Composite sulfur positive electrode material and preparation method and application thereof

Abstract

The application relates to the technical field of lithium-sulfur battery positive electrode materials, and discloses a composite sulfur positive electrode material and a preparation method and application thereof. The composite sulfur positive electrode material comprises a carbon-based host material, sulfur combined on the surface of the carbon-based host material and an organic conductive small molecule; the mass ratio of the organic conductive small molecule, the sulfur and the carbon-based host material is (0.1-20):(30-90):(10-40). The composite sulfur positive electrode material reduces the solubility of the sulfur positive electrode material, inhibits the volume change of the sulfur positive electrode material and improves the conductivity of the sulfur positive electrode material through the synergistic effect of the organic conductive small molecule and the carbon-based host material. The cyanide in the organic conductive small molecule fixes the polysulfide intermediate in the charging and discharging through electrostatic adsorption, and the porous conductive carbon material can inhibit the dissolution and shuttling of the polysulfide as a physical barrier; in addition, the composite sulfur positive electrode material containing the metal-modified organic conductive small molecule also has the function of quickly catalyzing the conversion reaction, realizes the high specific capacity, high cycle stability and high rate performance of the lithium-sulfur battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium-sulfur battery positive electrode materials, in particular to a composite sulfur positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in portable electronic devices, electric vehicles and energy storage fields due to their light weight, high energy density and no memory effect; however, the theoretical specific capacity of traditional lithium ion battery electrode materials is limited, and the inclusion of heavy metal elements brings problems in resources and environment, limiting their large-scale sustainable development. Compared with lithium ion batteries, lithium-sulfur batteries have high theoretical specific capacity and no heavy metals, and are expected to become an important direction for large-scale development of future high-energy density batteries.

[0003] Lithium-sulfur batteries are composed of a sulfur positive electrode and a lithium negative electrode, and the sulfur positive electrode undergoes reversible redox reactions during charging and discharging to generate lithium polysulfide intermediates and then generate Li2S, with a theoretical specific capacity of 1672 mAh g -1 , and at the same time, the resources are abundant, the cost is low, and the pollution is small; the lithium negative electrode reaction is with a theoretical specific capacity of 3860 mAh g -1 . The average output voltage of lithium-sulfur batteries is about 2.1 V, and the theoretical energy density is 2600 Wh kg -1 , which has excellent electrochemical performance, and is expected to bring new breakthroughs and changes to the energy storage field and help the construction and improvement of sustainable energy systems.

[0004] However, existing lithium-sulfur batteries still face a series of challenges. First, the lithium polysulfide intermediates LiPSs generated by the sulfur positive electrode during charging and discharging have high solubility in the electrolyte, and the positive active material is continuously lost during the cycle process. LiPSs dissolved in the electrolyte will shuttle through the separator to the negative electrode side and undergo a series of side reactions on the negative electrode surface, resulting in self-discharge, specific capacity decay and poor cycle stability of the battery. Secondly, the positive electrode material S8 and its discharge product Li2S have a large density difference, and the electrode will undergo serious volume change during charging and discharging, resulting in the cracking and differentiation of the electrode material and the reduction of the cycle life of the battery. In addition, insoluble S8 and Li2S have poor conductivity, and the conversion reaction kinetics of polysulfides is poor, which seriously affects the reaction kinetics of the battery and limits its rate performance.

[0005] Therefore, it is urgent to develop a composite sulfur positive electrode material. SUMMARY

[0006] The application provides a composite sulfur positive electrode material and a preparation method and application thereof, and aims to solve the problems of capacity attenuation, poor cycle stability and poor rate performance of existing lithium-sulfur batteries due to high solubility, easy cracking and poor conductivity of the sulfur positive electrode material.

[0007] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions.

[0008] In a first aspect, the application provides a composite sulfur positive electrode material, which comprises a carbon-based host material and sulfur and an organic conductive small molecule combined on the surface of the carbon-based host material.

[0009] The mass ratio of the organic conductive small molecule, the sulfur and the carbon-based host material is (0.1-20):(30-90):(10-40).

[0010] Preferably, the organic conductive small molecule comprises at least one of TNCQ, a TNCQ derivative, tetrathiafulvalene or tetracyanoethylene.

[0011] Preferably, the organic conductive small molecule has the chemical structure shown in the following formula:

[0012]

[0013] wherein R1, R2, R3 and R4 are each independently selected from a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted C1-C 12 alkyl group or a substituted or unsubstituted C2-C 12 alkenyl group;

[0014] or,

[0015] the organic conductive small molecule is a composite of TCNQ and tetrathiafulvalene in a mass ratio of (0-20):(0-20);

[0016] or,

[0017] the organic conductive small molecule is a composite of TCNQ and tetracyanoethylene in a mass ratio of (0-20):(0-20).

[0018] Preferably, the organic conductive small molecule has the chemical structure shown in the following formula:

[0019]

[0020] wherein M is any one or more of Li, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.

[0021] Preferably, the carbon-based host material comprises at least one of graphene, carbon nanotubes, nitrogen-doped graphene and Ketjen black.

[0022] In a second aspect of the present application, a preparation method of the composite sulfur cathode material is provided, comprising:

[0023] S1, dispersing the organic conductive small molecule, sulfur powder and carbon-based host material in an organic solvent, and performing a reaction under an inert atmosphere, collecting a solid-phase product to obtain a precursor;

[0024] S2, adding the precursor into a reaction kettle, and performing a reaction under an inert atmosphere to obtain the composite sulfur cathode material.

[0025] Preferably, the organic solvent comprises at least one of carbon disulfide, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, toluene or ethylene glycol;

[0026] and / or,

[0027] The inert atmosphere is a nitrogen or argon atmosphere.

[0028] Preferably, the reaction temperature in step S1 is 20-50℃, and the reaction time is 12-48h; the reaction temperature in step S2 is 145-200℃, and the reaction time is 6-36h.

[0029] In a third aspect of the present application, the composite sulfur cathode material is applied in a lithium-sulfur battery.

[0030] In a fourth aspect of the present application, a lithium-sulfur battery is provided, wherein the cathode comprises the composite sulfur cathode material.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The composite sulfur cathode material of the present application reduces the solubility of the sulfur cathode material, inhibits the volume change of the sulfur cathode material and improves the conductivity thereof through the synergistic effect of the organic conductive small molecule and the carbon-based host material. In the composite sulfur cathode material of the present application, the organic conductive small molecule is uniformly dispersed on the surface of the porous conductive carbon material, the cyan group in the organic conductive small molecule can fix the polysulfide intermediate through electrostatic adsorption, and the porous conductive carbon material can inhibit the dissolution and shuttling of the polysulfide as a physical barrier. In addition, the composite sulfur cathode material comprising the metal-modified organic conductive small molecule also has the effect of rapidly catalyzing the conversion reaction, which can relieve the volume change of the composite sulfur cathode material during the charging and discharging process, and further improve the stability and reaction kinetics thereof.

[0033] The composite sulfur cathode material of the present application has low solubility, small volume change and excellent conductivity, and is particularly suitable for lithium-sulfur batteries; the lithium-sulfur battery comprising the cathode active material has high specific capacity, high cycle stability and high rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0035] Figure 1 Thermogravimetric analysis test graph of the organic sulfide prepared for Example 1;

[0036] Figure 2 Charge-discharge cycle test graph of lithium-sulfur battery 1;

[0037] Figure 3 EIS test graph of lithium-sulfur battery 1;

[0038] Figure 4 Charge-discharge cycle test graph of lithium-sulfur battery 2;

[0039] Figure 5 Charge-discharge cycle test graph of lithium-sulfur battery 3;

[0040] Figure 6 Charge-discharge cycle test graph of lithium-sulfur battery D1

[0041] Figure 7 EIS test graph of lithium-sulfur battery D1. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely in the following description of the embodiments of the present application in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0043] In the following description of the present embodiment, the terms "include", "contain", "have" and "comprise" and the like are all open terms, that is, they mean including but not limited to.

[0044] In the following description of the present embodiment, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following three cases: A exists alone, B exists alone and A and B exist at the same time. Wherein A, B can be singular or plural. The character " / " generally represents that the associated objects before and after are in an "or" relationship.

[0045] In the following description of the present embodiments, the term "at least one" means one or more and the term "multiple" means two or more. The phrase "at least one of A, B, and C" or similar phrases can refer to a combination of any of the items in the list A, B, and C, including only one item in the list, only two items in the list, or all three items in the list.

[0046] The terminology used in the present embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of the present embodiments. As used in the description of the present embodiments and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0047] It should be understood by those skilled in the art that the order of the numbers in the following description of the present embodiments does not mean the order of execution, and some or all steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the present embodiments.

[0048] It should be understood by those skilled in the art that the numerical range in the present embodiments should be understood as each intermediate value between the upper limit and the lower limit of the range. Each smaller range between any stated value or intermediate value in the range and any other stated value or intermediate value in the range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0049] Unless otherwise defined, technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are concerned. In the event of conflict between the content of this specification and any incorporated document, the content of this specification controls.

[0050] In a first aspect, the present application provides a composite sulfur positive electrode material, comprising a carbon-based host material and sulfur and an organic conductive small molecule combined on the surface of the carbon-based host material.

[0051] The mass ratio of the organic conductive small molecule, sulfur and carbon-based host material is (0.1-20):(30-90):(10-40).

[0052] In the present application, the organic conductive small molecule is preferably at least one of TNCQ, a TNCQ derivative, tetrathiafulvalene or tetracyanoethylene, such as TNCQ, a halogen-substituted TNCQ, an alkyl- or alkenyl-substituted TNCQ, a complex of TNCQ with a metal ion, and a complex of TNCQ with tetrathiafulvalene (TTF) or tetracyanoethylene (TCNE).

[0053] Specifically, the organic conductive small molecule has a chemical structure as shown below:

[0054]

[0055] wherein R1, R2, R3 and R4 are each independently selected from a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted C1-C 12 alkyl group or a substituted or unsubstituted C2-C 12 alkenyl group.

[0056] Alternatively, the organic conductive small molecule is a complex of TCNQ and tetrathiafulvalene in a mass ratio of (0-20):(0-20), which has a chemical structure as shown below:

[0057]

[0058] Alternatively, the organic conductive small molecule is a complex of TCNQ and tetracyanoethylene in a mass ratio of (0-20):(0-20), which has a chemical structure as shown below:

[0059]

[0060] As a more preferred technical solution, the organic conductive small molecule has a chemical structure as shown below:

[0061]

[0062] wherein M is any one or more of Li, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.

[0063] In the present application, the carbon-based host material includes at least one of graphene, carbon nanotubes, nitrogen-doped graphene and Ketjen black.

[0064] The composite sulfur positive electrode material of the present application reduces the solubility of the sulfur positive electrode material, inhibits the volume change of the sulfur positive electrode material and improves the conductivity thereof through the synergistic effect of the organic conductive small molecule and the carbon-based host material. Specifically, the cyano group in the organic conductive small molecule can fix the polysulfide intermediate in the charging and discharging through electrostatic adsorption, and improve the conductivity of the positive electrode; and the carbon-based host material can inhibit the dissolution and shuttling of the polysulfide as a physical barrier; under the synergistic effect of the organic conductive small molecule and the carbon-based host material, the specific capacity, cycle stability and rate performance of the lithium-sulfur battery are improved.

[0065] In the preferred scheme of the present application, the composite sulfur positive electrode material containing the metal-modified organic conductive small molecule also has the effect of rapidly catalyzing the conversion reaction, can also alleviate the volume change of the composite sulfur positive electrode material in the charging and discharging process, further improves the stability and reaction kinetics thereof, and thus realizes high specific capacity, high cycle stability and high rate performance of the lithium-sulfur battery.

[0066] In a second aspect, the present application provides a preparation method of the above-mentioned composite sulfur positive electrode material, comprising:

[0067] S1, dispersing the organic conductive small molecule, sulfur powder and carbon-based host material in an organic solvent, and performing a reaction under an inert atmosphere to collect a solid-phase product to obtain a precursor;

[0068] In the present application, the organic solvent provides a reaction site for the reaction principle and promotes the progress of the reaction; the organic solvent includes at least one of carbon disulfide, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, toluene or ethylene glycol.

[0069] In the present application, the inert atmosphere is preferably a nitrogen or argon atmosphere.

[0070] In the present application, the reaction temperature is 20-50℃, the reaction time is 12-48h, and the mass ratio of the organic conductive small molecule, sulfur and carbon-based host material is (0.1-20):(30-90):(10-40). After the reaction is completed, the solid-phase product is collected through solid-liquid separation such as drying, filtration and the like.

[0071] S2, adding the precursor into a reaction kettle and performing a reaction under an inert atmosphere to obtain a composite sulfur positive electrode material.

[0072] In the present application, the sulfur and the organic conductive small molecule are infiltrated into the surface of the carbon-based host material through a melting sulfur infiltration treatment at 145-200℃ for 6-36h, and a composite sulfur positive electrode material with a stable structure is formed.

[0073] The composite sulfur cathode material of the present application has low solubility, small volume change and excellent electrical conductivity, and can be used to prepare electrodes for lithium-sulfur batteries. The lithium-sulfur battery comprising the cathode active material has high specific capacity, high cycle stability and high rate performance.

[0074] The present application also provides a lithium-sulfur battery, wherein the cathode comprises the composite sulfur cathode material described above.

[0075] The lithium-sulfur battery can be prepared by conventional techniques in the art. Specifically, the preparation method of the lithium-sulfur battery of the present application comprises:

[0076] The composite sulfur cathode material of the organic conductive small molecule, the conductive additive and the binder are uniformly mixed in N-methyl pyrrolidone (NMP) to form a slurry, the slurry is coated on the surface of a carbon-coated aluminum foil current collector, and the slurry is dried by heating to prepare a cathode electrode film. The cathode electrode film is cut into a circular shape to prepare a cathode electrode sheet; the cathode electrode sheet and the negative lithium foil are separated by a separator, an electrolyte is added, and a button lithium-sulfur battery is assembled.

[0077] The mass ratio of the composite sulfur cathode material, the conductive additive and the binder is (40-80):(50-10):10; the conductive additive can be at least one of SuperP, Ketjen black or carbon nanotubes; the electrolyte is a solution obtained by dissolving lithium salt in an organic solvent, and further comprises an additive. The concentration of lithium salt in the electrolyte is 0.5-2.0 mol / L, and the preferred concentration is 1.0 mol / L. The lithium salt is selected from one or a mixture of several of lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium hexafluorophosphate (LiPF6) in any ratio, and the organic solvent is selected from one or a mixture of several of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), ethylene carbonate (EC) or dimethyl carbonate (DMC) in any ratio; the additive is selected from one or a mixture of several of lithium nitrate (LiNO3), lithium tetrafluoroborate (LiBF4), lithium bisoxalate borate (LiBOB) or lithium difluoro oxalate borate (LiDFOB) in any ratio.

[0078] The present application is further illustrated by the following examples.

[0079] Example 1

[0080] The present example provides a preparation method of a composite sulfur cathode material, comprising:

[0081] 30mg of TCNQ, 770mg of sulfur powder and 200mg of Ketjenblack were sequentially added into a 50mL round-bottom flask, 20mL of carbon disulfide was added, stirred at 25°C for 24 hours, after the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was reserved, the product was vacuum dried at 60°C for 6 hours, transferred into a 100ml polytetrafluoroethylene reaction kettle, and kept at 155°C in a vacuum oven for 12 hours, and after natural cooling, a composite sulfur positive electrode material was obtained.

[0082] Example 2

[0083] The embodiment provides a preparation method of a composite sulfur positive electrode material, comprising the following steps:

[0084] 50mg of TCNQ, 750mg of sulfur powder and 200mg of Ketjenblack were sequentially added into a 50mL round-bottom flask, 20mL of dimethyl sulfoxide was added, stirred at 25°C for 24 hours, after the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was reserved, the product was vacuum dried at 60°C for 6 hours, transferred into a 100ml polytetrafluoroethylene reaction kettle, and kept at 155°C in a vacuum oven for 12 hours, and after natural cooling, a composite sulfur positive electrode material was obtained.

[0085] Example 3

[0086] The embodiment provides a preparation method of a composite sulfur positive electrode material, comprising the following steps:

[0087] 30mg of F-TCNQ, 750mg of sulfur powder and 200mg of Ketjenblack were sequentially added into a 50mL round-bottom flask, 20mL of N,N-dimethylformamide was added, stirred at 25°C for 24 hours, after the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was reserved, the product was vacuum dried at 60°C for 6 hours, transferred into a 100ml polytetrafluoroethylene reaction kettle, and kept at 155°C in a vacuum oven for 12 hours, and after natural cooling, a composite sulfur positive electrode material was obtained.

[0088] Example 4

[0089] The embodiment provides a preparation method of a composite sulfur positive electrode material, comprising the following steps:

[0090] 30mg of F4-TCNQ, 730mg of sulfur powder and 200mg of Ketjenblack were sequentially added into a 50mL round-bottom flask, 20mL of carbon disulfide was added, stirred at 25°C for 24 hours, after the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was reserved, the product was vacuum dried at 60°C for 6 hours, transferred into a 100ml polytetrafluoroethylene reaction kettle, and kept at 155°C in a vacuum oven for 12 hours, and after natural cooling, a composite sulfur positive electrode material was obtained.

[0091] Example 5

[0092] This embodiment provides a method for preparing a composite sulfur cathode material, comprising:

[0093] 30 mg of TCNQ-TTF (1:1), 770 mg of sulfur powder and 200 mg of Ketjen black were added to a 50 mL round-bottom flask in sequence, and then 20 mL of carbon disulfide was added. The mixture was stirred at 25 ° C for 24 hours. After the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was retained. The product was vacuum dried at 60 ° C for 6 hours, transferred to a 100 ml polytetrafluoroethylene reactor, and kept at 155 ° C in a vacuum oven for 12 hours. After natural cooling, a composite sulfur positive electrode material was obtained.

[0094] Example 6

[0095] This embodiment provides a method for preparing a composite sulfur cathode material, comprising:

[0096] 30 mg of TCNE, 770 mg of sulfur powder and 200 mg of Ketjen black were added to a 50 mL round-bottom flask in sequence, and then 20 mL of carbon disulfide was added. The mixture was stirred at 25 ° C for 24 hours. After the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was retained. The product was vacuum dried at 60 ° C for 6 hours, transferred to a 100 ml polytetrafluoroethylene reactor, and kept at 155 ° C in a vacuum oven for 12 hours. After natural cooling, a composite sulfur positive electrode material was obtained.

[0097] Example 7

[0098] This embodiment provides a method for preparing a composite sulfur cathode material, comprising:

[0099] 30 mg of CuTCNQ, 770 mg of sulfur powder and 200 mg of Ketjen black were added to a 50 mL round-bottom flask in sequence, and then 20 mL of carbon disulfide was added. The mixture was stirred at 25 ° C for 24 hours. After the reaction was completed, the reaction system was allowed to stand, the solvent was removed and the solid product was retained. The product was vacuum dried at 60 ° C for 6 hours, transferred to a 100 ml polytetrafluoroethylene reactor, and kept at 155 ° C in a vacuum oven for 12 hours. After natural cooling, a composite sulfur positive electrode material was obtained.

[0100] The composite sulfur cathode material prepared in Example 1 was subjected to thermogravimetric analysis, and the thermogravimetric analysis test results are as follows: Figure 1 As shown. Figure 1 It can be seen that the composite sulfur cathode material of organic conductive small molecules exhibits a mass retention rate of more than 96% at 200°C and has high thermal stability.

[0101] Example 8

[0102] The embodiment provides a lithium-sulfur battery, a positive electrode active material of which is a composite sulfur positive electrode material prepared in the embodiment 1, and a preparation method of the lithium-sulfur battery comprises the following steps:

[0103] The composite sulfur positive electrode material, Ketjen black and PVDF are mixed according to a mass ratio of 8:1:1 to prepare a slurry, the slurry is coated on the surface of a carbon-coated aluminum foil current collector, and after drying at 60 DEG C, a positive electrode film is obtained, and a positive electrode wafer is obtained through cutting.

[0104] Metal lithium foil is used as a negative electrode, and Celgard2325 is used as a diaphragm; LiTFSI is used as an electrolyte, DME and DOL are mixed according to a volume ratio of 1:1 to be used as a solvent, an electrolyte with a molar concentration of 1M is prepared, an additive LiNO3 is added into the electrolyte, and the concentration of the additive is 2wt%. A button-type (Cion-type 2032) lithium-sulfur battery is assembled in an argon-filled glove box, and is recorded as lithium-sulfur battery 1.

[0105] Embodiment 9

[0106] The embodiment provides a lithium-sulfur battery, a positive electrode active material of which is a composite sulfur positive electrode material prepared in the embodiment 3, and a preparation method of the lithium-sulfur battery comprises the following steps:

[0107] The composite sulfur positive electrode material, Super P and PVDF are mixed according to a mass ratio of 7:2:1 to prepare a slurry, the slurry is coated on the surface of a carbon-coated aluminum foil current collector, and after drying at 60 DEG C, a positive electrode film is obtained, and a positive electrode wafer is obtained through cutting.

[0108] Metal lithium foil is used as a negative electrode, and Celgard2325 is used as a diaphragm; LiTFSI is used as an electrolyte, DME and DOL are mixed according to a volume ratio of 1:1 to be used as a solvent, an electrolyte with a molar concentration of 1M is prepared, an additive LiNO3 is added into the electrolyte, and the concentration of the additive is 2wt%. A button-type (Cion-type 2032) lithium-sulfur battery is assembled in an argon-filled glove box, and is recorded as lithium-sulfur battery 2.

[0109] Embodiment 10

[0110] The embodiment provides a lithium-sulfur battery, a positive electrode active material of which is a composite sulfur positive electrode material prepared in the embodiment 7. A preparation method of the lithium-sulfur battery comprises the following steps:

[0111] The composite sulfur positive electrode material, Super P and PVDF are mixed according to a mass ratio of 8:1:1 to prepare a slurry,

[0112] The slurry is coated on the surface of a carbon-coated aluminum foil current collector, and after drying at 60 DEG C, a positive electrode film is obtained, and a positive electrode wafer is obtained through cutting.

[0113] A lithium-sulfur battery was assembled in an argon-filled glove box with lithium foil as the anode, Celgard 2325 as the separator, and the electrolyte being a gel electrolyte prepared in situ. The electrolyte precursor was a 1.5 M LiFSI solution in DOL. After the battery was assembled, it was heated at 60 °C. The ring-opening polymerization of DOL initiated by LiFSI occurred in situ to produce a gel polymer electrolyte. The lithium-sulfur battery obtained in Example 10 is referred to as lithium-sulfur battery 3.

[0114] Comparative Example 1

[0115] This comparative example provides a conventional lithium-sulfur battery with sulfur as the positive active material. The preparation method comprises:

[0116] Sulfur powder, Super P and PVDF were mixed in a mass ratio of 7:2:1 to prepare a slurry, which was coated on the surface of a carbon-coated aluminum foil current collector. After drying at 60 °C, a positive electrode film was obtained, and the positive electrode round sheet was obtained after cutting.

[0117] A lithium-sulfur battery was assembled in an argon-filled glove box with lithium foil as the anode, Celgard 2325 as the separator, and the electrolyte being a gel electrolyte prepared in situ. The electrolyte precursor was a 1.5 M LiFSI solution in DOL. After the battery was assembled, it was heated at 60 °C. The ring-opening polymerization of DOL initiated by LiFSI occurred in situ to produce a gel polymer electrolyte. The lithium-sulfur battery obtained in Example 10 is referred to as lithium-sulfur battery 3.

[0118] The lithium-sulfur batteries 1-3 prepared in Examples 8-10 and the lithium-sulfur battery D1 prepared in Comparative Example 1 were subjected to electrochemical performance tests, and the test results are shown in Table 1.

[0119] Table 1: Cycle performance results of lithium-sulfur batteries

[0120] Initial specific capacity 100 cycle specific capacity 200 cycle specific capacity Capacity retention Lithium sulfur battery 1 799.7 mAh g -1 ]] 578.4 mAh g -1 ]] 488.2 mAh g -1 ]] 61.0％ Lithium sulfur battery 2 725.9 mAh g -1 ]] 583.1 mAh g -1 ]] 496.1 mAh / g -1 ]] 68.3％ Lithium sulfur battery 3 520.4 mAh g -1 ]] 459.8 mAh g -1 ]] 416.7 mAh / g -1 ]] 80.1％ Lithium sulfur battery D1 550.9 mAh g -1 ]] 330.3 mAh / g -1 ]] 283.6 mAh g -1 ]] 51.5％

[0121] As can be seen from Table 1, compared with the conventional lithium-sulfur battery, the lithium-sulfur battery containing the composite sulfur positive electrode material of the present application has better cycle performance, and the capacity retention rate after 200 cycles is higher than that of the conventional lithium-sulfur battery. Among them, the lithium-sulfur battery using the composite sulfur positive electrode material containing the metal-modified organic conductive small molecule has a capacity retention rate as high as 80.1% after 200 cycles.

[0122] The test results of lithium-sulfur battery 1 are shown in Figure 2 and Figure 3 As can be seen from Figure 2 , within the test voltage window range of 1.7-2.8 V (vs Li / Li + ), the discharge capacity of the lithium-sulfur battery 1 is 836 mAg -1At the current density (0.5C), the battery’s discharge capacity is 799.7 mAh g -1 , showing higher specific capacity and improved capacity utilization, while also showing higher cycle stability. Figure 3 It can be seen that in the EIS spectrum, the resistance of the two semicircles is relatively low, indicating that the addition of organic conductive small molecules can reduce the surface passivation film resistance and charge transfer resistance of the material.

[0123] The test results of lithium-sulfur battery 2 are as follows Figure 4 As shown. Figure 4 It can be seen that in the test voltage window range of 1.7-2.8V (vsLi / Li + ) in 836mAg -1 At the current density (0.5C), its first cycle discharge capacity can reach 725.9mAh g -1 , showing good charge-discharge cycle stability.

[0124] The test results of lithium-sulfur battery 3 are as follows Figure 5 As shown. Figure 5 It can be seen that in the test voltage window range of 1.7-2.8V (vsLi / Li + ) in 836mAg -1 Under the current density (0.5C), in the 200-cycle charge-discharge cycle test, the capacity retention rate can reach 80.1%, and the charge-discharge cycle stability is very high.

[0125] The test results of the lithium-sulfur battery D1 prepared in Comparative Example 1 are as follows: Figure 6 and Figure 7 As shown. Figure 6 It can be seen that in the test voltage window range of 1.7-2.8V (vs Li / Li + ) in 836mAg -1 At a current density of 0.5C, the lithium-sulfur battery D1 exhibited a capacity of 550.9 mAh g -1 The initial discharge capacity is 283.6 mAh g after 200 cycles. -1 , the capacity retention rate is only 51.4%, the capacity utilization is low and the cycle stability is poor. Figure 7 It can be seen that in the EIS spectrum, the resistance of the two semicircles is relatively large, indicating that the surface passivation film resistance and charge transfer resistance of the material are large, the internal reaction kinetics of the positive electrode are insufficient, and the diffusion of lithium ions in the material structure is poor, resulting in its poor specific capacity and cycle performance.

[0126] It can be known from the above test results that the composite sulfur positive electrode material of the organic conductive small molecule used as the lithium sulfur battery positive electrode active material has high specific capacity, high cycle stability and high rate performance.

[0127] Although the present application has been described in detail in the foregoing description with general principles and specific embodiments thereof, it should be further appreciated that modifications and improvements to the application embodied therein can be made by those skilled in the art, without departing from the spirit and scope of the application. Accordingly, such modifications and improvements are intended to be included within the scope of the application.

Claims

1. A composite sulfur cathode material, characterized in that, The carbon-based host material and sulfur and organic conductive small molecules combined on the surface of the carbon-based host material; The mass ratio of the organic conductive small molecule, sulfur and the carbon-based host material is (0.1-20):(30-90):(10-40); The organic conductive small molecule includes at least one of TNCQ, a TNCQ derivative, tetrathiafulvalene or tetracyanoethylene.

2. The composite sulfur cathode material of claim 1, wherein, The organic conductive small molecule has a chemical structure as shown in the following formula: ； wherein R1, R2, R3 and R4 are each independently selected from a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted C1-C 12 Alkyl or substituted or unsubstituted C2-C 12 alkenyl; Or, The organic conductive small molecule is a compound of TCNQ and tetrathiafulvalene in a mass ratio of (0-20):(0-20). Or, The organic conductive small molecule is a compound of TCNQ and tetracyanoethylene in a mass ratio of (0-20):(0-20).

3. The composite sulfur cathode material of claim 1, wherein, The organic conductive small molecule has a chemical structure as shown in the following formula: ； Wherein M is any one or more of Li, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.

4. The composite sulfur cathode material of claim 1, wherein, The carbon-based host material includes at least one of graphene, carbon nanotubes, nitrogen-doped graphene and Ketjen black.

5. The method of producing a composite sulfur cathode material according to any one of claims 1 to 4, characterized in that, Comprising: S1, dispersing the organic conductive small molecule, sulfur powder and carbon-based host material in an organic solvent, and reacting under an inert atmosphere to collect a solid-phase product to obtain a precursor; S2, adding the precursor into a reaction kettle and heating to react under an inert atmosphere to obtain a composite sulfur positive electrode material.

6. The production method according to claim 5, wherein The organic solvent includes at least one of carbon disulfide, chloroform, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, toluene or ethylene glycol; And / or, The inert atmosphere is a nitrogen or argon atmosphere.

7. The preparation method according to claim 5, characterized in that In step S1, the reaction temperature is 20-50℃ and the reaction time is 12-48h; In step S2, the reaction temperature is 145-200℃ and the reaction time is 6-36h.

8. Use of the composite sulfur positive electrode material according to any one of claims 1-4 in a lithium-sulfur battery.

9. A lithium-sulfur battery, characterized by, The positive electrode includes the composite sulfur positive electrode material according to any one of claims 1-4.

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