Preparation method of battery-grade lithium tetrafluoroborate and lithium ion battery

Abstract

To overcome the problems existing in the preparation of lithium tetrafluoroborate using the current aqueous solution method, this invention provides a method for preparing battery-grade lithium tetrafluoroborate and a lithium-ion battery. The preparation method includes the following steps: adding and dispersing boric acid and lithium salt in an alcohol solvent, while simultaneously adding hydrofluoric acid dropwise to react and obtain a reaction solution containing lithium tetrafluoroborate. The reaction solution is then subjected to azeotropic removal of water using the alcohol solvent to obtain crude lithium tetrafluoroborate. The crude product is then purified by removing the alcohol solvent to obtain battery-grade lithium tetrafluoroborate. This invention also provides the application of the above preparation method in lithium-ion battery electrolytes. The method for preparing lithium tetrafluoroborate provided by this invention introduces an alcohol solvent during the reaction process, which reduces the complexation of the product with water in the traditional aqueous solution method. This significantly improves the yield and purity of the obtained lithium tetrafluoroborate, and simultaneously meets the stricter requirements for the content of impurities such as water, acid, and alcohol in battery-grade lithium tetrafluoroborate, thus facilitating industrial application.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium battery electrolytes, specifically relating to a method for preparing battery-grade lithium tetrafluoroborate and a lithium-ion battery. Background Technology

[0002] Lithium tetrafluoroborate possesses high thermal stability, insensitivity to moisture, and low toxicity, effectively preventing electrode corrosion. It can broaden the operating temperature range of lithium-ion batteries and improve their high and low temperature discharge performance, making it widely used in lithium battery electrolytes. As a battery additive, battery-grade lithium tetrafluoroborate products generally need to meet requirements such as water content ≤150ppm, acid content ≤50ppm, and main content ≥99.5%. Strict control of residual methanol and ethanol (≤100ppm) is also required, and it should be used in conjunction with carbonate solvents.

[0003] Common methods for preparing lithium tetrafluoroborate include the aqueous solution method, the solid-gas contact method, and the organic solvent method. The aqueous solution method involves reacting tetrafluoroboric acid (also known as fluoroboric acid, typically obtained by reacting hydrogen fluoride with boric acid) with a lithium source in an aqueous phase. By controlling the feed ratio, an aqueous solution of lithium tetrafluoroborate is obtained, which is then dehydrated to finally obtain lithium tetrafluoroborate. The solid-gas contact method uses boron trifluoride and lithium fluoride as raw materials. Lithium fluoride is often complexed with anhydrous hydrogen fluoride to increase its solubility. Boron trifluoride gas is then introduced into the solution, and the final product is obtained through filtration, degassing, concentration, crystallization, and drying to obtain solid lithium tetrafluoroborate. The organic solvent method involves complexing boron trifluoride with diethyl ether, using the ether as a carrier, and then adding lithium fluoride to react under reflux. After drying, solid lithium tetrafluoroborate is obtained. The reaction mechanism is similar to that of the solid-gas contact method.

[0004] Analysis of the above methods reveals that the aqueous solution method has the advantage of inexpensive raw materials, minimal organic solvent pollution, and the use of water as a green solvent. Its challenge lies in the fact that lithium tetrafluoroborate often exists in the form of water of crystallization, increasing the difficulty of drying and making it difficult to obtain products with water content meeting battery-grade standards. The solid-gas contact method suffers from the disadvantages of high-temperature synthesis, requiring sophisticated equipment, strict process control, high synthesis difficulty, and low reaction efficiency, thus hindering large-scale production. The non-aqueous solution method, due to the use of organic solvents, generates side reactions during the reaction process, affecting product quality. Furthermore, its high production cost, high synthesis difficulty, and high energy consumption for organic solvent recovery limit its application.

[0005] Both CN 115385352A and CN 117945437A employ an aqueous solution method to prepare lithium tetrafluoroborate in steps. In the crude product purification process, ethanol is used for crystallization to remove water, resulting in lithium tetrafluoroborate products with low water content. However, the presence of residual alcohol prevents the production of products that meet battery-grade requirements, and the low product yield is not conducive to industrial applications.

[0006] CN 102030339 A also employs a stepwise aqueous solution method, heating the lithium tetrafluoroborate at 95°C with an infrared lamp to obtain hydrated lithium tetrafluoroborate, then dissolving it in ethanol, evaporating it with an infrared lamp to remove water, and neutralizing it with alkali to remove acid, yielding anhydrous lithium tetrafluoroborate. This method suffers from high energy consumption, severe product decomposition, and numerous byproducts. Furthermore, the product obtained by this method still has a high water content (0.02%), and also suffers from residual alcohol.

[0007] Although the aqueous solution method for manufacturing lithium tetrafluoroborate has been greatly improved and has initially met the requirements for electrolyte production, with the increasing demands for lithium-ion battery electrolytes, there is a desire to use anhydrous lithium tetrafluoroborate with a water content of less than 0.005% (50ppm), while also requiring acid content, main content, and alcohol residue to meet the requirements for battery-grade lithium tetrafluoroborate products. Therefore, the aqueous solution method still needs improvement. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing battery-grade lithium tetrafluoroborate and a lithium-ion battery. Based on the aqueous solution method, this method not only removes a large amount of water from the aqueous system in an economical and efficient manner, but also ensures that the product quality meets the requirements of battery grade.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0010] On one hand, the present invention provides a method for preparing battery-grade lithium tetrafluoroborate, comprising the following steps:

[0011] (S1) Boric acid and lithium salt are added and dispersed in an alcohol solvent, and hydrofluoric acid is added dropwise to react and obtain a reaction solution containing lithium tetrafluoroborate.

[0012] (S2) The crude lithium tetrafluoroborate was obtained by azeotropic distillation of the reaction solution with an alcohol solvent to remove water.

[0013] (S3) Crude lithium tetrafluoroborate was purified by removing alcohol solvent to obtain battery-grade lithium tetrafluoroborate.

[0014] The reaction equations involved are as follows:

[0015] HF + H3BO3 + LiX → LiBF4

[0016] Preferably, in step (S1), the molar ratio of the boric acid, the lithium salt, the alcohol solvent, and the HF in the hydrofluoric acid is 1:(0.5-2):(0.5-4):(2-6).

[0017] Preferably, the lithium salt in step (S1) is selected from one or more combinations of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium fluoride, and lithium fluoride.

[0018] The alcohol solvents mentioned in steps (S1) and (S2) are independently selected from one or more combinations of methanol, ethanol, n-propanol, isopropanol, tert-butanol, and n-butanol;

[0019] The alcohol removal solvent mentioned in step (S3) is a carbonate solvent.

[0020] Preferably, the carbonate solvent is dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, or propylene carbonate.

[0021] Preferably, the concentration of the hydrofluoric acid is 10-70%, more preferably 30-50%.

[0022] Preferably, in step (S2), the alcohol solvent content in the crude lithium tetrafluoroborate is less than 5 wt%, more preferably less than 2 wt%.

[0023] Preferably, in step (S3), the amount of alcohol removal solvent used is 1 to 10 times the mass of the crude lithium tetrafluoroborate, more preferably 2 to 5 times.

[0024] Preferably, the method for preparing battery-grade lithium tetrafluoroborate provided by the present invention includes the following steps:

[0025] (S1) Add boric acid and lithium salt to and disperse them in an alcohol solvent, and simultaneously add hydrofluoric acid dropwise to carry out the reaction. Use a water bath to control the dropwise temperature of hydrofluoric acid at 10-50°C and the reaction temperature at 20-60°C. The reaction time is 1-4 hours to obtain a reaction solution containing lithium tetrafluoroborate.

[0026] (S2) First, the reaction solution is concentrated by vacuum distillation to remove water, and the concentration is controlled to be 40-80%, more preferably 65-80%, to obtain a concentrate; then, an alcohol solvent is added to the concentrate and vacuum distillation is continued to obtain crude lithium tetrafluoroborate.

[0027] (S3) Add alcohol-free solvent to crude lithium tetrafluoroborate, dissolve and filter, and distill the filtrate under reduced pressure to obtain battery-grade lithium tetrafluoroborate.

[0028] Preferably, the vacuum distillation conditions for the reaction solution to the concentrate, the concentrate to the crude product, and the crude product to battery-grade lithium tetrafluoroborate are all 1-30 mbar vacuum and 40-110°C temperature.

[0029] Preferably, the total amount of alcohol solvent added to the concentrate is 1 to 10 times the mass of the concentrate, more preferably 2 to 5 times.

[0030] On the other hand, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises lithium tetrafluoroborate prepared by the preparation method described above.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1) The preparation method of the present invention combines one-pot reaction, alcohol solvent azeotropic water removal and alcohol removal drying processes, which reduces the number of feeding steps and equipment, and has the effects of simplifying the process, making the process convenient, safe and environmentally friendly.

[0033] 2) In this invention, an alcohol solvent is introduced during the reaction process. The water generated in the reaction is preferentially dissolved in the alcohol solvent, which can reduce the contact between the product and water in the traditional aqueous solution method, reduce the formation of hydrates, reduce the occurrence of decomposition, thereby reducing the energy consumption for water removal and increasing the product yield.

[0034] 3) This invention uses an alcohol solvent azeotropic water removal method, which utilizes the alcohol solvent and water to form an azeotropic mixture to remove water. First, the water removal effect is good; second, the process and equipment are simple and easy to control; and third, the organic solvent produced by the azeotropic reaction can be recycled and reused without being consumed.

[0035] 4) The prepared lithium tetrafluoroborate has a product yield of over 90%, a main content of over 99.5%, a water content of ≤50ppm, an acid content of ≤50ppm, and an alcohol residue of ≤50ppm. It can simultaneously meet the stricter requirements for the content of impurities such as water, acid, and alcohol in battery-grade lithium tetrafluoroborate. The overall process conditions are mild and easy to industrialize. Detailed Implementation

[0036] To make the technical problems solved, technical solutions, and beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described herein are only some, not all, embodiments of the present invention, and are merely illustrative and not intended to limit the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0037] It should be noted that, since hydrofluoric acid is an aqueous solution of HF, the amount of hydrofluoric acid added in this invention is calculated based on the number of moles of HF in the hydrofluoric acid. The concentrations in this invention are mass percentage concentrations; for example, the concentration of hydrofluoric acid is the percentage of the mass of HF in the hydrofluoric acid to the mass of its aqueous solution. The water content of the alcohol solvent used in this invention has little impact; generally, ≤5% is sufficient.

[0038] On one hand, the present invention provides a method for preparing battery-grade lithium tetrafluoroborate, comprising the following steps:

[0039] (S1) Boric acid and lithium salt are added and dispersed in an alcohol solvent, and hydrofluoric acid is added dropwise to react and obtain a reaction solution containing lithium tetrafluoroborate.

[0040] (S2) The crude lithium tetrafluoroborate was obtained by azeotropic distillation of the reaction solution with an alcohol solvent to remove water.

[0041] (S3) Crude lithium tetrafluoroborate was purified by removing alcohol solvent to obtain battery-grade lithium tetrafluoroborate.

[0042] In some embodiments, in step (S1), the molar ratio of boric acid, lithium salt, alcohol solvent, and HF in hydrofluoric acid is 1:(0.5-2):(0.5-4):(2-6). Specifically, the molar ratio can be 1:0.5:1:4, 1:1:2:3, 1:1.5:3:5, 1:2:2:6, 1:2:4:6, etc. Both excessively high and low feed ratios will affect the yield and purity. For example, too much HF will increase the acid content of the product, making it unqualified; too much lithium salt will decrease the yield, etc.

[0043] In some embodiments, the lithium salt in step (S1) is selected from one or more combinations of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium fluoride, and lithium hydrofluoride.

[0044] The concentration of hydrofluoric acid is 10-70%, specifically, it can be 10%, 15%, 30%, 40%, 50%, 65%, 70%, etc. If the concentration of hydrofluoric acid is too low, too much water is introduced, exceeding the dehydration process capacity, leading to increased water content in the product and making it substandard; if the concentration is too high, severe reaction decomposition will occur, reducing both yield and purity. A more preferable concentration of hydrofluoric acid is 30-50%.

[0045] In some embodiments, in step (S2), the alcohol solvent content in the crude lithium tetrafluoroborate is less than 5 wt%. Specifically, the content can be 4.95 wt%, 4.5 wt%, 3.1 wt%, 2.5 wt%, 2 wt%, 1.5 wt%, 1 wt%, or lower, more preferably less than 2 wt%. The alcohol solvent content in the crude lithium tetrafluoroborate affects the alcohol removal process; an excessively high alcohol solvent content will lead to an increased alcohol content in the final product, resulting in it being substandard.

[0046] In some embodiments, the method for preparing battery-grade lithium tetrafluoroborate provided by the present invention includes the following steps:

[0047] (S1) Boric acid and lithium salt are added and dispersed in an alcohol solvent, while hydrofluoric acid is added dropwise to carry out the reaction. The dropping temperature of hydrofluoric acid is controlled at 10-50℃ using a water bath, and the reaction temperature is controlled at 20-60℃ using a water bath. The reaction time is 1-4 hours to obtain a reaction solution containing lithium tetrafluoroborate. Specifically, the dropping temperature can be 10℃, 20℃, 30℃, 40℃, 50℃, etc., more preferably 10-30℃; the reaction temperature can be 20℃, 25℃, 32℃, 41℃, 52℃, 60℃, etc., more preferably 30-50℃; the reaction time can be 1 hour, 2 hours, 2.5 hours, 3.5 hours, 4 hours, etc. If the reaction temperature is too high, decomposition occurs; if the reaction temperature is too low, the reaction is incomplete, resulting in a low yield. If the reaction time is too long, decomposition occurs; if the reaction time is too short, the reaction is incomplete.

[0048] (S2) First, the reaction solution is concentrated by vacuum distillation to remove water. The concentration of the concentrate will affect the effect of the water removal process. The concentration is controlled at 40-80%. Specifically, the concentration can be 40%, 45%, 50%, 56%, 62%, 70%, 75%, 80%, etc., and more preferably 65-80% to obtain a concentrate. Then, an alcohol solvent is added to the concentrate, and vacuum distillation and drying are continued to obtain crude lithium tetrafluoroborate.

[0049] (S3) Add alcohol-free solvent to crude lithium tetrafluoroborate, dissolve and filter, and distill the filtrate under reduced pressure to obtain battery-grade lithium tetrafluoroborate.

[0050] In some embodiments, the vacuum distillation conditions for the process from reaction solution to concentrate, from concentrate to crude product, and from crude product to battery-grade lithium tetrafluoroborate are all 1–30 mbar vacuum degree and 40–110°C temperature. Specifically, the vacuum degree can be 1 mbar, 5 mbar, 12 mbar, 17 mbar, 23 mbar, 30 mbar, etc., more preferably 15–25 mbar; the temperature can be 40°C, 50°C, 60°C, 70°C, 85°C, 95°C, 105°C, 110°C, etc., more preferably 50–80°C. If the vacuum degree is too low, the operation time is prolonged and decomposition increases; if the vacuum degree is too high, it is difficult to achieve, and solvent contact is incomplete, resulting in poor water or alcohol removal. High temperatures facilitate decomposition, while low temperatures prolong the operation time and increase decomposition.

[0051] In some embodiments, the alcohol solvents used in steps (S1) and (S2) are independently selected from one or more combinations of methanol, ethanol, n-propanol, isopropanol, tert-butanol, and n-butanol.

[0052] In some embodiments, in step (S2), the total amount of alcohol solvent added to the concentrate is 1 to 10 times the mass of the concentrate. Specifically, it can be 1, 2, 3, 4.3, 5.7, 7.2, 8, 9, or 10 times, and more preferably 2 to 5 times. The amount of alcohol solvent used affects the dehydration effect; if it is too low, the product will have high residual water content; if it is too high, it is uneconomical and exceeds the capacity of subsequent alcohol removal processes.

[0053] In step (S3) of this invention, the alcohol removal solvent is a carbonate solvent. Choosing a carbonate solvent can effectively remove alcohol and water from the crude product. Moreover, since the solvent for lithium electrolytes is usually a carbonate, even if there is residual carbonate, it will not affect the quality of lithium tetrafluoroborate.

[0054] In some embodiments, the carbonate solvent is dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, or propylene carbonate. The amount of the carbonate solvent used is 1 to 10 times the mass of the crude lithium tetrafluoroborate, specifically, it can be 1, 2.2, 3.5, 4.6, 5.1, 5, 7, 8.3, or 10 times, more preferably 2 to 5 times.

[0055] The aqueous solution method involves a stepwise reaction where the first two materials react before reacting with the third. In contrast, this invention first disperses boric acid and lithium carbonate in an alcohol solvent, then adds hydrofluoric acid. This ensures the reaction occurs during the addition of hydrofluoric acid, achieving a "one-pot" reaction and increasing yield. Furthermore, the presence of the alcohol solvent inhibits hydration during the reaction, reducing the water content of the final product or the difficulty of dehydration.

[0056] On the other hand, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises lithium tetrafluoroborate prepared by the preparation method described above.

[0057] Because the preparation method described above is used, it is beneficial to reduce the impurities in the prepared lithium tetrafluoroborate, resulting in lithium tetrafluoroborate with higher purity, thereby meeting the standards for use as battery-grade lithium tetrafluoroborate and avoiding the impact of impurities in lithium tetrafluoroborate on the performance of lithium-ion batteries.

[0058] The present invention will be further illustrated by the following examples.

[0059] Example 1

[0060] S1: Synthesis reaction

[0061] Boric acid, lithium carbonate, and isopropanol were weighed into a three-necked flask and dispersed by stirring in a water bath. Simultaneously, 50% hydrofluoric acid (HF aqueous solution) was weighed into a dropping funnel, and the hydrofluoric acid was added dropwise at a temperature controlled at 15°C using a water bath. The molar ratio of boric acid, lithium carbonate, isopropanol, and HF in the hydrofluoric acid was 1:0.5:1:4. The reaction temperature was controlled at 40°C in a water bath, and the mixture was stirred for 1 hour. The resulting reaction solution containing lithium tetrafluoroborate was obtained in a one-pot reaction.

[0062] S2: Dehydration of the reaction solution

[0063] 1) Concentration and dehydration: The reaction solution is transferred to a distillation apparatus, and vacuum distillation is carried out at a vacuum of 20 mbar and a temperature of 65°C. The concentration is controlled to 75% by pausing the weighing process to obtain the concentrate.

[0064] 2) Azeotropic distillation with water in alcohol solvent: n-Butanol was added to the concentrate, with the total amount of n-Butanol being 4 times the amount of the concentrate. After stirring, vacuum distillation and drying were carried out under vacuum conditions of 20 mbar and 65°C. The alcohol solvent content in the product was controlled to be 3 wt%, and crude lithium tetrafluoroborate was obtained.

[0065] S3: Remove alcohol from crude product

[0066] Diethyl carbonate was added to crude lithium tetrafluoroborate, with the amount of diethyl carbonate being 4 times the mass of crude lithium tetrafluoroborate. The mixture was stirred to dissolve and then filtered. The filtrate was then subjected to vacuum distillation and drying at a vacuum degree of 20 mbar and a temperature of 65 °C to obtain battery-grade lithium tetrafluoroborate.

[0067] Example 2-21

[0068] Examples 2-21 include most of the operational steps in Example 1, with the differences being: the alcohol solvent and amount selected in steps (S1) and (S2), and the alcohol removal solvent and amount selected in step (S3), etc. Specifically, see Table 1.

[0069] Comparative Examples 1 to 4 are used to illustrate the preparation method of lithium tetrafluoroborate disclosed in this invention, including most of the operation steps in Example 1. The differences are shown in Table 1 and the following explanation.

[0070] Comparative Example 1

[0071] Comparative Example 1 includes most of the steps in Example 1, except that step (S1) is a stepwise reaction using an aqueous solution and no alcohol solvent is used.

[0072] Comparative Example 2

[0073] Comparative Example 2 includes most of the operating steps in Example 1, except that: in step (S2), the reaction solution is dehydrated, and the concentrate is directly distilled and dried under reduced pressure at a vacuum of 20 mbar and a temperature of 65°C. The alcohol solvent is not used for azeotropic water removal, and the water content in the product is controlled to be 3%, thus obtaining crude lithium tetrafluoroborate.

[0074] Comparative Example 3

[0075] Comparative Example 3 includes most of the operating steps in Example 1, except that in step (S3), the crude lithium tetrafluoroborate is directly distilled and dried under reduced pressure at a vacuum of 20 mbar and a temperature of 65°C, without the addition of carbonate solvents to remove the alcohol solvent.

[0076] Comparative Example 4

[0077] Comparative Example 4 is a commonly used method in the prior art for preparing lithium tetrafluoroborate by aqueous solution, including most of the operation steps in Example 1. The difference is that: in step (S1), the reaction solution containing lithium tetrafluoroborate is reacted stepwise by aqueous solution, and in step (S3), the crude lithium tetrafluoroborate is directly dried without adding carbonate solvents to remove alcohol solvent.

[0078] Table 1:

[0079]

[0080]

[0081] Performance testing

[0082] The instrument parameters and test methods are as follows:

[0083] Instrument models: JF-3 moisture analyzer, TL2300 turbidity meter, Dionex ICS-900 ion chromatograph, Bruker AvanceCore nuclear magnetic resonance spectrometer;

[0084] Test methods: Coulometric moisture analyzer was used to test the water content of the product at the ppm level; methyl red / tri-n-propylamine method was used to titrate the acid content of the product; a 1% dimethyl carbonate solution was prepared and tested 5 times with a turbidity analyzer and the average value was taken; a product / deuterated acetonitrile sample was prepared and tested with 1H NMR to quantify the alcohol-soluble residue.

[0085] The product yield of lithium tetrafluoroborate prepared in the above examples and comparative examples was calculated, and the water content, acid content, turbidity, main content, and alcohol content were tested. The test results are shown in Table 2.

[0086] Table 2:

[0087]

[0088]

[0089] As can be seen from Examples 2, 3, 6, and 7, when the alcohol solvent and amount selected in steps (S1) and (S2), and the alcohol removal solvent and amount selected in step (S3) are within the preferred range disclosed in this invention, the purity and yield of the product are relatively better.

[0090] As can be seen from the implementation of steps 4, 5, 12-14, and 19-21, when the alcohol solvent and dosage selected in steps (S1) and (S2), and the alcohol removal solvent and dosage selected in step (S3) are not within the scope of the present invention, the yield and purity of lithium tetrafluoroborate decrease to varying degrees, the acid content and alcohol content do not reach the standard value, and the moisture content cannot meet the more stringent requirement of below 0.005% (50ppm).

[0091] As can be seen from Examples 1 and 2 and Comparative Example 1, using the traditional aqueous solution method for stepwise reaction, the reactants are easily decomposed due to being surrounded by a large amount of water, resulting in poor quality lithium tetrafluoroborate. The acid content and main component content do not meet the standard values, and the yield is significantly reduced. However, by adding an alcohol removal solvent in step (S3), the alcohol content reaches the standard value. This also demonstrates that adding an alcohol removal solvent during the crude product alcohol removal process can reduce the alcohol content.

[0092] As can be seen from Examples 1 and 2 and Comparative Example 2, without the use of an alcohol solvent for azeotropic water removal during the dehydration process, the water content, acid content, and main component content of the resulting lithium tetrafluoroborate were far below the standard values. Excessive water content also led to product decomposition, resulting in a significant decrease in yield. Because the total amount of alcohol solvent introduced was relatively small, both direct drying in the dehydration stage and the addition of an alcohol-removing solvent in step (S3) could remove the alcohol, reducing the alcohol content in the product to undetectable levels (alcohol content of 0).

[0093] As can be seen from the implementation of Examples 1 and 2 and Comparative Example 3, when carbonate solvents were not used to remove alcohol solvents during the crude product purification, the resulting lithium tetrafluoroborate was inferior in both acid and alcohol content, especially with the alcohol content being seriously excessive, resulting in a significant decrease in yield.

[0094] As can be seen from Examples 1 and 2 and Comparative Example 4, compared with the prior art, the lithium tetrafluoroborate prepared by the present invention has a higher yield and purity, which can meet the requirements of the battery-grade lithium tetrafluoroborate standard for the content of impurities such as water, acid, and alcohol, and has significant advantages.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of battery grade lithium tetrafluoroborate, characterized in that, The method comprises the following steps: (S1) adding and dispersing boric acid and lithium salt in an alcohol solvent, and adding hydrofluoric acid dropwise to react, to obtain a reaction solution containing lithium tetrafluoroborate; (S2) removing water from the reaction solution by alcohol solvent azeotropy to obtain lithium tetrafluoroborate crude product; (S3) purifying the lithium tetrafluoroborate crude product by removing alcohol solvent to obtain battery-grade lithium tetrafluoroborate.

2. The method for preparing battery-grade lithium tetrafluoroborate according to claim 1, characterized in that, In step (S1), the molar ratio of the boric acid, the lithium salt, the alcohol solvent, and HF in the hydrofluoric acid is 1:(0.5-2):(0.5-4):(2-6).

3. The method for preparing battery-grade lithium tetrafluoroborate according to claim 1, characterized in that, The lithium salt in step (S1) is selected from one or a combination of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium fluoride, and lithium hydrofluoride. The alcohol solvent in steps (S1) and (S2) is independently selected from one or a combination of methanol, ethanol, n-propanol, isopropanol, tert-butanol, and n-butanol. The alcohol solvent removing agent in step (S3) is a carbonic ester solvent.

4. The method for preparing battery-grade lithium tetrafluoroborate according to claim 1, characterized in that, The concentration of the hydrofluoric acid is 10-70%.

5. The method for preparing battery-grade lithium tetrafluoroborate according to claim 1, characterized in that, In step (S2), the alcohol solvent content in the lithium tetrafluoroborate crude product is less than 5wt%.

6. The method for preparing battery-grade lithium tetrafluoroborate according to claim 1, characterized in that, In step (S3), the amount of the alcohol solvent removing agent is 1-10 times the mass of the lithium tetrafluoroborate crude product.

7. The process for producing battery-grade lithium tetrafluoroborate according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: (S1) adding and dispersing boric acid and lithium salt in an alcohol solvent, and adding hydrofluoric acid dropwise to react, to obtain a reaction solution containing lithium tetrafluoroborate; (S2) removing water from the reaction solution by alcohol solvent azeotropy to obtain lithium tetrafluoroborate crude product; (S3) purifying the lithium tetrafluoroborate crude product by removing alcohol solvent to obtain battery-grade lithium tetrafluoroborate.

8. The process for the preparation of battery grade lithium tetrafluoroborate according to claim 7, characterized in that, The conditions of the vacuum distillation from the reaction solution to the concentrate, from the concentrate to the crude product, and from the crude product to the battery-grade lithium tetrafluoroborate are all vacuum degree 1-30 mbar and temperature 40-110℃.

9. The method for preparing battery-grade lithium tetrafluoroborate according to claim 7, characterized in that, The total amount of the alcohol solvent added to the concentrate is 1-10 times the mass of the concentrate.

10. A lithium-ion battery, characterized by, The battery comprises a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte comprises the lithium tetrafluoroborate prepared by the preparation method in any one of claims 1-9.

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