Method for synchronously constructing and preparing solid electrolyte membrane through phase separation-amidation

Abstract

The invention discloses a method for synchronously constructing and preparing a solid electrolyte membrane through phase separation-amidation, and belongs to the technical field of electrochemical energy storage materials, and the method comprises the following steps: preparing a primary membrane by taking PVDF-HFP and a styrene-maleic anhydride copolymer as matrixes, and then completing phase separation and synchronous in-situ grafting on the primary membrane under the action of EDTA to obtain the solid electrolyte membrane. And finally, carrying out post-treatment and lithium salt loading to obtain the solid-state electrolyte membrane. The electrolyte membrane prepared by the invention has a three-dimensional interpenetrating network structure, not only endows the membrane with good mechanical strength and toughness, but also provides a rich pore structure, is beneficial to interface contact and ion transmission, inhibits dendritic crystal growth, and is suitable for the next generation of all-solid-state lithium batteries with high energy density and high safety; and particularly, the method has important application value in the fields of electric automobiles and portable electronic equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage materials, and relates to a method for preparing a solid-state electrolyte membrane by synchronous construction through phase separation-amination. BACKGROUND

[0002] With the rapid development of electric vehicles and portable electronic devices, there is an increasing demand for lithium ion batteries with high energy density and high safety. Traditional liquid lithium ion batteries have safety hazards such as leakage, combustion and explosion due to the use of organic electrolyte. Solid-state electrolyte is considered an ideal alternative solution to solve the above problems due to its non-flammability and no leakage.

[0003] Among various solid-state electrolytes, polymer-based electrolytes have attracted widespread attention due to their good film-forming property and flexibility. For example, a Chinese invention patent with the authorization announcement number CN106910939B discloses a preparation method of a high-conductivity lithium battery polymer electrolyte. Polyvinylidene fluoride (PVDF) is used as the matrix, polyvinylpyrrolidone (PVP) and ethylenediaminetetraacetic acid (EDTA) are physically blended as additives, and lithium salt is supplemented. Finally, a film is formed by solution casting and heat drying. This technology uses the electron-donating groups in PVP and EDTA to form hydrogen bonds with PVDF, destroy its crystalline structure, and promote the dissociation of lithium salt, thereby improving the ionic conductivity of the electrolyte to a certain extent.

[0004] However, this kind of physical blending method has obvious limitations. First, EDTA as a small molecule organic compound has poor compatibility and dispersibility in the polymer matrix (such as PVDF), and is prone to aggregation due to phase separation, resulting in uneven distribution in the film. This unevenness can make the distribution of functional sites (carboxyl and amine groups) present in a locally dense or sparse state, not only limiting the overall efficiency of its destruction of polymer crystallinity and promotion of lithium salt dissociation, but also more likely to become a bottleneck for ion transport and a cause of local current density unevenness, affecting the cycle stability and safety of the battery. Second, the additives and the polymer matrix in physical blending are mainly combined through weak intermolecular forces (such as hydrogen bonds), which may have the risk of interface instability or component loss under long-term cycling or stress, limiting its long-term electrochemical stability. In addition, existing methods usually focus on reducing crystallinity to improve ionic conductivity, but fail to systematically construct stable, continuous and functional ion transport channels in the polymer backbone, resulting in a low lithium ion transference number and limited performance improvement.

[0005] Therefore, there is an urgent need in the art to develop a method that can fundamentally solve the problem of dispersion uniformity and binding stability of functional additives (such as EDTA). The ideal method should be able to precisely and uniformly anchor the functional molecules in the polymer backbone through firm chemical bonding, thereby simultaneously constructing a stable three-dimensional porous physical structure and in-situ constructing a continuous, efficient and functional ion transport "highway", ultimately realizing the synergistic leap of solid-state electrolyte ionic conductivity, lithium ion transference number and mechanical / interface stability. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for synchronously constructing and preparing a solid-state electrolyte membrane through phase separation-amidation, so as to solve the problems of uneven dispersion and poor binding stability of functional additives added in the preparation process of the solid-state electrolyte.

[0007] The technical scheme is specifically as follows:

[0008] A method for synchronously constructing and preparing a solid-state electrolyte membrane through phase separation-amidation, comprising the following steps: preparing a nascent membrane with polyvinylidene fluoride-co-hexafluoropropylene and styrene-maleic anhydride copolymer as the matrix, then completing phase separation and synchronous in-situ grafting of the nascent membrane under the action of EDTA, and finally preparing a three-dimensional porous PVDF-HFP / SMA-EDTA solid-state electrolyte membrane through lithium salt loading.

[0009] The specific steps are as follows:

[0010] (1) Preparation of nascent membrane: weigh PVDF-HFP, styrene-maleic anhydride copolymer (SMA), water-insoluble diluent and organic solvent, mix them in a three-necked flask, continuously heat and stir until completely dissolved, and then obtain the casting solution after complete degassing by standing at room temperature; under room temperature conditions, cast the casting solution on a glass plate, control the thickness with a doctor blade, and scrape it into a flat wet film at a speed of 0.1 m / s-5 m / s;

[0011] (2) Phase separation and synchronous in-situ grafting: immediately immerse the nascent membrane prepared in step (1) in an EDTA aqueous solution with a concentration of 1%-5% to perform phase separation and solidification; the EDTA aqueous solution acts as a non-solvent to induce phase separation of the casting solution, forming a three-dimensional porous skeleton prototype; at the same time, it triggers the ring-opening reaction of the anhydride on the SMA chain as a Lewis base, generating SMA derivatives containing carboxyl groups, which undergo in-situ amidation reaction with the amine groups on the EDTA molecules, thereby grafting the EDTA molecules onto the polymer skeleton in the form of covalent bonds;

[0012] (3) Post-treatment and lithium salt loading: the membrane obtained in step (2) is immersed in deionized water to remove residual solvents, soaked for 24-48 h, and then taken out and dried to remove water, to obtain a three-dimensional porous membrane with a thickness of 10-100 μm; then it is immersed in an alcohol solution containing lithium salt, to extract the residual diluent and achieve loading and fixation of the lithium salt, and finally dried to obtain the solid-state electrolyte membrane.

[0013] Two key roles occur in this process:

[0014] a. Diluent replacement: the original water-insoluble diluent in the membrane obtained in step (2) is extracted by the alcohol solvent.

[0015] b. Lithium salt loading and chelation fixation: the lithium salt in the solution enters the porous structure of the membrane, and most importantly, the EDTA molecules pre-grafted on the skeleton, with multiple carboxyl and amine functional groups, can act as a high-efficiency "molecular anchor point" to actively capture lithium ions (Li⁺) through strong coordination (chelation), thereby achieving uniform and stable fixation of the lithium salt on the surface and in the bulk of the membrane.

[0016] Further, the PVDF-HFP in step (1) accounts for 10-25% of the total casting solution.

[0017] Further, the styrene-maleic anhydride copolymer accounts for 0.5-5% of the total casting solution.

[0018] Further, the diluent is poorly soluble with PVDF-HFP, and accounts for 5-25% of the total casting solution.

[0019] Further, the diluent is any one of dimethyl phthalate (DMP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), acetyl tri-butyl citrate (ATBC), and diphenyl ether (DPE).

[0020] Further, the organic solvent is one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide DMF, and N-methyl pyrrolidone NMP.

[0021] Further, the organic solvent accounts for 25-45% of the total casting solution.

[0022] Further, the continuous heating and stirring is at 40-80°C for 6-24 h.

[0023] Further, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the lithium salt concentration is 0.1-3%.

[0024] Further, the drying temperature is 30-50℃.

[0025] Invention principle: The core mechanism of the patent lies in developing a "diluent pore-forming-interfacial reaction grafting" one-step in-situ synchronous strategy. Among them, the water-immiscible diluent plays a dual role: at the physical level, as a pore-forming agent, it is trapped and then extracted in the water-induced composite thermal-induced phase separation process, thereby dominating the construction of three-dimensional macroscopic pores throughout the membrane body, providing a physical channel for ion transport; at the chemical level, its compatibility with the polymer regulates the phase separation kinetics, affecting the aggregation state of the polymer network, thereby indirectly providing a more optimal interfacial area and reaction site for the subsequent interfacial ring-opening-amidation reaction. On this basis, the EDTA aqueous solution not only serves as a non-solvent, but also as a Lewis base to trigger the SMA ring-opening, and the newly generated carboxyl group undergoes in-situ amidation reaction with the amine group of EDTA itself, thereby firmly and uniformly grafting EDTA with strong metal ion chelating ability to the surface of the newly generated pores in the form of a covalent bond, upgrading the physical pores to the "ion highway" with functionalized inner walls. Finally, during the subsequent alcohol solution extraction of the diluent and lithium salt loading process, the remaining pores are uniformly modified by the covalently fixed EDTA molecules and serve as efficient "molecular anchoring points", promoting the stable fixation of lithium salts on the membrane surface and in the matrix, ultimately forming a three-dimensional porous PVDF-HFP / SMA-EDTA / lithium salt solid-state electrolyte membrane. As a result, the three-dimensional porous framework in the membrane is upgraded from a simple physical pore to a "functionalized ion highway" constructed by covalently grafted EDTA. These uniformly distributed EDTA along the pores can actively capture lithium ions and strongly promote lithium salt dissociation through their multi-dentate chelation, thereby building a uniform and continuous lithium ion transport channel in the membrane. This not only significantly improves the ionic conductivity and lithium ion transference number, but also ensures the excellent structural and interfacial stability of the material. This design enables the physical pore formation, chemical grafting, and ion anchoring transmission to be highly synergistic in time and space, transforming the traditional passive physical channel into an intelligent structure that can actively regulate ion transport, fundamentally solving the problems of uneven distribution, poor bonding, and single function of additives. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a cross-sectional view of the solid-state electrolyte membrane prepared in Example 1

[0027] Beneficial effects

[0028] 1. By using a specific diluent as a pore-forming template, ideal three-dimensional through physical channels are constructed through phase separation and selective extraction. On this basis, these physical channels are successfully upgraded to functional channels that can actively capture and transport lithium ions by in-situ grafting of EDTA, realizing the perfect unity of "physical channel construction" and "chemical functionalization". The preparation efficiency is high, and the subsequent complex modification steps are avoided.

[0029] 3. EDTA molecules are uniformly grafted on the polymer backbone through strong covalent bonds, realizing the uniform distribution of EDTA at the molecular level, completely avoiding the problems of agglomeration, uneven distribution and easy loss during long-term use caused by physical blending, and providing a large number of uniform active sites for ion transport.

[0030] 4. By using the multi-dentate coordination ability of EDTA, strong coordination anchoring of lithium ions is realized during the diluent exchange stage, so that the lithium salt is stably fixed on the membrane surface and the matrix channel, avoiding the precipitation or uneven distribution of the salt during use, and enhancing the electrochemical stability.

[0031] 5. The three-dimensional porous network constructed by covalent grafting of EDTA not only has a stable structure, but also has a rich surface of strong coordination groups (carboxyl and amine groups) uniformly distributed in the channel. Its strong chelating effect can efficiently and uniformly capture lithium ions during application, significantly promote the dissociation of lithium salt, and provide a continuous and efficient transport channel for lithium ion migration, thereby simultaneously realizing high ionic conductivity and high lithium ion transference number.

[0032] 6. The electrolyte membrane prepared by the present application has good mechanical strength, excellent thermal stability and stable electrode / electrolyte interface. Uniform ion flow distribution can effectively inhibit the growth of lithium dendrites, combined with the intrinsic safety of solid-state electrolyte, making it very suitable for constructing high-energy-density and high-safety solid-state lithium batteries, especially showing great application potential in electric vehicles and flexible electronic devices. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described in detail below in combination with several embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0034] Embodiment 1

[0035] A method for synchronously constructing and preparing a solid-state electrolyte membrane by phase separation-amidation, comprising the following steps:

[0036] (1) Configuration of casting solution: take 25 kg of PVDF-HFP, 5 kg of styrene-maleic anhydride copolymer (SMA), 25 kg of dibutyl phthalate (DBP), and 45 kg of N, N-dimethylformamide DMF as the total amount of casting solution, mix them in a three-necked flask, continuously heat and stir at 80°C for 24 h until completely dissolved, and then obtain the casting solution after complete degassing by standing;

[0037] (2) Film scraping and curing: under room temperature conditions, cast the above-mentioned casting solution on a glass plate, control the thickness by using a scraper, scrape a flat wet film at a speed of 5 m / s, and then immediately immerse it in an ethylenediaminetetraacetic acid aqueous solution with a concentration of 5% for phase separation and curing;

[0038] (3) Solvent removal by immersion: transfer the cured film to deionized water, immerse it for 48 h, and then control the moisture after taking it out, to obtain a three-dimensional porous membrane with a thickness of 100 μm.

[0039] (4) Preparation of solid electrolyte membrane: place the prepared three-dimensional porous membrane in a mixed solution of ethanol and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) with a concentration of 0.1%, perform extraction of the diluent and loading and chelation of the lithium salt, and then place the treated membrane in a vacuum oven at 50°C for drying, to obtain the solid electrolyte membrane.

[0040] Example 2

[0041] A method for preparing a solid electrolyte membrane by simultaneous construction through phase separation-acylation, comprising the following steps:

[0042] (1) Configuration of casting solution: take 25 kg of PVDF-HFP, 5 kg of styrene-maleic anhydride copolymer (SMA), 25 kg of dibutyl phthalate (DBP), and 45 kg of N, N-dimethylformamide DMF as the total amount of casting solution, mix them in a three-necked flask, continuously heat and stir at 80°C for 24 h until completely dissolved, and then obtain the casting solution after complete degassing by standing;

[0043] (2) Film scraping and curing: under room temperature conditions, cast the above-mentioned casting solution on a glass plate, control the thickness by using a scraper, scrape a flat wet film at a speed of 5 m / s, and then immediately immerse it in an ethylenediaminetetraacetic acid aqueous solution with a concentration of 5% for phase separation and curing;

[0044] (3) Solvent removal by immersion: transfer the cured film to deionized water, immerse it for 48 h, and then control the moisture after taking it out, to obtain a three-dimensional porous membrane with a thickness of 100 μm.

[0045] (4) Preparation of solid electrolyte membrane: The prepared three-dimensional porous membrane is placed in a mixed solution of methanol and 0.2% LiTFSI to extract the diluent and load and chelate the lithium salt. Then the treated membrane is dried in a vacuum oven at 30°C to obtain the solid electrolyte membrane.

[0046] Example 3

[0047] A method for preparing a solid electrolyte membrane by simultaneous phase separation and amidation includes the following steps:

[0048] (1) Preparation of casting solution: Weigh 20 kg of PVDF-HFP, 3 kg of styrene-maleic anhydride copolymer (SMA), 20 kg of dioctyl phthalate (DOP), and 35 kg of N-methylpyrrolidone (NMP) into a three-necked flask, and heat and stir at 60°C for 10 h until completely dissolved. After standing and degassing completely, the casting solution is obtained.

[0049] (2) Film casting and curing: At room temperature, the above casting liquid is cast onto a glass plate, and the thickness is controlled by a scraper. The film is scraped into a smooth wet film at a speed of 1 m / s. Then, it is immersed in a 3% ethylenediaminetetraacetic acid aqueous solution for phase separation and curing.

[0050] (3) Solvent removal by immersion: The cured membrane is transferred to deionized water and soaked for 30 hours. After being taken out and drained, a three-dimensional porous membrane with a thickness of 50 μm is obtained.

[0051] (4) Preparation of solid electrolyte membrane: The prepared three-dimensional porous membrane is placed in a mixed solution of propanol and 2% LiTFSI to extract the diluent and load and chelate the lithium salt. Then the treated membrane is dried in a vacuum oven at 40°C to obtain the solid electrolyte membrane.

[0052] Example 4

[0053] A method for preparing a solid electrolyte membrane by simultaneous phase separation and amidation includes the following steps:

[0054] (1) Preparation of casting solution: Weigh 25 kg of PVDF-HFP, 0.5 kg of styrene-maleic anhydride copolymer (SMA), 25 kg of acetylated tributyl citrate (ATBC), and 30 kg of N-methylpyrrolidone (NMP) into a three-necked flask, and heat and stir at 80°C for 20 h until completely dissolved. After standing and degassing completely, the casting solution is obtained.

[0055] (2) Film casting and curing: At room temperature, the above casting liquid is cast onto a glass plate, and the thickness is controlled by a scraper. The film is scraped into a smooth wet film at a speed of 2 m / s. Then, it is immersed in a 5% ethylenediaminetetraacetic acid aqueous solution for phase separation and curing.

[0056] (3) Soaking to remove solvent: Transfer the cured membrane to deionized water and soak for 24 hours. After taking it out, drain the water to obtain a three-dimensional porous membrane with a thickness of 70 μm.

[0057] (4) Preparation of solid electrolyte membrane: The prepared three-dimensional porous membrane is placed in a mixed solution of ethanol and 1% LiTFSI to extract the diluent and load and chelate the lithium salt. Then the treated membrane is dried in a vacuum oven at 50°C to obtain the solid electrolyte membrane.

[0058] Example 5

[0059] A method for preparing a solid electrolyte membrane by simultaneous phase separation and amidation includes the following steps:

[0060] (1) Preparation of casting solution: Weigh out 10 kg of PVDF-HFP, 5 kg of styrene-maleic anhydride copolymer (SMA), 15 kg of diphenyl ether (DPE), and 45 kg of N-methylpyrrolidone (NMP) according to the total amount of casting solution, mix them in a three-necked flask, and continue to heat and stir at 50°C for 6 h until completely dissolved. After standing and degassing completely, the casting solution is obtained.

[0061] (2) Film casting and curing: At room temperature, the above casting liquid is cast onto a glass plate, and the thickness is controlled by a scraper. The film is scraped into a smooth wet film at a speed of 4 m / s. Then, it is immersed in a 2% ethylenediaminetetraacetic acid aqueous solution for phase separation and curing.

[0062] (3) Solvent removal by immersion: The cured membrane is transferred to deionized water and soaked for 30 hours. After being taken out and drained, a three-dimensional porous membrane with a thickness of 60 μm is obtained.

[0063] (4) Preparation of solid electrolyte membrane: The prepared three-dimensional porous membrane is placed in a mixed solution of propanol and 3% LiTFSI to extract the diluent and load and chelate the lithium salt. Then the treated membrane is dried in a vacuum oven at 35°C to obtain the solid electrolyte membrane.

[0064] Comparative Example 1 (used to demonstrate that a simple blend electrolyte membrane with a three-dimensional porous structure constructed without SMA-EDTA modification and without diluent has performance (such as ionic conductivity and lithium-ion transference number) that is far lower than that of this application)

[0065] Preparation of casting solution: Weigh out the same amount of PVDF-HFP polymer, EDTA and LiTFSI lithium salt as in Example 1, dissolve them in N,N-dimethylformamide (DMF) solvent, and heat and stir continuously at 80°C until completely dissolved. After standing to remove bubbles, a uniform and transparent casting solution is obtained.

[0066] Key difference: This comparative example does not contain styrene-maleic anhydride copolymer (SMA) and does not use any water-insoluble diluents (such as DBP).

[0067] Film casting and curing: At room temperature, the above casting liquid is cast onto a glass plate, and the thickness is controlled by a doctor blade to form a smooth wet film.

[0068] Drying and film formation: The wet film is directly transferred to a vacuum oven and dried at 50°C to completely remove the DMF solvent, finally obtaining a dense, non-porous PVDF-HFP / LiTFSI solid electrolyte membrane.

[0069] Comparative Example 2 (used to demonstrate that the performance of an electrolyte membrane that only undergoes physical pore formation without SMA-EDTA chemical grafting modification is still inferior to that of the present invention)

[0070] Preparation of casting solution: Weigh out the same amount of PVDF-HFP polymer and dibutyl phthalate (DBP) diluent as in Example 1, dissolve them in N,N-dimethylformamide (DMF) solvent, and heat and stir continuously at 80°C until completely dissolved. After standing to remove bubbles, the casting solution is obtained.

[0071] Key difference: This comparative example does not include styrene-maleic anhydride copolymer (SMA).

[0072] Film casting and curing: At room temperature, the above casting solution is cast onto a glass plate, and the thickness is controlled by a doctor blade to form a smooth wet film. The film is then immersed in an EDTA aqueous solution for phase separation and curing to form a three-dimensional porous framework.

[0073] Key difference: It can only induce physical phase separation to form a porous structure and random deposition of EDTA, but cannot induce ring opening of SMA and grafting reaction of EDTA.

[0074] Solvent removal by immersion: The cured membrane is transferred to deionized water and immersed for 48 hours to remove residual solvent and diluent. After removal, the water is drained to obtain pure PVDF-HFP three-dimensional porous membrane.

[0075] Preparation of the electrolyte membrane: The prepared pure PVDF-HFP porous membrane was placed in a mixed solution of ethanol and 0.1% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) for diluent extraction and lithium salt loading. The treated membrane was then dried in a vacuum oven at 50°C to obtain a porous PVDF-HFP / LiTFSI electrolyte membrane.

[0076] Key difference: Due to the weak interaction between EDTA in the membrane skeleton and the membrane matrix, its dispersibility and stability are poor.

[0077] Experimental results

[0078] The performance of the solid electrolyte membranes prepared in Examples 1-5 and Comparative Examples 1-2 was tested, and the test results are shown in Table 1.

[0079] Table 1

[0080] Electrical conductivity (mS / cm) Lithium ion transference number (t Li+ ) Electrochemical window voltage (V) Discharge capacity (0.5 C, 25 o C) (mAh / g) Capacity retention rate (0.5 C, 25 o C, 200 cycles) Tensile strength (MPa) Example 1 0.56 0.49 4.43 116.18 98.7% 6.44 Example 2 1.28 0.64 4.56 119.26 98.9% 7.75 Example 3 1.55 0.66 4.65 124.28 99.1% 8.38 Example 4 1.98 0.73 4.81 138.0 99.7% 9.94 Example 5 1.66 0.69 4.72 126.05 99.3% 8.84 Comparative Example 1 0.26 0.34 4.32 90.87 67.5% 0.82 Comparative Example 2 0.11 0.23 4.21 75.71 43.2% 0.79

[0081] As shown in Table 1, the solid electrolyte membranes prepared in Examples 1-5 of this invention exhibit significant advantages in all key performance aspects. Specifically, by constructing a three-dimensional porous structure and utilizing SMA ring-opening and in-situ chemical grafting anchoring with EDTA, this invention achieves a high degree of synergy between physical structure and chemical function. On the one hand, this strategy completely solves the problems of uniform dispersion and interfacial stability of EDTA molecules in the polymer matrix, allowing them to be firmly bound to the porous framework surface in the form of covalent bonds; on the other hand, the in-situ grafting reaction simultaneously strengthens the polymer framework, forming a more stable cross-linked network structure. As a result, the prepared electrolyte membranes show significant improvements in ionic conductivity, lithium-ion transference number, and mechanical strength, with performance far superior to Comparative Example 1 and Comparative Example 2. Benefiting from this, the electrolyte system exhibits high initial discharge capacity and excellent long-term cycling stability, with capacity retention maintained above 98.7% after 200 cycles. The above data fully demonstrate that the integrated in-situ design strategy proposed in this invention has significant effectiveness and technological advancement in simultaneously improving ion transport efficiency, structural stability, and electrochemical cycling performance.

Claims

1. A method for simultaneously constructing a solid electrolyte membrane via phase separation and amidation, characterized in that, Includes the following steps: A primary membrane was prepared using PVDF-HFP and styrene-maleic anhydride copolymer as the matrix. The primary membrane was then subjected to phase separation and simultaneous in-situ grafting under the action of EDTA. Finally, a solid electrolyte membrane was prepared by post-treatment and lithium salt loading.

2. The method as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of primary film: Weigh PVDF-HFP, styrene-maleic anhydride copolymer, water-insoluble diluent and organic solvent according to the proportions, mix them in a three-necked flask, and continue heating and stirring until completely dissolved. After standing and degassing, the casting solution is obtained. At room temperature, the casting solution is cast on a glass plate, and the thickness is controlled by a doctor blade. The film is scraped into a smooth wet film at a speed of 0.1 m / s-5 m / s. (2) Phase separation and synchronous in-situ grafting: The nascent membrane prepared in step (1) was then immersed in an EDTA aqueous solution with a concentration of 1%-5%; (3) Post-treatment and lithium salt loading: The membrane obtained in step (2) is immersed in deionized water to remove residual solvent for 24h-48h. After being taken out and drained, a three-dimensional porous membrane with a thickness of 10μm-100μm is obtained. Then it is immersed in an alcohol solution containing lithium salt to extract residual diluent and achieve lithium salt loading and fixation. Finally, it is dried to obtain the solid electrolyte membrane.

3. The method as described in claim 2, characterized in that, The content of PVDF-HFP in step (1) is 10%-25% of the total amount of casting solution.

4. The method as described in claim 2, characterized in that, The styrene-maleic anhydride copolymer (SMA) has a content of 0.5%-5% of the total casting solution.

5. The method as described in claim 2, characterized in that, The diluent has poor solubility with PVDF-HFP and its content is 5%-25% of the total casting solution.

6. The method as described in claim 2, characterized in that, The diluent is any one of dimethyl phthalate (DMP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), tributyl acetyl citrate (ATBC), and diphenyl ether (DPE).

7. The method as described in claim 2, characterized in that, The organic solvent casting solution comprises 25%-45% of the total volume.

8. The method as described in claim 2, characterized in that, The continuous heating and stirring conditions are 40℃-80℃, and stirring time is 6h-24h.

9. The method as described in claim 1, characterized in that, The lithium salt is lithium bis(trifluoromethanesulfonylimide), and the lithium salt concentration is 0.1-3%.

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