A flame-retardant gel electrolyte, its preparation method, and a lithium-ion battery

Abstract

This invention belongs to the field of lithium-ion battery technology, and relates to a flame-retardant gel electrolyte, its preparation method, and a lithium-ion battery. The flame-retardant gel electrolyte is a gel structure in which a three-dimensional cross-linked network encapsulates the electrolyte. The three-dimensional cross-linked network is formed by in-situ polymerization of fluoroacrylate, octavinyl-POSS, and methylenebisacrylamide. The three-dimensional cross-linked network formed by the in-situ polymerization of fluoroacrylate, octavinyl-POSS, and methylenebisacrylamide encapsulates the electrolyte, making it less prone to leakage and improving the flame-retardant effect of the gel electrolyte. Simultaneously, the three-dimensional cross-linked network structure provides a structural basis for ion transport, ensuring ionic conductivity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a flame-retardant gel electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries use liquid electrolytes as ion transport media. The good fluidity and interfacial wettability of liquid electrolytes enable them to have high ionic conductivity. However, most liquid electrolytes use alkyl carbonates or ether solvents. These solvents generally have disadvantages such as easy volatility, easy leakage, low flash point, and easy combustion, which can easily induce battery thermal runaway or even cause fire or explosion.

[0003] To address these safety concerns, researchers are dedicated to developing novel electrolyte systems, with gel electrolytes and solid-state electrolytes being two core research directions. Solid-state electrolytes, a promising solution, completely eliminate the need for liquid organic solvents, theoretically achieving ultimate safety through non-flammability and non-explosion, and are compatible with high-capacity lithium metal anodes, potentially significantly improving battery energy density. However, current solid-state electrolytes still face significant technical bottlenecks, such as prominent interfacial contact issues, with numerous micropores and cracks existing between the solid electrolyte and the electrode. Furthermore, defects such as grain boundaries and pores within inorganic solid-state electrolytes can induce lithium metal deposition and form conductive pathways, undergoing an irreversible transition from soft to hard short circuits, ultimately leading to battery failure. This mechanism is prevalent in mainstream inorganic solid-state electrolytes. Gel polymer electrolytes, as a transitional form between liquid and solid states, encapsulate organic solvents within a polymer framework, solving the problem of electrolyte evaporation and leakage while possessing the high conductivity of liquid electrolytes and the mechanical stability of polymer solids, making them a current research hotspot.

[0004] However, existing gel polymer electrolytes still have significant limitations. The large amount of liquid plasticizers they contain are still flammable, and the gel is prone to thermal decomposition and discharging at high temperatures. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant gel electrolyte, its preparation method, and a lithium-ion battery. This application uses a three-dimensional cross-linked network formed by in-situ polymerization of fluorinated acrylate, octavinyl-POSS (inorganic silica cage core), and methylenebisacrylamide to encapsulate the electrolyte, making it difficult for the electrolyte to flow out and improving the flame-retardant effect of the flame-retardant gel electrolyte. At the same time, the three-dimensional cross-linked network structure provides a structural basis for ion transport and ensures ionic conductivity.

[0006] In a first aspect, the present invention provides a flame-retardant gel electrolyte, wherein the flame-retardant gel electrolyte is a gel structure in which an electrolyte is encapsulated by a three-dimensional cross-linked network, wherein the three-dimensional cross-linked network is formed by in-situ polymerization of fluoroacrylate, octavinyl-POSS and methylenebisacrylamide.

[0007] A three-dimensional cross-linked network, formed by in-situ polymerization of fluoroacrylate, octavinyl-POSS, and methylenebisacrylamide, encapsulates the electrolyte, making it less prone to leakage and improving the flame-retardant effect of the flame-retardant gel electrolyte. At the same time, the three-dimensional cross-linked network structure provides a structural basis for ion transport, ensuring ionic conductivity.

[0008] In some embodiments, the flame-retardant gel electrolyte has a self-extinguishing time of 0 s, an electrochemical window of ≥5.0 V, and an ionic conductivity of ≥5.30 mS / cm.

[0009] The self-extinguishing time of 0 s indicates excellent flame-retardant properties of the flame-retardant gel electrolyte. The electrochemical window ≥ 5.0 V indicates good electrochemical stability, meeting the application requirements of high-voltage cathodes, and the electrolyte is not easily oxidized or decomposed under high voltage. The ionic conductivity ≥ 5.30 mS / cm indicates that the flame-retardant gel electrolyte has a continuous lithium-ion transport channel, ensuring efficient ion transport.

[0010] In a second aspect, the present invention provides a method for preparing the flame-retardant gel electrolyte, comprising the following steps:

[0011] Preparation of electrolyte: Dissolve fluorinated lithium salt in fluorocarbonate and stir at room temperature for 10 min to 30 min until completely dissolved to obtain electrolyte;

[0012] Preparation of flame-retardant gel electrolyte prepolymer: Add crosslinking agent methylenebisacrylamide, octavinyl-POSS and fluoroacrylate to the electrolyte, stir at room temperature for 30 min to 120 min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0013] Preparation of flame-retardant gel electrolyte precursor solution: Add an azo initiator to the flame-retardant gel electrolyte prepolymer solution and stir at room temperature for 5 min to 15 min to obtain the flame-retardant gel electrolyte precursor solution.

[0014] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, positive electrode and negative electrode, and left to stand until the positive electrode and negative electrode are fully wetted. Then, it is heated to 30℃~60℃ to solidify and obtain the flame-retardant gel electrolyte.

[0015] First, the lithium salt is dissolved in a plasticizer. The high solubility of the plasticizer disperses the lithium salt. After the basic electrolyte system is stable, polymerization-related components are added, avoiding compatibility issues caused by direct contact between the monomers, crosslinking agents, and lithium salt. The initiator is added last to prevent premature decomposition, which could cause the polymerization reaction to start before battery injection. Finally, through impregnation followed by polymerization, the precursor solution fully fills the electrode pores and adheres to the electrode surface. Heating then initiates the polymerization reaction, achieving in-situ molding of the electrolyte inside the battery. Heating and curing at 30℃~60℃ ensures the polymerization reaction proceeds fully, forming a complete and dense three-dimensional crosslinked network structure, while avoiding electrolyte decomposition or electrode active material failure caused by high temperatures, thus ensuring stable electrolyte performance.

[0016] In some embodiments, the fluorinated lithium salt accounts for 1% to 20% of the total mass of the flame-retardant gel electrolyte precursor solution; the fluorinated lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0017] Fluorine-containing lithium salts with a content of 1% to 20% balance ion concentration and transport efficiency, providing sufficient active lithium ions to ensure effective lithium ion transport, while avoiding crystallization caused by excessive lithium salt aggregation.

[0018] In some embodiments, the fluorocarbonate accounts for 70% to 80% of the total mass of the flame-retardant gel electrolyte precursor solution, and the fluorocarbonate is any one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0019] The flame-retardant gel electrolyte precursor solution contains a high proportion of 70%~80% fluorocarbonate, which provides an ample ion transport medium. Its small molecular structure fills the pores of the three-dimensional cross-linked network, constructing an efficient lithium-ion channel. Combined with fluorinated lithium salt, it ensures an ionic conductivity of ≥5.30mS / cm, meeting the battery charging and discharging requirements.

[0020] In some embodiments, the methylenebisacrylamide accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution; the octavinyl-POSS accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution; and the fluoroacrylate accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution.

[0021] Within this ratio range, the three components ensure that the flame-retardant gel electrolyte has an ionic conductivity of ≥5.30mS / cm, an electrochemical window of ≥5.0V, and a self-extinguishing time of 0s. It is also compatible with high-voltage positive electrodes and lithium metal negative electrodes, ensuring the long-cycle stability of the battery.

[0022] In some embodiments, the fluoroacrylate is any one or more of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, and heptafluorobutyl acrylate.

[0023] The carbon-based backbone of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, and heptafluorobutyl acrylate can form weak interactions with fluorinated lithium salts and fluorinated carbonates, ensuring compatibility between components and providing channels for ion transport. Fluorine atoms further enhance flame retardancy and electrochemical stability.

[0024] In some embodiments, the azo initiator accounts for 0.001% to 0.075% of the total mass of the flame-retardant gel electrolyte precursor solution, and the azo initiator is any one or more of dimethyl azobisisobutyrate, azobisisoheptanenitrile, and azobisisobutyronitrile.

[0025] Azo initiators with a mass ratio of 0.001% to 0.075% make the polymerization reaction mild and controllable.

[0026] In some embodiments, the separator is selected from any one of cellulose separator, polyethylene battery separator, polypropylene battery separator, and polyethylene / polypropylene composite battery separator;

[0027] The positive electrode is selected from any one of lithium iron phosphate positive electrode, lithium manganese iron phosphate positive electrode, lithium cobalt oxide positive electrode, and nickel cobalt manganese 811 positive electrode.

[0028] Cellulose separators, polyethylene battery separators, polypropylene battery separators, and polyethylene / polypropylene composite battery separators enable rapid and uniform wetting of the gel precursor solution, avoiding ion transport obstruction caused by unfilled local pores. Lithium iron phosphate cathodes, lithium manganese iron phosphate cathodes, lithium cobalt oxide cathodes, and nickel-cobalt-manganese 811 cathodes are highly compatible with the flame-retardant gel electrolyte's wide electrochemical window of ≥5.0V, preventing electrolyte oxidative decomposition under high voltage.

[0029] In a third aspect, the present invention provides a lithium-ion battery, wherein the electrolyte of the lithium-ion battery is a flame-retardant gel electrolyte as described in any one of the above claims, or a flame-retardant gel electrolyte prepared by any one of the above methods.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] This application utilizes a three-dimensional cross-linked network formed by in-situ polymerization of fluorinated acrylates, octavinyl-POSS, and methylenebisacrylamide to encapsulate the electrolyte, making it difficult for the electrolyte to flow out and improving the flame retardant effect of the flame-retardant gel electrolyte. At the same time, the three-dimensional cross-linked network structure provides a structural basis for ion transport and ensures ionic conductivity. Detailed Implementation

[0032] The following specific embodiments further illustrate the technical solution of the present invention. These specific embodiments do not represent a limitation on the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the scope of protection of the present invention.

[0033] This application provides a flame-retardant gel electrolyte, which is a gel structure in which an electrolyte is encapsulated by a three-dimensional cross-linked network. The three-dimensional cross-linked network is formed by in-situ polymerization of fluoroacrylate, octavinyl-POSS and methylenebisacrylamide.

[0034] Specifically, fluoroacrylates, as polymerizing monomers, provide carbon-carbon double bonds as active sites for the polymerization reaction. Octadecyl-POSS (inorganic silica cage core), as a polymerizing monomer and functional modifier, contains eight carbon-carbon double bonds and can participate in polymerization as a multifunctional monomer. Methylenebisacrylamide crosslinking agent contains two polymerizable double bonds and acts as a "bridge" to connect the long chains of fluoroacrylates and octavincyl-POSS during polymerization, constructing a three-dimensional crosslinking network to bind the electrolyte within and reduce the risk of leakage.

[0035] The fluorine groups in fluorinated acrylate molecules remain in the three-dimensional cross-linked network after polymerization, enhancing the electrochemical stability of the electrolyte. Simultaneously, the fluorine groups break down under the high temperatures of the initial combustion phase, releasing fluorine free radicals. These free radicals combine with hydrogen and hydroxyl radicals generated during combustion to form stable HF molecules. Hydrogen and hydroxyl radicals are key reactive species for maintaining the combustion chain reaction, preventing sustained flame combustion through free radical quenching. The three-dimensional cross-linked network formed by the polymerization of fluorinated acrylates and cross-linking agents undergoes a carbonization reaction at high temperatures, generating a fluorinated carbon layer. Octadecyl-POSS (inorganic silica cage core) is uniformly dispersed in a three-dimensional cross-linked network after polymerization. The core of octavinyl-POSS is an octahedral silica cage. After the organic vinyl segments burn at high temperatures, the silica cages aggregate to form a dense amorphous SiO2 ceramic layer. The SiO2 ceramic layer interweaves with the fluorocarbon layer to form an inorganic-organic composite protective barrier. This barrier utilizes the high heat resistance of SiO2 to block heat transfer, preventing the continuous decomposition and volatilization of the internal electrolyte. Simultaneously, the dense fluorocarbon layer isolates oxygen and prevents the leakage of internal combustible components, such as unpolymerized plasticizers, thus completely cutting off the supply of substances for combustion. Octadecyl-POSS decomposes at high temperatures; these substances dilute the oxygen concentration in the combustion zone, further interrupting the chain reaction.

[0036] Hydrogen bonds in the three-dimensional cross-linked network structure can immobilize lithium salt anions, increase lithium ion transference number, and optimize ion transport kinetics. The carbon-based structure of fluoroacrylates can also interact with lithium salt anions, promoting lithium salt dissociation and ensuring lithium ion transport efficiency. Simultaneously, octavinyl-POSS can reduce gel crystallinity and optimize ion transport channels. Fluoroacrylates, octavinyl-POSS, and methylenebisacrylamide synergistically improve the flame retardant effect and ionic conductivity of the flame-retardant gel electrolyte.

[0037] Furthermore, the flame-retardant gel electrolyte has a self-extinguishing time of 0 s, an electrochemical window of ≥5.0 V, and an ionic conductivity of ≥5.30 mS / cm.

[0038] This indicates that the flame-retardant gel electrolyte of this application has excellent flame-retardant effect and good electrochemical stability, meeting the application requirements of high-voltage cathodes. The electrolyte is not easily oxidized and decomposed under high voltage, and has a continuous lithium-ion transport channel to ensure ion transport efficiency.

[0039] Furthermore, this application provides a method for preparing a flame-retardant gel electrolyte, comprising the following steps:

[0040] Preparation of electrolyte: Dissolve fluorinated lithium salt in fluorocarbonate and stir at room temperature for 10 min to 30 min until completely dissolved to obtain electrolyte;

[0041] Preparation of flame-retardant gel electrolyte prepolymer: Add crosslinking agent methylenebisacrylamide, octavinyl-POSS and fluoroacrylate to the electrolyte, stir at room temperature for 30 min to 120 min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0042] Preparation of flame-retardant gel electrolyte precursor solution: Add an azo initiator to the flame-retardant gel electrolyte prepolymer solution and stir at room temperature for 5 min to 15 min to obtain the flame-retardant gel electrolyte precursor solution.

[0043] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, positive electrode and negative electrode. After standing until the positive electrode and negative electrode are fully wetted, it is heated at 30℃~60℃ to solidify and obtain flame-retardant gel electrolyte.

[0044] Fluorinated lithium salt and fluorinated plasticizer first form a synergistic system, pre-constructing preliminary ion transport channels. Simultaneously, the interaction of fluorine groups lays the foundation for subsequent SEI film formation. Then, crosslinking agents methylenebisacrylamide, octavinyl-POSS, and fluoroacrylates are added. Methylenebisacrylamide and fluoroacrylates undergo weak secondary interactions, such as hydrogen bonding, in the electrolyte, providing pre-assembly sites for the rapid formation of a three-dimensional crosslinked network in the subsequent polymerization reaction, thus improving polymerization efficiency. The azo initiator is added late to ensure that the flame-retardant gel electrolyte precursor solution is fully wetted by the battery and electrodes before polymerization is initiated by heating, avoiding premature polymerization that could clog electrode pores. Finally, an in-situ polymerization process ensures tight adhesion between the flame-retardant gel electrolyte and the electrodes. Static wetting facilitates the filling of electrode pores by the flame-retardant gel electrolyte, while the three-dimensional crosslinked network formed by heating and curing fixes the electrolyte, reducing the possibility of electrolyte leakage and ensuring efficient ion transport. In-situ polymerization enables the flame-retardant gel electrolyte to be highly compatible with the battery structure, forming an integrated electrode-electrolyte structure. This not only fixes the electrolyte to prevent leakage but also ensures interface stability, significantly improving the battery's safety performance and cycle life.

[0045] In the electrolyte preparation step, stirring at room temperature for 10 to 30 minutes is beneficial for the uniform dispersion of lithium salt and avoids excessively high local concentrations that may affect ion transport. The stirring time can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, etc.

[0046] In the preparation of the flame-retardant gel electrolyte prepolymer, prolonged stirring for 30 to 120 minutes is required to ensure that the crosslinking agent (methylenebisacrylamide), octavinyl-POSS, and fluoroacrylate are fully dissolved and uniformly dispersed. This prevents uneven local crosslinking density during polymerization and ensures a complete and dense three-dimensional crosslinked network structure. Stirring times can be 30, 35, 40, 45, 50, 60, 65, 70, 80, 85, 90, 100, 110, or 120 minutes.

[0047] In the preparation of the flame-retardant gel electrolyte precursor solution, stirring at room temperature for 5 to 15 minutes ensures uniform dispersion of the initiator while preventing premature polymerization. Stirring times can be 5 minutes, 8 minutes, 10 minutes, 13 minutes, 15 minutes, etc.

[0048] In-situ polymerization of methylenebisacrylamide, fluoroacrylates, and octavinyl-POSS forms a three-dimensional cross-linked network. Fluorocarbonates, acting as film-forming additives and plasticizers, can co-form a solid electrolyte interface film rich in lithium fluoride and lithium nitride with methylenebisacrylamide. This film can induce uniform lithium ion deposition and stripping, inhibit lithium dendrite formation, and alleviate the volume expansion of the lithium metal anode. Simultaneously, the small-molecule structure of the fluorocarbonate fills the pores of the three-dimensional cross-linked network, serving as a channel for lithium ion transport, while the fluorinated lithium salt provides active lithium ions for ion transport.

[0049] The methylenebisacrylamide molecule contains nitrogen-hydrogen bonds, which allow it to interact with fluoroacrylates via secondary interactions, forming a more stable three-dimensional cross-linked network. This enhances the binding capacity of the electrolyte and reduces the risk of leakage. The formation of this three-dimensional cross-linked network also facilitates interaction with lithium salt anions through hydrogen bonds, effectively immobilizing the anions within the network and increasing the lithium-ion transference number, thus improving lithium-ion migration kinetics. The presence of carbon groups also promotes lithium salt dissociation, aiding in lithium-ion conduction.

[0050] Octadecyl-POSS is a derivative obtained by introducing eight vinyl groups at the vertices of the silica-oxygen cage core of POSS. It retains the inorganic silica-oxygen cage core of POSS (which imparts flame retardancy and mechanical reinforcement) while also giving it polymerizability through the vinyl groups. Since POSS itself has excellent flame retardant properties, its introduction into flame-retardant gel electrolytes can significantly improve the flame retardancy of the electrolyte. Furthermore, the eight vinyl groups in octavincyl-POSS constitute more reaction sites, which also reduces the amount of polymerizable monomers used in the flame-retardant gel electrolyte, helping to reduce the battery's internal resistance.

[0051] The three-dimensional cross-linked network formed by fluoroacrylates has excellent flame retardant properties. The fluorine content of the polymer also facilitates the formation of hydrogen bonds, resulting in a more stable three-dimensional cross-linked network that can better bind the electrolyte. Fluorine compounds also help to improve the electrochemical window of the electrolyte. In addition, similar to the role of the carbon group in the methylenebisacrylamide cross-linking agent, the carbon group of fluoroacrylates also facilitates the dissociation of lithium salts and helps lithium ion conduction.

[0052] Furthermore, in the electrolyte preparation step, the fluorinated lithium salt accounts for 1% to 20% of the total mass of the flame-retardant gel electrolyte precursor solution, and the fluorinated lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0053] Fluorinated lithium salts serve as the core source of lithium ions in flame-retardant gel electrolytes, ensuring the material basis for ion transport during battery charging and discharging. Fluorinated groups can participate in the construction of a solid electrolyte interphase (SEI) film rich in lithium fluoride (LiF). This film has a dense and stable structure, inhibiting lithium dendrite formation and growth, mitigating the volume expansion of the lithium metal anode (avoiding SEI film rupture due to expansion), and reducing side reactions between the electrolyte and the anode, thus improving battery cycle stability. Lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate exhibit excellent chemical stability and are not easily oxidized and decomposed under high pressure. In synergy with fluorinated acrylates and fluorocarbonates, they ensure the stable application of electrolytes in high-voltage cathode systems (such as nickel-cobalt-manganese 811), avoiding performance degradation or safety risks caused by lithium salt decomposition.

[0054] Fluorinated lithium salts comprising 1% to 20%, such as 1%, 5%, 10%, 15%, and 20%, provide the necessary concentration for ion transport. This avoids insufficient ionic conductivity due to a low concentration, while preventing excessive viscosity and lithium salt agglomeration from negatively impacting ion migration efficiency due to a high concentration. A concentration ≥1% provides sufficient active lithium ions, ensuring effective lithium ion transport and maintaining a stable ionic conductivity ≥5.30 mS / cm, meeting the ion transport requirements for lithium battery charging and discharging. A concentration <1% results in a small ion concentration gradient, a sharp drop in ionic conductivity, and insufficient battery power density. A concentration ≤20% avoids excessive lithium salt aggregation leading to crystallization: excessive lithium salt exceeds the solubility of fluorocarbonate, forming localized crystalline particles that block ion transport channels, increase electrolyte viscosity, and reduce lithium ion migration rate.

[0055] Furthermore, in the electrolyte preparation step, fluorocarbonate accounts for 70% to 80% of the total mass of the flame-retardant gel electrolyte precursor solution, and the fluorocarbonate is any one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0056] The synergistic effect of fluorocarbonate and fluorinated lithium salt further optimizes the SEI film composition (rich in LiF and lithium nitride), enhances the film's flexibility and ionic conductivity, can induce uniform deposition or stripping of lithium ions, and can resist the mechanical stress caused by the volume expansion of lithium metal, thus avoiding SEI film rupture and failure.

[0057] Fluorinated ethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate exhibit good compatibility with methylenebisacrylamide crosslinking agents and polymer monomers (octavinyl-POSS, fluoroacrylates), preventing phase separation and ensuring uniform dispersion within a three-dimensional crosslinked network, thus guaranteeing the uniformity of electrolyte performance. Simultaneously, their film-forming properties improve the interfacial contact between the electrolyte and electrode, reducing interfacial impedance. Fluorinated ethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate are small-molecule fluorocarbonates with excellent flowability and lithium salt solubility, providing a smooth channel for lithium-ion transport, improving electrolyte ionic conductivity, and solving the problem of decreased conductivity in traditional flame-retardant gel electrolytes due to insufficient plasticizers. Meanwhile, the fluorinated groups of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate form a synergistic effect with the fluorine elements of octavinyl-POSS and fluoroacrylate, quenching combustion-active free radicals, assisting in gas-phase flame retardancy, reducing the exposure of flammable components, and improving the flame retardant effect in conjunction with the inorganic flame-retardant skeleton of POSS, thus avoiding the safety hazards of flammability of traditional carbonate plasticizers such as alkyl carbonates.

[0058] A high proportion of fluorocarbonate in the flame-retardant gel electrolyte precursor solution, ranging from 70% to 80% by mass (e.g., 70%, 75%, 78%, 80%), effectively plasticizes the three-dimensional cross-linked network, providing ample ion transport channels. Furthermore, through synergy with the flame-retardant components, it ensures the flame-retardant effect without compromising conductivity. Simultaneously, this ratio gives the precursor solution a suitable viscosity, guaranteeing the uniform dispersion and dissolution of subsequent cross-linking agents, octavinyl-POSS, fluoroacrylates, and other components. It also avoids the risk of leakage due to an excessively high plasticizer content, which could prevent the three-dimensional cross-linked network from effectively binding the electrolyte, or an excessively low plasticizer content, which could lead to an overly dense network that blocks ion transport channels.

[0059] Furthermore, methylenebisacrylamide accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution; octavinyl-POSS accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution; and fluoroacrylates account for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution.

[0060] Methylenebisacrylamide, comprising 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution, creates a complementary synergy among the three components, such as 1%, 5%, and 10%. Insufficient concentrations of monomers and crosslinking agents prevent the formation of a complete three-dimensional crosslinked network, completely negating the core functions of leak prevention and lithium dendrite resistance. Simultaneously, insufficient flame-retardant content disrupts the dual flame-retardant mechanism, significantly prolonging self-extinguishing time, narrowing the electrochemical window, and drastically reducing ionic conductivity, failing to meet the basic performance and safety requirements of lithium batteries. Excessive methylenebisacrylamide leads to excessive crosslinking, reduced gel porosity, blockage of ion transport channels, and hardening and brittleness of the gel, making it unable to accommodate electrode volume expansion. Excessive octavinyl-POSS results in an excessively high proportion of inorganic components, decreased gel flexibility, increased interfacial impedance, and a tendency for aggregation, leading to uneven flame-retardant performance. Excessive fluoroacrylates make the polymer skeleton too dense, hindering lithium-ion migration. Simultaneously, excessive fluorine leads to an excessively thick SEI film, a sharp increase in interfacial impedance, and a significant decrease in battery charge-discharge efficiency.

[0061] Furthermore, the fluoroacrylate is any one or more of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, and heptafluorobutyl acrylate.

[0062] All of the aforementioned fluorinated acrylates contain carbon-carbon double bonds and synergistically polymerize with methylenebisacrylamide and octavinyl-POSS to form a stable three-dimensional cross-linked network, preventing electrolyte leakage. The aforementioned fluorinated alkyl side chains all break at high temperatures, releasing fluorine radicals. These fluorine radicals preferentially combine with hydrogen radicals and hydroxyl radicals generated during combustion to form stable HF molecules, interrupting the combustion chain reaction.

[0063] Furthermore, the azo initiator accounts for 0.001% to 0.075% of the total mass of the flame-retardant gel electrolyte precursor solution, and the azo initiator is any one or more of dimethyl azobisisobutyrate, azobisisoheptanenitrile, and azobisisobutyronitrile.

[0064] Under heating and curing conditions such as 60°C, azo initiators can decompose smoothly to generate free radicals, efficiently initiating the polymerization reaction of fluoroacrylates, octavinyl-POSS, and the crosslinking agent methylenebisacrylamide. This ensures the formation of a complete and dense three-dimensional crosslinked network, which is beneficial for the transformation of the flame-retardant gel electrolyte from a liquid precursor to a solid gel. A mass percentage of 0.001%~0.075% of azo initiators makes the polymerization reaction mild and controllable. For example, concentrations of 0.001%, 0.005%, 0.065%, and 0.075% ensure that the decomposition temperature and reaction rate of dimethyl azobisisobutyrate, azobisisoheptanenitrile, and azobisisobutyronitrile are well-matched. This avoids excessively rapid decomposition leading to high free radical concentrations, resulting in uneven crosslinking of the three-dimensional crosslinked network, causing pores or cracks, or excessively slow decomposition leading to insufficient polymerization, insufficient gel strength, and inability to effectively bind the electrolyte. Ultimately, this ensures a uniform structure and stable mechanical properties of the flame-retardant gel electrolyte.

[0065] Furthermore, the separator is selected from any one of cellulose separator, polyethylene battery separator, polypropylene battery separator, and polyethylene / polypropylene composite battery separator; the positive electrode is selected from any one of lithium iron phosphate positive electrode, lithium manganese iron phosphate positive electrode, lithium cobalt oxide positive electrode, and nickel cobalt manganese 811 positive electrode.

[0066] The surface material of the aforementioned diaphragm is compatible with the flame-retardant gel electrolyte formed by the polymerization of fluorocarbonate and fluoroacrylate, enabling rapid and uniform wetting of the gel precursor solution and avoiding ion transport obstruction caused by unfilled local pores. The selected positive electrode is highly compatible with the wide electrochemical window of the flame-retardant gel electrolyte (≥5.0V), preventing electrolyte oxidative decomposition under high voltage.

[0067] Example 1

[0068] A method for preparing a flame-retardant gel electrolyte includes the following steps:

[0069] Preparation of electrolyte: Dissolve 1g of lithium hexafluorophosphate (fluorinated lithium salt) in 8.0g of fluoroethylene carbonate (fluorocarbonate), stir at room temperature for 30min until completely dissolved to obtain electrolyte;

[0070] Preparation of flame-retardant gel electrolyte prepolymer: Add 0.5g methylenebisacrylamide (crosslinking agent), 0.25g octavinyl-POSS and 0.25g trifluoroethyl acrylate (fluoroacrylate) to the electrolyte, stir at room temperature for 60min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0071] Preparation of flame-retardant gel electrolyte precursor solution: 7.5 mg of azobisisobutyronitrile (azo initiator) was added to the flame-retardant gel electrolyte prepolymer solution and stirred at room temperature for 10 min to obtain the flame-retardant gel electrolyte precursor solution.

[0072] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, a positive electrode and a negative electrode. The separator is a polyethylene battery separator, the positive electrode is a lithium iron phosphate positive electrode and the negative electrode is lithium metal. After standing until the electrode materials are fully wetted, it is heated and cured at 30°C to obtain the flame-retardant gel electrolyte.

[0073] Example 2

[0074] A method for preparing a flame-retardant gel electrolyte includes the following steps:

[0075] Preparation of electrolyte: Dissolve 1g of lithium bis(fluorosulfonyl)imide (fluorinated lithium salt) in 8.0g of difluoropropylene carbonate (fluorocarbonate), stir at room temperature for 30min until completely dissolved to obtain electrolyte;

[0076] Preparation of flame-retardant gel electrolyte prepolymer: Add 0.5g methylenebisacrylamide (crosslinking agent), 0.25g octavinyl-POSS and 0.25g trifluoroethyl methacrylate (fluoroacrylate) to the electrolyte, stir at room temperature for 60min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0077] Preparation of flame-retardant gel electrolyte precursor solution: 7.5 mg of azobisisoheptanenitrile (azo initiator) was added to the flame-retardant gel electrolyte prepolymer solution and stirred at room temperature for 10 min to obtain the flame-retardant gel electrolyte precursor solution.

[0078] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, positive electrode and negative electrode. The battery separator is a polyethylene battery separator, the positive electrode is lithium iron phosphate positive electrode and the negative electrode is lithium metal. After standing until the electrode materials are fully wetted, it is heated at 50°C to solidify and obtain the flame-retardant gel electrolyte.

[0079] Example 3

[0080] A method for preparing a flame-retardant gel electrolyte includes the following steps:

[0081] Preparation of electrolyte: Dissolve 1g of lithium tetrafluoroborate (fluorinated lithium salt) in 8.0g of propylene trifluorocarbonate (fluorocarbonate), stir at room temperature for 30min until completely dissolved to obtain electrolyte;

[0082] Preparation of flame-retardant gel electrolyte prepolymer: Add 0.5g methylenebisacrylamide (crosslinking agent), 0.25g octavinyl-POSS and 0.25g hexafluoroisopropyl acrylate (fluoroacrylate) to the electrolyte, stir at room temperature for 60min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0083] Preparation of flame-retardant gel electrolyte precursor solution: Add 7.5 mg of dimethyl azobisisobutyrate (azo initiator) to the flame-retardant gel electrolyte prepolymer solution and stir at room temperature for 10 min to obtain the flame-retardant gel electrolyte precursor solution.

[0084] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, positive electrode and negative electrode. The battery separator is a polyethylene battery separator, the positive electrode is lithium iron phosphate positive electrode and the negative electrode is lithium metal. After standing until the electrode materials are fully wetted, it is heated at 60°C to solidify and obtain the flame-retardant gel electrolyte.

[0085] Example 4

[0086] A method for preparing a flame-retardant gel electrolyte includes the following steps:

[0087] Preparation of electrolyte: Dissolve 1g of lithium difluorooxalate borate (fluorinated lithium salt) in 8.0g of propylene trifluorocarbonate (fluorocarbonate), stir at room temperature for 30min until completely dissolved to obtain electrolyte;

[0088] Preparation of flame-retardant gel electrolyte prepolymer: Add 0.5g methylenebisacrylamide (crosslinking agent), 0.25g octavinyl-POSS and 0.25g pentafluoropropyl acrylate (fluoroacrylate) to the electrolyte, stir at room temperature for 60min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0089] Preparation of flame-retardant gel electrolyte precursor solution: 7.5 mg of azobisisobutyronitrile (azo initiator) was added to the flame-retardant gel electrolyte prepolymer solution and stirred at room temperature for 10 min to obtain the flame-retardant gel electrolyte precursor solution.

[0090] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, positive electrode and negative electrode. The battery separator is a polyethylene battery separator, the positive electrode is lithium iron phosphate positive electrode and the negative electrode is lithium metal. After standing until the electrode materials are fully wetted, it is heated at 60°C to solidify and obtain the flame-retardant gel electrolyte.

[0091] Example 5

[0092] A method for preparing a flame-retardant gel electrolyte includes the following steps:

[0093] Preparation of electrolyte: Dissolve 1g of lithium difluorooxalate borate (fluorinated lithium salt) in 8.0g of propylene trifluorocarbonate (fluorocarbonate), stir at room temperature for 30min until completely dissolved to obtain electrolyte;

[0094] Preparation of flame-retardant gel electrolyte prepolymer: Add 0.5g methylenebisacrylamide (crosslinking agent), 0.25g octavinyl-POSS and 0.25g heptafluorobutyl acrylate (fluoroacrylate) to the electrolyte, stir at room temperature for 60min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer;

[0095] Preparation of flame-retardant gel electrolyte precursor solution: 7.5 mg of azobisisobutyronitrile (azo initiator) was added to the flame-retardant gel electrolyte prepolymer solution and stirred at room temperature for 10 min to obtain the flame-retardant gel electrolyte precursor solution.

[0096] In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, a positive electrode and a negative electrode. The battery separator is a polyethylene battery separator, the positive electrode is a lithium iron phosphate positive electrode and the negative electrode is lithium metal. After standing until the electrode materials are fully wetted, it is heated and cured at 55°C to obtain the flame-retardant gel electrolyte.

[0097] Comparative Example 1

[0098] A method for preparing a flame-retardant gel electrolyte differs from Example 1 in that, after obtaining the electrolyte, it is directly injected into the battery containing a separator, a positive electrode, and a negative electrode. The battery separator is a polyethylene battery separator, the positive electrode is a lithium iron phosphate positive electrode, and the negative electrode is a lithium metal electrode. After standing until the electrode materials are fully wetted, it is heated and solidified to obtain the flame-retardant gel electrolyte.

[0099] Comparative Example 2

[0100] A method for preparing a flame-retardant gel electrolyte differs from Example 1 in that, in the step of preparing the flame-retardant gel electrolyte prepolymer, 1g of methylenebisacrylamide (crosslinking agent) is added to the electrolyte, but octavinyl-POSS and trifluoroethyl acrylate (fluoroacrylate) are not added, and other conditions are the same as in Example 1.

[0101] Comparative Example 3

[0102] A method for preparing a flame-retardant gel electrolyte differs from Example 1 in that, in the step of preparing the flame-retardant gel electrolyte prepolymer, 1g of trifluoroethyl acrylate (fluoroacrylate) is added to the electrolyte, but octavinyl-POSS and methylenebisacrylamide (crosslinking agent) are not added, and other conditions are the same as in Example 1.

[0103] Comparative Example 4

[0104] A method for preparing a flame-retardant gel electrolyte differs from Example 1 in that, in the step of preparing the flame-retardant gel electrolyte prepolymer, 1g of octavinyl-POSS is added to the electrolyte, but methylenebisacrylamide (crosslinking agent) and trifluoroethyl acrylate (fluoroacrylate) are not added. Other conditions are the same as in Example 1.

[0105] Comparative Example 5

[0106] A method for preparing a flame-retardant gel electrolyte differs from Example 1 in that, in the step of preparing the flame-retardant gel electrolyte prepolymer, 0.05 g of octavinyl-POSS is added to the electrolyte, while other conditions are the same as in Example 1.

[0107] Performance testing

[0108] I. Sample Preparation

[0109] Preparation environment: The flame-retardant gel electrolyte precursor solutions corresponding to the examples and comparative examples were all assembled into coin cells in a glove box environment, avoiding interference from moisture and oxygen throughout the process.

[0110] Button battery materials: The positive and negative electrode shells are made of CR2025, with a 12mm diameter composite positive electrode sheet, a 19mm diameter separator, a 15.8mm diameter stainless steel sheet and a 15.8mm outer diameter stainless steel spring sheet. The core electrolyte is the flame-retardant gel electrolyte precursor solution corresponding to each embodiment and comparative example.

[0111] Assembly and Packaging: After assembling according to the different battery types and hierarchical order, use a battery sealing machine to pressurize and seal the batteries until the inner ring of the equipment reaches 500 psi, ensuring good battery sealing performance.

[0112] II. Test Battery Type and Structure

[0113] Based on performance testing requirements, four different button cell structures were built, with the specific hierarchical order as follows:

[0114] 1. Dual-blocking battery: positive electrode shell, stainless steel sheet, electrolyte, separator, electrolyte, stainless steel sheet, spring sheet, negative electrode shell;

[0115] 2. Single-blocking battery: positive electrode shell, lithium plate, electrolyte, separator, electrolyte, stainless steel plate, spring plate, negative electrode shell;

[0116] 3. Lithium symmetric battery: positive electrode shell, lithium sheet, electrolyte, separator, electrolyte, lithium sheet, stainless steel sheet, spring sheet, negative electrode shell;

[0117] 4. Lithium metal full battery: positive electrode shell, positive electrode plate, electrolyte, separator, lithium plate, stainless steel plate, spring plate, negative electrode shell.

[0118] III. Test Items and Methods

[0119] (a) Ionic conductivity test

[0120] A dual-blocking battery was used for testing. The assembled battery was connected to an electrochemical workstation, and the scanning frequency range was set to 1MHz~0.1Hz. Electrochemical impedance spectroscopy (EIS) was performed at room temperature, and the ionic conductivity of the flame-retardant gel electrolyte was calculated by fitting the impedance data.

[0121] (ii) Electrochemical window testing

[0122] Testing was conducted using a single-blocked battery, with a lithium-ion sheet as the reference electrode and a stainless steel sheet as the working electrode. The test was performed using linear sweep voltammetry (LSV) at a scan rate of 0.5 mV / s, covering a voltage range of 1.2 V to 6.0 V (vs Li). + / Li), the upper limit of the electrochemical window of the electrolyte is determined based on the current abrupt change node.

[0123] (III) Flame retardant performance test

[0124] Flame-retardant gel electrolyte samples from each experimental group were directly selected, and the vertical combustion test method was used to observe the self-extinguishing time after the samples were ignited to evaluate the flame-retardant effect of the electrolyte. The self-extinguishing time of 0s was determined to be the optimal flame-retardant level.

[0125] Results Analysis

[0126] The performance test results of the flame-retardant gel electrolytes prepared in the examples and comparative examples are shown in Table 1 below:

[0127] Table 1 Performance test results of the flame-retardant gel electrolytes prepared in the examples and comparative examples

[0128]

[0129] As shown in Table 1, the self-extinguishing time of Examples 1-5 is 0 s, achieving a completely non-flammable flame-retardant effect. This indicates that the synergistic effect of octavinyl-POSS, fluoroacrylate, and methylenebisacrylamide in this invention effectively interrupts the combustion chain reaction. Meanwhile, the ionic conductivity of the flame-retardant gel electrolytes corresponding to Examples 1-5 is between 5.31 and 5.40 mS / cm, exhibiting stable and high performance. This demonstrates that the fluorocarbonate, octavinyl-POSS, and fluoroacrylate system used in this invention can effectively construct a continuous lithium-ion transport channel, ensuring the ion transport efficiency of the electrolyte. Furthermore, the electrochemical windows of Examples 1-5 are all between 5.03 and 5.19 V, all greater than 5.0 V, meeting the application requirements of high-voltage cathodes (such as nickel-cobalt-manganese 811). This indicates that the fluoroacrylate in the system of this invention can effectively inhibit the oxidative decomposition of the electrolyte under high voltage, improving the high-voltage resistance of the electrolyte.

[0130] Comparative Example 1 (without monomers and crosslinking agents) exhibits a high ionic conductivity of 9.10 mS / cm, but due to the lack of a three-dimensional crosslinking network, there is a risk of electrolyte leakage. Furthermore, the electrolyte only extinguishes after complete combustion, demonstrating no flame-retardant capability. This confirms the necessity of a three-dimensional crosslinking network and flame-retardant components for safety performance. Comparative Examples 2 and 3 (containing only crosslinking agents or fluorinated acrylates) have self-extinguishing times of 50s and 40s, respectively, indicating poor flame-retardant performance. This demonstrates that a single component cannot achieve effective flame retardancy, requiring synergistic effects from multiple components. The electrochemical windows of Comparative Examples 1, 2, and 3 are all below 5.0V, indicating poor electrochemical stability and unsuitability for high-voltage battery systems.

[0131] Comparative Example 4 (containing only octavinyl-POSS) had a self-extinguishing time of 0 s, exhibiting excellent flame retardant properties, but its ionic conductivity was only 2.08 mS / cm, significantly lower than that of the Example group. This indicates that while octavinyl-POSS alone can provide flame retardancy, the lack of synergistic effects from components such as fluoroacrylates limits the construction of ion transport channels. Comparative Example 5 (octavinyl-POSS content reduced to 0.5%) had an ionic conductivity of 5.66 mS / cm, slightly higher than that of the Example group, but its self-extinguishing time was extended to 5 s, resulting in a decrease in flame retardant properties. This sacrifices flame retardant performance, indicating that the amount of octavinyl-POSS added needs to be maintained within a reasonable range (1~10%) to ensure the flame retardant effect. This further confirms the crucial role of the synergistic effect of each component in balancing ionic conductivity and flame retardancy. Although the electrochemical windows of Comparative Examples 4 and 5 reached 5.14V and 5.13V respectively, they had defects such as low ionic conductivity or insufficient flame retardancy. This further demonstrates the synergistic effect of the multi-component combination of the present invention on optimizing the comprehensive performance of high voltage resistance, safety and ionic conductivity.

[0132] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A flame-retardant gel electrolyte, characterized in that, The flame-retardant gel electrolyte is a gel structure in which the electrolyte is encapsulated by a three-dimensional cross-linked network. The three-dimensional cross-linked network is formed by in-situ polymerization of fluoroacrylate, octavinyl-POSS and methylenebisacrylamide. The methylenebisacrylamide is linked to the fluoroacrylate and octavinyl-POSS. The mass ratio of the methylenebisacrylamide, octavinyl-POSS and fluoroacrylate is 1~10:1~10:1~10.

2. The flame-retardant gel electrolyte as described in claim 1, characterized in that, The flame-retardant gel electrolyte has a self-extinguishing time of 0 s, an electrochemical window of ≥5.0 V, and an ionic conductivity of ≥5.30 mS / cm.

3. A method for preparing a flame-retardant gel electrolyte as described in any one of claims 1-2, characterized in that, Includes the following steps: Preparation of electrolyte: Dissolve fluorinated lithium salt in fluorocarbonate and stir at room temperature for 10 min to 30 min until completely dissolved to obtain electrolyte; Preparation of flame-retardant gel electrolyte prepolymer: Add methylenebisacrylamide, octavinyl-POSS and fluoroacrylate to the electrolyte, stir at room temperature for 30 min to 120 min until completely dissolved to obtain flame-retardant gel electrolyte prepolymer; Preparation of flame-retardant gel electrolyte precursor solution: Add an azo initiator to the flame-retardant gel electrolyte prepolymer solution and stir at room temperature for 5 min to 15 min to obtain the flame-retardant gel electrolyte precursor solution. In-situ polymerization preparation of flame-retardant gel electrolyte: The flame-retardant gel electrolyte precursor solution is injected into the battery containing a separator, positive electrode and negative electrode, and left to stand until the positive electrode and negative electrode are fully wetted. Then, it is heated and solidified at 30℃~60℃ to obtain the flame-retardant gel electrolyte.

4. The method for preparing the flame-retardant gel electrolyte as described in claim 3, characterized in that, The fluorinated lithium salt accounts for 1% to 20% of the total mass of the flame-retardant gel electrolyte precursor solution; the fluorinated lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorooxalateborate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

5. The method for preparing the flame-retardant gel electrolyte as described in claim 3, characterized in that, The fluorocarbonate accounts for 70% to 80% of the total mass of the flame-retardant gel electrolyte precursor solution, and the fluorocarbonate is any one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

6. The method for preparing the flame-retardant gel electrolyte as described in claim 3, characterized in that, The methylenebisacrylamide accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution; the octavinyl-POSS accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution; and the fluoroacrylate accounts for 1% to 10% of the total mass of the flame-retardant gel electrolyte precursor solution.

7. The method for preparing the flame-retardant gel electrolyte as described in claim 3, characterized in that, The fluoroacrylate is any one or more of trifluoroethyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, and heptafluorobutyl acrylate.

8. The method for preparing the flame-retardant gel electrolyte as described in claim 3, characterized in that, The azo initiator accounts for 0.001% to 0.075% of the total mass of the flame-retardant gel electrolyte precursor solution, and the azo initiator is any one or more of dimethyl azobisisobutyrate, azobisisoheptanenitrile, and azobisisobutyronitrile.

9. The method for preparing the flame-retardant gel electrolyte according to any one of claims 3-8, characterized in that, The separator is selected from any one of cellulose separator, polyethylene battery separator, polypropylene battery separator, and polyethylene / polypropylene composite battery separator; The positive electrode is selected from any one of lithium iron phosphate positive electrode, lithium manganese iron phosphate positive electrode, lithium cobalt oxide positive electrode, and nickel cobalt manganese 811 positive electrode.

10. A lithium-ion battery, characterized in that, The electrolyte of the lithium-ion battery is the flame-retardant gel electrolyte according to any one of claims 1-2, or the flame-retardant gel electrolyte prepared by the preparation method of the flame-retardant gel electrolyte according to any one of claims 3-9.

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