Preparation method of lithium tetrafluoroborate

Abstract

The invention discloses a preparation method of lithium tetrafluoroborate. The preparation method of the lithium tetrafluoroborate comprises the following steps: (1) dissolving lithium borohydride in an organic solvent to obtain a lithium borohydride organic solution; (2) reacting the lithium borohydride organic solution with silicon tetrafluoride in a protective atmosphere to obtain a reaction solution after the reaction is finished; and (3) carrying out cooling crystallization on the reaction liquid, carrying out solid-liquid separation on crystal mush to obtain a solid phase, and drying the solid phase to obtain the lithium tetrafluoroborate. Compared with the traditional technology for preparing lithium tetrafluoroborate by using boron trifluoride and hydrogen fluoride as raw materials, the method provided by the invention has the advantages that the silicon tetrafluoride gas with lower danger is used as the fluorine source, the safety production risk can be reduced, the reaction is simple, and the obtained finished product has higher purity and is easy to purify subsequently.

Description

Technical Field

[0001] The invention belongs to the field of battery electrolyte additives, and in particular relates to a method for preparing lithium tetrafluoroborate. Background Art

[0002] At present, with the development of new energy technologies, lithium-ion batteries, as a new type of power energy, are widely used in digital products such as mobile phones, computers, and new energy vehicles, and have good development prospects. Lithium tetrafluoroborate (LiBF4), as a lithium salt additive, has good chemical stability and thermal stability, and is insensitive to moisture. At present, the preparation methods of lithium tetrafluoroborate mainly include aqueous phase method, solid-phase gas contact method and non-aqueous solution method. The aqueous phase method is prepared by using hydrofluoric acid, boric acid and lithium carbonate as raw materials to react in an aqueous medium. Although the process conditions of this method are relatively mild, the impurity content of the obtained product is high, so the purification process is relatively complicated; the solid-phase gas contact method is to use basic lithium salts as raw materials for synthesis under high temperature conditions. This method has high requirements for equipment and requires strict process control. It is difficult to synthesize, the reaction efficiency is low, and it is difficult to achieve large-scale production; the non-aqueous solution method is to form a suspension of lithium fluoride in an organic solvent, and then react with BF3 gas or its solution to generate LiBF4. However, this method is prone to side reactions during the reaction, which makes the product easy to form a complex with the solvent, thereby increasing the difficulty of purification.

[0003] In view of the fact that the current method has certain safety risks, and the conversion rate and product purity need to be improved, it is necessary to provide a preparation method with higher safety, simple operation, higher product conversion rate and higher purity. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing lithium tetrafluoroborate. The present invention utilizes silicon tetrafluoride as a fluorine source, adopts reducible lithium borohydride to provide a boron source and a lithium source, and performs reaction preparation under specific conditions. The present invention does not use highly dangerous hydrofluoric acid and boron trifluoride, thereby reducing the safety risks in the production process. In addition, the reaction operation is simple, and the purity and conversion efficiency of the obtained product are both high. In addition, silicon tetrafluoride as a fluorine source can be prepared by pyrolysis of fluorosilicates from a wide range of sources, which not only helps to reduce environmental pollution, but also recovers useful resources, reduces the environmental burden and economic pressure of enterprises, and therefore has important environmental, economic and social significance.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for preparing lithium tetrafluoroborate comprises the following steps: (1) dissolving lithium borohydride in an organic solvent to obtain a lithium borohydride organic solution; (2) reacting a lithium borohydride organic solution with silicon tetrafluoride under a protective atmosphere to obtain a reaction solution after the reaction is completed; (3) The reaction solution is cooled and crystallized, and the slurry is separated into a solid and liquid phase, and the obtained solid phase is dried to obtain lithium tetrafluoroborate.

[0006] Preferably, in step (1), the mass ratio of lithium borohydride to the organic solvent is 1:20-25.

[0007] Preferably, in step (1), the dissolution temperature is 15-55°C.

[0008] In some embodiments, lithium borohydride is added to an organic solvent and dissolved for 1 to 4 hours at a stirring rate of 15 to 30 r / min to obtain a lithium borohydride organic solution.

[0009] Preferably, in step (1), the organic solvent is dehydrated by passing through a molecular sieve before use to ensure that the water content of the organic solvent after the dehydration treatment is not higher than 100 ppm.

[0010] In some embodiments, the mass ratio of molecular sieve to organic solvent is 1:4-5, and the dehydration treatment time is 12-24 hours.

[0011] Preferably, in step (1), the organic solvent is at least one of diethyl ether, tetrahydrofuran and ethylene glycol dimethyl ether.

[0012] Preferably, in step (2), the protective atmosphere is nitrogen.

[0013] Preferably, in step (2), the molar ratio of silicon tetrafluoride to lithium borohydride in the lithium borohydride organic solution is 1.0-1.1:1.

[0014] Preferably, in step (2), the reaction temperature is 25-55° C., the reaction pressure is 5 KPa-60 KPa (G), and the reaction time is 24-30 h.

[0015] In some embodiments, in step (2), the lithium borohydride organic solution is put into a reactor that has been replaced with nitrogen, and then silicon tetrafluoride is put into the reactor to react.

[0016] Preferably, in step (3), the cooling rate of the cooling crystallization is 1 to 2°C / h, and the final temperature is -20 to -10°C.

[0017] Preferably, in step (3), the drying pressure is -0.08 to -0.095 MPa (G), the drying temperature is 80 to 120° C., and the drying time is 2 to 4 hours.

[0018] Preferably, in step (3), after the solid-liquid separation of the slurry, the obtained liquid phase is dehydrated and then recycled to step (1) to be circulated as an organic solvent.

[0019] Compared with the prior art, the beneficial effects of the present invention include: (1) The present invention prepares a crude product with higher purity, which reduces the technical difficulty and purification cost of the subsequent purification process.

[0020] (2) The fluorine source of the present invention uses silicon tetrafluoride gas obtained by thermal decomposition of fluorosilicate, which replaces more harmful hydrogen fluoride and boron trifluoride, thereby reducing production safety risks and helping to reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a comparison of the XRD diffraction spectra of the finished product obtained in Example 1 and a lithium tetrafluoroborate standard sample.

[0022] Figure 2 The figure is a comparison of the XRD diffraction spectra of the finished product obtained in Example 2 and a lithium tetrafluoroborate standard sample.

[0023] Figure 3 The figure is a comparison chart of the XRD diffraction spectra of the finished product obtained in Example 3 and a lithium tetrafluoroborate standard sample. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] The molecular sieve used in the embodiment is 3A molecular sieve purchased from China National Pharmaceutical Group Corporation.

[0026] Example 1 A method for preparing lithium tetrafluoroborate, the specific steps are as follows: (1) Weigh 600 g of analytically pure ethylene glycol dimethyl ether, add 150 g of molecular sieve and leave for 16 hours, and measure the water content to be 73 ppm, thereby obtaining dehydrated ethylene glycol dimethyl ether; add 30 g of lithium borohydride solid to the dehydrated ethylene glycol dimethyl ether, maintain the temperature at 55° C., and dissolve at a stirring rate of 20 r / min for 1.5 hours to obtain a lithium borohydride organic solution; (2) placing the lithium borohydride organic solution in a gas-liquid reactor, keeping the equipment temperature at 55°C, stirring at a speed of 30 r / min, introducing high-purity nitrogen for replacement for 1 hour, and then introducing 155 g of silicon tetrafluoride gas for reaction at a ventilation rate of 20 mL / min for 28 hours. The reaction pressure is 5-15 KPa. After the reaction is completed, introducing high-purity nitrogen for replacement for another 1 hour to obtain a reaction liquid; (3) The reaction solution is placed in a crystallizer, and a refrigerant is introduced to cool and crystallize. The initial temperature of the refrigerant is 20°C, the cooling rate is 1.5°C / h, and the final temperature is -20°C. High-purity nitrogen is then introduced for pressure filtration at a gas pressure of 0.25 MPa to obtain a filtrate and a filter residue. The filtrate is dehydrated through a molecular sieve and then reused in step (1) as an organic solvent. The filter residue is dried at 120°C to obtain 123.1 g of a finished product.

[0027] The finished product described in Example 1 was subjected to XRD diffraction analysis, and the analysis results are as follows Figure 1 As shown. Figure 1 It can be known that the peak shape of the product spectrum is basically the same as that of the standard sample, indicating that the finished product has a high content. After analysis, the main content is 99.3% and the yield is 94.66%. It should be noted that the main content is determined by a chemical titration method. The yield refers to the ratio of the mass of lithium tetrafluoroborate actually obtained after analyzing the reaction solution to the theoretical amount calculated according to the raw material feed amount.

[0028] Example 2 A method for preparing lithium tetrafluoroborate, the specific steps are as follows: (1) Weigh 600 g of tetrahydrofuran solvent, add 120 g of molecular sieve and leave for 24 hours, measure the water content of the solvent to be 57 ppm, and obtain dehydrated tetrahydrofuran; add 30 g of lithium borohydride solid to the dehydrated tetrahydrofuran, maintain the temperature at 35° C., and dissolve the solvent at a stirring rate of 30 r / min for 2 hours to obtain a lithium borohydride organic solution; (2) placing the lithium borohydride organic solution in a gas-liquid reactor, keeping the equipment temperature at 45°C, stirring at a speed of 35 r / min, introducing high-purity nitrogen for replacement for 1.5 hours, and then introducing 150 g of silicon tetrafluoride gas for reaction at a ventilation speed of 18 mL / min for 30 hours. The reaction pressure is 5-20 KPa. After the reaction is completed, introducing high-purity nitrogen for replacement for another 1.5 hours to obtain a reaction liquid; (3) The reaction solution is placed in a crystallizer, and a refrigerant is introduced to cool and crystallize. The initial temperature of the refrigerant is 20°C, the cooling rate is 1°C / h, and the final temperature is -20°C. High-purity nitrogen is then introduced for pressure filtration at a gas pressure of 0.35 MPa to obtain a filtrate and a filter residue. The filtrate is dehydrated through a molecular sieve and then reused in step (1) as an organic solvent. The filter residue is dried at 100°C to obtain 119.5 g of a finished product.

[0029] The finished product described in Example 2 was subjected to XRD diffraction analysis, and the analysis results are as follows Figure 2 As shown. Figure 2 It can be seen that the spectrum of the product has a very small amount of impurity peaks compared with the standard sample, indicating that there are a certain amount of impurities in the finished product. After analysis, the main content is 99.0% and the yield is 91.71%.

[0030] Example 3 A method for preparing lithium tetrafluoroborate, the specific steps are as follows: (1) Weigh 600.5 g of ether solvent, add 135 g of molecular sieve and leave for 20 h, measure the water content to be 49 ppm, and obtain dehydrated ether; add 30 g of lithium borohydride solid to the dehydrated ether, maintain the temperature at 15° C., and dissolve at a stirring rate of 15 r / min for 42 h to obtain a lithium borohydride organic solution; (2) placing the lithium borohydride organic solution in a gas-liquid reactor, keeping the equipment temperature at 25°C, stirring at a speed of 40 r / min, introducing high-purity nitrogen for replacement for 30 minutes, and then introducing 145 g of silicon tetrafluoride gas for reaction at a ventilation rate of 21.5 mL / min for 24 hours. The reaction pressure is 10-25 KPa. After the reaction is completed, introducing high-purity nitrogen for replacement for another 30 minutes to obtain a reaction liquid; (3) The reaction solution was placed in a crystallizer, and a refrigerant was introduced to cool and crystallize. The initial temperature of the refrigerant was 20°C, the cooling rate was 1.2°C / h, and the final temperature was -20°C. High-purity nitrogen was then introduced for pressure filtration at a gas pressure of 0.40 MPa to obtain a filtrate and a filter residue. The filtrate was dehydrated by a molecular sieve and then reused in step (1) as an organic solvent. The filter residue was dried at 80°C to obtain 114.1 g of a finished product.

[0031] The finished product described in Example 3 was subjected to XRD diffraction analysis, and the analysis results are as follows Figure 3 As shown. Figure 3 It can be seen that the spectrum of the product has a very small amount of impurity peaks compared with the standard sample, indicating that there are a certain amount of impurities in the finished product. After analysis, the main content is 98.5% and the yield is 87.30%.

[0032] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing lithium tetrafluoroborate, characterized in that: The steps include: (1) dissolving lithium borohydride in an organic solvent to obtain a lithium borohydride organic solution; (2) reacting a lithium borohydride organic solution with silicon tetrafluoride under a protective atmosphere to obtain a reaction solution after the reaction is completed; (3) The reaction solution is cooled and crystallized, and the slurry is subjected to solid-liquid separation, and the obtained solid phase is then dried to obtain the lithium tetrafluoroborate.

2. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The mass ratio of lithium borohydride to organic solvent in step (1) is 1:20-25.

3. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The dissolving temperature in step (1) is 15-55°C.

4. The method for preparing lithium tetrafluoroborate according to any one of claims 1 to 3, characterized in that: The organic solvent in step (1) is dehydrated by passing through a molecular sieve before use to ensure that the water content of the organic solvent after the dehydration treatment is not higher than 100 ppm.

5. The method for preparing lithium tetrafluoroborate according to claim 4, characterized in that: The organic solvent in step (1) is at least one of diethyl ether, tetrahydrofuran and ethylene glycol dimethyl ether; The protective atmosphere in step (2) is nitrogen.

6. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The molar ratio of silicon tetrafluoride to lithium borohydride in the lithium borohydride organic solution in step (2) is 1.0-1.1:

1.

7. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The reaction temperature of step (2) is 25-55°C, the reaction pressure is 5KPa-60KPa (G), and the reaction time is 24-30h.

8. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The cooling rate of the cooling crystallization in step (3) is 1 to 2°C / h, and the final temperature is -20 to -10°C.

9. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The drying pressure in step (3) is -0.08 to -0.095 MPa (G), the drying temperature is 80 to 120° C., and the drying time is 2 to 4 hours.

10. The method for preparing lithium tetrafluoroborate according to any one of claims 1 to 3, characterized in that: After the solid-liquid separation of the slurry in step (3), the obtained liquid phase is dehydrated and then recycled to step (1) for recycling as an organic solvent.

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