Preparation method and application of cobalt-coated spherical nickel hydroxide with cobalt oxide on surface and nickel oxide on inner core

Abstract

The invention discloses a preparation method and application of cobalt-coated spherical nickel hydroxide with cobalt oxide on the surface and nickel oxide on the inner core, and the specific preparation process is as follows: firstly, spherical nickel hydroxide is partially oxidized into nickel oxide in the presence of air / oxygen and a strong oxidant, and then cobalt hydroxide is coated on the surface; the preparation method comprises the following steps: preparing spherical nickel hydroxide, then oxidizing cobalt on the surface into cobalt oxide in the presence of an oxidizing agent, and finally preparing the cobalt-coated spherical nickel hydroxide with cobalt oxide on the surface and nickel oxide on the inner core part, and the cobalt-coated spherical nickel hydroxide prepared by the method can be used as a positive electrode active material for assembling a nickel-series secondary battery. And the over-discharge resistance, the capacity performance and the cycle stability of the lithium ion battery are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of positive electrode active materials for nickel-based secondary batteries, and relates to the preparation of cobalt-coated spherical nickel hydroxide positive electrode active materials, and specifically to a preparation method and application of cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core. Background Art

[0002] With the development of science and technology, various new types of electrification products have been born one after another, and the application of secondary energy storage batteries has become more extensive. At the same time, higher requirements have been put forward for the performance of secondary energy storage batteries. Spherical nickel hydroxide is the positive electrode active material of various alkaline secondary batteries (such as Ni / Cd, Ni / Mn, Ni / H, etc.), and plays a vital role in the excellent performance of secondary energy storage batteries. Ordinary nickel hydroxide is a low-conductivity P-type semiconductor with low charge and discharge efficiency and poor electrode performance. Its performance improvement has always been a major research direction. In order to improve the conductivity between spherical nickel hydroxide particles, between active substances and conductive skeletons, and between active substances and electrolytes, and improve the performance of electrodes, R&D personnel use different additives to modify spherical nickel hydroxide. Cobalt-coated spherical nickel hydroxide is one of the fastest-growing and most mature materials, and it has the advantages of strong large current charge and discharge capability, good cycle performance, high discharge platform and excellent conductivity.

[0003] At present, most of the methods for producing high-performance spherical nickel hydroxide adopt ammonia complex precipitation method, and the modification methods to improve its performance mainly include mechanical mixing, electrochemical co-deposition, surface plating, chemical co-precipitation method, etc. Conductive substances such as CoO are doped into the nickel hydroxide active material by mechanical mixing. Due to the limitation of mixing process conditions, the nickel hydroxide active material and the conductive substance are mixed unevenly, and the improvement effect is limited. Co coating on the surface of nickel hydroxide particles by chemical plating can better solve the problem that Ni(OH)2 generated during discharge accumulates at the electrode / solution interface to form high interface resistance and prevent further discharge. It is an effective way to improve the conductivity of nickel electrodes, but surface-coated Co is easily converted into poorly active CoO(OH) and Co3O4, which reduces the performance of nickel electrodes, and the production process is complicated and the cost is high. Coating Co(OH)2 on the surface of spherical nickel hydroxide by chemical method can improve the electrical properties of spherical nickel hydroxide. Co(OH)2 is uniformly deposited on the surface of spherical nickel hydroxide. Appropriate coating method and amount of cobalt coating can effectively improve the electrochemical cycle stability and capacity retention rate of spherical nickel hydroxide.

[0004] Patent document No. 200810048260.0 discloses a method for uniformly, tightly and firmly coating the surface of powdered nickel hydroxide particles used as positive active materials for alkaline storage batteries with a layer of CoOOH for improving conductivity. The method comprises adding powdered nickel hydroxide to an aqueous solution of a soluble cobalt salt, stirring and reacting at 40-100°C for 0.5-10 hours in the presence of hydrogen peroxide, filtering and separating, and drying at 40-200°C for 1-48 hours, thereby obtaining a powdered cobalt-coated nickel hydroxide electrode material. The powdered cobalt-coated nickel hydroxide electrode material prepared by the method has good conductivity, strong large current charge and discharge capability, and good cycle stability. However, the process realizes the coating of CoOOH on the surface of nickel hydroxide in the presence of hydrogen peroxide, and does not perform oxidation modification of the inner core nickel hydroxide, so its cycle stability still needs to be further improved.

[0005] Patent document No. 200510048557.3 discloses a method for coating cobalt hydroxide oxide on the surface of spherical nickel hydroxide. The process flow is as follows: 0.5-2 mol / L cobalt sulfate solution, 3-8 mol / L sodium hydroxide solution and 6-10 mol / L ammonia water are prepared, and 1 part of spherical nickel hydroxide is added into a reactor which has been previously added with 6-12 parts of deionized water according to a weight ratio. The temperature of the reactor is controlled at 30-70°C during stirring, and a metering pump is used to adjust the molar ratio. 1 part of cobalt sulfate solution, 2-2.5 parts of sodium hydroxide solution, and 0.8-1.5 parts of ammonia water are added to the reactor to react, and the pH value is maintained at 10-11. The reaction is carried out for 3-8 hours, and the feeding of cobalt sulfate solution is stopped. Sodium hydroxide solution is continued to be added to raise the pH value to 12-13.6. After the temperature rises to 80-90°C, 1%-5% of the weight of spherical nickel hydroxide sodium hypochlorite is added, and the reaction is stirred for 30-60 minutes. The solution after the reaction is completed is separated from the solid and dried. The capacity recovery ability of the material prepared by this method after making the battery is improved by 15%-30% compared with that of conventional spherical nickel hydroxide. However, after the process of cobalt hydroxide coating on the surface of nickel hydroxide is completed, the surface of nickel hydroxide is oxidized to cobalt hydroxide oxide in the presence of the oxidant sodium hypochlorite, and the oxidation modification of the inner core nickel hydroxide is not carried out, so its cycle stability performance needs to be further improved.

[0006] Patent document No. 201310150593.5 discloses a method for preparing spherical nickel hydroxide coated with γ-hydroxy cobalt oxide, and the process is as follows: first, spherical nickel hydroxide coated with cobalt hydroxide is prepared, and then, in a reactor, oxygen is introduced under stirring conditions, and pre-oxidation is performed until the color of the material in the reactor stops changing, and the temperature in the reactor is controlled to be 40-150°C; then, an alkali metal hydroxide solution is added to the reactor, and oxygen is continuously introduced under stirring conditions. After the oxidation reaction lasts for a certain period of time, the product obtained by oxidation is washed and dried with pure water to obtain nickel hydroxide coated with γ-hydroxy cobalt oxide. This method can inhibit the cobalt dissolution reaction in the initial stage of oxidation, and a large amount of water is not generated during the preparation process, and the material has less sieve material when sieving. However, after the process of coating the surface of nickel hydroxide with cobalt hydroxide, the process realizes the oxidation of the surface of nickel hydroxide with cobalt to γ-hydroxy cobalt oxide under the conditions of the presence of alkali metal hydroxide and oxygen, and does not carry out oxidation modification of the inner core nickel hydroxide, so its cyclic stability needs to be further improved.

[0007] Patent document No. 200710035313.0 discloses a method for preparing nickel hydroxide coated with γ-hydroxy cobalt oxide, and the process is as follows: firstly, a layer of cobalt hydroxide is coated on the surface of spherical nickel hydroxide, and then the surface-coated cobalt hydroxide layer is oxidized into γ-hydroxy cobalt oxide under the conditions of high concentration of sodium hydroxide and oxygen, or the γ-hydroxy cobalt oxide layer is treated with metal embedding. The method mainly controls the coating layer to present a flaky structure of cobalt hydroxide, so that the conductive network of the γ-hydroxy cobalt oxide coating layer finally prepared is more uniform, more complete, and has better conductivity, so that the nickel hydroxide positive electrode active material coated with γ-hydroxy cobalt oxide has the characteristics of high over-discharge capacity recovery rate, good large current discharge performance, low self-discharge, and good cycle life. However, after the process of coating the nickel hydroxide with cobalt hydroxide on the surface is completed, the process realizes the oxidation of the cobalt-coated nickel hydroxide surface to γ-hydroxy cobalt oxide under the conditions of high concentration of sodium hydroxide and oxygen, and does not carry out oxidation modification of the inner core nickel hydroxide, so its cycle stability performance needs to be further improved. Summary of the invention

[0008] The technical problem solved by the present invention is to provide a method for preparing cobalt-coated spherical nickel hydroxide with surface cobalt oxidation and inner core nickel oxidation, which is simple in process and low in cost. The cobalt-coated spherical nickel hydroxide prepared by the method can be used as a positive electrode active material for assembling nickel-based secondary batteries, and its over-discharge resistance, capacity performance and cycle stability performance are effectively improved.

[0009] The present invention adopts the following technical solution to solve the above technical problems, a method for preparing cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the core, characterized by the specific steps of: Step S1: adding pure water and spherical nickel hydroxide to a reactor, setting the temperature of the reactor to 30-70° C., continuously introducing oxygen or air into the reactor, and then adding a strong oxidant and an alkaline solution to the reactor in parallel and stirring the reaction for 30-60 minutes, maintaining the pH of the mixed system in the reactor at 10-11.5 by controlling the amount of the alkaline solution added, and controlling the oxidation amount of the spherical nickel hydroxide in the reactor to 5wt%-30wt% by controlling the amount of the strong oxidant added, wherein the strong oxidant is one or more of sodium perchlorate, sodium hypochlorite, sodium persulfate or ammonium persulfate; Step S2, stop introducing oxygen or air into the reactor, add a soluble cobalt salt solution, an alkaline solution and a complexing agent solution into the reactor in parallel, keep the pH of the mixed system in the reactor at 10-11.5 and the concentration of the complexing agent at 0.5-10 g / L by controlling the amount of the alkaline solution and the complexing agent solution added, stop feeding the soluble cobalt salt solution after the amount of cobalt coating reaches the requirement, continue to add the alkaline solution to raise the pH of the mixed system to 12-13.6, and at the same time increase the temperature of the reactor to 80-90° C., then add an oxidant in an amount of 1wt%-5wt% of the weight of the spherical nickel hydroxide and stir the reaction for 30-60 min to obtain spherical nickel hydroxide with cobalt oxyhydroxide coated on the surface, wherein the oxidant is one or more of sodium hypochlorite or hydrogen peroxide; Step S3, after the reaction is completed, the material is subjected to solid-liquid separation, washing, and drying to obtain the target product, a cobalt-coated spherical nickel hydroxide with a cobalt-oxidized surface and a nickel-oxidized core.

[0010] It is further defined that the stirring speed of the reactor in step S1 and step S2 is 200-1000 r / min.

[0011] It is further defined that the mass ratio of pure water to spherical nickel hydroxide in step S1 is 1:0.5-3, the alkali in the alkaline solution is one or more of sodium hydroxide or potassium hydroxide, and the concentration of the alkaline solution is 2-10 mol / L.

[0012] It is further defined that the cobalt coating amount in step S2 is regulated by controlling the feed amount of the soluble cobalt salt solution, specifically by controlling the feed amount of the soluble cobalt salt to 0.2wt%~5wt% of the weight of the spherical nickel hydroxide to achieve the regulation of the cobalt coating amount, thereby meeting the production indicators required by customers.

[0013] It is further defined that the soluble cobalt salt in the soluble cobalt salt solution in step S2 is one or more of cobalt sulfate, cobalt chloride or cobalt nitrate, and the concentration of the soluble cobalt salt solution is 0.5~3 mol / L; the alkali in the alkaline solution is one or more of sodium hydroxide or potassium hydroxide, and the concentration of the alkaline solution is 2~10 mol / L; the complexing agent in the complexing agent solution is one or more of ammonia water, EDTA, citric acid or sodium citrate, and the concentration of the complexing agent solution is 2~10 mol / L.

[0014] The cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core of the invention is used as a positive electrode active material for preparing a nickel-based secondary battery.

[0015] It is further specified that the nickel-based secondary battery is a nickel-hydrogen secondary battery.

[0016] In the positive electrode active material of nickel-hydrogen secondary batteries, oxidation of a portion of spherical nickel hydroxide can form nickel oxide with a specific structure (such as NiO or NiOOH, etc.), which helps to improve the cycle stability of nickel-hydrogen secondary batteries and reduce self-discharge. The specific reasons are as follows: 1. Improve electrochemical performance: Nickel oxide can participate in electrochemical reactions as an active substance during the charge and discharge process of nickel-hydrogen secondary batteries. The presence of nickel oxide can improve the conductivity of the positive electrode active material, thereby improving the charge and discharge efficiency and cycle stability of nickel-hydrogen secondary batteries. 2. Improve structural stability: The introduction of nickel oxide can increase the structural stability of the positive electrode active material and reduce the structural collapse caused by volume change during the charge and discharge process, which helps to extend the cycle life of nickel-hydrogen secondary batteries. 3. Reduce self-discharge: Self-discharge is the phenomenon that the battery discharges itself without an external load. The oxidation of a portion of nickel hydroxide to nickel oxide can reduce the number of mobile nickel ions in the positive electrode active material, thereby reducing the self-discharge rate. 4. Adjusting the potential window: The potential of nickel oxide is higher than that of nickel hydroxide. Introducing it into the positive electrode active material can adjust the potential window, making the nickel-hydrogen secondary battery more stable during charging and discharging, and effectively reducing the occurrence of side reactions. 5. Synergistic effect: The synergistic effect of nickel and cobalt in hydroxide can optimize the comprehensive performance of nickel-hydrogen secondary batteries. The introduction of nickel oxide in the positive electrode active material can enhance this synergistic effect and further improve the electrochemical performance and cycle stability of nickel-hydrogen secondary batteries. In short, by introducing nickel oxide into the positive electrode active material of nickel-hydrogen secondary batteries, the electrochemical performance of nickel-hydrogen secondary batteries can be effectively improved, their structural stability can be improved, self-discharge can be reduced, and the potential window can be adjusted, thereby improving the overall performance of nickel-hydrogen secondary batteries.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: nickel participates in the redox reaction during the charging and discharging process of the nickel-hydrogen secondary battery. During the charging process, nickel is oxidized from Ni(II) to Ni(III) or Ni(IV), and during the discharging process, nickel is reduced from Ni(III) or Ni(IV) back to Ni(II). This redox reaction ability enables nickel to store and release charges, thereby realizing the energy storage and release functions of the nickel-hydrogen secondary battery. Nickel is not only a key element for charge storage and release in the positive electrode active material of the nickel-hydrogen secondary battery, but also significantly affects the overall performance of the nickel-hydrogen secondary battery through its redox activity, structural stability, conductivity and synergy with other metal elements. The invention adds strong oxidants such as sodium thiosulfate and sodium perchlorate to spherical nickel hydroxide, then adds an alkaline solution, and introduces oxygen, firstly oxidizes 5wt% to 30wt% of the spherical nickel hydroxide, then coats cobalt hydroxide and performs oxidation modification on the cobalt hydroxide, and finally forms cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation on the inner core. The cobalt-coated spherical nickel hydroxide can be used as a positive electrode active material for a nickel-hydrogen secondary battery to manufacture an ultra-low self-discharge battery, has the performance of over-discharge resistance and high capacity, and the cycle stability performance can be improved by 10% to 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a SEM image of the cobalt-coated spherical nickel hydroxide prepared in Example 1; Figure 2 This is the SEM image of the cobalt-coated spherical nickel hydroxide prepared in Example 2. DETAILED DESCRIPTION

[0019] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Example 1

[0020] Step S1, preparing 2.0 mol / L cobalt sulfate solution, 8 mol / L sodium hydroxide solution, and 10 mol / L ammonia solution; Step S2, adding 40 kg of pure water and 40 kg of spherical nickel hydroxide into the reactor, maintaining the stirring speed of the reactor at 800 r / min and the temperature of the reactor at 50° C.; Step S3, continuously introducing oxygen into the reactor at a flow rate of 10 L / min, adding sodium perchlorate solution (4.0 mol / L, flow rate 120 mL / min) and sodium hydroxide solution into the reactor in parallel, maintaining the pH of the mixed system in the reactor at 10.5 by controlling the amount of sodium hydroxide solution added, stirring the reaction for 30 minutes, adding a certain amount of sodium perchlorate according to the chemical reaction stoichiometric ratio of sodium perchlorate and nickel hydroxide, and controlling the oxidation amount of nickel hydroxide to 20wt%; Step S4, turning off the oxygen, adding the cobalt sulfate solution (flow rate 60 mL / min), the sodium hydroxide solution and the ammonia solution into the reactor in parallel, and maintaining the pH of the mixed system in the reactor at 10.5 and the ammonia concentration at 2 g / L by controlling the addition amount of the sodium hydroxide solution and the ammonia solution; Step S5, after the cobalt coating amount reaches the requirement (the cobalt coating amount is controlled according to the production index of the customer's requirements, and the cobalt coating amount is controlled by controlling the amount of cobalt sulfate added to 2wt% of the weight of the spherical nickel hydroxide), the cobalt sulfate solution is stopped from being fed, and the sodium hydroxide solution is continuously added to raise the pH of the mixed system to 12, and the temperature of the reactor is raised to 80°C; Step S6, adding hydrogen peroxide in an amount of 2 wt% of the weight of the spherical nickel hydroxide, maintaining the stirring speed of the reactor at 600 r / min, and stirring the reaction for 30 minutes to obtain spherical nickel hydroxide with cobalt oxyhydroxide coated on the surface; Step S7, after the reaction is completed, the material is subjected to solid-liquid separation, washed, and dried at 100° C. to obtain the target product, spherical nickel hydroxide coated with cobalt with the surface oxidized by cobalt and the inner core partially oxidized by nickel. Figure 1 This is the SEM image of the prepared cobalt-coated spherical nickel hydroxide. It can be seen from the image that the coating layer is evenly and densely coated on the surface of the spherical nickel hydroxide matrix without falling off or peeling off.

[0021] The prepared cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core was used as the positive electrode active material to make a nickel-hydrogen secondary battery with a 0.2C discharge capacity of 277 mAh / g, a self-discharge of 49% at 60℃*7 days, and a capacity retention rate of 94% for 300 cycles at 1C. Example 2

[0022] Step S1, preparing 1.5 mol / L cobalt sulfate solution, 10 mol / L sodium hydroxide solution, and 5 mol / L sodium citrate solution.

[0023] Step S2, adding 40 kg of pure water and 80 kg of spherical nickel hydroxide into the reactor, maintaining the stirring speed of the reactor at 600 r / min and the temperature of the reactor at 60° C.; Step S3, continuously introducing oxygen into the reactor at a flow rate of 10 L / min, adding sodium persulfate solution (2.0 mol / L, 120 mL / min) and sodium hydroxide solution into the reactor in parallel, maintaining the pH of the mixed system in the reactor at 11.0 by controlling the amount of sodium hydroxide solution added, stirring the reaction for 60 minutes, adding a certain amount of sodium persulfate according to the chemical reaction stoichiometric ratio of sodium persulfate and nickel hydroxide, and controlling the oxidation amount of nickel hydroxide to 10 wt%; Step S4, turning off the air, adding cobalt sulfate solution (60 mL / min), sodium hydroxide solution and sodium citrate solution into the reactor in parallel, and maintaining the pH of the mixed system in the reactor at 11.0 and the sodium citrate concentration at 4 g / L by controlling the amount of sodium hydroxide solution and ammonia solution added; Step S5, after the cobalt coating amount reaches the requirement (the cobalt coating amount is controlled according to the production index of the customer's requirements, and the cobalt coating amount is controlled by controlling the amount of cobalt sulfate added to 1wt% of the weight of the spherical nickel hydroxide), the cobalt sulfate solution is stopped from being fed, and the sodium hydroxide solution is continuously added to raise the pH of the mixed system to 12.5, and the temperature of the reactor is raised to 85°C; Step S6, adding sodium hypochlorite at 1 wt% of the weight of the spherical nickel hydroxide, maintaining the stirring speed of the reactor at 500 r / min, and stirring the reaction for 40 minutes to obtain spherical nickel hydroxide with cobalt oxyhydroxide coated on the surface; Step S7, after the reaction is completed, the material is subjected to solid-liquid separation, washed, and dried at 110° C. to obtain the target product, spherical nickel hydroxide coated with cobalt with the surface oxidized by cobalt and the inner core partially oxidized by nickel. Figure 2 This is the SEM image of the prepared cobalt-coated spherical nickel hydroxide. It can be seen from the figure that the surface of the coating layer is smooth without obvious defects such as cracks and bubbles. It is evenly and densely coated on the surface of the spherical nickel hydroxide matrix without falling off or peeling.

[0024] The prepared cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core was used as the positive electrode active material to make a nickel-hydrogen secondary battery with a 0.2C discharge capacity of 278 mAh / g, a self-discharge of 53% at 60℃*7 days, and a capacity retention rate of 89% for 300 cycles at 1C.

[0025] Comparative Example 1 Step S1, preparing 2.0 mol / L cobalt sulfate solution, 8 mol / L sodium hydroxide solution, and 10 mol / L ammonia solution; Step S2, adding 40 kg of pure water and 40 kg of spherical nickel hydroxide into the reactor, maintaining the stirring speed of the reactor at 800 r / min and the temperature of the reactor at 50° C.; Step S3, adding cobalt sulfate solution (60 mL / min), sodium hydroxide solution and ammonia solution into the reactor in parallel, and maintaining the pH of the mixed system in the reactor at 10.5 and the concentration of ammonia solution at 2 g / L by controlling the amount of sodium hydroxide solution and ammonia solution added; Step S4, after the cobalt coating amount reaches the requirement (the cobalt coating amount is controlled according to the production index of the customer's requirements, and the cobalt coating amount is controlled by controlling the addition amount of cobalt sulfate to 2wt% of the weight of the spherical nickel hydroxide), the cobalt sulfate solution is stopped from being fed, and the sodium hydroxide solution is continuously added to raise the pH of the mixed system to 12, and the temperature of the reactor is raised to 80°C; Step S5, adding hydrogen peroxide in an amount of 2 wt% of the weight of the spherical nickel hydroxide, maintaining the stirring speed of the reactor at 600 r / min, and stirring the reaction for 30 minutes to obtain spherical nickel hydroxide with cobalt oxyhydroxide coated on the surface; Step S6, after the reaction is completed, the material is subjected to solid-liquid separation, washed, and dried at 100° C. to obtain spherical nickel hydroxide with cobalt oxyhydroxide coated on the surface.

[0026] The prepared spherical nickel hydroxide with surface coated with cobalt oxyhydroxide was used as the positive electrode active material to make a nickel-hydrogen secondary battery. The 0.2C discharge capacity was 279 mAh / g, the self-discharge at 60℃*7 days was 67%, and the capacity retention rate at 1C 300 cycles was 78%.

[0027] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the core, characterized in that The specific steps are: Step S1: adding pure water and spherical nickel hydroxide to a reactor, setting the temperature of the reactor to 30-70° C., continuously introducing oxygen or air into the reactor, and then adding a strong oxidant and an alkaline solution to the reactor in parallel and stirring the reaction for 30-60 minutes, maintaining the pH of the mixed system in the reactor at 10-11.5 by controlling the amount of the alkaline solution added, and controlling the oxidation amount of the spherical nickel hydroxide in the reactor to 5wt%-30wt% by controlling the amount of the strong oxidant added, wherein the strong oxidant is one or more of sodium perchlorate, sodium hypochlorite, sodium persulfate or ammonium persulfate; Step S2, stop introducing oxygen or air into the reactor, add a soluble cobalt salt solution, an alkaline solution and a complexing agent solution into the reactor in parallel, keep the pH of the mixed system in the reactor at 10-11.5 and the concentration of the complexing agent at 0.5-10 g / L by controlling the amount of the alkaline solution and the complexing agent solution added, stop feeding the soluble cobalt salt solution after the amount of cobalt coating reaches the requirement, continue to add the alkaline solution to raise the pH of the mixed system to 12-13.6, and at the same time increase the temperature of the reactor to 80-90° C., then add an oxidant in an amount of 1wt%-5wt% of the weight of the spherical nickel hydroxide and stir the reaction for 30-60 min to obtain spherical nickel hydroxide with cobalt oxyhydroxide coated on the surface, wherein the oxidant is one or more of sodium hypochlorite or hydrogen peroxide; Step S3, after the reaction is completed, the material is subjected to solid-liquid separation, washing, and drying to obtain the target product, a cobalt-coated spherical nickel hydroxide with a cobalt-oxidized surface and a nickel-oxidized core.

2. The method for preparing cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core according to claim 1, characterized in that: The stirring speed of the reactor in step S1 and step S2 is 200-1000 r / min.

3. The method for preparing cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core according to claim 1, characterized in that: In step S1, the mass ratio of pure water to spherical nickel hydroxide is 1:0.5-3, the alkali in the alkali solution is one or more of sodium hydroxide or potassium hydroxide, and the concentration of the alkali solution is 2-10 mol / L.

4. The method for preparing cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core according to claim 1, characterized in that: The cobalt coating amount in step S2 is regulated by controlling the feed amount of the soluble cobalt salt solution, specifically by controlling the feed amount of the soluble cobalt salt to 0.2wt%~5wt% of the weight of the spherical nickel hydroxide to achieve the regulation of the cobalt coating amount, thereby meeting the production indicators required by customers.

5. The method for preparing cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the inner core according to claim 1, characterized in that: In step S2, the soluble cobalt salt in the soluble cobalt salt solution is one or more of cobalt sulfate, cobalt chloride or cobalt nitrate, and the concentration of the soluble cobalt salt solution is 0.5-3 mol / L; the alkali in the alkaline solution is one or more of sodium hydroxide or potassium hydroxide, and the concentration of the alkaline solution is 2-10 mol / L; the complexing agent in the complexing agent solution is one or more of ammonia water, EDTA, citric acid or sodium citrate, and the concentration of the complexing agent solution is 2-10 mol / L.

6. The cobalt-coated spherical nickel hydroxide with a cobalt-oxidized surface and a nickel-oxidized core prepared by the method according to any one of claims 1 to 5 is used as a positive electrode active material in the preparation of nickel-based secondary batteries.

7. The use according to claim 6, characterized in that: The nickel-based secondary battery is a nickel-hydrogen secondary battery.

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