A sulfide solid-state electrolyte based on in-situ construction of a gradient interface layer by grain boundary engineering and molecular bridging and a preparation method thereof

Abstract

The application discloses a sulfide solid-state electrolyte based on a grain boundary engineering and a molecular bridging in-situ gradient interface layer and a preparation method thereof, and belongs to the technical field of solid-state battery materials. The method is characterized in that: firstly, a silane-polyethylene glycol-mercapto coupling agent is used to perform surface modification on a grain boundary modifier, so that the coupling agent is anchored and mercapto active sites are reserved; secondly, the modified modifier is ball-milled with a sulfide electrolyte, and the grain boundary is activated and annealed to reserve coupling activity; then, the ball-milled modified modifier is ball-milled with a phosphorus-free sulfide precursor, and a chemical bridging is formed between the mercapto and the precursor, so that the precursor is uniformly adsorbed in the grain boundary in a directional manner; finally, a phosphorus-free sulfide interface layer with a gradient change in composition and density is generated in-situ through gradient heat treatment. The application can enhance the air stability of the electrolyte and the electrode compatibility, and solves the problems of weak bonding force, easy peeling and high interface impedance of a traditional coating layer.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery materials technology, and in particular to a sulfide solid electrolyte and its preparation method based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging. Background Technology

[0002] In the field of solid-state batteries, sulfide solid electrolytes of the silver-germanium sulfide type have attracted much attention due to their high ionic conductivity, among which Li6PS5Cl X (0≤x≤3) This sulfide electrolyte system possesses advantages such as high ionic conductivity, good mechanical ductility and processability, excellent compatibility with high-voltage cathodes, and low raw material costs, making it suitable for large-scale applications and possessing great industrialization potential. However, Li6PS5Cl X Significant drawbacks remain in practical applications: insufficient interparticle contact leads to high grain boundary impedance, resulting in poor interfacial stability with lithium-rich manganese-based high-voltage cathodes, and easy reduction by metallic lithium to generate conductive byproducts such as lithium sulfide and lithium phosphide; it is also highly sensitive to moisture, readily decomposing in air and releasing highly toxic hydrogen sulfide gas, requiring preparation and storage in a harsh anhydrous environment with a dew point below -60°C, significantly increasing production and transportation costs. Therefore, there is an urgent need to improve the ionic conductivity of Li6PS5Cl without reducing its ionic conductivity. X Air stability.

[0003] In existing technologies, modification methods for sulfide electrolytes mostly focus on doping or surface coating, but both suffer from insurmountable drawbacks: On the one hand, traditional coating materials have poor interfacial compatibility and weak bonding with the sulfide electrolyte matrix, making them prone to coating layer peeling during long-term battery cycling and failing to achieve long-term protection. Simultaneously, these coating materials themselves have extremely poor ionic conductivity, easily forming a high-resistance interfacial layer on the substrate surface, significantly hindering lithium-ion transport and resulting in a substantial decrease in the overall ionic conductivity of the electrolyte. Furthermore, achieving a uniform and dense coating effect is difficult, limiting protective performance. On the other hand, even using phosphorus-free sulfides for physical mixing and coating can improve the electrolyte's air stability to some extent, but this method is merely a simple physical composite without chemical bonding, resulting in insufficient interfacial bonding strength. This leads to problems such as interfacial separation and failure during long-term cycling, failing to fundamentally solve the stability problem. In addition, in terms of grain boundary modification, commonly used grain boundary modifiers such as LiCl are prone to agglomeration and uneven distribution in the electrolyte matrix. This not only fails to fully exert the effects of grain boundary activation and reducing interfacial impedance, resulting in limited modification effects, but also introduces additional interfacial defects, further deteriorating the ion transport performance and structural stability of the electrolyte. Summary of the Invention

[0004] This invention provides a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, and its preparation method. This method improves air stability by constructing an in-situ composite coating layer with molecular bridging-induced and gradually changing composition and structure at the grain boundaries of the electrolyte matrix.

[0005] In a first aspect, the present invention provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. Dissolve silane-polyethylene glycol-mercapto (Si-PEG-SH) in anhydrous ethanol, add grain boundary modifier powder, stir ultrasonically to react, centrifuge, wash, and dry to obtain modified grain boundary modifier. S2. The modified grain boundary modifier and the sulfide solid electrolyte are ball-milled and mixed, annealed under an inert atmosphere, and cooled to obtain a grain boundary activated matrix. S3. The phosphorus-free sulfide precursor and the grain boundary activated matrix are ball-milled and mixed to obtain a mixture; S4. The mixture is subjected to gradient heat treatment and then cooled to obtain a sulfide solid electrolyte.

[0006] Further, in step S1, the ratio of silane-polyethylene glycol-mercapto, anhydrous ethanol, and grain boundary modifier powder is 0.002-0.004g: 10-50mL: 0.02-0.04g.

[0007] Further, in step S1, the degree of polymerization n of the polyethylene glycol segment in the silane-polyethylene glycol-mercapto group is 2 to 10.

[0008] Further, in step S1, the grain boundary modifier powder is any one or more of LiCl, LiBr, LiI, LiF, and Li2S.

[0009] Furthermore, in step S1, the temperature of the stirring reaction is 55–70°C, and the time is 2–4 hours.

[0010] Further, in step S2, the mass ratio of the modified grain boundary modifier to the sulfide solid electrolyte is 1:(20-50).

[0011] Further, in step S2, the sulfide solid electrolyte is Li6PS5Cl or Li 10 GeP2S 12 (LGPS), Li6PS5Br, Li7P3S 11 Any one or more of them.

[0012] Furthermore, in step S2, the ball milling speed is 100-500 rpm, and the ball milling time is 1-3 hours.

[0013] Furthermore, in step S2, the inert atmosphere is any one of nitrogen, argon, or helium.

[0014] Furthermore, in step S2, the annealing temperature is 300–500°C, and the time is 1–5 hours.

[0015] Further, in step S3, the mass ratio of the phosphorus-free sulfide precursor to the grain boundary activated matrix is ​​(1-5):100.

[0016] Furthermore, in step S3, the phosphorus-free sulfide precursor is any one or more of SnS2 nanosheets, Sb2S5 nanosheets, and GeS2 nanosheets.

[0017] Furthermore, in step S3, the ball milling speed is 100-500 rpm, and the ball milling time is 1-3 hours.

[0018] Further, in step S4, the specific steps of the gradient heat treatment are as follows: S41. First stage: Increase the temperature to 200-350℃ at a rate of 2-10℃ / min, and hold for 0.5-3 hours; S42, Second stage: Continue to heat up to 400-550℃ at a rate of 2-10℃ / min, and hold for 1-5 hours.

[0019] Secondly, the present invention provides a sulfide solid electrolyte based on in-situ construction of a gradient interface layer through grain boundary engineering and molecular bridging, which is prepared by any of the preparation methods described above.

[0020] The beneficial effects of this invention are: 1. In this invention, S1 modifies the surface of the grain boundary modifier using a Si-PEG-SH coupling agent. The PEG chains of the coupling agent interact with the LiCl surface. +Coordination adsorption occurs, and simultaneously, the silanol groups generated at the silane end form a hydrogen bond network with the water molecules adsorbed on the LiCl surface, allowing the coupling agent molecules to be uniformly coated on the LiCl particle surface. This significantly improves the dispersibility of the modifier and avoids aggregation. The thiol groups at the end of the coupling agent, as key active sites, are retained, providing a basis for subsequent chemical bridging with the phosphorus-free sulfide precursor. S2 achieves grain boundary activation and structural reconstruction through annealing in an inert atmosphere, which not only optimizes the electrolyte grain boundary contact state and reduces the initial grain boundary impedance, but also further anchors the coupling agent to the sulfide matrix surface, further preserving active sites. S3 achieves molecular bridging between the phosphorus-free sulfide precursor and the grain boundary activated matrix through ball milling. The S atoms on the precursor surface and the thiol groups at the end of the coupling agent... The matrix interacts to form bonds, constructing a stable chemical bridging network to ensure that the precursor is preferentially and firmly adsorbed in the grain boundary region, avoiding precursor aggregation or uneven distribution. S4 generates a gradient interface layer in situ through gradient heat treatment. The first stage of heat preservation promotes the cross-linking and curing of the coupling agent and ensures the stability of the bridging structure. The second stage of high temperature realizes the complete crystallization of the precursor and diffuses along the grain boundary gradient, ultimately forming a phosphorus-free sulfide interface layer (such as Li4SnS4, Li3SbS4 or Li4GeS4) that is tightly bonded to the matrix and has a gradient of composition or density. This significantly improves ionic conductivity, reduces grain boundary impedance, enhances the air stability of the electrolyte and the compatibility of the electrode interface, and avoids the defects of traditional coating layers such as easy peeling and high interface impedance.

[0021] 2. This invention significantly improves the air stability and safety of sulfide solid electrolytes, while simultaneously achieving a revolutionary enhancement of interfacial bonding. On one hand, the constructed gradient interface layer is primarily composed of phosphorus-free sulfides (such as Li4SnS4), whose [SnS4]... 4- The tetrahedral structure exhibits tight chemical bonds, making it resistant to hydrolysis or oxidation by moisture and oxygen in the air, thus preventing the generation of toxic H2S gas at the source. This interface layer also demonstrates good compatibility with matrices such as Li6PS5Cl, effectively isolating the matrix from air erosion while maintaining high ionic conductivity, significantly improving the material's operational safety and environmental tolerance. Furthermore, the molecular bridging technology forms a strong chemical bond network between the matrix, coupling agent, and precursor before heat treatment, enhancing the adhesion between the final coating layer and the matrix and solving the problems of easy peeling and poor interfacial contact inherent in traditional coatings.

[0022] 3. This invention achieves both maintenance and optimization of ionic conductivity while possessing significant cost advantages. On one hand, the PEG segments in the coupling agent have lithium-ion coordination capabilities, effectively improving interfacial ion transport kinetics; the uniformly dispersed grain boundary modifier (LiCl) significantly reduces grain boundary resistance, ensuring the overall ionic conductivity remains stably at a high level of 4–6 mS / cm. On the other hand, the raw materials used in this invention (such as LiCl, SnS2, Li6PS5Cl, etc.) are widely available and inexpensive, and the preparation process has low energy consumption; the integrated construction of the gradient interface layer is achieved through programmed temperature-controlled heat treatment, eliminating the need for complex post-processing steps, significantly reducing production costs. This provides a simple, efficient, and economical solution for the practical modification of sulfide solid electrolytes, and can be widely applied in the field of high-safety all-solid-state lithium batteries. Attached Figure Description

[0023] Figure 1 EIS diagrams of the sulfide solid electrolytes prepared in Examples 1-5 of this invention; Figure 2 EIS images of the sulfide solid electrolytes prepared in Examples 1-5 of this invention after exposure to air at 3% relative humidity for 30 min; Figure 3 This is a mapping diagram of the sulfide solid electrolyte prepared in Example 1 of the present invention; Figure 4 EIS images of the sulfide solid electrolyte prepared in Comparative Example 1 before and after exposure treatment; Figure 5 EIS images of the sulfide solid electrolyte prepared in Comparative Example 2 before and after exposure treatment; Figure 6 EIS images of the sulfide solid electrolyte prepared in Comparative Example 3 before and after exposure treatment; Figure 7 EIS diagrams of the sulfide solid electrolytes prepared in Comparative Examples 4-8; Figure 8 EIS images of the sulfide solid electrolytes prepared in Comparative Examples 4-8 after exposure to air at 3% relative humidity for 30 min. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0025] In a first aspect, the present invention provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. Dissolve silane-polyethylene glycol-mercapto (Si-PEG-SH) in anhydrous ethanol, add grain boundary modifier powder, stir ultrasonically to react, centrifuge, wash, and dry to obtain modified grain boundary modifier. Grain boundary modifiers (such as LiCl) can optimize the grain boundary structure of sulfide electrolytes, reduce interfacial impedance, and improve ion transport efficiency, and the raw materials are inexpensive and easy to industrialize. However, traditional LiCl has poor dispersibility, is prone to agglomeration, and is difficult to form a stable bond with the electrolyte matrix and phosphorus-free sulfide precursors, resulting in weak interfacial bonding. Therefore, this invention uses a Si-PEG-SH coupling agent to modify the grain boundary modifier: in an anhydrous ethanol system, the PEG chains of the coupling agent bind to the LiCl surface... + Coordination adsorption occurs, and simultaneously, the silanol groups generated at the silane end form a hydrogen bond network with water molecules adsorbed on the LiCl surface. This allows the coupling agent molecules to be uniformly coated on the LiCl particle surface, significantly improving its dispersibility and preventing aggregation. The thiol groups at the coupling agent end are retained as active sites, providing a foundation for the subsequent construction of molecular bridging networks. This step achieves surface functionalization of LiCl, laying the foundation for the precise delivery of thiol sites in subsequent processes, thereby enhancing interfacial binding strength and simultaneously improving electrolyte ionic conductivity and air stability.

[0026] S2. The modified grain boundary modifier and the sulfide solid electrolyte are ball-milled and mixed, annealed under an inert atmosphere, and cooled to obtain a grain boundary activated matrix. The modified grain boundary modifier was ball-milled and mixed with the sulfide solid electrolyte matrix to ensure uniform distribution at the matrix grain boundaries. Annealing under an inert atmosphere induced the reconstruction of the electrolyte grain boundary structure, generated highly active sites, and further anchored the Si-PEG-SH coupling agent to the matrix surface. At this temperature, the terminal thiol groups of the coupling agent exhibited poor thermal stability and weak bonding ability with the matrix. Appropriate annealing achieved a balance between grain boundary activation and thiol group activity retention. This step effectively optimized grain boundary contact, reduced grain boundary impedance, and improved the binding strength between the modifier and the matrix, providing a stable activation interface for the subsequent directional adsorption and molecular bridging of the phosphorus-free sulfide precursor.

[0027] S3. The phosphorus-free sulfide precursor and the grain boundary activated matrix are ball-milled and mixed to obtain a mixture; The phosphorus-free sulfide precursor and the grain boundary activated matrix are ball-milled together. The mechanical force generated by ball milling ensures the precursor is uniformly dispersed and fully contacts the active sites at the grain boundaries of the matrix. During this process, the sulfur atoms on the precursor surface interact with the thiol groups (-SH) retained at the ends of the coupling agent on the grain boundary activated matrix surface, forming coordination bonds and constructing a stable matrix-modifier-precursor molecular bridging network. This step achieves preferential and robust adsorption of the precursor in the grain boundary region through molecular bridging, effectively preventing precursor aggregation or uneven distribution. This ensures that the precursor can react in situ at the grain boundaries to form an interfacial layer during subsequent gradient heat treatment, while further enhancing the stability of the grain boundary structure. This lays the foundation for the formation of the subsequent gradient interfacial layer and the improvement of electrolyte performance.

[0028] S4. The mixture is subjected to gradient heat treatment and then cooled to obtain a sulfide solid electrolyte.

[0029] The resulting mixture is subjected to gradient heat treatment. The first stage, low-temperature holding, allows the coupling agent to fully cross-link and solidify, stabilizing the previously constructed molecular bridging structure. The second stage, high-temperature holding, promotes an in-situ solid-state reaction between the phosphorus-free sulfide precursor and the matrix, resulting in complete crystallization and slow diffusion along the grain boundaries into the grain interior. Ultimately, an in-situ phosphorus-free sulfide interface layer is generated, with its composition and density varying gradient from the grain boundaries to the grain interior. This step can construct a tightly bonded gradient coating structure without obvious interface defects, significantly reducing grain boundary impedance and increasing ionic conductivity. Simultaneously, it greatly enhances the air stability of the solid electrolyte, fundamentally suppressing the generation of hydrogen sulfide gas and solving the problems of easy peeling and high interface impedance in traditional coatings.

[0030] In some embodiments, in step S1, the ratio of silane-polyethylene glycol-mercapto, anhydrous ethanol, and grain boundary modifier powder is 0.002–0.004 g: 10–50 mL: 0.02–0.04 g. This ensures that the coupling agent is fully dissolved and uniformly grafted onto the surface of the grain boundary modifier. If the amount of silane-polyethylene glycol-mercapto is too low, the grain boundary modifier cannot be fully modified, making it difficult to form a complete surface modification layer and reducing the subsequent molecular bridging effect. If the amount is too high, it easily leads to raw material waste and may also cause agglomeration due to excessive coupling agent, affecting dispersibility and interfacial interaction. Too little grain boundary modifier results in insufficient grain boundary modification and cannot effectively reduce impedance; too much easily leads to particle aggregation and uneven distribution. Too little solvent makes it difficult to fully dissolve and disperse, while too much reduces reaction efficiency and increases the burden of post-processing. Controlling the ratio of the three components within the range of this invention can ensure the modification effect while improving material dispersibility and process economy.

[0031] In some embodiments, in step S1, the degree of polymerization n of the polyethylene glycol segment in the silane-polyethylene glycol-mercapto group is 2 to 10. This allows the coupling agent to possess good solubility, lithium-ion coordination ability, and structural stability. If the polymerization degree is too low, the polyethylene glycol segment is too short, resulting in insufficient lithium-ion coordination sites, making it difficult to effectively improve interfacial ion transport, and the molecular flexibility is poor, which is not conducive to interfacial adaptation. If the polymerization degree is too high, the segment is too long, which increases steric hindrance, reduces the anchoring efficiency of the coupling agent on the surface of the grain boundary modifier, and increases interfacial impedance, affecting the rapid conduction of lithium ions. Controlling the degree of polymerization within the range of this invention can ensure the dispersion and grafting effect of the coupling agent, and significantly improve the interfacial ion transport ability, enabling the solid electrolyte to possess both excellent structural stability and high ionic conductivity. In some embodiments, in step S1, the grain boundary modifier powder is any one or more of LiCl, LiBr, LiI, LiF, and Li2S. Using the above-mentioned lithium-based compounds as grain boundary modifiers can effectively regulate grain boundary defects and reduce interfacial impedance. Simultaneously, they exhibit excellent compatibility with sulfide electrolytes, which is beneficial for improving ionic conductivity and structural stability.

[0032] In some embodiments, in step S1, the temperature of the stirring reaction is 55–70°C, and the time is 2–4 hours. This ensures that the coupling agent is fully grafted and not destroyed; too low a temperature or too short a time will lead to insufficient modification, while too high a temperature or too long a time will easily cause the coupling agent to decompose and the structure to be destroyed. This condition can ensure the optimal modification efficiency and effect.

[0033] In some embodiments, in step S2, the mass ratio of the modified grain boundary modifier to the sulfide solid electrolyte is 1:(20-50). This balances grain boundary modification and ion transport performance. If the modifier ratio is too high, it is prone to excessive accumulation and agglomeration at the grain boundaries, increasing grain boundary impedance and reducing the overall ionic conductivity of the electrolyte. If the modifier ratio is too low, the grain boundaries cannot be fully activated, making it difficult to form effective modification and limiting the improvement of interface performance. Within this ratio range, sufficient activation and modification of the electrolyte grain boundaries can be achieved while avoiding agglomeration and increased impedance, thus maximizing the optimization of interface structure and ion transport performance.

[0034] In some embodiments, in step S2, the sulfide solid electrolyte is Li6PS5Cl or Li 10 GeP2S 12 (LGPS), Li6PS5Br, Li7P3S 11 Any one or more of the above-mentioned sulfide solid electrolytes. The selected sulfide solid electrolytes possess the characteristics of high ionic conductivity, good electrochemical stability, and excellent compatibility with the modified system of this invention, ensuring that the final electrolyte exhibits both high ionic conductivity and good structural stability.

[0035] In some embodiments, in step S2, the ball milling speed is 100–500 rpm, and the ball milling time is 1–3 hours. Within this range of ball milling speed and time, the material can be mixed evenly without damaging its structure; too low a speed or too short a time will lead to uneven mixing, while too high a speed or too long a time will easily damage the material structure and introduce defects, thus ensuring the best grain boundary activation effect.

[0036] In some embodiments, in step S2, the inert atmosphere is any one of nitrogen, argon, or helium. This effectively prevents the materials from being oxidized or decomposed during annealing, ensuring a stable and controllable reaction and maintaining the structural integrity of the electrolyte and coupling agent.

[0037] In some embodiments, in step S2, the annealing temperature is 300–500°C and the time is 1–5 h; this can effectively achieve grain boundary reconstruction and coupling agent anchoring; if the temperature is too low or the time is too short, the grain boundary activation will be insufficient and sufficient active sites cannot be formed; if the temperature is too high or the time is too long, it will aggravate the desorption of thiol groups and even destroy the electrolyte matrix structure; within this range, both grain boundary activation and active site retention can be taken into account, and the optimal interface modification effect can be obtained.

[0038] In some embodiments, in step S3, the mass ratio of the phosphorus-free sulfide precursor to the grain boundary activated matrix is ​​(1-5):100. Controlling the mass ratio of the phosphorus-free sulfide precursor to the grain boundary activated matrix at (1-5):100 ensures the in-situ formation of a uniform and dense phosphorus-free interface layer. If the amount of precursor added is too small, a complete coating layer cannot be formed, limiting its effect on improving air stability; if the amount added is too large, it is prone to excessive enrichment on the surface, generating impurities, increasing interfacial impedance, and reducing ionic conductivity. This ratio effectively improves the air stability of the electrolyte without hindering lithium-ion transport, resulting in optimal overall performance.

[0039] In some embodiments, in step S3, the phosphorus-free sulfide precursor is any one or more of SnS2 nanosheets, Sb2S5 nanosheets, and GeS2 nanosheets. Using the aforementioned nanosheet-structured phosphorus-free sulfides as precursors results in a large specific surface area, high reactivity, and good compatibility with the system. This allows for the in-situ formation of a uniform and dense gradient interface layer, significantly improving the electrolyte's air stability and ion transport performance.

[0040] In some embodiments, in step S3, the ball milling speed is 100–500 rpm, and the ball milling time is 1–3 h. Controlling the ball milling speed and time can ensure that the precursor is uniformly dispersed and completes molecular bridging; if the speed is too low or the time is too short, the mixing will be insufficient and the bridging will be inadequate, while if the speed is too high or the time is too long, the activation interface and active sites will be easily damaged, ensuring the best effect of subsequent in-situ reactions.

[0041] In some embodiments, the specific steps of the gradient heat treatment in step S4 are as follows: S41. First Stage: Heat to 200–350℃ at a rate of 2–10℃ / min and hold for 0.5–3 hours. This stage is mainly used to ensure the coupling agent is fully cross-linked and cured, stabilizing the molecular bridging structure, while slowly removing residual solvents and small molecules from the system. Excessive heating rate, excessively high temperature, or excessively long holding time can easily lead to premature decomposition of the coupling agent and significant loss of thiol groups; excessively slow heating, excessively low temperature, or insufficient time will result in incomplete cross-linking and curing, and an unstable bridging structure. This condition can protect the active sites while providing a stable interfacial structure for subsequent high-temperature in-situ reactions.

[0042] S42, Second Stage: Continue heating at a rate of 2–10 °C / min to 400–550 °C and hold for 1–5 hours. This allows the phosphorus-free sulfide precursor to fully crystallize and react in situ with the matrix, forming a gradient interface layer along the grain boundaries. Excessive temperature or time will damage the electrolyte matrix, causing over-reaction at the interface and the formation of impurity phases; excessive temperature or time will result in incomplete reaction and failure to form a dense and stable interface layer. Within this parameter range, a tightly bonded, low-impedance, and highly stable gradient interface layer can be prepared, significantly improving the electrolyte's ionic conductivity and air stability.

[0043] Secondly, the present invention provides a sulfide solid electrolyte based on in-situ construction of a gradient interface layer through grain boundary engineering and molecular bridging, which is prepared by any of the preparation methods described above.

[0044] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0045] Example 1 This embodiment provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.002 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, 0.02 g of LiCl powder was added, and the mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing and drying, the modified grain boundary modifier was obtained. S2. Mix 0.022g of modified grain boundary modifier with 0.978g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix; S3. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0046] Elemental analysis of the sulfide solid electrolyte was performed using scanning electron microscopy (SEM). Figure 3 This is a mapping image of the sulfide solid electrolyte obtained in this embodiment, from... Figure 3 As can be seen, S and Sn elements are present on the surface of the Li6PS5Cl crystal, indicating that the sulfide solid electrolyte was successfully generated.

[0047] Example 2 This embodiment provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.003 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, and 0.03 g of LiCl powder was added. The mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing, and drying, the modified grain boundary modifier was obtained. S2. Mix 0.033g of modified grain boundary modifier with 0.967g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix. S3. 0.03g SnS2 and 1g grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0048] Example 3 This embodiment provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.004 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, and 0.04 g of LiCl powder was added. The mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing and drying, the modified grain boundary modifier was obtained. S2. Mix 0.044g of modified grain boundary modifier with 0.956g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix. S3. 0.03g SnS2 and 1g grain boundary activation matrix are ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0049] Example 4 This embodiment provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.002 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, 0.02 g of LiCl powder was added, and the mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing and drying, the modified grain boundary modifier was obtained. S2. Mix 0.022g of modified grain boundary modifier with 0.978g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix; S3. 0.03g of Sb2S5 and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0050] Example 5 This embodiment provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.002 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, 0.02 g of LiCl powder was added, and the mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing and drying, the modified grain boundary modifier was obtained. S2. Mix 0.022g of modified grain boundary modifier with 0.978g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix; S3. 0.03g GeS2 and 1g grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0051] Comparative Example 1 This comparative example directly uses Li6PS5Cl as the sulfide solid electrolyte.

[0052] Comparative Example 2 This comparative example provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.001g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10mL of anhydrous ethanol, and 0.01g of LiCl powder was added. The mixture was sonicated and stirred at 60℃ for 3h. After centrifugation, washing, and drying, the modified grain boundary modifier was obtained. S2. Mix 0.011g of modified grain boundary modifier with 0.989g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix. S3. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0053] Comparative Example 3 This comparative example provides a method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, comprising the following steps: S1. In an argon glove box, 0.005 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, and 0.05 g of LiCl powder was added. The mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing, and drying, the modified grain boundary modifier was obtained. S2. Mix 0.055g of modified grain boundary modifier with 0.945g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix. S3. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0054] Comparative Example 4 The only difference between this comparative example and Example 1 is that the silane-polyethylene glycol-thiol group is omitted. The specific steps are as follows: S1. 0.022g LiCl and 0.978g Li6PS5Cl were ball-milled at 200rpm for 2h, annealed at 300℃ for 2h under argon atmosphere, and cooled to obtain a grain boundary activated matrix. S2. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S3. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, a sulfide solid electrolyte is obtained.

[0055] Comparative Example 5 The only difference between this comparative example and Example 1 is that an equal amount of "3-mercaptopropyltrimethoxysilane" is used to replace "silane-polyethylene glycol-mercapto" in step S1. The specific steps are as follows: S1. In an argon glove box, 0.002 g of 3-mercaptopropyltrimethoxysilane was dissolved in 10 mL of anhydrous ethanol, and 0.02 g of LiCl powder was added. The mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing, and drying, the modified grain boundary modifier was obtained. S2. Mix 0.022g of modified grain boundary modifier with 0.978g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix; S3. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0056] Comparative Example 6 The only difference between this comparative example and Example 1 is that an equal amount of "silane-polyethylene glycol-silane (polyethylene glycol segment degree of polymerization n is 3)" is used to replace "silane-polyethylene glycol-thiol (polyethylene glycol segment degree of polymerization n is 3)" in step S1. The specific steps are as follows: S1. In an argon glove box, 0.002 g of silane-polyethylene glycol-silane (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, and 0.02 g of LiCl powder was added. The mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing and drying, the modified grain boundary modifier was obtained. S2. Mix 0.022g of modified grain boundary modifier with 0.978g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix; S3. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, the sulfide solid electrolyte is obtained.

[0057] Comparative Example 7 The only difference between this comparative example and Example 1 is that the modified grain boundary modifier is omitted. The specific steps are as follows: S1. Add 0.03g of SnS2 nanosheets to 1g of Li6PS5Cl and ball mill the mixture at 200rpm for 1h to obtain a mixture. S2. The mixture is heated to 350°C at a rate of 5°C / min and held for 1 hour. Then, it is heated to 480°C at a rate of 5°C / min and held for 3 hours. After cooling, a sulfide solid electrolyte is obtained.

[0058] Comparative Example 8 The only difference between this comparative example and Example 1 is that the segmented heat treatment is omitted. The specific steps are as follows: S1. In an argon glove box, 0.002 g of silane-polyethylene glycol-mercapto (the degree of polymerization of the polyethylene glycol segment n is 3) was dissolved in 10 mL of anhydrous ethanol, 0.02 g of LiCl powder was added, and the mixture was sonicated and stirred at 60 °C for 3 h. After centrifugation, washing and drying, the modified grain boundary modifier was obtained. S2. Mix 0.022g of modified grain boundary modifier with 0.978g of Li6PS5Cl by ball milling at 200rpm for 2h, anneal at 300℃ for 2h under argon atmosphere, and cool to obtain grain boundary activated matrix; S3. 0.03g of SnS2 nanosheets and 1g of grain boundary activation matrix were ball-milled at 200rpm for 1h to obtain a mixture; S4. The mixture is heated to 480°C at a rate of 5°C / min, held at that temperature for 4 hours, and then cooled to obtain a sulfide solid electrolyte.

[0059] Test case (1) The ionic conductivity of the sulfide solid electrolytes obtained in Examples 1 to 5 and Comparative Examples 1 to 8 was tested by electrochemical impedance spectroscopy (EIS); (2) The sulfide solid electrolytes obtained in Examples 1 to 5 and Comparative Examples 1 to 8 were exposed to air with a relative humidity of 3% for 30 min. The room temperature ionic conductivity before and after exposure to air was tested by electrochemical impedance spectroscopy (EIS). The above test results are presented in detail in Figure 1 , Figure 2, Figures 4-8 See Table 1 for details.

[0060] Table 1

[0061] As can be seen from the data in Table 1, the sulfide solid electrolyte prepared in the embodiments of the present invention is superior to all comparative examples in terms of air stability.

[0062] Examples 1 through 5 all employ the complete technical solution of this invention, differing only in the amount of modifier and the type of phosphorus-free sulfide precursor. The overall performance exhibits a regular variation: In Examples 1 through 3, the initial conductivity slightly decreases with increasing modifier dosage, but the decrease is very small, indicating that the modified layer does not significantly hinder ion transport. The conductivity remains highly stable after exposure, proving that the density of the coating layer increases with increasing dosage, effectively blocking air erosion. The trends in the difference and retention rate further confirm that appropriately increasing the amount of modifier can enhance the protective effect. Examples 4 and 5 use Sb₂S₅ and GeS₂ as precursors, respectively. Their initial conductivity and air stability are lower than those of Example 1 using SnS₂, indicating that SnS₂ is a preferred precursor for constructing a gradient interface layer.

[0063] Comparative Example 1 is pure Li6PS5Cl without any modification. Its initial ionic conductivity is 5.24 mS / cm (the highest among all samples), but after exposure, the conductivity drops sharply to 0.33 mS / cm, a decrease of 4.91 mS / cm. This comparative example is a blank control, which directly reflects the core defects of pure sulfide electrolytes, such as extreme sensitivity to moisture and easy hydrolysis, proving the necessity of the modification process of this invention.

[0064] In Comparative Example 2, the amount of modifier added was insufficient, resulting in an initial ionic conductivity of 5.14 mS / cm (close to that of pure electrolyte) and a conductivity of 0.70 mS / cm after exposure, with a decrease of 4.44 mS / cm. Because the amount of modifier was below the limit specified in this invention, a complete molecular bridging network and gradient interface layer could not be formed, resulting in a weak protective effect. This verifies the rationality of the lower limit of the modifier dosage.

[0065] In Comparative Example 3, the amount of modifier added was excessive. The initial ionic conductivity was 4.50 mS / cm, and the conductivity after exposure was 1.71 mS / cm, with a decrease of 2.79 mS / cm. This indicates that the excessive modifier caused particle agglomeration, increased grain boundary impedance, and obstructed ion transport. At the same time, the interface layer was overgrown, and the overall performance was inferior to that of the example, which verifies the rationality of the upper limit of modifier dosage.

[0066] Comparative Example 4, which omits the silane-polyethylene glycol-thiol group, showed an initial ionic conductivity of 3.18 mS / cm and a conductivity of 0.46 mS / cm after exposure, a decrease of 2.72 mS / cm. This comparative example lacks the core molecular bridging component, making it impossible to achieve chemical bonding between the precursor and the matrix. The grain boundary modifier is prone to agglomeration, the interface layer cannot be formed, and the performance is significantly degraded, demonstrating the irreplaceable nature of the silane-polyethylene glycol-thiol group.

[0067] Comparative Example 5 was replaced with a monofunctional silane. The initial ionic conductivity was 2.94 mS / cm, and the conductivity after exposure was 0.45 mS / cm, a decrease of 2.49 mS / cm. This indicates that the monofunctional silane lacks the lithium-ion coordination effect of the PEG segment, resulting in weak molecular bridging, poor interfacial binding, and inability to optimize ion transport and air stability. This demonstrates the unique advantages of the difunctional silane of this invention.

[0068] Comparative Example 6 was replaced with a mercapto-free silane. The initial ionic conductivity was 2.80 mS / cm, and the conductivity after exposure was 0.42 mS / cm, a decrease of 2.38 mS / cm. This indicates that without a mercapto-active site, it is impossible to form a chemical bridge with the phosphorus-free sulfide precursor. The precursor cannot be directionally adsorbed, and the interfacial layer is not dense enough. This verifies the necessity of mercapto as a bridging active site.

[0069] Comparative Example 7, without the modified grain boundary modifier, had an initial ionic conductivity of 3.41 mS / cm and a conductivity of 0.40 mS / cm after exposure, a decrease of 3.01 mS / cm. This indicates that without the grain boundary modifier, grain boundaries cannot be activated or dispersion improved, the precursor cannot be uniformly adsorbed, grain boundary impedance is high, and there is no effective protective layer, resulting in extremely poor stability. This demonstrates the necessity of the modified grain boundary modifier. Its initial conductivity is higher than that of Comparative Examples 4-6 because it avoids the ion blocking defects formed by LiCl agglomeration.

[0070] Comparative Example 8, omitting the segmented gradient heat treatment, had an initial ionic conductivity of 4.10 mS / cm and a post-exposure conductivity of 1.52 mS / cm, a decrease of 2.58 mS / cm. This indicates that single-temperature heat treatment cannot achieve the synergistic effect of the low-temperature cross-linking bridging structure and the high-temperature crystallization gradient interface layer. The precursor crystallization was insufficient, the interface layer lacked a gradient structure, and the density was inadequate, resulting in performance inferior to the examples. This verifies the necessity of segmented gradient heat treatment. Its initial conductivity is higher than that of Comparative Examples 4-6 because the complete modifier system ensures good dispersion of LiCl, and the blocking effect of carbon residue is less than that of LiCl agglomeration.

[0071] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, characterized in that, Includes the following steps: S1. Dissolve silane-polyethylene glycol-mercapto in anhydrous ethanol, add grain boundary modifier powder, stir ultrasonically to react, centrifuge, wash, and dry to obtain modified grain boundary modifier. S2. The modified grain boundary modifier and the sulfide solid electrolyte are ball-milled and mixed, annealed under an inert atmosphere, and cooled to obtain a grain boundary activated matrix. S3. The phosphorus-free sulfide precursor and the grain boundary activated matrix are ball-milled and mixed to obtain a mixture; S4. The mixture is subjected to gradient heat treatment and then cooled to obtain a sulfide solid electrolyte.

2. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that, In step S1, the ratio of silane-polyethylene glycol-mercapto, anhydrous ethanol, and grain boundary modifier powder is 0.002-0.004g: 10-50mL: 0.02-0.04g.

3. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that... In step S1, the degree of polymerization n of the polyethylene glycol segment in the silane-polyethylene glycol-mercapto group is 2 to 10. The grain boundary modifier powder is any one or more of LiCl, LiBr, LiI, LiF, and Li2S; The stirring reaction is carried out at a temperature of 55–70°C for 2–4 hours.

4. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that, In step S2, the mass ratio of the modified grain boundary modifier to the sulfide solid electrolyte is 1:(20-50).

5. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that... In step S2, the sulfide solid electrolyte is Li6PS5Cl or Li 10 GeP2S 12 Li6PS5Br, Li7P3S 11 Any one or more of them.

6. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that, In step S2, the ball mill rotates at a speed of 100-500 rpm and the milling time is 1-3 hours. The inert atmosphere is any one of nitrogen, argon, and helium; The annealing temperature is 300–500°C, and the time is 1–5 hours.

7. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that, In step S3, the mass ratio of the phosphorus-free sulfide precursor to the grain boundary activated matrix is ​​(1-5):

100.

8. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that, In step S3, the phosphorus-free sulfide precursor is any one or more of SnS2 nanosheets, Sb2S5 nanosheets, and GeS2 nanosheets. The ball mill rotates at a speed of 100–500 rpm and the milling time is 1–3 hours.

9. The method for preparing a sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging as described in claim 1, characterized in that, In step S4, the specific steps of the gradient heat treatment are as follows: S41. First stage: Increase the temperature to 200-350℃ at a rate of 2-10℃ / min, and hold for 0.5-3 hours; S42, Second stage: Continue to heat up to 400-550℃ at a rate of 2-10℃ / min, and hold for 1-5 hours.

10. A sulfide solid electrolyte based on in-situ construction of a gradient interface layer using grain boundary engineering and molecular bridging, characterized in that... It is prepared by the preparation method according to any one of claims 1-9.

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