Preparation method of lithium difluoro (oxalato) borate

Abstract

The invention discloses a preparation method of lithium difluoro (oxalato) borate and belongs to the field of lithium ion battery electrolyte materials. According to the preparation method, a lithium oxalate (Li2C2O4) solution, a sodium oxalate (Na2C2O4) solution and a boron trifluoride acetonitrile (BF3.CH3CN) solution are used as reaction raw materials, a lithium atom conversion path is optimized, cyclic utilization of a byproduct LiBF4 is achieved, and the product yield is remarkably improved; the NaBF4 is directly filtered and removed on the basis of the solubility difference between the NaBF4 and the product, so that the post-treatment process is simplified; a gradient cooling crystallization technology is adopted, high-purity LiDFOB is directly obtained from a crude product, and yield loss caused by traditional multiple recrystallization is avoided; the method is simple, efficient, environment-friendly and easy for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion battery electrolyte materials, and particularly relates to a preparation method of lithium difluorooxalate borate. BACKGROUND

[0002] As a new type of lithium ion battery electrolyte material, lithium difluorooxalate borate has excellent high and low temperature performance, high electrical conductivity and good thermal stability. Its unique molecular structure combines the advantages of lithium bisoxalate borate and lithium tetrafluoroborate, can maintain excellent electrochemical performance in the range of-20℃ to 60℃, and can form a stable SEI film at the electrolyte-electrode interface, thereby improving the electrical conductivity of the electrolyte and the cycle performance of the battery. Therefore, it has broad application prospects in the field of lithium ion batteries.

[0003] At present, there are many preparation methods of lithium difluorooxalate borate (LiC2O4BF2, LiDFOB). Some preparation methods need to use catalysts or reaction aids, which may lead to the introduction of impurities and affect the purity of the product. Some preparation methods need to be recrystallized or complex purification process several times, which increases the complexity and energy consumption of the production process. However, most of them have the disadvantages of immature process, harsh reaction conditions or expensive raw materials, which are not conducive to large-scale industrial production. Therefore, developing a simple, efficient and environmentally friendly preparation method of lithium difluorooxalate borate has become the focus and difficulty of current research. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of lithium difluorooxalate borate, which has the advantages of simple process, high yield and mild reaction conditions. The specific steps are as follows: Li2C2O4+2BF3→LiC2O4BF2+LiBF4 Na2C2O4+2BF3→NaC2O4BF2+NaBF4 LiBF4+NaC2O4BF2→LiC2O4BF2+NaBF4 A preparation method of lithium difluorooxalate borate, the process is as follows: (1) Add organic solvent to the reaction kettle, and then add lithium oxalate and boron trifluoride acetonitrile, stir at 50-80℃ for 2-14h, to obtain a mixed system containing lithium difluorooxalate borate and lithium tetrafluoroborate; (2) Add organic solvent to the reaction kettle, and then add sodium oxalate and boron trifluoride acetonitrile, stir at 50-80℃ for 2-14h, to obtain a mixed system containing sodium difluorooxalate borate and sodium tetrafluoroborate; (3) slowly drop the mixed system of lithium difluorooxalate borate and lithium tetrafluoroborate obtained in step (1) into the mixed system of sodium difluorooxalate borate and sodium tetrafluoroborate obtained in step (2) and react at 50-80℃ for 4-24h; (4) after the reaction, filter, concentrate the filtrate under vacuum, then crystallize at 5-20℃ for 1-5h, filter, and dry the filter cake to obtain lithium difluorooxalate borate.

[0005] Further, the organic solvent in step (1) and step (2) is at least one selected from acetonitrile (ACN), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethyl acetate (EA), and the amount of the organic solvent is 2-10 times of the mass of lithium difluorooxalate borate or sodium difluorooxalate borate.

[0006] Further, the molar ratio of lithium oxalate or sodium oxalate to boron trifluoride acetonitrile is 1:(1.1-3), and the molar ratio of lithium oxalate to sodium oxalate is 1:1.

[0007] Further, in step (4), the cooling rate is 1-5℃ / min.

[0008] Further, in step (4), the drying temperature is 100-120℃, and the drying time is 1-5h.

[0009] Further, in step (1) and step (2), the stirring rate is 100-600r / min.

[0010] Further, in step (1) and step (2), the mass concentration of boron trifluoride acetonitrile complex in the boron trifluoride acetonitrile solution is 15-25%.

[0011] Further, in step (4), the filtrate is concentrated under vacuum to 1 / 2-1 / 3 of the original volume.

[0012] The present application provides a high-efficiency and economical method for preparing lithium difluorooxalate borate. The method uses lithium oxalate (Li2C2O4), sodium oxalate (Na2C2O4) and boron trifluoride acetonitrile (BF3·CH3CN) solution as raw materials, optimizes the lithium atom conversion path, realizes the recycling of by-product LiBF4, and significantly improves the yield of the product; based on the difference in solubility of NaBF4 and the product, NaBF4 is directly removed by filtration, which simplifies the post-processing process; gradient cooling crystallization technology is used to obtain high-purity LiDFOB directly from the crude product, which avoids the yield loss caused by traditional multiple recrystallization; the method is simple, efficient, environmentally friendly and easy to industrialize. DETAILED DESCRIPTION

[0013] The technical solutions of the present application are further described below in combination with examples.

[0014] In the following examples and comparative examples, the mass concentration of boron trifluoride acetonitrile complex in the boron trifluoride acetonitrile solution is 20%.

[0015] Example 1 A preparation method of lithium difluorooxalate borate, the process is as follows: (1) 360 g of acetonitrile was added to the reaction kettle, and then 51 g (0.5 mol) of lithium oxalate and 558.63 g (1.025 mol) of boron trifluoride acetonitrile solution were added in sequence, and the reaction was carried out at 70°C for 4 h, with a stirring rate of 300 r / min, to obtain a mixed system containing lithium difluorooxalate borate and lithium tetrafluoroborate; (2) 480 g of acetonitrile was added to the reaction kettle, and then 67 g (0.5 mol) of sodium oxalate and 572.25 g (1.05 mol) of boron trifluoride acetonitrile solution were added in sequence, and the reaction was carried out at 75°C for 6 h, with a stirring rate of 400 r / min, to obtain a mixed system containing sodium difluorooxalate borate and sodium tetrafluoroborate; (3) The mixed system of lithium difluorooxalate borate and lithium tetrafluoroborate obtained in step (1) was slowly added to the mixed system of sodium difluorooxalate borate and sodium tetrafluoroborate obtained in step (2), and the reaction was carried out at 80°C for 8 h; (4) After the reaction was completed, filtration was carried out, the filtrate was concentrated to one half of the original volume under vacuum, then it was cooled to 20°C at a rate of 5°C / min, and crystallization was carried out at 20°C for 4 h, with a crystallization rate of 100 r / min, then filtration was carried out, and the filter cake was dried at 110°C for 2 h, to obtain 143.86 g of white lithium difluorooxalate borate with a purity of 99.8%, and the yield was 99.7%.

[0016] Example 2 A preparation method of lithium difluorooxalate borate, the process is as follows: (1) 432 g of dimethyl carbonate was added to the reaction kettle, and then 51 g (0.5 mol) of lithium oxalate and 626.75 g (1.15 mol) of boron trifluoride acetonitrile solution were added in sequence, and the reaction was carried out at 75°C for 3 h, with a stirring rate of 400 r / min, to obtain a mixed system containing lithium difluorooxalate borate and lithium tetrafluoroborate; (2) 320 g of dimethyl carbonate was added to the reaction kettle, and then 67 g (0.5 mol) of sodium oxalate and 599.5 g (1.1 mol) of boron trifluoride acetonitrile solution were added in sequence, and the reaction was carried out at 75°C for 4 h, with a stirring rate of 400 r / min, to obtain a mixed system containing sodium difluorooxalate borate and sodium tetrafluoroborate; (3) The mixed system of lithium difluorooxalate borate and lithium tetrafluoroborate obtained in step (1) was slowly added to the mixed system of sodium difluorooxalate borate and sodium tetrafluoroborate obtained in step (2), and the reaction was carried out at 80°C for 6 h; (4) After the reaction, filter, concentrate the filtrate to half of the original volume under vacuum, then cool down to 20°C at a rate of 5°C / min, crystallize for 2h at a crystallization rate of 100r / min, filter, dry the filter cake at 110°C for 4h, to obtain 142.99g of white lithium difluorooxalate borate with a purity of 99.6% and a yield of 98.9%.

[0017] Example 3 A method for preparing lithium difluorooxalate borate, the process being as follows: (1) Add 576g of ethyl acetate to the reaction kettle, then add 51g (0.5mol) of lithium oxalate and 572.65g (1.05mol) of boron trifluoride acetonitrile solution, react at 65°C for 6h at a stirring rate of 300r / min, to obtain a mixed system containing lithium difluorooxalate borate and lithium tetrafluoroborate; (2) Add 560g of ethyl acetate to the reaction kettle, then add 67g (0.5mol) of sodium oxalate and 681.25g (1.25mol) of boron trifluoride acetonitrile solution, react at 70°C for 5h at a stirring rate of 400r / min, to obtain a mixed system containing sodium difluorooxalate borate and sodium tetrafluoroborate; (3) Slowly drop the mixed system of lithium difluorooxalate borate and lithium tetrafluoroborate obtained in step (1) into the mixed system of sodium difluorooxalate borate and sodium tetrafluoroborate obtained in step (2), react at 75°C for 7h; (4) After the reaction, filter, concentrate the filtrate to half of the original volume under vacuum, then cool down to 20°C at a rate of 5°C / min, crystallize for 2h at a crystallization rate of 100r / min, filter, dry the filter cake at 110°C for 4h, to obtain 143.42g of white lithium difluorooxalate borate with a purity of 99.5% and a yield of 99.1%.

[0018] Example 4 A method for preparing lithium difluorooxalate borate, the process being as follows: (1) Add 504g of dimethyl carbonate to the reaction kettle, then add 51g (0.5mol) of lithium oxalate and 681.25g (1.25mol) of boron trifluoride acetonitrile solution, react at 80°C for 5h at a stirring rate of 300r / min, to obtain a mixed system containing lithium difluorooxalate borate and lithium tetrafluoroborate; (2) Add 768g of dimethyl carbonate to the reaction kettle, then add 80.4g (0.6mol) of sodium oxalate and 680.16g (1.248mol) of boron trifluoride acetonitrile solution, react at 80°C for 5h at a stirring rate of 300r / min, to obtain a mixed system containing sodium difluorooxalate borate and sodium tetrafluoroborate; (3) The mixed system of lithium difluoroboric acid oxalate and lithium tetrafluoroborate obtained in step (1) is slowly added to the mixed system of sodium difluoroboric acid oxalate and sodium tetrafluoroborate obtained in step (2) at 80℃ for 4h.

[0019] (4) After the reaction, the filtrate is concentrated to half of the original volume under vacuum, then cooled to 20℃ at a rate of 5℃ / min for 5h, the crystallization rate is 100r / min, filtered, and the filter cake is dried at 110℃ for 4h to obtain 143.34g of white lithium difluoroboric acid oxalate with a purity of 99.76% and a yield of 99.3%.

[0020] Comparative Example 1 A method for preparing lithium difluoroboric acid oxalate, the process is as follows: (1) 360g of acetonitrile is added to a reaction kettle, then 51g (0.5mol) of lithium oxalate and 558.63g (1.025mol) of boron trifluoride acetonitrile solution are added in sequence, and the reaction is carried out at 70℃ for 4h with a stirring rate of 300r / min to obtain a mixed system containing lithium difluoroboric acid oxalate and lithium tetrafluoroborate; (2) After the reaction, the filtrate is concentrated to half of the original volume under vacuum, then cooled to 20℃ at a rate of 5℃ / min for 4h, the crystallization rate is 100r / min, filtered, and the filter cake is dried at 110℃ for 2h to obtain 49.47g of lithium difluoroboric acid oxalate with a purity of 94.5% and a yield of 49.47%.

[0021] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the embodiments of the present application and not to limit them, and those skilled in the art should understand that any equivalent replacement or obvious modification of the embodiments of the present application without changing the performance or purpose thereof should be covered within the scope of the present application.

Claims

1. A method for preparing lithium difluorooxalatoborate, characterized in that: The process is as follows: (1) Add an organic solvent to a reaction kettle, and then add lithium oxalate and boron trifluoride acetonitrile solution in sequence, and stir the mixture at 50-80°C for 2-14 hours to obtain a mixed system containing lithium difluorooxalatoborate and lithium tetrafluoroborate; (2) Adding an organic solvent to a reaction kettle, followed by sodium oxalate and boron trifluoride acetonitrile solution, stirring and reacting at 50-80°C for 2-14 hours to obtain a mixed system containing sodium difluorooxalatoborate and sodium tetrafluoroborate; (3) slowly adding the mixed system of lithium difluorooxalatoborate and lithium tetrafluoroborate obtained in step (1) dropwise to the mixed system of sodium difluorooxalatoborate and sodium tetrafluoroborate obtained in step (2), and reacting at 50-80° C. for 4-24 h; (4) After the reaction is completed, the reaction mixture is filtered and the filtrate is concentrated in vacuo. The temperature is then lowered to 5-20°C for crystallization for 1-5 hours. The mixture is filtered and the filter cake is dried to obtain lithium difluorooxalatoborate.

2. The method for preparing lithium difluorooxalatoborate according to claim 1, wherein: The organic solvent in step (1) and step (2) is selected from at least one of acetonitrile (ACN), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethyl acetate (EA), and the amount of the organic solvent is 2 to 10 times the mass of lithium difluorooxalatoborate or sodium difluorooxalatoborate.

3. The method for preparing lithium difluorooxalatoborate according to claim 1, wherein: The molar ratio of lithium oxalate or sodium oxalate to boron trifluoride and acetonitrile is 1:(1.1-3), and the molar ratio of lithium oxalate to sodium oxalate is 1:

1.

4. The method for preparing lithium difluorooxalatoborate according to claim 1, wherein: In step (4), the cooling rate is 1~5℃ / min.

5. The method for preparing lithium difluorooxalatoborate according to claim 1, wherein: In step (4), the drying temperature is 100-120° C., and the drying time is 1-5 hours.

6. The method for preparing lithium difluorooxalatoborate according to claim 1, wherein: The stirring rate in step (1) and step (2) is 100-600 r / min.