Battery-grade lithium difluoro (oxalato) borate as well as preparation method and application thereof

Abstract

The invention belongs to the field of battery materials, and provides battery-grade lithium difluoro (oxalato) borate as well as a preparation method and application thereof.The battery-grade lithium difluoro (oxalato) borate is prepared by mixing lithium fluoride, ethyl acetate and boron trifluoride gas for a first reaction to obtain a first reaction solution containing lithium tetrafluoroborate, mixing the first reaction solution with oxalic acid and silicon tetrachloride for a second reaction to obtain a second reaction solution containing lithium tetrafluoroborate; a second reaction solution containing a lithium difluoro (oxalato) borate component is obtained; the lithium difluoro (oxalato) borate is subjected to vacuum rectification and then mixed with dichloromethane for crystallization, a lithium difluoro (oxalato) borate crude product is obtained, the crude product is washed with a dichloromethane and ethyl acetate mixed washing agent and dried, and a battery-grade finished product is obtained. According to the method, gas boron trifluoride is used for reacting in a gas-liquid system, specific ethyl acetate is used as a solvent, specific dichloromethane is adopted for devitrification, a mixed washing agent of dichloromethane and ethyl acetate is used for washing a crude product, and various improved procedures are matched, so that the reaction is more sufficient, impurities are effectively removed, and the yield is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and relates to a battery-grade lithium bisdifluorooxalate borate as well as a preparation method and application thereof. BACKGROUND

[0002] At present, the new energy automobile industry develops rapidly, and has made great progress in the related research on key technologies, key materials and products of power lithium batteries. The demand and shipment of batteries are rapidly increasing. Lithium ion batteries have high energy density, large capacity, no memory effect and long service life, and have very high practical value. As one of the important component materials of the battery, the solubility, stability and ionic conductivity of the electrolyte lithium salt have an important influence on the comprehensive electrochemical performance of the lithium ion battery.

[0003] Traditional electrolyte lithium salts such as lithium hexafluorophosphate (LiPF6) often have the problems of poor thermal stability and chemical stability. Therefore, a variety of new electrolyte lithium salts have been developed in the field, and the most representative ones are lithium tetrafluoroborate (LiBF4) and lithium bisoxalate borate (LiBOB). Among them, LiBOB has the advantages of not being easy to decompose at high temperature, being not sensitive to moisture, simple and pollution-free synthesis process, wide electrochemical stability window and being able to form a good SEI film on the negative electrode surface. However, the solubility of the electrolyte in linear carbonate solvents is small, which leads to a low conductivity, especially poor low-temperature performance. It has been found through research that LiBF4 has a large solubility in carbonate solvents due to its small molecular volume, which can effectively improve the low-temperature performance of lithium batteries. However, it cannot form an SEI film on the negative electrode surface.

[0004] In view of the problems of LiBF4 and LiBOB, researchers have proposed a new type of electrolyte lithium salt, lithium bisdifluorooxalate borate (LiODFB), through molecular structure design. LiODFB combines the advantages of LiBOB and LiBF4 in structure and performance, not only has a large solubility in linear carbonate solvents, but also can reduce the viscosity and increase the conductivity of the electrolyte, thereby further improving the low-temperature performance and rate performance of lithium ion batteries. Moreover, LiODFB, like LiBOB, can form a layer of SEI film with good structure and performance on the negative electrode surface, thereby improving the high-temperature performance of lithium ion batteries. In addition, LiODFB has another very important advantage, that is, the SEI film formed by LiODFB on the negative electrode surface can effectively prevent the formation of co-insertion of propylene carbonate on the negative electrode surface, so that propylene carbonate can be used to replace ethylene carbonate when formulating the electrolyte, thereby significantly reducing the viscosity of the electrolyte and improving the low-temperature performance of lithium batteries.

[0005] In summary, lithium difluoro(oxalato)borate (LiDFOB) is not only thermally stable, insensitive to moisture, and easy to form a film, but also not prone to outgassing, which can enhance the stability of the battery, reduce the impedance, improve the cycle life and rate performance, and has good ionic conductivity in a wide temperature range. It is considered to be the most promising electrolyte lithium salt to replace lithium hexafluorophosphate. However, the existing preparation process of LiDFOB currently has problems such as low yield, low purity, high acid content, large solvent consumption, and tail gas pollution, which seriously affects the high-quality production of LiDFOB and cannot meet the demand of promoting its large-scale application. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to provide a battery-grade lithium difluoro(oxalato)borate and its preparation method and use. The preparation method mixes lithium fluoride, ethyl acetate and gaseous boron trifluoride to perform a first reaction to obtain a first reaction liquid containing lithium tetrafluoroborate component; then mixes with oxalic acid and silicon tetrachloride to perform a second reaction to obtain a second reaction liquid containing lithium difluoro(oxalato)borate component; after vacuum rectification, mixes with dichloromethane to perform crystallization, after solid-liquid separation, obtains lithium difluoro(oxalato)borate crude product, then uses a mixed washing agent of dichloromethane and ethyl acetate to wash and dry the crude product to obtain a battery-grade finished product. The present application uses gaseous boron trifluoride to react in a gas-liquid system, uses specific ethyl acetate as a solvent, uses specific dichloromethane for crystallization, and uses a mixed washing agent of dichloromethane and ethyl acetate to wash the crude product, and multiple improved processes are matched, which can make the reaction more sufficient, effectively remove impurities, and improve the yield.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a preparation method of battery-grade lithium difluoro(oxalato)borate, comprising:

[0009] S1. Mixing lithium fluoride, ethyl acetate and gaseous boron trifluoride to perform a first reaction to obtain a first reaction liquid containing lithium tetrafluoroborate component;

[0010] S2. Mixing the first reaction liquid with oxalic acid and silicon tetrachloride to perform a second reaction to obtain a second reaction liquid containing lithium difluoro(oxalato)borate component;

[0011] S3. After vacuum rectification of the second reaction liquid, a rectification bottom product is obtained;

[0012] S4. Mixing the rectification bottom product with dichloromethane to perform crystallization to obtain a solid-liquid mixture;

[0013] S5. After solid-liquid separation of the solid-liquid mixture, a lithium difluoro(oxalato)borate crude product is obtained;

[0014] S6. The crude lithium difluoro(oxalato)borate is washed and dried, the washing agent of the washing including a mixed washing agent of dichloromethane and ethyl acetate, to obtain the battery-grade lithium difluoro(oxalato)borate.

[0015] In the existing process for preparing lithium difluoro(oxalato)borate, dimethyl carbonate is usually used as the solvent, but the solvent component forms a complex with lithium difluoro(oxalato)borate at room temperature, in the form of a hard solid, which can wrap a large amount of impurities, thereby affecting the reaction, and it is difficult to realize purification and separation at room temperature, and high filtration requirements. The preparation method disclosed in the present application uses ethyl acetate as the solvent, which does not form a complex with lithium difluoro(oxalato)borate, can be filtered at room temperature, and can effectively improve the yield and product quality, and has higher yield and purity compared with dimethyl carbonate. The reaction system of the existing process is a solid-liquid reaction or a liquid-liquid reaction, and the reaction time is long, while the present application uses gaseous boron trifluoride, so that the first reaction is a gas-liquid reaction system, to optimize the quality and state of the generated lithium tetrafluoroborate component, and the gas-liquid reaction time is short, the reaction is more complete, and the yield is high. In the existing process, dimethyl carbonate is used for crystallization, which results in low yield (only 40%~50%) due to a large amount of lithium difluoro(oxalato)borate dissolved therein. The present application uses dichloromethane for crystallization, which facilitates the complete precipitation of lithium difluoro(oxalato)borate, and can significantly improve the yield; at the same time, the present application uses a mixed washing agent of ethyl acetate and dichloromethane for washing, which can dissolve the acid component and impurities such as lithium tetrafluoroborate in the material in the mixed solvent to remove them, and at the same time, since dichloromethane has a crystallization effect, it will not cause a decrease in yield, and can effectively improve the purity and yield.

[0016] The following is a preferred technical solution of the present application, but not as a limitation of the technical solution provided by the present application. Through the following technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0017] As a preferred technical solution of the present application, the processes in the preparation method are carried out under the protection of an inert atmosphere.

[0018] Preferably, the inert atmosphere includes nitrogen.

[0019] As a preferred technical solution of the present application, in step S1, the lithium fluoride is first mixed with the ethyl acetate, the temperature is raised to the temperature of the first reaction, then the gaseous boron trifluoride is introduced for mixing, and the first reaction is started, and the introduction of the gaseous boron trifluoride is maintained until the first reaction is completed.

[0020] Preferably, the moisture content of the ethyl acetate is ≤200ppm, for example, it can be 200ppm, 180ppm, 160ppm, 130ppm, 100ppm, 80ppm, 50ppm, 10ppm or 0ppm (water-free), etc.

[0021] Preferably, the mass ratio of the ethyl acetate to the lithium difluoro(oxalato)borate component theoretically generated in the second reaction is (2.5-25):1, and the amount of the ethyl acetate is controlled, such as 2.5:1, 5:1, 8:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, or 25:1, etc.

[0022] In the present application, too much ethyl acetate will cause waste; too little will easily lead to the generated lithium difluoro(oxalato)borate not completely dissolved in ethyl acetate, incomplete reaction, and wrapping impurities.

[0023] Preferably, the molar ratio of the gaseous boron trifluoride to the lithium fluoride is (1-1.2):1, such as 1:1, 1.03:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.14:1, 1.16:1, 1.18:1, or 1.2:1, etc.

[0024] Preferably, the temperature of the first reaction is 20-70℃, such as 20℃, 30℃, 40℃, 50℃, 60℃, or 70℃, etc., and the time is 0.25-3h, such as 0.25h, 0.5h, 0.8h, 1h, 1.1h, 1.3h, 1.5h, 1.8h, 2h, 2.3h, 2.5h, 2.8h, or 3h, etc.

[0025] In the process of the first reaction of the present application, the following chemical reaction is included: BF3+LiF=LiBF4.

[0026] Preferably, the tail gas of the gaseous boron trifluoride is absorbed by a first absorbent.

[0027] Preferably, the first absorbent includes at least one of acetonitrile, dimethyl carbonate, diethyl ether, diethyl carbonate, or acetic acid.

[0028] In the present application, after the first absorbent absorbs the boron trifluoride tail gas, it can be used as a byproduct, such as boron trifluoride dimethyl carbonate or boron trifluoride diethyl ether.

[0029] Preferably, the first reaction liquid is first filtered to obtain a first filtrate containing a lithium tetrafluoroborate component, and then the first filtrate is mixed with the oxalic acid and silicon tetrachloride in step S2 to perform the second reaction.

[0030] Preferably, the first filtration temperature is 0-70℃, such as 0℃, 5℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃ or 70℃, etc., and the filter membrane pore size is 0.1-1μm, such as 0.1μm, 0.3μm, 0.5μm, 0.7μm, 0.9μm or 1μm, etc.

[0031] As a preferred technical solution of the present application, in step S2, the first reaction solution is first mixed with the oxalic acid, then the temperature is raised to the second reaction temperature, the silicon tetrachloride is added and the second reaction is started, and the feeding of silicon tetrachloride is maintained until the second reaction is completed.

[0032] Preferably, the molar ratio of the oxalic acid to the lithium tetrafluoroborate component in the first reaction solution is (0.9-1.1):1, and the amount of oxalic acid is controlled, such as 0.9:1, 0.92:1, 0.95:1, 0.98:1, 1:1, 1.02:1, 1.05:1, 1.08:1 or 1.1:1, etc.

[0033] Preferably, the molar ratio of the silicon tetrachloride to the lithium tetrafluoroborate component in the first reaction solution is (0.45-0.55):1, and the amount of silicon tetrachloride is controlled, such as 0.45:1, 0.46:1, 0.47:1, 0.48:1, 0.49:1, 0.5:1, 0.51:1, 0.52:1, 0.53:1, 0.54:1 or 0.55:1, etc.

[0034] In the existing process, lithium fluoride and silicon tetrachloride are often used in excess, causing waste of lithium source or high silicon and chlorine indexes, and the present application strictly controls the dosage ratio.

[0035] Preferably, the second reaction temperature is 20-50℃, such as 20℃, 23℃, 25℃, 28℃, 30℃, 33℃, 35℃, 38℃, 40℃, 43℃, 48℃ or 50℃, etc., and the time is 0.25-3h, such as 0.25h, 0.5h, 0.8h, 1h, 1.1h, 1.3h, 1.5h, 1.8h, 2h, 2.3h, 2.5h, 2.8h or 3h, etc.

[0036] In the process of the two reactions of the present application, the following chemical reaction is included: 2H2C2O4+2LiBF4+SiCl4=2LiBF2C2O4+SiF4↑+4HCl↑.

[0037] As a preferred technical solution of the present application, in step S2, after the second reaction is completed, the second reaction solution is first incubated, then second filtration is performed to obtain a second filtrate containing a lithium difluoroxalate borate component, and then the second filtrate is subjected to the vacuum rectification in step S3.

[0038] Preferably, the insulation temperature is 20-70°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C or 70°C, and the insulation time is 1-6h, for example, 1h, 2h, 3h, 4h, 5h, 6h or 7h.

[0039] Preferably, the temperature of the second filtration is 0-70°C, for example, 0°C, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C or 70°C, and the pore size of the filter membrane is 0.1-1 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm or 1 μm, etc.

[0040] Preferably, the tail gas generated by the second reaction is absorbed by a second absorbent.

[0041] Preferably, the second absorbent comprises hydrofluoric acid with a mass concentration of 0.5% to 5%, for example, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0042] Exhaust gas generated in existing processes is often absorbed by alkali, which is prone to inadequate absorption and causes exhaust gas overflow. The present invention uses weak acid for absorption, which ensures sufficient absorption and allows the absorption liquid to be subsequently used to synthesize by-products such as potassium fluorosilicate. This shows that the preparation method of the present invention is cleaner and pollution-free, and all the waste gas (exhaust gas) generated can be absorbed and treated.

[0043] As a preferred technical solution of the present invention, in step S3, the process of the vacuum distillation includes first performing low vacuum distillation with a vacuum degree of 200 to 800 mbar, for example, 200 mbar, 300 mbar, 400 mbar, 500 mbar, 600 mbar, 700 mbar or 800 mbar, and then performing high vacuum distillation with a vacuum degree of 10 to 100 mbar, for example, 10 mbar, 20 mbar, 30 mbar, 40 mbar, 50 mbar, 60 mbar, 70 mbar, 80 mbar, 90 mbar or 100 mbar, and the temperature of the vacuum distillation is 20 to 70° C., for example, 20° C., 30° C., 40° C., 50° C., 60° C. or 70° C.

[0044] In the present invention, hydrogen chloride gas generated during the reaction is dissolved in the reaction liquid, so the hydrogen chloride gas is first extracted by low vacuum reduced pressure distillation to reduce the acid content of the reaction liquid; then high vacuum distillation is performed to extract excess ethyl acetate solvent, reduce the solvent and further concentrate the material dissolved in ethyl acetate.

[0045] Preferably, the distillate of the high-vacuum reduced-pressure rectification is collected by a condenser, and the collected ethyl acetate (ethyl acetate moisture ≤200 ppm, acid content ≤10 ppm) can be returned to step S1 for reuse, which can greatly reduce the amount and consumption of solvent.

[0046] Preferably, the low-vacuum rectification time is 2-6 h, for example, 2 h, 3 h, 4 h, 5 h, 6 h, or 7 h, etc.

[0047] Preferably, the high-vacuum rectification makes the molar ratio of ethyl acetate to lithium difluoroboric acid oxalate in the rectification substrate reach (2-8):1, for example, 2:1, 2.3:1, 2.5:1, 2.8:1, 3:1, 3.3:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, 5.2:1, 5.5:1, 5.8:1, 6:1, 6.3:1, 6.5:1, 6.8:1, 7:1, 7.2:1, 7.5:1, 7.8:1, or 8:1, etc.

[0048] Preferably, in step S4, the moisture content of the dichloromethane is ≤200 ppm, for example, it can be 200 ppm, 180 ppm, 160 ppm, 130 ppm, 100 ppm, 80 ppm, 50 ppm, 10 ppm, or 0 ppm (water-free), etc.

[0049] Preferably, the amount of dichloromethane is controlled according to the mass ratio of dichloromethane to ethyl acetate in the rectification substrate, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, etc.

[0050] In the present application, too much dichloromethane in the crystallization process leads to waste of dichloromethane and easy precipitation of unreacted lithium tetrafluoroborate, thereby reducing the purity; too little dichloromethane easily leads to less precipitated material and reduces the yield.

[0051] Preferably, in step S5, the solid-liquid separation also obtains a mother liquor, which is treated and then returned to the first reaction in step S1.

[0052] In the present application, the mother liquor contains dichloromethane, ethyl acetate, and a small amount of unreacted lithium tetrafluoroborate, which can be separated by atmospheric rectification at 55-65℃, and the dichloromethane is separated, and the ethyl acetate and lithium tetrafluoroborate are reused, and the collected dichloromethane is used for the crystallization of the next batch of dichloromethane in step S4.

[0053] As a preferred technical scheme of the present application, in step S6, the mass ratio of dichloromethane to ethyl acetate in the mixed washing agent is (1-10):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc.

[0054] Preferably, the amount of the mixed washing agent is controlled according to the mass ratio of the mixed washing agent to the crude lithium bis(fluorosulfonyl)imide of (1-5):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc.

[0055] Preferably, the number of washing is 2-5 times, for example, 2 times, 3 times or 5 times, etc.

[0056] Preferably, the drying temperature is 40-120℃, for example, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃ or 120℃, etc.

[0057] Preferably, the purity of the battery-grade lithium bis(fluorosulfonyl)imide is up to 99.95%, the acid content is ≤30ppm, for example, 30ppm, 28ppm, 25ppm, 22ppm, 20ppm, 18ppm, 16ppm, 14ppm, 12ppm, 10ppm, 8ppm, 6ppm, 4ppm, 3ppm or 1ppm, etc., the water content is ≤20ppm, for example, 20ppm, 18ppm, 16ppm, 13ppm, 10ppm, 8ppm, 5ppm, 3ppm or 1ppm, etc.

[0058] In a second aspect, the present application provides a battery-grade lithium bis(fluorosulfonyl)imide prepared according to the preparation method of the first aspect.

[0059] In a third aspect, the present application provides an electrolyte containing the battery-grade lithium bis(fluorosulfonyl)imide of the second aspect.

[0060] In a fourth aspect, the present application provides a battery containing the battery-grade lithium bis(fluorosulfonyl)imide of the second aspect or containing the electrolyte of the third aspect.

[0061] It should be noted that, due to the limitation of the page length and in order to avoid redundancy, the present application does not exhaustively list all applicable point values within the above numerical range, but is also not limited to the listed values, and other unlisted values within the above numerical range are also applicable.

[0062] Compared with the prior art, the present application has at least the following beneficial effects:

[0063] The application can make the reaction more sufficient, effectively remove impurities and improve the yield by a plurality of improved processes in combination, such as the reaction of gas boron trifluoride in a gas-liquid system, the use of specific ethyl acetate as a solvent, the use of specific dichloromethane for crystallization, and the use of a mixed washing agent of dichloromethane and ethyl acetate for washing the crude product. The yield of the battery-grade lithium difluoro(oxalato)borate prepared by the preparation method can be up to 99%, the purity can be up to 99.95%, the acid content is ≤30 ppm, the water content is ≤20 ppm, the solvent can be recycled and used, the consumption is low, the tail gas can be collected and treated, it is cleaner and less polluting, and it is suitable for large-scale industrial application. DETAILED DESCRIPTION

[0064] The technical solutions of the application are further described below through specific embodiments.

[0065] Those skilled in the art should understand that the embodiments are only used to help understand the application and should not be regarded as specific limitations on the application.

[0066] Embodiment 1

[0067] The embodiment provides a preparation method of battery-grade lithium difluoro(oxalato)borate, comprising the following steps:

[0068] S1. Under a nitrogen atmosphere, ethyl acetate and lithium fluoride are put into a three-necked flask, the water content of the ethyl acetate is 10 ppm, the amount of the ethyl acetate is controlled according to the mass ratio of the ethyl acetate to the theoretical generated lithium difluoro(oxalato)borate component is 16:1; then the three-necked flask is transferred into an oil bath, heated to 50℃, and gas boron trifluoride is continuously introduced into the three-necked flask, stirring is kept, the molar ratio of the total amount of the gas boron trifluoride to the lithium fluoride is controlled to be 1.1:1, the first reaction is kept for 1.5 h to be completed, a first reaction liquid containing lithium tetrafluoroborate component is obtained, and the tail gas is absorbed by a first absorbent acetonitrile; after the first reaction is completed, the first reaction liquid is subjected to a first filtration at 25℃ by using a filter membrane with a pore size of 0.45 μm, and a first filtrate containing lithium tetrafluoroborate component is obtained;

[0069] S2. The first filtrate is transferred into a PFA reaction bottle, oxalic acid is added into the reaction bottle, the amount of the oxalic acid is controlled according to the molar ratio of the oxalic acid to the lithium tetrafluoroborate component in the first filtrate being 0.95:1, then the reaction bottle is transferred into an oil bath, heated to 40℃, and continuously adding example silicon tetrachloride into the reaction bottle while stirring, the total amount of the silicon tetrachloride is controlled according to the molar ratio of the silicon tetrachloride to the lithium tetrafluoroborate component in the first filtrate being 0.47:1, the second reaction is kept going and completed for 1.5h, to obtain a second reaction liquid containing a lithium difluorooxalato borate component, and the tail gas is absorbed by using a second absorbent of 2% hydrofluoric acid;

[0070] S3. The obtained second filtrate is subjected to vacuum rectification, the temperature is kept at 50℃, first, low vacuum rectification is carried out at a vacuum degree of 500mbar for 3.6h, and the distillate is returned into the three-necked flask of step S1 through the rectification column; then high vacuum rectification is carried out at a vacuum degree of 60mbar, the distillate is collected through a condenser, and the high vacuum rectification is stopped when the molar ratio of ethyl acetate to the lithium difluorooxalato borate component reaches 5:1, to obtain a rectification residue;

[0071] S4. Dichloromethane is added into the rectification residue, the water content of the dichloromethane is 10ppm, and the amount of the dichloromethane is controlled according to the mass ratio of the dichloromethane to the ethyl acetate in the rectification residue being 4.5:1, and the mixture is stirred to carry out crystallization, to obtain a solid-liquid mixture;

[0072] S5. The obtained solid-liquid mixture is subjected to filtration to separate the solid and the liquid, to obtain a lithium difluorooxalato borate crude product, and the obtained mother liquor is treated and then reused in the first reaction of step S1;

[0073] S6. The obtained lithium difluorooxalato borate crude product is washed with a mixed washing agent of dichloromethane and ethyl acetate, the mass ratio of the dichloromethane to the ethyl acetate in the mixed washing agent is 8:1, and the amount of the mixed washing agent is controlled according to the mass ratio of the mixed washing agent to the lithium difluorooxalato borate crude product being 2:1, a total of 3 times of washing is carried out, after the washing is completed, the wet product is obtained through filtration, and then vacuum drying is carried out at 80℃, to obtain a battery-grade lithium difluorooxalato borate finished product.

[0074] Example 2

[0075] The embodiment provides a preparation method of battery-grade lithium bis (fluorosulfonyl) borate, in step S1 of the preparation method, the amount of ethyl acetate is adjusted, so that the mass ratio of ethyl acetate to theoretically generated lithium bis (fluorosulfonyl) borate component is changed from 16:1 to 1:1, and other conditions are completely same with those in example 1.

[0076] Example 3

[0077] The embodiment provides a preparation method of battery-grade lithium bis (fluorosulfonyl) borate, in step S1 of the preparation method, the amount of ethyl acetate is adjusted, so that the mass ratio of ethyl acetate to theoretically generated lithium bis (fluorosulfonyl) borate component is changed from 16:1 to 2.5:1, and other conditions are completely same with those in example 1.

[0078] Example 4

[0079] The embodiment provides a preparation method of battery-grade lithium bis (fluorosulfonyl) borate, in step S1 of the preparation method, the amount of ethyl acetate is adjusted, so that the mass ratio of ethyl acetate to theoretically generated lithium bis (fluorosulfonyl) borate component is changed from 16:1 to 25:1, and other conditions are completely same with those in example 1.

[0080] Example 5

[0081] The embodiment provides a preparation method of battery-grade lithium bis (fluorosulfonyl) borate, in step S1 of the preparation method, the amount of ethyl acetate is adjusted, so that the mass ratio of ethyl acetate to theoretically generated lithium bis (fluorosulfonyl) borate component is changed from 16:1 to 32:1, and other conditions are completely same with those in example 1.

[0082] Example 6

[0083] The embodiment provides a preparation method of battery-grade lithium bis (fluorosulfonyl) borate, in step S4 of the preparation method, the amount of dichloromethane is adjusted, so that the mass ratio of dichloromethane to ethyl acetate in a rectification substrate is changed from 4.5:1 to 0.5:1, and other conditions are completely same with those in example 1.

[0084] Example 7

[0085] The embodiment provides a preparation method of battery-grade lithium bis (fluorosulfonyl) borate, in step S4 of the preparation method, the amount of dichloromethane is adjusted, so that the mass ratio of dichloromethane to ethyl acetate in a rectification substrate is changed from 4.5:1 to 1:1, and other conditions are completely same with those in example 1.

[0086] Example 8

[0087] The embodiment provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S4 of the preparation method, the amount of dichloromethane is adjusted, so that the mass ratio of dichloromethane to ethyl acetate in a rectification substrate is changed from 4.5:1 to 10:1, and other conditions are completely same with those in example 1 except the above.

[0088] Example 9

[0089] The embodiment provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S4 of the preparation method, the amount of dichloromethane is adjusted, so that the mass ratio of dichloromethane to ethyl acetate in a rectification substrate is changed from 4.5:1 to 13:1, and other conditions are completely same with those in example 1 except the above.

[0090] Example 10

[0091] The embodiment provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S6 of the preparation method, the mass ratio of dichloromethane to ethyl acetate in a mixed washing agent is changed from 8:1 to 0.5:1, and other conditions are completely same with those in example 1 except the above.

[0092] Example 11

[0093] The embodiment provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S6 of the preparation method, the mass ratio of dichloromethane to ethyl acetate in a mixed washing agent is changed from 8:1 to 1:1, and other conditions are completely same with those in example 1 except the above.

[0094] Example 12

[0095] The embodiment provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S6 of the preparation method, the mass ratio of dichloromethane to ethyl acetate in a mixed washing agent is changed from 8:1 to 10:1, and other conditions are completely same with those in example 1 except the above.

[0096] Example 13

[0097] The embodiment provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S6 of the preparation method, the mass ratio of dichloromethane to ethyl acetate in a mixed washing agent is changed from 8:1 to 13:1, and other conditions are completely same with those in example 1 except the above.

[0098] Comparative Example 1

[0099] The comparative example provides a preparation method of battery-grade lithium bis (fluorooxalato) borate, in step S1 of the preparation method, dimethyl carbonate is used instead of the ethyl acetate, and other conditions are completely same with those in example 1 except the above.

[0100] Comparative Example 2

[0101] The comparative example provides a preparation method of battery-grade lithium bis (difluoro oxalato) borate, in step S1, boron trifluoride methanol solution is used instead of the gas boron trifluoride, and other conditions are the same as those in example 1.

[0102] Comparative example 3

[0103] The comparative example provides a preparation method of battery-grade lithium bis (difluoro oxalato) borate, in step S4, dimethyl carbonate is used instead of dichloromethane, and other conditions are the same as those in example 1.

[0104] Comparative example 4

[0105] The comparative example provides a preparation method of battery-grade lithium bis (difluoro oxalato) borate, in step S6, dimethyl carbonate is used instead of the mixed washing agent of dichloromethane and ethyl acetate, and other conditions are the same as those in example 1.

[0106] The yield (= (actual mass / theoretical mass generated) x 100%) of battery-grade lithium bis (difluoro oxalate) borate obtained in the examples and comparative examples, purity (using ICP equipment), acid content (using acetonitrile-triethylamine reagent titration) and moisture (using a moisture meter) are detected, and the results are shown in Table 1.

[0107] Table 1

[0108] Group Yield (%) Purity (%) Acid content (ppm) Moisture content (ppm) Example 1 99.83 99.993 2.1 3.6 Example 2 98.3 99.2 37.6 17.3 Example 3 99.14 99.952 29.5 18.6 Example 4 99.02 99.96 5 16 Example 5 96.9 99.968 13.6 11.3 Example 6 93.9 99.981 24.7 13.5 Example 7 99.03 99.963 14.9 9.7 Example 8 99.81 99.95 6.8 14.8 Example 9 99.5 99.1 45.8 15.6 Example 10 93.5 99.973 21.6 11.3 Example 11 99.03 99.958 24.6 9.6 Example 12 99.43 99.953 28.4 8.5 Example 13 99.24 99.15 35.6 19.5 Comparative Example 1 92.6 94.63 56.1 34.7 Comparative Example 2 91.8 89.6 184.6 55.6 Comparative Example 3 45.62 99.56 95.1 42.6 Comparative Example 4 51.3 97.6 62.4 39.7

[0109] As can be seen from Table 1:

[0110] Comparing example 1 with comparative examples 1-4, it is found that using ethyl acetate as a solvent can significantly improve the yield and the quality of the product; using boron trifluoride methanol solution instead of the gas boron trifluoride can easily cause insufficient reaction, which seriously affects the yield and purity of the product; using dimethyl carbonate as a crystallizing agent cannot crystallize, resulting in low yield; using dimethyl carbonate as a washing agent can also cause the material to be completely dissolved in dimethyl carbonate, resulting in particularly low yield.

[0111] Comparing example 1 with examples 2-5, it is found that the ratio of ethyl acetate to lithium bis (difluoro oxalate) borate can affect the purity and acid content of the material to some extent, the amount of dichloromethane used in the crystallization process can affect the yield and purity to some extent, and the ratio of dichloromethane to ethyl acetate in the mixed solvent during washing can also affect the purity, yield and acid content to some extent. On the basis of sufficient amount, the effects of various aspects can be improved and guaranteed, but excessive use should be avoided to cause waste and lead to cost increase.

[0112] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0113] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0114] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A method for preparing battery-grade lithium difluorooxalatoborate, characterized in that: include: S1. Lithium fluoride, ethyl acetate and boron trifluoride gas are mixed to perform a first reaction to obtain a first reaction solution containing a lithium tetrafluoroborate component; S2. The first reaction solution is mixed with oxalic acid and silicon tetrachloride, and a second reaction is performed to obtain a second reaction solution containing lithium difluorooxalatoborate component; S3. The second reaction solution is subjected to vacuum distillation to obtain a distillation substrate; S4. The distillation substrate is mixed with dichloromethane and crystallized to obtain a solid-liquid mixture; S5. After the solid-liquid mixture is subjected to solid-liquid separation, a crude product of lithium difluorooxalatoborate is obtained; S6. Washing and drying the crude lithium difluorooxalatoborate product, wherein the washing detergent comprises a mixed detergent of dichloromethane and ethyl acetate, to obtain battery-grade lithium difluorooxalatoborate.

2. The method for preparing battery-grade lithium difluorooxalatoborate according to claim 1, wherein: All the processes in the preparation method are carried out under the protection of an inert atmosphere; Preferably, the inert atmosphere comprises nitrogen.

3. The method for preparing battery-grade lithium difluorooxalatoborate according to claim 1 or 2, characterized in that: In step S1, the lithium fluoride and the ethyl acetate are first mixed, and then the temperature is raised to the temperature of the first reaction, and then the boron trifluoride gas is introduced to mix, and the first reaction is started, and the introduction of the boron trifluoride gas is maintained until the first reaction is completed; Preferably, the moisture content of the ethyl acetate is ≤200ppm; Preferably, the amount of the ethyl acetate is controlled according to the mass ratio of the ethyl acetate to the lithium difluorooxalatoborate component theoretically generated in the second reaction of (2.5-25):1; Preferably, the molar ratio of the gaseous boron trifluoride to the lithium fluoride is (1-1.2):1; Preferably, the temperature of the first reaction is 20-70°C and the time is 0.25-3h; Preferably, the tail gas remaining from the boron trifluoride gas is absorbed using a first absorbent; Preferably, the first absorbent comprises at least one of acetonitrile, dimethyl carbonate, diethyl ether, diethyl carbonate or acetic acid; Preferably, the first reaction liquid is first filtered to obtain a first filtrate containing lithium tetrafluoroborate, and then the first filtrate is mixed with the oxalic acid and silicon tetrachloride in step S2 to perform the second reaction; Preferably, the temperature of the first filtration is 0-70° C., and the pore size of the filter membrane is 0.1-1 μm.

4. The method for preparing battery-grade lithium difluorooxalatoborate according to any one of claims 1 to 3, characterized in that: In step S2, the first reaction liquid is first mixed with the oxalic acid, and then the temperature is raised to the temperature of the second reaction, and then the silicon tetrachloride is added and mixed, and the second reaction is started, and the silicon tetrachloride is kept added until the second reaction is completed; Preferably, the amount of oxalic acid is controlled according to a molar ratio of oxalic acid to lithium tetrafluoroborate in the first reaction solution of (0.9-1.1):1; Preferably, the amount of the silicon tetrachloride is controlled according to a molar ratio of the silicon tetrachloride to the lithium tetrafluoroborate component in the first reaction solution of (0.45-0.55):1; Preferably, the temperature of the second reaction is 20-50° C., and the time is 0.25-3 h.

5. The method for preparing battery-grade lithium difluorooxalatoborate according to any one of claims 1 to 4, characterized in that: In step S2, after the second reaction is completed, the second reaction liquid is first kept warm, and then subjected to a second filtration to obtain a second filtrate containing lithium difluorooxalatoborate, and the second filtrate is then subjected to the vacuum distillation in step S3; Preferably, the temperature of the insulation is 20-70°C and the time is 1-6 hours. Preferably, the temperature of the second filtration is 0-70°C, and the pore size of the filter membrane is 0.1-1 μm; Preferably, the tail gas generated by the second reaction is absorbed by a second absorbent; Preferably, the second absorbent comprises hydrofluoric acid with a mass concentration of 0.5% to 5%.

6. The method for preparing battery-grade lithium difluorooxalatoborate according to any one of claims 1 to 5, characterized in that: In step S3, the vacuum distillation process includes first performing low vacuum distillation with a vacuum degree of 200-800 mbar, and then performing high vacuum distillation with a vacuum degree of 10-100 mbar; the temperature of the vacuum distillation is 20-70°C; Preferably, the low vacuum distillation time is 2 to 6 hours, and the high vacuum distillation is performed so that the molar ratio of ethyl acetate to lithium difluorooxalatoborate in the distillation substrate reaches (2 to 8):1; Preferably, in step S4, the water content of the dichloromethane is ≤20 ppm; Preferably, the amount of the dichloromethane is controlled according to a mass ratio of the dichloromethane to the ethyl acetate in the distillation bottoms of (1-10):1; Preferably, in step S5, the solid-liquid separation further obtains a mother liquor, which is processed and then reused in the first reaction in step S1.

7. The method for preparing battery-grade lithium difluorooxalatoborate according to any one of claims 1 to 6, characterized in that: In step S6, in the mixed lotion, the mass ratio of the dichloromethane to the ethyl acetate is (1-10):1; Preferably, the amount of the mixed lotion is controlled according to the mass ratio of the mixed lotion to the crude lithium difluorooxalatoborate product of (1-5):1; Preferably, the number of washings is 2 to 5 times; Preferably, the drying temperature is 40 to 120°C; Preferably, the purity of the battery-grade lithium difluorooxalatoborate can be as high as 99.95%, the acid content is ≤30ppm, and the moisture content is ≤20ppm.

8. A battery-grade lithium difluorooxalatoborate, characterized in that: Obtained according to the preparation method according to any one of claims 1 to 7.

9. An electrolyte, characterized in that The electrolyte contains the battery-grade lithium difluorooxalatoborate according to claim 8.

10. A battery, characterized in that: The battery contains the battery-grade lithium difluorooxalatoborate according to claim 8 or the electrolyte according to claim 9.