Core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode and its preparation method

Abstract

This invention discloses a core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode and its preparation method, relating to the fields of materials engineering and manufacturing technology. The preparation method includes the following steps: adding nickel nitrate hexahydrate, cobalt nitrate hexahydrate, sodium citrate, potassium hydroxide, and ammonia to deionized water, and stirring to react to obtain nickel-cobalt hydroxide; placing sodium hypophosphite and nickel-cobalt hydroxide in a tube furnace and treating at high temperature under argon to obtain a nickel-cobalt phosphide composite material; mixing the nickel-cobalt phosphide composite material, PVDF, and carbon black to obtain a slurry, coating it on carbon cloth, and electrochemically activating it to obtain the composite electrode. The composite electrode of this invention has a large specific surface area and high resistance to OH-. ‑ It has strong adsorption capacity and abundant reactive sites; nickel cobalt hydroxide and nickel cobalt phosphide synergistically participate in the electrode reaction, giving the electrode an extremely high specific capacity; due to the heterostructure and the high conductivity of nickel cobalt phosphide, the electrode has excellent conductivity and excellent rate performance.

Description

Technical Field

[0001] This invention relates to the fields of materials engineering and manufacturing technology, specifically to a core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode and its preparation method. Background Technology

[0002] Due to the gradual depletion of non-renewable energy sources and the intermittent and dispersed nature of new energy sources such as wind and solar power, the development of advanced and efficient energy storage devices is of great significance. As an excellent electrochemical energy storage device, rechargeable batteries have attracted widespread attention due to their high stability, high energy efficiency, and excellent scalability. Currently, lithium-ion batteries dominate the portable electronic device and electric vehicle markets due to their high energy density and stable discharge platform; however, the low abundance and high cost of lithium, as well as the safety issues of electrolyte toxicity and flammability, severely limit the further development of lithium-ion batteries. Aqueous zinc batteries, with their high safety, low cost, relatively high energy density, and environmental friendliness, have attracted much attention in the energy storage field and have great development potential. However, the research and optimization of high-efficiency cathode materials remains one of the core challenges and difficulties in achieving large-scale application of aqueous zinc batteries.

[0003] Currently, common cathode materials in zinc batteries include manganese oxides, vanadium oxides, Prussian blue analogues, and nickel-based hydroxides. Among these, MnO2 suffers from three main problems: structural instability, severe manganese dissolution, and poor conductivity. Furthermore, the zinc storage mechanism involved in the reaction process is complex and subject to some controversy. Vanadium oxides consistently exhibit poor ion diffusion and sluggish kinetics; more seriously, long-term Zn… 2+ The strain generated by repeated insertion and extraction within its lattice eventually induces the destruction and failure of the vanadium oxide microstructure. Prussian blue analogues, on the other hand, face problems such as insufficient redox sites, structural instability, and very limited capacity, with significant capacity decay during cycling. Nickel-based hydroxides, however, possess pseudocapacitive properties, a large specific surface area and interlayer spacing, and two-dimensional ion diffusion channels, showing great application potential. However, they are currently mainly limited by limited energy supply and slow reaction kinetics.

[0004] Therefore, modifying nickel-based cathodes to improve their energy supply and accelerate their reaction kinetics, resulting in modified nickel cathodes with high specific capacity and excellent rate performance, is of great significance for the further application of aqueous zinc batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode and its preparation method. This electrode yields a core-shell structured NiCo-LDH@NiCo-P nanocomposite material on a carbon cloth substrate, which can be directly used in aqueous zinc batteries and exhibits high specific capacity and excellent rate performance.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode is provided, comprising the following steps:

[0007] (1) Add nickel nitrate hexahydrate, cobalt nitrate hexahydrate, sodium citrate, potassium hydroxide and ammonia to deionized water, react under mechanical stirring, cool to room temperature, remove the supernatant, wash and dry to obtain nickel cobalt hydroxide NiCo-LDH;

[0008] (2) Sodium hypophosphite and the nickel-cobalt hydroxide obtained in step (1) are placed in a ceramic boat, and then placed in a tube furnace. The ceramic boat containing sodium hypophosphite is placed upstream of the gas and kept warm in an argon atmosphere. It is then cooled to room temperature with the furnace to obtain the nickel-cobalt-phosphite composite material NiCo-Px.

[0009] (3) Mix the nickel cobalt phosphorus composite material, polyvinylidene fluoride and carbon black obtained in step (2) evenly to obtain a slurry; then coat the slurry onto the carbon cloth and dry it to obtain a carbon cloth coated with nickel cobalt phosphorus composite material.

[0010] (4) Using the carbon cloth coated with nickel cobalt phosphorus composite material obtained in step (3) as the working electrode, perform three-electrode CV electrochemical activation to obtain a core-shell structure nickel cobalt hydroxide / nickel cobalt phosphorus composite electrode NiCo-LDH@NiCo-P.

[0011] Furthermore, in step (1), the molar ratio of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, sodium citrate, potassium hydroxide, and ammonia is 4:1:8:16:40.

[0012] Furthermore, in step (1), the reaction is carried out at a temperature of 50-60 °C for 10 h under mechanical stirring conditions.

[0013] Furthermore, in step (2), the mass ratio of sodium hypophosphite to nickel cobalt hydroxide is 0.5-1.5:1.

[0014] Furthermore, in step (2), the temperature is increased to 350 ℃ at 1 ℃ / min and held for 3 h in an argon atmosphere.

[0015] Furthermore, in step (2), the nickel-cobalt-phosphorus composite material NiCo-Px, where x represents the mass ratio of sodium hypophosphite to nickel-cobalt hydroxide, can be 0.5, 0.75, 1.0, 1.25, or 1.5.

[0016] Furthermore, in step (3), the mass ratio of nickel-cobalt-phosphorus composite material, polyvinylidene fluoride and carbon black is 8:1:1.

[0017] Furthermore, in step (3), the counter electrode is a platinum sheet electrode, the reference electrode is a mercury / mercury oxide electrode, and the electrolyte is a 3 mol / L potassium hydroxide solution.

[0018] Furthermore, in step (3), during the three-electrode CV electrochemical activation, the voltage is 0-0.9 V, the scan rate is 10 mV / s, and the cycle scan is 100 times.

[0019] The present invention also provides a method for preparing the above-mentioned core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode, resulting in a core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode.

[0020] The present invention has the following beneficial effects:

[0021] 1. Compared to NiCo-LDH, the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P exhibits a larger specific surface area and higher resistance to OH groups. - The adsorption capacity of the composite material gives it a rich number of reactive sites.

[0022] 2. The core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P not only benefits from the high conductivity of NiCo-P due to its metal-like properties, but also has a large number of heterostructures. It can improve the electronic structure through charge transfer, ultimately resulting in good electronic conductivity and fast reaction kinetics.

[0023] 3. In the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P, both NiCo-LDH and NiCo-P exhibit electrochemical activity and can synergistically participate in the electrode reaction. Compared with NiCo-LDH, it has a larger specific capacity, which improves the energy supply of the electrode.

[0024] 4. The nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode of the present invention can be directly used as an electrode for aqueous zinc electrodes. When used as an electrode, the specific capacity can reach 286.64 mAh / g at a current density of 1 C (1 C = 289 mA / g), which is close to its theoretical capacity of 289 mAh / g. Furthermore, it retains 72.22% of the specific capacity even when the current density is increased to 40 C. After 1000 charge-discharge cycles at a current density of 5 C, the capacity retention rate is as high as 70.1%. Attached Figure Description

[0025] Figure 1 SEM image of the product obtained in Example 3;

[0026] Figure 2 TEM image of the product obtained in Example 3;

[0027] Figure 3 The CV curves of the products obtained in Example 3 and Comparative Examples 1-2 at a scan rate of 1 mV / s are shown.

[0028] Figure 4 The CV curves of the product obtained in Example 3 at different scanning speeds are shown below.

[0029] Figure 5 This is the GCD diagram of the product obtained in Example 3. Detailed Implementation

[0030] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0031] Example 1

[0032] A core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode is prepared by the following steps:

[0033] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0034] (2) Place 0.5 g of sodium hypophosphite and 1 g of nickel-cobalt hydroxide obtained in step (1) into a ceramic boat, and then place them in a tube furnace. The ceramic boat containing sodium hypophosphite is placed upstream of the gas. In an argon atmosphere, the temperature is increased to 350 °C at 1 °C / min and held for 3 h. The furnace is then cooled to room temperature to obtain the nickel-cobalt-phosphorus composite material NiCo-P0.5.

[0035] (3) Add the nickel cobalt phosphorus composite material obtained in step (2), polyvinylidene fluoride and carbon black to N-methylpyrrolidone solution at a mass ratio of 8:1:1, mix evenly to obtain a slurry; then coat the slurry onto carbon cloth and dry it at 60 ℃ to obtain carbon cloth coated with nickel cobalt phosphorus composite material.

[0036] (4) Using the carbon cloth coated with nickel cobalt phosphorus composite material obtained in step (3) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed. The voltage was 0-0.9 V, the scanning speed was 10 mV / s, and 100 cycles were performed to obtain the core-shell structure nickel cobalt hydroxide / nickel cobalt phosphide composite electrode NiCo-LDH@NiCo-P0.5.

[0037] Example 2

[0038] A core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode is prepared by the following steps:

[0039] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0040] (2) Place 0.75 g of sodium hypophosphite and 1 g of nickel-cobalt hydroxide obtained in step (1) into a ceramic boat, then place them in a tube furnace, with the ceramic boat containing sodium hypophosphite placed upstream of the gas. In an argon atmosphere, heat the furnace to 350 °C at 1 °C / min and hold for 3 h. Cool the furnace to room temperature to obtain the nickel-cobalt-phosphorus composite material NiCo-P0.75.

[0041] (3) Add the nickel cobalt phosphorus composite material obtained in step (2), polyvinylidene fluoride and carbon black to N-methylpyrrolidone solution at a mass ratio of 8:1:1, mix evenly to obtain a slurry; then coat the slurry onto carbon cloth and dry it at 60 ℃ to obtain carbon cloth coated with nickel cobalt phosphorus composite material.

[0042] (4) Using the carbon cloth coated with nickel cobalt phosphorus composite material obtained in step (3) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed. The voltage was 0-0.9 V, the scan rate was 10 mV / s, and 100 cycles were performed to obtain the core-shell structure nickel cobalt hydroxide / nickel cobalt phosphorus composite electrode NiCo-LDH@NiCo-P0.75.

[0043] Example 3

[0044] A core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode is prepared by the following steps:

[0045] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0046] (2) Place 1 g of sodium hypophosphite and 1 g of nickel cobalt hydroxide obtained in step (1) into a ceramic boat, then place them in a tube furnace, with the ceramic boat containing sodium hypophosphite placed upstream of the gas. In an argon atmosphere, heat the material to 350°C at 1 °C / min and hold for 3 h. Then cool the material to room temperature with the furnace to obtain the nickel cobalt phosphorus composite material NiCo-P1.0.

[0047] (3) Add the nickel cobalt phosphorus composite material obtained in step (2), polyvinylidene fluoride and carbon black to N-methylpyrrolidone solution at a mass ratio of 8:1:1, mix evenly to obtain a slurry; then coat the slurry onto carbon cloth and dry it at 60 ℃ to obtain carbon cloth coated with nickel cobalt phosphorus composite material.

[0048] (4) Using the carbon cloth coated with nickel cobalt phosphorus composite material obtained in step (3) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed. The voltage was 0-0.9 V, the scan rate was 10 mV / s, and 100 cycles were performed to obtain the core-shell structure nickel cobalt hydroxide / nickel cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.0.

[0049] Example 4

[0050] A core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode is prepared by the following steps:

[0051] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0052] (2) 1.25 g of sodium hypophosphite and 1 g of nickel cobalt hydroxide obtained in step (1) were placed in a ceramic boat, and then placed in a tube furnace. The ceramic boat containing sodium hypophosphite was placed upstream of the gas. In an argon atmosphere, the temperature was increased to 350 °C at 1 °C / min and held for 3 h. The furnace was then cooled to room temperature to obtain the nickel cobalt phosphorus composite material NiCo-P1.25.

[0053] (3) Add the nickel cobalt phosphorus composite material obtained in step (2), polyvinylidene fluoride and carbon black to N-methylpyrrolidone solution at a mass ratio of 8:1:1, mix evenly to obtain a slurry; then coat the slurry onto carbon cloth and dry it at 60 ℃ to obtain carbon cloth coated with nickel cobalt phosphorus composite material.

[0054] (4) Using the carbon cloth coated with nickel cobalt phosphorus composite material obtained in step (3) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed. The voltage was 0-0.9 V, the scanning speed was 10 mV / s, and 100 cycles were performed to obtain the core-shell structure nickel cobalt hydroxide / nickel cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.25.

[0055] Example 5

[0056] A core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode is prepared by the following steps:

[0057] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0058] (2) Place 1.5 g of sodium hypophosphite and 1 g of nickel cobalt hydroxide obtained in step (1) into a ceramic boat, and then place them in a tube furnace. The ceramic boat containing sodium hypophosphite is placed upstream of the gas. In an argon atmosphere, the temperature is increased to 350 °C at 1 °C / min and held for 3 h. The furnace is then cooled to room temperature to obtain the nickel cobalt phosphorus composite material NiCo-P1.5.

[0059] (3) Add the nickel cobalt phosphorus composite material obtained in step (2), polyvinylidene fluoride and carbon black to N-methylpyrrolidone solution at a mass ratio of 8:1:1, mix evenly to obtain a slurry; then coat the slurry onto carbon cloth and dry it at 60 ℃ to obtain carbon cloth coated with nickel cobalt phosphorus composite material.

[0060] (4) Using the carbon cloth coated with nickel cobalt phosphide composite material obtained in step (3) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed. The voltage was 0-0.9 V, the scanning speed was 10 mV / s, and 100 cycles were performed to obtain the core-shell structure nickel cobalt hydroxide / nickel cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.5.

[0061] Comparative Example 1

[0062] A composite electrode, the preparation method of which includes the following steps:

[0063] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0064] (2) Add the nickel cobalt hydroxide, polyvinylidene fluoride and carbon black obtained in step (1) to N-methylpyrrolidone solution in a mass ratio of 8:1:1, mix evenly to obtain a slurry; then coat the slurry onto carbon cloth and dry it at 60 ℃ to obtain carbon cloth coated with nickel cobalt hydroxide.

[0065] (3) Using the carbon cloth coated with nickel cobalt hydroxide obtained in step (2) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed with a voltage of 0-0.9 V, a scan rate of 10 mV / s, and 100 cyclic scans to obtain the composite electrode NiCo-LDH.

[0066] Comparative Example 2

[0067] A composite electrode, the preparation method of which includes the following steps:

[0068] (1) Add 50 mmol nickel nitrate hexahydrate, 12.5 mmol cobalt nitrate hexahydrate, 100 mmol sodium citrate, 200 mmol potassium hydroxide and 500 mmol ammonia water to 100 mL deionized water, and react at 50 °C for 10 h under mechanical stirring. Cool to room temperature, remove the supernatant, centrifuge and wash the lower green solution, and dry at 90 °C to obtain nickel cobalt hydroxide NiCo-LDH;

[0069] (2) Place 1 g of the nickel-cobalt hydroxide obtained in step (1) in a ceramic boat, and then place it in a tube furnace with the ceramic boat downstream of the gas. In an argon environment, heat the furnace to 350 °C at 1 °C / min and hold for 3 h. Then cool the furnace to room temperature to obtain NiCo-PO.

[0070] (3) The NiCo-PO, polyvinylidene fluoride and carbon black obtained in step (2) are added to the N-methylpyrrolidone solution in a mass ratio of 8:1:1 and mixed evenly to obtain a slurry; then the slurry is coated on carbon cloth and dried at 60 °C to obtain carbon cloth coated with NiCo-PO.

[0071] (4) Using the carbon cloth coated with NiCo-P0 obtained in step (3) as the working electrode, the counter electrode as a platinum sheet electrode, the reference electrode as a mercury / mercury oxide electrode, and the electrolyte as a 3 mol / L potassium hydroxide solution, a three-electrode CV electrochemical activation was performed. The voltage was 0-0.9 V, the scan rate was 10 mV / s, and the cycle scan was performed for 100 times to obtain the composite electrode NiCo-LDH@NiCo-P0.

[0072] Test case

[0073] 1. Obtain SEM and TEM images of the product obtained in Example 3 (core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.0), as shown below. Figure 1-2 As shown.

[0074] Meanwhile, the products obtained in Example 3 and Comparative Examples 1-2 were used as electrodes for electrochemical performance testing. The counter electrode was a platinum sheet electrode, the reference electrode was a mercury / mercury oxide electrode, and the electrolyte was a 3 mol / L potassium hydroxide solution. The CV comparison graphs at a scan rate of 1 mV / s are shown below. Figure 3 As shown.

[0075] The product obtained in Example 3 (core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.0) was subjected to CV testing at different scan rates, and the results are as follows: Figure 4 As shown. And the GCD diagram of the product obtained in Example 3, as shown. Figure 5 As shown.

[0076] Depend on Figure 1 As can be seen, the material exhibits a nanosheet morphology with its surface covered.

[0077] Depend on Figure 2It can be seen that the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.0 obtained in Example 3 has nickel-cobalt phosphide Ni2P / Co2P on the outside and NiCo-LDH on the inside, proving that the obtained nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode material has a core-shell structure, wherein the shell is nickel-cobalt phosphide NiCo-P and the inside is nickel-cobalt hydroxide NiCo-LDH; in addition, there are a large number of heterostructures in the material, which is beneficial to adjust its electronic structure through charge transfer, thereby improving the electronic conductivity of the material.

[0078] Depend on Figure 3 It can be seen that the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode NiCo-LDH@NiCo-P1.0 obtained in Example 3 has the largest specific capacity (area of ​​CV curve), followed by the NiCo-LDH electrode in Comparative Example 1, and the NiCo-LDH@NiCo-P0 electrode in Comparative Example 2 has the smallest specific capacity. Furthermore, the CV curves of both the NiCo-LDH and NiCo-LDH@NiCo-P0 electrodes show only one pair of redox peaks, corresponding to the electrode reaction of nickel-cobalt hydroxide NiCo-LDH. However, the CV curve of the NiCo-LDH@NiCoP1.0 electrode shows two distinct pairs of redox peaks, one pair representing the electrode reaction of nickel-cobalt hydroxide NiCo-LDH and the other pair representing the electrode reaction of nickel-cobalt phosphide NiCo-P. This indicates that the synergistic reaction of NiCo-LDH and NiCo-P in the NiCo-LDH@NiCoP1.0 electrode enhances the specific capacity of the composite electrode.

[0079] Depend on Figure 4 As can be seen, two pairs of distinct redox peaks can be observed, one pair being the electrode reaction of NiCo-LDH and the other pair being the electrode reaction of NiCo-P. Furthermore, when the scan rate increases from 1 mV / s to 5 mV / s, the CV curve maintains a good shape, indicating that NiCo-LDH@NiCo-P1.0 has good rate potential.

[0080] Depend on Figure 5 It can be seen that the NiCo-LDH@NiCo-P1.0 composite electrode has excellent specific capacity and rate performance.

[0081] 2. The products obtained in Examples 1-5 and Comparative Examples 1-2 were used as electrodes for electrochemical performance testing. The counter electrode was a platinum sheet electrode, the reference electrode was a mercury / mercury oxide electrode, and the electrolyte was a 3 mol / L potassium hydroxide solution. The results are shown in Table 1.

[0082] Table 1. Electrochemical performance test results of Examples 1-5 and Comparative Examples 1-2

[0083]

[0084] As shown in Table 1, when NiCo-LDH is used as an electrode, its specific capacity is approximately 198.1 mAh / g at a current density of 1 C, and the capacity retention rate is 59.5% when the current density increases to 40 C. When NiCo-LDH@NiCo-P0 is used as an electrode, its specific capacity is approximately 169.8 mAh / g at a current density of 1 C, and the capacity retention rate is 61.0% when the current density increases to 40 C. In comparison, the core-shell structure NiCo-LDH@NiCo-P1.0 electrode obtained in Example 3 has a large specific surface area, abundant reactive sites, and the metal-like properties of NiCo-P itself, as well as the large number of heterostructures between NiCo-LDH and NiCo-P, which greatly improves the electronic conductivity of the material, giving the electrode ultrafast reaction kinetics and excellent rate performance. In addition, both NiCo-LDH and NiCo-P exhibit reactivity and synergistically participate in the electrode reaction, improving the electrode's specific capacity and energy density. When used as an electrode, the specific capacity at a current density of 1 C is approximately 286.6 mAh / g, close to its theoretical specific capacity of 289 mAh / g; and the capacity retention is 72.2% when the current density increases to 40 C, which is far superior to the electrochemical activity when NiCo-LDH or NiCo-LDH@NiCoP0 are used as electrodes. Furthermore, NiCo-LDH@NiCo-P1.0 exhibits good structural stability. After 1150 charge-discharge cycles at a current density of 5 C, the capacity retention is as high as 70.1%.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode, characterized in that, Includes the following steps: (1) Add nickel nitrate hexahydrate, cobalt nitrate hexahydrate, sodium citrate, potassium hydroxide and ammonia to deionized water, react under mechanical stirring, cool to room temperature, remove the supernatant, wash and dry to obtain nickel cobalt hydroxide; (2) Sodium hypophosphite and the nickel-cobalt hydroxide obtained in step (1) are placed in a ceramic boat, and then placed in a tube furnace. The ceramic boat containing sodium hypophosphite is placed upstream of the gas and kept warm in an argon atmosphere. It is then cooled to room temperature with the furnace to obtain a nickel-cobalt-phosphite composite material. (3) Mix the nickel cobalt phosphorus composite material, polyvinylidene fluoride and carbon black obtained in step (2) evenly to obtain a slurry; then coat the slurry onto the carbon cloth and dry it to obtain a carbon cloth coated with nickel cobalt phosphorus composite material. (4) Using the carbon cloth coated with nickel cobalt phosphorus composite material obtained in step (3) as the working electrode, perform three-electrode CV electrochemical activation to obtain a core-shell structure nickel cobalt hydroxide / nickel cobalt phosphorus composite electrode.

2. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (1), the molar ratio of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, sodium citrate, potassium hydroxide and ammonia is 4:1:8:16:

40.

3. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (1), the reaction is carried out at 50-60 °C for 10 h under mechanical stirring.

4. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (2), the mass ratio of sodium hypophosphite to nickel cobalt hydroxide is 0.5-1.5:

1.

5. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (2), the temperature is increased to 350 ℃ at 1 ℃ / min and held for 3 h in an argon atmosphere.

6. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (3), the mass ratio of nickel-cobalt-phosphorus composite material, polyvinylidene fluoride and carbon black is 8:1:

1.

7. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (4), the counter electrode is a platinum sheet electrode, the reference electrode is a mercury / mercury oxide electrode, and the electrolyte is a 3 mol / L potassium hydroxide solution.

8. The method for preparing the core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode as described in claim 1, characterized in that, In step (4), during the three-electrode CV electrochemical activation, the voltage is 0-0.9 V, the scan rate is 10 mV / s, and the cycle scan is 100 times.

9. The core-shell structured nickel-cobalt hydroxide / nickel-cobalt phosphide composite electrode prepared by the method of any one of claims 1-8.

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