In-situ polymerized flame-retardant perfluorogel electrolyte, lithium metal battery and preparation method

Abstract

The invention relates to an in-situ polymerized flame-retardant perfluorogel electrolyte, a lithium metal battery and a preparation method, the in-situ polymerized flame-retardant perfluorogel electrolyte is prepared from a fluorinated organic solvent, a lithium salt, a fluorine-containing polymer precursor and a thermal initiator, and the fluorine-containing polymer precursor further comprises a fluorine-containing polymer and a cross-linking agent. Compared with the prior art, the composite material has a high electrochemical window and excellent flame retardant property, and can realize matching with a high-voltage high-nickel positive electrode at room temperature and stable circulation of a high-voltage lithium metal battery; the preparation method is simple, the interface performance is optimized, and large-scale preparation is easy to realize.

Description

Technical Field

[0001] The invention relates to the technical field of gel polymer electrolytes, and in particular to an in-situ polymerized flame-retardant perfluoro gel electrolyte, a lithium metal battery and a preparation method thereof. Background Art

[0002] Liquid electrolytes commonly used in commercial lithium batteries have safety hazards such as flammability and leakage, and the development of highly safe solid electrolytes is urgent. Inorganic solid electrolytes have high safety because they do not add any liquid components, but their large interfacial impedance and complex preparation process limit their large-scale production and application. All-solid polymer electrolytes can greatly improve the interface contact between electrodes and electrolytes while ensuring safety, but their low room temperature ionic conductivity cannot meet the needs of practical applications. Gel polymer electrolytes can effectively avoid leakage of electrolytes, and have high room temperature ionic conductivity and low interfacial impedance. They are considered to be one of the most likely electrolyte systems to be used in practical applications.

[0003] At present, there are two main routes for the preparation of gel polymer electrolytes: non-in-situ and in-situ. The non-in-situ route requires first preparing a polymer skeleton that can absorb electrolyte, and then adding electrolyte to achieve gelation. The electrolyte obtained by this route is generally thicker (50-200μm), which is not conducive to improving the volume energy density of the battery. The in-situ preparation route that achieves gelation through in-situ polymerization after injection can not only obtain ultra-thin electrolytes (20-30μm), but also further reduce the interfacial impedance. More importantly, this route is compatible with the current industrial injection and formation processes, so it can be quickly put into large-scale production.

[0004] However, most gel electrolytes are not compatible with high-voltage, high-energy-density nickel-rich cathodes (LiNi x Co y Mn z O2,x+y+z=1,x≥0.6), there are still problems such as electrolyte oxidation decomposition, irreversible lattice oxygen release and structural transformation of the positive electrode. The continuous side reaction between the gel electrolyte and the nickel-rich positive electrode will lead to a significant increase in the interface impedance and a rapid decay of the battery capacity, making it impossible to achieve practical application. The uneven deposition / stripping of lithium ions on the lithium metal negative electrode side and the continuous dendrite growth will also lead to serious safety hazards and performance degradation. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the existing gel electrolyte and to provide an in-situ polymerized flame retardant perfluoro gel electrolyte, a lithium metal battery and a preparation method.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide an in-situ polymerized flame retardant perfluorogel electrolyte, which is prepared from a fluorinated organic solvent, a lithium salt, a fluorinated polymer precursor and a thermal initiator, wherein the fluorinated polymer precursor also includes a fluorinated polymer and a crosslinking agent; wherein the fluorinated organic solvent is selected from fluoroethylene carbonate, 2,2,2-trifluoroethyl methyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 3,3,3-trifluoropropionate, ethyl 2-fluoropropionate, difluorocarbon any one or more of vinyl acrylate, bis(2,2,2-trifluoroethyl) carbonate, and ethyl difluoroacetate; the fluorine-containing polymer is selected from any one or more of 2,2,2-trifluoroethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, hexafluorobutyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, hexafluoropolyether triethoxysilane, and hexafluoropolyether trimethoxysilane.

[0008] In some specific embodiments, the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0009] In some specific embodiments, the cross-linking agent is selected from any one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, pentaerythritol tetraacrylate, and tetra(ethylene glycol) diacrylate.

[0010] In some specific embodiments, the thermal initiator is selected from any one or more of azobisisobutyronitrile (AIBN), dimethyl azobisisobutyrate (AIBME), and dibenzoyl peroxide (BPO).

[0011] In some specific embodiments, the mass percentages of the fluorinated organic solvent, lithium salt, fluorinated polymer precursor and thermal initiator in the flame retardant perfluorogel electrolyte are: the fluorinated organic solvent is 20-85wt%, the lithium salt is 5-30wt%, the fluorinated polymer precursor is 5-50wt%, and the thermal initiator is 0.5-2.5wt%.

[0012] In some specific embodiments, the molar ratio of the crosslinking agent in the fluorine-containing polymer precursor is 1-10 mol %.

[0013] The second technical solution of the present invention is to provide a lithium metal battery, comprising a positive electrode, a negative electrode, and an in-situ polymerized flame-retardant perfluorogel electrolyte as described in one of the above technical solutions and arranged between the positive electrode and the negative electrode.

[0014] The third technical solution of the present invention is to provide a method for preparing a lithium metal battery as described in the second technical solution above, comprising the following steps:

[0015] S1. In a protective gas atmosphere, a thermal initiator, a lithium salt, and a fluorinated organic solvent are stirred evenly, and then a fluorinated polymer precursor is added, and the mixture is stirred and mixed to obtain a precursor solution;

[0016] S2. In a protective gas atmosphere, the precursor solution obtained in step S2 is injected into the separator between the negative electrode and the positive electrode of the lithium metal battery, and allowed to stand to allow the precursor solution to fully penetrate into the lithium metal battery. Finally, the lithium metal battery is heated to initiate polymerization to form an in-situ polymerized flame retardant perfluorogel electrolyte, thereby preparing an in-situ polymerized flame retardant perfluorogel electrolyte battery.

[0017] In some specific embodiments, in step S1 and step S2, the protective gas atmosphere is argon gas with oxygen and water contents both less than 1 ppm.

[0018] In some specific embodiments, in step S1, the stirring and mixing temperature is room temperature, and the stirring and mixing time is 5-12 hours.

[0019] In some specific embodiments, in step S2, the positive electrode material of the lithium metal battery is selected from LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622) and LiNi 0.83 Co 0.12 Mn 0.05 Any one of O2(NCM83).

[0020] In some specific embodiments, in step S2, the separator is selected from any one of polyethylene (PE), polypropylene (PP), and cellulose.

[0021] In some specific embodiments, in step S2, the standing temperature is room temperature, and the standing time is 0.5-2 h; the heating temperature is 60-80° C., and the heating time is 4-10 h.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention provides an in-situ polymerized flame-retardant perfluorinated gel electrolyte, in which all fluorinated components are used, so that it has good oxidation stability and a high electrochemical window (over 4.5V), which can match with a high-voltage high-nickel positive electrode at room temperature. In addition, a large amount of fluorinated components in the electrolyte promotes the formation of a high-fluorine interface layer, effectively alleviating the continuous side reactions between the electrolyte and the highly active nickel-rich positive electrode and the lithium metal negative electrode, such as effectively inhibiting the oxidation of the electrolyte on the positive electrode side and the dissolution of transition metal ions and the uncontrollable lithium dendrite growth on the negative electrode side, and realizing the stable cycle of a high-voltage lithium metal battery at room temperature.

[0024] (2) The preparation process of the flame-retardant perfluorogel electrolyte prepared by in-situ polymerization provided by the present invention is simple and suitable for mass production. The cross-linked network obtained by in-situ polymerization can effectively prevent leakage of the electrolyte, and the perfluoro component gives the electrolyte excellent flame-retardant properties, which can ensure the high safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a physical picture of the gel electrolyte prepared in Example 1.

[0026] Figure 2 The conductivity diagram of the gel electrolyte prepared in Example 1.

[0027] Figure 3 The electrochemical window test results of Example 1 and commercial electrolytes are shown in FIG.

[0028] Figure 4 Cycling performance of high-voltage lithium metal batteries assembled with Example 1 and commercial electrolytes.

[0029] Figure 5 The combustion test comparison between Example 1 and commercial electrolyte is shown in FIG. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0031] In the following examples and comparative examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0032] 1. The commercial electrolyte is 1M LiPF6 dissolved in an organic solvent of ethylene carbonate / dimethyl carbonate (EC / DMC) with a volume ratio of 3:7.

[0033] 2. Conductivity test: The CHI660E electrochemical workstation of Shanghai Chenhua Instrument Co., Ltd. was used for AC impedance test. The test conditions were as follows: the test voltage was 0V, the test frequency range was 0.1Hz-1 MHz, and the test amplitude was 5mV; the ionic conductivity was calculated according to formula (1-1):

[0034]

[0035] Wherein, δ is the ionic conductivity, L is the electrolyte thickness, R is the resistance obtained by the test, and S is the working electrode area.

[0036] 3. Test of electrochemical window: Linear sweep voltammetry (LSV) test was performed using CHI660E electrochemical workstation of Shanghai Chenhua Instrument Co., Ltd. The test conditions were as follows: voltage range was 0-6V, and scan rate was 0.1mV / s.

[0037] 4. Electrochemical cycle test: The LAND battery test system of Wuhan Landian Electronics Co., Ltd. was used to perform charge and discharge cycles on the tested battery. The test conditions were as follows: the test temperature was 25°C, the charge and discharge voltage range was 3-4.3V, and the cycle was performed at 0.5C.

[0038] 5. All batteries involved are assembled in a glove box filled with argon, where the oxygen and water content are less than 1ppm.

[0039] Embodiment 1:

[0040] (1) Preparation of NCM811 positive electrode sheet:

[0041] Dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone to obtain a PVDF binder solution with a mass fraction of 5wt%; grind NCM811, conductive carbon black and PVDF binder in a mortar at a mass ratio of 8:1:1 to obtain a honey-like positive electrode slurry; evenly coat the positive electrode slurry on aluminum foil with a scraper, place it in a vacuum drying oven at 110°C and dry it for 24 hours, and cut it into discs with a diameter of 12mm after drying to obtain NCM811 positive electrode sheets.

[0042] (2) Preparation of precursor solution:

[0043] In a glove box filled with argon (oxygen and water contents are both less than 1 ppm), 0.01 g of thermal initiator (AIBN) and 0.3 g of lithium salt (LiTFSI) were dissolved in 0.783 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate), respectively. After stirring evenly, 0.417 g of fluorinated polymer precursor (a mixture of 2,2,2-trifluoroethyl methacrylate and polyethylene glycol diacrylate, wherein the content of polyethylene glycol diacrylate is 5.8 mol% of the content of the fluorinated polymer precursor) was added, and the mixture was stirred at room temperature for 12 h to obtain a precursor solution.

[0044] (3) Preparation of perfluorogel electrolyte:

[0045] In a glove box filled with argon (oxygen and water content are both less than 1ppm), 200μL of the precursor solution was injected into the positive electrode (NCM811 positive electrode sheet) of the lithium metal battery and the separator (PP separator) between the negative electrode (lithium metal) to assemble into a button battery. After standing at room temperature for 2h, the assembled battery was placed in a constant temperature oven and heated at 70℃ for 8h to obtain a fully cured in-situ polymerized flame-retardant perfluorogel electrolyte and an in-situ polymerized flame-retardant perfluorogel electrolyte battery.

[0046] The flame retardant perfluorogel electrolyte prepared in Example 1 was observed and tested as follows:

[0047] (1) Figure 1 The flame retardant perfluoro gel electrolyte is obtained after the precursor solution in step (2) is solidified. The flame retardant perfluoro gel electrolyte is transparent, and the liquid component is well wrapped in the polymer matrix without obvious fluidity.

[0048] (2) The room temperature ionic conductivity is calculated from the impedance of the flame retardant perfluorogel electrolyte. The room temperature impedance of the flame retardant perfluorogel electrolyte is shown in Figure 2 , it can be seen that the impedance of the flame retardant perfluorogel electrolyte is 9.05Ω. It is known that the thickness of the flame retardant perfluorogel electrolyte is equivalent to the thickness of the PP diaphragm (25μm). According to formula (1-1), the room temperature ionic conductivity of the flame retardant perfluorogel electrolyte is 1.45×10 -4 S cm -1 , more than 10 -4 S cm -1 , indicating that it meets the conditions for circulation at room temperature.

[0049] (3) The electrochemical window test results of the flame retardant perfluorogel electrolyte prepared in Example 1 and the commercial electrolyte are shown in Figure 3 It can be seen that the electrochemical window of the flame-retardant perfluorogel electrolyte reaches 5.21V, which has good antioxidant stability and can match the high-voltage positive electrode, while the commercial electrolyte begins to decompose at 4.49V.

[0050] (4) Battery charge and discharge cycle test of the flame retardant perfluorogel electrolyte prepared in Example 1 and commercial electrolyte Figure 4 The high-voltage lithium metal battery assembled with flame-retardant perfluorinated gel electrolyte has a capacity retention rate of up to 97.7% after 200 cycles at 0.5C, with basically no capacity decay, while the capacity of the battery assembled with commercial electrolyte decays rapidly, with a capacity retention of only 84.5% after 200 cycles.

[0051] (5) The flame retardant performance of the flame retardant perfluorogel electrolyte prepared in Example 1 was verified by using a flame torch ignition test with commercial electrolyte as a control. The test results are shown in Figure 5 The commercial electrolyte was quickly burned out when the spray gun was removed 0.5s after ignition, while the flame-retardant perfluorogel electrolyte quickly self-extinguished after the spray gun was removed 10s after ignition, showing excellent flame retardant properties.

[0052] Embodiment 2:

[0053] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to 0.654 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate); 0.417 g of polymer precursor is changed to 0.546 g.

[0054] Embodiment 3:

[0055] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to 0.712 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate); 0.417 g of polymer precursor is changed to 0.488 g.

[0056] Embodiment 4:

[0057] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to 0.805 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate); 0.417 g of polymer precursor is changed to 0.395 g.

[0058] Embodiment 5:

[0059] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to 0.889 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate); 0.417 g of polymer precursor is changed to 0.311 g.

[0060] Embodiment 6:

[0061] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to 0.923 g of fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate); 0.417 g of polymer precursor is changed to 0.277 g.

[0062] Embodiment 7:

[0063] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of the fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to a mixture of ethyl 3,3,3-trifluoropropionate and fluoroethylene carbonate of the same mass, wherein the content of fluoroethylene carbonate is 5 wt % of the total content of the precursor solution.

[0064] Embodiment 8:

[0065] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of the fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to a mixture of ethyl 3,3,3-trifluoropropionate and fluoroethylene carbonate of the same mass, wherein the content of fluoroethylene carbonate is 10 wt % of the total content of the precursor solution.

[0066] Embodiment 9:

[0067] Compared with Example 1, most of them are the same, except that in step (2), 0.783 g of the fluorinated organic solvent (ethyl 3,3,3-trifluoropropionate) is changed to a mixture of ethyl 3,3,3-trifluoropropionate and fluoroethylene carbonate of the same mass, wherein the content of fluoroethylene carbonate is 20 wt % of the total content of the precursor solution.

[0068] Referring to the test method of Example 1, the in-situ polymerized perfluorogel electrolytes of Examples 1 to 9 were tested respectively, and the test results are shown in Table 1 below:

[0069] Table 1 Performance statistics of flame retardant perfluorinated gel electrolyte

[0070]

[0071] It can be seen from the above table that by adjusting the type and content of the fluorinated organic solvent and the polymer precursor, a gel can be formed after heating at 70°C for 8 hours.

[0072] Comparing Examples 1-6, the results show that with the increase of the content of fluorinated organic solvent 3,3,3-trifluoropropionic acid ethyl ester and the decrease of the content of fluorinated polymer precursor, the room temperature ionic conductivity of the flame retardant perfluorogel polymer electrolyte gradually increases and the electrochemical window gradually decreases.

[0073] Comparing Examples 1, 7-9, the results show that adding fluoroethylene carbonate to the fluorinated organic solvent can significantly improve the room temperature ionic conductivity of the flame retardant perfluorogel electrolyte, but with the continuous increase of the fluoroethylene carbonate content, the electrochemical window decreases slightly.

[0074] The voltage windows of the flame-retardant perfluorogel polymer electrolytes prepared in Examples 1-9 are all higher than those of commercial electrolytes, and they all show good cycle stability when matched with high-nickel ternary positive electrodes. The capacity retention rate of the lithium metal battery assembled with commercial electrolytes is only 84.5% after 200 cycles at 0.5C. This is because EC continues to oxidize and decompose on the surface of the positive electrode, generating a large amount of by-products, resulting in an increase in interfacial impedance, making it difficult to achieve stable cycling. The capacity retention rates of the batteries assembled with flame-retardant perfluorogel electrolytes are all above 96%, which shows that the flame-retardant perfluorogel electrolyte can form a stable interface layer on the surface of the NCM811 positive electrode, preventing continuous side reactions between the electrolyte and the positive electrode.

[0075] The flame-retardant perfluorogel electrolytes prepared in Examples 1-9 all have good flame-retardant effects and can be self-extinguished 10 seconds after being ignited by a spray gun, indicating that the flame-retardant perfluorogel electrolytes have excellent safety.

[0076] Comparative Example 1:

[0077] Compared with Example 1, most of the contents are the same, except that the fluorinated organic solvent is replaced with a conventional organic solvent of the same mass percentage, and the conventional organic solvent is ethyl propionate.

[0078] Comparative Example 2:

[0079] Compared with Example 1, most of them are the same, except that the fluorine-containing polymer precursor is replaced with a conventional polymer precursor with the same mass percentage, and the conventional polymer precursor is ethyl methacrylate.

[0080] Referring to the test method of Example 1, the in-situ polymerized gel electrolytes prepared in Comparative Example 1 and Comparative Example 2 were tested respectively. The test results are shown in Table 2 below:

[0081] Table 2 Performance statistics of gel electrolyte

[0082]

[0083] By comparing Example 1 and Comparative Example 1, it can be seen that whether the organic solvent contains fluorine has little effect on the ionic conductivity. However, after replacing the fluorinated organic solvent with a conventional organic solvent, the electrochemical window of the electrolyte is significantly reduced, and self-extinguishing cannot be achieved 10 seconds after the spray gun is ignited. The capacity decay of the battery is aggravated during the cycle.

[0084] By comparing Example 1 and Comparative Example 2, it can be seen that whether the polymer precursor contains fluorine has little effect on the ionic conductivity. However, after replacing the fluorine-containing polymer precursor with a conventional polymer precursor, the electrochemical window of the electrolyte is significantly reduced, and the capacity decay of the battery is aggravated during the cycle.

[0085] The comparative results show that the introduction of fluorine atoms in the electrolyte system can significantly enhance the electrochemical window. The highest electrochemical window can be obtained when fluorinated organic solvents and fluorinated polymer precursors are used together. Fluorinated organic solvents are the key to determining the flame retardant properties of electrolytes. In addition, both fluorinated organic solvents and fluorinated polymer precursors play an important role in the construction of weakly solvated electrolytes, and weakly solvated structures can dominate the formation of stable interface layers. Fluorine in organic solvents and polymer precursors can also directly participate in the formation of LiF in the interface layer. Therefore, the most stable cycle performance can be obtained when fluorinated organic solvents and fluorinated polymer precursors are used together.

[0086] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. An in-situ polymerized flame retardant perfluorogel electrolyte, characterized in that: The invention is prepared from a fluorinated organic solvent, a lithium salt, a fluorinated polymer precursor and a thermal initiator, wherein the fluorinated polymer precursor also includes a fluorinated polymer and a crosslinking agent; wherein the fluorinated organic solvent is selected from any one or more of fluoroethylene carbonate, 2,2,2-trifluoroethyl methyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 3,3,3-trifluoroethyl propionate, ethyl 2-fluoropropionate, bisfluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and ethyl difluoroacetate; and the fluorinated polymer is selected from any one or more of 2,2,2-trifluoroethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, hexafluorobutyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, hexafluoropolyether triethoxysilane, and hexafluoropolyether trimethoxysilane.

2. The in-situ polymerized flame retardant perfluorogel electrolyte according to claim 1, characterized in that: The lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

3. The in-situ polymerized flame retardant perfluorogel electrolyte according to claim 1, characterized in that: The cross-linking agent is selected from any one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, pentaerythritol tetraacrylate, and tetra(ethylene glycol) diacrylate.

4. The in-situ polymerized flame retardant perfluorogel electrolyte according to claim 1, characterized in that: The thermal initiator is selected from any one or more of azobisisobutyronitrile, dimethyl azobisisobutyrate, and dibenzoyl peroxide.

5. The in-situ polymerized flame retardant perfluorogel electrolyte according to claim 1, characterized in that: The mass percentages of the fluorinated organic solvent, lithium salt, fluorinated polymer precursor and thermal initiator in the flame retardant perfluorogel electrolyte are: 20-85wt% of the fluorinated organic solvent, 5-30wt% of the lithium salt, 5-50wt% of the fluorinated polymer precursor and 0.5-2.5wt% of the thermal initiator.

6. The in-situ polymerized flame retardant perfluorogel electrolyte according to claim 1, characterized in that: The molar ratio of the crosslinking agent in the fluorine-containing polymer precursor is 1-10 mol%.

7. A lithium metal battery, characterized in that: The invention comprises a positive electrode, a negative electrode, and an in-situ polymerized flame-retardant perfluoro gel electrolyte as claimed in any one of claims 1 to 6 arranged between the positive electrode and the negative electrode.

8. A method for preparing a lithium metal battery according to claim 7, characterized in that: The steps include: S1. In a protective gas atmosphere, a thermal initiator, a lithium salt, and a fluorinated organic solvent are stirred evenly, and then a fluorinated polymer precursor is added, and the mixture is stirred and mixed to obtain a precursor solution; S2. In a protective gas atmosphere, the precursor solution obtained in step S2 is injected into the separator between the negative electrode and the positive electrode of the lithium metal battery, and allowed to stand to allow the precursor solution to fully penetrate into the lithium metal battery. Finally, the lithium metal battery is heated to initiate polymerization to form an in-situ polymerized flame retardant perfluorogel electrolyte, thereby preparing an in-situ polymerized flame retardant perfluorogel electrolyte battery.

9. The preparation method according to claim 8, characterized in that: In step S1, the stirring and mixing temperature is room temperature, and the stirring and mixing time is 5-12 hours; In step S2, the standing temperature is room temperature and the standing time is 0.5-2 hours; the heating temperature is 60-80° C. and the heating time is 4-10 hours; In step S1 and step S2, the protective gas atmosphere is argon gas with oxygen and water contents both less than 1 ppm.

10. The preparation method according to claim 8, characterized in that: In step S2, the positive electrode material of the lithium metal battery is selected from LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.83 Co 0.12 Mn 0.05 Any one of O2; the diaphragm is selected from any one of polyethylene, polypropylene, and cellulose.

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