Flaky nickel-cobalt sulfide array / multilayer graphene composite material, preparation method and supercapacitor

Abstract

The invention discloses a flaky nickel-cobalt sulfide array / multilayer graphene composite material, a preparation method and a supercapacitor. Nickel-cobalt sulfide prepared on the surface of multilayer graphene is flaky and is uniformly distributed on the surface of the multilayer graphene in an array manner. The nickel-cobalt sulfide sheet is composed of multiple phase structures (NiS, Ni3S2 and Co3S4) of nickel and cobalt, and the formed heterojunction structure enables the activity of Ni and Co ions to be enhanced. The nickel-cobalt sulfide sheets are uniformly distributed on the surface of the multilayer graphene, so that the electron transfer speed between the nickel-cobalt sulfide and the multilayer graphene is increased. Nickel-cobalt sulfide sheets grow upwards on the surface of the multi-layer graphene, and gaps are formed between the sheets, so that the contact area between the electrolyte and the nickel-cobalt sulfide is increased, and the active sites of Ni and Co are increased. The composite material obtained by adopting the technical scheme of the invention has excellent supercapacitor performance.

Description

Technical Field

[0001] The present invention belongs to the field of material technology, and in particular relates to a flaky nickel-cobalt sulfide array / multilayer graphene composite material, a preparation method, and a supercapacitor. The composite material of the present invention has potential application in supercapacitors. Background Art

[0002] Transition metal sulfides have good conductivity, adjustable electronic structure, high specific capacitance, excellent electrocatalytic performance, a wide variety of crystal structures and low price, making them a research hotspot in the field of supercapacitors.

[0003] Preparing three-dimensional nanostructures allows metal sulfides to fully contact the electrolyte, resulting in more active sites and thus improving the specific capacitance and charge transfer rate of supercapacitors. Although metal sulfides have better conductivity than metal oxides and metal hydroxides, they still result in higher internal resistance and charge transfer rate when used as electrode materials. Therefore, to improve the electrochemical performance of metal sulfides, compounding them with carbon materials has become a major approach. However, current research on compounding metal sulfides with carbon materials still has many shortcomings.

[0004] In the preparation of composite materials, it is often necessary to activate the carbon material. The current mainstream method is to perform an oxidation treatment to introduce oxygen-containing functional groups on the surface of the carbon material, thereby increasing the chemical activity of the carbon material surface. In the subsequent preparation of the composite material, these oxygen-containing functional groups become active sites, and metal sulfides mainly grow at these active sites. However, the oxidation treatment not only increases the preparation cost, but also greatly reduces the electrical conductivity of the carbon material, affecting its electrochemical performance. Secondly, the composite material of the carbon material and the sulfide have low composite uniformity, which affects the synergistic effect between the two and reduces the electrochemical performance. The performance of the composite sulfide is often better than that of a single sulfide. At present, there is a lack of a simple preparation method for preparing nickel-cobalt sulfide on the graphene surface, and the distribution of the sulfide is uneven, which affects the performance. Moreover, the preparation of composite materials often adopts the hydrothermal method, and the high temperature conditions and high-pressure containers are not conducive to large-scale production. Summary of the Invention

[0005] To address the technical problems encountered in the prior art, the present invention discloses a flaky nickel-cobalt sulfide array / multilayer graphene composite material, a preparation method, and a supercapacitor. The nickel-cobalt sulfide prepared on the multilayer graphene surface is flaky and evenly distributed in an array. The nickel-cobalt sulfide flakes are composed of multiple nickel-cobalt phases (NiS, Ni3S2, and Co3S4), forming a heterojunction structure that enhances the activity of Ni and Co ions. The uniform distribution of the nickel-cobalt sulfide flakes on the multilayer graphene surface increases the electron transfer rate between the nickel-cobalt sulfide and the multilayer graphene. The multilayer graphene enhances the conductivity of the composite material. The nickel-cobalt sulfide flakes grow upward on the multilayer graphene surface, with pores between the flakes. This increases the contact area between the electrolyte and the nickel-cobalt sulfide, thereby increasing the number of active sites for Ni and Co.

[0006] In order to solve the technical problems existing in the prior art, the technical solutions of the present invention are as follows: A method for preparing a flaky nickel-cobalt sulfide array / multilayer graphene composite material comprises the following steps: 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: Weigh Ni powder and Co powder, with the total mass of Ni and Co powder relative to the mixed solvent at 4 mg / mL, and a Ni:Co mass ratio of 7:3 to 8:2. Weigh 2.2 to 2.7 mg / mL of S powder and add it to the multilayer graphene solution. Add 20% acetic acid aqueous solution, with a volume ratio of 1:15 to 1:30 to the mixed solvent. Magnetic stirring is then performed at room temperature for 15 minutes. Preferably, the diameters of the Ni, Co, and S powders are between 10 and 50 μm.

[0007] 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.

[0008] Step S40: After the reaction is complete, the product is removed from the oven and cooled to room temperature. After cooling, the product is centrifuged three times with deionized water and three times with alcohol at 6000 rpm. After cleaning, the product is dried in an oven at 70°C for 24 hours. After drying, a flaky nickel-cobalt sulfide array / multilayer graphene composite material is obtained.

[0009] The preparation mechanism of the above method is as follows: at the reaction temperature, sulfur powder is dissolved in DMF, and the sulfur molecules in the solution are fully contacted with nickel powder and cobalt powder under stirring conditions. Nickel powder, cobalt powder and sulfur molecules undergo redox reaction to produce divalent and trivalent nickel ions, cobalt ions and sulfur ions. Nickel ions, cobalt ions, sulfur ions, DMF and water molecules form complexes, which generate molecular forces with the surface of multilayer graphene and are adsorbed to the surface of multilayer graphene. Due to the synergistic effect of nickel and cobalt ions, nickel and cobalt complexes grow upward from the surface of multilayer graphene to form a sheet array. At the same time, under heating, the polymerization reaction between the complexes will remove DMF molecules and water molecules, and ultimately form the phases NiS, Ni3S2 and Co3S4.

[0010] As a further improvement, multilayer graphene does not require activation treatment and can be directly prepared uniformly through the action of molecular forces on the surface of multilayer graphene. Since molecular forces exist uniformly on the surface of multilayer graphene, nickel cobalt sulfide is evenly distributed on the surface of multilayer graphene.

[0011] As a further improvement, nickel powder, cobalt powder and sulfur powder are used as nickel source, cobalt source and sulfur source. Preferably, the diameter of Ni powder, Co powder and S powder is 10~50μm.

[0012] As a further improvement, the synergistic effect between nickel and cobalt plays an important role in the formation of sheet arrays.

[0013] The present invention also discloses a flaky nickel-cobalt sulfide array / multilayer graphene composite material, which uses flaky multilayer graphene as a substrate and has nickel-cobalt sulfide distributed on the surface of the multilayer graphene; wherein the nickel-cobalt sulfide is in flaky form and is evenly distributed on the surface of the multilayer graphene.

[0014] As a further improvement, multilayer graphene is obtained by mechanically exfoliating expanded graphite in a mixed solvent using ultrasonic technology. The mechanically exfoliated multilayer graphene has a complete carbon ring structure on its surface, fewer than 100 graphite layers, and minimal surface oxygen functional groups, resulting in excellent electrical conductivity.

[0015] As a further improvement, nickel cobalt sulfide is in the form of flakes and evenly distributed in an array on the surface of multilayer graphene, which enhances the synergistic effect between nickel cobalt sulfide and multilayer graphene.

[0016] As a further improvement, nickel-cobalt sulfide sheets are composed of NiS, Ni3S2 and Co3S4, which form a heterojunction structure, thereby improving the activity of Ni and Co.

[0017] As a further improvement, nickel-cobalt sulfide sheets grow upward on the surface of multilayer graphene, with gaps between the sheets, which increases the contact area between the electrolyte and nickel-cobalt sulfide, thereby increasing the active sites of Ni and Co.

[0018] The invention also discloses a supercapacitor obtained by adopting the composite material.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation of substrate multilayer graphene is simple and low-cost. There is no need to activate the surface of the multilayer graphene, and there is no requirement for the number of layers of the multilayer graphene, which reduces the preparation cost of carbon materials.

[0020] (2) Nickel cobalt sulfide sheets are evenly distributed in an array on the surface of multilayer graphene, which enhances the synergistic effect between nickel cobalt sulfide and multilayer graphene.

[0021] (3) Nickel-cobalt sulfide sheets are composed of multiple phases, NiS, Ni3S2, and Co3S4, and the heterojunction formed between them increases the activity of Ni and Co ions.

[0022] (4) Nickel-cobalt sulfide sheets grow upward from the surface of multilayer graphene, with gaps between the sheets, allowing the electrolyte to fully contact the active sites of Ni and Co, thereby increasing the number of active sites.

[0023] (5) The present invention uses nickel powder, cobalt powder, and sulfur powder as nickel, cobalt, and sulfur sources, which are lower in cost than nickel salts, cobalt salts, and sulfur salts (sulfur-containing organic matter). Furthermore, the present invention is convenient to transport and has low transportation costs.

[0024] (6) The present invention adopts a chemical deposition method, which does not require the high-pressure equipment required by the hydrothermal method. Therefore, the required preparation cost is low. It is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flow chart of the preparation steps of the flaky nickel-cobalt sulfide array / multilayer graphene composite material of the present invention; Figure 2 The XRD pattern of the flaky nickel-cobalt sulfide array / multilayer graphene composite material prepared in Example 1 of the present invention; Figure 3 This is a low-magnification scanning electron microscope image of the flaky nickel-cobalt sulfide array / multilayer graphene composite material prepared in Example 1 of the present invention; Figure 4 This is a high-magnification scanning electron microscope image of the flaky nickel-cobalt sulfide array / multilayer graphene composite material prepared in Example 1 of the present invention; Figure 5CV curve of nickel cobalt sulfide sheet array / multilayer graphene prepared in Example 1 of the present invention; Figure 6 The charge-discharge curves of the sheet-like nickel-cobalt sulfide array / multilayer graphene composite material prepared in Example 1 of the present invention at different current densities; Figure 7 This is the rate curve of the flaky nickel-cobalt sulfide array / multilayer graphene composite prepared in Example 1 of the present invention; Figure 8 Cyclic performance test curve of the nickel cobalt sulfide array / multilayer graphene prepared in Example 1 of the present invention at a charge and discharge current density of 2 A / g; DETAILED DESCRIPTION

[0026] In order to better illustrate the process and scheme of the present invention, the following invention is further described in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] In order to solve the technical problems existing in the prior art, see Figure 1 , shown is a flow chart of the steps of the preparation method of the sheet-like nickel cobalt sulfide array / multilayer graphene composite material proposed by the present invention, comprising the following steps: 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: Weigh Ni powder and Co powder, with the total mass of Ni and Co powder relative to the mixed solvent at 4 mg / mL, and a Ni:Co mass ratio of 7:3 to 8:2. Weigh 2.2 to 2.7 mg / mL of S powder and add it to the multilayer graphene solution. Add 20% acetic acid aqueous solution, with a volume ratio of 0.035:1 to 0.065:1 to the mixed solvent. Magnetic stirring is then performed at room temperature for 15 minutes. Preferably, the diameters of the Ni, Co, and S powders are between 10 and 50 μm.

[0028] 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.

[0029] Step S40: After the reaction is complete, the product is removed from the oven and cooled to room temperature. After cooling, the product is centrifuged three times with deionized water and three times with alcohol at 6000 rpm. After cleaning, the product is dried in an oven at 70°C for 24 hours. After drying, a flaky nickel-cobalt sulfide array / multilayer graphene composite material is obtained.

[0030] The preparation mechanism of the above method is as follows: at the reaction temperature, sulfur powder is dissolved in DMF, and the sulfur molecules in the solution are fully contacted with nickel powder and cobalt powder under stirring conditions. Nickel powder, cobalt powder and sulfur molecules undergo redox reaction to produce divalent and trivalent nickel ions, cobalt ions and sulfur ions. Nickel ions, cobalt ions, sulfur ions, DMF and water molecules form complexes, which generate molecular forces with the surface of multilayer graphene and are adsorbed to the surface of multilayer graphene. Due to the synergistic effect of nickel and cobalt ions, nickel and cobalt complexes grow upward from the surface of multilayer graphene to form a sheet array. At the same time, under heating, the polymerization reaction between the complexes will remove DMF molecules and water molecules, and ultimately form the phases NiS, Ni3S2 and Co3S4.

[0031] 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. 32 mg of Ni powder, 8 mg of Co powder, and 25 mg of S powder (the Ni, Co, 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 20% aqueous 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 waterbath 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 sheet-like nickel-cobalt sulfide array / multilayer graphene composite material was obtained.

[0032] The XRD pattern of the sheet-like nickel cobalt sulfide array / multilayer graphene composite material synthesized in this example is shown in Figure 2 As shown in the figure, it can be seen that the composite material consists of four phases: multilayer graphene, NiS, Ni3S2 and Co3O4. The low-magnification scanning electron microscope and high-magnification scanning electron microscope photos of the composite material are shown in Figure 3 and 4 Scanning electron microscopy images show the uniform distribution of nickel-cobalt sulfide sheets across the multilayer graphene surface, with uniform growth and consistent nanosheet size. The sheets grow upward on the multilayer graphene surface, partially cross-linked with each other and with gaps between them. This nanosheet array structure provides stable support and significantly increases the specific surface area of ​​the composite material, providing more electrochemically active sites and effectively improving charge transport.

[0033] A nickel-cobalt sulfide array / multilayer graphene composite material, acetylene black, and PVDF binder (at a mass ratio of 8:1:1) were weighed and mixed thoroughly with NMP as the solvent to obtain a slurry of suitable viscosity. The slurry was applied to nickel foam and dried in a vacuum oven at 100°C for 12 hours. The slurry was then pressed using a tablet press at a pressure of 10 MPa to obtain a composite electrode sheet. Standard three-electrode electrochemical performance testing was performed using the prepared electrode sheet as the working electrode, the nickel foam as the counter electrode, and silver and silver chloride as reference electrodes (via a salt bridge).

[0034] Figure 5 The CV curves of the composite material obtained at different scanning speeds show that the composite material has a pair of redox peaks and has very good redox properties. Figure 6 This is the charge-discharge curve of the composite material. As can be seen from the figure, the curve has a good charge-discharge platform, indicating that the active material nickel-cobalt sulfide has good redox reversibility. Figure 7 is the rate performance of the composite material at 1, 2, 4, 6, 8, 10 A g −1 In the constant current charge and discharge test, the discharge specific capacitance is 2592.5, 2313.0, 2110.5, 2047.0, 1921.5, 1877.5 F g −1 . Figure 7 is the rate curve obtained from the GCD curve. 10 A g −1 The specific capacitance retention rate is 72.4% under the above conditions, and the composite material exhibits excellent specific capacitance and rate performance. Figure 8 This is the cycle performance test result of the composite material electrode. Under the constant current charge and discharge of 2A / g, the remaining capacity after 3000 times is 72.2%, showing excellent cycle performance.

[0035] Example 2: 8 mL of DMF and 2 mL of deionized water were mixed and used as the mixed solvent. 15 mg of expanded graphite was weighed and added to the mixed solvent. The mixture was ultrasonically treated at 200 W for 4 hours to obtain a multilayer graphene dispersion. 28 mg of Ni powder, 12 mg of Co powder, and 22 mg of S powder (the Ni, Co, and S powders had particle sizes primarily ranging from 10 to 50 μm) were weighed and added to the multilayer graphene solution. 0.35 mL of 20% aqueous 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 waterbath 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 sheet-like nickel-cobalt sulfide array / multilayer graphene composite material was obtained.

[0036] Example 3: 8 mL of DMF and 2 mL of deionized water were mixed and used as the mixed solvent. 5 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, 10 mg of Co powder, and 27 mg of S powder (the Ni, Co, and S powders had particle sizes primarily ranging from 10 to 50 μm) were weighed and added to the multilayer graphene solution. 0.65 mL of 20% aqueous 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 waterbath 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 sheet-like nickel-cobalt sulfide array / multilayer graphene composite material was obtained.

[0037] Example 4: 8 mL of DMF and 2 mL of deionized water were mixed and used as the mixed solvent. 10 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. 31 mg of Ni powder, 9 mg of Co powder, and 22 mg of S powder (the Ni, Co, and S powders had particle sizes primarily ranging from 10 to 50 μm) were weighed and added to the multilayer graphene solution. 0.6 mL of 20% aqueous 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 waterbath 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 sheet-like nickel-cobalt sulfide array / multilayer graphene composite material was obtained.

[0038] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0039] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a flaky nickel-cobalt sulfide array / multilayer graphene 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 Ni powder and Co powder, the total mass of Ni powder and Co powder relative to the mixed solvent is 4 mg / mL, and the Ni:Co mass ratio is 7:3-8:2; weighing 2.2-2.7 mg / mL of S powder and adding it to the multilayer graphene solution; adding 20% ​​acetic acid aqueous solution, the volume ratio of which to the mixed solvent is 1:15-1:30; and magnetic 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 flaky nickel cobalt sulfide array / multilayer graphene composite material.

2. The method for preparing the flaky nickel-cobalt sulfide array / multilayer graphene composite material according to claim 1, wherein: It is directly prepared uniformly through the action of molecular forces on the surface of multilayer graphene; wherein, the molecular forces exist uniformly on the surface of multilayer graphene, and nickel cobalt sulfide is uniformly distributed on the surface of multilayer graphene.

3. The method for preparing the flaky nickel-cobalt sulfide array / multilayer graphene composite material according to claim 1, wherein: Ni powder, Co powder and S powder are used as nickel source, cobalt source and sulfur source, wherein the diameters of Ni powder, Co powder and S powder are between 10 and 50 μm.

4. The method for preparing the flaky nickel-cobalt sulfide array / multilayer graphene composite material according to claim 1, wherein: The synergistic effect between nickel and cobalt is utilized to form a sheet array.

5. The flaky nickel-cobalt sulfide array / multilayer graphene composite material prepared by the method of any one of claims 1 to 4, characterized in that: The substrate is a flaky multilayer graphene, and nickel cobalt sulfide is distributed on the surface of the multilayer graphene. The nickel cobalt sulfide is in a flaky shape and is evenly distributed on the surface of the multilayer graphene.

6. The flaky nickel-cobalt sulfide array / multilayer graphene composite material according to claim 5, characterized in that: Nickel cobalt sulfide sheets are composed of NiS, Ni3S2 and Co3S4, forming a heterojunction structure, which improves the activity of Ni and Co.

7. The flaky nickel cobalt sulfide array / multilayer graphene composite material according to claim 6, characterized in that: Nickel cobalt sulfide sheets grow upward on the surface of multilayer graphene, with a porous structure and gaps between the sheets to increase the contact area between the electrolyte and the nickel cobalt sulfide, thereby increasing the active sites of Ni and Co.

8. The flaky nickel cobalt sulfide array / multilayer graphene composite material according to claim 7, characterized in that: Nickel cobalt sulfide sheets are evenly distributed in an array on the surface of multilayer graphene, thereby enhancing the synergistic effect between nickel cobalt sulfide and multilayer graphene.

9. The flaky nickel-cobalt sulfide array / multilayer graphene composite material according to claim 5, characterized in that: The multilayer graphene is obtained by mechanically exfoliating expanded graphite in a mixed solvent through an ultrasonic method; the carbon ring structure on the surface of the multilayer graphene obtained by mechanical exfoliation is complete, and the number of graphite layers of the multilayer graphene is less than 100.

10. A supercapacitor, characterized in that: The supercapacitor adopts the composite material according to any one of claims 5 to 9.

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