阅读说明：本技术 一种超小碳化钼@碳复合材料及其制备方法和应用 (Ultra-small molybdenum carbide @ carbon composite material and preparation method and application thereof ) 是由 顾栋 张星 于 2021-07-22 设计创作，主要内容包括：本发明公开了一种超小碳化钼@碳复合材料及其制备方法和应用。该方法制备的复合材料是由超小的碳化钼(Mo-(2)C)纳米颗粒和介孔碳组成,其中超小的Mo-(2)C纳米颗粒均匀地分布在有序介孔碳中。本发明是要解决现有的碳化钼制备条件苛刻、易团聚、比表面积较小的问题。本发明制备的超小碳化钼@碳复合材料既具备多级结构优势,有效增加了比表面积与孔体积；又具有较好导电性,并对LiPSs具有较好的化学吸附能力,可提供反应的结合位点,同时良好的电子传递可有效催化其向放电终端产物的转化,减缓“穿梭效应”。基于这种协同效应,对于锂硫电池电化学性能的提高具有重要意义。(The invention discloses an ultra-small molybdenum carbide @ carbon composite material and a preparation method and application thereof. The composite material prepared by the method is made of ultra-small molybdenum carbide (Mo) 2 C) Nanoparticles and mesoporous carbon, with ultra-small Mo 2 The C nanoparticles are uniformly distributed in the ordered mesoporous carbon. The invention aims to solve the problems of harsh preparation conditions, easy agglomeration and small specific surface area of the existing molybdenum carbide. The ultra-small molybdenum carbide @ carbon composite material prepared by the invention has moreThe hierarchical structure has the advantages that the specific surface area and the pore volume are effectively increased; the conductive material has good conductivity, has good chemical adsorption capacity on LiPSs, can provide a binding site for reaction, and simultaneously has good electron transfer, so that the conversion of the conductive material to a discharge terminal product can be effectively catalyzed, and the shuttle effect is slowed down. Based on the synergistic effect, the method has important significance for improving the electrochemical performance of the lithium-sulfur battery.)

1. A preparation method of an ultra-small molybdenum carbide @ carbon composite material is characterized by comprising the following steps:

(1) adding tetraethyl orthosilicate into an acidic solution containing the amphiphilic block copolymer, stirring in a water bath, reacting, and then filtering;

(2) filtering the filtrate obtained in the step (1) and keeping part of mother liquor for hydrothermal aging, and then filtering and drying;

(3) adding concentrated nitric acid and hydrogen peroxide into the product obtained in the step (2), stirring in a water bath to react completely, adding distilled water to dilute the mixed solution, performing suction filtration, and performing water washing, suction filtration and drying to obtain a silicon dioxide template;

(4) adding a carbon source into the silica template, fully mixing, and preserving heat to fully polymerize the carbon source to obtain a polymer @ silica template;

(5) dissolving a molybdenum source in water, adding a polymer @ silicon dioxide template, continuing stirring at room temperature, and evaporating the solvent until the solvent is completely dried to obtain a precursor;

(6) transferring the precursor to calcine in hydrogen atmosphere; after calcining, cooling to room temperature, and taking out a product;

(7) and (4) removing the silicon dioxide template in the product obtained in the step (6), and freeze-drying to obtain the final ultra-small molybdenum carbide @ carbon composite material.

2. The method of claim 1, wherein: the amphiphilic block copolymer contained in the step (1) comprises P123, F127 and F108; the silicon dioxide template in the step (3) comprises SBA-15-OH, KIT-6-OH, MCF-OH, P-SBA-15-OH, FDU-12-OH and SBA-16-OH.

3. The method of claim 1, wherein: the concentration of the hydrogen peroxide in the step (3) is 40 wt%, the water bath reaction temperature is 80 ℃, and the reaction time is 3 hours.

4. The method of claim 1, wherein: the carbon source used in the step (4) is selected from furfuryl alcohol, phenolic resin, 2-thiophene methanol, tryptophan, cysteine, tyrosine and dopamine.

5. The method of claim 4, wherein: selecting different solvents for the carbon source in the step (4) according to properties;

wherein, when furfuryl alcohol is used as a carbon source, Trimethylbenzene (TMB) is selected as a solvent and oxalic acid is selected as a catalyst for promoting polymerization; selecting ethanol as a solvent when phenolic resin and 2-thiophene methanol are used as carbon sources; when tryptophan, cysteine, tyrosine and dopamine are selected as carbon sources, distilled water is selected as a solvent.

6. The method of claim 1, wherein: the polymerization temperature of the polymer @ silica template in said step (4) is from room temperature to 130 ℃.

7. The method of claim 1, wherein: in the step (5), the molybdenum source is phosphomolybdic acid, molybdenum acetylacetonate, ammonium molybdate or sodium molybdate.

8. The method of claim 1, wherein: the content of hydrogen in the hydrogen atmosphere in the step (6) is 10-100% (v/v).

9. The ultra-small molybdenum carbide @ carbon composite material is characterized in that: prepared by the process of any one of claims 1 to 8.

10. Use of the ultra-small molybdenum carbide @ carbon composite of claim 9 as a catalyst and support in alkali metal ion batteries and lithium sulfur batteries.

Technical Field

The invention belongs to the technical field of nano composite materials, and particularly relates to an ultra-small molybdenum carbide @ carbon composite material as well as a preparation method and application thereof.

Background

When the elemental sulfur is used as the anode material of the lithium-sulfur battery, the elemental sulfur has very high theoretical specific capacity (1675mAh g)^-1) And theoretical specific energy (2600Wh kg)^-1) It is considered to be one of the best choices for the next-generation high energy density secondary battery. However, the lithium-sulfur battery cathode material still faces many challenges in commercialization, such as: 1) s₈And Li₂S has low conductivity. S₈And its discharge product Li₂S pair of electrons and Li⁺Are all insulating, which limits the redox kinetics on the positive side. This results in low sulfur utilization and ultimately low specific capacity. 2) Dissolution and shuttling effects of intermediate polysulfides (LiPSs). The intermediate LiPSs produced during cycling readily dissolved into the electrolyte and then shuttled from the positive to the negative side. This results in low coulombic efficiency and severe capacity fade. 3) From S₈To Li₂Volume expansion during lithiation of S. In view of S₈(2.07g cm^-3) And Li₂S(1.66g cm^-3) Of different density, S₈A large volume expansion of about 80% is experienced upon full lithiation. This may cause pulverization of the electrode after repeated volume changes of the positive electrode during cycling, resulting in poor cycle performance. In order to solve the above problems, it is imperative to improve the conductivity of elemental sulfur and suppress the shuttle effect in the electrode reaction. The ideal sulfur positive electrode matrix should satisfy the following preconditions: 1) high electronic and ionic conductivity; 2) high specific surface area and large pore volume to accommodate sulfur and LiPS; 3) optimal affinity for LiPS, since too weak anchoring leads to severe shuttling effects, while too strong binding leads to slow diffusion processes of LiPSs; 4) abundant catalytic active centers to accelerate redox kinetics.

The porous carbon material with a specific topological structure is constructed, so that the porous carbon material with a specific topological structure is a common method for improving poor conductivity and relieving volume effect by utilizing good conductivity, large specific surface area and adjustable porous structure, such as one-dimensional Carbon Nanotubes (CNTs) or Carbon Nanowires (CNFs), two-dimensional graphene or carbon nanosheets, three-dimensional porous carbon materials and the like. However, the nonpolar surface of these materials and the polar polysulfidesThe interaction is weak, and problems of LiPSs dissolution loss and rapid capacity fading are faced when the sulfur loading is increased. To suppress the problems of low sulfur utilization and capacity fade caused by the "shuttle effect", the introduction of active substances with adsorptive or catalytic capabilities is an effective strategy. Metal carbides such as Mo, as compared to weakly adsorbing non-polar carbon materials and poorly conducting polar active substances₂The C has better conductivity, better chemical adsorption capacity to the LiPSs, can provide a binding site for reaction, and simultaneously good electron transfer can effectively catalyze the conversion of the LiPSs to a discharge terminal product and slow down the shuttle effect. By constructing the molybdenum carbide @ carbon composite integrated electrode with an optimized structure, the synergistic promotion effect of all materials can be comprehensively exerted, the electrochemical performance and the cycling stability are effectively improved, and the service life of the battery is prolonged. Currently, the preparation methods of molybdenum carbide generally comprise the following steps: 1. temperature programmed reaction method, namely, molybdenum oxide precursor is added into light hydrocarbon or light hydrocarbon/H₂The mixed gas is heated and carbonized. The method is simple and easy to regulate, and the product is purer, but the method is easy to cause the surface area of the catalyst to be carbonized, and the specific surface area of the obtained molybdenum carbide is smaller; 2. the method comprises the following steps of (1) carrying out a carbothermic reduction method, wherein molybdenum oxide and a proper amount of carbon carriers react in a protective atmosphere or a reducing atmosphere, and the obtained product has a large specific surface area, but the reaction temperature is usually high; 3. a solvent thermal reduction method, which adopts a substance (KBH) with strong reducing power₄) The method is simple and easy to control, the temperature is low, but the product is impure; 4. the metal precursor cracking method is prepared by using a metal organic compound and a mixture of ammonium molybdate and hexamethylenetetramine for high-temperature cracking, but the precursor is complex to prepare, and the prepared particles are large. In addition, there are reports of CVD, hydrothermal method, ultrasonic method, microwave method, etc., but these methods also have problems of small yield, insufficient reaction, large product particles, and impure product. The above methods have limitations and inherent characteristics and have great disadvantages in practical applications, particularly in mass production of catalysts.

Disclosure of Invention

In order to solve the technical problems, the invention provides an ultra-small molybdenum carbide @ carbon composite material and a preparation method and application thereof.

The invention provides an effective, controllable, low-cost and environment-friendly modification method, which can overcome the defects in the prior art. The ultra-small molybdenum carbide @ carbon composite material prepared by the method has the characteristics of high purity, small particles and regular and uniform appearance, and shows excellent electrochemical performance when assembled into a lithium-sulfur battery. The invention prepares the nano composite material which simultaneously has the characteristics of carbon composite, high specific surface area, large pore volume, ultra-small particles, uniform distribution and the like by a hard template method. The existence of the carbon skeleton can prevent the molybdenum carbide from being enlarged in particles in the preparation process and increase catalytic active sites; the conductivity of the electrode material can also be enhanced, thereby improving the electrochemical performance of the lithium sulfur battery. The ultra-small molybdenum carbide @ carbon composite material prepared by the method has the advantages of a multi-stage structure, and the specific surface area and the pore volume are effectively increased; the conductive material has good conductivity, has good chemical adsorption capacity on LiPSs, can provide a binding site for reaction, and simultaneously has good electron transfer, so that the conversion of the conductive material to a discharge terminal product can be effectively catalyzed, and the shuttle effect is slowed down. Based on the synergistic effect, the method has important significance for improving the electrochemical performance of the lithium-sulfur battery.

The technical scheme provided by the invention is as follows:

in a first aspect, the invention provides a preparation method of an ultra-small molybdenum carbide @ carbon composite material, which comprises the following steps:

(1) adding tetraethyl orthosilicate (TEOS) into an acidic solution containing the amphiphilic block copolymer, stirring in a water bath, reacting, and filtering;

(2) filtering the filtrate obtained in the step (1) and keeping part of mother liquor for hydrothermal aging, and then filtering and drying;

(3) adding concentrated nitric acid and hydrogen peroxide into the product obtained in the step (2), stirring in a water bath to react completely, adding distilled water to dilute the mixed solution, performing suction filtration, and performing water washing, suction filtration and drying to obtain a silicon dioxide template;

(4) adding a carbon source into the silica template, fully mixing, and preserving heat to fully polymerize the carbon source to obtain a polymer @ silica template;

(5) dissolving a molybdenum source in water, adding a polymer @ silicon dioxide template, continuing stirring at room temperature, and evaporating the solvent until the solvent is completely dried to obtain a precursor;

(6) transferring the precursor to calcine in hydrogen atmosphere; after calcining, cooling to room temperature, and taking out a product;

(7) removing the silicon dioxide template in the product obtained in the step (6), and freeze-drying to obtain the final ultra-small molybdenum carbide @ carbon composite material named Mo₂[email protected]。

Further, the amphiphilic block copolymer contained in the step (1) comprises P123, F127 and F108.

Further, the water bath temperature in the step (1) is 35-38 ℃, and the stirring reaction time is 2-4 h.

Further, the silica template in the step (3) comprises SBA-15-OH, KIT-6-OH, MCF-OH, FDU-12-OH, SBA-16-OH and P-SBA-15-OH.

Further, in the step (3), the concentration of hydrogen peroxide is 40 wt%, the water bath reaction temperature is 80 ℃, and the reaction time is 3 hours.

Further, in the step (3), the usage ratio of the product in the step (2), the concentrated nitric acid and the hydrogen peroxide is as follows: 1.0g, 15mL, 5 mL; the water bath temperature is 80 ℃, and the reaction time is 3 h.

Further, in the step (4), the carbon source is selected from furfuryl alcohol, phenolic resin, 2-thiophenemethanol, tryptophan, cysteine, tyrosine and dopamine.

Further, when the carbon source is used in the step (4), different solvents should be selected according to different properties. Preferably, when furfuryl alcohol is used as a carbon source, Trimethylbenzene (TMB) is selected as a solvent and oxalic acid is selected as a catalyst for promoting polymerization; selecting ethanol as a solvent when phenolic resin and 2-thiophene methanol are used as carbon sources; when tryptophan, cysteine, tyrosine and dopamine are used as carbon sources, distilled water is selected as a solvent.

Further, the polymerization temperature of the polymer @ silica template in said step (4) is from room temperature to 130 ℃.

Further, in the step (5), the molybdenum source is phosphomolybdic acid, molybdenum acetylacetonate, ammonium molybdate or sodium molybdate.

Further, in the step (6), when calcining is carried out in a hydrogen atmosphere, the temperature is raised from room temperature to 700-900 ℃ at the temperature raising speed of 1-10 ℃/min, and the temperature is kept for 2-7 h.

Further, in the step (6), when the reduction is performed in a hydrogen atmosphere, the hydrogen content is 10-100% (v/v).

Further, in the step (7), 5 to 20 wt% of HF or 0.2 to 2.0mol/L of NaOH solution is used for removing the silica template.

Further, in the step (7), the final product is obtained by freeze drying for 12-48 hours at the temperature of-45 to-85 ℃.

In a second aspect, the present invention provides an ultra-small molybdenum carbide @ carbon composite prepared by the method of the first aspect.

In a third aspect, the present invention provides the use of the ultra-small molybdenum carbide @ carbon composite of the second aspect as a catalyst and support in alkali metal ion batteries and lithium sulfur batteries.

The invention has the beneficial effects that:

1) the present invention mainly utilizes silica (such as: the pore channel in the template of SBA-15) is a micro-reactor, a certain amount of carbon source is filled into the pore channel in advance and polymerized, and then the molybdenum source is filled into the pore channel. During the temperature programming, the polymer gradually carbonizes and ultra-small molybdenum carbide nanoparticles are generated in situ due to the reduction of hydrogen.

2) According to the invention, the electronic structure of the molybdenum carbide @ carbon composite material can be regulated and controlled by using carbon sources with different heteroatoms, so that the adsorption and catalysis effects of molybdenum carbide on polysulfide are improved.

3) The method can prepare the molybdenum carbide in the hydrogen atmosphere, so that the preparation process is simpler, safer and more environment-friendly.

4) The invention is also suitable for different types of mesoporous silica templates, such as SBA-15-OH, KIT-6-OH, MCF-OH, FDU-12-OH, SBA-16-OH and P-SBA-15-OH.

5) The material prepared by the invention shows excellent cycling stability and higher specific capacity in the aspect of electrochemical performance.

6) The material prepared by the invention has a high specific surface, large pore volume and uniform pore channel structure, wherein the size of the generated molybdenum carbide nano particles is uniform and the distribution is uniform due to the limitation of the pore channels.

7) The invention has the advantages of environmental protection, low cost, high safety, high yield and the like in the preparation process.

Drawings

FIG. 1 is a TEM, HRTEM, and particle size distribution plot of ultra-small molybdenum carbide @ carbon composite.

Figure 2 is an XRD pattern of ultra-small molybdenum carbide @ carbon composite.

FIG. 3 shows that when the ultra-small molybdenum carbide @ carbon composite material is applied to a lithium-sulfur battery, the composite material is 1.0Ag^-1Current density of (a).

Detailed Description

The following further describes the specific implementation steps of the present invention with reference to the drawings, and the present invention is not limited thereto at all.

Taking an SBA-15 template as an example, the main steps are as follows:

1. preparation of Polymer @ SBA-15 template:

1) 20.0g of the block copolymer P123 was added to a mixed solution containing 650mL of distilled water and 100mL of 37 wt% hydrochloric acid, and stirred in a water bath at 35 to 38 ℃ for 2 hours. After P123 had dissolved sufficiently, 41.6g of tetraethyl orthosilicate (TEOS) were added to the solution and stirring was continued for 24h, with a speed of 500 rpm. And after stirring, carrying out suction filtration on the solution, transferring the solution into a 500mL polytetrafluoroethylene hydrothermal kettle, and carrying out hydrothermal treatment for 24-48 h at the temperature of 90-130 ℃ in a blast drying oven. And (3) cooling the hydrothermal kettle to room temperature, carrying out suction filtration on the aged SBA-15 template by using a Buchner funnel, drying in a forced air drying oven at 50-80 ℃, and then keeping for later use.

2) And (2) taking 8.0g of the product dried in the step 2), putting the product into a 1L round-bottom flask, adding 120mL of concentrated nitric acid and 40mL of 40 wt% hydrogen peroxide, stirring in a water bath at 80 ℃ for 3 hours, adding distilled water, diluting, performing suction filtration, continuously washing with water, performing suction filtration, drying at 50-80 ℃ to obtain an SBA-15 template (named as SBA-15-OH) with a surface rich in-OH, and then reserving for later use.

3) 5.0mL of Trimethylbenzene (TMB) and 5.0mL of Furfuryl Alcohol (FA) were pipetted using a pipette and 25.0mg of oxalic acid was added to make a 50% (v/v) furfuryl alcohol solution.

4) Putting 0.5g of SBA-15-OH dried in the step 3) into a 20mL glass bottle by using an electronic balance scale, then adding 0.337-2.211 mL of 50% (v/v) furfuryl alcohol solution into the bottle, manually stirring for 10-20 min until the solution and the SBA-15-OH template are fully mixed, sealing the glass bottle, putting the glass bottle into a forced air drying oven, preserving the heat at 50 ℃ for 1 day, and then regulating the temperature to 90 ℃ and preserving the heat for 2 days to obtain the polymer @ SBA-15 template.

2. Preparing an ultra-small molybdenum carbide @ carbon composite material: and filling a molybdenum source into the polymer @ SBA-15 template, and filling a precursor into pore channels of the template through a solvent volatilization process. And then reducing the mixture by high-temperature hydrogen to obtain the ultra-small molybdenum carbide @ carbon composite material.

3. Removing the silicon dioxide template by taking a certain amount of 5-20 wt% of HF or 0.2-2.0 mol/L NaOH solution, and then putting the silicon dioxide template into a freeze dryer for freeze drying to obtain the final ultra-small molybdenum carbide @ carbon composite material.

Example 1

1) Preparation of Polymer @ SBA-15 template: and (2) putting 0.5g of the dried SBA-15-OH template into a 20mL glass bottle by using an electronic balance scale, then adding 0.337mL of 50% (v/v) furfuryl alcohol solution into the bottle, manually stirring for 10min until the solution and the SBA-15-OH template are fully mixed, sealing the glass bottle, putting the glass bottle into a forced air drying oven, preserving the temperature for 1 day at 50 ℃, and then adjusting the temperature to 90 ℃ and preserving the temperature for 2 days to obtain the polymer @ SBA-15 template.

2) Preparing an ultra-small molybdenum carbide @ carbon composite material: 0.7556g of phosphomolybdic acid is added into a beaker (50mL) containing 10mL of water, magnetic stirring is carried out at room temperature, after full dissolution and dispersion, 1.0g of polymer @ SBA-15 template is added, stirring is carried out for 2h, and the mixture is transferred to an air drying oven at 80 ℃ to be stirred until all water is volatilized. The obtained powder precursor is transferred to a tube furnace and calcined for 2h at the temperature of 700 ℃ and at the speed of 2 ℃/min under the atmosphere of 20 percent (v/v) hydrogen. And (3) removing the silicon dioxide template by taking 40mL of 5 wt% HF, and then putting the silicon dioxide template into a freeze dryer at the temperature of-85 ℃ for freeze drying for 24 hours to obtain the final ultra-small molybdenum carbide @ carbon composite material. As shown in FIGS. 1 and 2, the obtained ultra-small nickel phosphide nanoparticles are uniformly distributed on a carbon skeleton, and the average particle size of the ultra-small nickel phosphide nanoparticles is about 2.0 nm.

Example 2

0.7556g of molybdenum acetylacetonate was added to a beaker (50mL) containing 20mL of water, and magnetic stirring was carried out at room temperature, after sufficient dissolution and dispersion, 1.0g of the polymer @ SBA-15 template prepared in step (1) of example 1 was added, and stirring was carried out for 2 hours, and the mixture was transferred to an air-blast drying oven at 80 ℃ and stirred until all the water was evaporated. And transferring the obtained powder precursor into a constant-temperature tube furnace, and calcining for 2h at 800 ℃ at 5 ℃/min under the atmosphere of 10% (v/v) hydrogen. And (3) removing the silicon dioxide template by taking 80mL of 0.5mol/L NaOH solution, and then putting the silicon dioxide template into a freeze dryer at the temperature of-85 ℃ for freeze drying for 24 hours to obtain the final ultra-small molybdenum carbide @ carbon composite material.

Example 3

MCF-OH is used as a template to prepare the ultra-small molybdenum carbide @ carbon composite material.

1) Preparation of polymer @ MCF template: putting 0.5g of the dried MCF-OH template into a 20mL glass bottle by using an electronic balance, then adding 0.674mL of 50% (v/v) furfuryl alcohol solution into the bottle, manually stirring for 15min until the solution and the MCF-OH template are fully mixed, sealing the glass bottle, putting the glass bottle into a forced air drying oven, preserving the temperature at 50 ℃ for 1 day, and then regulating the temperature to 90 ℃ for 2 days to obtain the polymer @ MCF template.

2) Preparing an ultra-small molybdenum carbide @ carbon composite material: 0.7846g of phosphomolybdic acid was added to a beaker (50mL) containing 10mL of water, magnetic stirring was carried out at room temperature, after sufficient dissolution and dispersion, 1.0g of polymer @ MCF template was added, stirring was carried out for 2h, and the mixture was transferred to an air-blown dry box at 80 ℃ and stirred until all the water was evaporated. And putting the obtained powder precursor into a constant-temperature tubular furnace, and calcining for 2h at the temperature of 700 ℃ and at the speed of 2 ℃/min under the atmosphere of 10% (v/v) hydrogen. And (3) removing the silicon dioxide template by taking 40mL of 5 wt% HF, and then putting the silicon dioxide template into a freeze dryer at the temperature of-85 ℃ for freeze drying for 24 hours to obtain the final ultra-small molybdenum carbide @ carbon composite material.

Application example 1

The prepared ultra-small molybdenum carbide @ carbon composite material is used for preparing a CR2025 button type potassium ion battery, electrochemical performance tests are carried out, such as testing the cycle life, the coulombic efficiency, the alternating current impedance and the like of the battery under different current densities, and the reason for the excellent electrochemical performance is analyzed. The preparation method comprises the following steps:

1) mixing a molybdenum carbide @ carbon composite material and sulfur powder in a mass fraction of 3: 7 in a mass ratio. Then transferring the mixture into a constant-temperature tube furnace, keeping the temperature of 155 ℃ for 12h under the argon atmosphere, melting and pouring the elemental sulfur into the pore channel of the molybdenum carbide @ carbon composite material to obtain S @ Mo₂C @ C composite.

2) Uniformly mixing an active substance, acetylene black and 5% by mass of polytetrafluoroethylene aqueous dispersion emulsion together to obtain a mixture; dropwise adding N-methyl pyrrolidone into the mixture to obtain a mixture for coating;

the active substance in the step 2) is S @ Mo prepared in the step 1)₂C @ C composite;

the mass fraction of active substances in the mixture in the step 2) is 70%, the mass fraction of acetylene black is 20%, and the mass fraction of polytetrafluoroethylene is 10%;

the mass ratio of the volume of the N-methylpyrrolidone to the active substance in the step 1) is (1-2 mL): (5-10 mg);

3) uniformly coating the mixture for coating obtained in the step 2) on an aluminum foil with the diameter of 14mm, and then carrying out vacuum drying at the temperature of 60 ℃ for 12h to obtain a pole piece with the surface containing active substances; obtaining the mass of the active substance on the pole piece by using a difference method;

4) and transferring the pole piece with the surface containing the active substances into a vacuum glove box to complete the assembly of the button cell, wherein the PP diaphragm is a cell diaphragm, the lithium piece is a counter electrode, the pole piece with the surface containing the active substances is a working electrode, assembling the working electrode, the diaphragm, the counter electrode, a gasket and a cell shell into the CR2025 button cell in the glove box, sealing the button cell by using a sealing machine, and finally standing the prepared button cell at room temperature for 12h to activate the cell, thus completing the preparation of the CR2025 button cell.

FIG. 3 shows a lithium-sulfur battery at 1.0A g, prepared by applying example 1^-1Long cycle life test plots at current density. As shown in FIG. 3, when the ultra-small molybdenum carbide @ carbon composite material is applied to a lithium-sulfur battery, the current density is 1.0A g^-1When the material is circulated for 100 circles, the reversible specific capacity is still maintained at 760mAh g^-1And the composite material shows high reversible specific capacity and excellent rate performance and cycling stability.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made by those skilled in the art within the technical scope of the present invention should be included in the scope of the present invention.