Solid-state electrolyte membrane in an energy storage system and preparation method and application thereof

Abstract

This invention belongs to the field of solid polymer electrolyte membrane materials for lithium-ion batteries, and discloses a solid electrolyte membrane for energy storage systems, its preparation method, and its application. The solid electrolyte membrane is obtained by preparing lithium 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate, formulating a mixture of dual polymer backbone monomers, adding an initiator and degassing treatment, UV-initiated polymerization and film formation, and ion site activation treatment. This invention utilizes the "imidazolium-boronphenyl" synergistic structure in lithium 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate to enhance the performance of lithium-ion batteries. + Its selective conduction, combined with the mechanical support and channel regulation of the dual-framework, meets the core requirements of lithium batteries for "high ion conduction and stable cycling".

Description

Technical Field

[0001] This invention belongs to the field of solid polymer electrolyte membrane materials for lithium-ion batteries, and relates to a solid electrolyte membrane in an energy storage system, its preparation method and application. Background Technology

[0002] With the rapid development of new energy vehicles, portable electronic devices, and energy storage power stations, the requirements for energy density, cycle life, and safety performance of lithium batteries are continuously increasing. Traditional liquid electrolytes, due to inherent defects such as easy leakage and flammability and explosiveness, have become a core bottleneck restricting the development of lithium batteries towards higher safety and higher energy density. Solid electrolytes, as a key material to replace liquid electrolytes, have become a research hotspot in the current lithium battery field due to their advantages such as no risk of leakage, high mechanical strength, and ability to suppress lithium dendrite growth.

[0003] Single-ion conductor solid electrolytes can selectively conduct lithium ions (lithium ion transport number t). + ≈1), which can effectively avoid interfacial polarization caused by anion migration, significantly improve battery cycle stability and rate performance, and is considered an important development direction for the next generation of high-performance solid electrolytes. However, existing single-ion conductor solid electrolytes still have many technical pain points: First, the functional site design is simple. Most single-ion conductors rely on single groups such as sulfonates and carboxylates to fix anions, resulting in limited lithium-ion conduction efficiency and insufficient redox stability, making it difficult to adapt to high-voltage cathode systems; Second, the polymer backbone and single-ion conductors have poor compatibility. Traditional preparation methods mostly use physical blending to introduce single-ion conductors, lacking chemical bonding, which leads to easy dissolution and phase separation of functional components, resulting in severe performance degradation after long-term cycling; Third, performance balancing is difficult. Although a single polyether backbone is beneficial for ion conduction, its mechanical strength is weak and it is prone to brittleness during battery assembly or cycling; a single polyester, fluorinated, or polyolefin backbone has insufficient ion conduction channels, resulting in low conductivity (usually below 1×10). -4 Fourth, the preparation process is complex. Some high-performance single-ion conductors rely on expensive special monomers or complex synthesis routes. The polymerization process requires high temperature and high pressure conditions, solvent recovery is difficult, production costs are high, and it is difficult to achieve large-scale industrial production.

[0004] In addition, although existing dual-ion conductor solid electrolytes (such as LiTFSI / polymer systems) are simple to prepare, their lithium-ion transference number is only 0.3~0.5. The migration of anions with lithium ions causes severe interfacial polarization and lithium dendrite growth, resulting in short battery cycle life and increased safety risks.

[0005] Therefore, developing a single-ion conductor solid electrolyte that combines high lithium-ion transference number, high conductivity, excellent mechanical properties and cycle stability, and has a simple preparation process and controllable cost is of great significance for promoting the industrial application of solid-state lithium batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a solid electrolyte membrane for energy storage systems, its preparation method and application, and to solve the problems of existing solid electrolytes, such as reliance on dual-ion conduction, low lithium-ion transference number, difficulty in balancing mechanical properties and conductivity, and poor cycle stability.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a solid electrolyte membrane in an energy storage system, comprising: 4-Borophenylimidazolium was mixed with vinyl bromide, and acetonitrile was added as a solvent to carry out the reflux reaction. After cooling, 1-vinyl-3-(4-boronphenyl)imidazolium bromide was collected and recrystallized with acetonitrile to obtain purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide. The purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide was dissolved in deionized water, lithium hexafluorophosphate was added, and after ion exchange, the filtrate was concentrated by distillation to a viscous state. Anhydrous ethanol was added, and the solution was heated to dissolve. After cooling, the solution was allowed to stand and crystallize. The crystals were collected, washed, and dried to obtain 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate lithium monomer. 1-Vinyl-3-(4-Borophenyl)imidazolium hexafluorophosphate lithium was mixed with polyethylene glycol methacrylate, polycaprolactone and a crosslinking agent, toluene was added as a solvent and stirred to form a homogeneous and transparent mixture of two polymer backbone monomers. The photoinitiator was dissolved in a mixture of two polymer backbone monomers and degassed to obtain a polymerization precursor solution. The polymerization precursor solution was coated onto a substrate, subjected to ultraviolet light irradiation, and subjected to free radical copolymerization reaction. After drying, a single-ion conductor electrolyte membrane was obtained as a preliminary product. The initial sample of the single-ion conductor electrolyte membrane was statically immersed in LiTFSI / DMC activation solution for Li + After co-coordination with the imidazolium-borate sites within the membrane, and washing and drying, a solid electrolyte membrane is obtained.

[0008] Furthermore, the molar ratio of 4-boronphenylimidazolium, ethylene bromide, and lithium hexafluorophosphate is 1:1.1:1; The total mass ratio of the mixture of 4-boronphenylimidazolium and ethylene bromide to the volume ratio of acetonitrile is 1:8~12; The mass ratio of purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide to deionized water is 1:8~10; The volume ratio of the filtrate, which is concentrated to a viscous state by distillation, to anhydrous ethanol is 1:3~5.

[0009] Furthermore, during the reflux reaction, the stirring speed is 250~300 r / min, the reaction temperature is 65~75℃, and the reaction time is 10~14 h; After the reflux reaction is complete, cool to room temperature.

[0010] Furthermore, during the ion exchange process, the temperature was room temperature, the time was 5-7 hours, and the stirring speed was 200-250 r / min; After ion exchange, the heating dissolution temperature is 40~50℃, the cooling temperature is 0~5℃, the static crystallization time is 8~12h, the drying temperature is 45~55℃, and the drying time is 10~12h.

[0011] Furthermore, in the mixture of the two polymer backbone monomers, 40-60 parts of polyethylene glycol methacrylate, 20-35 parts of polycaprolactone, 25-35 parts of lithium 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate, 1.5-3 parts of crosslinking agent and 100-150 parts of toluene are added respectively. The photoinitiator accounts for 1.5% to 2.5% of the total mass of lithium 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate, polyethylene glycol methacrylate, polycaprolactone, and crosslinking agent. The crosslinking agent is trimethylolpropane triacrylate; The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0012] Furthermore, the stirring speed of the dual polymer skeleton monomer mixture is 250~350 r / min, the stirring temperature is 25~35℃, and the stirring time is 30~50 min; During the degassing process, the vacuum degree is -0.1~-0.08MPa, the temperature is 25~35℃, and the time is 1.5~2.5 h, with a venting interval of 30 min during the process.

[0013] Furthermore, the ultraviolet irradiation wavelength is 340~380nm, and the power is 25~35mW / cm². 2 The time is 30-50 minutes; After the free radical copolymerization reaction, the drying temperature is 55~65℃, the drying vacuum degree is 0.07~0.09MPa, and the drying time is 5~7h.

[0014] Furthermore, the concentration of the LiTFSI / DMC activation solution is 0.08~0.12 mol / L; The static soaking temperature is 20~30℃, and the static soaking time is 6~10 h; After static soaking, the drying temperature is 45~55℃, the drying vacuum degree is 0.07~0.09MPa, and the drying time is 6~10h.

[0015] A solid electrolyte membrane prepared by the aforementioned method has a tensile strength ≥13MPa, an elongation at break ≥121%, and a lithium-ion transference number ≥0.83.

[0016] A solid-state lithium battery made of the aforementioned solid electrolyte membrane.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a solid electrolyte membrane in an energy storage system. Using lithium 1-vinyl-3-(4-boronylphenyl)imidazolium hexafluorophosphate (VBIM-BF3Li) as an innovative single-ion conductor functional monomer, polyethylene glycol methacrylate (PEGMA) and polycaprolactone (PCL) as dual polymer backbone monomers, and trimethylolpropane triacrylate (TMPTA) as a crosslinking agent, an integrated covalent network structure solid electrolyte membrane is prepared through a process of "precise synthesis of single-ion conductor - copolymerization of dual monomers, prepolymerization - UV-initiated graft polymerization - ion site activation". This invention utilizes the "imidazolium-boronylphenyl" synergistic structure of VBIM-BF3Li to enhance the performance of Li... +The selective conduction of lithium-ion batteries, combined with the mechanical support and channel regulation of the PEGMA-PCL dual framework, meets the core requirements of "high ion conduction and stable cycling." It achieves covalent integration of functional sites and the polymer framework, breaking through the performance bottlenecks of traditional physical blends or single-framework electrolytes. The vinyl groups of lithium 1-vinyl-3-(4-boronylphenyl)imidazolium hexafluorophosphate undergo free radical copolymerization with the double bonds of polyethylene glycol methacrylate and polycaprolactone, forming a stable covalent network of "imidazolium-borate single-ion conductor-polyether-polyester dual framework," mechanistically solving the problems of functional component dissolution and phase separation. Simultaneously, the high-density and uniform distribution of imidazolium-borate synergistic sites, in conjunction with polyether segments, constructs continuous lithium-ion transport channels, achieving a synergy between high lithium-ion transport number and structural stability. This solves the problem that traditional single-ion conductors, which often introduce functional components through physical blending, are prone to functional site loss and severe phase separation due to lack of chemical bonding, leading to easily broken ion conduction channels. Furthermore, the synergistic mechanism of ion conduction and mechanical properties better aligns with the core requirements of solid-state lithium batteries. By using a polyether-polyester dual-backbone copolymer, the polyether segments provide flexible ion conduction channels and lower the lithium-ion migration barrier, while the polyester segments provide rigid support and enhance the membrane's mechanical strength. Combined with a crosslinking agent, a three-dimensional network structure is constructed, significantly improving the electrolyte membrane's tensile strength and deformation resistance. Simultaneously, imidazolium cations immobilize anions, and boron phenyl groups dynamically coordinate lithium ions, achieving highly selective single-ion conduction and fundamentally suppressing interfacial polarization and lithium dendrite growth caused by anion migration. This invention solves the problems of traditional solid-state electrolytes, which struggle to balance ion conduction and mechanical strength, suffer from poor mechanical properties with a single polyether backbone, and lack ion channels with a single polyester backbone. The preparation process of this invention is mild and controllable, significantly improving economic efficiency and practicality, making it suitable for industrial production. The monomers, crosslinking agents, and photoinitiators used are all conventional chemical reagents. The functional monomers are synthesized using a reflux reaction-ion exchange-low-temperature crystallization route, which is mild and yields high results. The polymerization is initiated by UV light at room temperature, eliminating the need for high-temperature and high-pressure equipment. The vacuum drying and activation processes are simple and easy to control, and the solvents can be recycled and reused. The entire process is free of harsh conditions and toxic byproducts. While ensuring the high performance of the electrolyte membrane, the process is significantly simplified and costs are reduced, making it more conducive to the large-scale preparation and application of high-performance solid-state electrolytes. In addition, no harmful byproducts are generated during the preparation process, the material structure is controllable, and it combines safety, high efficiency, and long cycle life, providing excellent material support for the industrialization of high-performance solid-state lithium batteries.

[0018] Furthermore, the molar ratio of 4-boronphenylimidazolium, ethylene bromide, and lithium hexafluorophosphate is limited to optimize the ratio of core raw materials, ensuring sufficient reaction of the imidazolium bromide intermediate, improving ion exchange efficiency, and reducing byproducts and impurities caused by excess or insufficient raw materials. At the same time, the range of raw material ratios for each process is limited to standardize the material proportions in the synthesis process, effectively control the synthesis purity and yield of functional monomers, avoid structural defects caused by material imbalance, ensure the uniformity of subsequent copolymerization reactions, and improve the consistency and stability of the finished electrolyte membrane performance.

[0019] Furthermore, by limiting the stirring speed, reaction temperature, reaction time, and cooling conditions during the synthesis of imidazole bromide, and optimizing the reflux reaction process parameters, we can ensure that 4-boronphenylimidazolium and ethylene bromide undergo a full addition reaction, promoting the stable formation of intermediates. Mild and controllable temperature and speed conditions can avoid over-reaction, raw material degradation, or structural damage, inhibit side reactions, ensure the integrity of intermediate molecular structure, improve product purification, and lay the foundation for the subsequent synthesis of functional monomers.

[0020] Furthermore, by clarifying key parameters such as temperature, time, and rotation speed in processes such as ion exchange, crystallization, and drying, the cation and anion exchange processes can be precisely controlled to ensure that lithium hexafluorophosphate fully completes ion replacement and improves the purity of the imidazolium-borate lithium monomer. Low-temperature crystallization and gradient drying conditions can regulate the monomer crystal structure, reduce the content of impurities and residual solvents, reduce the interference of free impurities on electrochemical performance, and ensure the ionic activity and chemical stability of the functional monomer.

[0021] Furthermore, the ratio range of dual-framework monomers, functional lithium monomers, crosslinking agents, and solvents is limited, as well as the addition ratio of photoinitiators and the types of functional materials; the polyether-polyester composite complements each other, taking into account both ion transport capacity and membrane mechanical strength; specific crosslinking agents construct a dense three-dimensional network structure, improving the mechanical strength, deformation resistance, and thermal stability of the electrolyte membrane; dedicated photoinitiators ensure efficient and stable ultraviolet light polymerization reaction, and reasonable ratio parameters balance the degree of polymerization and matrix flexibility, effectively optimizing the framework structure and ion transport channels of the solid electrolyte.

[0022] Furthermore, the process parameters for preparing the mixture and vacuum degassing are limited, and constant temperature stirring ensures that all monomers and additives are mixed uniformly to form a homogeneous and stable precursor liquid system. The controllable vacuum degassing process effectively eliminates air bubbles and voids inside the membrane, avoids leakage, breakdown risks and uneven ion conduction caused by micropore defects, ensures that the electrolyte membrane has a dense and uniform microstructure, improves the integrity and electrochemical stability of the membrane, and ensures the quality of subsequent photocuring molding.

[0023] Furthermore, by limiting the wavelength, power, reaction time, and vacuum drying parameters after curing of ultraviolet irradiation, and matching the response characteristics of the photoinitiator, the free radical copolymerization reaction can be carried out uniformly and fully, ensuring that the polymer skeleton is densely cross-linked and structurally uniform. Controllable vacuum drying effectively removes residual solvents and volatile impurities from the system, reduces the content of residual small molecules in the membrane, inhibits aging and side reactions of solid electrolytes during long-term use, and improves the dimensional stability and electrochemical durability of the membrane.

[0024] Furthermore, by limiting the concentration of the LiTFSI / DMC activation solution, immersion conditions, and post-drying parameters, the activation treatment achieves directional coordination between lithium ions and the functional sites of imidazolium-borate in the membrane, optimizes the lithium ion migration channel, and enhances single-ion conductivity. Mild immersion conditions avoid swelling and damage to the membrane structure, and vacuum drying in the later stage removes residual activation solvent, reduces the risk of internal side reactions in the battery, improves the interfacial contact characteristics between the electrolyte and the electrode, and enhances the cycle stability and charge-discharge performance of the solid-state battery.

[0025] This invention also provides a solid electrolyte membrane with a maximum room temperature ionic conductivity of 1.3 × 10⁻⁶. -3 S / cm, lithium-ion transference number (t) + The electrolyte exhibits a conductivity of 0.93, a tensile strength of 21 MPa, a capacity retention of 90.1% after 100 cycles at 0.5C, and an electrochemical stability window ≥ 5.5 V. In comparison, the room-temperature ionic conductivity of traditional dual-ion conductor electrolyte membranes is only 3.8 × 10⁻⁶. -4 S / cm, lithium-ion transference number (t) + The single-polymer backbone single-ion conductor film has a tensile strength of only 8 MPa, is easily brittle, and has a capacity retention of 79.2% after 100 cycles at 0.5C. The physically blended single-ion conductor film has a conductivity of only 4.2 × 10⁻⁶ due to phase separation. -4 With a capacity retention rate of only 68.4% after 50 cycles at 0.5C, the solid electrolyte membrane prepared in this invention provides a core material for high-performance solid-state lithium batteries that combines high conductivity, strong mechanical properties, and a wide stability window.

[0026] This invention also provides a solid-state lithium battery made from the aforementioned solid electrolyte membrane. The polyether-polyester copolymer framework combines flexibility and structural stability, ensuring both membrane processability and electrode interface adhesion while suppressing lithium dendrite growth and improving battery safety. The imidazolium-borate single-ion conductor structure can efficiently dissociate lithium salts, and combined with the synergistic coordination effect after LiTFSI activation, it can significantly improve lithium-ion transference number and ionic conductivity, reduce battery polarization loss, and optimize rate performance. Its unique chemical structure endows the electrolyte membrane with a wide electrochemical stability window, making it compatible with high-voltage cathode materials and reducing interfacial side reactions. Simultaneously, the covalently grafted ion conduction sites are evenly distributed, forming continuous and ordered ion transport channels, further improving ion transport efficiency. Through the synergistic effect of the framework and ion conductor, this invention can induce the formation of a stable interfacial layer on the electrode surface, enhancing interfacial compatibility, suppressing transition metal dissolution and electrode structure degradation, and significantly extending battery cycle life. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The impedance spectra of Examples 2, 3 and Comparative Example 1 at room temperature are shown below.

[0029] Figure 2 This is an electrochemical window curve of Example 3 of the present invention.

[0030] Figure 3 The stress-strain curves of Embodiment 3, Comparative Example 2, and Comparative Example 3 of the present invention are shown. Detailed Implementation

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0033] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0034] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0035] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0038] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a method for preparing a solid electrolyte membrane in an energy storage system, specifically including the following steps: Step 1: Preparation of lithium hexafluorophosphate (VBIM-BF3Li) of 1-vinyl-3-(4-boronphenyl)imidazolium.

[0039] Weigh 4-boronphenylimidazolium, vinyl bromide, and lithium hexafluorophosphate (LiPF6) in a molar ratio of 1:1.1:1, and prepare the mixture in two steps: First, add 4-boronphenylimidazolium and vinyl bromide to a 500 mL round-bottom flask, add acetonitrile as a solvent, install a reflux condenser, and reflux the mixture on a magnetic stirrer at a speed of 250-300 r / min and a temperature of 65-75 °C for 10-14 minutes. h; After the reaction is completed, cool to room temperature, filter and collect the solid product 1-vinyl-3-(4-boronphenyl)imidazolium bromide (VBIM-Br), recrystallize 2-3 times with acetonitrile; dissolve the purified VBIM-Br in deionized water, add LiPF6, and stir for 5-7 h at room temperature and 200-250 r / min for ion exchange; filter to remove the precipitate, transfer the filtrate to a rotary evaporator, and distill and concentrate to a viscous state at 45-55℃ and a vacuum of 0.08-0.09 MPa; add anhydrous ethanol to the viscous liquid, heat to 40-50℃ and stir to dissolve, cool to 0-5℃, let stand for crystallization for 8-12 h, filter and collect the crystals, wash 2-3 times with cold anhydrous ethanol, and finally dry in a vacuum drying oven at 45-55℃ for 10-12 h to obtain VBIM-BF3Li monomer, which is sealed and protected from light for later use.

[0040] Step 2: Preparation of the mixture of dual polymer backbone monomers.

[0041] Weigh out 40-60 parts by weight of polyethylene glycol methacrylate (PEGMA), 20-35 parts by weight of polycaprolactone (PCL), 25-35 parts by weight of self-made VBIM-BF3Li, and 1.5-3 parts by weight of crosslinking agent trimethylolpropane triacrylate (TMPTA). Place them in a three-necked flask, add 100-150 parts by weight of toluene as solvent, and magnetically stir for 30-50 min at a speed of 250-350 r / min and a temperature of 25-35℃ to form a homogeneous and transparent mixture of two polymer backbone monomers for later use.

[0042] Step 3: Initiator addition and degassing treatment.

[0043] Weigh 1.5% to 2.5% of the total monomers (PEGMA+PCL+VBIM-BF3Li+TMPTA) as the photoinitiator and add it to the mixed solution of the two polymer backbone monomers prepared in step two. Stir at 200 to 300 r / min for 20 to 40 min in a dark environment until the initiator is completely dissolved. Transfer the mixture to a vacuum degassing machine and degas for 1.5 to 2.5 h under a vacuum of -0.08 to -0.1 MPa and a temperature of 25 to 35 °C, releasing gas once every 30 min during the process to remove bubbles from the solution and obtain the polymerization precursor solution.

[0044] Step 4: Ultraviolet light initiates polymerization and film formation.

[0045] Cut the quartz substrate into 5-7cm x 5-7cm pieces, and ultrasonically clean it sequentially with acetone, ethanol, and deionized water for 10-20 minutes each (ultrasonic power 200-500W). Dry it in a vacuum drying oven at 50-70℃ for 1-3 hours to complete the pretreatment. Lay the pretreated quartz substrate flat on a horizontal worktable and fix it in place. Use a 180-220μm thickness coater to uniformly coat the polymerization precursor solution from step three in the same direction. Place the coated substrate in an ultraviolet irradiation device at a wavelength of 340-380nm and a power of 25-35mW / cm². 2 Irradiate for 30-50 min under the specified conditions to initiate a free radical copolymerization reaction (to achieve VBIM-BF3Li grafting onto the dual polymer backbone); after irradiation, transfer the substrate-film composite to a vacuum drying oven and dry for 5-7 h at 55-65℃ and a vacuum of 0.07-0.09 MPa to remove residual solvent, and obtain a preliminary single-ion conductor electrolyte membrane with a thickness of 90-110 μm.

[0046] Step 5: Ion site activation treatment.

[0047] Prepare a 0.08-0.12 mol / L LiTFSI dimethyl carbonate (DMC) solution as the activation solution. After peeling the initial electrolyte membrane sample obtained in step four from the quartz substrate, completely immerse it in the solution and statically soak it in a constant temperature water bath at 20-30°C for 6-10 hours to promote Li... + Co-coordination with imidazolium-borate sites within the membrane; remove the membrane sample and wash it repeatedly with anhydrous ethanol 3-5 times, each wash lasting ≥5 min, to remove residual LiTFSI on the surface; spread the washed membrane sample flat on a glass slide, place it in a vacuum drying oven, and dry it at 45-55℃ and a vacuum of 0.07-0.09 MPa for 6-10 h until the membrane mass is constant, thus obtaining a solid electrolyte membrane.

[0048] Preferably, the total mass ratio of the mixture of 4-boronphenylimidazolium and ethylene bromide to the volume ratio of acetonitrile is 1:8~12; The mass ratio of purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide to deionized water is 1:8~10; The volume ratio of the filtrate, which is concentrated to a viscous state by distillation, to anhydrous ethanol is 1:3~5.

[0049] The technical solution of the present invention will be further described in detail below through specific embodiments: Example 1: Accurately weigh 0.1 mol of 4-boronphenylimidazolium, 0.11 mol of vinyl bromide, and 0.1 mol of lithium hexafluorophosphate (LiPF6) in a molar ratio of 1:1.1:1. First, add 4-boronphenylimidazolium and vinyl bromide to a 500 mL round-bottom flask, add 180 mL of acetonitrile as solvent, install a reflux condenser, and set a magnetic stirrer to a speed of 280 r / min and a temperature of 70 °C. Reflux the reaction for 12 minutes. h; After the reaction was completed, the mixture was cooled to room temperature, and the solid product 1-vinyl-3-(4-boronphenyl)imidazolium bromide (VBIM-Br) was collected by vacuum filtration and recrystallized three times with acetonitrile; The purified VBIM-Br was dissolved in 110 mL of deionized water, and LiPF6 was added. Ion exchange was carried out by stirring at room temperature and 220 r / min for 6 h; The precipitate was removed by vacuum filtration, and the filtrate was transferred to a rotary evaporator and concentrated to a viscous state by distillation at 50 °C and a vacuum of 0.08 MPa; 130 mL of anhydrous ethanol was added to the viscous liquid, and the mixture was heated to 45 °C and stirred to dissolve. The mixture was cooled to 3 °C and allowed to stand for crystallization for 10 h. The crystals were collected by vacuum filtration, washed three times with cold anhydrous ethanol, and finally dried in a vacuum drying oven at 50 °C for 12 h to obtain the VBIM-BF3Li monomer, which was sealed and stored in the dark for later use.

[0050] Weigh out 50 parts of PEGMA, 28 parts of PCL, 30 parts of VBIM-BF3Li, and 2 parts of TMPTA by mass, place them in a three-necked flask, add 130 parts of toluene as solvent, and magnetically stir for 40 min at 300 r / min and 30℃ to form a homogeneous and transparent mixture of two polymer backbone monomers for later use.

[0051] The photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone was added at a rate of 2.0% of the total monomer mass and added to the mixed solution of the dual polymer backbone monomers prepared in step two. The mixture was stirred at 250 r / min for 30 min in a light-protected environment until the initiator was completely dissolved. The mixture was then transferred to a vacuum degassing machine and degassed for 2 h at a vacuum of -0.09 MPa and a temperature of 30 °C, with the gas being released once every 30 min during the process to remove bubbles from the solution and obtain the polymerization precursor solution.

[0052] Quartz substrates were cut to 6cm x 6cm dimensions and ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 15 minutes each (ultrasonic power 200-500W). They were then dried in a 60℃ vacuum oven for 2 hours to complete the pretreatment. The pretreated quartz substrates were then laid flat on a horizontal worktable and fixed. Using a 200μm thickness coater, the polymerization precursor solution from step three was uniformly coated in the same direction at a constant speed. The coated substrates were then placed in an ultraviolet irradiation device with an irradiation wavelength of 365nm and a power of 30mW / cm². 2The irradiation time was 40 min to initiate a free radical copolymerization reaction (to achieve VBIM-BF3Li grafting onto the dual polymer backbone); after irradiation, the substrate-film composite was transferred to a vacuum drying oven and dried at 60℃ and 0.08MPa for 6 h to remove residual solvent, resulting in a preliminary single-ion conductor electrolyte membrane with a thickness of 100 μm.

[0053] A LiTFSI / DMC activation solution with a concentration of 0.1 mol / L was prepared. The initial electrolyte membrane sample obtained in step four was completely immersed in the solution after being peeled from the quartz substrate and statically soaked in a 25°C constant temperature water bath for 8 hours to promote Li… + Co-coordination with imidazolium-borate sites within the membrane; remove the membrane sample and wash it repeatedly with anhydrous ethanol 5 times, each time for 10 min, to remove residual LiTFSI on the surface; spread the washed membrane sample flat on a glass slide, place it in a vacuum drying oven, and dry it at 50℃ and 0.08MPa for 8 h until the membrane mass is constant, thus obtaining a solid electrolyte membrane.

[0054] Example 2: The only difference from Example 1 is that the amount of VBIM-BF3Li was changed to 25 parts and the amount of PEGMA was changed to 55 parts, while the other parameters remained the same.

[0055] Example 3: The only difference from Example 1 is that the amount of VBIM-BF3Li is changed to 35 parts and the amount of PCL is changed to 32 parts, while the other parameters remain unchanged.

[0056] Example 4: The only difference from Example 1 is that the amount of crosslinking agent TMPTA is changed to 1.5 parts, while the other parameters remain the same.

[0057] Example 5: The only difference from Example 1 is that the amount of crosslinking agent TMPTA is changed to 3 parts, while the other parameters remain the same.

[0058] Example 6: The only difference from Example 1 is that the ultraviolet irradiation time was changed to 30 minutes, while the other parameters remained the same.

[0059] Example 7: The only difference from Example 1 is that the ultraviolet irradiation time was changed to 50 minutes, while the other parameters remained the same.

[0060] Example 8: The only difference from Example 1 is that the soaking time of the LiTFSI / DMC activation solution was changed to 6 hours, while the other parameters remained the same.

[0061] Example 9: The only difference from Example 1 is that the soaking time of the LiTFSI / DMC activation solution was changed to 10 hours, while the other parameters remained the same.

[0062] Example 10: The only difference from Example 1 is that the amount of photoinitiator added is changed to 1.5%, while the other parameters remain the same.

[0063] Comparative Example 1: Unlike Example 1, the single-ion conductor VBIM-BF3Li was replaced with an equal mass of the conventional dual-ion conductor LiTFSI, and the amount of PEGMA was adjusted to 65 parts and the amount of PCL to 35 parts, while the other parameters remained unchanged, to obtain a dual-ion conductor electrolyte membrane.

[0064] Comparative Example 2: Unlike Example 1, the dual polymer backbone was replaced with a single PEGMA and PCL was removed. The composition was 78 parts PEGMA, 30 parts VBIM-BF3Li, and 2 parts TMPTA, with the other parameters remaining unchanged, to obtain a single polymer backbone single ion conductor electrolyte membrane.

[0065] Comparative Example 3: Unlike Example 1, each monomer was physically blended (without UV-initiated copolymerization, but directly formed into a film and dried after mixing and dissolving), while the other parameters remained unchanged, to obtain a physically blended single-ion conductor electrolyte membrane.

[0066] The performance of the solid electrolyte membranes prepared in Examples 1-10 and the electrolyte membranes prepared in Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0067] Table 1. Performance test results of electrolyte membranes prepared in Examples 1-10 and Comparative Examples 1-3

[0068] As can be seen from the test results in Table 1, the lithium-ion transference number (t) of Examples 1-10 is... + The values ​​were all ≥0.83, significantly higher than those of Comparative Example 1 (0.43) and Comparative Example 3 (0.61). The core reason lies in the "imidazolium-boronylphenyl" synergistic structure of VBIM-BF3Li: the imidazolium cation fixes hexafluorophosphate (PF6) ions through electrostatic interaction. - ), preventing anions from following Li + Migration, while the empty p orbital of boron phenyl interacts with Li + Formation of dynamic coordination (B→Li) + ), constructing continuous Li + Transmission channel, enabling Li +Directional conduction can be achieved without relying on anion migration, a synergistic mechanism that traditional dual-ion conductors (LiTFSI in Comparative Example 1) cannot achieve. Regarding dosage, Example 3 (VBIM-BF3Li = 35 parts) showed a conductivity of 1.3 × 10⁻⁶. -3 S / cm) and t + (0.93) is optimal because the increased concentration of the single-ion conductor makes Li... + The density of transport sites was increased, while the performance of Example 2 (25 copies) was slightly reduced due to insufficient sites, which verified that "30~35 copies" is the optimal dosage range. Excessive dosage may lead to site aggregation and hinder conduction.

[0069] Furthermore, the tensile strength of Examples 1-10 was ≥13 MPa and the elongation at break was ≥121%, significantly better than Comparative Example 2 (8 MPa, 85%). The mechanism lies in the synergistic effect of PEGMA and PCL: the polyether segment (-O-CH2-CH2-) of PEGMA provides Li + The transport channel, and synergistically with the boron phenyl group of VBIM-BF3Li to reduce Li + The migration barrier is mitigated by the strong crystallinity of the polyester segments (-O-(CH2)5-CO-) in PCL, which form physical cross-linking points, enhancing the mechanical strength of the membrane. The copolymerization of these two components creates a composite structure of "flexible transport channels - rigid support network," solving the problem of the incompatibility between conductivity and mechanical properties in a single polymer backbone. Regarding ratio optimization, in Example 1, a PEGMA:PCL ratio of 50:28 achieved the optimal balance between conductivity and mechanical strength. In Example 3, increasing the PCL ratio to 32 parts resulted in a tensile strength of 21 MPa, while the conductivity only slightly decreased to 1.3 × 10⁻⁶. -3 S / cm reflects the dual-framework's ability to flexibly control performance.

[0070] Regarding UV irradiation, the tensile strength (19 MPa) of Example 7 (50 min) was higher than that of Example 6 (30 min, 13 MPa). This is because longer irradiation allows for more complete free radical copolymerization, resulting in increased VBIM-BF3Li grafting rate and a denser film structure. However, excessively long irradiation (over 60 min) can lead to over-crosslinking, increasing the rigidity of the polyether segments and hindering Li + For transmission, 40-50 minutes is the optimal range. Regarding activation soaking, Example 9 (10 h) has a t... + (0.92) is slightly higher than in Example 8 (6h, 0.85), because during the immersion in the LiTFSI / DMC solution, Li + It will form "B-Li" with the boron phenyl group of VBIM-BF3Li. + -O(PEGMA)" co-coordination, extending the soaking time can enable Li + It fully occupies the active site, but after more than 10 hours, excessive Li... +It can form ion clusters, reducing conductivity; regarding the amount of crosslinking agent, Example 5 (TMPTA = 3 parts) had the highest tensile strength (23 MPa), but the electrical conductivity decreased slightly to 9.2 × 10⁻⁶. -4 S / cm, due to the increase in crosslinking degree, the membrane porosity decreases and the transport channel narrows. In Example 4 (1.5 parts), the mechanical strength drops to 14 MPa due to insufficient crosslinking, which verifies that "2 parts" is the optimal value for crosslinking degree, which ensures structural stability and does not hinder ion conduction.

[0071] Comparative Examples 1-3 further demonstrate the innovativeness and rationality of this invention: In Comparative Example 1, VBIM-BF3Li was missing, but after being replaced with the traditional dual-ion conductor LiTFSI, Li... + With TFSI - Cooperative migration leads to t + With a value of only 0.43, and severe interfacial polarization caused by anion migration, the cycle capacity retention rate was only 72.6%, confirming the crucial role of the single-ion conductor in "selective conduction" of this invention. In Comparative Example 2, without PCL, the lack of rigid support from the polyester chain resulted in low crystallinity, mechanical property degradation, a tensile strength of only 8 MPa, and easy brittleness, failing to meet battery assembly requirements, thus verifying the synergistic necessity of the dual polymer framework. Comparative Example 3 used physical blending instead of UV-induced covalent grafting; the interaction between VBIM-BF3Li and the polymer framework was purely physical, easily leading to phase separation and Li... + The transmission channel is broken, and the conductivity is only 4.2 × 10⁻⁶. -4 The extremely poor S / cm and cycling stability (capacity retention of 68.4%) confirm that "covalent grafting" is the core means to improve compatibility and conduction stability.

[0072] from Figure 1 It can be seen that the radius of the impedance spectrum directly corresponds to the ion migration resistance. The radius of the arc in Example 3 is significantly smaller than that in Example 2 and Comparative Example 1, corresponding to its room temperature ionic conductivity (1.3 × 10⁻⁶). -3 The S / cm ratio was significantly higher than that of Example 2 (8.5 × 10⁻⁶). -4 S / cm) and Comparative Example 1 (3.8×10 -4 S / cm). The core mechanism lies in the high dosage of VBIM-BF3Li (35 parts) in Example 3, which results in a high-density and uniform distribution of imidazolium-borate sites in the polyether-polyester covalent network, synergistically constructing a continuous Li with the polyether segments of PEGMA. + The transport channel significantly reduces the ion migration barrier; however, in Example 2, due to insufficient VBIM-BF3Li (25 parts), the transport site density was low. In Comparative Example 1, due to the lack of a single-ion conductor and reliance on dual-ion conduction, the ion migration resistance increased significantly, ultimately resulting in a hierarchical difference in conductivity.

[0073] Figure 2Example 3 showed no significant current abrupt change within 5.5V, demonstrating a wide electrochemical stability window of ≥5.5V. This performance stems from the synergistic mechanism of the single-ion conductor structure and the dual-framework characteristics: the stable coordination structure formed by the imidazolium cation and boron phenyl group of VBIM-BF3Li can suppress the anion oxidative decomposition under high voltage; at the same time, the covalent network of the PEGMA-PCL dual-framework has excellent redox resistance, avoiding the segmental degradation of traditional polyether frameworks under high voltage. This ensures the stability of the electrolyte membrane in high-voltage systems from the molecular structure level, making it suitable for the application requirements of high-voltage cathode materials such as LiCoO2.

[0074] Figure 3 The tensile strength (21 MPa) and elongation at break (170%) of Example 3 significantly exceeded those of Comparative Example 2 (8 MPa, 85%) and Comparative Example 3 (11 MPa, 100%). The mechanism lies in the synergistic effect of the two polymer backbones: the polyether segments of PEGMA provide flexible segments, giving the film excellent ductility; the polyester segments of PCL, due to their high crystallinity, form physical crosslinking points, strengthening the rigid support of the film. The two form a composite network of "flexible transport-rigid support" through covalent copolymerization. In contrast, Comparative Example 2 (physical blend) lacks chemical bonding, and the single ionic conductor and backbone easily separate, resulting in poor structural integrity; Comparative Example 3 (single polymer backbone) lacks the rigid support of PCL, and the flexible segments of PEGMA alone cannot withstand high stress, ultimately resulting in significant deterioration of mechanical properties.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a solid electrolyte membrane in an energy storage system, characterized in that, include: 4-Borophenylimidazolium was mixed with vinyl bromide, and acetonitrile was added as a solvent to carry out the reflux reaction. After cooling, 1-vinyl-3-(4-boronphenyl)imidazolium bromide was collected and recrystallized with acetonitrile to obtain purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide. The purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide was dissolved in deionized water, lithium hexafluorophosphate was added, and after ion exchange, the filtrate was concentrated by distillation to a viscous state. Anhydrous ethanol was added, and the solution was heated to dissolve. After cooling, the solution was allowed to stand and crystallize. The crystals were collected, washed, and dried to obtain 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate lithium monomer. 1-Vinyl-3-(4-Borophenyl)imidazolium hexafluorophosphate lithium was mixed with polyethylene glycol methacrylate, polycaprolactone and a crosslinking agent, toluene was added as a solvent and stirred to form a homogeneous and transparent mixture of two polymer backbone monomers. The photoinitiator was dissolved in a mixture of two polymer backbone monomers and degassed to obtain a polymerization precursor solution. The polymerization precursor solution was coated onto a substrate, subjected to ultraviolet light irradiation, and subjected to free radical copolymerization reaction. After drying, a single-ion conductor electrolyte membrane was obtained as a preliminary product. The initial sample of the single-ion conductor electrolyte membrane was statically immersed in LiTFSI / DMC activation solution for Li + After co-coordination with the imidazolium-borate sites within the membrane, and washing and drying, a solid electrolyte membrane is obtained.

2. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, The molar ratio of 4-boronphenylimidazolium, ethylene bromide, and lithium hexafluorophosphate is 1:1.1:1; The total mass ratio of the mixture of 4-boronphenylimidazolium and ethylene bromide to the volume ratio of acetonitrile is 1:8~12; The mass ratio of purified 1-vinyl-3-(4-boronphenyl)imidazolium bromide to deionized water is 1:8~10; The volume ratio of the filtrate, which is concentrated to a viscous state by distillation, to anhydrous ethanol is 1:3~5.

3. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, During the reflux reaction, the stirring speed is 250~300 r / min, the reaction temperature is 65~75℃, and the reaction time is 10~14 h; After the reflux reaction is complete, cool to room temperature.

4. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, During the ion exchange process, the temperature was room temperature, the time was 5-7 hours, and the stirring speed was 200-250 r / min; After ion exchange, the heating dissolution temperature is 40~50℃, the cooling temperature is 0~5℃, the static crystallization time is 8~12h, the drying temperature is 45~55℃, and the drying time is 10~12h.

5. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, In the mixture of dual polymer backbone monomers, 40-60 parts of polyethylene glycol methacrylate, 20-35 parts of polycaprolactone, 25-35 parts of lithium 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate, 1.5-3 parts of crosslinking agent and 100-150 parts of toluene are added respectively. The photoinitiator accounts for 1.5% to 2.5% of the total mass of lithium 1-vinyl-3-(4-boronphenyl)imidazolium hexafluorophosphate, polyethylene glycol methacrylate, polycaprolactone, and crosslinking agent. The crosslinking agent is trimethylolpropane triacrylate; The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

6. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, The stirring speed of the dual polymer backbone monomer mixture is 250~350 r / min, the stirring temperature is 25~35℃, and the stirring time is 30~50 min; During the degassing process, the vacuum degree is (-0.1)~(-0.08)MPa, the temperature is 25~35℃, the time is 1.5~2.5 h, and the gas is released once every 30 min.

7. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, The ultraviolet light irradiation wavelength is 340~380nm, and the power is 25~35mW / cm. 2 The time is 30-50 minutes; After the free radical copolymerization reaction, the drying temperature is 55~65℃, the drying vacuum degree is 0.07~0.09MPa, and the drying time is 5~7h.

8. The method for preparing a solid electrolyte membrane in an energy storage system according to claim 1, characterized in that, The concentration of the LiTFSI / DMC activation solution is 0.08~0.12 mol / L; The static soaking temperature is 20~30℃, and the static soaking time is 6~10 h; After static soaking, the drying temperature is 45~55℃, the drying vacuum degree is 0.07~0.09MPa, and the drying time is 6~10 h.

9. A solid electrolyte membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that, Tensile strength ≥13MPa, elongation at break ≥121%, and lithium-ion transference number ≥0.

83.

10. A solid-state lithium battery, characterized in that, It is made from the solid electrolyte membrane as described in claim 9.

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