Carbon-supported molybdenum sulfide nanosheets and nickel disulfide nanocrystals composite materials, preparation and application

Abstract

This invention belongs to the field of functional nanocomposite material preparation technology, specifically relating to a carbon-supported molybdenum sulfide nanosheet and nickel disulfide nanocrystal composite material, its preparation and application. The preparation method of this composite material includes (1) mixing nickel salt with a complexing agent and preparing a carbon framework composite material by a hard template method; (2) mixing the carbon framework composite material, ammonium heptamolybdate and thiourea, and preparing carbon-supported MoS2 by a hydrothermal reaction. x Nanosheet composite material; (3) under the action of a vulcanizing agent, the carbon-supported MoS x The nanosheet composite material is calcined to obtain a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material; wherein the calcination temperature is 300-350℃. When the composite material obtained by this invention is used in sodium-ion batteries or sodium-ion capacitors, it exhibits high specific capacity, good rate performance, and good cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of functional nanocomposite material preparation technology, specifically relating to a carbon-supported molybdenum sulfide nanosheet and nickel disulfide nanocrystal composite material, its preparation and application. Background Technology

[0002] With the rapid development of the electronics and electric vehicle industries, people have put forward higher requirements for the performance of energy storage devices. Lithium-ion batteries themselves are facing growth limits, especially the increasing difficulty in improving service life and energy density, creating a natural demand for new alternative technologies. Sodium-ion batteries achieve charge transfer through the insertion and extraction of sodium ions between the positive and negative electrodes. Compared with lithium-ion batteries, sodium-ion batteries have the following advantages: (1) Sodium resources are abundant, and the mining cost is only one percent of that of lithium; (2) The charging time of sodium-ion batteries can theoretically be shortened to 1 / 5 of that of lithium-ion batteries; (3) Due to the characteristics of sodium salts, low-concentration electrolytes can be used, reducing costs; (4) Sodium ions do not form alloys with aluminum, and aluminum foil can be used as the current collector for the negative electrode, reducing costs and battery weight. Therefore, sodium-ion batteries have become a substitute for lithium-ion batteries, and their research and development has become a hot area of ​​competition.

[0003] The difference in radii between sodium and lithium ions results in sodium-ion batteries performing worse than lithium-ion batteries. Sodium-ion batteries often exhibit poor rate performance and low power density due to their slow reaction kinetics. Graphite, a traditional anode material for lithium-ion batteries, can combine with Li to form a LiC6 compound with a theoretical specific capacity of 372 mAh / g. However, sodium ions can hardly intercalate or deintercalate in graphite, meaning graphite can only store a limited number of sodium ions. In the long run, sodium-ion batteries still have a very broad application prospect. Achieving higher energy and power densities in sodium-ion batteries and finding a stable anode material remains the biggest challenge for sodium-ion batteries.

[0004] In recent years, transition metal sulfides have attracted widespread attention due to their high specific capacity, environmental friendliness, and low cost. Nickel-based sulfides, in particular, are abundant and inexpensive. Among sulfides, nickel disulfide boasts a theoretical specific capacity as high as 879 mAh / g; molybdenum disulfide has also been extensively studied, exhibiting a graphite-like layered structure with a large interlayer spacing of 0.62 nm, facilitating sodium ion transport and possessing a high theoretical specific capacity (670 mAh / g). However, transition metal sulfides suffer from significant volume expansion, hindering the achievement of optimal sodium storage performance. Three-dimensional porous structures, with their abundant pores, provide pathways for electron and ion transport, and the internal space can buffer volume expansion, resulting in better rate performance and cycle stability during electrochemical reactions. Based on these factors, the development of composite materials combining transition metal sulfides with graphene-like carbon materials possessing three-dimensional porous structures, high specific surface area, and excellent conductivity to achieve higher energy and power densities in sodium-ion batteries is of great significance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of low energy density and power density of sodium-ion batteries and the need to further improve the performance of electrode materials in the prior art, so as to provide a carbon-supported molybdenum sulfide nanosheet and nickel disulfide nanocrystal composite material, its preparation and application.

[0006] To this end, the present invention provides the following technical solution.

[0007] This invention provides a method for preparing a composite material of carbon-supported MoS2 nanosheets and NiS2 nanocrystals, comprising the following steps:

[0008] (1) A carbon framework composite material was prepared by mixing nickel salt with a complexing agent and using a hard template method;

[0009] (2) The carbon framework composite material, ammonium heptamolybdate, and thiourea are mixed and subjected to a hydrothermal reaction to obtain carbon-supported MoS2. x Nanosheet composite materials;

[0010] (3) Under the action of the sulfiding agent, the carbon-supported MoS x The nanosheet composite material was calcined to obtain a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material.

[0011] The roasting temperature is 300-350℃.

[0012] Further, in step (2), the mass ratio of the carbon framework composite material to the ammonium heptamolybdate is 1:(1-5.5);

[0013] Preferably, the mass ratio of ammonium heptamolybdate to thiourea is 1:(1-2.5).

[0014] Furthermore, step (2) satisfies at least one of A and B.

[0015] A. The mass ratio of the carbon framework composite material to the ammonium heptamolybdate is 1:(4.8-5.2); preferably 1:5;

[0016] B. The mass ratio of the ammonium heptamolybdate to the thiourea is 1:(1.8-2.2); preferably 1:2.

[0017] Furthermore, step (3) satisfies at least one of AE.

[0018] A. The carbon-supported MoS x The mass ratio of the nanosheet composite material to the vulcanizing agent is 1:(3-5);

[0019] B. In step (3), the temperature is increased to 300-350℃ at a heating rate of 5-10℃ / min for the calcination.

[0020] C. The roasting time is 180-360 min;

[0021] D. The roasting temperature is 350℃;

[0022] E. The vulcanizing agent is thiourea.

[0023] Furthermore, in step (1), at least one of AC is satisfied.

[0024] A. The molar ratio of the nickel salt to the complexing agent is (1-2):1; preferably 2:1.

[0025] B. The complexing agent is citric acid;

[0026] C. The nickel salt is at least one of nickel nitrate, nickel chloride, and nickel citrate.

[0027] Further, step (1) includes mixing a nickel salt with a complexing agent to form a first solution, immersing a template agent in the first solution, removing and drying the solution, carbonizing the solution, and obtaining a carbon framework composite material.

[0028] Furthermore, step (1) satisfies at least one of AE.

[0029] A. The soaking time shall be no less than 4 hours; preferably 24 hours.

[0030] B. The specific steps of the carbonization include heating to 400-600℃ at a heating rate of 2-10℃ / min and holding at that temperature for 30-60min;

[0031] C. The carbonization is carried out under an inert atmosphere;

[0032] D. The template agent is polymethyl methacrylate microspheres or polystyrene microspheres; wherein, the amount of template agent is not specifically limited, as long as the first solution can completely immerse the template agent;

[0033] E. The concentration of nickel salt in the first solution is 1.5-2.5 mol / L;

[0034] Preferably, the concentration of the complexing agent in the first solution is 1-2 mol / L; more preferably, it is 1 mol / L.

[0035] Furthermore, the hydrothermal reaction is carried out at a temperature of 180-200℃ for a duration of 10-13 hours.

[0036] Preferably, the hydrothermal reaction is carried out at a temperature of 190°C for 12 hours.

[0037] The present invention also provides a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material prepared by the above preparation method.

[0038] Furthermore, this invention provides the application of the carbon-supported MoS2 nanosheets and NiS2 nanocrystal composite material prepared by the above preparation method, or the above carbon-supported MoS2 nanosheets and NiS2 nanocrystal composite material, in sodium-ion batteries or sodium-ion capacitors.

[0039] The technical solution of this invention has the following advantages:

[0040] 1. The present invention provides a method for preparing carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite materials, the method comprising (1) mixing nickel salt and a complexing agent, and preparing a carbon framework composite material by a hard template method; (2) mixing the carbon framework composite material, ammonium heptamolybdate, and thiourea, and preparing carbon-supported MoS2 nanosheets by a hydrothermal reaction. x Nanosheet composite material; (3) under the action of a vulcanizing agent, the carbon-supported MoS xThe nanosheet composite material is calcined to obtain a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material; wherein the calcination temperature is 300-350℃. When the composite material obtained by this invention is used in sodium-ion batteries or sodium-ion capacitors, it exhibits high specific capacity, good rate performance, and good cycle performance. When used as a negative electrode material in sodium-ion batteries, its excellent kinetics can achieve good matching with the activated carbon positive electrode, improving electrochemical performance. This invention combines in-situ hard template method, hydrothermal treatment, and pyrolytic sulfidation (achieved through calcination) techniques to prepare a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material. This material has a highly regular pore structure, and its large pore size and specific surface area provide abundant channels for ion transport, enabling more convenient mass transfer and ion diffusion. Simultaneously, the well-developed nanoporous structure of this material provides sufficient space for the volume expansion of MoS2 and NiS2, avoiding damage to the electrode material structure. This material also possesses a stable carbon framework, achieving both coating of NiS2 and, leveraging the excellent conductivity of carbon materials, improving the reaction kinetics of sodium ion insertion / extraction in NiS2. Furthermore, its large interlayer spacing provides a convenient channel for sodium ion migration. In addition, both MoS2 nanosheets and NiS2 nanocrystals have sufficiently small nanoscale dimensions, which not only significantly reduces structural damage caused by volume changes during ion insertion / extraction but also significantly reduces ion diffusion distance. The heterojunction formed between the two disulfides further accelerates the ion diffusion rate. Based on these structural advantages, the material prepared by this method, when applied as a sodium-ion battery anode, exhibits high specific capacity, good rate performance, and excellent cycle stability.

[0041] Compared to lithium ions, sodium ions have a larger ionic radius, resulting in slower kinetics during electrochemical processes and placing higher demands on the design of battery anodes. This invention uses ammonium heptamolybdate and thiourea as molybdenum and sulfur sources, respectively, to prepare a graphene-like carbon material homogeneously loaded with MoS2 nanosheets and NiS2 nanocrystals. This allows both sulfides to have sufficiently small nanoscale dimensions, shortening the diffusion distance of sodium ions in the material lattice. It also allows the MoS2 nanosheets to be uniformly and tightly wrapped around the pore walls of the carbon framework, rather than nested within the pores. This not only enables more thorough contact between the poorly conductive molybdenum sulfide and the conductive carbon material but also facilitates the effective construction of multiple heterostructures among the three components—molybdenum sulfide, nickel disulfide, and graphene-like carbon—significantly improving the diffusion and charge transfer processes of sodium ions, thereby achieving faster reaction kinetics. Furthermore, thanks to the excellent water solubility of the raw materials, ammonium heptamolybdate and thiourea can achieve a larger loading of molybdenum sulfide and the formation of high sulfide components, thereby significantly increasing the content of each chemical component and further improving the theoretical specific capacity of the composite material; while thiourea, in addition to providing sulfur, can also provide nitrogen to achieve heterogeneous element doping of the carbon framework, which can also further improve the conductivity of the material.

[0042] The different raw materials used result in differences in reaction principles and dispersion levels, leading to variations in the nanoscale and chemical composition of sulfides, which in turn greatly affect the electrochemical performance of the products. This invention uses ammonium heptamolybdate and thiourea as raw materials, which can enable the target material to have a higher theoretical specific capacity and better rate performance and cycle performance.

[0043] The initially obtained carbon-supported MoS x Calcination of nanosheet materials and vulcanizing agents at a relatively mild temperature of 300-350℃ can better maintain the morphology of nanosheets obtained from the hydrothermal reaction, preventing them from being damaged, collapsing, stacking, or growing. This is similar to the preparation of carbon-supported MoS2 using ammonium tetrathiomolybdate. x Compared to existing technologies, the present invention employs a lower calcination temperature, which not only better preserves the morphology of the nanosheets but also retains more defects (i.e., sodium storage sites) within the nanosheets, thus achieving higher capacity retention. By calcining at 300-350°C, the present invention also enables thorough sulfidation of nickel and molybdenum, and achieves trace sulfur doping of the carbon component. At this calcination temperature, the hydrogen sulfide gas generated from the pyrolysis of the sulfiding agent reacts with a large amount of unsulfided nickel nanocrystals and molybdenum oxide intermediates after the hydrothermal reaction, thereby fully converting them into nickel disulfide and molybdenum disulfide with higher theoretical specific capacities, further improving the overall material's specific capacity and conductivity. Furthermore, the hydrogen sulfide gas also reacts with graphene-like carbon to achieve a small amount of sulfur doping, which also contributes to the generation of more sodium storage sites and increases the overall material's specific capacity.

[0044] The present invention utilizes a heterogeneous structure between molybdenum sulfide and nickel sulfide, which synergistically enhances the rate performance of graphene-like carbon materials. By selecting ammonium heptamolybdate and thiourea as specific raw materials and calcining them at 300-350℃, the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material exhibits superior rate performance, specific capacity, and cycle performance.

[0045] 2. The preparation method of carbon-supported MoS2 nanosheets and NiS2 nanocrystals provided by the present invention first achieves the optimization of the chemical composition of each component of the target material by controlling the proportion of carbon framework composite material, ammonium heptamolybdate, thiourea, etc., namely: (1) nickel and molybdenum elements both generate disulfides with higher sulfur content, thus having higher theoretical specific capacity; (2) the carbon framework carrier achieves higher content of heteroatoms doping, thereby optimizing the physical properties such as sodium storage sites, conductivity and interlayer spacing, which helps the material achieve higher rate performance.

[0046] Secondly, as mentioned above, due to the tight encapsulation and bonding of small-sized molybdenum disulfide nanosheets on the pore walls of the carbonaceous framework, the mechanical stability is ensured while forming a more effective heterojunction structure among the three components: molybdenum disulfide, graphene-like carbon, and nickel disulfide. Combined with the nanoscale size of these three components and the high conductivity of the carbonaceous support, the entire material can achieve very convenient and rapid ion-electron synchronous transport, thereby further ensuring the excellent rate performance and cycle stability of the overall material. In summary, this preparation method and strategy can realize the creation of sodium storage anode materials with excellent overall energy storage performance, and the synergistic integration of more active components will also help to continuously improve its volumetric energy storage performance.

[0047] 3. The carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material provided by the present invention has a three-dimensional ordered macroporous structure with a primary pore size of approximately 300 nm and a secondary pore size of approximately 100 nm. The composite material is composed of three active components: graphene-like carbon, molybdenum disulfide, and nickel disulfide. Among them, nickel disulfide is encapsulated in the graphene-like carbon matrix, while molybdenum disulfide is uniformly coated on the carbon skeleton. When the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material is applied to the anode of sodium-ion batteries, it exhibits high specific capacity, good rate performance, and excellent cycle stability. Attached Figure Description

[0048] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0049] Figure 1 The results are X-ray diffraction (XRD) test results of the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material in Example 1 of this invention;

[0050] Figure 2 The results are obtained by scanning electron microscopy (SEM) of the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material in Example 1 of this invention.

[0051] Figure 3 These are the electrochemical performance test results of the sodium-ion battery in Test Example 1 of this invention;

[0052] Figure 4 These are the cycle performance test results of the sodium-ion battery in Test Example 1 of this invention;

[0053] Figure 5 These are the electrochemical performance test results of the sodium-ion capacitor in Test Example 2 of this invention;

[0054] Figure 6 This is the result of the constant current charge-discharge test of the sodium-ion capacitor in Test Example 2 of this invention;

[0055] Figure 7 This is the result of the cycle performance test of the sodium-ion capacitor in Test Example 2 of this invention. Detailed Implementation

[0056] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0057] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0058] Example 1

[0059] This embodiment provides a method for preparing carbon-supported MoS2 nanosheets and NiS2 nanocrystals, including the following steps:

[0060] (1) Take 0.1 mol of nickel nitrate and 0.05 mol of citric acid and add them to 50 ml of deionized water. Stir for 24 h to form the first solution. Completely immerse the polymethyl methacrylate microsphere template in the first solution. After immersion for 24 h, filter it and let it dry naturally for 3 days. Then place it in a tube furnace and heat it to 500 °C at a heating rate of 2 °C / min under an argon atmosphere and keep it at that temperature for 30 min for carbonization. After carbonization, let it cool down naturally to obtain a carbon framework composite material with a three-dimensional ordered macroporous structure.

[0061] (2) The above-mentioned carbon framework composite material, ammonium heptamolybdate, and thiourea were mixed in a mass ratio of 1:5:10, stirred evenly in water, and then transferred to a reaction vessel. The mixture was reacted at 190°C for 12 hours. After naturally cooling to room temperature, the reaction solution was filtered, and the resulting solid product was washed multiple times with water and ethanol. After being thoroughly dried in an oven at 50°C, carbon-supported amorphous MoS2 was obtained. x Nanosheet composite materials.

[0062] (3) Mix the above carbon-supported MoS at a mass ratio of 1:5. x The nanosheet composite material and thiourea were placed in a covered corundum boat, and then placed in a tube furnace with argon protective gas. The temperature was increased to 350℃ at a heating rate of 5℃ / min and held for 180min. After cooling to room temperature, carbon-supported MoS2 two-dimensional nanosheets and NiS2 zero-dimensional nanocrystal composite materials were obtained. Thiourea was placed on one side of the gas inlet. The carbon-supported amorphous MoS2 obtained in step (2) x The nanosheet composite material is placed on one side of the air outlet, and a certain distance is maintained between the two materials.

[0063] Figure 1 These are the X-ray diffraction test results of the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material prepared in this embodiment. Figure 1 The material is mainly composed of graphene-like carbon, nickel disulfide, and molybdenum disulfide.

[0064] Figure 2 These are scanning electron microscope (SEM) images of the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material prepared in this embodiment. Figure 2 Combination Figure 1 It can be seen that this material uses three-dimensional ordered macroporous carbon as a matrix, and its pore walls are coated with homogeneous, fine MoS2 nanosheets. The length of the MoS2 nanosheets is about 55 μm. Figure 2 Within the frame, NiS2 nanoparticles are encapsulated within a carbon matrix.

[0065] Example 2

[0066] This embodiment provides a method for preparing a composite material of carbon-supported MoS2 nanosheets and NiS2 nanocrystals, including the following steps:

[0067] (1) Take 0.1 mol of nickel nitrate and 0.1 mol of citric acid and add them to 50 ml of deionized water. Stir for 24 h to form the first solution. Completely immerse the polymethyl methacrylate microsphere template in the first solution. After immersion for 24 h, filter it and let it dry naturally for 3 days. Then place it in a tube furnace and heat it to 450 °C at a heating rate of 8 °C / min under an argon atmosphere and keep it at that temperature for 40 min for carbonization. After carbonization, let it cool down naturally to obtain a carbon framework composite material with a three-dimensional ordered macroporous structure.

[0068] (2) The above-mentioned carbon framework composite material, ammonium heptamolybdate, and thiourea were mixed in a mass ratio of 1:3:6, stirred evenly in water, transferred to a reaction vessel, and reacted at 190℃ for 12 hours. After naturally cooling to room temperature, the reaction solution was filtered, and the resulting solid product was washed multiple times with water and ethanol. After being thoroughly dried in an oven at 50℃, carbon-supported amorphous MoS2 was obtained. x Nanosheet composite materials.

[0069] (3) Mix the above carbon-supported MoS at a mass ratio of 1:3. x The nanosheet composite material and thiourea were placed in a covered corundum boat, and then placed in a tube furnace with argon protective gas. The temperature was increased to 325°C at a heating rate of 8°C / min and held for 180 min for calcination and sulfidation. After cooling to room temperature, a graphene-like carbon composite material of carbon-supported MoS2 two-dimensional nanosheets and NiS2 zero-dimensional nanocrystals was obtained. Among them, thiourea was placed on one side of the gas inlet. The carbon-supported amorphous MoS2 obtained in step (2) x The nanosheet composite material is placed on one side of the air outlet, with a certain distance between the two materials.

[0070] Experimental Example 1

[0071] This experimental example uses the composite material obtained in Example 1 to fabricate a sodium-ion battery and tests its performance, including:

[0072] Electrode sheets were fabricated from carbon-supported MoS2 nanosheets and NiS2 nanocrystals, and sodium-ion half-cells were assembled and their performance was tested. Specifically, the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material obtained in Example 1, conductive carbon black, and polyvinylidene fluoride were first added to N-methylpyrrolidone in a mass ratio of 1:1:1 and stirred until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was then coated onto copper foil using a spatula and dried in an oven at 80°C. The target electrode sheet was then obtained using a die-casting machine.

[0073] Then, using sodium foil as the counter electrode, glass fiber as the separator, and a 0.8 mol / L NaPF6 solution as the electrolyte (diethylene glycol dimethyl ether as the solvent), the 2430 button cell was assembled in an argon-protected glove box (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0074] Electrochemical performance testing of sodium-ion batteries: The electrochemical performance of the assembled batteries was tested using a CT2001A sodium-ion battery testing system at room temperature using a constant current charge-discharge method. The results are shown in [Figure number missing]. Figure 3 .from Figure 3 It can be seen that when the current density is 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, 5A / g, 10A / g and 20A / g, the maximum reversible specific capacity of the target carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material reaches 672mAh / g, 425mAh / g, 306mAh / g, 244mAh / g, 212mAh / g, 180mAh / g and 137mAh / g, respectively.

[0075] Cycling performance testing of sodium-ion batteries: The cycle performance of the batteries was tested at 5 A / g, and the results are shown in [the table below]. Figure 4 After the initial activation stage (about 80 cycles), the performance of the target carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material remained basically unchanged, and the reversible specific capacity still reached 273 mAh / g after 1000 cycles.

[0076] The above results demonstrate that the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material prepared in Example 1 has high specific capacity and excellent cycle stability as an electrode material for sodium-ion batteries.

[0077] Experimental Example 2

[0078] This experimental example uses the composite material obtained in Example 1 to fabricate a sodium-ion capacitor and tests its performance, including...

[0079] A 2430-type button sodium-ion capacitor was assembled in an argon-protected glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). Specifically, the sodium-ion half-cell was first assembled to pre-sodium-encapsulate the prepared electrode sheets. This involved assembling the electrode sheets obtained in Example 1, sodium foil as the counter electrode, a separator (glass fiber), and an electrolyte (0.8 mol / L NaPF6 solution, diethylene glycol dimethyl ether as the solvent) to form a sodium-ion half-cell. After five charge-discharge cycles at 0.1 A / g, the cell was discharged to 0.01 V. The cell was then disassembled to obtain a pre-sodium-encapsulated electrode sheet containing the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material from Example 1. This pre-sodium-encapsulated electrode sheet was then used as the negative electrode, an activated carbon electrode as the positive electrode, and a sodium-ion capacitor was assembled using glass fiber as the separator and 0.8 mol / L NaPF6 solution as the electrolyte (diethylene glycol dimethyl ether as the solvent). The mass ratio of activated carbon to carbon-supported MoS2 nanosheets to NiS2 nanocrystals composite material is 2.7:1.

[0080] Electrochemical performance testing of sodium-ion capacitors: Cyclic voltammetry tests were performed on sodium-ion capacitors at room temperature, voltages ranging from 0.01 to 4.0 V, and a scan rate of 0.5 Mv / s. The results are shown in [Figure number missing]. Figure 5 . Figure 5 This indicates that at a scan rate of 0.5 mV / s, its nearly rectangular cyclic voltammetry curve demonstrates good capacitance characteristics.

[0081] Sodium-ion capacitor charge-discharge test: The sodium-ion capacitor was subjected to constant current charge-discharge tests at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g, respectively. The results are shown in [Figure number missing]. Figure 6 The specific capacitances of the sodium-ion capacitors are 48 F / g, 42 F / g, 38 F / g, 35 F / g, 33 F / g, 30 F / g, and 26 F / g, respectively.

[0082] Sodium-ion capacitor cycling performance test: Cyclic performance was tested at 10 A / g, and the results are shown below. Figure 7 .from Figure 7 It can be seen that the final coulombic efficiency of the sodium-ion capacitor is still greater than 94%, while the specific capacitance decreases from 26.6 F / g to 20.1 F / g. Figure 7 The scaled-down graph shows the curves of some voltage changes over time.

[0083] Figures 5-7 This invention demonstrates that the carbon-supported MoS2 nanosheets and NiS2 nanocrystals composite material prepared in this invention, when used as the negative electrode material for sodium-ion capacitors, can enable sodium-ion capacitors to exhibit excellent rate performance and cycle stability.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a composite material of carbon-supported molybdenum sulfide nanosheets and nickel disulfide nanocrystals, characterized in that, Includes the following steps, (1) A carbon framework composite material was prepared by mixing nickel salt with a complexing agent and using a hard template method; (2) The carbon framework composite material, ammonium heptamolybdate, and thiourea are mixed and subjected to a hydrothermal reaction to obtain carbon-supported MoS2. x Nanosheet composite materials; (3) Under the action of the sulfiding agent, the carbon-supported MoS x The nanosheet composite material was calcined to obtain a carbon-supported MoS2 nanosheet and NiS2 nanocrystal composite material. The roasting temperature is 300-350℃.

2. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the carbon framework composite material to the ammonium heptamolybdate is 1:(1-5.5).

3. The preparation method according to claim 2, characterized in that, The mass ratio of ammonium heptamolybdate to thiourea is 1:(1-2.5).

4. The preparation method according to claim 2, characterized in that, Step (2) satisfies at least one of A and B. A. The mass ratio of the carbon framework composite material to the ammonium heptamolybdate is 1:(4.8-5.2); B. The mass ratio of the ammonium heptamolybdate to the thiourea is 1:(1.8-2.2).

5. The preparation method according to claim 4, characterized in that, Step (2) satisfies at least one of A and B. A. The mass ratio of the carbon framework composite material to the ammonium heptamolybdate is 1:5; B. The mass ratio of the ammonium heptamolybdate to the thiourea is 1:

2.

6. The preparation method according to any one of claims 1-5, characterized in that, Step (3) satisfies at least one of A-E. A. The carbon-supported MoS x The mass ratio of the nanosheet composite material to the vulcanizing agent is 1:(3-5); B. In step (3), the temperature is increased to 300-350℃ at a heating rate of 5-10℃ / min for the calcination. C. The roasting time is 180-360 min; D. The roasting temperature is 350℃; E. The vulcanizing agent is thiourea.

7. The preparation method according to any one of claims 1-5, characterized in that, In step (1), at least one of A-C is satisfied. A. The molar ratio of the nickel salt to the complexing agent is (1-2):1; B. The complexing agent is citric acid; C. The nickel salt is at least one of nickel nitrate, nickel chloride, and nickel citrate.

8. The preparation method according to claim 7, characterized in that, The molar ratio of the nickel salt to the complexing agent is 2:

1.

9. The preparation method according to any one of claims 1-5, characterized in that, Step (1) includes mixing a nickel salt with a complexing agent to form a first solution, immersing a template agent in the first solution, removing and drying the solution, carbonizing the solution, and obtaining a carbon framework composite material.

10. The preparation method according to claim 9, characterized in that, Step (1) satisfies at least one of A-E. A. The soaking time shall not be less than 4 hours; B. The specific steps of the carbonization include heating to 400-600℃ at a heating rate of 2-10℃ / min and holding at that temperature for 30-60min; C. The carbonization is carried out under an inert atmosphere; D. The template agent is polymethyl methacrylate microspheres or polystyrene microspheres; E. The concentration of nickel salt in the first solution is 1.5-2.5 mol / L.

11. The preparation method according to claim 10, characterized in that, Step (1) satisfies at least one of A-B. A. The soaking time is 24 hours; B. The concentration of the complexing agent in the first solution is 1-2 mol / L.

12. The preparation method according to claim 11, characterized in that, The concentration of the complexing agent in the first solution is 1 mol / L.

13. The preparation method according to any one of claims 1-5, characterized in that, The hydrothermal reaction is carried out at a temperature of 180-200℃ for 10-13 hours.

14. The preparation method according to claim 13, characterized in that, The hydrothermal reaction was carried out at a temperature of 190°C for 12 hours.

15. The carbon-supported molybdenum sulfide nanosheets and nickel disulfide nanocrystals composite material prepared by the preparation method according to any one of claims 1-14.

16. The application of the carbon-supported molybdenum sulfide nanosheets and nickel disulfide nanocrystals composite material as described in claim 15 in sodium-ion batteries or sodium-ion capacitors.

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