Organic Sulfide, Graphene-Organic Sulfide Composite Material, Active Cathode Material, and Preparation Method and Application Thereof

Abstract

This application relates to the technical field of lithium-sulfur battery cathode materials, and discloses an organic sulfide, a graphene-organic sulfide composite material, an active cathode material, and their preparation methods and applications. The organic sulfide is prepared by a substitution reaction of 1,2,3,4,5,6-hexamercaptobenzene and sulfur in a solvent; the graphene-organic sulfide composite material includes a carbon-based host material and an organic sulfide adsorbed on the surface of the carbon-based host material. The organic sulfide of this application chemically fixes a large number of redox-active polysulfide chains on the aromatic skeleton of 1,2,3,4,5,6-hexamercaptobenzene through S-S bonds. The carbon-based host material and 1,2,3,4,5,6-hexamercaptobenzene jointly provide a physical barrier, chemical adsorption, and stable chemical bonds, effectively inhibiting the shuttle and dissolution of polysulfides, which are charge-discharge intermediates; at the same time, the carbon-based host material modified with metal compounds and doped with heteroatoms has the functions of enhancing conductivity and rapidly catalyzing conversion reactions, realizing high specific capacity, high cycle stability, and high rate performance of lithium-sulfur batteries.

Description

Technical Field

[0001] This application relates to the technical field of lithium-sulfur battery cathode materials, and specifically relates to an organic sulfide, a graphene-organic sulfide composite material, an active cathode material, and their preparation methods and applications. Background Art

[0002] Lithium-ion batteries have advantages such as a light mass, a high energy density, and zero memory effect, and are widely used in fields such as portable electronic devices, transportation, and large-scale energy storage. Traditional lithium-ion batteries use inorganic intercalation-type cathode materials, such as lithium cobalt oxide (LiCoO 2 ), lithium manganese oxide (LiMn 2 O 4 ), and lithium iron phosphate (LiFePO 4 ), etc., and graphite and lithium titanate (Li 4 Ti 5 O 12 ) etc. for the anode. Further improvement of the theoretical specific capacity of these electrode materials has reached a bottleneck period, and the heavy metal elements among them also face serious resource and environmental problems, which is not conducive to their future large-scale sustainable development.

[0003] A lithium-sulfur battery consists of a conversion-type sulfur cathode and a lithium anode. The sulfur cathode undergoes a reversible redox reaction with multiple electron transfers during charge and discharge A series of lithium polysulfide intermediates (LiPSs) are generated during the redox process, and finally Li 2 S products are formed, with a high theoretical specific capacity of 1672 mAh g -1 , and having advantages such as rich resources, low cost, and low environmental pollution; the lithium anode undergoes a reaction process during charge and discharge, with a high theoretical specific capacity of 3860 mAh g -1 . The average output voltage of a lithium-sulfur battery is about 2.1 V, with a high theoretical energy density of 2600 Wh kg -1 . Therefore, lithium-sulfur batteries are expected to become an important direction for the large-scale development of future high-energy density batteries.

[0004] A variety of lithium-sulfur batteries have been developed and shown excellent electrochemical performance. However, their further development and large-scale commercialization also face a series of challenges. First, the lithium polysulfide intermediate LiPSs generated by the sulfur cathode during charge and discharge have a high solubility in the electrolyte. During the cycling process, the active cathode material is continuously lost. The LiPSs dissolved in the electrolyte will shuttle through the separator to the anode side and undergo a series of side reactions on the anode surface, resulting in self-discharge, specific capacity decay, and poor cycle stability of the battery. Second, the cathode material S 8 and its discharge product Li 2S has a large density difference, and the electrode will undergo severe volume changes during charge and discharge, resulting in the cracking and differentiation of the electrode material and the reduction of the battery cycle life. In addition, insoluble S 8 and Li 2 S has poor conductivity, and the conversion reaction kinetics of polysulfides is poor. These factors seriously affect the battery reaction kinetics and limit its rate performance.

[0005] Based on this, there is an urgent need to develop a sulfur cathode host material. Summary of the Invention

[0006] This application provides an organic sulfide, a graphene-organic sulfide composite material, an active cathode material, and their preparation methods and applications, aiming to solve the problems of specific capacity attenuation, poor cycle stability, and poor rate performance of existing lithium-sulfur batteries due to the high solubility, easy cracking and differentiation, and poor conductivity of the cathode material.

[0007] To achieve the above object, this application adopts the following technical solutions.

[0008] In the first aspect of this application, an organic sulfide is provided, which has the chemical structure shown in formula (1):

[0009]

[0010] Among them, n is the number of sulfur atoms, and 2 ≤ n ≤ 8.

[0011] In some embodiments, it is prepared by the substitution reaction of 1,2,3,4,5,6-hexamercaptobenzene and sulfur in a solvent;

[0012] The mass ratio of 1,2,3,4,5,6-hexamercaptobenzene to sulfur is 1:(1.5 - 6).

[0013] In some embodiments, the solvent includes carbon disulfide or toluene.

[0014] In some embodiments, the temperature of the reaction is 20 - 50 °C, and the reaction time is 12 - 48 h.

[0015] In the second aspect of this application, a graphene-organic sulfide composite material is provided, which includes a carbon-based host material and an active component adsorbed on the surface of the carbon-based host material;

[0016] The active component includes the above-mentioned organic sulfide.

[0017] In some embodiments, the carbon-based host material includes graphene, carbon nanotubes, nitrogen-doped graphene, Ketjen black, MoS 2 modified nitrogen-doped graphene or CoS 2At least one of the modified graphene.

[0018] In a third aspect of the present application, there is provided a method for preparing the above graphene-organic sulfide composite material, including:

[0019] Disperse 1,2,3,4,5,6-hexamercaptobenzene, sulfur and a carbon-based host material in a solvent, react at 20 - 50 °C for 12 - 48 h under an inert atmosphere, collect the solid phase after the reaction, and dry it to obtain the graphene-organic sulfide composite material.

[0020] In another aspect of the present application, there is provided an active cathode material, including the above organic sulfide or the above graphene-organic sulfide composite material.

[0021] In another aspect of the present application, there is provided the application of the above active cathode material in a lithium-sulfur battery.

[0022] In another aspect of the present application, there is provided a lithium-sulfur battery, the cathode of which includes the above active cathode material.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] The organic sulfide and the graphene-organic sulfide composite material of the present application have specific structures and functions. They are alternately composed of 1,2,3,4,5,6-hexamercaptobenzene and polysulfide chains, and the two units are connected by S-S bonds. A large number of redox-active polysulfide chains are chemically fixed on the aromatic skeleton of 1,2,3,4,5,6-hexamercaptobenzene through S-S bonds. The carbon-based host material and 1,2,3,4,5,6-hexamercaptobenzene jointly provide a physical barrier, chemical adsorption and stable chemical bonds, effectively inhibiting the shuttle and dissolution of polysulfide intermediates during charge and discharge; at the same time, the carbon-based host material modified by metal compounds and doped with heteroatoms has the functions of enhancing conductivity and rapidly catalyzing conversion reactions, and can also alleviate the volume change of the organic sulfide or the graphene-organic sulfide composite material during charge and discharge, further improving its stability and reaction kinetics, and thus realizing the high specific capacity, high cycle stability and high rate performance of the lithium-sulfur battery.

[0025] The organic sulfide and the graphene-organic sulfide composite material of the present application contain redox-reactive polysulfide bonds connected by aromatic rings, and are particularly suitable for use as the active cathode material of a lithium-sulfur battery. The lithium-sulfur battery containing this active cathode material has a high specific capacity, high cycle stability and high rate performance. Description of the Drawings

[0026] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0027] Figure 1 Infrared spectrum diagram of the organic sulfide prepared in Example 1;

[0028] Figure 2 Thermogravimetric analysis test diagram of the organic sulfide prepared in Example 1;

[0029] Figure 3 Infrared spectrum diagram of the graphene-organic sulfide composite prepared in Example 3;

[0030] Figure 4 Charge-discharge cycle test diagram of lithium-sulfur battery 1;

[0031] Figure 5 Capacity-voltage curve diagram of lithium-sulfur battery 2;

[0032] Figure 6 Charge-discharge cycle test diagram of lithium-sulfur battery 2;

[0033] Figure 7 Charge-discharge cycle test diagram of lithium-sulfur battery 3;

[0034] Figure 8 Charge-discharge cycle test diagram of lithium-sulfur battery D1. Detailed implementation manners

[0035] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0036] In the following description of this embodiment, the terms "include", "comprise", "have" and "contain" are all open-ended terms, that is, they are intended to include but not limited to.

[0037] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and both A and B exist simultaneously. Where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are an "or" relationship.

[0038] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0039] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0040] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence numbers do not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic and should not constitute any limitation to the implementation process of the embodiments of this application.

[0041] Those skilled in the art should understand that the numerical ranges in the embodiments of this application should be understood as specifically disclosing each intermediate value between the upper and lower limits of the range. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in this application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0042] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0043] In a first aspect, this application provides an organic sulfide having a chemical structure shown in formula (1):

[0044]

[0045] Wherein, n is the number of sulfur atoms, and 2 ≤ n ≤ 8.

[0046] The organic sulfide represented by formula (1) is composed of 1,2,3,4,5,6 - hexamercaptobenzene and polysulfide chains alternatingly, and the two units are connected by S - S bonds. The six mercapto groups on each 1,2,3,4,5,6 - hexamercaptobenzene can be substituted by polysulfide chains, and the number of polysulfide substitutions is 1, 2, 3, 4, 5, or 6. Each polysulfide chain contains 2 - 8 sulfur atoms. The polysulfide chains fixed by S - S bonds are chemically fixed on the aromatic skeleton of 1,2,3,4,5,6 - hexamercaptobenzene, effectively inhibiting the dissolution and shuttle of polysulfide intermediates, improving the stability of the material, and thus enhancing the cycling performance of the battery.

[0047] The organic sulfide of the present application is prepared by a substitution reaction of 1,2,3,4,5,6 - hexamercaptobenzene and a series of stoichiometric sulfur in a solvent. Among them, the reaction is preferably carried out under anaerobic conditions, the reaction temperature is 20 - 50 °C, preferably 20 - 30 °C; the reaction time is 12 - 48 h, preferably 18 - 36 h.

[0048] The present application preferably has a mass ratio of 1,2,3,4,5,6 - hexamercaptobenzene to sulfur of 1:(1.5 - 6); preferably the solvent includes carbon disulfide or toluene.

[0049] In a second aspect, the present application provides a graphene - organic sulfide composite material, including a carbon - based host material and an active ingredient adsorbed on the surface of the carbon - based host material; the active ingredient includes the above - mentioned organic sulfide; the carbon - based host material includes at least one of graphene, carbon nanotubes, nitrogen - doped graphene, Ketjen black, MoS 2 modified nitrogen - doped graphene or CoS 2 modified graphene.

[0050] In the present application, the preparation method of the graphene - organic sulfide composite material includes:

[0051] Weigh 1,2,3,4,5,6 - hexamercaptobenzene, sulfur, and the carbon - based host material according to a mass ratio of 1:(1.5 - 6):(0.2 - 2), and add them into a round - bottom flask respectively, and introduce an inert gas to protect the reaction system; add a solvent to the system, and stir at a constant temperature for reaction; after the reaction is completed, let the reaction system stand, discard the supernatant, collect the lower - layer solid precipitate, and heat - dry it under vacuum to obtain the product, which is the graphene - organic sulfide composite material. Among them, the inert gas is preferably argon.

[0052] The present application provides an active cathode material, including the above - mentioned organic sulfide or the above - mentioned graphene - organic sulfide composite material.

[0053] The active cathode material of this application, namely organic sulfides and their composites, has a stable structure, that is, the structure shown in formula (1). This structure contains redox-active polysulfide bonds connected by aromatic rings and is suitable for lithium-sulfur batteries, especially as the active cathode material for lithium-sulfur batteries. The active cathode material of this application can be applied to lithium-sulfur batteries. The lithium-sulfur battery containing the active cathode material has a high specific capacity, high cycle stability, and rate performance.

[0054] For the graphene-organic sulfide composite of the active cathode material of this application, when the organic sulfide is compounded with the carbon-based host material, the active material is dispersed on the surface of the porous conductive carbon material. The porous conductive carbon material can act as a physical barrier to inhibit the dissolution and shuttle of polysulfides, and at the same time can relieve the volume change of the electrode during charge and discharge, further improving the cycle stability of the material. In addition, the material also has enhanced conductivity and improved kinetics, which is beneficial to improving its rate performance. Among them, when the organic sulfide is compounded with a heteroatom-doped carbon-based host material modified with a metal compound, the host material provides both a physical barrier and chemical adsorption for polysulfides. The metal compound is beneficial to catalyze the conversion reaction of polysulfides, synergistically improving the reaction kinetics and cycle stability of the material.

[0055] This application also provides a lithium-sulfur battery, the cathode of which includes the above-mentioned active cathode material. The lithium-sulfur battery prepared using the organic sulfides and their composites of this application has a high mass specific capacity, good cycle stability, and rate performance.

[0056] In this application, the lithium-sulfur battery can be prepared by conventional techniques in the art.

[0057] Specifically, the preparation method of the lithium-sulfur battery includes: grinding and mixing an organic sulfide or a graphene-organic sulfide composite with a conductive additive and a binder in N-methylpyrrolidone (NMP) to form a slurry, coating the slurry on the surface of a carbon-coated aluminum foil current collector, heating and drying to make a positive electrode film, and cutting the positive electrode film into a circle to make a positive electrode sheet; separating the positive electrode sheet and the negative lithium foil through a separator, adding an electrolyte, and assembling to obtain a button-type lithium-sulfur battery. Among them, the mass ratio of the organic sulfide or graphene-organic sulfide composite, the conductive additive, and the binder is (40-80):(50-10):10.

[0058] Among them, the conductive additive can be selected from at least one of SuperP, Ketjenblack, or carbon nanotubes; the electrolyte is a solution obtained by dissolving a lithium salt in an organic solvent, and the concentration of the electrolyte salt is 0.5-2.0 mol / L, preferably 1.0 mol / L. The lithium salt is selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium hexafluorophosphate (LiPF 6A mixed salt made by mixing one or several of the salts in any proportion, and the organic solvent is a mixed solvent made by mixing one or several of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), ethylene carbonate (EC) or dimethyl carbonate (DMC) in any proportion.

[0059] The following further illustrates the present application through examples.

[0060] Example 1

[0061] This example provides a method for preparing an organic sulfide, including:

[0062] 50 mg of 1,2,3,4,5,6-hexamercaptobenzene and 200 mg of sulfur powder were successively added to a 50 mL round-bottom flask, then 20 mL of carbon disulfide was added, and the mixture was stirred at 25 °C for 24 hours. After the reaction was completed, the reaction system was allowed to stand, the supernatant was removed and the solid precipitate product was retained. The product was vacuum dried at 60 °C for 6 hours to obtain organic sulfur compound 1.

[0063] Example 2

[0064] This example provides a method for preparing an organic sulfide, including:

[0065] 50 mg of 1,2,3,4,5,6-hexamercaptobenzene and 150 mg of sulfur powder were successively added to a 25 mL round-bottom flask to make the reaction system under argon protection, then 10 mL of toluene was added, and the mixture was stirred at 50 °C for 12 hours. After the reaction was completed, the reaction system was allowed to stand. After the liquid was separated, the supernatant was removed, and the solid precipitate product was collected. The product was vacuum dried at 60 °C for 12 hours to obtain organic sulfur compound 2.

[0066] Example 3

[0067] This example provides a method for preparing a graphene-organic sulfide composite material, including:

[0068] 50 mg of 1,2,3,4,5,6-hexamercaptobenzene, 200 mg of sulfur powder and 50 mg of MoS 2 Modified nitrogen-doped graphene host material were successively added to a 50 mL round-bottom flask to make the reaction system under argon protection, 20 mL of carbon disulfide solvent was added, and the mixture was stirred at 25 °C for 24 hours. After the reaction was completed, the reaction system was allowed to stand. After the liquid was separated, the supernatant was removed, and the solid precipitate product was collected. The product was vacuum dried at 60 °C for 12 hours to obtain organic sulfur compound composite material 3.

[0069] Example 4

[0070] This embodiment provides a method for preparing a graphene-organic sulfide composite material, including:

[0071] Add 75 mg of 1,2,3,4,5,6-hexamercaptobenzene, 200 mg of sulfur powder, and 25 mg of MoS 2 Modified graphene host material into a 50 mL round-bottom flask in sequence, make the reaction system in an argon-protected state, then add 20 mL of carbon disulfide, stir at 25 °C for 24 hours, after the reaction is completed, let the reaction system stand still, remove the supernatant after the liquid is stratified, collect the solid precipitation product, and vacuum-dry the product at 60 °C for 12 hours to obtain the organic sulfur compound composite material 4.

[0072] Example 5

[0073] This embodiment provides a method for preparing a graphene-organic sulfide composite material, including:

[0074] Add 50 mg of 1,2,3,4,5,6-hexamercaptobenzene, 200 mg of sulfur powder, and 50 mg of CoS 2 Modified graphene host material into a 50 mL round-bottom flask in sequence, make the reaction system in an argon-protected state, then add 20 mL of carbon disulfide, stir at 30 °C for 18 hours, after the reaction is completed, let the reaction system stand still, remove the supernatant after the liquid is stratified, collect the solid precipitation product, and vacuum-dry the product at 60 °C for 8 hours to obtain the organic sulfur compound composite material 5.

[0075] Perform performance and structure characterization on the organic sulfide prepared in Example 1, including infrared spectroscopy test and thermogravimetric analysis.

[0076] Among them, the infrared spectrum is as Figure 1 shown. From Figure 1 it can be seen that an infrared characteristic peak of S-S appears at 468 cm -1 indicating that a substitution reaction occurred between 1,2,3,4,5,6-hexamercaptobenzene and sulfur, generating an S-S linkage bond.

[0077] The thermogravimetric analysis test results are as Figure 2 shown. From Figure 2 it can be seen that the organic sulfur polymer shows a mass retention rate of more than 96% at 200 °C, having relatively high thermal stability.

[0078] Perform an infrared spectroscopy test on the graphene-organic sulfide composite material prepared in Example 3, and the results are as Figure 3 shown. From Figure 3 it can be seen that the graphene-organic sulfide composite material has an infrared absorption peak at 468 cm -1The infrared peak with S-S bonds indicates that substitution reaction has occurred between 1,2,3,4,5,6-hexanethiolbenzene and sulfur, forming a polymer containing S-S linkage bonds.

[0079] Example 6

[0080] This example provides a lithium-sulfur battery, whose positive electrode active material is the organic sulfide prepared in Example 1. Its preparation method includes:

[0081] Prepare a slurry using the organic sulfide prepared in Example 1 as the positive electrode active material, Ketjen black as the conductive additive, and PVDF as the binder, where the mass ratio of the positive electrode active material, Ketjen black, and PVDF is 7:2:1. Coat the slurry on the surface of a carbon-coated aluminum foil current collector, and after drying at 60 °C, obtain a positive electrode membrane, which is cut into circular positive electrode wafers.

[0082] Use a metallic lithium foil as the negative electrode and Celgard 2325 as the separator; use LiTFSI as the electrolyte, and a mixture of DME and DOL with a volume ratio of 1:1 as the solvent to prepare an electrolyte solution with a molar concentration of 1 M, and add an additive LiNO 3 , with a concentration of 1 wt%. Assemble a coin-type (Cion-type 2025) lithium-sulfur battery in a glove box filled with argon gas, denoted as lithium-sulfur battery 1.

[0083] Example 7

[0084] This example provides a lithium-sulfur battery, whose positive electrode active material is the graphene-organic sulfide composite material prepared in Example 3. Its preparation method includes:

[0085] Prepare a slurry using the graphene-organic sulfide composite material prepared in Example 3 as the positive electrode active material, Ketjen black as the conductive additive, and PVDF as the binder, where the mass ratio of the positive electrode active material, Ketjen black, and PVDF is 7:2:1. Coat the slurry on the surface of a carbon-coated aluminum foil current collector, and after drying at 60 °C, obtain a positive electrode membrane, which is cut into circular positive electrode wafers.

[0086] Use a metallic lithium foil as the negative electrode and Celgard 2325 as the separator; use LiTFSI as the electrolyte, and a mixture of DME and DOL with a volume ratio of 1:1 as the solvent to prepare an electrolyte solution with a molar concentration of 1 M, and add an additive LiNO 3 , with a concentration of 1 wt%. Assemble a coin-type (Cion-type 2025) lithium-sulfur battery in a glove box filled with argon gas, denoted as lithium-sulfur battery 2.

[0087] Example 8

[0088] This embodiment provides a lithium-sulfur battery, and its positive electrode active material is the graphene-organic sulfide composite material prepared in Example 3. Its preparation method includes:

[0089] Using the graphene-organic sulfide composite material prepared in Example 3 as the positive electrode active material, Ketjen black as the conductive additive, and PVDF as the binder to prepare a slurry, where the mass ratio of the positive electrode active material, Ketjen black, and PVDF is 7:2:1. Coating the slurry on the surface of a carbon-coated aluminum foil current collector, drying at 60 °C to obtain a positive electrode film, and cutting it to obtain a positive electrode wafer.

[0090] Using a lithium metal foil as the negative electrode and Celgard 2325 as the separator; using an in-situ polymerized gel electrolyte, and the electrolyte precursor solution is a DOL solution of 1 M LiTFSI + 0.5 M LiFSI. Assembling it into a coin-type (Cion-type 2025) lithium-sulfur battery in a glove box filled with argon. After the battery is assembled, it is left to stand and heated at 60 °C, and DOL undergoes a ring-opening polymerization reaction under the initiation of LiFSI to in-situ generate a gel polymer electrolyte. The obtained lithium-sulfur battery is denoted as lithium-sulfur battery 3.

[0091] Comparative Example 1

[0092] This comparative example provides a conventional lithium-sulfur battery, and its positive electrode active material is sulfur. Its preparation method includes:

[0093] Using sulfur as the positive electrode active material, Ketjen black as the conductive additive, and PVDF as the binder to prepare a slurry, where the mass ratio of the positive electrode active material, Ketjen black, and PVDF is 7:2:1. Coating the slurry on the surface of a carbon-coated aluminum foil current collector, drying at 60 °C to obtain a positive electrode film, and cutting it to obtain a positive electrode wafer.

[0094] Using a lithium metal foil as the negative electrode and Celgard 2325 as the separator; using LiTFSI as the electrolyte, and a mixture of DME and DOL with a volume ratio of 1:1 as the solvent to prepare an electrolyte with a molar concentration of 1 M, and adding an additive LiNO3 to the electrolyte with a concentration of 1 wt%. Assembling it into a coin-type (Cion-type 2025) lithium-sulfur battery in a glove box filled with argon, denoted as lithium-sulfur battery D1.

[0095] The lithium-sulfur batteries 1-3 prepared in Examples 1-3 and the lithium-sulfur battery D1 prepared in Comparative Example 1 are respectively subjected to electrochemical performance tests.

[0096] The test results of lithium-sulfur battery 1 are as Figure 4 shown. It can be seen from Figure 4 that within the test voltage window range of 1.7 - 2.8 V (vs Li / Li + )), at 1672 mA g-1 At a current density of 1.0 C, the discharge specific capacity of the battery can reach 516.7 mAh g -1 , showing a relatively high specific capacity and improved capacity utilization, and also exhibiting high cycle stability.

[0097] The test results of Lithium-sulfur battery 2 are as Figure 5 and Figure 6 shown. As Figure 5 can be seen, within the test voltage window range of 1.7 - 2.8 V (vs Li / Li + ), at a current density of 83.6 mA g -1 (0.05 C), the discharge specific capacity of the battery can reach 1573.8 mAh g -1 . As Figure 6 can be seen, at a current density of 1672 mA g -1 (1.0 C), its initial discharge specific capacity can reach 844.5 mAh g -1 . During the 500-cycle charge-discharge cycle test, the capacity retention rate per cycle on average can reach 99.94%, showing good charge-discharge cycle stability.

[0098] The test results of Lithium-sulfur battery 3 are as Figure 7 shown. As Figure 7 can be seen, within the test voltage window range of 1.7 - 2.8 V (vs Li / Li + ), at a current density of 167.2 mA g -1 (0.1 C), the initial discharge specific capacity can reach 1341.5 mAh g -1 .

[0099] The test results of Lithium-sulfur battery D1 prepared in Comparative Example 1 are as Figure 8 shown. As Figure 8 can be seen, within the test voltage window range of 1.7 - 2.8 V (vs Li / Li + ), at a current density of 1672 mA g -1 (1.0 C), Lithium-sulfur battery D1 shows an initial discharge specific capacity of 322.3 mAh g -1 . After 500 cycles, the remaining specific capacity is 120.6 mAh g -1 , with relatively low capacity utilization and poor cycle stability.

[0100] From the above test results, it can be seen that the organic sulfide and graphene-organic sulfide composite of the present application are used as the positive electrode active material of the lithium-sulfur battery, and various lithium-sulfur batteries containing this positive electrode active material all have high specific capacity, high cycle stability and high rate performance. In particular, when the graphene-organic sulfide composite is used as the positive electrode active material of the lithium-sulfur battery, within the test voltage window range of 1.7 - 2.8 V (vs Li / Li + ), at a current density of 83.6 mA g -1 (0.05 C), the discharge specific capacity of the battery can reach 1573.8 mAh g -1 , showing a very high discharge specific capacity; at a current density of 1672 mA g -1 (1.0 C), its initial discharge specific capacity can reach 844.5 mAh g -1 , and in the charge-discharge cycle test of 500 cycles, the capacity retention rate per cycle on average can reach 99.94%, indicating very high charge-discharge cycle stability.

[0101] Although the present application has been described in detail in the specification with general descriptions and specific implementation examples, based on the present application, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present application all fall within the scope of protection required by the present application.

Claims

1. An organic sulfide, characterized in that It has the chemical structure shown in formula (1): Here, n is the number of sulfur atoms, 2≤n≤8.

2. The organic sulfide according to claim 1, characterized in that It is prepared by a substitution reaction between 1,2,3,4,5,6-hexamercaptobenzene and sulfur in a solvent; The mass ratio of 1,2,3,4,5,6-hexamercaptobenzene to sulfur is 1:(1.5-6); The solvent includes carbon disulfide or toluene.

3. The organic sulfide according to claim 2, characterized in that The reaction temperature is 20-50°C and the reaction time is 12-48h.

4. A graphene-organic sulfide composite material, characterized in that: It includes a carbon-based host material and an active component adsorbed on the surface of the carbon-based host material; The active ingredient comprises the organic sulfide according to claim 1.

5. The graphene-organosulfide composite material according to claim 4, characterized in that: The carbon-based host material includes at least one of graphene, carbon nanotubes, nitrogen-doped graphene, Ketjen black, MoS2-modified nitrogen-doped graphene or CoS2-modified graphene.

6. The method for preparing the graphene-organosulfide composite material according to claim 4, characterized in that: include: 1,2,3,4,5,6-hexamercaptobenzene, sulfur and carbon-based host materials are dispersed in a solvent, reacted at 20-50° C. under an inert atmosphere for 12-48 hours, and after the reaction, the solid phase is collected and dried to obtain a graphene-organic sulfide composite material.

7. An active positive electrode material, characterized in that The method comprises the organic sulfide according to any one of claims 1 to 3, or the graphene-organic sulfide composite material according to any one of claims 4 to 5.

8. Use of the active positive electrode material according to claim 7 in a lithium-sulfur battery.

9. A lithium-sulfur battery, characterized in that: The positive electrode thereof comprises the active positive electrode material as claimed in claim 7.

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