Cobalt-coated spherical nickel hydroxide positive electrode material for low-temperature power batteries and preparation method thereof

Abstract

Cobalt-coated spherical nickel hydroxide positive electrode material for low-temperature power batteries and its preparation method belong to the technical field of spherical nickel hydroxide. The present invention prepares spherical nickel hydroxide with a uniform and dense layer of β-Co(OH)2 coated on the surface by improving the operating process conditions, and then prepares spherical nickel hydroxide with a uniform and dense surface coating and few coating defects and high conductivity γ-CoOOH. Compared with similar products on the market, the positive electrode material prepared by the present invention has higher capacity, better low-temperature performance, smaller self-discharge, and longer cycle life, and is fully capable of adapting to the capacity retention of batteries in low-temperature environments. By controlling the pH value during the coating of β-Co(OH)2, it is helpful to form a coating layer with a uniform and dense surface coating. On this basis, by adding a pre-oxygenation process, the coating layer is oxidized to a uniform and dense γ-CoOOH, reducing the formation of low-conductivity β-CoOOH and meeting the use requirements of low-temperature power batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of spherical nickel hydroxide, and in particular relates to a cobalt-coated spherical nickel hydroxide positive electrode material for low-temperature power batteries and a preparation method thereof. Background Art

[0002] Nickel hydroxide is widely used as a positive electrode active material in alkaline batteries such as MH-Ni. Since it is a semiconductor, it is necessary to add conductive materials to it or coat its surface to improve its chemical properties. During charge and discharge, a highly conductive CoOOH conductive network is generated on the surface of the active material, which facilitates the transfer of protons and electrons, thereby achieving the purpose of improving the conductivity of the electrode. 2+ / Co 3+ The electrode reaction is irreversible, so CoOOH can exist on the surface of nickel hydroxide for a long time and act as a conductive network. Existing research results show that the process of Co(OH)2 converting into CoOOH during the initial activation of the battery will cause the irreversible capacity of the battery, so directly coating the surface with CoOOH can further improve the electrochemical capacity and performance of Ni(OH)2.

[0003] At present, domestic manufacturers of spherical nickel hydroxide usually dope other elements through three methods: chemical coprecipitation, mechanical mixing, and surface modification. Although intracrystalline doping of nickel hydroxide active material by chemical coprecipitation can improve its intracrystalline electron and proton conductivity by increasing the crystal defects of nickel hydroxide and control the crystal transformation of the active material during the electrode reaction, it does not improve the conductivity between active material particles, between active material and conductive skeleton, and between active material and electrolyte. Moreover, the conventional chemical coprecipitation is very strict to the process requirements for coating β-Co(OH)2 on the surface of spherical nickel hydroxide. Temperature, alkalinity, and flow rate are all important factors that restrict the coating state of the cobalt coating layer. Moreover, the growth of the coated crystal bundle is chaotic and a large number of heterogeneous nuclei will be formed, resulting in loose coating, which in turn leads to blockage of the surface-coated cobalt conductive network structure, resulting in high current charge and discharge performance, cycle life, charge retention rate, etc., which cannot meet the requirements of low-temperature power batteries.

[0004] In addition, there is a major problem in the existing chemical coprecipitation process: the oxidation valence problem of Co in the coating layer. Through research, it was found that γ-CoOOH has better electrical conductivity than β-CoOOH, and has a lower reduction potential in alkaline electrolyte than β-CoOOH, is not easily reduced, and the conductive layer formed is more stable. Existing processes such as the process method mentioned in patents CN100448074C, CN102800859A, and CN105552350A, when oxidized, are still mainly based on generating β-CoOOH, and γ-CoOOH can not be effectively formed. The most intuitive characterization method is to measure the valence of Co in the coating layer. The valence of cobalt in β-CoOOH is +3 valence, and when forming γ-CoOOH, the valence of cobalt is higher than +3 valence, and can reach more than 3.2 valence. How to improve the chemical coprecipitation process so that the γ-CoOOH coating layer can be effectively produced is a problem that needs to be solved urgently. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a cobalt-coated spherical nickel hydroxide positive electrode material for low-temperature power batteries and a preparation method to solve the technical problem that the existing chemical coprecipitation process cannot effectively form γ-CoOOH in the coating layer and cannot well meet the requirements of low-temperature power batteries.

[0006] A cobalt-coated spherical nickel hydroxide positive electrode material for a low-temperature power battery. The spherical nickel hydroxide matrix of the positive electrode material has a Ni content of 58.5±0.5%, a Co content of 0.70±0.05%, and a Zn content of 3.0±0.15%. The surface of the spherical nickel hydroxide matrix is ​​coated with a highly conductive γ-CoOOH coating layer, and the Co content in the coating layer is 4% to 6%.

[0007] A method for preparing a cobalt-coated spherical nickel hydroxide positive electrode material for a low-temperature power battery comprises the following steps, which are performed in sequence:

[0008] Step 1: Preparation of spherical nickel hydroxide matrix:

[0009] First, add 1mol / L to 5mol / L ammonia solution as the bottom liquid into the reactor, adjust the temperature of the reactor to 50℃ to 65℃, and the speed of the stirring blade to 140r / min to 180r / min. A mixed solution of nickel, cobalt and zinc salts with a concentration of 4mol / L to 6mol / L, a sodium hydroxide solution with a concentration of 3mol / L to 6mol / L and a 1mol / L to 5mol / L ammonia solution are continuously added into the reactor by continuous overflow. The flow rate of the combined solution is 4 L / min to 14 L / min, the flow rate of the sodium hydroxide solution is 0.5 L / min to 6 L / min, and the flow rate of the ammonia solution is 0.3 L / min to 3 L / min. The pH of the system is controlled at 11 to 14. Spherical nickel hydroxide is output while the reaction is continued to prepare spherical nickel hydroxide having a particle size D50 of 10±3 μm, a Ni content of 58.5±0.5%, a Co content of 0.70±0.05%, and a Zn content of 3.0±0.15%.

[0010] Step 2: Wash and dry the prepared spherical nickel hydroxide, screen and remove impurities, and then use the spherical nickel hydroxide with a particle size D50 of 10±3 μm as the production matrix of cobalt-coated spherical nickel for standby use;

[0011] Step 3: Preparation of spherical nickel hydroxide coated with β-Co(OH)2:

[0012] The reaction temperature of the reactor is set to 50°C to 58°C, the alkalinity is adjusted to 10g / L to 25g / L, the stirring speed is 120r / min to 200r / min, the production matrix in step 2 is placed in the reactor, 1mol / L to 6mol / L cobalt solution, 1mol / L to 5mol / L ammonia solution, and 3mol / L to 6mol / L sodium hydroxide solution are continuously added, and the pH value is controlled to decrease by 0.1-0.15 every 20min on average until the reaction is completed. The coating time is 120min to 300min, and a layer of β-Co(OH)2 with a cobalt content of 4% to 6% is coated on the surface of the spherical nickel hydroxide. The coated spherical nickel hydroxide is injected into a filter press for washing, filter pressing, and then dried;

[0013] Step 4: Preparation of γ-CoOOH coated spherical nickel hydroxide:

[0014] The cobalt-coated spherical nickel hydroxide dried in step 3 is put into an oxidizer and heated to 90°C to 110°C. The oxidizer is pre-filled with oxygen for 2 minutes to 5 minutes. A sodium hydroxide solution at 95°C to 105°C and a concentration of 25 mol / L to 35 mol / L is added. Under the combined action of hot alkali and oxygen, the β-Co(OH)2 coating layer on the surface of the spherical nickel hydroxide is oxidized into γ-CoOOH with high conductivity.

[0015] The mixed solution of nickel, cobalt and zinc salts in step 1 is a sulfate solution or a nitrate solution.

[0016] The cobalt solution in step 3 is a cobalt sulfate solution or a cobalt nitrate solution.

[0017] Through the above design scheme, the present invention can bring the following beneficial effects:

[0018] The present invention can prepare a spherical nickel hydroxide with a uniform and dense layer of β-Co(OH)2 coated on the surface by improving the operating process conditions, and then prepare a spherical nickel hydroxide with a high conductivity γ-CoOOH with a uniform and dense surface coating and few coating defects. Compared with similar products on the market, the positive electrode material prepared by the present invention has higher capacity, better low-temperature performance, smaller self-discharge, and longer cycle life, and is fully capable of adapting to the capacity retention of batteries in low-temperature environments. By controlling the production process during the β-Co(OH)2 coating process, especially the precise control of the pH value, the system pH value is controlled to decrease by 0.1 to 0.15 every 20 minutes during the coating process, which helps to form a uniform and dense coating layer on the surface. On this basis, by controlling the conditions of the oxidation process and adding a pre-oxygenation process, the coating layer is oxidized to a uniform and dense γ-CoOOH, effectively reducing the formation of low-conductivity β-CoOOH and meeting the use requirements of low-temperature power batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0020] Figure 1 This is a comparison diagram of the electron microscope image of the coated β-Co(OH)2 spherical nickel hydroxide prepared by the conventional process in the cobalt-coated spherical nickel hydroxide positive electrode material and preparation method for low-temperature power batteries of the present invention and the electron microscope image of the coated β-Co(OH)2 spherical nickel hydroxide prepared by the present invention. DETAILED DESCRIPTION

[0021] Example 1

[0022] (1) Preparation of ordinary spherical nickel hydroxide: 1500 liters of pure water were added to a reactor with a volume of 3300 liters, and 650 liters of 3 mol / L ammonia solution was added as a base liquid. The speed of the stirring paddle was 160 r / min. At the same time, a mixed solution of 5 mol / L nickel, cobalt and zinc salts was added to the reactor at a flow rate of 4.5 L / min, 3 mol / L ammonia solution was added at a flow rate of 0.4 L / min, and 4 mol / L sodium hydroxide solution was added at a flow rate of about 0.6 L / min. The temperature of the reactor was controlled at 57°C and the pH value was 12.5. Samples were taken from the reactor every 2 hours to monitor the actual pH value and various flow rates were adjusted to ensure pH stability. The reaction was continued for 7 days in a continuous overflow manner until the planned production of spherical nickel hydroxide product was achieved, and spherical nickel hydroxide with a particle size D50 of 10±3 μm, a Zn content of 58.5%, a Zn content of 3%, and a Co content of 0.7% was obtained.

[0023] (2) The prepared spherical nickel hydroxide is washed and dried, and then screened to remove impurities and products with excessively large particle sizes before being used as a matrix.

[0024] (3) Prepare 4 mol / L cobalt solution, use spherical nickel hydroxide screened in (2) as the matrix, adjust the alkalinity to 25 g / L, the pH to 12.5, and during the coating process, the pH value decreases by 0.1 every 20 minutes on average. The stirring blade speed is 160 r / min, and the reactor temperature is controlled to be 56°C. 4 mol / L cobalt solution, 3 mol / L ammonia solution, and 4 mol / L sodium hydroxide solution are continuously added. The coating time is 150 minutes. During the coating process, the pH value of the system is controlled to decrease by 0.1 every 20 minutes on average until the reaction is completed. A layer of 3% β-Co(OH)2 is coated on the surface of the spherical nickel hydroxide. The coated spherical nickel hydroxide is injected into a filter press for washing, filtration, and drying for use.

[0025] (4) Preparation of γ-CoOOH-coated spherical nickel hydroxide: The spherical nickel hydroxide prepared in step (3) was placed in an oxidizer, the material was heated to 100°C, and pre-oxygenated for 3 minutes. Under the combined action of a 35 mol / L sodium hydroxide solution heated to 103°C and oxygen, the β-Co(OH)2 coating layer on the surface of the spherical nickel hydroxide was oxidized into γ-CoOOH with high conductivity. After washing and drying, sample 1 was obtained.

[0026] Example 2

[0027] (1) Preparation of ordinary spherical nickel hydroxide: 1500 liters of pure water were added to a reactor with a volume of 3300 liters, 650 liters of 3 mol / L ammonia solution was added as the base liquid, the speed of the stirring paddle was 160 r / min, and at the same time, a 5 mol / L mixed solution of nickel, cobalt and zinc salts was added to the reactor at a flow rate of 4.5 L / min, a 3 mol / L ammonia solution was added at a flow rate of 0.4 L / min, and a 4 mol / L sodium hydroxide solution was added at a flow rate of about 0.6 L / min. The temperature of the reactor was controlled at 57°C and the pH value was 12.5. Samples were taken from the reactor every 2 hours to monitor the actual pH. The product was output while the reaction was in progress by a continuous overflow method. The reaction was continued for 7 days until the predetermined output of the spherical nickel hydroxide product was reached, and spherical nickel hydroxide with a particle size D50 of 10±3 μm, a Zn content of 58.5%, a Zn content of 3%, and a Co content of 0.7% was obtained.

[0028] (2) The prepared spherical nickel hydroxide is washed and dried, and then the mixed material is screened and impurities are removed, and the spherical nickel hydroxide with a particle size D50 of 10±3 μm is taken as a matrix for use.

[0029] (3) Prepare 4 mol / L cobalt solution, use the spherical nickel hydroxide screened in (2) as the matrix, adjust the alkalinity to 10 g / L, the pH to 12.5, the stirring blade speed to 160 r / min, control the reactor temperature to 52 ° C, continuously add 4 mol / L cobalt solution, 3 mol / L ammonia solution, and 4 mol / L sodium hydroxide solution. During the coating process, the pH value of the system is controlled to decrease by 0.15 every 20 minutes on average. The coating time is 120 minutes. A layer of 3% β-Co(OH)2 is coated on the surface of the spherical nickel hydroxide. The coated spherical nickel hydroxide is injected into a filter press for washing, filtration, and then dried for use.

[0030] (4) Preparation of γ-CoOOH coated spherical nickel hydroxide: The spherical nickel hydroxide prepared in (3) was placed in an oxidizer, the material was heated to 100°C, and pre-oxygenated for 3 minutes. Under the combined action of a 35 mol / L sodium hydroxide solution heated to 103°C and oxygen, the β-Co(OH)2 coating layer on the surface of the spherical nickel hydroxide was oxidized into γ-CoOOH with high conductivity. After washing and drying, sample 2 was obtained.

[0031] Experimental comparison

[0032] We tested the common Zn3 cobalt-coated spherical nickel hydroxide on the market, and samples 1 and 2, respectively, in AA1330 nickel-metal hydride batteries. The results are as follows:

[0033] Table 1 Comparison of electrical performance test results

[0034] Spherical nickel model Sample 1 Sample 2 Current products 1C gram capacity 242.9 244.4 241.6 0.2C gram capacity 250.9 254.1 250.6 1C gram capacity 230.5 231.6 229.2 0.2C gram capacity 239.2 242.1 239.2 1.2V gram capacity 157.1 156.9 155.7 Median voltage 1.221 1.222 1.221 DC resistance 27.71 27.34 27.55 65℃*7 days charge retention test 78.9％ 79.2％ 76.5％ 1C charge and discharge cycles up to 80% capacity 588 650 553 Low temperature output 5s 99.0％ 100.2％ 98.5％ Low temperature output 10s 99.8％ 100.26％ 99.0％ Low temperature performance -20℃ discharge 1C 97.5％ 99.1％ 96.8％ Low temperature performance -20℃ discharge 3C 96.4％ 99.3％ 94.6％ Low temperature performance -20℃ discharge 5C 96.4％ 99.3％ 87.6％

[0035] Note: Except for DC resistance, the higher the value, the better the performance.

[0036] The cobalt-coated spherical nickel prepared by conventional process was compared with sample 2 under scanning electron microscope. It can be seen that in sample 2 prepared by the process of the present invention, the surface coating of the β-Co(OH)2-coated spherical nickel hydroxide prepared in step (3) is more uniform and dense. Based on this, the γ-CoOOH-coated spherical nickel hydroxide sample 2 with high conductivity was prepared, and the surface coating is more uniform, dense and has fewer coating defects.

[0037] The comparison of the valence of cobalt in the γ-CoOOH spherical nickel hydroxide coating layer prepared by conventional process and the valence of cobalt in the γ-CoOOH spherical nickel hydroxide coating layer prepared by the present invention is shown in Table 2:

[0038] Table 2 Comparison of valence states of cobalt in the coating layer

[0039]

[0040] In summary, the capacity, low-temperature performance, large-current charge and discharge performance, cycle life, and charge retention rate of the cobalt-coated spherical nickel prepared by the present invention are significantly better than similar products on the market. The comprehensive performance of the product coated by using a low-temperature, low-alkalinity, and large-flow process during coating is further improved, and the product can better meet the requirements of low-temperature power batteries.

Claims

1. A method for preparing a cobalt-coated spherical nickel hydroxide positive electrode material for a low-temperature power battery, wherein the cobalt-coated spherical nickel hydroxide positive electrode material for a low-temperature power battery comprises a spherical nickel hydroxide matrix having a Ni content of 58.5±0.5%, a Co content of 0.70±0.05%, and a Zn content of 3.0±0.15%. The surface of the spherical nickel hydroxide matrix is ​​coated with a highly conductive γ-CoOOH coating layer, wherein the Co content of the coating layer is 4% to 6%. The method is characterized by: Including the following Steps, and the following steps are performed in sequence, Step 1: Preparation of spherical nickel hydroxide matrix: First add 1mol / L~5mol / L ammonia solution as the bottom liquid into the reactor, adjust the temperature of the reactor to 50℃~65℃, and the stirring speed to 140r / min~180r / min. A mixed solution of nickel, cobalt and zinc salts with a concentration of 4 mol / L to 6 mol / L, a sodium hydroxide solution with a concentration of 3 mol / L to 6 mol / L and an ammonia solution with a concentration of 1 mol / L to 5 mol / L are continuously added into a reactor in a continuous overflow manner, wherein the flow rate of the mixed solution of nickel, cobalt and zinc salts is 4 L / min to 14 L / min, the flow rate of the sodium hydroxide solution is 0.5 L / min to 6 L / min, and the flow rate of the ammonia solution is 0.3 L / min to 3 L / min. The pH of the system is controlled at 11 to 14. Spherical nickel hydroxide is output while the reaction is continued, thereby preparing spherical nickel hydroxide with a particle size D50 of 10±3 μm, a Ni content of 58.5±0.5%, a Co content of 0.70±0.05% and a Zn content of 3.0±0.15%. Step 2: Wash and dry the prepared spherical nickel hydroxide, screen and remove impurities, and then use the spherical nickel hydroxide with a particle size D50 of 10±3 μm as the production matrix of cobalt-coated spherical nickel hydroxide for standby use; Step 3: Preparation of spherical nickel hydroxide coated with β-Co(OH)2: The reaction temperature of the reactor is set to 50°C to 58°C, the alkalinity is adjusted to 10 g / L to 25 g / L, the stirring speed is 120 r / min to 200 r / min, the production matrix in step 2 is placed in the reactor, and 1 mol / L to 6 mol / L cobalt solution, 1 mol / L to 5 mol / L ammonia solution, and 3 mol / L to 6 mol / L sodium hydroxide solution are continuously added, and the pH value is controlled to decrease by 0.1-0.15 every 20 minutes on average until the reaction is completed. The coating time is 120 min to 300 min, and a layer of β-Co(OH)2 with a cobalt content of 4% to 6% is coated on the surface of the spherical nickel hydroxide. The coated spherical nickel hydroxide is injected into a filter press for washing, filter pressing, and then dried; Step 4: Preparation of γ-CoOOH coated spherical nickel hydroxide: The cobalt-coated spherical nickel hydroxide dried in step 3 is put into an oxidizer and heated to 90°C to 110°C. The oxidizer is pre-filled with oxygen for 2 minutes to 5 minutes. A sodium hydroxide solution at 95°C to 105°C and a concentration of 25 mol / L to 35 mol / L is added. Under the combined action of hot alkali and oxygen, the β-Co(OH)2 coating layer on the surface of the spherical nickel hydroxide is oxidized into γ-CoOOH with high conductivity.

2. The method for preparing the cobalt-coated spherical nickel hydroxide positive electrode material for low-temperature power batteries according to claim 1, characterized in that: The mixed solution of nickel, cobalt and zinc salts in step 1 is a sulfate solution or a nitrate solution.

3. The method for preparing the cobalt-coated spherical nickel hydroxide positive electrode material for low-temperature power batteries according to claim 1, characterized in that: The cobalt solution in step 3 is a cobalt sulfate solution or a cobalt nitrate solution.

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