Lithium sulfide composite positive electrode material with difunctional network structure as well as preparation method and application of lithium sulfide composite positive electrode material

Abstract

The invention belongs to the technical field of all-solid-state lithium-sulfur battery materials, and relates to a bifunctional network structure lithium sulfide positive electrode material and a preparation method and application thereof. The invention aims to overcome the defects of the lithium sulfide positive electrode material in the aspects of ion and electron conductivity, and through the electron / ion bifunctional network structure design, the redox reaction kinetics of the lithium sulfide positive electrode is improved, so that the rate capability and the cycle capacity of the battery are improved. The lithium sulfide composite positive electrode material is prepared by adopting an in-situ synthesis method, the obtained composite material is provided with an in-situ solid electrolyte layer which is coated on the surface of a lithium sulfide matrix, a layer of carbon is uniformly coated on the surface, and the finally obtained lithium sulfide composite positive electrode shows relatively high reversible capacity and excellent rate capability. The method has the characteristics of uniform coating, simple process and the like, is suitable for large-scale production, and has a wide application prospect in the field of all-solid-state lithium-sulfur batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of all-solid-state lithium-sulfur battery materials, and particularly relates to a bifunctional network structure lithium sulfide composite cathode material and a preparation method and application thereof. BACKGROUND

[0002] The lithium ion secondary battery with chargeable and dischargeable functions has become one of the most important energy storage systems due to its high energy density and high working voltage advantages, and has developed into a mature stage. Compared with the traditional lithium ion battery, the lithium-sulfur battery is concerned based on its higher theoretical energy density (2800 Wh L -1 ) and economic benefits brought by abundant sulfur element (S). However, the "shuttle effect" of polysulfides produced in the discharge process of the lithium-sulfur battery and the combustion problem of the organic electrolyte when the battery is short-circuited seriously hinder the further development of the lithium-sulfur battery.

[0003] The all-solid-state lithium-sulfur battery can effectively solve the performance deterioration caused by the "shuttle effect" and the safety problem caused by the combustion of the organic electrolyte by using a solid-state electrolyte to replace the organic electrolyte. The cathode active material involved in the all-solid-state lithium-sulfur battery is elemental sulfur or lithium sulfide (Li2S), wherein the room temperature electronic conductivity (<10 -14 S cm -1 ) and ionic conductivity (negligible) of elemental sulfur are extremely low, which leads to slow reaction kinetics, limits the cycle capacity and rate performance of the battery, and serious volume expansion (~80%) occurs in the S-Li2S conversion process during the charge and discharge process. The contact between particles is lost due to the volume expansion and shrinkage, forming "dead" sulfur that cannot function.

[0004] The lithium sulfide, which is the lithiation product of elemental sulfur, introduces a lithium source as the cathode active material, so that it can be compatible with lithium-free anodes (such as graphite anodes, silicon anodes, etc.), effectively solving the short circuit problem caused by lithium dendrite growth, and due to its high melting point (938℃), it is often used for synthesis of sulfide solid-state electrolytes and high-temperature modification. Compared with elemental sulfur, lithium sulfide has improved ionic conductivity (10 -8 ~10 -10 S cm -1 ) and electronic conductivity (10 -7 ~10 -8 S cm -1 ), but it still cannot meet the electronic and ionic transmission in the charge and discharge process, and the problem of slow reaction kinetics still exists.

[0005] In order to overcome the obstacle of low electronic and ionic conductivity of lithium sulfide cathode, researchers have proposed various implementation strategies, including nanostructure composite, core-shell encapsulation design and redox medium catalysis, and have made some progress in these directions. Patent CN119252909A obtains a multi-level porous carbon composite by one-step calcination of a carbon source and a metal salt, using the reaction between urea and the metal salt as a double catalyst to synergistically promote the redox of lithium sulfide. Patent CN115714169B prepares lithium sulfate pellets by spray drying, then fully mixes them with a carbon source precursor, and then obtains carbon-coated lithium sulfide hollow sphere materials by in-situ redox. However, a single modification cannot completely solve the problems existing in lithium sulfide cathodes. Therefore, the present application provides a dual-functional network structure lithium sulfide composite cathode material. SUMMARY

[0006] In order to overcome the problems of low electronic and ionic conductivity and slow reaction kinetics of lithium sulfide cathode materials still existing in the prior art, the present application provides a dual-functional network structure lithium sulfide composite cathode material, a preparation method thereof and its application in a full solid-state lithium-sulfur battery.

[0007] The present application first performs in-situ reaction of lithium sulfide and metal sulfide, and then performs carbon layer coating, thereby obtaining a lithium sulfide composite cathode material with both electronic and ionic transmission channels.

[0008] To achieve the above technical purpose, the present application provides the following specific technical solutions: The present application relates to a preparation method of a dual-functional network structure lithium sulfide composite cathode material, comprising the following steps: (1) Mixing: thoroughly mix lithium sulfide and metal sulfide to obtain a mixed material; (2) Annealing treatment: perform annealing treatment on the mixed material obtained in step (1) to obtain a lithium sulfide composite cathode material with an in-situ solid-state electrolyte layer; (3) Carbon coating treatment: thoroughly mix the lithium sulfide composite cathode material obtained in step (2) with a carbon source to obtain a dual-functional network structure lithium sulfide composite cathode material.

[0009] By employing the above technical solution, this invention, through mixing lithium sulfide with metal sulfides, enables a chemical reaction between the two phases during annealing, resulting in the in-situ formation of a solid electrolyte layer with high ionic conductivity on the lithium sulfide surface. Due to the low hardness and high ductility of metal sulfides, they can form a tight solid-solid contact with lithium sulfide during mixing, achieving close adhesion and increasing the active area. This compensates for the insufficient ionic conductivity of lithium sulfide cathode materials, making it more efficient than point-to-point contact through direct mixing of solid electrolytes. The material performance is further improved, and it also reduces interfacial impedance in the cathode system. Furthermore, unlike traditional methods that often rely on the first charge of the battery… Compared to the method of forming a solid electrolyte layer by driving an interfacial reaction during discharge, this invention effectively solves the problems of low controllability and poor stability of traditional solid electrolyte layers. The solid electrolyte layer of this invention exhibits excellent controllability and stability. Subsequently, by mixing with a carbon source, such as amorphous carbon, the electronic conductivity of the lithium sulfide cathode material is effectively improved, while simultaneously constructing dual channels for ions and electrons, overcoming the problem of slow reaction kinetics, and further enhancing battery performance. Traditional methods mostly utilize the first charge and discharge of the battery to drive an interfacial reaction to form a solid electrolyte layer. Such solid electrolyte layers have the characteristics of low controllability and poor stability, while the solid electrolyte layer of this invention exhibits excellent controllability and stability. The following are further preferred technical solutions of the present invention: Preferably, in step (1), the metal sulfide is selected from at least one of titanium disulfide (TiS2), germanium disulfide (GeS2), tin disulfide (SnS2), tin sulfide (SnS), zirconium disulfide (ZrS2), tantalum disulfide (TaS2), niobium disulfide (NbS2), niobium trisulfide (NbS3), molybdenum disulfide (MoS2), molybdenum trisulfide (MoS3), tungsten trisulfide (WS3), pentavanium octasulfide (V5S8), vanadium disulfide (V2S3), vanadium disulfide (VS2), aluminum disulfide (Al2S3), and antimony disulfide (Sb2S3). And / or, the mass ratio of lithium sulfide to metal sulfide is 1~20:1.

[0010] Preferably, in step (1), the mixture is thoroughly mixed by ball milling. The ball milling conditions are: a ball milling speed of 100~1500 rpm and a ball milling time of 1~50 h; more preferably, a ball milling speed of 300~1500 rpm and a ball milling time of 3~50 h. By using ball milling, the metal sulfide and lithium sulfide can be thoroughly mixed and reacted. If the mixing is uneven, the reaction will be insufficient or non-reaction will occur, and lithium sulfide and metal sulfide will separate into phases, resulting in the inability to form a solid electrolyte layer and construct an effective structural network, thus leading to poor electrochemical performance.

[0011] Preferably, in step (2), the annealing conditions are: annealing temperature of 200-1500℃; holding time of 2-24h; heating rate of 2~10℃ / min; more preferably, annealing temperature of 300~1500℃.

[0012] Preferably, in step (2), the size of the composite cathode material prepared is ≤100nm and the thickness of the solid electrolyte layer is 1~10 nm.

[0013] Preferably, in step (3), the carbon source material is a conventional coated carbon material, more preferably selected from at least one of multi-walled carbon nanotubes (WMCNTs), acetylene black (AB), activated carbon (AC), conductive carbon black (Super P), reduced graphene oxide (rGo), carbon fiber (VGCF), and mesoporous carbon (MCFC). And / or, the mass ratio of carbon source to lithium sulfide composite cathode material is (1~30):60, more preferably (5-15):60.

[0014] Preferably, in step (3), the mixture is thoroughly mixed by ball milling to achieve carbon coating. The ball milling conditions are: ball milling speed of 100~700 rpm and ball milling time of 4~20 h; more preferably, the ball milling speed is 300-500 rpm and the ball milling time is 6-12 h. In the carbon coating step, the degree of bonding between different solid electrolyte layers and lithium sulfide is not consistent. It is necessary to ensure that carbon is coated without damaging the structure of the solid electrolyte layer. The ball milling parameters need to be strictly controlled and optimized to further ensure the stable realization of battery performance.

[0015] Further preferably, the preparation method includes the following steps: (1) Ball milling and mixing: In an environment where the water and oxygen content is less than 0.01 ppm, such as in an argon atmosphere glove box, weigh a certain amount of lithium sulfide and metal sulfide, seal them in a ball mill jar, and ball mill them at a certain speed for several hours. (2) Annealing treatment: The mixed material obtained after ball milling in step (1) is placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace to obtain lithium sulfide composite cathode material with an in-situ solid electrolyte layer. (3) Carbon coating treatment: Weigh a certain amount of carbon source material, seal the composite cathode material obtained after annealing in step (2) with carbon in a ball mill jar, and ball mill it at a certain speed for several hours to obtain a bifunctional network structure lithium sulfide composite cathode material.

[0016] The present invention also provides a bifunctional network structure lithium sulfide composite cathode material prepared by any of the above preparation methods.

[0017] This invention also provides an application of the bifunctional network structure lithium sulfide composite cathode material prepared by any of the above preparation methods in the field of all-solid-state lithium-sulfur batteries.

[0018] Preferably, the application includes a sulfide all-solid-state lithium-sulfur battery, which includes the above-described bifunctional network structure lithium sulfide composite cathode material.

[0019] This invention aims to address the shortcomings of lithium sulfide cathode materials in terms of electronic and ionic conductivity. By employing the technical solution of this invention, a solid electrolyte layer can be generated in situ during the reaction process, achieving tight adhesion and increasing the active area, thus compensating for the insufficient ionic conductivity of lithium sulfide cathode materials. Subsequently, by mixing with carbon, the electronic conductivity of the lithium sulfide cathode material is effectively improved. Simultaneously, a dual-channel system for ions and electrons is constructed, overcoming the problem of slow reaction kinetics. The resulting lithium sulfide composite cathode material exhibits high reversible capacity and excellent rate performance. This invention features uniform coating and a simple process, making it suitable for large-scale production and possessing broad application prospects in the field of all-solid-state lithium-sulfur batteries.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The method for preparing a bifunctional network structure lithium sulfide composite cathode material provided by this invention forms a solid electrolyte layer on the surface of lithium sulfide through in-situ reaction while simultaneously constructing electron transport channels using carbon coating. This invention features a simple process and yields a uniformly coated composite material. Furthermore, the in-situ generation of the solid electrolyte layer makes the interface more stable. The preparation method is convenient, efficient, and easy to operate, making it suitable for large-scale industrial production.

[0021] 2. Existing technologies all involve single modifications to lithium sulfide cathode materials, including nanostructure design, core-shell encapsulation, and redox medium catalysis. This invention combines the advantages of these three strategies to synthesize a bifunctional network structure lithium sulfide composite cathode material in situ. Furthermore, this invention does not simply combine the three strategies, but rather achieves a uniformly coated composite material through precise design of raw materials for in-situ synthesis.

[0022] 3. The modified composite material of this invention has excellent ionic conductivity while satisfying electronic conductivity, which enhances the redox reaction kinetics of lithium sulfide cathode, reduces polarization during charge and discharge, and has excellent rate performance and reversibility, thus having broad market application prospects. Attached Figure Description

[0023] Figure 1 This is a refined XRD pattern of the bifunctional network structure lithium sulfide composite cathode material in Embodiment 1 of the present invention. Figure 2This is a SEM image of the bifunctional network structure lithium sulfide composite cathode material in Embodiment 1 of the present invention; Figure 3 This is a comparison chart of the lithium-ion conductivity of the bifunctional network structure lithium sulfide composite cathode material in Embodiment 1 of the present invention. Figure 4 This refers to the performance tests of the two materials in Example 1 and Comparative Example 1 of this invention at different current densities; Figure 5 This is Example 1 of the present invention in 1A g -1 Long-cycle plot at current density; Figure 6 This is a comparison graph of the electrochemical polarization curves of Example 1 and Comparative Example 1 after 150 cycles. Detailed Implementation

[0024] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, and instruments used in the embodiments, unless otherwise specified, can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0026] Example 1

[0027] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.1 g of tin disulfide (SnS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 500 rpm for 12 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 450℃ for 10 h with a heating rate of 2℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Sn-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 40~80 nm and the solid electrolyte layer thickness was 5~8 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Sn-S cathode composite material obtained in step (2) and 0.035 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill at 500 rpm for 12 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Sn-S@AB). The amorphous carbon coating thickness is 3~6 nm. SEM image is shown below. Figure 2 As shown.

[0028] Example 2

[0029] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.3 g of vanadium disulfide (VS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 1500 rpm for 1 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 200℃ for 24h at a heating rate of 10℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-VS) with an in-situ solid electrolyte layer, the composite cathode particle size being 60~100 nm and the solid electrolyte layer thickness being 7~10 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-VS cathode composite material and 0.15 g of multi-walled carbon nanotubes (WMCNTs) obtained in step (2) in a glove box, seal them in a ball mill jar with a ball-to-material ratio of 10:1, and ball mill them at 700 rpm for 4 hours to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-VS@WMCNTs) with an amorphous carbon coating thickness of 6~9 nm.

[0030] Example 3

[0031] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.02 g of germanium disulfide (GeS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 200 rpm for 40 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 700℃ for 8 h with a heating rate of 10 ℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Ge-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 30~70 nm and the solid electrolyte layer thickness was 4~7 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Ge-S cathode composite material obtained in step (2) and 0.1 g of activated carbon (AC) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Mill the materials at 300 rpm for 14 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Ge-S@AC). The thickness of the amorphous carbon coating layer is 5~8 nm.

[0032] Example 4

[0033] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.1 g of niobium disulfide (NbS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 1200 rpm for 3 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 750℃ for 4 h with a heating rate of 5℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Nb-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 50~90 nm and the solid electrolyte layer thickness was 6~9 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Nb-S cathode composite material obtained in step (2) and 0.05 g of activated carbon (AC) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Mill the materials at 600 rpm for 6 h to obtain a bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Nb-S@AC) with an amorphous carbon coating thickness of 2~4 nm.

[0034] Example 5

[0035] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.03 g of molybdenum disulfide (MoS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 400 rpm for 18 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 600℃ for 8 h with a heating rate of 3℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Mo-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 20~60 nm and the solid electrolyte layer thickness was 1~4 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Mo-S cathode composite material obtained in step (2) and 0.005 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill the materials at 200 rpm for 18 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Mo-S@AB) with an amorphous carbon coating thickness of 1~2 nm.

[0036] Example 6

[0037] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.025 g of tungsten trisulfide (WS3) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 100 rpm for 50 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 200℃ for 24 h with a heating rate of 8℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-WS) with an in-situ solid electrolyte layer, the composite cathode particle size being 10~50 nm and the solid electrolyte layer thickness being 2~5 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-WS cathode composite material obtained in step (2) and 0.025 g of multi-walled carbon nanotubes (WMCNTs) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Mill the materials at 100 rpm for 20 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-WS@WMCNTs) with an amorphous carbon coating thickness of 2~3 nm.

[0038] Example 7

[0039] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.08 g of titanium disulfide (TiS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball milled at 900 rpm for 10 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 1300 °C for 6 h with a heating rate of 4 °C / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Ti-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 30~70 nm and the solid electrolyte layer thickness was 4~6 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Ti-S cathode composite material obtained in step (2) and 0.025 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill the materials at 400 rpm for 10 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Ti-S@AB). The thickness of the amorphous carbon coating layer is 2~5 nm.

[0040] Example 8

[0041] Based on Example 1, the metal sulfide tin disulfide was replaced with at least one of titanium disulfide (TiS2), germanium disulfide (GeS2), tin sulfide (SnS), zirconium disulfide (ZrS2), tantalum disulfide (TaS2), niobium disulfide (NbS2), niobium trisulfide (NbS3), molybdenum disulfide (MoS2), molybdenum trisulfide (MoS3), tungsten trisulfide (WS3), vanadium octasulfide (V5S8), vanadium trisulfide (V2S3), vanadium disulfide (VS2), aluminum trisulfide (Al2S3), and antimony trisulfide (Sb2S3). The mass ratio of lithium sulfide to metal sulfide was the same as in Example 1, and other conditions were the same as in Example 1. The resulting bifunctional network structure lithium sulfide composite cathode material had a particle size of 10-100 nm and a solid electrolyte layer thickness of 1-10 nm.

[0042] Comparative Example 1

[0043] The lithium sulfide cathode material used is untreated and can be used as other lithium sulfide materials. The particle size of this material is 2~4 μm. It is a lithium sulfide material (Li2S) synthesized by conventional methods of lithium hydride (LiH) and sulfur (S).

[0044] Comparative Example 2

[0045] (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.3 g of solid electrolyte (Li3VS4) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 1500 rpm for 1 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 200℃ for 24h at a heating rate of 10℃ / min. The composite positive electrode has a particle size of 60~100 nm and a solid electrolyte layer thickness of 7~10 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li3VS4 cathode composite material and 0.15 g of multi-walled carbon nanotubes (WMCNTs) obtained in step (2) in a glove box, seal them in a ball mill jar with a ball-to-material ratio of 10:1, and ball mill them at 700 rpm for 4 hours to obtain the composite cathode material (Li2S@Li3VS4@WMCNTs) with an amorphous carbon coating thickness of 6~9 nm.

[0046] Comparative Example 3: No annealing treatment (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.02 g of germanium disulfide (GeS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 200 rpm for 40 h. (2) Amorphous carbon coating treatment Weigh 0.3 g of the mixed material obtained in step (2) and 0.1 g of activated carbon (AC) in a glove box, seal them in a ball mill jar with a ball-to-material ratio of 10:1, and ball mill them at 300 rpm for 14 h to obtain a bifunctional network structure lithium sulfide composite cathode material (Li2S@GeS2@AC) with an amorphous carbon coating thickness of 5~8 nm.

[0047] Comparative Example 4: Construction of Solid Electrolyte Layers Using Traditional Methods (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.1 g of niobium disulfide (NbS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 1200 rpm for 3 h. (2) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@NbS2 cathode composite material obtained in step (1) and 0.05 g of activated carbon (AC) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill at 600 rpm for 6 h to obtain lithium sulfide composite cathode material (Li2S@NbS2@AC) with an amorphous carbon coating thickness of 2~4 nm.

[0048] (3) Activation reaction during the first charge and discharge In a glove box, the lithium sulfide composite cathode material (Li2S@NbS2@AC) obtained in step (2) was ball-milled with sulfide solid electrolyte (Li6PS5Cl) and activated carbon (AC) at a mass ratio of 67:10:3 at 500 rpm for 2 h to obtain an electrode composite material. Subsequently, carbon-coated aluminum foil, electrode composite material, sulfide solid electrolyte (Li6PS5Cl), and lithium indium sheet were sequentially cold-pressed to assemble an all-solid-state lithium-sulfur battery. Then, the battery was mounted on a battery rack at 20 mA g. -1 Electrochemical discharge was performed at a current density of 0.3–3.0 V, and the first charge-discharge was conducted to construct an in-situ solid electrolyte layer, thus obtaining the lithium sulfide composite cathode material (Li2S@Li-Nb-S@AC). The thickness of the solid electrolyte layer was 4–7 nm.

[0049] Effect of grinding and mixing conditions on Comparative Example 5 (1) Grinding and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.6 g of lithium sulfide (Li2S) and 0.1 g of molybdenum disulfide (MoS2) from Comparative Example 1 were weighed, and the two were placed in a mortar and ground for 1 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 600℃ for 8 h with a heating rate of 3℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Mo-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 80~100 nm and the solid electrolyte layer thickness was 1~4 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Mo-S cathode composite material obtained in step (2) and 0.005 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill the materials at 200 rpm for 18 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Mo-S@AB) with an amorphous carbon coating thickness of 1~2 nm.

[0050] Effect of annealing conditions on comparison example 6 (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.025 g of tungsten trisulfide (WS3) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 100 rpm for 50 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 100°C for 24 h with a heating rate of 2°C / min. The resulting lithium sulfide composite cathode material (Li2S@WS3) had a particle size of 10~50 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-WS cathode composite material obtained in step (2) and 0.025 g of multi-walled carbon nanotubes (WMCNTs) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill at 100 rpm for 20 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-WS@WMCNTs) with an amorphous carbon coating thickness of 1~3 nm.

[0051] The effect of treatment order on comparison example 7 (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.4 g of lithium sulfide (Li2S) and 0.08 g of titanium disulfide (TiS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball milled at 900 rpm for 10 h. (2) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@TiS2 cathode composite material obtained in step (2) and 0.025 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Mill the materials in a ball mill at 400 rpm for 10 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@TiS2@AB) with an amorphous carbon coating thickness of 2~5 nm.

[0052] (3) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 1300 °C for 6 h with a heating rate of 4 °C / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Ti-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 30–70 nm, and the solid electrolyte layer thickness was 4–6 nm.

[0053] Effect of coating ball milling parameters on Comparative Example 8 (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.1 g of tin disulfide (SnS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 500 rpm for 12 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 450℃ for 10 h with a heating rate of 2℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Sn-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 40~80 nm and the solid electrolyte layer thickness was 5~8 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Sn-S cathode composite material obtained in step (2) and 0.035 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill the materials at 1000 rpm for 12 h to obtain the bifunctional network structure lithium sulfide composite cathode material (Li2S@Li-Sn-S@AB). The thickness of the amorphous carbon coating layer is 3~6 nm.

[0054] Comparative Example 9 uses other sulfides (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.1 g of copper disulfide (CuS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 500 rpm for 12 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 450℃ for 10 h with a heating rate of 2℃ / min. The resulting lithium sulfide composite cathode material (Li2S@CuS2) was obtained with a composite cathode particle size of 40~80 nm. (3) Amorphous carbon coating treatment Weigh 0.3 g of the Li2S@Li-Sn-S cathode composite material obtained in step (2) and 0.035 g of acetylene black (AB) in a glove box. Seal the two materials in a ball mill jar with a ball-to-material ratio of 10:1. Ball mill the materials at 500 rpm for 12 h to obtain the lithium sulfide composite cathode material (Li2S@CuS2@AB) with an amorphous carbon coating thickness of 3~6 nm.

[0055] Comparative Example 10: No electronic pathway construction treatment performed. (1) Ball milling and mixing In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 0.3 g of lithium sulfide (Li2S) and 0.1 g of tin disulfide (SnS2) from Comparative Example 1 were weighed, sealed in a ball mill jar with a ball-to-material ratio of 10:1, and ball-milled at 500 rpm for 12 h. (2) Annealing treatment The mixed material obtained after ball milling in step (1) was placed in a corundum ceramic boat in a glove box and annealed in a muffle furnace at 450℃ for 10 h with a heating rate of 2℃ / min. This yielded a lithium sulfide composite cathode material (Li2S@Li-Sn-S) with an in-situ solid electrolyte layer. The composite cathode particle size was 40~80 nm and the solid electrolyte layer thickness was 5~8 nm.

[0056] Test Example: Battery Assembly and Performance Testing

[0057] All-solid-state lithium-sulfur battery assembly: The electrode composite material was prepared by ball milling a mixture of the composite cathode material (Li2S@Li-XS@C, where X is a metal atom) in each example or the pure lithium sulfide material of Comparative Example 1, a sulfide solid electrolyte, and conductive carbon in a mass ratio of 67:10:3. In an argon atmosphere glove box with water and oxygen content both less than 0.01 ppm, 120 mg of the sulfide solid electrolyte was placed in a 12 mm diameter PTFE mold and compressed into a sheet under a pressure of 20 MPa. Then, 5-10 mg of the electrode composite material was uniformly coated onto a carbon-coated aluminum foil, placed on the upper surface of the mold, and a pressure of 10 MPa was applied. Finally, a 10 mm diameter lithium indium sheet was placed on the back of the mold, and the assembly was cold-pressed under a pressure of 10 MPa.

[0058] Place the assembled battery on the Xinwei Battery Tester. First, perform an in-situ electrochemical reduction reaction at 50 mAg. -1 The first activation cycle was performed using current density, with a voltage range of 0.6–2.9 V. Subsequent charge / discharge tests were conducted with a voltage range of 0.8–2.4 V for two activation cycles, followed by a 0.1 A g-current test. -1 The current density was used for charge-discharge cycles, with a voltage range of 0.8 to 2.4 V. The rate test current density was 0.1 A g. -1 0.2 A g -1 0.5A g -1 1A g -1 .

[0059] The battery performance was prepared and tested according to the above method, and the results are shown in Table 1:

[0060] The materials described in each embodiment of the present invention were tested under the test conditions of the test examples, and all met the following requirements: at 1A g -1 The initial discharge specific capacity at current density is not less than 400 mA hg -1 1A g -1 The discharge specific capacity after 150 cycles at current density is not less than 420 mA hg -1 The cycle capacity retention rate is no less than 102%. In contrast, the batteries tested in Comparative Examples 1-7, at 1A g... -1 The initial discharge specific capacity at current density is below 400 mA hg. -1Furthermore, the capacity retention rate after 150 cycles was less than 67%; Comparative Example 8 shows that the difference from Example 1 lies in the different ball milling parameters used for coating. Although it has certain advantages over Comparative Examples 1-7 in both initial discharge specific capacity and cycle performance, Example 1 has superior electrochemical performance; Comparative Example 9 uses copper sulfide as the sulfide, and although it has advantages over Example 1 in terms of 50 mA g... -1 The first-amplifier specific capacity under current density conditions shows a significant advantage, but its cycle performance is significantly weaker than that of Example 1, although it still has an advantage compared to Comparative Examples 1-7. Although Comparative Example 10 has a good advantage in first-amplifier specific capacity compared to Comparative Examples 1-7, the cycle performance of Example 1 has a significant advantage compared to it. It can be seen that the overall synergistic effect of the technical solution of the present invention can have a significant and excellent effect.

[0061] The bifunctional network structure lithium sulfide composite cathode material in Example 1 was tested at 0.1 A g. -1 0.2 A g -1 0.5Ag -1 1 A g -1 The discharge specific capacity that can be achieved at the current density is 657.75 mA hg. -1 677.7 mA hg -1 629.26 mA hg -1 559.11 mA hg -1 The performance of Examples 2-6 shows the same trend as that of Example 1. In Comparative Example 1, the material at 0.1 Ag... -1 0.2 A g -1 0.5A g -1 1 A g -1 The discharge specific capacity that can be achieved at the current density is 373.38 mA hg. -1 358.18 mA hg -1 289.94 mA hg -1 193.08 mA hg -1 The capacity utilization was lower than that of the examples, and in Comparative Examples 2-10 it was lower than that of 1A g. -1 The discharge specific capacity and capacity retention after 150 cycles at current density are both lower than those of the example.

[0062] Figure 1 XRD refinement results show that the lattice diffraction fringes of the solid electrolyte layer formed by annealing are clearly observable. According to... Figure 3 It can be seen that constructing a solid electrolyte layer in situ can significantly increase the ionic conductivity of the cathode material, from 1.61 × 10⁻⁶. -5 S cm-1 Increased to 7.51×10 -5 S cm -1 The ionic conductivity increased by 4.66 times. The advantages of the bifunctional network can be clearly observed from rate testing, high-current long-cycle testing, and electrochemical polarization comparisons. Figure 4 The results show that Example 1 outperforms Comparative Example 1 in terms of capacity performance at different scaling rates. Figure 5 Example 1 is in 1A g -1 Long cycling at current densities demonstrates that even at 1 A g -1 It exhibits good capacity performance even under high current density conditions, and shows no capacity decay after 150 cycles. The electrochemical polarization of Example 1 is significantly less than that of Comparative Example 1, demonstrating that this bifunctional network structure can significantly reduce electrochemical polarization, thereby reducing energy loss, improving charge and discharge efficiency, and extending battery life. Figure 6 This is a comparison graph of the electrochemical polarization curves of Example 1 and Comparative Example 1 after 150 cycles.

[0063] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims, and all such variations and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for preparing a bifunctional network structure lithium sulfide composite cathode material, characterized in that, Includes the following steps: (1) Mixing: Lithium sulfide and metal sulfide are thoroughly mixed to obtain a mixed material; (2) Annealing treatment: The mixed materials are annealed to obtain lithium sulfide composite cathode material with an in-situ solid electrolyte layer; (3) Carbon coating treatment: The lithium sulfide composite cathode material and the carbon source are mixed to obtain a bifunctional network structure lithium sulfide composite cathode material.

2. The method for preparing a bifunctional network structure lithium sulfide composite cathode material according to claim 1, characterized in that, In step (1), the metal sulfide is at least one of titanium disulfide, germanium disulfide, tin disulfide, tin sulfide, zirconium disulfide, tantalum disulfide, niobium disulfide, niobium trisulfide, molybdenum disulfide, molybdenum trisulfide, tungsten trisulfide, pentavanadium octasulfide, vanadium trisulfide, vanadium disulfide, aluminum trisulfide, and antimony trisulfide; And / or, the mass ratio of lithium sulfide to metal sulfide is 1~20:

1.

3. The method for preparing a bifunctional network lithium sulfide composite cathode material according to claim 1, characterized in that, In step (1), the mixture is fully mixed by ball milling. The ball milling conditions are: ball milling speed of 100~1500 rpm and ball milling time of 1~50 h.

4. The method for preparing a bifunctional network structure lithium sulfide composite cathode material according to claim 3, characterized in that, The ball milling speed is 300-1500 rpm, and the ball milling time is 3-50 h.

5. The method for preparing a bifunctional network structure lithium sulfide composite cathode material according to claim 1, characterized in that, The annealing conditions described in step (2) are: annealing temperature of 200-1500℃; holding time of 2-24h; and heating rate of 2~10℃ / min.

6. The method for preparing a bifunctional network lithium sulfide composite cathode material according to claim 1, characterized in that, The lithium sulfide composite cathode material obtained in step (2) has a particle size ≤100 nm and a solid electrolyte layer thickness of 1~10 nm.

7. The method for preparing a bifunctional network structure lithium sulfide composite cathode material according to claim 1, characterized in that, In step (3), the carbon source is at least one of multi-walled carbon nanotubes, acetylene black, and activated carbon; And / or, the mass ratio of the carbon source to the lithium sulfide composite cathode material is (1~30):

60.

8. The method for preparing a bifunctional network structure lithium sulfide composite cathode material according to claim 1, characterized in that, In step (3), the mixture is fully mixed by ball milling. The ball milling conditions are: ball milling speed of 100~700 rpm and ball milling time of 4~20 h.

9. A bifunctional network structure lithium sulfide composite cathode material prepared by the preparation method according to any one of claims 1-8.

10. The application of a bifunctional network structure lithium sulfide composite cathode material prepared by the preparation method according to any one of claims 1-8 in the field of all-solid-state lithium-sulfur batteries.

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