Fluorine-containing chain modified composite electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a fluorine-containing chain modified composite electrolyte as well as a preparation method and application thereof, and relates to the technical field of lithium batteries, the surfaces of inorganic particles are covalently grafted with a C4-C6 short-chain perfluorinated compound through an S-O-M bond, a P-O-M bond or an M-OOC bond, so that the surface free energy is reduced, the inorganic particles can be stably dispersed in a polymer matrix, and the performance of the electrolyte is improved. The ion transmission performance of the composite electrolyte can be effectively improved; according to the fluorine-containing chain modified composite electrolyte prepared by the invention, in the charging and discharging process, fluorine-containing molecular chains on the surfaces of inorganic particles and a fluorine-containing polymer matrix can realize gradual electrochemical reduction, a LiF-rich layer is formed on a lithium negative electrode interface, lithium dendrites are inhibited, and a long-acting stabilizing effect is achieved. According to the invention, after the organic electrolyte is uniformly mixed with the polymer matrix containing the fluorinated acrylate, the electrolyte is cured through the in-situ polymerization reaction, so that the battery interface resistance is low, and the rate capability and the safety of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a fluorine-chain modified composite electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, a secondary power source that emerged in the early 1990s, have a wide range of applications. With the development and advancement of technology, the energy density of lithium-ion batteries has been increasingly demanded. To increase battery energy density, it is crucial to improve the energy density of both the positive and negative electrodes. Commonly used lithium-ion battery anode materials include graphite, lithium titanate, silicon-carbon anodes, and lithium metal. Lithium metal, due to its highest energy density, has attracted considerable attention as the ultimate anode material. However, the lithium metal anode exhibits extreme metallic activity and is prone to side reactions with the electrolyte, forming an unstable solid electrolyte interface (SEI) film. This leads to rapid electrolyte depletion and battery degradation over cycling. Furthermore, during lithium stripping and deposition, interfacial side reactions cause uneven lithium deposition, resulting in the formation of lithium dendrites, which can lead to battery failure and safety incidents. One of the greatest challenges facing lithium metal batteries is interfacial instability of the lithium metal anode.

[0003] A key approach to addressing these issues is the development of novel electrolyte materials. For example, dense ceramic sheets made of inorganic oxide solid electrolytes exhibit excellent chemical and electrochemical stability toward lithium metal, high ionic conductivity, and an elastic modulus significantly higher than that of lithium metal. These advantages have led to promising applications for inorganic oxide solid electrolytes in stabilizing lithium metal anodes (Advanced Energy Materials 2020, 2002689). For example, highly concentrated electrolytes with high lithium salt concentrations can alter the SEI formation mechanism, shifting from a solvent-induced SEI in conventional electrolytes to a salt-induced SEI, thereby forming a LiF-rich SEI on the lithium metal surface and stabilizing the lithium metal (Nature Energy 2019, 4, 269). For example, the addition of fluorinated additives (such as LiDFOB and methyl benzoates) to the electrolyte can form a LiF-rich SEI at the electrode interface (Patent: CN202410242707.7).

[0004] However, the current lithium metal battery electrolyte system has three major technical bottlenecks: (1) Dense ceramic sheets of inorganic oxide solid electrolytes face the intrinsic problems of brittleness, difficult processing, high density, and large thickness, and also face the difficulties of high interface resistance with electrodes and interface bonding breakdown during battery cycling; (2) High-concentration electrolytes with high lithium salt concentrations face the problems of high viscosity, poor wetting of diaphragms / electrodes, poor battery rate performance, and high cost; (3) Traditional fluorinated additives in the electrolyte decompose instantaneously during the first charge and discharge, and cannot form a long-term stable interface. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a fluorine-chain-modified composite electrolyte and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: A method for preparing a fluorine-containing chain-modified composite electrolyte is provided, comprising the following steps: S1: dissolving a perfluorinated compound in ethanol to obtain a perfluorinated compound-ethanol solution, adding a non-garnet fast ion conductor to the perfluorinated compound-ethanol solution, and stirring the reaction at 30-80°C for 0.5-12 hours; S2: mixing a fluorinated acrylate monomer, a crosslinking agent, and an initiator to form a polymer matrix, and mixing the polymer matrix with an organic electrolyte to obtain a precursor solution; S3: Add modified particles grafted with fluorine-containing chains to the precursor solution, and perform polymerization reaction at 50-80°C for 1-12 hours to obtain a fluorine-containing chain-modified composite electrolyte.

[0007] Furthermore, the perfluorinated compound is a liquid short-chain perfluorinated compound containing a sulfonic acid group, a phosphonic acid group or a carboxyl end group, wherein the short chain has 4 to 6 carbon atoms; and includes any one of perfluorobutanesulfonic acid, 1H,1H,2H,2H-perfluorohexylphosphonic acid or perfluoropentanoic acid.

[0008] Furthermore, the non-garnet fast ion conductor is any one of a sodium fast ion conductor and a perovskite electrolyte.

[0009] Furthermore, in step S1, the volume ratio of the perfluorinated compound to ethanol is 1:1-19, that is, the concentration of the perfluorinated compound in ethanol is 5-50 vol.%.

[0010] Furthermore, the mass ratio of the non-garnet fast ion conductor to the perfluorinated compound-ethanol solution is 3:7-97, that is, the concentration of the non-garnet fast ion conductor in the perfluorinated compound-ethanol solution is 3-30 wt.%.

[0011] Furthermore, the fluorine-containing acrylate monomer is 2,2,2-trifluoroethyl acrylate, the crosslinking agent is polyethylene glycol diacrylate, and the initiator is azobisisobutyronitrile; and the molar ratio of 2,2,2-trifluoroethyl acrylate, polyethylene glycol diacrylate and azobisisobutyronitrile is 100:1~2:0.25~1; that is, polyethylene glycol diacrylate is 1~2 mol% of 2,2,2-trifluoroethyl acrylate, and azobisisobutyronitrile is 0.25~1 mol% of 2,2,2-trifluoroethyl acrylate.

[0012] Furthermore, the organic electrolyte is a mixed solution of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 4:6, and the mixed solution also contains 0.4M LiBOB, 0.05M LiPF6 and 0.6M LiTFSI.

[0013] Furthermore, the volume ratio of the polymer matrix to the organic electrolyte is 1:5-10, that is, the volume ratio of the polymer matrix in the precursor solution is 10-20 vol.%.

[0014] The present invention also provides a fluorine-chain-modified composite electrolyte prepared by the above-mentioned preparation method.

[0015] The present invention also provides a use of the above-mentioned fluorine-containing chain-modified composite electrolyte in the preparation of a solid-state lithium metal battery, wherein the fluorine-containing chain-modified composite electrolyte is used as the electrolyte layer of the solid-state lithium metal battery, and the polymerization of the fluorine-containing chain-modified composite electrolyte is carried out after the battery is packaged; The specific preparation steps of the solid-state lithium metal battery are as follows: adding modified particles grafted with fluorine chains to the precursor solution, mixing them evenly as a precursor, dripping the precursor on both sides of the battery separator, and then encapsulating the positive electrode sheet and the metal lithium negative electrode on both sides of the separator. The encapsulated semi-finished battery is reacted at 50-80°C for 1-12 hours to complete the preparation of the solid-state lithium metal battery. The positive electrode is one of nickel-cobalt-manganese ternary materials, lithium iron phosphate and lithium cobalt oxide.

[0016] The beneficial effects of the present invention are: The present invention covalently grafts C4-C6 short-chain perfluorinated compounds on the surface of inorganic particles through SOM bonds, POM bonds or M-OOC bonds, thereby reducing the surface free energy, allowing the inorganic particles to be stably dispersed in the polymer matrix, and effectively improving the ion transport performance of the composite electrolyte; The fluorine-containing chain-modified composite electrolyte prepared by the present invention can achieve gradual electrochemical reduction of the fluorine-containing molecular chains on the surface of the inorganic particles and the fluorine-containing polymer matrix during the charge and discharge process, forming a LiF-rich layer at the lithium negative electrode interface, inhibiting lithium dendrites and playing a long-term stabilizing role.

[0017] This invention uniformly mixes an organic electrolyte with a fluorinated acrylate polymer matrix, then solidifies the electrolyte through an in-situ polymerization reaction. This reduces the interfacial resistance of the battery, improving its rate performance and safety. Furthermore, the process allows for encapsulation followed by polymerization, making it suitable for existing battery manufacturing processes and conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a high-resolution transmission electron micrograph of LATP and the prepared modified LATP particles in Example 1; Figure 2This is a diagram showing the high-resolution energy spectrum test results of the modified LATP particles prepared in Example 1; Figure 3 This is the AC impedance spectrum of the fluorine-containing chain-modified composite electrolyte prepared in Example 1; Figure 4 This is a test graph of the ion migration number of the fluorine-containing chain-modified composite electrolyte prepared in Example 1; Figure 5 This is a high-resolution transmission electron microscopy image of the modified LATP particles prepared in Example 2; Figure 6 The charge and discharge cycle curve of the lithium metal battery prepared in Example 3; Figure 7 This is a scanning electron microscope image of lithium metal in the lithium metal battery prepared in Example 3 after 200 cycles; Figure 8 The charge and discharge cycle curve of the lithium metal battery prepared in Comparative Example 1; Figure 9 This is a scanning electron microscope image of lithium metal in the lithium metal battery prepared in Comparative Example 1 after 120 cycles; Figure 10 High-resolution X-ray photoelectron spectroscopy of F1s of lithium metal in the lithium metal batteries prepared in Example 3 and Comparative Example 1 after 20 cycles; Figure 11 The charge and discharge cycle curve of the lithium metal battery prepared in Comparative Example 2; Figure 12 This is a scanning electron microscope image of lithium metal in the lithium metal battery prepared in Comparative Example 2 after 150 cycles. DETAILED DESCRIPTION

[0019] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0020] The raw material sources used in the embodiments of the present invention are shown in Table 1 below. Table 1

[0021] Example 1 The fluorinated chain-modified composite electrolyte was prepared using the following steps: S1: 1 mL of perfluorobutanesulfonic acid is mixed with 9 mL of anhydrous ethanol, and stirred at room temperature for 0.5 h to obtain a perfluorobutanesulfonic acid-ethanol solution; in a specific implementation, the perfluoro compound may also be 1H, 1H, 2H, 2H-perfluorohexylphosphonic acid or perfluoropentanoic acid; and the volume ratio of the perfluoro compound to ethanol may also be 1:1, 1:5, 1:13, or 1:19; Then, the existing solid phase synthesis method (Chem. Mater. 2002, 14, 3, 1091–1097) was used to synthesize the NASICON type fast ion conductor Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (hereinafter referred to as LATP); Add 1g of LATP to the perfluorobutanesulfonic acid-ethanol solution and stir the reaction at 60℃ for 2h. In this reaction, the sulfonic acid group (-SO3H) of perfluorobutanesulfonic acid forms a sub-SOM covalent bond with the surface of LATP, where M is the metal cation Al of LATP. 3+ or Ti 4+ In specific implementation, the temperature can also be selected from 30°C, 40°C, 50°C, 70°C or 80°C; and the stirring time can also be selected from 0.5h, 4h, 6h, 8h, 10h or 12h; After centrifugal washing, the mixture was dried at 120°C in vacuum to obtain modified LATP particles grafted with fluorine-containing chains.

[0022] The unmodified LATP and modified LATP particles were photographed using a high-resolution transmission electron microscope (Talos F200S) from Thermo Fisher Scientific. Figure 1 As shown, Figure 1 a is the electron microscope image of LATP, Figure 1 b is the electron microscope image of modified LATP; Figure 1 It can be seen that the surface of the original LATP particles is smooth, while the surface of the modified LATP particles has an obvious coating layer (such as Figure 1 The area divided by the red line in b) has a thickness of about 10 nm.

[0023] The modified LATP particles were tested by high-resolution energy spectrum using Thermo Fisher Scientific Talos F200S. Specifically, the high-resolution mode was used, the magnification was magnified to the level of a particle, and characteristic elements F and Ti were selected for scanning. The results are as follows: Figure 2 As shown by Figure 2 It can be seen that in addition to the bulk element Ti of LATP (the purple part in the figure), the surface of the modified LATP particles also has the F element from perfluorobutane sulfonic acid (the green part in the figure), and the F element is evenly distributed, indicating that through this process, a layer of fluorine-containing molecular chains with a thickness of about 10 nanometers is prepared on the surface of the LATP particles.

[0024] S2: 2,2,2-trifluoroethyl acrylate monomer (TFEA), crosslinker polyethylene glycol diacrylate (PEGDA), and initiator azobisisobutyronitrile (AIBN) are uniformly mixed to obtain a polymer matrix, wherein the molar amounts of PEGDA and AIBN are 1 mol% and 0.25 mol% of the molar amount of TFEA, respectively; in specific implementation, the molar amount of PEGDA can also be 1.5 mol% or 2 mol% of the molar amount of TFEA, and the molar amount of AIBN can also be 0.5 mol%, 0.75 mol% or 1 mol% of the molar amount of TFEA.

[0025] The polymer matrix and the organic electrolyte are mixed uniformly in a volume ratio of 1:9 to obtain a precursor solution; In a specific implementation, the volume ratio of the polymer matrix to the organic electrolyte can also be 1:5, 1:6, 1:7, 1:8 or 1:10; The organic electrolyte is prepared by dissolving LiBOB, LiPF6, and LiTFSI in ethylene carbonate and ethyl methyl carbonate, wherein the concentration of LiBOB is 0.4M, the concentration of LiPF6 is 0.05M, the concentration of LiTFSI is 0.6M, and the mass ratio of ethylene carbonate to ethyl methyl carbonate is 4:6. S3: Add the modified LATP particles prepared in S1 to the precursor solution prepared in S2, with the modified LATP particles accounting for 5 wt.% by weight. Stir at room temperature for 5 hours to obtain a precursor. Then, heat the precursor to 60°C and polymerize for 12 hours to obtain a fluorine-chain-modified composite electrolyte. In specific implementations, the modified LATP particles can account for 2 wt.%, 10 wt.%, 15 wt.%, 18 wt.%, 25 wt.%, or 30 wt.%.

[0026] The polymerization temperature can also be 50°C, 70°C or 80°C; the polymerization time can also be 1h, 3h, 5h, 7h, 9h or 11h; The obtained fluorinated chain modified composite electrolyte was tested by AC impedance spectroscopy using Autolab 302N electrochemical workstation. Specifically, two stainless steel sheets were used as blocking electrodes, the test frequency was 1MHz-1Hz, and the applied bias voltage was 10mV. The results are as follows: Figure 3 As shown, the horizontal axis is the real part of impedance, the ordinate is the imaginary part of impedance, the intercept of the curve on the horizontal axis is the resistance R, ionic conductivity = L / (S*R), L is the sample thickness, S is the sample area, and Figure 3 It can be seen that the ionic conductivity of the fluorinated chain modified composite electrolyte at room temperature reaches 6.2×10 -3 S / cm.

[0027] The fluorine chain modified composite electrolyte was also tested for ion mobility using an Autolab 302N electrochemical workstation. Specifically, lithium metal was used as a reversible electrode, a symmetrical cell was assembled, and the polarization voltage was set to 10mV. A DC polarization test was performed, and the impedance was tested before and after polarization. The results are as follows: Figure 4 As shown, Figure 4 a is the current-time curve, Figure 4 b is the impedance spectrum; Figure 4 a to obtain the initial current and steady-state current of DC polarization (I SS ), and by Figure 4 b Obtain the interfacial resistance of the battery before and after polarization and substitute it into the following formula: ; in, t + is the lithium ion migration number, I 0 and I s They represent the initial current and steady-state current of DC polarization, △V is the polarization voltage, R 0 and R s are the interfacial resistances of the symmetric cell before and after polarization, respectively; Calculations show that the lithium-ion transference number of the fluorinated chain-modified composite electrolyte prepared in this example can reach 0.61. Lithium ions carry 61% of the current transported. A higher transference number enhances lithium-ion conductivity, reducing concentration polarization and interfacial side reactions caused by anion migration, which is beneficial to the battery's rate performance, cycle stability, and safety.

[0028] In summary, the ion transport performance of composite electrolytes has significant advantages.

[0029] Example 2 The difference between this embodiment and embodiment 1 is that in step S1, 3 mL of perfluorobutanesulfonic acid and 7 mL of anhydrous ethanol are used to prepare a perfluorobutanesulfonic acid-ethanol solution. Other parameters are the same as those in embodiment 1. The electron microscope image of the modified LATP particles prepared in this embodiment is as follows: Figure 5 As shown by Figure 5 It can be seen that the surface of the modified LATP particles prepared by the method of this embodiment has a uniform coating layer with a thickness of about 15 nanometers.

[0030] Example 3 The fluorine-containing chain-modified composite electrolyte prepared in Example 1 was used to prepare a solid-state lithium metal battery. Specifically: A1: Nickel-cobalt-manganese ternary material NCM811, conductive agent SP, and binder PVDF were mixed into a slurry at a mass ratio of 90:5:5, and then coated onto an aluminum current collector. After drying, a positive electrode sheet was obtained. The positive electrode sheet had a diameter of 10 mm and an active material loading of 18 mg / cm 2 .

[0031] A2: The precursor prepared in step S3 of Example 1 was added dropwise to both sides of the PE diaphragm, with a dosage of 10 μL each.

[0032] A3: Cover with a positive electrode sheet and metal lithium foil, add a steel sheet, and encapsulate the button battery shell. After a static aging process of about 12 hours, initiate a polymerization reaction at 60°C for 12 hours to obtain the lithium metal battery of this embodiment.

[0033] The prepared lithium metal battery was subjected to charge and discharge cycle test using a four-range button cell tester, the Xinwei CT-4000. Specifically, the constant current mode was adopted, with the first cycle charged and discharged at 0.1C, and the second cycle charged and discharged at 1C, where 1C = 200mA / g. The results are shown in Figure 2. Figure 6 As shown by Figure 6 It can be seen that at 0.1C (0.36mA / cm 2 ) rate charge and discharge, the first discharge capacity of the lithium metal battery is 191mAh / g, and the 2 High current density cycling, cycle 200 cycles, the capacity retention rate is 90%. The surface of lithium metal after 200 cycles was scanned by electron microscope, and the results are as follows Figure 7 As shown by Figure 7 It can be seen that the lithium metal negative electrode is still in bulk form with a dense structure and no dendrites and holes appear, indicating that the fluorine-containing chain-modified composite electrolyte has good compatibility with the lithium metal negative electrode.

[0034] Comparative Example 1 The difference between this embodiment and embodiment 3 is that in step A2, the precursor solution prepared in step S2 of embodiment 1 is directly dripped onto both sides of the PE separator without adding modified LATP particles, and the amount used is 10 μL. The prepared lithium metal battery is subjected to charge and discharge cycle test, and the results are as follows: Figure 8 As shown by Figure 8 It can be seen that at 0.1C (0.36mA / cm 2 ) rate charge and discharge, the first discharge capacity of the lithium metal battery is 188mAh / g, and the discharge capacity is 1.08mA / cm 2 After 75 cycles of high current density cycling, the battery begins to fail and the capacity rapidly declines. The surface of the lithium metal is scanned by electron microscope after 120 cycles. The results are as follows Figure 9 As shown by Figure 9It can be seen that the surface of the lithium metal negative electrode is fibrous, indicating the formation of dendrites, and there are many pores, which means that the pure electrolyte without modified inorganic particles will have adverse side reactions with the lithium metal negative electrode during the battery cycle, generating lithium dendrites, and eventually leading to battery failure.

[0035] The F1s binding energy of lithium metal was tested after the lithium metal batteries of Example 3 and this example were cycled for 20 cycles. Figure 10 As shown, Figure 10 The left side shows the F1s binding energy detection results of Example 3. Figure 10 The right side shows the F1s binding energy test results of Comparative Example 1. Figure 10 It can be seen that during the battery cycle, the F-containing components generated by the electrolyte on the surface of the lithium metal negative electrode are mainly SF, LixPOyFz, and LiF. LiF, as the most important SEI component, has high interfacial energy, thereby effectively inhibiting the formation of lithium dendrites. In Comparative Example 1, the content of LiF in the F-containing components is 23.9%, while in Example 3, the content of LiF is as high as 35.4%. It is proved that the fluorine-containing molecular chains and fluorine-containing polymer matrix in the present invention are gradually electrochemically decomposed during the lithium metal battery cycle, and a long-lasting stable layer rich in LiF can be formed at the lithium metal negative electrode interface.

[0036] Comparative Example 2 The difference between this embodiment and embodiment 3 is that in step A2, the modified LATP particles in step S3 of embodiment 1 are replaced with the original LATP particles, and the precursor solution prepared is dripped onto both sides of the PE diaphragm, with the amount of 10 μL each.

[0037] The prepared lithium metal battery was subjected to charge and discharge cycle tests, and the results were as follows: Figure 11 As shown by Figure 11 It can be seen that at 0.1C (0.36mA / cm 2 ) rate charge and discharge, the first discharge capacity of the lithium metal battery is 179mAh / g, and the 2 After 120 cycles of high current density cycling, the battery begins to fail and the capacity rapidly declines. The surface of the lithium metal is scanned by electron microscope after 150 cycles. The results are as follows Figure 12 As shown by Figure 12 It can be seen that there are no fibrous dendrites on the surface of the lithium metal negative electrode, but there are still many holes, indicating that adding LATP particles that have not undergone any modification to the organic electrolyte can inhibit the formation of lithium dendrites to a certain extent. However, the composite electrolyte will still continue to have adverse side reactions with the lithium metal negative electrode, generating holes, and eventually leading to battery failure.

Claims

1. A method for preparing a fluorine-containing chain-modified composite electrolyte, characterized in that: The steps include: S1: dissolving a perfluorinated compound in ethanol to obtain a perfluorinated compound-ethanol solution, adding a non-garnet fast ion conductor to the perfluorinated compound-ethanol solution, and stirring the reaction at 30-80°C for 0.5-12 hours; after the reaction is completed, centrifuging, washing, and drying to obtain modified particles grafted with fluorinated chains; S2: mixing a fluorinated acrylate monomer, a crosslinking agent, and an initiator to form a polymer matrix, and mixing the polymer matrix with an organic electrolyte to obtain a precursor solution; S3: Add modified particles grafted with fluorine-containing chains to the precursor solution, and perform polymerization reaction at 50-80°C for 1-12 hours to obtain a fluorine-containing chain-modified composite electrolyte.

2. The preparation method according to claim 1, characterized in that The perfluorinated compound is a liquid short-chain perfluorinated compound containing a sulfonic acid group, a phosphonic acid group or a carboxyl end group, wherein the short chain has 4 to 6 carbon atoms; the perfluorinated compound includes any one of perfluorobutanesulfonic acid, 1H,1H,2H,2H-perfluorohexylphosphonic acid or perfluoropentanoic acid; the non-garnet fast ion conductor is any one of a sodium fast ion conductor or a perovskite electrolyte.

3. The preparation method according to claim 2, characterized in that In step S1 , the volume ratio of the perfluorinated compound to ethanol is 1:1-19, that is, the concentration of the perfluorinated compound in the ethanol is 5-50 vol.%.

4. The preparation method according to claim 3, characterized in that The mass ratio of the non-garnet fast ion conductor to the perfluorinated compound-ethanol solution is 3:7~97, that is, the concentration of the non-garnet fast ion conductor in the perfluorinated compound-ethanol solution is 3~30wt.%.

5. The preparation method according to claim 4, characterized in that In step S2, the fluorine-containing acrylate monomer is 2,2,2-trifluoroethyl acrylate, the cross-linking agent is polyethylene glycol diacrylate, and the initiator is azobisisobutyronitrile; and the molar ratio of 2,2,2-trifluoroethyl acrylate, polyethylene glycol diacrylate, and azobisisobutyronitrile is 100:1-2:0.25-1; that is, the polyethylene glycol diacrylate is 1-2 mol% of the 2,2,2-trifluoroethyl acrylate, and the azobisisobutyronitrile is 0.25-1 mol% of the 2,2,2-trifluoroethyl acrylate.

6. The preparation method according to claim 5, characterized in that The organic electrolyte is a mixed solution of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 4:6, and the mixed solution also contains 0.4M LiBOB, 0.05M LiPF6 and 0.6M LiTFSI.

7. The preparation method according to claim 6, characterized in that In step S2 , the volume ratio of the polymer matrix to the organic electrolyte is 1:5-10, that is, the volume ratio of the polymer matrix in the precursor solution is 10-20 vol.%.

8. The preparation method according to claim 7, characterized in that In step S3 , the mass ratio of the modified particles grafted with fluorine-containing chains to the precursor solution is 1-30:100; that is, the modified particles grafted with fluorine-containing chains account for 1-30 wt.% of the mass of the precursor solution.

9. A fluorine-chain-modified composite electrolyte prepared by the preparation method according to claim 8.

10. Use of the fluorine-containing chain-modified composite electrolyte according to claim 9 in the preparation of a solid-state lithium metal battery, characterized in that: A fluorine-containing chain-modified composite electrolyte is used as the electrolyte layer of a solid-state lithium metal battery, and the polymerization of the fluorine-containing chain-modified composite electrolyte is carried out after the battery is encapsulated; The specific preparation steps of the solid-state lithium metal battery are as follows: adding modified particles grafted with fluorine chains to the precursor solution, mixing them evenly as a precursor, dripping the precursor on both sides of the battery separator, and then encapsulating the positive electrode sheet and the metal lithium negative electrode on both sides of the separator. The encapsulated semi-finished battery is reacted at 50-80°C for 1-12 hours to complete the preparation of the solid-state lithium metal battery. The positive electrode is one of nickel-cobalt-manganese ternary materials, lithium iron phosphate and lithium cobalt oxide.

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