Preparation method of lithium difluoro (oxalato) borate
By combining ionic liquid media and plasma activation technology with supercritical carbon dioxide extraction, the problems of cumbersome synthesis process and difficulty in removing impurities of lithium difluorooxalate borate have been solved, achieving a highly efficient and environmentally friendly production process.
Patent Information
- Application Number
- CN202511281277.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-09
- Publication Date
- 2025-11-11
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a method for preparing lithium difluorooxalate borate. Background Technology
[0002] In lithium-ion battery electrolytes, lithium difluorooxalate borate has emerged as a potential high-performance lithium salt alternative due to its combination of the low-temperature performance of lithium tetrafluoroborate and the high-temperature film-forming properties of lithium dioxalate borate. However, existing synthesis processes still have significant limitations.
[0003] In the traditional route, when boron trifluoride complexes react with lithium oxalate, lithium tetrafluoroborate byproducts are generated, requiring multiple recrystallizations for separation and purification, which is cumbersome and results in limited yield. Another method, using lithium tetrafluoroborate as a raw material and reacting it with oxalic acid with silicon tetrachloride or aluminum trichloride as an aid, has simpler raw materials, but the reaction process generates hydrogen chloride gas, which not only corrodes the equipment but also results in residual chloride ion impurities in the product, affecting the electrochemical performance of the electrolyte.
[0004] In addition, existing processes mostly rely on volatile organic solvents, such as dimethyl carbonate, which is highly hygroscopic and easily introduces moisture, leading to increased product moisture content. Furthermore, the solvent recovery rate is low, increasing industrialization costs and environmental pressure. Therefore, developing a synthesis method that can reduce impurity introduction, simplify purification steps, and reduce equipment corrosion is of great significance for promoting the large-scale application of lithium difluorooxalate borate. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing lithium difluorooxalate borate, which solves the problems mentioned in the background section.
[0006] This invention provides a method for preparing lithium difluorooxalate borate, the method comprising: (1) Lithium source, boron source, oxalic acid source and fluorine source are selected as raw materials, and ionic liquid is used as medium. Specifically, lithium source is lithium hydroxide; boron source is trimethyl borate; oxalic acid source is dimethyl oxalate; fluorine source is ammonium hydrogen fluoride vapor; and ionic liquid is imidazole imine salt ionic liquid. (2) Dry lithium hydroxide at 120~140℃ for 4~6 h to remove water of crystallization, avoiding the introduction of moisture which would cause the fluorine source to hydrolyze and generate HF, corroding the equipment and increasing the acidity of the product. Trimethyl borate and dimethyl oxalate were dehydrated by molecular sieves and then transferred to the reaction vessel under Ar inert gas protection to prevent moisture from the air from entering. (3) In a flask lined with polytetrafluoroethylene (to prevent fluorine corrosion), add ionic liquid, pretreated lithium hydroxide, trimethyl borate and dimethyl oxalate in sequence, and stir until a homogeneous transparent solution is formed; introduce Ar into the flask, turn on the plasma power supply and set the power to 300~400W; continuously introduce ammonium fluoride vapor into the reaction system through Ar to carry ammonium fluoride into the reaction system for reaction, and the plasma activates the reactivity of fluoride ions, promoting the coordination of fluoride ions with boron atoms and the combination of oxalate ions with boron atoms; (4) After the reaction is completed, the ionic liquid reaction solution of lithium difluorooxalate borate is obtained. After centrifugation, the supernatant is filtered. The filtered liquid is purified by supercritical carbon dioxide extraction. The product is collected by two-stage separation and dried to obtain the final product.
[0007] Furthermore, the purity of lithium hydroxide is >99.9%, the purity of dimethyl oxalate is >99%, and the water content of the ionic liquid is <10ppm.
[0008] Further, the amount of lithium hydroxide used is measured at 1.05 to 1.1 times the theoretical molar amount of the target product; the molar ratio of trimethyl borate to lithium hydroxide is (1 to 1.2):1; the molar ratio of dimethyl oxalate to lithium hydroxide is (1 to 1.2):1; and the molar ratio of ammonium bifluoride vapor to lithium hydroxide is (1.5 to 3):1.
[0009] Preferably, the molar ratio of trimethyl borate to lithium hydroxide is 1:1; and the molar ratio of ammonium bifluoride vapor to lithium hydroxide is 2:1.
[0010] Furthermore, the ionic liquid is 1-butyl-3-methylimidazolium diimide salt, and the amount of 1-butyl-3-methylimidazolium diimide salt is 2.5 to 3.5 times the total mass of the lithium source, boron source, oxalic acid source and fluorine source.
[0011] Preferably, the amount of 1-butyl-3-methylimidazolium diimide salt is three times the total mass of the raw materials to ensure homogeneous dispersion of the system and resistance to fluorine corrosion.
[0012] Furthermore, in step (3), the reaction temperature is -5~10℃, the Ar introduction time is 30~50 min, and ammonium hydrogen fluoride vapor is continuously introduced for 3~5 h.
[0013] Furthermore, in step (4), supercritical carbon dioxide extraction and purification refers to pumping the filtered liquid into the extraction vessel, introducing carbon dioxide gas with a purity of 99.9% or higher, heating to the critical temperature of carbon dioxide, pressurizing to the critical pressure of carbon dioxide, and maintaining the supercritical state for 20 to 40 minutes.
[0014] Further, in step (4), the two-stage separation refers to controlling the carbon dioxide flow rate to 40~60g / min, introducing the supercritical carbon dioxide of the dissolved product into a first-stage separation vessel at 35~45℃ and 7.5~8.5MPa, and the liquid carbon dioxide in the first-stage separation vessel enters a second-stage separation vessel at 20~30℃ and 4.5~5.5MPa; the solid in the two-stage separation vessel is collected, which is lithium difluorooxalate borate.
[0015] Furthermore, in step (4), supernatant filtration refers to filtration through a 0.2~0.3μm polytetrafluoroethylene filter membrane.
[0016] Furthermore, in step (4), the drying is carried out at 70~80℃.
[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: Utilizing plasma activation technology, the chemical bond-breaking activation reaction can be achieved through high-energy particles without traditional heating, allowing for efficient operation at low temperatures. This not only shortens the reaction cycle but also suppresses side reactions such as fluorine source decomposition and oxalate ester hydrolysis, improving the selectivity of the target product. Furthermore, by selecting a chlorine-free raw material system, the generation of hydrogen chloride gas caused by chlorosilanes or silicon tetrachloride in traditional processes is avoided, reducing chloride ion impurities at the source and minimizing corrosion of reaction equipment, thus extending equipment lifespan. Using ionic liquid as the reaction medium, its high polarity and low volatility ensure uniform dispersion of raw materials, reducing moisture introduced by solvent evaporation or moisture absorption, and lowering product acidity. Simultaneously, supercritical carbon dioxide extraction replaces traditional recrystallization, utilizing its selective dissolution characteristics to achieve one-step purification, simplifying process steps, reducing solvent residue, and allowing the ionic liquid to be recycled, thus reducing production costs and environmental pressure. Detailed Implementation
[0018] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.
[0019] Example 1 A method for preparing lithium difluorooxalate borate, the process is as follows: 15.3 g of lithium hydroxide monohydrate (0.364 mol, purity > 99.9%, theoretical molar amount of target product is 0.34 mol), 37.8 g of trimethyl borate (0.363 mol), and 51.6 g of dimethyl oxalate (0.437 mol, purity > 99%) were added to a three-necked flask lined with polytetrafluoroethylene (PTFE) (to prevent fluorine corrosion). 438.8 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (CAS No.: 174899-83-3) (water content < 10 ppm) was added in proportion. The mixture was stirred at 300 rpm for 30 min to form a homogeneous, transparent solution. Argon gas was then used to purge the mixture for 30 min, and the flask was placed in a -5°C cryogenic bath. At -5°C, anhydrous ammonium fluoride vapor was continuously introduced into the reaction system via Ar gas at a power of 400 W and a frequency of 2.45 Hz. The reaction was activated by a GHz plasma generator for 3.5 hours. After the reaction, the plasma power supply was turned off, and argon gas was continuously introduced until the system temperature returned to room temperature to avoid abnormal crystallization morphology of the product due to sudden temperature changes. The reaction solution was transferred to a centrifuge tube and centrifuged at 8000 r / min for 10 min to remove a small amount of unreacted solid impurities, such as excess lithium hydroxide, to obtain a clear ionic liquid-product mixture. The supernatant was taken and filtered through a 0.22 μm polytetrafluoroethylene filter membrane to further remove colloidal impurities. The filtered mixture was pumped into an extraction vessel, the vessel was closed, and 99.99% pure carbon dioxide was introduced. The temperature was raised to the critical temperature of carbon dioxide, 31°C. The pressure was increased to the critical carbon dioxide pressure of 7.38 MPa and maintained in a supercritical state for 30 min. The outlet valve of the extraction vessel was opened, and the carbon dioxide flow rate was controlled at 50 g / min. The supercritical carbon dioxide containing the dissolved product was introduced into a primary separation vessel at 40 °C and 8 MPa. Most of the product precipitated out due to the decrease in solubility and remained in the primary separation vessel. The remaining liquid entered a secondary separation vessel at 25 °C and 5 MPa to further recover the residual product. The liquid flowing out of the secondary separation vessel was the ionic liquid. The white crystalline lithium difluorooxalate borate in the two separation vessels was collected, combined, and dried in a vacuum drying oven at 70-80 °C and -0.09 MPa for 2 h to remove residual carbon dioxide, yielding 45.85 g of lithium difluorooxalate borate.
[0020] Example 2 A method for preparing lithium difluorooxalatoborate, the method comprising: Plasma-free control group: Except for the reaction method being changed to 60°C oil bath heating, the other steps were completely the same as in Example 1.
[0021] Example 3 A method for preparing lithium difluorooxalatoborate, the method comprising: In the conventional recrystallization control group, the synthesis steps were the same as in Example 1. After centrifugation and filtration, the reaction solution was recrystallized with dimethyl carbonate and filtered. The filter cake was vacuum dried at 120°C for 4 hours. The product was lithium difluorooxalate borate. The filtrate was distilled at 90°C to recover dimethyl carbonate and ionic liquid.
[0022] Example 4 A method for preparing lithium difluorooxalatoborate, the method comprising: Control group of existing technology: Synthesis of silane oxalic acid condensate: 50g oxalic acid and 71.7g dimethyldichlorosilane were reacted at 80℃ for 24h, HCl was purged with nitrogen, and the condensate was obtained by vacuum distillation at 120℃; 20g lithium tetrafluoroborate and 32.7g condensate were reacted in 150g dimethyl carbonate at 30℃ for 8h, filtered and then vacuum distilled to obtain crude product; the solvent dimethyl carbonate obtained by vacuum distillation can be recycled, and the crude dimethyl carbonate is recrystallized and vacuum dried at 150℃ for 12h.
[0023] In summary, the results of each embodiment are shown in Table 1 below: Table 1 The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing lithium difluorooxalate borate, characterized in that, The process is as follows: (1) Lithium hydroxide, trimethyl borate, dimethyl oxalate, and ammonium hydrogen fluoride vapor were selected as raw materials, and ionic liquid was selected as medium. The ionic liquid was an imidazole imine salt ionic liquid. (2) The lithium hydroxide was dried at 120~140℃ for 4~6 h. Trimethyl borate and dimethyl oxalate were dehydrated by molecular sieve and then transferred to the reaction vessel under a protective atmosphere. (3) In a fluorine-resistant flask, add ionic liquid, pretreated lithium hydroxide, trimethyl borate and dimethyl oxalate in sequence, and stir until a homogeneous transparent solution is formed; introduce Ar into the flask, turn on the power of the plasma generator, set the power to 300~400W, and continuously introduce ammonium bifluoride vapor into the reaction system through Ar to carry ammonium bifluoride into the reaction system for reaction. (4) After the reaction is completed, the ionic liquid reaction solution of lithium difluorooxalate borate is obtained. After centrifugation, the supernatant is filtered. The filtered liquid is purified by supercritical carbon dioxide extraction. The product is collected by two-stage separation and dried to obtain the final product.
2. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, The purity of lithium hydroxide is >99.9%, the purity of dimethyl oxalate is >99%, and the water content of the ionic liquid is <10ppm.
3. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, The amount of lithium hydroxide used is 1.05 to 1.1 times the theoretical molar amount of the target product; the molar ratio of trimethyl borate to lithium hydroxide is (1 to 1.2):1; the molar ratio of dimethyl oxalate to lithium hydroxide is (1 to 1.2):1; and the molar ratio of ammonium bifluoride vapor to lithium hydroxide is (1.5 to 3):
1.
4. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, The ionic liquid is 1-butyl-3-methylimidazolium diimide salt, and the amount of 1-butyl-3-methylimidazolium diimide salt is 2.5 to 3.5 times the total mass of the lithium source, boron source, oxalic acid source and fluorine source.
5. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, In step (3), the reaction temperature is -5~10℃, the Ar is introduced for 30~50 min, and ammonium hydrogen fluoride vapor is continuously introduced for 3~5 h.
6. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, In step (4), supercritical carbon dioxide extraction and purification refers to pumping the filtered liquid into the extraction vessel, introducing carbon dioxide gas with a purity of 99.9% or higher, heating to the critical temperature of carbon dioxide, pressurizing to the critical pressure of carbon dioxide, and maintaining the supercritical state for 20 to 40 minutes.
7. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, In step (4), the two-stage separation refers to controlling the carbon dioxide flow rate to 40~60g / min, introducing the supercritical carbon dioxide of the dissolved product into a primary separation vessel at 35~45℃ and 7.5~8.5MPa, and then the liquid carbon dioxide in the primary separation vessel enters a secondary separation vessel at 20~30℃ and 4.5~5.5MPa; the solid in the two-stage separation vessel is collected, which is lithium difluorooxalate borate.
8. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, In step (4), supernatant filtration refers to filtration through a 0.2~0.3μm polytetrafluoroethylene filter membrane.
9. The method for preparing lithium difluorooxalatoborate according to claim 1, characterized in that, In step (4), the drying is carried out at 70~80℃.