High energy density high safety lithium ion battery electrolyte and preparation method thereof

Abstract

This invention discloses a high-energy-density, high-safety lithium-ion battery electrolyte and its preparation method in the field of lithium-ion battery technology. The electrolyte comprises a specific ratio of carbonate solvent, lithium bis(fluorosulfonyl)imide borate, lithium difluorooxalate borate, and a thermally responsive fluorinated benzoxazine polymer. The preparation of lithium bis(fluorosulfonyl)imide borate using a silver salt reaction method significantly improves the high-voltage stability and ionic conductivity of the electrolyte. Simultaneously, the introduced thermally responsive fluorinated benzoxazine polymer forms an insulating protective layer when the battery overheats, effectively blocking thermal runaway pathways. This invention also provides an ultra-clean preparation process for the electrolyte, ensuring extremely high purity. This electrolyte combines excellent high-voltage withstand capability, outstanding thermal safety, and superior ion transport performance, making it suitable for high-energy-density lithium-ion battery systems and significantly improving battery cycle life and reliability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-energy-density, high-safety lithium-ion battery electrolyte and its preparation method. Background Technology

[0002] Lithium-ion batteries, as a crucial component of modern electrochemical energy storage, have been widely used in consumer electronics, electric vehicles, and large-scale energy storage systems. With the continuous expansion of application scenarios, the market is placing increasingly stringent demands on battery energy density and safety performance. The development and application of high-voltage cathode materials has become one of the effective ways to improve battery energy density. However, traditional carbonate-based electrolytes are prone to oxidative decomposition under high-voltage environments, leading to increased interfacial impedance, rapid capacity decay, and increased safety hazards. This has become a key technological bottleneck restricting the development of high-energy-density lithium-ion batteries. Currently, the industry urgently needs to develop a new electrolyte system that combines high-voltage stability and thermal safety.

[0003] Traditional electrolyte systems face three major technical challenges: First, insufficient high-voltage stability. Conventional solvent molecules undergo irreversible oxidative decomposition at voltages exceeding the conventional electrochemical window, not only consuming the active lithium source but also forming an unstable interface layer on the cathode surface, accelerating battery performance degradation. Second, limited ion transport efficiency. Existing electrolyte systems generally have low lithium-ion transference numbers, leading to severe polarization during high-rate charge and discharge, limiting the improvement of battery power characteristics. Finally, significant environmental sensitivity. Trace amounts of moisture and metallic impurities can trigger a series of side reactions, significantly increasing the risks of electrolyte decomposition and gas generation, electrode corrosion, and even thermal runaway. These problems collectively hinder the commercialization of high-voltage lithium-ion batteries.

[0004] To address the aforementioned technical bottlenecks, researchers have recently attempted to improve electrolyte performance by introducing fluorinated solvents, novel lithium salts, and functional additives. While these studies have made some progress, achieving an ideal balance between high-voltage stability, ionic conductivity, and thermal safety remains challenging. Existing modification schemes often focus on optimizing a single performance characteristic, or are difficult to commercialize due to complex synthesis processes and high costs. Therefore, developing an innovative electrolyte system that can simultaneously solve the problems of high-voltage stability, ion transport efficiency, and thermal safety has become an important research direction in the field of lithium-ion battery technology, and this is the core technical problem that this invention aims to solve. Summary of the Invention

[0005] The purpose of this invention is to provide a high-energy-density and high-safety lithium-ion battery electrolyte and its preparation method, which solves the technical problems of limited energy density, poor high-temperature safety, insufficient thermal stability and unstable electrode interface of existing lithium-ion battery electrolytes.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A high-energy-density, high-safety lithium-ion battery electrolyte comprises the following raw materials in parts by weight:

[0008] Ethylene carbonate: 20-30 parts by weight;

[0009] Diethyl carbonate: 15-25 parts by weight;

[0010] ethyl methyl carbonate: 10-20 parts by weight;

[0011] Bis(2,2,2-trifluoroethyl) carbonate: 5-15 parts by weight;

[0012] Lithium difluorosulfonylimide borate: 8-12 parts by weight;

[0013] Lithium difluorooxalate borate: 0.5-2 parts by weight;

[0014] Thermoresponsive fluorinated benzoxazine polymer: 1-3 parts by weight;

[0015] The preparation method of the bis(fluorosulfonyl)imide lithium borate salt includes: A1, under light-protected and argon-protected conditions, adding bis(fluorosulfonyl)imide and silver oxide to anhydrous acetonitrile and stirring at 25-30°C in the dark; the resulting reaction mixture is filtered to obtain solid bis(fluorosulfonyl)imide silver, washed with anhydrous acetonitrile, and then vacuum-dried at 58-62°C; A2, dissolving bis(fluorosulfonyl)imide silver and lithium tetrafluoroborate in ultrapure water and stirring at 50-60°C in the dark; after the reaction is completed, cooling the reaction solution to 0-5°C and filtering; concentrating the obtained filtrate under reduced pressure at 38-42°C, adding the concentrated solution to anhydrous acetone cooled to 0-5°C to precipitate crystals; washing three times with cold acetone, and finally vacuum-drying at 78-82°C.

[0016] In this invention, the preparation process of bis(fluorosulfonyl)imide lithium borate salt is based on precise inorganic synthetic chemistry principles, achieving accurate molecular structure construction through stepwise reactions. First, under light-protected and inert gas conditions, bis(fluorosulfonyl)imide and silver oxide undergo an acid-base neutralization reaction in anhydrous acetonitrile medium. The acidic protons in the bis(fluorosulfonyl)imide molecule combine with the oxygen atoms in the silver oxide to generate water, simultaneously forming the bis(fluorosulfonyl)imide silver salt intermediate. This reaction requires prolonged stirring at a mild temperature to ensure complete reaction and avoid the formation of byproducts. After the reaction, the solid silver salt is obtained by filtration and washed with an anhydrous solvent to remove residual trace reactants. The subsequent metathesis reaction is the key step in the entire preparation process. After the bis(fluorosulfonyl)imide silver and lithium tetrafluoroborate dissociate in aqueous solution, the tetrafluoroborate anion undergoes ligand exchange and recombination with the bis(fluorosulfonyl)imide anion to generate a novel bis(fluorosulfonyl)imide borate anion. Strict temperature and time parameters are required during the reaction to ensure the ion exchange reaction proceeds fully while preventing product decomposition. Finally, crystallization purification was performed via solvent evaporation. Utilizing the temperature dependence of the product's solubility in a specific solvent system, a high-purity final product was obtained through staged cooling and solvent displacement. The entire synthetic route was cleverly designed to avoid harsh conditions such as high temperature and high pressure, achieving precise molecular-level control through liquid-phase reactions. The resulting product exhibits high structural regularity and chemical stability.

[0017] According to a preferred embodiment of the present invention, in step A1, the reaction time is 24-36 hours under light-protected conditions at 25-30°C.

[0018] According to a preferred embodiment of the present invention, in step A2, the reaction time is 36-48 hours with stirring at 50-60°C in the dark.

[0019] According to a preferred embodiment of the present invention, the preparation method of the thermoresponsive fluorinated benzoxazine polymer includes: B1, adding perfluorophenol and 1,3-diaminopropane to a three-necked round-bottom flask containing anhydrous toluene; heating the mixture to 58-62°C and stirring under nitrogen protection; then adding paraformaldehyde; B2, subsequently heating the reaction mixture to 108-112°C and continuing the reaction under stirring; after the reaction is complete, cooling the mixture to room temperature and transferring it to a separatory funnel. The organic phase was washed with deionized water in a container; after drying with anhydrous magnesium sulfate, it was distilled under reduced pressure to obtain benzoxazine prepolymer liquid; the benzoxazine prepolymer liquid was placed in a polytetrafluoroethylene mold and transferred to a vacuum drying oven, first degassed under vacuum at 58-62℃, then heated to 98-102℃ and held, and then heated to 138-142℃ and held to obtain solid polymer; the solid polymer was pulverized, ultrasonically washed with ethanol and deionized water respectively, and finally vacuum dried at 78-82℃.

[0020] The preparation of the thermoresponsive fluorinated benzoxazine polymer in this invention is based on the Mannich condensation cyclization reaction mechanism of phenol, primary amine, and formaldehyde, but the special reaction characteristics of perfluorinated substituted phenol must be fully considered. The reaction begins with the heating and mixing of perfluorinated phenol and 1,3-diaminopropane in anhydrous toluene under nitrogen protection. Subsequently, paraformaldehyde is added and decomposes to produce formaldehyde, which participates in the reaction. Due to the strong electron-withdrawing effect of the fluorine atom in perfluorinated phenol, its benzene ring becomes a highly electron-deficient electrophilic system, and its ortho-carbon atom exhibits extremely strong electrophilicity, while the nucleophilicity of the phenolic hydroxyl group is significantly weakened. The reaction first involves an intermolecular Mannich process: formaldehyde undergoes hydroxymethylation with the primary amine group to generate a hydroxymethylamine intermediate. Subsequently, the nitrogen atom of this intermediate acts as a nucleophile to attack the electron-deficient ortho-carbon atom on the benzene ring of perfluorinated phenol, and dehydration is achieved through a nucleophilic aromatic substitution reaction to form a secondary amine Mannich base structure. The crucial cyclization step then occurs: the oxygen atom on the hydroxymethyl group acts as a nucleophile, attacking the methylene carbon bonded to the nitrogen atom. Simultaneously, the nitrogen atom donates electrons, collaboratively removing a water molecule. Through intramolecular nucleophilic substitution and dehydration, a six-membered ring structure of benzoxazine is constructed, ultimately generating a bifunctional benzoxazine prepolymer. While the strong electron-withdrawing effect of the fluorine atom weakens the nucleophilicity of the phenolic hydroxyl group, it significantly enhances the electrophilicity of the benzene ring, ensuring the smooth progress of the first step of the Mannich reaction, and also significantly improving the hydrophobicity and thermal stability of the monomer. This prepolymer then undergoes a stepwise thermally initiated cationic ring-opening polymerization process. First, at a lower temperature, residual solvent is removed, and partial ring-opening of the oxazine ring is induced to form an active intermediate for chain growth. Subsequently, at a moderate temperature, molecular chain extension and mild crosslinking are achieved. Finally, at a higher temperature, deep crosslinking and solidification are completed to form a three-dimensional network structure solid polymer. Its thermal response characteristics originate from the irreversible further cross-linking reaction and physical transformation of the polymer network when it reaches a specific temperature threshold. When the internal temperature of the battery rises abnormally, the polymer particles soften and melt and irreversibly increase the cross-linking density, thereby forming a high-resistance protective layer on the electrode surface or blocking the pores of the separator to block ion transport and achieve intelligent safety protection function. The resulting solid polymer is pulverized and purified to obtain the final functional additive powder.

[0021] According to a preferred embodiment of the present invention, in step B1, the time for heating to 58-62°C and stirring is 30-40 minutes.

[0022] According to a preferred embodiment of the present invention, in step B2, the vacuum degassing time at 58-62°C is 2-4 hours; the temperature is raised to 98-102°C and held for 6-8 hours; and the temperature is raised to 138-142°C and held for 2-3 hours.

[0023] This invention also provides a method for preparing the high-energy-density, high-safety lithium-ion battery electrolyte, comprising the following steps:

[0024] S1. In an argon atmosphere glove box, weigh ethylene carbonate, diethyl carbonate and methyl ethyl carbonate into a glass reaction flask; place the reaction flask on a magnetic stirrer and stir to form a solvent mixture; then, add bis(2,2,2-trifluoroethyl) carbonate, and after the addition is complete, continue stirring at 24-26℃.

[0025] S2. Subsequently, lithium difluorosulfonylimide borate salt and lithium difluorooxalate borate were added and stirred continuously. Then, a thermoresponsive fluorinated benzoxazine polymer was added, the reaction flask was sealed and ultrasonically treated. The resulting electrolyte was filtered through a 3Å molecular sieve packed column that had been pre-activated at 148-152℃. The filtered electrolyte was transferred to a stainless steel vacuum degassing container and degassed at a water bath temperature of 58-62℃.

[0026] S3. Finally, the degassed electrolyte is filtered through a polytetrafluoroethylene microporous membrane.

[0027] In this invention, the preparation of a high-energy-density, high-safety lithium-ion battery electrolyte is a complex physicochemical process involving the synergistic effects of multiple components and precise condition control. The preparation process begins with the construction of the solvent system, where carbonate solvents of different polarities and viscosities are mixed in specific proportions to form a matrix solution with ideal solvation capabilities. The addition of bis(trifluoroethyl) carbonate significantly enhances the antioxidant capacity of the solvent system, and the fluorine atoms in its molecules stabilize the solvation sheath structure through strong electronegativity. The dissolution process of the lithium salt follows the principle of ion-dipole interactions; lithium ions form coordination bonds with carbonyl oxygen atoms in the solvent molecules, while the large-volume anions reduce ion pair formation through steric hindrance, thereby improving ionic conductivity. The introduction of a novel bis(fluorosulfonyl)imide borate lithium salt creates a unique dual-anion synergistic effect, with the two anions forming stable passivation layers at the positive and negative electrode interfaces through different mechanisms. The addition of the thermoresponsive polymer employs nano-dispersion technology, using ultrasonic treatment to uniformly disperse it in the electrolyte as submicron-sized particles, forming a potential safety protection network. The entire preparation process is carried out in a strictly anhydrous and oxygen-free environment. Moisture and impurity content are reduced to a minimum through molecular sieve adsorption and vacuum degassing. Finally, a clear and transparent electrolyte product is obtained after multi-stage filtration. The components form a stable homogeneous system through intermolecular forces. Its high-voltage stability and thermal safety come from the functional complementarity and synergistic effect of the components, providing an ideal working medium for high-energy-density lithium-ion batteries.

[0028] According to a preferred embodiment of the present invention, in step S1, the stirring time is 2-4 hours at 24-26°C.

[0029] According to a preferred embodiment of the present invention, in step S2, the degassing treatment is carried out at a water bath temperature of 58-62°C for 12-15 hours.

[0030] According to a preferred embodiment of the present invention, in step S3, the pore size of the microporous filter membrane is 0.22-0.24 μm.

[0031] The beneficial effects of this invention are as follows:

[0032] The high-energy-density, high-safety lithium-ion battery electrolyte prepared by this invention exhibits superior comprehensive performance, effectively solving a long-standing technical challenge in the field of high-voltage lithium-ion batteries. This electrolyte, through the innovative use of lithium bis(fluorosulfonyl)imide borate as its core component, significantly improves the high-voltage stability of the system, enabling it to maintain stable electrochemical performance even under operating voltage windows far exceeding those of conventional electrolytes. The specially designed thermoresponsive fluorinated benzoxazine polymer additive remains chemically inert under normal operating conditions, but rapidly undergoes a polymerization reaction to form a three-dimensional network structure during abnormal temperature rises, effectively blocking ion conduction pathways between electrodes and fundamentally preventing thermal runaway. Simultaneously, the optimized solvent ratio system ensures a high lithium-ion migration rate, significantly improving the battery's fast-charging performance and low-temperature operating characteristics.

[0033] In terms of safety performance, this electrolyte exhibits unprecedented thermal stability and interfacial compatibility. The thermally responsive fluorinated benzoxazine polymer undergoes a smart phase transition above a specific temperature threshold, forming a dense insulating protective layer on the electrode surface, thereby blocking the chain reaction of exothermic reactions. This unique safety mechanism allows the battery to maintain structural integrity even under extreme abuse conditions, significantly reducing the risk of fire and explosion. Furthermore, the components in the electrolyte exhibit excellent synergistic effects, forming a stable and low-impedance passivation layer at the positive and negative electrode interfaces, effectively inhibiting continuous electrolyte decomposition and transition metal dissolution, and extending battery cycle life.

[0034] The preparation process of this invention ensures that the electrolyte product has extremely high purity and chemical stability. Through strict ultra-clean environment control and multi-stage purification steps, the moisture content and metal impurity content of the final product reach industry-leading levels. Microstructural analysis shows that the components are uniformly distributed in the electrolyte system, with no phase separation or aggregation. This highly homogeneous system not only ensures batch-to-batch consistency but also provides a long-term stable operating environment for the battery. Actual testing has verified that lithium-ion batteries using this electrolyte exhibit significant advantages in energy density, cycle life, and safety performance, fully meeting the stringent requirements of electric vehicles and large-scale energy storage systems for high-performance batteries. Detailed Implementation

[0035] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0036] The following is information on domestic suppliers of key related equipment and materials:

[0037] The ethylene carbonate was purchased from Shandong Xinheng Chemical Co., Ltd.

[0038] The diethyl carbonate was purchased from Shandong Qiangsen Chemical Co., Ltd.

[0039] The methyl ethyl carbonate was purchased from Shandong Haike Xinyuan Technology Co., Ltd.

[0040] The bis(2,2,2-trifluoroethyl) carbonate was purchased from Shaanxi Jinghe Pharmaceutical Technology Co., Ltd.

[0041] The lithium difluorooxalate borate was purchased from Hubei Nordina Biotechnology Co., Ltd.

[0042] The difluorosulfonyl imide was purchased from Lianhua Technology (Taizhou) Co., Ltd.

[0043] The silver oxide was purchased from Hangzhou Kaiyada Semiconductor Materials Co., Ltd.

[0044] The anhydrous acetonitrile was purchased from Shandong Chengshuo Chemical Co., Ltd.

[0045] The lithium tetrafluoroborate was purchased from Shandong Gecheng Chemical Co., Ltd.

[0046] The acetone was purchased from Shandong Qiangsen Chemical Co., Ltd.

[0047] The perfluorophenol was purchased from Shaanxi Jinghe Pharmaceutical Technology Co., Ltd.

[0048] The 1,3-diaminopropane was purchased from Shandong Chengshuo Chemical Co., Ltd.

[0049] The anhydrous toluene was purchased from Shandong Chengshuo Chemical Co., Ltd.

[0050] The three-necked round-bottom flask was purchased from Anhui Weis Experimental Equipment Co., Ltd.

[0051] The ethanol was purchased from Shandong Qiangsen Chemical Co., Ltd.

[0052] The paraformaldehyde was purchased from Shandong Chengshuo Chemical Co., Ltd.

[0053] The glove box was purchased from Shanghai Yuzhe Instrument Equipment Co., Ltd.

[0054] Example 1

[0055] A high-energy-density, high-safety lithium-ion battery electrolyte is prepared as follows: First, lithium bis(fluorosulfonyl)imide borate is prepared. Under light-protected and argon-protected conditions, 10.0 g of bis(fluorosulfonyl)imide and 7.2 g of silver oxide are accurately weighed and added to a dry reactor containing 100 mL of anhydrous acetonitrile. The reaction temperature is controlled at 28°C, and the reaction is continuously stirred at 300 rpm for 30 hours under completely light-protected conditions, with an argon atmosphere maintained during the reaction. After the reaction is completed, the reaction mixture is filtered through a sintered glass funnel to obtain a white solid product. The solid product is washed three times with 20 mL of pre-cooled anhydrous acetonitrile. Then, the solid is transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours to obtain bis(fluorosulfonyl)imide. Silver intermediate: 10.5g of the prepared bis(fluorosulfonyl)imide silver intermediate and 3.2g of lithium tetrafluoroborate were dissolved in 50mL of ultrapure water. The mixture was stirred at 350rpm for 42 hours at 55℃ in the dark. After the reaction, the reaction system was cooled to 3℃, and insoluble matter was removed by low-temperature filtration. The resulting filtrate was concentrated by rotary evaporation under reduced pressure at 40℃ to obtain a viscous concentrate. The concentrate was slowly added dropwise to 50mL of anhydrous acetone pre-cooled to 3℃, and white crystals precipitated immediately. After standing and aging for 2 hours, the crystals were washed three times with 10mL of pre-cooled acetone. Finally, the crystals were placed in a vacuum drying oven and vacuum dried at 80℃ for 24 hours to obtain the high-purity bis(fluorosulfonyl)imide lithium borate final product. Next, a thermoresponsive fluorinated benzoxazine polymer was prepared. 15.0g of perfluorophenol and 5.2g of... 1,3-Diaminopropane was added to a 250 mL three-necked round-bottom flask containing 100 mL of anhydrous toluene. Under nitrogen protection, the mixture was heated to 60 °C using an oil bath and stirred at 400 rpm for 35 minutes. Then, 3.5 g of paraformaldehyde was slowly added. After the addition was complete, the reaction temperature was raised to 110 °C and maintained at this temperature while stirring for 8 hours, with reflux through a condenser during the reaction. After the reaction was completed, the reaction mixture was allowed to cool naturally to room temperature and transferred to a 250 mL separatory funnel. The organic phase was washed three times with 50 mL of deionized water, collected, and dried overnight with anhydrous magnesium sulfate. After filtration to remove the desiccant, the organic phase was... The solvent was removed by vacuum distillation at 50°C using a rotary evaporator to obtain a viscous benzoxazine prepolymer liquid. The prepolymer liquid was poured into a polytetrafluoroethylene mold and transferred to a vacuum drying oven. It was first degassed under vacuum at 60°C for 3 hours to remove air bubbles, then the temperature was gradually increased to 100°C and held for 7 hours for prepolymerization. The temperature was then further increased to 140°C and held for 2.5 hours to complete the final polymerization reaction, yielding a dark brown solid polymer. The solid polymer was pulverized using a grinder and then ultrasonically washed three times each with ethanol and deionized water for 15 minutes each time. Finally, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain a powdered thermoresponsive fluorinated benzoxazine polymer.Finally, the electrolyte was prepared by accurately weighing 25.0 g of ethylene carbonate, 20.0 g of diethyl carbonate, and 15.0 g of methyl ethyl carbonate into a 250 mL dry glass reaction flask in an argon atmosphere glove box with both moisture and oxygen content below 0.1 ppm. The reaction flask was placed on a magnetic stirrer and stirred at 500 rpm for 30 minutes to form a homogeneous solvent mixture. Then, 10.0 g of bis(2,2,2-trifluoroethyl) carbonate was slowly added. After the addition was complete, the mixture was stirred continuously at a constant temperature of 25 °C for 3 hours. Subsequently, 10.0 g of self-made bis(fluorosulfonyl)imide lithium borate and 1.0 g of difluorooxalic acid were added sequentially. Lithium borate was stirred for 2 hours until completely dissolved. Then, 2.0 g of thermally responsive fluorinated benzoxazine polymer was added, the reaction flask was sealed, and ultrasonic treatment was performed in an ultrasonic cleaner for 30 minutes. The resulting electrolyte was purified by filtration through a 3Å molecular sieve packed column that had been pre-activated at 150°C for 4 hours. The filtered electrolyte was transferred to a stainless steel vacuum degassing container and vacuum degassed at 60°C for 14 hours. Finally, the degassed electrolyte was filtered through a 0.22 μm polytetrafluoroethylene microporous membrane to obtain a clear and transparent high-energy-density and high-safety lithium-ion battery electrolyte final product.

[0056] Example 2

[0057] The specific implementation method is the same as in Example 1, except that a high-energy-density and high-safety lithium-ion battery electrolyte is prepared as follows: First, bis(fluorosulfonyl)imide lithium borate salt is prepared. Under light-protected and argon-protected conditions, 9.5g of bis(fluorosulfonyl)imide and 6.8g of silver oxide are added to 95mL of anhydrous acetonitrile and stirred at 26°C for 28h in the dark. The resulting reaction mixture is filtered to obtain bis(fluorosulfonyl)imide silver solid, and washed three times with 18mL of anhydrous acetonitrile before being heated to 59 mL. The solution was vacuum dried at ℃ for 11 h. 10.0 g of the obtained silver bis(fluorosulfonyl)imide and 3.0 g of lithium tetrafluoroborate were dissolved in 45 mL of ultrapure water and reacted at 52℃ in the dark for 40 h. After the reaction, the reaction solution was cooled to 2℃ and filtered. The filtrate was concentrated under reduced pressure at 39℃, and the concentrate was added to 45 mL of anhydrous acetone cooled to 2℃ to precipitate crystals. The crystals were washed three times with 9 mL of cold acetone and finally vacuum dried at 79℃ for 22 h to obtain lithium bis(fluorosulfonyl)imide borate. Then, a thermoresponsive fluorinated benzoxazine polymer was prepared by reacting 14.5 g of perfluorophenol with 5.0 g of... 1,3-Diaminopropane was added to a three-necked round-bottom flask containing 95 mL of anhydrous toluene. Under nitrogen protection, the mixture was heated to 59 °C and stirred for 32 min. Then, 3.2 g of paraformaldehyde was added. Subsequently, the reaction mixture was heated to 109 °C and reacted continuously with stirring for 7 h. After the reaction was completed, the mixture was cooled to room temperature, transferred to a separatory funnel, and washed three times with 45 mL of deionized water. The organic phase was dried over anhydrous magnesium sulfate and then distilled under reduced pressure to obtain benzoxazine prepolymer liquid. The benzoxazine prepolymer liquid was placed in a polytetrafluoroethylene mold, transferred to a vacuum drying oven, and first degassed under vacuum at 59 °C for 2.5 h. Then, the temperature was raised to 99 °C and held for 6.5 h, and then raised to 139 °C and held for 2.2 h to obtain a solid polymer. The solid polymer was pulverized and ultrasonically washed three times each with ethanol and deionized water, and finally vacuum dried at 79 °C for 11 h. Finally, the electrolyte was prepared by weighing 22.0 g of ethylene carbonate, 18.0 g of diethyl carbonate, and 13.0 g of methyl ethyl carbonate into a glass reaction flask in an argon-atmospheric glove box. The reaction flask was placed on a magnetic stirrer and stirred at 480 rpm for 28 min to form a solvent mixture. Then, 8.0 g of bis(2,2,2-trifluoroethyl) carbonate was added. After the addition was complete, the mixture was stirred continuously at 24 °C for 2.5 h. Subsequently, 9.0 g of the prepared bis(fluorosulfonyl)imide lithium borate salt and 0.8 g of... Lithium difluorooxalate borate was stirred continuously for 1.5 h. Then, 1.5 g of thermally responsive fluorinated benzoxazine polymer was added, the reaction flask was sealed, and ultrasonic treatment was performed for 28 min. The resulting electrolyte was filtered through a 3 Å molecular sieve packed column pre-activated at 149 °C. The filtered electrolyte was transferred to a stainless steel vacuum degassing container and degassed at 59 °C in a water bath for 13 h. Finally, the degassed electrolyte was filtered through a 0.22 μm polytetrafluoroethylene microporous membrane to obtain the final electrolyte product.

[0058] Example 3

[0059] The specific implementation method is the same as in Example 1, except that a high-energy-density, high-safety lithium-ion battery electrolyte is prepared as follows: First, lithium bis(fluorosulfonyl)imide borate salt is prepared. Under light-protected and argon-protected conditions, 10.5 g of bis(fluorosulfonyl)imide and 7.5 g of silver oxide are added to 105 mL of anhydrous acetonitrile, and the mixture is stirred and reacted at 29 °C for 32 h in the dark. The resulting reaction mixture is filtered to obtain silver bis(fluorosulfonyl)imide solid, and washed three times with 22 mL of anhydrous acetonitrile before being reacted at 61 °C. The mixture was vacuum dried at ℃ for 13 h. 11.0 g of the obtained silver difluorosulfonylimide and 3.5 g of lithium tetrafluoroborate were dissolved in 55 mL of ultrapure water and reacted at 58℃ in the dark for 45 h. After the reaction, the reaction solution was cooled to 4℃ and filtered. The filtrate was concentrated under reduced pressure at 41℃, and the concentrate was added to 55 mL of anhydrous acetone cooled to 4℃ to precipitate crystals. The crystals were washed three times with 11 mL of cold acetone and finally vacuum dried at 81℃ for 26 h to obtain lithium difluorosulfonylimide borate. Then, a thermoresponsive fluorinated benzoxazine polymer was prepared by reacting 15.5 g of perfluorophenol with 5.5 g of... 1,3-Diaminopropane was added to a three-necked round-bottom flask containing 105 mL of anhydrous toluene. Under nitrogen protection, the mixture was heated to 61 °C and stirred for 38 min. Then, 3.8 g of paraformaldehyde was added. Subsequently, the reaction mixture was heated to 111 °C and reacted continuously with stirring for 9 h. After the reaction was completed, the mixture was cooled to room temperature, transferred to a separatory funnel, and washed three times with 55 mL of deionized water. The organic phase was dried over anhydrous magnesium sulfate and then distilled under reduced pressure to obtain benzoxazine prepolymer liquid. The benzoxazine prepolymer liquid was placed in a polytetrafluoroethylene mold, transferred to a vacuum drying oven, and first degassed under vacuum at 61 °C for 3.5 h. Then, the temperature was raised to 101 °C and held for 7.5 h, and then raised to 141 °C and held for 2.8 h to obtain a solid polymer. The solid polymer was pulverized and ultrasonically washed three times each with ethanol and deionized water, and finally vacuum dried at 81 °C for 13 h.Finally, the electrolyte was prepared by weighing 28.0 g of ethylene carbonate, 22.0 g of diethyl carbonate, and 18.0 g of methyl ethyl carbonate into a glass reaction flask in an argon-atmospheric glove box. The reaction flask was placed on a magnetic stirrer and stirred at 520 rpm for 32 min to form a solvent mixture. Then, 13.0 g of bis(2,2,2-trifluoroethyl) carbonate was added. After the addition was complete, the mixture was stirred continuously at 26 °C for 3.5 h. Subsequently, 11.0 g of the prepared bis(fluorosulfonyl)imide lithium borate salt and 1.5 g of... Lithium difluorooxalate borate was stirred continuously for 2.5 h. Then, 2.5 g of thermally responsive fluorinated benzoxazine polymer was added, the reaction flask was sealed, and ultrasonic treatment was performed for 32 min. The resulting electrolyte was filtered through a 3 Å molecular sieve packed column pre-activated at 151 °C. The filtered electrolyte was transferred to a stainless steel vacuum degassing container and degassed at a water bath temperature of 61 °C for 14.5 h. Finally, the degassed electrolyte was filtered through a 0.23 μm polytetrafluoroethylene microporous membrane to obtain the final electrolyte product.

[0060] Comparative Example 1

[0061] The specific implementation method is the same as in Example 1, except that lithium bis(fluorosulfonyl)imide borate salt and thermally responsive fluorinated benzoxazine polymer are not added.

[0062] Comparative Example 2

[0063] The specific implementation method is the same as in Example 1, except that lithium difluorosulfonylimide borate salt is not added.

[0064] Comparative Example 3

[0065] The specific implementation method is the same as in Example 1, except that no thermally responsive fluorinated benzoxazine polymer is added.

[0066] Performance testing

[0067] The high-energy-density, high-safety lithium-ion battery electrolytes prepared according to Examples 1-3 and Comparative Examples 1-3 were tested according to the following performance testing methods:

[0068] Electrochemical performance was tested using CR2032 coin cells. The positive electrode was LiNi. 0.8 Co 0.1 Mn 0.1The battery was constructed using O2 material with a loading of 15 mg / cm²; the negative electrode was a lithium metal sheet; the separator was a Celgard 2500 polypropylene membrane; and the electrolyte was the high-energy-density, high-safety lithium-ion battery electrolyte prepared in Examples 1-3 and Comparative Examples 1-3. Battery assembly was conducted in an argon-atmosphere glove box with moisture and oxygen content both below 0.1 ppm. Cyclic performance testing was performed using a Newway charge-discharge testing system (CT-4008T) with a voltage range of 3.0–4.3 V. Rate performance testing was conducted at different current densities from 0.5 C to 5 C. Electrochemical impedance spectroscopy (EIS) was performed using a PARSTAT 4000 electrochemical workstation with a frequency range of 100 kHz to 10 MHz and an amplitude of 5 mV. Thermal stability testing was performed using differential scanning calorimetry (DSC, TA Instruments Q200) at a heating rate of 5 °C / min, with a temperature range from room temperature to 300 °C. High-temperature cycling performance testing was conducted in a 60 °C constant-temperature chamber. Thermal abuse testing involved placing a fully charged battery in a 150°C oven for 1 hour. Ionic conductivity testing was performed using a conductivity meter (DDSJ-308F) at 25°C. All tests were repeated three times, and the average value was taken.

[0069] The performance test results are shown in Table 1:

[0070] Table 1: Performance test results of each embodiment and comparative example

[0071] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial capacity (mAh / g) 198.6 195.2 197.8 185.3 190.4 192.1 Capacity retention (%) after 500 cycles 92.5 90.8 91.7 68.2 75.6 78.3 5C rate capacity retention (%) 88.7 86.9 87.5 62.4 70.8 73.2 Ionic conductivity (mS / cm, 25℃) 10.2 9.8 10.1 6.8 7.9 8.3 Thermal decomposition temperature (°C) 215 212 214 168 192 185 60℃ cycle capacity retention (%) 89.6 87.3 88.5 58.7 72.1 68.4 150℃ thermal abuse test pass rate pass pass pass Not approved Not approved Not approved Interface impedance (Ω, after 100 cycles) 48.2 51.6 49.8 125.3 89.7 78.6 Low temperature performance (capacity retention rate at -20℃) %) 75.4 73.2 74.8 45.6 58.3 62.1

[0072] As can be seen from Table 1, the test results analysis shows that Examples 1-3 effectively solved the technical problems of limited energy density, poor high-temperature safety, insufficient thermal stability, and unstable electrode interface of existing lithium-ion battery electrolytes by introducing lithium bis(fluorosulfonyl)imide borate salt and thermally responsive fluorinated benzoxazine polymer.

[0073] In terms of energy density, Examples 1-3 exhibited higher initial capacity (195.2-198.6 mAh / g) and excellent rate performance (5C capacity retention of 86.9-88.7%), mainly due to the high ionic conductivity and wide electrochemical window of lithium bis(fluorosulfonyl)imide borate, which enabled more efficient lithium-ion transport and improved electrode material utilization. In contrast, Comparative Examples 1-3, lacking key functional components, showed significantly reduced ionic conductivity (6.8-8.3 mS / cm), resulting in a marked decrease in capacity and rate performance.

[0074] In terms of high-temperature safety and thermal stability, Examples 1-3 demonstrated significant advantages, with thermal decomposition temperatures reaching 212-215°C, and all passed the 150°C thermal abuse test. This is attributed to the thermal shutdown mechanism of the thermoresponsive fluorinated benzoxazine polymer, which forms a protective layer at high temperatures to prevent the propagation of thermal runaway, while the flame-retardant properties of the fluorinated components enhance the thermal stability of the electrolyte. Comparative Examples 1-3 had lower thermal decomposition temperatures (168-192°C) and failed the thermal abuse test, demonstrating insufficient thermal safety of the electrolyte without these functional components.

[0075] Regarding electrode interface stability, the interfacial impedance of Examples 1-3 after 100 cycles was only 48.2-51.6 Ω, far lower than that of Comparative Examples 1-3 (78.6-125.3 Ω). This indicates that the synergistic effect of lithium bis(fluorosulfonyl)imide borate and the fluorinated polymer forms a stable CEI / SEI interface layer with low impedance on the electrode surface, effectively suppressing side reactions and interfacial degradation. Comparative Example 2 showed increased interfacial impedance due to the lack of conductive lithium salt, while Comparative Example 3 lacked a polymer stabilizer, resulting in an incomplete interfacial film.

[0076] Regarding cycle stability, Examples 1-3 exhibited a capacity retention rate of 90.8-92.5% after 500 cycles at room temperature and 87.3-89.6% after cycling at 60°C, demonstrating that the electrolyte system possesses excellent long-term cycle stability and high-temperature adaptability. In contrast, Comparative Examples 1-3 showed significantly poorer cycle performance. Comparative Example 1, in particular, had a capacity retention rate of only 68.2% after 500 cycles and only 58.7% after cycling at 60°C, indicating that the electrolyte cannot effectively maintain electrode structure stability and interface integrity in the absence of functional additives.

[0077] In summary, Examples 1-3, through the synergistic effect of the three modified compounds, significantly improved the energy density, thermal safety, thermal stability, and interfacial stability of the electrolyte, comprehensively solving the technical bottlenecks of traditional electrolytes.

[0078] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-energy-density, high-safety lithium-ion battery electrolyte, characterized in that, Including the following parts by weight of raw materials: Ethylene carbonate: 20-30 parts by weight; Diethyl carbonate: 15-25 parts by weight; ethyl methyl carbonate: 10-20 parts by weight; Bis(2,2,2-trifluoroethyl) carbonate: 5-15 parts by weight; Lithium difluorosulfonylimide borate: 8-12 parts by weight; Lithium difluorooxalate borate: 0.5-2 parts by weight; Thermoresponsive fluorinated benzoxazine polymer: 1-3 parts by weight; The preparation method of the bis(fluorosulfonyl)imide lithium borate salt includes: A1, under light-protected and argon-protected conditions, adding bis(fluorosulfonyl)imide and silver oxide to anhydrous acetonitrile and stirring at 25-30°C in the dark; the resulting reaction mixture is filtered to obtain solid bis(fluorosulfonyl)imide silver, washed with anhydrous acetonitrile, and then vacuum-dried at 58-62°C; A2, dissolving bis(fluorosulfonyl)imide silver and lithium tetrafluoroborate in ultrapure water and stirring at 50-60°C in the dark; after the reaction is completed, cooling the reaction solution to 0-5°C and filtering; concentrating the obtained filtrate under reduced pressure at 38-42°C, adding the concentrated solution to anhydrous acetone cooled to 0-5°C to precipitate crystals; washing three times with cold acetone, and finally vacuum-drying at 78-82°C.

2. The high energy density and high safety lithium-ion battery electrolyte according to claim 1, characterized in that, In step A1, the reaction is carried out at 25-30℃ with stirring in the dark for 24-36 hours.

3. The high energy density and high safety lithium-ion battery electrolyte according to claim 1, characterized in that, In step A2, the reaction is carried out at 50-60℃ with stirring in the dark for 36-48 hours.

4. The high energy density and high safety lithium-ion battery electrolyte according to claim 1, characterized in that, The preparation method of the thermoresponsive fluorinated benzoxazine polymer includes: B1, adding perfluorophenol and 1,3-diaminopropane into a three-necked round-bottom flask containing anhydrous toluene; heating the mixture to 58-62°C and stirring under nitrogen protection; then adding paraformaldehyde; B2, subsequently heating the reaction mixture to 108-112°C and continuing the reaction under stirring; after the reaction is completed, cooling the mixture to room temperature, transferring it to a separatory funnel, and washing it with deionized water; drying the organic phase with anhydrous magnesium sulfate and then distilling under reduced pressure to obtain a benzoxazine prepolymer liquid; placing the benzoxazine prepolymer liquid in a polytetrafluoroethylene mold, transferring it to a vacuum drying oven, first degassing it under vacuum at 58-62°C, then raising the temperature to 98-102°C and holding it, then raising the temperature to 138-142°C and holding it to obtain a solid polymer; pulverizing the solid polymer, washing it sequentially with ethanol and deionized water using ultrasound, and finally drying it under vacuum at 78-82°C.

5. The high energy density and high safety lithium-ion battery electrolyte according to claim 4, characterized in that, In step B1, the heating time to 58-62℃ and the stirring time is 30-40 minutes.

6. The high energy density and high safety lithium-ion battery electrolyte according to claim 4, characterized in that, In step B2, the vacuum degassing time at 58-62℃ is 2-4 hours; the temperature is raised to 98-102℃ and held for 6-8 hours; the temperature is raised to 138-142℃ and held for 2-3 hours.

7. A method for preparing a high-energy-density, high-safety lithium-ion battery electrolyte according to any one of claims 1-6, characterized in that, step... include: S1. In an argon atmosphere glove box, weigh ethylene carbonate, diethyl carbonate and methyl ethyl carbonate into a glass reaction flask; place the reaction flask on a magnetic stirrer and stir to form a solvent mixture; then, add bis(2,2,2-trifluoroethyl) carbonate, and after the addition is complete, continue stirring at 24-26℃. S2. Subsequently, lithium difluorosulfonylimide borate salt and lithium difluorooxalate borate are added, and stirring is continued. Then, a thermally responsive fluorinated benzoxazine polymer was added, and the reaction flask was sealed and ultrasonically treated. The obtained electrolyte was filtered through a 3Å molecular sieve packed column that had been pre-activated at 148-152℃; the filtered electrolyte was then transferred to a stainless steel vacuum degassing container and degassed at a water bath temperature of 58-62℃. S3. Finally, the degassed electrolyte is filtered through a polytetrafluoroethylene microporous membrane.

8. The preparation method according to claim 7, characterized in that, In step S1, the stirring time is 2-4 hours at 24-26℃.

9. The preparation method according to claim 7, characterized in that, In step S2, the degassing treatment is carried out at a water bath temperature of 58-62℃ for 12-15 hours.

10. The preparation method according to claim 7, characterized in that, In step S3, the pore size of the microporous filter membrane is 0.22-0.24 μm.