Method for manufacturing positive electrode active material for lithium secondary battery

Abstract

To provide a method for manufacturing a positive electrode active material for a lithium secondary battery with high initial charge capacity and initial charge / discharge efficiency.SOLUTION: A method for manufacturing a positive electrode active material for a lithium secondary battery includes the steps of obtaining a slurry containing a lithium metal composite oxide containing at least Li and Ni, performing solid-liquid separation of the slurry to obtain a first wet cake, crushing the first wet cake to obtain a second wet cake having a shortest dimension of 10 mm or less, maintaining the second wet cake in an atmosphere having a carbon dioxide concentration of 400 ppm or less to obtain a third wet cake, and heat-treating the third wet cake at 500°C or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery. [Background technology]

[0002] The positive electrode constituting the lithium secondary battery contains a positive electrode active material for lithium secondary batteries. The method for producing a positive electrode active material for a lithium secondary battery includes a raw material mixing step and a calcination step. In the method for producing a positive electrode active material for a lithium secondary battery, the lithium metal composite oxide obtained after calcination is further washed with water or the like to remove lithium compounds and the like that remain unreacted during calcination.

[0003] For example, Patent Document 1 describes a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which includes a step of calcining a lithium metal composite oxide of a specific composition, and then stirring and washing the calcined lithium metal composite oxide with 50 to 200 parts by weight of water per 100 parts by weight of the lithium metal composite oxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP-A-2007-242288 Summary of the Invention [Problem to be solved by the invention]

[0005] The lithium metal composite oxide after washing is in a slurry state, and the water is removed from the slurry by heat treatment or the like to dry it. However, if the amount of liquid contained in the slurry subjected to heat treatment is large, the surface of the slurry will dry, but the inside of the slurry may not dry sufficiently. As a result, the crystallinity and composition of the resulting positive electrode active material for lithium secondary batteries will be non-uniform, causing a decrease in the initial charge capacity and initial charge / discharge efficiency of the lithium secondary battery.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery that has a high initial charge capacity and a high initial charge-discharge efficiency. [Means for solving the problem]

[0007] One aspect of the present invention includes [1] to [9]. [1] A method for producing a positive electrode active material for a lithium secondary battery, comprising: a step of obtaining a slurry containing a lithium metal composite oxide containing at least Li and Ni; a step of performing solid-liquid separation of the slurry to obtain a first wet cake; a step of crushing the first wet cake to obtain a second wet cake having a shortest dimension of 10 mm or less; a step of maintaining the second wet cake in an atmosphere having a carbon dioxide concentration of 400 ppm or less to obtain a third wet cake; and a step of heat-treating the third wet cake at 500°C or less. [2] The method for producing a positive electrode active material for a lithium secondary battery according to [1], wherein the water content of the positive electrode active material for a lithium secondary battery is 1% by mass or more and 15% by mass or less, based on the total mass of the positive electrode active material for a lithium secondary battery. [3] The method for producing a positive electrode active material for a lithium secondary battery according to [1] or [2], wherein the step of obtaining the slurry includes a washing step of mixing and stirring the lithium metal composite oxide with a washing solution. [4] The method for producing a positive electrode active material for a lithium secondary battery according to [3], wherein the temperature of the cleaning solution in the cleaning step is less than 10°C. [5] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [1] to [4], wherein the step of obtaining the first wet cake is a step of obtaining a first wet cake by feeding a solution containing element M2 to a solid-liquid separated product obtained by solid-liquid separation of the slurry, and the element M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P. [6] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [1] to [5], wherein the dew point of the atmosphere is −30° C. or lower. [7] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [1] to [6], wherein the atmosphere contains oxygen. [8] The method for producing a positive electrode active material for a lithium secondary battery according to any one of [1] to [7], wherein the heat treatment is performed once in the heat treatment step. [Effects of the Invention]

[0008] According to the above aspect, it is possible to provide a method for producing a positive electrode active material for a lithium secondary battery that has a high initial charge capacity and a high initial charge / discharge efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart showing steps from a slurry production step to a heat treatment step in one embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of a lithium secondary battery. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of an all-solid-state lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0010] The metal composite compound according to one aspect of the present invention will be described below. Preferred examples and conditions may be shared among the following embodiments. In this specification, each term is defined as follows.

[0011] In this specification, metal composite compound will be referred to as "MCC", lithium metal composite oxide will be referred to as "LiMO", and cathode active material for lithium secondary batteries will be referred to as "CAM".

[0012] "Ni" refers to nickel atoms, not nickel metal. Similarly, "Li" and "Al" refer to lithium atoms and aluminum atoms, respectively. The lithium secondary battery refers to a lithium ion secondary battery.

[0013] For example, when a numerical range is described as "1-10 μm" or "1 to 10 μm," it means a range from 1 μm to 10 μm, including the lower limit of 1 μm and the upper limit of 10 μm. The upper and lower limits of the numerical range can be combined arbitrarily. Furthermore, the mutual numerical ranges for the respective physical properties, compositions, manufacturing conditions, etc. can be combined arbitrarily.

[0014] The "composition analysis of CAM" is performed by the following method. For example, CAM powder is dissolved in hydrochloric acid, and then the composition is measured using an ICP optical emission spectrometer. For example, an Optima 7300 manufactured by PerkinElmer Co., Ltd. can be used as the ICP optical emission spectrometer.

[0015] In this specification, "high initial charge capacity" means an initial charge capacity of 223.0 mAh / g or more, and "high initial charge / discharge efficiency" means an initial charge / discharge efficiency of 91.0% or more.

[0016] [Preparation of positive electrodes for lithium secondary batteries] A paste-like positive electrode mixture is prepared by mixing CAM, a conductive material (acetylene black), and a binder (PVdF) in a mass ratio of CAM:conductive material:binder = 92:5:3. N-methyl-2-pyrrolidone is used as the organic solvent when preparing the positive electrode mixture.

[0017] The resulting positive electrode mixture is applied to a 40 μm thick Al foil as a current collector and dried in a vacuum at 150°C for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of ​​this positive electrode for a lithium secondary battery is 1.65 cm2. 2 Let's say.

[0018] [Fabrication of lithium secondary batteries] Perform the following operations inside a glove box under an argon atmosphere. Place the above-mentioned positive electrode for a lithium secondary battery with the aluminum foil side facing down on the lower lid of parts for a coin-type battery R2032 (manufactured by Takizawa Co., Ltd.), and place a separator (porous film made of polypropylene, thickness 25 μm) on top of it. Inject 300 μl of an electrolytic solution here. The electrolytic solution used is a liquid in which LiPF6 is dissolved to a concentration of 1 mol / l in a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate mixed at a volume ratio of 30:35:35.

[0019] Next, use metallic lithium as the negative electrode, place it above the separator, cover it with an upper lid through a gasket, and crimp it with a crimping machine to fabricate a lithium secondary battery (coin-type half cell R2032).

[0020] [Charge and Discharge Test] Leave the lithium secondary battery fabricated above at room temperature for 12 hours to sufficiently impregnate the separator and the positive electrode mixture with the electrolytic solution.

[0021] Next, set the current set value to 0.2 CA both for charging and discharging at room temperature, and perform constant current constant voltage charging and constant current discharging respectively. The maximum charging voltage is 4.3 V, and the minimum discharging voltage is 2.5 V. Measure the charging capacity, and take the obtained value as the "initial charging capacity" (mAh / g). Further, measure the discharging capacity, and take the obtained value as the "initial discharging capacity" (mAh / g).

[0022] Calculate the initial charge-discharge efficiency using the following formula (1) from the above-mentioned initial charging capacity and initial discharging capacity. The higher the initial charge-discharge efficiency, the higher the utilization efficiency of CAM, which means it is desirable as battery performance. Initial charge-discharge efficiency (%) = Initial discharging capacity (mAh / g) / Initial charging capacity (mAh / g) × 100 …(1)

[0023] [Manufacturing Method of CAM The method for manufacturing a CAM includes a step of obtaining a slurry containing LiMO containing at least Li and Ni (hereinafter sometimes referred to as a slurry manufacturing step), a step of performing solid-liquid separation on the slurry to obtain a first wet cake (hereinafter sometimes referred to as a first wet cake manufacturing step), a step of crushing the first wet cake to obtain a second wet cake having a shortest dimension of 10 mm or less (hereinafter sometimes referred to as a second wet cake manufacturing step), a step of holding the second wet cake in an atmosphere having a carbon dioxide concentration of 400 ppm or less to obtain a third wet cake (hereinafter sometimes referred to as a holding step), and a step of heat-treating the third wet cake at 500°C or lower (hereinafter sometimes referred to as a heat treatment step).

[0024] LiMO is obtained by firing a mixture of MCC and a lithium compound. First, the method for manufacturing MCC will be described below.

[0025] (1) Method for manufacturing MCC MCC may be any of a metal composite hydroxide, a metal composite oxide, and a mixture thereof. MCC contains at least Ni. As an example, MCC contains Ni and M1 in a molar ratio represented by the following formula (A'), and is represented by the following formula (A''). Ni:M1=(1-x):x (A')[[]]END]] Ni (1-x) M1 x O α (OH)[[]]END]] 2-β (A'')[[]]END]] (In formula (A') and formula (A''), M1 is one or more elements selected from the group consisting of Co, Mn, and Al, and preferably satisfies 0 < x ≦ 0.3. Formula (A'') preferably satisfies 0 ≦ α ≦ 3, -0.5 ≦ β ≦ 2, and β - α < 2.)

[0026] Hereinafter, as an example, the method for manufacturing MCC containing Ni and M1 will be described. First, a metal composite hydroxide containing Ni and M1 is manufactured. The metal composite hydroxide can be manufactured by a batch-type coprecipitation method or a continuous-type coprecipitation method.

[0027] For example, a continuous coprecipitation method described in JP-A-2002-201028 involves reacting a nickel salt solution with a metal salt solution of M1 to form Ni (1-x) M1 x A metal complex hydroxide represented by (OH)2 is produced.

[0028] As the nickel salt that is the solute of the nickel salt solution, for example, at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used.

[0029] Examples of the metal salt solution of M1 include an aluminum salt solution, a cobalt salt solution, and a manganese salt solution. As the aluminum salt, which 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.

[0030] 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.

[0031] As the manganese salt that is the solute of the manganese salt solution, for example, at least one of manganese sulfate, manganese nitrate, and manganese chloride can be used.

[0032] The nickel salt solution and the metal salt solution of M1 are used in a mixed solution containing them such that the molar ratio of Ni to M1 corresponds to the above formula (A'), and water is used as the solvent.

[0033] The complexing agent is capable of forming a complex with nickel ions and ions of M1 in an aqueous solution, and examples thereof include ammonium ion donors (ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

[0034] 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 metal salt solution of M1, and the complexing agent is, for example, such that the molar ratio of the amount of the complexing agent to the total number of moles of the metal salts (nickel salt and metal salt of M1) is greater than 0 and less than or equal to 2.0.

[0035] In the co-precipitation method, an aqueous solution of an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, is added to the mixture before the pH of the mixture changes from alkaline to neutral in order to adjust the pH of the mixture.

[0036] The pH value in this specification is defined as the value measured when the temperature of the mixed solution 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 sampled mixed solution is not at 40°C, the mixed solution is heated or cooled to 40°C and then the pH is measured.

[0037] During the reaction, the temperature of the reaction vessel is controlled within the range of, for example, 20 to 80°C, preferably 30 to 70°C.

[0038] During the reaction, the pH value of the mixture in the reaction vessel is controlled within the range of, for example, 10-13, preferably 10-12, and the pH fluctuation is controlled within ±0.5.

[0039] The reaction vessel used in the continuous coprecipitation method can be an overflow type reaction vessel in order to separate the formed reaction precipitate.

[0040] When a metal composite hydroxide is produced by a batch coprecipitation method, examples of the reaction tank include a reaction tank without an overflow pipe and an apparatus having a mechanism for concentrating the overflowed reaction precipitate in a concentration tank connected to an overflow pipe and circulating it back to the reaction tank.

[0041] Various gases, for example, inert gases such as nitrogen, argon, or carbon dioxide, oxidizing gases such as air or oxygen, or a mixture thereof may be supplied into the reaction vessel.

[0042] After the reaction, the resulting reaction precipitate is washed and isolated, for example, by dehydrating the slurry containing the reaction precipitate by centrifugation or suction filtration.

[0043] The isolated reaction precipitate is dried and sieved appropriately to obtain a metal composite hydroxide containing Ni and M1.

[0044] The reaction precipitate is preferably washed with water or an alkaline washing solution, more preferably with an alkaline washing solution, and even more preferably with an aqueous sodium hydroxide solution. Alternatively, the reaction precipitate may be washed with a washing solution containing sulfur. Examples of the washing solution containing sulfur include aqueous solutions of potassium or sodium sulfate.

[0045] When MCC is a metal composite oxide, the metal composite hydroxide is heated to produce the metal composite oxide. If necessary, the metal composite hydroxide may be heated multiple times. In this specification, the heating temperature refers to the set temperature of the heating device. When heating multiple times, the heating temperature refers to the temperature at which the metal composite oxide is heated at the highest temperature.

[0046] The heating temperature is preferably 400 to 700° C., more preferably 450 to 680° C. When the heating temperature is 400 to 700° C., the metal composite hydroxide is sufficiently oxidized.

[0047] The time for maintaining the heating temperature is, for example, 0.1 to 20 hours, preferably 0.5 to 10 hours. The rate of temperature increase to the heating temperature is, for example, 50 to 400°C / hour. The heating atmosphere can be air, oxygen, nitrogen, argon, or a mixture thereof.

[0048] The interior of the heating device may be an atmosphere containing a moderate amount of oxygen. The oxygen-containing atmosphere may be a mixed gas atmosphere of an inert gas and oxygen, or may be an inert gas atmosphere in the presence of an oxidizing agent. By providing an atmosphere containing a moderate amount of oxygen inside the heating device, the transition metal contained in the metal composite hydroxide is oxidized appropriately, making it easier to control the morphology of the metal composite oxide.

[0049] The oxygen or oxidizing agent in the oxygen-containing atmosphere should have enough oxygen atoms to oxidize the transition metal.

[0050] When the oxygen-containing atmosphere is a mixed gas atmosphere of an inert gas and oxygen, the atmosphere in the heating device can be controlled by a method such as passing oxygen through the heating device or bubbling oxygen into the mixed liquid.

[0051] As the oxidizing agent, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, ozone, or the like can be used.

[0052] MCC can be produced by the above steps.

[0053] (2) Mixing MCC with lithium compounds Next, the lithium compound and MCC are mixed to obtain a mixture.

[0054] The lithium compound may be at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride, and lithium fluoride. Of these, either lithium hydroxide or lithium carbonate, or a mixture thereof, is preferred.

[0055] The lithium compound and MCC are mixed in consideration of the composition ratio of the final target product to obtain a mixture. The amount (molar ratio) of Li contained in the lithium compound relative to the total amount of metal elements contained in MCC is preferably 1.00 or more, more preferably 1.02 or more, and even more preferably 1.05 or more.

[0056] (3) Firing the mixture LiMO can be obtained by firing a mixture of MCC and a lithium compound. The firing may include multiple firing stages with different firing temperatures. For example, pre-firing and main firing, which is performed at a higher temperature than the pre-firing, may be performed independently. Furthermore, firing stages with different firing temperatures and firing times may be performed. Furthermore, after the main firing, post-firing, which is performed at a temperature lower than the main firing, may be performed.

[0057] In this specification, the firing temperature refers to the temperature of the atmosphere in the firing furnace and also refers to the highest temperature maintained during firing (hereinafter sometimes referred to as the highest maintained temperature). When there are multiple firing stages, the firing temperature refers to the temperature of the stage at which firing is performed at the highest maintained temperature among the firing stages.

[0058] The firing temperature is preferably 600-1100°C. The firing temperature during the main firing is preferably 700°C or higher, more preferably 700-1100°C. When the firing temperature is 700°C or higher, LiMO having a strong crystal structure can be obtained. When the firing temperature is 1100°C or lower, the volatilization of lithium ions on the particle surface can be reduced.

[0059] The holding time during firing is preferably 1 to 50 hours. If the holding time during firing is 1 hour or more, the reaction between unreacted MCC in the reactant and the lithium compound can be sufficiently enhanced. If the holding time during firing is 50 hours or less, volatilization of lithium ions is unlikely to occur, improving battery performance.

[0060] The mixture of MCC and a lithium compound may be calcined in the presence of an inert flux. The inert flux may remain in the calcined product or may be removed by washing with a cleaning solution after calcination, as described below. Examples of inert fluxes that can be used include those described in WO2019 / 177032A1.

[0061] After firing, the mixture may be crushed as needed. By the above steps, LiMO containing at least Li and Ni is obtained.

[0062] The steps from the slurry production step to the heat treatment step will be described below with reference to Fig. 1. Fig. 1 is a flowchart showing the steps from the slurry production step to the heat treatment step in one embodiment of the present invention. The LiMO described above is treated in the following order: a slurry production step 41, a first wet cake production step 42, a second wet cake production step 43, a holding step 44, and a heat treatment step 45.

[0063] (4) Slurry manufacturing process The slurry production process preferably includes a washing step in which the LiMO and a washing solution are mixed and stirred. The washing solution may be water or an alkaline washing solution. Examples of the alkaline washing solution include an aqueous solution of one or more anhydrides or hydrates thereof selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate. Ammonia water may also be used as the alkaline washing solution.

[0064] The temperature of the cleaning solution is preferably less than 10° C., more preferably not more than 8° C., and even more preferably not more than 5° C. By controlling the temperature of the cleaning solution within the above range so that the cleaning solution does not freeze, excessive elution of lithium ions from the crystal structure of LiMO into the cleaning solution during cleaning can be suppressed, and a CAM with high initial charge capacity and initial charge / discharge efficiency can be obtained.

[0065] Methods for mixing and stirring the cleaning solutions with LiMO include adding LiMO to each cleaning solution and stirring, showering each cleaning solution onto the LiMO, and adding LiMO to each cleaning solution and stirring, then separating the LiMO from each cleaning solution, and then showering each cleaning solution onto the separated LiMO.These methods may also be combined to perform the cleaning step.

[0066] In the cleaning process, it is preferable to mix and stir the cleaning solution and LiMO for an appropriate time. The "appropriate time" in the cleaning process refers to a time sufficient to disperse the individual particles of LiMO while removing unreacted lithium compounds and inert fluxing agents remaining on the surface of the LiMO. The cleaning time is preferably adjusted depending on the aggregation state of the LiMO. The cleaning time is more preferably in the range of 5 minutes to 1 hour.

[0067] The proportion of LiMO relative to the total mass of the slurry is preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably greater than 30% by mass. The proportion of LiMO relative to the total mass of the slurry is preferably 70% by mass or less, more preferably 65% ​​by mass or less. Examples of the proportion of LiMO relative to the total mass of the slurry include 5-70% by mass, 20-65% by mass, and greater than 30% by mass but not greater than 65% by mass. When the proportion of LiMO is within the above range, unreacted lithium compound and inactive fluxing agent can be removed, resulting in a CAM with high initial charge capacity and initial charge / discharge efficiency.

[0068] (5) First wet cake manufacturing process

[0069] In the first wet cake production step 42, the slurry obtained in the slurry production step 41 is subjected to solid-liquid separation to obtain a first wet cake. Preferably, in the first wet cake production step 42, a solution containing element M2 is transferred to the solid-liquid separated product obtained by solid-liquid separation of the slurry to obtain a first wet cake. Examples of devices used during solid-liquid separation and liquid transfer include a filter press, a suction filtration device, a pressure filtration device, and a centrifuge. The atmosphere during solid-liquid separation and liquid transfer is not particularly limited, and examples include air atmosphere, oxygen atmosphere, and the like.

[0070] With regard to the solution containing the element M2, the element M2 may be one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P. From the viewpoint of obtaining a lithium secondary battery with high initial charge-discharge efficiency, the element M2 is preferably one or more elements selected from the group consisting of Ti, Mg, Mo, Nb, Zr, B, Si, and S. The solution containing the element M2 is, for example, an aqueous solution of a compound containing the element M2. Examples of compounds containing the element M2 include oxides of the element M2 and compounds containing the element M2 and Li, such as titanium oxide, magnesium oxide, molybdenum oxide, niobium oxide, zirconium oxide, boron oxide, silicon dioxide, lithium molybdate, lithium borate, lithium niobate, lithium titanate, lithium silicate, and lithium sulfate. The molar concentration of element M2 in the solution containing element M2 is preferably 0.05 mol% or more, more preferably 0.1 mol% or more, and even more preferably 0.2 mol% or more. The molar concentration of element M2 in the solution containing element M2 is preferably 2.0 mol% or less, more preferably 1.5 mol% or less, and even more preferably 1.0 mol% or less. Examples of the molar concentration of element M2 in the solution containing element M2 include 0.05-2.0 mol%, 0.1-1.5 mol%, 0.1-1.0 mol%, and 0.2-1.0 mol%. By transferring the solution containing element M2, a CAM with high initial charge capacity and initial charge / discharge efficiency can be obtained.

[0071] The shape of the first wet cake obtained in the first wet cake production step 42 may vary widely. The shortest dimension of the first wet cake is preferably 0.1 mm or more and 30 mm or less. The shortest dimension of the first wet cake is, for example, 0.1 to 30 mm. When the shortest dimension of the first wet cake is within the above range, a second wet cake having the desired shortest dimension is easily obtained in the second wet cake production step described below, and as a result, a CAM with high initial charge capacity and initial charge / discharge efficiency can be obtained.

[0072] (6) Second wet cake manufacturing process In the second wet cake production step 43, the first wet cake is crushed to obtain a second wet cake having a shortest dimension of 10 mm or less. The crushing device used to crush the first wet cake may be, for example, a roll mill, a jaw crusher, or a hammer mill. The atmosphere in which the crushing is carried out is not particularly limited, and examples thereof include an atmosphere having a carbon dioxide concentration of 400 ppm or less, an air atmosphere, or a vacuum atmosphere, but an atmosphere having a carbon dioxide concentration of 400 ppm or less is preferred. Note that the carbon dioxide concentration (unit: ppm = cm 3 / m 3 ) is a certain atmosphere 1m 3 The volume of carbon dioxide contained in the 3 ) is shown. The dew point of the atmosphere in which the crushing is performed is preferably −30° C. or lower, more preferably −35° C. or lower, even more preferably −40° C. or lower, and particularly preferably −50° C. or lower. The lower limit of the dew point of the atmosphere in which the crushing is performed is not particularly limited, and may be, for example, −80° C. The dew point of the atmosphere in which the crushing is performed may be, for example, −80 to −30° C., −80 to −35° C., or −80 to −40° C. In an atmosphere having a carbon dioxide concentration and a dew point within the above ranges, Li on the surface of the second wet cake obtained after crushing is less likely to react with carbon dioxide and moisture, and loss of Li in the CAM can be prevented, resulting in a CAM with a high initial charge capacity and initial charge / discharge efficiency.

[0073] The shortest dimension of the second wet cake is preferably 8 mm or less, more preferably 5 mm or less. When the shortest dimension of the second wet cake is 10 mm or less, preferably the above upper limit or less, liquid is likely to evaporate uniformly from the second wet cake in the subsequent holding step, and uniform heat treatment is likely to be performed in the heat treatment step described below. Therefore, a CAM with high initial charge capacity and initial charge / discharge efficiency can be obtained. The shortest dimension of the second wet cake is preferably 0.1 mm or more. When the shortest dimension of the second wet cake is 0.1 mm or more, this has the effect of preventing unnecessary evaporation of liquid from the second wet cake. Examples of the shortest dimension of the second wet cake include 0.1-10 mm, 0.1-8 mm, and 0.1-5 mm. When the shortest dimension of the second wet cake is within the above range, a CAM with high initial charge capacity and initial charge / discharge efficiency can be obtained.

[0074] In this specification, the "shortest dimension of the wet cake" is defined as a value measured by the following method. When the length, width, and height of the wet cake are defined as the x-axis, y-axis, and z-axis, respectively, planar images of at least three planes, the xy plane, the yz plane, and the xz plane, are obtained. For each planar image of the wet cake, the shortest dimension passing through the center of gravity of the planar image is measured. Of the shortest dimensions determined for each planar image, the shortest dimension is defined as the shortest dimension of the wet cake.

[0075] (7) Holding process The second wet cake is transported from the disintegrator to a holding tank via a transport device. In the holding step 44, the second wet cake is held in the holding tank in an atmosphere with a carbon dioxide concentration of 400 ppm or less to obtain a third wet cake. Note that the second wet cake may also be held in an atmosphere with a carbon dioxide concentration of 400 ppm or less while being transported by the transport device.

[0076] The carbon dioxide concentration in the atmosphere during the holding step is preferably 100 ppm or less, more preferably 50 ppm or less. When the carbon dioxide concentration in the atmosphere is 400 ppm or less, preferably below the upper limit, Li on the surface of the second wet cake is less likely to react with carbon dioxide, preventing Li loss. Therefore, a CAM with a high initial charge capacity and initial charge-discharge efficiency can be obtained. The carbon dioxide concentration in the atmosphere during the holding step is preferably 0 ppm or more, more preferably 10 ppm or more. When the carbon dioxide concentration in the atmosphere during the holding step is 0 ppm or more, the device can be operated stably. Examples of the carbon dioxide concentration in the atmosphere during the holding step include 0-400 ppm, 0-100 ppm, and 10-100 ppm. When the carbon dioxide concentration in the atmosphere during the holding step is within the above range, a CAM with a high initial charge capacity and initial charge-discharge efficiency can be obtained.

[0077] The time for which the second wet cake is held in the atmosphere is preferably 15 hours or less, more preferably 10 hours or less, and even more preferably 2 hours or less. When the time for which the second wet cake is held in the atmosphere is equal to or less than the upper limit, a third wet cake can be obtained in which the liquid has evaporated to such an extent that LiMO does not scatter in the subsequent heat treatment step.

[0078] Furthermore, the time for which the second wet cake is maintained in the atmosphere is preferably 0.3 hours or more, more preferably 0.5 hours or more, and even more preferably 1 hour or more. When the time for which the second wet cake is maintained in the atmosphere is equal to or greater than the above lower limit, the liquid evaporates from the second wet cake appropriately, thereby reducing the difference in Li distribution on the surface of the resulting CAM. The time for which the second wet cake is maintained in the atmosphere can be, for example, 0.3-2 hours, 0.5-2 hours, or 1-2 hours.

[0079] The dew point of the atmosphere during the holding step is preferably -30°C or lower, more preferably -35°C or lower, even more preferably -40°C or lower, and particularly preferably -50°C or lower. When the dew point of the atmosphere during the holding step is -30°C or lower, performance degradation caused by contact of the second wet cake with moisture in the atmosphere can be suppressed, and a CAM with high initial charge capacity and initial charge-discharge efficiency can be obtained. The lower limit of the dew point of the atmosphere during the holding step is not particularly limited, and can be, for example, -80°C. The dew point of the atmosphere during the holding step can be, for example, -80 to -30°C, -80 to -35°C, or -80 to -40°C.

[0080] The atmosphere in the maintaining step preferably contains oxygen. The atmosphere in the maintaining step may be a mixed gas atmosphere of an inert gas and oxygen, or may be an inert gas atmosphere in the presence of an oxidizing agent. When the atmosphere in the maintaining step contains oxygen, it is possible to suppress excessive evaporation of the liquid and also suppress a decrease in the initial charge capacity of the CAM.

[0081] When the atmosphere in the holding step contains oxygen, the oxygen concentration is not particularly limited as long as the carbon dioxide concentration in the atmosphere satisfies the above condition.

[0082] The oxygen concentration is 1 x 10 4 ~100×10 4 ppm is preferred, and 10×10 4 ~25×10 4 More preferably, it is ppm.

[0083] When the atmosphere in the holding step is a mixed gas atmosphere of an inert gas and oxygen, the atmosphere in the heating device can be controlled by a method such as passing oxygen through the heating device or bubbling oxygen into the mixed liquid.

[0084] As the oxidizing agent, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, ozone, or the like can be used.

[0085] (8) Heat treatment process The third wet cake is transported to a heat treatment device via a transport device. In heat treatment step 45, the third wet cake is heat-treated at 500°C or less in the heat treatment device. The third wet cake is preferably maintained in an atmosphere with a carbon dioxide concentration of 400 ppm or less even during transport between the holding tank and the heat treatment device. The heat treatment device is not particularly limited, and examples thereof include a fluidized bed dryer, a tray dryer, a continuous dryer, a vacuum dryer, and a vibration dryer.

[0086] The temperature at which the third wet cake is heat-treated (heat treatment temperature) is preferably 450°C or lower, and more preferably 400°C or lower, from the viewpoint of preventing a decrease in the initial charge capacity. From the viewpoint of preventing a decrease in the initial charge capacity, the heat treatment temperature is preferably 100°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher. Examples of heat treatment temperatures include 100-500°C, 130-450°C, and 150-400°C. A heat treatment temperature within the above range can produce a CAM with a high initial charge capacity and initial charge-discharge efficiency. The heat treatment temperature refers to the set temperature of the heat treatment device. The heat treatment time at the heat treatment temperature is preferably 0.1 hours or more, more preferably 0.3 hours or more, even more preferably 1 hour or more, and is preferably 50 hours or less, for example, 0.1 to 50 hours, 0.3 to 50 hours, or 1 to 50 hours.

[0087] Regarding the number of heat treatments in the heat treatment step 45, if one cycle is defined as raising the temperature to a set heat treatment temperature, maintaining the temperature, and lowering the temperature, the number of heat treatments in the heat treatment step 45 is preferably one. Note that if heat treatment is performed at a certain set temperature and then at another set temperature without lowering the temperature, the number of heat treatments is calculated as two. For example, if heat treatment is performed for a predetermined time at a set temperature of 100°C, and then the set temperature is changed to 200°C and heat treatment is performed, the number of heat treatments is defined as two. By performing heat treatment once in the heat treatment step 45, excessive thermal load on the third wet cake can be prevented, and a CAM with high initial charge capacity and initial charge / discharge efficiency can be obtained.

[0088] 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 in such an atmosphere, the reaction between the CAM and moisture or carbon dioxide in the atmosphere during the heat treatment is suppressed, and the CAM with few impurities can be obtained.

[0089] The moisture content of the resulting CAM is preferably 1% by mass or more, more preferably 3% by mass or more, based on the total mass of the CAM. The moisture content of the CAM is preferably 15% by mass or less, more preferably 11% by mass or less. Examples of the moisture content of the CAM include 1-15% by mass or 3-11% by mass. When the moisture content of the CAM is within the above range, the third wet cake can be uniformly heat-treated in the heat treatment step. As a result, the variation in Li present on the surface of the resulting CAM can be suppressed, and the initial discharge capacity and initial charge / discharge efficiency can be improved. The moisture content of the CAM can be measured using an infrared moisture meter. For example, the FD-610 manufactured by Kett Electric Laboratory can be used. The moisture content of the CAM can be adjusted by adjusting the various conditions in the above-mentioned CAM production method (particularly, the holding time in the holding step and the dew point of the atmosphere).

[0090] According to the above-described method for producing a CAM, it is possible to produce a CAM having improved crystallinity and composition uniformity, and having a high initial charge capacity and initial charge-discharge efficiency.

[0091] <Positive electrode active material for lithium secondary battery> CAM is represented by, for example, the following compositional formula (A). Li (1+m) Ni (1-a-y) M1 a X y O2(A) (In formula (A), M1 is one or more elements selected from the group consisting of Co, Mn, and Al, X is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P, and -0.1 ≦ m ≦ 0.2, 0 < a ≦ 0.3, 0 ≦ y ≦ 0.1, and 0 < a + y ≦ 0.3 are satisfied.)

[0092] From the viewpoint of obtaining a lithium secondary battery with a high initial charge capacity, m in the formula (A) is more preferably -0.05 or more, and even more preferably more than 0. Also, from the viewpoint of obtaining a lithium secondary battery with a higher initial Coulomb efficiency, m in the formula (A) is preferably 0.08 or less, and more preferably 0.06 or less.

[0093] Examples of m include more than 0 and 0.2 or less, -0.05 to 0.08, more than 0 and 0.06 or less, etc.

[0094] Also, from the viewpoint of obtaining a lithium secondary battery with a high initial charge capacity, a in the formula (A) is preferably 0.01 or more, and more preferably 0.02 or more. Also, a is preferably 0.20 or less, and more preferably 0.17 or less.

[0095] Examples of a include 0.01 to 0.20, or 0.02 to 0.17, etc.

[0096] When CAM contains X, from the viewpoint of obtaining a lithium secondary battery with high initial charge-discharge efficiency, y in the formula (A) is preferably 0.001 or more, more preferably 0.002 or more, and even more preferably 0.003 or more. y is preferably 0.08 or less, and more preferably 0.05 or less.

[0097] For example, y may be 0 to 0.08, 0.001 to 0.08, 0.002 to 0.08, or 0.003 to 0.05.

[0098] The value of a+y in the formula (I) is preferably 0.25 or less, and more preferably 0.20 or less, from the viewpoint of obtaining a lithium secondary battery with a high initial charge capacity. The value of a+y is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.05 or more, from the viewpoint of suppressing a decrease in the initial charge-discharge efficiency.

[0099] Examples of a+y include 0.01 to 0.3, 0.02 to 0.25, and 0.05 to 0.20.

[0100] From the viewpoint of obtaining a lithium secondary battery with high initial charge-discharge efficiency, X is preferably one or more elements selected from the group consisting of Ti, Mg, W, Mo, Nb, Zr, B, Si, and S.

[0101] The crystal structure of the CAM is preferably a layered structure, and more preferably a hexagonal crystal structure or a monoclinic crystal structure.

[0102] The hexagonal crystal structure is P3, P31, P32, R3, P-3, R-3, P312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P 31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63 , P-6, P6 / m, P63 / m, P622, P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P63 / mcm, and P63 / mmc.

[0103] Furthermore, the monoclinic crystal structure belongs to any one space group selected from the group consisting of P2, P21, C2, Pm, Pc, Cm, Cc, P2 / m, P21 / m, C2 / m, P2 / c, P21 / c, and C2 / c.

[0104] Among these, in order to obtain a lithium secondary battery having a high initial charge capacity and a high initial charge / discharge efficiency, it is more preferable that CAM has a hexagonal crystal structure belonging to the space group R-3m or a monoclinic crystal structure belonging to the space group C2 / m.

[0105] <Lithium secondary battery> Next, a positive electrode for a lithium secondary battery (hereinafter, sometimes referred to as a positive electrode) suitable for use with the CAM produced according to this embodiment will be described. Furthermore, a lithium secondary battery suitable for use as a positive electrode will be described.

[0106] An example of a suitable lithium secondary battery when using the CAM manufactured by this embodiment has a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

[0107] An example of a lithium secondary battery has a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

[0108] 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.

[0109] 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 stacked in this order: separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0110] Next, the electrode group 4 and an insulator (not shown) are placed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with an electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing member 8, whereby a lithium secondary battery 10 can be manufactured.

[0111] The shape of the electrode group 4 can be, for example, a columnar shape such that the cross section of the electrode group 4 cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0112] The shape of a lithium secondary battery having such an electrode group 4 can be any shape specified by IEC60086, a standard for batteries established by the International Electrotechnical Commission (IEC), or JIS C 8500. Examples of shapes include a cylindrical shape and a rectangular shape.

[0113] Furthermore, the lithium secondary battery is not limited to the above-mentioned wound type configuration, and may be a laminated type configuration in which a laminated 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.

[0114] Each component will be described below in order. (positive electrode) The positive electrode of this embodiment can be produced by first preparing a positive electrode mixture containing CAM, a conductive material, and a binder, and then supporting the positive electrode mixture on a positive electrode current collector.

[0115] (Negative electrode) The negative electrode of the lithium secondary battery of the present embodiment may be any electrode capable of doping and dedoping lithium ions at a potential lower than that of the positive electrode, and examples thereof include an electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector, and an electrode made of the negative electrode active material alone.

[0116] The positive electrode, separator, negative electrode, and electrolyte constituting the lithium secondary battery can be, for example, the configuration, materials, and manufacturing method described in

[0113] to

[0140] of WO2022 / 113904A1.

[0117] <All-solid-state lithium secondary battery> The CAM produced according to this embodiment can be used as a CAM for an all-solid-state lithium secondary battery.

[0118] Fig. 3 is a schematic diagram showing an example of an all-solid-state lithium secondary battery according to 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 that houses the laminate 100. The all-solid-state lithium secondary battery 1000 may also have a bipolar structure in which a positive electrode active material and a negative electrode active material are disposed on both sides of a current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400. The materials constituting each component will be described later.

[0119] The laminate 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may have a separator between the positive electrode 110 and the negative electrode 120.

[0120] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the exterior body 200 , and a sealing body (not shown) that seals the opening 200 a of the exterior body 200 .

[0121] A container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel can be used as exterior body 200. Alternatively, a container formed into a bag shape from a laminate film with corrosion resistance applied to at least one surface can also be used as exterior body 200.

[0122] The all-solid-state lithium secondary battery 1000 may have any shape, such as a coin shape, a button shape, a paper shape (or a sheet shape), a cylindrical shape, a square shape, or a laminate shape (pouch shape).

[0123] 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 (laminated bodies 100) are sealed inside an exterior body 200.

[0124] (positive electrode) The positive electrode 110 of this embodiment includes a positive electrode active material layer 111 and a positive electrode current collector 112 .

[0125] The positive electrode active material layer 111 includes a CAM and a solid electrolyte manufactured by a manufacturing method according to one embodiment of the present invention. The positive electrode active material layer 111 may also include a conductive material and a binder.

[0126] (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. The negative electrode active material layer 121 may also contain a solid electrolyte and a conductive material. The negative electrode active material, negative electrode current collector, solid electrolyte, conductive material, and binder may be those described above.

[0127] Regarding the all-solid-state lithium secondary battery, for example, the configurations, materials, and manufacturing methods described in

[0151] to

[0181] of WO2022 / 113904A1 can be used.

[0128] Since the lithium secondary battery with the above configuration uses the above-mentioned CAM, the initial charge capacity and the initial charge-discharge efficiency can be improved.

Example

[0129] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following description.

[0130] <Composition analysis of CAM> The composition analysis of CAM was performed by the method described in the above-mentioned "Composition analysis of CAM".

[0131] <Measurement of the shortest dimensions of the first wet cake and the second wet cake> The shortest dimensions of the first wet cake and the second wet cake were measured by the method described in the above-mentioned "Shortest dimensions of the wet cake".

[0132] <Water content of CAM> The water content of CAM was measured using fd-610 manufactured by Kett Scientific Research Institute Co., Ltd.

[0133] <Initial charge capacity and initial charge-discharge efficiency> The initial charge capacity and the initial charge-discharge efficiency were measured by the method described in [Charge-discharge test].

[0134] (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.

[0135] A mixed raw material liquid was prepared by mixing an aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, and an aqueous aluminum sulfate solution so that the molar ratio of Ni to Co was 0.88:0.09. Furthermore, an aqueous aluminum sulfate solution was prepared as a raw material liquid containing Al.

[0136] Next, the mixed raw material solution and an aluminum sulfate aqueous solution were continuously added to the reaction vessel under stirring so that the molar ratio of Ni, Co, and Al was 0.88:0.09:0.03, and an ammonium sulfate aqueous solution was continuously added as a complexing agent. An aqueous sodium hydroxide solution was added dropwise at appropriate times so that the pH of the mixed solution in the reaction vessel became 11.7 (measurement temperature: 40°C), and reaction precipitate 1 was obtained.

[0137] The reaction precipitate 1 was washed, dehydrated, dried and sieved to obtain a metal composite hydroxide 1.

[0138] Metal composite hydroxide 1 was heated and held at 650°C for 5 hours, and then cooled to room temperature to obtain metal composite oxide MCC1.

[0139] MCC1 and lithium hydroxide were mixed so that the amount (molar ratio) of Li contained in lithium hydroxide relative to the total amount of Ni, Co, and Al contained in MCC1 was 1.05, thereby obtaining mixture 1.

[0140] This mixture 1 was pre-fired at 670±30°C for 5 hours in an atmosphere containing oxygen gas, and then fired at 740°C for 5 hours. The fired product was then crushed to obtain LiMO-1.

[0141] 50 g of LiMO-1 was mixed with 33 g of water (liquid temperature 5°C) and stirred to obtain slurry 1. This slurry 1 was subjected to solid-liquid separation using a pressure filter in an atmospheric environment to obtain solid-liquid separated product 1. Next, 11.1 g of lithium molybdate was added and dissolved per 63.9 g of water to prepare Mo solution 1 having a Mo molar concentration of 0.50 mol%. Mo solution 1 was transferred to solid-liquid separated product 1 using a pressure filter in an atmospheric environment to obtain first wet cake 1 having a minimum dimension of 20 mm. First wet cake 1 was crushed in an oxygen-containing atmosphere with a carbon dioxide concentration of less than 50 ppm and a dew point of -50°C to obtain second wet cake 1 having a minimum dimension of 5 mm. Second wet cake 1 was held in a holding tank in an atmosphere with a carbon dioxide concentration of less than 50 ppm and a dew point of -50°C for 2 hours to obtain third wet cake 1.

[0142] The third wet cake 1 was heat-treated at 190°C for 3 hours using a vacuum dryer to obtain CAM-1.

[0143] Example 2 Water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous solution of sodium hydroxide was added thereto, and the liquid temperature was maintained at 70°C.

[0144] A mixed raw material solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate so that the molar ratio of Ni to Co to Mn was 0.83:0.12:0.05.

[0145] Next, this mixed raw material solution and an aqueous solution of ammonium sulfate as a complexing agent were continuously added to the reaction vessel under stirring. An aqueous solution of sodium hydroxide was added dropwise at appropriate times so that the pH of the solution in the reaction vessel became 11.2 (measurement temperature: 40°C), and reaction precipitate 2 was obtained.

[0146] The reaction precipitate 2 was washed, dehydrated and dried to obtain a metal composite hydroxide MCC2.

[0147] Mixture 2 was obtained by mixing MCC2 and lithium hydroxide so that the amount (molar ratio) of Li contained in lithium hydroxide relative to the total amount of Ni, Co, and Mn contained in MCC2 was 1.05.

[0148] This mixture 2 was pre-fired at 670±30°C for 2 hours in an atmosphere containing oxygen gas, and then fired at 800°C for 5 hours. The fired product was then crushed to obtain LiMO-2.

[0149] LiMO-2 was mixed with 33 g of water (liquid temperature 5°C) and stirred to obtain slurry 2. This slurry 2 was subjected to solid-liquid separation in an atmospheric environment using a pressure filter to obtain solid-liquid separated material 2. The above Mo solution 1 was transferred to the solid-liquid separated material 2 using a pressure filter in an atmospheric environment to obtain a first wet cake 2 having a shortest dimension of 20 mm. The first wet cake 2 was crushed under the conditions shown in Table 1 to obtain a second wet cake 2. The second wet cake 2 was held in a holding tank under the conditions shown in Table 1 to obtain a third wet cake 2. The third wet cake 2 was heat-treated under the conditions shown in Table 1 to obtain CAM-2.

[0150] Example 3 The Mo solution 1 was fed to the solid-liquid separated material 2 using a pressure filtration device under atmospheric conditions to obtain a first wet cake 3 having a shortest dimension of 10 mm. The first wet cake 3 was crushed under the conditions shown in Table 1 to obtain a second wet cake 3. The second wet cake 3 was held in a holding tank under the conditions shown in Table 1 to obtain a third wet cake 3.

[0151] The third wet cake 3 was heat-treated using a vacuum dryer at 60°C for 0.5 hours and then at 190°C for 3 hours to obtain CAM-3.

[0152] (Comparative Example 1) The third wet cake 2 was heat-treated in an electric furnace at 600° C. for 1 hour to obtain CAM-C1.

[0153] (Comparative Example 2) The above-mentioned slurry 2 was subjected to solid-liquid separation using a Nutsche in an atmospheric environment to obtain a solid-liquid separated product C2. Next, the above-mentioned Mo solution 1 was transferred to the solid-liquid separated product C2 using a Nutsche in an atmospheric environment to obtain a first wet cake C2 having a shortest dimension of 10 mm. The same procedure as in Example 1 was carried out using the first wet cake C2, except that the conditions were changed as shown in Table 1, to obtain CAM-C2.

[0154] (Comparative Example 3) After dissolving 3.03 g of lithium hydroxide monohydrate in 67.3 g of water, 4.71 g of sodium silicate was added and stirred to dissolve the sodium silicate, producing a Si solution with a molar concentration of 0.35 mol%. The Si solution was transferred to the solid-liquid separated product 2 using a pressure filtration device under atmospheric conditions, yielding a first wet cake C3 with a minimum dimension of 10 mm. CAM-C3 was obtained by the same procedure as in Example 1, except that the first wet cake C3 was used and the conditions were changed as shown in Table 1.

[0155] Table 1 shows the shortest dimensions of the first wet cake (referred to as WC1 in Table 1) and the second wet cake (referred to as WC2 in Table 1) in the manufacturing methods of CAM-1 to CAM-3 in Examples 1 to 3 and CAM-C1 to CAM-C3 in Comparative Examples 1 to 3, the crushing conditions for the second wet cake, the conditions for the holding step and heat treatment step for the third wet cake (referred to as WC3 in Table 1), the water content and composition of the CAM, and the initial charge capacity and initial charge / discharge efficiency of the lithium secondary batteries using each CAM.

[0156] [Table 1]

[0157] The initial charge capacities of the lithium secondary batteries using CAM-1 to CAM-3 of Examples 1 to 3 were 223.7 to 226.3 mAh / g, and the initial charge / discharge efficiencies were 91.1 to 91.9%.

[0158] On the other hand, in Comparative Example 1, in which the third wet cake was heat-treated at 600°C, the initial charge capacity was 220.5 mAh / g. In Comparative Example 2, in which the third wet cake was kept in an atmosphere with a carbon dioxide concentration higher than 400 ppm, the initial charge capacity was 221.0 mAh / g. In Comparative Example 3, in which the shortest dimension of the second wet cake was 20 mm, the initial charge / discharge efficiency was 90.5%. [Industrial Applicability]

[0159] According to the present invention, a CAM having a high initial charge capacity and a high initial charge / discharge efficiency can be provided. [Explanation of symbols]

[0160] DESCRIPTION OF SYMBOLS 1... separator, 2... positive electrode, 2a... positive electrode active material layer, 2b... positive electrode current collector, 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, 41... solid-liquid separator, 42... crusher, 43... holding tank, 44... heat treatment device, 100... laminate, 110... positive electrode, 111... positive electrode active material layer, 112... positive electrode current collector, 113... external terminal, 120... negative electrode, 121... negative electrode active material layer, 122... negative electrode current collector, 123... external terminal, 130... solid electrolyte layer, 200... exterior body, 200a... opening, 1000... all-solid-state lithium secondary battery.

Claims

1. obtaining a slurry containing a lithium metal composite oxide containing at least Li and Ni; performing solid-liquid separation of the slurry to obtain a first wet cake; crushing the first wet cake to obtain a second wet cake having a shortest dimension of 10 mm or less; maintaining the second wet cake in an atmosphere having a carbon dioxide concentration of 400 ppm or less to obtain a third wet cake; and heat-treating the third wet cake at 500°C or less.

2. 2. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the water content of the positive electrode active material for a lithium secondary battery is 1 mass % or more and 15 mass % or less with respect to the total mass of the positive electrode active material for a lithium secondary battery.

3. 3. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the step of obtaining the slurry includes a washing step of mixing and stirring the lithium metal composite oxide with a washing solution.

4. The method for producing a positive electrode active material for a lithium secondary battery according to claim 3 , wherein the temperature of the cleaning solution in the cleaning step is lower than 10° C.

5. 3. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the step of obtaining a first wet cake is a step of obtaining a first wet cake by feeding a solution containing element M2 to a solid-liquid separated product obtained by solid-liquid separation of the slurry, and the element M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P.

6. 3. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the dew point of the atmosphere is −30° C. or lower.

7. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the atmosphere contains oxygen.

8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the heat treatment is performed once in the heat treatment step.

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