A method for coating the surface of nickel hydroxide particles with cobalt

Abstract

The application discloses a method for coating cobalt on the surface of nickel hydroxide particles, and belongs to the technical field of nickel-hydrogen battery preparation. The method solves the problem that trivalent nickel impurities are easily mixed on the surface of particles during the coating of cobalt, and greatly improves the electrochemical performance of the battery. The steps of the method are as follows: 50% of the volume of a reaction kettle is filled with a basic bottom solution containing Ni(OH)2 particles, a CoSO4 solution is prepared, Na2SO3 is added into the CoSO4 solution, a mixed solution is prepared, inert gas is introduced into the reaction kettle, a feeding valve of the reaction kettle is opened, N2H4·H2O solution is added as a strong reducing agent, a stirrer of the reaction kettle is started, CoSO4 solution and NaOH solution are added, after the addition of the CoSO4 solution is completed, all the feeding is stopped, and the stirring and ripening are continued, finally, the reactants are taken out, washed and dried to obtain a cobalt-coated nickel hydroxide precursor. The method is convenient to operate, efficient in process, stable in the obtained cobalt-coated nickel hydroxide precursor, uniform in the color of the coating layer on the surface of the particles, good in electrochemical performance, and has strong practicability and wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of nickel-hydrogen battery preparation technology, specifically relating to a method for coating cobalt on the surface of nickel hydroxide particles. Background Technology

[0002] In the preparation of spherical nickel hydroxide, a precursor for nickel-metal hydride battery cathode materials, a layer of trivalent cobalt hydroxide is often coated onto the surface of its particles. This process is called "cobalt coating" or "cobalt cladding." The introduction of the coating layer aims to improve the rate performance, cycle stability, and structural integrity of the final sintered product. Ideally, the coating layer should be pure-phase trivalent cobalt hydroxide, which has good electronic conductivity and helps to improve electrode reaction kinetics.

[0003] However, during the cobalt coating reaction in an alkaline aqueous environment, the nickel hydroxide core is extremely sensitive to oxygen. Under stirring conditions and when the slurry is in contact with air, the divalent nickel on the particle surface is easily locally oxidized by oxygen in the air, generating trivalent nickel hydroxide with high resistance and poor conductivity. This trivalent nickel hydroxide, intercalated within the trivalent cobalt hydroxide coating layer, will severely reduce the overall electronic conductivity of the cathode material, leading to a decrease in specific capacity and ultimately degrading the electrochemical performance of the battery.

[0004] Currently, most common cobalt coating processes are carried out in an air atmosphere or with only simple inert gas protection, which is difficult to effectively isolate oxygen. Especially in reaction systems with high pH values ​​and high stirring intensity, the contact area between the slurry and air increases significantly, thereby increasing the risk of oxidation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for coating nickel hydroxide particles with cobalt, in order to solve the problem that trivalent nickel impurities are easily trapped on the particle surface during existing cobalt coating processes, which greatly affects the electrochemical performance of the battery.

[0006] The technical solution of the present invention is: a method for coating the surface of nickel hydroxide particles with cobalt, characterized by comprising the following steps: A. Add an alkaline bottom solution containing Ni(OH)2 particles, accounting for 50% of the volume of the reactor, and add 0.1 kg to 0.5 kg of Na2SO3 per cubic meter to the reactor to prepare a mixed alkaline bottom solution. At the same time, prepare a CoSO4 solution with a concentration of 1.4 mol / L to 1.5 mol / L, and add 0.1 kg to 0.5 kg of Na2SO3 per cubic meter to the CoSO4 solution to prepare a mixed solution of CoSO4 and Na2SO3. B. Tightly close the feed port of the reactor, and feed at a rate of 0.5m. 3 / h~2m 3 Inert gas is introduced into the reactor at a rate of / h, so that the inert gas will expel the air from the reactor. C. After introducing inert gas for 10 to 30 minutes, open the other feed port of the reactor and add a 10% N2H4·H2O solution as a strong reducing agent at a rate of 0.5 L / h to 2.0 L / h to maintain a strong reducing environment in the reactor. D. After adding N2H4·H2O solution for 5 to 15 minutes, start the reactor stirrer and control the stirring speed of the reactor stirrer to 130 r / min to 150 r / min. At the same time, turn on the feed pumps of CoSO4 solution and NaOH solution and add the mixed solution of CoSO4 and Na2SO3 prepared in step A and NaOH solution into the reactor. Set the temperature in the reactor to 55℃ to 60℃ and control the pH value in the reactor to 11.0 to 11.5. The precipitation and coating reaction of Co(OH)3 on the surface of Ni(OH)2 particles will take place. During the reaction, the addition of inert gas and N2H4·H2O solution will be maintained and the reaction will continue for 5.5 h to 6.5 h. E. After the CoSO4 solution is added, turn off the feed pumps for the CoSO4 solution and NaOH solution, and at the same time stop the introduction of inert gas and the addition of N2H4·H2O solution into the reactor. Continue stirring and aging, and finally take out the reactants, wash and dry them to obtain the cobalt-coated nickel hydroxide precursor.

[0007] As a further improvement of the present invention, in step A, the alkaline bottom solution containing Ni(OH)2 particles also contains an ammonia-containing complexing agent to maintain the stability of the solution.

[0008] As a further improvement of the present invention, in step B, the inert gas introduced is nitrogen or argon.

[0009] As a further improvement of the present invention, in step C, hydrazine hydrate can preferentially react with trace amounts of oxygen that may invade the system or the small amount of trivalent cobalt species that have already been generated, thereby maintaining the strong reducing environment of the system.

[0010] As a further improvement of the present invention, in step D, the amount of CoSO4 solution added to the reactor is 40% of the reactor volume.

[0011] As a further improvement of the present invention, in step E, the stirring and maturation time is continued for at least 30 minutes.

[0012] As a further improvement of the present invention, the reactor is equipped with a folded disc stirring paddle and an upper baffle is provided above the stirring paddle, which helps to reduce the contact and renewal area between the slurry and the gas phase in the reactor, and generate a coating layer with good crystallinity.

[0013] The beneficial effects of this invention are: 1. This invention uses inert gas and N2H4·H2O solution in the reactor to maintain an oxygen-free, strongly reducing environment, ensuring that divalent nickel is not oxidized to trivalent nickel during the process of coating cobalt hydroxide on the surface of nickel hydroxide, thus improving the cobalt coating effect and avoiding affecting the electrochemical performance after cobalt coating.

[0014] 2. The present invention also adds sodium sulfite, an auxiliary reducing agent, to the solution and base solution during preparation to remove dissolved oxygen during solution preparation and transportation, thereby reducing the source of oxidation from the source and ensuring the effect of subsequent cobalt coating.

[0015] 3. This invention adopts an updated reactor structure. By combining the stirring paddle and baffle structure, it ensures uniform mixing of materials and suspension of particles, while reducing the degree of turbulence and eddies on the liquid surface, reducing the contact and renewal area between the slurry and the gas phase in the reactor, thereby reducing the opportunity for oxygen to transfer mass to the liquid phase, and is conducive to the formation of a coating layer with good crystallinity.

[0016] 4. This invention is easy to operate and efficient. By creating an oxygen-free, strongly reducing environment in the reactor, the obtained cobalt-coated nickel hydroxide precursor is stable, the particle surface coating is uniform in color, and the electrochemical performance is good. It has strong practicality and broad application prospects. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope image of the cobalt-coated nickel hydroxide precursor of Example 1 of the present invention; Figure 2 This is a finished product image of the cobalt-coated nickel hydroxide precursor of Example 1 of the present invention; Figure 3 This is a cross-sectional view of the reactor of the present invention.

[0018] In the diagram: 1. Cover plate; 2. Disc agitator. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1 A method for cobalt coating on the surface of nickel hydroxide particles, selecting 5m 3 The reactor was filled with 2.5 ml of [material / resource]. 3 An alkaline solution containing Ni(OH)₂ particles was prepared. This alkaline solution contained an ammonia-containing complexing agent, and 0.25 kg of Na₂SO₃ was added to dissolve it, thus preparing a mixed solution. Separately, 2 mL of a 1.4 mol / L CoSO₄ solution was prepared. 3 Add 0.2 kg of Na2SO3 to dissolve it.

[0021] Close the reactor and bring the pressure to 0.5m. 3Nitrogen gas is introduced into the reactor at a rate of 0.5 L / h to displace the air inside. After 10 min of nitrogen introduction, the reactor feeding valve is opened, and a 10% N2H4·H2O solution is added to the reactor as a strong reducing agent at a rate of 0.5 L / h. Five min after adding the N2H4·H2O solution, the reactor stirrer is started and its speed is controlled at 130 r / min. Simultaneously, the feed pumps for CoSO4 solution and NaOH solution are turned on, and 1.4 mol / L CoSO4 solution and NaOH solution are added to the reactor. At the same time, the reactor temperature is set to 55℃, and the pH value inside the reactor is controlled to 11.0. The precipitation and coating reaction of Co(OH)3 on the surface of Ni(OH)2 particles continues for 5.5 h.

[0022] After adding all the prepared CoSO4 solution to the reactor, the feed pumps for the CoSO4 solution and NaOH solution were turned off. At the same time, the introduction of inert gas and the addition of N2H4·H2O solution into the reactor were stopped. Stirring and aging continued. Finally, the reactants were taken out, washed, and dried to obtain the cobalt-coated nickel hydroxide precursor.

[0023] like Figure 1-2 As shown, the obtained cobalt-coated nickel hydroxide precursor exhibits a uniform color coating on the particle surface. XPS and chemical titration analysis revealed that almost all nickel in the core is divalent, and after further analysis, the trivalent nickel content is 0.42%, which is lower than 0.5%. The cathode material prepared in this manner exhibits significantly better specific capacity and rate performance than the comparative sample prepared using conventional methods.

[0024] like Figure 3 As shown, the reactor is equipped with a folding disc agitator 2, and an upper baffle 1 is set above the agitator. While the material is uniformly mixed and the particles are suspended, the turbulence and eddies on the liquid surface are reduced, the contact and renewal area between the slurry and the gas phase in the reactor are reduced, thereby reducing the chance of oxygen mass transfer to the liquid phase and facilitating the formation of a coating layer with good crystallinity.

[0025] Example 2 A method for coating cobalt onto the surface of nickel hydroxide particles, selecting 10m 3 Add 5m to the reactor. 3 An alkaline solution containing Ni(OH)₂ particles was prepared. This alkaline solution contained an ammonia-containing complexing agent, and 2.5 kg of Na₂SO₃ was added to dissolve it, thus preparing a mixed solution. Separately, 4 mL of a 1.5 mol / L CoSO₄ solution was prepared. 3 Add 2 kg of Na2SO3 to dissolve it.

[0026] Shut down the reactor, at 2m 3Nitrogen gas is introduced into the reactor at a rate of 1 h to displace the air inside. After 30 min of nitrogen introduction, the reactor feeding valve is opened, and a 10% N2H4·H2O solution is added to the reactor at a rate of 2 L / h as a strong reducing agent. 15 min after adding the N2H4·H2O solution, the reactor stirrer is started and the stirring speed is controlled at 150 r / min. At the same time, the feed pumps for CoSO4 solution and NaOH solution are turned on, and 1.5 mol / L CoSO4 solution and NaOH solution are added to the reactor. The reactor temperature is set to 60℃ and the pH value is controlled to 11.5. The precipitation and coating reaction of Co(OH)3 on the surface of Ni(OH)2 particles continues for 6.5 h.

[0027] After adding all the prepared CoSO4 solution to the reactor, the feed pumps for the CoSO4 solution and NaOH solution were turned off. At the same time, the introduction of inert gas and the addition of N2H4·H2O solution into the reactor were stopped. Stirring and aging continued. Finally, the reactants were taken out, washed, and dried to obtain the cobalt-coated nickel hydroxide precursor.

[0028] The obtained cobalt-coated nickel hydroxide precursor showed a uniform color of coating on the particle surface. XPS and chemical titration analysis revealed that almost all nickel in the core was divalent, and after further analysis, the trivalent nickel content was 0.38%, lower than 0.5%. The cathode material prepared in this manner exhibited significantly better specific capacity and rate performance than the comparative sample prepared using conventional methods.

[0029] Example 3 A method for coating cobalt onto the surface of nickel hydroxide particles involves selecting a 10 m³ reactor, adding 5 m³ of alkaline bottom solution containing Ni(OH)₂ particles to the reactor, the alkaline solution containing an ammonia complexing agent, and adding 1.25 kg of Na₂SO₃ to dissolve and prepare a mixed solution. Separately, prepare 4 m³ of a 1.5 mol / L CoSO₄ solution and add 1 kg of Na₂SO₃ to dissolve it.

[0030] Close the reactor, at 1m 3Nitrogen gas is introduced into the reactor at a rate of 1 L / h to displace the air inside. After 15 minutes of nitrogen introduction, the reactor feeding valve is opened, and a 10% N2H4·H2O solution is added to the reactor as a strong reducing agent at a rate of 1 L / h. Eight minutes after adding the N2H4·H2O solution, the reactor stirrer is started, and the stirring speed is controlled at 140 r / min. Simultaneously, the feed pumps for CoSO4 solution and NaOH solution are turned on, and 1.5 mol / L CoSO4 solution and NaOH solution are added to the reactor. At the same time, the reactor temperature is set to 58℃, and the pH value inside the reactor is controlled to 11.2. The precipitation and coating reaction of Co(OH)3 on the surface of Ni(OH)2 particles continues for 6 hours.

[0031] After adding all the prepared CoSO4 solution to the reactor, the feed pumps for the CoSO4 solution and NaOH solution were turned off. At the same time, the introduction of inert gas and the addition of N2H4·H2O solution into the reactor were stopped. Stirring and aging continued. Finally, the reactants were taken out, washed, and dried to obtain the cobalt-coated nickel hydroxide precursor.

[0032] The obtained cobalt-coated nickel hydroxide precursor showed a uniform color of coating on the particle surface. XPS and chemical titration analysis revealed that almost all nickel in the core was divalent, and after further analysis, the trivalent nickel content was 0.35%, which is lower than 0.5%. The cathode material prepared in this manner exhibited significantly better specific capacity and rate performance than the comparative sample prepared using conventional methods.

[0033] Therefore, by taking multiple measures and synergistically preventing oxidation, the oxidation of divalent cobalt during the cobalt coating process can be effectively suppressed, ensuring the formation of a stable and pure divalent cobalt hydroxide coating layer. The resulting cobalt-coated nickel hydroxide precursor coating layer exhibits the normal characteristic color of divalent cobalt (such as pink or rose), without any impurities, effectively improving the electrochemical performance of nickel hydroxide.

Claims

1. A method for coating the surface of nickel hydroxide particles with cobalt, characterized in that, Includes the following steps: A. Add an alkaline bottom solution containing Ni(OH)2 particles, accounting for 50% of the volume of the reactor, and add 0.1 kg to 0.5 kg of Na2SO3 per cubic meter to the reactor to prepare a mixed alkaline bottom solution. At the same time, prepare a CoSO4 solution with a concentration of 1.4 mol / L to 1.5 mol / L, and add 0.1 kg to 0.5 kg of Na2SO3 per cubic meter to the CoSO4 solution to prepare a mixed solution of CoSO4 and Na2SO3. B. Close the feed port of the reactor tightly and introduce inert gas into the reactor at a rate of 0.5 m³ / h to 2 m³ / h to expel the air from the reactor. C. After introducing inert gas for 10 to 30 minutes, open the other feed port of the reactor and add a 10% N2H4·H2O solution as a strong reducing agent at a rate of 0.5 L / h to 2.0 L / h to maintain a strong reducing environment in the reactor. D. After adding N2H4·H2O solution for 5 to 15 minutes, start the reactor stirrer and control the stirring speed of the reactor stirrer to 130 r / min to 150 r / min. At the same time, turn on the feed pumps of CoSO4 solution and NaOH solution and add the mixed solution of CoSO4 and Na2SO3 prepared in step A and NaOH solution into the reactor. Set the temperature in the reactor to 55℃ to 60℃ and control the pH value in the reactor to 11.0 to 11.

5. The precipitation and coating reaction of Co(OH)3 on the surface of Ni(OH)2 particles will take place. During the reaction, the addition of inert gas and N2H4·H2O solution will be maintained and the reaction will continue for 5.5 h to 6.5 h. E. After the CoSO4 solution is added, turn off the feed pumps for the CoSO4 solution and NaOH solution, and at the same time stop the introduction of inert gas and the addition of N2H4·H2O solution into the reactor. Continue stirring and aging, and finally take out the reactants, wash and dry them to obtain the cobalt-coated nickel hydroxide precursor.

2. The method for coating cobalt onto the surface of nickel hydroxide particles according to claim 1, characterized in that: In step A, the alkaline solution containing Ni(OH)2 particles also contains an ammonia-containing complexing agent.

3. The method for coating cobalt onto the surface of nickel hydroxide particles according to claim 1, characterized in that: In step B, the inert gas introduced is either nitrogen or argon.

4. The method for coating cobalt onto the surface of nickel hydroxide particles according to claim 1, characterized in that: In step D, the amount of CoSO4 solution added to the reactor is 40% of the reactor volume.

5. The method for coating cobalt onto the surface of nickel hydroxide particles according to claim 1, characterized in that: In step E, the stirring and maturation time shall be continued for ≥30 minutes.

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