A method for preparing a full solid-state lithium-sulfur battery cathode containing a transition metal sulfide

Abstract

The application provides a preparation method of a transition metal sulfide-containing full-solid-state lithium-sulfur battery positive electrode, and belongs to the technical field of full-solid-state lithium-sulfur batteries. The method first prepares a carbon / sulfur composite material through ball milling and sealed melt infiltration compounding, and then adopts a mixing strategy of "two-stage ball milling and graded addition": in the first stage, the transition metal sulfide is fully dispersed with the carbon / sulfur composite material and the conductive agent and a continuous conductive framework is constructed by using medium energy; in the second stage, the sulfide solid-state electrolyte is introduced by using lower energy, so that the solid-state electrolyte is prevented from being excessively broken or the defects from being increased under high-energy mixing, thereby reducing the interface impedance and maintaining the ion transmission capacity. Through the above energy window control and addition sequence design, the application realizes the synergistic consideration of high dispersibility of the transition metal sulfide and the structural integrity of the solid-state electrolyte, and further improves the solid-solid interface stability and the battery cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state lithium-sulfur battery technology, specifically relating to a method for preparing an all-solid-state lithium-sulfur battery cathode containing transition metal sulfides. Background Technology

[0002] Lithium-sulfur batteries, with their theoretical specific capacity of up to 1675 mAh / g at the sulfur cathode and a theoretical energy density of approximately 2600 Wh / kg, are considered a crucial development direction for next-generation high-energy-density energy storage devices. However, traditional liquid lithium-sulfur battery systems suffer from severe polysulfide shuttle effects, rapid electrolyte consumption, and insufficient safety, resulting in cycle life and coulombic efficiency that fail to meet practical application requirements. To address the safety and shuttle effect issues in liquid systems, all-solid-state lithium-sulfur batteries, by replacing the liquid electrolyte with a solid electrolyte, are gradually becoming an important research direction for lithium-sulfur batteries. Solid electrolytes possess advantages such as non-flammability, good chemical stability, and high thermal stability, which can significantly improve battery safety and, to some extent, suppress polysulfide migration.

[0003] However, all-solid-state lithium-sulfur batteries still face a series of key technical challenges in actual operation. First, sulfur and its discharge products have extremely poor electronic conductivity. In an all-solid-state system, the lack of ion buffering and interfacial wetting provided by a liquid electrolyte restricts electron and lithium-ion transport within the cathode, significantly increasing electrode polarization and leading to insufficient capacity release and a drop in voltage plateau. Second, all-solid-state lithium-sulfur batteries are typical solid-solid reaction systems, requiring stable and continuous interfacial contacts at the microscale between the sulfur cathode active material, the solid electrolyte, and the conductive agent. However, during actual preparation and cycling, due to differences in the mechanical properties of different materials and insufficient interfacial compatibility, poor contact, debonding, and even microcracks easily occur at the solid-solid interface, severely hindering the effective migration of lithium ions at the interface, thus causing increased internal resistance and rapid capacity decay. Furthermore, the sulfur cathode undergoes significant volume expansion and contraction during charging and discharging, with volume changes exceeding 70%. In an all-solid-state system, solid electrolytes cannot effectively buffer volume changes like liquid electrolytes. Sulfur cathodes are more prone to structural pulverization and interface damage during repeated cycling, leading to the breakage of the conductive network and the gradual failure of active materials, which seriously affects the cycle stability of the battery.

[0004] To address the aforementioned issues, patent CN113206255A improves electron and ion transport within the electrode by increasing the content of conductive agents and constructing a porous conductive framework structure. However, this method often requires sacrificing the proportion of sulfur active material, reducing the overall energy density. Furthermore, the fabrication process for complex structures is difficult to integrate with existing battery manufacturing processes, increasing process complexity and production costs. In recent years, some studies have attempted to introduce polar or catalytically active inorganic materials into sulfur cathode systems, such as patent CN108832098A, aiming to improve the reaction kinetics of sulfur and its discharge products through interfacial interactions. However, existing inorganic materials are mostly concentrated in oxide, nitride, or carbon-based composite material systems, which have limited electronic conductivity or ion transport capabilities and insufficient interfacial compatibility with sulfur and solid electrolytes, making it difficult to simultaneously achieve interfacial stability and long-cycle performance in an all-solid-state system.

[0005] In contrast, transition metal sulfide materials with layered structures have gradually attracted attention due to their unique crystal structure and electronic properties. These materials exhibit metalloid or quasi-metallic conductivity in certain configurations, while their interlayer structure facilitates lithium-ion insertion and migration, and they possess good chemical compatibility and structural stability within the sulfide system. However, although existing technologies offer systematic applications of these materials in the cathode structure of all-solid-state lithium-sulfur batteries, the mixing and ball milling process typically involves a single high-energy ball milling operation. Transition metal sulfides are prone to agglomeration in composite sulfur cathodes, and the sulfide solid electrolyte is easily damaged under high-energy ball milling conditions.

[0006] Therefore, how to rationally introduce functional materials with good electronic conductivity, lithium-ion transport capability and interface stabilization into all-solid-state lithium-sulfur batteries to achieve synergistic optimization of sulfur cathode structural stability and electrochemical performance improvement remains an important technical problem to be solved in this field. Summary of the Invention

[0007] To address the problems existing in the background technology, the present invention aims to provide a method for preparing a transition metal sulfide composite sulfur cathode for all-solid-state lithium-sulfur batteries. This method first prepares a carbon / sulfur composite material through ball milling and sealed melt infiltration composite processing. Then, a "two-stage ball milling, graded addition" mixing strategy is adopted: in the first stage, medium energy is used to fully disperse the transition metal sulfide, carbon / sulfur composite material, and conductive agent to construct a continuous conductive framework; in the second stage, a sulfide solid electrolyte is introduced at a lower energy level to avoid excessive fragmentation or increased defects in the solid electrolyte under high-energy mixing, thereby reducing interfacial impedance and maintaining ion transport capability. Through the above-mentioned energy window control and addition sequence design, the present invention achieves a synergistic balance between the high dispersibility of the transition metal sulfide and the structural integrity of the solid electrolyte, thereby improving solid-solid interface stability and battery cycle stability.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for preparing an all-solid-state lithium-sulfur battery cathode containing transition metal sulfides includes the following steps:

[0010] Step 1. Mix elemental sulfur and a conductive agent and then ball-mill them to obtain a sulfur-carbon mixture;

[0011] Step 2. Place the sulfur-carbon mixture in a sealed environment for melt infiltration composite treatment, so that the molten sulfur infiltrates and is fixed in the conductive agent skeleton under capillary action to obtain a carbon-sulfur composite material;

[0012] Step 3. Mix the carbon-sulfur composite material, transition metal sulfide, and conductive agent, and then perform the first stage of ball milling; the ball milling speed is 350~500 r / min, and the ball milling time is 0.5~2h;

[0013] The transition metal sulfide is tantalum sulfide or tungsten sulfide;

[0014] Step 4. Add solid electrolyte to the material obtained after the first stage of ball milling and mixing, and then carry out the second stage of ball milling and mixing. The ball milling speed is 100~250 r / min and the ball milling time is 2~4 h. After the ball milling is completed, the desired all-solid-state lithium-sulfur battery cathode is obtained.

[0015] Furthermore, the conductive agent is any one or two of vapor-grown carbon fibers and carbon nanotubes.

[0016] Furthermore, the mass ratio of elemental sulfur to conductive agent is 1:(0.2~0.4). Since elemental sulfur is an insulating material, too low carbon content in the conductive agent will lead to reduced sulfur utilization and incomplete capacity release. Since carbon has a high specific surface area, is porous and has a low density, too high carbon content will lead to easy cracking of high-load electrodes and reduce the overall energy density.

[0017] Furthermore, in step 1, the ball milling speed is 20~40 r / min, and the time is 5~10 min.

[0018] Furthermore, the mass fraction of transition metal sulfides in the cathode of all-solid-state lithium-sulfur batteries is 3% to 10%.

[0019] Furthermore, the mass ratio of carbon-sulfur composite material, conductive agent, solid electrolyte and transition metal sulfide is (3~4):(0.7~1):(4~5):(0.3~1).

[0020] Furthermore, the solid electrolyte is a lithium phosphorus sulfide chlorine sulfide electrolyte or a lithium phosphorus sulfide chlorine bromine sulfide electrolyte.

[0021] Furthermore, in step 2, the temperature of the melt infiltration composite treatment is 155~180℃, and the time is 12~14h.

[0022] Furthermore, apart from the difference in rotation speed and time, the ball milling equipment type, ball-to-material ratio, and grinding ball specifications remain the same in the first stage of ball milling and the second stage of ball milling, so as to ensure that the energy difference between the two stages of ball milling is mainly controlled by the rotation speed and time window.

[0023] Furthermore, both the first-stage ball milling and the second-stage ball milling were carried out using a vibrating ball mill; the grinding media were grinding balls, the ball-to-material ratio was 10:1, and the diameter of the grinding balls was 10 mm.

[0024] The mechanism of this invention is as follows:

[0025] This invention preferably incorporates tantalum sulfide (TaS2) and / or tungsten sulfide (WS2) as transition metal sulfide functional phases. Compared to common transition metal sulfides, TaS2 / WS2 exhibits superior layered crystal structure stability and higher electronic conductivity, and demonstrates better chemical compatibility in sulfur and sulfide solid electrolyte systems, making it more suitable for simultaneously serving as a "conductive bridging" and "interface stabilizing" element in the composite cathode of all-solid-state lithium-sulfur batteries. Specifically, the layered structure of TaS2 / WS2 can form more continuous contact and bridging pathways between the carbon / sulfur composite material, the conductive agent, and the sulfide solid electrolyte, reducing solid-solid interface contact impedance and promoting the co-transport of electrons and lithium ions. Simultaneously, its layered structure can buffer the interfacial debonding tendency caused by volume changes in the sulfur active material during cycling, effectively buffering the volume expansion of the all-solid-state lithium-sulfur battery cathode, thereby improving the battery's cycle stability.

[0026] While TaS2 / WS2 possesses the aforementioned advantages, its sheet-like materials are prone to stacking and agglomeration. If the conventional "one-step ball milling method" is used to simultaneously perform high-energy ball milling on TaS2 / WS2, sulfide solid electrolyte, and C / S, the ball milling intensity often needs to be increased to achieve dispersion. This can easily lead to excessive breakage of sulfide solid electrolyte particles, an increase in surface defects, or an abnormal increase in interfacial activity, resulting in increased interfacial impedance and deterioration of cycle performance. Conversely, if the ball milling intensity is reduced to protect the solid electrolyte, TaS2 / WS2 will be difficult to fully deagglomerate and disperse, forming local enrichment, discontinuous conductive network, and failing to leverage its interfacial bridging advantages. To address this, the present invention employs a two-stage ball milling and phased addition energy window process: In the first stage, higher energy is used to fully depolymerize and uniformly anchor TaS2 / WS2 within the framework of the carbon / sulfur composite material and the conductive agent, constructing a continuous electron transport pathway. In the second stage, lower energy ball milling gently introduces the sulfide solid electrolyte, preventing excessive electrolyte breakage, increased surface defects, or abnormally enhanced interfacial activity under high-energy impact, which could lead to increased solid-solid interface contact impedance. This balances electron and ion transport while improving cycle stability. The synergistic combination of material selection and process window enables the composite cathode to achieve a synergistic improvement in conductivity, interfacial stability, and structural stability without significantly increasing the proportion of inactive components, thereby significantly improving the capacity release and cycle retention performance of the all-solid-state lithium-sulfur battery.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] The all-solid-state lithium-sulfur battery prepared based on the composite cathode of this invention exhibits good electrochemical stability and cycle reliability within the operating voltage range of 0.4–3.0 V: at a rate of 0.1C, the initial specific capacity of the battery can reach 1242.5 mAh / g, and the capacity retention rate is 100% after 100 cycles; it also has good repeatability and system stability; at the same time, the preparation method of this invention is simple and easy to operate, adopting a dry process route of "melt composite preparation of C / S + two-stage ball milling and graded addition", and with the key process parameters, it can effectively reduce batch fluctuations and maintain consistent material dispersion and interface state during scale-up production, thus making it easier to achieve consistent battery performance at a large production scale. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the surface of the tantalum sulfide composite sulfur positive electrode sheet prepared in Example 1 of the present invention;

[0030] Figure 2 This is a scanning electron microscope image of the surface of the composite sulfur cathode prepared in Comparative Example 1 of the present invention.

[0031] Figure 3This is a scanning electron microscope cross-sectional image (before cycling) of the surface of the tantalum sulfide-containing composite sulfur positive electrode sheet prepared in Example 1 of the present invention.

[0032] Figure 4 This is a scanning electron microscope cross-sectional view (after 100 cycles) of the surface of the tantalum sulfide composite sulfur cathode prepared in Example 1 of the present invention.

[0033] Figure 5 This is a scanning electron microscope cross-sectional view (before cycling) of the surface of the composite sulfur positive electrode sheet prepared in Comparative Example 1 of the present invention.

[0034] Figure 6 This is a scanning electron microscope cross-sectional view (after 100 cycles) of the surface of the composite sulfur positive electrode sheet prepared in Comparative Example 1 of the present invention.

[0035] Figure 7 The graphs show the cycle performance of the all-solid-state lithium-sulfur batteries obtained in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0037] Example 1

[0038] A method for preparing an all-solid-state lithium-sulfur battery cathode containing transition metal sulfides includes the following steps:

[0039] Step 1. Mix elemental sulfur and vapor-grown carbon fiber (VGCF) powder at a mass ratio of 3:1, and then ball mill the mixture at a speed of 30 r / min for 5 min to obtain a sulfur-carbon mixture.

[0040] Step 2. The sulfur-carbon mixture is subjected to high-temperature melt infiltration composite treatment at a temperature of 155℃ for 14 hours to obtain carbon-sulfur composite material C / S.

[0041] Step 3. Mix C / S, TaS2, and carbon nanotubes (CNTs) and place them in a vibrating ball mill for the first stage of ball milling and mixing. The mass ratio of C / S:CNTs:TaS2 is 37:10:3; the ball-to-material ratio is 10:1; the diameter of the grinding balls is 10 mm; the ball milling speed is 400 r / min; and the ball milling time is 1 h.

[0042] Step 4. Add sulfide solid electrolyte LPSC powder to the composite material obtained after the first stage of ball milling and mixing. The mass ratio of composite material to LPSC is 1:1. Then, carry out the second stage of ball milling and mixing. The ball-to-material ratio is 10:1, the diameter of the grinding ball is 10 mm, the ball milling speed is 200 r / min, and the ball milling time is 3 h. After the ball milling is completed, the desired all-solid-state lithium-sulfur battery cathode is obtained.

[0043] The prepared all-solid-state lithium-sulfur battery cathode, lithium foil, and solid electrolyte were assembled into an all-solid-state battery. The lithium foil was 100 μm thick, and the electrolyte was a lithium phosphorus sulfide chlorine sulfide solid electrolyte. The lithium phosphorus sulfide chlorine sulfide solid electrolyte was pressed into a sheet at a pressure of 400 MPa. Then, the solid electrolyte was placed on top of the prepared cathode and a pressure of 500 MPa was applied. Subsequently, the lithium foil was placed on the other side, and the battery was sealed. After sealing, it was stored at 45°C for 24 hours to obtain the all-solid-state lithium-sulfur battery.

[0044] Example 2

[0045] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the proportion of TaS2 is increased from 3% to 5%, while the other steps remain unchanged.

[0046] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0047] Example 3

[0048] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the proportion of TaS2 is increased from 3% to 10%, while the other steps remain unchanged.

[0049] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0050] Example 4

[0051] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the ball milling time in the first stage is changed from 1 hour to 0.5 hours, while the other steps remain unchanged.

[0052] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0053] Example 5

[0054] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the ball milling time in the first stage is changed from 1 hour to 2 hours, while the other steps remain unchanged.

[0055] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0056] Example 6

[0057] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the ball milling time in the second stage is changed from 3 hours to 2 hours, while the other steps remain the same.

[0058] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0059] Example 7

[0060] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the ball milling time in the second stage is changed from 3 hours to 4 hours, while the other steps remain the same.

[0061] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0062] Example 8

[0063] A method for preparing a composite sulfur cathode containing transition metal sulfides differs from Example 1 only in that the transition metal sulfide TaS2 is replaced with WS2, while the other steps remain unchanged.

[0064] Referring to the all-solid-state lithium-sulfur battery preparation method of Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode containing transition metal sulfides in this example to prepare an all-solid-state lithium-sulfur battery.

[0065] Comparative Example 1

[0066] A sulfur composite cathode differs from Example 1 only in that no transition metal sulfides were added during ball milling.

[0067] Referring to the preparation method of the all-solid-state lithium-sulfur battery in Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode of this example to prepare an all-solid-state lithium-sulfur battery.

[0068] Comparative Example 2

[0069] A composite sulfur cathode differs from Example 1 only in that: a sulfide solid electrolyte LPSC is added simultaneously during the first stage of ball milling and mixing, so that the LPSC undergoes the same high-energy ball milling process as the transition metal sulfide.

[0070] Specifically, the C / S, CNTs, TaS2, and LPSC obtained in step one were added to a ball mill jar and ball-milled at 400 r / min for 1 h, followed by ball milling at 200 r / min for 3 h to obtain the composite sulfur cathode material. The remaining battery assembly and testing conditions were the same as in Example 1.

[0071] Comparative Example 3

[0072] A composite sulfur cathode differs from Example 1 only in that: during the first stage of ball milling, C / S, CNTs and LPSC are first ball milled and mixed, and then TaS2 is added in the second stage, so that TaS2 only undergoes a low-energy ball milling process.

[0073] Specifically, the C / S, CNTs, and LPSC obtained in step one were added to a ball mill jar and ball-milled at 400 r / min for 1 h; then TaS2 was added, and the mixture was ball-milled again at 200 r / min for 3 h to obtain the composite sulfur cathode material. The remaining battery assembly and testing conditions were the same as in Example 1.

[0074] Comparative Example 4

[0075] A composite sulfur cathode differs from Example 1 only in that both the first and second stages of ball milling use lower energy conditions.

[0076] Specifically, the C / S, CNTs, and TaS2 prepared in step one were ball-milled at 200 r / min for 1 h in the first stage; then LPSC was added and ball-milled at 200 r / min for 3 h in the second stage to obtain the composite sulfur cathode material. The remaining battery assembly and testing conditions were the same as in Example 1.

[0077] Comparative Example 5

[0078] A sulfur composite cathode differs from Example 1 only in that MoS2 transition metal sulfide is added during ball milling.

[0079] Referring to the preparation method of the all-solid-state lithium-sulfur battery in Example 1, the composite sulfur cathode containing transition metal sulfides in Example 1 was replaced with the composite sulfur cathode of this example to prepare an all-solid-state lithium-sulfur battery.

[0080] Performance testing:

[0081] Morphological characterization: The surface of the composite sulfur cathode containing transition metal sulfides prepared in Example 1 was observed, and its scanning electron microscope image is shown below. Figure 1 ,from Figure 1 It can be seen that the surface of the composite sulfur cathode containing transition metal sulfides remains continuous and dense, forming a continuous network, and there is no tendency for the surface to "powder".

[0082] The surface of the composite sulfur positive electrode sheet prepared in Comparative Example 1 was observed, and its scanning electron microscope image is shown below. Figure 2 ,from Figure 2 It can be seen that there are obvious pores on the surface, and the local structure is loose, showing "sponge-like / porous" characteristics. Figure 1 and Figure 2 The comparison shows that there is a significant difference in the density of the electrodes prepared by the two methods, and density affects the cycle stability of the final battery.

[0083] The cross-section of the composite sulfur cathode containing tantalum sulfide prepared in Example 1 was observed, and the scanning electron microscope cross-sectional images before and after cycling are shown below. Figure 3 and Figure 4 ,from Figure 3 and Figure 4 It can be seen that after 100 cycles, the cross-sectional thickness changed from 91.73 μm to 96.47 μm, and the volume expansion rate was only 5.2%, which shows that the volume expansion was well suppressed after the introduction of tantalum sulfide.

[0084] The cross-section of the composite sulfur positive electrode sheet prepared in Comparative Example 1 was observed, and the scanning electron microscope cross-sectional images before and after cycling are shown below. Figure 5 and Figure 6 ,from Figure 5 and Figure 6 It can be seen that after 100 cycles, the cross-sectional thickness changed from 73.18 μm to 87.36 μm, and the volume expansion rate was approximately 17.1%.

[0085] The all-solid-state lithium-sulfur batteries prepared in the above embodiments and comparative examples were subjected to capacity retention tests: the voltage range was 0.4~3.0V, and the current rate was 0.1C. The test results are shown in Table 1.

[0086] Table 1

[0087] plan Initial capacity (mAh / g) Capacity retention rate (%) after 100 cycles Example 1 1242.5 100 Example 2 1150.8 95.5 Example 3 1120.6 94.9 Example 4 1088.9 95.6 Example 5 1105.4 97.3 Example 6 1111.3 92.6 Example 7 1059.6 92.8 Example 8 1058.7 90.8 Comparative Example 1 950.4 77.5 Comparative Example 2 941.6 72.7 Comparative Example 3 920.5 70.6 Comparative Example 4 937.1 70.3 Comparative Example 5 1020.6 80.1

[0088] The cycle performance (cycle rate of 0.1C) of the all-solid-state lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 can be found in [reference needed]. Figure 7It can be observed that the cycle performance of the tantalum sulfide-containing all-solid-state lithium-sulfur battery in Example 1 is significantly improved compared to that of the all-solid-state lithium-sulfur battery in Comparative Example 1. It maintains 100% of its cycle specific capacity after 100 cycles, while the specific capacity of the lithium all-solid-state sulfur battery in Comparative Example 1 decreases significantly during cycling. This is because, in Example 1 of this invention, on the one hand, transition metal sulfides (taking TaS2 as an example) have high electronic conductivity and good chemical stability, providing a continuous electron transport channel and stabilizing the solid-solid interface in the composite cathode; on the other hand, this invention employs a two-stage ball milling energy window process: firstly, a first-stage medium-energy ball milling process fully disperses TaS2 with the carbon / sulfur composite material and conductive agent to form a continuous conductive framework; then, a second-stage low-energy ball milling process introduces the sulfide solid electrolyte, thereby avoiding defects and increased interfacial impedance in the solid electrolyte under high-energy ball milling conditions. The synergistic effect of the above material properties and process window results in slower polarization growth and more stable solid-solid interface contact during cycling, thus significantly improving the cycle performance compared to the comparative example.

[0089] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A method for preparing an all-solid-state lithium-sulfur battery cathode containing transition metal sulfides, characterized in that, Includes the following steps: Step 1. Mix elemental sulfur and a conductive agent and then ball-mill them to obtain a sulfur-carbon mixture; Step 2. Place the sulfur-carbon mixture in a sealed environment for melt infiltration composite treatment, so that the molten sulfur infiltrates and is fixed in the conductive agent skeleton under capillary action to obtain a carbon-sulfur composite material; Step 3. Mix the carbon-sulfur composite material, transition metal sulfide, and conductive agent, and then perform the first stage of ball milling; the ball milling speed is 350~500 r / min, and the ball milling time is 0.5~2h; The transition metal sulfide is tantalum sulfide or tungsten sulfide; Step 4. Add solid electrolyte to the material obtained after the first stage of ball milling and mixing, and then carry out the second stage of ball milling and mixing. The ball milling speed is 100~250 r / min and the ball milling time is 2~4 h. After the ball milling is completed, the desired all-solid-state lithium-sulfur battery cathode is obtained.

2. The preparation method according to claim 1, characterized in that, The conductive agent is any one or two of vapor-grown carbon fibers and carbon nanotubes.

3. The preparation method according to claim 1, characterized in that, The mass ratio of elemental sulfur to conductive agent is 1:(0.2~0.4).

4. The preparation method according to claim 1, characterized in that, In step 1, the ball milling speed is 20~40 r / min and the time is 5~10 min.

5. The preparation method according to claim 1, characterized in that, The mass fraction of transition metal sulfides in the cathode of all-solid-state lithium-sulfur batteries is 3% to 10%.

6. The preparation method according to claim 1, characterized in that, The mass ratio of carbon-sulfur composite material, conductive agent, solid electrolyte and transition metal sulfide is (3~4):(0.7~1):(4~5):(0.3~1).

7. The preparation method according to claim 1, characterized in that, The solid electrolyte is a lithium phosphorus sulfide chlorine sulfide electrolyte or a lithium phosphorus sulfide chlorine bromine sulfide electrolyte.

8. The preparation method according to claim 1, characterized in that, In step 2, the temperature of the melt infiltration composite treatment is 155~180℃ and the time is 12~14h.

9. The preparation method according to claim 1, characterized in that, The first stage of ball milling and the second stage of ball milling are identical except for the rotation speed and time. The other aspects, such as the type of ball milling equipment, the ball-to-material ratio, and the specifications of the grinding balls, are kept the same to ensure that the energy difference between the two stages of ball milling is mainly controlled by the rotation speed and time window.

10. The preparation method according to claim 9, characterized in that, The first stage of ball milling and the second stage of ball milling were both carried out using a vibrating ball mill; the grinding media were grinding balls, the ball-to-material ratio was 10:1, and the diameter of the grinding balls was 10 mm.

Images