Flame-retardant electrolyte for high-rate sodium metal battery as well as preparation method and application of flame-retardant electrolyte

Abstract

The invention discloses a flame-retardant electrolyte for a high-rate sodium metal battery as well as a preparation method and application of the flame-retardant electrolyte, belongs to the technical field of sodium metal batteries, and solves the problems that a fluorine-containing solvent in an existing sodium metal battery electrolyte is poor in flame retardance and relatively high in cost, and a phosphorus-containing solvent is poor in compatibility with a sodium metal negative electrode. The flame-retardant electrolyte is prepared from the following components in percentage by mass: 6.63 to 31.1 percent of sodium salt and the balance of a mixed solvent, wherein the mixed solvent comprises a phosphate ester solvent, a fluoro-carbonic ester solvent, a carbonic ester solvent, a fluoro-carboxylic ester solvent and a silane coupling agent; the volume ratio of the phosphate ester solvent to the fluoro-carbonic ester solvent to the carbonic ester solvent to the fluoro-carboxylic ester solvent to the silane coupling agent solvent in the mixed solvent is (1-5): 1: (1-5): (1-5): 1. According to the electrolyte, a firm artificial SEI film can be formed on the sodium metal negative electrode side, side reactions are reduced, and the cycle life of the sodium metal battery is greatly prolonged; the material not only has the characteristic of flame retardance, but also can realize high-magnification long circulation.

Description

Technical Field

[0001] The invention relates to a flame retardant electrolyte for a sodium metal battery, in particular to a flame retardant electrolyte for a high-rate sodium metal battery and a preparation method and application thereof, belonging to the technical field of sodium metal batteries. Background Art

[0002] With the rapid growth of portable electronic products and the global push for automotive electrification and smart grids, traditional battery technology faces many challenges. People's demand for electricity is increasing, and renewable energy sources such as wind power, hydropower, and solar energy cannot be stably connected to the grid for power distribution due to the constraints of the external environment. Electrochemical energy storage provides an important carrier for renewable energy and is increasingly valued, developing rapidly like "mushrooms after rain". Among them, lithium batteries have significant advantages such as high energy density, excellent cycle performance, high operating voltage and long service life. However, due to the limited and uneven distribution of lithium resources, they cannot adapt to the rapid growth of the energy storage market. Sodium resources are abundant, evenly distributed, and low in cost, and are expected to become an important supplement to lithium batteries in the future.

[0003] The electrolyte in the battery is known as the "blood" of the battery. It is responsible for the ion transport task during the battery's charge and discharge process. It is the medium for the chemical reaction inside the battery and has a direct impact on the battery's performance and life. However, during extreme applications, the battery is prone to overcharge, over discharge, and inevitable collisions that can cause the battery to burn and explode.

[0004] At present, in the process of selecting key materials for sodium metal batteries, phosphorus- or fluorine-containing solvents are often considered to improve the flame retardancy of electrolytes. However, fluorine-containing solvents have the disadvantages of poor flame retardancy and high cost in practical applications. In contrast, phosphate ester solvents such as TMP or TEP are not only cheaper, but also show excellent flame retardancy. Therefore, these phosphate ester solvents are considered to be ideal choices for developing flame-retardant electrolytes. However, for example, Zhao XM, Yan YW, Ren XX, Chen L, Xu SD, Liu SB, Wang XM, Zhang D. TrimethylPhosphate forNonflammable Carbonate-Based Electrolytes for Safer Room-Temperature Sodium-Sulfur Batteries[J]. Chemelectrochem, 2019, 6(4): 1229-1234., due to the poor compatibility of phosphates with sodium metal negative electrodes, they are prone to side reactions with the electrode surface, making it difficult to form an effective SEI film on the negative electrode side, resulting in uneven sodium deposition and continuous decomposition of phosphates on the anode, leading to serious capacity decay.

[0005] Therefore, it is urgent to design a flame-retardant electrolyte for sodium metal batteries that can form a strong artificial SEI film on the sodium metal negative electrode side to improve the cycle life of sodium metal batteries. Summary of the invention

[0006] The purpose of the present invention is to solve the problems that the fluorine-containing solvent in the existing sodium metal battery electrolyte has poor flame retardancy and high cost, and the phosphorus-containing solvent has poor compatibility with the sodium metal negative electrode, and to provide a flame-retardant electrolyte for a high-rate sodium metal battery and a preparation method and application thereof. The flame-retardant electrolyte is formed by mixing a phosphorus-containing solvent and a fluorine-containing solvent with a silane coupling agent, and the amino group in the silane is used to react and polymerize with fluoroethylene carbonate, and grafted on the surface of the sodium metal, so that in-situ polymerization can occur on the side of the sodium metal negative electrode to form a solid artificial SEI film, reduce interface resistance, and greatly improve the cycle life of the sodium metal battery; the flame-retardant electrolyte not only has flame retardant properties, but also can achieve high-rate long cycle.

[0007] To achieve the above object, the present invention adopts the following technical scheme: a flame retardant electrolyte for a high-rate sodium metal battery, the flame retardant electrolyte consisting of 6.63% to 31.1% of a sodium salt and the remainder of a mixed solvent by mass percentage, the mixed solvent comprising a phosphate solvent, a fluorocarbonate solvent, a carbonate solvent, a fluorocarboxylate solvent and a silane coupling agent; The fluorocarbonate solvent is fluoroethylene carbonate (FEC); The volume ratio of the phosphate solvent, the fluorinated carbonate solvent, the carbonate solvent, the fluorinated carboxylate solvent and the silane coupling agent solvent in the mixed solvent is 1-5:1:1-5:1-5:1.

[0008] Furthermore, the volume ratio of the phosphate solvent, the fluorocarbonate solvent, the carbonate solvent, the fluorocarboxylate solvent and the silane coupling agent solvent in the mixed solvent is 3:1:3:2:1.

[0009] Furthermore, the concentration of the sodium salt is 0.6-2.5 mol / L, and the sodium salt is at least one of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium tetrafluoroborate (NaBF4) and sodium difluorooxalatoborate (NaDFOB).

[0010] Furthermore, the sodium salt is a mixed solution of sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI), wherein the concentration of sodium hexafluorophosphate (NaPF6) is 0.6 mol / L, and the concentration of sodium bis(fluorosulfonyl)imide (NaFSI) is 0.6 mol / L.

[0011] Further, the phosphate ester solvent is at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TPP), tributyl phosphate (TBP), dimethyl methyl phosphate (DMMP), and diethyl methyl phosphate (DEEP); The carbonate solvent is one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and diethyl carbonate (DEC); The fluorocarboxylic acid ester solvent is one of methyl trifluoroacetate (MTFA), ethyl trifluoroacetate (ETFA), and propyl trifluoroacetate (PTFA); The silane coupling agent solvent is 3-aminopropyltriethoxysilane (APTES).

[0012] The present invention also provides a method for preparing a flame retardant electrolyte for a high-rate sodium metal battery, comprising the following steps: S1. Under argon atmosphere, add phosphate solvent, fluorocarbonate solvent, carbonate solvent, fluorocarboxylate solvent and silane coupling agent solvent in sequence, mix well, and stir for 1 hour to obtain a pre-solution; S2, fully dissolving the sodium salt into the pre-solution obtained in the above step S1 to form a basic solution; S3, adding the molecular sieve to the basic solution obtained in step S2, standing for 24 hours, and finally removing the molecular sieve to obtain a flame retardant electrolytic solution; Furthermore, the molecular sieve is a 3Å or 4Å molecular sieve.

[0013] The present invention also provides the use of the flame retardant electrolyte prepared by the above preparation method in a sodium metal battery, wherein the sodium metal battery consists of a positive electrode sheet, a separator, a flame retardant electrolyte and positive and negative electrode sheets.

[0014] The beneficial effects of the present invention are: 1) The present invention mixes a phosphorus-containing solvent and a fluorine-containing solvent with a silane coupling agent to form a flame-retardant electrolyte, utilizes the amino group in the silane to react and polymerize with fluoroethylene carbonate, and grafts on the surface of the sodium metal. In-situ polymerization can occur on the negative electrode side of the sodium metal to form a solid artificial SEI film, thereby reducing the interface resistance and greatly improving the cycle life of the sodium metal battery. The invention not only has flame-retardant properties, but also can achieve high-rate long cycles.

[0015] 2) The present invention utilizes APTES and FEC to slowly polymerize in ETFA dispersant to form a small molecule polymer, which undergoes in-situ polymerization during the battery cycle to form an interface film, effectively reducing the battery interface impedance, reducing the side reactions of the battery, and inhibiting the excessive growth of sodium dendrites; it can greatly increase the migration number of sodium ions, the interface exchange current density, and the cycle stability of the charge and discharge process.

[0016] 3) In the present invention, a phosphorus-containing solvent and a fluorine-containing solvent are mixed together with a silane coupling agent and then applied to a sodium metal battery system, and the chemical stability is improved by utilizing the synergistic effect of multiple molecules. Compared with a sodium metal battery with a phosphate electrolyte without a silane coupling agent solvent, the battery not only has an extremely flame-retardant property but also exhibits good rate performance and a long cycle life.

[0017] Among them, carbonate electrolytes have a high dielectric constant and can dissociate sodium salts well; the silane coupling agent APTES has amino groups and silicon-oxygen bonds, which can react with FEC to generate polymers and generate a lot of heat. By optimizing the content of different salts and mixed solvents, the electrolyte solvation structure can be precisely controlled and the chemical composition of the interface can be optimized, thereby obtaining an electrolyte that is both flame-retardant and highly compatible with the negative electrode, greatly improving the safety and cycle stability of sodium metal batteries.

[0018] 4) In the preparation method of the present invention, the addition sequence is controlled to slowly polymerize in the ETFA dispersant to form a small molecule polymer, which is grafted on the surface of the sodium metal material to form a stable interface film that can inhibit the growth of sodium dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a long cycle data diagram of Example 1 of the present invention and Comparative Example 1 at 20C rate; Figure 2 Schematic diagram of the reaction mechanism of FEC and APTES in the present invention; Figure 3 This is an infrared data diagram of the slow polymerization of FEC and APTES in the solution ETFA in the present invention; Figure 4 This is a graph of NMR silicon spectrum data after slow polymerization of FEC and APTES in the solution ETFA in the present invention. DETAILED DESCRIPTION

[0020] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0021] In the following embodiments and comparative examples, the specific preparation method of the positive electrode sheet is as follows: the positive electrode active material Na3V2(PO4)3, the conductive agent Super P, and the adhesive PVDF are dissolved in the solvent NMP in a mass ratio of 8:1:1, and the initial positive electrode slurry is obtained after stirring evenly, with a slurry viscosity of 5000±1000cP and a solid content of 65wt%; the additives prepared in each embodiment and comparative example are respectively added to the initial positive electrode slurry and stirred for 8h, and then coated on the positive electrode collector aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0022] Abbreviations: Sodium hexafluorophosphate: NaPF6, sodium bis(fluorosulfonyl)imide: NaFSI, triethyl phosphate: TEP, fluoroethylene carbonate: FEC, dimethyl carbonate: DMC, ethyl trifluoroacetate: ETFA, 3-aminopropyltriethoxysilane: APTES.

[0023] Example 1: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:3:2:1 are added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0024] Example 2: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:2:3:1 are added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0025] Example 3: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 5:1:1:2:1 are added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0026] Example 4: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: adding TEP:FEC:DMC:ETFA:APTES in a volume ratio of 1:1:1:1:1 in order and mixing them evenly, adding 100.8 mg of NaPF6 and 121.87 mg of NaFSI and dissolving them in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then mixing the solution evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0027] Example 5: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 2:1:5:1:1 are added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0028] Example 6: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 2:1:1:5:1 are added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0029] Example 7: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:3:2:1 are added in sequence and mixed evenly, 168 mg of NaPF6 is first dissolved in 1 ml of the mixed solution so that the salt concentration is 1 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0030] Example 8: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:2:3:1 are added in sequence and mixed evenly, 168 mg of NaPF6 is first dissolved in 1 ml of the mixed solution so that the salt concentration is 1 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0031] Example 9: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:3:2:1 are added in sequence and mixed evenly, 203.12 mg of NaFSI is first dissolved in 1 ml of the mixed solution so that the salt concentration is 1 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0032] Example 10: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:3:2:1 are added in sequence and mixed evenly, 201.6 mg of NaPF6 and 244.8 mg of NaFSI are first dissolved in 1 ml of the mixed solution to make the salt concentration 2.4 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0033] Example 11: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA:APTES with a volume ratio of 3:1:3:2:1 are added in sequence and mixed evenly, 50.4 mg of NaPF6 and 60.935 mg of NaFSI are first dissolved in 1 ml of the mixed solution to make its salt concentration 0.6 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0034] Comparative Example 1: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA with a volume ratio of 3:1:4:2 is added in order and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0035] Comparative Example 2: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:FEC:DMC:ETFA with a volume ratio of 3:4:2:1 are added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0036] Comparative Example 3: A flame retardant electrolyte for a high-rate sodium metal battery, the preparation method of which comprises the following steps: TEP:DMC:ETFA with a volume ratio of 4:4:2 is added in sequence and mixed evenly, 100.8 mg of NaPF6 and 121.87 mg of NaFSI are first dissolved in 1 ml of the mixed solution so that the salt concentration is 1.2 mol / L, and then the solution is mixed evenly at room temperature to obtain a sodium metal battery electrolyte with flame retardant function.

[0037] Table 1 below is a summary chart of the long cycle performance of Na||NVP full batteries assembled with different embodiments and different comparative electrolytes at a 1 C rate.

[0038] Group Average charge and discharge efficiency (%) Charge and discharge rate Number of cycles Capacity retention rate Example 1 99.85 1C 2300 95.01% Example 2 97.49 1C 1450 95.08% Example 3 99.08 1C 200 97.46% Example 4 97.81 1C 185 97.43% Example 5 98.56 1C 182 97.97% Example 6 98.96 1C 210 99.05% Example 7 98.89 1C 1450 87.71% Example 8 98.24 1C 1450 92.63% Example 9 97.99 1C 210 96.76% Example 10 98.93 1C 230 98.11% Embodiment 11 98.29 1C 350 97.2% Comparative Example 1 99.11 1C 550 96.53% Comparative Example 2 98.99 1C 120 98.56 Comparative Example 3 99.70 1C 163 93.4% According to the performance test results, the capacity retention rate of Experimental Example 1 is 95.01% after 2300 cycles at a 1C rate. Compared with the comparative example, it can maintain better electrochemical long-cycle stability and ensure a high cycle life of the battery.

[0039] Examples 1 to 11 are mixed solutions with different salt concentrations and different volumes of solvents. Compared to the comparative examples, the experimental examples all contain FEC and APTES, which can react on the sodium metal negative electrode to form a strong interface and film to resist the growth of sodium dendrites. Examples 1, 2, 7, and 8 all achieve long cycles at a 1C rate, while during the test of comparative examples 1 to 3, short circuits occurred because they could not resist the growth of sodium dendrites.

[0040] The following is a detailed analysis of the data content in Table 1: Examples 1 to 6 are the performance results of mixed solvents in different proportions under a salt concentration of 1.2 mol / L and two salt solutions, and their capacity retention rates can all reach more than 95%. According to the performance test results, the capacity retention rate of Experimental Example 1 is 95.01% after 2300 cycles at a rate of 1C. Compared with the comparative example, it can maintain better electrochemical long-cycle stability and ensure a high cycle life of the battery.

[0041] Examples 7 to 9 are the performance results of mixed solvents in different proportions under a salt concentration of 1.0 mol / L and a salt solution. Because it contains both FEC and APTES, it can stably circulate 1450 times at a 1C rate.

[0042] Examples 10 to 11 are the performance results of the solvent under the same two salt concentrations of 2.4 mol / L and 0.6 mol / L, respectively. It can be concluded from the examples that the performance is best under the condition of having two salts at the same time.

[0043] Comparative Examples 1 to 3 have the same salt concentration as Example 1, but do not contain both FEC and APTES. They cannot form a strong interface film during the cycle and are prone to internal short circuits.

[0044] Figure 1 It is a long cycle data diagram of Example 1 and Comparative Example 1 at 20C rate.

[0045] Compared with Comparative Example 1, Example 1 has better electrochemical stability and better fast charging stability at 20C.

[0046] Figure 2Schematic diagram of the polymerization of FEC and APTES. The polymerized organosilicon has a high Young's modulus, a fast ion transmission channel, and can dissolve fluorinated organic matter well to form a fluorinated organic-inorganic hybrid SEI at the interface.

[0047] Figure 3 and Figure 4 for Figure 2 Mechanistic polymerization support information application, in which the amino group in APTES attacks FEC, and FEC defluorination promotes silane self-polymerization. (C. Tretbar, J. Castro, K. Yokoyama, Z. Guan, Fluoride-CatalyzedSiloxane Exchange as a Robust Dynamic Chemistry forHigh-PerformanceVitrimers. Adv. Mater. 2023, 35, 2303280.) In the present invention, a phosphorus-containing solvent and a fluorine-containing solvent are mixed with a silane coupling agent to form a flame-retardant electrolyte, and the amino group in the silane is used to react and polymerize with fluoroethylene carbonate, and grafted on the surface of the sodium metal. In-situ polymerization can occur on the negative electrode side of the sodium metal to form a solid artificial SEI film, reduce interface resistance, and greatly improve the cycle life of the sodium metal battery; it not only has flame-retardant properties, but also can achieve high-rate long cycles.

[0048] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A flame retardant electrolyte for a high rate sodium metal battery, characterized in that: The flame retardant electrolyte is composed of 6.63% to 31.1% of sodium salt and the remainder of a mixed solvent by mass percentage, and the mixed solvent includes a phosphate solvent, a fluorocarbonate solvent, a carbonate solvent, a fluorocarboxylate solvent and a silane coupling agent; The fluorocarbonate solvent is fluoroethylene carbonate (FEC); The volume ratio of the phosphate solvent, the fluorinated carbonate solvent, the carbonate solvent, the fluorinated carboxylate solvent and the silane coupling agent solvent in the mixed solvent is 1-5:1:1-5:1-5:

1.

2. The flame retardant electrolyte for high rate sodium metal battery according to claim 1, characterized in that: The volume ratio of the phosphate solvent, the fluorocarbonate solvent, the carbonate solvent, the fluorocarboxylate solvent and the silane coupling agent solvent in the mixed solvent is 3:1:3:2:

1.

3. The flame retardant electrolyte for high rate sodium metal battery according to claim 1, characterized in that: The concentration of the sodium salt is 0.6-2.5 mol / L, and the sodium salt is at least one of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium tetrafluoroborate (NaBF4) and sodium difluorooxalatoborate (NaDFOB).

4. The flame retardant electrolyte for high rate sodium metal battery according to claim 3, characterized in that: The sodium salt is a mixed solution of sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI), wherein the concentration of sodium hexafluorophosphate (NaPF6) is 0.6 mol / L, and the concentration of sodium bis(fluorosulfonyl)imide (NaFSI) is 0.6 mol / L.

5. The flame retardant electrolyte for high rate sodium metal battery according to claim 1, characterized in that: The phosphate ester solvent is at least one of trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TPP), tributyl phosphate (TBP), dimethyl methyl phosphate (DMMP), and diethyl methyl phosphate (DEEP); The carbonate solvent is one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and diethyl carbonate (DEC); The fluorocarboxylic acid ester solvent is one of methyl trifluoroacetate (MTFA), ethyl trifluoroacetate (ETFA), and propyl trifluoroacetate (PTFA); The silane coupling agent solvent is 3-aminopropyltriethoxysilane (APTES).

6. A method for preparing a flame retardant electrolyte for a high rate sodium metal battery according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Under argon atmosphere, add phosphate solvent, fluorocarbonate solvent, carbonate solvent, fluorocarboxylate solvent and silane coupling agent solvent in sequence, mix well, and stir for 1 hour to obtain a pre-solution; S2, fully dissolving the sodium salt into the pre-solution obtained in the above step S1 to form a basic solution; S3, adding the molecular sieve to the basic solution obtained in step S2, standing for 24 hours, and finally removing the molecular sieve to obtain a flame retardant electrolytic solution; The preparation method according to claim 6, characterized in that the molecular sieve is a 3Å or 4Å molecular sieve.

7. Application of the flame-retardant electrolyte prepared by the preparation method according to claim 6 in a sodium metal battery, characterized in that: The sodium metal battery is composed of a positive electrode sheet, a separator, a flame retardant electrolyte and positive and negative electrode sheets.

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