Molybdenum Phosphide-Molybdenum Sulfide / Graphene Composite Material, Microwave Ultra-Fast Preparation and Electrochemical Application

Abstract

A molybdenum phosphide-molybdenum sulfide / graphene composite material, microwave ultra-fast preparation and electrochemical application. The composite material includes reduced graphene oxide, and molybdenum phosphide-molybdenum sulfide is formed on the surface of the reduced graphene oxide. The solid-phase microwave preparation method utilizes the microwave absorption ability of the reduced graphene oxide, enabling molybdenum sulfide to absorb microwave energy in a short time to generate heat and reach a high temperature. At the same time, the precursor containing phosphorus element is thermally decomposed to partially phosphorize molybdenum sulfide. A molybdenum phosphide-molybdenum sulfide composite structure is formed on the surface of the reduced graphene oxide, realizing ultra-fast and low-energy consumption preparation. The molybdenum phosphide-molybdenum sulfide / graphene composite material, when applied as a modification layer or a cathode additive to a lithium-sulfur battery, exhibits excellent electrochemical performance. Compared with traditional hydrothermal synthesis and high-temperature calcination methods, it has been greatly improved in terms of convenience, simplicity, and economy.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage materials, and specifically relates to a molybdenum phosphide-molybdenum sulfide / graphene composite material, microwave ultra-fast preparation and electrochemical application. Background Art

[0002] Compared to traditional lithium-ion batteries, lithium-sulfur batteries (LiS) have become a candidate for the next generation of new energy batteries due to their higher capacity and energy density. However, the insulating properties of elemental sulfur, the volume expansion of the sulfur cathode during charge and discharge, and the shuttle effect of polysulfides have hindered the development and application of LiS batteries. The shuttle effect of polysulfides and the slow "liquid-solid" redox reaction kinetics cause the battery capacity to decay rapidly, shortening the service life of LiS batteries.

[0003] To address the shuttling effect of polysulfides, metal compounds that accelerate redox kinetics have been widely studied. Molybdenum sulfide (MS) exhibits rapid lithium ion diffusion on its surface and exhibits favorable polar reactions with polysulfides. However, its poor conductivity leads to slow redox kinetics. Furthermore, MS exhibits volume expansion during charge and discharge, all of which limit its application in lithium-sulfur batteries. Recent research indicates that MS has excellent conductivity, strong chemical adsorption to polysulfides, and can accelerate the reaction kinetics of the active sulfur species to lithium sulfide.

[0004] The common preparation method of molybdenum phosphide materials (Journal of Energy Chemistry 72(2022)479–486, Journal of Membrane Scienace 642(2022)120003, Chemical Engineering Journal 431(2022)133923) is to use high-temperature heat treatment in a tubular furnace, thermally decompose the precursor upstream, and phosphate other metal compounds downstream. This method has the disadvantages of high energy consumption, long time consumption, and high requirements for experimental equipment. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a molybdenum phosphide-molybdenum sulfide / graphene composite material, microwave ultra-fast preparation and electrochemical application. The molybdenum phosphide-molybdenum sulfide / graphene composite material can be applied as a modification layer and positive electrode additive to lithium-sulfur batteries to exhibit excellent electrochemical performance; at the same time, it can achieve ultra-fast and low-energy preparation of the molybdenum phosphide-molybdenum sulfide / graphene composite material, which has greatly improved convenience, simplicity and economy compared with traditional hydrothermal synthesis and high-temperature calcination methods.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A molybdenum phosphide-molybdenum sulfide / graphene composite material, including reduced graphene oxide, on the surface of which molybdenum phosphide-molybdenum sulfide is in-situ generated.

[0008] A microwave ultra-fast preparation method of a molybdenum phosphide-molybdenum sulfide / graphene composite material, by using the microwave absorption ability of reduced graphene oxide, enabling molybdenum sulfide to absorb microwave energy within 50 - 100 s to generate heat reaching above 400 °C, and the precursor containing phosphorus element is thermally decomposed to partially phosphide molybdenum sulfide; a molybdenum phosphide-molybdenum sulfide composite structure is in-situ generated on the surface of reduced graphene oxide.

[0009] The microwave ultra-fast preparation method of the described molybdenum phosphide-molybdenum sulfide / graphene composite material includes the following steps:

[0010] S1. Disperse reduced graphene oxide powder and ammonium tetrathiomolybdate powder in ethanol and deionized water with the same volume respectively. After ultrasonic treatment and stirring, obtain the corresponding dispersions.

[0011] S2. Add the ammonium tetrathiomolybdate dispersion prepared in step S1 to the reduced graphene oxide dispersion, stir and heat, and then dry to obtain powder.

[0012] S3. Perform heat treatment on the powder prepared in step S2, and thermally decompose to obtain molybdenum sulfide-graphene powder.

[0013] S4. Grind reduced graphene oxide powder and sodium hypophosphite powder evenly, and perform tabletting treatment to obtain a precursor tablet.

[0014] S5. Perform argon-sealed microwave radiation treatment on the precursor tablet prepared in step S4 and the molybdenum sulfide-graphene powder prepared in step S3. The sodium hypophosphite in the precursor tablet thermally decomposes to produce phosphine gas, which reacts with molybdenum sulfide to in-situ generate a molybdenum sulfide-molybdenum phosphide composite structure on the reduced graphene oxide sheet layer, obtaining the molybdenum phosphide-molybdenum sulfide / graphene composite material.

[0015] In step S1, the mass ratio of reduced graphene oxide powder to ammonium tetrathiomolybdate powder is 1:(1 - 3); the reduced graphene oxide powder uses graphene prepared by chemical method, that is, few-layer graphene is selected; the mass concentration of the reduced graphene oxide powder dispersion is 2 - 4 mg / mL -1 , and the mass concentration of the ammonium tetrathiomolybdate powder dispersion is 4 - 6 mg / mL -1 ; the ultrasonic time is 1 - 2 h.

[0016] In step S2, stir, heat and dry the mixture of ammonium tetrathiomolybdate and reduced graphene oxide at 65 - 85 °C.

[0017] In step S3, the powder obtained in step S2 is put into a tube furnace for heat treatment for 1 - 2 h; the heat treatment temperature is 600 - 700 °C, and a hydrogen-argon mixed gas is introduced into the tube furnace.

[0018] In step S4, the mass ratio of the reduced graphene oxide powder to the sodium hypophosphite powder is 1:(7.5 - 10).

[0019] In step S5, the mass ratio of the molybdenum sulfide-graphene powder prepared in step S3 to the precursor sheet prepared in step S4 is (5 - 6):(8.5 - 11); the two are encapsulated in a protective gas atmosphere for microwave radiation treatment; the protective atmosphere is nitrogen or argon; the power of the microwave treatment is 600 W - 800 W, the reaction time is 50 - 100 s, and the reaction temperature is above 400 °C.

[0020] The electrochemical application of the molybdenum phosphide-molybdenum sulfide / graphene composite material, as a separator modification layer or a cathode additive of a lithium-sulfur battery, can improve the adsorption capacity for polysulfides, accelerate the reaction kinetics, and improve the battery cycle life.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] After simple pretreatment steps such as liquid-phase mixing, heat treatment, and tablet pressing in the preparation method of the present invention, through the action of microwave radiation, the molybdenum phosphide-molybdenum sulfide / graphene composite material can be efficiently and rapidly prepared. The preparation process is simple in operation and short in time consumption, and conforms to the principle of green chemistry; the prepared molybdenum phosphide-molybdenum sulfide / graphene composite material realizes the in-situ generation of a nanoscale molybdenum phosphide-molybdenum sulfide composite structure on the reduced graphene oxide sheet, with simple operation, short time consumption, energy conservation and environmental protection, and is conducive to future large-scale commercial production; the prepared molybdenum phosphide-molybdenum sulfide / graphene composite material can be applied to the separator modification layer and the cathode additive of a lithium-sulfur battery, which can improve the adsorption capacity and catalytic capacity for polysulfides, thereby inhibiting the shuttle effect of polysulfides, accelerating the reaction kinetics, and greatly improving the cycle life of the lithium-sulfur battery.

[0023] The preparation method of the present invention controls the mass ratio of the reduced graphene oxide powder to the ammonium tetrathiomolybdate powder at 1:(1 - 3), ensuring that the composite material has good electrical conductivity and catalytic performance.

[0024] The reduced graphene oxide powder used in the preparation method of the present invention selects few-layer graphene and is dispersed in the mixed solution, making the in-situ growth of molybdenum sulfide on the graphene surface more uniform.

[0025] The preparation method of the present invention heats and stirs the mixed solution of ammonium tetrathiomolybdate and graphene at 65 - 85 °C to accelerate the solvent volatilization.

[0026] The preparation method of the present invention places the dried sodium tetrathiomolybdate and graphene powder in a tube furnace for heat treatment at 600 - 700 °C for 1 - 2 h, and introduces a hydrogen-argon mixed gas into the tube furnace to ensure that the prepared powder is a molybdenum sulfide / graphene material.

[0027] In the preparation method of the present invention, the mass of the precursor sheet is 85 - 110 mg, and the diameter size is 10 - 12.7 mm, so that the precursor sheet can be fully compounded with graphene to construct a wave absorption and heat conduction network, and make sodium hypophosphite decompose fully.

[0028] In the preparation method of the present invention, the pressure of tablet pressing treatment is less than or equal to 6 MPa, and the time is less than or equal to 1 minute. On the basis of maintaining a stable shape, it ensures the construction of a heat conduction network and leaves sufficient overflow channels for gas.

[0029] In the preparation method of the present invention, the dried powder and the precursor sheet are encapsulated in a quartz glass bottle filled with a protective gas atmosphere to prevent molybdenum sulfide from being oxidized at high temperatures.

[0030] In the preparation method of the present invention, the power of microwave treatment is 600 W - 800 W, the reaction time is 50 - 100 s, and the reaction temperature is above 400 °C to ensure that the precursor material can decompose fully.

[0031] The preparation method of the present invention uses solid-phase microwave technology to prepare a molybdenum phosphide-molybdenum sulfide / graphene composite material with excellent adsorption and catalytic capabilities for polysulfides. Applying this material to the separator modification layer or the cathode additive of a lithium-sulfur battery can greatly improve the battery capacity and cycle life.

[0032] In summary, compared with the traditional tube furnace high-temperature heat treatment method, the preparation process of the present invention has the advantages of simple operation, fast speed, high efficiency, energy conservation and environmental protection while achieving the ultra-fast preparation of composite materials. Brief Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the preparation method of the embodiment of the present invention.

[0034] Figure 2 It is an X-ray diffraction (XRD) spectrum of the molybdenum phosphide-molybdenum sulfide / graphene composite material prepared in Example 1 of the present invention.

[0035] Figure 3 It is a Raman spectrum of the molybdenum phosphide-molybdenum sulfide / graphene composite material prepared in Example 1 of the present invention.

[0036] Figure 4 It is a scanning electron microscope image of the molybdenum phosphide-molybdenum sulfide / graphene composite material prepared in Example 1 of the present invention.

[0037] Figure 5TEM image of the molybdenum phosphide-molybdenum sulfide / graphene composite prepared in Example 1 of the present invention.

[0038] Figure 6 TGA curve of the molybdenum phosphide-molybdenum sulfide / graphene composite prepared in Example 1 of the present invention.

[0039] Figure 7 Cycling performance graph of the lithium-sulfur battery assembled with the separator modified by the molybdenum phosphide-molybdenum sulfide / graphene composite prepared in Example 1 of the present invention at a current of 0.2C.

[0040] Figure 8 Cycling performance graph of the lithium-sulfur battery assembled with the molybdenum phosphide-molybdenum sulfide / graphene composite as a cathode additive prepared in Example 1 of the present invention at a current of 0.2C.

[0041] Figure 9 Cyclic voltammogram of the Li2S6 symmetric battery with the molybdenum phosphide-molybdenum sulfide / graphene composite prepared in Example 1 of the present invention.

[0042] Figure 10 XRD patterns of the molybdenum phosphide-molybdenum sulfide / graphene composites prepared in Examples 3 and 4 of the present invention. Detailed implementation mode

[0043] The technical solution of the present invention will be clearly and completely described below with reference to the drawings and embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] Example 1, a microwave ultra-fast preparation method of a molybdenum phosphide-molybdenum sulfide / graphene composite, comprising the following steps:

[0045] S1. Weigh 80 mg of reduced graphene oxide and disperse it in 20 ml of ethanol, and perform ultrasonic treatment; weigh 80 mg of ammonium tetrathiomolybdate and dissolve it in 20 ml of deionized water. After ultrasonic treatment and stirring, the ultrasonic time is 1.5 h to obtain the corresponding dispersion.

[0046] S2. Add the ammonium tetrathiomolybdate dispersion prepared in step S1 to the reduced graphene oxide dispersion with a dropper, stir and heat at 65 °C, and dry to obtain a powder.

[0047] S3. Put the powder prepared in step S2 into a tube furnace and perform heat treatment at 700 °C for 1 h to thermally decompose and obtain molybdenum sulfide-graphene powder.

[0048] S4. Grind 10 mg of reduced graphene oxide powder and 75 mg of sodium hypophosphite powder evenly, and perform tablet pressing to obtain a precursor tablet with a mass of 85 mg and a diameter of 10 mm; the pressure for tablet pressing is 6 MPa and the time is 1 minute.

[0049] S5. Take 50 mg of the molybdenum sulfide-graphene powder prepared in step S3, encapsulate it with the precursor tablet prepared in step S4 in a quartz glass bottle filled with a protective gas atmosphere, and then place it in a microwave synthesizer for microwave radiation treatment. As Figure 1 shown, the microwave power is 600 W, the time is 90 s, and the protective atmosphere is nitrogen; the sodium hypophosphite in the precursor tablet thermally decomposes to produce phosphine gas, which reacts with molybdenum sulfide. The reaction temperature is above 400 °C, and a molybdenum sulfide-molybdenum phosphide composite structure is in-situ generated on the reduced graphene oxide sheet layer to obtain a molybdenum phosphide-molybdenum sulfide / graphene composite material.

[0050] Experimental characterization 1: Take 16 mg of the molybdenum phosphide-molybdenum sulfide / graphene powder prepared in Example 1, and then add reduced graphene oxide / molybdenum sulfide powder, Cabot carbon black, and binder (PVDF) according to a ratio of 5:1, make a slurry, and then filter or coat it on a commercial polypropylene separator, and dry it to make a modified separator.

[0051] Assemble a lithium-sulfur full cell: Stack the composite sulfur positive electrode sheet, the modified separator, and the lithium sheet in sequence, add 45 μL of electrolyte, seal it, and let it stand for 10 h.

[0052] Electrochemical test: Use a Blue Power battery test system to test the cycling performance of the battery at a current of 0.2 C (1 C = 1675 mAh g -1 ).

[0053] Experimental characterization 2: Take 112 mg of sulfur-carbon composite material, 16 mg of the molybdenum phosphide-molybdenum sulfide / graphene powder prepared in Example 1, Cabot carbon black, and binder (PVDF), and then make a slurry according to a ratio of 7:1:1:1 and coat it on a carbon-coated aluminum foil to prepare a sulfur-carbon composite positive electrode.

[0054] Assemble a lithium-sulfur full cell: Stack the composite sulfur positive electrode sheet, the modified separator, and the lithium sheet in sequence, add 45 μL of electrolyte, seal it, and let it stand for 10 h.

[0055] Electrochemical test: Use a Blue Power battery test system to test the cycling performance of the battery at a current of 0.2 C (1 C = 1675 mAh g -1 ).

[0056] The molybdenum phosphide-molybdenum sulfide / graphene composite material obtained in Example 1 includes MoP-MoS2 / rGO, through Figure 2The XRD spectrum shows obvious characteristic diffraction peaks of MoP, MoS2 and rGO, indicating that the composite material was successfully prepared by microwave.

[0057] The molybdenum phosphide-molybdenum sulfide / graphene composite material obtained in Example 1 includes MoP-MoS2 / rGO. Figure 3 The Raman spectrum clearly shows the characteristic peaks of rGO and MoS2.

[0058] In Example 1, the surface of the reduced graphene oxide sheet is attached with MoP-MoS2 composite material and the scale is at the nanometer level. Figure 4 Scanning electron microscopy and Figure 5 Transmission electron microscopy can reveal the presence and size of the composite material.

[0059] The content of the molybdenum phosphide-molybdenum sulfide / graphene composite material in Example 1 is determined by Figure 6 The thermogravimetric curve was confirmed.

[0060] In Example 1, the lithium-sulfur battery using the molybdenum phosphide-molybdenum sulfide / graphene composite material as the modified layer and after adding it to the positive electrode side showed a high initial specific capacity and excellent cycle stability, such as Figure 7 , as shown in the test results of 8.

[0061] In Example 1, the symmetrical battery assembled using the molybdenum phosphide-molybdenum sulfide / graphene composite material has an obvious left shift in the oxidation peak and an obvious right shift in the reduction peak, which indicates that the molybdenum phosphide-molybdenum sulfide / graphene composite material accelerates the conversion process of polysulfides, reduces the polarization of the battery, and exhibits a good catalytic effect. Figure 9 shown.

[0062] Example 2, a microwave ultrafast preparation method for a molybdenum phosphide-molybdenum sulfide / graphene composite material, wherein the ultrasonic time in step S1 of Example 1 is changed to 1 h; the stirring and heating temperature in step S2 is changed to 70°C; the temperature and time of the heat treatment in step S3 are changed to 600°C and 2 h, respectively; the microwave power in step S5 is changed to 700 W and the time is changed to 70 s; the rest are the same as in Example 1.

[0063] Beneficial effects of this embodiment: Adjusting the temperature and microwaves will not have much impact on the experimental results, refer to the results of Example 1.

[0064] Example 3. A method for the microwave ultra-fast preparation of molybdenum phosphide-molybdenum sulfide / graphene composite materials. In this example, the reduced graphene oxide in step S1 of Example 1 is changed to 40 mg, ammonium tetrathiomolybdate is changed to 120 mg, and the ultrasonic time is changed to 2 h; the stirring and heating temperature in step S2 is changed to 75 °C; the diameter of the precursor tablet in step S4 is changed to 12.7 mm, the pressure for tablet pressing is 5 MPa, and the time is 0.5 minutes; in step S5, 60 mg of molybdenum sulfide-graphene powder is taken, the microwave power is changed to 800 W, and the time is changed to 50 s; other conditions are the same as in Example 1.

[0065] The beneficial effect of this example: By adjusting the dosages of graphene and ammonium tetrathiomolybdate, as can be seen from the XRD pattern Figure 10 in this example, as the amount of ammonium tetrathiomolybdate increases, the relative intensity of the characteristic peak of molybdenum phosphide will decrease. Since the proportion of graphene decreases, the thermal energy provided during the microwave process becomes relatively less, so the content of molybdenum phosphide also decreases.

[0066] Example 4. A method for the microwave ultra-fast preparation of molybdenum phosphide-molybdenum sulfide / graphene composite materials. In this example, the reduced graphene oxide in step S1 of Example 1 is changed to 40 mg, ammonium tetrathiomolybdate is changed to 120 mg; the stirring and heating temperature in step S2 is changed to 80 °C; the temperature and time of heat treatment in step S3 are respectively changed to 650 °C and 2 h; in step S4, 10 mg of reduced graphene oxide powder, 100 mg of sodium hypophosphite powder, and the mass of the precursor tablet is 110 mg; in step S5, the microwave power is changed to 800 W, and the time is changed to 50 s; other conditions are the same as in Example 1.

[0067] The beneficial effect of this example: Referring to Figure 10 this example, simply adjusting the temperature basically does not affect the experimental results, and the generated molybdenum phosphide-molybdenum sulfide / graphene composite material is basically the same as that in Example 3.

[0068] Example 5. A method for the microwave ultra-fast preparation of molybdenum phosphide-molybdenum sulfide / graphene composite materials. In this example, the stirring and heating temperature in step S2 of Example 1 is changed to 85 °C; in step S4, 10 mg of reduced graphene oxide powder, 100 mg of sodium hypophosphite powder, the mass of the precursor tablet is 110 mg, and the diameter is changed to 11.7 mm; in step S5, 55 mg of molybdenum sulfide-graphene powder is taken, the microwave power is changed to 600 W, and the time is changed to 100 s; other conditions are the same as in Example 1.

[0069] The beneficial effect of this example: Compared with Example 4, after the microwave power is reduced, the microwave time is correspondingly increased, referring to the results of Example 1.

[0070] Example 6. A method for the microwave ultra-fast preparation of molybdenum phosphide-molybdenum sulfide / graphene composite materials. In this example, the reduced graphene oxide in step S1 of Example 1 is changed to 40 mg, ammonium tetrathiomolybdate is changed to 80 mg; other conditions are the same as in Example 1.

[0071] Advantages of this embodiment: Similar to the results of Embodiment 1.

[0072] In summary, the molybdenum phosphide-molybdenum disulfide / graphene composite material, microwave ultra-fast preparation and electrochemical application of the present invention have the following characteristics:

[0073] (1) The preparation method of the present invention can simply, quickly and greenly realize the preparation of molybdenum phosphide-molybdenum disulfide / graphene composite materials;

[0074] (2) The molybdenum phosphide-molybdenum disulfide / graphene composite material prepared by the present invention is used as a separator modification layer or a cathode additive, and can achieve the effects of inhibiting the shuttle effect, accelerating the conversion of polysulfides, and improving the cycle stability in lithium-sulfur batteries;

[0075] (3) The preparation method of the present invention uses microwave irradiation of graphene-based materials to achieve rapid element doping, which is universal for materials that decompose thermally below 600 degrees Celsius.

[0076] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A microwave ultra-fast preparation method of a molybdenum phosphide-molybdenum sulfide / graphene composite material, characterized by: A molybdenum phosphide-molybdenum sulfide / graphene composite material comprises reduced graphene oxide, wherein molybdenum phosphide-molybdenum sulfide is formed on the surface of the reduced graphene oxide; The microwave ultra-fast preparation method comprises: utilizing the microwave absorption capability of reduced graphene oxide to cause molybdenum sulfide to absorb microwave energy within 50 to 100 seconds to generate heat reaching above 400°C, thereby thermally decomposing a precursor containing phosphorus to partially phosphate the molybdenum sulfide; and in-situ generating a molybdenum phosphide-molybdenum sulfide composite structure on the surface of the reduced graphene oxide; The microwave ultra-fast preparation method comprises the following steps: S1. Dispersing reduced graphene oxide powder and ammonium tetrathiomolybdate powder in equal volumes of ethanol and deionized water, respectively, and obtaining corresponding dispersions after ultrasonication and stirring; S2. Add the ammonium tetrathiomolybdate dispersion prepared in step S1 to the reduced graphene oxide dispersion, stir and heat, and dry to obtain a powder; S3, heat-treating the powder prepared in step S2 and thermally decomposing it to obtain molybdenum sulfide-graphene powder; S4, grinding the reduced graphene oxide powder and the sodium hypophosphite powder uniformly, and performing tableting to obtain a precursor sheet; S5. The precursor sheet prepared in step S4 and the molybdenum sulfide-graphene powder prepared in step S3 are subjected to argon-sealed microwave radiation treatment. The sodium hypophosphite in the precursor sheet is thermally decomposed to produce phosphine gas, which reacts with molybdenum sulfide to form a molybdenum sulfide-molybdenum phosphide composite structure on the reduced graphene oxide sheet, thereby obtaining a molybdenum phosphide-molybdenum sulfide / graphene composite material.

2. The microwave ultrafast preparation method according to claim 1, characterized in that: In step S1, the mass ratio of reduced graphene oxide powder to ammonium tetrathiomolybdate powder is 1:(1-3); the reduced graphene oxide powder is chemically prepared graphene, i.e., few-layer graphene; the mass concentration of the reduced graphene oxide powder dispersion is 2-4 mg mL -1 The mass concentration of ammonium tetrathiomolybdate powder dispersion is 4-6 mg mL -1 ; Ultrasound time is 1-2 h.

3. The microwave ultrafast preparation method according to claim 1, wherein: In step S2, the mixed solution of ammonium tetrathiomolybdate and reduced graphene oxide is stirred, heated and dried at 65-85°C.

4. The microwave ultrafast preparation method according to claim 1, wherein: In step S3, the powder obtained in step S2 is placed in a tube furnace for heat treatment for 1-2 hours; the heat treatment temperature is 600-700° C., and a hydrogen-argon mixed gas is introduced into the tube furnace.

5. The microwave ultrafast preparation method according to claim 1, characterized in that: In step S4, the mass ratio of the reduced graphene oxide powder to the sodium hypophosphite powder is 1:(7.5-10).

6. The microwave ultrafast preparation method according to claim 1, characterized in that: The mass ratio of the molybdenum sulfide-graphene powder prepared in step S3 to the precursor sheet prepared in step S4 is (5-6):(8.5-11); both are encapsulated in a protective gas atmosphere and subjected to microwave radiation treatment; the protective atmosphere is nitrogen or argon; the microwave treatment power is 600W~800W, the reaction time is 50~100s, and the reaction temperature is above 400°C.

7. The microwave ultrafast preparation method according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Weigh 80 mg of reduced graphene oxide and disperse it in 20 ml of ethanol, and then sonicate it. Weigh 80 mg of tetrathiomolybdate amine and dissolve it in 20 ml of deionized water, and then sonicate and stir to obtain the corresponding dispersion. S2. Add the ammonium tetrathiomolybdate dispersion prepared in step S1 to the reduced graphene oxide dispersion using a dropper, stir and heat at 65° C., and dry to obtain a powder; S3, placing the powder prepared in step S2 into a tube furnace and heat-treating it at 700° C. for 1 h to obtain molybdenum sulfide-graphene powder by thermal decomposition; S4. Grind 10 mg of reduced graphene oxide powder and 75 mg of sodium hypophosphite powder evenly, and press them into tablets to obtain precursor tablets with a diameter of 10 mm. The tableting process is performed at a pressure of 6 MPa for 1 minute. S5. Take 50 mg of the molybdenum sulfide-graphene powder prepared in step S3, and encapsulate it with 85 mg of the precursor sheet prepared in step S4 in a quartz glass bottle filled with a protective gas atmosphere, and then place it in a microwave synthesizer for microwave radiation treatment with a microwave power of 600 W for 90 s in a nitrogen protective atmosphere; the sodium hypophosphite in the precursor sheet is thermally decomposed to produce phosphine gas, which reacts with molybdenum sulfide at a reaction temperature of above 400° C. to form a molybdenum sulfide-molybdenum phosphide composite structure on the reduced graphene oxide sheet, thereby obtaining a molybdenum phosphide-molybdenum sulfide / graphene composite material.

8. Electrochemical application of the molybdenum phosphide-molybdenum sulfide / graphene composite material prepared by the method according to any one of claims 1 to 7, characterized in that: As a separator modification layer or positive electrode additive for lithium-sulfur batteries.

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