A lithium sulfide material with high ionic conductivity and a warm isostatic pressing treatment method for preparing the lithium sulfide

Abstract

This application relates to the field of lithium battery technology, providing a lithium sulfide material with high ionic conductivity and a warm isostatic pressing (WIP) method for preparing the lithium sulfide. The lithium sulfide material has a multilayer structure, comprising at least one sulfide functional layer and at least one buffer layer. The multilayer structure is densified by WIP, and the interlayer interfaces have a modifying phase that forms a short-range liquid phase. After cooling and solidification, the modifying phase forms a Li-rich or S-rich amorphous or fine-grained conductive phase, reducing the ion migration barrier at grain boundaries and interfaces and decreasing interfacial resistance. WIP increases the overall density, and the buffer layer absorbs cyclic volumetric strain and thermal stress, suppressing interlayer cracks and delamination, thereby significantly improving the material's ionic conductivity, critical current density, and cycling stability.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a lithium sulfide material with high ionic conductivity and a method for preparing the lithium sulfide by temperature isostatic pressing. Background Technology

[0002] With the increasing demands for high energy density and high safety from electric vehicles and wearable devices, all-solid-state lithium-ion batteries have attracted widespread attention due to their non-flammability and the significant energy density improvement achievable when matched with lithium metal anodes. Among various solid electrolytes, sulfide systems are considered one of the most promising technological routes due to their intrinsic high ionic conductivity and excellent interfacial compatibility. Realizing their device applications depends not only on the conductivity of the materials themselves but also on low interfacial impedance, high density, and reliable mechanical stability between the multilayer electrolyte and functional layers to meet the stringent requirements of high-rate operation and long cycle life.

[0003] Currently, although material doping and particle structure optimization can improve the bulk conductivity of sulfide electrolytes to some extent, high interlayer and grain boundary interfacial impedances still exist, becoming a key bottleneck restricting the ion transport efficiency of full cells. Traditional pressing or sintering processes cannot achieve sufficient wetting and tight bonding between layers at the microscale, resulting in porosity, microcracks, and grain boundary barriers at the interface. This leads to discontinuous effective ion transport channels, resulting in high interfacial resistance, low critical current density, and easy interface degradation and performance decline during cycling.

[0004] Therefore, there is an urgent need for a solution that can effectively reduce the interlayer ion migration barrier and construct continuous and stable low-resistivity ion channels in sulfide multilayer structures. Summary of the Invention

[0005] In view of the above-mentioned shortcomings in the prior art, the purpose of this application is to provide a lithium sulfide material with high ionic conductivity and a warm isostatic pressing method for preparing the lithium sulfide.

[0006] To achieve the aforementioned objectives, the technical solution adopted in this application is as follows: At least one sulfide functional layer and at least one buffer layer are disposed in a multilayer lithium sulfide material, and the multilayer structure is densified using a warm isostatic pressing (WIP) process. A short-range liquid phase modification phase is generated at the interlayer interfaces, thereby wetting and bonding adjacent layers at the microscale, filling pores and constructing continuous lithium-ion transport channels. After cooling and solidification, this short-range liquid phase modification phase can form a Li-rich or S-rich amorphous or fine-grained conductive phase, reducing the migration energy barrier between grain boundaries and layers and significantly reducing interfacial resistance. Simultaneously, WIP provides a uniform compaction effect, further reducing macroscopic and microscopic porosity and improving overall density. The buffer layer, as a chemical and mechanical transition zone, can absorb volumetric strain and thermal stress during cycling, suppressing interfacial cracks and peeling, and mitigating side reactions between the functional layer and the active metal, thereby significantly improving the ionic conductivity, critical current density, and cycling stability of the material.

[0007] In a first aspect, embodiments of this application provide a lithium sulfide material with high ionic conductivity. The lithium sulfide material has a multilayer structure, including at least one sulfide functional layer and at least one buffer layer. The multilayer structure is densified by isostatic pressing, and the interlayer interfaces have a modified phase formed by short-range liquid phase.

[0008] In an optional implementation, the sulfide functional layer includes a Li2S-P2S5 system, Li6PS5X, and Li 10 GeP2S 12 At least one of microcrystalline or corresponding glass-ceramic precursors, wherein X includes Cl, Br or I; the buffer layer includes at least one of Li3PO4, LiNbO3, Al2O3, lithium phosphate or inorganic glass precursor.

[0009] In one alternative implementation, the thickness of the sulfide functional layer is 5-500 μm; the thickness of the buffer layer is 50 nm-1 μm; and the total thickness of the multilayer structure is 0.1-5 mm.

[0010] In an alternative embodiment, the material further contains a short-range liquid phase aid, which includes at least one of LiI, LiBr, or LiCl.

[0011] In an optional implementation, the lithium sulfide material has an ionic conductivity greater than 1 × 10⁻⁶ at 25°C. -4 S / cm.

[0012] Secondly, embodiments of this application provide a warm isostatic pressing method for lithium sulfide materials with high ionic conductivity, comprising the following steps: S100, preparing monolayer green bodies of sulfide functional layer and buffer functional layer; S200, in an inert atmosphere, alternately stacking monolayer green bodies of sulfide functional layer and buffer functional layer, and pre-encapsulating them to form a pre-encapsulated blank; S300, subjecting the pre-encapsulated blank to warm isostatic pressing, and after cooling, obtaining lithium sulfide material.

[0013] In an alternative implementation, the monolayer chloroplast is prepared by blade coating, spraying, screen printing, or sheet preforming.

[0014] In an optional implementation, in step S200, during the alternating stacking process, a short-range liquid phase additive is introduced at the interlayer interface, with the amount of the short-range liquid phase additive being 0.1-10 wt% based on the total mass of the solid raw materials of the sulfide functional layer and the buffer functional layer.

[0015] In an optional implementation, in step S300, the warm isostatic pressing conditions are: pressure 50-300 MPa, temperature 150-350 °C, and holding time 5-180 min.

[0016] In an optional implementation, after step S300, the lithium sulfide material is further subjected to an annealing treatment at a temperature of 100-250°C for a time of 1-12 hours.

[0017] The beneficial effects of this application include at least the following: (1) This application uses a warm isostatic pressing process to induce the generation of a short-range liquid phase at the interlayer interface, which can wet and penetrate into the micropores and grain boundaries of adjacent layers. After cooling and solidification, a lithium-rich or sulfur-rich amorphous phase or fine-grained phase is formed as an interface modification phase, thereby reducing the migration activation energy of lithium ions at the grain boundaries and interfaces, enabling ions to achieve rapid and continuous transitions between layers. (2) The isostatic pressing process provides an isotropic high pressure field, which can effectively eliminate pores of different sizes, including gaps between particles and contact defects between layers, thereby achieving ultra-high densification close to the theoretical density; it not only provides a low-resistance bulk ion transport path, but also works in synergy with low-resistance interface modification to build a seamless and highly continuous lithium-ion transport network in three-dimensional space, ensuring the high-efficiency operation of the full cell at high rates; (3) The buffer layer introduced in this application can effectively absorb and dissipate volumetric strain and local thermal stress during cycling, prevent stress concentration, and thus inhibit the initiation and propagation of microcracks and the tendency of interlayer delamination. At the chemical level, it acts as a physical barrier to slow down the side reactions between the sulfide functional layer and the highly active electrode material, improve the chemical stability of the interface, and lay a solid material foundation for the practical application of all-solid-state batteries. Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are only for explaining this application, but the implementation of this application is not limited thereto.

[0019] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this application pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; the amounts of experimental reagents used are, unless otherwise specified, the amounts used in conventional experimental operations; and the experimental methods used are, unless otherwise specified, conventional methods.

[0020] With the increasing demand for high energy density and safety in electric vehicles and wearable devices, all-solid-state lithium-ion batteries, especially sulfide electrolyte systems with high intrinsic ionic conductivity, have become a highly anticipated technological direction. However, although existing technologies have improved the bulk conductivity of materials through doping and particle engineering, high interfacial impedance exists at the interlayer and grain boundaries of multilayer structures. Traditional processes struggle to achieve sufficient wetting and densification at the microscale, resulting in porosity, microcracks, and discontinuous ion channels at the interfaces, severely limiting overall ion transport efficiency and cycle stability. To address the aforementioned shortcomings in the existing technology, this embodiment provides a lithium sulfide material with high ionic conductivity and a warm isostatic pressing method for preparing the lithium sulfide. By modifying the phase and solidifying it upon cooling, an amorphous or fine-grained conductive phase rich in Li or S is formed, which reduces the ion migration barrier at grain boundaries and interfaces and decreases the interfacial resistance. Warm isostatic pressing improves the overall density, and the buffer layer absorbs cyclic volumetric strain and thermal stress, suppressing interlayer cracks and delamination, thereby significantly improving the ionic conductivity, critical current density, and cycling stability of the material.

[0021] In a first aspect, embodiments of this application provide a lithium sulfide material with high ionic conductivity. The lithium sulfide material has a multilayer structure, including at least one sulfide functional layer and at least one buffer layer. The multilayer structure is densified by isostatic pressing, and the interlayer interfaces have a modified phase formed by short-range liquid phase.

[0022] Preferably, the lithium sulfide material is composed of at least one sulfide functional layer and at least one buffer layer stacked alternately; the multilayer structure is not a simple physical superposition, but solves the inherent contradiction of ionic conductivity and mechanical stability in a single material system through the combination and synergistic effect of different functional layers; the warm isostatic pressing process promotes the overall densification of the multilayer structure by applying isotropic ultra-high pressure in a heated environment, and induces a short-range liquid phase at the interlayer interface, ultimately forming an interface modification phase with unique functions.

[0023] Preferably, the sulfide functional layer is the main body for ion transport, and its material system is selected from sulfides with intrinsically high ionic conductivity, specifically including but not limited to the Li2S-P2S5 system, Li6PS5X, and Li 10 GeP2S 12 At least one of microcrystalline or corresponding glass-ceramic precursors, wherein X includes Cl, Br, or I; on the one hand, the aforementioned sulfide phase itself possesses an open crystal structure and abundant lithium vacancies, which is conducive to achieving a low ion migration barrier and high bulk conductivity; on the other hand, through reasonable composition and microstructure control, the crystalline phase and amorphous phase in the functional layer can jointly construct an atomic-scale fast lithium-ion channel. Specifically, lithium ions can achieve efficient transitions through lattice interstices, vacancy defects, and soft coordination networks composed of sulfur or halogens; when the functional layer is in close contact with other layers and modified by a short-range liquid phase during warm isostatic pressing, the ion migration barrier at its grain boundaries is significantly reduced, thereby forming a continuous low-resistivity ion transport network in both the bulk phase and the interface.

[0024] Preferably, the buffer layer includes at least one of Li3PO4, LiNbO3, Al2O3, lithium phosphate, or inorganic glass precursor. The buffer layer serves as a chemical and mechanical buffer transition zone: chemically, it can inhibit direct contact and violent chemical reactions between the functional layer and metallic lithium or the active electrode, forming a stable interfacial chemical barrier; mechanically, it has relatively good elasticity or adhesion, which can absorb volumetric strain and thermal stress caused by electrochemical cycling and temperature changes, reducing stress concentration at the interface, thereby inhibiting crack initiation and interlayer delamination; under isostatic pressing, this thin-layer structure can form a tight interface with the functional layer, promoting short-range liquid relative wetting and structural reconstruction at the interface, achieving simultaneous improvement in the chemical stability and mechanical compliance of the interface without significantly increasing the interfacial resistance, thus ensuring ion transport efficiency.

[0025] Furthermore, to optimize interfacial properties during warm isostatic pressing (WIP), short-range liquid phase additives can be added to the material. These additives include at least one of LiI, LiBr, or LiCl. Under specific temperatures and pressures during WIP, these additives can undergo localized melting at the interlayer interface, forming a transient liquid phase. This short-range liquid phase fills micropores and wets the interlayer interface during the pressure holding and temperature holding stages, enhancing the actual contact area between layers. After cooling and solidification, it forms a Li-rich or S-rich amorphous or fine-grained conductive phase, thereby establishing continuous conductive bridges and low-barrier channels at the interface. By reducing local interfacial energy, promoting ion and composition rearrangement, weakening the potential barrier at grain boundaries, and lowering the lithium-ion migration activation energy, short-range liquid phase additives significantly reduce interfacial impedance and improve overall ionic conductivity. In addition, appropriate amounts of halides can optimize the interfacial chemical state through doping / ion exchange, improving the long-term stability of the interface.

[0026] Preferably, the thickness of the sulfide functional layer is 5-500 μm. A thinner functional layer helps shorten the ion transport path and reduce bulk resistance, making it suitable for high-power devices; a thicker functional layer helps enhance mechanical strength and process tolerance, facilitating battery assembly and mechanical support. Within this range, the functional layer can construct a continuous bulk ion transport path while ensuring sufficient mechanical integrity. The thickness of the buffer layer is 50 nm-1 μm, ensuring that it acts as an interface transition layer without significantly increasing the system's series resistance. That is, while effectively performing mechanical buffering and chemical isolation functions, it avoids significant negative impacts on the overall ionic conductivity and energy density. The total thickness of the multilayer structure is 0.1-5 mm. This range meets the requirements of solid-state electrolyte layers in terms of mechanical integrity and electrical insulation, and also facilitates large-area densification and large-scale fabrication through processes such as isostatic pressing, thus adapting to the device design needs of different types of all-solid-state batteries.

[0027] Secondly, embodiments of this application also provide a method for the warm isostatic pressing of lithium sulfide materials with high ionic conductivity, comprising the following steps: S100, preparation of monolayer chloroplasts with sulfide functional layers and buffer functional layers; S200. In an inert atmosphere, the monolayer green body of the sulfide functional layer and the monolayer green body of the buffer layer are alternately stacked and pre-encapsulated to form a pre-encapsulated blank. S300: The pre-packaged blank is subjected to warm isostatic pressing and then cooled to obtain lithium sulfide material.

[0028] Preferably, in step S100, the single-layer green body refers to a preform that has not undergone final densification and sintering. A single-layer green body containing a sulfide functional layer and a buffer layer is prepared using methods such as blade coating, spraying, screen printing, or sheet preforming. By uniformly distributing the materials of each layer on the substrate according to the target composition, thickness, and microstructure, a foundation is laid for subsequent orderly stacking and densification of the interlayers. Using solvent dispersion-coating or sheet preforming processes can achieve uniform composition, controllable thickness, and a smooth surface, thus providing a structural basis for constructing a high-quality multilayer interface and avoiding stress or cracks generated during the co-forming process due to differences in the shrinkage rates of different materials.

[0029] Furthermore, the solid content of the slurry is controlled between 45% and 55%, and through appropriate dispersing agents and grinding processes, the slurry possesses good dispersibility and viscosity stability. Higher solid content results in lower organic solvent and volatile content in the dry film, leading to smaller drying shrinkage and porosity after coating, which is beneficial for subsequent warm isostatic pressing densification. High solid content also reduces interlayer organic residue and lowers the source of interfacial resistance. However, excessively high solid content can cause a sharp increase in slurry viscosity, affecting flowability and self-leveling properties, causing coating defects, and impacting coating uniformity and thickness control; simultaneously, insufficient powder dispersion can easily lead to agglomeration.

[0030] Preferably, in step S200, the functional layer chloroplasts and the buffer layer chloroplasts are alternately stacked and pre-encapsulated in an inert atmosphere to form a pre-encapsulated preform. Alternating stacking avoids component migration or uncontrolled diffusion during the mixing process, while minimizing macroscopic voids between layers and ensuring good initial contact. Pre-encapsulation methods include using inert gas sealed bags, metal containers, or vacuum argon-filled encapsulation to block air and moisture, preventing oxidation, hydrolysis, or halide volatilization of the sulfide phase, thereby protecting water- and oxygen-sensitive components.

[0031] Furthermore, during the alternating stacking process, a short-range liquid phase additive can be introduced at the interlayer interface. Based on the total mass of the solid raw materials of the sulfide functional layer and the buffer functional layer, the additive addition amount is 0.1% to 10%. During isostatic pressing, this additive can induce localized softening, limited melting, or vitrification of the interface, forming a short-range liquid phase that wets and fills the interlayer micropores. Under high temperature and high pressure conditions, the short-range liquid phase can reduce the interfacial free energy and enhance wettability, enabling a larger actual contact area between particles and the interlayer interface. Kinetically, the short-range liquid phase promotes component diffusion and ion rearrangement, contributing to the formation of lithium-rich or sulfur-rich amorphous or fine-grained conductive phases. After cooling and solidification, low-activation-energy ion transport channels can be established at grain boundaries and between layers; an appropriate amount of additive can significantly reduce the grain boundary migration barrier and interfacial resistance, and can also adjust the interfacial composition and electrical properties through chemical doping or ion exchange. However, if the amount of additive is too small, it will not be able to wet the phase sufficiently, while if it is too large, it may lead to continuous liquid phase or component segregation. Therefore, it is recommended to control the amount within the above range in order to balance the wetting effect and phase stability.

[0032] Preferably, in step S300, a warm isostatic pressing is applied to the pre-encapsulated preform at a pressure of 50-300 MPa, a temperature of 150-350°C, and a holding time of 5-180 min to achieve integrated densification and interfacial bonding of the multilayer structure. Isostatic pressing promotes pore closure, particle rearrangement, and plastic flow through an isotropic high-pressure field; a suitable temperature activates the surface of solid particles, causing the short-range liquid phase to exhibit wetting behavior and undergo bonding or diffusion welding, thereby eliminating pores and reconstructing grain boundary or interfacial structures at the microscale. This process includes bonding and diffusion at particle contact surfaces, wetting of the short-range liquid phase and formation of a conductive phase after solidification, reduction of grain boundary migration barriers, and high-pressure-promoted pore closure and increased bulk density. The combination of temperature, pressure, and time directly affects the degree of liquid phase formation, interfacial diffusion depth, and grain growth: higher temperatures or longer holding times are beneficial for liquid phase wetting and interfacial compaction, but too high or too long temperatures can lead to phase decomposition or excessive grain growth; higher pressure helps to eliminate porosity and uniform stress distribution, but it needs to be matched with temperature to avoid brittleness; therefore, the best lithium sulfide materials can be obtained within the above range.

[0033] Furthermore, after step S300, annealing is performed at a temperature of 100-250℃ for 1-12 hours. This heat treatment further reduces residual stress, promotes interfacial phase homogenization, and completes phase transformation or crystallization processes, or relaxes the structure of the amorphous phase, thereby improving the long-term electrochemical stability and mechanical integrity of the material. Under medium-low temperature annealing conditions, the short-range liquid phase undergoes structural rearrangement and local densification, and the chemical composition at the interface tends to be homogenized through diffusion, forming a stable lithium-rich or sulfur-rich amorphous phase or fine-grained phase. Simultaneously, thermal stress release reduces internal stress concentration, lowering the risk of crack initiation in subsequent cycles. Annealing also helps to further remove volatile residues or organic binders, reducing the increase in interfacial resistance caused by impurities. Appropriate annealing can significantly enhance cycle durability and interfacial stability while maintaining or slightly increasing ionic conductivity. However, excessively high annealing temperatures or excessively long annealing times can lead to the complete consumption of the beneficial short-range liquid phase or excessive grain growth and embrittlement.

[0034] This application has undergone multiple experiments, and some of the test results are presented here for reference to further describe the invention in detail. The following is a detailed description in conjunction with specific embodiments.

[0035] Example 1 This embodiment provides a lithium sulfide material with high ionic conductivity and a method for preparing the lithium sulfide by temperature isostatic pressing, specifically including the following steps: S100, Preparation of sulfide functional layer: Li6PS5Cl powder is mixed with anhydrous heptane solvent and styrene-butadiene rubber binder, and stirred in a planetary mixer to form a slurry with a solid content of 50%. The slurry is coated on a polyimide substrate by a doctor blade coating method, and after drying, a sulfide functional layer monolayer with a thickness of 100μm is obtained. Preparation of buffer layer: Li3PO4 was mixed with anhydrous heptane solvent and polyacrylate binder and stirred in a planetary mixer to form a slurry with a solid content of 50%. The slurry was then coated by a doctor blade coating method to obtain a single-layer green body with a thickness of 0.5 μm. S200. In an argon-atmospheric glove box, sulfide functional layer monolayers and buffer layer monolayers are stacked alternately, with a structure of: functional layer-buffer layer-functional layer-buffer layer-functional layer, for a total of 5 layers. During the stacking process, LiBr powder is evenly sprinkled at the interface of each layer as a short-range liquid phase aid, with an addition amount accounting for 2% of the total solid mass. After stacking, the pre-packaged blank is sealed in an inert gas sealed bag to form a pre-packaged blank. S300. The pre-packaged blank is placed in a warm isostatic pressing apparatus. The processing conditions are: temperature 250℃, pressure 200MPa, holding time 30min, followed by natural cooling to room temperature, and annealing at 200℃ for 4h to obtain lithium sulfide material.

[0036] Example 2 This embodiment provides a lithium sulfide material with high ionic conductivity and a method for preparing the lithium sulfide by temperature isostatic pressing, specifically including the following steps: S100, Preparation of sulfide functional layer: Li 10 GeP2S 12 Microcrystalline powder was mixed with anhydrous heptane solvent and styrene-butadiene rubber binder and stirred in a planetary mixer to form a slurry with a solid content of 45%. The slurry was then coated on a polyimide substrate by a doctor blade coating method and dried to obtain a sulfide functional layer monolayer green body with a thickness of 80 μm. Preparation of buffer layer: LiNbO3 was mixed with anhydrous ethanol solvent and polyvinylidene fluoride binder and stirred in a planetary mixer to form a slurry with a solid content of 45%. A single-layer green body with a thickness of 0.2 μm was prepared by doctor blade coating method. S200. In an argon-atmospheric glove box, sulfide functional layer monolayers and buffer layer monolayers are stacked alternately, with a structure of: functional layer-buffer layer-functional layer-buffer layer-functional layer, for a total of 5 layers. During the stacking process, LiI powder is evenly sprinkled at the interface of each layer as a short-range liquid phase aid, with an addition amount accounting for 3% of the total solid mass. After stacking, an aluminum-plastic composite film is used for vacuum sealing to form a pre-packaged blank. S300. The pre-packaged blank is placed in a warm isostatic pressing apparatus. The processing conditions are: temperature 280℃, pressure 150MPa, holding time 60min, followed by natural cooling to room temperature, and annealing at 180℃ for 6h to obtain lithium sulfide material.

[0037] Example 3 This embodiment provides a lithium sulfide material with high ionic conductivity and a method for preparing the lithium sulfide by temperature isostatic pressing, specifically including the following steps: S100, Preparation of sulfide functional layer: 75 mol% Li2S and 25 mol% P2S5 glass ceramic precursor powders are mixed with anhydrous heptane solvent and styrene-butadiene rubber binder, and stirred in a planetary mixer to form a slurry with a solid content of 50%. The slurry is coated on a polyimide substrate by a doctor blade coating method, and after drying, a sulfide functional layer monolayer with a thickness of 150 μm is obtained. Preparation of buffer layer: Al2O3 nanopowder was mixed with anhydrous ethanol solvent and polyvinyl butyral binder, and ball milled to form a uniformly dispersed slurry. The slurry was then sprayed onto another polyimide substrate and dried to obtain a 100nm thick buffer layer monolayer green body. S200. In an argon-atmospheric glove box, sulfide functional layer monolayers and buffer layer monolayers are stacked alternately, with a structure of: functional layer-buffer layer-functional layer, for a total of 3 layers. During the stacking process, LiBr powder is evenly sprinkled at the interface of each layer as a short-range liquid phase aid, with an addition amount accounting for 1% of the total solid mass. After stacking, aluminum-plastic composite film is used for vacuum sealing to form a pre-packaged blank. S300. The pre-packaged blank is placed in a warm isostatic pressing apparatus. The processing conditions are: temperature 200℃, pressure 280MPa, holding time 15min, followed by natural cooling to room temperature, and annealing at 150℃ for 10h to obtain lithium sulfide material.

[0038] Example 4 This embodiment provides a lithium sulfide material with high ionic conductivity and a method for preparing the lithium sulfide by temperature isostatic pressing, specifically including the following steps: S100, Preparation of sulfide functional layer: Li6PS5I is mixed with anhydrous heptane solvent and styrene-butadiene rubber binder, and stirred in a planetary mixer to form a slurry with a solid content of 50%. The slurry is coated on a polyimide substrate by a doctor blade coating method, and after drying, a sulfide functional layer monolayer with a thickness of 150μm is obtained. Preparation of buffer layer: Al2O3 nanopowder was mixed with anhydrous ethanol solvent and polyvinyl butyral binder, and ball milled to form a uniformly dispersed slurry. The slurry was then sprayed onto another polyimide substrate and dried to obtain a 100nm thick buffer layer monolayer green body. S200. In an argon-atmospheric glove box, sulfide functional layer monolayers and buffer layer monolayers are stacked alternately, with a structure of: functional layer-buffer layer-functional layer-buffer layer-functional layer, for a total of 5 layers. During the stacking process, LiCl powder is evenly sprinkled at the interface of each layer as a short-range liquid phase aid, with an addition amount accounting for 2% of the total solid mass. After stacking, an aluminum-plastic composite film is used for vacuum sealing to form a pre-sealed blank. S300. The pre-packaged blank is placed in a warm isostatic pressing apparatus. The processing conditions are: temperature 240℃, pressure 260MPa, holding time 20min, followed by natural cooling to room temperature, and annealing at 180℃ for 6h to obtain lithium sulfide material.

[0039] Comparative Example 1 This comparative example provides a lithium sulfide material with high ionic conductivity and a warm isostatic pressing method for preparing the lithium sulfide. The lithium sulfide material and preparation method are the same as those in Example 1, except that only a single layer of sulfide functional layer is used to stack three layers, that is, in step S100, there is no Li3PO4 buffer layer.

[0040] Comparative Example 2 This comparative example provides a lithium sulfide material with high ionic conductivity and a warm isostatic pressing method for preparing the lithium sulfide. The lithium sulfide material and preparation method are the same as those in Example 1, except that the stacking structure is the same as in Example 1. The pre-packaged blank is cold-pressed on a uniaxial press at a pressure of 300 MPa and room temperature, and then placed in a tube furnace for sintering at 250°C and atmospheric pressure for 1 hour.

[0041] Comparative Example 3 This comparative example provides a lithium sulfide material with high ionic conductivity and a warm isostatic pressing method for preparing the lithium sulfide. The lithium sulfide material and preparation method are the same as those shown in Example 1, except that no annealing treatment is performed.

[0042] Comparative Example 4 This comparative example provides a lithium sulfide material with high ionic conductivity and a warm isostatic pressing method for preparing the lithium sulfide. The lithium sulfide material and preparation method are the same as those shown in Example 1, except that the temperature of the warm isostatic pressing conditions is 400°C, the pressure is 200 MPa, and the holding time is 30 min.

[0043] Test method: The lithium sulfide materials of Examples 1-4 and Comparative Examples 1-4 were subjected to the following tests, and the test results are shown in Table 1: Ionic conductivity testing: The AC impedance method was used. The sample was placed between two stainless steel blocking electrodes and tested at 25°C using an electrochemical workstation with a frequency range of 0.1 Hz-1 MHz and an amplitude of 10 mV. The ionic conductivity was calculated by fitting the impedance spectrum. Critical current density test: Assemble a Li / sample / Li symmetric cell and perform constant current charge-discharge test with a step-increasing current density. Each step lasts for 10 minutes. Observe voltage change or short circuit phenomenon to determine the critical current density. Cyclic performance testing: Assembling all-solid-state batteries with LiNi 0.8 Mn 0.1 Co 0.1 Using O2 as the positive electrode and lithium metal as the negative electrode, a long-cycle test was conducted at 0.5C rate and 25℃, and the capacity retention rate was recorded. Density test: The actual density of the sample was measured using the Archimedes displacement method, and the relative density was calculated by comparing it with the theoretical density.

[0044] Table 1 As shown in Table 1, the ionic conductivity of all embodiments is higher than that of the comparative example, and reaches greater than 1×10⁻⁶. -4 The S / cm ratio indicates that the dense structure and interface-modified phase formed by warm isostatic pressing effectively reduce the ion migration barrier. The critical current density of the examples is significantly higher than that of the comparative example, indicating better interface stability and the ability to withstand higher currents without short circuits. The examples maintained high capacity retention after 100 cycles, far superior to the comparative example, demonstrating that the combination of multilayer structure and warm isostatic pressing effectively suppresses interface degradation, crack initiation, and interlayer delamination, thereby improving the material's cycle stability. The density of the examples is all above 97%, significantly better than Comparative Example 2, which uses a traditional cold pressing sintering process, verifying the effectiveness of warm isostatic pressing in achieving high material densification under isotropic high pressure.

[0045] Comparative Example 1 showed a significant decline in all performance aspects, especially in cycling performance, demonstrating the indispensable role of the buffer layer in absorbing strain, suppressing interfacial side reactions, and preventing interlayer delamination. Comparative Example 2 exhibited the worst performance, indicating that traditional processes cannot achieve sufficient densification and interfacial bonding at the microscale, resulting in high interfacial impedance and poor mechanical integrity. Although Comparative Example 3 had acceptable initial conductivity, its cycling performance declined, demonstrating that annealing is crucial for releasing residual stress, stabilizing the interfacial structure, and improving long-term cycling stability. Comparative Example 4 showed deteriorating performance, indicating that excessively high isostatic pressing temperatures led to material decomposition, abnormal grain growth, or unfavorable phase transitions, damaging the material's structure and interfacial stability.

[0046] In summary, the test results fully demonstrate that the lithium sulfide material and its preparation method provided by this invention can effectively solve the technical problems of high interlayer impedance and poor interface stability of sulfide solid electrolytes, and achieve the expected high ionic conductivity, high critical current density and excellent cycle stability.

[0047] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A lithium sulfide material with high ionic conductivity, characterized in that, The lithium sulfide material has a multilayer structure, comprising at least one sulfide functional layer and at least one buffer layer: The multilayer structure is densified by isostatic pressing, and the interlayer interfaces have a modified phase formed by short-range liquid phase.

2. The lithium sulfide material according to claim 1, characterized in that, The sulfide functional layer includes the Li2S-P2S5 system, Li6PS5X, and Li 10 GeP2S 12 At least one of microcrystalline or corresponding glass-ceramic precursors, wherein X includes Cl, Br or I; The buffer layer includes at least one of Li3PO4, LiNbO3, Al2O3, lithium phosphate, or inorganic glass precursor.

3. The lithium sulfide material according to claim 1, characterized in that, The thickness of the sulfide functional layer is 5-500 μm; The thickness of the buffer layer is 50nm-1μm; The total thickness of the multilayer structure is 0.1-5mm.

4. The lithium sulfide material according to claim 1, characterized in that, The material also contains a short-range liquid phase aid, which includes at least one of LiI, LiBr, or LiCl.

5. The lithium sulfide material according to claim 1, characterized in that, The lithium sulfide material has an ionic conductivity greater than 1×10⁻⁶ at 25°C. -4 S / cm.

6. A method for warm isostatic pressing of lithium sulfide materials with high ionic conductivity, characterized in that, The processing method is used to prepare lithium sulfide materials as described in any one of claims 1-5, and includes the following steps: S100, preparation of monolayer chloroplasts with sulfide functional layers and buffer functional layers; S200. In an inert atmosphere, the monolayer green body of the sulfide functional layer and the monolayer green body of the buffer layer are alternately stacked and pre-encapsulated to form a pre-encapsulated blank. S300. The pre-packaged blank is subjected to warm isostatic pressing and then cooled to obtain lithium sulfide material.

7. The processing method according to claim 6, characterized in that, The single-layer green body is prepared by blade coating, spraying, screen printing or sheet preforming.

8. The processing method according to claim 6, characterized in that, In step S200, during the alternating stacking process, a short-range liquid phase additive is introduced at the interlayer interface. Based on the total mass of the solid raw materials of the sulfide functional layer and the buffer functional layer, the amount of the short-range liquid phase additive added is 0.1-10 wt%.

9. The processing method according to claim 6, characterized in that, In step S300, the processing conditions for the isostatic pressing treatment are: pressure 50-300MPa, temperature 150-350℃, and holding time 5-180min.

10. The processing method according to claim 6, characterized in that, After step S300, the process further includes an annealing step for the lithium sulfide material, with an annealing temperature of 100-250°C and an annealing time of 1-12 hours.

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