Sulfide solid electrolyte membranes, their preparation methods and applications

Abstract

This disclosure belongs to the field of solid-state battery technology, and provides a sulfide solid electrolyte membrane, its preparation method, and its application. Preparation method: Sulfide solid electrolyte powder and a binder are ball-milled and mixed under an inert atmosphere to obtain a mixture; a perfluoropolyether additive and a optionally volatile main solvent are added to the mixture, and the materials are plasticized and mixed to obtain a slurry; the slurry is then rolled and dried to obtain the final product. The sulfide solid electrolyte membrane prepared according to the above method is also disclosed, as well as an all-solid-state battery including the membrane. This disclosure achieves a balance between the film-forming performance, electrochemical performance, and large-scale production capability of sulfide solid electrolytes through the selection of perfluoropolyether additives and the synergistic optimization of process parameters, solving the core technical problems of existing sulfide solid electrolytes, such as difficulty in film formation, high brittleness, poor interfacial stability, and low industrial adaptability.

Description

Technical Field

[0001] This disclosure relates to the field of solid-state battery technology, and in particular to sulfide solid electrolyte membranes, their preparation methods, and applications. Background Technology

[0002] In the field of new energy storage, all-solid-state lithium batteries are regarded as the core development direction of the next generation of power batteries due to their higher energy density and better safety performance. Sulfide solid electrolytes, with their high ionic conductivity and good mechanical ductility close to that of liquid electrolytes, have become one of the key materials for the commercial application of all-solid-state lithium batteries. Breakthroughs in their large-scale preparation technology are of great strategic significance.

[0003] Currently, the film-forming process of sulfide solid electrolytes mainly revolves around two technical routes: wet and dry methods. However, both have fundamental defects that are difficult to overcome, which seriously restrict the industrialization process of sulfide solid electrolytes.

[0004] While wet processes are mature in the fabrication of traditional lithium-ion battery electrodes, they suffer from inherent chemical incompatibility with sulfide electrolyte systems, which are extremely sensitive to solvents, resulting in significant technical drawbacks. On one hand, the polar or aprotic solvents used in wet processes (such as N-methylpyrrolidone) react with active sulfur species (such as PS bonds, S bonds, etc.) in the sulfide electrolyte. 2- Irreversible nucleophilic substitution or Lewis acid-base reactions can occur, leading to the collapse of the electrolyte crystal structure and a sharp decrease in ionic conductivity. This is accompanied by the release of toxic H₂S gas, posing serious safety and environmental hazards. Furthermore, even with high-temperature vacuum drying processes, high-boiling-point solvent molecules are difficult to completely remove, and residual solvents can occupy the Li₂ between electrolyte particles. + Migration channels significantly reduce bulk ionic conductivity. During battery cycling, especially when in contact with the lithium metal anode at low potentials, residual solvents undergo electrochemical decomposition, continuously consuming active lithium, increasing interfacial impedance, and severely deteriorating battery cycle life and coulombic efficiency. Furthermore, to ensure an anhydrous environment, the entire slurry preparation, coating, and drying process must be carried out in a strictly controlled glove box or drying room, and a complex solvent recovery system is required, resulting in high equipment investment and operating costs, which cannot meet the needs of large-scale production.

[0005] To avoid the solvent degradation problem of wet processes, pure dry processes were developed. This process eliminates the risk of chemical incompatibility in principle, but introduces serious physical processing challenges. During high-energy ball milling, intense mechanical impact and shearing forces can easily cause lattice defects or even amorphization transformation in sulfide electrolytes, resulting in irreversible loss of their intrinsic ionic conductivity. Simultaneously, the lack of solvent lubrication and mediating effect makes it difficult for binders (such as PTFE fibers) to uniformly disperse and encapsulate electrolyte particles, easily forming microscale "island structures." This leads to high interparticle friction and uneven stress distribution during subsequent cold pressing, causing microcracks and pores within the electrolyte membrane and low bulk density. Furthermore, electrolyte membranes prepared by the pure dry method are extremely brittle and have almost zero flexibility, making them prone to cracking and breakage during demolding or subsequent operations. This makes it difficult to prepare large-area, self-supporting films, resulting in extremely low yields. Moreover, the molding process requires ultra-high pressures of hundreds of megapascals, leading to high equipment wear, high energy consumption, and low production efficiency, severely restricting its industrial application.

[0006] To balance processability and chemical stability, solvent-assisted dry processes (such as systems using PTFE binder and low-polarity solvents like n-heptane) have been proposed as a compromise. By introducing trace amounts of volatile solvents, the processing effect can be improved. However, this improved approach has not completely solved key problems such as poor slurry uniformity, narrow rolling process window, insufficient film flexibility, and low production efficiency. It has failed to fundamentally break through the technical bottleneck of sulfide solid electrolyte film formation.

[0007] In summary, the "chemical incompatibility" of traditional wet processes, the "physical processing difficulties" of dry processes, and the inherent defects of improved processes together constitute the core obstacles to the large-scale application of sulfide electrolytes. Developing a technical solution that can overcome the poor processability of dry processes while avoiding the chemical damage risks of wet processes, and achieve efficient and high-quality preparation of sulfide electrolyte membranes with excellent mechanical properties, high ionic conductivity, and good interfacial stability, has become an urgent need to promote the industrialization of all-solid-state lithium batteries. Summary of the Invention

[0008] This disclosure provides sulfide solid electrolyte membranes, their preparation methods, and applications, in order to at least solve the above-mentioned technical problems existing in the prior art.

[0009] According to a first aspect of this disclosure, a method for preparing a sulfide solid electrolyte membrane is provided, comprising the following steps:

[0010] S1: Under an inert atmosphere, the sulfide solid electrolyte powder and the binder are ball-milled and mixed to obtain a mixture;

[0011] S2: Add perfluoropolyether (PFPE) additive and optional volatile main solvent to the mixture described in step S1, and obtain a slurry after plasticizing and mixing treatment; the amount of perfluoropolyether additive added accounts for 0.5~5.0 wt% of the mass of the mixture; the shear force of the plasticizing and mixing treatment is 0.05~1 MPa;

[0012] S3: Roll the slurry described in step S2 to obtain a solid electrolyte membrane green body; dry the solid electrolyte membrane green body to obtain the sulfide solid electrolyte membrane.

[0013] Specifically, step S1 of this disclosure explicitly defines inert atmosphere protection, preventing the reaction between sulfide solid electrolyte powder and water and oxygen in the air from the source, thus preventing damage to the electrolyte crystal structure and attenuation of ionic conductivity, and solving the key problem of the environmental sensitivity of sulfide electrolytes. The PFPE additive introduced in step S2 combines low surface tension, high chemical inertness, and volatility. Working synergistically with the volatile main solvent, it reduces interfacial tension between material particles and provides temporary plasticization, improving the rheological properties of the slurry and avoiding the defect of uneven binder dispersion forming an "island structure" in traditional dry processes. Simultaneously, the chemical inertness of PFPE ensures that it does not react with the sulfide electrolyte, avoiding the risk of solvent-induced chemical side reactions in wet processes. The material plasticizing and mixing treatment uses low to medium shear force, achieving both uniform mixing of materials and inducing fibrillation of the fibrous binder to form a three-dimensional network structure, enhancing the cohesiveness of the slurry and the mechanical strength of the subsequent film; it also avoids electrolyte lattice defects or amorphization problems caused by processes such as high-energy ball milling, ensuring the intrinsic ionic conductivity of the electrolyte. Finally, step S3 involves rolling to eliminate voids in the slurry, achieving densification of the electrolyte preform and improving the ion transport efficiency of the membrane. The drying process efficiently removes volatile main solvents and most PFPE additives, ensuring a low total residual amount of organic solvents in the membrane and preventing residues from clogging the Li. + Migration channels may trigger interfacial reactions, ensuring the electrochemical stability of the electrolyte membrane.

[0014] In one embodiment, the inert atmosphere in step S1 is selected from at least one of argon and nitrogen, and the water oxygen content of the inert atmosphere is <0.1ppm.

[0015] In one embodiment, the mass of the binder in step S1 is 2% to 10% of the mass of the sulfide solid electrolyte powder.

[0016] In a preferred embodiment, the mass of the binder in step S1 is 3% to 5% of the mass of the sulfide solid electrolyte powder.

[0017] In one embodiment, the sulfide solid electrolyte powder is selected from Li6PS5Cl and its derivatives, Li 10 GeP2S 12 At least one of its derivatives.

[0018] Specifically, derivatives of Li6PS5Cl such as Li6PS5Br and Li6PS5I.

[0019] Specifically, Li 10 GeP2S 12 The derivative is Li 6+x P 1-x M x S5X, 0 < x ≤ 0.5; where M is selected from at least one of Si, Ge, and Sn.

[0020] In one embodiment, the adhesive is selected from at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and hydrogenated nitrile rubber.

[0021] In a preferred embodiment, the adhesive is selected from at least one of polytetrafluoroethylene and polyvinylidene fluoride.

[0022] In one embodiment, the ball milling speed in step S1 is 200~250 rpm, and the time is 10~30 min.

[0023] In one embodiment, the perfluoropolyether additive is selected from at least one of polyperfluoromethyl isopropyl ether, and linear or branched perfluoropolyethers with a surface tension <20mN / m, chemical inertness, and volatilization at 50~80℃; the molecular weight of the perfluoropolyether additive is 500~2500g / mol.

[0024] Specifically, the aforementioned linear and branched perfluoropolyethers have high chemical inertness and can be essentially volatilized at 50~80°C.

[0025] In a preferred embodiment, the amount of the perfluoropolyether additive added accounts for 1.5 to 3.5 wt% of the mass of the mixture.

[0026] In one embodiment, the volatile primary solvent is selected from at least one of n-heptane, n-hexane, and toluene; the amount of the volatile primary solvent added accounts for 5 to 20 wt% of the mass of the mixture.

[0027] Specifically, the volatile primary solvent has low polarity and is easily volatile. Its function is to further adjust the consistency of the slurry. It is used in small quantities and is usually used in conjunction with PFPE. The volatile primary solvent can be added or not added as needed, and its amount can be adjusted according to the state of the slurry.

[0028] In one embodiment, the material plasticizing and mixing process in step S2 is performed by shearing and plasticizing through at least one of kneading, twin-screw extruder, kneader, and high-shear mixer.

[0029] Specifically, kneading is a mixing method that applies low to medium shear force (0.05~1MPa). It not only achieves uniform mixing of materials, but more importantly, it promotes the fibrillation of fibrous binders such as PTFE, enabling them to form a three-dimensional network structure, thereby significantly improving the cohesiveness of the slurry and the mechanical strength of the final film. In large-scale production, equipment that can provide similar shearing and kneading effects, such as twin-screw extruders, kneaders, and high-shear mixers, can be used.

[0030] In one embodiment, the linear pressure of the rolling process in step S3 is 20~80MPa, and the number of times is 2~5; the thickness of the solid electrolyte membrane preform is 50~200μm.

[0031] Specifically, the rolling process uses a double-roll mill; repeated rolling can increase density.

[0032] In one embodiment, the vacuum degree of the drying process in step S3 is <100 Pa, the temperature is 50~90℃, and the time is 4~24h.

[0033] Specifically, after drying, the volatile main solvent and most of the PFPE additives can be removed.

[0034] In one embodiment, the total residual amount of organic solvent in the sulfide solid electrolyte membrane obtained after the drying treatment in step S3 is <200ppm.

[0035] According to a second aspect of this disclosure, a sulfide solid electrolyte membrane prepared according to the above-described preparation method is provided.

[0036] According to a third aspect of this disclosure, an all-solid-state battery is provided, comprising a positive electrode, the aforementioned sulfide solid electrolyte membrane, and a negative electrode.

[0037] According to one possible implementation of this disclosure, at least the following beneficial effects are achieved:

[0038] 1. The PFPE additive selected in this disclosure has the characteristics of low surface tension and high chemical inertness. During the plasticizing and mixing process with low to medium shear force, it can form a uniform lubricating modified layer on the surface of sulfide solid electrolyte powder and binder particles, effectively reducing the cohesive resistance and shear friction resistance between materials. With the control of shear force parameters of 0.05~1MPa, it avoids the destruction of sulfide electrolyte crystal phase and particle pulverization caused by high shear force, and can achieve full plasticizing and fusion of materials, so that the mixture forms a uniform slurry with good extensibility. After roll pressing, the slurry can be directly formed into a self-supporting film with a thickness of 50~200μm. The film layer has high density and no cracks or delamination defects. At the same time, the plasticizing and toughening effect of PFPE additive on binder greatly improves the tensile strength and bending flexibility of electrolyte film, solving the technical pain points of traditional sulfide solid electrolyte film such as high brittleness, high film formation difficulty, and easy breakage during roll pressing.

[0039] 2. The molecular weight of PFPE additives is precisely controlled between 500 and 2500 g / mol, and it is essentially volatile at 50-80℃, playing only a plasticizing and lubricating role during the film-forming stage. After drying, there is no residue or only trace residue in the film layer, and it will not form an ion transport blocking phase. At the same time, the high chemical inertness of PFPE ensures that it does not have adverse chemical reactions with sulfide electrolytes and binders, and will not destroy the ion transport channels of sulfide electrolytes, thus ensuring the high ionic conductivity of the electrolyte membrane. In addition, the dense electrolyte membrane formed after PFPE modification can effectively inhibit the growth and penetration of lithium dendrites, improve the critical current density of the electrolyte membrane, and its chemical inertness also enhances the interfacial compatibility between the electrolyte membrane and the positive and negative electrode materials, reduces the occurrence of interfacial side reactions, and significantly improves the cycle stability and rate performance of all-solid-state batteries.

[0040] 3. This disclosure uses low to medium shear force plasticizing and mixing equipment such as kneading, twin-screw extruders, and kneaders to replace the traditional high-shear mixing process. Combined with the lubrication and drag reduction effect of PFPE additives, it achieves uniform mixing of materials while minimizing mechanical wear and crystal phase destruction of sulfide electrolyte particles during the mixing process. It retains the intrinsic ionic conductivity of sulfide electrolytes, solves the problems of electrolyte performance degradation and high material loss rate caused by traditional high-shear mixing, and reduces equipment wear during the production process, extending the service life of the equipment.

[0041] 4. The preparation process disclosed herein has clearly defined and controllable parameters throughout. The inert atmosphere protection conditions, ball milling parameters, shear force range for shear plasticizing mixing, roller pressing line pressure, and drying process parameters are all conditions that are easily achievable in industrial production. At the same time, the plasticizing mixing treatment with low to medium shear force can be achieved through conventional industrial mixing equipment such as kneading, twin-screw extruders, kneaders, and high-shear mixers, without the need for customized special equipment. The process has strong compatibility and can be directly connected to existing large-scale battery production lines to achieve continuous and standardized production, which greatly reduces the technical difficulty and production cost of industrial scale-up. Furthermore, the total residual organic solvent content in the dried film is less than 200 ppm, which meets the industrial quality standards for power batteries.

[0042] 5. The PFPE additive is selected from polyperfluoromethyl isopropyl ether or other composite linear / branched perfluoropolyethers with low surface tension, high chemical inertness, and low-temperature volatility. The addition amount is only 0.5~5.0wt% of the total mass of the sulfide solid electrolyte and binder. A small amount of addition can achieve significant plasticizing and film-forming enhancement effects without the need for a large amount of additives, which would reduce the proportion of effective components in the electrolyte membrane. At the same time, the low polarity volatile main solvent can be selected from at least one of n-heptane, n-hexane, and toluene, which can be flexibly adjusted according to actual production needs, further improving the practicality and adaptability of the process.

[0043] 6. The sulfide solid electrolyte membrane prepared in this disclosure is a highly dense, flexible, and self-supporting film that can be used directly as an independent electrolyte separator component in the stacking assembly of all-solid-state batteries without the need for additional substrate support, thus simplifying the assembly process of all-solid-state batteries. The tensile strength, ionic conductivity, critical current density, and cycle stability of this electrolyte membrane are all superior to those prepared without the addition of PFPE additives or with other alternative additives. When applied to all-solid-state batteries, it can significantly improve the energy density, cycle life, and safety performance of the battery. It is suitable for the preparation of various all-solid-state batteries such as power batteries, energy storage batteries, and consumer electronics batteries, and has broad application prospects.

[0044] In summary, this disclosure achieves a balance between the film-forming performance, electrochemical performance, and large-scale production capability of sulfide solid electrolytes through precise selection of PFPE additives and synergistic optimization of process parameters. It solves the core technical problems of existing technologies, such as the difficulty in film formation, high brittleness, poor interface stability, and low industrial adaptability of sulfide solid electrolytes. It provides a feasible technical solution for the industrial mass production of high-performance sulfide-based all-solid-state batteries, and has significant technological innovation and industrial application value.

[0045] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0046] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of this disclosure are illustrated in the drawings by way of example and not limitation, in which:

[0047] In the accompanying drawings, the same or corresponding reference numerals indicate the same or corresponding parts.

[0048] Figure 1 Photographs and scanning electron micrographs of the sulfide solid electrolyte membranes of Embodiment 1 and Comparative Example 1 of this disclosure are shown; wherein, (a) is of Comparative Example 1 and (b) is of Embodiment 1;

[0049] Figure 2 The EIS and IT curves of the sulfide solid electrolyte membrane in Embodiment 1 of this disclosure are shown; wherein, (a) is the EIS curve and (b) is the IT curve.

[0050] Figure 3 The CCD test curve and the corresponding EIS curve of the sulfide solid electrolyte membrane in Embodiment 1 of this disclosure are shown; wherein, (a) is the CCD test curve and (b) is the EIS curve.

[0051] Figure 4 The electrochemical performance test results of the all-solid-state batteries assembled in Example 1 and Comparative Example 1 of this disclosure are shown in the figure; wherein, (a) is the voltage-specific capacity curve of the battery of Example 1 during the first charge-discharge cycle, (b) is the rate performance curve of the battery of Example 1, and (c) is the cycle life curve of the batteries of Example 1 and Comparative Example 1 at 1C rate. Detailed Implementation

[0052] To make the objectives, features, and advantages of this disclosure more apparent and understandable, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0053] Example 1

[0054] This embodiment prepares a sulfide solid electrolyte membrane, as detailed below:

[0055] (1) In an argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm) glove box, 1.0 g of Li6PS5Cl electrolyte powder and 30 mg of PTFE binder were initially mixed by low-speed ball milling to obtain a mixture; wherein the ball milling speed was 200 rpm and the time was 15 min.

[0056] (2) Subsequently, 3.0 wt% of polyperfluoromethyl isopropyl ether was added to the mixture in step (1), and the mixture was kneaded manually for 30 minutes to obtain a slurry. It was observed that the slurry gradually changed from a powder to a uniform, fine paste with significant viscoelasticity and extensibility, which could be drawn into threads and was not easily broken.

[0057] (3) The slurry from step (2) was placed in a two-roller press and rolled continuously 5 times under a rolling pressure of 30 MPa to obtain a green electrolyte membrane preform with a thickness of about 100 ± 10 μm, a smooth surface, and self-supporting. The green solid electrolyte membrane preform was placed in a vacuum drying oven and dried at 70 °C and a vacuum degree of <10 Pa for 8 h to obtain a sulfide solid electrolyte membrane (labeled as S-1).

[0058] Example 2

[0059] This embodiment prepares a sulfide solid electrolyte membrane, as detailed below:

[0060] (1) In an argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm) glove box, 1.0 g of Li6PS5Cl electrolyte powder and 30 mg of PTFE binder were initially mixed by low-speed ball milling to obtain a mixture; wherein the ball milling speed was 200 rpm and the time was 10 min.

[0061] (2) Subsequently, 2.0 wt% of poly(perfluoromethyl isopropyl ether) of the mixture in step (1) was added and kneaded manually for 40 min to obtain a slurry. It was observed that the slurry gradually changed from a powder to a uniform, fine paste with significant viscoelasticity and extensibility, which could be drawn into threads and was not easily broken.

[0062] (3) The slurry from step (2) was placed in a two-roller press and rolled continuously four times under a rolling pressure of 50 MPa to obtain a green electrolyte membrane preform with a thickness of approximately 100 ± 10 μm, a smooth surface, and self-supporting structure. The green solid electrolyte membrane preform was placed in a vacuum drying oven and dried at 70 °C and a vacuum degree of <10 Pa for 8 hours to obtain a sulfide solid electrolyte membrane (labeled as S-2).

[0063] Example 3

[0064] This embodiment prepares a sulfide solid electrolyte membrane, as detailed below:

[0065] (1) In an argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm) glove box, 1.0 g of Li6PS5Cl electrolyte powder and 30 mg of PTFE binder were initially mixed by low-speed ball milling to obtain a mixture; wherein the ball milling speed was 200 rpm and the time was 30 min.

[0066] (2) Subsequently, 0.10 mL of anhydrous n-heptane (9.6 wt% of the mass of the mixture in step (1)) was added using a pipette, followed by 2.0 wt% of poly(perfluoromethyl isopropyl ether) (2.0 wt% of the mass of the mixture in step (1)). The mixture was kneaded manually for 20 min to obtain a slurry. The slurry was observed to have excellent uniformity and extensibility, with slightly better fluidity than in Example 1.

[0067] (3) The slurry from step (2) was placed in a two-roller press and rolled twice under a rolling pressure of 60 MPa to obtain a green electrolyte membrane preform with a thickness of approximately 100 ± 10 μm, a smooth surface, and self-supporting structure. The green solid electrolyte membrane preform was placed in a vacuum drying oven and dried for 8 hours at 70°C and a vacuum degree of <10 Pa to obtain a sulfide solid electrolyte membrane (labeled as S-3).

[0068] Example 4

[0069] This embodiment prepares a sulfide solid electrolyte membrane, as detailed below:

[0070] (1) In a glove box under an argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm), 1.0 g of Li 10 GeP2S 12 (LGPS) electrolyte powder and 50 mg of polyvinylidene fluoride (PVDF) powder binder were initially mixed by low-speed ball milling to obtain a mixture; wherein the ball milling speed was 200 rpm and the time was 25 min.

[0071] (2) Subsequently, 2.5 wt% of poly(perfluoromethyl isopropyl ether) of the mixture in step (1) was added and kneaded manually for 25 min to obtain a slurry. It was observed that the film-forming mechanism of the PVDF system was slightly different from that of PTFE. During the kneading process, the slurry gradually became sticky and eventually formed a uniform paste with a certain elasticity.

[0072] (3) The slurry from step (2) was placed in a two-roller press and rolled continuously 5 times under a rolling pressure of 30 MPa to obtain a green electrolyte membrane preform with a thickness of about 100 ± 10 μm, a smooth surface, and self-supporting. The green solid electrolyte membrane preform was placed in a vacuum drying oven and dried at 80 °C and a vacuum degree of <10 Pa for 10 h to obtain a sulfide solid electrolyte membrane (labeled as S-4).

[0073] Comparative Example 1

[0074] This comparative example prepared a sulfide solid electrolyte membrane. The difference from Example 1 is that this comparative example did not add poly(perfluoromethyl isopropyl ether), otherwise it was the same as Example 1. During the preparation process, it was found that the slurry was difficult to mix, the binder was unevenly distributed, and it was prone to cracking during rolling, making it difficult to obtain a complete large-area film. The product of this comparative example is labeled C-1.

[0075] Comparative Example 2

[0076] This comparative example prepared a sulfide solid electrolyte membrane. The difference from Example 1 is that the amount of poly(perfluoromethyl isopropyl ether) added in this comparative example was excessively high, accounting for 86 wt% of the mixture. The rest was the same as in Example 1. During the preparation process, it was found that the slurry was too slippery, causing severe sticking to the rollers during rolling. The resulting green membrane had extremely low strength, resembling wet dough, and was difficult to peel off completely. After barely drying, the membrane was very soft, easily deformed, and had poor mechanical strength. The product of this comparative example is designated C-2.

[0077] Comparative Example 3

[0078] This comparative example prepared a sulfide solid electrolyte membrane. The difference from Example 1 is that polyethylene oxide (PEO) was used instead of polytetrafluoroethylene (PTFE) in this comparative example; otherwise, the process was the same as in Example 1. During the preparation process, it was found that PEO had weak mechanical strength, was difficult to disperse uniformly, and still left a large amount of residue after drying, severely affecting electrochemical performance. This indicates that PEO and the sulfide electrolyte have interfacial compatibility issues, and its plasticizing properties have poor synergistic effect with PFPE. As a binder, it leads to low electrolyte membrane density and a significant decrease in ionic conductivity. The product of this comparative example is labeled C-3.

[0079] Comparative Example 4

[0080] This comparative example prepared a sulfide solid electrolyte membrane. The difference from Example 1 is that perfluoropolyether carboxylic acid was used instead of polyperfluoromethyl isopropyl ether in this comparative example; otherwise, the process was the same as in Example 1. During the preparation process, an abnormality was observed immediately upon starting kneading. The material rapidly agglomerated, becoming a hard, non-plastic block, completely losing its fluidity; continued kneading did not improve the situation. The product of this comparative example is labeled C-4.

[0081] Comparative Example 5

[0082] This comparative example prepared a sulfide solid electrolyte membrane. The difference from Example 1 is that this comparative example used low-speed ball milling instead of a kneading step. After mixing, the material rapidly agglomerated, forming a collection of moist, small particles that failed to form a continuous slurry mass. Upon being poured into a roller press, the particles slid between the rollers, failing to combine into a film, resulting in broken flakes and particles. The product of this comparative example is designated C-5.

[0083] Test case

[0084] 1. The microstructure of the sulfide solid electrolyte membranes prepared in Example 1 and Comparative Example 1 was tested.

[0085] The sulfide solid electrolyte membranes prepared in Example 1 and Comparative Example 1 were placed under a scanning electron microscope (SEM) to observe their respective morphology and structure. The structures are as follows: Figure 1 As shown. Figure 1 The comparison example 1 (i.e.) shows that Figure 1 The electrolyte membrane in Example (a) exhibits obvious cracks and wrinkles on its surface, irregular edges, high overall brittleness, poor flexibility, and is prone to breakage. The microstructure (SEM image) shows a loosely distributed particle structure with numerous obvious pores and interparticle spaces, weak interparticle bonding, and low membrane density. In contrast, Example 1 (i.e....) Figure 1 The electrolyte membrane in (b) has a smooth and flat surface, free of cracks and wrinkles, exhibiting a uniform and continuous self-supporting state, significantly improving its flexibility and integrity. Microstructural analysis shows that the particles are tightly packed, with a substantial reduction in pores and gaps, resulting in significantly increased membrane density and stronger interparticle bonding. This demonstrates that the lubricating effect of the PFPE additive leads to more uniform material mixing, resulting in a dense, defect-free membrane after rolling, solving the problems of brittleness and easy breakage inherent in traditional sulfide electrolyte membranes. The modified layer formed by the PFPE additive on the particle surface enhances interparticle bonding, significantly reduces membrane porosity, provides a more continuous channel for ion transport, and simultaneously strengthens the membrane's mechanical stability.

[0086] 2. Test the tensile strength of the sulfide solid electrolyte membranes prepared in Examples 1-4 and Comparative Examples 1-5.

[0087] Referring to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets" and the general test requirements for solid electrolyte membranes for batteries, the tensile strength was determined by uniaxial tensile test. The test results are shown in Table 1.

[0088] Table 1

[0089]

[0090] Table 1 shows that the tensile strength of the sulfide solid electrolyte membranes in Examples 1-4 ranged from 3.9 to 5.2 MPa, with an average of approximately 4.5 MPa; while the tensile strength of the sulfide solid electrolyte membranes in Comparative Examples 1-5 ranged from 1.6 to 2.6 MPa, with an average of approximately 2.12 MPa. It is evident that the tensile strength of the samples in Examples 1-4 was significantly better than that in Comparative Examples 1-5. This indicates that the plasticizing and mixing process under low to medium shear forces in this embodiment effectively improves the flexibility and tensile strength of the electrolyte membrane by forming a lubricating modified layer of PFPE on the particle surface, thus solving the problem of high brittleness in traditional sulfide electrolyte membranes. The low to medium shear force mixing process avoids the damage to electrolyte particles caused by high shear forces, significantly improving mechanical properties while ensuring electrochemical performance.

[0091] 3. Test ionic conductivity and electronic conductivity.

[0092] Assembly method of symmetrical battery (blocking electrode): 100 mg of sulfide solid electrolyte membrane was accurately weighed and placed in a mold cavity with an inner diameter of 10 mm. Then, a 10 mm diameter carbon-coated aluminum foil was placed on each of the upper and lower surfaces of the powder to serve as the blocking electrode. Finally, the battery was held at 150 MPa for 10 min to complete the integrated molding of the battery and optimize the electrode interface contact. The assembled battery was then connected to an electrochemical workstation for EIS (electrochemical impedance spectroscopy) and IT (current-time polarization) curve testing.

[0093] Formula for calculating ionic conductivity: σ i = ;

[0094] Where, σ i Ω is the ionic conductivity, in mS / cm; L is the thickness of the electrolyte membrane, in cm; R is the impedance, in Ω; r is the radius of the electrode plate, in cm.

[0095] Formula for calculating electronic conductivity: σ e = ;

[0096] Where, σ e ρ is electronic conductivity, in S / cm; L is the thickness of the electrolyte membrane, in cm; I is the current, in A; U is the voltage, in V; r is the radius of the electrode plate, in cm.

[0097] The EIS and IT test results of the electrolyte membrane in Example 1 are as follows: Figure 2 As shown. Figure 2 The EIS curve (shows) Figure 2In (a) of the curve, an arc appears in the high-frequency region, reflecting the bulk resistance and interfacial resistance of the electrolyte membrane. The smaller the diameter of the arc, the lower the resistance. It then extends into the low-frequency region and gradually bends upward, which is related to the ion diffusion process at the electrode / electrolyte interface. The ionic conductivity of the electrolyte membrane in Example 1 was calculated to be 2.23 mS / cm using impedance spectroscopy fitting, which falls within the typical performance range of sulfide solid electrolytes, indicating that the electrolyte membrane possesses good ion transport capabilities. (IT curve) Figure 2 In (b) of the experiment, the current drops rapidly in the initial stage, enters a stable plateau after about 500 s, and eventually approaches 0. The rapid drop in current is due to the accumulation of interfacial charge and changes in concentration gradient during polarization, while the subsequent current stabilization reflects the electrochemical stability of the electrolyte membrane. Extremely low steady-state current is a key indicator for sulfide solid electrolytes to meet battery application requirements. The electronic conductivity obtained after polarization testing is 7.60 × 10⁻⁶. -9 The value of S / cm is extremely low, indicating that the electrolyte membrane of Example 1 has excellent electronic insulation properties, which can effectively prevent electrons from directly conducting between the positive and negative electrodes and avoid short circuits inside the battery.

[0098] Meanwhile, the ionic conductivity and electronic conductivity of the electrolyte membranes of Examples 1-4 and Comparative Examples 1-5 were tested using the above method, and the results are shown in Table 2.

[0099] Table 2

[0100]

[0101] Table 2 shows that the ionic conductivity of samples 1-4 ranged from 1.62 to 2.23 mS / cm, with an average of approximately 1.91 mS / cm; while the ionic conductivity of samples 1-5 ranged from 0.46 to 1.32 mS / cm, with an average of approximately 1.124 mS / cm. It is evident that the ionic conductivity of samples 1-4 was approximately 70% higher than that of samples 1-5 on average, indicating that the technical solution of PFPE additives for synergistic plasticization and film-forming enhancement effectively preserves the intrinsic ion transport efficiency of the sulfide solid electrolyte membrane and significantly improves the ionic conductivity of the electrolyte membrane. The electronic conductivity of samples 1-4 ranged from 7.60E-09 to 1.84E-08 S / cm, with an average of approximately 1.26E-08 S / cm; while the electronic conductivity of samples 1-5 ranged from 3.95E-09 to 1.72E-08 S / cm, with an average of approximately 1.29E-08 S / cm. As can be seen, the electronic conductivity of both the example and comparative samples is within 10. -8 ~10 -9 The extremely low S / cm level indicates that the modification process disclosed herein does not introduce additional electronic conduction pathways, and the electrolyte membrane can still effectively suppress electronic conduction, ensuring the coulombic efficiency and safety of the all-solid-state battery.

[0102] 4. Test the critical current density (CCD).

[0103] Assembly method of lithium symmetric battery: 100mg of sulfide solid electrolyte membrane is accurately weighed and filled into a mold cavity with an inner diameter of 10mm. A pressure of 250MPa is applied and held for 5-10 minutes until the electrolyte membrane is densely stacked. Subsequently, a 10mm diameter ultrathin lithium foil is placed on the upper and lower surfaces of the electrolyte membrane as symmetric electrodes. Then, a uniaxial pressure of 50MPa is applied for 1 minute to achieve battery structure densification and optimized electrode / electrolyte interface contact. The assembled battery is then connected to the Blue Electric testing system for constant current charge-discharge (CCD) testing.

[0104] Example 1: The CCD test curve of the electrolyte membrane and its corresponding EIS curve are as follows. Figure 3 As shown. Figure 3 The display shows the CCD curve ( Figure 3 In (a) of the diagram, during the current density increase phase, the polarization voltage remained within a small fluctuation range without any sudden voltage changes or sharp increases, indicating that at this current density, the electrolyte membrane effectively suppressed the growth and penetration of lithium dendrites, demonstrating good interface stability. When the current density reached 1.8 mA cm⁻¹... -2 No short circuit occurred during this period, indicating that the sulfide solid electrolyte membrane possesses a high critical current density, which is a key basis for its compatibility with high-rate all-solid-state batteries. (ESI curve) Figure 3 (b) exhibits typical single-arc characteristics, with the arc diameter corresponding to the battery's interface impedance. As the test progresses, the diameter of the impedance arc gradually increases, indicating a certain degree of increase in interface resistance, but the overall increase is controllable. This phenomenon suggests that although there are certain interface side reactions or uneven lithium deposition / stripping during the charging and discharging process between the electrolyte membrane and the lithium metal anode, no serious interface failure occurs. This is consistent with the stable polarization voltage result in (a), further demonstrating the interface stability of the electrolyte membrane.

[0105] Meanwhile, the critical current density of the electrolyte membranes of Examples 1-4 and Comparative Examples 1-5 was tested using the above method, and the results are shown in Table 3.

[0106] Table 3

[0107]

[0108] Table 3 shows that the critical current density range for samples in Examples 1-4 is 1.4~1.8 mA / cm². 2This demonstrates that the sulfide solid electrolyte membrane prepared in this disclosure possesses excellent resistance to lithium dendrite penetration, making it suitable for high-rate charge-discharge scenarios. The critical current density range of the comparative examples 1-5 is 0.4~1.0 mA / cm². 2 The overall level is far lower than that of the examples, indicating that the electrolyte membrane without the PFPE synergistic additive plasticizing process disclosed in this paper has significantly insufficient resistance to lithium dendrite formation.

[0109] 5. Test the rate performance of the full battery.

[0110] Assembly method of sulfide all-solid-state battery: (1) Preparation of positive electrode material: VGCF, sulfide solid electrolyte LPSC and NCM are placed in an agate mortar in a weight ratio of 5:25:70 and mixed evenly for 50 min to obtain composite positive electrode. (2) Assembly of sulfide all-solid-state battery: 100 mg of sulfide solid electrolyte membrane is added to a mold with a diameter of 10 mm and pressed at 50 MPa for 10 min to form a solid electrolyte layer. Then, 10 mg of composite positive electrode is evenly spread on one side of the electrolyte layer and pressed at 300 MPa for 10 min to make it in close contact with the solid electrolyte layer. Finally, Li negative electrode is evenly spread on the other side of the solid electrolyte layer and pressed at 30 MPa for 1 min to complete the assembly of solid-state battery.

[0111] The electrochemical performance test results of the all-solid-state batteries assembled in Example 1 and Comparative Example 1 are as follows: Figure 4 As shown. Figure 4 In the middle, the voltage-specific capacity curve of the first charge-discharge cycle ( Figure 4 (a) shows a clear charge-discharge plateau and high specific capacity in Example 1 battery, indicating good interfacial compatibility between the electrolyte membrane and the positive and negative electrodes, and high initial coulombic efficiency. Rate performance curve ( Figure 4 (b) shows that as the current rate increases, the specific capacity of the battery in the example decreases, but the decrease is gradual, and it can still maintain a high capacity after recovering from the high rate, indicating that the battery has excellent rate performance and can adapt to the needs of different discharge rates. Cycle life curve at 1C rate ( Figure 4 (c) shows that the capacity decay of the battery in Example 1 after 600 cycles is significantly less than that in Comparative Example 1, indicating that the battery in Example 1 has better structural and interface stability during long-term charge and discharge and has excellent long-cycle stability.

[0112] Meanwhile, the first-cycle coulombic efficiency and first-cycle charge-discharge capacity of all-solid-state batteries assembled from the electrolyte membranes of Examples 1-4 and Comparative Examples 1-5 were tested, and the results are shown in Table 4.

[0113] Table 4

[0114]

[0115] Table 4 shows that the first discharge capacity of the batteries corresponding to Examples 1-4 is consistently 173 mAh·g. -1 Of the above, the optimal one reaches 182.2 mAh·g. -1 The first-cycle discharge capacity of the batteries corresponding to Comparative Examples 1-5 was generally lower than 160 mAh·g. -1 The lowest is only 142.4 mAh·g -1 This difference indicates that the sulfide solid electrolyte membrane prepared by the present disclosure through PFPE additive synergistic low-to-medium shear plasticization process can effectively reduce interfacial impedance, optimize ion transport channels, and significantly improve the initial lithium intercalation utilization rate of the positive electrode active material, solving the technical pain point of low active material utilization rate in traditional processes. The first-cycle coulombic efficiency of the batteries corresponding to Examples 1-4 is ≥75%, while the first-cycle coulombic efficiency of the batteries corresponding to Comparative Examples 1-5 is below 75%. This demonstrates that the high chemical inertness of the PFPE additive and the construction of a dense electrolyte membrane effectively suppress the first-cycle interfacial side reactions between the electrolyte and the positive / negative electrode materials, reduce irreversible lithium consumption, improve the energy conversion efficiency of the battery, and lay the foundation for subsequent cycle stability.

[0116] Through comparative analysis of the above examples and comparative examples, the crucial role of PFPE additive in solvent-assisted dry processes is clearly evident. Appropriate amounts of PFPE not only significantly improve the uniformity and processability of the slurry but also effectively enhance the mechanical properties and electrochemical stability of the final electrolyte membrane. Specifically, the introduction of PFPE solves the problems of uneven binder dispersion, high interparticle friction, and easy film cracking in traditional dry processes, while avoiding side reactions and interface deterioration caused by solvent residues in wet processes. Furthermore, PFPE possesses excellent chemical inertness and thermal stability, and its low surface tension helps achieve more uniform wetting and encapsulation during mixing, thereby further optimizing the microstructure of the electrolyte membrane. Experiments controlling different PFPE addition amounts revealed that optimal overall performance was achieved when its mass fraction was controlled within the range of 2% to 4%. Excessive or insufficient addition amounts adversely affect the rheological properties of the slurry and the quality of the film. For example, excessive addition amounts result in membranes that are too soft and difficult to handle, while insufficient addition amounts fail to fully realize their modifying effects. These results fully verify the scientific validity and practicality of the disclosed technical solution.

[0117] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this is not limited herein.

[0118] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0119] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing a sulfide solid electrolyte membrane, characterized in that, Includes the following steps: S1: Under an inert atmosphere, the sulfide solid electrolyte powder and the binder are ball-milled and mixed to obtain a mixture; the binder is selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, and hydrogenated nitrile rubber. S2: Add a perfluoropolyether additive and an optional volatile main solvent to the mixture described in step S1, and obtain a slurry after plasticizing and mixing treatment; the perfluoropolyether additive is selected from at least one of polyperfluoromethyl isopropyl ether, and linear or branched perfluoropolyethers with a surface tension <20mN / m, chemical inertness, and volatilization at 50~80℃; the molecular weight of the perfluoropolyether additive is 500~2500g / mol; the amount of the perfluoropolyether additive added is 0.5~5.0wt% of the mass of the mixture; the volatile main solvent is selected from at least one of n-heptane, n-hexane, and toluene; the material plasticizing and mixing treatment is carried out by at least one of kneading, twin-screw extruder, kneader, and high-shear mixer for shearing and plasticizing; the shear force of the material plasticizing and mixing treatment is 0.05~1MPa; S3: Roll the slurry from step S2 to obtain a solid electrolyte membrane green body; dry the solid electrolyte membrane green body to obtain the sulfide solid electrolyte membrane; the drying temperature is 50~90℃.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass of the binder is 2% to 10% of the mass of the sulfide solid electrolyte powder; The sulfide solid-state electrolyte powder is selected from at least one of Li6PS5CI and derivatives thereof, Li 10 GeP2S 12 and derivatives thereof.

3. The preparation method according to claim 1, characterized in that, The ball milling speed in step S1 is 200~250 rpm, and the time is 10~30 min.

4. The preparation method according to claim 1, characterized in that, The amount of the volatile primary solvent added is 5 to 20 wt% of the mass of the mixture.

5. The preparation method according to claim 1, characterized in that, The linear pressure of the rolling process in step S3 is 20~80MPa, and the number of times is 2~5; the thickness of the solid electrolyte membrane preform is 50~200μm.

6. The preparation method according to claim 1, characterized in that, The vacuum degree of the drying process in step S3 is <100Pa, and the time is 4~24h.

7. A sulfide solid electrolyte membrane prepared by any one of claims 1 to 6.

8. An all-solid-state battery, characterized in that, The all-solid-state battery includes a positive electrode, a sulfide solid electrolyte membrane as described in claim 7, and a negative electrode.

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