JP7455795B2 - Positive electrode active materials for lithium secondary batteries, positive electrodes for lithium secondary batteries, and lithium secondary batteries - Google Patents

Description

The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, 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 and insertion reactions of lithium ions occur from the surface of a positive electrode active material for a lithium secondary battery. Therefore, the surface shape of the positive electrode active material for a lithium secondary battery affects the performance of the lithium secondary battery.

For example, Patent Document 1 discloses that by controlling the secondary particle shape of a positive electrode active material for a lithium secondary battery, wettability with respect to a non-aqueous electrolyte (electrolyte 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 vertices of the convex part of the two-dimensional image with respect to the area of the two-dimensional image of the secondary particle, exceeds 1, It is disclosed that the number is less than 2.

JP-A-2004-362781

There is room to further improve the performance of lithium secondary batteries by controlling the shape of secondary particles of positive electrode active materials 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 secondary particles, the stability of a positive electrode active material for a lithium secondary battery is improved, and a lithium secondary battery with a high cycle maintenance rate is achieved. An object of the present invention is to provide a positive electrode active material for a lithium secondary battery that can obtain the same, and a positive electrode for a lithium secondary battery and a lithium secondary battery using the same.

The present invention has the following aspects.
[1] A positive electrode active material for a lithium secondary battery having a layered structure, wherein the first average aspect ratio, which is the 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 average degree of envelopment of the positive electrode active material for a lithium secondary battery is 0.983 or more and 1.000 or less.
[2] The positive electrode active material for a lithium secondary battery according to [1], wherein the average circularity of the positive electrode active material for a lithium secondary battery is 0.910 or more and 1.000 or less.
[3] The positive electrode active material for a lithium secondary battery 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 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, [ 3], the positive electrode active material for a lithium secondary battery.
[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 size equal to or larger than the average particle size. Cathode active material for use.
[6] The positive electrode active material for a lithium secondary battery according to any one of [1] to [5], which is represented by formula (A).
Li [Li _x (Ni _(1-y-z) 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. It 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 a lithium secondary battery, comprising the positive electrode active material for a lithium secondary battery 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].

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 with a high cycle maintenance rate, and a positive electrode for a lithium secondary battery and a lithium secondary battery using the same. can.

FIG. 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-state lithium secondary battery according to the present embodiment.

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

In this specification, the metal composite compound is hereinafter referred to as "MCC" and the cathode active material for lithium secondary batteries is hereinafter referred to as "CAM."

"Ni" refers to a nickel atom, not nickel metal. Similarly, "Co" and "Li" etc. refer to a cobalt atom, a lithium atom, etc., 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, and a numerical range 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, the measurement can be performed using an inductively coupled plasma emission spectrometer (for example, SPS3000 manufactured by SII Nano Technology Co., Ltd.).

"Cycle maintenance rate" refers to the initial discharge capacity of a lithium secondary battery after a cycle test in which the lithium secondary battery is charged and discharged a predetermined number of times under specific conditions. It means the percentage of discharge capacity of a lithium secondary battery.
In this specification, a value measured by conducting a test in which charging and discharging cycles are repeated 50 times under the conditions shown below is defined as a cycle maintenance rate.

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

The discharge capacity at the 1st cycle is taken 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 taken as the cycle maintenance rate (%).

<Cathode active material for lithium secondary batteries>
The CAM of this 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 an average aspect ratio of the CAM, of 0.755 or more and 1.000 or less, and a lithium secondary The average degree of envelopment of the battery positive electrode active material is 0.983 or more and 1.000 or less.

The CAM in this embodiment is an aggregate of a plurality of 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.

"Primary particles" refer to particles that do not have grain boundaries in appearance when observed using a scanning electron microscope or the like with a field of view of 5,000 times or more and 20,000 times or less.

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

The aspect ratio of a CAM is the ratio of the short axis to the long axis measured in a planar image of the CAM. It can be determined that the smaller the aspect ratio is, the flatter the CAM is, and the closer the aspect ratio is to 1, the closer the shape of the CAM is to a perfect 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. Hereinafter, the average aspect ratio of the CAM may be referred to as a "first average aspect ratio."

The degree of envelope of a CAM is the ratio of the envelope length to the circumferential length measured in a planar image of the CAM. The smaller the degree of envelopment, the larger the amount of unevenness in the CAM, and the closer the degree of envelopment is to 1, the smaller the amount of unevenness between the vertices of the CAM. The average degree of envelopment of a CAM is a value obtained by measuring and calculating the degree of envelopment of particles to be measured, specifically, the degree of envelopment of 200 or more CAMs, and calculating the average value.

The circularity of the CAM is a value expressed by 4π×(area)/(perimeter) ² measured in a planar image of the CAM. The smaller the circularity is, the flatter the CAM is, 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 particles to be measured, specifically, 200 or more CAMs, and calculating the average value.

The average particle diameter of the CAM is a value expressed by the diameter of a circle having the same area as the area of the particles imaged in the plane image of the CAM. The average particle diameter of CAM is a value obtained by measuring and calculating the diameters of particles to be measured, specifically, diameters of 200 or more CAMs, and calculating the average value.

The first average aspect ratio, average degree of envelopment, average circularity, and average particle diameter of the CAM, as well as the average aspect ratio of the particles in the CAM (second average aspect ratio and third average aspect ratio to be described later) are calculated using static automatic images. It can be measured using an analyzer (for example, Morphologi 4, Malvern Panalytical).

Specifically, it can be measured by the following method. More than 200 CAM particles are introduced into the analyzer supply and sprayed onto the preparation to be fixed. The fixed particles are observed using an optical microscope and images are obtained. The acquired image is analyzed to calculate the first average aspect ratio, average envelope degree, and average circularity 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 this embodiment is 0.755-1.000, preferably 0.755-0.999, and 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 maintenance 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 larger than the first average aspect ratio, more preferably 0.004 or more larger, and 0.005 or more larger. is even more preferable. Hereinafter, the average aspect ratio of particles having a particle size smaller than the average particle size of CAM may be referred to as a "second average aspect ratio." When the second average aspect ratio is larger than the first average aspect ratio by 0.002 or more, it can be said that particles having a particle diameter smaller than the average particle diameter of CAM have a shape closer to a true sphere. As a result, the packing density of the CAM can be increased, and the cycle maintenance rate of the lithium secondary battery can be improved.

The first average aspect ratio is preferably 0.004 or more larger, more preferably 0.005 or more, and 0.006 or more larger than the average aspect ratio of particles having a particle size larger than or equal to the average particle size of CAM. is even more preferable. Hereinafter, the average aspect ratio of particles having a particle size larger than the average particle size of CAM may be referred to as a "third average aspect ratio." When the first average aspect ratio is larger than the third average aspect ratio by 0.004 or more, it can be said that the particles having a particle size equal to or larger than the average particle size of CAM have a relatively flat shape. Spaces between flat particles can be filled with particles that are more spherical and have a smaller particle diameter, increasing the packing density of CAM. As a result, the cycle maintenance rate of the lithium secondary battery is improved.

The average particle diameter of CAM is preferably 4-16 μm, more preferably 4.5-15 μm, and even more preferably 5-14 μm. When the average particle diameter of CAM is 4-16 μm, the cycle retention rate is improved.

The average envelope degree of CAM is 0.983-1.000, preferably 0.983-0.995, and more preferably 0.983-0.990. When the average degree of envelopment 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 vertices. As a result, the cycle maintenance rate of the lithium secondary battery is improved.

The average circularity of the CAM is 0.910-1.000, preferably 0.915-0.980, and more preferably 0.920-0.950. When the average circularity is 0.910-1.000, it can be said that the secondary particles in the CAM have a shape close to a sphere. As a result, the packing density of the CAM can be increased, and the cycle maintenance rate of the lithium secondary battery can be improved.

It is preferable that the CAM of this embodiment has a certain range of particle size distribution. If the particle size distribution of the secondary particles has a wide range, when the CAM is formed into a layer, the spaces between the secondary particles with a large particle size can be filled with the secondary particles with a small particle size, and the packing density of the CAM can be increased. can. As a result, the cycle maintenance rate of the lithium secondary battery is improved.

The width of the particle size distribution is expressed, for example, by (D ₁₀₀ −D ₀ ). 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, manufactured by Malvern Panalytical). D ₁₀₀ means the largest particle diameter among the CAMs to be measured, and D ₀ means the smallest particle diameter excluding measurement artifacts among the CAMs to be measured.

CAM includes LiMO represented by formula (A).
Li [Li _x (Ni _(1-y-z) 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. The above elements 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, more preferably -0.05 or more, and even more preferably more than 0. Moreover, from the viewpoint of obtaining a lithium secondary battery with higher initial coulombic efficiency, x is 0.2 or less, preferably 0.15 or less, and more preferably 0.10 or less.

The upper and lower limits of x can be arbitrarily combined. Examples of combinations include x being -0.1 to 0.2, more than 0 and less than 0.2, -0.05 to 0.15, more than 0 and less than 0.10.

From the viewpoint of obtaining a lithium secondary battery with low internal resistance, y is 0 or more, preferably more than 0, more preferably 0.005 or more, and even more 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 and lower limits of y can be arbitrarily combined. Examples of combinations include y being 0 to 0.4, more than 0 to 0.35 or less, 0.005 to 0.35, 0.05 to 0.30, etc.

From the viewpoint of obtaining a lithium secondary battery with a high cycle maintenance rate, z is 0 or more, preferably 0.01 or more, more preferably 0.02 or more, and 0.1 or more. is even more preferable. Further, 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 and lower limits of z can be arbitrarily combined. z is 0 to 0.5, preferably 0.01 to 0.45, more preferably 0.02 to 0.40, and even more preferably 0.05 to 0.35. preferable.

From the viewpoint of obtaining a lithium secondary battery with a high cycle maintenance 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 even more preferable, and particularly preferably 0.3 or less.

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

From the viewpoint of obtaining a lithium secondary battery with a high cycle maintenance 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 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, P6 mm, P6 cc, P6 ₃ cm, P6 ₃ mc, P- 6m2, P-6c2, P-62m, P-62c, P6/mmm, P6/mcc, P6 ₃ /mcm, and P6 ₃ /mmc.

The monoclinic crystal structure is 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, the crystal structure is a hexagonal crystal structure belonging to space group R-3m or a monoclinic crystal structure belonging to C2/m. Particularly preferred is the structure.

<CAM manufacturing method>
Next, a method for manufacturing the CAM will be explained. The method for producing CAM includes at least production of MCC, mixing of MCC and a lithium compound, primary calcination of the mixture of MCC and lithium compound, and secondary calcination of the reaction product obtained by the primary calcination.

(1) Production of MCC MCC may be a metal composite hydroxide, a metal composite oxide, or a mixture thereof. The metal composite hydroxide and the metal composite oxide contain Ni, Co, and X in a molar ratio represented by the following formula (A'), for example.
Ni:Co:X=(1-y-z):y:z (A')
(In formula (A'), X is 1 selected from the group consisting of Mn, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S, and P. It is an element that is more than a species, and satisfies 0≦y≦0.4, 0≦z≦0.5, and y+z<1.)

Hereinafter, a method for manufacturing MCC containing Ni, Co, and Al will be described as an example. First, a metal composite hydroxide containing Ni, Co and Al is prepared. The metal composite hydroxide can be produced by a commonly 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 form Ni _(1-yz). A metal composite hydroxide represented by Co _y Al _z (OH) ₂ is produced.

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

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

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

The above metal salts are used in a proportion corresponding to the composition ratio of Ni _(1-yz) Co _y Al _z (OH) ₂ described above. That is, the amount of each metal salt is 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 of formula (A'). do. Also, water is used as a solvent.

The complexing agent is one that can form a complex with nickel ions, cobalt ions, and aluminum ions in an aqueous solution, such as an ammonium ion donor (ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride). etc.), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid and uracil diacetic acid and glycine.

In the process for producing the metal composite hydroxide, a complexing agent may or may not be used. When a complexing agent is used, the amount of the complexing agent contained in the mixed solution containing the nickel salt solution, the cobalt salt solution, the aluminum salt solution, and the complexing agent is, for example, a molar ratio of the amount of the complexing agent to the total number of moles of the metal salts (nickel salt, cobalt salt, and aluminum salt) that is greater than 0 and less than or equal to 2.0.

In the coprecipitation method, in order to adjust the pH value of the mixed solution containing the nickel salt solution, cobalt salt solution, aluminum salt solution, and complexing agent, the mixed solution should be adjusted before the pH of the mixed solution changes from alkaline to neutral. Add an alkali metal hydroxide to. The alkali metal hydroxide is, for example, sodium hydroxide or potassium hydroxide.

Note that the pH value in this specification is defined as a value measured when the temperature of the liquid mixture is 40°C. 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 temperature of the sampled liquid mixture is lower than 40°C, the mixed liquid is heated to 40°C and the pH is measured. If the temperature of the sampled mixed liquid exceeds 40°C, the mixed liquid is cooled to 40°C and the pH is measured.

In addition to the above nickel salt solution, cobalt salt solution, and aluminum salt solution, when a complexing agent is continuously supplied to the reaction tank, Ni, Co, and Al react, forming Ni _(1-y-z) Co _y Al _z (OH) ₂ is generated.

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

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

The reaction precipitate formed in the reaction tank is neutralized while stirring. The time for neutralizing the reaction precipitate is, for example, 1 to 20 hours.

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

When producing a metal composite hydroxide by a batch coprecipitation method, a reaction tank is equipped with a reaction tank without an overflow pipe and a concentration tank connected to the overflow pipe, and the overflowing reaction precipitate is collected in the concentration tank. Examples include devices that have a mechanism for concentrating and circulating it back to the reaction tank.

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

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

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

The reaction precipitate is preferably washed with water or an alkaline washing liquid. In this embodiment, it is preferable to wash with an alkaline cleaning liquid, and more preferably to wash with an aqueous sodium hydroxide solution. Alternatively, cleaning may be performed using a cleaning liquid containing elemental sulfur. Examples of the cleaning liquid containing elemental sulfur include K and Na sulfate aqueous solutions.

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 necessary. The heating temperature in this specification means the set temperature of the heating device. When there are multiple heating steps, it means the temperature at the time of heating at the highest holding temperature among 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, there is a risk that the metal composite hydroxide will be excessively oxidized.

The time for holding at the heating temperature may be 0.1 to 20 hours, preferably 0.5 to 10 hours. The rate of temperature increase to the heating temperature is, for example, 50-400° C./hour. Further, as the heating atmosphere, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used.

The inside of the heating device may have an appropriate 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. By providing an appropriate oxygen-containing atmosphere within the heating device, the transition metal contained in the metal composite hydroxide is appropriately oxidized, making it easier to control the form of the metal composite oxide.

The oxygen and oxidizing agent in the oxygen-containing atmosphere need only contain 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 inside the heating device can be controlled by venting the oxidizing gas into the heating device or bubbling the oxidizing gas into the mixed liquid. This can be done using the following method.

As the oxidizing agent, peroxides such as hydrogen peroxide, peroxide salts such as permanganates, perchlorates, hypochlorites, nitric acid, halogens, or ozone can be used.

(2) Mixing 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, classification may be performed as appropriate.

As the lithium compound used in this embodiment, at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride, and lithium fluoride can be used. Among these, either lithium hydroxide or lithium carbonate or a mixture thereof is preferred. Further, when lithium hydroxide contains lithium carbonate, the content of lithium carbonate in lithium hydroxide is preferably 5% by mass or less.

A lithium compound and MCC are mixed in consideration of the composition ratio of the final target product to obtain a mixture. Specifically, the lithium compound and MCC are mixed in a ratio corresponding to the composition ratio of the above composition formula (A). The amount (mole ratio) of Li with respect to the total amount 1 of metal atoms contained in the 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 explained later.

(3) Primary firing of mixture The mixture of MCC and lithium compound is primary fired to form a reactant. In this embodiment, primary firing refers to firing at a temperature lower than the firing temperature in the secondary firing described below (if the firing process has multiple firing stages, the firing temperature in the lowest firing stage) That's true. The primary firing may be performed multiple times.

The firing device used during the primary firing is a fluidized firing furnace. A rotary kiln or a fluidized bed kiln may be used as the fluidized kiln. In the fluidized 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 to the object to be fired in the same direction, and it is easy to control the first to third average aspect ratios, average degree of envelopment, and average degree of circularity of the CAM to be finally produced within the above-mentioned ranges.

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

Here, it is preferable to appropriately set the rotational speed and firing temperature of the rotary cylinder according to the inner diameter of the rotary cylinder. For example, when the inner diameter of the rotary tube is 50-2000 mm, the rotation speed of the rotary tube is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, and 0.52-4.9 rpm. More preferably, the speed is 4.8 rpm. Further, the temperature of the primary firing is preferably 400°C or more and 700°C or less, 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 envelope degree, and average circularity of the finally produced CAM within the above-mentioned ranges.

The firing temperature in this specification means the temperature of the atmosphere inside the firing furnace, and is the maximum temperature held in the firing process (hereinafter sometimes referred to as maximum holding temperature). In the case of a firing process having a plurality of heating steps, the firing temperature means the temperature at which heating is performed at the highest holding temperature among each heating process. The upper and lower limits of the firing temperature can be arbitrarily combined.

The holding time in the 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 holding time during firing is 50 hours or less, lithium is less likely to volatilize and battery performance is improved.

The firing atmosphere for the primary firing can be selected from air, oxygen, nitrogen, argon, or a mixed gas thereof 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 calcination may be crushed to the extent that bonded secondary particles are separated from each other.

Examples of the crushing of the reactant include crushing using a pin mill, a disk mill, and the like. Conditions for crushing the reactant using a pin mill include, for example, operating the pin mill at a rotation speed of 300 to 20,000 rpm. Conditions for crushing the reactant using a disk mill include, for example, operating the disk mill at a rotation speed of 12 to 1200 rpm. By crushing the reactants under such conditions, it is easy to control the first to third average aspect ratios, average degree of envelopment, and average circularity of the CAM within the above-mentioned ranges.

(5) Secondary calcination of reactant The crushed reactant is subjected to secondary calcination. The secondary firing is performed using the above-mentioned fluidized firing furnace. When a rotary kiln is used as the firing furnace, the inner diameter of the rotary cylinder serving as the firing furnace is preferably 50-2000 mm, more preferably 60-1900 mm. As the firing atmosphere for the secondary firing, air, oxygen, nitrogen, argon, a mixed gas thereof, or the like is used 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 include multiple firing stages with different firing temperatures. For example, a first firing stage and a second firing stage in which firing is performed at a higher temperature than the first firing stage 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 rotation speed and firing temperature of the rotary cylinder depending on the inner diameter of the rotary cylinder. For example, when the inner diameter of the rotary tube is 50-250 mm, the rotation speed of the rotary tube is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, and more preferably 0.52-4.9 rpm. More preferably, the speed is 4.8 rpm. Further, the temperature of the secondary firing is preferably higher than 700°C and lower than 750°C, 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, it is easy to control the first to third average aspect ratios, average envelope degree, and average circularity of the finally produced CAM within the above-mentioned ranges.

When the inner diameter of the rotary tube is 250-2000 mm, the rotation speed of the rotary tube is preferably 0.5-5 rpm, more preferably 0.51-4.9 rpm, and 0.52-4. More preferably, the speed is 8 rpm. Further, the temperature of the secondary firing is preferably higher than 700°C and lower than or equal to 1000°C, more preferably higher than 700°C and lower than or equal to 990°C. When the secondary firing temperature is higher than 700° C., a CAM having a strong crystal structure can be obtained. Furthermore, when the firing temperature is 1000° C. or lower, the first to third average aspect ratios, average degree of envelope, and average degree of circularity of the finally produced CAM can be easily controlled within the above-mentioned ranges. Further, volatilization of lithium ions on the surface of secondary particles included in the CAM can be reduced.

The holding time during firing is preferably 1 to 50 hours. When the holding time during firing is 1 hour or more, crystals are sufficiently developed and battery performance is improved. When the holding time during firing is 50 hours or less, lithium ions are less likely to volatilize and battery performance is improved.

The reaction product 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 below. As the inert melting agent, for example, those described in WO2019/177032A1 can be used.

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

(4) Other steps After performing the secondary firing, the CAM may be crushed. Examples of the crushing of CAM include crushing using a pin mill, a disk mill, and the like. Conditions for crushing the reactant using a pin mill include, for example, operating the pin mill at a rotation speed of 300 to 20,000 rpm. Conditions for crushing the reactant using a disk mill include, for example, operating a pin mill at a rotation speed of 12 to 1200 rpm. By crushing the CAM after the secondary firing under such conditions, it is easy to control the first to third average aspect ratios, average envelope degree, and average circularity of the CAM within the above-mentioned ranges.

After performing the secondary firing, the CAM may be washed to remove residual unreacted lithium compounds and inert melting agents. For cleaning, pure water or alkaline cleaning liquid can be used. As the alkaline cleaning liquid, for example, an aqueous solution of one or more anhydrides and hydrates thereof selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate. can be mentioned. Moreover, ammonia water can also be used as an 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. By controlling the temperature of the cleaning liquid within the above range without freezing the cleaning liquid, excessive elution of lithium ions from the crystal structure of the CAM into the cleaning liquid during cleaning can be suppressed.

Examples of the method for bringing the cleaning liquid and the CAM into contact include a method of adding the CAM into each cleaning liquid and stirring the mixture. Alternatively, each cleaning liquid may be used as shower water and applied to the CAM. Furthermore, a method may be adopted in which the CAM is added to the cleaning liquid and stirred, the CAM is separated from each cleaning liquid, and then each cleaning liquid is used as shower water to be applied to the separated CAM.

In cleaning, it is preferable that the cleaning liquid and CAM are brought into contact for an appropriate period of time. The "appropriate time" in cleaning refers to the time required to disperse each particle of the CAM while removing the unreacted lithium compound and inert melting agent remaining on the surface of the CAM. The washing time is preferably adjusted depending on the aggregation state of CAM. For example, a preliminary experiment may be performed to set an appropriate washing time. The washing time is particularly preferably in the range of, for example, 5 minutes to 1 hour.

The proportion of CAM in 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 is more preferable. When the proportion of CAM is 10-60% by mass, unreacted lithium compounds and inert melting agents can be removed.

After cleaning the CAM, it is preferable to heat-treat the CAM. The temperature and method of heat treatment are not particularly limited, but from the viewpoint of preventing a decrease in charging capacity, the temperature is preferably 150°C or higher, more preferably 175°C or higher, and even more preferably 200°C or higher. Further, although there is no particular restriction, 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 this embodiment.
The amount of volatization of lithium ions can be controlled by the heat treatment temperature.

The upper and lower limits of the heat treatment temperature can be arbitrarily combined. 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 the heat treatment may be 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, the reaction between the CAM and the moisture or carbon dioxide in the atmosphere during the heat treatment is suppressed, and a CAM with less impurities can be obtained.

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

An example of a suitable lithium secondary battery using the CAM of this embodiment includes 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.

An example of a lithium secondary battery includes 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 band-shaped separators 1, a band-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a band-shaped negative electrode 3 having a negative electrode lead 31 at one end are placed between the separator 1, the positive electrode 2, and the separator. 1 and negative electrode 3 are laminated 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 bottom of the can is sealed, the electrode group 4 is impregnated with the electrolyte 6, and the electrolyte is placed between the positive electrode 2 and the negative electrode 3. . Furthermore, by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8, the lithium secondary battery 10 can be manufactured.

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

Further, 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 established by the International Electrotechnical Commission (IEC), or JIS C 8500 can be adopted. . For example, the shape may be cylindrical or square.

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

Each configuration will be explained in order below.
(positive electrode)
The positive electrode can be manufactured by first preparing a positive electrode mixture containing a CAM, a conductive material, and a binder, and then supporting the positive electrode mixture on a positive electrode current collector.

(conductive material)
A carbon material can be used as the conductive material included in 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 based on 100 parts by mass of CAM.

(binder)
A thermoplastic resin can be used as the binder included in the positive electrode. Examples of this thermoplastic resin include polyimide resins; fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) and polytetrafluoroethylene; polyolefin resins such as polyethylene and polypropylene; described in WO2019/098384A1 or US2020/0274158A1 The following resins can be mentioned.

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

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, and the resulting paste of the positive electrode mixture is applied to at least one side of the positive electrode current collector and dried. An example of this method is to perform an electrode pressing process to fix the electrode.

When the positive electrode mixture is made into a paste, an example of an organic solvent that can be used is 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 listed above.

(Negative electrode)
The negative electrode of a lithium secondary battery may be an electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector, as long as it is capable of doping and dedoping lithium ions at a potential lower than that of the positive electrode. Examples include electrodes made of a negative electrode active material alone.

(Negative electrode active material)
Examples of the negative electrode active material included in the negative electrode include carbon materials, chalcogen compounds (oxides or sulfides, etc.), nitrides, metals, or alloys, which can be doped and dedoped with lithium ions at a lower potential than the positive electrode. It will 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 fired bodies of organic polymer compounds.

Oxides that can be used as negative electrode active materials include silicon oxides 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 ;

Furthermore, examples of 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. Carbon materials whose main component is graphite, such as natural graphite or artificial graphite, are preferably used for reasons such as high cycle performance (good cycle characteristics). The shape of the carbon material may be, for example, flaky like natural graphite, spherical like mesocarbon microbeads, fibrous like graphitized carbon fiber, or aggregates of fine powder.

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

(Negative electrode current collector)
Examples of the negative electrode current collector included in the negative electrode include a band-shaped member made of a metal material such as Cu, Ni, or stainless steel.

The negative electrode mixture can be supported on such a negative electrode current collector, as in the case of the positive electrode, by pressure molding, by forming a paste using a solvent, applying it on the negative electrode current collector, or by pressing after drying. An example is a method of crimping.

(Separator)
The separator of the lithium secondary battery may be a porous membrane, nonwoven fabric, or woven fabric made of polyolefin resin such as polyethylene and polypropylene, fluororesin, or nitrogen-containing aromatic polymer. Can be used. Further, the separator may be formed using two or more of these materials, or may be formed by laminating these materials. Alternatively, a separator described in JP-A-2000-030686 or US20090111025A1 may be used.

(electrolyte)
The electrolytic solution of a lithium secondary battery contains an electrolyte and an organic solvent.

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

Further, 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 these, mixed solvents containing carbonates are preferred, and mixed solvents of cyclic carbonates and acyclic carbonates and mixed solvents of cyclic carbonates and ethers are more preferred.

Further, as the electrolytic solution, it is preferable to use an electrolytic solution containing a lithium salt containing fluorine such as LiPF ₆ and an organic solvent having a fluorine substituent, in order to increase the safety of the obtained lithium secondary battery. 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-state lithium secondary battery>
Next, while explaining the configuration of an all-solid-state lithium secondary battery, a positive electrode using a CAM according to one embodiment of the present invention and an all-solid-state lithium secondary battery having this positive electrode will be described.

FIG. 3 is a schematic diagram showing an example of the all-solid-state lithium secondary battery of this embodiment. The all-solid-state lithium secondary battery 1000 shown in FIG. 3 includes a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an exterior body 200 housing the laminate 100. Furthermore, the all-solid-state 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. A specific example of the bipolar structure is, for example, the structure described in JP-A-2004-95400. The materials constituting each member will be described later.

The laminate 100 may include 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, the all-solid-state lithium secondary battery 1000 may include a separator between the positive electrode 110 and the negative electrode 120.

The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the stacked body 100 and the exterior body 200 and a sealing body (not shown) that seals the opening 200a of the exterior body 200.

For the exterior body 200, a container made of a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel can be used. Further, as the exterior body 200, a container formed by processing a laminate film into a bag shape, which has been subjected to anti-corrosion treatment on at least one surface, can also be used.

Examples of the shape of the all-solid-state lithium secondary battery 1000 include a coin shape, a button shape, a paper shape (or sheet shape), a cylindrical shape, a square shape, and a laminate shape (pouch shape).

Although the all-solid-state lithium secondary battery 1000 is illustrated as having one laminate 100 as an example, 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 (the laminate 100) are sealed inside an exterior body 200.

Each configuration will be explained in order below.

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

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

(solid electrolyte)
As the solid electrolyte included in the CAM layer 111 of this embodiment, a solid electrolyte that has lithium ion conductivity and is used in known all-solid-state lithium secondary batteries can be used. Such solid electrolytes include inorganic electrolytes and organic electrolytes. Examples of the inorganic electrolyte include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hydride-based solid electrolytes. Examples of the organic electrolyte include polymer solid electrolytes. As each electrolyte, WO2020/208872A1, US2016/02335
10A1, US2012/0251871A1, and US2018/0159169A1, and examples thereof include the following compounds.

(Oxide solid electrolyte)
Examples of the oxide-based solid electrolyte include perovskite-type oxides, NASICON-type oxides, LISICON-type oxides, and garnet-type oxides. Specific examples of each oxide are WO2020/208872A1, US2016/0233510A1, US2
Examples include the compounds described in 020/0259213A1, including the following compounds.

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

Examples of the NASICON type oxide include Li _1+d Al _d Ti _2-d (PO ₄ ) ₃ (0≦d≦1). NASICON type oxide is Li _m M ¹ _n M ² _o P _p O _q (wherein M ¹ is from the group consisting of B, Al, Ga, In, C, Si, Ge, Sn, Sb and Se). One or more elements selected. ^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).

The LISICON type oxide is 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 , As, and one or more elements selected from the group consisting of V).

Examples of the garnet type oxide include Li-La-Zr-based oxides such as Li ₇ La ₃ Zr ₂ O ₁₂ (also referred to as LLZ).

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

(Sulfide solid electrolyte)
Sulfide-based solid electrolytes include Li ₂ S-P 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- Examples include Si ₂ S-P 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. I can do it.

In this specification, the expression "compound" referring to a sulfide-based solid electrolyte refers to a solid electrolyte mainly containing raw materials such as "Li ₂ S" and "P ₂ S ₅ " described before "compound". Used as a general term for For example, the Li ₂ S--P ₂ S _5- based compound includes a solid electrolyte that mainly contains Li ₂ S and P ₂ S ₅ and further contains other raw materials. The proportion of Li ₂ S contained in the Li ₂ SP ₂ S ₅ compound is, for example, 50 to 90% by mass based on the entire Li ₂ SP ₂ S ₅ compound. The proportion of P ₂ S ₅ contained in the Li ₂ SP ₂ S ₅ compound is, for example, 10 to 50% by mass based on the entire Li ₂ SP ₂ S ₅ compound. Further, the proportion of other raw materials contained in the Li ₂ S--P ₂ S ₅ -based compound is, for example, 0 to 30% by mass with respect to the entire Li ₂ S--P ₂ S ₅ -based compound. Furthermore, the Li ₂ S--P ₂ S _5- based compounds also include solid electrolytes in which the mixing ratio of Li ₂ S and P ₂ S ₅ is varied.

Examples of Li ₂ S-P ₂ S _5- based compounds include Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -LiBr, Li ₂ S-P ₂ S ₅ -LiI-LiBr, Li ₂ S-P ₂ S ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI and Li ₂ S- Examples include P ₂ S ₅ -Z _m S _n (m and n are positive numbers. Z is Ge, Zn or Ga).

Examples of Li ₂ S-SiS _2- based 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 -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiCl, Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-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 ).

Examples of the Li ₂ S-GeS _2- based compound 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 the polymer-based solid electrolyte include organic polymer electrolytes such as polyethylene oxide-based polymer compounds and polymer compounds containing one or more types selected from the group consisting of polyorganosiloxane chains and polyoxyalkylene chains. . Furthermore, a so-called gel type material in which a non-aqueous electrolyte is held in a polymer compound can also be used.

Two or more types 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) above can be used. Moreover, the ratio explained in the above-mentioned (electrically conductive material) can be similarly applied to the ratio of the conductive material in the positive electrode mixture. Further, as the binder included in the positive electrode, the material 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 (Positive electrode current collector) above can be used.

A method for supporting the CAM layer 111 on the positive electrode current collector 112 includes a method of pressure-molding the CAM layer 111 on the positive electrode current collector 112. Cold press or hot press can be used for pressure molding.

Further, a mixture of CAM, solid electrolyte, conductive material, and binder is made into a paste using an organic solvent to form a positive electrode mixture, and the resulting positive electrode mixture is applied onto 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 fixing the CAM layer 111 to the positive electrode current collector 112.

Further, the mixture of CAM, solid electrolyte, and conductive material is made into a paste using an organic solvent to form a positive electrode mixture, and the resulting positive electrode mixture is applied onto at least one surface of the positive electrode current collector 112, dried, and sintered. In this way, the CAM layer 111 may be supported on the positive electrode current collector 112.

As the organic solvent that can be used for the positive electrode mixture, the same organic solvent that can be used when making a paste of the positive electrode mixture explained in the above (positive electrode current collector) can be used.

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

The positive electrode 110 can be manufactured by the method listed above. Specific combinations of materials used for the positive electrode 110 include the CAM described in this embodiment and the combinations listed in Tables 1 to 3.

(Negative electrode)
The negative electrode 120 includes a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 includes a negative electrode active material. Further, the negative electrode active material layer 121 may include a solid electrolyte and a conductive material. As the negative electrode active material, negative electrode current collector, solid electrolyte, conductive material, and 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, a method of pressure molding, a method of applying a paste-like negative electrode mixture containing a negative electrode active material onto the negative electrode current collector 122, Examples include a method in which a paste-like negative electrode mixture containing a negative electrode active material is applied on the negative electrode current collector 122, dried, and then sintered.

(Solid electrolyte layer)
The solid electrolyte layer 130 includes 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 above-described positive electrode 110 by sputtering.

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

In the laminate 100, the negative electrode 120 is stacked on the solid electrolyte layer 130 provided on the positive electrode 110 using a known method so that the negative electrode active material layer 121 is in contact with the surface of the 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 maintenance rate of the lithium secondary battery can be improved.

Furthermore, since the positive electrode having the above configuration includes the CAM having the above-described configuration, it is possible to improve the cycle maintenance rate of the lithium secondary battery.

Furthermore, since the lithium secondary battery configured as described above has the above-described positive electrode, it becomes a secondary battery with a high cycle maintenance rate.

In another aspect, the present invention includes the following embodiments.
[1] A positive electrode active material for a lithium secondary battery having a layered structure, wherein the first average aspect ratio, which is the average aspect ratio of the positive electrode active material for a lithium secondary battery, is 0.760-0.998 or less. , a positive electrode active material for a lithium secondary battery, wherein the average degree of envelopment of the positive electrode active material for a lithium secondary battery is 0.983-0.998 or less.
[2] The positive electrode active material for a lithium secondary battery according to [1], wherein the average circularity of the positive electrode active material for a lithium secondary battery is 0.915-0.998 or less.
[3] 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, [ 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 size equal to or larger than the average particle size. Cathode active material for use.
[5] The positive electrode active material for a lithium secondary battery according to any one of [1] to [4], which is represented by formula (A).
Li [Li _x (Ni _(1-y-z) 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. It 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 a lithium secondary battery, comprising the positive electrode active material for a lithium secondary battery 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 Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited by the following description.

<Composition analysis>
The compositional analysis of the CAM manufactured by the method described below was performed by the method of "Compositional analysis of CAM" described above.

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

<Production of positive electrode for lithium secondary battery>
CAM obtained by the manufacturing method described below, 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 paste-like positive electrode mixture was prepared. When preparing the positive electrode mixture, NMP was used as an organic solvent.

The obtained positive electrode mixture was applied to a 40 μm thick Al foil serving 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 a glove box with an argon atmosphere.
Place the positive electrode for a lithium secondary battery prepared in <Preparation of a positive electrode for a lithium secondary battery> on the bottom cover of a coin-type battery R2032 part (manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down. A laminated film separator (a laminate with a thickness of 16 μm in which a heat-resistant porous layer was laminated on a polyethylene porous film) was placed on top. 300 μl of electrolyte was injected here. The electrolyte was a 16:10:74 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, in which LiPF ₆ was dissolved at a concentration of 1.3 mol/L and vinylene carbonate was dissolved at 1.0%. I used the one that I made.
Next, using metal lithium as the negative electrode, place the negative electrode on the upper side of the laminated film separator, cover the top with a gasket, and swage it with a crimping machine to form a lithium secondary battery (coin-type half cell R2032; hereinafter referred to as "coin-type"). (sometimes referred to as "half cell") was produced.

<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 maintenance rate" described above.

(Example 1)
After putting water into a reaction tank 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 mixed raw material solution was prepared by mixing a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and an aluminum sulfate aqueous solution so that the molar ratio of Ni, Co, and Al was 0.88:0.09:0.03.

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

Metal composite hydroxide 1 was maintained and heated at 650° C. for 5 hours in the air, and then cooled to room temperature to obtain metal composite oxide 1.

Lithium hydroxide was weighed so that the amount of Li (molar ratio) to the total amount of Ni, Co, and Al contained in the metal composite oxide 1 was 1.10. 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 rotary cylinder with an inner diameter of 300 mm, and the rotation speed was 0.67 rpm, the temperature inside the kiln was 690°C, and the mixture was kept in an oxygen-containing atmosphere for 2 hours to heat it. , Reactant 1 of metal composite oxide 1 and lithium hydroxide was obtained.

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

The crushed reaction product 1 was placed in a rotary kiln (manufactured by Tanabe Co., Ltd.) having a rotating cylinder with an inner diameter of 300 mm. The rotational speed was 0.67 rpm, the temperature in the firing furnace was 770° C., and the reactant 1 was fired by holding it in an oxygen-containing atmosphere for 2 hours to obtain a fired product 1.

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

A slurry prepared by mixing the crushed fired product 1 and pure water whose liquid temperature was adjusted to 5°C so that the ratio of the weight of the fired product to the total amount is 30% by mass 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 in the composition formula (A), x=0.04, y=0.089, and z=0.022, and 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) having a rotating cylinder with an inner diameter of 100 mm, the rotation speed was 1.08 rpm, the temperature inside the kiln was 680°C, and oxygen was added. The reaction product 2 was obtained by holding and heating the mixture for 2 hours in a containing atmosphere.

The obtained reaction product 2 was crushed using a disc mill (manufactured by Masuko Sangyo Co., Ltd., MKCA6-2) at 1200 rpm, and then crushed at 20000 rpm using a pin mill (manufactured by Mill System Co., Ltd., Impact Mill).

The crushed reaction product 2 was placed in a rotary kiln (manufactured by Noritake TCF) having a rotating cylinder with an inner diameter of 100 mm. The rotational speed was 1.08 rpm, the temperature in the firing furnace was 720° C., and the reaction product 2 was fired by holding it in an oxygen-containing atmosphere for 2 hours to obtain a fired product 2.

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

The crushed 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 in the composition formula (A), x=0.05, y=0.088, and z=0.023, and element X was Al.

(Comparative example 1)
Mixture 1 was obtained by the method described in Example 1. This mixture 1 was held in a firing furnace of a roller hearth kiln (manufactured by Noritake Company Limited) at 650°C for 5 hours in an oxygen-containing atmosphere to cause the mixture 1 to react with the metal composite oxide 1 and lithium hydroxide. Product C1 was obtained.

The obtained reaction product C1 was crushed using a disc mill (manufactured by Masuko Sangyo Co., Ltd., MKCA6-2) at 1200 rpm.

Next, the crushed reactant C1 was held at 720° C. for 6 hours in a roller hearth kiln (manufactured by Noritake Company Limited) to bake the reactant C1 to obtain a baked product C1.

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

The crushed calcined product C1 was washed, dehydrated, and heat treated by the method described in Example 1 to obtain CAM-C1.

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

(Comparative example 2)
After putting water into a reaction tank 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 mixed raw material solution was prepared by mixing a nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and an aluminum sulfate aqueous solution so that the molar ratio of Ni, Co, and Al was 0.885:0.09:0.025.

Next, this mixed raw material solution and an ammonium sulfate aqueous solution were continuously added as a complexing agent into the reaction tank while stirring. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the solution in the reaction tank became 11.6 (measurement temperature: 40° C.) to obtain a reaction precipitate 2.

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 maintained and heated at 650° C. for 5 hours in the air, and then cooled to room temperature to obtain the metal composite oxide C2.

Lithium hydroxide was weighed so that the amount of Li (molar ratio) to the total amount of Ni, Co, and Al contained in the metal composite oxide C2 was 1.10. Metal composite oxide C2 and lithium hydroxide were mixed in a mortar to obtain mixture C2.

CAM-C2 was obtained by carrying out the same method as in Comparative Example 1 except that this mixture C2 was used.

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

The CAMs obtained in Examples 1 and 2 and Comparative Examples 1 and 2 all had a layered structure.
Firing conditions for CAM of Examples 1 to 2 and Comparative Examples 1 to 2, first average aspect ratio, average degree of envelope, average particle size, particle size distribution, second average aspect ratio - first average aspect ratio, first average aspect Table 4 shows the third average aspect ratio, average circularity, and cycle retention rate of the coin-shaped half cell using each CAM.

In the firing process of Examples 1 and 2, a rotary kiln was used for primary firing and secondary firing. Further, when the inner diameter of the rotary cylinder was 300 mm, the firing conditions were adjusted to 0.67 rpm, and when the inner diameter of the rotary cylinder was 100 mm, the firing conditions were adjusted to 1.08 rpm. Such a CAM had a first average aspect ratio of 0.755-1.000 or less and an average degree of envelope of 0.983-1.000. Furthermore, the cycle maintenance rate of the coin-shaped half cell using CAM-1 and 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 degree of envelope did not satisfy the above range. This is thought to be because the mixture did not flow during firing and force was not applied isotropically to the secondary particles.

The cycle maintenance rate of the coin-shaped half cell using the above CAM-C1 to CAM-C2 was 87.9% or less.

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 with a high cycle maintenance 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... Electrolyte, 7... Top insulator, 8... Sealing body, 10... Lithium secondary battery, 21... Positive electrode lead, 31 ...Negative electrode lead, 100... Laminate, 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 (7)

A positive electrode active material for a lithium secondary battery having a layered structure,
A first average aspect ratio, which is an aspect ratio of the positive electrode active material for a lithium secondary battery determined from an image of the positive electrode active material for a lithium secondary battery, is 0.755 or more and 1.000 or less, and the lithium secondary battery The average degree of envelopment of the positive electrode active material for lithium secondary batteries is 0.983 or more and 1.000 or less, and (D ₁₀₀ −D ₀ ) of the positive electrode active material for lithium secondary batteries is 10 μm or more and 60 μm or less,
The image of the positive electrode active material for a lithium secondary battery is an image of 200 or more of the positive electrode active material for a lithium secondary battery obtained using a static automatic image analyzer,
The D ₁₀₀ is the particle diameter of the largest particle of the positive electrode active material for a lithium secondary battery included in the image,
The D ₀ is the smallest particle diameter of the positive electrode active material for a lithium secondary battery included in the image,
A positive electrode active material for a lithium secondary battery represented by formula (A).
Li [Li _x (Ni _(1-y-z) 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. It is an element and satisfies -0.1≦x≦0.2, 0≦y≦0.4, 0≦z≦0.5, and y+z<1.) The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average circularity of the positive electrode active material for a lithium secondary battery is 0.910 or more and 1.000 or less. 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. A second average aspect ratio, which is an aspect ratio of particles having a particle size smaller than an 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. The positive electrode active material for a lithium secondary battery as described above. 5. 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 a third average aspect ratio that is an aspect ratio of particles having a particle size larger than or equal to the average particle size. material. A positive electrode for a lithium secondary battery, comprising the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 6.

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