Sodium difluorophenylborate and its preparation method and application

Abstract

This invention provides sodium difluorodiphenylborate, its preparation method, and its application. The sodium difluorodiphenylborate has the molecular formula NaB(Ph)2F2. The two phenyl atoms and two fluorine atoms of the sodium difluorodiphenylborate of this invention can work synergistically to ensure good solubility in organic solvents and improve electrochemical stability and conductivity by introducing fluorine atoms, thus making it a promising candidate for use in sodium-ion battery electrolytes.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical materials and relates to a sodium difluorodiphenylborate, its preparation method, and its application. Background Technology

[0002] Currently, fluorinated borate electrolytes, particularly those used in sodium-ion battery electrolytes, have certain limitations and cannot fully meet the requirements of high-performance batteries for electrolyte materials. For example, traditional methods for preparing sodium tetrafluoroborate (NaBF4) typically require the use of highly corrosive hydrofluoric acid (HF) and boric acid, which not only imposes harsh process conditions and high operational risks but also easily generates highly toxic waste gases and wastewater, making them environmentally unfriendly. Furthermore, the solubility, ionic conductivity, and electrochemical stability of NaBF4 in electrolytes still have room for improvement in certain specific applications.

[0003] In the field of fluorinated organoborates, some literature and patents report the preparation of fluorinated and organoborates, but most rely on complex multi-step synthetic routes, expensive fluorinated reagents, or harsh reaction conditions. For example, CN117486912A discloses a process for synthesizing sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate. This method relies on the reaction of 3,5-bis(trifluoromethyl)phenyl Grignard reagent with boron trichloride under a catalyst, followed by multiple conversions including post-treatment with dihydrogen phosphate aqueous solution and reaction with sodium hydride. Although this method strives to simplify the post-treatment, its preparation route still involves expensive fluorinated Grignard reagents, the risk of catalyst residue, and multiple acid quenching and sodium treatment steps, making large-scale industrial production difficult and costly.

[0004] CN116588944A discloses a method for preparing sodium tetrafluoroborate, using hydrofluoric acid, boric acid, and soda ash as raw materials, and purifying it through steps such as evaporation, dissolution in a polar organic solvent, filtration, and cooling crystallization. The core product of this method is pure inorganic BF4. - Anions. Their preparation process requires the treatment of hydrofluoric acid waste gas, resulting in high energy consumption and stringent equipment requirements. Furthermore, the product has relatively low solubility and cannot be well miscible with many organic solvents, which limits its application in sodium-ion batteries.

[0005] CN111943968A discloses a method for preparing tetra(pentafluorophenyl)borate, which requires nitrogen protection and involves the reaction of pentafluorobromobenzo Grignard reagent with polyhalogenated boron or polyhalogenated borate. This method involves the preparation of expensive and complex fluorinated Grignard reagents, with harsh operating conditions, large equipment investment, and high production costs.

[0006] CN117603246A discloses a method for preparing sodium tetraphenylborate, which involves heating sodium phenolate and triphenylborate ester in a solvent, followed by purification by cyclohexane precipitation and washing with anhydrous ethanol. The core of this method is fluorine-free BPh4.- Anions. Although the route is simple, there is still room for improvement in oxidation stability and cycle performance of its products compared to fluoroborates in sodium-ion battery electrolytes.

[0007] In summary, existing borate electrolytes face the following prominent problems in their application as electrolytes in sodium-ion batteries: (1) The preparation of many high-performance fluorinated borates relies on multi-step conversion, expensive fluorinated reagents (such as fluorinated Grignard reagents) or highly corrosive substances (such as HF), resulting in high production costs and hindering industrial promotion.

[0008] (2) The use of highly corrosive or toxic reagents such as hydrofluoric acid can easily generate harmful waste gas and wastewater, which pose a threat to operators and the environment, and increase equipment maintenance costs.

[0009] (3) Traditional synthesis methods are prone to generating a variety of boron-oxygen / fluorine hybrid byproducts, making it difficult to separate the target product from the impurities. Residual impurities will seriously affect the electrochemical performance of the electrolyte and the cycle life of the battery.

[0010] Therefore, there is an urgent need in this field to develop an efficient, economical, and environmentally friendly preparation method to obtain high-purity sodium difluorodiphenylborate, in order to overcome the limitations of existing electrolyte salts. Summary of the Invention

[0011] In view of the shortcomings of the prior art, the purpose of this invention is to provide sodium difluorodiphenylborate, its preparation method and application.

[0012] To achieve this objective, the present invention adopts the following technical solution: On one hand, the present invention provides sodium difluorodiphenylborate with the molecular formula NaB(Ph)₂F₂ and the following structure: .

[0013] The two phenyl groups and two fluorine atoms of NaB(Ph)2F2 of the present invention can work synergistically to ensure good solubility in organic solvents and improve electrochemical stability by introducing fluorine atoms.

[0014] In the structural design of the target product, if there are too many phenyl atoms (such as NaBPh4), the electrochemical stability may be limited, especially at higher potentials where it is easily oxidized; if there are too many fluorine atoms (such as NaBF4), it is easy to decompose in trace amounts of water or at high temperatures to produce HF, and its solubility in organic solvents may be limited.

[0015] In this invention, the technical problem to be solved is how to achieve precise ligand exchange to obtain NaB(Ph)₂F₂ in a simple and efficient manner, while avoiding the drawbacks of traditional fluorination reactions. The preparation of organoborates via the reaction of Grignard reagents with boron halides typically requires an inert atmosphere, is complex, and the Grignard reagents themselves are expensive. Furthermore, when introducing fluorine atoms to improve the properties of borates, the use of highly corrosive fluorinating agents (such as HF) is often involved, posing significant risks, equipment corrosion, and difficulties in waste gas treatment. In addition, in traditional synthesis methods, if the solubility or volatility of byproducts is not significantly different from that of the target product, subsequent purification steps become extremely complex, sometimes requiring multiple recrystallizations or column chromatography, greatly increasing production costs and time, and potentially leading to reduced product yield and unstable purity. This invention solves these technical problems through the following preparation method, successfully obtaining sodium difluorodiphenylborate.

[0016] This invention provides a method for preparing sodium difluorodiphenylborate as described above, the method comprising the following steps: Sodium tetraphenylborate (NaBPh4) reacts with a fluorine source to yield sodium difluorodiphenylborate.

[0017] This invention is the first to synthesize sodium tetraphenylborate and fluorine source as the core raw material system through salt formation / ligand exchange. The route is short and the reaction logic is clear, avoiding the multi-step conversion path that relies on highly corrosive HF or complex fluorine-containing reagents. The product purity is ≥90%.

[0018] Preferably, the fluorine source is selected from any one or a combination of at least two of sodium fluoride, ammonium fluoride, and sodium bifluoride.

[0019] Preferably, the molar ratio of sodium tetraphenylborate to fluorine source is 1:0.5 to 1:4 (e.g., 1:0.5, 1:0.9, 1:1.3, 1:1.7, 1:2.1, 1:2.5, 1:2.9, 1:3.3, 1:3.7, or 1:4, etc.). When the proportion of fluorine source in the molar ratio of sodium tetraphenylborate to fluorine source is less than 0.5, the fluorination conversion is incomplete and the yield is low; when the proportion of fluorine source is greater than 4, the excess fluorine source leads to an increase in impurities and increases the difficulty of purification.

[0020] Preferably, the reaction is carried out in a first organic solvent.

[0021] Preferably, the first organic solvent is selected from one or a combination of at least two of methanol, ethanol, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ethylene glycol dimethyl ether, or diethylene glycol dimethyl ether.

[0022] Preferably, the mass ratio of the organic solvent to sodium tetraphenylborate is 10:1 to 20:1 (e.g., 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, or 20:1). When the mass ratio of the organic solvent to sodium tetraphenylborate is less than 10:1, the sodium tetraphenylborate and the fluorine source are not fully dissolved, the system becomes viscous, mass transfer is limited, and side reactions are easily induced. When the mass ratio of the organic solvent to sodium tetraphenylborate is greater than 20:1, the reaction rate decreases significantly, and the energy consumption and time cost of subsequent vacuum distillation increase.

[0023] Preferably, the mixture is stirred at 20-30°C (e.g., 20°C, 22°C, 25°C, 27°C, or 30°C) for 0.5-1 h (e.g., 0.5h, 0.6h, 0.7h, 0.8h, or 1h) to fully disperse and dissolve; subsequently, the reaction system is stirred at 30-150°C (e.g., 30°C, 40°C, 55°C, 60°C, 70°C, 80°C, 95°C, 100°C, 120°C, 140°C, or 150°C) for 2-15 h (e.g., 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 12h, or 15h) to carry out a salt formation reaction.

[0024] This invention proposes a segmented temperature control strategy of "low-temperature dispersion / dissolution-heating reaction" to improve solid-liquid mass transfer and reaction uniformity, reduce side reactions and batch-to-batch fluctuations caused by local overheating or agglomeration, and is suitable for scale-up production.

[0025] In the dispersion and dissolution stages, if the temperature is too low, the dissolution rate will be slow; if it is too high, side reactions may be triggered prematurely. In the reaction stage, if the temperature is too low, the reaction rate will be slow; if it is too high, decomposition or side reactions may be triggered. If the time is too short, the conversion will be insufficient; if it is too long, the number of by-products will increase.

[0026] Preferably, after the reaction is completed, the reaction solution is filtered to remove insoluble matter; the filtrate is subjected to a first vacuum distillation to remove the first organic solvent and the byproduct benzene, to obtain a crude product; a second organic solvent is added to the obtained crude product to dissolve it, to obtain a solution, and then the insoluble matter is removed by filtration; the filtrate is subjected to a second vacuum distillation to remove organic solvent B, and the obtained solid is dried to obtain sodium difluorodiphenylborate with a purity ≥90%.

[0027] The preparation method described in this invention uses only a simplified separation strategy of "filtration + vacuum distillation". It takes advantage of the difference in volatility and solubility between the target product and by-products (such as benzene, inorganic salts, etc.) to achieve efficient impurity removal and reduce fine purification steps.

[0028] Preferably, the second organic solvent is selected from one or a combination of at least two of acetonitrile, acetone, dichloromethane, tetrahydrofuran, or ethanol.

[0029] Preferably, the first and second vacuum distillations are carried out independently at temperatures of 60–100°C (e.g., 60°C, 70°C, 80°C, 90°C, or 100°C) and pressures of 20–50 mbar (e.g., 20 mbar, 24 mbar, 28 mbar, 32 mbar, 36 mbar, 40 mbar, 44 mbar, or 50 mbar). Distillations below 60°C or pressures above 50 mbar result in incomplete removal of the solvent and the byproduct benzene; temperatures above 100°C may trigger the thermal decomposition of sodium difluorodiphenylborate.

[0030] Preferably, during the first and second vacuum distillations, the condensation system maintains a condensation temperature of 5-15°C to improve the removal efficiency of water and benzene.

[0031] Preferably, the volume ratio of the second organic solvent to the crude product is 1:1 to 5:1, for example, 1:1, 1:2, 1:3, 1:4 or 1:5.

[0032] Preferably, the drying is vacuum drying.

[0033] Preferably, the drying temperature is 50~80℃ (e.g., 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc.), and the drying time is 24~48 h (e.g., 24h, 28h, 30h, 33h, 36h, 40h, 42h, 46h or 48h, etc.).

[0034] Preferably, the drying is carried out at a pressure of ≤10 mbar (e.g., 0 mbar, 2.5 mbar, 5 mbar, 7.5 mbar or 10 mbar, etc.).

[0035] In this invention, the drying intensity can be guaranteed under the drying temperature, drying pressure and time as described above, so as to avoid insufficient drying intensity leading to solvent residue, or excessive drying intensity leading to the risk of thermal decomposition.

[0036] On the other hand, the present invention provides a sodium-ion battery electrolyte, wherein the sodium-ion battery electrolyte comprises sodium difluorodiphenylborate as described above.

[0037] On the other hand, the present invention provides a sodium-ion battery, the sodium-ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte as described above.

[0038] Compared with the prior art, the present invention has the following beneficial effects: The two phenyl groups and two fluorine atoms of NaB(Ph)2F2 of the present invention can work synergistically to ensure good solubility in organic solvents and improve electrochemical stability and conductivity by introducing fluorine atoms, thus making it a promising candidate for use in sodium-ion battery electrolytes. Attached Figure Description

[0039] Figure 1 Sodium difluorodiphenylborate of Example 1 11 B. Liquid phase NMR spectrum.

[0040] Figure 2 This is a comparison chart of the solubility of sodium difluorodiphenylborate and sodium tetrafluoroborate in diethylene glycol dimethyl ether solvent, as shown in Example 1.

[0041] Figure 3 The diagram shows the charge-discharge curves of a sodium-ion battery using the sodium difluorodiphenylborate and sodium tetraphenylborate electrolyte from Example 1.

[0042] Figure 4 A sodium-ion battery cycle diagram using sodium difluorodiphenylborate electrolyte containing the electrolyte of Example 1. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0044] Example 1 This embodiment provides a sodium difluorodiphenylborate, the preparation method of which is as follows: Step 1: Weigh 0.10 mol of sodium tetraphenylborate (NaBPh4) and 0.05 mol of sodium hydrogen fluoride (NaHF2). Add both to a 500 mL flask, and add acetonitrile (NaBPh4 to acetonitrile mass ratio approximately 1:10). Stir at 25°C for 0.5 h to ensure complete dispersion and dissolution; then, raise the temperature of the reaction system to 80°C and stir at this temperature for 6 h.

[0045] Step 2: After the reaction is complete, the reaction solution is filtered through a sintered glass funnel to remove insoluble matter. The filtrate is then subjected to a rotary evaporator under reduced pressure (70℃ / 30 mbar) to remove acetonitrile and the byproduct benzene, yielding crude sodium difluorodiphenylborate.

[0046] Step 3: Add acetone (acetone to crude product volume ratio approximately 3:1) to the crude product to ensure complete dissolution. Filter the solution again to remove any remaining insoluble impurities. Then, remove the acetone from the filtrate by vacuum distillation (rotary evaporator, 80℃ / 40 mbar) to obtain a solid.

[0047] Step 4: Transfer the obtained solid to a vacuum drying oven and dry it at 60°C and 5 mbar for 36 h to obtain sodium difluorodiphenylborate.

[0048] Example 2 This embodiment provides a sodium difluorodiphenylborate, the preparation method of which is as follows: Step 1: Weigh 0.10 mol of sodium tetraphenylborate (NaBPh4) and 0.40 mol of ammonium fluoride (NH4F). Add both to a 500 mL flask, and add tetrahydrofuran (NaBPh4 to tetrahydrofuran mass ratio approximately 1:20). Stir at 27 °C for 0.8 h to ensure complete dispersion and dissolution; then, raise the temperature of the reaction system to 150 °C and stir at this temperature for 15 h.

[0049] Step 2: After the reaction is complete, the reaction solution is filtered to remove insoluble matter. The filtrate is then distilled under reduced pressure (100℃ / 50 mbar) to remove tetrahydrofuran and the byproduct benzene, yielding crude sodium difluorodiphenylborate.

[0050] Step 3: Add acetonitrile (acetonitrile to crude product volume ratio approximately 5:1) to the crude product to ensure complete dissolution. Filter the solution to remove any small amount of insoluble impurities. Then, distill the filtrate under reduced pressure (60℃ / 20 mbar) to remove the acetonitrile, yielding a solid.

[0051] Step 4: Dry the obtained solid at 80℃ and 8 mbar under vacuum for 48 h to obtain the product sodium difluorodiphenylborate.

[0052] Example 3 This embodiment provides a sodium difluorodiphenylborate, the preparation method of which is as follows: Step 1: Weigh 0.10 mol of sodium tetraphenylborate (NaBPh4) and 0.30 mol of sodium fluoride (NaF). Add both to a 500 mL flask, and add N,N-dimethylformamide (DMF) (NaBPh4 to DMF mass ratio approximately 1:15). Stir at 20 °C for 1 h to ensure complete dispersion and dissolution; subsequently, raise the reaction temperature to 30 °C and stir at this temperature for 2 h.

[0053] Step 2: After the reaction is complete, the reaction solution is filtered to remove insoluble matter. The filtrate is then distilled under reduced pressure (60℃ / 20 mbar) to remove DMF and the byproduct benzene, yielding crude sodium difluorodiphenylborate.

[0054] Step 3: Add ethanol (ethanol to crude product volume ratio approximately 1:1) to the crude product to ensure complete dissolution. Filter the solution to remove any small amount of insoluble impurities. Then, distill the filtrate under reduced pressure (100℃ / 50 mbar) to remove the ethanol, yielding a solid.

[0055] Step 4: The obtained solid was dried under vacuum at 75°C and 10 mbar for 24 h to obtain the product sodium difluorodiphenylborate. Example 4 This embodiment provides a sodium difluorodiphenylborate, the preparation method of which is as follows: Step 1: Weigh 0.10 mol of sodium tetraphenylborate (NaBPh4) and 0.20 mol of sodium fluoride (NaF). Add both to a 500 mL flask and add ethanol (NaBPh4 to DMF mass ratio approximately 1:12). Stir at 30 °C for 0.7 h to ensure complete dispersion and dissolution; then, raise the temperature of the reaction system to 120 °C and stir at this temperature for 8 h.

[0056] Step 2: After the reaction is complete, the reaction solution is filtered to remove insoluble matter. The filtrate is then distilled under reduced pressure (80℃ / 40 mbar) to remove ethanol and the byproduct benzene, yielding crude sodium difluorodiphenylborate.

[0057] Step 3: Add dichloromethane (dichloromethane to crude product volume ratio approximately 2:1) to the crude product to ensure complete dissolution. Filter the solution to remove any small amount of insoluble impurities. Then, distill the filtrate under reduced pressure (90℃ / 35 mbar) to remove the dichloromethane, yielding a solid.

[0058] Step 4: Dry the obtained solid at 70℃ and 2 mbar under vacuum for 42 h to obtain the product sodium difluorodiphenylborate.

[0059] Example 5 This embodiment provides a sodium difluorodiphenylborate, the preparation method of which is as follows: Step 1: Weigh 0.10 mol of sodium tetraphenylborate (NaBPh4) and 0.35 mol of sodium hydrogen fluoride (NaHF2). Add both to a 500 mL flask, and add dimethyl ethylene glycol (DME) (NaBPh4 to DME mass ratio approximately 1:18). Stir at 23°C for 0.6 h to ensure complete dispersion and dissolution; then, raise the temperature of the reaction system to 60°C and stir at this temperature for 5 h.

[0060] Step 2: After the reaction is complete, the reaction solution is filtered to remove insoluble matter. The filtrate is then distilled under reduced pressure (65℃ / 35 mbar) to remove DME and the byproduct benzene, yielding crude sodium difluorodiphenylborate.

[0061] Step 3: Add tetrahydrofuran (tetrahydrofuran to crude product volume ratio approximately 2.5:1) to the crude product and dissolve it completely. Filter the solution to remove any small amount of insoluble impurities. Then, distill the filtrate under reduced pressure (88℃ / 45 mbar) to remove the tetrahydrofuran, yielding a solid.

[0062] Step 4: Dry the obtained solid at 55℃ and 1 mbar under vacuum for 28 h to obtain the product sodium difluorodiphenylborate.

[0063] Liquid nuclear magnetic resonance (NMR) was used to determine the structure and purity of the synthesized product, specifically sodium difluorodiphenylborate prepared in Example 1. 11 B. Liquid phase NMR spectrum as shown Figure 1 As shown, only sodium difluorodiphenylborate contains the characteristic peak of boron, with no impurity peaks, indicating that the final product has high purity and can be used as a raw material for secondary battery electrolyte.

[0064] Comparative Example 1 The only difference from Example 1 is that the amount of sodium hydrogen fluoride (NaHF2) used is 0.01 mol.

[0065] Comparative Example 2 The only difference from Example 1 is that the amount of sodium hydrogen fluoride (NaHF2) used is 0.5 mol.

[0066] Comparative Example 3 The only difference from Example 1 is that the mass ratio of NaBPh4 to acetonitrile is 1:5.

[0067] The performance of sodium difluorodiphenylborate provided in the embodiments and comparative examples of the present invention was tested using the following methods: (1) Yield: The formula for calculating yield is: ; (2) Purity: The purity of the product is determined by nuclear magnetic resonance hydrogen spectroscopy (NMR spectroscopy). 1 The H NMR was used for determination. In the measured spectrum, the peak areas of the H signals in the product and the whole spectrum (excluding internal standard DMSO and water) were integrated, and the integrated values ​​were A and B, respectively. The purity was calculated according to the following formula: product purity: (A / B) × 100%.

[0068] The performance test results are shown in Table 1.

[0069] Table 1: Yield, yield, and purity of sodium difluorodiphenylborate in Examples 1-5 The yields and purities of sodium difluorodiphenylborate obtained in Examples 1-5 are shown in Table 1.

[0070] The products prepared in Examples 1-5 all achieved high yields (>90%) and purity (>90%), indicating the high feasibility of the preparation method mentioned in this invention. Sodium difluorodiphenylborate prepared in Example 1... 11 B. Liquid phase NMR spectrum as shown Figure 1 As shown, 11The chemical shift in the B spectrum differs from that of NaBPh4 and shifts to a higher field, indicating the successful substitution of F. The splitting into doublets is related to the number of F substitutions, indicating that exactly two Fs successfully substituted -Ph.

[0071] Furthermore, the sodium difluorodiphenylborate prepared in this invention exhibits good thermal stability and solubility in organic electrolytes, as well as an excellent electrochemical stability window. These properties make it a promising candidate for application in sodium-ion battery electrolytes.

[0072] like Figure 2 As shown, the prepared sodium difluorodiphenylborate has a solubility of over 1 mol / L in common organic solvents, while the solubility of sodium tetrafluoroborate is less than 0.8 mol / L. This indicates that sodium difluorodiphenylborate has a higher solubility in organic solvents, which is more conducive to meeting the requirements of sodium-ion batteries for higher electrolyte conductivity.

[0073] In addition, sodium difluorodiphenylborate was used as the main salt to prepare the electrolyte. The preparation process was carried out in an argon-atmosphere glove box (moisture content <1 ppm). The electrolyte included sodium difluorodiphenylborate and a salt solvent. The concentration of sodium difluorodiphenylborate in the salt solvent was 1 mol / L, and the salt solvent used was diethylene glycol dimethyl ether. The above electrolyte was used in the fabrication of sodium / sodium iron pyrophosphate button batteries. The positive electrode used was sodium iron pyrophosphate (NFPP), the negative electrode was a sodium sheet, and the separator was made of glass fiber (Whatman GF / F).

[0074] The charge / discharge performance test results of the fabricated sodium / iron phosphate pyrophosphate coin cells are as follows: Figure 3 As shown, the prepared sodium difluorodiphenylborate can be stably charged and discharged within an electrochemical window of 2 to 3.6 V, while sodium tetraphenylborate decomposes upon charging to 3.2 V and cannot be used normally.

[0075] The cycle performance test results of the fabricated sodium / iron phosphate pyrophosphate coin cells are as follows: Figure 4 As shown, the first 3 weeks were charged and discharged at 0.2C, and then cycled at 1C current density and 25°C. The average coulombic efficiency was 99.58% over 100 cycles, and the capacity retention rate at the 100th cycle was 81.62%, which demonstrates excellent battery cycle performance.

[0076] The applicant declares that the present invention illustrates the sodium difluorodiphenylborate, its preparation method, and its application through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A sodium difluorodiphenylborate, characterized in that, Its molecular formula is NaB(Ph)2F2, and its structure is as follows: 。 2. The method for preparing sodium difluorodiphenylborate according to claim 1, characterized in that, The preparation method includes the following steps: Sodium tetraphenylborate reacts with a fluorine source to yield sodium difluorodiphenylborate.

3. The preparation method according to claim 2, characterized in that, The fluorine source is selected from any one or a combination of at least two of sodium fluoride, ammonium fluoride, or sodium bifluoride; Preferably, the molar ratio of sodium tetraphenylborate to fluorine source is 1:0.5 to 1:

4.

4. The preparation method according to claim 2 or 3, characterized in that, The reaction is carried out in the first organic solvent; Preferably, the first organic solvent is selected from one or a combination of at least two of methanol, ethanol, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ethylene glycol dimethyl ether, or diethylene glycol dimethyl ether; Preferably, the mass ratio of the organic solvent to sodium tetraphenylborate is 10:1 to 20:

1.

5. The preparation method according to any one of claims 2-4, characterized in that, Sodium tetraphenylborate, a fluorine source, and a first solvent were stirred at 20–30 °C for 0.5–1 h to ensure complete dispersion and dissolution; subsequently, the reaction system was stirred at 30–150 °C for 2–15 h.

6. The preparation method according to any one of claims 2-5, characterized in that, After the reaction is completed, the reaction solution is filtered to remove insoluble matter; the filtrate is subjected to a first vacuum distillation to obtain a crude product, a second organic solvent is added to the crude product to dissolve it, a solution is obtained, and then the insoluble matter is removed by filtration; the filtrate is subjected to a second vacuum distillation, and the obtained solid is dried to obtain the product sodium difluorodiphenylborate.

7. The preparation method according to claim 6, characterized in that, The second organic solvent is selected from one or a combination of at least two of acetonitrile, acetone, dichloromethane, tetrahydrofuran, or ethanol; Preferably, the first and second vacuum distillations are carried out independently at temperatures of 60-100°C and pressures of 20-50 mbar. Preferably, the condensation system maintains a condensation temperature of 5~15℃ during the first and second vacuum distillations.

8. The preparation method according to claim 6, characterized in that, The volume ratio of the second organic solvent to the crude product is 1:1 to 5:1; Preferably, the drying is vacuum drying; Preferably, the drying temperature is 50~80℃ and the drying time is 24~48 h; Preferably, the drying is carried out at a pressure of ≤10 mbar.

9. A sodium-ion battery electrolyte, characterized in that, The sodium-ion battery electrolyte includes sodium difluorodiphenylborate as described in claim 1.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the sodium-ion battery electrolyte as described in claim 9.

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