Preparation method and application of conductive dual catalyst loaded nitrogen-doped hollow carbon / sulfur composite material

Abstract

A preparation method and application of a conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material. The present invention relates to a preparation method and application field of a conductive dual-catalyst loaded nitrogen-doped hollow carbon-based composite material. The present invention aims to solve the technical problems of low utilization of electrode active substances and rapid attenuation of battery cycle capacity caused by effective inhibition of lithium polysulfide shuttle in existing sulfur positive electrode materials prepared with metal compounds / porous carbon materials as carrier materials. Method: First, a dual-metal ion chelated organic phosphorus loaded hollow precursor material is prepared; then, a void-rich dual-metal phosphide loaded nitrogen-doped hollow carbon composite material is prepared by a one-step thermal reduction treatment, and sulfur is loaded. The composite material is used as a positive electrode material in lithium-sulfur batteries. It has low cost, simple process, environmental friendliness, low energy consumption, no toxic organic reagents, mature process, and can be used for large-scale production. The composite material prepared by the present invention is used as a positive electrode material in the field of lithium-sulfur batteries.

Description

Technical Field

[0001] The invention relates to a preparation method and application field of a conductive dual-catalyst loaded nitrogen-doped hollow carbon-based composite material. Background Art

[0002] Compared to many energy storage devices, such as traditional lithium-ion batteries, lithium-sulfur (Li-S) batteries have become one of the most promising and valuable next-generation energy storage candidates due to their significantly higher theoretical energy density (2500 W·h·kg⁻¹) and lower cost. Despite these advantages, Li-S batteries present several challenges due to their inherent properties. First, the sulfur cathode in Li-S batteries undergoes a multi-step sulfur redox reaction, which produces soluble lithium polysulfides and poorly soluble lithium sulfide. The electrode reaction involves multiple solid-liquid-solid phase transitions, which require overcoming high decomposition or nucleation energy barriers. Furthermore, the high electrical insulating properties of the reactant sulfur and the discharge product lithium sulfide result in slow electron transfer during the electrode reaction, inhibiting the electrode reaction kinetics. Furthermore, the highly soluble long-chain lithium polysulfides (LiPSs) produced during the reaction dissolve and diffuse in the organic electrolyte, and undergo irreversible side reactions with the metallic lithium anode. This leads to low active material utilization and rapid cycling capacity decay, hindering their widespread commercialization.

[0003] To address the inherent drawbacks of Li-S batteries, researchers have made extensive efforts to improve electrode cycling stability. For example, the introduction of highly conductive carbon-based conductive agents can enhance the electronic conductivity of the sulfur electrode; the use of support materials with high porosity and hollow structures can mitigate the volume effect caused by the significant density difference between sulfur and lithium sulfide during charge and discharge, thereby ensuring the structural integrity of the electrode during charge and discharge; the use of highly polar metal compounds and carbon-based materials in composites enhances the adsorption capacity of LiPSs and thus suppresses the shuttle effect; and the introduction of catalysts that promote electrode conversion reactions can improve the reaction kinetics of the electrode. While these approaches have improved the electrode electrochemical rate to a certain extent, inhibited the shuttle effect of LiPSs, and improved the cycling stability and active material utilization, for redox reactions requiring electron participation, the inert polar sites inhibit electron transport, increase the diffusion steps of the active species in the electrode reaction, and thus reduce the electrode reaction kinetics. Therefore, the electronic conductivity of polar sites has a significant impact on the reaction rate during the electrode reaction. Furthermore, for multiphase and multistep reactions, phase transitions have different conversion reaction barriers, so a single catalyst has significant limitations for multiple reactions. Currently, there are relatively few reports on conductive multiple catalysts. Therefore, the development of conductive dual-catalyst loaded nitrogen-doped hollow carbon composite materials for application in lithium-sulfur batteries has important research significance and value. Summary of the Invention

[0004] The present invention aims to solve the technical problems of low utilization of electrode active substances and rapid attenuation of battery cycle capacity caused by effective inhibition of lithium polysulfide shuttle in existing sulfur positive electrode materials prepared with metal compounds / porous carbon materials as carrier materials, and provide a preparation method and application of conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite materials.

[0005] The present invention first prepares a bimetallic ion chelated organic phosphorus loaded hollow precursor material; then prepares a void-rich bimetallic phosphide loaded nitrogen-doped hollow carbon composite material through a one-step thermal reduction treatment, and loads sulfur.

[0006] A method for preparing a conductive dual-catalyst-loaded nitrogen-doped hollow carbon / sulfur composite material, characterized in that the method is specifically carried out in the following steps:

[0007] Step 1: Disperse metal salt A in methanol to obtain a clear solution A; disperse metal salt B in anhydrous ethanol to obtain a clear solution B; disperse the ligand in methanol to form a clear solution C;

[0008] Step 2: Add solution C obtained in step 1 to solution A, mix evenly, and settle at room temperature to obtain a purple precipitate, which is then washed with methanol several times and dried to obtain a purple precipitate;

[0009] Step 3: Disperse the purple precipitate prepared in step 2 in anhydrous ethanol, then add solution B prepared in step 1, mix thoroughly, centrifuge, wash, and dry to obtain a hollow bimetallic precursor material;

[0010] Step 4: Disperse the hollow bimetallic precursor material prepared in step 3 in a nitrogen source solution, add an organic phosphoric acid solution, stir to fully react, centrifuge and wash, and dry to obtain a bimetallic ion chelated organic phosphorus hollow precursor material;

[0011] Step 5: Under a reducing atmosphere, the dual metal ion chelated organophosphorus hollow precursor material obtained in step 4 is placed in a tube furnace for thermal reduction. After cooling to room temperature, a hollow carbon composite material with rich voids and dual catalyst (metal phosphide) loaded with nitrogen doping is obtained;

[0012] Step 6: Mix the sublimated sulfur with the hollow carbon composite material described in step 5, preheat the mixture in an inert atmosphere until the sulfur is in a molten liquid state for 8-24 hours, then heat the mixture to 200-300°C and heat treat the mixture for 1-3 hours to obtain the conductive dual catalyst (metal phosphide) loaded nitrogen-doped carbon hollow carrier carbon / sulfur composite material. The preparation is completed.

[0013] The present invention provides a conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material, which is prepared by two-step ion etching combined with thermal reduction. The mass fraction of elemental sulfur in the carbon composite material is 70% to 80%.

[0014] Nitrogen is introduced in situ into the carbon composite material through the decomposition of a nitrogen source. The precursor material is then decomposed and reduced at high temperature to produce a highly conductive metal phosphide. By varying the metal salt concentration, amount of organophosphoric acid, and heat treatment temperature, a range of conductive dual-catalyst-loaded nitrogen-doped carbon composites with varying microstructures can be obtained.

[0015] Currently, the most widely studied method is to use conductive carbon materials and polymetallic compound materials as carrier materials to improve conductivity while suppressing the shuttle effect. 1. Although the surface of a single carbon material has good conductivity, it is highly non-polar and cannot effectively bind lithium polysulfides. 2. Polymetallic compounds are mostly inert metal oxides / nitrides, phosphides, etc., and the preparation process is complex and uses toxic and hazardous reagents, which is not environmentally friendly. This method solves the problems of conductivity, insufficient catalytic sites, polar adsorption, and volume expansion of polymetallic compounds, and the preparation method is simple and environmentally friendly.

[0016] The conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material is used as a positive electrode in the field of Li-S batteries.

[0017] The electrolyte in the Li-S battery is lithium trifluoromethanesulfonate or lithium bis-trifluoromethanesulfonimide.

[0018] Polyvinylidene fluoride (PVDF) was added to N-methylpyrrolidone (NMP) to prepare a 10% by mass PVDF solution. A conductive dual-catalyst-loaded nitrogen-doped hollow carbon / sulfur composite, Super P, and PVDF solution were slurried in a 70:20:10 mass ratio and coated onto aluminum foil. The thickness was adjusted to 100 μm to 650 μm. The resulting electrode sheets were then dried at 60°C and cut into circular shapes using a microtome. In a vacuum glove box, button cells were assembled using lithium metal as the positive electrode and a polytetrafluoroethylene microporous membrane as the separator, and their electrochemical performance was tested.

[0019] The beneficial effects of the present invention are:

[0020] 1. A conductive dual-catalyst-loaded nitrogen-doped hollow carbon composite material was obtained as a sulfur carrier by two-step ion etching combined with organic phosphoric acid chelation and heat treatment. The preparation cost is low, the process is simple, environmentally friendly, and can be mass-produced.

[0021] 2. The conductive dual-catalyst loaded nitrogen-doped hollow carbon composite material prepared by the present invention has a hollow structure and a rich void structure, which is conducive to the storage and dispersion of a large amount of elemental sulfur and the physical barrier to the diffusion and migration of lithium polysulfide; the nitrogen-doped carbon network structure cooperates with the bimetallic phosphide with good conductivity as a dual catalyst to form a large conductive network, and carry out rapid electron transport and ion diffusion at the reaction site; the selective adsorption of LiPSs by the dual catalyst can realize a variety of LiPSs adsorption modes through Ni-S, Co-S, and Li-N sites, and can effectively anchor LiPSs; the dual catalyst selectively promotes the behavior of multi-step electrode reactions, which is conducive to improving the utilization rate of active materials and inhibiting the diffusion of LiPSs; therefore, the battery exhibits high discharge specific capacity and excellent cycle stability.

[0022] 3. The conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material prepared by the present invention has a high discharge capacity and excellent cycle stability as the sulfur positive electrode of Li-S battery. This material is used to assemble the sulfur positive electrode into a button cell, and the discharge capacity reaches 1063mAh g at a current density of 1C. -1 After 1000 cycles, the capacity decay rate per cycle is 0.04%.

[0023] The conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material prepared by the present invention is used as a sulfur positive electrode in the field of Li-S batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Lithium sulfonate was used as the electrolyte, button cells were assembled, and their long cycle performance was tested.

[0025] Figure 1 The transmission electron microscope image of the hollow bimetallic precursor material obtained in step 3 of Example 1;

[0026] Figure 2 This is a transmission electron micrograph of the double metal ion chelated organophosphorus hollow precursor material obtained in step 4 of Example 1;

[0027] Figure 3 The transmission electron microscope image of the hollow carbon material obtained in step 5 of Example 1;

[0028] Figure 4 The XRD pattern of the hollow carbon material is obtained in step 5 of Example 1;

[0029] Figure 5 The N1s spectrum of the hollow carbon material is obtained in step 5 of Example 1;

[0030] Figure 6 This is the N1s spectrum obtained after the hollow carbon material adsorbs Li2S6 in step 5 of Example 1;

[0031] Figure 7The Co 2p spectra before and after the hollow carbon material adsorbs Li2S6 are obtained in step 5 of Example 1;

[0032] Figure 8 The Ni 2p spectra before and after the hollow carbon material adsorbs Li2S6 are obtained in step 5 of Example 1;

[0033] Figure 9 The S 2p spectra of the hollow carbon material before and after adsorption of Li2S6 are obtained in step 5 of Example 1;

[0034] Figure 10 The CV graph of the conductive dual catalyst supported nitrogen-doped carbon hollow support carbon / sulfur composite material obtained in step 6 of Example 1;

[0035] Figure 11 The long cycle performance diagram of the conductive dual-catalyst loaded nitrogen-doped carbon hollow carrier carbon / sulfur composite material at 1C current density is obtained in step six of Example 1. DETAILED DESCRIPTION

[0036] Specific embodiment 1: This embodiment is a method for preparing a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material, which is specifically carried out in the following steps:

[0037] Step 1: Disperse metal salt A in methanol to obtain a clear solution A; disperse metal salt B in anhydrous ethanol to obtain a clear solution B; disperse the ligand in methanol to form a clear solution C;

[0038] Step 2: Add solution C obtained in step 1 to solution A, mix evenly, and settle at room temperature to obtain a purple precipitate, which is then washed with methanol several times and dried to obtain a purple precipitate;

[0039] Step 3: Disperse the purple precipitate prepared in step 2 in anhydrous ethanol, then add solution B prepared in step 1, mix thoroughly, centrifuge, wash, and dry to obtain a hollow bimetallic precursor material;

[0040] Step 4: Disperse the hollow bimetallic precursor material prepared in step 3 in a nitrogen source solution, add an organic phosphoric acid solution, stir to fully react, centrifuge and wash, and dry to obtain a bimetallic ion chelated organic phosphorus hollow precursor material;

[0041] Step 5: Place the dual metal ion chelated organophosphorus hollow precursor material obtained in step 4 into a tubular furnace under a reducing atmosphere for thermal reduction. After cooling to room temperature, a hollow carbon composite material with rich voids and dual catalysts loaded with nitrogen doping is obtained.

[0042] Step 6: Mix the sublimed sulfur with the hollow carbon composite material described in step 5, with a mass ratio of sublimated sulfur to hollow carbon composite material of (3-4):1. Under an inert atmosphere, preheat the mixture until the sulfur is in a molten liquid state for 8-24 hours, then heat the mixture to 200-300°C and heat treat it for 1-3 hours to obtain the conductive dual-catalyst loaded nitrogen-doped carbon hollow carrier carbon / sulfur composite material. The preparation is completed.

[0043] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the metal salt A in step 1 is a nickel salt, an iron salt or a cerium salt. Other aspects are the same as specific embodiment 1.

[0044] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that: the metal salt B in step 1 is a cobalt salt, a nickel salt, an iron salt, or a cerium salt, and the concentration of the metal salt B in solution B is 0.0001 to 0.2 g / mL. Other aspects are the same as specific embodiments 1 or 2.

[0045] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the ligand in step 1 is an imidazole organic ligand. Other aspects are the same as specific embodiments 1 to 3.

[0046] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that step 3 uses stirring and ultrasonication to fully mix, and the temperature is controlled at 25° C. Other aspects are the same as specific embodiments 1 to 4.

[0047] Specific embodiment 6: This embodiment differs from Specific embodiments 1 to 5 in that: the washing process in step 3 is performed using anhydrous ethanol under stirring and ultrasonic conditions, washing 3 to 5 times; the drying temperature is 75°C and the drying time is 8 hours. Other aspects are the same as Specific embodiments 1 to 5.

[0048] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that the nitrogen source solution in step 4 is prepared from a nitrogen source and anhydrous ethanol, wherein the nitrogen source is dicyandiamide, melamine, or polyvinylpyrrolidone; and the organophosphoric acid solution is prepared from organophosphoric acid and anhydrous ethanol, wherein the concentration of the organophosphoric acid is 0.001 to 0.05 mL / mL. Other steps are the same as those of specific embodiments 1 to 6.

[0049] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the reducing atmosphere in step 5 is pure hydrogen or a mixture of Ar and H2; the thermal reduction temperature is 650-900°C, the time is 2-6 hours, and the heating rate is 2-10°C / min. Other aspects are the same as specific embodiments 1 to 7.

[0050] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the mass ratio of sublimated sulfur to hollow carbon composite material in step 6 is (3-4): 1. Other aspects are the same as specific embodiments 1 to 8.

[0051] Specific embodiment ten; This embodiment is an application of a conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material, and the conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material is used as a positive electrode in the field of Li-S batteries.

[0052] The content of the present invention is not limited to the content of the above-mentioned embodiments. The combination of one or more specific embodiments can also achieve the purpose of the invention.

[0053] Example 1:

[0054] This embodiment provides a method for preparing a conductive dual-catalyst-supported nitrogen-doped hollow carbon / sulfur composite material, which is specifically carried out by the following steps:

[0055] Step 1: Disperse metal salt A, cobalt nitrate, in methanol to obtain a clear solution A with a concentration of 0.0291 g / mL; disperse metal salt B, nickel nitrate, in anhydrous ethanol to obtain a clear solution B with a concentration of 0.03 g / mL; disperse ligand 2-methylimidazole in methanol to form a clear solution C with a concentration of 0.03 g / mL;

[0056] Step 2: Add 20 mL of solution C obtained in step 1 to 20 mL of solution A, mix evenly, and settle at room temperature to obtain a purple precipitate, which is then washed with methanol several times and dried at 75°C for 8 h to obtain a purple precipitate;

[0057] Step 3: Disperse 0.8 g of the purple precipitate prepared in step 2 in 200 mL of anhydrous ethanol, then add 10 mL of solution B prepared in step 1, mix thoroughly by stirring and ultrasonicating, control the temperature to 25 ° C, centrifuge, wash with anhydrous ethanol under stirring and ultrasonic conditions, and dry at 75 ° C for 8 h to obtain a hollow bimetallic precursor material;

[0058] Step 4: Disperse the hollow bimetallic precursor material prepared in step 3 in 200 mL of 0.015 g / mL melamine ethanol solution, and add 80 mL of 0.025 mL 磷酸 / mL 乙醇 An ethanol solution of an organic phosphoric acid, wherein the organic phosphoric acid is cyclohexane hexamethylenetetraphosphate (phytic acid), is stirred to react fully, centrifuged for washing, and dried to obtain a double metal ion chelated organic phosphorus hollow precursor material;

[0059] Step 5. Under a reducing atmosphere, the dual metal ion chelated organophosphorus hollow precursor material obtained in step 4 is placed in a tubular furnace for thermal reduction. The reducing atmosphere is a mixture of Ar and H2, wherein the H2 volume content is 10%; the thermal reduction temperature is 700°C, the time is 6h, the heating rate is 5°C / min, and then cooled to room temperature to obtain a hollow carbon composite material with rich voids and dual catalysts loaded with nitrogen doping;

[0060] Step 6: Mix the sublimed sulfur with the hollow carbon composite material described in step 5, with a mass ratio of sublimated sulfur to hollow carbon composite material of 4:1. Under an inert atmosphere, preheat the mixture until the sulfur is in a molten liquid state and maintain it for 12 hours. Then, heat it to 200°C and heat treat it for 2 hours to obtain the conductive dual-catalyst loaded nitrogen-doped carbon hollow carrier carbon / sulfur composite material. The preparation is completed.

[0061] According to the detection, the mass fraction of elemental sulfur loaded in the conductive dual catalyst (metal phosphide) loaded nitrogen-doped carbon hollow carrier carbon is 75.5%.

[0062] Polyvinylidene fluoride (PVDF) was added to N-methylpyrrolidone (NMP) to prepare a 10% by mass PVDF solution. A conductive dual-catalyst-loaded nitrogen-doped hollow carbon / sulfur composite, Super P, and PVDF solution were slurried in a mass ratio of 70:20:10 and coated onto aluminum foil with a thickness ranging from 100 μm to 650 μm. The resulting electrode sheets were then dried at 60°C and cut into circular shapes using a microtome. In a vacuum glove box, button cells were assembled using metallic lithium as the positive electrode, a polytetrafluoroethylene microporous membrane as the separator, and lithium trifluoromethanesulfonate as the electrolyte, and their long-cycle performance was tested.

[0063] Figure 1 The transmission electron microscope image of the hollow bimetallic precursor material is obtained in step 3 of Example 1; Figure 1 It can be seen that the precursor presents a significant hollow structure.

[0064] Figure 2 The transmission electron micrograph of the double metal ion chelated organophosphorus hollow precursor material obtained in step 4 of Example 1 is shown; Figure 2 It can be seen that the material still maintains a significant hollow structure after two-step etching.

[0065] Figure 3 The transmission electron microscope image of the hollow carbon material obtained in step 5 of Example 1 is as follows; Figure 3 It can be seen that the target carrier after calcination exhibits a significant hollow structure and has significant nanoparticle dispersion on the surface.

[0066] Figure 4 The XRD pattern of the hollow carbon material obtained in step 5 of Example 1 is shown. As can be seen from the pattern, the material has characteristic diffraction peaks of two metal phosphides, proving that the bimetallic phosphide is successfully synthesized.

[0067] Figure 5 The N1s spectrum of the hollow carbon material is obtained in step 5 of Example 1; Figure 5 It shows that N atoms are successfully doped into carbon materials and exist in the form of pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen.

[0068] Figure 6 This is the N1s spectrum obtained after the hollow carbon material adsorbs Li2S6 in step 5 of Example 1; Figure 6 It shows that the non-metallic N atomic sites in the carbon material combine with the active sulfur components to form N-Li bonds, indicating that they can play the role of anchoring polysulfide components to a certain extent.

[0069] Figure 7 The Co 2p spectra before and after the hollow carbon material adsorbs Li2S6 are obtained in step 5 of Example 1; Figure 7 This indicates that the Co atoms in the material can form Co-S interactions with the active sulfur components.

[0070] Figure 8 The Ni 2p spectra before and after the hollow carbon material adsorbs Li2S6 are obtained in step 5 of Example 1; Figure 8 This indicates that Ni atoms in the material can form Ni-S interactions with active sulfur components.

[0071] Figure 9 The S 2p spectra of the hollow carbon material before and after adsorption of Li2S6 are obtained in step 5 of Example 1; Figure 9 It further shows that the metal site atoms in the material can form Ni-S interactions with the active sulfur components.

[0072] Figure 10 The CV graph of the conductive dual catalyst supported nitrogen-doped carbon hollow support carbon / sulfur composite material obtained in step 6 of Example 1; Figure 10 It can be seen that the conductive dual catalyst loaded with nitrogen-doped hollow carbon / sulfur composite material as the sulfur positive electrode exhibits typical redox behavior: two reduction peaks and two oxidation peaks.

[0073] Figure 11 The long cycle performance diagram of the conductive dual-catalyst loaded nitrogen-doped carbon hollow carrier carbon / sulfur composite material at a current density of 1C was obtained in step six of Example 1; it can be seen from the figure that after 1000 cycles at a current density of 1C, the capacity decay rate per cycle is 0.04%, showing excellent long cycle stability.

Claims

1. A method for preparing a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material, characterized in that The method is specifically carried out in the following steps: Step 1: Disperse metal salt A in methanol to obtain a clear solution A; disperse metal salt B in anhydrous ethanol to obtain a clear solution B; disperse the ligand in methanol to form a clear solution C; Step 2: Add solution C obtained in step 1 to solution A, mix evenly, and settle at room temperature to obtain a purple precipitate, which is then washed with methanol several times and dried to obtain a purple precipitate; Step 3: Disperse the purple precipitate prepared in step 2 in anhydrous ethanol, then add solution B prepared in step 1, mix thoroughly, centrifuge, wash, and dry to obtain a hollow bimetallic precursor material; Step 4: Disperse the hollow bimetallic precursor material prepared in step 3 in a nitrogen source solution, add an organic phosphoric acid solution, stir to fully react, centrifuge and wash, and dry to obtain a bimetallic ion chelated organic phosphorus hollow precursor material; Step 5: Place the dual metal ion chelated organophosphorus hollow precursor material obtained in step 4 into a tubular furnace under a reducing atmosphere for thermal reduction. After cooling to room temperature, a hollow carbon composite material with rich voids and dual catalysts loaded with nitrogen doping is obtained. Step 6: mixing the sublimed sulfur with the hollow carbon composite material described in step 5, with a mass ratio of sublimed sulfur to hollow carbon composite material of (3-4):1, preheating under an inert atmosphere until the sulfur is in a molten liquid state for 8-24 hours, then heating to 200-300° C. and heat treating for 1-3 hours to obtain the conductive dual catalyst supported nitrogen-doped carbon hollow carrier carbon / sulfur composite material. The metal salt A in step 1 is a nickel salt, an iron salt or a cerium salt; The metal salt B in step 1 is a cobalt salt, a nickel salt, an iron salt or a cerium salt, and the concentration of the metal salt B in solution B is 0.0001 to 0.2 g / mL; The ligand in step 1 is an imidazole organic ligand; The nitrogen source solution in step 4 is prepared from a nitrogen source and anhydrous ethanol, wherein the nitrogen source is dicyandiamide, melamine or polyvinyl pyrrolidone; the organophosphoric acid solution is prepared from organophosphoric acid and anhydrous ethanol, wherein the concentration of the organophosphoric acid is 0.001 to 0.05 mL / mL, and the organophosphoric acid is phytic acid.

2. The method for preparing a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material according to claim 1, characterized in that Step 3: Stir and ultrasonicate to mix thoroughly, and control the temperature to 25°C.

3. The method for preparing a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material according to claim 1, characterized in that The washing process in step 3 is carried out using anhydrous ethanol under stirring and ultrasonic conditions for 3 to 5 times; the drying temperature is 75° C. and the drying time is 8 hours.

4. The method for preparing a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material according to claim 1, characterized in that The reducing atmosphere in step 5 is pure hydrogen or a mixture of Ar and H2; the thermal reduction temperature is 650-900°C, the time is 2-6h, and the heating rate is 2-10°C / min.

5. The method for preparing a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material according to claim 1, characterized in that Step 6: The mass ratio of sublimated sulfur to hollow carbon composite material is (3-4):

1.

6. The use of a conductive dual catalyst supported nitrogen-doped hollow carbon / sulfur composite material as claimed in claim 1, characterized in that The conductive dual-catalyst loaded nitrogen-doped hollow carbon / sulfur composite material is used as a positive electrode in the field of Li-S batteries.

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