A fluorine-containing zwitterionic polymer gel electrolyte and a preparation method and application thereof

Abstract

The application belongs to the technical field of electrolytes, and particularly relates to a fluorine-containing zwitterionic polymer gel electrolyte and a preparation method and application thereof. The fluorine-containing zwitterionic polymer gel electrolyte is prepared by using fluorine-containing monomers, zwitterionic monomers and 1-n-butyl-1-methyl pyrrolidine di(trifluoromethyl sulfone) imide ionic liquid as raw materials, mixing the three to form an ionic liquid system, mixing lithium salt in the ionic liquid system, and then initiating thermal polymerization by using an initiator. The fluorine-containing zwitterionic polymer gel electrolyte obtained by the application has high mechanical toughness, a wide electrochemical window and super-low-temperature ionic conduction characteristics, and can simultaneously realize lithium metal negative electrode dendrite growth inhibition, interface side reaction elimination and full-weather battery stability improvement.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically a fluorine-containing zwitterionic polymer gel electrolyte, its preparation method, and its application. Background Technology

[0002] Zwitterionic gel electrolytes, due to their unique molecular structure that integrates both cation and anion groups on the same polymer chain, have become an ideal choice for next-generation high-performance energy storage devices, with wide applications in flexible electronic devices, new energy vehicles, and high-energy-density battery systems. Compared to traditional electrolytes, zwitterionic gel electrolytes form highly efficient ion transport channels through electrostatic interactions, achieving up to 10... -3 S cm -1 The electrolyte exhibits high ionic conductivity, along with excellent interfacial stability and leakage resistance, significantly improving battery safety. However, the practical application of existing zwitterionic gel electrolytes still faces several technical bottlenecks: firstly, the insufficient mechanical properties of the gel network make it difficult to effectively suppress interfacial delamination caused by electrode volume changes; secondly, the ion transport rate decreases sharply at low temperatures, with conductivity typically below 10 at -20°C. -4 S cm -1 Third, the complex preparation process and high raw material costs restrict its large-scale production.

[0003] To overcome these problems, researchers have developed various strategies, including dual-network structure design, organic-inorganic composite toughening, and ionic liquid modification. Dual-network structures enhance mechanical strength through the synergistic effect of rigid polymers and flexible zwitterionic polymers; however, there is an inherent contradiction between crosslinking density and ionic conductivity—high crosslinking density, while enhancing mechanical properties, hinders ion migration. Organic-inorganic composite strategies (such as introducing ceramic nanoparticles) can improve interfacial stability, but inorganic fillers are prone to agglomeration, leading to uneven ion distribution. Ionic liquid modification strategies broaden the electrochemical window by introducing imidazole or pyrrolidine ionic liquids, but residual free ionic liquids can trigger side reactions and reduce coulombic efficiency.

[0004] Furthermore, existing zwitterionic gel electrolytes still lack sufficient adaptability to the dynamic electrode interface: during cycling, the continuous volume change of the metal anode leads to microcracks at the gel-electrode interface, with dendrites growing along the defects and eventually piercing the electrolyte. Simultaneously, free water molecules in traditional zwitterionic gels are prone to electrolytic reactions under high voltage, accelerating the corrosion of the metal anode and inducing capacity decay. Summary of the Invention

[0005] To address the shortcomings of existing zwitterionic gel electrolytes, such as insufficient mechanical strength, low ionic conductivity over a wide temperature range, and poor electrode-electrolyte interface stability, this invention provides a fluorinated zwitterionic polymer gel electrolyte, its preparation method, and its applications. Through the molecular-level synergistic effect of the hydrophobic segments of the fluorinated monomer, the zwitterionic groups, and the ionic liquid, the obtained fluorinated zwitterionic polymer gel electrolyte possesses high mechanical toughness, a wide electrochemical window, and ultra-low temperature ionic conductivity. This simultaneously achieves suppression of dendrite growth in the lithium metal anode, elimination of interfacial side reactions, and improvement of battery stability across all weather conditions.

[0006] To address the common problems of high interfacial impedance, weak lithium dendrite suppression, and poor high-temperature cycling performance in conventional gel electrolytes used in lithium metal batteries, this invention proposes a gel electrolyte based on dual-functionalized zwitterionic monomers. This gel electrolyte forms a stable three-dimensional network through the synergistic effect of fluorine-containing monomers and zwitterionic monomers, enhancing interfacial stability and ion transport efficiency. Specifically, this invention utilizes the fluorocarbon chain structure to provide chemical stability, the sulfonate betaine structure to achieve efficient lithium ion dissociation, and an adaptive interface layer integrated with the electrode is constructed through in-situ thermal polymerization, effectively suppressing lithium dendrite growth.

[0007] The dual functionality is divided into two core dimensions: 1) The dual functionality of the zwitterionic monomer itself: The same molecular chain of the zwitterionic monomer simultaneously carries a cationic quaternary ammonium group and anionic sulfonic acid (carboxylic acid / phosphate) group; among which, the anionic group can promote lithium salt dissociation through electrostatic interaction, improving lithium ion dissociation efficiency and transport number, while the cationic group can inhibit the migration of free anions in the system, reduce concentration polarization during battery cycling, and adsorb trace impurities and moisture in the system, reducing interfacial side reactions, thus achieving the dual function of "promoting lithium ion transport + inhibiting interfacial side reactions". 2) The dual functionality of the gel system: Through the copolymerization of fluorinated monomers and zwitterionic monomers, the gel electrolyte simultaneously possesses two core functions: first, excellent ion transport function, which can achieve stable lithium ion conduction at high rates; second, excellent interfacial stabilization function, which can adapt to the volume change of lithium metal anode, inhibit lithium dendrite growth, and at the same time possess high oxidation resistance and thermal stability, thus achieving the dual function of efficient ion conduction + stable interfacial adaptation.

[0008] Based on the above-mentioned technical objectives, the present invention provides the following technical solution: This invention protects a method for preparing a fluorinated zwitterionic polymer gel electrolyte, comprising the following steps: S1. In an inert atmosphere glove box, weigh out 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid with a purity of not less than 99.9% and place it in a reaction vessel. The core reasons for selecting this ionic liquid in this invention are as follows: First, this pyrrolidine-based ionic liquid has a wide electrochemical stability window of over 5.7V, a thermal decomposition temperature above 350℃, and strong chemical inertness, which can significantly improve the electrochemical stability and high-temperature safety of the gel electrolyte. Second, its glass transition temperature is as low as -85℃, maintaining low viscosity liquid characteristics even in ultra-low temperature environments, which is the core basis for achieving ultra-low temperature ionic conductivity of the gel electrolyte. Third, the bis(trifluoromethanesulfonyl)imide anion of this ionic liquid has a strong fluorine-fluorine interaction with the fluorocarbon segment of the fluorine-containing monomer, which can achieve molecular-level compatibility with the polymer system of this invention, avoiding the ionic liquid from leaching out and separating from the system phase. Fourth, this ionic liquid can effectively reduce the lithium-ion migration barrier, synergistically construct an efficient ion transport channel with zwitterionic monomers, and simultaneously form a stable LiF-rich SEI film on the lithium metal anode surface, suppressing interfacial side reactions and lithium dendrite growth, which is highly consistent with the technical objectives of this invention.

[0009] S2. Mix the fluorine-containing monomer and the zwitterionic monomer together in the above ionic liquid to obtain a mixed solution. Heat and stir until the fluorine-containing monomer and the zwitterionic monomer are completely dissolved in the ionic liquid to obtain an ionic liquid system.

[0010] S3. Cool the ionic liquid system from step S2 to room temperature, add lithium salt, and stir until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0011] S4. Mix the transparent premixed solution obtained in step S3 with the initiator (azobisisobutyronitrile AIBN / azobisisoheptanenitrile ABVN), stir at room temperature to form a homogeneous precursor solution.

[0012] S5. The homogeneous precursor solution is thermally polymerized to obtain a fluorinated zwitterionic polymer gel electrolyte. During the thermal polymerization process, a three-dimensional cross-linked network is formed based on the thermally initiated free radical copolymerization reaction. The specific mechanism consists of three steps: 1) Initiation stage: Under heating conditions, the initiator decomposes thermally, generating active species containing carbon free radicals. 2) Chain growth and cross-linking stage: Active free radicals attack the carbon-carbon double bonds on the fluorinated monomer and zwitterionic monomer molecules, causing the double bonds to open and forming new monomer free radicals; the new free radicals continue to attack the double bonds of other monomers, realizing chain growth; since both monomers are polymerizable acrylate monomers, they can form covalent cross-linking bonds between molecular chains, enabling the linear polymer chains to connect with each other and form a three-dimensional network cross-linked structure. 3) Gel formation: As the copolymerization reaction proceeds, the cross-linking density continuously increases, and the polymer chains entangle with each other to form a continuous three-dimensional polymer skeleton. At the same time, the ionic liquid and lithium salt are physically confined in the pores of the cross-linked network, the system loses its fluidity, completes the gel transformation, and finally forms a stable three-dimensional network of fluorinated zwitterionic polymer gel electrolyte.

[0013] Preferably, the fluorinated monomer is selected from 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate or hexafluorobutyl methacrylate, and the purity of the fluorinated monomer is not less than 98%.

[0014] Preferably, the zwitterionic monomer is selected from 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propane-1-sulfonate, 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propionate or 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propyl phosphate, and the purity of the zwitterionic monomer is not less than 97%.

[0015] Preferably, the total amount of fluorinated monomers and zwitterionic monomers to the mass ratio of the 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid is 1:4~9.

[0016] Preferably, the mass ratio of fluorinated monomer to zwitterionic monomer is 1:1~3.

[0017] Preferably, the water content in the ionic liquid system is less than 50 ppm. Moisture in the ionic liquid system has serious negative impacts on polymerization reaction, electrochemical performance, and safety, specifically as follows: 1) It disrupts free radical polymerization: This invention uses azo initiators for thermal free radical polymerization. Trace amounts of moisture quench the active free radicals in the polymerization reaction, reducing initiation efficiency, leading to incomplete monomer polymerization, insufficient crosslinking density, and ultimately, the inability to form a complete gel, resulting in a significant decrease in mechanical strength and leakage resistance. 2) It triggers lithium salt hydrolysis and interfacial side reactions: Moisture reacts with lithium salts (LiTFSI, LiFSI, LiPF6, etc.) in the system to generate corrosive substances such as hydrofluoric acid (HF). HF corrodes the electrode current collector and damages the SEI / CEI film on the electrode surface, leading to a continuous increase in interfacial impedance and rapid growth of lithium dendrites. Simultaneously, moisture reacts directly with the highly active lithium metal anode, consuming active lithium and reducing battery coulombic efficiency and cycle life. 3) Deterioration of battery safety and stability: Moisture undergoes electrolysis during high-voltage battery cycling, producing gases such as hydrogen and oxygen, leading to battery bulging, increased internal pressure, and even safety risks. Simultaneously, moisture reduces the thermal stability of the gel electrolyte, making it prone to decomposition at high temperatures and limiting the battery's operating temperature range. This invention controls the water content of the system to below 50 ppm, completely avoiding the above negative impacts and ensuring stable polymerization and long-term stable battery cycling.

[0018] Preferably, the purity of the lithium salt is not less than 99.95%, and it is pre-dried under vacuum at 60°C for at least 24 hours, and the molar concentration of the lithium salt in the premixed solution is 1 mol / L to 2 mol / L.

[0019] Preferably, the purity of the initiator is not less than 99%, and it needs to be recrystallized and purified before use; stirring should be carried out in a brown glass bottle in the dark.

[0020] Preferably, the polymerization temperature for thermal polymerization is controlled at 80±2℃, and the polymerization time is not less than 8 hours. Because the half-life of the azobisisobutyronitrile (AIBN) and azobisisoheptanenitrile (ABVN) initiators used in this invention increases significantly with decreasing temperature (the half-life of AIBN at 80℃ is approximately 1.5 hours), excessively low temperatures lead to extremely slow initiator decomposition rates, insufficient free radical generation, and a significant decrease in initiation efficiency. This results in incomplete monomer polymerization, insufficient crosslinking density, and the inability to form a complete gel, failing to meet design requirements for mechanical strength and structural stability. Excessively high polymerization temperatures lead to excessively rapid initiator decomposition, generating a large number of free radicals in a short time, causing uncontrolled polymerization rates, localized burst polymerization, uneven polymer crosslinking networks, numerous structural defects, and a significant decrease in the mechanical toughness and ion transport uniformity of the gel. Simultaneously, excessively high temperatures can cause trace thermal decomposition of ionic liquids and lithium salts within the system, generating impurities and worsening interfacial compatibility. Furthermore, it can cause the formation of bubbles within the system, damaging the structural integrity of the gel and affecting the electrode-electrolyte interfacial contact.

[0021] This invention also protects a fluorinated zwitterionic polymer gel electrolyte, which is prepared using the above-described method.

[0022] This invention also protects the application of fluorine-containing zwitterionic polymer gel electrolytes in the preparation of lithium-ion batteries. A homogeneous precursor solution is injected into a battery mold, thermally polymerized, and in-situ formed into a zwitterionic gel electrolyte; or a homogeneous precursor solution is injected into a glass mold, thermally polymerized, and in-situ formed into a zwitterionic gel electrolyte membrane.

[0023] When assembling a LiFePO4||Li full cell, the lithium metal anode has a thickness of 400 μm and a purity of 99.9%; the cathode is lithium iron phosphate with a loading of not less than 3 mg / cm³. 2 The LiFePO4||Li full cell assembly was carried out in an argon glove box with a water and oxygen concentration of less than 0.1 ppm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes the molecular-level synergistic effect of hydrophobic segments of fluorinated monomers, zwitterionic groups, and ionic liquids to obtain fluorinated zwitterionic polymer gel electrolytes that possess high mechanical toughness, a wide electrochemical window, and ultra-low temperature ionic conductivity. The molecular-level synergistic effect refers to the structural adaptation, functional complementarity, and performance synergy of the fluorinated monomers, the anionic / cationic groups of the zwitterionic monomers, and the ionic liquid at the molecular scale. The specific principle is divided into three dimensions: 1) Structural compatibility synergy: Both the fluorinated monomers and the zwitterionic monomers are methacrylates with the same polymerizable double bond structure, which can achieve molecular-level random copolymerization through free radical copolymerization, avoiding phase separation of components; at the same time, the fluorinated fluorocarbon chain and the TFSI⁻ anion of the ionic liquid have fluorine-fluorine interaction, which can stably confine the ionic liquid in the polymer cross-linking network, avoiding the precipitation and leakage of free ionic liquid. 2) Synergistic effect of ion transport: The anionic groups (sulfonic acid / carboxylic acid / phosphate groups) of zwitterionic monomers can promote the dissociation of lithium salts through electrostatic interactions, while the cationic quaternary ammonium groups can inhibit anion migration, thus constructing a continuous lithium-ion transport channel; the ionic liquid provides a low-viscosity ion migration environment, reducing the lithium-ion desolvation energy barrier; the strong electronegativity of the fluorinated segments can help regulate the lithium-ion solvation structure, and the three work together to achieve high ionic conductivity over a wide temperature range. 3) Synergistic effect of interface and stability: The strong hydrophobicity of the fluorinated fluorocarbon chains can isolate trace amounts of moisture and inhibit side reactions, while forming a stable LiF-rich SEI film on the lithium metal anode surface; the zwitterionic groups can alleviate concentration polarization at the electrode-electrolyte interface and inhibit lithium dendrite growth; the ionic liquid itself has a wide electrochemical window and high thermal stability, and the three work together to simultaneously improve the mechanical toughness, electrochemical stability, and interfacial compatibility of the gel electrolyte.

[0025] The fluorine-containing zwitterionic polymer gel electrolyte obtained by this invention possesses high mechanical toughness, a wide electrochemical window, and ultra-low temperature ionic conductivity, as specifically demonstrated below: High mechanical toughness: The core is based on a three-dimensional cross-linked polymer network formed by the copolymerization of fluorinated monomers and zwitterionic monomers. The fluorocarbon segments of the fluorinated monomers have strong intermolecular forces, which can improve the rigidity and deformation resistance of the polymer chain; the anionic / cationic groups of the zwitterionic monomers can form intermolecular electrostatic interactions and hydrogen bonds, giving the cross-linked network good flexibility and tear resistance; the interpenetrating network formed by the copolymerization of the two avoids the brittleness caused by high cross-linking degree and solves the problem of insufficient mechanical strength of traditional gel electrolytes, thus achieving high mechanical toughness.

[0026] Wide electrochemical window: The core is based on the synergistic effect of ionic liquids and fluorinated monomers. Pyr 14TFSI ionic liquids have an electrochemical stability window of >5V, which is far superior to traditional carbonate electrolytes. The fluorocarbon segments of fluorinated monomers have strong antioxidant properties, which can improve the high-voltage stability of the polymer matrix. At the same time, they form a stable CEI film on the cathode surface to inhibit oxidative decomposition under high voltage. The two work together to broaden the electrochemical window of the gel electrolyte, making it suitable for high-voltage cathode systems.

[0027] Ultra-low temperature ionic conductivity: The core is based on the synergistic solvation structure regulation of zwitterionic monomers, ionic liquids, and lithium salts. The continuous ion transport channels constructed by zwitterionic groups can reduce the lithium-ion migration energy barrier; the glass transition temperature of the ionic liquid is as low as <-80℃, maintaining low viscosity liquid characteristics even in ultra-low temperature environments, avoiding the problem of low-temperature solidification of traditional electrolytes; at the same time, zwitterionic groups can promote the low-temperature dissociation of lithium salts, preventing lithium salt crystallization and precipitation. The three factors work together to achieve high ionic conductivity in ultra-low temperature environments.

[0028] 2. The fluorinated zwitterionic polymer gel electrolyte constructed in this invention achieves excellent ion transport performance and electrochemical stability through the synergistic effect of multiple components. The anionic and cationic groups in the zwitterionic monomer can form ion transport sites, significantly enhancing the ion transport performance of Li. + Migration efficiency; the introduction of fluorine-containing monomers reduces the electrolyte-electrode interface impedance and enhances oxidation stability; the dual-salt ionic liquid system further broadens the electrochemical window, effectively solving the problems of low ionic conductivity, poor interfacial compatibility and easy decomposition under high voltage of traditional gel electrolytes, and significantly improving battery rate performance and cycle life.

[0029] The mechanism of action of fluorinated monomers can be divided into two dimensions: 1) Mechanism of reducing interfacial impedance: The fluorocarbon segments of fluorinated monomers have extremely low surface energy, which can significantly improve the wettability of the gel electrolyte to the electrode surface, reduce the electrode-electrolyte interfacial contact angle, and achieve tight interfacial contact, thereby significantly reducing the initial interfacial impedance; at the same time, the fluorocarbon segments can be oriented on the lithium metal anode surface, inducing the formation of a uniform, low-impedance LiF-rich SEI film, inhibiting the continuous growth of interfacial impedance during cycling. 2) Mechanism of enhancing oxidation resistance: Fluorine has extremely strong electronegativity and electron-withdrawing effect, which can increase the highest occupied molecular orbital (HOMO) energy level of the polymer matrix, reduce the possibility of polymer oxidation, and significantly improve the high-voltage oxidation resistance of the gel electrolyte; at the same time, the fluorinated segments can form a stable CEI film on the cathode surface, inhibiting the oxidative decomposition of the electrolyte under high voltage, and improving the electrochemical stability of long-term cycling.

[0030] The core principle of widening the electrochemical window is the synergistic enhancement of the oxidation / reduction stability of the system by multiple components: 1) The 1-n-butyl-1-methylpyrrolidine di(trifluoromethanesulfonyl)imide ionic liquid selected in this invention has an electrochemical stability window of up to 5.7V, which is far superior to traditional carbonate electrolytes and forms the basis for the wide window; 2) The fluorocarbon segments of the fluorinated monomer can enhance the oxidation resistance of the polymer matrix and form a stable passivation film on the positive and negative electrode surfaces, suppressing side reactions on the electrode surface and avoiding the decomposition of the electrolyte at high / low potentials; 3) The optional dual-salt lithium salt system can combine the advantages of different lithium salts to further optimize the composition and stability of the passivation film at the electrode interface, suppress interfacial side reactions, and ultimately achieve the widening of the electrochemical window.

[0031] Addressing the three core problems of traditional gel electrolytes—low ionic conductivity, poor interfacial compatibility, and easy decomposition under high pressure—this invention offers the following solutions: 1) Solving the problem of low ionic conductivity: By constructing continuous lithium-ion transport sites through the anionic / cationic groups of zwitterionic monomers, lithium salt dissociation is promoted and Li⁺ migration number is increased; combined with a low-viscosity, high-ionic-conductivity ionic liquid, the lithium-ion migration barrier is lowered, and the two synergistically significantly improve the ionic conductivity of the gel electrolyte. 2) Solving the problem of poor interfacial compatibility: The low surface energy fluorocarbon segments of fluorinated monomers enhance the wettability of the gel electrolyte to the electrode surface, achieving close contact with the electrode; simultaneously, in-situ polymerization constructs an integrated electrode-electrolyte interface, adapting to volume changes during electrode cycling, avoiding interfacial delamination, and significantly improving interfacial compatibility. 3) Solving the problem of easy decomposition under high pressure: The strong oxidation resistance of fluorinated monomers enhances the high pressure stability of the polymer matrix. Paired with pyrrolidine ionic liquids with a wide electrochemical window, a stable passivation film is formed on the electrode surface to suppress oxidative decomposition side reactions under high pressure, thus solving the problem of easy decomposition of traditional gel electrolytes under high pressure.

[0032] 3. The fluorinated zwitterionic polymer gel electrolyte of this invention achieves excellent mechanical properties and leak-proof characteristics through a cross-linked network structure. The three-dimensional cross-linked network formed by the polymerization of monomers (a collective term for fluorinated monomers and zwitterionic monomers) initiated by azobisisobutyronitrile (AIB) avoids the leakage risk of traditional liquid electrolytes, while also giving the fluorinated zwitterionic polymer gel electrolyte good flexibility, adapting to the bending and encapsulation requirements during battery assembly. The hydrophobic properties of the fluorinated monomer segments and the high stability of the ionic liquid work synergistically, enabling the fluorinated zwitterionic polymer gel electrolyte to maintain structural stability at 60℃~80℃, improving the safety of electrochemical devices.

[0033] 4. The preparation process of this invention is simple, efficient, and industrially adaptable. All raw materials are commercially available reagents, requiring no complex pretreatment; the dissolution and polymerization processes are under mild conditions, requiring no high temperature, high pressure, or special equipment, thus reducing production energy consumption; after the homogeneous precursor liquid is assembled into a battery, it can be directly compatible with existing battery preparation processes through in-situ polymerization, without the need for additional electrolyte coating or encapsulation steps; the resulting fluorinated zwitterionic polymer gel electrolyte is compatible with various electrochemical energy storage devices such as lithium metal batteries, lithium-ion batteries, and supercapacitors, exhibiting strong versatility and meeting the commercialization needs of high-stability energy storage devices in different scenarios. Attached Figure Description

[0034] Figure 1 To test the stainless steel-stainless steel coin cells assembled using the zwitterionic gel electrolytes of Examples 1 to 4 of this invention at 0.1 Hz to 10 Hz 5 Electrochemical impedance spectroscopy at Hz.

[0035] Figure 2 The figures shown are thermal stability test diagrams of the zwitterionic gel electrolyte membrane in Example 1 of the present invention, where figure a is a thermogravimetric diagram and figure b is a differential scanning calorimetry curve.

[0036] Figure 3 The time-voltage curve is shown for the Li||Li symmetric coin cell assembled using the zwitterionic gel electrolyte of Example 1 of the present invention.

[0037] Figure 4 The time-specific capacity curve of the LiFePO4||Li full cell assembled using the zwitterionic gel electrolyte of Example 1 of this invention is shown. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] This invention develops a novel zwitterionic gel electrolyte that combines high ionic conductivity, a wide electrochemical window, excellent mechanical toughness, and interfacial adaptability. Through molecular structure design (such as introducing fluorinated monomers to enhance hydrophobicity), solvation structure regulation (such as lowering the desolvation energy barrier), and innovative preparation processes (such as in-situ polymerization to achieve integrated electrode-electrolyte structure), it is expected to achieve a balance between dendrite suppression, side reaction elimination, and low-temperature performance improvement, thus promoting the practical application of high-performance battery systems.

[0040] The raw material information for this invention is as follows: The technical solution of the present invention will be further explained and described below with reference to the embodiments and accompanying drawings, as follows: Example 1 A method for preparing a fluorinated zwitterionic polymer gel electrolyte includes the following steps: Step 1: Weigh 1.094 g of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid in an inert atmosphere glove box and place it in a reaction vessel.

[0041] Step 2: Mix 0.114g of the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl methacrylate and 0.1094g of the zwitterionic monomer 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propane-1-sulfonate in the above ionic liquid to obtain a mixture. The water and oxygen content in the mixture is less than 50ppm. The mass ratio of monomer to ionic liquid is 1:5. The monomer consists of the fluorinated monomer and the zwitterionic monomer.

[0042] Step 3: Heat the mixture from Step 2 to 60°C and continuously stir magnetically for 1 hour until the monomer is completely dissolved to obtain an ionic liquid system; then cool the ionic liquid system to room temperature, and add 0.2066 g of lithium bis(trifluoromethanesulfonyl)imide, wherein the mass fraction of LiTFSI in the ionic liquid is 15%, and continue stirring at room temperature for at least 1 hour until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0043] Step 4: Mix the transparent premixed solution obtained in Step 3 with 0.0044 g of azobisisobutyronitrile initiator and stir at room temperature for 1 h to form a homogeneous precursor solution.

[0044] Step 5: Inject the homogeneous precursor solution from Step 4 into the battery mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form zwitterionic gel electrolyte in situ.

[0045] Step 6: Inject the homogeneous precursor solution from Step 4 into a glass mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form an in-situ zwitterionic gel electrolyte membrane.

[0046] Example 2 A method for preparing a fluorinated zwitterionic polymer gel electrolyte includes the following steps: Step 1: Weigh 1.094 g of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid in an inert atmosphere glove box and place it in a reaction vessel.

[0047] Step 2: Mix 0.114g of the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl methacrylate and 0.0945g of the zwitterionic monomer 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propionate in the above ionic liquid to obtain a mixture. The water and oxygen content in the mixture is less than 50ppm. The mass ratio of monomer to ionic liquid is 1:5. The monomer is composed of the fluorinated monomer and the zwitterionic monomer.

[0048] Step 3: Heat the mixture from Step 2 to 60°C and continuously stir magnetically for 1 hour until the monomer is completely dissolved to obtain an ionic liquid system; then cool the ionic liquid system to room temperature, and add 0.2066 g of lithium hexafluorophosphate, wherein the mass fraction of LiPF6 in the ionic liquid is 15%, and continue stirring at room temperature for at least 1 hour until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0049] Step 4: Mix the transparent premixed solution obtained in Step 3 with 0.0044 g of azobisisobutyronitrile initiator and stir at room temperature for 1 h to form a homogeneous precursor solution.

[0050] Step 5: Inject the homogeneous precursor solution from Step 4 into the battery mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form zwitterionic gel electrolyte in situ.

[0051] Step 6: Inject the homogeneous precursor solution from Step 4 into a glass mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form an in-situ zwitterionic gel electrolyte membrane.

[0052] Example 3 A method for preparing a fluorinated zwitterionic polymer gel electrolyte includes the following steps: Step 1: Weigh 1.094 g of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid in an inert atmosphere glove box and place it in a reaction vessel.

[0053] Step 2: Mix 0.155g of the fluorinated monomer 3,3,4,4,5,5,6,6,6-nonafluorohexyl methacrylate and 0.1152g of the zwitterionic monomer 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propyl phosphate in the above ionic liquid to obtain a mixture. The water and oxygen content in the mixture is less than 50ppm. The mass ratio of monomer to ionic liquid is 1:4. The monomer consists of the fluorinated monomer and the zwitterionic monomer.

[0054] Step 3: Heat the mixture from Step 2 to 60°C and continuously stir magnetically for 1 hour until the monomer is completely dissolved to obtain an ionic liquid system; then cool the ionic liquid system to room temperature, and add 0.2066 g of lithium bis(trifluoromethanesulfonyl)imide, wherein the mass fraction of LiTFSI in the ionic liquid is 15%, and continue stirring at room temperature for at least 1 hour until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0055] Step 4: Mix the transparent premixed solution obtained in Step 3 with 0.0044 g of azobisisobutyronitrile initiator and stir at room temperature for 1 h to form a homogeneous precursor solution.

[0056] Step 5: Inject the homogeneous precursor solution from Step 4 into the battery mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form zwitterionic gel electrolyte in situ.

[0057] Step 6: Inject the homogeneous precursor solution from Step 4 into a glass mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form an in-situ zwitterionic gel electrolyte membrane.

[0058] Example 4 A method for preparing a fluorinated zwitterionic polymer gel electrolyte includes the following steps: Step 1: Weigh 1.094 g of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid in an inert atmosphere glove box and place it in a reaction vessel.

[0059] Step 2: Mix 0.114g of the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl methacrylate and 0.1094g of the zwitterionic monomer 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propane-1-sulfonate in the above ionic liquid to obtain a mixture. The water and oxygen content in the mixture is less than 50ppm. The mass ratio of monomer to ionic liquid is 1:5. The monomer consists of the fluorinated monomer and the zwitterionic monomer.

[0060] Step 3: Heat the mixture from Step 2 to 60°C and continuously stir magnetically for 1 hour until the monomer is completely dissolved to obtain an ionic liquid system; then cool the ionic liquid system to room temperature, and add 0.2066 g of lithium bis(fluorosulfonyl)imide, wherein the mass fraction of LiFSI in the ionic liquid is 15%, and continue stirring at room temperature for at least 1 hour until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0061] Step 4: Mix the transparent premixed solution obtained in Step 3 with 0.0044 g of azobisisobutyronitrile initiator and stir at room temperature for 1 h to form a homogeneous precursor solution.

[0062] Step 5: Inject the homogeneous precursor solution from Step 4 into the battery mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form zwitterionic gel electrolyte in situ.

[0063] Step 6: Inject the homogeneous precursor solution from Step 4 into a glass mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form an in-situ zwitterionic gel electrolyte membrane.

[0064] Example 5 A method for preparing a fluorinated zwitterionic polymer gel electrolyte includes the following steps: Step 1: Weigh 2.052 g of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid in an inert atmosphere glove box and place it in a reaction vessel.

[0065] Step 2: Mix 0.114g of the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl methacrylate and 0.228g of the zwitterionic monomer 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propane-1-sulfonate in the above ionic liquid to obtain a mixture. The water and oxygen content in the mixture is less than 50ppm. The mass ratio of monomer to ionic liquid is 1:6. The monomer consists of the fluorinated monomer and the zwitterionic monomer.

[0066] Step 3: Heat the mixture from Step 2 to 60°C and continuously stir magnetically for 1 hour until the monomer is completely dissolved to obtain an ionic liquid system; then cool the ionic liquid system to room temperature, and continue to add lithium bis(fluorosulfonyl)imide, wherein the mass fraction of LiFSI in the ionic liquid is 15%, and continue stirring at room temperature for at least 1 hour until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0067] Step 4: Mix the transparent premixed solution obtained in Step 3 with 0.0044 g of azobisisobutyronitrile initiator and stir at room temperature for 1 h to form a homogeneous precursor solution.

[0068] Step 5: Inject the homogeneous precursor solution from Step 4 into the battery mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form zwitterionic gel electrolyte in situ.

[0069] Step 6: Inject the homogeneous precursor solution from Step 4 into a glass mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form an in-situ zwitterionic gel electrolyte membrane.

[0070] Example 6 A method for preparing a fluorinated zwitterionic polymer gel electrolyte includes the following steps: Step 1: Weigh 4.104 g of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid in an inert atmosphere glove box and place it in a reaction vessel.

[0071] Step 2: Mix 0.114g of the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl methacrylate and 0.342g of the zwitterionic monomer 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propane-1-sulfonate in the above ionic liquid to obtain a mixture. The water and oxygen content in the mixture is less than 50ppm. The mass ratio of monomer to ionic liquid is 1:9. The monomer is composed of fluorinated monomer and zwitterionic monomer.

[0072] Step 3: Heat the mixture from Step 2 to 60°C and continuously stir magnetically for 1 hour until the monomer is completely dissolved to obtain an ionic liquid system; then cool the ionic liquid system to room temperature, and continue to add lithium bis(fluorosulfonyl)imide, wherein the mass fraction of LiFSI in the ionic liquid is 15%, and continue stirring at room temperature for at least 1 hour until the lithium salt is completely dissolved to obtain a transparent premixed solution.

[0073] Step 4: Mix the transparent premixed solution obtained in Step 3 with 0.0044 g of azobisisobutyronitrile initiator and stir at room temperature for 1 h to form a homogeneous precursor solution.

[0074] Step 5: Inject the homogeneous precursor solution from Step 4 into the battery mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form zwitterionic gel electrolyte in situ.

[0075] Step 6: Inject the homogeneous precursor solution from Step 4 into a glass mold and place it in a constant temperature environment of 80℃ for thermal polymerization for 8 hours to form an in-situ zwitterionic gel electrolyte membrane.

[0076] Application Example 1: Assemble stainless steel-stainless steel button cells: Stainless steel is used as the positive and negative electrodes. The homogeneous precursor solution in Examples 1 to 4 above is injected. A 2025 type battery case is used. The stainless steel-stainless steel button cells are assembled in the following order: negative electrode case, stainless steel sheet, zwitterionic gel electrolyte, stainless steel sheet, gasket, spring sheet, and positive electrode case.

[0077] Electrochemical impedance spectroscopy (EIS) was performed on the assembled stainless steel-stainless steel coin cells using an electrochemical workstation, with a frequency range of 0.1 Hz to 10 Hz. 5 Hz. The test was conducted on a Chenhua CHI660E at a temperature of 30℃. The ionic conductivity of the zwitterionic gel electrolyte was further calculated. Where L is the thickness of the sample, S is the contact area between the sample and the stainless steel sheet, and R is the intrinsic impedance of the sample, which is obtained through testing.

[0078] Application Example 2: Assemble lithium-lithium symmetrical coin cells: Lithium metal is used as the positive and negative electrodes, and the homogeneous precursor solution in Examples 1 to 4 above is injected. A 2025 type battery case is used, and the lithium-lithium symmetrical coin cells are assembled in the following order: negative electrode case, lithium metal, zwitterionic gel electrolyte, lithium metal, gasket, spring sheet, and positive electrode case.

[0079] The assembled lithium-lithium symmetric coin cells were subjected to cycle testing on the Newway Battery test channel, with current density and capacity density of 1 mA cm⁻¹. -2 and 1mAh cm -2 .

[0080] Application Example 3: Assemble lithium iron phosphate-lithium coin cells: using lithium metal as the negative electrode, with 3mg cm⁻¹ -2 The lithium iron phosphate is used as the positive electrode, and the homogeneous precursor solution in Examples 1 to 4 above is injected. The lithium iron phosphate-lithium coin cell is assembled in the following order: negative electrode shell, lithium metal, zwitterionic gel electrolyte, lithium iron phosphate positive electrode, gasket, spring sheet, and positive electrode shell.

[0081] The self-healing and highly resilient zwitterionic gel electrolytes prepared in Examples 1 to 4 were subjected to performance tests. The results showed that they had the following significant characteristics: (1) Good ionic conductivity: about 1 mS / m at 30°C; (2) High thermal stability: no decomposition at temperatures above 100°C; (3) Good elastic behavior: glass transition temperature below -50°C; (4) Excellent lithium deposition and stripping ability: lithium-lithium symmetric coin cells can cycle stably; (5) Excellent cycle stability: the full cell can maintain stable capacity retention during cycling.

[0082] Example 1 is a preferred embodiment of the present invention, and the performance tests are as follows: (1) Good ionic conductivity: approximately 2.15 mS / m at 30℃; (2) High thermal stability: does not decompose at 180℃; (3) Good elastic behavior: glass transition temperature is -72.8℃; (4) Excellent lithium deposition and stripping ability: lithium-lithium symmetric coin cells can achieve current density and capacity density of 1 mA cm⁻¹. -2 and 1mAh cm -2 (5) Excellent cycle stability: The full cell can maintain a capacity of over 91% after 800 cycles at 1C rate.

[0083] See Figure 1The figures show the electrochemical impedance spectroscopy (EIS) spectra of the zwitterionic gel electrolytes prepared in Examples 1-4 at 30°C. Through corresponding calculations and analysis, these figures demonstrate that the prepared zwitterionic gel electrolytes possess good ionic conductivity (approximately 1 mS / m).

[0084] See Figure 2 The figure shows the sum-difference scanning calorimetry (SDC) curve of the zwitterionic gel electrolyte prepared in Example 1. This figure demonstrates that the prepared zwitterionic gel electrolyte has extremely high thermal stability (does not decompose at 180°C) and good elastic behavior (glass transition temperature of -72.8°C).

[0085] See Figure 3 The figure shows the time-voltage curve of the Li||Li symmetric coin cell assembled using the zwitterionic gel electrolyte of Example 1. This figure demonstrates that the prepared zwitterionic gel electrolyte-assembled lithium-lithium symmetric coin cell can achieve current and capacity densities of 1 mA cm⁻¹. -2 and 1mAh cm -2 The stable cycle time exceeded 1100 hours.

[0086] See Figure 4 The figure shows the time-specific capacity curve of the LiFePO4||Li full cell assembled using the zwitterionic gel electrolyte of Example 1. The figure shows that the full cell assembled using the zwitterionic gel electrolyte can retain more than 91% of its capacity after 800 cycles at 1C rate.

[0087] It is worth noting that the zwitterionic gel electrolyte prepared by the method of the present invention does not contain any commercial electrolyte solvent components, thereby improving its safety and stability in use.

[0088] Although specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the spirit and scope of the present invention, which is defined only by the appended claims.

Claims

1. A method for preparing a fluorinated zwitterionic polymer gel electrolyte, characterized in that, Includes the following steps: Under an inert atmosphere, a fluorine-containing monomer and a zwitterionic monomer are dissolved together in a 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid to obtain an ionic liquid system; Among them, the same molecular chain of the zwitterionic monomer has both cationic quaternary ammonium groups and anionic groups, and the anionic groups are selected from sulfonic acid groups, carboxylic acid groups or phosphate groups. At room temperature, lithium salts are dissolved in an ionic liquid system to obtain a premixed solution; The premixed solution is mixed with an initiator and then subjected to thermal polymerization. During the thermal polymerization process, the initiator decomposes to generate free radicals. The free radicals then open the double bonds of the fluorinated monomer and the zwitterionic monomer, and the two undergo free radical polymerization to form a cross-linked network, which locks in the ionic liquid, resulting in a fluorinated zwitterionic polymer gel electrolyte.

2. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, The fluorinated monomer is selected from 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate or hexafluorobutyl methacrylate.

3. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, The zwitterionic monomer is selected from 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propane-1-sulfonate, 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propionate or 3-((2-(methacryloyloxy)ethyl)dimethylammonium)propyl phosphate.

4. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, The total amount of fluorinated monomers and zwitterionic monomers is in a mass ratio of 1:4 to 9 to the mass of 1-n-butyl-1-methylpyrrolidine di(trifluoromethylsulfonyl)imide ionic liquid.

5. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, The mass ratio of fluorinated monomer to zwitterionic monomer is 1:1~3.

6. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, In the ionic liquid system, the water content is less than 50 ppm.

7. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, The molar concentration of lithium salt in the premixed solution is 1 mol / L to 2 mol / L.

8. The method for preparing the fluorinated zwitterionic polymer gel electrolyte according to claim 1, characterized in that, The conditions for thermal polymerization are: polymerization at 80±2℃ for ≥8h.

9. A fluorinated zwitterionic polymer gel electrolyte, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. The application of the fluorine-containing zwitterionic polymer gel electrolyte of claim 9 in the preparation of lithium-ion batteries.

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