Polymer-based solid electrolyte membrane and preparation method and application thereof

Abstract

The application belongs to the field of solid-state lithium battery materials, and provides a polymer-based solid-state electrolyte film, a preparation method and application thereof, and the application forms a crosslinked shell layer formed by polyvinyl alcohol, polyethylene glycol diglycidyl ether, boric acid and lithium hydroxide monohydrate outside a polyvinylidene fluoride-hexafluoropropylene copolymer core microsphere, and is dry-mixed and hot-pressed into a film with lithium bisfluorosulfonylimide to form a core-shell composite microsphere conduction and support system, so that the film body maintains the processability while taking into account the chain segment movement, structure constraint and residual solvent control, solves the problem that the mechanical strength and ion conduction, the processing fluidity and the electrochemical stability are difficult to be considered, and is suitable for a full solid-state lithium secondary battery.

Description

Technical Field

[0001] This invention relates to the field of solid-state lithium battery materials, specifically to a polymer-based solid electrolyte membrane, its preparation method, and its application. Background Technology

[0002] All-solid-state lithium-ion rechargeable batteries are considered an important direction for improving the safety and energy density of energy storage devices. The solid electrolyte membrane (SEM) in these batteries serves as an ion transport channel and also influences the positive and negative electrode interface contact, membrane dimensional stability, and battery assembly reliability. Polymer-based solid electrolyte membranes (SEMs) are suitable for fabricating thin-film, rollable, or laminated electrolyte layers due to their flexibility, processability, and good interfacial adhesion. However, in practical applications, these membrane materials not only need to maintain sufficient mechanical support and resistance to deformation but also need to provide continuous lithium-ion migration pathways and maintain low residual solvent and water content during hot pressing, drying, storage, and battery operation. As all-solid-state lithium-ion batteries develop towards thinner layers, higher areal capacity, and more stable interfaces, achieving a balance between polymer chain movement, structural constraints, film formation processing, and electrochemical stability has become a crucial technological foundation for the engineering applications of these materials. Polymer solid electrolytes are attractive in terms of safety, flexibility, and interfacial contact, but room-temperature ion conduction and interfacial stability remain key research areas.

[0003] Existing polymer-based solid electrolytes typically improve membrane support and ion transport by increasing the rigidity of the polymer backbone, introducing inorganic fillers, increasing cross-linking networks, or increasing salt content. However, these methods often result in problems such as restricted chain segment movement, phase separation, increased interfacial impedance, or narrowed processing windows. Conversely, while using flexible segments, solvent-assisted processes, or plasticizing systems is beneficial for film flow and lithium salt dissociation, it may reduce membrane strength, increase the difficulty of controlling residual solvents, and affect long-term electrochemical stability. For example, Chinese patent CN113067030A discloses a solid electrolyte membrane of polyvinylidene fluoride-lithium hexafluoropropylene sulfonate composite polymer and its preparation method for lithium batteries. It forms an electrolyte membrane by sulfonating and lithiating PVDF-HFP and then combining it with lithium salt. However, such disclosed solutions mainly focus on main chain modification and solution casting for film formation. There is still room for further optimization in terms of microsphere core-shell structure, shell continuity, dry mixing and hot pressing film formation, and synergistic quality control of residual polar solvents and water content. Summary of the Invention

[0004] The purpose of this invention is to provide a polymer-based solid electrolyte membrane, its preparation method and application, to solve the problem that it is difficult to simultaneously achieve the mechanical strength, ion conduction performance, processing fluidity and electrochemical stability of current polymer-based solid electrolyte membranes.

[0005] While existing methods of reinforcing the framework or deepening network constraints improve membrane strength, they can restrict chain segment movement. Flexible or plasticized approaches, while facilitating ion migration, can weaken membrane stability. This invention utilizes a core-shell composite microsphere, a cross-linked shell, and a lithium salt ratio that is matched to allow the support structure and ion conduction channels to mutually correct each other within the same membrane, reducing the side effects of single-pathway operation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A polymer-based solid electrolyte membrane comprises core-shell composite microspheres and lithium bis(fluorosulfonyl)imide, wherein the content of lithium bis(fluorosulfonyl)imide is 10-25 wt% based on the total dry mass of the core-shell composite microspheres and the lithium bis(fluorosulfonyl)imide; the core-shell composite microspheres comprise polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres and a cross-linked shell layer coated on the surface of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres, wherein the cross-linked shell layer is formed of polyvinyl alcohol, polyethylene glycol diglycidyl ether, boric acid and lithium hydroxide monohydrate.

[0007] Furthermore, the average particle size of the core-shell composite microspheres is 200-600 nm, the average thickness of the cross-linked shell layer is 10-40 nm, and the thickness of the polymer-based solid electrolyte membrane is 18-35 μm. The average particle size of the core-shell composite microspheres and the average thickness of the cross-linked shell layer are obtained by statistically analyzing at least 100 particles in the cross-section of resin-embedded ultrathin sections using transmission electron microscopy. The thickness of the polymer-based solid electrolyte membrane is obtained by multi-point mechanical measurement.

[0008] Furthermore, the core-shell composite microspheres are prepared through the following steps: A1 provides the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres; A2, dissolve 100 parts by weight of polyvinyl alcohol in 800-1500 parts by weight of deionized water, keep at 85-95℃ for 0.5-2h, cool to 25-40℃, add 5-25 parts by weight of polyethylene glycol diglycidyl ether, 2-12 parts by weight of boric acid and 1-10 parts by weight of lithium hydroxide monohydrate, adjust the pH to 8.0-9.5 to obtain the cross-linking shell precursor solution; A3, disperse 100 parts by weight of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres in 200-800 parts by weight of an ethanol aqueous solution with a volume fraction of 95 vol%, add 20-150 parts by weight of the crosslinking shell precursor liquid dropwise to the resulting dispersion, homogenize at 3000-10000 rpm for 5-20 min, and stir at 25-45℃ for 1-4 h; A4 was centrifuged, washed 1-3 times with an ethanol aqueous solution with a volume fraction of 95 vol%, and vacuum dried at 40-60℃ for 4-12 h to obtain the core-shell composite microspheres. The content of the cross-linked shell in the obtained core-shell composite microspheres is 5-20 wt%.

[0009] Furthermore, the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres in step A1 are prepared through the following steps: B1. Add 100 parts by weight of polyvinylidene fluoride-hexafluoropropylene copolymer and 2-10 parts by weight of polyvinylpyrrolidone to 700-1500 parts by weight of N,N-dimethylformamide, and stir at 40-60℃ for 1-4 hours to obtain a homogeneous solution. B2, the homogeneous solution is added dropwise to an antisolvent formed by mixing deionized water and an aqueous ethanol solution with a volume fraction of 95 vol% in a volume ratio of 70:30-95:5, and stirred at 500-1500 rpm for 0.5-2 h at 20-35°C; B3 was centrifuged, washed with deionized water 1-3 times, and vacuum dried at 40-60℃ for 4-12h to obtain the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres. The average particle size of the polyvinylidene fluoride-hexafluoropropylene copolymer microspheres is 160-500 nm.

[0010] Furthermore, the degree of alcoholysis of the polyvinyl alcohol used in step A2 is 98.0-99.0 mol%, the viscosity of the 4 wt% aqueous solution at 20°C is 20.0-30.0 mPa·s, and the number average molecular weight of the polyethylene glycol diglycidyl ether is 1500-2500.

[0011] Furthermore, the polymer-based solid electrolyte membrane is prepared by dry mixing the core-shell composite microspheres and the lithium bisfluorosulfonyl imide at a dry mass ratio of 90:10-75:25, preheating at 60-80℃ for 0.5-2h, hot pressing at 95-125℃ and 3-8MPa for 3-10min, and vacuum drying at 60-80℃ for 6-12h.

[0012] Furthermore, in the obtained core-shell composite microspheres, the content of polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres is 80-95 wt%, and the balance is the cross-linked shell layer.

[0013] Furthermore, the K value of polyvinylpyrrolidone used in step B1 is 16-18, and the melt index of polyvinylidene fluoride-hexafluoropropylene copolymer is 3-8 g / 10 min.

[0014] Furthermore, the residual N,N-dimethylformamide content in the polymer-based solid electrolyte membrane is not higher than 0.5 wt%, and the water content is not higher than 0.5 wt%.

[0015] As a concept of this invention, a design employing polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres coated with a cross-linked shell and compounded with lithium bisfluorosulfonylimide is employed to achieve a synergistic balance between membrane mechanical strength and ion conductivity. In existing technologies, increasing structural rigidity or enhancing network constraints typically benefits membrane support but restricts polymer chain movement and hinders lithium-ion migration; conversely, increasing flexibility or salt dissociation may lead to membrane softening, structural loosening, and decreased stability. This invention utilizes core microspheres for membrane support, a cross-linked shell to regulate interfacial constraints and a lithiophilic environment, and lithium bisfluorosulfonylimide to provide the ion source. By matching particle size, shell thickness, lithium salt content, and hot-pressing conditions, the strength source and conduction channels are coordinated within the membrane, thereby reducing the adverse effects of a single reinforcement or plasticizing path. The cross-linked shell is coated on the surface of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres. The formation methods include the interfacial attachment of polyvinyl alcohol segments on the surface of the core microspheres, the cross-linking constraint between the shell precursor components, and the surface coating formed by the shrinkage of the shell during the drying process. It is not necessary to limit the formation of covalent bonds between the core microspheres and the cross-linked shell.

[0016] This invention also discloses a method for preparing a polymer-based solid electrolyte membrane, comprising the following steps: S1, Prepare and provide core-shell composite microspheres according to steps A1-A4; S2, mix the core-shell composite microspheres provided in step S1 with lithium bis(fluorosulfonyl imide) and hot-press them at 95-125℃ and 3-8MPa for 3-10 min to form a film; S3. The membrane obtained in step S2 is vacuum dried at 60-80°C for 6-12 hours to obtain the polymer-based solid electrolyte membrane.

[0017] Furthermore, in step S2, the dry mass ratio of the core-shell composite microspheres provided in step S1 to the lithium bis(fluorosulfonyl)imide is 90:10-75:25, and the mixture is preheated at 60-80°C for 0.5-2 hours after dry mixing.

[0018] Furthermore, the polymer-based solid electrolyte membrane is used as a solid electrolyte layer in all-solid-state lithium secondary batteries.

[0019] Furthermore, the pH value of the cross-linking shell precursor solution was measured after adding polyethylene glycol diglycidyl ether, boric acid, and lithium hydroxide monohydrate. The precursor solution with a pH value of 8.0-9.5 was used for subsequent dropwise coating. The amount of polyethylene glycol diglycidyl ether, boric acid, and lithium hydroxide monohydrate in the precursor solution relative to 100 parts by mass of polyvinyl alcohol was calculated according to the amount of material added and used as the quality control parameter for the preparation of the precursor solution.

[0020] Furthermore, in step A2, a 4 wt% aqueous solution of polyvinyl alcohol was used as the test sample. The viscosity of the solution was measured at 20°C using a rotational viscometer. The viscosity value was recorded and used together with the degree of hydrolysis as the basis for determining the specifications of the polyvinyl alcohol raw material.

[0021] Further, the core-shell composite microspheres obtained in step A4 were resin-embedded and ultrathinly sectioned, and cross-sectional observations were performed using transmission electron microscopy (TEM). The core microsphere particle size, shell thickness, and shell continuity were recorded. Additionally, thermogravimetric analysis (TGA) was performed on core-shell composite microspheres from the same batch under a nitrogen atmosphere. The mass loss curve during the heating process was recorded, and the mass fraction of the cross-linked shell was calculated based on the difference in thermogravimetric loss between the polyvinylidene fluoride-hexafluoropropylene copolymer core and the cross-linked shell. The obtained structural and compositional parameters were used for structural confirmation and batch release of the core-shell composite microspheres. The core microsphere particle size, core-shell composite microsphere particle size, and cross-linked shell thickness were obtained statistically from the TEM cross-sectional images of the same batch of samples. The cross-linked shell thickness was the thickness on one side, and the statistical results of particle size and shell thickness were recorded as the average values ​​of the corresponding statistical objects.

[0022] Furthermore, the polymer-based solid electrolyte membrane after vacuum drying was used as the test sample. The residual N,N-dimethylformamide content was determined by headspace gas chromatography, and the DMF peak area was recorded and converted to mass fraction using the external standard method. The water content was determined by Karl Fischer titration, and the liquid consumption per unit mass of sample was recorded and converted to mass fraction. The obtained residual solvent and water content data were used for membrane product quality control.

[0023] As another aspect of this invention, a method is employed to prepare a film by dry mixing and preheating core-shell composite microspheres with lithium bis(fluorosulfonyl)imide, followed by hot pressing and vacuum drying. This method is primarily used to achieve, fix, or amplify the aforementioned synergistic effects. Instead of simply mixing lithium salt into a polymer system, this method first provides composite microspheres with a core and a cross-linked shell. Preheating reduces mixing resistance, and hot pressing allows the microspheres to accumulate and distribute with the lithium salt to form a continuous film. Subsequent vacuum drying controls residual N,N-dimethylformamide and water content. Compared to conventional processes that individually increase temperature, pressure, or lithium salt ratio, this approach utilizes the coordination between the feeding sequence, film-forming pressure, hot-pressing temperature, and drying conditions to reduce the adverse effects of improved processing fluidity on electrochemical stability. This ensures the product maintains a relatively stable structural state and a solid foundation for quality control in all-solid-state lithium secondary battery applications.

[0024] Polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres primarily serve as membrane support and the membrane-forming framework. While their use alone or in excessive proportions helps maintain structural integrity, insufficient interfacial constraint or uneven lithium salt distribution may limit effective ion conduction. The cross-linked shell formed by polyvinyl alcohol, polyethylene glycol diglycidyl ether, boric acid, and lithium hydroxide monohydrate, along with lithium difluorosulfonyl imide, mainly improves the interfacial lithiophilic environment and ion source. However, their individual enhancement or excessive proportions may lead to softening, hygroscopicity, localized salt enrichment, or decreased processing stability. This invention achieves a balance between the support contribution of the core microspheres and the conduction contribution of the shell and lithium salt by controlling the core-shell spatial distribution, shell thickness, matching lithium salt content, and the hot-pressing film-forming sequence, ultimately resolving the inherently contradictory performance.

[0025] Beneficial technical effects 1. This invention uses polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres as support units and constructs a cross-linked shell layer on their surface, so that the rigid support in the membrane no longer depends solely on the overall cross-linking deepening, which helps to reduce the ion conduction loss caused by the restriction of chain segment movement, thereby improving the contradiction between mechanical strength and ion migration.

[0026] 2. This invention uses polyvinyl alcohol, polyethylene glycol diglycidyl ether, boric acid, and lithium hydroxide monohydrate to form a cross-linked shell. By controlling the state of the precursor liquid through pH value and feed amount, the shell coating is more conducive to maintaining continuity and composition controllability, thereby providing a quality control basis for batch consistency of core-shell composite microspheres.

[0027] 3. This invention forms a film by dry mixing, preheating, hot pressing, and vacuum drying of core-shell composite microspheres and lithium difluorosulfonyl imide at a specific mass ratio. This avoids the residual polar solvent control pressure caused by simple solution casting, which helps to reduce the impact of residual N,N-dimethylformamide and water content on the stability of the membrane product while maintaining the processing fluidity.

[0028] 4. This invention uses transmission electron microscopy cross-sectional observation, thermogravimetric analysis, headspace gas chromatography, and Karl Fischer titration as structural and quality control methods, which allows the particle size of the core microspheres, shell thickness, shell mass fraction, residual solvent, and water content to be objectively recorded. This is beneficial for improving the sufficiency of disclosure in the specification and the reproducibility of product implementation. Attached Figure Description

[0029] Figure 1 This figure shows the effect of changing only the lithium bis(fluorosulfonyl)imide content on room temperature ionic conductivity and tensile strength, based on a fixed median parameter.

[0030] Figure 2 This diagram illustrates the effect of changing the cross-linked shell content on room temperature ionic conductivity and tensile strength, using fixed median parameters as a baseline.

[0031] Figure 3 This diagram illustrates the effect of changing the hot-pressing temperature on room temperature ionic conductivity and tensile strength, based on fixed median parameters.

[0032] Figure 4 This diagram illustrates the effect of this scheme, based on fixed median parameters, on room temperature ionic conductivity and tensile strength by only changing the homogenization rotation speed.

[0033] Figure 5 The image shows the particle size difference distribution of the composite microspheres in Example 1 and Comparative Example 11.

[0034] Figure 6 The cumulative particle size distribution diagrams of the composite microspheres in Example 1 and Comparative Example 11 are shown.

[0035] Figure 7 This is a verification diagram of the differential particle size distribution of the composite microspheres in Example 1 and Comparative Example 11.

[0036] Figure 8 The image shows the scatter plot of the continuous shell coverage of Example 1, Comparative Example 9, and Comparative Example 11.

[0037] Figure 9 The TGA residual mass curves of core-shell composite microspheres in Example 1, Comparative Example 5, and Comparative Example 11 are shown.

[0038] Figure 10 The graphs show the mass loss rate curves of DTG for core-shell composite microspheres in Examples 1, 5, and 11.

[0039] Figure 11 The Nyquist plots for the lithium / electrolyte membrane interface are shown for Example 1, Comparative Example 6, and Comparative Example 9.

[0040] Figure 12 The tensile stress-strain curves of the electrolyte membranes in Examples 1, 10, and 11 are shown.

[0041] Figure 13 The graphs show the LSV oxidation stability curves of the electrolyte membranes in Examples 1, 7, and 8.

[0042] Figure 14 The image shows the scatter plot of the film integrity rate of hot pressing in Examples 1, 7, 10 and 11.

[0043] Figure 15 The following are headspace gas chromatograms of residual DMF from Examples 2, 1, and 8.

[0044] Figure 16 The scatter plot shows the Karl Fischer water content mean values ​​for Example 2, Example 1, and Comparative Example 8.

[0045] Figure 17This is a comparison of macroscopic optical photographs of the final product of Example 1 and the final product of Comparative Example 11; wherein, Figure 17 In the image, 'a' is a macroscopic optical photograph of the polymer-based solid electrolyte membrane from Example 1. Figure 17 b in the image is a macroscopic optical photograph of the final product of Comparative Example 11.

[0046] Figure 18 The images show a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 11; wherein, Figure 18 In the image, 'a' is a low-magnification SEM image of the final product of Example 1; Figure 18 b in the image is a low-magnification SEM image of the final product of Comparative Example 11; Figure 18 In the image, c represents the magnified SEM image of the final product from Example 1; Figure 18 In the image, d represents the magnified SEM image of the final product in Comparative Example 11; Figure 18 In the image, 'e' represents a high-magnification SEM image of the final product from Example 1. Figure 18 f in the image is a high-magnification SEM image of the final product of Comparative Example 11.

[0047] Figure 19 The images show a comparison of the TEM structures of the final product of Example 1 and the final product of Comparative Example 11; where, Figure 19 In the image, 'a' is a bright-field TEM image of the final product of Example 1; Figure 19 b in the image is the bright-field TEM image of the final product of Comparative Example 11; Figure 19 c in the image is the HRTEM image of the final product of Example 1; Figure 19 In the image, d represents the HRTEM image of the final product of Comparative Example 11; Figure 19 In this context, 'e' represents the final product SAED and its elemental distribution results from Example 1. Figure 19 f in the figure represents the final product SAED and elemental distribution results of Comparative Example 11.

[0048] Figure 20 Macroscopic images of the preparation process of core-shell microspheres and core-shell composite microspheres; among them, Figure 20 a and Figure 20 In this context, 'c' represents the liquid system used in the preparation process. Figure 20 b and Figure 20 In this context, d represents the corresponding dried powder sample. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0050] Example 1 S1: Preparation of polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres. 100.0 g of commercially available battery-grade polyvinylidene fluoride-hexafluoropropylene copolymer with a melt index of 3 g / 10 min was used as the starting material. 2.0 g of commercially available polyvinylpyrrolidone (PVP) with a K value of 16 was weighed. The above two raw materials were added to 700.0 g of commercially available anhydrous N,N-dimethylformamide and stirred at 500 rpm for 1 h under closed stirring conditions at 40°C, normal pressure, and in the absence of air, to obtain a clear and homogeneous solution. The acceptance criterion was the absence of visible gel and undissolved particles in the solution.

[0051] S2: Deionized water and a 95 vol% ethanol aqueous solution were mixed at a volume ratio of 70:30 to form an antisolvent. The homogeneous solution obtained in S1 was added dropwise to the antisolvent at 20°C for 30 min, with continuous stirring at 500 rpm during the addition. After the addition was completed, stirring was continued for 0.5 h. The resulting suspension was centrifuged, washed once with deionized water, and vacuum dried at 40°C for 4 h to obtain polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres. The drying endpoint was determined by a mass change of no more than 0.2 wt% between two consecutive weighings.

[0052] S3: Preparation of cross-linking shell precursor solution. Weigh 100.0g of commercially available polyvinyl alcohol (PVA) with a degree of alcoholysis of 98.0 mol%. Use a 4wt% aqueous solution as the test sample. Measure the viscosity of the aqueous solution at 20℃ using a rotational viscometer; the PVA is added to 800.0g of deionized water and stirred at 600rpm for 0.5h at 85℃. The pass criterion is the absence of visible gel particles and undissolved solids in the solution. After cooling to 25℃, add 5.0g of commercially available polyethylene glycol diglycidyl ether with a number average molecular weight of 1500, 2.0g of commercially available analytical grade boric acid, and 1.0g of commercially available battery-grade lithium hydroxide monohydrate sequentially. Stir for 20min and adjust the pH to 8.0 to obtain the cross-linking shell precursor solution. The quality control parameters recorded based on the amount of raw materials are as follows: relative to 100.0g of polyvinyl alcohol, the amount of polyethylene glycol diglycidyl ether is 5.0g, the amount of boric acid is 2.0g, and the amount of lithium hydroxide monohydrate is 1.0g.

[0053] S4: Construction of core-shell composite microspheres. 100.0 g of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres obtained in S2 were weighed and dispersed in 200.0 g of 95 vol% ethanol aqueous solution, pre-dispersed at 3000 rpm for 5 min. 20.0 g of the cross-linked shell precursor solution obtained in S3 was added dropwise to the dispersion over 10 min, followed by homogenization at 3000 rpm for 5 min and stirring at 400 rpm for 1 h at 25 °C. The resulting product was centrifuged, washed once with 95 vol% ethanol aqueous solution, and vacuum dried at 40 °C for 4 h to obtain the core-shell composite microspheres.

[0054] S5: Hot-pressing film formation. 90.0 g of the core-shell composite microspheres obtained from S4 and 10.0 g of commercially available battery-grade lithium bis(fluorosulfonyl)imide were weighed and dry-mixed for 15 min in a dry environment to obtain a uniform powder. The mixture was preheated at 60°C for 0.5 h, then placed in a flat hot-press mold and hot-pressed at 95°C and 3 MPa for 3 min to form a film. The film was then vacuum-dried at 60°C for 6 h to obtain a polymer-based solid electrolyte membrane. After cooling to 25°C, the membrane was cut into sheet samples. The appearance acceptance criteria were continuous membrane surface, no obvious cracks, and no visible salt precipitation points.

[0055] Quality testing methods and results. Core-shell composite microspheres obtained from S4 were resin-embedded and ultrathin sections were prepared. Cross-sectional observation was performed using transmission electron microscopy, with at least 100 particles counted. The average particle size of the core microspheres was 160 nm, the average particle size of the core-shell composite microspheres was 200 nm, and the average thickness of the cross-linked shell layer was 10 nm, indicating a continuous coating state. Another batch of core-shell composite microspheres from the same batch underwent thermogravimetric analysis under a nitrogen atmosphere at a heating rate of 10 °C / min. The calculated cross-linked shell layer content was 5.0 wt%, and the polyvinylidene fluoride-hexafluoropropylene copolymer core microsphere content was 95.0 wt%. Membrane sample thickness was measured at five locations using a micrometer, with an average thickness of 18 μm. Residual N,N-dimethylformamide content was determined by headspace gas chromatography, with an external standard conversion result of 0.50 wt%. Water content was determined by Karl Fischer titration, with a result of 0.50 wt%.

[0056] Features and application scenarios of this embodiment. This embodiment adopts a relatively conservative low-ratio scheme and mild film-forming conditions. The particle size of the core-shell composite microspheres, the thickness of the cross-linked shell layer, and the film thickness are all in the low value range. The lithium bis(fluorosulfonyl)imide content is low, making it suitable for the preparation of all-solid-state lithium secondary battery electrolyte membranes that require thin film flexibility, low salt content, and mild hot-pressing conditions.

[0057] Example 2 Raw materials and proportions In this embodiment, 100.0 g of commercially available battery-grade polyvinylidene fluoride-hexafluoropropylene copolymer was used as the core microsphere matrix, and the melt index of the polyvinylidene fluoride-hexafluoropropylene copolymer was 8 g / 10 min; 10.0 g of commercially available polyvinylpyrrolidone was used as the dispersing auxiliary component, and the K value of the polyvinylpyrrolidone was 18; 100.0 g of commercially available polyvinyl alcohol was used as the shell material, and the degree of alcoholysis of the polyvinyl alcohol was 99.0 mol%. The viscosity of the 4 wt% aqueous solution was measured to be 30.0 mPa·s at 20 °C using a rotational viscometer; polyethylene glycol diglycidyl ether was a commercially available product with a number average molecular weight of 2500; boric acid, lithium hydroxide monohydrate, and lithium difluorosulfonyl imide were all commercially available battery or analytical grade raw materials.

[0058] Preparation process 100.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer and 10.0 g of polyvinylpyrrolidone were added to 1500.0 g of N,N-dimethylformamide and stirred at 800 rpm for 4 h at 60 °C to obtain a homogeneous solution. A 95 vol% ethanol aqueous solution was mixed with deionized water at a volume ratio of 95:5 as an antisolvent, and the homogeneous solution was added dropwise to the antisolvent at 35 °C over 60 min, with stirring at 1500 rpm during the addition. After the addition was completed, stirring was continued for 2 h. The resulting suspension was centrifuged, washed three times with deionized water, and vacuum dried at 60 °C for 12 h to obtain polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres.

[0059] Post-processing 100.0 g of polyvinyl alcohol was added to 1500.0 g of deionized water, kept at 95 °C for 2 h and stirred until clear. After cooling to 40 °C, 25.0 g of polyethylene glycol diglycidyl ether, 12.0 g of boric acid, and 10.0 g of lithium hydroxide monohydrate were added sequentially, and the pH was adjusted to 9.5 to obtain the cross-linking shell precursor solution. The quality control parameters recorded according to the feed amount were: relative to 100.0 g of polyvinylidene fluoride, the feed amount of polyethylene glycol diglycidyl ether was 25.0 g, the feed amount of boric acid was 12.0 g, and the feed amount of lithium hydroxide monohydrate was 10.0 g. 100.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres were dispersed in 800.0 g of ethanol aqueous solution with a volume fraction of 95 vol%, and 150.0 g of cross-linking shell precursor solution was added dropwise. The mixture was homogenized at 10000 rpm for 20 min and stirred at 45 °C for 4 h. The obtained product was centrifuged, washed three times with an ethanol aqueous solution with a volume fraction of 95 vol%, and vacuum dried at 60 °C for 12 h to obtain core-shell composite microspheres.

[0060] Film formation process 75.0 g of core-shell composite microspheres and 25.0 g of lithium bis(fluorosulfonyl)imide were dry-mixed for 20 min, with the mixing endpoint being uniform powder color and flowability. The dry mixture was preheated at 80 °C for 2 h, then hot-pressed at 125 °C and 8 MPa for 10 min, followed by vacuum drying at 80 °C for 12 h to obtain a polymer-based solid electrolyte membrane. After hot pressing, the membrane was cooled to 25 °C in a dry environment before dimensional cutting and quality inspection.

[0061] Quality testing methods and results The cross-section of the core-shell composite microspheres was observed using transmission electron microscopy (TEM). At least 100 particles were counted. The average particle size of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres was 500 nm, and the average particle size of the core-shell composite microspheres was 600 nm. The average thickness of the cross-linked shell layer was 40 nm, and the shell layer continuously covered the surface of the core microspheres. Thermogravimetric analysis (TGA) was performed under a nitrogen atmosphere, and the calculated cross-linked shell layer content was 20.0 wt%, and the polyvinylidene fluoride-hexafluoropropylene copolymer core microsphere content was 80.0 wt%. The average thickness of the polymer-based solid electrolyte membrane was 35 μm, and the lithium difluorosulfonyl imide content was 25.0 wt%. The residual N,N-dimethylformamide content was determined to be 0.08 wt% by headspace gas chromatography, and the water content was determined to be 0.08 wt% by Karl Fischer titration.

[0062] Features of the solution in this embodiment This embodiment adopts an optimized scheme with a relatively high load. The particle size of the core-shell composite microspheres, the thickness of the cross-linked shell, the content of the cross-linked shell, the lithium bis(fluorosulfonyl)imide content, and the hot-pressing strength are all in the high value range. It is suitable for all-solid-state lithium secondary battery electrolyte membrane applications that require membrane structure support, preparation of thicker membrane layers, and higher lithium salt content.

[0063] Example 3 The key parameters and sample form of this embodiment are as follows: the melt index of the polyvinylidene fluoride-hexafluoropropylene copolymer is 5 g / 10 min, the K value of polyvinylpyrrolidone is 17, the degree of alcoholysis of polyvinyl alcohol is 98.5 mol%, the viscosity of a 4 wt% aqueous solution of polyvinyl alcohol at 20°C is 25.0 mPa·s, and the number-average molecular weight of polyethylene glycol diglycidyl ether is 2000. The target product form is a sheet-like polymer-based solid electrolyte membrane. The total amount of the dry mixture before film formation is 100.0 g, and a single membrane sample with an area of ​​200 cm² is prepared by hot pressing a sample taken from the dry mixture.

[0064] Polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres were prepared as follows: 100.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer and 6.0 g of polyvinylpyrrolidone were added to 1100.0 g of N,N-dimethylformamide and stirred at 700 rpm for 2.5 h at 55 °C to obtain a homogeneous solution; this homogeneous solution was added dropwise to an antisolvent formed by mixing deionized water and ethanol aqueous solution with a volume ratio of 85:15 at 28 °C and a stirring speed of 1000 rpm. After the addition was completed, stirring was continued for 1.2 h; then centrifugation, washing twice with deionized water, and vacuum drying at 50 °C for 8 h were performed to obtain polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres with an average particle size of 300 nm.

[0065] The preparation process of the cross-linking shell precursor solution was as follows: 100.0 g of polyvinyl alcohol was added to 1100.0 g of deionized water and kept at 90℃ for 1.2 h. After cooling to 32℃, 15.0 g of polyethylene glycol diglycidyl ether, 7.0 g of boric acid, and 6.0 g of lithium hydroxide monohydrate were added. The mixture was stirred at 600 rpm for 30 min and the pH was adjusted to 8.8. The quality control parameters recorded according to the feed amounts were: relative to 100.0 g of polyvinyl alcohol, the feed amount of polyethylene glycol diglycidyl ether was 15.0 g, the feed amount of boric acid was 7.0 g, and the feed amount of lithium hydroxide monohydrate was 6.0 g. The pH value was measured after adding polyethylene glycol diglycidyl ether, boric acid, and lithium hydroxide monohydrate and stirring evenly.

[0066] The construction process of the core-shell composite microspheres was as follows: 100.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres were dispersed in 500.0 g of ethanol aqueous solution with a volume fraction of 95 vol%, and then 90.0 g of crosslinking shell precursor solution was added dropwise. The mixture was homogenized at 6500 rpm for 12 min and stirred at 500 rpm for 2.5 h at 35 °C. The resulting product was centrifuged, washed twice with ethanol aqueous solution with a volume fraction of 95 vol%, and vacuum dried at 50 °C for 8 h to obtain the core-shell composite microspheres.

[0067] During film formation, 82.0 g of core-shell composite microspheres and 18.0 g of lithium bis(fluorosulfonyl)imide were added to a dry mixing container and mixed for 18 min. After preheating at 70 °C for 1.2 h, the mixture was transferred to a hot press mold and hot-pressed at 110 °C and 5 MPa for 6 min, followed by vacuum drying at 70 °C for 9 h. The resulting polymer-based solid electrolyte membrane was cooled and cut with a clean cutter. The membrane sheets were placed in a desiccator for 2 h before testing.

[0068] Quality testing methods and results. Transmission electron microscopy (TEM) cross-sectional observation showed that the average particle size of the polyvinylidene fluoride (PVDF)-hexafluoropropylene (HFT) copolymer core microspheres was 300 nm, the average particle size of the core-shell composite microspheres was 360 nm, and the average thickness of the cross-linked shell layer was 25 nm, with good shell layer continuity. Thermogravimetric analysis under nitrogen atmosphere showed that the cross-linked shell layer content was 12.0 wt%, and the PVDF-HFT copolymer core microsphere content was 88.0 wt%. The film thickness was 26 μm, and the lithium difluorosulfonamide content was 18.0 wt%. Headspace gas chromatography determined the residual N,N-dimethylformamide content to be 0.20 wt%, and Karl Fischer titration determined the water content to be 0.24 wt%. Thickness measurements were taken at no fewer than 5 points for each sample, and solvent and water content measurements were performed on 3 samples each.

[0069] This embodiment is applicable to a specific scenario. It employs medium particle size, medium shell thickness, and medium hot-pressing conditions, making it suitable for demonstrating feasibility over a wide process window. This approach balances the efficiency of core-shell composite microsphere dispersion, dry mixing film formation, and vacuum drying, making it suitable for the preparation of all-solid-state lithium secondary battery electrolyte membranes where a balance needs to be struck between film thickness, lithium salt content, and hot-pressing conditions.

[0070] Example 4 I. Preparation Object and Raw Material State: 100.0g of commercially available battery-grade polyvinylidene fluoride-hexafluoropropylene copolymer was used as the core microsphere matrix, with a melt index of 4g / 10min; 8.0g of commercially available polyvinylpyrrolidone was used as the dispersing auxiliary component, with a K value of 16.5; polyvinyl alcohol was a commercially available raw material with a degree of alcoholysis of 98.8mol% and a viscosity of 28.0mPa·s for a 4wt% aqueous solution at 20℃; polyethylene glycol diglycidyl ether was a commercially available raw material with a number average molecular weight of 2200; boric acid, lithium hydroxide monohydrate, lithium difluorosulfonyl imide, N,N-dimethylformamide, deionized water, and an ethanol aqueous solution with a volume fraction of 95vol% were all commercially available raw materials.

[0071] II. Preparation of Core Microspheres: 100.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer and 8.0 g of polyvinylpyrrolidone were added to 900.0 g of N,N-dimethylformamide and stirred at 650 rpm for 3 h at 45 °C to form a homogeneous solution. This homogeneous solution was then added dropwise to an antisolvent prepared by mixing deionized water and ethanol aqueous solution with a volume ratio of 90:10 (95 vol%), and stirred at 750 rpm for 1.5 h at 25 °C. The resulting polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres were centrifuged, washed three times with deionized water, and vacuum dried at 45 °C for 10 h.

[0072] III. Preparation of Crosslinking Shell Precursor Solution: Dissolve 100.0g of polyvinyl alcohol in 1300.0g of deionized water, maintain at 88℃ for 1.8h, cool to 38℃, then add 20.0g of polyethylene glycol diglycidyl ether, 10.0g of boric acid, and 8.0g of lithium hydroxide monohydrate. Adjust the pH to 9.2 to obtain the crosslinking shell precursor solution. The quality control parameters recorded according to the feed amounts are as follows: relative to 100.0g of polyvinyl alcohol, the feed amount of polyethylene glycol diglycidyl ether is 20.0g, the feed amount of boric acid is 10.0g, and the feed amount of lithium hydroxide monohydrate is 8.0g.

[0073] IV. Construction of Core-Shell Structure: 100.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres were dispersed in 650.0 g of ethanol (95 vol%) aqueous solution. 120.0 g of crosslinking shell precursor solution was added dropwise to the resulting dispersion. The mixture was homogenized at 8500 rpm for 18 min and stirred at 40 °C for 3.5 h. The resulting product was centrifuged, washed twice with ethanol (95 vol%) aqueous solution, and vacuum dried at 55 °C for 10 h to obtain core-shell composite microspheres.

[0074] V. Hot-pressing and Drying: 78.0 g of core-shell composite microspheres and 22.0 g of lithium bis(fluorosulfonyl)imide were dry-mixed for 20 min. After dry mixing, the mixture was preheated at 75 °C for 1.5 h, and then hot-pressed at 120 °C and 7 MPa for 8 min to form a film. The hot-pressed film was then transferred to a vacuum drying environment and dried at 75 °C for 10 h to obtain a polymer-based solid electrolyte membrane. After drying, the membrane was cooled to 25 °C and sealed for storage, and equilibrated for 30 min before detection.

[0075] Quality testing methods and results. Transmission electron microscopy (TEM) cross-section observation and statistical analysis of no fewer than 100 particles revealed that the average particle size of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres was 420 nm, the average particle size of the core-shell composite microspheres was 520 nm, and the average thickness of the cross-linked shell layer was 35 nm, with the shell layer continuously covering the surface of the core microspheres. Nitrogen atmosphere thermogravimetric analysis showed that the cross-linked shell layer content was 16.0 wt%, and the polyvinylidene fluoride-hexafluoropropylene copolymer core microsphere content was 84.0 wt%. The membrane sample thickness was 32 μm, and the lithium difluorosulfonamide content was 22.0 wt%. Headspace gas chromatography determined the residual N,N-dimethylformamide content to be 0.12 wt%, and Karl Fischer titration determined the water content to be 0.15 wt%.

[0076] The process features and application directions of this embodiment. This embodiment adopts relatively high load and strong hot-pressing conditions, while maintaining the core-shell composite microsphere particle size, cross-linked shell thickness, and lithium salt content in a relatively high range. It is suitable for all-solid-state lithium secondary battery applications with high requirements for film thickness, structural stability, and battery assembly tolerance.

[0077] Comparative Example 1: Basically the same as Example 1, except that in step S1, 100.0g of commercially available battery-grade polyvinylidene fluoride-hexafluoropropylene copolymer was replaced with 100.0g of commercially available battery-grade polyvinylidene fluoride homopolymer, the melt index was 3g / 10min, and other conditions remained unchanged.

[0078] Comparative Example 2: It is basically the same as Example 1, except that the amount of commercially available polyvinylpyrrolidone added in step S1 is adjusted from 2.0g to 0.5g, the K value of polyvinylpyrrolidone is still 16, and other conditions remain unchanged.

[0079] Comparative Example 3: It is basically the same as Example 1, except that in step S2, the volume ratio of deionized water to ethanol aqueous solution with a volume fraction of 95 vol% is adjusted from 70:30 to 60:40, while other conditions remain unchanged.

[0080] Comparative Example 4: It is basically the same as Example 1, except that in step S4, after adding 20.0g of cross-linked shell precursor liquid to the dispersion, the homogenization speed is adjusted from 3000rpm to 1500rpm, the homogenization time is still 5min, and other conditions remain unchanged.

[0081] Comparative Example 5: It is basically the same as Example 1, except that the amount of cross-linking shell precursor solution added in step S4 is adjusted from 20.0g to 10.0g, the addition time is still 10min, and other conditions remain unchanged.

[0082] Comparative Example 6: It is basically the same as Example 1, except that in step S5, 95.0g of the core-shell composite microspheres obtained in S4 and 5.0g of commercially available battery-grade lithium bisfluorosulfonylimide are weighed and dry-mixed. The dry-mixing time is still 15min, and other conditions remain unchanged.

[0083] Comparative Example 7: It is basically the same as Example 1, except that in step S5, the hot pressing temperature is adjusted from 95°C to 85°C, the hot pressing pressure is still 3MPa, the hot pressing time is still 3min, and other conditions remain unchanged.

[0084] Comparative Example 8: It is basically the same as Example 1, except that the vacuum drying time after hot pressing film formation in step S5 is adjusted from 6h to 3h, the vacuum drying temperature is still 60℃, and other conditions remain unchanged.

[0085] Comparative Example 9: Essentially the same as Example 1, except that steps S3 and S4 (preparation of the crosslinking shell precursor solution and construction of the core-shell composite microspheres) were omitted. In step S5, 90.0 g of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres obtained in step S2 and 10.0 g of commercially available battery-grade lithium difluorosulfonylimide were directly weighed, dry-mixed, preheated, hot-pressed, and vacuum-dried, while other conditions remained unchanged. This comparative example was used to verify the synergistic effect of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres and the crosslinking shell.

[0086] Comparative Example 10: Essentially the same as Example 1, except that the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres were not added; only the cross-linked shell precursor liquid system obtained in step S3 was retained. The cross-linked shell precursor liquid obtained in step S3 was vacuum dried at 40°C for 4 hours and then pulverized and sieved. 90.0 g of the obtained cross-linked shell material was dry-mixed with 10.0 g of commercially available battery-grade lithium difluorosulfonylimide, preheated, hot-pressed, and vacuum-dried, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres and the cross-linked shell.

[0087] Comparative Example 11: This example is essentially the same as Example 1, except that the step of adding the cross-linking shell precursor liquid dropwise to the polyvinylidene fluoride-hexafluoropropylene copolymer core microsphere dispersion and homogenizing it to form a core-shell interface in step S4 is omitted. The cross-linking shell precursor liquid obtained in step S3 is vacuum dried at 40°C for 4 hours, pulverized, and sieved. 85.5g of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres obtained in step S2, 4.5g of the obtained cross-linking shell material, and 10.0g of commercially available battery-grade lithium bis(fluorosulfonyl)imide are directly dry-mixed and then hot-pressed into a film, with other conditions remaining unchanged. This comparative example is used to verify the synergistic effect between the core-shell interface construction method and the hot-pressing film formation of lithium bis(fluorosulfonyl)imide.

[0088] Characterization and performance testing: The room-temperature ionic conductivity of polymer-based solid electrolyte membranes was tested to evaluate their ion conduction performance. The sample was a circular membrane vacuum-dried at 60℃. The membrane was sandwiched between two stainless steel blocking electrodes and equilibrated for 2 hours at 25℃ and a dew point ≤ -40℃. Electrochemical impedance spectroscopy was used at 1MHz-0.1Hz with a perturbation voltage of 10mV. The high-frequency intercept resistance was read, and the conductivity was calculated based on the membrane thickness and effective area. For n=3, the average and standard deviation were recorded. The corresponding data recording fields are the average room-temperature ionic conductivity and the standard deviation of room-temperature ionic conductivity, in mS / cm. Higher values ​​indicate better ion conduction performance.

[0089] The tensile properties test of polymer-based solid electrolyte membranes is used to evaluate the membrane's strength and flexibility. Samples are cut into dumbbell or strip shapes and equilibrated for 24 hours at 23℃ and 50% relative humidity before testing. Membrane thickness is determined according to GB / T 6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets". Tensile conditions are set according to GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics Part 3: Test Conditions for Films and Sheets", with a tensile rate of 50 mm / min and n=5. The corresponding fields for this experiment are the average tensile strength, standard deviation of tensile strength, average elongation at break, and standard deviation of elongation at break, in MPa and %. Higher tensile strength and a reasonable elongation at break indicate better mechanical properties. The applicability of the standard version is based on the valid version on the actual test date.

[0090] The oxidation stability window test of polymer-based solid electrolyte membranes was used to evaluate electrochemical stability. Samples were vacuum-dried at 60℃ and then assembled into stainless steel sheet / electrolyte membrane / lithium-ion battery cells. After standing at 25℃ for 6 hours, linear sweep voltammetry was performed. The voltage range was 2.5–6.0 V, and the scan rate was 1 mV / s. The oxidation stability potential was defined as the potential at which the current density reached 0.05 mA / cm², with n=3. The corresponding fields for this experiment are the average oxidation stability potential and the standard deviation of the oxidation stability potential, in V. Higher values ​​indicate better electrochemical stability.

[0091] The hot-pressing processability test of polymer-based solid electrolyte membranes is used to evaluate the flow, spreading, and membrane continuity of powder mixtures under film-forming temperature and pressure. 100.0 g of dry-mixed powder is placed in a mold of fixed area and processed under the corresponding hot-pressing conditions in the examples. After cooling, images of the membrane surface are captured, and the thickness is measured at five locations. Image analysis is used to calculate the proportion of the crack-free continuous membrane area to the effective area of ​​the mold, and the thickness coefficient of variation is calculated. The corresponding fields for this experiment are the average film integrity rate, the standard deviation of the film integrity rate, the average thickness coefficient of variation, and the standard deviation of the thickness coefficient of variation, expressed in % and %. Higher film integrity rate and lower thickness coefficient of variation indicate better processability.

[0092] The lithium / electrolyte membrane interfacial impedance and lithium-ion transport number (LTU) tests were used to evaluate the interfacial compatibility of the membrane in all-solid-state lithium secondary batteries. A symmetrical battery was assembled by sandwiching a dried membrane between two lithium wafers. After standing at 25°C for 12 hours, the interfacial impedance was recorded using electrochemical impedance spectroscopy. Then, a 10mV DC polarization was applied, and the steady-state current was recorded. The LTU was calculated by combining the impedance before and after polarization, with n=3. The corresponding fields for this experiment are the average interfacial resistance, standard deviation of interfacial resistance, average LTU, and standard deviation of LTU, in units of Ω·cm² and dimensionless. Lower interfacial resistance and higher LTU indicate better interfacial transport performance.

[0093] The structural parameters of the core-shell composite microspheres were tested to confirm the particle size, shell thickness, and shell content. Dry microspheres were resin-embedded and ultrathinly sectioned. The cross-sections were observed using transmission electron microscopy (TEM). The particle size of the core microspheres, the particle size of the core-shell composite microspheres, the thickness of the cross-linked shell, and the shell continuity coverage were statistically analyzed for at least 100 particles. Separately, samples from the same batch were subjected to thermogravimetric analysis (TGA) at a nitrogen atmosphere with a heating rate of 10 °C / min. The shell mass fraction was calculated based on the difference in thermogravimetric loss between the polyvinylidene fluoride (PVDF)-hexafluoropropylene (HCF) copolymer core and cross-linked shell. The corresponding fields are composite microsphere particle size, cross-linked shell thickness, shell content, and shell continuity coverage, in nm, nm, wt%, and %. The composite microsphere particle size, core microsphere size, and cross-linked shell thickness were recorded separately for each statistical object; the statistical average of different particles was not used as the geometric pairing value for the same particle.

[0094] Residual N,N-dimethylformamide and moisture content tests are used for quality control. After sealing and weighing the membrane samples, DMF is detected by headspace gas chromatography using the external standard method. General chromatograph requirements are in accordance with GB / T 9722-2023 "General Rules for Gas Chromatography of Chemical Reagents". Moisture content is determined by Karl Fischer titration according to GB / T 6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method (General Method)", n=3. The corresponding fields are the average residual N,N-dimethylformamide, standard deviation of residual N,N-dimethylformamide, average moisture content, and standard deviation of moisture content, in wt%. Lower values ​​indicate better quality control. The applicability of the standard version is based on the valid version on the actual test date.

[0095] Figure 1 This diagram illustrates the effect of lithium bis(fluorosulfonyl)imide content on room temperature ionic conductivity and tensile strength in this design. Using fixed median parameters as a baseline, with a crosslinked shell content of approximately 12 wt%, a hot-pressing temperature of approximately 110°C, and a homogenization speed of approximately 6500 rpm, only the lithium bis(fluorosulfonyl)imide content was adjusted within the range of 8-30 wt%. Figure 1 It is evident that when the lithium salt content is too low, the number of migratable ions within the membrane is insufficient, limiting the room-temperature ionic conductivity. Conversely, when the lithium salt content is too high, although the ion source increases, it easily weakens the supporting effect of the polymer continuous phase and causes local salt enrichment, leading to a decrease in tensile strength. When the lithium salt content is approximately 16-21 wt%, both room-temperature ionic conductivity and tensile strength remain at optimal levels, indicating that a suitable lithium salt ratio can maintain the mechanical integrity of the membrane while providing ion conduction channels, thereby alleviating the contradiction between high conductivity and high strength.

[0096] Figure 2This diagram illustrates the effect of cross-linked shell content on room temperature ionic conductivity and tensile strength in this design. Using fixed median parameters as a baseline, with a lithium bis(fluorosulfonyl)imide content of approximately 18 wt%, a hot-pressing temperature of approximately 110°C, and a homogenization speed of approximately 6500 rpm, only the cross-linked shell content was varied, ranging from 3 to 24 wt%. Figure 2 It is evident that when the cross-linked shell content is too low, the interfacial constraint of the core-shell composite microspheres is insufficient, making it difficult to effectively improve the continuity and mechanical support of the intramembrane phase region; when the cross-linked shell content is too high, the cross-linked structure excessively restricts the movement of polymer chain segments, which is detrimental to lithium-ion migration. When the cross-linked shell content is approximately 11-14 wt%, the room temperature ionic conductivity and tensile strength reach a relatively balanced state, indicating that the cross-linked shell is not simply a reinforcing filler, but rather forms a synergy between mechanical support and ion transport through appropriate interfacial constraint.

[0097] Figure 3 This diagram illustrates the effect of hot-pressing temperature on room temperature ionic conductivity and tensile strength. Using fixed median parameters as a baseline, with a lithium bis(fluorosulfonyl)imide content of approximately 18 wt%, a cross-linked shell content of approximately 12 wt%, and a homogenization speed of approximately 6500 rpm, only the hot-pressing temperature was adjusted within the range of 85-135℃. Figure 3 It is evident that when the hot-pressing temperature is too low, the composite microspheres do not soften and fuse sufficiently, resulting in insufficient film density and interfacial contact, which affects both mechanical properties and the continuity of ion transport channels. When the hot-pressing temperature is too high, local structures may be over-compacted or thermally induced phase separation may occur, which is detrimental to maintaining stable conduction pathways. When the hot-pressing temperature is around 105-115℃, the film density, interfacial contact, and structural stability are well-matched, indicating that a moderate hot-pressing temperature is beneficial for improving film quality without compromising the advantages of the core-shell structure.

[0098] Figure 4 This diagram illustrates the effect of homogenization rotation speed on room temperature ionic conductivity and tensile strength in this design. Using fixed median parameters as a baseline, with a lithium bis(fluorosulfonyl)imide content of approximately 18 wt%, a cross-linked shell content of approximately 12 wt%, and a hot-pressing temperature of approximately 110 °C, only the homogenization rotation speed was varied, ranging from 2000 to 12000 rpm. Figure 4 It can be seen that when the homogenization speed is too low, the cross-linked shell precursor component does not adequately coat the core microspheres, resulting in poor dispersion uniformity of the composite microspheres. When the homogenization speed is too high, excessive shearing may damage the initially formed interface structure or cause fluctuations in particle size distribution. When the homogenization speed is around 6000-7500 rpm, the dispersion of the composite microspheres and the continuity of the film are better, indicating that moderate shearing helps to form a stable core-shell interface and provides uniform structural units for subsequent hot pressing film formation.

[0099] Figure 5 This is a particle size difference distribution diagram of the composite microspheres in Example 1 and Comparative Example 11 of this scheme. Figure 6This is a cumulative particle size distribution diagram of the composite microspheres in Example 1 and Comparative Example 11 of this scheme. Figure 5 and Figure 6 It can be seen that the particle size of the composite microspheres in Example 1 is mainly concentrated around 200 nm, with a narrow differential distribution and a steep rise in the cumulative distribution curve, indicating a high particle concentration near D50. In contrast, the particle size distribution of Comparative Example 11 is significantly wider, with a larger particle tail, indicating that the direct dry mixing method is more likely to cause particle agglomeration or uneven dispersion. The narrower particle size distribution means that the heating, pressure and contact behavior of each structural unit during hot pressing is more consistent, which is conducive to the formation of a uniform film layer and reduces the risk of local weaknesses, pores and salt enrichment from the source.

[0100] Figure 7 This is a verification diagram of the differential particle size distribution of the composite microspheres in Example 1 and Comparative Example 11. Figure 8 This is a scatter plot showing the mean of the shell coverage in Embodiment 1, Comparative Example 9, and Comparative Example 11 of this scheme. Figure 7 It can be seen that the composite microspheres in Example 1 have a more concentrated particle size distribution, while the composite microspheres in Comparative Example 11 have a wider particle size distribution; Figure 8 It can be seen that the shell continuity coverage of Example 1 is approximately 92.5%, which is significantly higher than that of samples without an effective shell or with discontinuous shells. These results show that the core-shell composite microspheres formed by cross-linking shell precursor droplet coating and homogenization can construct a continuous interface layer on the microsphere surface. This allows the reinforcement effect to no longer rely on disordered stacking, but rather to be dispersed within the membrane in a uniform coating form, thus providing a structural basis for balancing strength and ion conduction.

[0101] Figure 9 The above are TGA residual mass curves of core-shell composite microspheres in Example 1, Comparative Example 5, and Comparative Example 11 of this scheme. Figure 10 This is a graph showing the DTG mass loss rate of core-shell composite microspheres in Example 1, Comparative Example 5, and Comparative Example 11 of this scheme. (Source: [Insert Source Here]) Figure 9 and Figure 10 It can be seen that Example 1 exhibits relatively stable mass retention characteristics in the medium-high temperature range, with a relatively concentrated and stable DTG mass loss rate peak. Comparative Examples 5 and 11 show more pronounced changes in weight loss range and peak shape, indicating that their component binding and thermal decomposition processes are not uniform enough. These results demonstrate that continuous cross-linked shells not only improve the membrane structure at room temperature but also enhance the thermal stability of the composite microspheres during processing and use, enabling the membrane material to maintain a more reliable structure in hot-pressing and battery operating environments.

[0102] Figure 11 These are Nyquist plots of the lithium / electrolyte membrane interface from Example 1, Comparative Example 6, and Comparative Example 9 of this scheme. Figure 11It can be seen that the impedance semicircle diameter corresponding to Example 1 is smaller and the interface impedance is lower, indicating that there is more sufficient contact and smoother interfacial ion transport between lithium metal and the electrolyte membrane. The interface impedance of Comparative Examples 6 and 9 is significantly increased, indicating that when there is a lack of a suitable lithium salt ratio or continuous shell structure, the matching between the intramembrane conduction path and the lithium interface decreases. This result shows that the core-shell composite microspheres and lithium salt ratio in Example 1 can jointly improve the interfacial wetting contact and local ion distribution, which is beneficial to reducing the transport resistance of solid electrolyte membranes in actual electrochemical systems.

[0103] Figure 12 The images show the tensile stress-strain curves of the electrolyte membrane in Embodiment 1, Comparative Example 10, and Comparative Example 11 of this scheme. Figure 12 It can be seen that Example 1 has high tensile strength and moderate elongation at break, and can maintain good membrane integrity when subjected to external force; Comparative Example 10 has low strength, and Comparative Example 11 shows varying degrees of decrease in both toughness and strength. This result indicates that simply improving flexibility or using physical dry mixing cannot effectively solve the problem of insufficient membrane strength. However, Example 1, through a combination of core microsphere support, cross-linked shell interface constraint, and appropriate lithium salt plasticizing conduction, enables the membrane to have both necessary mechanical support and retain a certain degree of deformation adaptability.

[0104] Figure 13 This is a graph showing the LSV oxidation stability of the electrolyte membrane in Example 1, Comparative Example 7, and Comparative Example 8 of this scheme. (Source: [Insert Source Here]) Figure 13 It can be seen that Example 1 only shows a significant increase in oxidation current at a higher voltage region, while the oxidation current of Comparative Examples 7 and 8 increases earlier, indicating that Example 1 has better electrochemical oxidation stability. This result shows that appropriately controlling the lithium salt content, residual solvent, and water content, and reducing local enrichment and interface defects through a continuous shell, can reduce the risk of side reactions under high voltage conditions, allowing the membrane material to maintain good electrochemical stability while improving ion transport performance.

[0105] Figure 14 This is a scatter plot showing the average integrity rate of the hot-pressed film formed in Examples 1, 7, 10, and 11 of this scheme. Figure 14 It can be seen that the integrity rate of the hot-pressed film in Example 1 is approximately 93.2%, significantly higher than that of the comparative examples. This result indicates that the lithium salt ratio, core-shell composite microsphere structure, and hot-pressing process used in Example 1 have good compatibility, which can improve the flow, fusion, and support behavior of the powder or film system during the hot-pressing process. Compared with the approach of only increasing the degree of crosslinking or only increasing the flexible component, this method can simultaneously improve the processing stability and film structure integrity, further demonstrating that this scheme is suitable for preparing thin, continuous, and uniform polymer-based solid electrolyte membranes.

[0106] Figure 15The following are headspace gas chromatograms of residual DMF from Examples 2, 1, and 8 of this scheme. Figure 16 This is a scatter plot of the Karl Fischer moisture content average values ​​for Examples 2, 1, and 8 of this scheme. Figure 15 It can be seen that the DMF characteristic peak is lowest in Example 2, the residual DMF in Example 1 is at a controllable level, while the peak area of ​​Comparative Example 8 is larger, indicating that optimizing the drying conditions and formulation system can effectively reduce residual solvent. Figure 16 It can be seen that the water content of Example 2 is about 0.08 wt%, that of Example 1 is about 0.50 wt%, and that of Comparative Example 8 is about 0.68 wt%, further illustrating that moisture control has a significant impact on the stability of membrane materials. Excessive residual solvent and moisture will increase the risk of interfacial side reactions and electrochemical instability. Therefore, Example 2 further reduces the residual DMF and water content based on the structure of Example 1, which helps to improve the storage stability and electrochemical reliability of the electrolyte membrane.

[0107] Figure 17 This is a comparison of macroscopic optical photographs of the final product of Example 1 and the final product of Comparative Example 11. Figure 17 In Figure 'a', there is a macroscopic optical photograph of the polymer-based solid electrolyte membrane of Example 1. This membrane was prepared by hot pressing core-shell composite microspheres and lithium bis(fluorosulfonyl)imide at 95°C and 3MPa for 3 minutes. The average thickness is 18μm. The membrane surface is continuous, with no obvious cracks or visible salting-out points. This indicates that core-shell composite microspheres with an average particle size of about 200nm and a cross-linked shell thickness of about 10nm can form a complete film under mild hot pressing conditions. Figure 17 Figure b shows a macroscopic optical photograph of the final product of Comparative Example 11. This sample was formed by directly dry-mixing polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres, dry cross-linked shell material, and lithium bis(fluorosulfonyl)imide, followed by hot pressing. Because it lacked the pre-droplet coating of the cross-linked shell and the homogeneous construction of the core-shell interface, the film surface was more prone to localized roughness, uneven particle size, or salt enrichment defects. This comparison demonstrates that core-shell interface construction can directly improve the macroscopic integrity and uniformity of the film.

[0108] Figure 18 This is a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 11. Figure 18 In Figure 'a', the image is a low-magnification SEM image of the final product of Example 1, showing that the polymer-based solid electrolyte membrane with an average thickness of about 18 μm has a continuous surface or a uniform cross-section, indicating that the membrane layer is intact after hot pressing. Figure 18 b in the image is a low-magnification SEM image of the final product of Comparative Example 11, which shows that the direct dry-mix system is more prone to forming local agglomerates, pores, or uneven areas on the film surface, indicating that the lack of a continuous core-shell interface will weaken the uniformity of film formation over a large area. Figure 18c in the image is a magnified SEM image of the final product of Example 1, showing that the structural units inside the film are uniformly distributed and the phase regions are continuous, indicating that the approximately 200 nm core-shell composite microspheres form good interparticle contact during the hot pressing process. Figure 18 In the image d, which is a magnified SEM image of the final product of Comparative Example 11, it shows more obvious physical mixing traces and local phase separation between the core microspheres and the dry shell material, indicating that direct dry mixing is difficult to form a stable and continuous interface. Figure 18 In the image, 'e' is a high-magnification SEM image of the final product of Example 1, showing that the structural units of about 160-200 nm are relatively uniformly distributed, and no obvious salting-out particles or large-sized aggregates are observed locally. Figure 18 In Figure f, the final product of Comparative Example 11 is a high-magnification SEM image, showing that the shell material agglomerates, particle boundaries are discontinuous, or local microcracks are more obvious. The above SEM results show from the microscopic morphology level that the cross-linked shell introduced in a continuous coating state is more conducive to building a uniform intramembrane interface than physical dry mixing.

[0109] Figure 19 This is a comparison diagram of the TEM structure of the final product of Example 1 and the final product of Comparative Example 11. Figure 19 In Figure 'a', the final product of Example 1 is a bright-field TEM image, showing that the final film locally retains a core-shell interface structure composed of approximately 160 nm polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres and approximately 10 nm cross-linked shell layers, indicating that approximately 200 nm core-shell composite microspheres can provide continuous interface units for the hot-pressed film. Figure 19 b in the image is a bright-field TEM image of the final product of Comparative Example 11, which shows that the core microspheres and the dried cross-linked shell material are mainly in physical mixing contact, making it difficult to form a continuous coating layer. This indicates that canceling the coating homogenization step will destroy the spatial continuity of the core-shell interface. Figure 19 c in the image is the HRTEM image of the final product of Example 1, which shows that the local polymer crystal region and the cross-linked shell interface are relatively continuous, indicating that the core-shell structure is beneficial to reducing the disordered accumulation of the interface. Figure 19 In the image d, which is the HRTEM image of the final product of Comparative Example 11, it shows an increase in local interface discontinuities or amorphous agglomeration regions, indicating that physical mixing is not conducive to the formation of stable nano-interfaces. Figure 19 In the figure, 'e' represents the final product SAED and elemental distribution results of Example 1, showing that the polymer matrix and related elements of lithium bis(fluorosulfonylimide) are relatively uniformly distributed in local areas. Figure 19 In the figure, f represents the final SAED and elemental distribution results of Comparative Example 11, showing more pronounced local elemental enrichment or phase heterogeneity. Therefore, Example 1 achieves a synergistic effect of continuous nanostructure, uniform salt component dispersion, and stable intramembrane phase region through core-shell interface regulation. Figure 20It is evident that during the preparation of core-shell microspheres and core-shell composite microspheres, the resulting liquid systems exhibited a uniform dispersion, with no obvious stratification, flocculation, sedimentation, or large-scale gelation observed. Correspondingly, the dried samples were all uniformly shaped powders, without significant agglomeration, clustering, or phase separation. Figure 20 a and b in the figure indicate that polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres can be stably formed through the anti-solvent precipitation process, and the core microspheres can still maintain the powder morphology after centrifugation, washing and drying; Figure 20 Figures c and d further demonstrate that after adding the crosslinking shell precursor solution and homogenizing and stirring, the system remains stably dispersed, and the resulting core-shell composite microspheres remain uniform powder after drying. This indicates that the construction process of the crosslinking shell did not cause severe particle agglomeration or system instability. Combined with the transmission electron microscopy observation in Example 1, which showed an average particle size of 200 nm, an average crosslinking shell thickness of 10 nm, and a continuous shell coating, and the thermogravimetric analysis result showing a crosslinking shell content of 5.0 wt%, it can be proven that the antisolvent spheroidization, shell precursor solution coating crosslinking, and subsequent drying process used in this example can successfully obtain core-shell composite microspheres with stable structure, clear composition, and suitable for hot pressing film formation. This verifies the feasibility and correctness of this technical solution.

[0110] In conclusion, Figures 1 to 4 From the perspective of single factors in formulation and process, it can be seen that there are suitable matching ranges for lithium salt content, cross-linked shell content, hot pressing temperature and homogenization speed. Figures 5 to 10 Further evidence shows that this matching relationship can be transformed into core-shell composite microspheres with uniform particle size, continuous shell, and good thermal stability; Figures 11 to 16 The comprehensive performance of the final membrane material was verified from aspects such as interfacial impedance, mechanical properties, electrochemical stability, hot-pressing film integrity, and control of residual solvent and water content. Figures 17 to 20 Macroscopic photographs, SEM, and TEM morphology further demonstrate that the continuous core-shell interface improves film uniformity and internal phase distribution. These results collectively show that the proposed solution does not rely solely on reinforcement or plasticization to achieve performance enhancement, but rather achieves a more reasonable balance between mechanical strength, ion conductivity, processing fluidity, and electrochemical stability in the polymer-based solid electrolyte membrane through the synergistic effect of core-shell composite microspheres, cross-linked shells, lithium salt ratio, and hot-pressing process.

[0111] Table 1 Electrochemical performance Table 2 Mechanical / Film Formation / Shell Layer and Residual Properties As can be seen from the test trends of the examples and comparative examples in Tables 1 and 2, Examples 1-4 achieve a relatively balanced performance combination in core indicators such as ionic conductivity, tensile strength, oxidation stability potential, film integrity, interfacial resistance, and lithium-ion transference number. This indicates that the combination of core-shell composite microspheres, cross-linked shells, and lithium bis(fluorosulfonyl)imide can establish a continuous correlation around structural support, ion migration, and hot-pressing film formation. Comparative Examples 1-8, after changing the core material, dispersion auxiliary components, antisolvent ratio, homogenization speed, shell precursor solution dosage, lithium salt content, hot-pressing temperature, and drying time, mainly show that deviations in certain structural or process parameters lead to a decrease in the corresponding fields. Comparative Examples 9-11 further show that when the cross-linked shell is removed, only the cross-linked shell material is retained, or the core-shell interface construction method is disrupted, although some individual indicators may remain at a certain level, strength, film integrity, interfacial resistance, and stability are difficult to maintain simultaneously, reflecting the necessity of the synergistic unit to balance contradictory performance characteristics.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A polymer-based solid electrolyte membrane, characterized in that, The polymer-based solid electrolyte membrane comprises core-shell composite microspheres and lithium difluorosulfonyl imide, wherein the content of lithium difluorosulfonyl imide is 10-25 wt%, based on the total dry mass of the core-shell composite microspheres and the lithium difluorosulfonyl imide; the core-shell composite microspheres comprise polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres, and a cross-linked shell layer coated on the surface of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres, wherein the cross-linked shell layer is formed of polyvinyl alcohol, polyethylene glycol diglycidyl ether, boric acid and lithium hydroxide monohydrate.

2. The polymer-based solid electrolyte membrane according to claim 1, characterized in that, The core-shell composite microspheres have an average particle size of 200-600 nm, the cross-linked shell has an average thickness of 10-40 nm, and the polymer-based solid electrolyte membrane has a thickness of 18-35 μm. The average particle size of the core-shell composite microspheres and the average thickness of the cross-linked shell are obtained by statistically analyzing at least 100 particles in the resin-embedded section using transmission electron microscopy. The thickness of the polymer-based solid electrolyte membrane is obtained by multi-point mechanical measurement.

3. The polymer-based solid electrolyte membrane according to claim 1, characterized in that, The core-shell composite microspheres were prepared by the following steps: A1 provides the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres; A2, dissolve 100 parts by weight of polyvinyl alcohol in 800-1500 parts by weight of deionized water, keep at 85-95℃ for 0.5-2h, cool to 25-40℃, add 5-25 parts by weight of polyethylene glycol diglycidyl ether, 2-12 parts by weight of boric acid and 1-10 parts by weight of lithium hydroxide monohydrate, adjust the pH to 8.0-9.5 to obtain the cross-linking shell precursor solution; A3, disperse 100 parts by weight of the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres in 200-800 parts by weight of an ethanol aqueous solution with a volume fraction of 95 vol%, add 20-150 parts by weight of the crosslinking shell precursor liquid dropwise to the resulting dispersion, homogenize at 3000-10000 rpm for 5-20 min, and stir at 25-45℃ for 1-4 h; A4 was centrifuged, washed 1-3 times with an ethanol aqueous solution with a volume fraction of 95 vol%, and vacuum dried at 40-60℃ for 4-12 h to obtain the core-shell composite microspheres. The content of the cross-linked shell in the obtained core-shell composite microspheres is 5-20 wt%.

4. The polymer-based solid electrolyte membrane according to claim 3, characterized in that, The polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres in step A1 are prepared by the following steps: B1. Add 100 parts by weight of polyvinylidene fluoride-hexafluoropropylene copolymer and 2-10 parts by weight of polyvinylpyrrolidone to 700-1500 parts by weight of N,N-dimethylformamide, and stir at 40-60℃ for 1-4 hours to obtain a homogeneous solution. B2, the homogeneous solution is added dropwise to an antisolvent formed by mixing deionized water and an aqueous ethanol solution with a volume fraction of 95 vol% in a volume ratio of 70:30-95:5, and stirred at 500-1500 rpm for 0.5-2 h at 20-35°C; B3 was centrifuged, washed with deionized water 1-3 times, and vacuum dried at 40-60℃ for 4-12h to obtain the polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres. The average particle size of the polyvinylidene fluoride-hexafluoropropylene copolymer microspheres is 160-500 nm.

5. The polymer-based solid electrolyte membrane according to claim 3, characterized in that, The degree of alcoholysis of the polyvinyl alcohol used in step A2 is 98.0-99.0 mol%, the viscosity of the 4 wt% aqueous solution at 20°C is 20.0-30.0 mPa·s, and the number average molecular weight of the polyethylene glycol diglycidyl ether is 1500-2500.

6. The polymer-based solid electrolyte membrane according to claim 1, characterized in that, The polymer-based solid electrolyte membrane is prepared by dry mixing the core-shell composite microspheres with lithium bis(fluorosulfonyl)imide at a dry mass ratio of 90:10-75:25, preheating at 60-80℃ for 0.5-2h, hot pressing at 95-125℃ and 3-8MPa for 3-10min, and then vacuum drying at 60-80℃ for 6-12h.

7. The polymer-based solid electrolyte membrane according to claim 3, characterized in that, In the obtained core-shell composite microspheres, the content of polyvinylidene fluoride-hexafluoropropylene copolymer core microspheres is 80-95 wt%, and the balance is the cross-linked shell layer.

8. A method for preparing a polymer-based solid electrolyte membrane as described in any one of claims 1-7, characterized in that, Includes the following steps: S1, Core-shell composite microspheres are prepared and provided according to steps A1-A4 of claim 3; S2, mix the core-shell composite microspheres provided in step S1 with lithium bis(fluorosulfonyl imide) and hot-press them at 95-125℃ and 3-8MPa for 3-10 min to form a film; S3. The membrane obtained in step S2 is vacuum dried at 60-80°C for 6-12 hours to obtain the polymer-based solid electrolyte membrane.

9. The preparation method according to claim 8, characterized in that, In step S2, the dry mass ratio of the core-shell composite microspheres provided in step S1 to the lithium bis(fluorosulfonyl)imide is 90:10-75:25, and the mixture is preheated at 60-80°C for 0.5-2 hours after dry mixing.

10. The application of the polymer-based solid electrolyte membrane according to any one of claims 1-7 as a solid electrolyte layer in an all-solid-state lithium secondary battery.

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