Composite hydroxide and method for producing same, and positive electrode active material using composite hydroxide and method for producing same

Abstract

A composite hydroxide according to the present invention contains elemental nickel (Ni) and elemental manganese (Mn). The composite hydroxide has an oil absorption of 3.0 mL / 5 g to 6.5 mL / 5 g inclusive as determined in accordance with JIS K5101 (2004). It is preferable that the composite hydroxide has a density of 4.00 g / cm3 to 4.99 g / cm3 inclusive as determined by a gas replacement method. It is preferable that the volume cumulative particle diameter of the composite hydroxide at a cumulative volume of 50 vol% is 3.0 µm to 20.0 µm inclusive as determined by a laser diffraction / scattering particle size distribution measurement method. It is preferable that the composite hydroxide has a BET specific surface area of 15.0 m2 / g to 65.0 m2 / g inclusive.

Description

Composite hydroxide and method for producing the same, and positive electrode active material using the composite hydroxide and method for producing the same.

[0001] The present invention relates to a composite hydroxide and a method for producing the same, as well as a positive electrode active material using a composite hydroxide and a method for producing the same.

[0002] In recent years, rechargeable batteries have attracted attention as a means of preventing global warming by reducing carbon dioxide emissions. Among rechargeable batteries, lithium-ion batteries, which have high energy density and high voltage, are widely used.

[0003] Lithium manganese nickel oxide is known as one of the active materials to be included in the positive electrode of such batteries. For example, Patent Document 1 proposes a lithium manganese nickel oxide obtained by calcining a mixture of a compound containing nickel and manganese elements and lithium carbonate.

[0004] WO2020 / 127526A1

[0005] In recent years, there has been a growing demand for further improvements in the performance of lithium secondary batteries. However, when commercializing the lithium manganese nickel oxide described in Patent Document 1, there is a problem in that the metallic elements such as manganese contained in the oxide dissolve into the electrolyte, generating gas within the cell, which degrades the battery performance and prevents the acquisition of superior battery performance. Furthermore, in order to obtain a battery with improved performance, it is necessary that the raw materials of the active material used in the battery can come into sufficient contact with oxygen in the air when the active material is manufactured by calcination. However, the compounds described in the same document could not solve this problem. Therefore, the object of the present invention is to provide a composite hydroxide that can be used to obtain a positive electrode active material with reduced dissolution of metallic elements.

[0006] The present invention provides a composite hydroxide containing nickel (Ni) and manganese (Mn) elements, having an oil absorption capacity of 3.0 mL / 5 g or more and 6.5 mL / 5 g or less, as measured in accordance with JIS K 5101:2004.

[0007] The present invention also provides a method for producing a composite hydroxide, comprising a composite hydroxide generation reaction in which a composite hydroxide containing nickel (Ni) and manganese (Mn) elements is produced by adding a metal ion aqueous solution containing nickel ions and manganese ions and a basic aqueous solution to water charged in a reaction vessel while stirring the water, wherein the reaction vessel has an inner surface having a combination of three or more flat surfaces, and during the composite hydroxide generation reaction, the pH of the liquid in the reaction vessel is maintained at 9.0 or higher and 9.5 or lower, while the metal ion aqueous solution is continuously added to the water so as to maintain the following S / V value of 0.08 or higher and 0.50 or lower: V: Total volume of liquid in the reaction vessel at the end of the reaction (L). S: Addition rate of the metal ion aqueous solution (L / hr).

[0008] The present invention also provides a method for producing a positive electrode active material containing a composite oxide containing lithium (Li), nickel (Ni), and manganese (Mn) elements, wherein the reaction vessel has an inner surface having a combination of three or more flat surfaces, and during the composite hydroxide production reaction, the pH of the liquid in the reaction vessel is maintained at 9.0 or higher and 9.5 or lower, while the metal ion aqueous solution is continuously added to the water so as to maintain the S / V value defined below at 0.08 or higher and 0.50 or lower. V: Total volume of liquid in the reaction vessel at the end of the reaction (L). S: Addition rate of the metal ion aqueous solution (L / hr).

[0009] The present invention will be described below based on its preferred embodiments. The present invention relates to a composite hydroxide. In this specification, "composite hydroxide" refers to a compound consisting of hydroxides of two or more metal elements. According to the composite hydroxide of the present invention, a positive electrode active material with reduced elution of metal elements can be obtained, for example, by the manufacturing method described later.

[0010] The composite hydroxide of the present invention contains metal elements, and more specifically, it is preferable to contain at least nickel (Ni) and manganese (Mn). This makes it possible to obtain a composite hydroxide that can be used to obtain a positive electrode active material capable of manufacturing high-performance batteries. In the composite hydroxide of the present invention, it is desirable that the nickel and manganese elements exist in the form of hydroxides, but some of the nickel and / or manganese elements may exist in a state other than hydroxide, for example, in the form of oxides.

[0011] From the viewpoint of obtaining a positive electrode active material that can manufacture high-performance batteries, the nickel element content in the composite hydroxide of the present invention is preferably 12.0% by mass or more, more preferably 13.0% by mass or more, and even more preferably 14.0% by mass or more. From a similar viewpoint, the nickel element content in the composite hydroxide is preferably 20.0% by mass or less, more preferably 19.0% by mass or less, and even more preferably 18.0% by mass or less.

[0012] Furthermore, from the viewpoint of obtaining a positive electrode active material that can manufacture high-performance batteries, the manganese element content in the composite hydroxide of the present invention is preferably 40.0% by mass or more, more preferably 41.0% by mass or more, and even more preferably 42.0% by mass or more. From a similar viewpoint, the manganese element content in the composite hydroxide is preferably 50.0% by mass or less, more preferably 49.0% by mass or less, and even more preferably 48.0% by mass or less.

[0013] Furthermore, from the viewpoint of obtaining a positive electrode active material capable of manufacturing high-performance batteries, the molar ratio of manganese element to nickel element in the composite hydroxide of the present invention is preferably 2.60 or higher, more preferably 2.65 or higher, and even more preferably 2.70 or higher. Similarly, from the viewpoint of obtaining a positive electrode active material capable of manufacturing high-performance batteries, the molar ratio of manganese element to nickel element in the composite hydroxide of the present invention is preferably 3.40 or lower, more preferably 3.35 or lower, and even more preferably 3.30 or lower.

[0014] In order to set the nickel and manganese content within the above-mentioned ranges, it is preferable to adjust the concentration of nickel ions or manganese ions in the metal ion aqueous solution in the manufacturing method described later.

[0015] The composite hydroxide of the present invention may contain other elements in addition to nickel and manganese. This makes it possible to obtain a positive electrode active material that can successfully manufacture high-performance batteries. Examples of other elements include Na, Mg, B, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. One or more of these other elements may be used. When the composite hydroxide of the present invention contains other elements, there are no particular restrictions on the state in which these other elements exist. The other elements may exist, for example, in the form of hydroxides and oxides. Alternatively, the other elements may exist together with nickel and manganese in the form of a composite hydroxide.

[0016] If the composite hydroxide of the present invention contains other elements, it is preferable that their content be within a predetermined range. Specifically, from the viewpoint of obtaining a positive electrode active material that can successfully manufacture a high-performance battery, it is preferable that the content of other elements in the composite hydroxide of the present invention be 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. From a similar viewpoint, it is preferable that the content of other elements in the composite hydroxide is 8.0% by mass or less, more preferably 7.5% by mass or less, and even more preferably 7.0% by mass or less.

[0017] The presence and content of nickel, manganese, and other elements can be measured, for example, by ICP emission spectroscopy.

[0018] A preferred compositional formula for the composite hydroxide of the present invention is, for example, formula (I): Ni ｘ Mn ｙExamples include OOH (where x + y = 1). In equation (I), "x" is preferably 0.23 or more and 0.28 or less, and more preferably 0.24 or more and 0.27 or less. "y" is preferably 0.72 or more and 0.77 or less, and more preferably 0.73 or more and 0.76 or less.

[0019] The composite hydroxide of the present invention preferably has many voids in the aggregate of the composite hydroxide, that is, it has low packing capacity. Compounds with low packing capacity are more easily exposed to oxygen throughout the compound compared to compounds with high packing capacity. This is particularly advantageous when calcining the compound. For example, when calcining a composite hydroxide, it is possible to calcine it with a sufficient amount of oxygen permeating not only the outside but also the inside of the composite hydroxide, and as a result, a positive electrode active material that can successfully manufacture a high-performance battery can be obtained. The degree of packing capacity of a composite hydroxide can be evaluated by the amount of oil absorbed, measured in accordance with JIS K 5101:2004. A higher amount of oil absorbed means that the composite hydroxide has low packing capacity. Specifically, from the viewpoint of reducing packing capacity and calcining the composite hydroxide with oxygen permeating throughout, the amount of oil absorbed by the composite hydroxide is preferably 3.0 mL / 5 g or more, more preferably 3.2 mL / 5 g or more, even more preferably 3.4 mL / 5 g or more, and even more preferably 4.0 mL / 5 g or more. Furthermore, from the viewpoint of adjusting the reaction with oxygen when calcining the composite hydroxide, the oil absorption of the composite hydroxide is preferably 6.5 mL / 5 g or less, more preferably 6.3 mL / 5 g or less, even more preferably 6.0 mL / 5 g or less, and even more preferably 5.5 mL / 5 g or less.

[0020] The oil absorption of the composite hydroxide is measured by the following method. First, 5 g of the composite hydroxide is placed on a stainless steel plate. Then, using a burette, commercially available boiled linseed oil is dropped little by little onto the plate, and the mixture is spread evenly using a spatula. This spreading process is repeated until the small particles in the mixture of composite hydroxide and boiled linseed oil aggregate and form clumps of the sample. After the clumps of the sample are formed, one more drop of boiled linseed oil is added and mixed until a uniform putty-like consistency is achieved. This putty should be spreadable without cracking or crumbling, and should adhere lightly to the stainless steel plate. The value on the burette is read, and the amount of boiled linseed oil used is taken as the oil absorption amount.

[0021] The composite hydroxide of the present invention preferably exhibits high miscibility with other compounds (e.g., solids). Since substances with high miscibility with other compounds also have high dispersibility themselves, the degree of miscibility can be evaluated by the degree of dispersibility. It is known that there is a positive correlation between high dispersibility and high oil absorption. Therefore, the composite hydroxide of the present invention exhibits high miscibility with other compounds because its oil absorption falls within the above-mentioned range.

[0022] In order to keep the oil absorption within the above-mentioned range, it is preferable to generate turbulence in the liquid or adjust the pH of the reaction solution or the rate of addition of the metal ion aqueous solution in the manufacturing method described later.

[0023] The composite hydroxide of the present invention preferably has a density within a predetermined range. This makes it easier to mix the composite hydroxide with other compounds, for example, when using other compounds with a density close to the present density as raw materials for the positive electrode active material. As a result, the miscibility of these mixtures is improved, and a positive electrode active material that can successfully manufacture high-performance batteries can be obtained. From the viewpoint of making this effect even more pronounced, the density d of the composite hydroxide measured by the gas displacement method is ＯＨ 4.00 g / cm³ ３ Preferably, it is 4.05 g / cm³ or more. ３ It is even more preferable that the amount be greater than or equal to 4.10 g / cm³. ３It is more preferable that it is as described above. From the same viewpoint, the density d of the composite hydroxide measured by the gas replacement method ＯＨ is preferably 4.99 g / cm ３ or less, more preferably 4.95 g / cm ３ or less, even more preferably 4.90 g / cm ３ or less, and still more preferably 4.45 g / cm ３ or less. The density of lithium carbonate measured by the gas replacement method is approximately 2.00 g / cm ３ or more and 2.40 g / cm ３ or less. In this case, the above-mentioned density d of the composite hydroxide ＯＨ is sufficiently close to the density of lithium carbonate, and their miscibility is high. Therefore, for example, a spinel-type lithium transition metal composite oxide (hereinafter also referred to as "LNMO") can be effectively produced using the composite hydroxide. In this specification, when there are no closed pores in the composite hydroxide and lithium carbonate, the density d ＯＨ means the true density, and when there are closed pores, the density d ＯＨ means the apparent density.

[0024] The density d of the composite hydroxide ＯＨ is measured by the gas replacement method using a density measuring device ("BELPycn Ver1.04A" manufactured by Microtrac Bell Co., Ltd.). The pretreatment is carried out three times by purging. The measurement is performed in the true density mode. The composite hydroxide is measured as it is without being pulverized. For the measurement of the density, a dedicated sample basket attached is used, and the sample basket is filled with about 2 g of the composite hydroxide for measurement. In this way, the density d of the composite hydroxide ＯＨ (g / cm ３ ) is measured.

[0025] In order to make the density d ＯＨ within the above-mentioned range, it is preferable to adjust the pH of the reaction solution or the addition rate of the metal ion aqueous solution.

[0026] The composite hydroxide of the present invention preferably has a broad particle size distribution. This is because a broad particle size distribution allows for high mixability of the composite hydroxide. The degree of broad particle size distribution of the composite hydroxide is determined by the volume cumulative particle size at 10% of the cumulative volume, measured by laser diffraction scattering particle size distribution analysis. １０ (Hereafter simply referred to as "particle size D") １０ It is also called ". ) and the cumulative volume particle size D at 90% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ９０ (Hereafter simply referred to as "particle size D") ９０ It is also called ". ) When D ９０ / D １０ It can be defined by the following. Specifically, from the viewpoint of improving the miscibility of the complex hydroxide, D ９０ / D １０ It is preferable that it is 1.5 or higher, more preferably 1.8 or higher, and even more preferably 2.0 or higher. From a similar viewpoint, D ９０ / D １０ It is preferable that the value is 5.0 or less, more preferably 4.8 or less, and even more preferably 4.6 or less.

[0027] In the composite hydroxide of the present invention, it is preferable from the viewpoint of obtaining a composite hydroxide that can be used as a positive electrode active material for manufacturing high-performance batteries, such that the individual particle sizes constituting its particle size distribution are within a predetermined range. Specifically, from the viewpoint of durability when used as a positive electrode active material, the composite hydroxide of the present invention has a volume cumulative particle size D at 50% cumulative volume measured by laser diffraction scattering particle size distribution measurement. ５０ (Hereafter simply referred to as "particle size D") ５０ It is also called ". The particle size D of the composite hydroxide is preferably 3.0 μm or larger, more preferably 3.5 μm or larger, even more preferably 4.0 μm or larger, even more preferably 4.5 μm or larger, and particularly preferably 7.5 μm or larger. Furthermore, from the viewpoint of the output characteristics when used as a positive electrode active material, the particle size D of the composite hydroxide is also preferable. ５０ The particle size is preferably 20.0 μm or less, more preferably 19.0 μm or less, and even more preferably 18.0 μm or less.

[0028] Here, particle size D ５０This term has meaning as a surname for the average diameter of particles, including primary and secondary particles. "Primary particle" refers to the smallest unit of particle surrounded by grain boundaries when observed with an SEM (scanning electron microscope, e.g., 500 to 5000x magnification). On the other hand, in this specification, "secondary particle" refers to a particle that is independent of other particles, formed by the aggregation of multiple primary particles sharing a portion of their respective outer perimeters (grain boundaries).

[0029] Furthermore, from the viewpoint of durability when used as a positive electrode active material, the particle size D of the composite hydroxide of the present invention １０ The particle size D of the composite hydroxide is preferably 1.0 μm or larger, more preferably 1.2 μm or larger, and even more preferably 1.4 μm or larger. Furthermore, from the viewpoint of output characteristics when used as a positive electrode active material, the particle size D of the composite hydroxide is also important. １０ The particle size is preferably 10.0 μm or less, more preferably 9.5 μm or less, and even more preferably 9.0 μm or less.

[0030] Furthermore, from the viewpoint of durability when used as a positive electrode active material, the particle size D of the composite hydroxide of the present invention ９０ The particle size D of the composite hydroxide is preferably 6.0 μm or larger, more preferably 6.5 μm or larger, and even more preferably 7.0 μm or larger. Furthermore, from the viewpoint of output characteristics when used as a positive electrode active material, the particle size D of the composite hydroxide is also important. ９０ The particle size is preferably 37.0 μm or less, more preferably 36.0 μm or less, and even more preferably 35.0 μm or less. ５０ , particle size D １０ and particle size D ９０ The detailed measurement method will be explained in the examples described later.

[0031] Particle size D ５０ , particle size D ９０ and particle size D １０ In order to bring the range within the above-mentioned range, it is preferable to adjust the concentration of the basic aqueous solution, the concentration of the metal ion aqueous solution, or the peripheral speed of the stirring device in the manufacturing method described later.

[0032] The composite hydroxide of the present invention preferably has a BET specific surface area within a predetermined range. Specifically, from the viewpoint of increasing the oil absorption capacity and thereby improving the packing and mixing properties of the composite hydroxide, the BET specific surface area of ​​the composite hydroxide is 15.0 m². ２ It is preferable that the amount be 16.0 m or more. ２ It is even more preferable that the amount is 17.0 m or more per g. ２ It is even more preferable that the amount is 65.0 m² or more. Furthermore, in the manufacturing method described later, from the viewpoint of reducing the moisture content of the composite hydroxide during the drying process and lowering the energy cost associated with drying, the BET specific surface area of ​​the composite hydroxide is 65.0 m². ２ It is preferable that the amount be less than or equal to 64.0 m ２ It is even more preferable that it be less than or equal to 63.0 m ２ It is even more preferable that the amount is less than or equal to / g. The method for measuring the BET specific surface area will be explained in the examples described later.

[0033] As described above, the composite hydroxide of the present invention preferably has low packing properties. Therefore, it is also preferable that the apparent density of the composite hydroxide is low. Specifically, from the viewpoint of reducing packing properties and firing the composite hydroxide in a state where oxygen is distributed throughout, the apparent density of the composite hydroxide is 0.90 g / cm³. ３ Preferably, it is 0.80 g / cm³. ３ It is even more preferable that the following is the case: 0.70 g / cm³ ３ It is even more preferable that the following is the case: 0.50 g / cm³ ３ It is even more preferable that the following conditions are met. From the viewpoint of making the above-mentioned effects even more pronounced, the lower the apparent density of the composite hydroxide, the better. However, from the viewpoint of adjusting the reaction with oxygen when calcining the composite hydroxide, an apparent density of 0.30 g / cm³ of the composite hydroxide is preferable. ３ Preferably, it is 0.32 g / cm³ or more. ３ It is even more preferable that the concentration be greater than or equal to 0.34 g / cm³. ３ The above is even more preferable. The method for measuring apparent density will be explained in the examples described later.

[0034] Since the composite hydroxide of the present invention has low packing properties, a low tap density is also preferable. Specifically, from the viewpoint of reducing packing properties and allowing oxygen to be distributed throughout the composite hydroxide during firing, the tap density of the composite hydroxide is 1.30 g / cm³. ３ Preferably, it is 1.20 g / cm³. ３ It is even more preferable that the following is the case: 1.10 g / cm³ ３ It is even more preferable that the concentration be less than 1.00 g / cm³. ３ It is even more preferable that the following conditions are met. From the viewpoint of making the above-mentioned effects even more pronounced, the lower the tap density of the composite hydroxide, the better. However, from the viewpoint of adjusting the reaction with oxygen when calcining the composite hydroxide, a tap density of 0.50 g / cm³ of the composite hydroxide is preferable. ３ Preferably, it is 0.52 g / cm³ or more. ３ It is even more preferable that the concentration be greater than or equal to 0.54 g / cm³. ３ The above is even more preferable. In this specification, "tap density" refers to a value measured in accordance with JIS Z2512. A detailed method for measuring tap density will be described in the examples below.

[0035] In order to set the BET specific surface area, apparent density, and tap density within the above-mentioned range, it is preferable to adjust the pH of the reaction solution, the rate of addition of the metal salt, or the peripheral speed of the stirring device in the manufacturing method described later.

[0036] Next, a preferred method for producing the composite hydroxide of the present invention will be described. This production method includes a step of adding an aqueous solution of metal ions and an aqueous solution of a basic substance while stirring water to produce the composite hydroxide.

[0037] First, a basic aqueous solution is prepared. A basic aqueous solution can be prepared by mixing a basic compound with water. Examples of basic compounds include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, as well as ammonia. One basic compound or two or more basic compounds can be used. In the complex hydroxide formation reaction described later, it is preferable that the basic compound is at least one of sodium hydroxide and ammonia, and more preferably sodium hydroxide, in order to successfully obtain the desired complex hydroxide by forming a metal complex with nickel and manganese and facilitating the coprecipitation of nickel and manganese. This is because the coprecipitation of nickel and manganese tends to increase the packing efficiency of the desired complex hydroxide.

[0038] There are no particular restrictions on the method of mixing the basic compound with water. For example, one method is to stir the water and then add the basic compound to it and mix. When using two or more basic compounds in combination, they may be added simultaneously or sequentially.

[0039] From the viewpoint of successfully obtaining complex hydroxides, the concentration of the basic compound in the basic aqueous solution is preferably adjusted to 10.0 mol / L or higher, more preferably 11.0 mol / L or higher, and even more preferably 12.0 mol / L or higher. From a similar viewpoint, the concentration of the basic compound in the basic aqueous solution is preferably adjusted to 15.0 mol / L or lower, more preferably 14.0 mol / L or lower, and even more preferably 13.0 mol / L or lower.

[0040] Prepare a metal ion aqueous solution along with a basic aqueous solution. The metal ion aqueous solution can be prepared by mixing a metal ion source with water. As the metal ion source, a water-soluble salt of a metal element can be used. At least nickel and manganese are used as metal elements. In addition, other metal elements such as Na, Mg, B, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce may be used. As water-soluble salts of these metal elements, for example, salts, complexes, and chlorides of nickel, manganese, and other metal elements can be used. These can be used individually or in combination of two or more. As salts of nickel, manganese, and other metal elements, for example, oxo salts such as sulfates, nitrates, phosphates, and phosphates, and organic salts such as oxalates and acetates can be used. As complexes of nickel, manganese, and other metal elements, for example, ammine complex salts, as well as complexes and complex salts with other organic ligands can be used. From the viewpoint of successfully obtaining complex hydroxides, the metal ion source is preferably at least one of nickel and manganese sulfates, nitrates, and ammine complex salts, and more preferably nickel and manganese sulfates.

[0041] There are no particular restrictions on the method of mixing the metal ion source with water. For example, one method is to stir the water and then add the metal ion source and mix it. When using two or more metal ion sources in combination, they may be added together or simultaneously. This prepares an aqueous metal ion solution containing at least nickel ions and manganese ions.

[0042] It is preferable to use a metal ion source such that the concentrations of various metal ions in the metal ion aqueous solution are within a predetermined range. Specifically, from the viewpoint of successfully obtaining complex hydroxides, it is preferable to prepare the metal ion aqueous solution so that the concentration of nickel ions is 25.0 g / L or more, more preferably 25.5 g / L or more, and even more preferably 26.0 g / L or more. From a similar viewpoint, it is preferable to prepare the metal ion aqueous solution so that the concentration of nickel ions is 33.0 g / L or less, more preferably 32.5 g / L or less, and even more preferably 32.0 g / L or less. Furthermore, from the viewpoint of successfully obtaining complex hydroxides, it is preferable to prepare the metal ion aqueous solution so that the concentration of manganese ions is 80.0 g / L or more, more preferably 81.0 g / L or more, and even more preferably 82.0 g / L or more. From a similar viewpoint, it is preferable to prepare the metal ion aqueous solution so that the concentration of manganese ions is 88.0 g / L or less, more preferably 87.0 g / L or less, and even more preferably 86.0 g / L or less.

[0043] Furthermore, from the viewpoint of successfully obtaining complex hydroxides, the molar ratio of manganese ions to nickel ions in the metal ion aqueous solution is preferably 2.60 or higher, more preferably 2.65 or higher, and even more preferably 2.70 or higher. From a similar viewpoint, the molar ratio of nickel ions to manganese ions in the metal ion aqueous solution is preferably 3.40 or lower, more preferably 3.35 or lower, and even more preferably 3.30 or lower.

[0044] When using other metal elements as a metal ion source, from the viewpoint of successfully obtaining complex hydroxides, it is preferable to prepare the aqueous metal ion solution so that the concentration of other metal ions is 1 g / L or more, more preferably 2 g / L or more, and even more preferably 3 g / L or more. From a similar viewpoint, it is preferable to prepare the aqueous metal ion solution so that the concentration of other metal ions is 15 g / L or less, more preferably 12 g / L or less, and even more preferably 10 g / L or less.

[0045] Along with the above aqueous solutions, a reaction vessel is prepared, which serves as the reaction site for the basic aqueous solution and the metal ion aqueous solution. The reaction vessel used in this manufacturing method has a distinctive feature in the shape of its inner surface. Normally, when a reaction is carried out in the liquid phase, stirring of the liquid can cause vortices to be generated in the liquid. In this case, the crystal nuclei produced by the reaction rotate in the reaction vessel with the swirling water flow, making it difficult for the crystal nuclei to come into contact with each other. While the crystal nuclei can grow easily due to the reduced contact between them, aggregation caused by contact is less likely to occur, resulting in crystals with fewer voids, i.e., high packing efficiency. In contrast, this manufacturing method controls the water flow generated in the liquid during the reaction in the liquid phase. This allows for appropriate contact between the crystal nuclei produced by the reaction, enabling both crystal nucleus growth and aggregation. As a result, crystals with low packing efficiency can be obtained. The inventors have discovered for the first time that controlling the water flow can reduce the packing efficiency of composite hydroxides.

[0046] The water flow can be controlled by combining multiple planes to form the inner surface of the reaction vessel. For example, in a reaction vessel where the inner surface is integrally curved, water flow tends to occur along the inner surface, easily creating vortices. In contrast, in the reaction vessel of this embodiment, where the inner surface is a combination of planes, turbulence is more likely to occur due to changes in the angle of the inner surface. In this specification, "turbulence" refers to water flow with a Reynolds number of 2310 or higher. Specifically, from the viewpoint of generating turbulence in the liquid and achieving both nucleation growth and aggregation during the complex hydroxide formation reaction, it is preferable that the inner surface of the reaction vessel has a combination of three or more planes. From the viewpoint of effectively generating turbulence, it is preferable that the planes in the reaction vessel are connected in a series of three or more planes. In this case, the part where three or more planes are connected only needs to be at least a part of the inner surface, and the other parts may be curved. This part may be in any part of the reaction vessel, for example, the upper, middle, and lower parts of the inner surface of the reaction vessel. From the above viewpoint, it is even more preferable that the inner surface of the reaction vessel has a combination of four or more planes. Furthermore, from a similar viewpoint, it is preferable that the inner surface of the reaction vessel has a combination of seven or fewer surfaces, more preferably six or fewer surfaces, and even more preferably five or fewer surfaces. From the viewpoint of making the above-mentioned effects even more pronounced, it is particularly preferable that the inner surface of the reaction vessel consists only of a combination of flat surfaces.

[0047] In the process of producing complex hydroxides, water is placed in a reaction vessel, and while stirring the water in the reaction vessel, a metal ion aqueous solution and a basic aqueous solution are added to the water. This produces a complex hydroxide containing at least nickel and manganese elements in the reaction solution. In this process, the addition times of the metal ion aqueous solution and the basic aqueous solution may be different, as long as there is a period of time when they are added simultaneously. Specifically, (i) the start and end times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be the same, (ii) the start times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be the same, but the end times may be different, (iii) the start times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be different, but the end times may be the same, and (iv) the start and end times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be different.

[0048] There are no particular restrictions on the method of stirring the reaction solution in the reaction vessel, and known stirring devices can be used. The stirring of the reaction solution may be continuous or intermittent. Even when the reaction solution is stirred intermittently, if there is a short period of time during which the reaction solution is not stirred, such that turbulence can be considered to be generated in the liquid, it shall be considered as continuous stirring. From the viewpoint of effectively generating turbulence in the liquid and further achieving both nucleation growth and aggregation during the complex hydroxide formation reaction, it is preferable to stir the reaction solution continuously. When stirring the reaction solution using a stirring device, it is preferable to set the peripheral speed of the device within a predetermined range. Specifically, from the viewpoint of causing the reaction solution to collide with the inner surface of the reaction vessel and facilitating the generation of turbulence, it is preferable to stir the reaction solution with a peripheral speed of 2.5 m / s or more, more preferably 2.8 m / s or more, and even more preferably 3.0 m / s or more. From a similar viewpoint, it is preferable to stir the reaction solution at a peripheral speed of 5.5 m / s or less, more preferably 5.0 m / s or less, even more preferably 4.5 m / s or less, even more preferably 4.2 m / s or less, and particularly preferably 4.0 m / s or less.

[0049] During the complex hydroxide formation reaction, it is preferable to set the temperature of the reaction solution within a predetermined range. Specifically, from the viewpoint of successfully obtaining complex hydroxides by achieving an appropriate reaction rate, it is preferable to set the temperature of the reaction solution to 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. From a similar viewpoint, it is preferable to set the temperature of the reaction solution to 80°C or lower, more preferably 75°C or lower, and even more preferably 70°C or lower.

[0050] During the complex hydroxide formation reaction, it is preferable to maintain the pH of the reaction solution in the reaction vessel within a predetermined range. Specifically, it is preferable to maintain the pH of the reaction solution at 9.0 or higher, more preferably 9.1 or higher, and even more preferably 9.2 or higher, from the viewpoint of successfully obtaining complex hydroxides, within a pH range where the basic aqueous solution and the metal ion aqueous solution can react. Furthermore, if the pH is too high, the rate of complex hydroxide formation is fast, very fine particles are generated, and these particles strongly aggregate, resulting in high packing density. Therefore, from the viewpoint of successfully obtaining complex hydroxides with low packing density, it is preferable to maintain the pH of the reaction solution at 9.5 or lower, more preferably 9.4 or lower, and even more preferably 9.3 or lower. pH adjustment can be performed, for example, by adjusting the addition rate of the metal ion aqueous solution or the basic aqueous solution. More specifically, for example, by adding the metal ion aqueous solution at a constant rate while appropriately adjusting the addition rate of the basic aqueous solution to match the pH of the reaction solution, the pH of the reaction solution can be controlled within the above range. Alternatively, the pH of the reaction solution can be controlled within the above range by adding the basic aqueous solution at a constant rate while appropriately adjusting the rate of addition of the metal ion aqueous solution to match the pH of the reaction solution. The addition of the basic aqueous solution or the metal ion aqueous solution may be continuous or intermittent. From the viewpoint of successfully adjusting the pH of the reaction solution, it is preferable to add the metal ion aqueous solution at a constant rate while continuously or intermittently adding the basic aqueous solution.

[0051] The addition of the metal ion aqueous solution to the water may be continuous or intermittent. Even if the metal ion aqueous solution is added intermittently, if the duration is short enough to be considered as continuous addition, it will be treated as continuous addition. From the viewpoint of successfully producing complex hydroxides, it is preferable to continuously add the metal ion aqueous solution. When continuously adding the metal ion aqueous solution, it is preferable to slow down the rate of addition of the metal ion aqueous solution during the complex hydroxide formation reaction. This is because it is possible to successfully produce complex hydroxides with low packing density. The addition rate is determined by the value of S / V ((L / hr) / L) defined by the following formula (1). A smaller S / V value means that the rate of addition of the metal ion aqueous solution is slower, and a larger S / V value means that the rate of addition of the metal ion aqueous solution is faster. S / V (1) V: Total volume of liquid in the reaction vessel at the end of the reaction (L) S: Addition rate of metal ion aqueous solution (L / hr)

[0052] From the viewpoint of successfully setting the rate of addition of the metal ion aqueous solution, it is preferable to calculate the value of V in equation (1) before the start of the reaction. The value of V is defined by the following equation (2): V = V1 + V2 + V3 (2) In equation (2), V1 is the amount of water (L) added to the reaction vessel before the formation reaction of the complex hydroxide. V2 is the amount of metal ion aqueous solution added to the water (L). V3 is the amount of basic aqueous solution added to the water (L). The value of V2 can be set appropriately according to the desired amount of complex hydroxide to be produced. For example, the ratio of the amount of water to the amount of metal ion aqueous solution added, V1 / V2, can be set to 1 / 3 or more and 3 or less. The value of V3 is the amount of basic aqueous solution required to precipitate all of the metal ions in the metal ion aqueous solution.

[0053] From the perspective of successfully obtaining low-packing composite hydroxides by balancing the formation and aggregation of crystal nuclei, an S / V value of 0.50hr －１ Preferably, the following is true: 0.40hr －１ It is even more preferable that the following conditions apply: 0.35hr －１The following is even more preferable. From the viewpoint of making the above-mentioned effects even more pronounced, the smaller the S / V value, the better. However, from the viewpoint of obtaining a composite hydroxide with low packing properties, the S / V value should be 0.08hr. －１ Preferably, it is 0.09hr －１ It is even more preferable that the above be true, and 0.10hr －１ It is even more preferable that the above conditions are met.

[0054] It is preferable to add the metal ion aqueous solution to the reaction mixture in the reaction vessel while blowing in an inert gas. This suppresses the unintended oxidation of the generated complex hydroxide. Examples of inert gases include helium, nitrogen, neon, and argon. One or more inert gases can be used. From the viewpoint of simplicity and effectively suppressing the oxidation of the complex hydroxide, it is preferable to use at least nitrogen gas. From the viewpoint of effectively suppressing the oxidation of the complex hydroxide, it is preferable to blow in a predetermined amount of inert gas. The amount blown in is determined by the value of T / V ((L / min) / L) defined by the following formula (3). A smaller value of T / V means that less inert gas is blown in, and a larger value of T / V means that more inert gas is blown in. T / V (3) V: Total volume of liquid in the reaction vessel at the end of the reaction (L) T: Amount of inert gas blown in (L / min)

[0055] From the viewpoint of successfully setting the amount of inert gas to be injected, it is preferable to calculate the value of V in equation (3) before the reaction starts. The value of V is defined by equation (2) described above.

[0056] From the perspective of effectively suppressing the oxidation of complex hydroxides, the T / V value is 0.08 min. －１ Preferably, it is 0.09 min －１ It is even more preferable that the above be true, and 0.10 min －１ It is even more preferable that the above is true. From a similar viewpoint, the value of T / V is 0.25 min. －１ Preferably, the following: 0.24 min －１ It is even more preferable that the following conditions be met: 0.23 min －１The following is even more preferable:

[0057] The inert gas may be blown into the reaction mixture from one location in the reaction vessel, or from multiple locations simultaneously, depending on the volume of the reaction vessel. The inert gas may be blown into the reaction mixture continuously or intermittently. Even if the inert gas is blown in intermittently, if the duration is short enough to be considered as continuous blowing, it will be treated as continuous blowing. Only one type of inert gas may be blown into the reaction mixture, or two or more types of inert gases may be blown in. When two or more types of inert gases are blown into the reaction mixture, the value T mentioned above refers to the total amount of inert gas blown in.

[0058] Once the complex hydroxide is formed in the reaction solution, the reaction solution is then separated into solid and liquid components by decantation and filtration to remove the complex hydroxide from the reaction solution. After that, the complex hydroxide is washed with water and dried. From the viewpoint of successfully removing moisture from the complex hydroxide and obtaining a positive electrode active material that can easily manufacture high-performance batteries with high thermal efficiency, it is preferable to dry the complex hydroxide at 80°C or higher, more preferably at 90°C or higher, and even more preferably at 100°C or higher. From a similar viewpoint, it is preferable to dry the complex hydroxide at 200°C or lower, more preferably at 190°C or lower, and even more preferably at 180°C or lower. Furthermore, from the viewpoint of successfully removing moisture from the complex hydroxide and obtaining a positive electrode active material that can easily manufacture high-performance batteries with high thermal efficiency, it is preferable to dry it for 1 hour or more, more preferably at 8 hours or more, even more preferably at 10 hours or more, and even more preferably at 12 hours or more. From a similar viewpoint, it is preferable to dry the composite hydroxide for 1000 hours or less, more preferably 150 hours or less, even more preferably 120 hours or less, and even more preferably 100 hours or less. In this way, the desired composite hydroxide can be obtained.

[0059] A positive electrode active material can be obtained by using the composite hydroxide of the present invention. Details of the method for obtaining a positive electrode active material using the composite hydroxide will be described later. The positive electrode active material contains a composite oxide. This composite oxide contains lithium (Li), nickel, manganese, and oxygen (O). The composite oxide contained in the positive electrode active material is not particularly limited as long as it contains lithium, nickel, manganese, and oxygen, and various crystalline structures can be used. For example, lithium transition metal composite oxides having a spinel structure and lithium transition metal composite oxides having a layered rock salt structure can be used as composite oxides. In particular, using a lithium transition metal composite oxide having a spinel structure as the composite oxide is preferable because it has an operating potential of 4.5 V or higher at a metallic Li reference potential. "Having an operating potential of 4.5 V or higher at a metallic Li reference potential" does not mean that it is necessary to have an operating potential of 4.5 V or higher only in the plateau region, but also includes cases where it has an operating potential of 4.5 V or higher in part. Therefore, the positive electrode active material is not limited to a positive electrode active material consisting only of 5V-class positive electrode active material having an operating potential of 4.5V or higher as a plateau region. For example, the positive electrode active material may include positive electrode active material having an operating potential of less than 4.5V as a plateau region. Specifically, it is preferable that the 5V-class positive electrode active material accounts for, for example, 30% by mass or more, preferably 50% by mass or more, and particularly preferably 80% by mass or more (including 100% by mass) of the positive electrode active material.

[0060] Lithium transition metal composite oxides having a spinel structure include, for example, those with the general formula LiNi ｘ Mn ２－ｘ O ４ It can be expressed as (where x is a number greater than 0 and less than 2). Another example of a composite oxide is the spinel-type LiNi ｘ Mn ２－ｘ O ４ Another example is a spinel-type lithium manganese-containing composite oxide having a crystal structure in which some of the Mn sites in are substituted with lithium, nickel, and other M elements (details of the M elements will be described later). In addition, formula (4): Li１＋ｘ (Ni ｙ M ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ Examples include spinel-type lithium manganese-containing composite oxides represented by . In formula (4), element M is preferably one or more elements selected from the group consisting of Na, Mg, B, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Element M is a substitution element that mainly contributes to stabilizing the crystal structure and improving its properties. By selecting element M from the elements described above, the crystal structure can be stabilized and the amount of metal elements leached out can be reduced. From this viewpoint, it is preferable that element M contains element Ti.

[0061] In formula (4), it is preferable that "x" is between 0.001 and 0.200, "y" is between 0.20 and 1.20, and "z" is between 0.000 and 0.500. Furthermore, "4-δ" indicates that oxygen deficiency may be present, and it is preferable that δ is between 0 and 0.2.

[0062] The types of metal elements contained in the composite oxide and their content can be analyzed, for example, by ICP emission spectroscopy.

[0063] The positive electrode active material of this embodiment may contain components other than the composite oxide described above. However, from the viewpoint of sufficiently improving the various performance aspects of the battery into which the positive electrode active material is incorporated, the positive electrode active material preferably contains 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more of the composite oxide.

[0064] As a result of our investigations, we have found that if there is a deficiency of oxygen atoms in the crystal structure of the composite oxide constituting the positive electrode active material, the crystal structure becomes unstable, and the amount of metal elements leached from the positive electrode active material (particularly the amount of manganese leached) tends to increase. In contrast, in the positive electrode active material of this embodiment, oxygen atoms are sufficiently contained in the crystal structure of the composite oxide, so the amount of metal elements leached from the positive electrode active material is reduced. This is advantageous from the viewpoint of further suppressing gas generation from the battery.

[0065] Whether the crystal structure of the composite oxide contains sufficient oxygen atoms can be evaluated by thermogravimetric measurement. Specifically, let the mass of the positive electrode active material at 400 °C measured by the thermogravimetric measurement be W1, the maximum mass of the positive electrode active material at a temperature of 500 °C or higher and 600 °C or lower measured by the same thermogravimetric measurement be W2, and the surface area of the positive electrode active material subjected to the thermogravimetric measurement be SA. When (W2 - W1) / SA, which is the ratio of the mass increase amount W2 - W1 to the surface area SA, is 0.25 mg / m ２ is as follows. (W2 - W1) / SA being 0.25 mg / m ２ or less indicates that W2 - W1 is sufficiently small, that is, when heated to 500 °C or higher and 600 °C or lower, the amount of oxygen atoms incorporated into the crystal structure of the composite oxide is sufficiently small. In other words, (W2 - W1) / SA being 0.25 mg / m ２ or less indicates that the crystal structure of the composite oxide constituting the positive electrode active material of the present embodiment already contains a sufficient amount of oxygen atoms before heating. From this perspective, (W2 - W1) / SA is preferably 0.25 mg / m ２ or less, more preferably 0.15 mg / m ２ or less, even more preferably 0.10 mg / m ２ or less, still more preferably 0.05 mg / m ２ or less, and even still more preferably 0.05 mg / m or less. Also, (W2 - W1) / SA is typically 0 (zero) mg / m ２ or more, but when actually measured, it may sometimes be a negative value.

[0066] The reason for adopting 400 °C instead of room temperature as the measurement temperature of the mass W1 is to exclude the influence of moisture adsorbed on the positive electrode active material.

[0067] The thermogravimetric measurement can be carried out, for example, using STA - 2500 Regulus manufactured by NETZSCH under an air atmosphere and at a heating rate of 5 °C / min. Also, the mass of the positive electrode active material subjected to the thermogravimetric measurement can be, for example, 40 mg.

[0068] The surface area SA of the positive electrode active material used for thermogravimetric analysis is calculated as the product of the BET specific surface area of ​​the positive electrode active material and the mass of the positive electrode active material used for thermogravimetric analysis (e.g., 40 mg). The BET specific surface area of ​​the positive electrode active material can be measured in the same way as the BET specific surface area of ​​the composite hydroxide.

[0069] To set (W2 - W1) / SA within the above numerical range, for example, a positive electrode active material can be produced by calcining a mixture containing the composite hydroxide of the present invention and a lithium compound.

[0070] Furthermore, it can sometimes be confirmed by X-ray diffraction measurement that the composite oxide constituting the positive electrode active material of this embodiment contains a sufficient amount of oxygen atoms within its crystal structure. More specifically, it is preferable that the full width at half maximum (FWHM) of the diffraction peak originating from the (111) plane is 0.2 deg. or less, and the full width at half maximum (FWHM) of the diffraction peak originating from the (400) plane is 0.2 deg. or less, when X-ray diffraction measurement is performed on the positive electrode active material of this embodiment. The diffraction peak originating from the (111) plane is a diffraction peak originating from the Li-O bond in the spinel-type crystal structure, and the diffraction peak originating from the (400) plane is a diffraction peak originating from the M-O bond (M represents Ni or Mn) in the spinel-type crystal structure. Therefore, the fact that the full width at half maximum of the diffraction peak originating from the (111) plane is 0.2 deg. or less, and the full width at half maximum of the diffraction peak originating from the (400) plane is 0.2 deg. or less, indicates that the composite oxide having a spinel-type crystal structure has few oxygen vacancies and that the amount of oxygen atoms contained within the crystal structure is close to the stoichiometric amount.

[0071] From the above viewpoints, it is more preferable that the full width at half maximum of the diffraction peak derived from the (111) plane is 0.15 deg. or less, and even more preferable that it is 0.08 deg. or less. Similarly, it is more preferable that the full width at half maximum of the diffraction peak derived from the (400) plane is 0.15 deg. or less, and even more preferable that it is 0.09 deg. or less. There is no particular limitation on the lower limit value of the full width at half maximum of the diffraction peaks derived from the (111) plane and the (400) plane, but it is practical that they are each independently 0.05 deg. or more, or 0.06 deg. or more. The measurement conditions for X-ray diffraction measurement will be described in the examples described later.

[0072] In order to set the full width at half maximum of the diffraction peaks derived from the (111) plane and the (400) plane within the above numerical ranges, for example, the positive electrode active material may be produced by the production method described later.

[0073] From the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the ratio TD / SSA of the tap density TD to the BET specific surface area SSA of the positive electrode active material of the present embodiment is 1.5 kg ２ / m ５ or more is preferable, 1.7 kg ２ / m ５ or more is more preferable, and 2.0 kg ２ / m ５ or more is even more preferable. Also, the upper limit value of TD / SSA is not particularly limited, but for example, it is practical to set it to 3.0 kg ２ / m ５ or less. The tap density of the positive electrode active material can be measured in the same manner as the tap density of the composite hydroxide.

[0074] From the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the BET specific surface area of the positive electrode active material of the present embodiment is preferably 2.0 m ２ / g or less, more preferably 1.5 m ２ / g or less, and even more preferably 1.0 m ２It is even more preferable that the amount is less than or equal to / g. Furthermore, from the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the BET specific surface area of ​​the positive electrode active material in this embodiment is 0.1 m². ２ It is preferable that the amount be 0.2 m or more. ２ It is even more preferable that it be 0.3 m or more per gram. ２ It is even more preferable that the amount is greater than or equal to / g. In order to set the BET specific surface area of ​​the positive electrode active material within the above range, for example, the firing temperature in the manufacturing method described later can be appropriately controlled.

[0075] From the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the tap density of the positive electrode active material in this embodiment is 1.0 g / cm³. ３ Preferably, it should be 1.1 g / cm³ or more. ３ It is even more preferable that the concentration be greater than or equal to 1.2 g / cm³. ３ It is even more preferable that the above conditions are met. Furthermore, from the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the tap density of the positive electrode active material in this embodiment is 3.0 g / cm³. ３ Preferably, it is 2.5 g / cm³. ３ It is even more preferable that the following conditions be met: 2.0 g / cm³ ３ The following is even more preferable. In order to set the tap density of the positive electrode active material within the above range, for example, the firing temperature can be appropriately controlled in the manufacturing method described later.

[0076] The positive electrode active material of this embodiment may be, for example, particulate. In this case, the particle size of the positive electrode active material is particle size D. ５０ Expressed as such, the particle size D is preferably 0.5 μm or larger, more preferably 3 μm or larger, and even more preferably 5 μm or larger. This is because excessive aggregation of particles is suppressed, resulting in good dispersibility. On the other hand, the particle size D of the positive electrode active material ５０ The particle size D is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. This is because it ensures sufficient contact between the positive electrode active material particles and between the positive electrode active material particles and the electrolyte.５０ The particle size D of the positive electrode active material may be 10.0 μm or less. ５０ The particle size D of the composite hydroxide ５０ It can be measured using a similar method.

[0077] To improve the various properties of the positive electrode active material in this embodiment, part or all of its surface may be coated with another substance. As a coating layer for the positive electrode active material, for example, a coating layer containing Li (lithium), A (where A represents one or more elements selected from the group consisting of Ti, B, P, Zr, Ta, Nb, Zn, W, La, and Al), and O (oxygen) can be used. Specifically, to suppress the increase in reaction resistance and deterioration of cycle characteristics during high-temperature storage, the surface of the positive electrode active material can be coated with one or more substances selected from the group consisting of, for example, lithium niobate, lithium titanate, lithium lanthanuzirconate, lithium tantalate, and lithium tungstate. The elements contained in the coating layer can be detected by analytical methods such as ICP emission spectrometry, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). For example, when detecting elements contained in the coating layer using ICP emission spectrometry, a solution obtained by dissolving the particle surface of the positive electrode active material in a solvent and a solution obtained by dissolving the remaining particles after removing the particle surface in the solvent are analyzed by ICP emission spectrometry. If an element is present in a higher concentration in the solution containing the particle surface than in the solution containing the remaining particles, it can be concluded that the element is contained in the coating layer. Alternatively, when detecting elements contained in the coating layer using XPS analysis, XPS analysis combined with ion sputtering is performed. Specifically, XPS analysis and ion sputtering are repeatedly performed on the sample. In the XPS analysis before ion sputtering, elements contained in the coating layer are detected. In contrast, as ion sputtering is repeated, the coating layer is gradually removed, and finally, elements contained in the part of the positive electrode active material that is inside the coating layer are detected by XPS analysis. By observing this change in the detected elements, the elements contained in the coating layer can be confirmed. Even when using AES, elements contained in the coating layer can be detected in a similar manner to XPS.

[0078] Next, a suitable method for producing the positive electrode active material will be described. Once the composite hydroxide is obtained by the method described above, it is then mixed with a lithium compound to obtain a mixture. Examples of lithium compounds to be mixed with the composite oxide include lithium hydroxide (LiOH) and lithium carbonate (Li... ２ CO ３ ), lithium nitrate (LiNO) ３ ), LiOH・H ２ O, Lithium oxide (Li ２ Examples include lithium fatty acids and lithium halides. Among these, lithium carbonate is preferred. The mixing ratio of the composite hydroxide and the lithium compound can be appropriately adjusted according to the elemental composition of the desired composite oxide. There are no particular restrictions on the method of mixing the composite hydroxide and the lithium compound; wet mixing or dry mixing is acceptable.

[0079] The mixture may contain other components besides the composite hydroxide, lithium compound, and sintering aid described above. Examples of such components include titanium(IV) oxide. By including titanium(IV) oxide in the mixture, the crystal structure of the resulting composite oxide can be reinforced, and the elution of metal elements from the composite oxide can be suppressed. From this viewpoint, the titanium(IV) oxide content in the mixture is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. On the other hand, from the viewpoint of ensuring a balance between reinforcing the crystal structure and the battery characteristics due to the amount of composite oxide, the content of other components such as titanium(IV) oxide in the mixture is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0080] From the viewpoint of facilitating smoother mixing of the complex hydroxide and the lithium compound, it is preferable that the density of the complex hydroxide and the density of the lithium compound do not differ significantly. Specifically, when mixing the complex hydroxide and the lithium compound, the density of the lithium compound d Ｌｉ The density d of the complex hydroxide relative to ＯＨ ratio d ＯＨ / d ＬｉIt is preferable to mix the two so that the ratio is 2.10 or less, more preferably 2.00 or less, and even more preferably 1.90 or less. Also, the density ratio d ＯＨ / d Ｌｉ A value closer to 1 is preferable, but a value of 1.80 or higher, or 1.82 or higher, is more practical. Ｌｉ is, d ＯＨ Similarly, this is the density measured by the gas displacement method. Therefore, d Ｌｉ This refers to the apparent density when closed pores exist in the lithium compound, and the true density when closed pores do not exist. d ＯＨ The value and d Ｌｉ The value of the ratio d varies depending on the state of each substance. ＯＨ / d Ｌｉ The measured d ＯＨ The maximum value and d Ｌｉ This is the value obtained by comparing the maximum values ​​of the two values.

[0081] The composite hydroxide produced by the method described above has a density d as described above. ＯＨ Preferably 4.00 g / cm³ ３ 4.99g / cm or more ３ The following applies: By using a composite hydroxide having such density in a mixture with a lithium compound, the density ratio d of the two compounds is obtained. ＯＨ / d Ｌｉ This can be easily set within the above-mentioned numerical range.

[0082] Next, the mixture is calcined in an oxygen-containing atmosphere to produce a positive electrode active material having a desired crystalline structure (typically spinel type). The calcination temperature is preferably 600°C or higher, more preferably 700°C or higher, and even more preferably 750°C or higher. Alternatively, the calcination temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower. The calcination time is preferably 0.5 hours or more, more preferably 3 hours or more, and even more preferably 5 hours or more. Alternatively, the calcination time is preferably 50 hours or less, more preferably 45 hours or less, and even more preferably 40 hours or less. The calcination atmosphere is not particularly limited as long as it is an oxygen-containing atmosphere; for example, an air atmosphere or an oxygen atmosphere can be used. From the viewpoint of allowing sufficient reaction between the mixture and oxygen, it is preferable to calcine the mixture while circulating the atmosphere. During the heating process until the target calcination temperature is reached, the temperature may be continuously increased over time, or a period of time may be provided during the heating process when the temperature becomes constant.

[0083] Calcination can be carried out, for example, with the mixture contained in a reaction vessel that is open at the top. As mentioned above, the complex hydroxides contained in the mixture contained in the reaction vessel have relatively low packing density. Therefore, the packing density of the mixture in the reaction vessel will be relatively small.

[0084] When a mixture is calcined, its volume gradually decreases. For example, if lithium carbonate is used as the lithium compound, carbon dioxide is gradually released from the lithium carbonate during calcination, causing the volume of the mixture to decrease. As the volume of the mixture decreases, multiple cracks develop in the mixture within the reaction vessel, due to the relatively low packing density of the mixture in the reaction vessel, as described above. These cracks typically extend from the top to the bottom of the mixture, allowing oxygen to be supplied to the entire mixture from above through these cracks. Therefore, the mixture reacts sufficiently with oxygen during calcination, and the resulting composite oxide crystal structure contains a sufficient amount of oxygen atoms. A composite oxide containing a sufficient amount of oxygen atoms in its crystal structure has increased crystal structure stability, thus reducing the amount of metal elements leached from the composite oxide.

[0085] After calcining the mixture, a re-oxidation treatment may be performed as needed. By performing a re-oxidation treatment, the amount of oxygen deficiency in the composite oxide constituting the positive electrode active material can be reduced. The re-oxidation treatment is carried out by heat-treating the composite oxide after calcination. The temperature of the re-oxidation treatment is preferably 300°C or higher, more preferably 400°C or higher, and even more preferably 500°C or higher. Alternatively, the temperature of the re-oxidation treatment is preferably 900°C or lower, more preferably 850°C or lower, and even more preferably 800°C or lower. In particular, performing the re-oxidation treatment at a high temperature tends to further promote sintering between particles, resulting in a decrease in the BET specific surface area of ​​the resulting positive electrode active material. The duration of the re-oxidation treatment is preferably 0.5 hours or more, more preferably 2 hours or more, and even more preferably 5 hours or more. Alternatively, the duration of the re-oxidation treatment is preferably 50 hours or less, more preferably 45 hours or less, and even more preferably 40 hours or less. The atmosphere for the re-oxidation treatment can be an air atmosphere or an oxygen-containing atmosphere such as an oxygen atmosphere.

[0086] The re-oxidation treatment may be carried out by firing the mixture at the firing temperature and then lowering the temperature to the re-oxidation treatment temperature, or by firing the mixture at the firing temperature, cooling it to room temperature, and then raising the temperature again to the re-oxidation treatment temperature. In either case, during the process of reaching the target temperature, the temperature may be continuously changed over time, or a period of time may be provided during the temperature change when the temperature becomes constant.

[0087] In this way, the desired positive electrode active material can be obtained. The positive electrode active material obtained by the above manufacturing method can be crushed or classified if necessary to obtain a powder with a desired particle size.

[0088] The positive electrode active material of this embodiment can be used, for example, in the form of an electrode mixture containing the positive electrode active material and an electrolyte. The electrolyte may be solid or liquid. When a solid electrolyte is used, the content of the positive electrode active material in the electrode mixture may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, when the total solid content is considered to be 100% by mass. Alternatively, the content of the positive electrode active material may be, for example, 98% by mass or less, 90% by mass or less, or 85% by mass or less. By having the content of the positive electrode active material within the above range, the electrode can fully perform its function.

[0089] The electrolyte that can be used in the present invention can be the same as the electrolyte used in general liquid-type batteries, and may be a non-aqueous electrolyte or an aqueous electrolyte. For example, organic electrolytes, polymer solid electrolytes, molten salts, etc. can be used. Examples of organic electrolytes include esters such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, etc. as solvents, substituted tetrahydrofurans such as tetrahydrofuran and 2-methyltetrahydrofuran, ethers such as dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, etc., dimethyl sulfoxide, sulfolane, methylsulfolane, acetonitrile, methyl formate, methyl acetate, etc., and one or more of these as mixed solvents can be used. In addition, examples of electrolyte salts that dissolve in organic solvents include lithium perchlorate, lithium borofluoride, lithium hexafluoride phosphate (hereinafter referred to as "LiPF") ６ Examples include lithium salts such as lithium hexafluoride, lithium trifluoromethanesulfonate, lithium halides, and lithium aluminate chloride.

[0090] The solid electrolyte that can be used in the present invention can be the same as the solid electrolyte used in general solid batteries, as long as it has lithium ion conductivity. Examples include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, but sulfide solid electrolytes are preferred. The sulfide solid electrolyte may contain lithium and sulfur (S) and have lithium ion conductivity, or it may contain lithium, phosphorus (P), and sulfur and have lithium ion conductivity. The sulfide solid electrolyte may be a crystalline material, glass ceramic, or glass. The sulfide solid electrolyte may have a crystalline phase with an argyrodite-type structure. Examples of such sulfide solid electrolytes include Li ２ S-P ２ S ５ Li ２ S-P ２ S ５ - LiX (where "X" indicates one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ Li ２ S-Li ３ PO ４ -P ２ S ５ Li ３ PS ４ Li ４ P ２ S ６ Li １０ GeP ２ S １２ Li ３．２５ Ge ０．２５ P ０．７５ S ４ Li ７ P ３ S １１ Li ３．２５ P ０．９５ S ４ Li ａ PS ｂ X ｃExamples include compounds represented by (X is at least one halogen element; a represents a number between 3.0 and 6.0; b represents a number between 3.5 and 4.8; c represents a number between 0.1 and 3.0). In addition, examples include sulfide solid electrolytes described in WO2013 / 099834A1 and WO2015 / 001818A1.

[0091] The positive electrode active material contained in the electrode mixture may consist solely of the positive electrode active material of this embodiment, or it may be a combination of the positive electrode active material of this embodiment and other positive electrode active materials. Examples of other positive electrode active materials include particles made of known lithium transition metal composite oxides. When using the positive electrode active material of this embodiment in combination with other positive electrode active materials, it is preferable that the positive electrode active material of the present invention is contained in an amount of 50% by mass or more, and particularly 70% by mass or more, relative to the total positive electrode active material.

[0092] The positive electrode active material of this embodiment can be suitably used as a positive electrode active material for a battery. The battery may be a primary battery or a secondary battery. The battery of the present invention may, for example, have a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing an electrolyte. The positive electrode layer contains the positive electrode active material of this embodiment. The positive electrode active material of this embodiment is particularly suitably used as a positive electrode active material for a non-aqueous electrolyte secondary battery in which the electrolyte is liquid.

[0093] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments.

[0094] Further disclosure relating to the above embodiments is provided for copper powder and a method for producing the same. [1] A composite hydroxide containing nickel (Ni) and manganese (Mn) elements, having an oil absorption capacity of 3.0 mL / 5 g or more and 6.5 mL / 5 g or less as measured in accordance with JIS K 5101:2004. [2] A density of 4.00 g / cm³ as measured by the gas displacement method. ３ 4.99g / cm or more ３The following composite hydroxides are available: [1] [3] The composite hydroxides available in [1] or [2], wherein the cumulative volume particle size at 50% of the cumulative volume measured by laser diffraction scattering particle size distribution analysis is 3.0 μm or more and 20.0 μm or less. [4] The BET specific surface area is 15.0 m². ２ / g or more 65.0m ２ A composite hydroxide according to any one of [1] to [3], having a density of 0.30 g / cm³ or less. [5] Apparent density of 0.30 g / cm³ ３ 0.90g / cm or more ３ The following is a composite hydroxide as described in any one of [1] to [4].

[0095] [6] Tap density is 0.50 g / cm³ ３ 1.30g / cm or more ３ The following composite hydroxides are described in any one of [1] to [5]: [7] A positive electrode active material obtained using the composite hydroxide described in any one of [1] to [6]: [8] An electrode mixture comprising the positive electrode active material described in [7] and an electrolyte: [9] A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing an electrolyte, wherein the positive electrode layer comprises the positive electrode active material described in [7].

[10] A method for producing a composite hydroxide, comprising: stirring water charged in a reaction vessel, adding a metal ion aqueous solution containing nickel ions and manganese ions and a basic aqueous solution to the water to produce a composite hydroxide containing nickel (Ni) and manganese (Mn) elements, wherein the reaction vessel has an inner surface having a combination of three or more flat surfaces, and during the composite hydroxide production reaction, the pH of the liquid in the reaction vessel is maintained at 9.0 or higher and 9.5 or lower, while the metal ion aqueous solution is continuously added to the water to maintain the S / V value defined below at 0.08 or higher and 0.50 or lower. V: Total volume of liquid in the reaction vessel at the end of the reaction (L). S: Addition rate of the metal ion aqueous solution (L / hr).

[0096]

[11] The manufacturing method according to

[10] , wherein the metal ion aqueous solution is added while blowing an inert gas into the liquid in the reaction vessel.

[12] The manufacturing method according to

[10] or

[11] , wherein the concentration of nickel ions in the metal ion aqueous solution is 25.0 g / L or more and 33.0 g / L or less, and the concentration of manganese ions is 80.0 g / L or more and 88.0 g / L or less.

[13] A method for producing a positive electrode active material containing a composite oxide containing lithium (Li), nickel (Ni), and manganese (Mn) elements, comprising: stirring water charged in a reaction vessel while adding a metal ion aqueous solution containing nickel ions and manganese ions and a basic aqueous solution to the water to produce a composite hydroxide reaction containing nickel and manganese; mixing the composite hydroxide with a lithium compound to obtain a mixture; and then calcining the mixture in an oxygen-containing atmosphere, wherein the reaction vessel has an inner surface having a combination of three or more flat surfaces, and during the composite hydroxide reaction, the pH of the liquid in the reaction vessel is maintained at 9.0 or more and 9.5 or less while the metal ion aqueous solution is continuously added to the water so as to maintain the S / V value defined below at 0.08 or more and 0.50 or less. V: Total volume of liquid in the reaction vessel at the end of the reaction (L). S: Addition rate of the metal ion aqueous solution (L / hr).

[14] The manufacturing method according to

[13] , wherein the composite hydroxide and the lithium compound are mixed such that the ratio of the density of the composite hydroxide measured by the gas displacement method to the density of the lithium compound measured by the gas displacement method is 1.80 or more and 2.10 or less.

[15] The density measured by the gas displacement method is 4.00 g / cm³ ３ 4.99g / cm or more ３ The manufacturing method according to

[13] or

[14] , comprising mixing the composite hydroxide, which is as follows, with the lithium compound.

[0097] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0098] [Example 1] 9600 g of nickel sulfate hexahydrate and 19400 g of manganese sulfate monohydrate were added to 75 L of pure water and stirred to prepare a metal ion aqueous solution. The total molar concentrations of nickel and manganese in the metal ion aqueous solution are shown in Table 1. Water was added to a reaction vessel consisting of a combination of four flat inner surfaces (i.e., a reaction vessel with a rectangular cross-section), and the water was stirred to generate turbulence. While continuously blowing nitrogen gas into this reaction vessel, the metal ion aqueous solution and a 12.5 mol / L sodium hydroxide aqueous solution were added simultaneously to generate a complex hydroxide. Subsequently, the addition of the metal ion aqueous solution and the sodium hydroxide aqueous solution was stopped simultaneously. The metal ion aqueous solution was added continuously, and the addition rate S was set so that S / V was as shown in Table 1. The amount of water V1, the amount of metal ion aqueous solution added V2, and the amount of sodium hydroxide aqueous solution added V3 are as shown in Table 1. The sodium hydroxide aqueous solution was added at an addition rate such that the pH of the reaction solution was maintained at the value shown in Table 1. The amount of nitrogen gas injected was as shown in Table 1, and the peripheral speed and temperature of the reaction mixture were also adjusted to the values ​​shown in the same table. The reaction mixture was separated into solid and liquid by decantation to separate the complex hydroxide. This was heated and dried under the conditions shown in Table 1 to obtain the desired complex hydroxide. X-ray diffraction (XRD) analysis of this complex hydroxide confirmed the presence of nickel and manganese elements in the form of hydroxides.

[0099] [Example 2 and Comparative Example 1] In Example 1, the conditions for generating the composite hydroxide were changed as shown in Table 1. Otherwise, the desired composite hydroxide was obtained in the same manner as in Example 1. When this composite hydroxide was measured by XRD, it was confirmed that nickel and manganese elements were present in the form of hydroxides.

[0100] [Example 3] In Example 1, the ratio of nickel sulfate hexahydrate and manganese sulfate was changed so that the composition of the starter was as shown in Table 2. In addition, the conditions for generating the composite hydroxide were changed as shown in Table 1. The target composite hydroxide was obtained in the same manner as in Example 1. When this composite hydroxide was measured by XRD, it was confirmed that nickel and manganese elements were present in the form of hydroxides.

[0101] [Example 4] In Example 1, the conditions for generating the composite hydroxide were changed as shown in Table 1. Otherwise, the desired composite hydroxide was obtained in the same manner as in Example 1. When this composite hydroxide was measured by XRD, it was confirmed that nickel and manganese elements were present in the form of hydroxides.

[0102] [Comparative Example 2] In Example 1, instead of a reaction vessel with a combination of flat inner surfaces, a reaction vessel with an integrally curved inner surface (i.e., a reaction vessel with a circular cross-section) was used. Also, the conditions for generating the composite hydroxide were changed as shown in Table 1. Except for these changes, the desired composite hydroxide was obtained in the same manner as in Example 1. When this composite hydroxide was measured by XRD, it was confirmed that nickel and manganese elements were present in the form of hydroxides.

[0103] [Evaluation] The composite hydroxides obtained in the examples and comparative examples were evaluated according to the method described above, determining the oil absorption amount and density d ＯＨ The following was measured: the composition of the composite hydroxide, the content of nickel and manganese elements, and the particle size D. １０ , particle size D ５０ and particle size D ９０ The BET specific surface area, apparent density, and tap density were measured. Furthermore, the miscibility of the composite hydroxide was evaluated according to the method described later. In addition, a positive electrode active material was manufactured using the composite hydroxide, and the amount of manganese element leached was measured. These results are shown in Table 2.

[0104] [Composition of the composite hydroxide, nickel and manganese content] The nickel content (%) and manganese content (%) were measured by ICP emission spectrometry in accordance with JIS K 0116:2014.

[0105] [Particle size D １０ , particle size D ５０ and particle size D ９０ Using an automated sample feeder for laser diffraction particle size distribution analyzers (Microtrac SDC, manufactured by Microtrac-Bell Corporation), the composite hydroxide powder was introduced into a solvent mixture of 20% ethanol and 0.1% hexametaphosphoric acid. After irradiating with 40W ultrasound for 360 seconds at a flow rate of 40%, the particle size distribution was measured using the Microtrac-Bell Corporation laser diffraction particle size distribution analyzer "MT33000EXII," and the particle size D was determined from the obtained volume-based particle size distribution chart. １０ , particle size D ５０ and particle size D ９０ The particle size was measured. The water-soluble solvent used for measuring particle size was passed through a 60 μm filter, with a solvent refractive index of 1.33, particle permeability set to "permeable," particle shape set to "non-spherical," particle refractive index set to 2.46, measurement range set to 0.243 μm to 704.0 μm, and measurement time set to 30 seconds. The average of two measurements was used as the particle size D. １０ , particle size D ５０ and particle size D ９０ Let's assume that.

[0106] [BET Specific Surface Area] The specific surface area was measured using a nitrogen-helium mixed gas containing 30% by volume of nitrogen as the adsorbent gas and 70% by volume of helium as the carrier gas, and a specific surface area measuring device (e.g., Macorb manufactured by Mountec Co., Ltd.), according to "(3.5) Single Point Method" of "6.2 Flow Method" in JIS R 1626 "Method for Measuring Specific Surface Area of ​​Fine Ceramic Powders by Gas Adsorption BET Method". The preliminary degassing conditions were atmospheric pressure and 100°C for 10 minutes. Degassing was also performed at 100°C for 1 minute before the main measurement.

[0107] [Apparent Density] The apparent density was measured in accordance with JIS Z2512 using a tapping machine (model: KSR-406, manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). In detail, a volume of 150 cm³ was measured.３ 50g of composite hydroxide was placed in a graduated cylinder. The tap stroke was set to 6cm and the number of taps to 100 for measurement.

[0108] [Tap Density] Tap density was measured in accordance with JIS Z2512 using a tapping machine (model: KSR-406, manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). In detail, a volume of 150 cm³ was measured. ３ 50 g of composite hydroxide was placed in a graduated cylinder. The tap stroke was set to 6 cm and the number of taps to 510 for measurement.

[0109] [Mixability of the Composite Hydroxide] Mixability was evaluated in accordance with JIS K 5600:1999. First, a sample was prepared by mixing 99 g of composite hydroxide and 21 g of lithium carbonate for 2000 seconds at setting 1 using an Extreme Mill (WARING MODEL MX1200XTSLJ). Approximately half a spatula-sized portion of the sample was placed on the deeper end of a grind gauge (maximum groove depth 100 μm, scale interval 10 μm). The long side of the scraper was made parallel to the width direction of the grind gauge, and the tip of the scraper was brought into contact with the aforementioned end of the grind gauge. The scraper was then pulled toward the shallower end of the groove on the grind gauge. The stretched sample was visually inspected, and the groove depth at which streaks appeared due to the aggregation of particles in the sample was read. A small value or no streaks observed indicates good mixability.

[0110] [Amount of manganese element leaching] (1) The density d of the composite hydroxides of manufacturing examples 1 to 4 and comparative examples 1 and 2 of the positive electrode active material was measured by gas displacement method. Ｌｉ 2.20 g / cm³ ３A mixture was obtained by mixing the composite hydroxide with lithium carbonate and titanium(IV) oxide. The mixing ratio of the composite hydroxide, lithium carbonate, and titanium(IV) oxide was such that the molar ratio of Li, Ni, Mn, and Ti in the resulting positive electrode active material was Li:Ni:Mn:Ti = 1:0.4:1.2:0.2. This mixture was calcined at 880°C. The calcination time was 37 hours, and the calcination atmosphere was an air atmosphere, with air circulating while the mixture was calcined. Next, a re-oxidation treatment was performed at 740°C for 37 hours. The atmosphere for the re-oxidation treatment was also an air atmosphere. The calcined material obtained by the re-oxidation treatment was pulverized using a pin mill, and then classified using a sieve with a mesh size of 53 μm, and the sieved material was collected to obtain the positive electrode active material.

[0111] (2) Measurement of elution amount 1 mol / L LiPF ６ One g of positive electrode active material was dispersed in 10 mL of an organic solvent (ethylene carbonate / dimethyl carbonate = volume ratio 3 / 7) containing the above-mentioned substance, and left at 85°C for 144 hours. Subsequently, the amount of Mn element in the organic solvent (i.e., the amount of Mn element eluted from the positive electrode active material) was measured by ICP emission spectrometry. The above measurement was performed twice, and the arithmetic mean of the measured Mn element elution amounts is shown in Table 2.

[0112]

[0113]

[0114] As is clear from the results shown in Table 2, the composite hydroxide of the example had better miscibility than the composite hydroxide of the comparative example. Furthermore, the positive electrode active material obtained using the composite hydroxide of the example had less manganese leaching compared to the positive electrode active material obtained using the composite hydroxide of the comparative example. Therefore, it can be seen that the composite hydroxide of the present invention makes it possible to obtain a positive electrode active material with reduced metal element leaching.

[0115] The present invention provides a composite hydroxide capable of producing a positive electrode active material with reduced leaching of metal elements, and a method for producing the same. Furthermore, the present invention provides a positive electrode active material with reduced leaching of metal elements.

[0116] The composite hydroxide of the present invention exhibits excellent mixability in the production of positive electrode active materials, and therefore the amount of manganese element leached into the resulting positive electrode active material is low. Consequently, the composite hydroxide of the present invention can suppress product defects in the positive electrode active material and subsequent battery manufacturing, thereby extending the battery life. By suppressing the rate of defective products and extending battery life, waste can be reduced and energy costs can be lowered. In these respects, the composite hydroxide of the present invention enables the sustainable management and efficient use of natural resources, leading to the achievement of decarbonization (carbon neutrality).

Claims

1. A composite hydroxide containing nickel (Ni) and manganese (Mn), with an oil absorption capacity of 3.0 mL / 5 g or more and 6.5 mL / 5 g or less, as measured in accordance with JIS K 5101:2004.

2. The density measured by the gas displacement method was 4.00 g / cm³. ３ 4.99g / cm or more ３ The composite hydroxide according to claim 1, which is as follows:

3. The composite hydroxide according to claim 1, wherein the cumulative volume particle size at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis, is 3.0 μm or more and 20.0 μm or less.

4. BET specific surface area is 15.0 m² ２ / g or more 65.0m ２ The composite hydroxide according to claim 1, wherein the amount is less than or equal to / g.

5. Apparent density is 0.30 g / cm³ ３ 0.90g / cm or more ３ The composite hydroxide according to claim 1, which is as follows:

6. Tap density is 0.50 g / cm³ ３ 1.30g / cm or more ３ The composite hydroxide according to claim 1, which is as follows:

7. A positive electrode active material obtained using the composite hydroxide described in claim 1.

8. An electrode mixture comprising the positive electrode active material and electrolyte according to claim 7.

9. A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing an electrolyte, wherein the positive electrode layer contains the positive electrode active material described in claim 7.

10. A method for producing a composite hydroxide, comprising: carrying out a composite hydroxide production reaction in which water charged in a reaction vessel is stirred and a metal ion aqueous solution containing nickel ions and manganese ions and a basic aqueous solution are added to the water to produce a composite hydroxide containing nickel (Ni) and manganese (Mn) elements, wherein the inner surface of the reaction vessel has a combination of three or more flat surfaces, and during the composite hydroxide production reaction, the pH of the liquid in the reaction vessel is maintained at 9.0 or higher and 9.5 or lower, while the metal ion aqueous solution is continuously added to the water to maintain the S / V value defined below at 0.08 or higher and 0.50 or lower. V: Total volume of liquid in the reaction vessel at the end of the reaction (L). S: Addition rate of the metal ion aqueous solution (L / hr).

11. The manufacturing method according to claim 10, wherein the metal ion aqueous solution is added while blowing an inert gas into the liquid in the reaction vessel.

12. The manufacturing method according to claim 10 or 11, wherein the concentration of nickel ions in the metal ion aqueous solution is 25.0 g / L or more and 33.0 g / L or less, and the concentration of manganese ions is 80.0 g / L or more and 88.0 g / L or less.

13. A method for producing a positive electrode active material containing a composite oxide containing lithium (Li), nickel (Ni), and manganese (Mn) elements, comprising: stirring water charged in a reaction vessel while adding a metal ion aqueous solution containing nickel ions and manganese ions and a basic aqueous solution to the water to produce a composite hydroxide reaction containing nickel and manganese; mixing the composite hydroxide with a lithium compound to obtain a mixture; and then calcining the mixture in an oxygen-containing atmosphere, wherein the reaction vessel has an inner surface having a combination of three or more flat surfaces; and during the composite hydroxide reaction, the pH of the liquid in the reaction vessel is maintained at 9.0 or higher and 9.5 or lower while continuously adding the metal ion aqueous solution to the water so as to maintain the S / V value defined below at 0.08 or higher and 0.50 or lower. V: Total volume of liquid in the reaction vessel at the end of the reaction (L). S: Addition rate of the metal ion aqueous solution (L / hr).

14. The manufacturing method according to claim 13, wherein the composite hydroxide and the lithium compound are mixed such that the ratio of the density of the composite hydroxide, as measured by the gas displacement method, to the density of the lithium compound, as measured by the gas displacement method, is 1.80 or more and 2.10 or less.

15. The composite hydroxide having a density measured by the gas replacement method of 4.00 g / cm ３ or more and 4.99 g / cm ３ or less is mixed with the lithium compound, and the production method according to claim 13 or 14.

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