Nickel-cobalt phosphide electrode and preparation method thereof

Abstract

The invention provides a nickel-cobalt phosphide electrode and a preparation method thereof, a foamed nickel base material is immersed in a mixed solution A for a first hydrothermal reaction, and the mixed solution A contains nickel ions, cobalt ions, sodium hypophosphite, urea and an ion regulating agent; an ion stabilizer is at least one of thiourea, selenourea, potassium iodide and sodium aluminate, a mixed solution B is obtained and subjected to a second hydrothermal reaction, a foamed nickel base material coated with a nickel-cobalt phosphide electrode material is obtained, and the ion stabilizer is at least one of thiourea, selenourea, potassium iodide and sodium aluminate; and uniformly distributing an ion dispersing agent on the surface of the foamed nickel base material coated with the nickel-cobalt phosphide electrode material, and then drying. Two hydrothermal reactions are combined, and the second hydrothermal reaction is performed through ion stabilizers of thiourea, selenourea, potassium iodide and sodium aluminate, so that nickel-cobalt phosphide ions are better combined with one another, and then a dispersion layer of sodium citrate and polyvinylpyrrolidone is formed on the surface of the material; and the capacitance, the conductivity and the cycle performance of the nickel-cobalt phosphide electrode are improved through mutual cooperation.

Description

Technical Field

[0001] The present invention relates to the field of electrode materials, and in particular to a nickel-cobalt-phosphide electrode and a preparation method thereof. Background Art

[0002] Nickel cobalt phosphide has a high specific capacitance due to its reasonable mesopore size distribution, high specific surface area, the valence of the two elements nickel and cobalt, and the synergistic effect of the two elements.

[0003] Invention patent 201811429925.2 discloses a method for preparing a nickel-cobalt-phosphorus-carbon-nickel hydroxide ternary composite electrode material. The method comprises: growing a nickel-cobalt sheet-line nanoarray matrix on the surface of nickel foam using nickel nitrate hexahydrate, cobalt nitrate hexahydrate, ammonium fluoride, and urea; then infiltrating the matrix with a glucose solution and heat-treating it in an argon atmosphere; and then reacting it with sodium hypophosphite to produce a nickel-cobalt-phosphorus-carbon nanoarray; and then reacting the matrix with nickel chloride hexahydrate and urea to produce a nickel foam loaded with nickel-cobalt-phosphorus-carbon-nickel hydroxide nanoarrays. The preparation method of the present invention is simple and highly operational. Nanoarrays can be grown directly on a nickel foam substrate, and the resulting electrode can be directly used as a supercapacitor electrode, thus showing broad application prospects in supercapacitors. The method can improve the cycling performance, overall specific capacitance, and energy density of the electrode material, resulting in higher energy density and superior cycling performance.

[0004] However, the nickel cobalt phosphide electrode prepared by adjusting ammonium fluoride and urea has poor conductivity, especially at higher rates. Its dynamics is controlled by diffusion-controlled processes and phase change processes, resulting in its unstable structure and loss of active materials, which directly leads to poor cycle performance of the energy storage device. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a nickel cobalt phosphide electrode and a preparation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a nickel cobalt phosphide electrode, the preparation method comprising the following steps: (1) Submerging the nickel foam substrate in a mixed solution A and performing a first hydrothermal reaction at 100° C. to 150° C. under closed conditions for 2 to 5 hours, wherein the mixed solution A contains nickel ions, cobalt ions and sodium hypophosphite, wherein the molar ratio of nickel ions, cobalt ions and sodium hypophosphite is 1.2 to 1.8:1:4 to 6, and the mixed solution A further contains 0.5 to 1 mol / L of urea and 0.10 to 0.3 mol / L of an ion regulator, wherein the ion regulator is one or more selenium halides, and the selenium halide is selenium chloride, selenium fluoride or selenium bromide; (2) After the first hydrothermal reaction is completed, an ion stabilizer is added to the mixed solution A to obtain a mixed solution B, and the foamed nickel substrate treated in step (1) is immersed in the mixed solution B and subjected to a second hydrothermal reaction at 80° C. to 100° C. under closed conditions for 45 to 90 minutes to obtain a foamed nickel substrate coated with a nickel cobalt phosphide electrode material, wherein the ion stabilizer is at least one of thiourea, selenourea, potassium iodide, and sodium aluminate, and the mass concentration of the ion stabilizer is 0.1% to 0.5%; (3) Evenly distributing an ion dispersant on the surface of the nickel foam substrate coated with the nickel cobalt phosphide electrode material obtained in step (2) and then drying the substrate to obtain a nickel cobalt phosphide electrode, wherein the ion dispersant is a mixed aqueous solution of sodium citrate and polyvinyl pyrrolidone (PVP).

[0007] The preparation method of the above-mentioned nickel cobalt phosphide electrode uses nickel foam as a substrate and combines two hydrothermal reactions. In the first hydrothermal reaction, nickel nitrate, cobalt nitrate, and sodium hypophosphite are adjusted on the nickel foam by using selenium halide and urea. In the second hydrothermal reaction, thiourea, selenourea, potassium iodide, and sodium aluminate are used as ion stabilizers for hydrothermal reaction, so that the nickel cobalt phosphide ions are better combined with each other, and the ions on the surface of the nickel foam are embedded in the inner layer of the nickel foam, so that the nickel cobalt phosphide ions are better combined with the nickel foam. Moreover, after the second hydrothermal reaction, a dispersion layer of sodium citrate and polyvinyl pyrrolidone is formed on the surface of the material by drying, which synergistically improves the capacitance, conductivity and cycle performance of the nickel cobalt phosphide electrode.

[0008] Preferably, in step (1), the concentration of nickel ions is 3-6 mmol / L.

[0009] Preferably, in step (2), the ionic stabilizer is at least one of thiourea, selenourea, potassium iodide, and sodium aluminate and must contain selenourea or sodium aluminate.

[0010] The inventors have found through research that selenourea or sodium aluminate in step (2) can make the hydrothermal reaction in step (2) more effective, thereby improving the capacitance, conductivity and cycle performance of the nickel cobalt phosphide electrode.

[0011] Preferably, in step (2), the ionic stabilizer is at least two of thiourea, selenourea, potassium iodide, and sodium aluminate, and must contain selenourea and sodium aluminate.

[0012] The inventors have found through research that the combination of selenourea and sodium aluminate in the hydrothermal reaction of step (2) can make the hydrothermal reaction in step (2) more effective, thereby improving the capacitance, conductivity and cycle performance of the nickel cobalt phosphide electrode.

[0013] Preferably, in step (2), the molar amount of each compound in the ionic stabilizer is 0.5 to 2 times the molar amount of any other compound.

[0014] Those skilled in the art can clearly understand that the molar amount of each compound in the ionic stabilizer is 0.5 to 2 times the molar amount of any other compound, which means that when the ionic stabilizer is a combination of two or more of thiourea, selenourea, potassium iodide, and sodium aluminate, the molar amount of compound A is 0.5 to 2 times that of compound B. Similarly, when the molar amount of compound B is 2 to 0.5 times that of compound A, and when compound A is 0.5 times that of compound B, the molar amount of compound B is 2 times that of compound A.

[0015] Preferably, in step (2), the ionic stabilizer is a combination of thiourea, selenourea and sodium aluminate, or the ionic stabilizer is a combination of selenourea, potassium iodide and sodium aluminate.

[0016] The inventors have found through research that, in step (2), the combination of the above-mentioned ion stabilizers participating in the hydrothermal reaction of step (2) can make the hydrothermal reaction in step (2) more effective, thereby improving the capacitance, conductivity and cycle performance of the nickel cobalt phosphide electrode.

[0017] Preferably, in step (1), the molar ratio of nickel ions, cobalt ions, and sodium hypophosphite is 1.5-1.75:1:4.5-5.5.

[0018] Preferably, in step (1), the concentration of urea in the mixed solution A is 0.6-0.8 mol / L, and the concentration of the ion regulator in the mixed solution A is 0.15-0.25 mol / L.

[0019] Preferably, in step (2), the mass concentration of the ionic stabilizer is 0.2% to 0.4%.

[0020] Preferably, in step (3), the thickness of the ion dispersant on the surface of the nickel-cobalt phosphide electrode material obtained in step (2) is controlled to be 100-200 μm.

[0021] Preferably, in step (3), the concentration of sodium citrate in the ionic dispersant is 0.08% to 0.15%, and the concentration of polyvinyl pyrrolidone is 0.4% to 0.8%.

[0022] Preferably, in step (3), the drying temperature is 80-100° C., and the drying time is 45-90 minutes.

[0023] Preferably, the first hydrothermal reaction and the second hydrothermal reaction are both carried out in a closed high-pressure reactor.

[0024] Preferably, the temperature of the first hydrothermal reaction is 120-140° C., and the time of the first hydrothermal reaction is 2.5-4 hours.

[0025] Preferably, the temperature of the second hydrothermal reaction is 85-95° C., and the time of the second hydrothermal reaction is 50-80 minutes.

[0026] A nickel cobalt phosphide electrode prepared by any of the above methods for preparing a nickel cobalt phosphide electrode.

[0027] The nickel cobalt phosphide electrode of the present invention forms a dispersion layer of sodium citrate and polyvinyl pyrrolidone on the surface of the material through drying after two hydrothermal reactions, which synergistically improves the capacitance, conductivity and cycle performance of the nickel cobalt phosphide electrode.

[0028] The beneficial effects of the present invention are: the present invention provides a nickel cobalt phosphide electrode and a preparation method thereof. The preparation method of the nickel cobalt phosphide electrode uses foam nickel as a substrate and combines two hydrothermal reactions. In the first hydrothermal reaction, nickel nitrate, cobalt nitrate, and sodium hypophosphite are loaded on the nickel foam by adjusting selenium halide and urea. In the second hydrothermal reaction, an ion stabilizer such as thiourea, selenourea, potassium iodide, and sodium aluminate is used for hydrothermal reaction, so that the nickel cobalt phosphide ions are better combined with each other, the ions on the surface of the nickel foam are embedded in the inner layer of the nickel foam, and the nickel cobalt phosphide ions are better combined with the nickel foam. Moreover, after the second hydrothermal reaction, a dispersion layer of sodium citrate and polyvinyl pyrrolidone is formed on the surface of the material by drying, which synergistically improves the capacitance, conductivity, and cycle performance of the nickel cobalt phosphide electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 1 is a charge and discharge comparison diagram of Example 1 of the present invention and the comparative example at the same current density.

[0030] Figure 2 2 is a charge and discharge comparison diagram of Example 1 and Example 14 of the present invention at the same current density. DETAILED DESCRIPTION

[0031] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0032] Example 1

[0033] As a preparation method of a nickel cobalt phosphide electrode according to an embodiment of the present invention, the preparation method comprises the following steps: (1) The nickel foam was sequentially placed in a beaker containing deionized water and anhydrous ethanol, ultrasonically cleaned for 10 minutes, and then dried to form a nickel foam substrate. The nickel foam substrate was immersed in a mixed solution A and subjected to a first hydrothermal reaction at 125° C. in a high-pressure reactor under closed conditions for 3 hours. The mixed solution A contained nickel ions, cobalt ions, and sodium hypophosphite, wherein the molar ratio of nickel ions, cobalt ions, and sodium hypophosphite was 1.5:1:5, wherein the concentration of nickel ions was 4.5 mmol / L, and the mixed solution A also contained 0.8 mol / L of urea and 0.2 mol / L of an ion regulator, wherein the ion regulator was selenium fluoride; (2) After the first hydrothermal reaction is completed, an ion stabilizer is added to the mixed solution A to obtain a mixed solution B. The foamed nickel substrate treated in step (1) is rinsed with deionized water and then dried. Then, the foamed nickel substrate is immersed in the mixed solution B and subjected to a second hydrothermal reaction at 90° C. under closed conditions for 60 minutes to obtain a foamed nickel substrate coated with a nickel cobalt phosphide electrode material. The ion stabilizer is thiourea, and the mass concentration of the ion stabilizer is 0.3%; (3) An ion dispersant is uniformly coated on the surface of the nickel foam substrate coated with the nickel cobalt phosphide electrode material obtained in step (2) and then dried to obtain a nickel cobalt phosphide electrode. The ion dispersant is a mixed aqueous solution of sodium citrate and polyvinyl pyrrolidone (PVP). The concentration of sodium citrate in the ion dispersant is 0.12%, and the concentration of polyvinyl pyrrolidone is 0.5%. The drying temperature is 100°C and the drying time is 60 minutes. The thickness of the ion dispersant on the surface of the nickel cobalt phosphide electrode material obtained in step (2) is controlled to be 200 μm±1 μm.

[0034] The obtained nickel cobalt phosphide electrode was retained and kept for subsequent chemical performance testing.

[0035] Example 2

[0036] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is potassium iodide.

[0037] Example 3

[0038] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is selenourea.

[0039] Example 4

[0040] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is sodium aluminate.

[0041] Example 5

[0042] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is potassium iodide and thiourea in a mass ratio of 1:1.

[0043] Example 6

[0044] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is potassium iodide and selenourea in a mass ratio of 1:1.

[0045] Example 7

[0046] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is potassium iodide and sodium aluminate in a mass ratio of 1:1.

[0047] Example 8

[0048] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is thiourea and selenourea in a mass ratio of 1:1.

[0049] Example 9

[0050] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 1 is that in step (2), the ion stabilizer is selenourea and sodium aluminate in a mass ratio of 1:1.

[0051] Example 10

[0052] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 9 is that the molar ratio of nickel ions, cobalt ions, and sodium hypophosphite is 1.7:1:5.

[0053] Example 11

[0054] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 9 is that the mass concentration of the ion stabilizer is 0.1%.

[0055] Example 12

[0056] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 9 is that the mass concentration of the ion stabilizer is 0.2%.

[0057] Example 13

[0058] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 9 is that the mass concentration of the ion stabilizer is 0.4%.

[0059] Example 14

[0060] As a method for preparing a nickel cobalt phosphide electrode according to an embodiment of the present invention, the only difference between this embodiment and Example 9 is that the mass concentration of the ion stabilizer is 0.5%.

[0061] Comparative Example 1 As a preparation method of a nickel cobalt phosphide electrode of a comparative example of the present invention, the only difference between this comparative example and Example 1 is that the preparation method does not include step (3), and the material after drying in step (2) is used as the nickel cobalt phosphide electrode of this comparative example.

[0062] Comparative Example 2 As a preparation method of a nickel cobalt phosphide electrode of a comparative example of the present invention, the only difference between this comparative example and Example 1 is that the preparation method does not include step (2), and the material after drying in step (1) is directly subjected to the operation of step (3) to obtain the nickel cobalt phosphide electrode of this comparative example.

[0063] Comparative Example 3 As a comparative example of the present invention, the preparation method of a nickel cobalt phosphide electrode is different from Example 1 only in that the mixed solution A in step (1) of the preparation method does not contain urea.

[0064] Comparative Example 4 As a preparation method of a nickel cobalt phosphide electrode as a comparative example of the present invention, the only difference between this comparative example and Example 1 is that the mixed solution A in step (1) of the preparation method does not contain an ion regulator.

[0065] Comparative Example 5 As a preparation method of a nickel cobalt phosphide electrode of a comparative example of the present invention, the preparation method of this comparative example is a one-step hydrothermal method: (1) The nickel foam was sequentially placed in a beaker containing deionized water and anhydrous ethanol, ultrasonically cleaned for 10 minutes, and then dried to form a nickel foam substrate. The nickel foam substrate was immersed in a mixed solution A and subjected to a first hydrothermal reaction at 125° C. in a high-pressure reactor under closed conditions for 3 hours. The mixed solution contained nickel ions, cobalt ions, and sodium hypophosphite, wherein the molar ratio of nickel ions, cobalt ions, and sodium hypophosphite was 1.5:1:5, wherein the concentration of nickel ions was 4.5 mmol / L, and the mixed solution A also contained 0.8 mol / L of urea and 0.2 mol / L of an ion regulator, wherein the ion regulator was selenium fluoride; the mixed solution A also contained an ion stabilizer, wherein the ion stabilizer was thiourea, and the mass concentration of the ion stabilizer was 0.3%; (2) An ion dispersant is uniformly coated on the surface of the nickel foam substrate coated with the nickel cobalt phosphide electrode material obtained in step (1) and then dried to obtain a nickel cobalt phosphide electrode. The ion dispersant is a mixed aqueous solution of sodium citrate and polyvinyl pyrrolidone (PVP). The concentration of sodium citrate in the ion dispersant is 0.12%, and the concentration of polyvinyl pyrrolidone is 0.5%. The drying temperature is 100°C and the drying time is 60 minutes. The thickness of the ion dispersant on the surface of the nickel cobalt phosphide electrode material obtained in step (1) is controlled to be 200 μm±1 μm.

[0066] Experimental methods: Test samples: Examples 1 to 14, Comparative Examples 1 to 5, nickel cobalt phosphide electrodes with a size of 1×2 cm 2 .

[0067] Test method: The prepared electrode materials were subjected to electrochemical performance tests. The above-mentioned test samples were used as working electrodes, composite zinc sheets as counter electrodes, zinc wires as reference electrodes, and 1 mol / L KOH solution as electrolyte. Battery charge and discharge tests were performed at 25°C ± 1°C.

[0068] The capacitance, conductivity, rate capability, and cycle performance of the tested samples were shown in Table 1. The discharge rate (C) of each sample was 5.00 ± 0.05.

[0069] As can be seen from Table 1, the preparation method of the nickel cobalt phosphide electrode of the present invention uses nickel foam as a substrate and combines two hydrothermal reactions. In the first hydrothermal reaction, nickel nitrate, cobalt nitrate, and sodium hypophosphite are loaded on the nickel foam by adjusting selenium halide and urea. In the second hydrothermal reaction, thiourea, selenourea, potassium iodide, and sodium aluminate are used as ion stabilizers for hydrothermal reaction, so that the nickel cobalt phosphide ions are better combined with each other, the ions on the surface of the nickel foam are embedded in the inner layer of the nickel foam, and the nickel cobalt phosphide ions are better combined with the nickel foam. Moreover, after the second hydrothermal reaction, a dispersion layer of sodium citrate and polyvinyl pyrrolidone is formed on the surface of the material by drying, which synergistically improves the capacitance, conductivity, and cycle performance of the nickel cobalt phosphide electrode.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a nickel-cobalt phosphide electrode, characterized in that: The preparation method comprises the following steps: (1) Submerging the nickel foam substrate in a mixed solution A and performing a first hydrothermal reaction at 100° C. to 150° C. under closed conditions for 2 to 5 hours, wherein the mixed solution A contains nickel ions, cobalt ions and sodium hypophosphite, wherein the molar ratio of nickel ions, cobalt ions and sodium hypophosphite is 1.2 to 1.8:1:4 to 6, and the mixed solution A further contains 0.5 to 1 mol / L of urea and 0.10 to 0.3 mol / L of an ion regulator, wherein the ion regulator is one or more selenium halides, and the selenium halide is selenium chloride, selenium fluoride or selenium bromide; (2) After the first hydrothermal reaction is completed, an ion stabilizer is added to the mixed solution A to obtain a mixed solution B, and the foamed nickel substrate treated in step (1) is immersed in the mixed solution B and subjected to a second hydrothermal reaction at 80° C. to 100° C. under closed conditions for 45 to 90 minutes to obtain a foamed nickel substrate coated with a nickel cobalt phosphide electrode material, wherein the ion stabilizer is at least one of thiourea, selenourea, potassium iodide, and sodium aluminate, and the mass concentration of the ion stabilizer is 0.1% to 0.5%; (3) Evenly distributing an ion dispersant on the surface of the nickel foam substrate coated with the nickel cobalt phosphide electrode material obtained in step (2) and then drying the substrate to obtain a nickel cobalt phosphide electrode, wherein the ion dispersant is a mixed aqueous solution of sodium citrate and polyvinyl pyrrolidone (PVP).

2. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: In step (2), the ionic stabilizer is at least one of thiourea, selenourea, potassium iodide, and sodium aluminate and must contain selenourea or sodium aluminate.

3. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: In step (2), the ionic stabilizer is at least two of thiourea, selenourea, potassium iodide, and sodium aluminate and must contain selenourea and sodium aluminate.

4. The method for preparing the nickel-cobalt phosphide electrode according to claim 3, characterized in that: In step (2), the molar amount of each compound in the ionic stabilizer is 0.5 to 2 times the molar amount of any other compound.

5. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: In step (2), the ionic stabilizer is a combination of thiourea, selenourea and sodium aluminate, or the ionic stabilizer is a combination of selenourea, potassium iodide and sodium aluminate.

6. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: In step (1), the concentration of nickel ions is 3-6 mmol / L; the molar ratio of nickel ions, cobalt ions, and sodium hypophosphite is 1.5-1.75:1:4.5-5.5; the concentration of urea in the mixed solution A is 0.6-0.8 mol / L, and the concentration of the ion regulator in the mixed solution A is 0.15-0.25 mol / L.

7. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: The mass concentration of the ionic stabilizer in step (2) is 0.2% to 0.4%.

8. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: In step (3), the thickness of the ion dispersant on the surface of the nickel cobalt phosphide electrode material obtained in step (2) is controlled to be 100-200 μm, the concentration of sodium citrate in the ion dispersant is 0.08%-0.15%, the concentration of polyvinyl pyrrolidone is 0.4%-0.8%, and the drying temperature is 80-100°C.

9. The method for preparing the nickel-cobalt phosphide electrode according to claim 1, characterized in that: The first hydrothermal reaction and the second hydrothermal reaction are both carried out in a high-pressure reactor; the temperature of the first hydrothermal reaction is 120~140°C, and the time of the first hydrothermal reaction is 2.5~4 hours; the temperature of the second hydrothermal reaction is 85~95°C, and the time of the second hydrothermal reaction is 50~80 minutes.

10. A nickel cobalt phosphide electrode prepared by the method for preparing a nickel cobalt phosphide electrode according to any one of claims 1 to 9.

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