A flame-retardant phosphate-based gel electrolyte, its preparation method and application

Abstract

The present invention relates to the technical field of solid electrolytes, and particularly relates to a preparation method of a flame-retardant phosphate-based gel electrolyte, which is obtained by polymerizing a raw material solution containing unsaturated phosphate, an initiating lithium salt, and an organic solvent and not containing an azo initiator at 50 to 70 °C; the initiating lithium salt is at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium bis(oxalate) borate, and lithium difluoro(bis(oxalato))phosphate; in the raw material solution, the volume ratio of the unsaturated phosphate of formula 1 to the organic solvent is 0.5 to 2.5:1; the concentration of the initiating lithium salt is 1.5 to 3.5 M. The present invention also relates to the material prepared by the preparation method and its application in a solid electrolyte. The technical solution of the present invention can be synergistic, can initiate polymerization without an initiator, and moreover, can unexpectedly improve the high-temperature cycling performance of the prepared battery.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and particularly relates to the field of solid-state lithium secondary batteries. Background Art

[0002] In recent years, with the development of the economy and the improvement of living standards, people's demand for energy has been increasing continuously. Lithium batteries have been favored due to their advantages such as safety, environmental protection, high specific energy, and good electrochemical performance. The currently used lithium batteries adopt liquid electrolytes, and during the use process, there will be situations such as liquid leakage, volatilization, combustion, and even explosion, causing great potential safety hazards. To ensure the safety and stability of the battery during use, the development direction of lithium battery electrolytes has gradually shifted towards the gel state and the solid state. All-solid-state batteries can well solve the safety performance of the battery, but compared with the conventional solid-liquid interface, their interface contact is poor, which will cause a significant increase in the interface impedance between the electrode and the solid electrolyte, and their room-temperature ionic conductivity is low, thus greatly affecting the performance of the battery.

[0003] To solve the above problems, a feasible method is to introduce an organic electrolyte into a polymer framework and form a gel electrolyte through an in-situ curing method. This not only retains the advantages of high ionic conductivity and good cycle stability of the liquid electrolyte but also has the excellent safety characteristics, good mechanical strength, and flexible processing performance of the solid electrolyte, and has excellent development prospects. The existing preparation processes mostly adopt the solution casting method. This preparation method requires separate film formation, activation by soaking in the electrolyte, and then volatilization of the solvent to obtain the gel electrolyte. The process is cumbersome, the technology is complex, and it is not green and environmentally friendly. Patent CN101475663B adopts an in-situ polymerization strategy to prepare the gel electrolyte. The in-situ polymerization technology is simple and convenient to operate, has strong controllability, can well solve the interface contact problem between the electrolyte and the electrode material, and also has a higher compatibility with the existing battery production processes, and has certain industrialization development prospects. However, currently, most gel electrolytes adopt the method of initiating polymerization with an external initiator. For example, patent CN113234195A uses azobisisobutyronitrile as the initiator for monomer polymerization, but the electrochemical performance of the solid electrolyte prepared by this method needs to be improved. Summary of the Invention

[0004] To solve the problems of the existing technology, the first object of the present invention is to provide a preparation method of a flame-retardant phosphate-based gel electrolyte, aiming to provide a gel electrolyte that can be polymerized without an external initiator and can obtain better electrochemical performance, especially high-temperature performance.

[0005] The second object of the present invention is to provide the flame-retardant phosphate-based gel electrolyte prepared by the above preparation method.

[0006] The third object of the present invention is to provide an application of the flame-retardant phosphate-based gel electrolyte in a solid-state lithium secondary battery.

[0007] The fourth object of the present invention is to provide a solid-state lithium secondary battery containing the gel electrolyte and a preparation method thereof.

[0008] Existing solid electrolytes crosslinked with unsaturated monomers (such as olefin monomers) all need to be polymerized under an azo initiator. However, the inventors of the present invention have found through research that the flame retardancy and electrochemical performance of the solid electrolytes constructed by this process need to be improved. In view of this problem, through in-depth research, the present invention provides the following solutions:

[0009] A preparation method of a flame-retardant phosphate-based gel electrolyte, which is obtained by polymerizing a raw material solution containing an unsaturated phosphoester of formula 1, an initiator lithium salt, and an organic solvent and containing no azo initiator at 50-70 °C;

[0010]

[0011] A is P or P=O; at least one of the substituents of R1-R3 contains an unsaturated double bond; the remaining substituents are at least one of H, C1-C

[0012] ,

[0011] , , , , , 10 , ,

[0010] , 10 ,

[0015] , , ,

[0009] ,

[0014] , ,

[0013] alkyl of, alkoxy of C1-C 10 at least one of;

[0012] The initiator lithium salt is at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluoro(bis(oxalato))phosphate;

[0013] In the raw material solution, the volume ratio of the unsaturated phosphoester of formula 1 to the organic solvent is 0.5-2.5:1; the concentration of the initiator lithium salt is 1.5-3.5 M.

[0014] The present invention breaks away from the inherent preparation idea of azo initiator initiation in the industry and proposes a preparation idea without azo initiator: it innovatively uses the special cross-linked lithium salt as the initiation material, and further cooperates with the combined control of the dosage of the cross-linked lithium salt, the type and dosage of the monomer, and the temperature parameter of the cross-linking reaction, so that synergy can be achieved, and the monomers can be successfully cross-linked without an azo initiator. Moreover, it helps to regulate the polymer network structure and improve the solvation structure of the electrolyte, which is helpful for the transmission of lithium ions and helps to synergistically improve the electrochemical performance of the prepared material unexpectedly, especially beneficial to improving the electrochemical performance of the prepared material under extreme conditions such as high temperature.

[0015] In the present invention, through the combined control of the initiator lithium salt, monomer type, dosage ratio, and temperature, the problem of difficult cross-linking polymerization caused by the absence of azo initiators is overcome, and monomer initiation polymerization can be synergistically achieved. Moreover, it can unexpectedly adjust the polymerization network structure and further improve the electrochemical performance of the prepared material at high temperatures.

[0016] In the present invention, for the monomer of Formula 1, the unsaturated double bond is, for example, a single double bond or a conjugated double bond. The number of the unsaturated double bonds is, for example, 1 to 3. In the present invention, the unsaturated double bond and A are connected by an -O- bond, -C-, or -C-O- bond.

[0017] Preferably, the unsaturated phosphonate of Formula 1 is at least one compound having Formula 1-A, Formula 1-B, or Formula 1-C below;

[0018]

[0019] In Formula 1-A, Formula 1-B, and Formula 1-C, at least one of the substituents R4 to R6 is vinyl, allyl, or substituted allyl; the remaining substituents are H, C1-C6 alkyl, or alkoxyalkyl. In the present invention, the substituted allyl is, for example, substituted with a substituent on the double bond, and the substituent is, for example, at least one of C1-C6 alkyl, alkoxy, halogen, and nitro.

[0020] More preferably, the unsaturated phospholipid is a compound of Formula 1-A, at least one of R4 to R5 is allyl, and the remaining substituents are C1-C6 alkyl; or, the unsaturated phospholipid is a compound of Formula 1-B, and R5 is vinyl, and R4 or R6 is C1-C6 alkyl. Or, the

[0021] Preferably, in the raw material solution, the volume ratio of the unsaturated phosphonate of Formula 1 to the organic solvent is 1 to 2:1; more preferably 1 to 1.5:1; even more preferably 1 to 1.2:1. At the preferred ratio, it is helpful to further cooperate with the process, more conducive to successful initiation of polymerization without initiator, and more conducive to improving the performance of the prepared material at high temperatures.

[0022] In the present invention, the combined control of the initiator lithium salt type and the various conditions is the key to synergistically achieving initiation polymerization without azo initiator, regulating the polymer network structure, and improving the high-temperature performance.

[0023] Preferably, the initiating lithium salt is a mixture of two or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluoro(oxalato)borate; more preferably, it is a complex of lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide. The present invention has found that the use of the combined initiating lithium salt helps to further improve the initiation polymerization of the monomers, helps to improve the polymerization structure, and helps to further improve the high-temperature electrochemical performance.

[0024] In the present invention, in the initiating lithium salt, when a combined initiating lithium salt component is used, the molar percentage content of each single component is 30-60%.

[0025] Preferably, in the raw material solution, the content of the initiating lithium salt is 2-2.5 M. In the present invention, within the preferred range, it helps to further synergistically improve the high-temperature electrochemical performance of the material without initiation.

[0026] There are no particular requirements for the organic solvent described in the present invention. For example, the organic solvent is at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyltrifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl propionate, methyl acetate, and ethyl acetate;

[0027] Preferably, the organic solvent is at least one of ethylene carbonate, fluorinated ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyltrifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0028] More preferably, the organic solvent is a ternary solvent of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1-2:1-2:1-2; or a composite solvent of fluorinated ethylene carbonate, methyltrifluoroethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 1-3:5-7:1-3.

[0029] In the present invention, the raw material solution is a system without the addition of a conventional initiator such as an azo initiator, and it is more preferably a solution composed of the unsaturated phosphoester of formula 1, the initiating lithium salt, and the organic solvent.

[0030] In the present invention, under the combined control of the components and proportions of the raw material solution, further combined with the control of the polymerization reaction temperature, it is unexpectedly possible to achieve the successful initiation of the crosslinked lithium salt, which helps to improve the polymerization network and the electrochemical performance of the prepared electrolyte, especially beneficial to improving the high-temperature electrochemical performance of the prepared material.

[0031] In the present invention, during the polymerization process, the first-stage polymerization is carried out at 50-55°C in advance, and then the second-stage polymerization is carried out at 65-70°C. The present invention has found through research that under the gradient polymerization process described above, the synergy of the components and the process can be unexpectedly further improved, which helps to further improve the electrochemical performance of the prepared electrolyte, especially the high-temperature electrochemical performance.

[0032] In the present invention, the polymerization time is 6-36 h; more preferably 8-16 h.

[0033] Preferably, when a two-stage polymerization process is adopted, the time of the first-stage polymerization stage is 1-3 h; the time of the second-stage polymerization is 6-10 h.

[0034] The present invention also provides a flame-retardant phosphate-based gel electrolyte prepared by the above preparation method.

[0035] Under the combined control of the preparation process and parameters described in the present invention, the product can be given a special network structure. Moreover, the prepared gel electrolyte can also exhibit better high-temperature cycle stability.

[0036] The present invention also provides an application of the above flame-retardant phosphate-based gel electrolyte to prepare a solid-state lithium secondary battery.

[0037] The present invention also provides a solid-state lithium secondary battery, which includes the above flame-retardant phosphate-based gel electrolyte.

[0038] For the solid-state lithium secondary battery described in the present invention, except that the solid electrolyte is the flame-retardant phosphate-based gel electrolyte described in the present invention, other components and component structures can be the same as those in the prior art.

[0039] The present invention also provides a preparation method of a solid-state lithium secondary battery, in which a positive electrode, a separator, and a negative electrode are combined to form an electrode core, the electrode core is placed in a battery case, and then by using the above method, the raw material solution is injected into the battery case and in-situ polymerization is carried out to obtain it.

[0040] In the present invention, under the raw material solution described above and in combination with the in-situ polymerization method, the performance of the solid-state lithium secondary battery can be unexpectedly further improved.

[0041] In the present invention, the positive electrode, the separator, and the negative electrode can be sequentially combined and loaded into the battery case, then the raw material solution is injected, and after encapsulation, it is pre-stationed to fully infiltrate the electrode core components with the raw material solution, and then in-situ polymerization is carried out at the above temperature.

[0042] The specific preparation steps of the solid-state secondary battery described in the present invention include:

[0043] 1. Add the monomer of Formula 1 to an organic solvent to prepare Solution 1;

[0044] 2. Add an initiating lithium salt to the prepared Solution 1 and continuously stir until the lithium salt dissolves to obtain a raw material solution;

[0045] 3. Assemble a battery in the order of positive electrode, separator, negative electrode, injection of liquid (the solution in Step 2), and encapsulation;

[0046] 4. Subsequently, polymerize at 50 - 70 °C.

[0047] Among them, the positive electrode includes a positive electrode current collector and a positive electrode material composite on the surface of the positive electrode current collector; the positive electrode material is obtained by curing a slurry of a positive electrode active material, a conductive agent, and a binder.

[0048] The weight ratio among the positive electrode active material, the conductive agent, and the binder is 7 - 9.5:0.5 - 2:1.

[0049] Preferably, the positive electrode active material is at least one of NCA, NCM111, NCM523, NCM622, NCM811, lithium iron phosphate, lithium cobaltate, lithium-rich manganese-based, lithium nickelate, lithium manganate, lithium vanadium phosphate, lithium fluorophosphate vanadate, elemental sulfur, sulfur-containing polymer, and lithium sulfide.

[0050] Preferably, the conductive agent is one or more of Surper P, acetylene black, KS - 6, CNT, or graphene;

[0051] Preferably, the binder is one or more of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose;

[0052] Preferably, the negative electrode is one of graphite, silicon, silicon-carbon composite, lithium metal, lithium alloy, and lithium titanate.

[0053] Preferably, the separator is one or more of polypropylene, polyethylene, and glass fiber.

[0054] The beneficial effects of the present invention are as follows:

[0055] It is first discovered in the present invention that the initiating lithium salt has an initiating polymerization effect on the monomer under the combined control of the ratio, monomer, and polymerization temperature. Thus, the monomer can be polymerized without adding an external initiator. Moreover, it helps to regulate the polymerization structure and can bring better performance, especially the cycle stability at high temperatures. Description of the Drawings

[0056] Figure 1 It is the SEM image of the flame-retardant phosphate-based gel electrolyte membrane obtained in Example 1;

[0057] Figure 2It is a photo of the flame retardancy test of the flame retardant phosphate-based gel electrolyte obtained in Example 1;

[0058] Figure 3 It is the cycle performance graph of the lithium battery obtained in Example 1; Specific Embodiments

[0059] The following examples are intended to further illustrate the content of the present invention in detail; however, the protection scope of the claims of the present invention is not limited by the examples.

[0060] Example 1:

[0061] Preparation of Flame Retardant Phosphate-Based Gel Electrolyte and Its Application in Lithium Secondary Batteries

[0062] (I) Preparation of Flame Retardant Phosphate-Based Gel Electrolyte

[0063] An unsaturated phospholipid and an organic solvent were mixed at a volume ratio of 1:1 to obtain a precursor solution. The unsaturated phospholipid was of formula A, and the organic solvent was ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1). Then, a lithium salt was initiated in the precursor solution. The initiated lithium salt was lithium hexafluorophosphate (LiPF6), and the mixture was stirred evenly to obtain a raw material solution (solution B). Among them, the concentration of the initiated lithium salt was 2 M. Subsequently, it was heated at 60 °C for 10 h to obtain the flame retardant phosphate-based gel electrolyte (SEM is shown in Figure 1 ).

[0064]

[0065] (II) Flame Retardancy Test

[0066] The prepared flame retardant phosphate-based gel electrolyte was ignited with a high-temperature torch for 5 s, and it was observed whether the electrolyte was flammable. The combustion experiment of the flame retardant phosphate-based gel electrolyte prepared in this case is shown in Figure 2 , reaching the non-flammable level.

[0067] (III) Assembly of Lithium Battery Using Flame Retardant Phosphate-Based Gel Electrolyte

[0068] (1) Preparation of the positive electrode: Lithium iron phosphate, acetylene black, and PVDF were mixed at a mass ratio of 8:1:1, and then an appropriate volume of N-methylpyrrolidone (NMP) was added and placed in a homogenizer and stirred for 15 min at a rotation speed of 15 kr / min to form a stable and uniform positive electrode paste. This paste was coated on aluminum foil using a scraper and placed in an oven at 60 °C for 12 h until NMP was completely volatilized.

[0069] (2) Assembly of the battery: The prepared positive electrode sheet is punched into a circular electrode sheet with a diameter of Φ10 mm. In an argon atmosphere, a lithium metal sheet is used as the negative electrode, and a polypropylene microporous membrane of model Celgard 2400 is selected as the separator. The positive electrode, separator, and negative electrode are sequentially laminated and then placed into the battery case. Subsequently, the raw material solution (i.e., the above-mentioned solution B) is injected, and a CR2025 lithium battery (precursor battery) is encapsulated.

[0070] (3) In-situ polymerization

[0071] The battery case is completely sealed and left standing for 2 h to allow the electrolyte to fully infiltrate. Then, it is heated at 60 °C for 10 h to obtain a flame-retardant phosphate-based gel electrolyte by in-situ polymerization.

[0072] (IV) Electrochemical performance test of the lithium battery

[0073] Charge-discharge cycle tests are carried out on a Blue Electric test charge-discharge tester. The test conditions are charge-discharge cycles at a rate of 1C (1C = 170 mAh / g), the electrochemical window is set to 3 - 4.2 V, and the test temperature is 65 °C. The cycle stability is shown in Figure 3 ; The test results obtained are listed in Table 1.

[0074] Example 2:

[0075] Other conditions are the same as those in Example 1, except that in the raw material solution, the initiating lithium salt is LiTFSI, and the molar concentration of the initiating lithium salt is 2 M. The test results obtained are listed in Table 1.

[0076] Example 3:

[0077] Other conditions are the same as those in Example 1, except that in the raw material solution, the initiating lithium salts are LiPF6 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a molar ratio of 1:1. The test results obtained are listed in Table 1.

[0078] Example 4:

[0079] Other conditions are the same as those in Example 1, except that in the raw material solution, the initiating lithium salts are LiTFSI and lithium difluoro(oxalato)borate (LiODFB) with a molar ratio of 1:1. The test results obtained are listed in Table 1.

[0080] Example 5:

[0081] Other conditions are the same as those in Example 1, except that in the raw material solution, the initiating lithium salts are LiPF6 and lithium bis(fluorosulfonyl)imide (LiFSI) with a molar ratio of 1:1. The test results obtained are listed in Table 1.

[0082] Example 6:

[0083] Other conditions are the same as those in Example 1, except that the concentration of the initiating lithium salt in the raw material solution is 2.5 mol / L. The test results obtained are listed in Table 1.

[0084] Example 7:

[0085] Other conditions are the same as those in Example 1, except that in the raw material solution, the volume ratio of the unsaturated phospholipid to the organic solvent is 1.5:1. The test results obtained are listed in Table 1.

[0086] Example 8:

[0087] Other conditions are the same as those in Example 1, except that in the raw material solution, the unsaturated phospholipid is of formula B.

[0088] The test results obtained are listed in Table 1.

[0089]

[0090] Example 9:

[0091] Other conditions are the same as those in Example 1, except that the organic solvents are vinylidene fluoride carbonate, methyl trifluoroethyl carbonate, and 1,1,2,2 - tetrafluoroethyl - 2,2,3,3 - tetrafluoropropyl ether, and the volume ratio is 2:6:2. The test results obtained are listed in Table 1.

[0092] Example 10:

[0093] Other conditions are the same as those in Example 1, except that in step (3) of (iii), the first - stage polymerization is carried out at 50 °C for 2 h in advance, and then the second - stage polymerization is carried out at 70 °C for 8 h. The test results obtained are listed in Table 1.

[0094] Example 11:

[0095] Other conditions are the same as those in Example 3, except that in step (3) of (iii), the first - stage polymerization is carried out at 55 °C in advance, and then the second - stage polymerization is carried out at 65 °C. The test results obtained are listed in Table 1.

[0096] Comparative Example 1:

[0097] Other conditions are the same as those in Example 1, except that 1% by mass of azobisisobutyronitrile (AIBN) is additionally added to the raw material solution as an initiator. The test results obtained are listed in Table 1.

[0098] Comparative Example 2:

[0099] Other conditions are the same as those in Example 1, except that the concentration of the initiating lithium salt in the raw material solution is 5 mol / L. The test results obtained are listed in Table 1.

[0100] Comparative Example 3:

[0101] Other conditions were the same as those in Example 1, except that the concentration of the initiating lithium salt in the raw material solution was 1 mol / L. The test results obtained are listed in Table 1.

[0102] Comparative Example 4:

[0103] Other conditions were the same as those in Example 1, except that the volume ratio of the unsaturated phospholipid to the organic solvent was 3:1. The test results obtained are listed in Table 1.

[0104] Comparative Example 5:

[0105] Other conditions were the same as those in Example 1, except that the unsaturated phospholipid was replaced with the conventional polymer monomer isopentyl tetraacrylate, and then 1% of AIBN by mass of the polymer monomer was added as an initiator. The test results obtained are listed in Table 1.

[0106] Comparative Example 6:

[0107] Other conditions were the same as those in Example 1, except that the initiating lithium salt was replaced with the non-initiating lithium salt lithium perchlorate (LiClO4). The test results obtained are listed in Table 1.

[0108] Comparative Example 7:

[0109] Other conditions were the same as those in Example 1, except that the assembled battery was kept heated at 40 °C for 10 h. After returning to room temperature, electrochemical performance tests were then carried out. The test results obtained are listed in Table 1.

[0110] Comparative Example 8:

[0111] Other conditions were the same as those in Example 1, except that monomer A was not added to the raw material solution and no heating was required. The test results obtained are listed in Table 1.

[0112] Table 1 Performance test results of Examples and Comparative Examples

[0113]

[0114] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a flame-retardant phosphate-based gel electrolyte, characterized in that, It is obtained by polymerizing a raw material solution composed of the unsaturated phosphoester of Formula 1, an initiating lithium salt, and an organic solvent at 50 to 70 °C; Formula 1 A is P or P=O; at least one of the substituents R1 to R3 contains an unsaturated double bond; the remaining substituents are at least one of H, an alkyl group having 1 to C 10 alkyl group, an alkoxy group having 1 to C 10 ; The initiating lithium salt is at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium bis(oxalate) borate, and lithium difluoro bis(oxalato) phosphate; In the raw material solution, the volume ratio of the unsaturated phosphoester of Formula 1 to the organic solvent is 0.5 to 2.5:1; the concentration of the initiating lithium salt is 1.5 to 3.5 M.

2. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, wherein, The unsaturated phosphoester of Formula 1 is at least one compound having Formula 1-A, Formula 1-B, or Formula 1-C below; In Formula 1-A, Formula 1-B, and Formula 1-C, at least one of the substituents R4 to R6 is vinyl, allyl, or a substituted allyl; the remaining substituents are H, an alkyl group having 1 to 6 carbon atoms, or an alkoxyalkyl group.

3. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, wherein, In the raw material solution, the volume ratio of the unsaturated phosphoester of Formula 1 to the organic solvent is 1 to 2:

1.

4. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, wherein, In the raw material solution, the volume ratio of the unsaturated phosphoester of Formula 1 to the organic solvent is 1 to 1.5:

1.

5. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, characterized in that, In the raw material solution, the volume ratio of the unsaturated phosphoester of Formula 1 to the organic solvent is 1 to 1.2:

1.

6. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, wherein, The initiating lithium salt is a mixture of two or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorooxalate borate.

7. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, characterized in that, In the raw material solution, the concentration of the initiating lithium salt is 2 to 2.5 M.

8. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, characterized in that, The organic solvent is at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl propionate, methyl acetate, and ethyl acetate.

9. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, characterized in that, The organic solvent is a ternary solvent of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate with a volume ratio of 1 to 2:1 to 2:1 to 2; or a composite solvent of fluorinated ethylene carbonate, methyl trifluoroethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether with a volume ratio of 1 to 3:5 to 7:1 to 3.

10. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 1, characterized in that, The total polymerization time is 6 to 36 h.

11. The preparation method of the flame-retardant phosphate-based gel electrolyte according to any one of claims 1 to 10, characterized in that, During the polymerization process, the first-stage polymerization is carried out at 50 to 55 °C in advance, and then the second-stage polymerization is carried out at 65 to 70 °C.

12. The preparation method of the flame-retardant phosphate-based gel electrolyte according to claim 11, wherein, The time of the first-stage polymerization stage is 1 to 3 h; the time of the second-stage polymerization is 6 to 10 h.

13. A flame-retardant phosphoester-based gel electrolyte prepared by the preparation method according to any one of claims 1 to 12.

14. Use of the flame-retardant phosphate-based gel electrolyte according to claim 13, characterized in that, It is used to prepare a solid-state lithium secondary battery.

15. A solid-state lithium secondary battery, characterized in that, It includes the flame-retardant phosphoester-based gel electrolyte according to claim 13.

16. A method for preparing a solid-state lithium secondary battery, characterized in that, The positive electrode, separator, and negative electrode are combined to form an electrode core, the electrode core is placed in a battery case, and then the raw material solution is injected into the battery case by the method according to any one of claims 1 to 12, and in-situ polymerization is carried out to obtain it.

Images