Method of producing positive electrode active material, method of producing positive electrode plate, and method of producing non-aqueous electrolyte secondary battery

Abstract

To provide a method of producing a positive electrode active material capable of suppressing introduction of Cr, which is an impurity.SOLUTION: A method of producing a positive electrode active material includes: a first step of obtaining a mixture by mixing a nickel-containing compound and a lithium compound, the nickel-containing compound being at least one of a nickel-containing hydroxide and a nickel-containing oxide; a second step of obtaining a molded body by molding the mixture; and a third step of calcining the molded body at 750 to 1000°C under an oxygen atmosphere using a rotary kiln having a furnace having an inner wall composed of an alloy including Cr. A maximum diameter of the molded body is 18 to 50 mm, and a density of the molded body is 1.5 to 4 g / cm3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a positive electrode active material, a method for producing a positive electrode plate, and a method for producing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] A rotary kiln is sometimes used in the firing process to mass-produce positive electrode active materials for lithium secondary batteries. For example, Patent Document 1 discloses that lithium compounds, which are raw materials for positive electrode active materials, can corrode the alloy on the inner wall of the rotary kiln furnace, and that corrosion of the alloy on the inner wall of the furnace can be prevented by performing the firing process using lithium compounds under specific conditions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-91093 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to provide a method for producing a positive electrode active material that can suppress the inclusion of Cr as an impurity, even when a rotary kiln is used in which the inner wall of the furnace is made of an alloy containing Cr. [Means for solving the problem]

[0005] [1] A method for producing a positive electrode active material containing a first lithium transition metal composite oxide, A first step of mixing a nickel-containing compound, which is at least one of a nickel-containing hydroxide and a nickel-containing oxide, with a lithium compound to obtain a mixture; a second step of molding the mixture to obtain a molded body; a third step of firing the compact at 750 to 1000°C in an oxygen atmosphere using a rotary kiln whose inner wall is formed of an alloy containing Cr; The maximum diameter of the molded body is 18 to 50 mm, The density of the molded body is 1.5 to 4 g / cm 3 The method for producing a positive electrode active material is as follows. [2] The molded body has a core layer formed by molding the mixture and a coating layer that coats the core layer, The method for producing a positive electrode active material according to [1], wherein the coating layer contains a second lithium transition metal composite oxide. [3] The method for producing a positive electrode active material according to [1] or [2], wherein the first lithium transition metal composite oxide has a Cr content of 50 ppm or less. [4] The method for producing a positive electrode active material according to any one of [1] to [3], wherein the first lithium transition metal composite oxide has a Cr content of 1 ppm or less. [5] The method for producing a positive electrode active material according to any one of [1] to [4], wherein the shape of the molded body is a sphere, an oval sphere, or a cylinder. [6] The method for producing a positive electrode active material according to any one of [1] to [5], wherein the Cr-containing alloy further contains Fe and Ni. [7] The method for producing a positive electrode active material according to any one of [1] to [6], wherein the lithium compound is at least one of lithium hydroxide and lithium carbonate. [8] The method for producing a positive electrode active material according to any one of [1] to [7], wherein the first lithium transition metal composite oxide contains Li, Ni, and Mn. [9] The first lithium transition metal composite oxide is Li, Ni, Mn, Co, and M (M is one or more metallic elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W, and Y), and The molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t [where a, x, y, z, and t satisfy 1.0 ≤ a ≤ 1.3, x + y + z + t = 1, 0.25 ≤ x ≤ 0.9, 0 < y ≤ 0.6, 0 < z ≤ 0.6, and 0 < t ≤ 0.1]. The method for producing a positive electrode active material according to any one of [1] to [8].

[10] A method for producing a positive electrode plate using a positive electrode active material, comprising: The method for producing a positive electrode plate, wherein the positive electrode active material is produced by the method for producing a positive electrode active material according to any one of [1] to [9].

[11] A method for producing a non-aqueous electrolyte secondary battery including a positive electrode plate, comprising: The method for producing a non-aqueous electrolyte secondary battery, wherein the positive electrode plate is produced by the method for producing a positive electrode plate according to

[10] . [Advantages of the Invention]

[0006] According to the method for producing a positive electrode active material of the present disclosure, a positive electrode active material with suppressed incorporation of Cr, which is an impurity, can be produced. [Brief Description of the Drawings]

[0007] [Figure 1] It is a flowchart showing an example of the method for producing a positive electrode active material according to an embodiment. [Embodiments for Carrying Out the Invention]

[0008] In this specification, a numerical range such as "m to n" includes upper and lower limit values unless otherwise specified. That is, "m to n" represents a numerical range of "m or more and n or less". A numerical value arbitrarily selected from within the numerical range may be used as a new upper limit value or lower limit value. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described in another part of this specification, in a table, or in a figure, etc.

[0009] (Method for Producing Positive Electrode Active Material) FIG. 1 is a flowchart showing an example of a method for manufacturing a positive electrode active material according to an embodiment. The positive electrode active material manufactured by the method for manufacturing a positive electrode active material of the present embodiment (hereinafter also referred to as "the present method") is used for a positive electrode plate of a non-aqueous electrolyte secondary battery such as a lithium ion battery (hereinafter also referred to as "secondary battery").

[0010] The positive electrode active material manufactured by the present method contains a first lithium transition metal composite oxide (hereinafter also referred to as "the first composite oxide"). The content of Cr in the first composite oxide may be 80 ppm or less, preferably 50 ppm or less, may be 30 ppm or less, may be 20 ppm or less, may be 15 ppm or less, may be 10 ppm or less, may be 5 ppm, more preferably 1 ppm or less, and may be 0.9 ppm or less. The content of Cr in the first composite oxide refers to the mass ratio to the total mass of the first composite oxide. The content of Cr in the first composite oxide can be adjusted, for example, by manufacturing the positive electrode active material by the present method described later.

[0011] The composition of the first composite oxide is not particularly limited, but the first composite oxide preferably contains Ni and Mn as transition metals in addition to Li. The first composite oxide is more preferably Li, Ni, Mn, Co, and M [M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W, and Y.], and The molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t [a, x, y, z, and t are 1.0 ≦ a ≦ 1.3, x + y + z + t = 1, 0.25 ≦ x ≦ 0.9, 0 < y ≦ 0.6, 0 < z ≦ 0.6, and 0 < t ≦ 0.1.].

[0012] The molar ratio of Li is 1.0 ≤ a ≤ 1.3, and it may also be 1.0 ≤ a ≤ 1.25, 1.01 ≤ a ≤ 1.2, 1.03 ≤ a ≤ 1.15, or 1.04 ≤ a ≤ 1.1. The molar ratio of Ni is 0.25 ≤ x ≤ 0.9, and it may also be 0.3 ≤ x ≤ 0.9, 0.4 ≤ x ≤ 0.88, or 0.5 ≤ x ≤ 0.85. The molar ratio of Mn is 0 < y ≤ 0.6, and it may also be 0.05 ≤ y ≤ 0.5, 0.08 ≤ y ≤ 0.3, or 0.10 ≤ y ≤ 0.2. The molar ratio of Co is 0 < z ≤ 0.6, and it may also be 0 < z ≤ 0.5, 0.01 ≤ z ≤ 0.3, or 0.02 ≤ z ≤ 0.1. The molar ratio of M is 0 < t ≤ 0.1, and it may also be 0 < t ≤ 0.08, 0.001 ≤ t ≤ 0.05, or 0.002 ≤ t ≤ 0.01. When the first composite oxide contains two or more metal elements M, the molar ratio of M refers to the total amount of two or more metal elements.

[0013] The composition of the first composite oxide can be adjusted by the types of raw materials and the blending amounts of the raw materials used in producing the first composite oxide. The composition of the first composite oxide can be determined by ICP (Inductively Coupled Plasma) optical emission spectrometry (ICP-AES).

[0014] The positive electrode active material may contain only the first composite oxide, or may contain an active material other than the first composite oxide. The content of the first composite oxide in the positive electrode active material may be 85 to 100% by mass, 90 to 100% by mass, 92 to 99% by mass, or 95 to 98% by mass based on the total amount of the positive electrode active material.

[0015] As shown in FIG. 1, this method includes the following first step, second step, and third step. First step: A step of mixing a nickel-containing compound, which is at least one of a nickel-containing hydroxide and a nickel-containing oxide, and a lithium compound to obtain a mixture. Second step: A step of molding the mixture to obtain a molded body, the maximum diameter of which is 18 to 50 mm and the density of which is 1.5 to 4 g / cm 3 This is the process. Third step: A step of firing the compact at 750 to 1000°C in an oxygen atmosphere using a rotary kiln whose inner wall is made of an alloy containing Cr.

[0016] The calcination of a mixture of a lithium compound and a nickel-containing compound is carried out under high-temperature conditions. Therefore, when the lithium compound comes into contact with the inner wall of the rotary kiln, it may react with the Cr-containing alloy forming the inner wall, resulting in the elution of metals such as Cr. In this method, the mixture is formed into a compact and then calcined in a rotary kiln. Therefore, compared to when a compact is not formed, the degree of direct contact between the lithium compound and the Cr-containing alloy forming the inner wall of the furnace can be reduced. This prevents the alloy forming the inner wall of the furnace from being corroded by the lithium compound. Therefore, it is possible to prevent Cr contained in the alloy forming the inner wall of the furnace from being mixed into the first composite oxide as an impurity, making it easier to obtain a first composite oxide having a Cr content within the above-mentioned range.

[0017] Each step of this method will now be described in detail. (1st step) The first step is to mix a nickel-containing compound with a lithium compound to obtain a mixture. The nickel-containing compound and the lithium compound are compounds that serve as raw materials for a composite oxide. The mixture is usually in the form of a powder or particles.

[0018] The nickel-containing compound is at least one of a nickel-containing hydroxide and a nickel-containing oxide, and more preferably contains a nickel-containing oxide or is a nickel-containing oxide. The nickel-containing compound may contain a metal element other than Ni in addition to Ni, preferably a transition metal element other than Ni, more preferably at least one of Mn and Co, and may contain Mn and Co. The Cr content in the nickel-containing compound is preferably 0.001% by mass or less, and may be 0.0001% by mass or less.

[0019] The nickel-containing hydroxide is preferably a nickel composite hydroxide containing Ni and a metal element other than Ni. The nickel-containing oxide is preferably a nickel composite oxide containing Ni and a metal element other than Ni. The metal element other than Ni contained in the nickel composite hydroxide and nickel composite oxide is preferably a transition metal element other than Ni, more preferably at least one of Mn and Co, and may be Mn and Co. The nickel-containing compound is preferably a nickel composite oxide.

[0020] The lithium compound may be one or more selected from the group consisting of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate. The Cr content in the lithium compound is preferably 0.001% by mass or less, and may be 0.0001% by mass or less. The lithium compound is preferably at least one of lithium hydroxide and lithium carbonate, and more preferably lithium hydroxide. The lithium compound may be anhydrous or hydrated. When the lithium compound is lithium hydroxide, the lithium hydroxide may be anhydrous lithium hydroxide or lithium hydroxide hydrate. An example of the lithium hydroxide hydrate is lithium hydroxide monohydrate.

[0021] The average particle size (D50) of the lithium compound is, for example, 3 to 20 μm, or may be 5 to 18 μm, or may be 8 to 15 μm. In this specification, the average particle size is the particle size (D50) at which the cumulative frequency of particles with smaller sizes in a volume-based particle size distribution reaches 50%. The volume-based particle size distribution can be measured using a laser diffraction particle size distribution analyzer.

[0022] The contents of the nickel-containing compound and the lithium compound in the mixture may be set so as to obtain a first composite oxide having the desired composition.

[0023] The mixture can be obtained by mixing the nickel-containing compound and the lithium compound using, for example, a mixer. The mixer can be a general mixer, such as a jet mill, a ball mill, a rocking mixer, a shaker mixer, a V-blender, a ribbon mixer, a Julia mixer, or a Loedige mixer.

[0024] (2nd process) The second step is a step of forming a molded body by molding the mixture obtained in the first step. The method of forming the mixture is not limited as long as it can form a molded body having the density described below, but compression molding is preferred.

[0025] The maximum diameter of the compact obtained in the second step is 18 to 50 mm, and may be 20 to 48 mm, 21 to 45 mm, or 22 to 40 mm. When the maximum diameter of the compact is within the above range, the contact area of ​​the lithium compound with the inner wall of the rotary kiln furnace can be reduced, thereby reducing the amount of Cr mixed into the first composite oxide. In addition, the compact can be fired efficiently. On the other hand, when the maximum diameter of the compact is smaller, the contact area of ​​the lithium compound with the inner wall of the furnace tends to increase. When the maximum diameter of the compact is larger, it becomes difficult to sufficiently fire the interior of the compact, or the firing takes a long time, making it difficult to fire the compact efficiently. In this specification, the maximum diameter of the compact refers to the longest length among the lengths connecting any two points on the periphery of the compact (the length when connecting two points passing through the interior of the compact).

[0026] The density of the compact obtained in the second step is 1.5 to 4 g / cm 3 and preferably 1.6 to 3.5 g / cm 3 and 1.8 to 3.0 g / cm 3 and 2.0 to 2.8 g / cm 3 and 2.0 to 2.5 g / cm 3When the density of the molded body is within the above range, cracking of the molded body during firing can be suppressed, and firing can be performed efficiently. On the other hand, when the density of the molded body is low, the molded body is more likely to crack during firing in the third step. When the density of the molded body is high, oxygen is less likely to enter the interior of the molded body, making it difficult to fire the molded body sufficiently to the inside, or firing takes a long time, making it difficult to fire the molded body efficiently.

[0027] The shape of the compact is not particularly limited, but is preferably spherical, elliptical, or cylindrical, and is preferably elliptical or cylindrical. The above-mentioned shapes of the compact can reduce the contact area with the inner wall of the rotary kiln furnace, thereby reducing the amount of Cr mixed into the first composite oxide. Furthermore, compacts of the above shapes have reduced corners compared to prismatic shapes, etc., and therefore can prevent the compact from being powdered due to chipping of the corners when fired in the rotary kiln in the third step. Elliptical or cylindrical compacts are preferred because they are more likely to move at a speed suitable for firing in the rotary kiln used in the third step than spherical compacts.

[0028] The molded article may have a single-layer structure formed by molding the mixture, or may have a multi-layer structure of two or more layers, including a core layer formed by molding the mixture and a coating layer covering the core layer. The core layer may be formed by compression molding the mixture. In a molded article having a core layer and a coating layer (hereinafter also referred to as a "multi-layer molded article"), the coating layer may cover the entire surface of the core layer, or may cover only a portion of the core layer. The coating layer may cover preferably 70% or more, or may cover 80% or more, or may cover 90% or more of the entire surface of the core layer. The multi-layer molded article may have, for example, a three-layer structure in which a coating layer, a core layer, and a coating layer are laminated in this order.

[0029] The coating layer preferably contains a second lithium transition metal composite oxide (hereinafter also referred to as "second composite oxide"), and more preferably contains the second composite oxide and a binder. When the coating layer contains the second composite oxide, the core layer formed using a mixture containing a lithium compound is less likely to be exposed. Therefore, in the firing step (third step), direct contact between the inner wall of the rotary kiln furnace and the lithium compound is less likely to occur, and the incorporation of Cr as an impurity into the first composite oxide can be further suppressed.

[0030] The second composite oxide is not particularly limited as long as it is an oxide containing lithium and a transition metal. The second composite oxide preferably has the composition described for the first composite oxide, and is more preferably the first composite oxide produced by the present method. The second composite oxide may have the same composition as the first composite oxide contained in the molded body, or may have a different composition. The coating layer may contain, for example, a cathode active material produced by the present method, i.e., a cathode active material containing the first composite oxide. The composition of the second composite oxide can be determined by ICP-AES, as described for the first composite oxide.

[0031] The coating layer may contain a binder to improve the coverage of the core layer. Mixing the second composite oxide with a binder improves the granulation properties of the second composite oxide, thereby improving the coverage of the core layer with the coating layer.

[0032] The binder contains one or more selected from the group consisting of polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyacrylamide (PAM), and preferably contains PVdF. The binder is used to improve the granulation properties of the second composite oxide, and may be present in an amount of 0.1 to 5 mass %, 0.5 to 3 mass %, or 0.8 to 2 mass % relative to the total amount of the second composite oxide.

[0033] The compact can be obtained by molding the mixture using a molding machine, for example, by compression molding the mixture using a powder molding machine. As the powder molding machine, a general powder molding machine can be used, for example, a hydraulic press, a hydrostatic press, a briquetting machine, a single-punch tablet press, a rotary tablet press, or the like.

[0034] The method for forming the multilayer molded body is not particularly limited, and it can be obtained, for example, by simultaneously molding the material for forming the coating layer and the mixture for forming the core layer. For example, a layer of a material containing the second composite oxide and a layer of the mixture are laminated, and then the laminate is molded to obtain a multilayer molded body. When the coating layer contains a binder, for example, the multilayer molded body can be obtained as follows. First, the second composite oxide and the binder are mixed, dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP), and then the NMP is volatilized and removed by heating to obtain a granulated material containing the second composite oxide and the binder. Next, the granulated material is charged into a mold, the mixture is charged thereon, and the granulated material is further charged, and the resulting mixture is molded to obtain a multilayer molded body. The molding used to form the multilayer molded body may be compression molding.

[0035] (3rd step) The third step is a step of firing the molded body obtained in the second step using a rotary kiln. In the third step, the molded body is introduced into the furnace of the rotary kiln, and the atmosphere inside the furnace is made an oxygen atmosphere and the temperature inside the furnace is adjusted to 750 to 1000°C, where the molded body is fired. The rotary kiln can be an externally heated type.

[0036] The inner wall of the rotary kiln furnace is formed of an alloy containing Cr. The outermost surface of the inner wall of the furnace may be an alloy containing Cr, and a chromium oxide film may be deposited on the outermost surface by firing the Cr-containing alloy. The Cr-containing alloy may contain, in addition to Cr, one or more metals selected from the group consisting of Fe, Ni, Mn, and Mo, and preferably contains Fe and Ni. The Cr-containing alloy may contain non-metallic elements such as Si, P, S, and C, as long as the alloy exhibits its alloy properties. Examples of the Cr-containing alloy include at least one of SUS310S and SUS316L.

[0037] The sintering of the molded body is carried out in an oxygen atmosphere. The oxygen atmosphere can be formed, for example, by supplying oxygen into the furnace of a rotary kiln. The third step is preferably carried out while continuously supplying oxygen into the furnace.

[0038] The firing temperature of the compact is 750 to 1000° C., and may be 760 to 950° C., 770 to 900° C., 780 to 880° C., or 790 to 850° C. The firing time at the above firing temperature is, for example, 1 to 20 hours, may be 5 to 15 hours, or may be 8 to 12 hours.

[0039] (Manufacturing method of positive electrode plate) The method for manufacturing a positive electrode plate according to this embodiment is a method for manufacturing a positive electrode plate using a positive electrode active material, and the positive electrode active material is manufactured by this method.

[0040] The positive electrode plate can have a positive electrode current collector foil and a positive electrode active material formed on one or both sides of the positive electrode current collector foil. The positive electrode active material is contained in a positive electrode active material layer, and the positive electrode active material layer can further include at least one of a binder and a conductive material. The positive electrode active material layer can be formed by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to materials that form the positive electrode active material layer, such as the positive electrode active material, binder, and conductive material, to form a positive electrode slurry, applying the slurry to the positive electrode current collector foil, drying, and compressing the slurry.

[0041] The positive electrode current collector foil is, for example, a metal foil made of an Al material such as Al or an Al alloy. Examples of binders include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; cellulose-based resins such as carboxymethyl cellulose (CMC), methyl cellulose, and hydroxypropyl cellulose; and styrene butadiene rubber, and one or more of these can be used. Examples of conductive materials include carbon materials. Examples of carbon materials include fibrous carbon such as carbon nanotubes and carbon black, and one or more of these can be used.

[0042] (Method of manufacturing non-aqueous electrolyte secondary battery) The method for manufacturing a non-aqueous electrolyte secondary battery (secondary battery) of this embodiment is a method for manufacturing a secondary battery using the above-described positive electrode plate, and the positive electrode plate is manufactured by the above-described method for manufacturing a positive electrode plate.

[0043] The secondary battery may include an electrode assembly including a positive electrode plate and a non-aqueous electrolyte, and may have a battery case that accommodates the electrode assembly and the non-aqueous electrolyte. The battery case and the non-aqueous electrolyte may be any known battery case and non-aqueous electrolyte used in secondary batteries.

[0044] The electrode assembly may include the above-described positive electrode plate, negative electrode plate, and separator. In the electrode assembly, the positive electrode active material layer of the positive electrode plate and the negative electrode active material layer of the negative electrode plate face each other via the separator. The electrode assembly may be a laminated type in which a positive electrode plate, a negative electrode plate, and a separator are stacked, or a wound type in which a strip-shaped laminate in which a strip-shaped positive electrode plate, a strip-shaped negative electrode plate, and a strip-shaped separator are stacked is wound. The wound type electrode assembly may have a flat shape that is pressed after rolling the laminate. The negative electrode plate usually has a negative electrode current collector foil and a negative electrode active material layer. The negative electrode current collector foil, negative electrode active material layer, and separator may be known negative electrode current collector foils, negative electrode active material layers, and separators used in secondary batteries. [Example]

[0045] Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples.

[0046] Example 1 A nickel composite oxide containing Ni, Co, and Mn in a molar ratio of Ni:Co:Mn = 83:5:12 was prepared as the nickel-containing compound, and lithium hydroxide monohydrate (average particle size (D50): 10 μm) was prepared as the lithium compound. The nickel-containing compound and the lithium compound were mixed to a molar ratio of Li:Ni:Co:Mn = 1.06:0.83:0.05:0.12 to obtain a mixture (first step).

[0047] 5.0 g of the mixture was placed in a powder molding die ("DT6025A-2025" manufactured by NPA Systems Co., Ltd.). The mixture in the die was compression molded at 20 MPa using a hydraulic press (manufactured by Riken Kikai) to produce a cylindrical powder with a diameter of 20 mm, a height of 10 mm, and a density of 2.2 g / cm. 3 A molded body (1) having the following maximum diameter was obtained (second step).

[0048] A 100mm x 100mm SUS310S plate was prepared to simulate the inner wall of a rotary kiln, a Cr-containing alloy. The compact (1) was placed on the SUS310S plate, which was then placed in an electric furnace and fired at 805°C for 10 hours in an oxygen atmosphere (Step 3), yielding a first lithium-transition metal composite oxide as the positive electrode active material. The Cr content of the positive electrode active material was measured by inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES). Specifically, measurements were performed in accordance with JIS K 0116:2014, General Rules for Optical Emission Spectroscopy. The first lithium-transition metal composite oxide was dissolved by alkali fusion using a high-resolution ICP atomic emission spectrometer (Hitachi High-Tech Science Corporation, PS3500DDII), and then diluted to a predetermined volume with ultrapure water, tartaric acid, or hydrochloric acid. The results are shown in Table 1.

[0049] Example 2 A mixture was obtained according to the procedure described in Example 1 (first step).

[0050] The first lithium transition metal composite oxide produced by the procedure of Example 1 was prepared as the second lithium transition metal composite oxide (second composite oxide) for forming the coating layer. The second composite oxide and polyvinylidene fluoride (PVdF) were mixed at a ratio of second composite oxide:PVdF = 99:1, and the mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a dispersion. The dispersion was heated to 100°C using a hot plate, and the NMP was volatilized to obtain a granulated product containing the second composite oxide and a binder.

[0051] 0.2 g of granules, 5.0 g of the mixture, and 0.2 g of granules were placed in a powder molding die ("DT6025A-2025" manufactured by NPA Systems Co., Ltd.) in this order, and a laminate with a three-layer structure of granules / mixture / granules was formed in the die. The laminate in the die was compression-molded at 20 MPa using a hydraulic press (manufactured by Riken Kikai) to form a cylindrical product with a diameter of 20 mm, a height of 10 mm, and a density of 2.2 g / cm. 3 A molded body (2) was obtained (second step). The molded body (2) had a three-layer structure in which a coating layer, a core layer, and another coating layer were laminated in this order. The maximum diameter of the molded body (2) was 22.4 mm.

[0052] The compact (2) was fired (third step) in the same manner as in Example 1, except that the compact (1) was replaced with the compact (2), to obtain a lithium transition metal composite oxide as a positive electrode active material. The Cr content in the positive electrode active material was measured by ICP-AES as in Example 1. The results are shown in Table 1.

[0053] Comparative Example 1 A mixture was obtained using the procedure described in Example 1. The mixture was placed on a 100 mm × 100 mm SUS310S plate, which was then placed in an electric furnace and fired at 805°C for 10 hours in an oxygen atmosphere to obtain a lithium transition metal composite oxide as a positive electrode active material. As described in Example 1, the Cr content in the positive electrode active material was measured by ICP-AES. The results are shown in Table 1.

[0054] [Table 1]

Claims

1. A method for producing a positive electrode active material including a first lithium transition metal composite oxide, comprising: A first step of mixing a nickel-containing compound, which is at least one of a nickel-containing hydroxide and a nickel-containing oxide, with a lithium compound to obtain a mixture; a second step of molding the mixture to obtain a molded body; a third step of firing the compact at 750 to 1000°C in an oxygen atmosphere using a rotary kiln whose inner wall is formed of an alloy containing Cr; The maximum diameter of the molded body is 18 to 50 mm, The density of the molded body is 1.5 to 4 g / cm ３ The method for producing a positive electrode active material is as follows.

2. the molded body has a core layer formed by molding the mixture and a coating layer that coats the core layer, The method for producing a positive electrode active material according to claim 1 , wherein the coating layer contains a second lithium transition metal composite oxide.

3. 2. The method for producing a positive electrode active material according to claim 1, wherein the first lithium transition metal composite oxide has a Cr content of 50 ppm or less.

4. 2 . The method for producing a positive electrode active material according to claim 1 , wherein the first lithium transition metal composite oxide has a Cr content of 1 ppm or less.

5. The method for producing a positive electrode active material according to claim 1 , wherein the molded body has a spherical, oval sphere, or cylindrical shape.

6. The method for producing a positive electrode active material according to claim 1 , wherein the alloy containing Cr further contains Fe and Ni.

7. The method for producing a positive electrode active material according to claim 1 , wherein the lithium compound is at least one of lithium hydroxide and lithium carbonate.

8. The method for producing a positive electrode active material according to claim 1 , wherein the first lithium transition metal composite oxide contains Li, Ni, and Mn.

9. The first lithium transition metal composite oxide is Li, Ni, Mn, Co, and M (M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W, and Y), and 2. The method for producing a positive electrode active material according to claim 1, wherein a molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M=a:x:y:z:t, where a, x, y, z, and t are 1.0≦a≦1.3, x+y+z+t=1, 0.25≦x≦0.9, 0<y≦0.6, 0<z≦0.6, and 0<t≦0.

1.

10. A method for manufacturing a positive electrode plate using a positive electrode active material, A method for producing a positive electrode plate, wherein the positive electrode active material is produced by the method for producing a positive electrode active material according to any one of claims 1 to 9.

11. A method for manufacturing a nonaqueous electrolyte secondary battery including a positive electrode plate, comprising: A method for producing a non-aqueous electrolyte secondary battery, comprising producing the positive electrode plate by the method for producing a positive electrode plate according to claim 10.

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