Self-supporting nitrogen-doped carbon layer coated nickel-cobalt sulfide nanobelt / foamed nickel electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of electrode material preparation, in particular to a self-supporting nitrogen-doped carbon layer coated nickel-cobalt sulfide nanobelt / foamed nickel electrode material and a preparation method and application thereof, a nickel-cobalt sulfide nanobelt grows on the surface of foamed nickel in situ, and the surface of the nickel-cobalt sulfide nanobelt is coated with a nitrogen-doped carbon layer. The preparation method comprises the following steps: growing a nickel-cobalt nanobelt precursor with controllable morphology on a foamed nickel skeleton in situ, coating the surface of the nanobelt with polydopamine in situ at room temperature by virtue of electrostatic interaction between negative charges (OH <-> and CO3 < 2->) in the precursor and amino positive charges in dopamine hydrochloride, and vulcanizing and carbonizing to obtain a target product. The nitrogen-doped carbon layer is beneficial to accelerating the electron conduction rate of the nickel-cobalt sulfide, providing abundant reaction active sites, accelerating the kinetics of ion transmission in the oxidation-reduction reaction process, improving the structural stability of the electrode material, inhibiting the volume expansion of an active substance in the circulation process, and improving the specific capacitance, the rate and the circulation stability of the electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state supercapacitor electrode material preparation, and specifically relates to a self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material, and a preparation method and application thereof. Background Art

[0002] As a new type of energy storage device, supercapacitors have the advantages of high power density, long cycle life and high safety compared with lithium-ion batteries, and are increasingly valued by people. Compared with traditional liquid electrolyte supercapacitors, solid-state supercapacitors usually use gel electrolytes, which will not cause faults such as electrolyte leakage, and can be integrated on a single chip in various geometric shapes. They are fast energy storage devices used in the field of future smart wearable electronic devices. Electrode materials have a crucial impact on the performance of supercapacitors. Optimizing and regulating the morphology, composition and size of electrode materials is the main research direction of current electrode materials. Nickel-cobalt transition bimetallic sulfide has high electrochemical activity and specific capacity, and is a potential pseudocapacitive electrode material. However, it is affected by the material morphology and low intrinsic conductivity, and faces problems such as slow kinetics, inability to buffer volume changes, and unstable structure during charging and discharging. Therefore, it is necessary to develop a new electrode material to solve the above problems by designing and optimizing the material structure and simultaneously obtain a larger specific capacity, rate and cycle stability of the electrode material. Summary of the invention

[0003] The purpose of the present invention is to provide a self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material and its preparation method and application, using nickel foam as a substrate, in-situ growth of a nickel cobalt nanobelt precursor with controllable morphology through a hydrothermal reaction, coating polydopamine on the surface of the nickel cobalt nanobelt through an in-situ polymerization reaction at room temperature, and then sulfurizing and carbonizing to form a nickel cobalt sulfide nanobelt / nickel foam electrode material coated with a nitrogen-doped carbon layer. The thickness of the nitrogen-doped carbon layer can be controlled by adjusting the time of coating with polydopamine, and an electrode material with high specific capacitance, good rate performance and excellent cycle stability is obtained.

[0004] The primary purpose of the present invention is to provide a self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material, in which the nickel-cobalt sulfide nanobelt is in-situ grown on the surface of nickel foam, and the surface of the nickel-cobalt sulfide nanobelt is coated with a nitrogen-doped carbon layer, the nickel-cobalt sulfide is an edge-containing nanobelt structure, and the width of the nickel-cobalt sulfide nanobelt is 150~200 nm.

[0005] Another object of the present invention is to provide a method for preparing a self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material, which specifically comprises the following steps: (1) Pretreatment of nickel foam NF; (2) Preparation of nickel-cobalt nanobelt precursor / NF: dissolving hydrated nickel salt, hydrated cobalt salt, urea and ammonium fluoride in deionized water to form solution A; immersing the nickel foam pretreated in step (1) in solution A, and then transferring it to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the nickel foam is naturally cooled to room temperature. The nickel foam after the reaction is taken out, washed with deionized water, and then dried to obtain a nickel-cobalt nanobelt precursor in situ grown on the nickel foam, which is recorded as nickel-cobalt nanobelt precursor / NF; (3) Preparation of nickel-cobalt nanobelt precursor @PDA / NF: Add tris(hydroxymethyl)aminomethane to an ethanol aqueous solution and stir to dissolve it uniformly, adjust the pH value of the solution to 8.5, and then add dopamine hydrochloride thereto to dissolve it, thereby obtaining solution B; put the nickel-cobalt nanobelt precursor / NF obtained in step (2) into solution B, and allow it to react at room temperature for 24 to 96 h, replace it with a new solution B every 24 h, take out the nickel foam after the reaction, wash it with deionized water, and then dry it to obtain a nickel foam with polydopamine in situ coated on the surface of the nickel-cobalt nanobelt precursor, which is recorded as nickel-cobalt nanobelt precursor @PDA / NF; (4) Preparation of nickel cobalt sulfide nanobelts @PDA / NF: dissolving sodium sulfide nonahydrate in deionized water to form a solution C, immersing the nickel cobalt nanobelt precursor @PDA / NF obtained in step (3) in the solution C and transferring the whole of the solution into a hydrothermal reactor for a hydrothermal sulfidation reaction. After the reaction is completed, the solution is naturally cooled to room temperature. The nickel foam after the reaction is taken out, washed with deionized water, and then dried to obtain nickel cobalt sulfide nanobelts @PDA / NF; (5) Preparation of NCS@NC / NF electrode material: The nickel cobalt sulfide nanobelt@PDA / NF obtained in step (4) was calcined in an argon atmosphere at a temperature of 480-600°C, a heating rate of 2°C / min, and a holding time of 60-180 min. After the calcination, the material was naturally cooled to room temperature and taken out to obtain a self-supporting nitrogen-doped carbon layer-coated nickel cobalt sulfide nanobelt / nickel foam electrode material, denoted as NCS@NC / NF.

[0006] Furthermore, in step (1) of the above preparation method, the pretreatment process of the nickel foam includes: rinsing the nickel foam with deionized water and then immersing it in a hydrochloric acid solution with a concentration of 1 mol / L for ultrasonic washing for 20 to 30 minutes, then washing it with deionized water and anhydrous ethanol alternately for 3 times, then immersing the nickel foam in an acetone solvent for ultrasonic washing for 20 to 30 minutes, then washing it with deionized water and anhydrous ethanol alternately for 3 times, and finally placing the nickel foam in a drying oven for drying.

[0007] Furthermore, in step (2) of the above preparation method, the nickel salt is selected from one of nickel nitrate hexahydrate and nickel chloride hexahydrate, the cobalt salt is selected from one of cobalt nitrate hexahydrate and cobalt chloride hexahydrate, and the temperature of the hydrothermal reaction in step (2) is 120° C. and the reaction time is 8 h.

[0008] Furthermore, the concentration of the hydrated nickel salt in solution A is 0.01-0.03 mol / L, and the concentration of the hydrated cobalt salt is 0.02-0.06 mol / L; and the molar ratio of the hydrated nickel salt, the hydrated cobalt salt, urea, and ammonium fluoride in solution A is 1:2:4:4.

[0009] Furthermore, in step (3) of the above preparation method, the concentration of tris(hydroxymethyl)aminomethane in solution B is 0.01 to 0.03 mol / L, the concentration of dopamine hydrochloride is 0.01 to 0.06 mol / L, and the ethanol aqueous solution is obtained by mixing anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is 1:1 to 1:4.

[0010] Furthermore, in step (4) of the above preparation method, the concentration of sodium sulfide nonahydrate in solution C is 0.2-0.6 mol / L, the temperature of the hydrothermal sulfidation reaction is 160° C., and the reaction time is 6 h.

[0011] Another object of the present invention is to provide a self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material obtained according to the above preparation method as an energy storage electrode material in a supercapacitor, and the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material can be directly used as a working electrode.

[0012] In the above application, the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material was used as the working electrode, the platinum electrode was used as the counter electrode, the Hg / HgO electrode was used as the reference electrode, the electrolyte was 6 mol / L KOH, and the current was 1 mA / cm 2 When the area specific capacitance of the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material is 3100~5100mF / cm 2 ; 10 mA / cm 2 When the area specific capacitance of the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material is 2200~4500 mF / cm 2 .

[0013] Compared with the prior art, the present invention has obvious advantages and beneficial effects. By means of the above technical solution, the present invention can achieve considerable technical progress and practicality, and has a wide range of utilization value, and has at least the following advantages: (1) In the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam (NCS@NC / NF) electrode material prepared by the present invention, the nickel cobalt sulfide nanobelt is in-situ uniformly grown on the nickel foam, and the nickel cobalt nanobelt is firmly bonded to the nickel foam substrate, and can be directly used as a working electrode. Compared with the preparation process of powder-based electrode materials, the present invention does not require solvent and adhesive mixing, stirring, coating and drying operations, thereby saving the time for electrode preparation, and at the same time avoiding the problem that the electrode material obtained by the traditional preparation method in the electrode preparation process is unevenly coated with the electrode material and the active material is not firmly bonded to the nickel foam substrate, resulting in the active material falling off the nickel foam surface during the test process and the low repeatability and poor stability of the results.

[0014] (2) The contact area between the electrode materials with nanoneedle structure and nanosheet structure and the electrolyte is small. In the NCS@NC / NF electrode material prepared by the present invention, the nickel-cobalt sulfide is an edge-containing nanobelt structure, which has a large specific surface area and can increase the contact area with OH in alkaline electrolyte. - The larger contact area provides more active sites for redox reactions and generates a larger Faradaic pseudocapacitance.

[0015] (3) In the NCS@NC / NF electrode prepared by the present invention, the surface of the nickel cobalt sulfide nanobelt is coated with a nitrogen-doped carbon layer. The nitrogen-doped carbon layer is an excellent conductive substrate. Coating it on the surface of the high specific capacity nickel cobalt sulfide is conducive to accelerating the electron conduction rate of the nickel cobalt sulfide. At the same time, the high specific surface area can provide abundant reactive active sites to accelerate the kinetics of ion transport in the redox reaction in the electrolyte, which is conducive to improving the structural stability of the electrode material and inhibiting the volume expansion of the active material during the cycle. It can better play the synergistic effect of the high theoretical specific capacity of nickel cobalt sulfide and the excellent conductivity of carbon materials, and make up for the defects of poor conductivity of nickel cobalt sulfide and low specific capacity of carbon materials. The thickness of the nitrogen-doped carbon layer can be effectively controlled by adjusting the polydopamine coating time, thereby optimizing the synthesis of energy storage electrode materials with optimal conductivity and electrochemical active sites, which can be used in hybrid solid-state supercapacitors.

[0016] (4) Compared with the nickel cobalt sulfide / nickel foam (NC / NF) electrode without nitrogen-doped carbon layer, the NCS@NC / NF electrode prepared in the present invention has relatively excellent specific capacity and rate performance, and can maintain good cycle stability, which is superior to the nickel cobalt sulfide electrodes prepared by other methods reported so far.

[0017] (5) The preparation method of the NCS@NC / NF electrode of the present invention is simple, repeatable and universal. The nickel salt, cobalt salt and urea raw materials used are cheap and easily available, and the cost is low. It is also applicable to the preparation of other transition monometallic sulfide, bimetallic sulfide and polymetallic sulfide electrodes with foam as the substrate and coated with a nitrogen-doped carbon layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 (a) and (b) are SEM images of the nickel-cobalt nanobelt precursor / NF prepared in step (2) of Example 1 at magnifications of 50,000 times and 700 times, respectively.

[0019] Figure 2 (a), (b), (c), and (d) are SEM images of the nickel-cobalt nanobelt precursor @PDA / NF prepared after coating with polydopamine in step (3) of Example 1, Example 2, Example 3, and Example 4, respectively.

[0020] Figure 3 (a) and (b) are SEM images of the nickel cobalt sulfide / NF electrode prepared in the comparative example at magnifications of 50,000 times and 700 times, respectively.

[0021] Figure 4 (a), (b), (c), and (d) are SEM images of nickel cobalt sulfide nanobelts@PDA / NF prepared in Example 1, Example 2, Example 3, and Example 4, respectively.

[0022] Figure 5 3 are SEM images of NCS@NC / NF electrode materials prepared in Example 2 and Example 3, wherein (a) and (b) represent Example 2, and (c) and (d) represent Example 3.

[0023] Figure 6 1 is the XRD curve of the NCS@NC / NF electrode prepared in Example 2 and the nickel cobalt sulfide / NF electrode material prepared in the comparative example.

[0024] FIG. 7 is a full XPS spectrum of the NCS@NC / NF electrode material prepared in Example 2.

[0025] Figure 8 It is the CV curve of the nickel cobalt sulfide / NF electrode material prepared in comparative example at different scanning rates.

[0026] Fig. 9 CV curves of the NCS@NC / NF electrode material prepared in Example 2 at different scanning rates.

[0027] Fig.10 The electrode materials prepared in Examples 1 to 4 and the comparative example are 2 Comparison of constant current charge and discharge (GCD) curves under.

[0028] Fig.11 The electrode materials prepared in Example 2 and the comparative example are 5Hz, comparison of electrochemical impedance spectroscopy (EIS) curves at an amplitude of 5 mV.

[0029] Fig.12 yes Fig.11 Enlarged comparison of the mid- and high-frequency areas.

[0030] Fig.13 The NCS@NC / NF electrode material prepared in Example 2 and the nickel cobalt sulfide / NF electrode material prepared in the comparative example were subjected to a current density of 5 mA / cm 2 Comparison of specific capacitance retention rate after 5000 charge and discharge cycles. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention is described in detail with specific examples below. If no specific conditions are specified in the following examples, they are all carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials and reagents used without specifying the manufacturer are all conventional products that can be purchased from the market.

[0033] Embodiment 1: (1) Pretreatment of nickel foam (NF): Prepare a 15×20×1 mm 3 The nickel foam was first rinsed with deionized water and then immersed in a 1 mol / L hydrochloric acid solution for ultrasonic washing for 20 min, then washed alternately with deionized water and anhydrous ethanol for 3 times, then immersed in an acetone solvent for ultrasonic washing for 20 min, then washed alternately with deionized water and anhydrous ethanol for 3 times, finally, the NF was placed in a drying oven and dried at 60 °C for 12 h to obtain the pretreated nickel foam.

[0034] (2) Preparation of nickel-cobalt nanobelt precursor / NF: 0.291 g nickel nitrate hexahydrate, 0.582 g cobalt nitrate hexahydrate, 0.24 g urea, and 0.148 g ammonium fluoride were dissolved in 50 mL deionized water to form solution A; the NF pretreated in step (1) was immersed in solution A and transferred to a hydrothermal reactor, and hydrothermally reacted in an oven at 120°C for 8 h. After the reaction was completed, the NF was naturally cooled to room temperature. The nickel foam NF after the reaction in solution A was taken out and washed with deionized water three times, and then placed in a vacuum oven at 60°C for 12 h to obtain nickel-cobalt nanobelt precursor / NF.

[0035] (3) Preparation of nickel-cobalt nanobelt precursor @PDA / NF: 0.0726 g of tris(hydroxymethyl)aminomethane was added to 60 mL of ethanol aqueous solution (the volume ratio of ethanol to water was 1:1), and the mixture was dissolved and stirred evenly. Ammonia water was added dropwise to adjust the pH value of the solution to 8.5. Then, 0.2 g of dopamine hydrochloride was added thereto to dissolve the solution, and solution B was obtained. The nickel-cobalt nanobelt precursor / NF obtained in step (2) was placed in solution B and allowed to react at room temperature for 24 h. The nickel foam in solution B after the reaction was taken out and washed with deionized water for 3 times. The nickel foam was placed in a vacuum oven at 60°C and dried for 12 h to obtain a nickel foam with polydopamine in situ coated on the surface of the nickel-cobalt nanobelt precursor, which was recorded as nickel-cobalt nanobelt precursor @PDA / NF.

[0036] (4) Preparation of nickel cobalt sulfide nanobelts @PDA / NF: 2.4 g of sodium sulfide nonahydrate was dissolved in 50 mL of deionized water to form solution C. The nickel cobalt nanobelt precursor @PDA / NF obtained in step (3) was immersed in solution C and transferred to a hydrothermal reactor. The precursor was subjected to hydrothermal sulfurization in an oven at 160 °C for 6 h. After the reaction, the precursor was naturally cooled to room temperature. The nickel foam NF after the reaction in solution C was taken out and washed with deionized water for 3 times. The foamed nickel NF was then dried in an oven at 60 °C for 12 h to obtain nickel cobalt sulfide nanobelts @PDA / NF.

[0037] (5) Preparation of NCS@NC / NF: The nickel cobalt sulfide nanobelt@PDA / NF obtained in step (4) was calcined and carbonized in an argon atmosphere at a temperature of 480°C, a heating rate of 2°C / min, and a holding time of 120 min. After the calcination, the nanobelt was naturally cooled to room temperature and taken out to obtain a self-supporting nitrogen-doped carbon layer-coated nickel cobalt sulfide nanobelt / nickel foam electrode material, which was labeled as NCS@NC / NF.

[0038] The self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode (NCS@NC / NF) prepared in step (5) was used as the working electrode, the platinum electrode was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. Cyclic voltammetry (CV), constant current charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle stability tests were performed at different scan rates in 6 mol / L KOH electrolyte. Based on the GCD curve, 1 mA / cm 2 The area specific capacitance is 3102.2 mF / cm 2 , 10 mA / cm 2 The area specific capacitance is 2210.5 mF / cm 2 The rate performance is 71.2%, and the area specific capacitance retention rate after 5000 cycles is 85.8%.

[0039] Embodiment 2: (1) Pretreatment of nickel foam (NF): The specific operation is the same as step (1) of Example 1.

[0040] (2) Preparation of nickel-cobalt nanobelt precursor / NF: The specific operation is the same as step (2) of Example 1.

[0041] (3) Preparation of nickel-cobalt nanobelt precursor @PDA / NF: The reaction was allowed to stand at room temperature for 48 h, and solution B was replaced every 24 h. The remaining operations were the same as step (3) of Example 1.

[0042] (4) Preparation of nickel cobalt sulfide nanobelts @PDA / NF: The specific operation is the same as step (4) of Example 1.

[0043] (5) Preparation of NCS@NC / NF: The calcination temperature was 500°C, and the remaining operations were the same as step (5) of Example 1.

[0044] The self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode (NCS@NC / NF) prepared in step (5) was used as the working electrode, the platinum electrode was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. Cyclic voltammetry (CV), constant current charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle stability tests were performed at different scan rates in 6 mol / L KOH electrolyte. Based on the GCD curve, 1 mA / cm 2 The area specific capacitance is 5082.6 mF / cm 2 , 10 mA / cm 2 The area specific capacitance is 4460.1 mF / cm 2 The rate performance is 87.8%, and the area specific capacitance retention rate after 5000 cycles is 98.6%.

[0045] Embodiment 3: (1) Pretreatment of nickel foam (NF): The specific operation is the same as step (1) of Example 1.

[0046] (2) Preparation of nickel-cobalt nanobelt precursor / NF: The specific operation is the same as step (2) of Example 1.

[0047] (3) Preparation of nickel-cobalt nanobelt precursor @PDA / NF: The reaction was allowed to stand at room temperature for 72 h, and solution B was replaced every 24 h. The remaining operations were the same as step (3) of Example 1.

[0048] (4) Preparation of nickel cobalt sulfide nanobelts @PDA / NF: The specific operation is the same as step (4) of Example 1.

[0049] (5) Preparation of NCS@NC / NF: The calcination temperature was 550°C, and the remaining operations were the same as step (5) of Example 1.

[0050] The self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode (NCS@NC / NF) prepared in step (5) was used as the working electrode, the platinum electrode was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. Cyclic voltammetry (CV), constant current charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle stability tests were performed at different scan rates in 6 mol / L KOH electrolyte. Based on the GCD curve, 1 mA / cm 2 The area specific capacitance is 5051.2 mF / cm 2 , 10 mA / cm 2 The area specific capacitance is 4196.5 mF / cm 2 The rate performance is 83.1%, and the area specific capacitance retention rate after 5000 cycles is 99.1%.

[0051] Embodiment 4: (1) Pretreatment of nickel foam (NF): The specific operation is the same as step (1) of Example 1.

[0052] (2) Preparation of nickel-cobalt nanobelt precursor / NF: The specific operation is the same as step (2) of Example 1.

[0053] (3) Preparation of nickel-cobalt nanobelt precursor @PDA / NF: The reaction was allowed to stand at room temperature for 96 h, with solution B replaced every 24 h. The remaining operations were the same as step (3) of Example 1.

[0054] (4) Preparation of nickel cobalt sulfide nanobelts @PDA / NF: The specific operation is the same as step (4) of Example 1.

[0055] (5) Preparation of NCS@NC / NF: The specific operation is the same as step (5) of Example 1.

[0056] The self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode (NCS@NC / NF) prepared in step (5) was used as the working electrode, the platinum electrode was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. Cyclic voltammetry (CV), constant current charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle stability tests were performed at different scan rates in 6 mol / L KOH electrolyte. Based on the GCD curve, 1 mA / cm 2 The area specific capacitance is 4548.9 mF / cm 2 , 10 mA / cm 2 The area specific capacitance is 3602.7 mF / cm 2The rate performance is 79.2%, and the area specific capacitance retention rate after 5000 cycles is 96.3%.

[0057] Comparative Example: (1) Pretreatment of nickel foam (NF): The specific operation is the same as step (1) of Example 1.

[0058] (2) Preparation of nickel-cobalt nanobelt precursor / NF: The specific operation is the same as step (2) of Example 1.

[0059] (3) 2.4 g of sodium sulfide nonahydrate was dissolved in 50 mL of deionized water to form solution C. The nickel cobalt nanobelt precursor / NF obtained in step (2) was immersed in solution C and transferred to a hydrothermal reactor. The hydrothermal sulfurization reaction was carried out in an oven at 160° C. for 6 h. After the reaction was completed, the foamed nickel NF was naturally cooled to room temperature. The foamed nickel NF after the reaction in solution C was taken out and washed with deionized water for 3 times. Then, it was placed in an oven and dried at 60° C. for 12 h to obtain a nickel cobalt sulfide / foamed nickel electrode, which was recorded as nickel cobalt sulfide / NF.

[0060] The nickel cobalt sulfide / NF prepared in step (3) was used as the working electrode, the platinum electrode as the counter electrode, and the Hg / HgO electrode as the reference electrode. Cyclic voltammetry (CV), constant current charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle stability tests were performed at different scan rates in 6 mol / L KOH electrolyte. The 1 mA / cm 2 The area specific capacitance is 2597.8 mF / cm 2 , 10 mA / cm 2 When the area specific capacitance is 1623.1 mF / cm 2 The rate performance is 62.5%, and the area specific capacitance retention rate after 5000 cycles is 69.4%.

[0061] The comparative example is nickel cobalt sulfide / NF prepared by two-step hydrothermal reaction, and is not coated with a nitrogen-doped carbon layer.

[0062] The morphology of the nickel-cobalt nanobelt precursor / NF before and after polydopamine coating, hydrothermal sulfidation and calcination in the examples and comparative examples was characterized using a German ZEISS Sigma 360 scanning electron microscope (SEM). 2 For small pieces, there is no need to distinguish the front and back sides. They can be glued to the conductive glue on the sample stage and then sprayed with gold for testing.

[0063] Figure 1 This is a SEM image of the nickel-cobalt nanobelt precursor / NF prepared in step (2) of Example 1. Figure 1 The magnification of (a) is 50,000 times. Figure 1The magnification of (b) is 700 times. Figure 1 It can be seen that the pretreated nickel foam can uniformly grow nanobelt-shaped nickel-cobalt precursor in situ through hydrothermal reaction. The surface of the nickel-cobalt nanobelt is smooth with thin prisms.

[0064] Figure 2 The SEM images of the nickel-cobalt nanobelt precursor @PDA / NF prepared after coating with polydopamine in step (3) of Example 1, Example 2, Example 3, and Example 4 are all at a magnification of 50,000 times. Figure 2 (a) represents Example 1, the polydopamine coating time is 24 h, Figure 2 (b) represents Example 2, where the polydopamine coating time is 48 h. Figure 2 (c) represents Example 3, where the polydopamine coating time is 72 h. Figure 2 (d) represents Example 4, and the polydopamine coating time is 96 h. Figure 2 It can be seen that from Example 1 to Example 4, as the coating time increases from 24 h to 96 h, the surface of the nickel-cobalt nanobelt precursor becomes increasingly rough, indicating that the thickness of the coated polydopamine PDA gradually increases.

[0065] Figure 3 It is the SEM image of nickel-cobalt sulfide / NF prepared in comparative example. Figure 3 The magnification of (a) is 50,000 times. Figure 3 (b) is magnified 700 times. Figure 3 It can be seen in (a) that after the hydrothermal sulfurization process, the surface of the nickel-cobalt precursor nanobelt is etched, and the ribbon morphology changes to a hexagonal pyramid shape.

[0066] Figure 4 (a), (b), (c), and (d) are SEM images of nickel-cobalt sulfide nanobelts@PDA / NF prepared after hydrothermal sulfidation in step (4) of Example 1, Example 2, Example 3, and Example 4, respectively, and the magnification is 50,000 times. Figure 4 It can be seen that compared with Figure 3 The morphology of the product obtained by direct sulfurization without polydopamine coating in the comparative example, the nickel cobalt sulfide nanobelts @PDA / NF formed by sulfurization after coating polydopamine can better retain the morphology of nickel cobalt sulfide nanobelts. The coating time of polydopamine in Example 1 is 24 h, and the surface can be seen to be etched; the surface of Example 2 is not etched, and the surface is rough and ribbon-shaped; the surface of the nanobelt in Example 3 becomes rougher and is covered with granular polydopamine; in Example 4, the surface of the nanobelt is covered with a layer of nanosheet-like structured material, and the nanobelts in Examples 3 and 4 are accumulated.

[0067] Figure 5is a SEM image of the self-supporting nitrogen-doped carbon layer-coated nickel cobalt sulfide nanobelt / nickel foam electrode material (NCS@NC / NF) prepared after calcination in Example 2 and Example 3, Figure 5 (a) and (b) represent Example 2, Figure 5 (c) and (d) represent Example 3, the magnification of (a) and (c) is 50,000 times, and the magnification of (b) and (d) is 700 times. Figure 5 It can be seen that after calcination, nickel-cobalt sulfide still retains the nanobelt morphology and grows evenly on the nickel foam skeleton. The surface of the nanobelt is rough and has edges.

[0068] The XRD test was performed using a Japanese Rigaku SmartLab SE X-ray diffractometer, and the nickel foam loaded with active materials was placed on a sample table to analyze information such as the composition and crystal structure of the material. Figure 6 The XRD curves of the NCS@NC / NF prepared in Example 2 and the nickel cobalt sulfide / NF electrode material prepared in the comparative example are shown in Figure 2. The XRD curves of the two electrodes are very similar, and both have characteristic peaks of nickel cobalt sulfide Ni3S2, NiCo2S4 and Ni. Among them, 2θ at 21.8°, 31.1°, 37.8°, 44.5°, 49.8°, 50.2°, and 55.3° correspond to the (100), (-110), (111), (200), (210), (-210) and (211) crystal planes of Ni3S2, respectively; 2θ at 31.5°, 38.3°, 50.4° and 55.3° correspond to the (311), (400), (511) and (440) crystal planes of NiCo2S4, respectively, indicating that the loaded nickel cobalt sulfide product contains Ni3S2 and NiCo2S4. The remaining three 2θ diffraction peaks at 44.5°, 51.9° and 76.4° correspond to Ni (111), (200) and (220), respectively, which are attributed to Ni in nickel foam. Since the carbon in the nitrogen-doped carbon layer is amorphous carbon, the diffraction peak is weak and is not observed in the XRD pattern of NCS@NC / NF.

[0069] XPS testing was performed using a Thermo Scientific K-Alpha X-ray photoelectron spectrometer from the United States. The nickel foam loaded with active materials was placed on a sample stage to analyze the valence state of the elements in the electrode and possible bonding interactions. Figure 7 This is the full XPS spectrum of the NCS@NC / NF electrode material prepared in Example 2, indicating that the NCS@NC / NF electrode contains Ni, Co, S, C, N, and O elements. The appearance of C and N elements indicates that the polydopamine coated on the surface of the nickel cobalt sulfide nanobelts forms a nitrogen-doped carbon layer coated on the surface of the nanobelts after calcination.

[0070] The material was subjected to a three-electrode test using a Shanghai Chenhua electrochemical workstation CHI760E, with the NCS@NC / NF electrode prepared in Example 2 or the nickel cobalt sulfide / NF electrode prepared in the comparative example as the working electrode, a platinum wire electrode as the counter electrode, and a Hg / HgO electrode as the reference electrode. Cyclic voltammetry (CV) tests and analyses were performed at different scan rates in a 6 mol / L KOH electrolyte. Figure 8 and Fig. 9 The CV curves of the electrode materials prepared in the comparative example and in Example 2 at different scanning rates are shown in FIG. Figure 8 It can be seen that when the scan rate increases from 2 mV / s to 20 mV / s, the CV curve shape of the self-supporting nickel cobalt sulfide / NF electrode material prepared in the comparative example can remain consistent, but when it continues to increase to 50 mV / s and 100 mV / s, the CV curve is severely deformed. Fig. 9 In the experiment, the scan rate increased from 2 mV / s to 300 mV / s, and the CV curve shape of the self-supporting NCS@NC / NF electrode material prepared in Example 2 remained consistent, indicating that coating the nitrogen-doped carbon layer on the surface of the nickel cobalt sulfide nanobelts can improve the rate performance of the electrode.

[0071] Fig.10 The electrode materials prepared in Examples 1 to 4 and the comparative example are 2 Comparison of constant current charge and discharge (GCD) curves under the current density of 1 mA / cm 2 When the area specific capacitance of the electrodes prepared in Example 1, Example 2, Example 3, Example 4 and the comparative example is 3102.2 mF / cm 2 , 5082.6 mF / cm 2 、5051.1 mF / cm 2 、4548.9 mF / cm 2 and 2597.8 mF / cm 2 , indicating that coating the surface of the nickel cobalt sulfide nanobelts with a nitrogen-doped carbon layer can significantly improve the specific capacitance of the electrode. In Example 2, the electrode with a coating time of 48 h has the largest area specific capacitance, indicating that the best coating effect has been achieved. The coating time is further extended to 72 h in Example 3 and 96 h in Example 4, and the thickness of the coated nitrogen-doped carbon layer is increased, and the nanobelts are partially agglomerated, resulting in a decrease in the area specific capacitance of the electrode material during discharge.

[0072] Fig.11 The electrode materials prepared in Example 2 and the comparative example are 5 Hz, comparison of electrochemical impedance spectroscopy (EIS) curves at an amplitude of 5 mV; Fig.12 yes Fig.11 A magnified comparison of the mid- and high-frequency regions. Fig.11 It can be seen that compared with the nickel cobalt sulfide / NF prepared in the comparative example, the impedance curve of the NCS@NC / NF electrode prepared in Example 2 presents a larger low-frequency slope, indicating that it has lower diffusion resistance and fast charge transfer capability in the Faraday redox process. Fig.12 It can be seen that the NCS@NC / NF electrode prepared in Example 2 is semicircular with a small radius in the high frequency region. R The s value (0.697Ω) is significantly smaller than that of the nickel-cobalt sulfide / NF electrode prepared in the comparative example. R s value (1.789Ω), proving that coating the carbon layer on the surface of nickel cobalt sulfide nanobelts reduces the charge transfer resistance between the electrode and the KOH electrolyte.

[0073] Fig.13 The electrode materials prepared in Example 2 and the comparative example were subjected to a current density of 5 mA / cm 2 The capacitance retention rate comparison chart of the self-supporting NCS@NC / NF electrode prepared in Example 2 after 5000 cycles is 98.6%, which is significantly better than the capacitance retention rate of 69.4% of the self-supporting nickel cobalt sulfide / NF electrode prepared in the comparative example, indicating that coating with nitrogen-doped carbon layer can significantly improve the cyclic stability of nickel cobalt sulfide nanobelt / NF electrode.

[0074] The self-supporting nitrogen-doped carbon layer coated nickel-cobalt sulfide nanobelt / nickel foam electrode material disclosed in the present invention uses pretreated nickel foam as a substrate, firstly grows a nickel-cobalt nanobelt precursor in situ on the surface of the nickel foam by hydrothermal reaction, then realizes in situ coating of polydopamine on the surface of the nickel-cobalt nanobelt precursor at room temperature in an ethanol / water solution containing trishydroxymethylaminomethane and dopamine hydrochloride, then undergoes hydrothermal ion exchange to undergo sulfurization reaction to obtain nickel foam coated with polydopamine nickel-cobalt sulfide nanobelt, and finally obtains a nickel foam electrode material coated with a nitrogen-doped carbon layer after polydopamine is decomposed and carbonized in a calcination process. The preparation method forms a nickel-cobalt precursor with a nanobelt morphology in a hydrothermal process by controlling the concentration of nickel salt and cobalt salt, then coats the surface of the nanobelt with polydopamine as a carbon source and a nitrogen source by a simple in situ polymerization reaction at room temperature, and then obtains a target product with a stable structure by hydrothermal sulfurization and carbonization. In NCS@NC / NF, the role of nickel foam is to serve as a substrate for the in-situ uniform growth of active materials to form nickel-cobalt sulfide nanobelts; the highly conductive and high specific surface area nitrogen-doped carbon layer coating the nickel-cobalt sulfide nanobelt structure can increase the contact area between the active material and the electrolyte, provide more active sites for redox reactions, and generate larger pseudocapacitors; at the same time, the excellent conductivity of the nitrogen-doped carbon layer can be brought into play, accelerating the synergistic energy storage effect of ion / electron transfer rates in the electrolyte, providing more adsorption sites, and generating larger double-layer capacitance, thereby improving the electrode specific capacity, rate and cycle stability. The nitrogen-doped carbon layer is an important protective layer for the stability of the nickel-cobalt nanobelt structure. The nitrogen-doped carbon layer and the nickel-cobalt sulfide nanobelt structure can be controlled by adjusting the polydopamine coating time.

[0075] The above is only an embodiment of the present invention, and does not limit the present invention in any form. The present invention can also have other forms of embodiments according to the above structures and functions, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material, characterized in that: The nickel-cobalt sulfide nanobelt is in-situ grown on the surface of nickel foam, and the surface of the nickel-cobalt sulfide nanobelt is coated with a nitrogen-doped carbon layer. The nickel-cobalt sulfide is an edge-containing nanobelt structure, and the width of the nickel-cobalt sulfide nanobelt is 150-200 nm.

2. A method for preparing a self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material, characterized in that: The following steps are involved: (1) Pretreatment of nickel foam NF; (2) Preparation of nickel-cobalt nanobelt precursor / NF: dissolving hydrated nickel salt, hydrated cobalt salt, urea and ammonium fluoride in deionized water to form solution A; immersing the nickel foam pretreated in step (1) in solution A, and then transferring it to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the nickel foam is naturally cooled to room temperature. The nickel foam after the reaction is taken out, washed with deionized water, and then dried to obtain a nickel-cobalt nanobelt precursor in situ grown on the nickel foam, which is recorded as nickel-cobalt nanobelt precursor / NF; (3) Preparation of nickel-cobalt nanobelt precursor @PDA / NF: Add tris(hydroxymethyl)aminomethane to an ethanol aqueous solution and stir to dissolve it uniformly, adjust the pH value of the solution to 8.5, and then add dopamine hydrochloride thereto to dissolve it, thereby obtaining solution B; put the nickel-cobalt nanobelt precursor / NF obtained in step (2) into solution B, and allow it to react at room temperature for 24 to 96 h, replace solution B every 24 h, take out the nickel foam after the reaction, wash it with deionized water, and then dry it to obtain a nickel foam with polydopamine in situ coated on the surface of the nickel-cobalt nanobelt precursor, which is recorded as nickel-cobalt nanobelt precursor @PDA / NF; (4) Preparation of nickel cobalt sulfide nanobelts @PDA / NF: dissolving sodium sulfide nonahydrate in deionized water to form a solution C, immersing the nickel cobalt nanobelt precursor @PDA / NF obtained in step (3) in the solution C and transferring the whole of the solution into a hydrothermal reactor for a hydrothermal sulfidation reaction. After the reaction is completed, the solution is naturally cooled to room temperature. The nickel foam after the reaction is taken out, washed with deionized water, and then dried to obtain nickel cobalt sulfide nanobelts @PDA / NF; (5) Preparation of NCS@NC / NF electrode material: The nickel cobalt sulfide nanobelt@PDA / NF obtained in step (4) was calcined in an argon atmosphere at a temperature of 480-600°C, a heating rate of 2°C / min, and a holding time of 60-180 min. After the calcination, the material was naturally cooled to room temperature and taken out to obtain a self-supporting nitrogen-doped carbon layer-coated nickel cobalt sulfide nanobelt / nickel foam electrode material, denoted as NCS@NC / NF.

3. The method for preparing the self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material according to claim 2, characterized in that: The pretreatment process of the nickel foam in step (1) includes: rinsing the nickel foam with deionized water and then immersing it in a hydrochloric acid solution with a concentration of 1 mol / L for ultrasonic washing for 20 to 30 minutes, then washing it with deionized water and anhydrous ethanol alternately for 3 times, then immersing the nickel foam in an acetone solvent for ultrasonic washing for 20 to 30 minutes, then washing it with deionized water and anhydrous ethanol alternately for 3 times, and finally drying the nickel foam in a drying oven.

4. The method for preparing the self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material according to claim 2, characterized in that: The nickel salt in step (2) is selected from one of nickel nitrate hexahydrate and nickel chloride hexahydrate, and the cobalt salt is selected from one of cobalt nitrate hexahydrate and cobalt chloride hexahydrate. The temperature of the hydrothermal reaction is 120° C. and the reaction time is 8 h.

5. The method for preparing the self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material according to claim 2 or 4, characterized in that: The concentration of the hydrated nickel salt in solution A is 0.01-0.03 mol / L, and the concentration of the hydrated cobalt salt is 0.02-0.06 mol / L; and the molar ratio of the hydrated nickel salt, the hydrated cobalt salt, urea, and ammonium fluoride in solution A is 1:2:4:

4.

6. The method for preparing the self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material according to claim 2, characterized in that: In step (3), the concentration of tris(hydroxymethyl)aminomethane in solution B is 0.01 to 0.03 mol / L, the concentration of dopamine hydrochloride is 0.01 to 0.06 mol / L, and the ethanol aqueous solution is obtained by mixing anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is 1:1 to 1:

4.

7. The method for preparing the self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material according to claim 2, characterized in that: In step (4), the concentration of sodium sulfide nonahydrate in solution C is 0.2-0.6 mol / L, the temperature of the hydrothermal sulfidation reaction is 160° C., and the reaction time is 6 h.

8. Application of the self-supporting nitrogen-doped carbon layer-coated nickel cobalt sulfide nanobelt / nickel foam electrode material obtained by the preparation method as claimed in claim 2 as an energy storage electrode material in a supercapacitor.

9. The use according to claim 8, characterized in that: The self-supporting nitrogen-doped carbon layer-coated nickel-cobalt sulfide nanobelt / nickel foam electrode material is directly used as a working electrode.

10. The use according to claim 8 or 9, characterized in that: The self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material was used as the working electrode, the platinum electrode was used as the counter electrode, the Hg / HgO electrode was used as the reference electrode, the electrolyte was 6 mol / L KOH, and the current was 1 mA / cm 2 The area specific capacitance of the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material is 3100~5100 mF / cm 2 ; 10 mA / cm 2 The area specific capacitance of the self-supporting nitrogen-doped carbon layer coated nickel cobalt sulfide nanobelt / nickel foam electrode material is 2200~4500 mF / cm 2 .

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