Preparation method of lithium tetrafluoroborate

Abstract

The invention provides a preparation method of lithium tetrafluoroborate, which comprises the following steps: S1, dissolving lithium alkoxide in a preset ratio in a corresponding alcohol solvent, then slowly adding a fluoboric acid solution, and continuously stirring to obtain a lithium tetrafluoroborate alcohol solution; s2, the lithium tetrafluoroborate alcoholic solution is filtered, evaporated, concentrated and crystallized to obtain a lithium tetrafluoroborate crude product, then a recrystallization solvent is added, the lithium tetrafluoroborate crude product is subjected to recrystallization, vacuum drying and other steps, and high-purity anhydrous lithium tetrafluoroborate is prepared. The lithium tetrafluoroborate prepared by the method is simple in technological process, convenient to operate and control, simple in post-treatment step, capable of being produced on a large scale and suitable for industrialization.

Description

Technical Field

[0001] The invention relates to the technical field of lithium salt preparation, and in particular to a method for preparing lithium tetrafluoroborate. Background Art

[0002] Among chemical energy storage batteries, lithium batteries have the best comprehensive performance, including energy density, power density, cycle life and safety. At present, lithium batteries have been maturely applied in various electronic products, power tools, transportation, energy storage and other fields. In the manufacture of lithium batteries, electrolyte is one of the key materials and is the medium for lithium ion migration and charge transfer. The most widely used electrolyte is LiPF 6 However, due to LiPF 6 The thermal stability is poor and decomposition reaction is prone to occur. A strong decomposition peak appears at 60°C. The side reaction products will destroy the SEI film on the electrode surface, dissolve the positive electrode active components, and cause the cycle capacity to decay. Therefore, long-term development requires better electrolytes to replace it.

[0003] At present, lithium tetrafluoroborate (LiBF 4 ) is considered to be one of the most promising lithium-ion battery electrolytes. Lithium tetrafluoroborate, with its advantages in thermal stability, temperature sensitivity and safety performance, meets the requirements of high-performance lithium-ion batteries and is expected to develop into a lithium salt widely used in lithium-ion batteries and energy storage fields, and has quickly become a hot spot for research and development. In addition, lithium tetrafluoroborate can also be used as an additive to broaden the operating temperature range of lithium-ion batteries and improve the high and low temperature discharge performance of batteries.

[0004] Currently LiBF 4 The main preparation methods are aqueous solution method and gas-solid reaction method. Among them, the aqueous solution method uses hydrofluoric acid, boric acid and lithium carbonate as reaction raw materials. This method has many steps, high process risks, and solid melting is prone to occur during the drying process, which affects the dehydration of the product and the product purity is low; while the gas-solid reaction is a reaction under high temperature conditions, which has high requirements for process equipment, low reaction efficiency, and is difficult to achieve large-scale production. Therefore, how to provide a preparation method for lithium tetrafluoroborate with simple steps, high synthesis yield and high purity is a technical problem that technicians in related fields urgently need to solve. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a method for preparing lithium tetrafluoroborate, which can solve the technical problems of the existing lithium tetrafluoroborate synthesis having many steps, complicated process and water molecule coating during drying.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing lithium tetrafluoroborate, comprising the following steps: S1, dissolving a preset proportion of lithium alcoholate in a corresponding alcohol solvent, then slowly adding a fluoroboric acid solution and stirring continuously to obtain a lithium tetrafluoroborate alcohol solution; S2, filtering, evaporating and concentrating the lithium tetrafluoroborate alcohol solution, and crystallizing to obtain a crude lithium tetrafluoroborate product, then adding a recrystallization solvent, and performing steps of recrystallization and vacuum drying on the crude lithium tetrafluoroborate product to prepare high-purity anhydrous lithium tetrafluoroborate.

[0007] Furthermore, in step S1, the molar ratio of the lithium alkoxide and the fluoroboric acid is added according to the ratio of Li to B element of 1:1 to 1.3, and the lithium alkoxide and the fluoroboric acid react with continuous stirring at a reaction temperature of 0 to 50°C and a reaction time of 1 to 8 hours.

[0008] Furthermore, in step S1, the lithium alcoholate is any one of lithium methanol, lithium ethoxide, lithium tert-butoxide, and lithium tert-amyl alcohol, and the alcohol solvent is any one of methanol, ethanol, tert-butanol, and tert-amyl alcohol.

[0009] Furthermore, in step S2, the evaporation concentration temperature is 50-100°C, the evaporation amount during the evaporation process reaches 70-95%, and the crystallization temperature is 10-30°C.

[0010] Furthermore, in step S2, the recrystallization solvent is any one of methanol, ethanol, tert-butanol, and tert-amyl alcohol, the evaporation amount during the recrystallization process is 60-85%, and the recrystallization temperature is 0-30°C.

[0011] Furthermore, in step S2, the vacuum drying temperature is 90 to 130°C, and the drying time is 4 to 24 hours.

[0012] The lithium tetrafluoroborate of the present invention is prepared by lithium alcoholate and fluoroboric acid. The reaction mechanism is that during the reaction of lithium alcoholate and fluoroboric acid, lithium ions combine with tetrafluoroborate ions to generate the target product lithium tetrafluoroborate, and at the same time generate another corresponding product alcohol. After filtering, concentrating, crystallizing, recrystallizing, vacuum drying and other steps, a high-purity lithium tetrafluoroborate product can be obtained, with high main content, qualified impurity ion content, moisture and free acid below 200ppm, and can be used for lithium battery electrolyte without further purification. Among them, the alcohol solvent is an alcohol reagent, such as methanol, ethanol, tert-butanol, etc., and lithium alcoholate is a lithium salt prepared and synthesized from metallic lithium and alcohol reagents, such as lithium methoxide, lithium ethoxide, lithium tert-butoxide, etc. In the reaction, by using lithium alcoholate as a reaction raw material, the reaction activity is strong, the reaction is sufficient, the raw material conversion rate is high, the product can be directly and quickly obtained, and it has the characteristics of mild reaction and high product purity. The reaction adopts the method of crystallization and recrystallization, which effectively improves the purity of the lithium tetrafluoroborate product. The alcohol solvent in the reaction process can be recycled and reused, which further saves production costs and is recyclable and environmentally friendly. The use of fluoroboric acid solution as a raw material reduces the difficulty of equipment, avoids the drawbacks of insufficient reaction and production danger of the gas-solid reaction system using gaseous boron trifluoride as a raw material, and makes the system operation simpler.

[0013] The lithium tetrafluoroborate and the preparation method thereof of the present invention have simple process, convenient operation and control, simple post-processing steps, mild reaction conditions, and the alcohol solvent can be recycled and reused. The invention has recyclability and environmental protection, can be produced on a large scale, and is suitable for industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The figure is a schematic diagram of the process for preparing lithium tetrafluoroborate. DETAILED DESCRIPTION

[0015] See also Figure 1 The present invention provides a method for preparing lithium tetrafluoroborate. In an alcohol solvent, lithium alcoholate and fluoroboric acid solution are added to react to obtain high-purity anhydrous lithium tetrafluoroborate.

[0016] Specifically, the present invention provides a method for preparing lithium tetrafluoroborate, comprising the following steps: S1, dissolving a preset proportion of lithium alcoholate in a corresponding alcohol solvent, then slowly adding a fluoroboric acid solution and stirring continuously to obtain a lithium tetrafluoroborate alcohol solution; S2, filtering, evaporating and concentrating the lithium tetrafluoroborate alcohol solution, and crystallizing to obtain a crude lithium tetrafluoroborate product, then adding a recrystallization solvent, and performing steps of recrystallization and vacuum drying on the crude lithium tetrafluoroborate product to prepare high-purity anhydrous lithium tetrafluoroborate.

[0017] Furthermore, in step S1, the molar ratio of the lithium alkoxide and the fluoroboric acid is added according to the ratio of Li to B element of 1:1 to 1.3, and the lithium alkoxide and the fluoroboric acid react with continuous stirring at a reaction temperature of 0 to 50°C and a reaction time of 1 to 8 hours.

[0018] Furthermore, in step S1, the lithium alcoholate is one of lithium methanolate, lithium ethoxide, lithium tert-butoxide or lithium tert-amyl alcoholate, and the alcohol solvent is one of methanol, ethanol, tert-butanol or tert-amyl alcohol.

[0019] Furthermore, in step S2, the evaporation concentration temperature is 50-100°C, the evaporation amount during the evaporation process reaches 70-95%, and the crystallization temperature is 10-30°C.

[0020] Furthermore, in step S2, the recrystallization solvent is one of methanol, ethanol, tert-butyl alcohol or tert-amyl alcohol, the evaporation amount during the recrystallization process is 60-85%, and the recrystallization temperature is 0-30°C.

[0021] Furthermore, in step S2, the vacuum drying temperature is 90 to 130°C, and the drying time is 4 to 24 hours. Example

[0022] Provided is a method for preparing lithium tetrafluoroborate, comprising the following specific steps: Step 1: Under the protection of inert gas, take 38g (1mol) lithium methoxide and dissolve it in 60mL methanol, slowly add 87.8g (1mol) fluoroboric acid, and react at 15℃ for 4 hours. Distill the reaction solution at 60℃ to evaporate 90% of the solvent, and place the remaining reaction solution at 0℃ for crystallization to obtain crude lithium tetrafluoroborate.

[0023] Step 2: Further, the solid-liquid mixture is filtered to obtain a wet product, methanol solvent is added to dissolve it again, and then distilled again. After 80% of the solvent is evaporated, it is placed at 0°C for crystallization to obtain lithium tetrafluoroborate. After filtering, it is placed at 100°C for drying in a vacuum environment for 10 hours to obtain a high-purity lithium tetrafluoroborate product with a content of 99.5%. Example

[0024] Provided is a method for preparing lithium tetrafluoroborate, comprising the following specific steps: Step 1: Under the protection of inert gas, take 38g (1mol) lithium methoxide and dissolve it in 60mL methanol, slowly add 96.6g (1.1mol) fluoroboric acid, and react at 15℃ for 4 hours. Distill the reaction solution at 60℃ to evaporate 90% of the solvent, and place the remaining reaction solution at 0℃ for crystallization to obtain crude lithium tetrafluoroborate.

[0025] Step 2: Further, the solid-liquid mixture is filtered to obtain a wet product, methanol solvent is added to dissolve it again, and then distilled again. After 80% of the solvent is evaporated, it is placed at 0°C for crystallization to obtain lithium tetrafluoroborate. After filtering, it is placed at 110°C for drying at a vacuum environment for 8 hours to obtain a high-purity lithium tetrafluoroborate product with a content of 99.8%. Example

[0026] Provided is a method for preparing lithium tetrafluoroborate, comprising the following specific steps: Step 1: Under the protection of inert gas, take 80g (1mol) of lithium tert-butoxide and dissolve it in 150mL of tert-butanol, slowly add 87.8g (1mol) of fluoroboric acid, and react at 30°C for 4 hours. Distill the reaction solution at 80°C to evaporate 80% of the solvent, and place the remaining reaction solution at 10°C for crystallization to obtain crude lithium tetrafluoroborate.

[0027] Step 2: Further, the solid-liquid mixture is filtered to obtain a wet product, tert-butanol solvent is added to dissolve it again, and then distilled again. After 70% of the solvent is evaporated, it is placed at 10°C for crystallization to obtain lithium tetrafluoroborate. After filtering, it is placed at 120°C for drying at a vacuum environment for 8 hours to obtain a high-purity lithium tetrafluoroborate product with a content of 99.3%. Example

[0028] Provided is a method for preparing lithium tetrafluoroborate, comprising the following specific steps: Step 1: Under the protection of inert gas, take 94g (1mol) of lithium tert-amyl alcohol and dissolve it in 200mL of tert-amyl alcohol, slowly add 114.1g (1.3mol) of fluoroboric acid, and react at 20°C for 3 hours. Distill the reaction solution at 100°C to evaporate 80% of the solvent, and place the remaining reaction solution at 20°C for crystallization to obtain crude lithium tetrafluoroborate.

[0029] Step 2: Further, the solid-liquid mixture is filtered to obtain a wet product, tert-amyl alcohol solvent is added to dissolve it again, and then distilled again. After 80% of the solvent is evaporated, it is placed at 20°C for crystallization to obtain lithium tetrafluoroborate. After filtering, it is placed at 130°C for drying for 4 hours under a vacuum environment to obtain a high-purity lithium tetrafluoroborate product with a content of 98.7%.

[0030] The lithium tetrafluoroborate of the present invention is prepared by lithium alcoholate and fluoroboric acid. The reaction mechanism is that during the reaction of lithium alcoholate and fluoroboric acid, lithium ions combine with tetrafluoroborate ions to generate the target product lithium tetrafluoroborate, and at the same time generate another corresponding product alcohol. After filtering, concentrating, crystallizing, recrystallizing, vacuum drying and other steps, a high-purity lithium tetrafluoroborate product can be obtained, with high main content, qualified impurity ion content, moisture and free acid below 200ppm, and can be used for lithium battery electrolyte without further purification. Among them, the alcohol solvent is an alcohol reagent, such as methanol, ethanol, tert-butanol, etc., and lithium alcoholate is a lithium salt prepared and synthesized from metallic lithium and alcohol reagents, such as lithium methoxide, lithium ethoxide, lithium tert-butoxide, etc. In the reaction, by using lithium alcoholate as a reaction raw material, the reaction activity is strong, the reaction is sufficient, the raw material conversion rate is high, the product can be directly and quickly obtained, and it has the characteristics of mild reaction and high product purity. The reaction adopts the method of crystallization and recrystallization, which effectively improves the purity of the lithium tetrafluoroborate product. The alcohol solvent in the reaction process can be recycled and reused, which further saves production costs and is recyclable and environmentally friendly. The use of fluoroboric acid solution as a raw material reduces the difficulty of equipment, avoids the drawbacks of insufficient reaction and production danger of the gas-solid reaction system using gaseous boron trifluoride as a raw material, and makes the system operation simpler.

[0031] The lithium tetrafluoroborate and the preparation method thereof of the present invention have simple process, convenient operation and control, simple post-processing steps, mild reaction conditions, and the alcohol solvent can be recycled and reused. The invention has recyclability and environmental protection, can be produced on a large scale, and is suitable for industrialization.

[0032] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not limited to the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing lithium tetrafluoroborate, characterized in that: In an alcohol solvent, lithium alcoholate and fluoroboric acid solution are added to react to prepare high-purity anhydrous lithium tetrafluoroborate.

2. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: The steps include: S1, dissolving a preset proportion of lithium alcoholate in a corresponding alcohol solvent, then slowly adding a fluoroboric acid solution and stirring continuously to obtain a lithium tetrafluoroborate alcohol solution; S2, filtering, evaporating and concentrating the lithium tetrafluoroborate alcohol solution, and crystallizing to obtain a crude lithium tetrafluoroborate product, then adding a recrystallization solvent, and performing steps of recrystallization and vacuum drying on the crude lithium tetrafluoroborate product to prepare high-purity anhydrous lithium tetrafluoroborate.

3. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: In step S1, the molar ratio of lithium alkoxide and fluoroboric acid is added according to the ratio of Li to B element of 1:1 to 1.3, and the lithium alkoxide and fluoroboric acid react with continuous stirring at a reaction temperature of 0 to 50° C. for 1 to 8 hours.

4. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: In step S1, the lithium alkoxide is at least one of lithium methoxide, lithium ethoxide, lithium tert-butoxide and lithium tert-amyl alcohol, and the alcohol solvent is at least one of methanol, ethanol, tert-butanol and tert-amyl alcohol.

5. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: In step S2, the evaporation concentration temperature is 50-100°C, the evaporation amount during the evaporation process reaches 70-95%, and the crystallization temperature is 10-30°C.

6. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: In step S2, the recrystallization solvent is at least one of methanol, ethanol, tert-butanol, and tert-amyl alcohol, the evaporation amount during the recrystallization process is 60-85%, and the recrystallization temperature is 0-30°C.

7. The method for preparing lithium tetrafluoroborate according to claim 1, characterized in that: In step S2, the vacuum drying temperature is 90-130°C, and the drying time is 4-24 hours.

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