Preparation method of sodium tetrafluoroborate and electrolyte

Abstract

The application discloses a preparation method of sodium tetrafluoroborate and an electrolyte, and the preparation method comprises the following steps: S1, preparation of an ionic raw material solution: mixing a boron source compound and a sodium source compound according to a stoichiometric ratio to obtain a raw material mixture, and dissolving the raw material mixture to form the ionic raw material solution; S2, preparation of sodium tetrafluoroborate crude product: performing a hydrothermal reaction on the ionic raw material solution obtained in the step S1, crystallizing, and vacuum drying to obtain the sodium tetrafluoroborate crude product; S3, purification of sodium tetrafluoroborate: dissolving and filtering the sodium tetrafluoroborate crude product obtained in the step S2, and crystallizing to obtain the final sodium tetrafluoroborate; and the sodium source compound is sodium fluoride and / or sodium hydrogen fluoride. The preparation method of the sodium tetrafluoroborate has the characteristics of low safety risk, green environmental protection, high product yield and strong process operability.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery electrolyte technology, specifically to a method for preparing sodium tetrafluoroborate and an electrolyte thereof. Background Technology

[0002] With the continuous development of society, people's demand for energy is increasing. However, traditional fossil fuel resources are gradually being depleted, and environmental pollution problems are becoming increasingly serious. Under these circumstances, new energy technologies have become the focus of attention. Battery technology, as an important component, has attracted much attention. Because batteries have many advantages such as high energy storage efficiency and cleanliness, they are highly favored.

[0003] Sodium tetrafluoroborate, as an important electrolyte, possesses high conductivity and low electrolyte viscosity, and can be used as a main salt or additive in sodium-ion battery electrolytes. It has wide applications in modern electrochemistry. Its emergence has greatly improved the performance and safety of sodium-ion batteries, playing a crucial role in promoting the development of new energy fields. Its main preparation methods are as follows: For example, the preparation method of sodium tetrafluoroborate in Chinese patent CN116588944A uses hydrofluoric acid, boric acid, and soda ash to prepare sodium tetrafluoroborate; and uses evaporation, dissolution with polar organic solvents, separation, filtration with a modified polytetrafluoroethylene membrane fine filter, and cooling crystallization to purify sodium tetrafluoroborate. This process route, involving the use of hydrofluoric acid, has the following drawbacks: High safety risks, as hydrofluoric acid is an extremely corrosive and toxic acid that easily corrodes skin, eyes, and respiratory mucous membranes; severe environmental pollution, as its strong corrosiveness and toxicity may generate toxic gases and waste liquids during use, causing environmental pollution; complex operation, as hydrofluoric acid reacts strongly with many substances, requiring extreme caution to ensure safety and precision; difficulty in controlling product purity, as the purity of the hydrofluoric acid reaction product can be affected by various factors such as reaction conditions, raw material quality, and operating techniques; and high equipment requirements, as hydrofluoric acid is a hazardous chemical requiring specialized operating equipment and safety measures, potentially leading to significant investment costs for equipment purchase and maintenance.

[0004] For example, Chinese patent CN116102029A describes a method for preparing battery-grade sodium tetrafluoroborate, which involves reacting boron trifluoride complexes with sodium fluoride in a methanol / ester mixed solvent. Molecular sieves are added to the reaction system simultaneously. After the reaction is complete, filtration, drying, and sieving are performed to obtain a high-purity sodium tetrafluoroborate product with low water content in one step. Another example is Chinese patent CN117303390A, which describes a method for preparing sodium tetrafluoroborate, which includes the following steps: passing boron trichloride gas into a sodium hydrogen fluoride solution, mixing, and concentrating to obtain the sodium tetrafluoroborate. A third example is Chinese patent CN102803142A, which describes a method for manufacturing tetrafluoroborate, which involves dissolving boron trifluoride in an organic solvent, reacting it with a metal fluoride to generate a tetrafluoroborate solution, and then returning the tetrafluoroborate solution to the first step to dissolve boron trifluoride gas in the tetrafluoroborate solution, thereby improving the production rate of tetrafluoroborate. All of the above synthetic methods involve the use of boron trichloride, which presents at least the following limitations: Safety hazards, as boron trichloride is highly toxic and corrosive, requiring strict control during operation; operational complexity, as gaseous reactions are generally more complex than liquid or solid reactions, necessitating strict operational control and precise techniques to ensure controlled reaction conditions and product purity; significant environmental impact, as boron trichloride is a commonly used reagent in organic synthesis, and its use may have negative environmental effects, including the emission of toxic gases and waste disposal; and difficulty in controlling product purity, as the purity of the product may be affected by various factors due to the special nature of the reaction, including reaction conditions, the purity of reactants, and operational techniques.

[0005] For example, the preparation method of lithium tetrafluoroborate in Chinese patent CN106082251A uses a two-step method. The first step synthesizes a chemically active weak acid lithium salt, which facilitates the second step of synthesizing lithium tetrafluoroborate. However, this synthetic route has the following drawbacks: the product purity is relatively low, as the weak acid lithium salt may introduce impurities, thereby reducing the purity of the obtained sodium tetrafluoroborate; the reaction selectivity is poor, as the weak acid lithium salt may have lower selectivity in the reaction compared to the strong acid lithium salt, potentially leading to the formation of other byproducts, thus affecting the reaction efficiency and product purity; and the operating conditions are demanding, as the synthesis of sodium tetrafluoroborate using the weak acid lithium salt may require stricter operating conditions and longer reaction times, increasing the complexity and time consumption of the process.

[0006] In summary, the existing synthesis process for sodium tetrafluoroborate needs improvement in terms of safety, environmental friendliness, product purity, and process operability. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing sodium tetrafluoroborate and an electrolyte, which has the characteristics of low safety risk, green and environmentally friendly, high product yield and strong process operability.

[0008] This invention can be achieved through the following technical solutions: This invention discloses a method for preparing sodium tetrafluoroborate, comprising the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. The sodium source compound is sodium fluoride and / or sodium hydrogen fluoride.

[0009] Further, in step S1, the molar ratio of B to Na in the boron source compound and the sodium source compound is 1:(2-4).

[0010] Furthermore, in step S1, the solvent for dissolving the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:(3-7). Under the condition that the raw materials can be completely dissolved, an appropriate reaction concentration can improve the product yield and reduce the by-products generated by excessive reaction time during the evaporation process.

[0011] Furthermore, in step S2, the hydrothermal reaction conditions are: temperature of 100-200 ℃ and reaction time of 1-20 h. Too long or too short a reaction time will increase the formation of byproducts.

[0012] Furthermore, in step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent. Both sodium tetrafluoroborate and impurities are readily soluble in water, and sodium tetrafluoroborate cannot be separated from impurities in an aqueous solvent.

[0013] Furthermore, the non-aqueous solvent is one or more of ethyl acetate, propylene carbonate, dimethyl carbonate, diethyl ether, ethylene glycol methyl ether, diethylene glycol dimethyl ether, and acetonitrile.

[0014] Furthermore, in step S2, the crystallization method is evaporation crystallization. The evaporation crystallization conditions are oil bath heating at 80-130 ℃. The appropriate evaporation temperature and evaporation time can quickly evaporate the water while avoiding the generation of more by-products through further reaction.

[0015] Furthermore, in step S3, the crystallization method is evaporation crystallization, and the evaporation crystallization conditions are vacuum distillation at 50-90℃. The vacuum distillation temperature will vary depending on the purification solvent.

[0016] Further, in step S1, the boron source compound is one or more of boric acid, anhydrous boric acid, boron oxide, sodium borate, and borax.

[0017] Another aspect of the present invention is to protect a sodium-ion battery electrolyte, comprising an electrolyte solvent and a sodium salt, wherein the sodium salt is sodium tetrafluoroborate prepared as described above.

[0018] Furthermore, in this electrolyte system, the solvent is one or more of trimethyl phosphate, triethyl phosphate, ethylene glycol dimethyl ether, ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0019] Furthermore, in this electrolyte system, the concentration of sodium tetrafluoroborate in the electrolyte solvent is 0.5 mol / L.

[0020] This invention discloses a method for preparing sodium tetrafluoroborate and an electrolyte, which have the following beneficial effects: First, the safety risk is low. This invention uses a boron-containing compound and a fluorine-containing sodium compound to carry out an ionic reaction in a liquid state, without the need to introduce highly toxic hydrofluoric acid or boron trifluoride, thus avoiding safety risks at the raw material level. Moreover, since the system does not involve the use of gases such as boron trifluoride, there is no high pressure risk, which effectively improves the safety of the overall process system.

[0021] Secondly, it is environmentally friendly. As mentioned above, the preparation process of this invention does not involve highly toxic hydrofluoric acid or boron trifluoride as raw materials or intermediate products, effectively avoiding the environmental impact of synthesizing such toxic components, ensuring the green and environmentally friendly nature of the process, and avoiding harm to operators.

[0022] Third, the product has high purity. This invention utilizes the high solubility of boric acid and fluorine-containing sodium compounds in solvents, and adopts the ionic reaction of boric and fluorine-containing compounds in solvents. The thorough mixing of the two compounds accelerates the reaction process, ensuring both high yield and product purity. Moreover, this synthesis process avoids the influence of the introduction of weak acid salts on the selectivity of the reaction system and side reactions, effectively ensuring the purity of the product.

[0023] Fourth, the process is highly operable. The entire reaction process, including the preparation of ionic raw material solutions, the preparation of crude sodium tetrafluoroborate, and the purification of crude sodium tetrafluoroborate, are all existing mature processes. They can all be controlled using existing mature equipment and operating procedures, without cumbersome and complex process control conditions, ensuring a high degree of process feasibility. Moreover, based on the non-toxic nature of the process, the solvents used in purification can also be recycled and reused, effectively reducing process costs. Attached Figure Description

[0024] Figure 1 Sodium tetrafluoroborate prepared in Example 319 F liquid phase NMR spectrum; Figure 2 The XRD pattern of sodium tetrafluoroborate prepared in Example 3; Figure 3 Electrochemical performance graph of sodium / vanadium phosphate button cell fabricated using Example 1. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0026] This invention discloses a method for preparing sodium tetrafluoroborate, comprising the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. The sodium source compound is sodium fluoride and / or sodium hydrogen fluoride.

[0027] Further, in step S1, the molar ratio of B to Na in the boron source compound and the sodium source compound is 1:(2-4).

[0028] Further, in step S1, the solvent for dissolving the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:(3-7).

[0029] Furthermore, in step S2, the hydrothermal reaction conditions are: temperature of 100-200 ℃ and reaction time of 1-20 h.

[0030] Furthermore, in step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent.

[0031] Furthermore, the non-aqueous solvent is one or more of ethyl acetate, propylene carbonate, dimethyl carbonate, diethyl ether, ethylene glycol methyl ether, diethylene glycol dimethyl ether, and acetonitrile.

[0032] Furthermore, in step S2, the crystallization method is evaporation crystallization, and the evaporation crystallization conditions are oil bath heating at 80-130 ℃.

[0033] Furthermore, in step S3, the crystallization method is evaporation crystallization, and the evaporation crystallization conditions are vacuum distillation at 50-90 °C.

[0034] Further, in step S1, the boron source compound is one or more of boric acid, anhydrous boric acid, boron oxide, sodium borate, and borax.

[0035] Another aspect of the present invention is to protect a sodium-ion battery electrolyte, comprising an electrolyte solvent and a sodium salt, wherein the sodium salt is sodium tetrafluoroborate prepared as described above.

[0036] In this invention, when boric acid is used as the boron source compound and sodium fluoride as the sodium source compound, the specific reaction process in steps S1 and S2 is as follows: H3BO3 + 2NaHF2 = NaBF4 + NaOH + 2H2O. After mixing in the ionic system, a hydrothermal reaction effectively accelerates the direct formation of the product, ensuring a high yield and purity.

[0037] Example 1 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: Prepare the raw materials according to the stoichiometric ratio of boric acid to sodium fluoride of 1:2. Add 3.86 g of boric acid and 7.74 g of sodium fluoride to a hydrothermal reactor, then add 50 mL of deionized water and stir to dissolve the raw materials. Then place the reactor in a 200 ℃ drying oven and react for 1 h. S2. Preparation of crude sodium tetrafluoroborate: The aqueous solution after the reaction is evaporated and crystallized to obtain a white solid, which is then ground into powder and dried in a vacuum drying oven at 100 ℃ to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Add crude sodium tetrafluoroborate to 500 mL of propylene carbonate, heat to 80 °C to dissolve, filter out insoluble substances, retain the liquid, rotary evaporate, and then place the obtained solid in a vacuum drying oven at 100 °C for 12 h to obtain about 3 g of sodium tetrafluoroborate, with a yield of about 43.8% and a purity of 99.1%. Example 2 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: Prepare the raw materials according to the stoichiometric ratio of boric acid to sodium fluoride of 1:2. Add 3.86 g of boric acid and 7.74 g of sodium fluoride to a hydrothermal reactor, then add 50 mL of deionized water and stir to dissolve the raw materials. Then place the reactor in a 180 ℃ forced-air drying oven and react for 7 h. S2. Preparation of crude sodium tetrafluoroborate: The aqueous solution after the reaction is evaporated and crystallized to obtain a white solid, which is then ground into powder and dried in a vacuum drying oven at 100 ℃ to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Add crude sodium tetrafluoroborate to 500 mL of ethylene glycol methyl ether, heat to 60 °C to dissolve, filter out insoluble substances, retain the liquid, evaporate by rotary evaporation, and then place the obtained solid in a vacuum drying oven at 100 °C for 12 h to obtain approximately 6 g of sodium tetrafluoroborate, with a yield of approximately 87.6% and a purity of 99.2%.

[0038] Example 3 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: Prepare the raw materials according to the stoichiometric ratio of boric acid to sodium fluoride of 1:2. Add 3.86 g of boric acid and 7.74 g of sodium fluoride to a hydrothermal reactor, then add 70 mL of deionized water and stir to dissolve the raw materials. Then place the reactor in a 200 ℃ forced-air drying oven and react for 20 h. S2. Preparation of crude sodium tetrafluoroborate: The aqueous solution after the reaction is evaporated and crystallized to obtain a white solid, which is then ground into powder and dried in a vacuum drying oven at 100 ℃ to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Crude sodium tetrafluoroborate was added to 500 mL of propylene carbonate, heated to 80 °C to dissolve, the insoluble substances were filtered out, the liquid was retained, and the mixture was rotary evaporated. The resulting solid was then placed in a vacuum drying oven at 100 °C and dried for 12 h to obtain approximately 6.8 g of sodium tetrafluoroborate, with a yield of approximately 99.3% and a purity of 99.8%.

[0039] Sodium tetrafluoroborate prepared in Example 3 19 The liquid phase NMR spectrum of F is as follows: Figure 1 As shown, only the characteristic peaks of fluorine in sodium tetrafluoroborate are present, with no impurity peaks, indicating that the final product has high purity. The XRD pattern is shown below. Figure 2 As shown, the diffraction peaks are sharp and there are no obvious impurity phase peaks, indicating that the obtained product is sodium tetrafluoroborate, which can be used as a raw material for secondary battery electrolyte.

[0040] Example 4 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: Prepare the raw materials according to the stoichiometric ratio of boric acid to sodium fluoride of 1:2. Add 3.86 g of boric acid and 7.74 g of sodium fluoride to a hydrothermal reactor, then add 70 mL of deionized water and stir to dissolve the raw materials. Then place the reactor in a 150 ℃ forced-air drying oven and react for 20 h. S2. Preparation of crude sodium tetrafluoroborate: The aqueous solution after the reaction is evaporated and crystallized to obtain a white solid, which is then ground into powder and dried in a vacuum drying oven at 100 ℃ to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Crude sodium tetrafluoroborate was added to 500 mL of diethylene glycol dimethyl ether, heated to 60 °C to dissolve, the insoluble substances were filtered out, the liquid was retained, and the solution was rotary evaporated. The resulting solid was then placed in a vacuum drying oven at 100 °C and dried for 12 h to obtain approximately 6.78 g of sodium tetrafluoroborate, with a yield of approximately 99% and a purity of 99.8%. Example 5 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. In this embodiment, the sodium source compound is sodium fluoride; the boron source compound is boric acid. The molar ratio of B to Na in the boron source compound and the sodium source compound is 1:4.

[0041] In step S1, the solvent used to dissolve the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:7.

[0042] In step S2, the hydrothermal reaction conditions are: temperature 200℃ and reaction time 10 h. The crystallization method is evaporative crystallization, which is carried out under oil bath heating at 80℃.

[0043] In step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent. The non-aqueous solvent is ethyl acetate. The crystallization method is evaporative crystallization, and the evaporative crystallization conditions are vacuum distillation at 90 °C.

[0044] Example 6 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. In this embodiment, the sodium source compound is sodium hydrogen fluoride; the boron source compound is anhydrous boric acid. The molar ratio of B to Na in the boron source compound and the sodium source compound is 1:3.

[0045] In step S1, the solvent used to dissolve the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:5.

[0046] In step S2, the hydrothermal reaction conditions are: temperature 150 ℃ and reaction time 1 h. The crystallization method is evaporative crystallization, which is carried out under oil bath heating at 130 ℃.

[0047] In step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent. The non-aqueous solvent is ethyl acetate or propylene carbonate. The crystallization method is evaporation crystallization, and the evaporation crystallization conditions are vacuum distillation at 70 °C.

[0048] Example 7 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. In this embodiment, the sodium source compounds are sodium fluoride and sodium hydrogen fluoride; the boron source compounds are boron oxide, sodium borate, and borax. The molar ratio of B to Na in the boron source compounds and sodium source compounds is 1:2.

[0049] In step S1, the solvent used to dissolve the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:3.

[0050] In step S2, the hydrothermal reaction conditions are: temperature 100 ℃ and reaction time 20 h. The crystallization method is evaporative crystallization, which is carried out under oil bath heating at 110 ℃.

[0051] In step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent. The non-aqueous solvents include dimethyl carbonate, diethyl ether, ethylene glycol methyl ether, diethylene glycol dimethyl ether, and acetonitrile. The crystallization method is evaporation crystallization, and the evaporation crystallization conditions are vacuum distillation at 50 °C.

[0052] Example 8 This embodiment relates to a method for preparing sodium tetrafluoroborate, including the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. In this embodiment, the sodium source compounds are sodium fluoride and sodium hydrogen fluoride; the boron source compounds are boric acid, anhydrous boric acid, boron oxide, and sodium borate. The molar ratio of B to Na in the boron source compounds and sodium source compounds is 1:3.

[0053] In step S1, the solvent used to dissolve the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:4.

[0054] In step S2, the hydrothermal reaction conditions are: temperature 130 ℃ and reaction time 12 h. The crystallization method is evaporative crystallization, which is carried out under oil bath heating at 100 ℃.

[0055] In step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent. The non-aqueous solvents include ethyl acetate, propylene carbonate, dimethyl carbonate, diethyl ether, and ethylene glycol methyl ether. The crystallization method is evaporation crystallization, and the evaporation crystallization conditions are vacuum distillation at 60 °C.

[0056] Application Example 1 The electrolyte was prepared using sodium tetrafluoroborate, the main salt prepared in Example 1, in an argon-atmosphere glove box (moisture content < 1 ppm). The electrolyte consisted of sodium tetrafluoroborate and a salt solvent. The concentration of sodium tetrafluoroborate in the salt solvent was 0.5 mol / L, and the salt solvent used was diethylene glycol dimethyl ether.

[0057] The above electrolyte was used in the fabrication of a sodium / vanadium phosphate coin cell. The positive electrode was sodium vanadium phosphate, the negative electrode was a sodium sheet, and the separator was made of glass fiber (Whatman GF / F). The cycle performance of the sodium / vanadium phosphate coin cell fabricated in this application example is as follows: Figure 3 The battery underwent a 0.5 C charge-discharge cycle in the first week, followed by a 1 C current density cycle. Over 200 weeks, the average coulombic efficiency was 99.7%, and the capacity retention rate reached 96% in the 200th week. This demonstrates excellent battery cycle performance.

[0058] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing sodium tetrafluoroborate, characterized in that... Includes the following steps: S1. Preparation of ionic raw material solution: The boron source compound and the sodium source compound are mixed in stoichiometric ratio to obtain a raw material mixture, which is then dissolved to form an ionic raw material solution; S2. Preparation of crude sodium tetrafluoroborate: The ionic raw material solution obtained in step S1 is subjected to hydrothermal reaction, crystallized, and vacuum dried to obtain crude sodium tetrafluoroborate. S3. Purification of sodium tetrafluoroborate: Dissolve and filter the crude sodium tetrafluoroborate obtained in step S2, and crystallize to obtain the final sodium tetrafluoroborate. The sodium source compound is sodium fluoride and / or sodium hydrogen fluoride.

2. The method for preparing sodium tetrafluoroborate according to claim 1, characterized in that: In step S1, the solvent used to dissolve the raw material mixture is deionized water, and the mass ratio of the raw material mixture to the solvent is 1:(3-7).

3. The method for preparing sodium tetrafluoroborate according to claim 1, characterized in that: In step S2, the conditions for the hydrothermal reaction are: temperature of 100-200 ℃ and reaction time of 1-20 h.

4. The method for preparing sodium tetrafluoroborate according to claim 1, characterized in that: In step S3, the solvent used to dissolve the crude sodium tetrafluoroborate is a non-aqueous solvent.

5. The method for preparing sodium tetrafluoroborate according to claim 4, characterized in that: The non-aqueous solvent is one or more of ethyl acetate, propylene carbonate, dimethyl carbonate, diethyl ether, ethylene glycol methyl ether, diethylene glycol dimethyl ether, and acetonitrile.

6. The method for preparing sodium tetrafluoroborate according to claim 1, characterized in that: In step S2, the crystallization method is evaporation crystallization, and the evaporation crystallization conditions are 80-130 ℃.

7. The method for preparing sodium tetrafluoroborate according to claim 1, characterized in that: In step S3, the crystallization method is evaporation crystallization, and the evaporation crystallization conditions are vacuum distillation at 50-90 °C.

8. The method for preparing sodium tetrafluoroborate according to claim 7, characterized in that: In step S1, the boron source compound is one or more of boric acid, boron oxide, sodium borate, and borax.

Images