Graphene-coated v3s4@NC material and preparation method therefor and use thereof

Abstract

A graphene-coated V3S4@NC material and a preparation method therefor and the use thereof. The material is composed of V3S4@NC and graphene coated on the surface of V3S4@NC, wherein V3S4@NC is of a core-shell structured nanofiber composite material with a V3S4 core and an NC shell. The method comprises the following steps: step I: adding a sulfur powder, vanadyl acetylacetonate (VO(acac)2), polyacrylonitrile (PAN), and graphene oxide to N-N dimethylformamide (DMF), stirring same for 12 h, followed by ultrasonic oscillation to obtain a mixed solution; step II: filling a syringe with the mixed solution obtained in step I, performing electrostatic spinning at a flow rate of 0.4 mL / h under a voltage of 18 kV, and collecting a product, so as to obtain a precursor; and step III: placing the collected precursor in a protective atmosphere, and annealing same at 800 ºC for 3 h to obtain a graphene-coated V3S4@NC material. The product can enable the reduced transport distance of sodium ions, and improvement of the electrochemical performance thereof.

Description

A graphene-coated V3S4@NC material, its preparation method and application Technical Field

[0001] This disclosure relates to the field of battery electrode composite materials technology, specifically to a graphene-coated V3S4@NC material, its preparation method, and its application. Background Technology

[0002] To date, many novel anode materials, such as Sb₂S₃, ZnS, Co₂GeO₄, P, CuCo₂S₄, and V₃S₄, have attracted considerable interest in sodium-ion storage. Among these anode materials, the monoclinic V₃S₄ structure is considered the most advanced sodium-ion storage electrode due to its large interlayer space and high theoretical capacity. However, pure V₃S₄ material exhibits slow kinetics and large volume changes, resulting in poor high-speed performance and poor cycle stability. In response, numerous strategies have been employed to address these drawbacks, including constructing specialized nanostructures and fabricating carbon composite materials.

[0003] The paper “V3S4 nanoparticles anchored on three-dimensional porous graphene gel for superior lithium storage, Electrochim. Acta 261(2018)35–41” discloses a V3S4 nanocrystal anchored on a conductive graphene sheet. The results show that graphene provides a continuous electronic network for electrons and suppresses volume changes during discharge / charge.

[0004] The paper “Insights into the storage mechanism of 3D nanoflower-like V3S4 anode in sodium-ion batteries, Chem. Eng. J. 427 (2022), 130936” discloses the preparation of three-dimensional nanoflower-like V3S4 material by a solvothermal method. The anode obtained has good sodium storage performance, with a discharge capacity as high as 299 mAh / g under 5 A / g conditions.

[0005] Although the aforementioned papers all used V3S4 to produce corresponding battery electrode composite materials, the performance of these composite materials is still not ideal, and the preparation methods are relatively complex and the synthesis environment is relatively harsh.

[0006] Summary of the Invention

[0007] To address the problems existing in the prior art, the present disclosure aims to provide a graphene-coated V3S4@NC material, its preparation method, and its application, so as to improve the electrical properties of V3S4 composite materials and provide a relatively simple preparation method.

[0008] The graphene-coated V3S4@NC material disclosed herein is composed of V3S4@NC and graphene coated on the surface of V3S4@NC. The V3S4@NC is a core-shell structured nanofiber composite material with V3S4 core and NC shell.

[0009] Preferably, the crystal structure of V3S4 is a monoclinic crystal structure.

[0010] This disclosure also provides a method for preparing the above-mentioned graphene-coated V3S4@NC material, including the following steps:

[0011] Step 1: Add sulfur powder, vanadium acetylacetonate (VO(acac)2), polyacrylonitrile (PAN) and graphene oxide to N,N-dimethylformamide (DMF) and stir for 12 hours, then sonicate to obtain a mixed solution.

[0012] Step 2: Fill the syringe with the mixed solution obtained in Step 1, perform electrospinning at a flow rate of 0.4 mL / h under 18 kV voltage, collect the product, and obtain the precursor;

[0013] Step 3: Place the collected precursor in a protective atmosphere and anneal at 800℃ for 3 hours to obtain graphene-coated V3S4@NC material.

[0014] Preferably, the sulfur powder has an average particle size of 400-800 mesh, the acetylacetone vanadium oxide powder has an average particle size of 600-1000 mesh, the sulfur powder and acetylacetone vanadium oxide powder are both analytical grade, the polyacrylonitrile powder has an average molecular weight of 50,000-200,000, and the graphene oxide has 15-20 layers.

[0015] Preferably, the protective atmosphere is an inert atmosphere.

[0016] Preferably, the inert atmosphere is a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 95:5.

[0017] This disclosure also provides a sodium-ion battery anode, comprising the above-mentioned graphene-coated V3S4@NC material, conductive carbon black, and polyvinylidene fluoride (PVDF), wherein the mass ratio of the graphene-coated V3S4@NC material, conductive carbon black, and polyvinylidene fluoride (PVDF) is 80:10:10.

[0018] This invention also provides the application of the above-mentioned graphene-coated V3S4@NC material, using it as an anode in a sodium-ion battery.

[0019] The advantages of the graphene-coated V3S4@NC material disclosed herein are as follows:

[0020] Graphene is coated onto the V3S4@NC composite material. The synergistic effect between V3S4@NC and graphene reduces the transport distance of sodium ions and improves the conductivity of the material. Since V3S4@NC is a core-shell structured nanofiber composite material with V3S4 core and NC shell, it has a large specific surface area, which helps to disperse and coat V3S4@NC graphene on the material.

[0021] Meanwhile, graphene may bind strongly to nitrogen-doped carbon fibers through van der Waals forces or π-π stacking interactions, which helps anchor graphene sheets, reduces the agglomeration effect of graphene, and also helps the dispersion and coating of graphene on V3S4@NC materials.

[0022] Since graphene is well dispersed on and coats the V3S4@NC material, the electrochemical performance of the graphene-coated V3S4@NC material is improved by the synergy of the conductivity of graphene and the electrochemical performance of the V3S4@NC material itself. Attached Figure Description

[0023] Figure 1 shows the SEM and TEM images of the V3S4@NC anode material;

[0024] a~c are SEM images of V3S4@NC anode material, and d~f are TEM images of V3S4@NC composite material;

[0025] Figure 2 shows the XRD pattern, Raman spectrum, and XPS spectrum of the V3S4@NC anode material;

[0026] a is the XRD pattern of the V3S4@NC anode material; b is the Raman spectrum of the V3S4@NC anode material; c to f are the XPS spectra of the V3S4@NC anode material;

[0027] Figure 3 shows the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements of the V3S4@NC anode material, and the charge-discharge curves of the V3S4@NC anode material at 0.1 A·g⁻¹.

[0028] a) Charge-discharge curves of the V3S4@NC electrode at 0.1 A·g⁻¹; b) Rate characteristics of the V3S4@NC electrode at different current densities; c) Long-term cycling stability of the V3S4@NC electrode at 10 A·g⁻¹; d) Electrochemical impedance spectroscopy (EIS) curves of the V3S4@NC electrode; e) Cyclic voltammetry curves of the V3S4@NC electrode. Detailed Implementation

[0029] The graphene-coated V3S4@NC material disclosed herein is composed of V3S4@NC and graphene coated on the surface of V3S4@NC. The V3S4@NC is a core-shell structured nanofiber composite material with V3S4 core and NC shell.

[0030] Specifically, V3S4 has a monoclinic crystal structure.

[0031] As is well known, graphene possesses excellent chemical and physical properties, such as a large theoretical specific surface area (≈2630 m²g⁻¹), high electronic conductivity, and high mechanical strength. Furthermore, doping with heteroatoms (such as N, B, S, and P) can further enhance conductivity and electrochemical sodium ion storage, making it not only a framework for the growth of other active materials but also contributing to sodium ion storage. Against this backdrop, constructing graphene-based composite electrodes can effectively improve the overall electronic / ionic conductivity of the electrode and increase the number of active sodium ion storage sites. Simultaneously, the synergistic effect of graphene with other active materials can enhance the charge-discharge platform, accelerate ion / electron transfer at the working interface, and enhance structural stability. Moreover, the introduction of graphene can effectively accommodate volume expansion and prevent the aggregation of active materials, thereby resulting in excellent electrochemical performance.

[0032] However, graphene is prone to agglomeration when combined with other materials, resulting in uneven dispersion and poor coating effect. Under these circumstances, the inventors unexpectedly discovered that graphene can effectively disperse and coat V3S4@NC materials, and the resulting graphene-coated V3S4@NC materials exhibit excellent electrochemical properties. The preparation method of the above materials is as follows:

[0033] Step 1: Add sulfur powder, vanadium acetylacetonate (VO(acac)2), polyacrylonitrile (PAN) and graphene oxide to N,N-dimethylformamide (DMF) and stir for 12 hours, then sonicate to obtain a mixed solution.

[0034] Step 2: Fill the syringe with the mixed solution obtained in Step 1, perform electrospinning at a flow rate of 0.4 mL / h under 18 kV voltage, collect the product, and obtain the precursor;

[0035] Step 3: Place the collected precursor in a protective atmosphere and anneal at 800℃ for 3 hours to obtain graphene-coated V3S4@NC material.

[0036] Specifically, the average particle size of the sulfur powder is 400-800 mesh, the average particle size of the acetylacetone vanadium oxide powder is 600-1000 mesh, the purity of both the sulfur powder and the acetylacetone vanadium oxide powder is analytical grade, the average molecular weight of the polyacrylonitrile powder is 50,000-200,000, the number of graphene oxide layers is 15-20, and the protective atmosphere is an inert atmosphere.

[0037] More specifically, sulfur powder, vanadium acetylacetonate (VO(acac)2), polyacrylonitrile (PAN), and graphene oxide were added to N,N-dimethylformamide (DMF) at a mass ratio of 1:4:5:2, stirred for 12 hours, and ultrasonically vibrated for 12 hours to obtain a mixed solution; the protective atmosphere was an inert atmosphere consisting of a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 95:5.

[0038] In step one, sulfur powder and acetylacetone vanadium oxide react in the mixed solution to obtain a mixed solution of V3S4 particles, unreacted polyacrylonitrile, and graphene oxide. In step two, the mixed solution is spun by electrospinning at a flow rate of 0.4 mL / h under 18 kV to obtain a precursor, which includes V3S4 fibers, polyacrylonitrile precursor fibers, and graphene. The precursor is then placed in a protective atmosphere and annealed at 800°C using a solid-state annealing method. During annealing, nitrogen-doped carbon (NC) fibers are formed and coated onto V3S4 filaments, forming a core-shell structure, namely V3S4@NC. Graphene oxide is reduced to graphene during annealing. Due to the strong capillary force between the V3S4@NC fibers and graphene, the graphene flakes are anchored, reducing the agglomeration effect and helping the graphene flakes to disperse better. This allows graphene to coat the outer surface of the V3S4@NC fibers, which is the graphene-coated V3S4@NC material described in this disclosure.

[0039] The above-mentioned materials or graphene-coated V3S4@NC materials prepared by the above method are applied to the anode of a sodium-ion battery. Specifically, the electrolyte of the sodium-ion battery is NaClO4, and the anode materials are conductive carbon black (super P), polyvinylidene fluoride (PVDF), and the above-mentioned materials or graphene-coated V3S4@NC materials prepared by the above method. More specifically, the mass ratio of graphene-coated V3S4@NC materials, conductive carbon black (super P), and polyvinylidene fluoride (PVDF) is 80:10:10. The above-mentioned graphene-coated V3S4@NC materials, conductive carbon black (super P), and polyvinylidene fluoride (PVDF) are mixed with N-methylpyrrolidone (NMP) at a mass ratio of 80:10:10 to obtain a mixed slurry. The mixed slurry is cast onto a clean copper foil and heated at 110°C for 16 hours as the working anode. Metallic sodium is selected as the cathode, 1M NaClO4 is selected as the electrolyte, and Celgard is selected as the electrolyte. 2400 is used as a battery separator to assemble a coin cell.

[0040] In the description of this disclosure, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing this disclosure and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this disclosure.

[0041] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims disclosed herein.

Claims

1. A graphene-coated V3S4@NC material, characterized in that, The V3S4@NC is a core-shell structure nanofiber composite material with a V3S4 core and an NC shell. 2.The graphene-coated V 3S 4@ NC material of claim 1, characterized in that, The crystal structure of the V3S4 is monoclinic crystal structure.

3. The method for preparing the graphene-coated V3S4@NC material according to claim 1 or 2, characterized in that, The method comprises the following steps: Step one: add sulfur powder, vanadium acetylacetonate (VO(acac)2), polyacrylonitrile (PAN) and graphene oxide into N-N dimethylformamide (DMF) and stir for 12 hours, and ultrasonic oscillation to obtain a mixed solution; Step two: fill the mixed solution obtained in step one into a syringe, and perform electrospinning at a flow rate of 0.4 mL / h under a voltage of 18 kV to collect the product to obtain a precursor; Step three: place the collected precursor in a protective atmosphere, and anneal at 800 DEG C for 3 hours to obtain a graphene-coated V3S4@NC material.

4. The production method according to claim 3, characterized by, The average particle size of the sulfur powder is 400-800 mesh, the average particle size of the vanadium acetylacetonate powder is 600-1000 mesh, the purity of the sulfur powder and the vanadium acetylacetonate powder is all analytical pure, the average molecular weight of the polyacrylonitrile powder is 50-200 thousand, and the number of layers of the graphene oxide is 15-20 layers.

5. The preparation method according to claim 3, characterized in that, The protective atmosphere is an inert atmosphere.

6. The preparation method according to claim 3, characterized in that, The inert atmosphere is a mixed gas of argon and hydrogen, and the volume ratio of the argon to the hydrogen is 95:

5.

7. Use of the graphene-coated V3S4@NC material according to any one of claims 1 to 2 or of the graphene-coated V3S4@NC material produced according to the production method according to any one of claims 3 to 6, characterized in that: It is used as a sodium ion battery anode.

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