JP2023085223A - Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

To provide a positive electrode active material for a lithium secondary battery which can form a lithium secondary battery with a high cycle retention rate.SOLUTION: A positive electrode active material for a lithium secondary battery has a layered structure. A first average aspect ratio, which is the aspect ratio of the positive electrode active material for a lithium secondary battery, is from 0.755 to 1.000 inclusive, and the average envelopment of the positive electrode active material for a lithium secondary battery is from 0.983 to 1.000 inclusive.SELECTED DRAWING: 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 an aggregate of secondary particles in which a plurality of 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, [ 3], the positive electrode active material for lithium secondary batteries.
[5] The lithium secondary battery according to [4], 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. positive electrode active material.
[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, 0≦z≦0.5 and y+z<1.)
[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].

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

"Ni" refers to nickel atoms rather than nickel metal. “Co” and “Li” and the like similarly refer to cobalt atoms and lithium 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.

"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, the cycle retention rate is defined as a value measured by repeating a charge/discharge cycle 50 times under the following conditions.

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 cycle capacity is calculated, and this value is defined as the cycle retention rate (%).

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

The CAM in this embodiment is an aggregate of multiple particles. In other words, CAM is in powder form. The aggregate of a plurality of particles may contain only secondary particles, or may be a mixture of primary particles and secondary particles.

The term "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. 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 CAM is a value obtained by measuring the aspect ratios of particles to be measured, specifically 200 or more 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. The smaller the enveloping degree, the larger the amount of unevenness of the CAM. The average envelopment of the CAM is a value obtained by measuring and calculating the envelopment of the particles to be measured, specifically 200 or more 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, and the closer the circularity is to 1, the closer the secondary particles are to a true sphere. The average circularity of CAM is a value obtained by measuring and calculating the circularity of 200 or more CAMs to be measured, and calculating the average value.

The CAM average particle diameter is a 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 diameter of particles to be measured, specifically 200 or more 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 by an analyzer (for example, Morphologi 4, Malvern Panalytical).

Specifically, it can be measured by the following method. 200 or more particles of CAM are introduced into the analyzer supply 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 a first average aspect ratio, an average degree of envelopment and an average degree of circularity of the CAM, as well as a second average aspect ratio and a third average aspect ratio which will be described later.

The first average aspect ratio of the CAM of this embodiment is 0.755-1.000, preferably 0.755-0.999, more preferably 0.760-0.998. When the first average aspect ratio is 0.755-1.000, it can be said that the secondary particles have 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.

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 0.002 or more larger than the first average aspect ratio, it can be said that 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 improved.

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 improved.

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 4-16 μm, the cycle retention rate is improved.

The average envelope of CAM is 0.983-1.000, preferably 0.983-0.995, more preferably 0.983-0.990. When the average enveloping degree is 0.983-1.000, it can be said that the secondary particles in the CAM have a shape with a small amount of unevenness between the vertexes. 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. When the average circularity is 0.910 to 1.000, it can be said that the secondary particles in the CAM have a nearly spherical shape. As a result, the packing density of the CAM can be increased, and the cycle retention rate of the lithium secondary battery is improved.

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

The width of the particle size distribution is represented by (D ₁₀₀ -D ₀ ), for example. The width of the particle size distribution is preferably 10-60 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, Malvern Panalytical). D ₁₀₀ means the largest particle size of the CAM to be measured, and D ₀ means the smallest particle size of the CAM to be measured excluding measurement artifacts.

CAM includes LiMO 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, 0 ≤ z ≤ 0.5, and y + z < 1.)

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, x is -0.1 or more, preferably -0.05 or more, and more preferably more than 0. From the viewpoint of obtaining a lithium secondary battery with a higher initial coulombic efficiency, x is 0.2 or less, preferably 0.15 or less, and more preferably 0.10 or less.

The upper limit and lower limit of x can be combined arbitrarily. Combinations include, for example, x being −0.1 to 0.2, over 0 to 0.2 or less, −0.05 to 0.15, over 0 to 0.10 or less.

From the viewpoint of obtaining a lithium secondary battery with low battery internal resistance, y is 0 or more, preferably more than 0, more preferably 0.005 or more, and further preferably 0.05 or more. preferable. y is 0.4 or less, 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 0 to 0.4, more than 0 to 0.35 or less, 0.005 to 0.35, 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 0 or more, preferably 0.01 or more, more preferably 0.02 or more, and 0.1 or more. is more preferred. Also, z is 0.5 or less, 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 0 to 0.5, preferably 0.01 to 0.45, more preferably 0.02 to 0.40, and further preferably 0.05 to 0.35 preferable.

From the viewpoint of obtaining a lithium secondary battery with a high cycle retention rate, y+z exceeds 0, preferably 0.01 or more, and more preferably 0.02 or more. From the viewpoint of obtaining a lithium secondary battery with high thermal stability, y+z is less than 1, preferably 0.9 or less, more preferably 0.75 or less, and 0.7 or less. is more preferable, and 0.3 or less is particularly preferable.

The upper and lower limits 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, M is preferably one or more metals selected from the group consisting of Ti, Mg, Al, W, B, Nb and Zr. More preferably, it is one or more metals selected from the group consisting of W, B, Nb and Zr.

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 diffraction (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 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>
Next, a method for manufacturing a CAM will be described. A method for producing CAM includes at least production of MCC, mixing of 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.
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 at least one element and satisfies 0≤y≤0.4, 0≤z≤0.5, and y+z<1.)

A method for manufacturing 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 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-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.

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.

The above metal salts are used in _proportions corresponding to the composition ratio of Ni _{(1-yz) CoyAlz} (OH) ₂ . That is, the amounts of each metal salt are defined so 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'). do. Also, water is used as a solvent.

The complexing agent is one capable of forming complexes with nickel ions, cobalt ions and aluminum 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, 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 solution containing the nickel salt solution, the cobalt salt solution, the aluminum salt solution, and the complexing agent, the mixed solution is added before the pH of the mixed solution changes from alkaline to neutral. Add an 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, 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 in the reaction vessel is controlled within the range of 9-13, for example.

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

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.

By appropriately controlling the concentration of the metal salt supplied to the reaction tank, stirring speed, reaction temperature, reaction pH, reaction neutralization time, etc., the average particle size of the finally obtained CAM can be controlled.

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, Co and Al.

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 solution containing elemental sulfur include an aqueous K and Na sulfate solution.

When MCC is a metal composite oxide, the metal composite hydroxide is heated to produce the metal composite oxide. 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. In the case of having a plurality of heating steps, it means the temperature when heated at the highest holding temperature in each heating step.

The heating temperature is preferably 400-700°C, more preferably 450-680°C. When the heating temperature is 400-700° C., the metal composite hydroxide is sufficiently oxidized. 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.

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, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, ozone, and 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) Primary Firing of Mixture The mixture of MCC and lithium compound is subjected to primary firing to form a reactant. 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 a 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 (in this embodiment, 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 the 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°C or higher and 700°C or lower, preferably 410-700°C, and 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 highest temperature held in the firing process (hereinafter sometimes referred to as the maximum held temperature). In the case of the firing process having a plurality of heating steps, the firing temperature means the temperature when heating is performed at the highest holding temperature in each heating step. The above upper limit and lower limit of the firing temperature can be combined arbitrarily.

The holding time in primary firing is preferably 0.01 to 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 firing is 50 hours or less, volatilization of lithium is less likely to occur, and battery performance is improved.

Air, oxygen, nitrogen, argon, or a mixture of these gases can be selected as the firing atmosphere for the primary firing 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 the primary firing may be pulverized to such an extent that the bound secondary particles are separated from each other.

Pulverization of the reaction product includes, for example, pulverization by a pin mill, a disc mill, or the like. 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. Air, oxygen, nitrogen, argon, or a mixed gas of these is used as the firing atmosphere for the secondary firing 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 secondary firing may have multiple firing stages with different firing 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.

As in the primary 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. 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. Further, the secondary firing temperature is preferably higher than 700°C and 750°C or lower, more preferably 710-750°C. 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 lower, 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 250-2000 mm, the rotating speed of the rotating barrel is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, and 0.52-4. More preferably 8 rpm. The secondary firing temperature is preferably above 700° C. and 1000° C. or less, and more preferably above 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 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 firing is preferably 1 to 50 hours. When the holding time in firing is 1 hour or more, crystals are sufficiently developed, and the battery performance is improved. When the retention time in the firing is 50 hours or less, volatilization of lithium ions is less likely to occur, resulting in improved battery performance.

The reaction of MCC and lithium compound may be calcined 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.

CAM is obtained by firing the reaction product of MCC and the lithium compound as described above.

(4) Other Steps After secondary firing, the CAM may be pulverized. Crushing of CAM includes, for example, crushing by a pin mill, disk mill, or the like. 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 disk mill include, for example, operating the pin mill at a rotational speed of 12 to 1200 rpm. By pulverizing the CAM after secondary firing under such conditions, it is easy to control the first to third average aspect ratios, the average degree of envelopment, and the average degree of circularity of the CAM within the ranges described above.

After secondary firing, the CAM may be washed to remove residual unreacted lithium compound and inert fusing agent. Pure water or an alkaline cleaning liquid can be used for cleaning. Examples of the alkaline cleaning solution include aqueous solutions of one or more anhydrides selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate and ammonium carbonate, and hydrates thereof. can be mentioned. Ammonia water can also be used as the alkaline cleaning liquid.

The temperature of the cleaning liquid is preferably 15° C. or lower, more preferably 10° C. or lower, and even more preferably 8° C. or lower. Excessive elution of lithium ions from the crystalline structure of the CAM into the cleaning liquid during cleaning can be suppressed by controlling the temperature of the cleaning liquid within the above range so that the cleaning liquid does not freeze.

As a method for contacting the cleaning liquid and the CAM, there is a method in which the CAM is put into each cleaning liquid and stirred. Alternatively, each cleaning liquid may be used as shower water and applied to the CAM. Furthermore, after the CAM is put into the cleaning liquid and stirred, the CAM may be separated from each cleaning liquid, and then each cleaning liquid may be used as shower water and poured over the separated CAM.

In cleaning, it is preferable to bring the cleaning solution and the CAM into contact for an appropriate time. The "appropriate time" in cleaning refers to a time sufficient to disperse the particles of the CAM while removing any unreacted lithium compound and inert melting agent remaining on the surface of the CAM. The washing time is preferably adjusted according to the aggregation state of the CAM. 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 CAM to the mixture of cleaning liquid and CAM (hereinafter sometimes referred to as slurry) is preferably 10-60% by mass, more preferably 20-50% by mass, and 30-50% by mass. % or less. A proportion of 10-60% by weight of CAM makes it possible to remove unreacted lithium compounds and inert melting agents.

After cleaning the CAM, it is preferred to heat treat the CAM. 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 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.

<Lithium secondary battery>
Next, the configuration of a lithium secondary battery suitable for using the CAM of this embodiment will be described.
When applying the CAM of the present embodiment to a lithium secondary battery, the CAM may include a CAM other than the CAM of the present embodiment. For example, the content of CAM in the present embodiment is preferably 70% by mass or more, more preferably 80% by mass or more, relative to the total mass of CAM (100% by mass).
Furthermore, a positive electrode for a lithium secondary battery (hereinafter sometimes referred to as a positive electrode) suitable for using the CAM of the present embodiment will be described.
Furthermore, a lithium secondary battery suitable for use as a positive electrode will be described.

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

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

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 step 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 can 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 enhanced. 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, 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. 3 is a schematic diagram showing an example of the all-solid lithium secondary battery of this embodiment. The all-solid lithium secondary battery 1000 shown in FIG. 3 has a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer package 200 that houses the laminate 100. Moreover, the all-solid lithium secondary battery 1000 may have a bipolar structure in which a CAM and a negative electrode active material are arranged on both sides of a current collector. Specific examples of bipolar structures include structures described in JP-A-2004-95400. The material forming each member will be described later.

The 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 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-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 .

Hereinafter, each configuration will be described in order.

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

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

(solid electrolyte)
As the solid electrolyte contained in the CAM 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 CAM 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 of supporting the CAM layer 111 on the positive electrode current collector 112 , a method of pressure-molding the CAM layer 111 on the positive electrode current collector 112 can be given. 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 CAM layer 111 may be supported on the positive electrode current collector 112 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 carry the CAM 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 combinations of the CAM described in this embodiment and those described in Tables 1 to 3.

(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 CAM 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 CAM 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

In the lithium secondary battery configured as described above, since the CAM manufactured according to the present embodiment described above is used, the cycle retention rate of the lithium secondary battery can be improved.

In addition, since the positive electrode configured as described above has the CAM configured as described above, the cycle retention rate of the lithium secondary battery can be improved.

Furthermore, since the lithium secondary battery having the above configuration has the above-described positive electrode, the secondary battery has a high cycle retention rate.

As another aspect, the present invention includes the following aspects.
[1] A positive electrode active material for lithium secondary batteries having a layered structure, wherein the first average aspect ratio, which is the average aspect ratio of the positive electrode active material for lithium secondary batteries, is 0.760 to 0.998 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 to 0.998 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 0.915 to 0.998 or less.
[3] 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] or the positive electrode active material for a lithium secondary battery according to [2].
[4] The lithium secondary battery according to [3], 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. positive electrode active material.
[5] The positive electrode active material for a lithium secondary battery according to any one of [1] to [4], 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<x≤0.10, 0.05≤y≤0.30, 0.05≤z≤0.35 and y+z<1.)
[6] A positive electrode for lithium secondary batteries containing the positive electrode active material for lithium secondary batteries according to any one of [1] to [5].
[7] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [6].

[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.

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

<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.) with the aluminum foil side facing down on the lower cover. A laminated film separator (a laminate having a thickness of 16 μm in which a heat-resistant porous layer is laminated on a polyethylene porous film) was placed thereon. 300 μl of electrolytic solution was injected here. The electrolytic solution is a 16:10:74 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, in which _LiPF6 is dissolved to a concentration of 1.3 mol/L, and vinylene carbonate is dissolved at a concentration of 1.0%. I used what I made.
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").

<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 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 tank 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 1 of the total amount of Ni, Co and Al contained in the metal composite oxide 1 was 1.10. A mixture 1 was obtained by mixing metal composite oxide 1 and lithium hydroxide in a mortar.

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

The obtained reactant 1 was pulverized at 1200 rpm using a disc mill (MKCA6-2, manufactured by Masuko Sangyo Co., Ltd.), and then pulverized at 7000 rpm using a pin mill (impact mill, manufactured by Mill System Co., Ltd.).

The pulverized reactant 1 was put into a rotary kiln (manufactured by Tanabe Co., Ltd.) 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 reaction product 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 disk mill (manufactured by Masuko Sangyo Co., Ltd., MKCA6-2).

The crushed baked product 1 and pure water adjusted to a liquid temperature of 5 ° C. are mixed so that the ratio of the baked product weight to the total amount is 30% by mass, and the prepared slurry is stirred for 20 minutes and washed. After that, it was dehydrated, heat-treated at 250° C., and the water remaining after dehydration was dried to obtain CAM-1.

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

(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 cylinder with an inner diameter of 100 mm, the rotation speed was 1.08 rpm, the temperature in the firing furnace was 680 ° C., and oxygen Reaction 2 was obtained by holding and heating under a containing atmosphere for 2 hours.

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

The pulverized baked product 2 was washed, dehydrated and heat-treated 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, and z=0.023 in the composition formula (A), and the 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 resulting reactant C1 was pulverized at 1200 rpm using a disk mill (manufactured by Masuko Sangyo Co., Ltd., MKCA6-2).

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

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

The pulverized fired product C1 was washed, dehydrated and heat-treated 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, and z=0.022 in the composition formula (A), and the element X was Al.

(Comparative example 2)
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 0.885:0.09:0.025 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 tank was 11.6 (measurement temperature: 40° C.), and a reaction precipitate 2 was obtained.

After washing the reaction precipitate 2, it was dehydrated, dried and sieved to obtain a metal composite hydroxide C2 containing Ni, Co and Al.

The metal composite hydroxide C2 was held at 650° C. for 5 hours in an air atmosphere, heated, and cooled to room temperature to obtain a metal composite oxide C2.

Lithium hydroxide was weighed so that the amount (molar ratio) of Li to 1 of the total amount of Ni, Co, and Al contained in the metal composite oxide C2 was 1.10. A mixture C2 was obtained by mixing the metal composite oxide C2 and lithium hydroxide in a mortar.

CAM-C2 was obtained in the same manner as in Comparative Example 1 except that this mixture C2 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.

All of the CAMs obtained in Examples 1 and 2 and Comparative Examples 1 and 2 had a layered structure.
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 Ratio-Third Average Aspect Ratio, Average Circularity, and Cycle Retention of Coin Half-Cells Using Each CAM are shown in Table 4.

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 or less and an average envelopment of 0.983-1.000. Furthermore, the cycle retention rate of the coin-shaped half-cells 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 the 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 the coin-type half-cells using the above CAM-C1 to CAM-C2 was 87.9% or less.

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.

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 CAM 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 (8)

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 a lithium secondary battery according to claim 1, wherein said positive electrode active material for a lithium secondary battery 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, wherein said first average aspect ratio is 0.755 or more and 0.999 or less. 4. The method according to claim 3, wherein a second average aspect ratio, which is an aspect ratio of particles having a particle size smaller than the average particle size of the positive electrode active material for a lithium secondary battery, is larger than the first average aspect ratio by 0.003 or more. A positive electrode active material for a lithium secondary battery as described. The positive electrode active for a lithium secondary battery according to claim 4, 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. material. 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, M 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, 0≦z≦0.5, and y+z<1.) 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 6. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 7 .

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