mixture.

The obtained positive electrode mixture was 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 was 1.65 cm ² .

<Production of lithium secondary battery (coin-type half cell)>
The following operations were 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.) on the lower lid with the aluminum foil side facing down. A laminated film separator (16 μm-thick laminate obtained by laminating a heat-resistant porous layer on a polyethylene porous film) was placed thereon. 300 μl of electrolytic solution was injected here. The electrolytic solution used was obtained by dissolving LiPF ₆ to 1 mol/l in a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate at a volume ratio of 30:35:35.
Next, using metallic lithium as the negative electrode, the negative electrode is placed on the upper side of the laminated film separator, the top lid is placed through a gasket, and the lithium secondary battery (coin type half cell R2032. Hereinafter, "coin type (sometimes referred to as "half cell").

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

(Example 1)
After putting water 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 were continuously added as a complexing agent into the reactor with stirring. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the solution in the reaction vessel was 11.6 (measurement temperature: 40° C.), and a reaction precipitate 1 was obtained.

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

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

Lithium hydroxide was weighed so that the amount (molar ratio) of Li to the total amount of Ni, Co and Al contained in the metal composite oxide 1 was 1.1. Mixture 1 was obtained by mixing metal composite oxide 1 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 6 hours in an oxygen atmosphere to obtain a calcined product 1.

The fired product 1 and pure water are mixed so that the mass ratio of the fired product 1 to the total amount is 30% by mass, and the slurry is stirred for 20 minutes and washed. C. for 10 hours, and the remaining moisture after dehydration was dried to obtain dried product 1.

The dried material 1 was supplied to a turbo screener at a feeding rate of 50 kg/hour and sieved to obtain CAM-1. During sieving by the turbo screener, air having a moisture concentration of 2566 ppm or less was continuously supplied to the inside of the turbo screener.

A composition analysis of CAM-1 revealed that m=0.03, x=0.03, y=0.09 in the composition formula (A), and the element X 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 calcination temperature of reactant 1 was 700°C.

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

(Example 3)
CAM-3 was obtained in the same manner as in Example 2, except that in the washing step, the mass ratio of the baked product 1 to the total mass was 40% by mass.

A composition analysis of CAM-3 revealed that m=0.04, x=0.03, y=0.09 in the composition formula (A), and the element X 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 the composition formula (A), and the element X was Co. LiMO contained in CAM-C1 had a layered structure.
(Comparative example 2)

Dried product 2 was prepared in the same manner as in Example 1, except that the heating step of metal composite hydroxide 1 was omitted, and the mass ratio of fired product 1 to the total amount was set to 40% by mass in the washing step. got

The dried product 2 was sieved with an ultrasonic vibrator to obtain CAM-C2. Before sieving with the ultrasonic vibrator, the atmosphere inside the ultrasonic vibrator was filled with air having a moisture concentration of 2566 ppm or less.

A composition analysis of CAM-C2 revealed that m=0.03, x=0.03, y=0.09 in the composition formula (A), and element X was Co. LiMO contained in CAM-C2 had a layered structure.

(Comparative Example 3)
A fired product 2 was obtained in the same manner as in Example 1, except that the firing conditions for the reactant 1 were 790° C. for 5 hours. The obtained fired product 2 and pure water are mixed so that the mass ratio of the fired product 2 to the total amount is 5% by mass, and the prepared slurry is stirred for 5 minutes, washed, dehydrated, and vacuumed. It was heat-treated at 120° C. for 10 hours in an atmosphere, dried to remove moisture remaining after dehydration, and ground in an agate mortar in an air atmosphere to obtain CAM-C3.

A composition analysis of CAM-C3 revealed that m = -0.01, x = 0.03, y = 0.09 in the composition formula (A), and the element X 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, D ₅₀ , D ₉₀ /D ₁₀ , ratio a, ratio b, ratio c , the diffraction peak intensity height ratio (H1/H2), and the initial discharge capacity and cycle efficiency of coin-shaped half-cells using each CAM are shown in Table 4.

In CAM-1-3 of Examples 1-3, the ratio a was 0.22-0.28% and the ratio b was 1.6-3.2%. Furthermore, the initial discharge capacity of the coin-shaped half-cells using CAM-1-3 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 ratio b was 5.8%. This is probably because the segregated Al did not sufficiently flow out due to the lack of washing. In Comparative Example 2, the ratio a was 0.01%, the ratio b was 0.9%, and the cycle maintenance rate was 80.1%. It is believed that CAM-C2 did not contain enough Al segregation parts and voids, and could not buffer the expansion and contraction of LiMO due to charging and discharging. In Comparative Example 3, the ratio a was 0.49% and the ratio b was 14.7%. As a result, the initial discharge capacity was 184.2 mAh/g. This is probably because CAM-C3 contained an excessive amount of Al segregation and voids.

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.

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 41 LiMO 42 Void and Al segregation portion 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 123 External terminal 130 Solid electrolyte layer 200 Exterior body 200a Opening 1000 All-solid lithium secondary battery

Claims (5)

A positive electrode active material for a lithium secondary battery containing a plurality of particles X containing a lithium metal composite oxide and an Al segregation part,
The particles X have voids,
The lithium metal composite oxide has a layered structure and contains at least Li, Ni and Al,
50% cumulative volume particle size of the positive electrode active material is 5-20 μm,
The composition formula of the positive electrode active material is represented by formula (A),
A positive electrode active material for a lithium secondary battery, wherein a cross-sectional image of the particles X obtained by a scanning electron microscope satisfies conditions (1) to (3) .
(1) In an image obtained by binarizing the cross-sectional image so that the lithium metal composite oxide is bright and the voids and the Al segregation part are dark, the area of the region surrounded by the outer periphery of the bright-colored portion The ratio of the sum of the areas of the dark-colored portions existing in the region surrounded by the outer periphery of the light-colored portion to the total sum is more than 0.05% and not more than 0.4%.
(2) In the binarized image, the ratio of the number of particles Y whose circularity represented by formula (i) to the total number of particles X is 0.33 or less is greater than 0% and 5.0. % or less.
(3) In the binarized image, the ratio of the number of particles Z having a circularity of 0.45 or more to the total number of particles X is 70% or more.
Circularity = 4πS/L ² (i)
In formula (i), S is the area of the region surrounded by the perimeter of the light-colored portion, and L is the perimeter length of the light-colored portion.
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.) The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the ratio of 90% cumulative volume particle size to 10% cumulative volume particle size of said positive electrode active material is 3 or less. In powder X-ray diffraction measurement (XRD) using CuKα rays of the positive electrode active material, 2θ = 18.5 ± 1 ° for the diffraction peak intensity height (H2) within the range of 2θ = 44.1 ± 1 ° 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the ratio (H1/H2) of the diffraction peak intensity heights (H1) within the range is 1.5 or more and 1.6 or less. A positive electrode for a lithium secondary battery containing the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 . A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 4 .

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