Flame-retardant gel polymer electrolyte and preparation method thereof, and supercapacitor using flame-retardant gel polymer electrolyte

Abstract

The invention discloses a flame-retardant gel polymer electrolyte, a preparation method of the flame-retardant gel polymer electrolyte and a supercapacitor using the flame-retardant gel polymer electrolyte, and belongs to the technical field of supercapacitors. The flame-retardant gel polymer electrolyte comprises a lithium salt, a carbonate solvent, a flame retardant and a cross-linked structure formed by polymerization of a cross-linking agent, wherein the flame retardant is hexa (1H, 1H, 2H-perfluoroethoxy) o-azene and hexa (p-cyanophenoxy)-cyclotriphosphazene. The preparation method comprises the following steps: dissolving a lithium salt in a carbonic ester solvent to form a uniform solution; adding a flame retardant, a cross-linking agent and a thermal initiator into the uniform solution, and stirring to obtain a uniform precursor solution; and dropwise adding the precursor solution on the surface of an electrode to assemble a supercapacitor, initiating polymerization through a heating method, and forming the flame-retardant gel polymer electrolyte with a cross-linked structure on the surface of the electrode in situ. By introducing the two flame retardants and utilizing the synergistic effect of the two flame retardants, the safety and the electrochemical performance are both improved.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, specifically relating to a flame-retardant gel polymer electrolyte, its preparation method, and its application in supercapacitors. Background Technology

[0002] Supercapacitors are increasingly used in electric vehicles, new energy storage systems, and portable electronic devices such as mobile phones and laptops. These fields not only have requirements for energy storage capacity and lifespan, but also place safety and reliability at the core. Among the core components of supercapacitors, the electrolyte plays a crucial role in ion transfer, directly affecting the overall performance of the device. Currently, the types of electrolytes most commonly researched and used in the industry include organic liquid electrolytes, solid electrolytes, and gel polymer electrolytes (GPE). Among them, gel polymer electrolytes have become one of the key research directions in recent years because they attempt to combine the ion conduction efficiency of liquid electrolytes with the structural stability of solid electrolytes.

[0003] Currently, most commercially available supercapacitors use traditional organic liquid electrolytes, which mostly employ carbonate compounds or acetonitrile as solvents. These solvents have two significant drawbacks: they are flammable and volatile. When supercapacitors encounter abnormal conditions during use, such as thermal abuse (e.g., excessively high ambient temperature or uncontrolled internal heating), overcharging (charging voltage exceeding the rated value), or short circuits in the internal electrodes, these flammable solvents can easily ignite, potentially causing explosions. This not only damages the equipment but also threatens personnel safety. This safety hazard has become a major obstacle limiting the adoption of supercapacitors in scenarios with higher safety requirements (such as energy storage modules for electric vehicles).

[0004] To address the safety issues of traditional organic liquid electrolytes, the industry has explored two main improvement paths: one is to develop solid-state electrolytes, which contain no liquid solvents, reducing flammable substances at the source and theoretically significantly improving the safety of supercapacitors; the other is to optimize GPE. Conventional GPEs are generally based on polyethylene oxide (PEO) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), which absorb an appropriate amount of liquid electrolyte to form a gel state. The aim is to ensure a certain ionic conductivity while possessing good flexibility, facilitating subsequent device assembly.

[0005] However, both of these improvement methods still have significant shortcomings: although solid electrolytes improve safety, they have low ionic conductivity and high interfacial impedance with electrode materials, which severely reduces the power characteristics of supercapacitors and cannot meet the equipment's requirements for rapid charging and discharging; the problem with conventional GPE is that its matrix materials (such as PEO and PVDF-HFP) are inherently flammable. Even if they absorb liquid electrolyte and form a gel, there is still a risk of electrolyte leakage and combustion, which fails to fundamentally solve the safety problem. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems and provide a flame-retardant gel polymer electrolyte, its preparation method and application in a supercapacitor. This supercapacitor can maintain high ionic conductivity and good interfacial contact while possessing self-extinguishing characteristics upon removal from the flame, thus resolving the contradiction between high energy density and high safety and meeting the extreme requirements for the reliability of energy storage devices under harsh operating conditions.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a flame-retardant gel polymer electrolyte comprising a lithium salt, a carbonate solvent, a flame retardant, and a cross-linked structure formed by polymerization of a cross-linking agent; The lithium salt is any one or two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, and lithium difluorosulfonylimide. The carbonate solvent includes cyclic carbonates and chain carbonates, the cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, and the chain carbonates include at least one of diethyl carbonate and methyl ethyl carbonate. The flame retardants are hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene and hexa(p-cyanophenoxy)-cyclotriphosphazene; The crosslinking agent is any one of isoprene tetraacrylate, pentaerythritol tetraacrylate, polyethylene glycol diacrylate, and pentaerythritol triacrylate.

[0008] A further improvement of the present invention is that the lithium salt accounts for 12%-14% of the total mass of the electrolyte.

[0009] A further improvement of the present invention is that, based on the total volume of the carbonate solvent as 100%, the total volume of the cyclic carbonate accounts for 20% to 25%, the volume of the diethyl carbonate accounts for 10% to 20%, and the volume of the methyl ethyl carbonate accounts for 55% to 65%.

[0010] A further improvement of the present invention is that, based on the total mass of the electrolyte, the amount of hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene added is 0.5%-2%, and the amount of hexa(p-cyanophenoxy)-cyclotriphosphazene added is 1%-3%.

[0011] A further improvement of the present invention is that, based on the total mass of the electrolyte, the amount of crosslinking agent added is 2%-5%.

[0012] A further improvement of the present invention is that it also includes a thermal initiator, wherein the thermal initiator is any one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and potassium persulfate; and the amount of the thermal initiator added is 0.3%-1% based on the total mass of the electrolyte.

[0013] Secondly, the present invention also provides a method for preparing a flame-retardant gel polymer electrolyte, comprising the following steps: S1, dissolve the lithium salt in a carbonate solvent to form a homogeneous solution; S2, add flame retardant, crosslinking agent and thermal initiator to the homogeneous solution, and stir to obtain a homogeneous precursor solution; S3, the precursor solution is dropped onto the electrode surface and assembled into a supercapacitor. Polymerization is initiated by heating to form a flame-retardant gel polymer electrolyte with a cross-linked structure in situ on the electrode surface.

[0014] A further improvement of the present invention is that, in step S3, the initiation temperature is 60-80°C.

[0015] A further improvement of the present invention is that, in S3, the supercapacitor is a CR2032 coin cell.

[0016] Thirdly, the present invention also provides a supercapacitor comprising the flame-retardant gel polymer electrolyte described above.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a flame-retardant gel polymer electrolyte that achieves dual improvements in safety and electrochemical performance by introducing two flame retardants and utilizing their synergistic effect. Its flame-retardant mechanism is mainly manifested in a gas-phase synergistic flame-retardant mechanism: Hexa(p-cyanophenoxy)-cyclotriphosphazene, upon thermal decomposition, releases phosphorus-containing free radicals (such as PO·) and nitrogen-containing gases (such as N2, NH3). The phosphorus-containing free radicals can efficiently capture hydrogen free radicals (H·) and hydroxyl free radicals (OH·) in the combustion chain reaction, thereby interrupting the free radical reaction; the nitrogen-containing gases can dilute the concentration of oxygen and combustible gases, inhibiting flame propagation. On the other hand, hexa(1H,1H,2H-perfluoroethoxy)o-azene decomposes at high temperatures, releasing perfluoroalkyl fragments (such as -C2F5, -CF3) and hydrogen fluoride (HF). These fluorinated components can further capture highly reactive free radicals in the gas phase, while non-flammable gases such as HF can effectively reduce the concentration of combustibles, enhancing the gas-phase flame-retardant effect. The phosphorus-nitrogen system and fluorine-based flame retardants work synergistically in the gas phase, forming a ternary synergistic effect of "phosphorus-nitrogen-fluorine," significantly improving free radical quenching efficiency and suffocation effect, thereby achieving highly efficient gas-phase flame suppression. In terms of electrochemical performance, the cyano group (-C≡N) exhibits high electrochemical stability, helping to broaden the electrochemical window of the electrolyte; simultaneously, the introduction of the phosphazene structure and perfluorinated components also helps to inhibit the oxidative decomposition of the electrolyte under high voltage. Both additives achieve effective flame retardancy without significantly sacrificing the ionic conductivity of the gel electrolyte, and may even reduce the ion migration barrier through interfacial modification, further optimizing the overall electrochemical performance.

[0018] This invention also provides a supercapacitor that effectively enhances its safety through a ternary synergistic flame-retardant mechanism of phosphorus-nitrogen-fluorine. Simultaneously, based on the inherent flexibility of the gel electrolyte and its good interfacial compatibility with the electrodes, the supercapacitor maintains stable electrochemical performance even under mechanical deformations such as bending and stretching, achieving a balance between high safety and good mechanical adaptability. Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] This invention provides a flame-retardant gel polymer electrolyte comprising a lithium salt, a carbonate solvent, a flame retardant, and a cross-linked structure formed by polymerization of a cross-linking agent; The lithium salt is any one or two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, and lithium difluorosulfonylimide. The carbonate solvent includes cyclic carbonates and chain carbonates, the cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, and the chain carbonates include at least one of diethyl carbonate and methyl ethyl carbonate. The flame retardants are hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene and hexa(p-cyanophenoxy)-cyclotriphosphazene; The crosslinking agent is any one of isoprene tetraacrylate, pentaerythritol tetraacrylate, polyethylene glycol diacrylate, and pentaerythritol triacrylate.

[0025] In some embodiments, the lithium salt accounts for 12%-14% of the total mass of the electrolyte.

[0026] In some embodiments, based on the total volume of the carbonate solvent being 100%, the total volume of the cyclic carbonate is 20% to 25%, the volume of the diethyl carbonate is 10% to 20%, and the volume of the methyl ethyl carbonate is 55% to 65%.

[0027] In some embodiments, based on the total mass of the electrolyte, the amount of hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene added is 0.5%-2%, and the amount of hexa(p-cyanophenoxy)-cyclotriphosphazene added is 1%-3%.

[0028] In some embodiments, the amount of crosslinking agent added is 2%-5% based on the total mass of the electrolyte.

[0029] In some embodiments, a thermal initiator is further included, which is any one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and potassium persulfate; the amount of thermal initiator added is 0.3%-1% based on the total mass of the electrolyte.

[0030] This invention also provides a method for preparing a flame-retardant gel polymer electrolyte, comprising the following steps: S1, dissolve the lithium salt in a carbonate solvent to form a homogeneous solution; S2, add flame retardant, crosslinking agent and thermal initiator to the homogeneous solution, and stir to obtain a homogeneous precursor solution; S3, the precursor solution is dropped onto the electrode surface and assembled into a CR2032 coin cell. Polymerization is initiated at 60-80°C by heating, and a flame-retardant gel polymer electrolyte with a cross-linked structure is formed in situ on the electrode surface.

[0031] The present invention also provides a supercapacitor comprising the flame-retardant gel polymer electrolyte described above.

[0032] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0033] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0034] This embodiment provides a method for preparing a flame-retardant gel polymer electrolyte, including the following steps: Step 1: Dissolve 14% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on a total volume of 100%, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0035] Step 2: Add 0.5% of hexa(1H,1H,2H-perfluoroethoxy)o-azine, 1% of hexa(p-cyanophenoxy)-cyclotriphosphazene, 2% of tetraacrylate crosslinking agent and 0.3% of azobisisoheptanenitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0036] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0037] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0038] The performance of the flame-retardant gel polymer electrolyte sample prepared in this embodiment was tested, and the test results are shown in Table 1.

[0039] Example 2 This embodiment provides a method for preparing a flame-retardant gel polymer electrolyte, including the following steps: Step 1: Dissolve 14% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on a total volume of 100%, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0040] Step 2: Add 2% hexa(1H,1H,2H-perfluoroethoxy)o-azine, 1% hexa(p-cyanophenoxy)-cyclotriphosphazene, 2% isoprene tetraacrylate crosslinking agent and 0.3% azobisisoheptanenitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0041] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0042] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0043] The performance of the flame-retardant gel polymer electrolyte sample prepared in this embodiment was tested, and the test results are shown in Table 1.

[0044] Example 3 This embodiment provides a method for preparing a flame-retardant gel polymer electrolyte, including the following steps: Step 1: Dissolve 14% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on a total volume of 100%, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0045] Step 2: Add 0.5% of hexa(1H,1H,2H-perfluoroethoxy)o-azine, 2% of hexa(p-cyanophenoxy)-cyclotriphosphazene, 2% of isoprene tetraacrylate crosslinking agent and 0.3% azobisisoheptanenitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0046] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0047] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0048] The performance of the flame-retardant gel polymer electrolyte sample prepared in this embodiment was tested, and the test results are shown in Table 1.

[0049] Example 4 This embodiment provides a method for preparing a flame-retardant gel polymer electrolyte, including the following steps: Step 1: Dissolve 14% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on a total volume of 100%, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0050] Step 2: Add 0.5% of hexa(1H,1H,2H-perfluoroethoxy)o-azine, 3% of hexa(p-cyanophenoxy)-cyclotriphosphazene, 2% of isoprene tetraacrylate crosslinking agent and 0.3% azobisisoheptanenitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0051] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0052] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0053] The performance of the flame-retardant gel polymer electrolyte sample prepared in this embodiment was tested, and the test results are shown in Table 1.

[0054] Example 5 This embodiment provides a method for preparing a flame-retardant gel polymer electrolyte, including the following steps: Step 1: Dissolve 12% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on 100% of the total volume, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0055] Step 2: Add 0.5% of hexa(1H,1H,2H-perfluoroethoxy)o-azine, 1% of hexa(p-cyanophenoxy)-cyclotriphosphazene, 2% of tetraacrylate crosslinking agent and 0.3% of azobisisoheptanenitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0056] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0057] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0058] The performance of the flame-retardant gel polymer electrolyte sample prepared in this embodiment was tested, and the test results are shown in Table 1.

[0059] Comparative Example 1 This comparative example provides a method for preparing a flame-retardant gel polymer electrolyte, comprising the following steps: Step 1: Dissolve 14% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on a total volume of 100%, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0060] Step 2: Add 2% isoprene tetraacrylate crosslinking agent and 0.3% azobisisobutyronitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0061] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0062] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0063] The performance of the gel polymer electrolyte sample prepared in this comparative example was tested, and the test results are shown in Table 1.

[0064] Comparative Example 2 This comparative example provides a method for preparing a flame-retardant gel polymer electrolyte, comprising the following steps: Step 1: Dissolve 14% lithium hexafluorophosphate in fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and methyl ethyl carbonate solvents to form a homogeneous solution. The solvents are calculated based on a total volume of 100%, with fluoroethylene carbonate accounting for 10%, ethylene carbonate accounting for 10%, diethyl carbonate accounting for 25% and methyl ethyl carbonate accounting for 55%.

[0065] Step 2: Add 0.5% of hexa(1H,1H,2H-perfluoroethoxy)o-azine, 2% of isoprene tetraacrylate crosslinking agent, and 0.3% azobisisoheptanenitrile to the homogeneous solution obtained in Step 1, and stir at room temperature for 2 hours to obtain the precursor solution.

[0066] Step 3: Assemble the CR2032 coin cell supercapacitor in the glove box in the following order: positive electrode shell, positive electrode plate (NCM811), separator, precursor solution, negative electrode plate (artificial graphite material), graphite sheet, stainless steel sheet, spring sheet, and negative electrode shell. During this process, the precursor solution must fully wet the positive and negative electrode plates and the separator.

[0067] Step 4: Place the assembled supercapacitor in a constant temperature environment of 70°C for 3 hours. Under this condition, the thermal initiator decomposes to generate free radicals, which trigger the polymerization reaction of the crosslinking agent monomers, and finally form a flame-retardant gel polymer electrolyte with a crosslinked structure in situ on the surface and inside of the electrode and separator.

[0068] The performance of the gel polymer electrolyte sample prepared in this comparative example was tested, and the test results are shown in Table 1.

[0069] Table 1 Performance test parameters of the gel polymer electrolytes prepared in the embodiments and comparative examples of the present invention.

[0070] As can be seen from the data in Table 1, compared with Comparative Example 1, the addition of hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene in Comparative Example 2 improved the electrolyte combustion time and electrochemical window. Compared with Comparative Example 2, the addition of hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene and hexa(p-cyanophenoxy)-cyclotriphosphazene in Examples 1-5 significantly improved the flame retardant performance and electrochemical window. This is mainly due to the synergistic effect of these two additives, which improves the safety and electrochemical performance of the supercapacitor.

[0071] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A flame-retardant gel polymer electrolyte, characterized in that, It contains lithium salts, carbonate solvents, flame retardants, and cross-linked structures formed by polymerization of cross-linking agents; The lithium salt is any one or two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, and lithium difluorosulfonylimide. The carbonate solvent includes cyclic carbonates and chain carbonates, the cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, and the chain carbonates include at least one of diethyl carbonate and methyl ethyl carbonate. The flame retardants are hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene and hexa(p-cyanophenoxy)-cyclotriphosphazene; The crosslinking agent is any one of isoprene tetraacrylate, pentaerythritol tetraacrylate, polyethylene glycol diacrylate, and pentaerythritol triacrylate.

2. The flame-retardant gel polymer electrolyte according to claim 1, characterized in that, The lithium salt accounts for 12%-14% of the total mass of the electrolyte.

3. The flame-retardant gel polymer electrolyte according to claim 1, characterized in that, Based on the total volume of the carbonate solvent being 100%, the total volume of the cyclic carbonate is 20% to 25%, the volume of the diethyl carbonate is 10% to 20%, and the volume of the methyl ethyl carbonate is 55% to 65%.

4. The flame-retardant gel polymer electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the amount of hexa(1H,1H,2H-perfluoroethoxy)o-nitrogenene added is 0.5%-2%, and the amount of hexa(p-cyanophenoxy)-cyclotriphosphazene added is 1%-3%.

5. The flame-retardant gel polymer electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the amount of crosslinking agent added is 2%-5%.

6. The flame-retardant gel polymer electrolyte according to claim 1, characterized in that, It also includes a thermal initiator, which is any one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and potassium persulfate; the amount of thermal initiator added is 0.3%-1% based on the total mass of the electrolyte.

7. A method for preparing a flame-retardant gel polymer electrolyte according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1, dissolve the lithium salt in a carbonate solvent to form a homogeneous solution; S2, add flame retardant, crosslinking agent and thermal initiator to the homogeneous solution, and stir to obtain a homogeneous precursor solution; S3, the precursor solution is dropped onto the electrode surface and assembled into a supercapacitor. Polymerization is initiated by heating to form a flame-retardant gel polymer electrolyte with a cross-linked structure in situ on the electrode surface.

8. The method for preparing a flame-retardant gel polymer electrolyte according to claim 7, characterized in that, In step S3, the initiation temperature is 60-80℃.

9. The method for preparing a flame-retardant gel polymer electrolyte according to claim 7, characterized in that, In S3, the supercapacitor is a CR2032 coin cell.

10. A supercapacitor, characterized in that, The flame-retardant gel polymer electrolyte includes any one of claims 1 to 6.

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