Fluorine-containing lithium borate compound, preparation method and application of fluorine-containing lithium borate compound in secondary battery

Abstract

The invention discloses a fluorine-containing lithium borate compound, a preparation method and application of the fluorine-containing lithium borate compound in a secondary battery. The fluorine-containing lithium borate compound has a structure as shown in a formula 1. The preparation method of the lithium fluoroborate-containing compound comprises the following steps: in a glove box, putting lithium tetrafluoroborate and a compound as shown in a formula II into a first solvent, carrying out stirring reaction, and after the reaction is finished, carrying out post-treatment on reaction liquid. The invention has the advantages of novel structure, mild reaction conditions, high product purity and good application scene, and can be applied to secondary batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of material synthesis, and in particular to a fluorine-containing lithium borate compound, a preparation method and application thereof in secondary batteries. Background Art

[0002] The electrolyte is the lifeblood of lithium-ion batteries, transferring lithium ions between the positive and negative electrode materials and the separator. It also plays a crucial role in the formation and impedance of the SEI and CEI at the interfaces of the positive and negative electrode materials. With the rapid development of pure electric and hybrid electric vehicles, demands for lithium-ion batteries' energy density, long cycle life, rate capability, and safety performance continue to rise.

[0003] Traditional lithium hexafluorophosphate (LiFPO), a commonly used commercial electrolyte lithium salt, is widely used in batteries and capacitors. However, it also has some critical drawbacks. In the presence of trace amounts of water, LiFPO produces hydrofluoric acid, which is corrosive to electrode materials, leading to severe degradation and failure of battery performance. Therefore, the development of new lithium salt additives with more stable electrochemical properties is currently a hot research and development direction. Summary of the Invention

[0004] In view of the above problems, the present invention aims to provide a fluorine-containing lithium borate compound, a preparation method and its application in secondary batteries. The fluorine-containing lithium borate compound of the present invention has a simple preparation process, mild reaction conditions, high product purity and novel structure, and can be used in secondary batteries.

[0005] To achieve the above objectives, the present invention provides a fluorine-containing lithium borate compound having a structure shown in Formula 1: .

[0006] Compared with the prior art, the fluorine-containing lithium borate compound of the present invention contains lithium, boron, fluorine, carbonyl and alkynyl structures, has a novel structure, has broad application prospects, and can be used in secondary batteries.

[0007] The second aspect of the present invention provides a method for preparing the aforementioned fluorine-containing lithium borate compound, comprising placing lithium tetrafluoroborate and a compound represented by Formula 2 in a first solvent in a glove box for stirring and reacting, and post-treating the reaction solution after the reaction is completed. .

[0008] Compared with the prior art, the preparation method of the present invention is simple and can be prepared by stirring and reacting lithium tetrafluoroborate and the compound shown in Formula 2. During the reaction, the compound shown in Formula 2 removes the trimethylsilyl group and lithium tetrafluoroborate to form trimethylsilyl fluoride. Subsequently, the parent compound that removes the trimethylsilyl group chelates with lithium tetrafluoroborate to obtain the target product. The obtained product has high purity and is easy to industrialize.

[0009] As a preferred technical solution, the stirring reaction temperature of the present invention is 20°C to 60°C, and the reaction time is 2h to 48h.

[0010] As a preferred technical solution, the molar ratio of lithium tetrafluoroborate to the compound represented by Formula 2 of the present invention is 1:1 to 1:5.

[0011] As a preferred technical solution, the first solvent of the present invention is selected from at least one of amide solvents, nitrile solvents, ether solvents, halogenated hydrocarbon solvents, ester solvents, sulfone solvents and aromatic hydrocarbon solvents.

[0012] As a preferred technical solution, the post-treatment of the present invention includes concentrating, crystallizing, filtering and washing the reaction solution.

[0013] As a preferred technical solution, the method for preparing the compound represented by Formula 2 of the present invention comprises the steps of: (1) In an ice bath, dimethyl malonate, sodium hydride, and a second solvent are mixed and stirred to form a first solution, and propargyl bromide and the second solvent are mixed to form a second solution. The second solution is added dropwise to the first solution and reacted at room temperature. After the reaction, the second solvent is removed, and then the intermediate A is obtained by extraction, drying, concentration, and crystallization; (2) Refluxing the intermediate A and sodium hydroxide in a third solvent, filtering to obtain a white solid after the reaction is completed, dissolving the white solid in water and adjusting the pH to acidic before extraction, collecting the organic phase and drying to obtain the intermediate B; (3) Dissolve the intermediate B in the fourth solvent, add triethylamine and trimethylsilyl chloride in sequence under ice bath conditions, and stir to react. After the reaction is completed, add water to quench the reaction. After extraction, separation, collection of the organic phase, and drying, the compound of formula 2 is obtained.

[0014] As a preferred technical solution, the molar ratio of dimethyl malonate, sodium hydride, and propyne bromide is 1:2~5:2~5.

[0015] As a preferred technical solution, the molar ratio of intermediate A to sodium hydroxide is 1:2 to 1:5.

[0016] As a preferred technical solution, the molar ratio of intermediate B, triethylamine and trimethylchlorosilane is 1:1~5:2~5.

[0017] As a preferred technical solution, the temperature of the reflux reaction is 50°C~80°C.

[0018] As a preferred technical solution, the second solvent, the third solvent and the fourth solvent are each independently selected from at least one of tetrahydrofuran, ethanol and dichloromethane.

[0019] A third aspect of the present invention provides a use of the aforementioned fluorine-containing lithium borate compound or the fluorine-containing lithium borate compound prepared by the aforementioned method for preparing the fluorine-containing lithium borate compound in a secondary battery. DETAILED DESCRIPTION

[0020] The fluorine-containing lithium borate compound of the present invention is mainly used in the field of lithium ion battery electrolyte additives, and can also be used in the fields of materials, pharmaceutical intermediates, etc.

[0021] The fluorine-containing lithium borate compound of the present invention has a structure shown in Formula 1: .

[0022] The preparation method of the fluorine-containing lithium borate compound of the present invention may include placing lithium tetrafluoroborate and the compound represented by Formula 2 in a first solvent in a glove box for stirring and reacting, and performing post-treatment on the reaction solution after the reaction is completed. .

[0023] Furthermore, the synthesis route of the fluorine-containing lithium borate compound can be shown in Reaction Scheme 1:

[0024] Furthermore, in the preparation method of the fluorine-containing lithium borate compound of the present invention, the molar ratio of lithium tetrafluoroborate to the compound shown in Formula 2 is 1:1 to 1:5. Preferably, the molar ratio of lithium tetrafluoroborate to the compound shown in Formula 2 is 1:1. As an example, the molar ratio of lithium tetrafluoroborate to the compound shown in Formula 2 can be, but is not limited to, 1:1, 1:2, 1:3, 1:4, or 1:5. The stirring reaction temperature is 20°C to 60°C. Specifically, the stirring reaction temperature can be, but is not limited to, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C. Preferably, the stirring reaction temperature is 48°C to 60°C. The stirring reaction time is 2h~48h. Specifically, the stirring reaction time can be, but is not limited to, 2h, 4h, 6h, 8h, 10h, 14h, 15h, 18h, 20h, 25h, 30h, 35h, 40h, 42h, 44h, 46h, and 48h. Preferably, the stirring reaction time is 24h~48h.

[0025] Furthermore, the first solvent is selected from at least one of an amide solvent, a nitrile solvent, an ether solvent, a halogenated hydrocarbon solvent, an ester solvent, a sulfone solvent, and an aromatic hydrocarbon solvent. Specifically, the amide solvent is N,N-dimethylformamide or N,N-dimethylacetamide, the nitrile solvent is acetonitrile, the ether solvent is 1,4-dioxane, diethyl ether, or tetrahydrofuran, the halogenated hydrocarbon solvent is dichloromethane or chloroform, the ester solvent is ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or propylene carbonate, the sulfone solvent is dimethyl sulfoxide, and the aromatic hydrocarbon solvent is benzene, toluene, or xylene.

[0026] Furthermore, post-treatment includes concentrating the reaction solution, crystallizing, filtering, and washing. Specifically, the post-treatment includes concentrating the reaction solution under reduced pressure to obtain an oily substance, adding a solvent to the oily substance for dissolution and crystallization to precipitate flocculent matter, and then filtering and washing. The solvent for dissolution and crystallization and the solvent for washing can be selected from toluene or dichloromethane.

[0027] Furthermore, the preparation method of the compound represented by Formula 2 of the present invention comprises the steps of: (1) In an ice bath, dimethyl malonate, sodium hydride and a second solvent are mixed and stirred to form a first solution, bromopropyne and a second solvent are mixed to form a second solution, the second solution is added dropwise to the first solution and reacted at room temperature, after which the second solvent is removed, and then the intermediate A is obtained by extraction, drying, concentration and crystallization; (2) Intermediate A and sodium hydroxide are refluxed in a third solvent, after which a white solid is obtained by filtration, the white solid is dissolved in water and the pH is adjusted to acidic, and then extraction is performed, the organic phase is collected and dried to obtain intermediate B; (3) Intermediate B is dissolved in a fourth solvent, triethylamine and trimethylsilyl chloride are added in sequence under ice bath conditions to react by stirring, after which water is added to quench the reaction, the organic phase is collected and dried to obtain the compound shown in formula 2.

[0028] Furthermore, in step (1), the synthesis route of intermediate A can be shown in Reaction Scheme 2:

[0029] Further, in step (1), the molar ratio of dimethyl malonate, sodium hydride and bromopropyne is 1:2-5:2-5, preferably, the molar ratio of dimethyl malonate, sodium hydride and bromopropyne is 1:2-4:2-3, for example, the molar ratio of dimethyl malonate, sodium hydride and bromopropyne can be, but is not limited to, 1:2:2, 1:2:3, 1:2:4, 1:2:5, 1:3:2, 1:3:3, 1:3:4, 1:3:5, 1:4:2, 1:4:3, 1:4:4, 1:4:5, 1:5:2, 1:5:3, 1:5:4, 1:5:5. The stirring reaction time can be 0.5 h. The room temperature reaction time can be 12-24 h, specifically, the room temperature reaction time can be, but is not limited to, 12, 14, 16, 18, 20, 22, 24, preferably, the room temperature reaction time is 16 h. The extraction, drying, concentration and crystallization include removing the second solvent from the reaction solution by reduced pressure distillation, then adding ethyl acetate and water for extraction, collecting the organic phase, adding anhydrous magnesium sulfate for drying, and then concentrating and crystallizing. The second solvent can be selected from at least one of tetrahydrofuran, ethanol and dichloromethane, preferably, the second solvent is selected from tetrahydrofuran.

[0030] Further, in step (2), the synthesis route of the intermediate B is shown in Reaction Formula III:

[0031] Further, in step (2), the molar ratio of the intermediate A and sodium hydroxide is 1:2-1:5. For example, the molar ratio of the intermediate A and sodium hydroxide can be, but is not limited to, 1:2, 1:3, 1:4, 1:5. The reflux reaction temperature can be 50-80°C, specifically, the reflux reaction temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C. Preferably, the reflux reaction temperature is 75-80°C. The reflux reaction time can be 2-10 h. Specifically, the reflux reaction time can be, but is not limited to, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h. Preferably, the reflux reaction time is 4-8 h. The organic solvent used for extraction can be an ester, preferably, the organic solvent used for extraction is ethyl acetate. The drying includes drying the organic phase with anhydrous magnesium sulfate to effectively remove the water contained in the organic phase. The third solvent can be selected from at least one of tetrahydrofuran, ethanol and dichloromethane, preferably, the third solvent is selected from ethanol.

[0032] Further, in step (3), the synthesis route of the compound shown in Formula II can be shown in Reaction Formula IV:

[0033] Furthermore, in step (3), the molar ratio of intermediate B, triethylamine and trimethylchlorosilane is 1:1~5:2~5. As an example, the molar ratio of intermediate B, triethylamine and trimethylchlorosilane can be, but is not limited to, 1:1:2, 1:2:2, 1:2:3, 1:2:4, 1:2:5, 1:3:2, 1:3:3, 1:3:4, 1:3:5, 1:4:2, 1:4:3, 1:4:4, 1:4:5, 1:5:2, 1:5:3, 1:5:4, 1:5:5. The stirring reaction time can be 12h~24h. Specifically, the stirring reaction time can be, but is not limited to, 12, 14, 16, 18, 20, 22, 24. Preferably, the stirring reaction time is 16h. The organic solvent used for extraction can be dichloromethane, and drying includes drying the organic phase with anhydrous magnesium sulfate. The fourth solvent may be selected from at least one of tetrahydrofuran, ethanol and dichloromethane. Preferably, the fourth solvent may be selected from dichloromethane.

[0034] Furthermore, the second solvent, the third solvent and the fourth solvent may be the same or different.

[0035] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0036] Part I: Preparation of the compound represented by Formula II Example 1 This embodiment provides a method for preparing a compound represented by Formula 2, comprising the steps of: (1) In a 500 mL three-necked flask under ice bath, 66 g of dimethyl malonate, 40 g of sodium hydride, and 300 mL of tetrahydrofuran were mixed and stirred to form a first solution. 119 g of propargyl bromide and 100 mL of tetrahydrofuran were mixed to form a second solution. The second solution was added dropwise to the first solution and reacted at room temperature for 16 h. After the reaction, the tetrahydrofuran was removed by vacuum distillation, and the mixture was extracted with ethyl acetate and water. The organic phase was collected, dried over anhydrous magnesium sulfate, and then concentrated and crystallized to obtain 83.28 g of white solid intermediate A. The hydrogen spectrum was: 1 H NMR (400 MHz, CDCl3, ppm): d 3.66 (s, 6H), 2.93 (t, 2H), 2.71 (d, 4H), yield: 79.8 %.

[0037] (2) 83.28 g of intermediate A, 32 g of sodium hydroxide and 300 mL of ethanol were placed in a 500 mL three-necked flask and stirred to dissolve, and the temperature was raised to 80°C to reflux for 6 h. After the reaction was completed, the solvent was removed by filtration to obtain a white solid, which was dissolved in water and adjusted to be acidic, and then extracted with ethyl acetate. The organic phase was collected, dried with anhydrous magnesium sulfate and concentrated to crystallize to obtain 61.3 g of intermediate B, and the hydrogen spectrum was: 1 H NMR (400 MHz, CDCl3, ppm): 2.93 (t, 2H),2.47 (d, 4H), the yield was 85.2 %.

[0038] (3) 61.3 g of intermediate B was dissolved in dichloromethane, and 34.4 g of triethylamine was added under ice bath condition at 0°C, and stirred for 0.5 h, and then 73.9 g of TMSCl was added, and the reaction was continued for 16 h. After the reaction was completed, water was added to quench the reaction, and then extracted, separated, and the organic phase was collected. After drying with anhydrous magnesium sulfate, it was concentrated to crystallize to obtain 81.64 g of the compound shown in formula II, and the hydrogen spectrum was: 1 H NMR (400 MHz, CDCl3, ppm): d 2.93 (t, 2H),2.47 (d, 4H),0.21((s,18H), the yield was 74.2 %.

[0039]

[0040] Second part: preparation of fluorine-containing lithium borate compound Example 2 The present example provides a preparation method of a fluorine-containing lithium borate compound, which comprises placing 28.9 g of lithium tetrafluoroborate and 150 mL of acetonitrile in a 500 mL three-necked flask in a glove box, stirring to dissolve, slowly adding 100 g of the compound shown in formula II at room temperature, and reacting at 60°C for 36 h. After the reaction was completed, a colorless oily liquid was obtained by concentration, 500 mL of toluene was added, a large amount of white flocculent precipitate was generated, and a white solid was obtained by filtration. After the white solid was washed with toluene and dried, 33.2 g of the fluorine-containing lithium borate compound was obtained, the yield was 49.2 %, and the purity was 99 %. The hydrogen spectrum data was: 1 H NMR (400 MHz, CDCl3, ppm): d 2.47 (d, 4H), 1.97 (t,2H). Example 3 ​This example provides a method for preparing a fluorine-containing lithium borate compound. The method comprises placing 28.9 g of lithium tetrafluoroborate and 150 mL of ethyl acetate in a 500 mL three-necked flask in a glove box and stirring to dissolve the mixture. Slowly adding 100 g of the compound represented by Formula 2 at room temperature and incubating at 60°C for 36 hours. After the reaction, the mixture is concentrated to obtain a colorless oily liquid. Adding 500 mL of dichloromethane produces a large amount of white flocculent precipitate, which is filtered to obtain a white solid. The resulting white solid is washed with dichloromethane and dried to obtain 42.1 g of the fluorine-containing lithium borate compound, with a yield of 62.5% and a purity of 99%. The hydrogen spectrum data are as follows: 1 H NMR (400MHz, CDCl3, ppm): d 2.47 (d, 4H), 1.97 (t,2H). Example 4 This example provides a method for preparing a fluorine-containing lithium borate compound. The method comprises placing 28.9 g of lithium tetrafluoroborate and 150 mL of 1,4-dioxane in a 500 mL three-necked flask and stirring to dissolve the mixture. Slowly adding 100 g of the compound represented by Formula 2 at room temperature and incubating at 60°C for 36 hours. After the reaction, the mixture is concentrated to obtain a colorless oily liquid. Adding 500 mL of dichloromethane produces a large amount of white flocculent precipitate, which is filtered to obtain a white solid. The resulting white solid is washed with dichloromethane and dried to obtain 35.4 g of the fluorine-containing lithium borate compound, with a yield of 52.5% and a purity of 99%. The hydrogen spectrum data are as follows: 1 HNMR (400 MHz, CDCl3, ppm): d 2.47 (d, 4H), 1.97 (t,2H). Example 5 This example provides a method for preparing a fluorine-containing lithium borate compound. The method comprises placing 28.9 g of lithium tetrafluoroborate and 150 mL of tetrahydrofuran in a 500 mL three-necked flask in a glove box and stirring to dissolve the mixture. Slowly adding 100 g of the compound represented by Formula 2 at room temperature and incubating at 60°C for 36 hours. After the reaction, the mixture is concentrated to obtain a colorless oily liquid. Adding 500 mL of toluene produces a large amount of white flocculent precipitate, which is filtered to obtain a white solid. The resulting white solid is washed with toluene and dried to obtain 31.1 g of the fluorine-containing lithium borate compound, with a yield of 46.2% and a purity of 98.5%. The hydrogen spectrum data are as follows: 1 H NMR (400 MHz,CDCl3, ppm): d 2.47 (d, 4H), 1.97 (t,2H). Example 6 This example provides a method for preparing a fluorine-containing lithium borate compound. The method comprises placing 28.9 g of lithium tetrafluoroborate and 150 mL of acetonitrile in a 500 mL three-necked flask in a glove box and stirring to dissolve the mixture. Slowly adding 80 g of the compound represented by Formula 2 at room temperature and incubating at 60°C for 36 hours. After the reaction, the mixture is concentrated to yield a colorless oily liquid. Adding 500 mL of toluene produces a large amount of white flocculent precipitate, which is filtered to yield a white solid. The resulting white solid is washed with toluene and dried to yield 33.2 g of the fluorine-containing lithium borate compound, with a yield of 49.2% and a purity of 98%. The hydrogen spectrum data are as follows: 1 H NMR (400 MHz,CDCl3, ppm): d 2.47 (d, 4H), 1.97 (t,2H). Example 7 This example provides a method for preparing a fluorine-containing lithium borate compound. The method comprises placing 28.9 g of lithium tetrafluoroborate and 150 mL of acetonitrile in a 500 mL three-necked flask in a glove box and stirring to dissolve the mixture. Slowly adding 150 g of the compound represented by Formula 2 at room temperature and incubating at 60°C for 36 hours. After the reaction, the mixture is concentrated to obtain a colorless oily liquid. Adding 500 mL of toluene produces a large amount of white flocculent precipitate, which is filtered to obtain a white solid. The resulting white solid is washed with toluene and dried to obtain 33.2 g of the fluorine-containing lithium borate compound, with a yield of 49.2% and a purity of 95%. The hydrogen spectrum data are as follows: 1 H NMR (400 MHz,CDCl3, ppm): d 2.47 (d, 4H), 1.97 (t,2H). Part III Application of Fluorinated Lithium Borate Compounds in Secondary Batteries 1 g of the fluorine-containing lithium borate compound prepared in Examples 2 to 7 and 87 g of a non-aqueous organic solvent (ethylene carbonate EC and ethyl methyl carbonate EMC in a mass ratio of 1:1) were respectively mixed evenly, and then 12 g of lithium hexafluorophosphate LiPF6 was added and mixed evenly to prepare non-aqueous electrolytes 1# to 6#.

[0041] 88 g of non-aqueous organic solvent (ethylene carbonate EC and ethyl methyl carbonate EMC in a mass ratio of 3:7) and 12 g of lithium hexafluorophosphate LiPF6 were mixed uniformly to prepare non-aqueous electrolyte solution 7#.

[0042] Lithium cobaltate was used as the positive electrode material and lithium metal as the counter electrode, and non-aqueous electrolyte 1#-7# was injected to assemble button cells 1#-7#. Under normal temperature (25℃) conditions, the button cells were subjected to 3.0C / 3.0C charging and discharging (the battery discharge capacity was recorded as C0) once, the upper limit voltage was 4.2V, then subjected to 3.0C / 3.0C charging and discharging for 300 cycles (the battery discharge capacity was recorded as C1), and the capacity retention rate was calculated.

[0043] Capacity retention rate = (battery capacity C1 after 300 cycles / battery initial capacity C0) x 100% Table 1: electrochemical performance test results of each example

[0044] From the results in Table 1, it can be seen that the cycle performance of button cells 1#-6# is better than that of button cell 7#, because the electrolyte of button cells 1#-6# contains a lithium fluoroborate compound, which does not decompose in water to produce substances harmful to the battery system, and does not contain hydrogen in the position of the methylene in the structure, and the acidity is weakened. At the same time, it contains a chelating oxalic acid structure, and the overall structure is relatively stable, which can form a passivation film on the electrode surface, protecting the electrode while not weakening the transport of lithium ions, and can effectively improve the cycle performance of the battery.

[0045] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the scope of protection of the present application, although the present application has been described in detail with reference to the preferred embodiments, but it is not limited to the examples listed in the embodiments, and those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A fluorine-containing lithium borate compound, characterized in that It has the structure shown in Formula 1: 。 2. A method for preparing a fluorine-containing lithium borate compound according to claim 1, characterized in that: The method comprises placing lithium tetrafluoroborate and the compound shown in Formula 2 in a first solvent in a glove box for stirring and reacting, and performing post-treatment on the reaction solution after the reaction is completed. 。 3. The method for preparing the fluorine-containing lithium borate compound according to claim 2, wherein: The stirring reaction temperature is 20° C. to 60° C., and the reaction time is 2 h to 48 h.

4. The method for preparing the fluorine-containing lithium borate compound according to claim 2, wherein The molar ratio of the lithium tetrafluoroborate to the compound represented by formula 2 is 1:1 to 1:

5.

5. The method for preparing the fluorine-containing lithium borate compound according to claim 2, wherein: The first solvent is selected from at least one of amide solvents, nitrile solvents, ether solvents, halogenated hydrocarbon solvents, ester solvents, sulfone solvents and aromatic hydrocarbon solvents.

6. The method for preparing the fluorine-containing lithium borate compound according to claim 2, wherein: The post-treatment includes concentrating, crystallizing, filtering and washing the reaction solution.

7. The method for preparing a fluorine-containing lithium borate compound according to claim 2, wherein: The method for preparing the compound represented by formula 2 comprises the steps of: (1) In an ice bath, dimethyl malonate, sodium hydride, and a second solvent are mixed and stirred to form a first solution, propargyl bromide and the second solvent are mixed to form a second solution, the second solution is added dropwise to the first solution and reacted at room temperature. After the reaction, the second solvent is removed, and then the intermediate A is obtained by extraction, drying, concentration, and crystallization; (2) The intermediate A and sodium hydroxide are subjected to reflux reaction in a third solvent. After the reaction is completed, a white solid is obtained by filtration. The white solid is dissolved in water and the pH is adjusted to acidic before extraction. The organic phase is collected and dried to obtain the intermediate B. (3) The intermediate B is dissolved in a fourth solvent, and triethylamine and trimethylsilyl chloride are added in sequence under ice bath conditions to carry out stirring reaction. After the reaction is completed, water is added to quench the reaction. After extraction, separation, collection of the organic phase, and drying, the compound shown in Formula 2 is obtained.

8. The method for preparing the fluorine-containing lithium borate compound according to claim 7, wherein: The molar ratio of the dimethyl malonate, the sodium hydride, and the propyne bromide is 1:2~5:2~5, the molar ratio of the intermediate A and the sodium hydroxide is 1:2~1:5, and the molar ratio of the intermediate B, the triethylamine, and the trimethylsilyl chloride is 1:1~5:2~5.

9. The method for preparing the fluorine-containing lithium borate compound according to claim 7, wherein: In step (2), the temperature of the reflux reaction is 50° C. to 80° C. The second solvent, the third solvent, and the fourth solvent are each independently selected from at least one of tetrahydrofuran, ethanol, and dichloromethane.

10. Use of the fluorine-containing lithium borate compound according to claim 1 or the fluorine-containing lithium borate compound prepared by the preparation method of the fluorine-containing lithium borate compound according to any one of claims 2 to 9 in a secondary battery.

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