Lithium-sulfur battery positive electrode material, preparation method thereof and lithium-sulfur battery

Abstract

The embodiment of the invention relates to a lithium-sulfur battery positive electrode material, a preparation method thereof and a lithium-sulfur battery. The preparation method comprises the following steps: dissolving cobalt salt and tin salt in deionized water according to a required molar ratio, carrying out ultrasonic treatment to obtain a mixed solution, adding a surfactant and a carbon material into the mixed solution, and continuously carrying out ultrasonic treatment to obtain a first suspension; dropwise adding an alkali solution into the first suspension, and stirring to obtain a second suspension; carrying out vacuum filtration on the second suspension, and washing to obtain CoSn (OH) 6 / C powder; uniformly grinding the CoSn (OH) 6 / C powder and excessive sublimed sulfur powder, putting the powder into a porcelain boat, and obtaining Co3Sn2S2 / C powder by a high-temperature vulcanization method; and further adding sublimed sulfur powder into the Co3Sn2S2 / C powder, uniformly grinding, loading into a porcelain boat, and obtaining the S / Co3Sn2S2 / C composite material through a melt diffusion method.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and particularly to a cathode material for a lithium-sulfur battery, a preparation method thereof, and a lithium-sulfur battery. Background Art

[0002] With the rapid development of large-scale energy storage technologies, electric vehicles, and various electronic devices, the energy density of existing commercial lithium-ion battery systems can no longer meet the growing demands of these fields. Lithium-sulfur (Li-S) batteries, with their advantages such as high energy density and high theoretical specific capacity, are considered to be one of the most promising next-generation energy storage systems in addition to conventional lithium-ion batteries.

[0003] Li-S batteries have high energy density and theoretical specific capacity, and sulfur is inexpensive and low-toxic, having theoretical technical advantages. However, there are still disadvantages that hinder the practical application of Li-S batteries. The main problems include: poor conductivity of sulfur and lithium sulfide; during the operation of Li-S batteries, soluble polysulfides are generated during the charge-discharge process, leading to the shuttle effect; due to the volume expansion of elemental sulfur during the electrochemical process, the structure becomes unstable, thus causing the formation of dendrites and triggering safety problems.

[0004] Recently, new scientific research has used composite materials combining polar metal compounds and carbon materials to solve the above drawbacks of Li-S batteries. Researchers use the polar bonds of metal compounds to form chemical adsorption with polysulfides to inhibit the shuttle effect. So far, the studied metal compounds mainly focus on binary metal oxides, metal sulfides, and metal nitrides. Research reports show that transition metal compounds have a large number of polar covalent bonds and adsorption sites, and such materials have excellent conductivity. However, the lithiation voltage of such materials is relatively high, and the adsorption of sulfur-containing substances is not ideal enough. Summary of the Invention

[0005] The purpose of the present invention is to provide a cathode material for a lithium-sulfur battery, a preparation method thereof, and a lithium-sulfur battery. By using Co3Sn2S2 / C composite material as a sulfur carrier material to prepare S / Co3Sn2S2 / C composite material, not only greatly enhances the intrinsic conductivity and extrinsic conductivity of S, improves the electron and ion diffusion-transport kinetics, and inhibits the polysulfide shuttle effect, but also enables the S / Co3Sn2S2 / C electrode to exhibit excellent cycle performance and rate performance.

[0006] To this end, in the first aspect, an embodiment of the present invention provides a preparation method of a cathode material for a lithium-sulfur battery. The cathode material for a lithium-sulfur battery is S / Co3Sn2S2 / C composite material, and the preparation method includes:

[0007] Dissolve cobalt salts and tin salts in deionized water according to the required molar ratio, and obtain a mixed solution after ultrasonic treatment. Add a surfactant and a carbon material to the mixed solution, and continue ultrasonic treatment to obtain a first suspension;

[0008] Dropwise add an alkali solution to the first suspension, and stir to obtain a second suspension;

[0009] Perform vacuum filtration and washing on the second suspension to obtain CoSn(OH)6 / C powder;

[0010] Grind the CoSn(OH)6 / C powder and an excessive amount of sublimed sulfur powder evenly, then load them into a porcelain boat, and obtain Co3Sn2S2 / C powder through high-temperature sulfidation;

[0011] Further add sublimed sulfur powder to the Co3Sn2S2 / C powder, grind them evenly and load them into a porcelain boat, and obtain an S / Co3Sn2S2 / C composite material through melt diffusion.

[0012] Preferably, the cobalt salt includes one of cobalt chloride, cobalt nitrate or cobalt sulfate; the tin salt includes tin chloride.

[0013] Preferably, the surfactant includes at least one or a combination of more than one of absolute ethanol, cetyltrimethylammonium bromide, polyvinylpyrrolidone, sodium citrate or sodium dodecylbenzenesulfonate, and the dosage of the surfactant is 1% - 5% of the total mass of the cobalt salt and the tin salt;

[0014] The carbon material includes at least one or a combination of more than one of nano-graphite, micro-graphite, hard carbon, soft carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, graphdiyne, and the dosage of the carbon material is 10% - 20% of the total mass of the cobalt salt and the tin salt;

[0015] The ultrasonic mixing is carried out in an ultrasonic disintegrator, the ultrasonic power is 110 - 180W, and the ultrasonic time is 0.5 - 2h.

[0016] Preferably, the alkali solution includes a NaOH solution with a concentration of 1 - 10 mol / L;

[0017] The stirring speed of the stirring is 300 - 800r / min; the stirring duration is 0.5 - 1.5h.

[0018] Preferably, the mass ratio of the CoSn(OH)6 / C powder to the excessive sublimed sulfur powder is 1:4 - 2:3;

[0019] The high-temperature vulcanization method includes: under a protective atmosphere, heating to 600-900°C at a heating rate of 3-5°C / min for calcination, and the holding time for calcination is 1.5-2.5 h; the protective atmosphere specifically includes at least one of a hydrogen-argon mixture, nitrogen, helium, neon, argon, krypton, and xenon.

[0020] Preferably, the mass ratio of the Co3Sn2S2 / C powder to the further added sublimed sulfur powder is 3:7;

[0021] The melt diffusion method includes: under a protective atmosphere, heating to 140-160°C at a heating rate of 1-5°C / min for heat preservation, and the holding time for heat preservation is 8-15 h; the protective atmosphere specifically includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0022] In a second aspect, an embodiment of the present invention provides a lithium-sulfur battery cathode material prepared by the preparation method described in the first aspect above.

[0023] In a third aspect, an embodiment of the present invention provides a lithium-sulfur battery, including the positive electrode sheet described in the second aspect above.

[0024] The lithium-sulfur battery cathode material provided by the embodiment of the present invention prepares an S / Co3Sn2S2 / C composite material by using Co3Sn2S2 / C as the carrier material of the active substance sulfur (S). Among them, Co3Sn2S2 is a Shandite compound (the general formula of this type of compound is M3A2Ch2, M is one of Co, Ni, Rh, or Pd, A is one of Sn, Pb, In, Tl, or Bi; Ch is S or Se), and has a quasi-two-dimensional Co3Sn ferromagnetic layer forming a sandwich structure with S atoms. This structure can not only store sulfur, but also relieve the volume expansion of sulfur during cycling, and physically confine polysulfides during cycling. At the same time, Co3Sn2S2, as a Weyl semimetal with a special topological protection effect, its energy band structure shows an obvious electronic structure of a topological semimetal, enabling it to obtain high electrical conductivity and providing active sites to adsorb polysulfides, promoting the adsorption of polysulfides, and further inhibiting the polysulfide shuttle effect. Therefore, S / Co3Sn2S2 / C as a lithium-sulfur battery cathode material can exhibit excellent cycle performance and rate performance. Description of the Drawings

[0025] Figure 1 It is a flowchart of the preparation method of the lithium-sulfur battery cathode material provided by the embodiment of the present invention;

[0026] Figure 2 It is a cycle curve graph of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention cycling 100 weeks at a current density of 0.5C. Detailed implementation manners

[0027] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0028] An embodiment of the present invention provides a preparation method for a cathode material of a lithium-sulfur battery. The main steps are as Figure 1 shown. The preparation method includes:

[0029] Step 110: Dissolve cobalt salt and tin salt in deionized water according to the required molar ratio, and obtain a mixed solution after ultrasonic treatment. Add a surfactant and a carbon material to the mixed solution, and continue ultrasonic treatment to obtain a first suspension.

[0030] Among them, the cobalt salt includes one of cobalt chloride, cobalt nitrate or cobalt sulfate, and the purity is not less than 98%; the tin salt includes tin chloride, and the purity is not less than 98%. The cobalt salt and the tin salt are added according to a molar ratio of Co:Sn = 3:2.

[0031] The surfactant includes at least one or a combination of anhydrous ethanol, cetyltrimethylammonium bromide, polyvinylpyrrolidone, sodium citrate or sodium dodecylbenzenesulfonate. The dosage of the surfactant is 1% - 5% of the total mass of the cobalt salt and the tin salt.

[0032] The carbon material includes at least one or a combination of nano-graphite, micro-graphite, hard carbon, soft carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, graphdiyne. The dosage of the carbon material is 10% - 20% of the total mass of the cobalt salt and the tin salt.

[0033] The ultrasonic mixing is carried out in an ultrasonic crusher, the ultrasonic power is 110 - 180W, and the ultrasonic time is 0.5 - 2h.

[0034] Step 120: Drop an alkali solution into the first suspension and stir to obtain a second suspension.

[0035] Among them, the alkali solution includes a NaOH solution with a concentration of 1 - 10 mol / L.

[0036] The stirring speed of the stirring is 300 - 800 r / min; the stirring duration is 0.5 - 1.5h.

[0037] Step 130: Perform vacuum filtration and washing on the second suspension to obtain CoSn(OH)6 / C powder.

[0038] Step 140: Grind the CoSn(OH)6 / C powder and an excessive amount of sublimed sulfur powder evenly and load them into a porcelain boat, and obtain Co3Sn2S2 / C powder through high-temperature sulfidation.

[0039] Specifically, the mass ratio of CoSn(OH)6 / C powder to excessive sublimed sulfur powder is 1:4 to 2:3.

[0040] The high-temperature vulcanization method includes: under a protective atmosphere, heating to 600 - 900 °C at a heating rate of 3 - 5 °C / min for calcination, and the holding time for calcination is 1.5 - 2.5 h; the protective atmosphere specifically includes at least one of a hydrogen-argon mixture, nitrogen, helium, neon, argon, krypton, and xenon.

[0041] Step 150: Further add sublimed sulfur powder to the Co3Sn2S2 / C powder, grind evenly and load it into a porcelain boat, and obtain the S / Co3Sn2S2 / C composite material through the melt diffusion method.

[0042] Among them, the mass ratio of the Co3Sn2S2 / C powder to the further added sublimed sulfur powder is 3:7.

[0043] The melt diffusion method includes: under a protective atmosphere, heating to 140 - 160 °C at a heating rate of 1 - 5 °C / min for heat preservation, and the holding time for heat preservation is 8 - 15 h; the protective atmosphere specifically includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0044] The lithium-sulfur battery cathode material provided by the embodiments of the present invention utilizes the strong adsorption of metal sulfides to sulfur-containing substances and the advantage of relatively low lithiation voltage. By using Co3Sn2S2 / C as the carrier material for the active substance sulfur (S) to prepare the S / Co3Sn2S2 / C composite material, where Co3Sn2S2 is a Shandite compound (the general formula of this type of compound is M3A2Ch2, M is one of Co, Ni, Rh, or Pd, A is one of Sn, Pb, In, Tl, or Bi; Ch is S or Se), and has a quasi-two-dimensional Co3Sn2 ferromagnetic layer forming a sandwich structure with S atoms. This structure can not only store sulfur but also relieve the volume expansion of sulfur during cycling and physically confine polysulfides during cycling. At the same time, Co3Sn2S2, as a Weyl semimetal with a special topological protection effect, its energy band structure presents an obvious electronic structure of a topological semimetal, enabling it to obtain high electrical conductivity and providing active sites to adsorb polysulfides, promoting the adsorption of polysulfides and further inhibiting the polysulfide shuttle effect. Therefore, applying the S / Co3Sn2S2 / C composite material prepared above in the present invention as the lithium-sulfur battery cathode material to a lithium-sulfur battery can exhibit excellent cycling performance and rate performance.

[0045] To more clearly illustrate the purpose and advantages of the present invention, the present invention will be further described below in conjunction with embodiments. In addition, the embodiments described in the present invention are only partial embodiments. All other embodiments obtained by those skilled in the art without creative efforts based on the embodiments described in the present invention fall within the protection scope of the present invention. Additionally, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any form, that is, it is not intended to limit the protection scope of the present invention.

[0046] Example 1

[0047] This example provides a preparation method for a cathode material of a lithium-sulfur battery:

[0048] Step 1, Take 7.14 g of CoCl₂·6H₂O and 5.22 g of SnCl₄ and dissolve them in 200 mL of deionized water. Use an ultrasonic cell disruptor to ultrasonicate for 0.8 h with an ultrasonic power of 120 W to obtain a uniform solution a. Add 2 g of nano-graphite and 0.25 g of cetyltrimethylammonium bromide, and then continue to ultrasonicate for 0.5 h to obtain a uniform suspension b.

[0049] Step 2, Slowly dropwise add 100 mL of 2 mol / L NaOH solution to the above suspension b, and stir at a stirring speed of 500 r / min for 0.5 h to obtain a suspension c. After vacuum filtration, washing, and drying, CoSn(OH)₆ / C powder is obtained.

[0050] Step 3, Take 5 g of the CoSn(OH)₆ / C powder obtained in Step 2 and 20 g of sublimed sulfur powder, mix them evenly and place them in a porcelain boat. Under an argon atmosphere, heat at a heating rate of 3 °C / min and hold at 750 °C for 2 h to obtain Co₃Sn₂S₂ / C powder.

[0051] Step 4, Mix 3 g of the Co₃Sn₂S₂ / C powder obtained in Step 3 and 7 g of sublimed sulfur powder evenly and place them in a porcelain boat. Under an argon atmosphere, heat at a heating rate of 1 °C / min and hold at 155 °C for 8 h to obtain S / Co₃Sn₂S₂ / C powder.

[0052] Example 2

[0053] This example provides a preparation method for a cathode material of a lithium-sulfur battery:

[0054] Step 1, Take 35.7 g of CoCl₂·6H₂O and 26.1 g of SnCl₄ and dissolve them in 500 mL of deionized water. Use an ultrasonic cell disruptor to ultrasonicate for 0.5 h with an ultrasonic power of 160 W to obtain a uniform solution a. Add 12.4 g of multi-walled carbon nanotubes and 3 g of polyvinylpyrrolidone, and then continue to ultrasonicate for 0.3 h to obtain a uniform suspension b.

[0055] Step 2: Slowly add 1000 mL of 1 mol / L NaOH solution drop by drop to the above-mentioned suspension b, and stir at a high speed of 450 r / min for 0.8 h to obtain suspension c. After vacuum filtration, washing, and drying, CoSn(OH)6 / C powder is obtained.

[0056] Step 3: Take 30 g of the CoSn(OH)6 / C powder obtained in Step 2 and 45 g of sublimed sulfur powder, mix them evenly, place them in a porcelain boat, and heat at a rate of 5 °C / min under a nitrogen atmosphere and hold at 650 °C for 1.5 h to obtain Co3Sn2S2 / C powder.

[0057] Step 4: Mix 15 g of the Co3Sn2S2 / C powder obtained in Step 3 and 35 g of sublimed sulfur powder evenly, place them in a porcelain boat, and heat at a rate of 2 °C / min under a nitrogen atmosphere and hold at 160 °C for 9 h to obtain S / Co3Sn2S2 / C powder.

[0058] Example 3

[0059] This example provides a method for preparing a cathode material for lithium-sulfur batteries:

[0060] Step 1: Dissolve 64.3 g of CoCl2·6H2O and 47.9 g of SnCl4 in 1000 mL of deionized water, and use an ultrasonic cell disruptor to ultrasonicate for 1.5 h with an ultrasonic power of 180 W to obtain a uniform solution a. Add 16.8 g of hard carbon 41 and 4.5 g of absolute ethanol, and continue ultrasonication for 0.5 h to obtain a uniform suspension b.

[0061] Step 2: Slowly add 420 mL of 4 mol / L NaOH solution drop by drop to the above-mentioned suspension b, and stir at a high speed of 600 r / min for 1.0 h to obtain suspension c. After vacuum filtration, washing, and drying, CoSn(OH)6 / C powder is obtained.

[0062] Step 3: Take 30 g of the CoSn(OH)6 / C powder obtained in Step 2 and 70 g of sublimed sulfur powder, mix them evenly, place them in a porcelain boat, and heat at a rate of 2 °C / min under an argon atmosphere and hold at 800 °C for 1.5 h to obtain Co3Sn2S2 / C powder.

[0063] Step 4: Mix 18 g of the Co3Sn2S2 / C powder obtained in Step 3 and 42 g of sublimed sulfur powder evenly, place them in a porcelain boat, and heat at a rate of 2 °C / min under an argon atmosphere and hold at 165 °C for 9 h to obtain S / Co3Sn2S2 / C powder.

[0064] Comparative Example 1

[0065] This comparative example provides a preparation method for a cathode material of a lithium-sulfur battery for comparison:

[0066] Step 1: Take 7.14 g of CoCl2·6H2O and 5.22 g of SnCl4 and dissolve them in 200 mL of deionized water. Use an ultrasonic cell disruptor to ultrasonicate for 0.8 h with an ultrasonic power of 120 W to obtain a uniform solution a.

[0067] Step 2: Gradually add 100 mL of 2 mol / L NaOH solution dropwise to the above solution a, and vigorously stir at a stirring speed of 500 r / min for 0.5 h. After vacuum filtration, washing, and drying, CoSn(OH)6 powder is obtained.

[0068] Step 3: Take 3 g of the CoSn(OH)6 powder obtained in Step 2 and 12 g of sublimed sulfur powder, mix them evenly, place them in a porcelain boat, and under an argon atmosphere, heat at a heating rate of 3 °C / min and hold at 750 °C for 2 h to obtain Co3Sn2S2 powder.

[0069] Step 4: Mix 3 g of the Co3Sn2S2 powder obtained in Step 3 and 7 g of sublimed sulfur powder evenly, place them in a porcelain boat, and under an argon atmosphere, heat at a heating rate of 1 °C / min and hold at 155 °C for 8 h to obtain S / Co3Sn2S2 powder.

[0070] Comparative Example 2

[0071] This comparative example provides a preparation method for a cathode material of a lithium-sulfur battery for comparison:

[0072] Mix 15 g of nano-graphite and 35 g of sublimed sulfur powder evenly, place them in a porcelain boat, and under an argon atmosphere, heat at a heating rate of 1 °C / min and hold at 155 °C for 8 h to obtain S / C powder.

[0073] Use the cathode materials obtained in the above-mentioned various examples and comparative examples as the cathode active materials, mix them with the conductive agent Ketjen black and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10 to obtain a cathode slurry. Use an automatic coater to coat the cathode slurry on the current collector aluminum foil with a coating thickness of 100 μm, and after drying, obtain a cathode sheet.

[0074] The battery assembly is completed in a glove box filled with high-purity argon gas, while controlling the content of water and oxygen in the glove box to be below 1-2 ppm. CR2032 button cells are used, with lithium sheets (purity > 99.9%) as the counter electrode, and the separator is a polyethylene PE / polypropylene PP separator. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a concentration of 1 mol / L is dissolved in 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME), with a solution volume ratio of 1:1, and 1.5% LiNO3 is added. The battery is assembled in the order of the positive electrode shell - a little electrolyte - the positive electrode material - the electrolyte - the separator - the lithium sheet - the shrapnel - the gasket - the negative electrode battery shell. Finally, the assembled battery is sealed with a battery encapsulation machine, and its electrochemical performance is tested after standing overnight.

[0075] In the voltage range of 1.7-2.8 V, the battery is activated by cycling at a current density of 0.1C for 2 cycles, and then cycled 100 times at a current density of 0.5C. The capacity retention rate after 100 cycles, the discharge specific capacity at 0.1C, and the discharge specific capacity at 0.5C of each example and comparative example are shown in Table 1. Figure 2 This is the cycling curve graph of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention at a current density of 0.5C for 100 cycles.

[0076]

[0077] Table 1

[0078] It can be seen from Table 1 above:

[0079] Compared with Comparative Examples 1 and 2, Example 1-3 has obvious advantages in the discharge specific capacity at 0.1C, the discharge specific capacity at 0.5C, and the capacity retention rate after 100 cycles at 0.5C. This shows that Co3Sn2S2 can provide active sites to adsorb polysulfides, promote the adsorption of polysulfides, and further inhibit the shuttle effect of polysulfides, thereby improving the cycling performance of the lithium-sulfur battery.

[0080] At the same time, when the current density is increased from 0.1C to 0.5C, the capacity retention rate of Example 1-3 is higher, indicating that the rate performance of Example 1-3 is more excellent. The main reason is that the energy band structure of Co3Sn2S2 shows an obvious topological semimetal electronic structure, enabling it to obtain high conductivity. After further compounding with carbon materials, it not only greatly enhances the intrinsic conductivity and extrinsic conductivity of the lithium-sulfur positive electrode, improves the electron and ion diffusion-transport kinetics, and enhances the rate performance of the lithium-sulfur battery.

[0081] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a cathode material for a lithium-sulfur battery, characterized in that The cathode material of the lithium-sulfur battery is an S / Co3Sn2S2 / C composite material, and the preparation method includes: Dissolve cobalt salt and tin salt in deionized water according to the required molar ratio, and obtain a mixed solution after ultrasonic treatment. Add a surfactant and a carbon material to the mixed solution, and continue ultrasonic treatment to obtain a first suspension; Dropwise add an alkali solution to the first suspension, and stir to obtain a second suspension; Perform vacuum filtration and washing on the second suspension to obtain CoSn(OH)6 / C powder; Grind the CoSn(OH)6 / C powder and an excessive amount of sublimed sulfur powder evenly, then load them into a porcelain boat, and obtain Co3Sn2S2 / C powder through high-temperature sulfidation; Further add sublimed sulfur powder to the Co3Sn2S2 / C powder, grind evenly and load it into a porcelain boat, and obtain the S / Co3Sn2S2 / C composite material through melt diffusion; 2. The preparation method according to claim 1, characterized in that, The cobalt salt includes one of cobalt chloride, cobalt nitrate or cobalt sulfate; the tin salt includes tin chloride.

3. The preparation method according to claim 1, characterized in that, The surfactant includes at least one or a combination of more than one of absolute ethanol, cetyltrimethylammonium bromide, polyvinylpyrrolidone, sodium citrate or sodium dodecylbenzenesulfonate, and the dosage of the surfactant is 1% - 5% of the total mass of the cobalt salt and the tin salt; The carbon material includes at least one or a combination of more than one of nano-graphite, micro-graphite, hard carbon, soft carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, graphdiyne, and the dosage of the carbon material is 10% - 20% of the total mass of the cobalt salt and the tin salt; The ultrasonic mixing is carried out in an ultrasonic crusher, the ultrasonic power is 110 - 180W, and the ultrasonic time is 0.5 - 2h.

4. The preparation method according to claim 1, characterized in that, The alkali solution includes a NaOH solution with a concentration of 1 - 10mol / L; The stirring speed of the stirring is 300 - 800r / min; the stirring duration is 0.5 - 1.5h.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the CoSn(OH)6 / C powder to the excessive sublimed sulfur powder is 1:4 - 2:3; The high-temperature sulfidation method includes: under a protective atmosphere, raise the temperature to 600 - 900°C at a heating rate of 3 - 5°C / min for calcination, and the holding time of the calcination is 1.5 - 2.5h; the protective atmosphere specifically includes at least one of a hydrogen-argon mixture, nitrogen, helium, neon, argon, krypton and xenon.

6. The preparation method according to claim 1, wherein, The mass ratio of the Co3Sn2S2 / C powder to the further added sublimed sulfur powder is 3:7; The melt diffusion method includes: under a protective atmosphere, raise the temperature to 140 - 160°C at a heating rate of 1 - 5°C / min for heat preservation, and the heat preservation time is 8 - 15h; the protective atmosphere specifically includes at least one of nitrogen, helium, neon, argon, krypton and xenon.

7. A cathode material of a lithium-sulfur battery prepared by the preparation method according to any one of claims 1 - 6 above.

8. A positive electrode plate, characterized in that, The positive electrode plate includes: the cathode material of the lithium-sulfur battery according to claim 7 above.

9. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes the positive electrode plate according to claim 8 above.

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