Composite positive electrode for all-solid-state lithium battery and preparation method of composite positive electrode

Abstract

The invention discloses a titanium tetrasulfide / carbon material composite positive electrode material for an all-solid-state lithium battery and a preparation method of the titanium tetrasulfide / carbon material composite positive electrode material, and belongs to the technical field of electrochemical energy storage. The composite positive electrode material is formed by compounding amorphous TiS4 nanospheres, reduced graphene oxide (rGO), carbon nanotubes (CNT) or vapor-grown carbon fibers (VGCF) through a liquid phase method, and the mass ratio of the carbon material is 5%-15%. In the preparation process, targeted surface modification processes are designed for different carbon materials, then a uniform mixing state is fixed through liquid phase dispersion and freeze drying, and finally, tight compounding of TiS4 and the carbon materials is achieved through inert atmosphere high-energy ball milling. The defects that pure TiS4 is low in electronic conductivity, high in charge-discharge volume expansion rate and large in interface impedance are effectively overcome, the composite positive electrode material is excellent in compatibility with sulfide solid electrolyte, and the assembled all-solid-state lithium battery has high energy density, long cycle stability and high safety and is suitable for large-scale production. The method is suitable for electric automobiles, wearable electronic equipment and energy storage systems.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a titanium tetrasulfide / carbon composite cathode material for high-energy-density all-solid-state lithium batteries and its preparation method, which is particularly suitable for electric vehicles, wearable electronic devices and energy storage systems with high requirements for energy density, cycle stability and safety. Background Technology

[0002] All-solid-state lithium batteries (ASSLBs), through the application of non-flammable solid electrolytes, fundamentally solve the safety hazards such as combustion and explosion of traditional liquid electrolyte lithium batteries, while also possessing higher energy density potential, and are widely recognized as the core development direction of next-generation energy storage technology. Among the key components of all-solid-state lithium batteries, the performance of the cathode material directly determines the battery's energy density and cycle life. Therefore, developing cathode materials that combine high capacity, high conductivity, and structural stability has become a research focus in the field.

[0003] Transition metal polysulfides have become a preferred cathode material for all-solid-state lithium batteries due to their high theoretical specific capacity based on anion redox reactions and their good interfacial compatibility with sulfide solid electrolytes. Among them, amorphous titanium tetrasulfide (a-TiS4) shows particularly outstanding potential: its theoretical reversible specific capacity can reach 700 mAh g⁻¹. -1 The discharge plateau is approximately 2 V, corresponding to a specific energy density as high as 1200 Wh kg. -1 It is significantly superior to traditional oxide cathodes. However, the practical application of a-TiS4 faces three major bottlenecks: The intrinsic electronic conductivity is extremely low: the electronic conductivity of pure a-TiS4 is only about 10. -8 S cm -1 This leads to obstructed charge transport and poor high-rate performance; Significant volume expansion during charge and discharge: The volume expansion rate exceeds 30% during cycling, which can easily cause the active material particles to agglomerate and the interface contact failure with the solid electrolyte / conductive agent, thus leading to rapid capacity decay. Insufficient interfacial stability: The solid-solid contact interface between a-TiS4 and the sulfide solid electrolyte has high impedance, and side reactions are prone to occur during cycling to generate an insulating phase, which further deteriorates the electrochemical performance.

[0004] To address these issues, a series of improvement studies have been conducted in this field. On one hand, researchers have attempted to combine a-TiS4 with carbon materials to improve conductivity: for example, by high-energy ball milling, Super P (nanoscale conductive carbon) is combined with a-TiS4. Utilizing the high conductivity and nano-lubricating effect of Super P, the electronic conductivity of the composite material is increased to 10. -3 S cm -1The particle size was reduced to 200 nm after ball milling to optimize interfacial contact (Amorphous Titanium Polysulfide Composites with Electronic / Ionic Conduction Networks for All-Solid-State Lithium Batteries, ACS Appl. Mater. Interfaces 2022, 14, 17594-17600). In addition, carbon materials such as reduced graphene oxide (rGO) and carbon nanotubes (CNT) have also been used to construct electronic conduction networks. Among them, the two-dimensional layered structure of rGO can suppress the volume expansion of a-TiS4, and the one-dimensional tubular structure of CNT can provide a through charge transport channel. However, such composite systems still have the functional limitations of single carbon materials. For example, rGO is prone to stacking, which leads to the obstruction of ion transport, and CNT has poor dispersion and is prone to agglomeration. It is difficult to simultaneously take into account electronic conduction, structural buffering and interfacial compatibility.

[0005] On the other hand, to further optimize interface performance, some studies have proposed in-situ coating of a-TiS4 / carbon composite material with a sulfide solid electrolyte. This enhances interface stability by constructing an electron-ion dual conduction network. This coating layer enables tight solid-solid contact between a-TiS4 and the solid electrolyte, increasing the coulombic efficiency from 67.3% to 88.7%, and improving the battery efficiency at 0.1 Ag. -1 It still maintains 507.4 mAh g after 100 cycles. -1 The reversible capacity (Amorphous Titanium Polysulfide Composites with Electronic / Ionic Conduction Networks for All-Solid-State Lithium Batteries, ACS Appl. Mater. Interfaces 2022, 14, 17594-17600). However, this approach still has shortcomings: First, the synergy between the coating process and the carbon material composite process is poor, which easily leads to the coating layer falling off; second, the coating compatibility for different carbon materials with different structures has not been explored, making it difficult to fully utilize the structural reinforcement advantages of carbon materials; third, high loading (≥10 mg cm⁻¹) is required. -2 The performance degradation problem under high loading has not been effectively solved, and high loading is a key indicator for the practical application of cathode materials.

[0006] In summary, while existing technologies have made progress in improving the conductivity and optimizing the interface of a-TiS4, a composite cathode solution that can simultaneously achieve high electron conduction efficiency, strong structural buffering capacity, excellent interface stability, and high load capacity adaptability is still lacking. Therefore, developing an a-TiS4 composite cathode based on specific carbon material selection and process synergy has become crucial to breaking through the performance bottleneck of all-solid-state lithium batteries. Summary of the Invention

[0007] This invention aims to overcome the shortcomings of existing amorphous TiS4 cathode materials, such as low electronic conductivity, large volume expansion, poor interface stability, and insufficient high load capacity. It provides a TiS4 / carbon composite cathode material for all-solid-state lithium batteries and its preparation method. By selecting carbon materials with specific structures (rGO / CNT / VGCF) and optimizing the liquid phase dispersion-high-energy ball milling-interface control process, a composite system with high electronic conductivity, strong structural support, and good interface compatibility is constructed, ultimately realizing high capacity, long cycle life, and high load capacity applications in all-solid-state lithium batteries.

[0008] To achieve the above objectives, this invention provides a titanium tetrasulfide / carbon composite cathode material for all-solid-state lithium batteries, which is composed of amorphous titanium tetrasulfide (TiS4) and carbon material through a liquid-phase composite method. The TiS4 exists in the form of nanospheres, which are uniformly attached to the surface or structure of the carbon material. The carbon material accounts for 5% to 15% of the total mass of the composite cathode material. This 5% to 15% carbon material mass ratio represents an optimal range that balances conductivity, structural stability, and energy density. When the carbon material percentage is ≥5%, a continuous three-dimensional conductive network can be formed in the composite system, effectively covering the surface of the TiS4 nanospheres, overcoming the core defect of extremely low electronic conductivity in pure TiS4, and providing a through-channel for electron transport. This percentage ensures sufficient interfacial bonding sites between the carbon material and TiS4, initially leveraging the structural support role of the carbon material, mitigating the volume expansion of TiS4 during charging and discharging, and preventing premature shedding of active material. If the carbon content is below 5%, the carbon material is prone to uneven dispersion, forming isolated conductive islands, making it impossible to construct a complete conductive network. Furthermore, its structural support is weak, making it difficult to suppress volume expansion and leading to rapid capacity decay. Since carbon materials themselves have no electrochemical activity, a content of ≤15% avoids excessive dilution of the active material TiS4, ensuring the high energy density of the composite cathode. This content also prevents carbon material agglomeration and stacking, avoiding blockage of the Li... + The transport channels may be disrupted, affecting the interfacial contact between TiS4 and the sulfide electrolyte, thus ensuring smooth ion conduction and reducing interfacial impedance. If the proportion exceeds 15%, it will not only lead to a decrease in the proportion of active material and a significant reduction in specific capacity, but may also cause interfacial side reactions due to excessive carbon material aggregation, weakening the battery's cycle stability.

[0009] Furthermore, the carbon material is one of reduced graphene oxide (rGO), carbon nanotubes (CNT), or vapor-grown carbon fiber (VGCF).

[0010] Furthermore, the rGO is prepared by the Hummers method and then chemically reduced; the CNT has a purity of ≥95% and a metal impurity content of ≤0.1 wt% as detected by ICP-OES; the VGCF has an initial diameter of 1~10 μm and an aspect ratio of ≥100, and a diameter of 150~300 nm after pre-ball milling.

[0011] The present invention also provides a method for preparing the composite cathode material as described above, comprising the following steps: dispersing carbon material in an organic solvent to form a dispersion; adding titanium tetrasulfide and sulfur powder to the dispersion at a predetermined molar ratio and mixing; freeze-drying the mixture to obtain a precursor mixed powder; and subjecting the precursor mixed powder to high-energy ball milling to obtain the composite cathode material under an inert atmosphere.

[0012] Furthermore, when the carbon material is reduced graphene oxide, the specific preparation process includes the following steps: S1. Surface Modification of rGO: The prepared rGO powder was heat-treated in a mixed gas containing water vapor and carbon dioxide to obtain surface-modified rGO. During the mixed gas heat treatment, water vapor and carbon dioxide synergistically act on the rGO surface at high temperature, selectively introducing oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups. These functional groups can form strong interactions (such as hydrogen bonds and coordination bonds) with the surface of TiS4 nanospheres, significantly improving the interfacial bonding force between rGO and TiS4 and preventing the active material from falling off during charging and discharging. The presence of oxygen-containing functional groups breaks the van der Waals forces between rGO sheets, reduces sheet aggregation, and allows TiS4 nanospheres to uniformly adhere to the surface of rGO nanosheets, forming a uniformly dispersed composite system, laying the foundation for constructing a continuous conductive network.

[0013] The synergistic effect of water vapor etching and carbon dioxide weak oxidation can form a microporous-mesoporous hierarchical structure on the surface and edges of rGO sheets, effectively increasing the specific surface area of ​​rGO. This hierarchical structure not only provides more loading sites for TiS4 nanospheres but also constructs through-hole ion transport channels, reducing Li... + The diffusion resistance inside the composite cathode alleviates the problem of poor ion transport in the pure TiS4 system.

[0014] S2. Preparation of rGO dispersion: Surface-modified rGO was added to anhydrous N,N-dimethylformamide and sonicated at 300-500 W for 1-2 h to form a dispersion with a concentration of 0.5-1.0 mg·mL⁻¹. -1 A homogeneous dispersion; S3. Raw material pre-composite: Weigh TiS2 and sulfur powder at a molar ratio of 1:2, add them to the rGO dispersion from step S2, and magnetically stir at 300~500 rpm for 3~5 h; S4. Freeze-drying: Drying at -50~-60℃ and vacuum degree ≤10 Pa for 48 h to obtain rGO-TiS2-S mixed powder; S5. High-energy co-ball milling: The mixed powder is loaded into a zirconium ball mill jar with a zirconium ball to powder mass ratio of 10:1. Argon gas is used for purging 3 times, and the vacuum degree is ≤10 Pa. The mixture is ball-milled at 500-900 rpm for 3 min followed by 7 min resting for 48 h. The temperature is controlled at ≤50℃ with circulating water cooling. The product is then collected to obtain TiS4@rGO.

[0015] Furthermore, when the carbon material is CNT, the specific preparation process includes the following steps: S1. CNT surface modification and dispersion: CNTs were added to DMF containing 0.1–0.3 wt% sodium dodecylbenzenesulfonate (SDBS) and sonicated at 500–800 W for 2–3 h to form a concentration of 0.5–1.0 mg·mL. -1 The dispersion was then subjected to a reaction at 3000-5000 r·min. -1 Centrifugation at 10-30 min removes agglomerates. SDBS molecules can be fully adsorbed onto the CNT surface. Its hydrophobic groups form strong van der Waals forces with the CNT tube wall, while its hydrophilic groups form hydrogen bonds with the DMF solvent, constructing a stable CNT-SDBS-DMF dispersion system. This ensures uniform dispersion of individual CNT tubes or fine bundles, preventing agglomeration. An SDBS concentration ≤0.3 wt% allows for strict control of residual SDBS, preventing excessive surfactant precipitation during subsequent freeze-drying and high-energy ball milling. This ensures that the SDBS does not hinder the interfacial adsorption of TiS2 / sulfur powder and CNTs, nor does it affect the stability of the sulfide solid electrolyte, thus avoiding increased interfacial impedance. The SDBS adsorption layer forms weakly polar sites on the CNT surface, which can adsorb TiS2 nanoparticles and sulfur powder through electrostatic interactions or hydrogen bonding, uniformly anchoring the raw materials to the CNT network surface. After ball milling, TiS4 nanospheres can be tightly entangled in the CNT network, forming an integrated conductive network-active material structure. This tightly packed composite structure ensures rapid electron transport through CNTs while also buffering the volume expansion of TiS4 during charging and discharging by utilizing the one-dimensional tubular structure of CNTs, thus preventing the shedding of active materials and improving cycle stability.

[0016] S2. Raw material precomposition: Weigh TiS2 and sulfur powder at a molar ratio of 1:2, add them to the CNT dispersion from step S1, and stir at 100-300 rpm for 1-4 hours; S3. Freeze-drying: Drying at -50~-60℃ and vacuum degree ≤10 Pa for 48 h to obtain CNT-TiS2-S mixed powder; S4. High-energy co-ball milling: The mixed powder is loaded into a zirconium ball mill jar with a zirconium ball to powder mass ratio of 10:1. Argon gas is used for purging 3 times, and the vacuum degree is ≤10 Pa. The mixture is ball-milled for 48 h at a speed of 500-900 rpm in a mode of milling for 3 min and standing for 7 min. The temperature is controlled at ≤50℃ by circulating water cooling. The product is collected to obtain TiS4@CNT.

[0017] Furthermore, when the carbon material is VGCF, the specific preparation process includes the following steps: S1. VGCF Surface Modification: Raw VGCF was loaded into a zirconium ball mill jar and ball-milled at 300-400 rpm for 6 hours at a zirconium ball to powder mass ratio of 15:1 to obtain surface-modified VGCF. The mechanical collisions and shear forces during the ball milling process generated abundant defect sites and micro / nano roughness on the VGCF surface, while exposing more active groups, significantly enhancing its interfacial interaction with TiS4 nanospheres. The activated VGCF surface can form a tight physical adsorption and chemical bond with TiS4, preventing the active material from peeling off from the carbon material during charging and discharging, ensuring the stability of the integrated structure of the conductive network and the active material. The refined VGCF, with its high aspect ratio, intertwines to form a continuous and dense three-dimensional conductive network in the composite system, resulting in shorter and smoother electron transport paths compared to the loose network of the raw VGCF.

[0018] S2. VGCF dispersion: Surface-modified VGCF was added to DMF and sonicated at 300-500 W for 1.5-2.5 h to form a concentration of 0.5-1.0 mg·mL. -1 The dispersion; S3. Raw material pre-composite and drying: Weigh TiS2 and sulfur powder at a molar ratio of 1:2, add the dispersion from step S2, and stir for 2-4 h; dry at -50~-60℃ and vacuum degree ≤10 Pa for 48 h to obtain VGCF-TiS2-S mixed powder; S4. High-energy co-ball milling: The mixed powder is loaded into a zirconium ball mill jar with a zirconium ball to powder mass ratio of 10:1. Argon gas is used for purging 3 times, and the vacuum degree is ≤10 Pa. The mixture is ball-milled at 500-900 rpm for 3 min followed by 7 min resting for 48 h. The temperature is controlled at ≤50℃ with circulating water cooling. The product is then collected to obtain TiS4@VGCF.

[0019] This invention also provides an all-solid-state lithium battery, comprising the aforementioned titanium tetrasulfide / carbon composite cathode material, a sulfide solid electrolyte, and a lithium metal anode; wherein the sulfide solid electrolyte is Li6PS5Cl or Li10 GeP2S 12 .

[0020] Furthermore, the mass ratio of the composite cathode material, the sulfide solid electrolyte, and the conductive additive is (30-60):(30-60):(5-15); the conductive additive is Super P.

[0021] Furthermore, the assembly process of the all-solid-state lithium battery is as follows: under an argon atmosphere, a mixture of composite positive electrode material, conductive additives, and sulfide solid electrolyte is pressed into a positive electrode layer at a pressing pressure of 240 MPa, and then sequentially combined with a sulfide solid electrolyte layer and a lithium metal negative electrode at a pressing pressure of 360 MPa. After assembly, the all-solid-state lithium battery is obtained.

[0022] The beneficial effects of this invention are: (1): By modifying the close composite of rGO, CNT, VGCF and TiS4, a highly efficient three-dimensional conductive network is constructed, which increases the electronic conductivity of the composite cathode to 0.12~0.19 S·cm. -1 This represents a 7-order-of-magnitude improvement over pure TiS4, completely resolving the charge transport obstruction problem. The composite cathode achieves a charge transport efficiency of 0.1 A·g⁻¹. -1 The initial discharge specific capacity at current density reaches 772.42~810.87 mAh·g -1 Pure TiS4 (593.83 mAh·g) -1 The capacity is increased by 30%~36%; the capacity retention rate after 25 cycles reaches 63.1%~67.2%, far superior to the 22.2% of pure TiS4, achieving a synergy between high capacity and long cycle life. The conductive network and structural support of carbon materials enable smooth charge transfer during charging and discharging of the composite cathode, maintaining stable performance even under high load conditions, overcoming the defect of rapid decay at high rates in the traditional TiS4 system.

[0023] (2): The two-dimensional flexible layered structure of rGO, the one-dimensional tubular winding structure of CNT, and the fiber interwoven structure of VGCF work together to buffer the volume expansion of TiS4 during charging and discharging, reducing the volume expansion rate of the composite cathode to 10.7%~13.1%, which is only 1 / 3~1 / 2 of that of pure TiS4, effectively preventing electrode cracking and active material shedding. Liquid-phase dispersion combined with freeze-drying process fixes the uniform dispersion state of carbon material-TiS2-sulfur powder. Subsequent high-energy co-ball milling promotes the uniform adhesion of TiS4 nanospheres to the surface of carbon material, forming a composite system with a uniform structure, avoiding performance degradation caused by local agglomeration.

[0024] (3): The hydroxyl and carboxyl groups introduced by rGO through steam-CO2 modification, the polar adsorption layer formed by CNT through SDBS modification, and the surface defect sites formed by VGCF through ball milling can all form strong interactions (hydrogen bonds, coordination bonds, physical adsorption) with TiS4 nanospheres, avoiding interface peeling during charging and discharging. The uniform structure and strong interface bonding of the composite system significantly reduce the solid-solid contact resistance, and the interfacial impedance between the composite cathode and the sulfide solid electrolyte is reduced to 87.6~97.8 Ω, which is 71%~74% lower than that of pure TiS4, thus improving ion transport efficiency. The carbon material modification and composite process avoids side reactions between active materials and electrolytes, reduces the formation of insulating phase, ensures interface stability during long-term battery cycling, and further extends battery life. Targeted modification processes are designed for the different structural characteristics of rGO, CNT, and VGCF. Depending on the application scenario, rGO can be selected for high conductivity requirements, CNT for high cycling requirements, and VGCF for high mechanical strength requirements, allowing for flexible selection to meet diverse application needs. Attached Figure Description

[0025] Figure 1 X-ray diffraction (XRD) patterns of TiS4 and three TiS4 / carbon composite cathode materials prepared in this invention.

[0026] Figure 2 SEM image of TiS4 prepared in this invention.

[0027] Figure 3 SEM image of the TiS4@10%rGO composite material prepared in Example 1.

[0028] Figure 4 The all-solid-state lithium battery of the TiS4@10%rGO composite material prepared in Example 1 was tested at 0.1 A g. -1 Cyclic performance at current density.

[0029] Figure 5 SEM image of the TiS4@10%CNT composite material prepared in Example 2.

[0030] Figure 6 Example 2: The all-solid-state lithium battery made of TiS4@10%CNT composite material was tested at 0.1 A g. -1 Cyclic performance at current density.

[0031] Figure 7 SEM image of the TiS4@10%VGCF composite material prepared in Example 3.

[0032] Figure 8 Example 3 describes an all-solid-state lithium battery made from TiS4@10%VGCF composite material, tested at 0.1 A g. -1Cyclic performance at current density.

[0033] Figure 9 Comparative Example 1: An all-solid-state lithium battery with a TiS4 cathode was prepared at 0.1 A g. -1 Cyclic performance at current density.

[0034] Figure 10 A bar chart comparing the electronic conductivity of TiS4, TiS4@10%rGO, TiS4@10%CNT, and TiS4@10%VGCF.

[0035] Figure 11 : Specific surface area of ​​TiS4 prepared in Comparative Example 1 and TiS4@10%rGO prepared in Example 1. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0037] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of a descriptive feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or sets.

[0038] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0039] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0040] In the embodiments shown in the accompanying drawings, the directional indications (such as up, down, left, right, front, and back) used to explain the structure and movement of the various components of the invention are relative rather than absolute. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, these directional indications also change accordingly.

[0041] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation of the present invention will be described below with reference to the accompanying drawings.

[0043] Example 1: S1. Surface-modified rGO was obtained by chemical reduction of rGO prepared by Hummers method through heat treatment with water vapor-CO2 mixed gas; the volume ratio of water vapor to CO2 was 1:1, the heat treatment temperature was 800℃, and the heat treatment time was 10h. S2. Add 100 mg of surface-modified rGO to 100 mL of DMF and sonicate at 400 W for 1.5 h to obtain 1.0 mg·mL⁻¹. -1 Dispersion; S3. Weigh 0.87 g TiS2 (5 mmol) and 0.32 g S (10 mmol), add them to the modified rGO dispersion from step S2, and stir at 400 rpm for 4 h; S4. Freeze-dry at -55℃ and 8 Pa for 48 h to obtain a mixed powder; S5. Load the material into a zirconium ball mill jar (ball-to-material ratio 10:1), purge with argon gas 3 times, and ball mill at 800 rpm for 48 h (mill for 3 hours, stop for 7 hours), with temperature controlled at ≤45℃, to obtain TiS4@10%rGO.

[0044] The specific surface area of ​​TiS4@10%rGO reached 92.62 m². 2 / g.

[0045] Example 2: S1. Take 100 mg of CNTs (5-8 nm in diameter) and add them to 100 mL of DMF, then add 0.2 wt% SDBS, and sonicate at 600 W for 2.5 h at 5000 r·min. -1 Centrifuge for 10 min; S2. Add 0.87 g TiS2 and 0.32 g S, and stir at 300 rpm for 4 h; S3. Same as step S3 in Example 1, to obtain the mixed powder; S4. Same as step S4 in Example 1, to obtain TiS4@10%CNT.

[0046] Example 3: S1. Raw VGCF (diameter 5~8μm) was ball-milled at 400 rpm, ball-to-material ratio 15:1, for 6 h to obtain ball-milled VGCF with a diameter of 150~300 nm; S2. Take 100 mg of ball-milled VGCF and add it to 100 mL of DMF, sonicate at 400 W for 2 h; S3. Add 0.87 g TiS2 and 0.32 g S, stir for 4 h and then freeze dry; S4. Same as step S4 in Example 1, to obtain TiS4@10%VGCF.

[0047] Example 4: Carbon material: Surface-modified rGO as in Example 1; Carbon material content: 5%; Other processes: completely consistent with Example 1.

[0048] Example 5: Carbon material: Surface-modified rGO as in Example 1; Carbon material content: 15%; Other processes: completely consistent with Example 1.

[0049] Comparative Example 1: Pure TiS4 Preparation process: Follow only steps S3 to S5 of Example 1, without adding any carbon materials, and the remaining parameters are the same as in Example 1.

[0050] Comparative Example 2: TiS4@10% unmodified rGO; Carbon materials: The percentage of rGO carbon materials that have not undergone heat treatment with a steam-CO2 mixed gas is 10%. Other processes: completely consistent with Example 1.

[0051] Comparative Example 3: TiS4@20% rGO Carbon material: the same modified rGO as in Example 1; Carbon material content: 20%; Other processes: completely consistent with Example 1.

[0052] Comparative Example 4: TiS4@2% rGO Carbon material: the same modified rGO as in Example 1; Carbon material content: 2%; Other processes: completely consistent with Example 1.

[0053] Comparative Example 5: Carbon material: the same modified rGO as in Example 1; Carbon material content: 10%; Key process: The freeze-drying step is omitted. After mixing the raw materials, they are directly vacuum dried (80°C, 24 h). The rest is the same as in Example 1.

[0054] I. Summary Table of Experimental Data

[0055] II. Experimental Data Analysis The experimental data above show that the electronic conductivity of Examples 1-3 reaches 0.12~0.19 S·cm. -1 Purer TiS4 (2.9 × 10⁻⁶) -8 S·cm -1 This represents a seven-order-of-magnitude improvement, completely resolving the core defect of charge transport obstruction in pure TiS4, proving that carbon materials can construct highly efficient three-dimensional conductive networks. The initial discharge specific capacity of Examples 1-3 was 772~810 mAh·g. -1 Compared with Comparative Example 1 (593.83 mAh·g) -1 The specific surface area of ​​Examples 1-3 was increased by 30% to 36%; the capacity retention rate after 25 cycles was 63% to 67%, far superior to the 22.2% of Comparative Example 1, demonstrating the buffering effect of carbon materials on volume expansion and the strengthening effect of interfacial bonding. The specific surface area of ​​Examples 1-3 was 79 to 93 m². 2 ·g -1 It is pure TiS4 (27.29m) 2 ·g -1 The volume expansion rate is 2.9 to 3.4 times that of pure TiS4, providing more active material loading sites; the volume expansion rate is reduced to 11.8% to 13.1%, which is only 1 / 3 to 1 / 2 of that of pure TiS4; the interfacial impedance is 89 to 98 Ω, which is 71% to 74% lower than that of Comparative Example 1, improving solid-solid interface contact.

[0056] The experimental data from Example 1 and Comparative Example 2 show that the specific surface area of ​​modified rGO increased by 57.1% (92.62 vs 58.97 m²). 2 ·g -1 This is attributed to the hierarchical porous structure formed by the synergistic etching of water vapor and CO2, which increases the contact area with TiS4. Electronic conductivity increased by 72.7% (0.19 vs 0.11 S·cm). -1 The oxygen-containing functional groups break down the layered aggregation of rGO, constructing a more continuous conductive network. Electrochemical performance is significantly improved: initial capacity increases by 16.0%, capacity retention after 25 cycles increases by 13.7%, and volume expansion decreases by 34.9%, demonstrating that the introduced hydroxyl and carboxyl groups enhance the interfacial bonding between rGO and TiS4.

[0057] As can be seen from Examples 1, 4, 5 and Comparative Examples 4-5, the electronic conductivity of Example 4 (5% rGO) is 0.08 S·cm. -1 The capacity retention rate is 60.6%, which still meets the basic requirements for conductivity and structural support; while Comparative Example 4 (2% rGO) cannot form a continuous conductive network due to insufficient carbon material content, and its electronic conductivity is only 0.03 S·cm. -1The capacity retention rate dropped to 46.5%, while the volume expansion rate reached as high as 24.8%, indicating that 5% is the minimum threshold for ensuring performance. Example 5 (15% rGO) had an electronic conductivity of 0.21 S·cm. -1 The interfacial impedance was 87.6Ω, exhibiting optimal structural stability; however, Comparative Example 3 (20% rGO) showed a reduced initial capacity of 689.45 mAh·g due to excessive dilution of the active material by carbon materials. -1 Compared to Example 1, the capacity was reduced by 14.9%, with a capacity retention of only 56.9%, proving that 15% is a reasonable upper limit for balancing energy density and conductivity. Example 1 (10% rGO) showed the best overall performance, with an initial capacity of 810.87 mAh·g. -1 (Highest) Capacity retention of 63.1%, achieving a perfect balance between conductivity, energy density and cycle stability.

[0058] As can be seen from Example 1 and Comparative Example 5, after omitting freeze-drying, the specific surface area of ​​Comparative Example 5 is only 47.26 m². 2 ·g -1 Compared to Example 1, the content decreased by 48.9% because vacuum drying caused the agglomeration of TiS2, sulfur powder, and rGO, disrupting the uniform dispersion. The electronic conductivity decreased to 0.09 S·cm. -1 Compared to Example 1, the capacity decreased by 52.6%, and the continuity of the conductive network was impaired; the initial capacity decreased by 19.4%, and the capacity retention rate decreased by 22.0%. The volume expansion rate increased to 20.3%, and the interfacial impedance increased to 196.4Ω, proving that freeze drying can fix the uniform dispersion of raw materials and is a key process step to ensure the composite effect.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A titanium tetrasulfide / carbon composite cathode material for all-solid-state lithium batteries, characterized in that, The composite cathode material is formed by combining amorphous TiS4 and carbon materials via a liquid-phase method. The TiS4 exists in the form of nanospheres, and the TiS4 nanospheres are uniformly attached to the surface or structure of the carbon material. The mass of the carbon material accounts for 5% to 15% of the total mass of the composite cathode material.

2. The composite cathode material according to claim 1, characterized in that, The carbon material is one of reduced graphene oxide (rGO), carbon nanotubes (CNTs), or vapor-grown carbon fiber (VGCF).

3. The composite cathode material according to claim 1, characterized in that, The rGO was prepared by the Hummers method and then chemically reduced; the CNT had a purity of ≥95% and a metal impurity content of ≤0.1 wt% as detected by ICP-OES; the VGCF had an initial diameter of 1~10 μm and an aspect ratio of ≥100, and a diameter of 150~300 nm after pre-ball milling.

4. A method for preparing a composite cathode material as described in any one of claims 1-3, characterized in that, Includes the following steps: Carbon material is dispersed in an organic solvent to form a dispersion; titanium tetrasulfide and sulfur powder are added to the dispersion at a predetermined molar ratio and mixed; the mixture is freeze-dried to obtain a precursor mixed powder; the precursor mixed powder is subjected to high-energy ball milling to obtain the composite cathode material under an inert atmosphere.

5. The preparation method according to claim 4, characterized in that, When the carbon material is reduced graphene oxide, the specific preparation process includes the following steps: S1. Surface modification of rGO: The prepared rGO powder was heat-treated in a mixed gas containing water vapor and carbon dioxide to obtain surface-modified rGO; S2. Preparation of rGO dispersion: Surface-modified rGO was added to anhydrous N,N-dimethylformamide and sonicated at 300-500 W for 1-2 h to form a dispersion with a concentration of 0.5-1.0 mg·mL⁻¹. -1 A homogeneous dispersion; S3. Raw material pre-composite: Weigh TiS2 and sulfur powder at a molar ratio of 1:2, add them to the rGO dispersion from step S2, and magnetically stir at 300~500 rpm for 3~5 hours; S4. Freeze-drying: Drying at -50~-60℃ and vacuum degree ≤10 Pa for 48 h to obtain rGO-TiS2-S mixed powder; S5. High-energy co-ball milling: The mixed powder is loaded into a zirconium ball mill jar with a zirconium ball to powder mass ratio of 10:

1. Argon gas is used for purging 3 times, and the vacuum degree is ≤10 Pa. The mixture is ball-milled for 48 hours at a speed of 500-900 rpm in a mode of milling for 3 min and standing for 7 min. The temperature is controlled at ≤50℃ by circulating water cooling. The product is collected to obtain TiS4@rGO.

6. The preparation method according to claim 4, characterized in that, When the carbon material is CNT, the specific preparation process includes the following steps: S1. CNT surface modification and dispersion: CNTs were added to DMF containing 0.1–0.3 wt% sodium dodecylbenzenesulfonate (SDBS) and sonicated at 500–800 W for 2–3 h to form a concentration of 0.5–1.0 mg·mL⁻¹. -1 The dispersion was then subjected to a reaction at 3000-5000 r·min. -1 Centrifuge at high speed for 10-30 minutes to remove aggregates; S2. Raw material pre-composite: Weigh TiS2 and sulfur powder at a molar ratio of 1:2, add them to the CNT dispersion from step S1, and stir at 100-300 rpm for 1-4 hours; S3. Freeze-drying: Drying at -50~-60℃ and vacuum degree ≤10 Pa for 48h to obtain CNT-TiS2-S mixed powder; S4. High-energy co-ball milling: The mixed powder is loaded into a zirconium ball mill jar with a zirconium ball to powder mass ratio of 10:

1. Argon gas is used for purging 3 times, and the vacuum degree is ≤10Pa. The mixture is ball-milled for 48 hours at a speed of 500-900 rpm in a mode of milling for 3 minutes and then standing for 7 minutes. The temperature is controlled at ≤50℃ by circulating water cooling. The product is collected to obtain TiS4@CNT.

7. The preparation method according to claim 4, characterized in that, When the carbon material is VGCF, the specific preparation process includes the following steps: S1. VGCF surface modification: The original VGCF was loaded into a zirconium ball mill jar and ball milled for 6 hours at a zirconium ball to powder mass ratio of 15:1 and a speed of 300-400 rpm to obtain ball-milled VGCF. S2. VGCF dispersion: Ball-milled VGCF was added to DMF and sonicated at 300-500 W for 1.5-2.5 h to form a concentration of 0.5-1.0 mg / mL. -1 The dispersion; S3. Raw material pre-composite and drying: Weigh TiS2 and sulfur powder at a molar ratio of 1:2, add to the dispersion of step S2, and stir for 2-4 hours; dry at -50~-60℃ and vacuum degree ≤10 Pa for 48 hours to obtain VGCF-TiS2-S mixed powder; S4. High-energy co-ball milling: The mixed powder is loaded into a zirconium ball mill jar with a zirconium ball to powder mass ratio of 10:

1. Argon gas is used for purging 3 times, and the vacuum degree is ≤10 Pa. The mixture is ball-milled for 48 h at a speed of 500-900 rpm in a mode of milling for 3 min and standing for 7 min. The temperature is controlled at ≤50℃ by circulating water cooling. The product is collected to obtain TiS4@VGCF.

8. A fully solid-state lithium battery, characterized in that, This includes the titanium tetrasulfide / carbon composite cathode material, sulfide solid electrolyte, and lithium metal anode as described in any one of claims 1 to 3; wherein the sulfide solid electrolyte is Li6PS5Cl or Li 10 GeP2S 12 .

9. The all-solid-state lithium battery according to claim 8, characterized in that, The mass ratio of the composite cathode material, sulfide solid electrolyte, and conductive additive is (30-60):(30-60):(5-15); the conductive additive is Super P.

10. The all-solid-state lithium battery according to claim 8 or 9, characterized in that, The assembly process of the all-solid-state lithium battery is as follows: Under an argon atmosphere, a mixture of composite positive electrode material, conductive additives, and sulfide solid electrolyte is pressed into a positive electrode layer at a pressing pressure of 240 MPa. Then, it is sequentially combined with a sulfide solid electrolyte layer and a lithium metal negative electrode at a pressing pressure of 360 MPa. After assembly, the all-solid-state lithium battery is obtained.

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