Cobalt-coated nickel-containing hydroxide and method for producing cobalt-coated nickel-containing hydroxide

Abstract

To provide cobalt-coated nickel-containing hydroxide that is capable of preventing an increase in battery resistance by reducing coating irregularity during positive electrode preparation, and that has reduced volume resistivity, and to provide a method for producing the cobalt-coated nickel-containing hydroxide.SOLUTION: Cobalt-coated nickel-containing hydroxide in which a coated layer containing cobalt oxyhydroxide is formed on nickel-containing hydroxide, wherein the average circularity of particles having a particle diameter not less than the particle diameter at a cumulative volume percentage of 50% (D50) is in the range of 0.900 to 0.990.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cobalt-coated nickel-containing hydroxide having an average circularity controlled within a predetermined range for particle diameters (D50) at a cumulative volume percentage of 50% by volume or more, thereby reducing coating unevenness of the cobalt-coated nickel-containing hydroxide, which is a positive electrode active material, during production of a positive electrode for a secondary battery, thereby preventing an increase in battery resistance and reducing volume resistivity. [Background technology]

[0002] In recent years, with the increasing sophistication of devices, there has been an increasing demand for improved battery characteristics of secondary batteries such as nickel-metal hydride secondary batteries. Therefore, in order to improve battery characteristics, nickel-containing hydroxides with an increased cobalt content have been developed as cobalt-coated nickel-containing hydroxides for use as positive electrode active materials for secondary batteries.

[0003] Furthermore, in order to increase the cobalt content, a coating layer of a cobalt compound has also been formed on nickel hydroxide particles. For example, Patent Document 1 proposes a coated nickel hydroxide powder for use as a positive electrode active material in alkaline secondary batteries, in which the particle surfaces of nickel hydroxide powder are coated with a cobalt compound mainly composed of cobalt oxyhydroxide or a mixture of cobalt oxyhydroxide and cobalt hydroxide to ensure uniformity and adhesion of the coating layer, wherein the valence of cobalt in the coating is 2.5 or more, and the amount of coating peeling off when 20 g of the coated nickel hydroxide powder is shaken in a sealed container for 1 hour is 20 mass % or less of the total coating amount.

[0004] On the other hand, since uneven coating of the cobalt-coated nickel-containing hydroxide, which is a positive electrode active material, during positive electrode production may increase battery resistance, it may be necessary to reduce the uneven coating of the cobalt-coated nickel-containing hydroxide in order to improve battery characteristics.Furthermore, it may be necessary to further reduce the volume resistivity of the cobalt-coated nickel-containing hydroxide in order to improve battery characteristics.

[0005] However, the coated nickel hydroxide powder for a positive electrode active material of an alkaline secondary battery disclosed in Patent Document 1 has room for improvement in terms of reducing coating unevenness of the coated nickel hydroxide powder for a positive electrode active material of an alkaline secondary battery during positive electrode production and further reducing the volume resistivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-103127 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above circumstances, the present invention aims to provide a cobalt-coated nickel-containing hydroxide in which the average circularity of particles having a cumulative volume percentage of 50 volume % or more (D50) is controlled within a predetermined range, thereby reducing coating unevenness during positive electrode production and preventing an increase in battery resistance, and also providing a method for producing the cobalt-coated nickel-containing hydroxide with reduced volume resistivity. [Means for solving the problem]

[0008] The gist of the configuration of the present invention is as follows. [1] A cobalt-coated nickel-containing hydroxide in which a coating layer containing cobalt oxyhydroxide is formed on a nickel-containing hydroxide, Cobalt-coated nickel-containing hydroxide in which the average circularity of particles having a cumulative volume percentage of 50% by volume or more is in the range of 0.900 or more and 0.990 or less. [2] The cobalt-coated nickel-containing hydroxide according to [1], wherein the particle diameter (D50) having a cumulative volume percentage of 50% by volume is 8.5 μm or more and 14.5 μm or less. [3] The cobalt-coated nickel-containing hydroxide according to [1] or [2], wherein the volume resistivity is 4.0 Ω·cm or less. [4] The cobalt-coated nickel-containing hydroxide according to any one of [1] to [3], wherein the nickel-containing hydroxide contains nickel (Ni) and one or more additive metal elements M selected from the group consisting of cobalt (Co) and zinc (Zn). [5] The cobalt-coated nickel-containing hydroxide according to [4], wherein the molar ratio of nickel (Ni) to additive metal element M is 100 - m:m (where 0.00 ≦ m ≦ 20.0). [6] The cobalt-coated nickel-containing hydroxide according to any one of [1] to [5], wherein the cobalt-coated nickel-containing hydroxide contains nickel (Ni) and cobalt (Co), or nickel (Ni), cobalt (Co), and zinc (Zn), and the molar ratio of nickel (Ni):cobalt (Co):zinc (Zn) is 100 - x - y:x:y (where 0.00 < x ≦ 10.0 and 0.00 ≦ y ≦ 10.0). [7] The BET specific surface area is 10.0 m 2 / g or more and 25.0 m 2 / g or less, and the cobalt-coated nickel-containing hydroxide according to any one of [1] to [6]. [8] The tap density is 1.5 g / cm 3 or more and 2.4 g / cm 3 or less, and the cobalt-coated nickel-containing hydroxide according to any one of [1] to [7]. [9] The cobalt-coated nickel-containing hydroxide according to any one of [1] to [8], which is used as a positive electrode active material for a nickel-hydrogen secondary battery.

[10] A positive electrode having the cobalt-coated nickel-containing hydroxide according to any one of [1] to [9] and a metal current collector.

[11] A nickel-metal hydride secondary battery comprising the positive electrode according to

[10] .

[12] A nickel-containing hydroxide preparation step of adding a nickel-containing metal salt solution, an alkali solution, and a complexing agent into a reaction vessel to prepare a nickel-containing hydroxide by a crystallization reaction; and a nickel-containing hydroxide preparation step of forming a coating layer containing cobalt on the surface of the nickel-containing hydroxide particles by adding the nickel-containing hydroxide, a cobalt salt solution, an alkali solution, and a complexing agent into a reaction vessel to form a coating layer containing divalent cobalt on the surface of the nickel-containing hydroxide particles by a crystallization reaction. an oxidation step of adding an alkaline solution to the nickel-containing hydroxide on which the coating layer containing cobalt has been formed under heating conditions, thereby chemically oxidizing the divalent cobalt in the coating layer; A method for producing a cobalt-coated nickel-containing hydroxide, comprising: A method for producing a cobalt-coated nickel-containing hydroxide, wherein the temperature (°C) of an alkaline solution-containing material obtained by adding the alkaline solution to the nickel-containing hydroxide having the coating layer containing cobalt formed thereon is measured every 20 seconds from the start of addition of the alkaline solution, at 0 seconds after the start of addition of the alkaline solution, and the temperature (°C) of the alkaline solution-containing material up to 280 seconds after the start of addition of the alkaline solution, and the sum of calculated values ​​A (°C x min) every 20 seconds, expressed as [temperature of alkaline solution-containing material (°C) x 20 (seconds)] / 60, from 0 seconds to 300 seconds after the start of addition of the alkaline solution, is 350 or more and 420 or less.

[13] The method for producing a cobalt-coated nickel-containing hydroxide according to

[12] , wherein the oxidation step is carried out in a reaction vessel, and the gas phase in the reaction vessel is replaced with a heated gas.

[14] The method for producing a cobalt-coated nickel-containing hydroxide according to

[12] or

[13] , wherein the oxidation step is carried out in a reaction tank, and the alkaline solution-containing material is dried in the reaction tank.

[0009] In the cobalt-coated nickel-containing hydroxide of the present invention, the nickel-containing hydroxide has a coating layer, and the coating layer contains a cobalt compound.

[0010] In the aspect of [1] above, the "average circularity" means, for cobalt-coated nickel-containing hydroxide particles, the circularity is measured by a static automatic image analyzer respectively, and it means the average value of the circularity of the measured cobalt-coated nickel-containing hydroxide powder.

Advantages of the Invention

[0011] According to the cobalt-coated nickel-containing hydroxide of the present invention, since the average circularity of particles with a particle diameter (D50) of 50% by volume or more in the cumulative volume percentage is in the range of 0.900 or more and 0.990 or less, it is possible to reduce the coating unevenness of the cobalt-coated nickel-containing hydroxide during the production of the positive electrode and prevent an increase in battery resistance, and it is also possible to obtain a cobalt-coated nickel-containing hydroxide with a reduced volume resistivity.

[0012] According to the cobalt-coated nickel-containing hydroxide of the present invention, since the volume resistivity is 4.0 Ω·cm or less, the electrical conductivity is further improved, and more excellent battery characteristics can be obtained.

[0013] According to the cobalt-coated nickel-containing hydroxide of the present invention, since the cobalt-coated nickel-containing hydroxide contains nickel (Ni) and cobalt (Co), or nickel (Ni), cobalt (Co) and zinc (Zn), and the molar ratio of nickel (Ni):cobalt (Co):zinc (Zn) is 100 - x - y:x:y (where 0.00 < x ≤ 10.0 and 0.00 ≤ y ≤ 10.0), high utilization rate and excellent charge-discharge characteristics can be obtained, and furthermore, more excellent electrical conductivity can be obtained.

[0014] According to the method for producing a cobalt-coated nickel-containing hydroxide of the present invention, an alkaline solution-containing material is obtained by adding an alkaline solution to a nickel-containing hydroxide having a coating layer containing cobalt. The temperature (°C) of the alkaline solution-containing material at 0 seconds after the start of addition of the alkaline solution and the temperature (°C) of the alkaline solution-containing material up to 280 seconds after the start of addition of the alkaline solution are measured every 20 seconds from the start of addition of the alkaline solution, and the sum of calculated values ​​A (°C × min) every 20 seconds, expressed as [temperature of alkaline solution-containing material (°C) × 20 (seconds)] / 60, from 0 seconds to 300 seconds after the start of addition of the alkaline solution is 350 or more and 420 or less. This makes it possible to reduce coating unevenness of the cobalt-coated nickel-containing hydroxide during production of a positive electrode, thereby preventing an increase in battery resistance and enabling the production of a cobalt-coated nickel-containing hydroxide with a reduced volume resistivity. DETAILED DESCRIPTION OF THE INVENTION

[0015] The cobalt-coated nickel-containing hydroxide of the present invention will be described in detail below. The cobalt-coated nickel-containing hydroxide of the present invention has a coating layer of a cobalt compound formed on the surface of nickel-containing hydroxide particles. That is, the nickel-containing hydroxide particles serve as core particles, and the core particles are coated with a layer of a cobalt compound, for example, mainly a layer of a cobalt compound in which the valence of cobalt is trivalent. An example of the cobalt compound in which the valence of cobalt is trivalent is cobalt oxyhydroxide. From the above, the cobalt-coated nickel-containing hydroxide of the present invention is a particle in which a coating layer containing cobalt oxyhydroxide is formed on nickel-containing hydroxide particles.

[0016] The shape of the cobalt-coated nickel-containing hydroxide particles is not particularly limited, but may be, for example, approximately spherical. The nickel-containing hydroxide particles are, for example, in the form of secondary particles formed by aggregation of a plurality of primary particles. The coating layer containing cobalt oxyhydroxide of the cobalt-coated nickel-containing hydroxide particles may cover the entire surface of the nickel-containing hydroxide particles, or may cover only a partial region of the surface of the nickel-containing hydroxide particles.

[0017] The cobalt-coated nickel-containing hydroxide of the present invention has an average circularity of 0.900 to 0.990 in terms of a particle diameter (D50) at a cumulative volume percentage of 50% by volume or more (hereinafter simply referred to as "D50"). By satisfying this range, coating unevenness of the cobalt-coated nickel-containing hydroxide during positive electrode production can be reduced, preventing an increase in battery resistance, and the volume resistivity of the cobalt-coated nickel-containing hydroxide can be reduced.

[0018] The average circularity of the cobalt-coated nickel-containing hydroxide powder of D50 or more is determined by measuring the circularity of 10,000 cobalt-coated nickel-containing hydroxide particles using a static automatic image analyzer (e.g., Morphologi 4, Malvern Panalytical), and the average circularity of the cobalt-coated nickel-containing hydroxide powder of D50 or more is the average value of the measured circularity. Specifically, the average circularity can be calculated by the following method. The cobalt-coated nickel-containing hydroxide powder is introduced into the analyzer supply section and sprayed onto a slide to fix it. 10,000 of the fixed cobalt-coated nickel-containing hydroxide particles are observed under an optical microscope to obtain images. The obtained images are analyzed to calculate the average circularity of the cobalt-coated nickel-containing hydroxide powder of D50 or more. Note that D50 refers to the particle size measured using a particle size distribution analyzer using a laser diffraction / scattering method.

[0019] As will be described later, the average circularity of D50 or more of the cobalt-coated nickel-containing hydroxide can be adjusted by controlling the heating conditions of the alkaline solution-containing material obtained by adding an alkaline solution to the nickel-containing hydroxide on which a coating layer containing cobalt has been formed in the oxidation step of the coating layer when producing the cobalt-coated nickel-containing hydroxide.

[0020] The average circularity of the cobalt-coated nickel-containing hydroxide at D50 or more is not particularly limited as long as it is in the range of 0.900 to 0.990. However, the lower limit is preferably 0.905, particularly preferably 0.910, from the viewpoint of further reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during positive electrode production, thereby further preventing an increase in battery resistance, and further reducing the volume resistivity of the cobalt-coated nickel-containing hydroxide. On the other hand, the upper limit of the average circularity of the cobalt-coated nickel-containing hydroxide at D50 or more is preferably 0.970, particularly preferably 0.950, from the viewpoint of reducing the volume resistivity of the cobalt-coated nickel-containing hydroxide. The above-mentioned lower and upper limits can be arbitrarily combined. The average circularity of the cobalt-coated nickel-containing hydroxide at D50 or more is, for example, preferably 0.905 to 0.970, particularly preferably 0.910 to 0.950.

[0021] The volume resistivity of the cobalt-coated nickel-containing hydroxide of the present invention is not particularly limited, but is preferably 4.0 Ω·cm or less, more preferably 3.9 Ω·cm or less, and particularly preferably 3.5 Ω·cm or less, in order to further improve the electrical conductivity of the cobalt-coated nickel-containing hydroxide and obtain even better battery characteristics. On the other hand, the lower the lower limit of the volume resistivity of the cobalt-coated nickel-containing hydroxide, the more preferable. An example of the lower limit of the volume resistivity of the cobalt-coated nickel-containing hydroxide is 0.4 Ω·cm. Note that the above upper and lower limits can be combined arbitrarily. The volume resistivity of the cobalt-coated nickel-containing hydroxide is, for example, preferably 0.4 Ω·cm or more and 4.0 Ω·cm or less, more preferably 0.4 Ω·cm or more and 3.9 Ω·cm or less, and particularly preferably 0.4 Ω·cm or more and 3.5 Ω·cm or less.

[0022] The D50 of the cobalt-coated nickel-containing hydroxide of the present invention is not particularly limited, but the lower limit is preferably 8.5 μm or more, more preferably 9.0 μm or more, and particularly preferably 9.5 μm or more, from the viewpoint of reducing coating unevenness of the cobalt-coated nickel-containing hydroxide while maintaining high circularity during positive electrode production. On the other hand, the upper limit of the D50 of the cobalt-coated nickel-containing hydroxide is preferably 14.5 μm or less, more preferably 14.0 μm or less, and particularly preferably 13.5 μm or less, from the viewpoint of reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during positive electrode production. The above-mentioned lower and upper limits can be arbitrarily combined. The D50 of the cobalt-coated nickel-containing hydroxide is, for example, preferably 8.5 μm or more and 14.5 μm or less, more preferably 9.0 μm or more and 14.0 μm or less, and particularly preferably 9.5 μm or more and 13.5 μm or less.

[0023] The particle diameter (D90) at a cumulative volume percentage of 90% by volume of the cobalt-coated nickel-containing hydroxide of the present invention (hereinafter simply referred to as "D90") is not particularly limited, but the lower limit is preferably 14.0 μm or more, and more preferably 14.5 μm or more, from the viewpoint of improving the packing density of the cobalt-coated nickel-containing hydroxide. On the other hand, the upper limit of D90 of the cobalt-coated nickel-containing hydroxide is preferably 20.0 μm or less, and more preferably 19.5 μm or less, from the viewpoint of reducing coating unevenness. The above-mentioned lower and upper limits can be arbitrarily combined. The D90 of the cobalt-coated nickel-containing hydroxide is, for example, preferably 14.0 μm or more and 20.0 μm or less, and more preferably 14.5 μm or more and 19.5 μm or less. D90 refers to the particle diameter measured by a laser diffraction / scattering method with a particle size distribution analyzer.

[0024] The particle diameter (D10) of the cobalt-coated nickel-containing hydroxide of the present invention at a cumulative volume percentage of 10% by volume (hereinafter simply referred to as "D10") is not particularly limited, but the lower limit is preferably 5.5 μm or more, and more preferably 6.0 μm or more, from the viewpoint of improving the packing density of the cobalt-coated nickel-containing hydroxide. On the other hand, the upper limit of D10 of the cobalt-coated nickel-containing hydroxide is preferably 10.0 μm or less, and more preferably 9.5 μm or less, from the viewpoint of ensuring a contact surface with the electrolyte. The above-mentioned lower and upper limits can be arbitrarily combined. The D10 of the cobalt-coated nickel-containing hydroxide is, for example, preferably 5.5 μm or more and 10.0 μm or less, and more preferably 6.0 μm or more and 9.5 μm or less. D10 refers to the particle diameter measured by a laser diffraction / scattering method with a particle size distribution analyzer.

[0025] The particle size distribution width ((D90-D10) / D50) of the cobalt-coated nickel-containing hydroxide of the present invention is not particularly limited, but is preferably 0.5 or more and 1.2 or less, particularly preferably 0.6 or more and 1.1 or less, from the viewpoint of further reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during production of the positive electrode.

[0026] The nickel-containing hydroxide core particles are not particularly limited in composition as long as they are hydroxides containing nickel (Ni), but from the viewpoint of obtaining high utilization rate, excellent charge / discharge characteristics, and electrical conductivity, they preferably contain nickel (Ni) and one or more additional metal elements M selected from the group consisting of cobalt (Co) and zinc (Zn). Furthermore, cobalt and zinc are preferably contained in the form of solid-dissolved cobalt and solid-dissolved zinc. In other words, the nickel-containing hydroxide core particles are preferably nickel hydroxide in which cobalt and / or zinc are solid-dissolved, i.e., nickel-containing hydroxides.

[0027] The molar ratio of nickel to the added metal element M is not particularly limited, but in order to obtain high utilization rate, excellent charge / discharge characteristics, and electrical conductivity, the molar ratio of nickel to the added metal element M is preferably 100-m:m (meaning 0.00≦m≦20.0), more preferably 2.00≦m≦18.0, and particularly preferably 4.00≦m≦15.0.

[0028] The cobalt-coated nickel-containing hydroxide preferably contains nickel and cobalt, or nickel, cobalt and zinc, from the viewpoint of further obtaining high utilization rate, excellent charge-discharge characteristics and electrical conductivity. The molar ratio of nickel:cobalt:zinc is not particularly limited, but the molar ratio of nickel:cobalt:zinc is preferably 100-x-y:x:y (where 0.00 < x ≤ 10.0 and 0.00 ≤ y ≤ 10.0) from the viewpoint of obtaining high utilization rate and excellent charge-discharge characteristics and further obtaining excellent electrical conductivity, more preferably 1.00 ≤ x ≤ 9.00 and 1.00 ≤ y ≤ 8.00, and particularly preferably 3.00 ≤ x ≤ 8.00 and 2.00 ≤ y ≤ 6.00.

[0029] In the cobalt-coated nickel-containing hydroxide of the present invention, the content of cobalt oxyhydroxide in the cobalt compound of the coating layer containing cobalt oxyhydroxide is not particularly limited, but the lower limit value is preferably 70% by mass or more, particularly preferably 80% by mass or more, from the viewpoint of further improving electrical conductivity. Also, the higher the upper limit value of the content of cobalt oxyhydroxide in the cobalt compound of the coating layer containing cobalt oxyhydroxide, the more preferable it is, and a coating layer composed of cobalt oxyhydroxide (the content of cobalt oxyhydroxide is about 100% by mass) is particularly preferable. In the coating layer containing cobalt oxyhydroxide, in addition to cobalt oxyhydroxide, cobalt oxide may be unavoidably contained in the production process.

[0030] The cobalt oxyhydroxide contained in the coating layer has a diffraction peak between diffraction angles of 65° to 66° represented by 2θ of the diffraction pattern obtained by X-ray diffraction measurement. Also, the cobalt content of the coating layer containing cobalt is not particularly limited, but the cobalt content of the coating layer containing cobalt is preferably more than 0% by mass and 6% by mass or less, particularly preferably 2% by mass or more and 5% by mass or less, from the viewpoint of obtaining high utilization rate, excellent charge-discharge characteristics and electrical conductivity.

[0031] In the cobalt-coated nickel-containing hydroxide of the present invention, the nickel content in the nickel-containing hydroxide is not particularly limited, but the lower limit is preferably 85 mol% or more, more preferably 87 mol% or more, and particularly preferably 90 mol% or more. On the other hand, the upper limit is preferably 100 mol% or less, and particularly preferably 97 mol% or less. The above-mentioned lower and upper limits can be combined arbitrarily. The nickel content in the nickel-containing hydroxide is, for example, preferably 85 mol% or more and 100 mol% or less, more preferably 87 mol% or more and 100 mol% or less, and particularly preferably 90 mol% or more and 97 mol% or less.

[0032] The BET specific surface area of ​​the cobalt-coated nickel-containing hydroxide of the present invention is not particularly limited, but the lower limit thereof is 10.0 m from the viewpoint of further reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during the production of the positive electrode while improving density and ensuring a contact surface with the electrolyte. 2 / g or more is preferable, and 10.5m 2 / g or more is more preferable, and 11.0m 2 On the other hand, the upper limit of the BET specific surface area of ​​the cobalt-coated nickel-containing hydroxide particles is 25.0 m / g or more from the viewpoint of obtaining particle strength while reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during the production of a positive electrode. 2 / g or less is preferable, and 24.5m 2 / g or less is more preferable, and 24.0m 2 / g or less is particularly preferred. The above-mentioned lower limit and upper limit values ​​can be combined arbitrarily. The BET specific surface area of ​​the cobalt-coated nickel-containing hydroxide is, for example, 10.0 m 2 / g or more 25.0m 2 / g or less is preferable, and 10.5m 2 / g or more 24.5m 2 / g or less is more preferable, and 11.0m 2 / g or more 24.0m 2 / g or less is particularly preferred.

[0033] The tap density of the cobalt-coated nickel-containing hydroxide of the present invention is not particularly limited, but the lower limit thereof is 1.5 g / cm from the viewpoint of improving the packing density and further reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during the production of the positive electrode. 3 More than 1.6g / cm is preferable. 3 More preferably, 1.7 g / cm 3 On the other hand, the upper limit is set to 2.4 g / cm from the viewpoint of obtaining particle strength of the cobalt-coated nickel-containing hydroxide while reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during the production of the positive electrode. 3 Preferably less than 2.3 g / cm 3 Less than 2.2 g / cm is more preferable. 3 The following is particularly preferred. The above-mentioned lower limit and upper limit values ​​can be combined arbitrarily. The tap density of the cobalt-coated nickel-containing hydroxide is, for example, 1.5 g / cm. 3 More than 2.4g / cm 3 Preferably less than 1.6 g / cm 3 More than 2.3g / cm 3 Less than 1.7 g / cm is more preferable. 3 More than 2.2g / cm 3 The following are particularly preferred:

[0034] The cobalt-coated nickel-containing hydroxide of the present invention can be used, for example, as a positive electrode active material for nickel-hydrogen secondary batteries.

[0035] Next, an example of a method for producing the cobalt-coated nickel-containing hydroxide of the present invention will be described.

[0036] The method for producing the cobalt-coated nickel-containing hydroxide of the present invention includes, for example, a nickel-containing hydroxide preparation step of adding a nickel-containing metal salt solution, an alkaline solution, and a complexing agent into a reaction vessel to prepare a nickel-containing hydroxide by a crystallization reaction; a nickel-containing hydroxide preparation step of adding the nickel-containing hydroxide, a cobalt salt solution, an alkaline solution, and a complexing agent into a reaction vessel to form a coating layer containing divalent cobalt on the surface of the nickel-containing hydroxide particles by a crystallization reaction; and an oxidation step of adding an alkaline solution to the nickel-containing hydroxide with the cobalt-containing coating layer formed thereon under heating conditions to chemically oxidize the divalent cobalt in the coating layer.

[0037] <Nickel-containing hydroxide preparation step> The process for preparing nickel-containing hydroxide, which is the core particle, will be described below. Here, a method for preparing nickel-containing hydroxide in which cobalt and zinc are dissolved will be described as an example. First, a salt solution of nickel, cobalt, and zinc (e.g., a sulfate solution) is reacted with a complexing agent and an alkaline solution by a coprecipitation method to produce nickel-containing hydroxide, thereby obtaining a slurry-like suspension containing nickel-containing hydroxide. Water, for example, is used as the solvent for the suspension.

[0038] The complexing agent is not particularly limited as long as it can form a complex with nickel, cobalt, and zinc ions in an aqueous solution, and examples thereof include ammonium ion donors (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine. The alkaline solution is not particularly limited as long as it adjusts the pH value of the aqueous solution during coprecipitation, and examples thereof include alkali metal hydroxides (e.g., sodium hydroxide and potassium hydroxide).

[0039] When an alkaline solution and a complexing agent are continuously supplied to the reaction vessel in addition to the salt solution, nickel, cobalt, and zinc undergo a crystallization reaction to produce a nickel-containing hydroxide. During the crystallization reaction, the temperature of the reaction vessel is controlled, for example, within a range of 10°C to 80°C, preferably 20 to 70°C, and the pH value in the reaction vessel is controlled, based on a liquid temperature of 40°C, within a range of, for example, pH 9 to pH 13, preferably pH 11 to 13, while the substances in the reaction vessel are appropriately stirred. The reaction vessel may, for example, be a continuous type, in which the formed nickel-containing hydroxide is overflowed to separate it.

[0040] <Step of preparing nickel-containing hydroxide having a coating layer containing cobalt formed thereon> Next, a suspension containing nickel-containing hydroxide, a cobalt salt solution (e.g., an aqueous solution of cobalt sulfate), an alkaline solution (e.g., an aqueous solution of sodium hydroxide), and a complexing agent (e.g., an aqueous solution of ammonium sulfate) are added while stirring with a stirrer, and a coating layer containing a cobalt compound, such as cobalt hydroxide, as a main component, in which cobalt has a valence of two, such as cobalt hydroxide, is formed on the surface of the nickel-containing hydroxide particles by neutralization crystallization, thereby preparing a nickel-containing hydroxide having a coating layer containing cobalt formed thereon. The pH of the step of forming the coating layer is preferably maintained in the range of 9 to 13 at a liquid temperature of 40°C. The nickel-containing hydroxide having a coating layer containing cobalt formed thereon can be obtained as a slurry suspension.

[0041] <Solid-liquid separation and drying process before the oxidation process> Furthermore, the method may further include, as necessary, a step of separating the suspension containing the nickel-containing hydroxide having the cobalt-containing coating layer formed thereon into a solid phase and a liquid phase before the oxidation step, and drying the solid phase containing the nickel-containing hydroxide having the cobalt-containing coating layer formed thereon to obtain a dry powder of the nickel-containing hydroxide having the cobalt-containing coating layer formed thereon. Furthermore, before drying the solid phase, the solid phase may be washed with water or the like as necessary.

[0042] <Oxidation process> Next, the nickel-containing hydroxide on which the cobalt-containing coating layer is formed is subjected to an oxidation treatment. Examples of the oxidation treatment method include chemical oxidation treatment in which an alkaline solution such as an aqueous sodium hydroxide solution is added to the nickel-containing hydroxide on which the cobalt-containing coating layer is formed, mixed, and heated. The oxidation treatment oxidizes the divalent cobalt in the nickel-containing hydroxide on which the cobalt-containing coating layer is formed, and can convert it to trivalent cobalt, i.e., cobalt oxyhydroxide. By oxidizing the divalent cobalt in the coating layer to cobalt oxyhydroxide, a cobalt-coated nickel-containing hydroxide on which the cobalt oxyhydroxide-containing coating layer is formed can be obtained. Note that, in the oxidation treatment, the addition of the alkaline solution, mixing, and heating may be performed simultaneously.

[0043] In the method for producing a cobalt-coated nickel-containing hydroxide of the present invention, in the oxidation step, the temperature (°C) of an alkaline solution-containing material obtained by adding an alkaline solution such as an aqueous sodium hydroxide solution to a nickel-containing hydroxide having a coating layer containing cobalt at 0 seconds after the start of addition of the alkaline solution and the temperature (°C) of the alkaline solution-containing material up to 280 seconds after the start of addition of the alkaline solution are measured every 20 seconds from the start of addition of the alkaline solution, and the sum of calculated values ​​A (°C × min) every 20 seconds, expressed as [temperature of alkaline solution-containing material (°C) × 20 (seconds)] / 60, from 0 seconds to 300 seconds after the start of addition of the alkaline solution is controlled to be 350 or more and 420 or less.

[0044] That is, [temperature of the alkaline solution-containing material at 0 seconds after the start of addition of the alkaline solution (i.e., immediately after the addition of the alkaline solution) (°C) × 20 (seconds)] / 60 is calculated as A1 (°C × min), [temperature of the alkaline solution-containing material 20 seconds after the start of addition of the alkaline solution (°C) × 20 (seconds)] / 60 is calculated as A2 (°C × min), [temperature of the alkaline solution-containing material 40 seconds after the start of addition of the alkaline solution (°C) × 20 (seconds)] / 60 is calculated as A3 (°C × min), and [temperature of the alkaline solution-containing material 60 seconds after the start of addition of the alkaline solution (°C) × 20 (seconds)] / 60 is calculated as A4 (°C × min). The following values ​​are calculated: value A4 (℃×min), calculated value A10 of [temperature of alkaline solution-containing material 180 seconds after start of addition of alkaline solution (℃)×20 (sec)] / 60, calculated value A11 of [temperature of alkaline solution-containing material 200 seconds after start of addition of alkaline solution (℃)×20 (sec)] / 60, calculated value A15 of [temperature of alkaline solution-containing material 280 seconds after start of addition of alkaline solution (℃)×20 (sec)] / 60, and the sum of the 15 calculated values ​​A1 to A15 is controlled to be between 350 (℃×min) and 420 (℃×min).

[0045] From the above, in the method for producing a cobalt-coated nickel-containing hydroxide of the present invention, by controlling the heating conditions when adding an alkaline solution in the oxidation step, a sudden temperature rise of the alkaline solution-containing material is prevented when the alkaline solution is added to the nickel-containing hydroxide on which a coating layer containing cobalt has been formed, and the degree of evaporation of the solvent such as water is adjusted, thereby making the progress of the oxidation reaction uniform.

[0046] In the method for producing a cobalt-coated nickel-containing hydroxide of the present invention, the total of A1 to A15 is controlled to be 350 or more and 420 or less, thereby making the progress of the oxidation reaction uniform and reducing unevenness in the coating of the cobalt-coated nickel-containing hydroxide during the production of a positive electrode. Furthermore, the uniform progress of the oxidation reaction makes it possible to obtain a cobalt-coated nickel-containing hydroxide with reduced volume resistivity.

[0047] The oxidation step is carried out, for example, in a reaction vessel. The temperature in the reaction vessel during the oxidation step is preferably 80°C to 150°C, more preferably 90°C to 140°C. The oxidation treatment time is preferably 0.5 hours to 10 hours, more preferably 1 hour to 5 hours. The temperature of the heated gas introduced into the gas phase in the reaction vessel is preferably 100°C to 150°C, more preferably 110°C to 140°C. By replacing the gas phase in the reaction vessel with heated gas, the degree of evaporation of solvents such as water can be adjusted or accelerated. The alkaline solution-containing material is thermally affected by the temperature in the reaction vessel or the temperature of the heated gas, but these do not have to be the same temperature.

[0048] In the oxidation step, the alkaline solution-containing material may be dried in the reaction vessel to evaporate the solvent such as water until a dry powder of the cobalt-coated nickel-containing hydroxide is obtained.

[0049] <Solid-liquid separation and drying process after oxidation process> Furthermore, after the oxidation step, the cobalt-coated nickel-containing hydroxide may be washed with water as necessary, and after washing with water, the cobalt-coated nickel-containing hydroxide may be separated into a solid phase and a liquid phase, and the solid phase containing the cobalt-coated nickel-containing hydroxide may be dried.

[0050] Next, a positive electrode using the cobalt-coated nickel-containing hydroxide of the present invention and a secondary battery using the positive electrode will be described. Here, a nickel-metal hydride secondary battery will be used as an example of the secondary battery. The nickel-metal hydride secondary battery includes a positive electrode using the cobalt-coated nickel-containing hydroxide of the present invention, a negative electrode, an alkaline electrolyte, and a separator.

[0051] The positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. The positive electrode active material layer comprises a cobalt-coated nickel-containing hydroxide, a binder, and, if necessary, a conductive additive. The conductive additive is not particularly limited as long as it is usable for nickel-metal hydride secondary batteries, and examples thereof include metallic cobalt and cobalt oxide. Examples of binders include, but are not limited to, polymer resins such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and combinations thereof. Examples of positive electrode current collectors include, but are not limited to, punched metal, expanded metal, wire mesh, foamed metal (e.g., nickel foam), mesh-like metal fiber sintered compacts, metal-plated resin sheets, and metal foils.

[0052] In a method for producing a positive electrode, for example, a cobalt-coated nickel-containing hydroxide, a conductive additive, a binder, and water are mixed together to prepare a positive electrode active material slurry, which is then filled into a positive electrode current collector by a known filling method, dried, and then rolled and fixed by a press or the like.

[0053] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector, the negative electrode active material being included in the negative electrode active material. The negative electrode active material is not particularly limited as long as it is a commonly used material, and examples thereof include hydrogen storage alloys. The negative electrode current collector may be made of the same conductive metal material as the positive electrode current collector, such as nickel, aluminum, or stainless steel.

[0054] Furthermore, the negative electrode active material layer may further contain, as necessary, a conductive additive, a binder, etc. Examples of the conductive additive and binder include the same ones as those used in the positive electrode active material layer.

[0055] In a method for producing a negative electrode, for example, a negative electrode active material is first mixed with an optional conductive additive, a binder, and water to prepare a negative electrode active material slurry, which is then filled into a negative electrode current collector by a known filling method, dried, and then rolled and fixed by a press or the like.

[0056] The alkaline electrolyte may contain, for example, water as a solvent and potassium hydroxide or sodium hydroxide as a solute to be dissolved in the solvent. The solutes may be used alone or in combination of two or more.

[0057] The separator is not particularly limited, but examples thereof include polyolefin nonwoven fabrics, such as polyethylene nonwoven fabrics and polypropylene nonwoven fabrics, polyamide nonwoven fabrics, and those which have been subjected to a hydrophilic treatment. [Example]

[0058] Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as they do not depart from the spirit of the present invention.

[0059] Example 1 Preparation of nickel-containing hydroxide An aqueous solution of zinc sulfate and nickel sulfate dissolved in a molar ratio of 4.0:96.0, an aqueous ammonium sulfate solution (complexing agent), and an aqueous sodium hydroxide solution were added dropwise to a reaction vessel having a predetermined volume, and the temperature in the reaction vessel was maintained at 45°C, and the pH in the reaction vessel was maintained at 11.5 to 12.5 based on a liquid temperature of 40°C, while the mixture was continuously stirred with a stirrer. The produced hydroxide was allowed to overflow from the overflow pipe of the reaction vessel and removed. The removed hydroxide was subjected to treatments of washing with water, dehydration, and drying to obtain a nickel-containing hydroxide.

[0060] Formation of a coating layer containing cobalt An aqueous solution of ammonium sulfate, a complexing agent, was added to a reaction vessel containing water so that the ammonia concentration in the reaction vessel was 9.0 to 13.0 g / L. The nickel-containing hydroxide obtained above was then added to form a slurry. An aqueous solution of sodium hydroxide was added dropwise to maintain the pH in the reaction vessel within a range of 9 to 13 at a liquid temperature of 40°C, while the mixture was continuously stirred with a stirrer. While stirring the solution in the reaction vessel with a stirring blade, an aqueous solution of cobalt sulfate with a concentration of 90 g / L was added dropwise. During this time, an aqueous solution of sodium hydroxide was appropriately added dropwise to maintain the pH of the solution in the reaction vessel within a range of 9 to 13 at a liquid temperature of 40°C, forming a coating layer of cobalt hydroxide on the surface of the nickel-containing hydroxide particles, thereby obtaining a suspension of nickel-containing hydroxide coated with cobalt hydroxide. The coated cobalt content was adjusted to be 3% by mass or more and 5% by mass or less.

[0061] Oxidation treatment of nickel-containing hydroxide coated with cobalt hydroxide The suspension of nickel-containing hydroxide coated with cobalt hydroxide obtained as described above was subjected to solid-liquid separation to obtain a dry powder of nickel-containing hydroxide coated with cobalt hydroxide. A 48% by mass aqueous sodium hydroxide solution was added to the obtained dry powder of nickel-containing hydroxide coated with cobalt hydroxide, and the mixture was mixed under heating conditions such that the sum of the above-mentioned A1 to A15 became 412.7 (°C × min). The mixture was then heated and dried at 120°C for 1 hour while mixing, thereby carrying out an oxidation treatment. Note that 0.10 parts by mass of a 48% by mass aqueous sodium hydroxide solution was added to 1.0 part by mass of the dry powder of nickel-containing hydroxide coated with cobalt hydroxide. In the oxidation treatment, the cobalt hydroxide in the coating layer formed on the surface of the nickel-containing hydroxide particles was oxidized to form cobalt oxyhydroxide, which is trivalent cobalt.

[0062] Solid-liquid separation and drying process Next, the nickel-containing hydroxide coated with cobalt oxyhydroxide obtained by the oxidation treatment was subjected to treatments of washing with water, dehydration, and drying, thereby obtaining the cobalt-coated nickel-containing hydroxide of Example 1.

[0063] Example 2 The cobalt-coated nickel-containing hydroxide of Example 2 was obtained in the same manner as in Example 1, except that the heating conditions were set so that the sum of the above A1 to A15 was 394.7 (°C x min).

[0064] Comparative Example 1 A cobalt-coated nickel-containing hydroxide of Comparative Example 1 was obtained in the same manner as in Example 1, except that the heating conditions were such that the total of the above-mentioned A1 to A15 was 424.2 (°C×min).

[0065] Comparative Example 2 A cobalt-coated nickel-containing hydroxide of Comparative Example 2 was obtained in the same manner as in Example 1, except that the heating conditions were such that the total of the above-mentioned A1 to A15 was 428.0 (°C×min).

[0066] Evaluation items (1) Average circularity of particle diameters with cumulative volume percentage of 50% or more (D50) The circularity of 10,000 cobalt-coated nickel-containing hydroxide particles was measured using a static automated image analyzer (Morphologi 4, Malvern Panalytical), and the average circularity of the measured cobalt-coated nickel-containing hydroxide particles of D50 or greater was calculated. Specifically, the cobalt-coated nickel-containing hydroxide powder was introduced into the feed section of the static automated image analyzer and sprayed onto a slide. 10,000 of the fixed cobalt-coated nickel-containing hydroxide particles were observed under an optical microscope, and images were captured. The captured images were analyzed, and the average circularity of the cobalt-coated nickel-containing hydroxide powder of D50 or greater was calculated. D50 was measured using a particle size distribution analyzer (LA-960, Horiba, Ltd.) using the laser diffraction / scattering method. The measurement conditions for the static automatic image analyzer are as follows. Magnification: ×50 (0.5 μm to 50 μm)

[0067] (2) D10, D50, D90 The cobalt-coated nickel-containing hydroxide was measured using a particle size distribution analyzer (LA-960, Horiba, Ltd.) as described above (based on the laser diffraction and scattering method). The measurement conditions were as follows: water was used as the solvent, 1 mL of sodium hexametaphosphate was added as a dispersant, the transmittance after adding the sample was set to 85±3%, and ultrasonic waves were generated to disperse the sample. The refractive index of the solvent used during analysis was 1.333, which is the refractive index of water.

[0068] (3) Volume resistivity The volume resistivity (Ω·cm) of the obtained cobalt-coated nickel-containing hydroxide powder was measured under the following conditions using a powder resistivity system (Loresta) model MCP-PD51 manufactured by Mitsubishi Chemical Analytech Corporation. Probe used: Four-point probe Electrode spacing: 3.0 mm Electrode radius: 0.7mm Sample radius: 10.0 mm Sample mass: 3.00 g Applied pressure: 20 kPa

[0069] (4) Prevents uneven coating A positive electrode active material slurry was prepared by mixing cobalt-coated nickel-containing hydroxide, binder (carboxymethyl cellulose (CMC)), and water in a mass ratio of 1:0.1:0.2. The positive electrode active material slurry was applied to a 0.015 mm aluminum foil using an applicator to a thickness of 0.1 mm to form a positive electrode active material layer on the aluminum foil surface. The thickness (unit: mm) of the positive electrode active material layer was measured at 10 random locations (n=10), and the thickness variation was calculated as the standard deviation.

[0070] (5) Tap density The tap density of the cobalt-coated nickel-containing hydroxide was measured by the constant mass measurement method, one of the methods described in JIS R1628, using a tap density analyzer (manufactured by Seishin Enterprise Co., Ltd., "KYT-4000").

[0071] (6) BET specific surface area 1 g of the cobalt-coated nickel-containing hydroxide was dried in a nitrogen atmosphere at 105° C. for 30 minutes, and then the specific surface area was measured by the one-point BET method using a specific surface area measuring device (Mountec Co., Ltd., "Macsorb").

[0072] (7) Composition of nickel-containing hydroxide The composition of 5 g of nickel-containing hydroxide was measured using a wavelength dispersive X-ray fluorescence spectrometer (Rigaku Corporation, "ZSX Primus").

[0073] Table 1 shows the average circularity of the cobalt-coated nickel-containing hydroxide at D50 or more, D50 of the cobalt-coated nickel-containing hydroxide, the volume resistivity of the cobalt-coated nickel-containing hydroxide, the standard deviation of the thickness variation of the positive electrode active material layer, the tap density of the cobalt-coated nickel-containing hydroxide, and the BET specific surface area of ​​the cobalt-coated nickel-containing hydroxide, and Table 2 shows data on the standard deviation of the thickness variation of the positive electrode active material layer (N=10).

[0074] [Table 1]

[0075] [Table 2]

[0076] As shown in Tables 1 and 2, in Examples 1 and 2 in which the average circularity of the cobalt-coated nickel-containing hydroxide at D50 or more was 0.900 or more and 0.990 or less, the standard deviation of the thickness variation of the positive electrode active material layer was reduced to 0.004 mm and 0.003 mm, respectively, thereby reducing coating unevenness of the cobalt-coated nickel-containing hydroxide during positive electrode fabrication and preventing an increase in battery resistance. Furthermore, in Examples 1 and 2, it was found that the volume resistivity was reduced to 2.3 Ω cm and 2.9 Ω cm, respectively.

[0077] Furthermore, as shown in Table 1, in Examples 1 and 2, the tap density was 2.17 g / cm 3 , and BET specific surface area are 14.7 m2 / g, 15.0m 2 / g. In Examples 1 and 2, the total of A1 to A15 in the alkaline oxidation treatment was controlled to a range of 350 or more and 420 or less, as described above.

[0078] On the other hand, as shown in Table 1, in Comparative Example 1 in which the average circularity of D50 or more of the cobalt-coated nickel-containing hydroxide was 0.892, and in Comparative Example 2 in which it was 0.861, the standard deviation of the thickness variation of the positive electrode active material layer was 0.011 mm and 0.014 mm, respectively, and it was not possible to reduce coating unevenness of the cobalt-coated nickel-containing hydroxide during positive electrode production, and it was not possible to sufficiently prevent an increase in battery resistance. Furthermore, in Comparative Example 2, the volume resistivity was 5.9 Ω cm, and it was found that a reduced volume resistivity could not be obtained.

[0079] Furthermore, as shown in Table 1, in Comparative Examples 1 and 2, the totals of A1 to A15 in the alkaline oxidation treatment were 424.2 and 428.0, respectively, and were not controlled within the range of 350 or more and 420 or less. [Industrial Applicability]

[0080] The cobalt-coated nickel-containing hydroxide of the present invention has an average circularity of D50 or more in the range of 0.900 to 0.990, which reduces coating unevenness of the cobalt-coated nickel-containing hydroxide during positive electrode production, thereby preventing an increase in battery resistance. Furthermore, the volume resistivity of the cobalt-coated nickel-containing hydroxide is reduced, so that the cobalt-coated nickel-containing hydroxide can be used in a wide range of secondary battery fields, and is highly useful, for example, in the field of nickel-metal hydride secondary batteries, which require high battery characteristics such as even higher output and improved utilization rate.

Claims

1. A cobalt-coated nickel-containing hydroxide in which a coating layer containing cobalt oxyhydroxide is formed on a nickel-containing hydroxide, wherein the average circularity of particles having a cumulative volume percentage of 50 volume % or more (D50) is in the range of 0.900 or more and 0.990 or less.

2. 2. The cobalt-coated nickel-containing hydroxide according to claim 1, wherein the particle diameter at a cumulative volume percentage of 50% by volume (D50) is 8.5 μm or more and 14.5 μm or less.

3. 3. The cobalt-coated nickel-containing hydroxide according to claim 1, wherein the volume resistivity is 4.0 Ω·cm or less.

4. 3. The cobalt-coated nickel-containing hydroxide according to claim 1, wherein the nickel-containing hydroxide contains nickel (Ni) and one or more additional metal elements M selected from the group consisting of cobalt (Co) and zinc (Zn).

5. 5. The cobalt-coated nickel-containing hydroxide according to claim 4, wherein the molar ratio of nickel (Ni):additional metal element M is 100-m:m (meaning 0.00≦m≦20.0).

6. 3. The cobalt-coated nickel-containing hydroxide according to claim 1, wherein the cobalt-coated nickel-containing hydroxide contains nickel (Ni) and cobalt (Co), or nickel (Ni), cobalt (Co), and zinc (Zn), and the molar ratio of nickel (Ni):cobalt (Co):zinc (Zn) is 100-x-y:x:y (meaning 0.00<x≦10.0, 0.00≦y≦10.0).

7. BET specific surface area is 10.0 m ２ / g or more 25.0m ２ 3. The cobalt-coated nickel-containing hydroxide according to claim 1, wherein the cobalt content is 1 / g or less.

8. Tap density is 1.5 g / cm ３ 2.4g / cm or more ３ 3. The cobalt-coated nickel-containing hydroxide according to claim 1, wherein:

9. 3. The cobalt-coated nickel-containing hydroxide according to claim 1, which is used as a positive electrode active material for a nickel-metal hydride secondary battery.

10. A positive electrode comprising the cobalt-coated nickel-containing hydroxide according to claim 1 or 2 and a metal current collector.

11. A nickel-metal hydride secondary battery comprising the positive electrode according to claim 10.

12. a nickel-containing hydroxide preparation step in which a nickel-containing metal salt solution, an alkaline solution, and a complexing agent are added to a reaction vessel to prepare a nickel-containing hydroxide by a crystallization reaction; a nickel-containing hydroxide preparation step in which the nickel-containing hydroxide, a cobalt salt solution, an alkaline solution, and a complexing agent are added to a reaction vessel to form a coating layer containing divalent cobalt on the surface of the nickel-containing hydroxide particles by a crystallization reaction; an oxidation step of adding an alkaline solution to the nickel-containing hydroxide on which the cobalt-containing coating layer has been formed under heating conditions, thereby chemically oxidizing the divalent cobalt in the coating layer; A method for producing a cobalt-coated nickel-containing hydroxide, comprising: The method for producing a cobalt-coated nickel-containing hydroxide includes measuring the temperature (°C) of an alkaline solution-containing material obtained by adding the alkaline solution to the nickel-containing hydroxide having the coating layer containing cobalt formed thereon at 0 seconds after the start of addition of the alkaline solution and the temperature (°C) of the alkaline solution-containing material up to 280 seconds after the start of addition of the alkaline solution every 20 seconds from the start of addition of the alkaline solution, and measuring calculated values ​​A (°C x min) every 20 seconds, which are calculated as [temperature of alkaline solution-containing material (°C) x 20 (seconds)] / 60, from 0 seconds to 300 seconds after the start of addition of the alkaline solution, such that the sum of these calculated values ​​A (°C x min) every 20 seconds from 0 seconds to 300 seconds after the start of addition of the alkaline solution is 350 or more and 420 or less.

13. 13. The method for producing a cobalt-coated nickel-containing hydroxide according to claim 12, wherein the oxidation step is carried out in a reaction vessel, and the gas phase in the reaction vessel is replaced with a heated gas.

14. The method for producing a cobalt-coated nickel-containing hydroxide according to claim 12 or 13, wherein the oxidation step is carried out in a reaction tank, and the alkaline solution-containing material is dried in the reaction tank.

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