A purification method of lithium difluoro(oxalato)borate
By mixing lithium difluoroxalic acid borate with liquid hydrogen fluoride, the impurity reaction is promoted to form lithium difluoroxalic acid borate, and purified with organic solvents, the complex problems of purification methods in the prior art are solved, and the impurities are efficiently removed and the product purity is improved.
Patent Information
- Application Number
- CN202310472561.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-04-27
- Publication Date
- 2025-07-01
- Estimated Expiration
- 2043-04-27
AI Technical Summary
The method of purifying lithium difluoroxalate borate in the prior art is complex, and it is difficult to effectively remove impurities such as lithium tetrafluoroborate and lithium dioxalate borate, which affects battery performance.
By mixing lithium difluoroxalate borate with liquid hydrogen fluoride, the reaction between lithium tetrafluoroxalate and lithium dioxalate is promoted to form lithium difluoroxalate borate, and the impurities are converted into removable substances by adding excess lithium oxalate, and finally purifying is performed using an organic solvent.
It achieves efficient purification of lithium difluoroxalate borate, removes impurities, improves the purity of the product, and meets the use requirements of the electrolyte.
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Figure BDA0004204544460000061
Abstract
Description
Technical Field
[0001] The present invention relates to a purification method of lithium difluorooxalate borate, belonging to the technical field of lithium ion battery materials. Background Art
[0002] Currently, the electrolyte industrially applied to lithium ion batteries is mainly lithium hexafluorophosphate (LiPF6). However, LiPF6 has some inherent disadvantages, such as poor thermal stability and sensitivity to water, which limit the application fields and further development of lithium batteries. Industry technicians have also explored other lithium salts, such as lithium tetrafluoroborate (LiBF4) and lithium bis(oxalato)borate (LiBOB). Both have their own advantages and disadvantages and have not been able to be mass-applied as the main electrolyte in lithium ion batteries. The battery made of LiBF4 has good low-temperature performance but poor cycle performance, while the battery made of LiBOB has good high-temperature performance but poor low-temperature performance. Lithium difluorooxalate borate (LiODFB) newly developed in recent years has a molecular structure containing half of LiBF4 and half of LiBOB, integrating the advantages of the two lithium salts: it has excellent high and low temperature performance in the range of -20°C to 60°C, has good film-forming performance, the SEI film is stable and has low impedance; using lithium difluorooxalate borate can significantly improve the cycle life and rate performance of the battery.
[0003] Among many preparation process routes of LiODFB, most of the prepared LiODFB has by-products, generally LiBF4 and LiF, and there are also traces of LiBOB in some LiODFB products. The solubility of the impurity LiBF4 and the target product LiODFB in common solvents is very similar, making it difficult to separate. And a relatively high-purity electrolyte is required in the lithium battery electrolyte, otherwise it will affect the performance of the battery. Chinese Patent Document CN101265176B purifies the product by means of crystallization from a mixed solvent. LiODFB is dissolved in acetonitrile, dimethyl carbonate, and propylene carbonate, and then mixed with diethyl ether, carbon tetrachloride, butyrolactone, etc. However, this kind of purification method generates a large amount of waste liquid. Chinese Patent Document CN106674261B uses a special solvent for washing and separation. The crude product of LiODFB is mixed with BF3 compounds and aprotic non-polar solvents, so that the by-product LiBF4 is better dissolved, while the target lithium salt LiODFB is insoluble, realizing the separation and purification of the LiODFB product and LiBF4. However, this method requires slow heating and reaction, and the process is relatively complex. There is also a purification method of converting by-product impurities into the target salt. For example, Chinese Patent Document CN109734735B filters out LiF from the LiODFB solution containing LiBF4 and LiF impurities, and then adds ammonium oxalate and trimethylchlorosilane to the filtrate to further convert LiBF4 into LiODFB, and then distillation and recrystallization are carried out. However, this method introduces new impurity elements such as silicon and chlorine.
[0004] Therefore, there is an urgent need to develop a simple and efficient purification method for lithium difluorooxalate borate. Summary of the Invention
[0005] The purpose of the present invention is to provide a purification method for lithium difluorooxalate borate, which can solve the problem of complex operation in the current purification of lithium difluorooxalate borate.
[0006] In order to achieve the above object, the technical solution adopted by the purification method of lithium difluorooxalate borate of the present invention is as follows:
[0007] A purification method for lithium difluorooxalate borate, comprising the following steps:
[0008] (1) Mix lithium difluorooxalate borate and liquid hydrogen fluoride until lithium difluorooxalate borate is completely dissolved and the mass fraction of lithium bis(oxalato)borate in the resulting liquid is not more than 0.005%, to obtain a first mixed liquid; the impurities in the lithium difluorooxalate borate include lithium tetrafluoroborate.
[0009] (2) Mix the first mixed liquid and lithium oxalate to remove lithium tetrafluoroborate in the first mixed liquid, to obtain a second mixed liquid, and then remove the liquid hydrogen fluoride in the second mixed liquid to obtain a solid product.
[0010] (3) Mix the solid product and an organic solvent until lithium difluorooxalate borate in the solid product is completely dissolved, perform solid-liquid separation, and then crystallize the liquid obtained from the solid-liquid separation to obtain a purified product of lithium difluorooxalate borate; the organic solvent is a good solvent for lithium difluorooxalate borate and a poor solvent for lithium fluoride and lithium oxalate.
[0011] Purification method of lithium difluorooxalate borate of the present invention: Dissolve lithium difluorooxalate borate containing impurities of lithium bis(oxalato)borate (LiBOB) and lithium tetrafluoroborate (LiBF4) in liquid hydrogen fluoride. Hydrogen fluoride is both a solvent and a catalyst, promoting the reaction of LiBF4 and LiBOB to generate lithium difluorooxalate borate (LiODFB). Moreover, the reaction rate of LiBF4 and LiBOB in the liquid phase is relatively fast, and the reaction formula is: LiBF4 + LiB(C2O4)2 → 2LiBF2C2O4. Since the molar ratio of lithium tetrafluoroborate to lithium bis(oxalato)borate in lithium difluorooxalate borate is greater than 1:1, and both lithium tetrafluoroborate and lithium bis(oxalato)borate are soluble in liquid hydrogen fluoride, and the reaction rate is fast and the reaction is complete in the liquid phase. Therefore, the lithium bis(oxalato)borate impurity in lithium difluorooxalate borate can be completely removed in step (1); then, an excessive amount of lithium oxalate is added to react with the remaining lithium tetrafluoroborate to obtain lithium difluorooxalate borate and lithium fluoride, and the reaction formula is: LiBF4 + Li2C2O4 → LiBF2C2O4 + 2LiF; Through the operations of step (1) and step (2), the lithium bis(oxalato)borate and lithium tetrafluoroborate impurities in lithium difluorooxalate borate are converted into lithium difluorooxalate borate, lithium fluoride, and lithium oxalate. Finally, by utilizing the solubility differences of lithium difluorooxalate borate, lithium fluoride, and lithium oxalate in organic solvents, lithium difluorooxalate borate is further purified to obtain a purified product of lithium difluorooxalate borate. The purification method of lithium difluorooxalate borate of the present invention is simple in operation, and the purity of the obtained lithium difluorooxalate borate product is high, which can meet the requirements for use in electrolytes.
[0012] Preferably, the impurities in the lithium difluorooxalate borate further include lithium bis(oxalato)borate, and the molar ratio of lithium bis(oxalato)borate to lithium tetrafluoroborate is less than 1:1.
[0013] It can be understood that when the impurities in lithium difluorooxalate borate contain lithium bis(oxalato)borate, during the process of dissolving lithium difluorooxalate borate in liquid hydrogen fluoride, lithium bis(oxalato)borate and lithium tetrafluoroborate are converted into lithium difluorooxalate borate through reaction; when the impurities in lithium difluorooxalate borate do not contain lithium bis(oxalato)borate, during the process of dissolving lithium difluorooxalate borate in liquid hydrogen fluoride, there is no reaction of converting lithium bis(oxalato)borate into lithium difluorooxalate borate.
[0014] When the impurities in lithium difluorooxalate borate contain lithium bis(oxalato)borate, if lithium difluorooxalate borate, lithium oxalate, and liquid hydrogen fluoride are mixed together, it will cause lithium oxalate to react preferentially with the lithium tetrafluoroborate impurity in lithium difluorooxalate borate. After consuming the lithium tetrafluoroborate, the lithium bis(oxalato)borate in lithium difluorooxalate borate cannot be effectively removed, thereby reducing the purity of the purified product.
[0015] It is understandable that in step (1), the concentration of lithium bis(oxalato)borate in the first mixture can be monitored in real time to determine whether lithium bis(oxalato)borate has been completely removed (whether lithium bis(oxalato)borate has completely reacted with lithium tetrafluoroborate); in step (2), the concentration of lithium tetrafluoroborate in the first mixture can be monitored in real time to determine whether lithium tetrafluoroborate has been completely removed (whether lithium tetrafluoroborate has completely reacted with lithium oxalate).
[0016] Preferably, the temperature of the mixing in step (1) and step (2) is independently not lower than 0 °C. If the temperature of the mixing in step (1) and step (2) is lower than 0 °C, the solubility of lithium difluoro(oxalato)borate in liquid hydrogen fluoride will be too low, resulting in excessive consumption of liquid hydrogen fluoride and reduced production capacity.
[0017] Preferably, the temperature of the mixing in step (1) and step (2) is independently 0 - 15 °C. The temperature of the mixing is slightly lower than the boiling point of liquid hydrogen fluoride to avoid a large amount of gasification of liquid hydrogen fluoride during operation, resulting in loss of liquid hydrogen fluoride and premature precipitation of lithium difluoro(oxalato)borate and its impurities, reducing the yield and purity of the product.
[0018] Preferably, in step (1), the temperature of the mixing is 0 - 15 °C.
[0019] Preferably, the operation in step (1) is carried out at 0 - 15 °C.
[0020] Preferably, in step (2), the temperature of the mixing is not lower than 0 °C.
[0021] Preferably, in step (2), the temperature of the mixing is 0 - 15 °C.
[0022] Preferably, the operations in step (1) and step (2) are carried out under closed conditions. Carrying out the operations in step (1) and step (2) under closed conditions can enable the recycling of hydrogen fluoride and generate no waste gas or waste liquid.
[0023] Preferably, in step (1), the mass ratio of lithium difluoro(oxalato)borate to liquid hydrogen fluoride is (80 - 100):500. Excessive use of liquid hydrogen fluoride will lead to complex post-treatment processes, reduced production capacity, and enrichment of impurities in liquid hydrogen fluoride, reducing the purity of the purified product of lithium difluoro(oxalato)borate. Insufficient use of liquid hydrogen fluoride will cause incomplete dissolution of lithium difluoro(oxalato)borate, resulting in insufficient reaction of lithium bis(oxalato)borate in lithium difluoro(oxalato)borate with lithium tetrafluoroborate, causing incomplete removal of lithium bis(oxalato)borate and reducing the product purity; experiments show that even if a small amount of liquid hydrogen fluoride can completely dissolve lithium difluoro(oxalato)borate, it will still lead to a high content of impurities in the product.
[0024] To ensure the complete removal of lithium tetrafluoroborate from the first mixture, preferably, in step (2), the molar ratio of lithium oxalate to lithium tetrafluoroborate in the first mixture is not less than 1:1.
[0025] Preferably, in step (2), the molar ratio of lithium oxalate to lithium tetrafluoroborate in the first mixture is (1.02 - 1.2):1. If the amount of lithium oxalate used is too small, lithium tetrafluoroborate in the first mixture cannot be fully removed. If the amount of lithium oxalate used is too large, new impurities will be introduced, increasing the difficulty of subsequent impurity removal and reducing the purity of the purified product of lithium difluoro(oxalato)borate.
[0026] Preferably, the organic solvent is selected from one of diethyl ether, acetonitrile, dimethyl carbonate, and propylene carbonate. When two or more of diethyl ether, acetonitrile, dimethyl carbonate, and propylene carbonate are mixed and used, the impurity removal effect will deteriorate, and it will be impossible to effectively separate lithium difluoro(oxalato)borate, lithium fluoride, and lithium oxalate.
[0027] Preferably, in step (3), the mass ratio of the solid product to the organic solvent is 1:(5 - 7.5). If the amount of the organic solvent used is too large, not only will the post-treatment process be complicated, but also the purity of the purified product will be reduced. If the amount of the organic solvent used is too small, lithium difluoro(oxalato)borate cannot be completely dissolved, reducing the product yield.
[0028] Preferably, the organic solvent is diethyl ether, and the mass ratio of the solid product to the organic solvent is 1:(5 - 5.5); the crystallization method includes the following steps: heating the liquid obtained by solid-liquid separation or placing it in a vacuum environment to evaporate the diethyl ether in the liquid obtained by solid-liquid separation to obtain a concentrated liquid, and then cooling the concentrated liquid to -20 to -15 °C for crystallization; the evaporation amount of diethyl ether is 70 - 80% of the total mass of diethyl ether;
[0029] Or the organic solvent is dimethyl carbonate or propylene carbonate, and the mass ratio of the solid product to the organic solvent is 1:(7 - 7.5); the temperature for mixing in step (3) is 50 - 55 °C; the crystallization method includes the following steps: cooling the liquid obtained by solid-liquid separation to 15 - 25 °C for crystallization. If the temperature for mixing in step (3) is too high, the product will decompose, resulting in a decrease in product purity. If the temperature for mixing in step (3) is too low, the separation effect will be poor, affecting the product quality.
[0030] It can be understood that when the organic solvent is dimethyl carbonate or propylene carbonate, the temperature of the liquid obtained by solid-liquid separation is 50 - 55 °C, and during crystallization, the temperature of the liquid obtained by solid-liquid separation is reduced from 50 - 55 °C to 15 - 25 °C. Specific embodiments
[0031] The technical solution of the present invention will be further described below in conjunction with specific embodiments.
[0032] Example 1
[0033] The purification method of lithium difluorooxalate borate in this example specifically includes the following steps:
[0034] (1) At 15°C, 100 g of crude lithium difluorooxalate borate and 500 g of anhydrous hydrogen fluoride are added to a closed container lined with polytetrafluoroethylene, and stirred until the crude lithium difluorooxalate borate is completely dissolved (during the dissolution process, a small amount of lithium bis(oxalato)borate contained in the crude lithium difluorooxalate borate is converted into lithium difluorooxalate borate through reaction), and the mass fraction of lithium bis(oxalato)borate in the resulting liquid is 0.002% to obtain a first mixed liquid;
[0035] Then lithium oxalate anhydrous (the molar ratio of lithium oxalate to lithium tetrafluoroborate in the first mixed liquid is 1.02:1) is added to the first mixed liquid, and stirred for 30 min to obtain a second mixed liquid; after detection, the mass fraction of lithium tetrafluoroborate in the second mixed liquid is less than 0.005%;
[0036] (2) Then the second mixed liquid is heated and concentrated under vacuum to remove hydrogen fluoride in the second mixed liquid to obtain a solid product;
[0037] (3) The solid product is added to ether (the mass ratio of the solid product to ether is 1:5), stirred to fully dissolve the solid product, then filtered (the solid obtained by filtration is lithium fluoride and lithium oxalate), and then the filtered liquid is placed in a vacuum environment (vacuum pumping) to evaporate the ether in the liquid. The mass of the evaporated ether is 80% of the total mass of the ether to obtain a concentrated liquid, and then the concentrated liquid is cooled to -20°C for crystallization, and finally the precipitated crystals are dried at 120°C for 2 h to obtain 87.2 g of purified product.
[0038] Example 2
[0039] The purification method of lithium difluorooxalate borate in this example specifically includes the following steps:
[0040] (1) At 0°C, 80 g of crude lithium difluorooxalate borate and 500 g of anhydrous hydrogen fluoride are added to a closed container lined with polytetrafluoroethylene, and stirred until the crude lithium difluorooxalate borate is completely dissolved (during the dissolution process, a small amount of lithium bis(oxalato)borate contained in the crude lithium difluorooxalate borate is converted into lithium difluorooxalate borate through reaction), and the mass fraction of lithium bis(oxalato)borate in the resulting liquid is 0.002% to obtain a first mixed liquid;
[0041] Then, lithium oxalate anhydrous was added to the first mixed solution (the molar ratio of lithium oxalate to lithium tetrafluoroborate in the first mixed solution was 1.2:1), and the mixture was stirred for 30 min to obtain a second mixed solution; after detection, the mass fraction of lithium tetrafluoroborate in the second mixed solution was less than 0.005%.
[0042] (2) Then, the second mixed solution was heated and concentrated under vacuum to remove hydrogen fluoride in the second mixed solution, obtaining a solid product.
[0043] (3) The solid product was added to dimethyl carbonate at 55 °C (the mass ratio of the solid product to dimethyl carbonate was 1:7.5), and the mixture was stirred to fully dissolve the solid product. Then, lithium fluoride, lithium oxalate and other solid impurities were removed by filtration. Next, the filtered liquid was cooled to 25 °C for crystallization. Finally, the precipitated crystals were dried at 120 °C for 2 h to obtain 66.4 g of a purified product.
[0044] Example 3
[0045] (1) Under the condition of 15 °C, 100 g of crude lithium difluorooxalate borate and 500 g of anhydrous hydrogen fluoride were added to a closed container lined with polytetrafluoroethylene, and the mixture was stirred until the crude lithium difluorooxalate borate was completely dissolved, obtaining a first mixed solution.
[0046] Then, lithium oxalate anhydrous was added to the first mixed solution (the molar ratio of lithium oxalate to lithium tetrafluoroborate in the first mixed solution was 1.02:1), and the mixture was stirred for 30 min to obtain a second mixed solution; after detection, the mass fraction of lithium tetrafluoroborate in the second mixed solution was 0.005%.
[0047] (2) Then, the second mixed solution was heated and concentrated under vacuum to remove hydrogen fluoride in the second mixed solution, obtaining a solid product.
[0048] (3) The solid product was added to propylene carbonate at 55 °C (the mass ratio of the solid product to propylene carbonate was 1:7.5), and the mixture was stirred to fully dissolve the solid product. Then, filtration was carried out. Next, the filtered liquid was cooled to 15 °C for crystallization. Finally, the precipitated crystals were dried at 120 °C for 2 h to obtain 85.6 g of a purified product.
[0049] Experimental Example
[0050] In order to evaluate the purification effect of the purification method of lithium difluorooxalate borate of the present invention, the mass fractions of lithium difluorooxalate borate and the mass fractions of various impurities in the crude lithium difluorooxalate borate used in Examples 1 - 3 and the purified products of lithium difluorooxalate borate purified in each example were listed in Table 1. In Table 1, Example 1, Example 2, and Example 3 respectively represent the purified products of lithium difluorooxalate borate purified in Examples 1 - 3.
[0051] Table 1 Mass fractions of lithium difluoro(oxalato)borate in the crude lithium difluoro(oxalato)borate and the purified products obtained in each example, as well as the mass fractions of various impurities
[0052]
Claims
1. A purification method of lithium difluorooxalate borate, characterized in that, It includes the following steps: (1) Mix lithium difluoro(oxalato)borate and liquid hydrogen fluoride until lithium difluoro(oxalato)borate is completely dissolved and the mass fraction of lithium bis(oxalato)borate in the resulting dissolved liquid is not more than 0.005%, to obtain a first mixed liquid; the impurities in the lithium difluoro(oxalato)borate include lithium tetrafluoroborate; (2) Mix the first mixed liquid and lithium oxalate to remove lithium tetrafluoroborate in the first mixed liquid, to obtain a second mixed liquid, and then remove the liquid hydrogen fluoride in the second mixed liquid to obtain a solid product; (3) Mix the solid product and an organic solvent until lithium difluoro(oxalato)borate in the solid product is completely dissolved, perform solid-liquid separation, and then crystallize the liquid obtained from the solid-liquid separation to obtain a purified product of lithium difluoro(oxalato)borate; the organic solvent is a good solvent for lithium difluoro(oxalato)borate and a poor solvent for lithium fluoride and lithium oxalate.
2. The purification method of lithium difluoro(oxalato)borate according to claim 1, characterized in that, The impurities in the lithium difluoro(oxalato)borate further include lithium bis(oxalato)borate, and the molar ratio of lithium bis(oxalato)borate to lithium tetrafluoroborate is less than 1:
1.
3. The purification method of lithium difluorooxalate borate according to claim 1, characterized in that, The temperature of the mixing in step (1) and step (2) is independently not lower than 0°C.
4. The purification method of lithium difluoro(oxalato)borate according to claim 2, characterized in that, The temperature of the mixing in step (1) and step (2) is independently 0 - 15°C.
5. The purification method of lithium difluoro(oxalato)borate according to any one of claims 1-4, characterized in that, In step (1), the mass ratio of the lithium difluoro(oxalato)borate to the liquid hydrogen fluoride is (80 - 100):
500.
6. The purification method of lithium difluoro(oxalato)borate according to any one of claims 1-4, characterized in that, In step (2), the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed liquid is not less than 1:
1.
7. The purification method of lithium difluorooxalate borate according to claim 6, wherein In step (2), the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed liquid is (1.02 - 1.2):
1.
8. The purification method of lithium difluoro(oxalato)borate according to any one of claims 1-4, characterized in that, The organic solvent is selected from one of diethyl ether, acetonitrile, dimethyl carbonate, and propylene carbonate.
9. The purification method of lithium difluoro(oxalato)borate according to claim 8, wherein, In step (3), the mass ratio of the solid product to the organic solvent is 1:(5 - 7.5).
10. The purification method of lithium difluorooxalate borate according to any one of claims 1-4, characterized in that, The organic solvent is diethyl ether, and the mass ratio of the solid product to the organic solvent is 1:(5 - 5.5); the crystallization method includes the following steps: heat the liquid obtained from the solid-liquid separation or place it in a vacuum environment to evaporate the diethyl ether in the liquid obtained from the solid-liquid separation to obtain a concentrated liquid, and then cool the concentrated liquid to -20 - -15°C for crystallization; the evaporation amount of the diethyl ether is 70 - 80% of the total mass of the diethyl ether; Or the organic solvent is dimethyl carbonate or propylene carbonate, the mass ratio of the solid product to the organic solvent is 1:(7 - 7.5); the temperature of the mixing in step (3) is 50 - 55°C; the crystallization method includes the following steps: cool the liquid obtained from the solid-liquid separation to 15 - 25°C for crystallization.
Citation Information
Patent Citations
Method for purifying LiODFB
CN101265176B
Purification method of lithium difluoroborate oxalate
CN106674261B
A purification method for lithium difluorooxalate borate
CN109734735B
Purification method of lithium difluoroborate
CN109734735A
Preparation method of lithium oxalyldifluoroborate
CN111943969A