Preparation method of polymer surfactant for lithium-sulfur battery

Abstract

The invention provides a preparation method of a polymer surfactant for a lithium-sulfur battery and a preparation method of a carbon-sulfur composite positive electrode material for the lithium-sulfur battery. The sulfur-lithium doped poly (ethylene glycol) methacrylate prepared by the preparation method disclosed by the invention is used as a polymer surfactant, and can optimize ion transmission and charge storage mechanisms in a battery, so that the charge-discharge efficiency and the cycle stability of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a preparation method of a polymer surfactant for lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur batteries are essentially a type of lithium battery with sulfur as the positive electrode and lithium metal as the negative electrode. Because of its extremely high theoretical capacity and energy density, low cost, and environmental friendliness, it is one of the most promising energy storage systems.

[0003] The patent application with the publication number CN119400842A discloses a preparation method and application of a lithium-sulfur battery positive electrode material. Chitosan and phytic acid are cross-linked to obtain a porous biochar aerogel; then it is combined with the catalyst nano-In 2 O 3 to obtain a porous biochar aerogel@In 2 O 3 composite material; then freeze-drying and microwave heating treatments are carried out to carbonize the aerogel to obtain an N, P co-doped three-dimensional porous biochar@In 2 O 3 composite material; then it is combined with elemental S to obtain an N, P co-doped three-dimensional porous biochar@In 2 O 3 @S composite material, which is the lithium-sulfur battery positive electrode material.

[0004] The patent application with the publication number CN119297217A discloses a composite positive electrode material applied to all-solid-state lithium-sulfur batteries. The composite positive electrode material includes elemental sulfur as the active substance, a sulfide solid electrolyte with high temperature and high ionic conductivity as the ion conductor to conduct lithium ions; a conductive carbon material, which conducts electrons as the electron conductor. The mass ratio among the elemental sulfur, the conductive carbon material, and the sulfide solid electrolyte can be 1:1:2.

[0005] The patent application with the publication number CN119230733A discloses a preparation method and application of a self-supporting positive electrode material for lithium-sulfur batteries. First, a self-supporting in-situ nitrogen-doped carbon nanofiber (PCNF) with a porous structure is obtained by electrospinning and carbon heat treatment. Then, the PCNF is impregnated in an ethanol solution of Co-ZIF-8, and a cobalt / zinc oxide-nitrogen-doped porous carbon-modified carbon nanofiber material (Co / ZnO-NC@PCNF) is obtained through calcination.

[0006] Although there are already many studies on lithium-sulfur battery positive electrode materials in the current prior art, there are still problems such as poor conductivity and poor stability in current lithium-sulfur batteries. Summary of the Invention

[0007] To solve the above technical problems existing in the prior art, the present invention provides a preparation method of a polymer surfactant for a lithium-sulfur battery, and a preparation method of a carbon-sulfur composite cathode material for a lithium-sulfur battery.

[0008] The present invention provides a preparation method of a polymer surfactant for a lithium-sulfur battery, comprising the following steps: (1) Under the protection of an inert gas, 100 - 120 parts by mass of poly(ethylene glycol) methacrylate (CAS: 25736 - 86 - 1), 0.01 - 0.2 parts by mass of zinc maleate, and 3 - 8 parts by mass of 2,5 - dimercapto - 1,3,4 - thiadiazole (CAS: 1072 - 71 - 5) are fully dissolved in 1000 - 1500 parts by mass of an organic solvent to obtain solution A; (2) 0.2 - 0.6 parts by mass of an initiator is added to solution A, and the reaction is carried out under the protection of an inert gas to obtain solution B; (3) The solvent is removed by vacuum distillation, and after washing and drying, the polymer surfactant for the lithium-sulfur battery is obtained.

[0009] Reaction principle: The mercapto groups in 2,5 - dimercapto - 1,3,4 - thiadiazole undergo an addition reaction with the double bonds in poly(ethylene glycol) methacrylate and zinc maleate.

[0010] Preferably, in step (2), the reaction temperature is 70 - 90 °C, and the reaction time is 8 - 10 hours.

[0011] Preferably, the initiator in step (2) is azobisisobutyronitrile (AIBN), benzoyl peroxide, or azodiisooctanenitrile.

[0012] Preferably, the organic solvent is N,N - dimethylformamide (DMF), N,N - dimethylacetamide, or N - methylpyrrolidone.

[0013] Preferably, the degree of polymerization of the poly(ethylene glycol) methacrylate is 300 - 1000.

[0014] The present invention also provides the polymer surfactant for the lithium-sulfur battery prepared by the above preparation method.

[0015] The present invention also provides a preparation method of a carbon-sulfur composite cathode material for a lithium-sulfur battery, which, by mass, comprises the following steps: (1) 10 - 80 parts of a nano conductive material, 0.5 - 2 parts of the polymer surfactant for the lithium-sulfur battery, 10 - 20 parts of a functional additive, and 400 - 500 parts of water are mixed evenly to obtain a mixed solution; (2) The mixed solution is dried to obtain a precursor, and the precursor is pre-oxidized under an inert atmosphere and then heat-treated to obtain nano carbon spheres; (3) Mix 50 - 80 parts of sulfur material with 10 - 20 parts of the nanocarbon spheres by ball milling. After uniform mixing, react under the conditions of a CO 2 atmosphere, a pressure of 7.29 - 15 MPa, and a temperature of 32 - 100 °C. Heat the powder obtained after the reaction to 300 - 380 °C under an inert atmosphere to obtain the carbon-sulfur composite cathode material for lithium-sulfur batteries.

[0016] Preferably, the nano-conductive material is selected from one or more of Super P, acetylene black, Ketjen black, conductive carbon black, mesophase carbon microspheres, carbon nanotubes, graphene, fullerenes, and nanofibers.

[0017] Preferably, the functional additive is selected from one of nano-fast ion conductors, soluble transition metal salts, inorganic templates, and anode materials with a relatively high lithium intercalation potential; the nano-fast ion conductors are Li 10 GeP 2 S 12 (LGPS), Li 7 La 3 Zr 2 O 12 (LLZO), and Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP); the soluble transition metal salts are Ni(OH) 2 , Ni(NO 3 ) 2 ·6H 2 O, NiSO 4 ·6(H 2 O), NiCl 2 ·6H 2 O, Fe(OH) 3 , Fe(NO 3 ) 3 , FeSO 4 ·7H 2 O, CoCl 2 and CoSO 4 ; the inorganic templates are SiO 2 , Al 2 O 3 , Fe 2 O 3 , TiO 2 and CaCO 3 ; the anode materials with a relatively high lithium intercalation potential are Si, SiO 2 and Li 4 Ti 5O 12 One or more of .

[0018] Preferably, the drying in step (2) is spray drying, and the conditions for the spray drying are an air inlet temperature of 105-350°C, an air outlet temperature of 80-200°C, an air inlet pressure of 0.2-0.6 MPa, and a flow rate controlled at 3-15 ml / min.

[0019] Preferably, the temperature of the pre-oxidation treatment in step (2) is 100-300°C and the time is 1-3 h; the conditions of the heat treatment are that the heating temperature is controlled at 500-1000°C and the insulation time is controlled at 6-12 h.

[0020] Preferably, the sulfur material in step (3) is selected from one or more of sublimated sulfur, precipitated sulfur, crystalline sulfur, colloidal sulfur, amorphous sulfur, microcrystalline sulfur, nano sulfur and molten sulfur.

[0021] The present invention also provides a carbon-sulfur composite positive electrode material for a lithium-sulfur battery prepared by the above preparation method.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The prepared sulfur-lithium doped poly(ethylene glycol) methacrylate as part of the carbon-sulfur composite positive electrode material of lithium-sulfur batteries can have a positive impact on the performance of lithium-sulfur batteries. The introduction of sulfur-containing lithium structural units helps to improve the energy density of the battery. Lithium is an important carrier in lithium-sulfur batteries. The lithium doping method can optimize the ion transport and charge storage mechanism inside the battery, thereby improving the battery's charge and discharge efficiency and cycle stability.

[0023] (2) Zinc maleate, as a cross-linking agent, can affect the molecular weight, molecular chain structure and degree of cross-linking of the polymer. The addition of zinc maleate helps to improve the stability and conductivity of the material. In lithium-sulfur batteries, good conductivity and structural stability are crucial for electrode materials, which can reduce battery polarization and improve battery rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The cycle performance curves of Example 4 and Comparative Example 3 at 0.5C.

[0025] Figure 2 The cycle performance curves of Example 4 and Comparative Example 3 at 1C. DETAILED DESCRIPTION

[0026] Example 1 A method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery comprises the following steps: Step 1: Preparation of carbon nanospheres According to the mass fractions, 80 g of nano-conductive material, 0.5 g of polymer surfactant and 10 g of functional additive were added into 400 g of deionized water, and the solution was stirred at 500 rpm for 1 h, and ultrasonic treatment was performed for 1 h during stirring to dissolve and disperse to obtain a mixed solution; The mixed solution is spray-dried to obtain a precursor; the precursor is pre-oxidized under an inert atmosphere and then heat-treated to obtain nano-carbon spheres; Step 2: Preparation of carbon-sulfur composite cathode materials According to the mass fraction, 50 g of sublimated sulfur and 10 g of nanocarbon balls were ball-milled and mixed evenly, and then placed in a high-temperature and high-pressure reactor, evacuated and filled with high-purity CO. 2 Into the kettle, adjust the gas pressure to 7.29 MPa, the temperature to 32 ℃, continue stirring for 1 h, lower the temperature of the reactor to below 30 ℃, release the gas until the pressure in the reactor returns to normal pressure, open the reactor, take out the powder and place it in a tubular furnace, introduce nitrogen atmosphere, heat to 300 ℃ and keep warm for 30 min to obtain a carbon-sulfur composite positive electrode material.

[0027] The nano conductive material is Super P.

[0028] The polymer surfactant is lithium sulfur-doped poly(ethylene glycol) methacrylate, and its preparation method is as follows: T1. Raw material preparation: according to the total amount, weigh 100 g of poly(ethylene glycol) methacrylate with a degree of polymerization of 300, add it to 1000 g of N,N-dimethylformamide (DMF), weigh 0.01 g of zinc maleate and 3 g of 2,5-dimercaptothiadiazole, add them to the above DMF solution, and weigh 0.2 g of azobisisobutyronitrile (AIBN) as an initiator; T2. Lithium-sulfur doping reaction: Under nitrogen protection, stir to fully dissolve and mix the raw materials for 45 minutes. Add initiator AIBN, continue to introduce nitrogen for 5 minutes to replace the air, then heat the reaction system to 70 °C and react for 8 hours; T3. Post-processing: After the reaction is completed, N,N-dimethylformamide is removed by distillation under reduced pressure, and then washed, centrifuged and dried to obtain lithium sulfur-doped poly(ethylene glycol) methacrylate.

[0029] The functional additive is a nano fast ion conductor powder; the nano fast ion conductor powder is Li 10 G 2 S 12 (LGPS).

[0030] The spray drying conditions are as follows: an air inlet temperature of 105°C, an air outlet temperature of 80°C, an air inlet pressure of 0.2 MPa, and a flow rate controlled at 3 ml / min.

[0031] The inert atmosphere in step 1 is nitrogen; The pre-oxidation treatment temperature is 100°C and the time is 1 hour; the heat treatment conditions are that the heating temperature is controlled at 500°C and the insulation time is controlled at 6 hours.

[0032] Example 2

[0033] A method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery comprises the following steps: Step 1: Preparation of carbon nanospheres According to the mass fractions, 50 g of nano-conductive material, 1 g of polymer surfactant, and 15 g of functional additive were added to 450 g of deionized water, and the solution was stirred at 2000 rpm for 10 h, and ultrasonic treatment was performed for 3 h during stirring to dissolve and disperse the mixture to obtain a mixed solution; The mixed solution is spray-dried to obtain a precursor; the precursor is pre-oxidized under an inert atmosphere and then heat-treated to obtain nano-carbon spheres; Step 2: Preparation of carbon-sulfur composite cathode materials According to the mass fraction, 60 g of precipitated sulfur and 13.5 g of nanocarbon spheres were ball-milled and mixed evenly, and then placed in a high-temperature and high-pressure reactor, evacuated and filled with high-purity CO. 2 Add the mixture into the kettle, adjust the gas pressure to 9 MPa and the temperature to 50 °C, continue stirring for 3 h, lower the temperature of the reactor to below 30 °C, release the gas until the pressure in the reactor returns to normal pressure, open the reactor, take out the powder and place it in a tubular furnace, introduce nitrogen atmosphere, heat to 300 °C and keep warm for 30 min to obtain a carbon-sulfur composite positive electrode material.

[0034] The nano conductive material is carbon nanotube.

[0035] The polymer surfactant is lithium sulfur-doped poly(ethylene glycol) methacrylate, and its preparation method is as follows: T1. Raw material preparation: according to the total amount, weigh 110 g of poly(ethylene glycol) methacrylate with a polymerization degree of 500, add it to 1250 g of N,N-dimethylacetamide, weigh 0.1 g of zinc maleate and 5 g of 2,5-dimercaptothiadiazole, add them to the above DMF solution, and weigh 0.4 g of azobisisobutyronitrile (AIBN) as an initiator; T2. Lithium-sulfur doping reaction: Under nitrogen protection, stir to fully dissolve and mix the raw materials for 60 minutes. Add initiator AIBN, continue to introduce nitrogen for 10 minutes to replace the air, then heat the reaction system to 80 °C and react for 9 hours; T3. Post-processing: After the reaction is completed, N,N-dimethylacetamide is removed by distillation under reduced pressure, and then washed, centrifuged and dried to obtain lithium sulfur-doped poly(ethylene glycol) methacrylate.

[0036] The functional additive is a soluble transition metal Ni(NO 3 ) 2 6H 2 O.

[0037] The spray drying conditions are as follows: an air inlet temperature of 200°C, an air outlet temperature of 120°C, an air inlet pressure of 0.4 MPa, and a flow rate controlled at 8 ml / min.

[0038] The inert atmosphere in step 1 is argon; The pre-oxidation treatment temperature is 200°C and the time is 1.5 hours; the heat treatment conditions are that the heating temperature is controlled at 650°C and the insulation time is controlled at 8 hours.

[0039] Example 3

[0040] A method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery comprises the following steps: Step 1: Preparation of carbon nanospheres According to the mass fractions, 35 g of nano-conductive material, 1.3 g of polymer surfactant, and 15 g of functional additive were added to 480 g of deionized water, and the solution was stirred at 4000 rpm for 20 h, and ultrasonic treatment was performed for 8 h during stirring to dissolve and disperse the mixture to obtain a mixed solution; The mixed solution is spray-dried to obtain a precursor; the precursor is pre-oxidized under an inert atmosphere and then heat-treated to obtain nano-carbon spheres; Step 2: Preparation of carbon-sulfur composite cathode materials According to the mass fraction, 70 g of amorphous sulfur and 17 g of nanocarbon spheres were ball-milled and mixed evenly, and then placed in a high-temperature and high-pressure reactor, evacuated and filled with high-purity CO. 2 Into the kettle, adjust the gas pressure to 12 MPa, the temperature to 80 ℃, continue stirring for 6 h, lower the temperature of the reactor to below 30 ℃, release the gas until the pressure in the reactor returns to normal pressure, open the reactor, take out the powder and place it in a tubular furnace, introduce nitrogen atmosphere, heat to 300 ℃ and keep warm for 30 min to obtain a carbon-sulfur composite positive electrode material.

[0041] The nano-conductive material is 20 g of Ketjen black and 10 g of nano-carbon fiber.

[0042] The polymer surfactant is lithium sulfur-doped poly(ethylene glycol) methacrylate, and its preparation method is as follows: T1. Raw material preparation: according to the total amount, weigh 115 g of poly(ethylene glycol) methacrylate with a degree of polymerization of 400, add it to 1400 g of N-methylpyrrolidone, weigh 0.15 g of zinc maleate and 6.5 g of 2,5-dimercaptothiadiazole, add them to the above DMF solution, and weigh 0.5 g of azobisisobutyronitrile (AIBN) as an initiator; T2. Lithium-sulfur doping reaction: Under nitrogen protection, stir to fully dissolve and mix the raw materials for 75 minutes, add initiator AIBN, continue to introduce nitrogen for 15 minutes to replace the air, then heat the reaction system to 85 °C and react for 9.5 hours; T3. Post-processing: After the reaction is completed, N-methylpyrrolidone is removed by distillation under reduced pressure, and then washed, centrifuged and dried to obtain lithium sulfur-doped poly(ethylene glycol) methacrylate.

[0043] The functional additive is 10 g of nano fast ion conductor powder and 5 g of a negative electrode material with a high lithium insertion potential; the nano fast ion conductor powder Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 In the LATP, the negative electrode material with a higher lithium insertion potential is SiO 2 .

[0044] The spray drying conditions are as follows: an air inlet temperature of 300°C, an air outlet temperature of 160°C, an air inlet pressure of 0.5 MPa, and a flow rate controlled at 12 ml / min.

[0045] The inert atmosphere in step 1 is nitrogen.

[0046] The pre-oxidation treatment temperature is 250°C and the time is 2.5 hours; the heat treatment conditions are that the heating temperature is controlled at 800°C and the insulation time is controlled at 10 h.

[0047] Example 4

[0048] A method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery comprises the following steps: Step 1: Preparation of carbon nanospheres According to the mass fractions, 10 g of nano-conductive material, 2 g of polymer surfactant, and 20 g of functional additive were added to 500 g of deionized water, and the solution was stirred at 6000 rpm for 24 h, and ultrasonic treatment was performed for 12 h during stirring to dissolve and disperse to obtain a mixed solution; The mixed solution is spray-dried to obtain a precursor; the precursor is pre-oxidized under an inert atmosphere and then heat-treated to obtain nano-carbon spheres; Step 2: Preparation of carbon-sulfur composite cathode materials According to the mass fraction, 80 g of nano-sulfur and 20 g of nano-carbon balls were ball-milled and mixed evenly, and then placed in a high-temperature and high-pressure reactor, evacuated and filled with high-purity CO. 2 Add the powder into the kettle, adjust the gas pressure to 15 MPa and the temperature to 100 °C, continue stirring for 10 h, lower the temperature of the reactor to below 30 °C, release the gas until the pressure in the reactor returns to normal pressure, open the reactor, take out the powder and place it in a tubular furnace, introduce nitrogen atmosphere, heat to 300 °C and keep warm for 30 min to obtain a carbon-sulfur composite positive electrode material.

[0049] The nano-conductive material is 5 g of conductive carbon black and 5 g of carbon nanotubes.

[0050] The polymer surfactant is lithium sulfur-doped poly(ethylene glycol) methacrylate, and its preparation method is as follows: T1. Raw material preparation: according to the total amount, weigh 120 g of poly(ethylene glycol) methacrylate with a polymerization degree of 1000, add it to 1500 g of N,N-dimethylformamide (DMF), weigh 0.2 g of zinc maleate and 8 g of 2,5-dimercaptothiadiazole, add them to the above DMF solution, and weigh 0.6 g of azobisisobutyronitrile (AIBN) as an initiator; T2. Lithium-sulfur doping reaction: Under nitrogen protection, stir to fully dissolve and mix the raw materials for 100 minutes. Add initiator AIBN, continue to introduce nitrogen for 20 minutes to replace the air, then heat the reaction system to 90 °C and react for 10 hours; T3. Post-processing: After the reaction is completed, N,N-dimethylformamide is removed by distillation under reduced pressure, and then washed, centrifuged and dried to obtain lithium sulfur-doped poly(ethylene glycol) methacrylate.

[0051] The functional additive is 10 g of soluble transition metal salt and 10 g of inorganic template, and the soluble transition metal salt is FeSO 4 7H 2 O; the inorganic template TiO 2 .

[0052] The spray drying conditions are as follows: an air inlet temperature of 350°C, an air outlet temperature of 200°C, an air inlet pressure of 0.6 MPa, and a flow rate controlled at 15 ml / min.

[0053] The inert atmosphere in step 1 is argon.

[0054] The pre-oxidation treatment temperature is 300°C and the time is 3 hours; the heat treatment conditions are that the heating temperature is controlled at 1000°C and the insulation time is controlled at 12 h.

[0055] Comparative Example 1 The polymer surfactant is 100 g of poly(ethylene glycol) methacrylate with a polymerization degree of 300, and the rest of the technical scheme is the same as Example 1.

[0056] Comparative Example 2 No zinc maleate is added to the polymer surfactant, and the rest of the technical scheme is the same as in Example 1.

[0057] Comparative Example 3 No 2,5-dimercaptothiadiazole is added to the polymer surfactant, and the rest of the technical scheme is the same as in Example 1.

[0058] Test Example 1 Electrochemical performance test: The carbon-sulfur composite positive electrode material, Super-P conductive agent and polyvinylidene fluoride (PVDF) prepared in Examples 1-4 and Comparative Examples 1-3 were ground and mixed in a mass ratio of 8:1:1, N-methylpyrrolidone (NMP) was added, stirred to a uniform slurry, coated on a copper foil current collector, placed in a vacuum drying oven, dried at a constant temperature of 60 ° C for 12 h, and then taken out to obtain a positive electrode sheet. It was mixed with a negative electrode metal lithium sheet, a separator, 1.0 M LiTFSI and 2.0% LiNO 3 The DME:DOL=1:1 Vol% lithium-sulfur electrolyte is made into a CR2032 button battery.

[0059] The obtained CR2032 button cell was placed on the battery test system and after standing for 12 h, the charge and discharge tests were performed at 0.5C and 1C rates, respectively, with the voltage cutoff range set to 1.8~2.6 V. The test results are shown in Tables 1 and 2.

[0060] Table 1 Cyclic performance of different embodiments at 0.5C

[0061] Table 2 Cyclic performance of different embodiments at 1C

[0062] The data in Table 1 show that the gram capacity data of the lithium-sulfur battery made of the carbon-sulfur composite positive electrode material for lithium-sulfur battery in Examples 1-4 before and after the 0.5C cycle test are significantly better than the data of the lithium-sulfur battery prepared by the conventional positive electrode material without doping. Among them, the cycle performance curves of Example 4 and Comparative Example 3 at 0.5C are shown in Table 1. Figure 1 ; and explored different polymer polymerization degrees, and the best result was achieved after doping with a polymer material with a polymerization degree of 1000 molecular weight.

[0063] The data in Table 2 show that the gram capacity data of the lithium-sulfur battery made of the carbon-sulfur composite positive electrode material for lithium-sulfur battery in Examples 1-4 before and after the 1C cycle test are significantly better than the data of the lithium-sulfur battery prepared by the conventional positive electrode material without doping. Among them, the cycle performance curves of Example 4 and Comparative Example 3 at 1C are shown in Figure 2 ; and explored different polymer polymerization degrees, and the best result was achieved after doping with a polymer material with a polymerization degree of 1000 molecular weight.

Claims

1. A method for preparing a polymer surfactant for lithium-sulfur batteries, characterized in that: The following steps are involved: (1) Under the protection of inert gas, 100-120 parts by mass of poly(ethylene glycol) methacrylate, 0.01-0.2 parts of zinc maleate and 3-8 parts of 2,5-dimercaptothiadiazole are fully dissolved in 1000-1500 parts of an organic solvent to obtain a solution A; (2) adding 0.2-0.6 parts of initiator to solution A and reacting under the protection of inert gas to obtain solution B; (3) removing the organic solvent by distillation under reduced pressure, washing and drying to obtain the polymer surfactant for lithium-sulfur battery.

2. The method for preparing a polymer surfactant for lithium-sulfur batteries according to claim 1, characterized in that: In step (2), the reaction temperature is 70-90°C and the reaction time is 8-10 hours.

3. The method for preparing a polymer surfactant for lithium-sulfur batteries according to claim 1, characterized in that: The organic solvent in step (1) is N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone, and the initiator in step (2) is azobisisobutyronitrile, benzoyl peroxide or azobisisoheptanenitrile.

4. A polymer surfactant for lithium-sulfur batteries prepared by the preparation method according to any one of claims 1 to 3.

5. A method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery, characterized in that: The polymer surfactant for lithium-sulfur batteries according to claim 4 is used; the preparation method comprises the following steps by weight: (1) mixing 10-80 parts of a nano-conductive material, 0.5-2 parts of a polymer surfactant for a lithium-sulfur battery, 10-20 parts of a functional additive and 400-500 parts of water to obtain a mixed solution; (2) drying the mixed solution to obtain a precursor, pre-oxidizing the precursor under an inert atmosphere and then heat-treating the precursor to obtain nano-carbon spheres; (3) 50-80 parts of the sulfur material and 10-20 parts of the nano-carbon spheres are ball-milled and mixed, and after the mixture is evenly mixed, the mixture is reacted in a CO2 atmosphere, a pressure of 7.29-15 MPa and a temperature of 32-100°C, and the powder obtained after the reaction is heated to 300-380°C in an inert atmosphere to obtain the carbon-sulfur composite positive electrode material for lithium-sulfur batteries.

6. The method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery according to claim 5, characterized in that: The nano-conductive material in step (1) is selected from one or more of Super P, acetylene black, Ketjen black, conductive carbon black, mesophase carbon microspheres, carbon nanotubes, graphene, fullerene and nano-carbon fibers; the sulfur material in step (3) is selected from one or more of sublimated sulfur, precipitated sulfur, crystalline sulfur, colloidal sulfur, amorphous sulfur, microcrystalline sulfur, nano-sulfur and molten sulfur.

7. The method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery according to claim 5, characterized in that: The functional additive is selected from one of a nano fast ion conductor, a soluble transition metal salt, an inorganic template, and a negative electrode material with a high lithium insertion potential; The nano fast ion conductor is Li 10 GeP2S 12 、Li7La3Zr2O 12 and Li 1.3 Al 0.3 Ti 1.7 (PO4)3 or more; The soluble transition metal salt is one or more of Ni(OH)2, Ni(NO3)2·6H2O, NiSO4·6(H2O), NiCl2·6H2O, Fe(OH)3, Fe(NO3)3, FeSO4·7H2O, CoCl2 and CoSO4; The inorganic template is one or more of SiO2, Al2O3, Fe2O3, TiO2 and CaCO3; The negative electrode material with high lithium insertion potential is Si, SiO2 and Li4Ti5O 12 One or more of .

8. The method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery according to claim 5, characterized in that: The drying in step (2) is spray drying, and the conditions of the spray drying are an air inlet temperature of 105-350°C, an air outlet temperature of 80-200°C, an air inlet pressure of 0.2-0.6 MPa, and a flow rate controlled at 3-15 ml / min.

9. The method for preparing a carbon-sulfur composite positive electrode material for a lithium-sulfur battery according to claim 5, characterized in that: The temperature of the pre-oxidation treatment in step (2) is 100-300°C and the time is 1-3 h; the conditions of the heat treatment are that the heating temperature is controlled at 500-1000°C and the insulation time is controlled at 6-12 h.

10. A carbon-sulfur composite positive electrode material for a lithium-sulfur battery prepared by the preparation method according to any one of claims 5 to 9.

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