Multilayer graphene coated NiS / Ni3S2 composite material, preparation method and supercapacitor

Abstract

The invention discloses a multilayer graphene-coated NiS / Ni3S2 composite material, a preparation method and a supercapacitor, NiS / Ni3S2 is uniformly laid on the surface of multilayer graphene to form a film, a small part of NiS / Ni3S2 forms raised nanosheets or nanosheet clusters, the nanosheets or nanosheet clusters are distributed sparsely in multilayer graphene sheets, the thickness of the multilayer graphene-coated NiS / Ni3S2 composite material is smaller than that of the multilayer graphene sheets, and the thickness of the multilayer graphene-coated NiS / Ni3S2 composite material is smaller than that of the multilayer graphene sheets. The distribution density on the edge of the multi-layer graphene sheet is relatively high. The weight ratio of the NiS and the Ni3S2 in the multi-composite material is 70 to 80 percent. The composite material provided by the technical scheme of the invention has excellent supercapacitor performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of materials, and particularly relates to a multilayer graphene@NiS / Ni3S2 composite material, a preparation method and a supercapacitor. BACKGROUND

[0002] Supercapacitors are a new type of energy storage device. In order to improve the energy density of supercapacitors, some materials with redox reaction performance (pseudocapacitive energy storage characteristics) are developed for supercapacitors. Nickel sulfide is a kind of electrode material with great potential due to its high theoretical specific capacitance, abundant electrochemical reaction sites, adjustable composition and low electronegativity. Although the conductivity of nickel sulfide is improved compared with nickel oxide and nickel hydroxide, its conductivity is still low compared with carbon materials. At the same time, when preparing pure nickel sulfide, the sulfide is easy to agglomerate and the volume expansion is easy to occur in the electrochemical process, which leads to its unsatisfactory electrochemical performance. In order to solve the above problems, the preparation of composite materials of sulfide and carbon materials has become a research hotspot.

[0003] The existing preparation method is relatively complex, mainly using a hydrothermal method to prepare the composite material. At the same time, before preparing the composite material, the carbon material also needs to be activated, such as oxidation or introduction of functional groups. Moreover, the composite of sulfide and carbon material is not uniform, and the contact area between them is not large enough, so that the good synergistic effect between the sulfide and the carbon material cannot be obtained.

[0004] In view of the defects in the prior art, the present application proposes a technical solution to solve the technical problems existing in the prior art. SUMMARY

[0005] In view of the problems in the background art, the present application discloses a multilayer graphene@NiS / Ni3S2 composite material, a preparation method and a supercapacitor. In the composite material, NiS / Ni3S2 is uniformly tiled on the surface of the multilayer graphene to form a film, and a small part of NiS / Ni3S2 forms a convex nanosheet or a nanosheet group. This nanosheet or nanosheet group is distributed relatively sparsely in the multilayer graphene sheet, and the distribution density is higher at the edge of the multilayer graphene sheet. The weight ratio of NiS / Ni3S2 in the composite material is 70-80%. The obtained nickel sulfide contains two phases of NiS and Ni3S2, and the heterojunction structure formed by the two is beneficial to the transport of electrons.

[0006] In order to solve the technical problems existing in the prior art, the technical solution of the present application is as follows: A preparation method of a multilayer graphene@NiS / Ni3S2 composite material, comprising the following steps: Step S10, measure the volume ratio of 8:2 of DMF and deionized water, mix uniformly, then take the expanded graphite, add to the mixed solvent, and perform 200W power ultrasonic treatment for 4 hours to obtain a multi-layer graphene dispersion liquid, and the concentration of the expanded graphite in the mixed solvent is 0.5-2mg / mL; Step S20, take Ni powder of 3-5mg / mL relative to the mixed solvent; take S powder, so that the molar ratio of Ni:S is 1:1-1:1.3. Add the two powders to the multi-layer graphene solution; measure acetic acid, and the volume ratio of acetic acid to the mixed solvent is 1:15-1:30; magnetically stir at room temperature for 15 minutes. Preferably, the diameter of the Ni powder and the S powder is 10-50μm.

[0007] Step S30, place the mixed solution into a 90℃ water bath for magnetic stirring reaction, the stirring speed is 500rpm, and the stirring reaction time is 4h.

[0008] Step S40, after the reaction is completed, take out and cool at room temperature. After cooling, perform 3 times of deionized water and 3 times of alcohol centrifugal cleaning, the centrifuge speed is 6000r / min, and after cleaning, place in an oven for drying at 70℃ for 24 hours. After drying, obtain the multi-layer graphene@NiS / Ni3S2 thin film composite material.

[0009] In the above preparation method, the multi-layer graphene mechanically exfoliated by the ultrasonic method is used as the carbon material, all the multi-layer graphene after ultrasonic treatment is used for the preparation of the composite material. And without activation treatment, the preparation of the composite material is greatly simplified. In order to overcome the preparation of the composite material on the surface of the carbon material without activation, the present application utilizes the molecular force on the surface of the multi-layer graphene to prepare nickel sulfide. At the same time, in order to obtain nickel sulfide with better morphology on the surface of the multi-layer graphene, the present application uses nickel powder and sulfur powder as nickel source and sulfur source, and adds acetic acid to control the morphology and crystallinity, and obtains the multi-layer graphene@NiS / Ni3S2 composite material with good electrochemical performance.

[0010] In the above preparation method, the multi-layer graphene is obtained by ultrasonic treatment of the expanded graphite. The carbon ring structure on the surface of the multi-layer graphene is complete, the oxygen-containing functional groups on the surface are few, and the multi-layer graphene has good conductivity.

[0011] The preparation mechanism of the above preparation method of the application is that at the reaction temperature, the sulfur powder is dissolved in DMF, and the sulfur atoms in the solution fully contact the nickel powder under stirring. The nickel powder and the sulfur atoms perform an oxidation-reduction reaction to generate nickel ions and sulfur ions. The nickel ions, the sulfur ions, DMF and water molecules generate a complex, and the complex is adsorbed to the surface of the multilayer graphene by molecular force generated by the carbon ring on the surface of the multilayer graphene. The polymerization reaction between the complexes removes the DMF molecules and the water molecules, and finally forms a NiS / Ni3S2 film laid on the surface of the multilayer graphene. In some places where the deposition is excessive on the surface of the multilayer graphene, the NiS / Ni3S2 nanosheets or nanosheet groups are finally grown into protrusions. Since there are more defects on the edges of the multilayer graphene, the excessive deposition is more likely to occur, and there are more nanosheet groups on the edges of the multilayer graphene. The addition of a proper amount of acetic acid can obtain a proper nucleation and growth rate of NiS / Ni3S2, so as to obtain the composite material of the application.

[0012] As a further improved scheme, the multilayer graphene does not need to be activated, but is directly prepared uniformly by the molecular force on the surface of the multilayer graphene. Since the molecular force uniformly exists on the surface of the multilayer graphene, the NiS / Ni3S2 is uniformly distributed on the surface of the multilayer graphene.

[0013] As a further improved scheme, the nickel powder and the sulfur powder are used as the nickel source and the sulfur source. Preferably, the diameter of the Ni powder and the S powder is 10-50 μm.

[0014] As a further improved scheme, at the reaction temperature, the sulfur powder is dissolved in DMF, and the sulfur atoms in the solution fully contact the nickel powder under stirring. The nickel powder and the sulfur atoms perform an oxidation-reduction reaction to generate nickel ions and sulfur ions. The nickel ions, the sulfur ions, DMF and water molecules generate a complex, and the complex is adsorbed to the surface of the multilayer graphene by molecular force generated by the carbon ring on the surface of the multilayer graphene. The polymerization reaction between the complexes removes the DMF molecules and the water molecules, and finally forms a NiS / Ni3S2 film.

[0015] As a further improved scheme, a certain amount of acetic acid solution is added to the solution. The addition of acetic acid can obtain a proper nucleation and growth rate of NiS / Ni3S2, so as to form the above characteristic NiS / Ni3S2 film on the surface of the multilayer graphene.

[0016] As a further improvement, the NiS / Ni3S2 is uniformly laid on the surface of the multi-layer graphene to form a film, and the contact area between the NiS / Ni3S2 and the multi-layer graphene is large, reducing the electronic transfer impedance between the NiS / Ni3S2 and the multi-layer graphene. A small part of the NiS / Ni3S2 in the composite material forms a protruding nanosheet or a nanosheet group, and the nanosheet or the nanosheet group is distributed sparsely in the multi-layer graphene sheet and has a high distribution density at the edge of the multi-layer graphene sheet. The protruding nanosheet or the nanosheet group is formed due to the presence of defects, thereby adsorbing too much nickel and sulfur ions in the area. The presence of the nanosheet is beneficial to the existence of a gap between the composite materials, the immersion of the electrolyte, and the increase of the contact area between the active material NiS / Ni3S2 and the electrolyte.

[0017] As a further improvement, the nickel sulfide is a heterojunction structure composed of NiS and Ni3S2, and the structure promotes the transport of electrons.

[0018] The application further discloses a multi-layer graphene@NiS / Ni3S2 composite material, wherein the NiS / Ni3S2 in the composite material is uniformly laid on the surface of the multi-layer graphene to form a film, and a small part of the NiS / Ni3S2 forms a protruding nanosheet or a nanosheet group, and the nanosheet or the nanosheet group is distributed sparsely in the multi-layer graphene sheet and has a high distribution density at the edge of the multi-layer graphene sheet.

[0019] As a further improvement, the multi-layer graphene in the composite material is obtained by mechanically exfoliating expanded graphite in a mixed solvent through an ultrasonic method. The obtained multi-layer graphene has an intact carbon ring structure on the surface, the number of graphite layers of the multi-layer graphene is less than 100, the surface contains few oxygen functional groups, and the multi-layer graphene has good conductivity.

[0020] As a further improvement, the weight ratio of the NiS and the Ni3S2 in the composite material is 70-80%.

[0021] As a further improvement, the nickel sulfide contains NiS and Ni3S2, and the heterojunction structure formed by the two is beneficial to the transport of electrons.

[0022] The application further discloses a supercapacitor, and the positive electrode material of the supercapacitor is the multi-layer graphene@NiS / Ni3S2 composite material prepared above, the specific capacity of the supercapacitor is high, and the rate performance of the supercapacitor is excellent.

[0023] Compared with the prior art, the application has the following beneficial effects: (1) The multi-layer graphene substrate is simple to prepare and low in cost, and does not need to be activated on the surface and does not have a layer number requirement, thereby reducing the preparation cost of the carbon material.

[0024] (2) NiS / Ni3S2 evenly laid on the surface of the multi-layer graphene forms a film, and the contact area between the multi-layer graphene and the film is large, reducing the electronic transmission impedance between the NiS / Ni3S2 and the multi-layer graphene.

[0025] (3) A small part of the protruding NiS / Ni3S2 in the composite material forms a nanosheet or a nanosheet group, and the nanosheet or the nanosheet group is distributed sparsely in the multi-layer graphene sheet and has a high distribution density at the edge of the multi-layer graphene sheet. The existence of the nanosheet is beneficial to the entry of the electrolyte, and the contact area between the active material NiS / Ni3S2 and the electrolyte is increased.

[0026] (4) The nickel powder and the sulfur powder are used as the nickel source and the sulfur source in the application, and the cost is lower than that of a nickel salt and a sulfur salt (or a sulfur-containing organic matter). Meanwhile, the transportation is convenient, and the transportation cost is low.

[0027] (5) The chemical deposition method is used in the application, and a high-pressure resistant device required by a hydrothermal method is not needed. Therefore, the preparation cost is low, and the application is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The preparation mechanism of the multi-layer graphene@NiS / Ni3S2 composite material in the application; Figure 2 The preparation step flow chart of the composite material in the application; Figure 3 The XRD spectrum of the multi-layer graphene@NiS / Ni3S2 composite material prepared in Example 1 of the application; Figure 4 The scanning electron microscope (SEM) image of the multi-layer graphene@NiS / Ni3S2 composite material prepared in Example 1 of the application, (a) a low-magnification image, and (b) a high-magnification image; Figure 5 The transmission electron microscope (TEM) image of the multi-layer graphene@NiS / Ni3S2 composite material prepared in Example 1 of the application, (a) a low-magnification image of the edge of the multi-layer graphene, (b) a low-magnification image of the surface of the multi-layer graphene, (c) a high-resolution image of the NiS / Ni3S2 sheet at the edge of the multi-layer graphene, and (d) a high-resolution image of the surface of the multi-layer graphene; Figure 6 The charge-discharge curve of the multi-layer graphene@NiS / Ni3S2 composite material prepared in Example 1 of the application under different current densities; Figure 7 The rate curve of the multi-layer graphene@NiS / Ni3S2 composite material prepared in Example 1 of the application; Figure 8The cycle performance test curve of the multilayer graphene@NiS / Ni3S2 composite material prepared for the embodiment 1 of the present application under a charge-discharge current density of 2 A / g is shown in the following table: DETAILED DESCRIPTION

[0029] In order to better illustrate the process and scheme of the present application, the following application is further described in combination with the drawings and embodiments. The specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0030] In order to solve the technical problems existing in the prior art, see Figure 2 The preparation method step flow chart of the multilayer graphene@NiS / Ni3S2 composite material is shown in the following table, which comprises the following steps: Step S10, the volume ratio of DMF and deionized water is 8:2, and after being mixed uniformly, the mixed solvent is obtained, the expanded graphite is weighed and added into the mixed solvent, and the multilayer graphene dispersion liquid is obtained by ultrasonic treatment at a power of 200 W for 4 hours, and the concentration of the expanded graphite in the mixed solvent is 0.5-2 mg / mL; Step S20, the Ni powder is weighed at 3-5 mg / mL with respect to the mixed solvent; the S powder is weighed, and the molar ratio of Ni:S is 1:1-1:1.3. The two powders are added into the multilayer graphene solution; the acetic acid is measured, and the volume ratio of acetic acid to mixed solvent is 1:15-1:30; and the magnetic stirring is performed at room temperature for 15 minutes. Preferably, the diameter of the Ni powder and the S powder is 10-50 μm.

[0031] Step S30, the mixed liquid is placed into a water bath at 90℃ for magnetic stirring reaction, the stirring speed is 500 rpm, and the stirring reaction time is 4 h.

[0032] Step S40, after the reaction is completed, the room temperature cooling is taken out. After cooling, the deionized water is washed for 3 times, the alcohol is washed for 3 times, the centrifuge speed is 6000 rpm / min, and the multilayer graphene@NiS / Ni3S2 composite material is obtained after drying in the oven at 70℃ for 24 hours.

[0033] The preparation mechanism of the above method of the present application is as follows: Figure 1As shown. Under the reaction temperature, sulfur powder dissolves in DMF, and the sulfur atoms in the solution fully contact the nickel powder under stirring. The nickel powder and sulfur atoms undergo an oxidation-reduction reaction to produce nickel ions and sulfide ions. The nickel ions, sulfide ions, DMF and water molecules produce complexes, which generate molecular forces with the carbon rings on the surface of the multilayer graphene and are adsorbed onto the surface of the multilayer graphene. The polymerization reaction between the complexes removes the DMF molecules and water molecules and eventually forms a thin film of NiS / Ni3S2 that is tiled on the surface of the multilayer graphene. In some places where there is excessive deposition on the surface of the multilayer graphene, raised NiS / Ni3S2 nanosheets or nanosheet clusters will eventually grow. Since there are more defects at the edges of the multilayer graphene, it is easier to obtain excessive deposition, and there are more nanosheet clusters at the edges of the multilayer graphene. Adding an appropriate amount of acetic acid can obtain appropriate NiS / Ni3S2 nucleation and growth rate, thereby obtaining the composite material of the present invention.

[0034] Example 1: 8 mL of DMF and 2 mL of deionized water were mixed and used as the mixed solvent. 20 mg of expanded graphite was weighed and added to the mixed solvent. Ultrasonic treatment was performed at 200 W for 4 hours to obtain a multilayer graphene dispersion. 30 mg of Ni powder and 20 mg of S powder (the Ni and S powders had particle sizes primarily ranging from 10 to 50 μm) were weighed and added to the multilayer graphene solution. 0.5 mL of acetic acid was added to the mixed solution and magnetically stirred at room temperature for 15 minutes. The mixture was placed in a 90°C water bath and magnetically stirred at 500 rpm for 4 hours. After the reaction, the mixture was cooled to room temperature. After cooling, the mixture was centrifuged three times with deionized water and three times with alcohol at 6000 rpm. After rinsing, the mixture was dried in an oven at 70°C for 24 hours. After drying, a multilayer graphene@NiS / Ni3S2 thin film composite material was obtained.

[0035] The XRD pattern of the multilayer graphene@NiS / Ni3S2 composite material synthesized in this example is shown in Figure 3 As shown in the figure, it can be seen that the composite material consists of three phases: carbon, NiS and Ni3S2. The low-magnification scanning electron microscope and high-magnification scanning electron microscope photos of the composite material are shown in Figure 4 As shown in the figure. Scanning electron microscopy images show that a small amount of NiS / Ni3S2 forms raised nanosheets or nanosheet clusters within the multilayer graphene surface. These nanosheets or nanosheet clusters are sparsely distributed within the multilayer graphene sheet and more densely distributed at the edges of the multilayer graphene sheet. NiS / Ni3S2 cannot be observed flattened on the multilayer graphene surface in the scanning electron microscopy images because the NiS / Ni3S2 is completely adhered to the multilayer graphene surface. Low-magnification and high-magnification transmission electron microscopy images of the composite material are shown in Figure 2. Figure 5The nanosheets and nanosheet groups are nearly vertically distributed. In the low-magnification transmission electron microscopy image, only nanosheets and nanosheet groups with nearly vertical distribution can be observed. In the high-resolution transmission electron microscopy observation of the smooth part of the multilayer graphene surface, the NiS / Ni3S2lattice can be observed in the part. It is illustrated that a layer of NiS / Ni3S2is tiled on the surface of the multilayer graphene.

[0036] The multilayer graphene@NiS / Ni3S2composite material, acetylene black and PVDF binder (according to the mass ratio of 8:1:1) are weighed, and a slurry with suitable viscosity is obtained after stirring uniformly with NMP as the solvent. The slurry is coated on the surface of the nickel foam and placed in a 100°C vacuum oven for drying for 12 h. After taking out, the tablet machine is used for tabletting, and the pressure is 10 Mpa. After tabletting, the composite material electrode sheet is obtained. The prepared electrode sheet is used as the working electrode, the nickel foam is used as the counter electrode, and the silver and silver chloride are used as the reference electrode (through the salt bridge) to perform the standard three-electrode electrochemical performance test. Figure 5 is the rate performance test result of the composite material electrode. As can be seen from the figure, in the constant current charge and discharge test at 1, 2, 4, 6, 8, , the discharge specific capacitance is 2455, 2135, 1897, 1726, 1650, 1567. The composite material shows excellent specific capacitance and rate performance. Figure 6 is the cycle performance test result of the composite material electrode. After 3000 times of constant current charge and discharge at 2 A / g, the remaining capacity is 56.8%. The capacity attenuation is mainly due to the dissolution of nickel ions into the electrolyte during the cycle charge and discharge process.

[0037] Example 2: 8 mL of DMF and 2 mL of deionized water are weighed and mixed uniformly to serve as a mixed solvent. 15 mg of expanded graphite is added to the mixed solvent, and ultrasonic treatment is performed at a power of 200 W for 4 hours to obtain a multilayer graphene dispersion solution. 40 mg of Ni powder and 25 mg of S powder (the particle size of the Ni powder and the S powder is mainly distributed in 10-50 μm) are added to the multilayer graphene solution. 0.60 mL of acetic acid is weighed and added to the mixed solution, and magnetic stirring is performed at room temperature for 15 minutes. The mixed solution is placed in a 90°C water bath for magnetic stirring reaction, the stirring speed is 500 rpm, and the stirring reaction time is 4 h. After the reaction is completed, the solution is taken out and cooled at room temperature. After cooling, 3 times of deionized water and 3 times of alcohol are used for centrifugal cleaning, the centrifugal machine speed is 6000 rpm, and after cleaning, the solution is placed in an oven for drying at 70°C for 24 hours. After drying, a multilayer graphene@NiS / Ni3S2thin film composite material is obtained.

[0038] Example 3: Take 8 mL of DMF and 2 mL of deionized water, mix evenly as mixed solvent. Take 5 mg of expanded graphite, add to the mixed solvent, ultrasonic treatment for 4 hours at 200W power, obtain multi-layer graphene dispersion. Take 35 mg of Ni powder and 24.7 mg of S powder (the particle size of Ni powder and S powder is mainly distributed in 10-50 μm), add to the multi-layer graphene solution. Take 0.33 mL of acetic acid and add to the mixed solution, magnetic stirring at room temperature for 15 minutes. Put the mixed solution into a 90°C water bath for magnetic stirring reaction, stirring speed is 500 rpm, stirring reaction time is 4 h. After the reaction is completed, take out and cool at room temperature. After cooling, perform 3 times of deionized water and 3 times of alcohol centrifugal cleaning, centrifuge speed is 6000 rpm / min, after cleaning, place in an oven for drying at 70°C for 24 hours. After drying, obtain multi-layer graphene@NiS / Ni3S2 thin film composite material.

[0039] Example 4: Take 8 mL of DMF and 2 mL of deionized water, mix evenly as mixed solvent. Take 5 mg of expanded graphite, add to the mixed solvent, ultrasonic treatment for 4 hours at 200W power, obtain multi-layer graphene dispersion. Take 35 mg of Ni powder and 24.7 mg of S powder (the particle size of Ni powder and S powder is mainly distributed in 10-50 μm), add to the multi-layer graphene solution. Take 0.33 mL of acetic acid and add to the mixed solution, magnetic stirring at room temperature for 15 minutes. Put the mixed solution into a 90°C water bath for magnetic stirring reaction, stirring speed is 500 rpm, stirring reaction time is 4 h. After the reaction is completed, take out and cool at room temperature. After cooling, perform 3 times of deionized water and 3 times of alcohol centrifugal cleaning, centrifuge speed is 6000 rpm / min, after cleaning, place in an oven for drying at 70°C for 24 hours. After drying, obtain multi-layer graphene@NiS / Ni3S2 thin film composite material.

[0040] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a multilayer graphene@NiS / Ni3S2 composite material, characterized in that: The following steps are involved: Step S10, measuring DMF and deionized water in a volume ratio of 8:2, mixing them uniformly as a mixed solvent, weighing expanded graphite, adding them to the mixed solvent, and performing ultrasonic treatment at 200 W power for 4 hours to obtain a multilayer graphene dispersion, wherein the concentration of expanded graphite relative to the mixed solvent is 0.5~2 mg / mL; Step S20, weighing 3-5 mg / mL Ni powder relative to the mixed solvent; weighing S powder to make the Ni:S molar ratio of 1:1 to 1:1.3; adding the two powders to the multilayer graphene solution; measuring acetic acid to make the volume ratio of acetic acid to the mixed solvent be 1:15 to 1:30; and magnetically stirring at room temperature for 15 minutes; Step S30, placing the mixed solution in a water bath at 90°C for magnetic stirring reaction at a stirring speed of 500 rpm for 4 h; Step S40, after the reaction is completed, take out and cool to room temperature; after cooling, perform deionized water three times and alcohol centrifugal cleaning three times, the centrifuge speed is 6000 rpm, and after cleaning, place in an oven at 70°C and dry for 24 hours; after drying, obtain a multilayer graphene@NiS / Ni3S2 composite material.

2. The method for preparing the multilayer graphene@NiS / Ni3S2 composite material according to claim 1, wherein It is directly prepared uniformly through the action of molecular forces on the surface of multilayer graphene. The molecular forces exist uniformly on the surface of multilayer graphene, and NiS / Ni3S2 is evenly distributed on the surface of multilayer graphene.

3. The method for preparing the multilayer graphene@NiS / Ni3S2 composite material according to claim 1, wherein Ni powder and S powder are used as nickel source and sulfur source, wherein the diameters of the Ni powder and the S powder are between 10 and 50 μm.

4. The method for preparing the multilayer graphene@NiS / Ni3S2 composite material according to claim 1, wherein At the reaction temperature, sulfur powder dissolves in DMF, and the sulfur atoms in the solution fully contact the nickel powder under stirring conditions; the nickel powder and sulfur atoms undergo an oxidation-reduction reaction to produce nickel ions and sulfur ions; among them, the nickel ions form complexes with the sulfur ions, DMF and water molecules, and the complexes produce molecular forces with the carbon rings on the surface of the multilayer graphene and are adsorbed to the surface of the multilayer graphene; the polymerization reaction between the complexes will remove DMF molecules and water molecules, and the appropriate NiS / Ni3S2 nucleation and growth rate are obtained by adding acetic acid, eventually forming a NiS / Ni3S2 film.

5. The method for preparing the multilayer graphene@NiS / Ni3S2 composite material according to claim 4, wherein NiS / Ni3S2 is evenly spread on the surface of the multilayer graphene to form a thin film. A small amount of NiS / Ni3S2 in the composite material forms raised nanosheets or nanosheet clusters. These nanosheets or nanosheet clusters are sparsely distributed within the multilayer graphene sheet and more densely distributed at the edges of the multilayer graphene sheet. This creates gaps in the composite material, which is conducive to the infiltration of the electrolyte, thereby increasing the contact area between the active material NiS / Ni3S2 and the electrolyte.

6. The method for preparing the multilayer graphene@NiS / Ni3S2 composite material according to claim 5, wherein: The NiS / Ni3S2 film is a heterojunction structure composed of two phases, NiS and Ni3S2.

7. A multilayer graphene@NiS / Ni3S2 composite material, characterized in that The NiS / Ni3S2 in the composite material is evenly spread on the surface of the multilayer graphene to form a NiS / Ni3S2 film, and a small portion of the NiS / Ni3S2 forms raised nanosheets or nanosheet clusters. These nanosheets or nanosheet clusters are sparsely distributed within the multilayer graphene sheet and have a higher distribution density at the edges of the multilayer graphene sheet.

8. The multilayer graphene@NiS / Ni3S2 composite material according to claim 7, characterized in that The NiS / Ni3S2 film contains two phases, NiS and Ni3S2, which form a heterojunction structure. The weight ratio of NiS and Ni3S2 in the composite material is 70~80%.

9. The multilayer graphene@NiS / Ni3S2 composite material according to claim 7, characterized in that The multilayer graphene in the composite material is obtained by mechanically exfoliating expanded graphite in a mixed solvent through an ultrasonic method, and the number of graphite layers of the multilayer graphene is less than 100.

10. A supercapacitor, characterized in that: The positive electrode material of the supercapacitor adopts any composite material according to claims 7 to 9.

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