WO2023106309A1 - 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 has a layered structure, and a first average aspect ratio, which is the aspect ratio of the positive electrode active material for a lithium secondary battery, is 0.755-1.000 inclusive, and the average envelopment of the positive electrode active material for a lithium secondary battery is 0.983-1.000 inclusive.

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. 2021-199651 filed in Japan on December 8, 2021, the contents of which are incorporated herein.

The positive electrode active material for lithium secondary batteries is an aggregate of secondary particles in which multiple primary particles are aggregated. During charging and discharging of a lithium secondary battery, desorption reaction and insertion reaction of lithium ions occur from the surface of the positive electrode active material for lithium secondary batteries. Therefore, the shape of the surface of the positive electrode active material for lithium secondary batteries affects the performance of the lithium secondary battery.

For example, Patent Document 1 discloses that by controlling the shape of the secondary particles of the positive electrode active material for lithium secondary batteries, the wettability with respect to the non-aqueous electrolyte (electrolytic solution) is improved, and high discharge load characteristics are achieved. are doing. Specifically, the average value of the shape factor, which is the area of the region surrounded by the shortest envelope connecting the vertexes of the convex portions of the two-dimensional image with respect to the area of the two-dimensional image of the secondary particle, exceeds 1, It is disclosed to be less than 2.

JP-A-2004-362781

There is room for further improving the performance of lithium secondary batteries by controlling the shape of the secondary particles of the positive electrode active material for lithium secondary batteries from another aspect.

The present invention has been made in view of the above circumstances, and by controlling the shape of the secondary particles, the stability of the positive electrode active material for lithium secondary batteries is improved, and the cycle maintenance rate is high. It is an object of the present invention to provide a positive electrode active material for a lithium secondary battery that can obtain a

The present invention has the following aspects.
[1] A positive electrode active material for a lithium secondary battery having a layered structure, wherein a first average aspect ratio, which is an average aspect ratio of the positive electrode active material for a lithium secondary battery, is 0.755 or more and 1.000 or less. A positive electrode active material for a lithium secondary battery, wherein the positive electrode active material for a lithium secondary battery has an average enveloping degree of 0.983 or more and 1.000 or less.
[2] The positive electrode active material for lithium secondary batteries according to [1], wherein the positive electrode active material for lithium secondary batteries has an average circularity of 0.910 or more and 1.000 or less.
[3] The positive electrode active material for lithium secondary batteries according to [1] or [2], wherein the first average aspect ratio is 0.755 or more and 0.999 or less.
[4] A second average aspect ratio, which is an aspect ratio of particles having a particle diameter smaller than the average particle diameter of the positive electrode active material for a lithium secondary battery, is greater than the first average aspect ratio by 0.003 or more, [ 1] to [3], the positive electrode active material for lithium secondary batteries.
[5] The first average aspect ratio is 0.004 or more larger than the third average aspect ratio, which is the aspect ratio of particles having a particle diameter equal to or larger than the average particle diameter of the positive electrode active material for a lithium secondary battery, [ 1] to [4], the positive electrode active material for lithium secondary batteries.
[6] The positive electrode active material for a lithium secondary battery according to any one of [1] to [5], represented by formula (A).
Li[Li _x (Ni _(1-yz) Co _y x _z ) _1-x ]O ₂ (A)
(In formula A, X is one or more selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P. is an element and satisfies -0.1 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.5.)
[7] D ₁₀₀ −D ₀ of the positive electrode active material for lithium secondary batteries is 10 μm or more and 60 μm or less, and the D ₁₀₀ is the particle diameter of the largest particle among the positive electrode active materials for lithium secondary batteries, The positive electrode active material for a lithium secondary battery according to any one of [1] to [6], wherein the D ₀ is the particle diameter of the smallest particles in the positive electrode active material for a lithium secondary battery.
[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].

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide a positive electrode active material for a lithium secondary battery that can obtain a lithium secondary battery having a high cycle retention rate, and a positive electrode for a lithium secondary battery and a lithium secondary battery using the same. can.

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", and a cathode active material for lithium secondary batteries is hereinafter referred to as "CAM".

"Ni" refers to nickel atoms, not nickel metal. “Co” and “Li” and the like similarly refer to cobalt atoms and lithium 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.

"CAM composition analysis" is performed by the following method. For example, after dissolving CAM in hydrochloric acid, an inductively coupled plasma emission spectrometer (for example, SII Nanotechnology Co., Ltd., SPS3000) can be used.

"Cycle retention rate" refers to the initial discharge capacity of a lithium secondary battery after performing a cycle test that repeats charging and discharging a predetermined number of times under specific conditions. It means the percentage of discharge capacity of a lithium secondary battery.

In the present specification, "cycle retention rate" refers to a lithium secondary battery produced by the method described in <Preparation of positive electrode for lithium secondary battery> and <Preparation of lithium secondary battery (coin-type half cell)> below. Then, the value measured by repeating the charging/discharging cycle 50 times under the following conditions is defined as the cycle retention rate.

Test temperature: 25°C
Maximum charge voltage 4.3V, charge current 0.5CA, constant current constant voltage charge Minimum discharge voltage 2.5V, discharge current 1CA, constant current discharge

The discharge capacity at the 1st cycle is defined as the initial discharge capacity, and the value obtained by dividing the discharge capacity at the 50th cycle by the initial discharge capacity is calculated, and this value is defined as the cycle retention rate (%).

<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 was prepared by dissolving LiPF ₆ in a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (16:10:74 (volume ratio) of 16:10:74 (volume ratio) so as to be 1.3 mol/L. A solution in which 1.0% by volume of vinylene is dissolved is used.
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).

<Positive electrode active material for lithium secondary battery>
The CAM of the present embodiment has a layered structure, a first average aspect ratio that is the average aspect ratio of the CAM is 0.755 or more and 1.000 or less, and an average envelopment degree is 0.983 or more and 1.000 or less. be.

The CAM in this embodiment is an aggregate of multiple particles. In other words, CAM is in powder form. The CAM may contain only secondary particles or may be a mixture of primary and secondary particles. At this time, the number of primary particles may be 0-10% of the total number of particles contained in the CAM.

"Primary particles" means particles that do not have grain boundaries in appearance when observed with a scanning electron microscope or the like in a field of view of 5000 times or more and 20000 times or less.

"Secondary particles" are particles in which the primary particles are agglomerated. That is, secondary particles are aggregates of primary particles.

The CAM aspect ratio is the ratio of the short axis to the long axis measured in the CAM planar image. Here, the major axis refers to the maximum diameter of CAM particles, and the minor axis refers to the maximum diameter among diameters orthogonal to the major axis. It can be determined that the smaller the aspect ratio, the flatter the CAM, and the closer the aspect ratio to 1, the closer the shape of the CAM to a true sphere. The average aspect ratio of the CAM is a value obtained by measuring the aspect ratios of 200 or more, preferably 200, CAMs and calculating the average value. Henceforth, the average aspect-ratio of CAM may be described as "1st average aspect-ratio."

The CAM envelope is the ratio of the envelope length to the perimeter measured in the CAM planar image. Here, the perimeter length refers to the length of the outer periphery of the shape of the CAM particle, and the envelope length refers to the distance between the points of contact with the protrusions in the closed curve that touches all the protrusions on the outer periphery of the CAM particle. Refers to the length of a closed curve for which all connecting lines are straight. The smaller the enveloping degree, the larger the amount of unevenness of the CAM. The average envelope of CAM is a value obtained by measuring and calculating the envelope of 200 or more, preferably 200, CAMs and calculating the average value.

The circularity of CAM is a value represented by 4π×(area)/(perimeter) ² measured in a plane image of CAM. The smaller the circularity, the flatter the CAM. As the circularity approaches 1, the secondary particles of the CAM become more spherical. The average circularity of CAM is a value obtained by measuring and calculating the circularity of 200 or more, preferably 200 CAMs, and calculating the average value.

The CAM particle diameter is the value represented by the diameter of a circle having the same area as the area of the particles captured in the CAM planar image. The average particle size of CAM is a value obtained by measuring and calculating the particle size of 200 or more, preferably 200, CAMs and calculating the average value.

The first average aspect ratio, average envelopment, average circularity and average particle size of the CAM, as well as the average aspect ratios of the particles in the CAM (second average aspect ratio and third average aspect ratio, described below) are calculated from static automated images. It can be measured with an analyzer (for example, Morphologi 4 manufactured by Malvern Panalytical).

Specifically, it can be measured by the following method. At least 200, preferably 200, particles of CAM are introduced into the feed section of the analyzer and fixed by spraying onto the preparation. Observe the fixed particles with an optical microscope and acquire an image. The obtained image is analyzed to calculate the first average aspect ratio, average degree of envelopment, average degree of circularity, and average particle size of the CAM, as well as the second average aspect ratio and third average aspect ratio, which will be described later.

The first average aspect ratio of the CAM of the present embodiment is 0.755-1.000, preferably 0.755-0.999, more preferably 0.760-0.998. When the first average aspect ratio is within the above range, it can be said that the secondary particles in the CAM have a nearly spherical shape. Further, when the first average aspect ratio is within the above range, it can be said that the plurality of particles in the CAM has a shape close to a sphere. As a result, the packing density of the CAM can be increased, and the cycle retention rate of the lithium secondary battery is improved. Moreover, the contact with the electrolytic solution is improved.

The average aspect ratio of particles having a particle size smaller than the average particle size of CAM is preferably 0.003 or more, more preferably 0.004 or more, and 0.005 or more than the first average aspect ratio. is more preferred. Hereinafter, the average aspect ratio of particles having a particle size smaller than the average particle size of CAM may be referred to as "second average aspect ratio". When the second average aspect ratio is 0.003 or more larger than the first average aspect ratio, it can be said that the particles having a particle size smaller than the average particle size of the CAM have a shape closer to a perfect sphere. As a result, the packing density of the CAM can be increased, and the cycle retention rate of the lithium secondary battery is further improved. Also, the difference between the second average aspect ratio and the first average aspect ratio is preferably 0.05 or less, more preferably 0.03 or less, and even more preferably 0.02 or less. The upper limit and lower limit of the difference between the second average aspect ratio and the first average aspect ratio can be combined arbitrarily. As a combination, for example, the difference between the second average aspect ratio and the first average aspect ratio is preferably 0.003 to 0.05, more preferably 0.003 to 0.03, and more preferably 0.003 to 0.03. 003 to 0.02 is more preferable.

The first average aspect ratio is preferably 0.004 or more, more preferably 0.005 or more, and 0.006 or more than the average aspect ratio of the particles having a particle diameter equal to or greater than the average particle diameter of the CAM. is more preferred. Hereinafter, the average aspect ratio of particles having a particle diameter equal to or larger than the average particle diameter of CAM may be referred to as "third average aspect ratio". When the first average aspect ratio is greater than the third average aspect ratio by 0.004 or more, it can be said that particles having a particle size equal to or larger than the average particle size of CAM have a relatively flat shape. The space between the flattened particles can be filled with particles that are closer to a spherical shape and have a smaller particle diameter, and the packing density of the CAM can be increased. As a result, the cycle retention rate of the lithium secondary battery is further improved. The difference between the first average aspect ratio and the third average aspect ratio is preferably 0.09 or less, more preferably 0.05 or less, and even more preferably 0.02 or less. The upper limit and lower limit of the difference between the first average aspect ratio and the third average aspect ratio can be combined arbitrarily. As a combination, for example, the difference between the first average aspect ratio and the third average aspect ratio is preferably 0.004 to 0.09, more preferably 0.004 to 0.05, and more preferably 0.004 to 0.05. 004 to 0.02 is more preferable.

The average particle size of CAM is preferably 4-16 μm, more preferably 4.5-15 μm, even more preferably 5-14 μm. When the average particle size of CAM is within the above range, the cycle retention rate is further improved.

The average envelope of CAM is 0.983-1.000, preferably 0.983-0.998, more preferably 0.983-0.995, and 0.983-0. 990 is more preferred. When the average envelopment is within the above range, it can be said that the secondary particles in the CAM have a shape with a small amount of unevenness between the vertexes. Further, when the average envelopment is within the above range, it can be said that the plurality of particles in the CAM has a shape close to a sphere. As a result, the cycle retention rate of the lithium secondary battery is improved.

The average circularity of CAM is 0.910-1.000, preferably 0.915-0.980, more preferably 0.920-0.950, and 0.920-0. 936 is more preferred. When the average circularity is within the above range, it can be said that the secondary particles in the CAM have a shape close to a sphere. Further, when the average circularity is within the above range, it can be said that the plurality of particles in the CAM has a shape close to a sphere. As a result, the packing density of the CAM can be increased, and the cycle retention rate of the lithium secondary battery is further improved.

The CAM of the present embodiment preferably has a certain width in particle size distribution. If the particle size distribution of the CAM has a wide range, secondary particles with a smaller particle size can be filled between the secondary particles with a larger particle size when the CAM is formed in layers, and the packing density of the CAM can be increased. As a result, the cycle retention rate of the lithium secondary battery is further improved.

The width of the particle size distribution is represented by (D ₁₀₀ -D ₀ ), for example. D ₁₀₀ -D ₀ is preferably 10-60 μm, more preferably 30-58 μm, even more preferably 45-55 μm. The particle size distribution of CAM can be measured by the static automatic image analyzer described above. Specifically, it can be calculated by analyzing an acquired image using a static automatic image analyzer (for example, Morphologi 4 manufactured by Malvern Panalytical). D ₁₀₀ means the particle size of the largest particle in CAM, and D ₀ means the particle size of the smallest particle in CAM excluding measurement artifacts. More specifically, D ₁₀₀ is the value represented by the diameter of a circle having the same area as the area of the largest particle imaged in the acquired image, and D ₀ is the diameter of the largest particle imaged in the acquired image. It is a value expressed by the diameter of a circle having the same area as the area of a small particle.

CAM preferably contains Li and Ni, and is preferably represented by formula (A).
Li[Li _x (Ni _(1-yz) Co _y x _z ) _1-x ]O ₂ (A)
(In formula (A), X is one selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P are the above elements and satisfy -0.1 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.5.)

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, x is preferably -0.05 or more, more preferably greater than 0. From the viewpoint of obtaining a lithium secondary battery with a higher initial coulombic efficiency, x is preferably 0.15 or less, more preferably 0.10 or less. Here, the initial coulombic efficiency is the ratio of the discharge capacity to the charge capacity when the secondary battery is charged for the first time under predetermined conditions and then discharged.

The upper and lower limits of x can be arbitrarily combined. Combinations include, for example, x being -0.05 to 0.15, more than 0 and not more than 0.10, and the like.

From the viewpoint of obtaining a lithium secondary battery with low battery internal resistance, y preferably exceeds 0, more preferably 0.005 or more, and even more preferably 0.05 or more. y is preferably 0.35 or less, more preferably 0.33 or less, and even more preferably 0.30 or less.

The upper limit and lower limit of y can be combined arbitrarily. Combinations include, for example, y being more than 0 and not more than 0.35, 0.005 to 0.35, 0.05 to 0.33, 0.05 to 0.30, and the like.

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, z is preferably 0.01 or more, more preferably 0.02 or more. Also, z is preferably 0.45 or less, more preferably 0.40 or less, and even more preferably 0.35 or less.

The upper limit and lower limit of z can be combined arbitrarily. z is preferably 0.01 to 0.45, more preferably 0.02 to 0.40, even more preferably 0.02 to 0.35.

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, y+z preferably exceeds 0, more preferably 0.01 or more, and even more preferably 0.02 or more. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, y+z is preferably 0.9 or less, more preferably 0.75 or less, even more preferably 0.7 or less, 0.3 or less is particularly preferred.

The upper limit and lower limit of y+z can be combined arbitrarily. y+z is preferably more than 0 and 0.9 or less, more preferably 0.01 to 0.75, still more preferably 0.02 to 0.7, and 0.02 to 0.75. 3 is particularly preferred.

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, X is preferably one or more elements selected from the group consisting of Mn, Ti, Mg, Al, W, B, Nb and Zr, More preferably, it is one or more elements selected from the group consisting of Mn, Al, W, B, Nb and Zr. X is one or more elements X1 selected from the group consisting of Mn and Al, and Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P and one or more elements X2 selected from the group consisting of

The crystal structure of CAM is a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure. The crystal structure of CAM can be confirmed by powder X-ray diffractometry (XRD).

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 high discharge capacity and cycle retention rate, 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>
Next, a method for manufacturing a CAM will be described. The CAM manufacturing method includes at least the steps of manufacturing MCC, mixing MCC and a lithium compound, primary firing of the mixture of MCC and lithium compound, and secondary firing of the reaction product obtained by the primary firing.

(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 contain Ni, Co, and X in molar ratios represented by the following formula (A′), for example. The preferred ranges of y, z, and y+z in formula (A′) are the same as the preferred ranges of y, z, and y+z in formula (A) above.
Ni:Co:X=(1-yz):y:z (A')
(In formula (A′), X is selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P. 1 is an element of at least one species and satisfies 0≤y≤0.4 and 0≤z≤0.5.)

A method for producing MCC containing Ni, Co and Al will be described below as an example. First, a composite metal hydroxide containing Ni, Co and Al 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-yz). A metal composite hydroxide represented _{by CoyAlz} (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 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.

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.

The nickel salt, cobalt salt, and aluminum salt used to produce the metal composite hydroxide can be combined arbitrarily. For example, the preferred combination is nickel sulphate, cobalt sulphate, aluminum sulphate.

The above metal salts are used in _proportions corresponding to the composition ratio of Ni _{(1-yz) CoyAlz} (OH) ₂ . That is, the amount of each metal salt is such that the molar ratio of Ni, Co and Al in the mixed solution containing the metal salt corresponds to (1-yz):y:z in formula (A'). Defined. Also, water is used as a solvent.

Examples of complexing agents include those that can form complexes with nickel ions, cobalt ions, and aluminum ions in an aqueous solution. Complexing agents include, for example, ammonium ion donors (such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid and uracildiacetic 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, cobalt salt solution, aluminum salt solution and complexing agent is, for example, metal salts (nickel salts, cobalt salts and aluminum salts). is greater than 0 and 2.0 or less.

In the coprecipitation method, in order to adjust the pH value of the mixed liquid containing the nickel salt solution, the cobalt salt solution, the aluminum salt solution, and the complexing agent, the alkali metal hydroxide is added so that the pH of the mixed liquid is from alkaline to neutral. is added to the mixture before the 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. If the temperature of the mixture sampled from the reaction vessel is not 40°C, the pH is measured by heating or cooling the mixture to 40°C.

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

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

Also, during the reaction, the pH value of the mixed liquid in the reaction tank is controlled within the range of 9-13, for example.

The reaction precipitate formed in the reaction tank is neutralized while stirring. The time for neutralization of the reaction precipitate is, for example, 1-20 hours.

In order to separate the formed reaction precipitate, the reaction tank used in the continuous coprecipitation method can be a reaction tank of the type that causes the reaction precipitate to overflow.

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 stirring speed, the temperature of the reaction tank, the pH of the mixed solution, the neutralization time, etc., the average particle size of the finally obtained CAM can be controlled. .

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 or suction filtration is used.

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

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 liquid containing elemental sulfur include an aqueous K or Na 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 400-700° C., the metal composite hydroxide is sufficiently oxidized.

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 an oxygen-containing atmosphere. The oxygen-containing atmosphere may be an oxidizing gas (atmosphere, oxygen, etc.) alone, or may be a mixed gas atmosphere of an inert gas (nitrogen, argon, etc.) and an oxidizing gas. and the oxidizing agent may be present. 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 the metal composite oxide.

The oxidizing gas 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, the lithium compound may be at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, lithium chloride and lithium fluoride. . Among these, any one of lithium hydroxide, lithium hydroxide hydrate, and lithium carbonate or a mixture thereof is preferable.

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 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) Primary Firing of Mixture The mixture of MCC and lithium compound is subjected to primary firing to form a reaction product of MCC and lithium compound. In the present embodiment, the primary firing means firing at a temperature lower than the firing temperature in the secondary firing described later (when the firing process has a plurality of firing steps, the firing temperature in the firing step performed at the lowest temperature). That is. The primary firing may be performed multiple times.

A fluidized-bed firing furnace is used as the firing device for the primary firing. A rotary kiln or a fluidized bed calcining furnace may be used as the fluidized calcining furnace. In the fluidized-bed firing furnace, the material to be fired (a mixture of MCC and a lithium compound) is fired while being stirred. Therefore, force is applied in the same direction to the object to be fired, and the first to third average aspect ratios, average enveloping degree and average circularity of the finally produced CAM can be easily controlled within the above ranges.

For example, when a rotary kiln is used as the firing furnace, the inner diameter of the rotating cylinder, which is the firing furnace, is preferably 50-2000 mm, more preferably 60-1900 mm. The volume of the rotary cylinder is preferably 0.002-100 m ³ , more preferably 0.003-99 m ³ , for example.

Here, it is preferable to appropriately set the rotational speed and firing temperature of the rotating shell according to the inner diameter of the rotating shell. For example, when the inner diameter of the rotating barrel is 50-2000 mm, the rotating speed of the rotating barrel is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, More preferably 4.8 rpm. The temperature of the primary firing is preferably 400-700°C, more preferably 410-700°C, even more preferably 420-700°C. When the primary firing temperature is 400° C. or higher, the reaction between MCC and the lithium compound is promoted. Further, when the primary firing temperature is 700° C. or lower, it is easy to control the first to third average aspect ratios, average degree of envelopment, and average degree of circularity of the finally produced CAM within the above ranges.

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 sintering process having a plurality of sintering steps, the sintering temperature means the temperature of the highest sintering step among the sintering steps. The above upper limit and lower limit of the firing temperature can be combined arbitrarily.

The holding time in the primary firing is preferably 0.01-50 hours. When the holding time in the primary firing is 0.01 hour or more, the reaction of the entire mixture of MCC and lithium compound proceeds. When the retention time in the primary firing is 50 hours or less, volatilization of lithium ions is less likely to occur, and the cycle retention rate is improved.

Air, oxygen, nitrogen, argon, or a mixed gas of these can be selected as the firing atmosphere for the primary firing and the secondary firing described later, depending on the desired composition. When the firing atmosphere is an oxygen-containing atmosphere, the oxygen concentration in the firing atmosphere is preferably 21-100% by volume, more preferably 25-100% by volume.

The reactant obtained by primary firing may be pulverized to the extent that secondary particles that are bound together are separated.

　The crushing of the reactant includes crushing by a pin mill, a disc mill, etc., for example. Conditions for pulverizing the reactant by the pin mill include, for example, operating the pin mill at a rotational speed of 300 to 20000 rpm. Conditions for pulverizing the reactant by the disc mill include, for example, operating the disc mill at a rotational speed of 12 to 1200 rpm. By pulverizing the reaction product under such conditions, it is easy to control the first to third average aspect ratios, average enveloping degree and average circularity of the CAM within the ranges described above.

(5) Secondary Firing of Reactant The pulverized reactant is subjected to secondary firing. Secondary firing is performed using the above-described fluidized bed firing furnace. When a rotary kiln is used as the firing furnace, the inner diameter of the rotating cylinder, which is the firing furnace, is preferably 50-2000 mm, more preferably 60-1900 mm.

The secondary firing may have multiple firing stages with different firing temperatures. For example, a first firing step and a second firing step of firing 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.

In the secondary firing, it is preferable to appropriately set the rotational speed of the rotating shell and the firing temperature according to the inner diameter of the rotating shell, as in the primary firing. For example, when the inner diameter of the rotating barrel is 50-250 mm, the rotational speed of the rotating barrel is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, More preferably 4.8 rpm. The secondary firing temperature at this time is preferably higher than 700.degree. C. and not higher than 750.degree. When the secondary firing temperature is higher than 700°C, a CAM having a strong crystal structure can be obtained. Further, when the secondary firing temperature is 750° C. or less, the first to third average aspect ratios, average enveloping degree and average circularity of the finally produced CAM can be easily controlled within the above ranges.

When the inner diameter of the rotating barrel is more than 250 mm and 2000 mm or less, the rotation speed of the rotating barrel is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, and 0.52- More preferably 4.8 rpm. The secondary firing temperature at this time is preferably over 700° C. and 1000° C. or less, and more preferably over 700° C. and 990° C. or less. When the secondary firing temperature is higher than 700°C, a CAM having a strong crystal structure can be obtained. Further, when the secondary firing temperature is 1000° C. or less, the first to third average aspect ratios, average degree of envelopment, and average degree of circularity of the finally produced CAM are likely to be controlled within the above ranges. In addition, volatilization of lithium ions on the surfaces of secondary particles contained in the CAM can be reduced.

The retention time in the secondary firing is preferably 1-50 hours. When the holding time in the secondary firing is 1 hour or more, crystals are sufficiently developed, and the cycle retention rate is improved. When the retention time in the secondary firing is 50 hours or less, volatilization of lithium ions is less likely to occur, and the cycle retention rate is improved.

The mixture or reactant 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.

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

(4) Other Steps After secondary firing, the fired product may be pulverized. The pulverization of the fired product includes, for example, pulverization by a pin mill, a disc mill, or the like. As conditions for pulverizing the fired product by the pin mill, for example, the pin mill is operated so that the number of revolutions is 300 to 20000 rpm. Conditions for pulverizing the reactant by the disc mill include, for example, operating the disc mill at a rotational speed of 12 to 1200 rpm. By pulverizing the fired product under such conditions, it is easy to control the first to third average aspect ratios, average degree of envelopment, and average degree of circularity of the CAM within the ranges described above.

After secondary firing and, if necessary, crushing, the fired product (or the crushed fired product) may be washed to remove the remaining unreacted lithium compound and inert melting agent. 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. The lower limit of the temperature of the cleaning liquid is 1° C., for example. 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 the baked product 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 in the fired material while removing any unreacted lithium compound and any inert melting agent remaining on the surface of the fired material. It is preferable to adjust the washing time according to the aggregation state of the baked product. For example, a preliminary experiment may be performed to set an appropriate washing time. 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 10-60% by mass, more preferably 20-50% by mass, and 30- More preferably, it is 50% by mass. A proportion of 10-60% by weight of calcined material allows removal of unreacted lithium compounds and any inert fusing agent.

After washing the fired product, the fired product is preferably heat-treated. The heat treatment temperature and method are not particularly limited, but from the viewpoint of preventing a decrease in charge capacity, the temperature is preferably 150° C. or higher, more preferably 175° C. or higher, and even more preferably 200° C. or higher. Although not particularly limited, the temperature is preferably 1000° C. or lower, more preferably 950° C. or lower, from the viewpoint of preventing volatilization of lithium ions and obtaining a CAM having the composition of the present embodiment.
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 150-1000°C, more preferably 175-950°C, even more preferably 200-950°C.

The holding time in the heat treatment is preferably 1-50 hours. When the holding time in the heat treatment is 1 hour or longer, the moisture in the baked product is removed, and a CAM with few impurities can be obtained. When the holding time in the heat treatment is 50 hours or less, the lithium ions are less likely to volatilize, and the cycle retention rate improves.

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 washing in the above atmosphere, the reaction between the fired product and moisture or carbon dioxide in the atmosphere is suppressed during the heat treatment, and a CAM with few impurities can be obtained.

The CAM can be obtained by crushing, washing, and heat-treating the fired material as necessary under the conditions described above. Moreover, it is good also considering a baked product as CAM.

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

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

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

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

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

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

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

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

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

<All-solid lithium secondary battery>
Next, a positive electrode using a CAM according to one embodiment of the present invention and an all-solid lithium secondary battery including the positive electrode will be described while describing the structure of the all-solid lithium secondary battery.

FIG. 2 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. 2 has a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer package 200 that accommodates the laminate 100. Moreover, the all-solid lithium secondary battery 1000 may have a bipolar structure in which a positive electrode active material 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 a high cycle retention rate.

Furthermore, the lithium secondary battery configured as described above has a high cycle retention rate because it has the positive electrode described above.

As another aspect, the present invention includes the following aspects.
<1> A CAM having a layered structure, wherein the first average aspect ratio of the CAM is 0.760 to 0.998 or less, and the average envelopment of the CAM is 0.983 to 0.990 or less. , CAM.
<2> The CAM according to <1>, wherein the CAM has an average circularity of 0.915 to 0.998 or less.
<3> The CAM according to <1> or <2>, wherein the second average aspect ratio is greater than the first average aspect ratio by 0.003 or more.
<4> The CAM according to any one of <1> to <3>, wherein the first average aspect ratio is greater than the third average aspect ratio by 0.004 or more.
<5> The CAM according to any one of <1> to <4>, represented by formula (A1).
Li[Li _x (Ni _(1-yz) Co _y x _z ) _1-x ]O ₂ (A1)
(In formula A, X is one or more selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P. is an element and satisfies 0<x≤0.10, 0.05≤y≤0.30, 0.05≤z≤0.35 and y+z≤0.3.)
<6> The CAM according to any one of <1> to <5>, wherein D ₁₀₀ -D ₀ is 10-60 μm.
<7> The CAM according to any one of <1> to <6>, wherein the average circularity is 0.915-0.936.
<8> A positive electrode for a lithium secondary battery, containing the CAM according to any one of <1> to <7>.
<9> A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to <8>.

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.

<Static automatic image analysis>
The first to third average aspect ratios, average envelopment, average circularity, average particle diameter and particle size distribution of CAM are measured by the above-described method using a static automatic image analyzer (manufactured by Malvern Panalytical, Morphologi 4). measured by

<Cycle maintenance rate>
The lithium secondary battery produced by the method described above was measured by the method described in the method for measuring the "cycle retention rate" described above.

(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 solution.

Next, this mixed 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 became 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 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 using a mortar.

This mixture 1 was put into a rotary kiln (manufactured by Tanabe) having a rotating cylinder with an inner diameter of 300 mm. The rotation speed was 0.67 rpm, the temperature in the firing furnace was 690° C., and the mixture 1 was heated by holding in an oxygen-containing atmosphere for 2 hours to obtain a reaction product 1 of metal composite oxide 1 and lithium hydroxide.

The obtained reactant 1 is crushed under the conditions of 1200 rpm using a disk mill (manufactured by Masuko Sangyo Co., Ltd., MKCA6-2), and then crushed under the conditions of 7000 rpm using a pin mill (impact mill manufactured by Mill System Co., Ltd.). bottom.

The pulverized reactant 1 was put into a rotary kiln (manufactured by Tanabe) having a rotating cylinder with an inner diameter of 300 mm. The rotation speed was 0.67 rpm, the temperature in the firing furnace was set at 770° C., and the reactant 1 was fired in an oxygen-containing atmosphere for 2 hours to obtain a fired product 1 .

The fired product 1 obtained was pulverized at 1200 rpm using a disc mill (MKCA6-2, manufactured by Masuko Sangyo Co., Ltd.).

A slurry was prepared by mixing the pulverized fired product 1 and pure water adjusted to a liquid temperature of 5°C so that the ratio of the fired product to the total amount was 30% by mass. The prepared slurry was washed with stirring for 20 minutes, dehydrated, heat-treated at 250° C., and dried to remove water remaining after dehydration to obtain CAM-1.

A composition analysis of CAM-1 revealed that x = 0.04, y = 0.089, z = 0.022 and X was Al in the composition formula (A).

(Example 2)
Mixture 1 obtained by the method described in Example 1 was put into a rotary kiln (manufactured by Noritake TCF Co., Ltd.) having a rotating barrel with an inner diameter of 100 mm. The rotation speed was 1.08 rpm, the temperature in the firing furnace was 680° C., and the mixture 1 was heated by holding it for 2 hours in an oxygen-containing atmosphere to obtain a reaction product 2 .

The obtained reactant 2 was pulverized at 1200 rpm using a disk mill (MKCA6-2, manufactured by Masuko Sangyo Co., Ltd.), and then pulverized at 20000 rpm using a pin mill (impact mill, manufactured by Mill System Co., Ltd.).

The pulverized reactant 2 was put into a rotary kiln (manufactured by Noritake TCF Co., Ltd.) having a rotating cylinder with an inner diameter of 100 mm. The rotation speed was 1.08 rpm, the temperature in the firing furnace was set to 720° C., and the reactant 2 was fired in an oxygen-containing atmosphere for 2 hours to obtain the fired product 2 .

The fired product 2 obtained was pulverized, washed, dehydrated, heat treated and dried by the method described in Example 1 to obtain CAM-2.

A composition analysis of CAM-2 revealed that x = 0.05, y = 0.088, z = 0.023 in composition formula (A), and element X was Al.

(Comparative example 1)
Mixture 1 was obtained by the method described in Example 1. This mixture 1 is held in a roller hearth kiln (manufactured by Noritake Co., Ltd.) in an oxygen-containing atmosphere at 650 ° C. for 5 hours to bake the mixture 1, and the metal composite oxide 1 reacts with lithium hydroxide. obtained product C1.

The obtained reactant C1 was pulverized at 1200 rpm using a disk mill (MKCA6-2, manufactured by Masuko Sangyo Co., Ltd.).

Next, the pulverized reactant C1 was fired at 720°C for 6 hours in a roller hearth kiln (manufactured by Noritake Co., Ltd.) to obtain a fired product C1.

The obtained fired product C1 was pulverized, washed, dehydrated, heat treated and dried by the method described in Example 1 to obtain CAM-C1.

A composition analysis of CAM-C1 revealed that x = 0.04, y = 0.089, z = 0.022 in composition formula (A), and element X was Al.

(Comparative example 2)
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 0.885:0.09:0.025, except that a mixed solution was prepared. A mixture 2 was obtained by the method described in Example 1. CAM-C2 was obtained in the same manner as in Comparative Example 1 except that the obtained mixture 2 was used.

A composition analysis of CAM-C2 revealed that x = 0.10, y = 0.09, and z = 0.025 in the composition formula (A), and the element X was Al.

The CAMs obtained in Examples 1 and 2 and Comparative Examples 1 and 2 all had a layered structure from the results of XRD.
CAM firing conditions of Examples 1 and 2 and Comparative Examples 1 and 2, first average aspect ratio, average enveloping degree, average particle diameter, particle size distribution, second average aspect ratio - first average aspect ratio, first average aspect Table 1 shows the ratio-third average aspect ratio, average circularity, and cycle retention rate of lithium secondary batteries using each CAM.

In the firing process of Examples 1 and 2, primary firing and secondary firing were performed using a rotary kiln. Furthermore, when the inner diameter of the rotating cylinder was 300 mm, the firing conditions were adjusted to 0.67 rpm, and when the inner diameter of the rotating cylinder was 100 mm, the firing conditions were adjusted to 1.08 rpm. Such CAMs had a first average aspect ratio of 0.755-1.000 and an average envelope of 0.983-1.000. Furthermore, the cycle retention rate of lithium secondary batteries using CAM-1 to CAM-2 was 88% or more.

On the other hand, in Comparative Examples 1 and 2 in which the primary firing and secondary firing were performed in a roller hearth kiln, the average aspect ratio or average enveloping degree did not satisfy the above ranges. It is considered that this is because the mixture did not flow during firing and no isotropic force was applied to the secondary particles.

The cycle retention rate of lithium secondary batteries using the above CAM-C1 to CAM-C2 was 87.9% or less.

According to the present invention, it is possible to provide a CAM capable of obtaining a lithium secondary battery with a high cycle retention rate, and a positive electrode for a lithium secondary battery and a lithium secondary battery using the CAM.

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)

1. A positive electrode active material for a lithium secondary battery having a layered structure, wherein a first average aspect ratio, which is an aspect ratio of the positive electrode active material for a lithium secondary battery, is 0.755 or more and 1.000 or less; A positive electrode active material for a lithium secondary battery, which has an average enveloping degree of 0.983 or more and 1.000 or less.
2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the positive electrode active material for lithium secondary batteries has an average circularity of 0.910 or more and 1.000 or less.
3. The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the first average aspect ratio is 0.755 or more and 0.999 or less.
4. Claims 1 to 1, wherein a second average aspect ratio, which is an aspect ratio of particles having a particle diameter smaller than the average particle diameter of the positive electrode active material for a lithium secondary battery, is greater than the first average aspect ratio by 0.003 or more. 4. The positive electrode active material for a lithium secondary battery according to any one of 3.
5. Claims 1 to 1, wherein the first average aspect ratio is 0.004 or more larger than the third average aspect ratio, which is the aspect ratio of particles having a particle diameter equal to or larger than the average particle diameter of the positive electrode active material for a lithium secondary battery. 5. The positive electrode active material for a lithium secondary battery according to any one of 4.
6. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5, represented by formula (A).
   Li[Li _x (Ni _(1-yz) Co _y x _z ) _1-x ]O ₂ (A)
   (In formula A, X is one or more selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S and P. is an element and satisfies -0.1 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.5.)
7. D ₁₀₀ −D ₀ of the positive electrode active material for a lithium secondary battery is 10 μm or more and 60 μm or less, the D ₁₀₀ is the particle diameter of the largest particle of the positive electrode active material for the lithium secondary battery, and the D ₀ The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6, wherein is the particle diameter of the smallest particles in the positive electrode active material for a lithium secondary battery.
8. 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.
9. A lithium secondary battery having the positive electrode for a lithium secondary battery according to claim 8.

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