Fluorine-rich flame-retardant gel polymer electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a fluorine-rich flame-retardant gel polymer electrolyte as well as a preparation method and application thereof. Dissolving a lithium salt in a fluorocarbonate solvent to form a uniform solution; then adding an unsaturated fluorine-based polymer monomer, a cross-linking agent and a thermal initiator into the obtained uniform solution, and stirring to obtain a uniform precursor solution; and dropwise adding the precursor solution on the surface of an electrode, assembling into a complete battery, initiating monomer polymerization by a heating method, and forming a gel polymer electrolyte with a cross-linked structure on the surface of the electrode in situ. Fluoro-carbonic ester is used as an electrolyte solvent, so that the flammability is reduced from the source of the solvent. The monomer rich in fluorine-based fragments is introduced, so that the thermal stability, the oxidation resistance and the mechanical strength of the gel polymer electrolyte are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes and batteries, and in particular to a fluorine-rich flame-retardant gel polymer electrolyte and a preparation method and application thereof. Background Art

[0002] At present, the rapid development of electric vehicles, wearable electronic devices, and smart devices (robots, drones, etc.) has put forward more stringent requirements on the energy density, cycle life and safety of lithium-ion batteries.

[0003] Traditional commercial lithium-ion batteries primarily utilize organic electrolytes. The low flash point and high volatility of common carbonate solvents (such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate) pose serious safety risks to batteries under extreme conditions such as high temperature, overcharging, and short circuits. These batteries are prone to thermal runaway and even explosion, directly impacting the battery's cycle life and safety. Furthermore, lithium metal and carbonate solvents are highly reactive, and side reactions can easily occur at the interface, generating lithium dendrites that can puncture and cause battery short circuits.

[0004] Compared to liquid electrolytes, solid polymer electrolytes effectively reduce the possibility of electrolyte leakage. They also possess excellent flexibility and interfacial compatibility, helping to inhibit lithium dendrite growth and reduce the risk of short circuits. Current approaches to improving the safety of polymer electrolytes primarily involve fixing flame-retardant groups within the polymer backbone through copolymerization and molecular design, or directly incorporating flame retardants into the polymer electrolyte. However, these approaches often suffer from reduced ionic conductivity and electrochemical stability, leading to decreased battery performance.

[0005] Therefore, the development of high-safety and high-performance polymer electrolytes is of vital importance to promoting the industrialization of lithium-ion batteries. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a fluorine-rich flame-retardant gel polymer electrolyte and its preparation method and application, so as to improve the thermal stability and other properties of the electrolyte as well as the safety and electrochemical stability of the battery.

[0007] To solve the above technical problems, according to one aspect of the present invention, a method for preparing a fluorine-rich flame-retardant gel polymer electrolyte is provided, comprising the following steps: Step 1, dissolving a lithium salt in a fluorocarbonate solvent to form a homogeneous solution; Step 2: adding an unsaturated fluorine-based polymer monomer, a crosslinking agent, and a thermal initiator to the uniform solution obtained in step 1, and stirring to obtain a uniform precursor solution; Step three: dripping the precursor solution onto the electrode surface and assembling a complete battery, initiating monomer polymerization by heating, and forming a gel polymer electrolyte with a cross-linked structure in situ on the electrode surface.

[0008] Furthermore, in step 1, the lithium salt is selected from one or a combination of lithium perchlorate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium hexafluorophosphate and lithium tetrafluoroborate.

[0009] Furthermore, in step 1, the fluorocarbonate solvent is selected from one or a combination of 2,2,2-trifluoroethyl methyl carbonate, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 4-(perfluorobutyl)ethylene carbonate, 4-(trifluoromethyl)ethylene carbonate, 4-(perfluorohexyl)ethylene carbonate, 4-(perfluorooctyl)ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate, perfluoropolyether carbonate and methyl fluorocarbonate.

[0010] Furthermore, in step 1, the molar ratio of the lithium salt to the fluorocarbonate solvent is 1:(5-50).

[0011] Furthermore, in step 2, the unsaturated fluorine-based polymer monomer is selected from one or a combination of tetrafluoroethylene, hexafluoropropylene, butyl hexafluoroacrylate, hexafluorobutyl methacrylate, heptafluorobutyl methacrylate, perfluorooctyl methacrylate and perfluoro-n-decyl methacrylate.

[0012] Furthermore, in step 2, the crosslinking agent is selected from one or a combination of ethoxylated trimethylolpropane triacrylate, isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol tetraacrylate, polyethylene glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate and pentaerythritol triacrylate.

[0013] Furthermore, in step 2, the thermal initiator is selected from one or a combination of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisobutylcyanamide, dibenzoyl peroxide, diethylhexyl peroxydicarbonate, potassium persulfate, lauroyl peroxide and benzophenone.

[0014] Furthermore, in step 2, the molar ratio of the unsaturated fluorine-based polymer monomer to the cross-linking agent is (1-10):1.

[0015] According to another aspect of the present invention, provided is a fluorine-rich flame-retardant gel polymer electrolyte obtained by the above method.

[0016] According to another aspect of the present invention, provided is the use of the fluorine-rich flame-retardant gel polymer electrolyte in the preparation of lithium-ion batteries.

[0017] The present invention utilizes fluorocarbonate as an electrolyte solvent to reduce flammability from the solvent source. The introduction of monomers rich in fluorine-based segments significantly improves the thermal stability, oxidation resistance, and mechanical strength of the gel polymer electrolyte. In addition, a cross-linking structure is constructed by in-situ polymerization using a cross-linking agent rich in ether oxygen groups, which improves the compatibility of the electrolyte / electrode interface, promotes the dissociation and transmission of lithium ions, and effectively overcomes the problem of slow lithium ion transmission caused by the low dielectric constant of fluorocarbonate solvents. At the same time, the cross-linking structure further improves the uniformity of lithium ion deposition, which is beneficial to inhibiting the growth of lithium dendrites and forming an effective electrolyte / electrode interface, thereby improving the overall safety and electrochemical stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of preparing fluorine-rich flame-retardant gel polymer electrolyte in the examples; Figure 2 This is a diagram of the ignition test of the fluorine-rich flame-retardant gel polymer electrolyte prepared in Example 1; Figure 3 AC impedance diagram of a CR2032 button cell assembled with the fluorine-rich flame-retardant gel polymer electrolyte prepared in Example 2; Figure 4 This is a cycling performance diagram of a CR2032 button-type battery assembled with the fluorine-rich flame-retardant gel polymer electrolyte prepared in Example 2.

[0019] Figure 5 This is an ignition test diagram of the fluorine-free gel polymer electrolyte prepared in Comparative Example 1; Figure 6 This is the AC impedance diagram of a CR2032 button cell assembled with the fluorine-free gel polymer electrolyte prepared in Comparative Example 1; Figure 7 This is a cycling performance diagram of a CR2032 button-type battery assembled with the fluorine-free gel polymer electrolyte prepared in Comparative Example 1. DETAILED DESCRIPTION

[0020] A typical embodiment of the present invention provides a method for preparing a fluorine-rich flame-retardant gel polymer electrolyte, comprising steps 1 to 3. In the following embodiments, unless otherwise specified, the term "a plurality of combinations" refers to two or more combinations.

[0021] Step 1: dissolving lithium salt in a fluorocarbonate solvent to form a uniform solution.

[0022] In this step, fluoroethylene carbonate (FEC) with good thermal stability is selected as the solvent to reduce flammability from the source of the solvent. The F• free radicals generated by the fluorocarbonate solvent during the heating process are used to remove the H• or O• free radicals generated during the combustion process, thereby terminating the chain reaction of combustion and having high flame retardant efficiency. As an efficient film-forming additive, the fluorocarbonate solvent can form a passivation layer rich in lithium fluoride components at the electrolyte / electrode interface, effectively inhibiting the penetration of lithium dendrites, thereby improving the long-cycle stability of lithium batteries. In addition, compared with phosphorus-containing and bromine-containing flame retardants, the fluorocarbonate solvent does not generate eutrophication and toxic and harmful substances during the heating process, and almost does not pollute the environment.

[0023] The lithium salt is selected from one or a combination of lithium perchlorate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium hexafluorophosphate and lithium tetrafluoroborate.

[0024] The fluorocarbonate solvent is selected from one or a combination of 2,2,2-trifluoroethyl methyl carbonate, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 4-(perfluorobutyl)ethylene carbonate, 4-(trifluoromethyl)ethylene carbonate, 4-(perfluorohexyl)ethylene carbonate, 4-(perfluorooctyl)ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate, perfluoropolyether carbonate and methyl fluorocarbonate.

[0025] The molar ratio of the lithium salt to the fluorocarbonate solvent is 1:(5-50), for example, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:40, 1:50, etc.

[0026] In a preferred embodiment, after the lithium salt is dissolved in the fluorocarbonate solvent, the solution is heated and stirred to form a uniform solution. The heating temperature is set to 50-70° C. and the stirring time is 5-48 h.

[0027] Step 2: Add unsaturated fluorine-based polymer monomer, crosslinking agent and thermal initiator to the uniform solution obtained in step 1, and stir to obtain a uniform precursor solution.

[0028] In this step, the introduction of monomers rich in fluorine-based fragments ensures the mechanical properties and non-flammability of the gel polymer. The introduction of fluorinated carbonate solvents and unsaturated fluorine-based polymer monomers improves the oxidation resistance of the gel polymer electrolyte and broadens its electrochemical stability window, enabling it to stably match high-voltage cathode materials.

[0029] The unsaturated fluorine-based polymer monomer is selected from one or a combination of tetrafluoroethylene, hexafluoropropylene, hexafluorobutyl methacrylate, heptafluorobutyl methacrylate, perfluorooctyl methacrylate and perfluoro-n-decyl methacrylate.

[0030] The crosslinking agent is selected from one or a combination of two of ethoxylated trimethylolpropane triacrylate, isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol tetraacrylate, polyethylene glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate and pentaerythritol triacrylate.

[0031] The molar ratio of the unsaturated fluorine-based polymer monomer and the crosslinking agent is (1-10):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0032] The initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisobutylcyanamide, dibenzoyl peroxide, diethylhexyl peroxydicarbonate, potassium persulfate, lauroyl peroxide and benzophenone.

[0033] The mass ratio of the initiator in the precursor solution is 0.5% to 1%.

[0034] Step three: dripping the precursor solution onto the electrode surface and assembling a complete battery, initiating monomer polymerization by heating, and forming a gel polymer electrolyte with a cross-linked structure in situ on the electrode surface.

[0035] In-situ thermal polymerization creates a cross-linked structure, effectively binding free solvents and improving the compatibility of the electrolyte / electrode interface. Furthermore, the cross-linked structure can further enhance the overall thermal stability and mechanical strength of the electrolyte, to a certain extent preventing thermal runaway under abusive testing conditions and improving battery safety. The presence of ether oxygen groups in the cross-linker promotes the dissociation and transport of lithium ions, effectively overcoming the slow lithium ion transport caused by the low dielectric constant of fluorocarbonate solvents, ensuring safety without sacrificing electrochemical performance.

[0036] In this step, the temperature for initiating monomer polymerization is preferably set to 60-90° C. and the time is 2-48 h.

[0037] The preferred applicable battery models are one or both of CR2032 button batteries and CR2025 button batteries.

[0038] The technical solutions claimed in the present invention are further illustrated below by means of some examples. However, the examples and comparative examples are intended to illustrate embodiments of the present invention and do not exceed the scope of the subject matter of the present invention. The scope of protection of the present invention is not limited by the examples. Unless otherwise specified, the materials and reagents used in the present invention can be obtained from commercial products in the art. Example 1

[0039] Lithium difluorooxalatoborate was dissolved in 2,2,2-trifluoroethyl methyl carbonate solvent at a molar ratio of 1:10 and magnetically stirred at 60°C for 12 h to prepare a stable homogeneous solution.

[0040] Hexafluorobutyl methacrylate and isopentaerythrityl tetraacrylate in a molar ratio of 4:1 were added to the above homogeneous solution, and then azobisisoheptanenitrile (the concentration in the precursor solution was 1 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0041] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0042] The monomer polymerization was initiated at 75 °C for 4 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface. Example 2

[0043] Lithium bis(trifluoromethanesulfonyl)imide was dissolved in 4-(perfluorobutyl)ethylene carbonate solvent at a molar ratio of 1:5 and magnetically stirred at 50°C for 48 h to form a stable homogeneous solution.

[0044] Butyl hexafluoroacrylate and ethoxylated trimethylolpropane triacrylate in a molar ratio of 1:1 were added to the above homogeneous solution, and then azobisisobutyronitrile (the concentration in the precursor solution was 0.5 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0045] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0046] The monomer polymerization was initiated at 60 °C for 48 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface. Example 3

[0047] Lithium perchlorate was dissolved in 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether solvent at a molar ratio of 1:50 and magnetically stirred at 70°C for 5 h to prepare a stable homogeneous solution.

[0048] Tetrafluoroethylene and di(trimethylolpropane)tetraacrylate in a molar ratio of 10:1 were added to the above homogeneous solution, and then azobisisobutylcyanamide (the concentration in the precursor solution was 1 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0049] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0050] The monomer polymerization was initiated at 90 °C for 2 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface. Example 4

[0051] Lithium dioxalatoborate was dissolved in fluoroethylene carbonate solvent at a molar ratio of 1:20 and magnetically stirred at 55 °C for 36 h to form a stable homogeneous solution.

[0052] Hexafluoropropylene and pentaerythritol tetraacrylate in a molar ratio of 3:1 were added to the above homogeneous solution, and then dibenzoyl peroxide (concentration in the precursor solution was 1 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0053] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0054] The monomer polymerization was initiated at 70 °C for 12 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface. Example 5

[0055] Lithium bis(fluorosulfonyl)imide was dissolved in fluoropropylene carbonate solvent at a molar ratio of 1:30 and magnetically stirred at 65 °C for 10 h to form a stable homogeneous solution.

[0056] Heptafluorobutyl methacrylate and polyethylene glycol diacrylate in a molar ratio of 6:1 were added to the above homogeneous solution, and then potassium persulfate (concentration in the precursor solution was 0.8 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0057] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0058] The monomer polymerization was initiated at 80 °C for 3 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface. Example 6

[0059] Lithium hexafluorophosphate was dissolved in 4-(trifluoromethyl)ethylene carbonate solvent at a molar ratio of 1:15 and magnetically stirred at 50 °C for 30 h to form a stable homogeneous solution.

[0060] Perfluorooctyl methacrylate and diethylene glycol diacrylate in a molar ratio of 8:1 were added to the above homogeneous solution, and then potassium persulfate (concentration in the precursor solution was 0.6 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0061] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0062] The monomer polymerization was initiated at 70 °C for 6 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface. Example 7

[0063] Lithium tetrafluoroborate was dissolved in 4-(trifluoromethyl)ethylene carbonate solvent at a molar ratio of 1:25 and magnetically stirred at 50 °C for 30 h to form a stable homogeneous solution.

[0064] Perfluoro-n-decyl methacrylate and ethylene glycol diacrylate in a molar ratio of 2:1 were added to the above homogeneous solution, and then benzophenone (the concentration in the precursor solution was 0.9 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0065] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0066] The monomer polymerization was initiated at 60 °C for 26 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface.

[0067] Comparative Example 1 Lithium hexafluorophosphate was dissolved in ethylene carbonate solvent at a molar ratio of 1:10 and magnetically stirred at 50 °C for 20 h to form a stable homogeneous solution.

[0068] Ethylene carbonate and ethoxylated trimethylolpropane triacrylate in a molar ratio of 4:1 were added to the above homogeneous solution, and then azobisisoheptanenitrile (the concentration in the precursor solution was 1 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0069] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0070] The monomer polymerization was initiated at 70 °C for 12 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface.

[0071] Comparative Example 2 Lithium difluorooxalatoborate was dissolved in dimethyl carbonate solvent at a molar ratio of 1:20 and magnetically stirred at 60°C for 10 h to prepare a stable homogeneous solution.

[0072] 1,3-Dioxolane and ethylene glycol diacrylate in a molar ratio of 4:1 were added to the above homogeneous solution, and then azobisisobutyronitrile (the concentration in the precursor solution was 0.8 wt.%) was added, and magnetic stirring was performed at room temperature for 2 h to prepare a GPE precursor solution.

[0073] Assemble the CR2032 button battery in the order of positive electrode shell, positive electrode sheet, GPE precursor solution, cellulose membrane, precursor solution, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) material is used to make electrode sheets according to the mass ratio of NCM811:Super P:PVDF=8:1:1.

[0074] The monomer polymerization was initiated at 60 °C for 24 h, and a gel polymer electrolyte with a cross-linked structure was formed in situ on the electrode surface.

[0075] Compared to the examples, the comparative examples, which replaced the fluorinated monomers with fluorine-free carbonate monomers, produced a fluorine-free gel polymer electrolyte prepared by in-situ polymerization. This electrolyte was easily ignited and continued to burn, exhibited lower ionic conductivity, and exhibited poorer cycling stability. The examples of the present invention exhibited significant improvements in both flame retardancy and electrochemical performance.

[0076] The scope of protection claimed by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention may have various variations and modifications. Any modifications, improvements and equivalent substitutions made within the concept and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a fluorine-rich flame-retardant gel polymer electrolyte, characterized in that: The following steps are involved: Step 1, dissolving a lithium salt in a fluorocarbonate solvent to form a homogeneous solution; Step 2: adding an unsaturated fluorine-based polymer monomer, a crosslinking agent, and a thermal initiator to the uniform solution obtained in step 1, and stirring to obtain a uniform precursor solution; Step three: dripping the precursor solution onto the electrode surface and assembling a complete battery, initiating monomer polymerization by heating, and forming a gel polymer electrolyte with a cross-linked structure in situ on the electrode surface.

2. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, wherein: In step 1, the lithium salt is selected from one or a combination of lithium perchlorate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium hexafluorophosphate and lithium tetrafluoroborate.

3. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, wherein: In step 1, the fluorocarbonate solvent is selected from one or a combination of 2,2,2-trifluoroethyl methyl carbonate, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 4-(perfluorobutyl)ethylene carbonate, 4-(trifluoromethyl)ethylene carbonate, 4-(perfluorohexyl)ethylene carbonate, 4-(perfluorooctyl)ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate, perfluoropolyether carbonate and methyl fluorocarbonate.

4. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, wherein: In step 1, the molar ratio of the lithium salt to the fluorocarbonate solvent is 1:(5-50).

5. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, wherein: In step 2, the unsaturated fluorine-based polymer monomer is selected from one or a combination of tetrafluoroethylene, hexafluoropropylene, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, heptafluorobutyl methacrylate, perfluorooctyl methacrylate and perfluoro-n-decyl methacrylate.

6. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, wherein: In step 2, the crosslinking agent is selected from one or a combination of ethoxylated trimethylolpropane triacrylate, isopentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol tetraacrylate, polyethylene glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate and pentaerythritol triacrylate.

7. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, characterized in that: In step 2, the thermal initiator is selected from one or a combination of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisobutylcyanamide, dibenzoyl peroxide, diethylhexyl peroxydicarbonate, potassium persulfate, lauroyl peroxide and benzophenone.

8. The method for preparing a fluorine-rich flame-retardant gel polymer electrolyte according to claim 1, wherein: In step 2, the molar ratio of the unsaturated fluorine-based polymer monomer to the cross-linking agent is (1-10):

1.

9. The fluorine-rich flame-retardant gel polymer electrolyte obtained by the method according to any one of claims 1 to 8.

10. Use of the fluorine-rich flame-retardant gel polymer electrolyte according to claim 9 in the preparation of lithium-ion batteries.

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