One-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts

Abstract

The application discloses a one-pot process for co-producing alkali metal tetrafluoroborate and difluorophosphate, comprising the following steps: reacting alkali metal oxide and / or carbonate, boron trifluoride gas and phosphorus pentafluoride gas in an ester solvent, and twice crystallizing the reaction product to obtain alkali metal tetrafluoroborate and difluorophosphate. The method is suitable for preparing lithium difluorophosphate and tetrafluoroborate, and is also suitable for preparing difluorophosphate and tetrafluoroborate of alkali metals such as sodium and potassium, and has very strong applicability and a wide application range. After reaction of the raw materials, all the raw materials are converted into the product, and no waste water, waste gas and waste residue are generated, so that the method is environment-friendly. The raw materials are metal oxides and / or carbonates, the raw materials are easy to obtain, and the cost is relatively low, so that the method is suitable for industrial popularization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of chemical synthesis, and particularly relates to a preparation method of tetrafluoroborate and difluorophosphate, and especially to a one-pot process for co-producing tetrafluoroborate and difluorophosphate. BACKGROUND

[0002] LiPF6 is the most widely used lithium salt in commercial applications. LiPF6-based electrolyte systems have good conductivity and can form stable solid electrolyte interface films (SEI films), etc. However, it also has the following shortcomings, such as complex preparation of battery-grade LiPF6, high price, excessive sensitivity to moisture, and instability to heat. LiBF4 is not sensitive to moisture in the environment, has good stability, low toxicity, and high safety, and LiBF4 can form a surface oxidation film on the surface of the electrode to prevent corrosion. Due to the above advantages of LiBF4, it has attracted widespread attention from researchers. The preparation methods of LiBF4 mainly include solid-gas contact method, non-aqueous solution method, aqueous solution method and ion exchange method. The solid-gas contact method is to synthesize with basic lithium salt as raw material at high temperature, which has high requirements for equipment, strict process control, great synthesis difficulty, low reaction efficiency and is difficult to realize large-scale production. The non-aqueous solution method is to form a suspension of lithium fluoride in an organic solvent, and react with BF3 to generate LiBF4, but this method has high requirements for equipment, and the raw materials are not easy to obtain, resulting in high production cost. The aqueous solution method uses boric acid and HF aqueous solution to react to prepare tetrafluoroboric acid, which is then reacted with carbonate to obtain lithium tetrafluoroborate solution, and then concentrated, crystallized and dried to obtain the product. However, in the preparation process using this method, lithium tetrafluoroborate exists in the form of monohydrate or trihydrate, the product has low purity, and it is difficult to dry and dehydrate. The ion exchange method uses the difference in solubility between potassium tetrafluoroborate and lithium tetrafluoroborate to obtain a crude product, which is further recrystallized to obtain a qualified product.

[0003] Lithium difluorophosphate (LiPO2F2) as an electrolyte additive can undergo redox reaction on the electrode surface before the electrolyte, generating a stable and dense protective film, avoiding the continuous decomposition of the electrolyte on the surface of the positive material, thereby improving the cycle performance of the lithium battery. The existing LiPO2F2 preparation processes mainly include: 1) LiPF6 and water are reacted to prepare LiPO2F2, but this process has many by-products, resulting in low product purity, and has high process control requirements; 2) using difluorophosphoric anhydride and lithium fluoride as raw materials to prepare LiPO2F2, but the raw material difluorophosphoric anhydride of this process is expensive, which is not conducive to industrial production; 3) using phosphoric anhydride and lithium fluoride as raw materials to prepare LiPO2F2, and the product of this process is a mixture of LiPO2F2 and LiPF6.

[0004] Currently, most of the research work is focused on optimizing the process of preparing lithium tetrafluoroborate or lithium difluorophosphate alone. Although the patent document CN107226463B discloses a combined preparation method of lithium difluorophosphate salt and lithium tetrafluoroborate salt, lithium hexafluorophosphate, lithium carbonate, boron trifluoride are reacted in the presence of a reaction solvent to prepare lithium difluorophosphate salt and lithium tetrafluoroborate salt, but using lithium hexafluorophosphate salt as raw material, the cost is high, and it is only limited to co-production of lithium difluorophosphate and lithium tetrafluoroborate, and the adaptability is narrow. SUMMARY

[0005] In view of the problems existing in the prior art, the purpose of the present application is to provide a one-pot process for co-producing alkali metal tetrafluoroborate salt and difluorophosphate salt with low cost.

[0006] To achieve the above-mentioned purpose, the present application provides the following specific technical solutions.

[0007] The one-pot process for co-producing alkali metal tetrafluoroborate salt and difluorophosphate salt comprises the following steps: reacting alkali metal oxide and / or carbonate, boron trifluoride gas and phosphorus pentafluoride gas in an organic solvent, and the reaction product is subjected to twice crystallization to obtain alkali metal tetrafluoroborate salt and difluorophosphate salt, respectively.

[0008] The reaction equation involved in the above preparation method is as follows:

[0009] PF5+2M2O+3BF3→3MBF4+MPO2F2

[0010] PF5+2M2CO3+3BF3→3MBF4+MPO2F2+2CO2

[0011] In the above reaction equation, M is an alkali metal element, preferably Li, Na or K.

[0012] In a further preferred embodiment, the reaction is carried out in a high-pressure reaction kettle.

[0013] In a further preferred embodiment, the organic solvent is an ester solvent; the amount of the ester solvent is 3-10 times, further preferably 3-6 times, of the theoretical mass yield of the tetrafluoroborate salt.

[0014] In a further preferred embodiment, the molar ratio of the amount of phosphorus pentafluoride to the amount of alkali metal oxide or carbonate is 1:1.5-2.5, further preferably 1:1.9-2.1; and the molar ratio of the amount of phosphorus pentafluoride to the amount of boron trifluoride is 1:2.5-3.6, further preferably 1:2.8-3.2.

[0015] In a further preferred embodiment, the alkali metal oxide and / or carbonate, the ester solvent and the boron trifluoride gas are mixed first, and then the phosphorus pentafluoride gas is introduced for reaction.

[0016] In a further preferred embodiment, the reaction temperature is 10-90℃ and the reaction time is 1-6h.

[0017] In a further preferred embodiment, the process further comprises the steps of filtering and concentrating the filtrate before the first and second crystallization.

[0018] In a further preferred embodiment, in the step of concentrating the filtrate, the filtrate is concentrated at 20-60℃ and -0.075 to -0.0095MPa for 1-6h.

[0019] In a further preferred embodiment, the first crystallization is carried out at -30 to -5℃ to obtain the alkali metal difluorophosphate salt, and the second crystallization is carried out using a poor solvent to obtain the alkali metal tetrafluoroborate salt. The poor solvent is at least one of dichloromethane, dichloroethane, toluene, dimethylbenzene, diethyl ether, and ethylene glycol dimethyl ether.

[0020] After the first crystallization, the filtrate is filtered, and the filter cake is the alkali metal difluorophosphate salt, and the filtrate is the alkali metal tetrafluoroborate ester solution. The tetrafluoroborate ester solution is concentrated, and the second crystallization is carried out, and the obtained crystals are filtered and dried to obtain the tetrafluoroborate salt solid.

[0021] In a further preferred embodiment, the poor solvent and the ester solvent in the mother liquor obtained from the second crystallization are separated, the ester solvent is recycled to the reaction, and the poor solvent is used for the second crystallization.

[0022] In a further preferred embodiment, the process further comprises the step of drying the filter cake.

[0023] In a further preferred embodiment, the drying process is carried out at 80-120℃ and -0.075 to -0.095MPa for 3-12h.

[0024] In a further preferred embodiment, the ester solvent is one or a combination of two or more of propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl acetate, and ethyl acetate.

[0025] Compared with the prior art, the present application has the following obvious beneficial effects:

[0026] (1) The present application reacts the alkali metal oxide and / or carbonate, boron trifluoride gas, and phosphorus pentafluoride gas in an ester solvent, and then crystallizes to obtain the alkali metal difluorophosphate salt and tetrafluoroborate salt in one pot, and the difluorophosphate salt and tetrafluoroborate salt can be completely separated to ensure the purity of each product.

[0027] (2) The method is not only suitable for the preparation of lithium difluorophosphate and tetrafluoroborate, but also suitable for the preparation of sodium, potassium and other alkali metal difluorophosphate and tetrafluoroborate, and has very strong applicability and wide application.

[0028] (3) Most of the raw materials in the present application are converted into products after reaction, and no waste water, waste gas and waste residue are generated, which is friendly to the environment.

[0029] (4) The raw materials used in the present application are metal oxides and / or carbonates, which are easy to obtain and have relatively low cost, and are suitable for industrialization.

[0030] (5) The process is simple and easy to operate and control. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The nuclear magnetic resonance spectrum of lithium tetrafluoroborate prepared in Example 1 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance B spectrum.

[0032] Figure 2 The nuclear magnetic resonance spectrum of lithium difluorophosphate prepared in Example 1 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance P spectrum.

[0033] Figure 3 The nuclear magnetic resonance spectrum of sodium tetrafluoroborate prepared in Example 2 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance B spectrum.

[0034] Figure 4 The nuclear magnetic resonance spectrum of sodium difluorophosphate prepared in Example 2 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance P spectrum.

[0035] Figure 5 The nuclear magnetic resonance spectrum of lithium tetrafluoroborate prepared in Example 3 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance B spectrum.

[0036] Figure 6 The nuclear magnetic resonance spectrum of lithium difluorophosphate prepared in Example 3 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance P spectrum.

[0037] Figure 7 The nuclear magnetic resonance spectrum of potassium tetrafluoroborate prepared in Example 4 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance B spectrum.

[0038] Figure 8 The nuclear magnetic resonance spectrum of potassium difluorophosphate prepared in Example 4 is shown in the figure, wherein figure (a) is the nuclear magnetic resonance F spectrum, and figure (b) is the nuclear magnetic resonance P spectrum. DETAILED DESCRIPTION

[0039] The inventors provide a one-pot process for co-production of alkali metal tetrafluoroborate and difluorophosphate, comprising the following steps: reacting alkali metal oxide and / or carbonate, boron trifluoride gas, phosphorus pentafluoride gas in an organic solvent, and the reaction product is subjected to twice crystallization to obtain alkali metal tetrafluoroborate and difluorophosphate, respectively.

[0040] The reaction equation involved in the above preparation method is as follows:

[0041] PF5+2M2O+3BF3→3MBF4+MPO2F2 (1)

[0042] PF5+2M2CO3+3BF3→3MBF4+MPO2F2+2CO2 (2)

[0043] The present application obtains two salts, tetrafluoroborate and difluorophosphate, through one-step reaction and simple separation, and the process is simple, efficient, and environmentally friendly, and is suitable for industrial production.

[0044] In the above reaction equation, M is an alkali metal element, preferably Li, Na, or K.

[0045] In the above preparation method, any equipment that can ensure the normal progress of the reaction can be used. In the embodiment of the present application, a high-pressure reaction kettle is used. The high-pressure reaction kettle can perform high-temperature and high-pressure reactions.

[0046] According to the reaction equations (1) and (2), the molar ratio of phosphorus pentafluoride, alkali metal oxide / carbonate, and boron trifluoride is 1:2:3. According to the actual reaction progress and reaction efficiency, in the present application, the molar ratio of the amount of phosphorus pentafluoride to alkali metal oxide or carbonate is 1:1.5-2.5, preferably 1:1.9-2.1; and the molar ratio of the amount of phosphorus pentafluoride to boron trifluoride is 1:2.5-3.6, preferably 1:2.8-3.2.

[0047] The reaction described in the present application is carried out in an organic solvent. The reaction product obtained from the reaction equations (1) and (2) is dissolved in an organic solvent, and then the product can be separated according to the difference in the crystallization process of the product in the organic solvent. In theory, any organic solvent that can ensure the normal progress of the reaction and effective separation of the product is suitable for the present application. In the specific embodiment of the present application, the organic solvent is further selected to be an ester solvent, and the ester solvent is further selected to be one or a combination of two or more of propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl acetate, and ethyl acetate. The reaction is carried out in an ester solvent, and the amount of solvent is 3-10 times, further preferably 3-6 times, the theoretical mass yield of tetrafluoroborate.

[0048] In the preferred embodiment of the present application, the alkali metal oxide and / or carbonate, the ester solvent and the boron trifluoride gas are mixed first, and then the phosphorus pentafluoride gas is introduced to react. The alkali metal oxide and / or carbonate has poor solubility in the ester solvent, and the introduction of the boron trifluoride gas increases the solubility to form a uniform solution, and then the phosphorus pentafluoride gas is introduced to form a gas-liquid reaction system, which promotes the reaction to occur, and generates tetrafluoroborate and difluorophosphate. The alkali metal oxide and / or carbonate, the ester solvent and the boron trifluoride gas can be added in sequence or simultaneously.

[0049] In the preferred embodiment of the present application, the reaction temperature is 10-90℃, further preferably 20-60℃, and more preferably 25-35℃. The reaction temperature can be ambient temperature, which is more conducive to industrial application. The reaction time can be appropriately adjusted by the person skilled in the art according to the reaction progress. The reaction time in the specific embodiment of the present application is 1-6h, which can be 1h, 2h, 3h, 4h, 5h, 6h, etc.

[0050] In the preferred embodiment of the present application, after the reaction is completed, to avoid that part of the alkali metal oxide and / or carbonate does not participate in the reaction, the reaction product is filtered to obtain a filtrate. And to ensure the efficiency of the first crystallization, the filtrate is further concentrated.

[0051] In the preferred embodiment of the present application, the filtrate of the reaction product before the first crystallization is concentrated at 20-60℃ and -0.075 to -0.0095MPa. During the concentration process, no solid phase is allowed to precipitate. If the concentration temperature is lower than 20℃ or the vacuum degree is lower than -0.075MPa, the concentration is not conducive, which is time-consuming and energy-consuming; if the concentration temperature is higher than 60℃ or the vacuum degree is higher than -0.0095MPa, the concentration is too fast, which is not conducive to crystallization, and the crystal particles precipitated during the crystallization process are not uniform, which affects the product quality. In the specific embodiment of the present application, the concentration temperature is further preferably 30-50℃. As for the concentration time, it can be adjusted adaptively according to the concentration of the reaction product. In the specific embodiment of the present application, the concentration time is 1-6h.

[0052] In the first crystallization process, the concentration of difluorophosphate and tetrafluoroborate in the solution and the crystallization temperature jointly affect the crystallization efficiency and purity of difluorophosphate. In the actual research and production process, the person skilled in the art can further determine the relationship between the concentration of the two products in the solution after the first concentration, the temperature and the crystallization separation process. In the specific embodiment of the present application, the filtrate is concentrated and crystallized at -30 to -5℃. Within this temperature range, the effective separation of the two salts can be achieved and the crystallization efficiency, yield and purity of difluorophosphate are ensured. In the preferred embodiment of the present application, the crystallization temperature is further preferably -30 to -20℃, and the crystallization effect is better. The crystallization time is adjusted according to the separation effect of difluorophosphate and tetrafluorophosphate in the crystallization process. The crystallization time of the present application is 0.5 to 5h.

[0053] In the preferred scheme of the present application, after the first crystallization is completed, filtration is performed, and the filter cake is an alkali metal difluorophosphate, and the filtrate is an alkali metal tetrafluoroborate ester solution. The tetrafluoroborate ester solution is further concentrated, and then crystallized by using a poor solvent to obtain a tetrafluoroborate solid phase. Specifically, the tetrafluoroborate ester solution is concentrated at 20 to 60℃ and -0.075 to -0.0095MPa for 1 to 6h, and then crystallized by using a poor solvent. The crystals obtained by crystallization are filtered and dried to obtain a lithium tetrafluoroborate solid. Further concentration increases the concentration of tetrafluoroborate in the solution, which is beneficial to improve the crystallization efficiency and product yield. By adding a poor solvent to reduce the solubility of tetrafluoroborate in the ester solvent, the purpose of crystallization and purification is achieved. Through a large number of screening experiments, in the specific embodiment of the present application, the poor solvent is at least one of dichloromethane, dichloroethane, toluene, xylene, diethyl ether and dimethyl ether, and the amount of the poor solvent is 3 to 10 times the mass of the solution to be treated. The time of the second crystallization can be adaptively adjusted according to the crystallization efficiency. In the specific embodiment of the present application, the time of the second crystallization is 1 to 4h.

[0054] The poor solvent and the ester solvent in the mother liquor after the second crystallization are separated, the ester solvent is recycled for the reaction process, and the poor solvent is used for the second crystallization.

[0055] In the preferred scheme of the present application, the step of drying the filter cake is further included. The drying process is carried out at 80 to 120℃ and -0.075 to -0.095MPa for 3 to 12h. The temperature in the drying process should not be too high to avoid decomposition of the product. Negative pressure drying can remove the ester solvent and at the same time achieve rapid drying.

[0056] The technical concept of the present application is further illustrated by specific specific embodiments. The person skilled in the art can understand the advantages of the present application from the disclosure of the specific embodiments provided in the specification. It should be understood that the present application can also be implemented and applied by other different specific embodiments.

[0057] Unless otherwise defined, all terms used in the description employ the same meaning as commonly understood by one of ordinary skill in the art. The professional terms used in the present specification are used only for the purpose of describing the specific embodiments and are not intended to limit the scope of protection of the present application.

[0058] Unless otherwise specified, the various materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0059] Example 1

[0060] In a high-pressure reactor, 78.3 g of lithium carbonate (1.06 mol), 101.7 g of boron trifluoride (1.5 mol) and 800 g of methyl ethyl carbonate were added, stirred for 1 h, and then 63.0 g of phosphorus pentafluoride (0.5 mol) was introduced. The reaction temperature was 40°C, and the reaction time was 4 h. After the reaction was completed, the temperature was lowered to 20°C, and after sufficient stirring, the filtrate was concentrated at 30°C and -0.095 MPa for 1.5 h. After concentration, the temperature was lowered to -30°C and crystallization was carried out for 2 h. After crystallization, filtration was carried out, and the filter cake was dried at 110°C and -0.095 MPa for 4 h to obtain 52.0 g of lithium difluorophosphate with a yield of 96.3% and a purity of 99.93%. The filtrate was 703 g of a lithium tetrafluoroborate-methyl ethyl carbonate solution (lithium tetrafluoroborate content 20%), which was concentrated at 60°C and -0.085 MPa for 3 h, and then 3 times the mass of the concentrated solution of the poor solvent dichloromethane was added and crystallization was carried out for 6 h. The crystals obtained by crystallization were filtered and dried to obtain 134.6 g of lithium tetrafluoroborate with a yield of 95.7% and a purity of 99.89%.

[0061] Figure 1 The nuclear magnetic resonance spectrum of lithium tetrafluoroborate prepared in Example 1 is shown in FIG. 1. According to the spectrum of FIG. 1, it can be determined that the substance obtained by secondary crystallization of Example 1 is lithium tetrafluoroborate. Figure 1

[0062] The nuclear magnetic resonance spectrum of lithium difluorophosphate prepared in Example 1 is shown in FIG. 2. Similarly, according to the spectrum of FIG. 2, it can be determined that the substance obtained by primary crystallization of Example 1 is lithium difluorophosphate. Figure 2 Figure 2

[0063] Example 2

[0064] ​​In a high-pressure reactor, 132.5 g of sodium carbonate (1.25 mol), 122.0 g of boron trifluoride (1.8 mol) and 1000 g of ethyl acetate were added, stirred for 2 h, then 63.0 g of phosphorus pentafluoride (0.5 mol) was introduced at a reaction temperature of 60°C and a reaction time of 2 h. After the reaction was completed, the temperature was lowered to 30°C, and after sufficient stirring, the filtrate was concentrated at 50°C and -0.095 MPa for 1 h. After concentration, the temperature was lowered to -20°C for crystallization for 3 h, and the filter cake was dried at 100°C and -0.095 MPa for 3 h to obtain 72.9 g of sodium difluorophosphate with a yield of 98.0% and a purity of 99.67%. The filtrate was 859.4 g of sodium tetrafluoroborate ethyl acetate solution (sodium tetrafluoroborate content 23%). The sodium tetrafluoroborate ethyl acetate solution was concentrated at 50°C and -0.095 MPa for 4 h, then 5 times the mass of poor solvent toluene and xylene was added to the concentrated solution for crystallization for 2 h, and the crystals were filtered and dried to obtain 189.6 g of sodium tetrafluoroborate solid with a yield of 95.9% and a purity of 99.44%.

[0065] Figure 3 The nuclear magnetic resonance spectrum of sodium tetrafluoroborate prepared in Example 2 was obtained. According to the spectrum of Figure 3 , it can be determined that the material obtained by secondary crystallization of Example 2 is sodium tetrafluoroborate.

[0066] Figure 4 The nuclear magnetic resonance spectrum of sodium difluorophosphate prepared in Example 2 was obtained. Similarly, according to the spectrum of Figure 4 , it can be determined that the material obtained by secondary crystallization of Example 2 is sodium difluorophosphate.

[0067] Example 3

[0068] In a high-pressure reactor, 33.5 g of lithium oxide (1.12 mol), 111.9 g of boron trifluoride (1.65 mol) and 1000 g of dimethyl carbonate were added, stirred for 1.5 h, then 69.3 g of phosphorus pentafluoride (0.55 mol) was introduced at a reaction temperature of 30°C and a reaction time of 3 h. After the reaction was completed, the temperature was lowered to 25°C, and after sufficient stirring, the filtrate was concentrated at 30°C and -0.095 MPa for 1 h. After concentration, the temperature was lowered to -30°C for crystallization for 2 h, and the filter cake was dried at 80°C and -0.095 MPa for 3 h to obtain 57.8 g of lithium difluorophosphate with a yield of 97.3% and a purity of 98.96%. The filtrate was 859 g of lithium tetrafluoroborate dimethyl carbonate solution (lithium tetrafluoroborate content 18%). The lithium tetrafluoroborate dimethyl carbonate solution was concentrated at 60°C and -0.095 MPa for 5 h, then 10 times the mass of poor solvent diethyl ether was added to the concentrated solution for crystallization for 1 h, and the crystals were filtered and dried to obtain 150.1 g of lithium tetrafluoroborate solid with a yield of 97.0% and a purity of 98.62%.

[0069] Figure 5 The NMR spectrum of lithium tetrafluoroborate prepared in Example 3 was measured. According to the spectrum of Figure 5 , it was determined that the substance obtained by the secondary crystallization of Example 3 was lithium tetrafluoroborate.

[0070] Figure 6 The NMR spectrum of lithium difluorophosphate prepared in Example 3 was measured. According to the spectrum of Figure 6 , it was determined that the substance obtained by the primary crystallization of Example 3 was sodium difluorophosphate.

[0071] Example 4

[0072] In a high-pressure reactor, 96.1 g of potassium oxide (1.02 mol), 101.7 g of boron trifluoride (1.5 mol) and 1000 g of propylene carbonate were added, and stirred for 1.5 h, and then 63.0 g of phosphorus pentafluoride (0.5 mol) was introduced at a reaction temperature of 20°C for 4 h. After the reaction was completed, the temperature was lowered to 30°C, and after sufficient stirring, the filtrate was concentrated at 45°C under -0.095 MPa for 3 h. After concentration, the temperature was lowered to -20°C, and crystallization was performed for 3 h, and the filter cake was dried at 70°C under -0.095 MPa for 4 h to obtain 68.5 g of potassium difluorophosphate at a yield of 97.8% and a purity of 99.42%. The filtrate was 900 g of a potassium tetrafluoroborate propylene carbonate solution (lithium tetrafluoroborate content: 21%). The potassium tetrafluoroborate propylene carbonate solution was concentrated at 50°C under -0.09 MPa for 4 h, and then 6 times the mass of the concentrated solution of the poor solvent ethylene glycol dimethyl ether was added, and crystallization was performed for 4 h. The crystallized potassium tetrafluoroborate was filtered and dried to obtain 181.8 g of potassium tetrafluoroborate at a yield of 96.2% and a purity of 99.31%.

[0073] Figure 7 The NMR spectrum of potassium tetrafluoroborate prepared in Example 4 was measured. According to the spectrum of Figure 7 , it was determined that the substance obtained by the secondary crystallization of Example 4 was potassium tetrafluoroborate.

[0074] Figure 8 The NMR spectrum of potassium difluorophosphate prepared in Example 4 was measured. According to the spectrum of Figure 8 , it was determined that the substance obtained by the primary crystallization of Example 4 was potassium difluorophosphate.

[0075] Example 5

[0076] In a high-pressure reactor, 44.3 g of lithium carbonate (0.6 mol), 14.9 g of lithium oxide (0.5 mol), 101.7 g of boron trifluoride (1.5 mol) and 800 g of methyl ethyl carbonate were added, stirred for 1 h, and then 63.0 g of phosphorus pentafluoride (0.5 mol) was introduced. The reaction temperature was 40°C, and the reaction time was 4 h. After the reaction was completed, the temperature was lowered to 20°C, and after sufficient stirring, the filtrate was concentrated at 30°C and -0.095 MPa for 1.5 h. After concentration, the temperature was lowered to -30°C for crystallization for 2 h. After crystallization was completed, filtration was performed, and the filter cake was dried at 110°C and -0.095 MPa for 4 h to obtain 46.1 g of lithium difluorophosphate, with a yield of 94.2% and a purity of 99.9%. The filtrate was 703 g of a lithium tetrafluoroborate-methyl ethyl carbonate solution (lithium tetrafluoroborate content: 20%), which was concentrated at 60°C and -0.085 MPa for 3 h. Then, 5 times the mass of the concentrated solution of a poor solvent, toluene, was added, and crystallization was performed for 2 h. The obtained crystals were filtered and dried to obtain 145.6 g of lithium tetrafluoroborate solid, with a yield of 95.1% and a purity of 99.5%.

[0077] The above only describes the preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of the present application.

Claims

1. A one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts, characterized in that, The process comprises the following steps: reacting alkali metal oxide and / or carbonate, boron trifluoride gas and phosphorus pentafluoride gas in an organic solvent, and twice crystallizing the reaction product to obtain alkali metal tetrafluoroborate and difluorophosphate, respectively.

2. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts according to claim 1, characterized in that, The alkali metal is Li, Na or K.

3. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts according to claim 1, characterized in that, The organic solvent is an ester solvent.

4. The one-pot process for co-producing alkali metal tetrafluoroborate and difluorophosphate according to claim 3, wherein the ester solvent is propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl acetate or ethyl acetate, or a combination of two or more thereof.

5. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts as claimed in claim 3, wherein, The amount of the ester solvent is 3-10 times the theoretical mass yield of the tetrafluoroborate; the molar ratio of the amount of phosphorus pentafluoride to the amount of alkali metal oxide and / or carbonate is 1:1.5-2.5; and the molar ratio of the amount of phosphorus pentafluoride to the amount of boron trifluoride is 1:2.5-3.

6.

6. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts according to any one of claims 1 to 5, characterized in that, The reaction temperature is 10-90℃ and the reaction time is 1-6h.

7. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts according to claim 1, characterized in that, The alkali metal difluorophosphate is obtained by first cooling and crystallization at a temperature of -30--5℃; and the alkali metal tetrafluoroborate is obtained by second crystallization using a poor solvent, which is at least one of dichloromethane, dichloroethane, toluene, xylene, diethyl ether or glycol dimethyl ether.

8. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts as claimed in claim 1 or 7, wherein, Before the first and second crystallization, the process further comprises the steps of filtering and concentrating the filtrate.

9. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts as claimed in claim 7, wherein, The poor solvent and the ester solvent in the mother liquor obtained in the second crystallization are separated, the ester solvent is recycled to the reaction, and the poor solvent is used for the second crystallization.

10. The one-pot process for the co-production of alkali metal tetrafluoroborate and difluorophosphate salts as claimed in claim 8, wherein, The process further comprises the step of drying the filter cake, and the drying process is carried out at 80-120℃ and -0.075--0.095MPa for 3-12h.

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