CN116496309A - Purification method of lithium difluoro oxalate borate - Google Patents
Purification method of lithium difluoro oxalate borate Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 36
- 238000000746 purification Methods 0.000 title claims abstract description 23
- NDZWKTKXYOWZML-UHFFFAOYSA-N trilithium;difluoro oxalate;borate Chemical compound [Li+].[Li+].[Li+].[O-]B([O-])[O-].FOC(=O)C(=O)OF NDZWKTKXYOWZML-UHFFFAOYSA-N 0.000 title abstract description 11
- -1 lithium tetrafluoroborate Chemical compound 0.000 claims abstract description 37
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 claims abstract description 34
- WXNUAYPPBQAQLR-UHFFFAOYSA-N B([O-])(F)F.[Li+] Chemical compound B([O-])(F)F.[Li+] WXNUAYPPBQAQLR-UHFFFAOYSA-N 0.000 claims abstract description 30
- YNQRWVCLAIUHHI-UHFFFAOYSA-L dilithium;oxalate Chemical compound [Li+].[Li+].[O-]C(=O)C([O-])=O YNQRWVCLAIUHHI-UHFFFAOYSA-L 0.000 claims abstract description 27
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 claims abstract description 26
- 239000012535 impurity Substances 0.000 claims abstract description 24
- 239000003960 organic solvent Substances 0.000 claims abstract description 21
- 239000012264 purified product Substances 0.000 claims abstract description 13
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 77
- 229910052744 lithium Inorganic materials 0.000 claims description 77
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 claims description 74
- 239000007788 liquid Substances 0.000 claims description 56
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 45
- 239000011259 mixed solution Substances 0.000 claims description 35
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 28
- 229910000040 hydrogen fluoride Inorganic materials 0.000 claims description 28
- 239000012265 solid product Substances 0.000 claims description 24
- 238000002156 mixing Methods 0.000 claims description 19
- 238000002425 crystallisation Methods 0.000 claims description 13
- 238000000926 separation method Methods 0.000 claims description 13
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims description 12
- 230000008025 crystallization Effects 0.000 claims description 9
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 9
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 claims description 9
- 239000000243 solution Substances 0.000 claims description 7
- 239000002904 solvent Substances 0.000 claims description 7
- 238000001816 cooling Methods 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 6
- 238000001704 evaporation Methods 0.000 claims description 2
- 230000008020 evaporation Effects 0.000 claims description 2
- 239000000047 product Substances 0.000 abstract description 14
- SYRDSFGUUQPYOB-UHFFFAOYSA-N [Li+].[Li+].[Li+].[O-]B([O-])[O-].FC(=O)C(F)=O Chemical compound [Li+].[Li+].[Li+].[O-]B([O-])[O-].FC(=O)C(F)=O SYRDSFGUUQPYOB-UHFFFAOYSA-N 0.000 abstract description 10
- 239000003792 electrolyte Substances 0.000 abstract description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 4
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 4
- 239000000463 material Substances 0.000 abstract description 2
- 229910013063 LiBF 4 Inorganic materials 0.000 description 10
- 239000012043 crude product Substances 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 9
- 238000003756 stirring Methods 0.000 description 8
- 238000001914 filtration Methods 0.000 description 7
- 239000006227 byproduct Substances 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 229910003002 lithium salt Inorganic materials 0.000 description 3
- 159000000002 lithium salts Chemical class 0.000 description 3
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 3
- 239000004810 polytetrafluoroethylene Substances 0.000 description 3
- YEJRWHAVMIAJKC-UHFFFAOYSA-N 4-Butyrolactone Chemical compound O=C1CCCO1 YEJRWHAVMIAJKC-UHFFFAOYSA-N 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
- IJOOHPMOJXWVHK-UHFFFAOYSA-N chlorotrimethylsilane Chemical compound C[Si](C)(C)Cl IJOOHPMOJXWVHK-UHFFFAOYSA-N 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000036632 reaction speed Effects 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- VBIXEXWLHSRNKB-UHFFFAOYSA-N ammonium oxalate Chemical compound [NH4+].[NH4+].[O-]C(=O)C([O-])=O VBIXEXWLHSRNKB-UHFFFAOYSA-N 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 229930188620 butyrolactone Natural products 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 239000012454 non-polar solvent Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000005051 trimethylchlorosilane Substances 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
- C07F5/00—Compounds containing elements of Groups 3 or 13 of the Periodic Table
- C07F5/02—Boron compounds
- C07F5/022—Boron compounds without C-boron linkages
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Primary Cells (AREA)
- Secondary Cells (AREA)
Abstract
The invention relates to a purification method of lithium difluoro oxalate borate, belonging to the technical field of lithium ion battery materials. According to the purification method of the lithium difluoroborate, impurities of the lithium difluoroborate and the lithium tetrafluoroborate in the lithium difluoroborate are converted into the lithium difluoroborate, the lithium fluoride and the lithium oxalate, and finally the lithium difluoroborate is further purified by utilizing the solubility difference of the lithium difluoroborate, the lithium fluoride and the lithium oxalate in an organic solvent to obtain a purified product of the lithium difluoroborate. The purification method of the lithium difluorooxalate borate is simple to operate, and the purity of the purified lithium difluorooxalate borate product is high, so that the use requirement of the electrolyte can be met.
Description
Technical Field
The invention relates to a purification method of lithium difluoro oxalate borate, belonging to the technical field of lithium ion battery materials.
Background
Currently, the electrolyte that has been industrially applied to lithium ion batteries is mainly lithium hexafluorophosphate (LiPF 6 ) But LiPF 6 There are some inherent disadvantages such as poor thermal stability, sensitivity to water, limiting the field of application and further development of lithium batteries. Other lithium salts have also been explored by those skilled in the art, such as lithium tetrafluoroborate (LiBF 4 ) And lithium bisoxalato borate (LiBOB), both of which have advantages and disadvantages, have not been used in bulk as a primary electrolyte in lithium ion batteries. LiBF 4 The battery manufactured by the method has good low-temperature performance but poor cycle performance, and the battery manufactured by LiBOB has good high-temperature performance but poor low-temperature performance. In recent years, newly developed lithium difluorooxalato borate (LiODFB) has a molecular structure comprising half LiBF4 and half LiBOB, and integrates the advantages of two lithium salts: the SEI film has excellent high and low temperature performance in the range of-20 ℃ to 60 ℃, good film forming performance, stable SEI film and low impedance; the cycle life and rate performance of the battery can be obviously improved by adopting the lithium difluorooxalato borate.
In many LiODFB preparation process routes, most of the LiODFB prepared by the preparation method has byproducts, generally LiBF 4 And LiF, also some LiODFB products have trace amounts of LiBOB, impurity LiBF 4 The solubility of the lithium battery electrolyte is very similar to that of the LiODFB target product in a general solvent, and the lithium battery electrolyte is difficult to separate, and the lithium battery electrolyte needs to use electrolyte with higher purity, otherwise, the performance of the battery is influenced. The Chinese patent document CN101265176B adopts a mixed solvent crystallization mode to purify a product, liODFB is dissolved in acetonitrile, dimethyl carbonate and propylene carbonate, and then the mixture is mixed with diethyl ether, carbon tetrachloride, butyrolactone and the like, but the amount of waste liquid generated by the purification mode is larger. Chinese patent document CN106674261B uses special solvent to wash and separate LiODFB crude product and BF 3 Mixing the class of compounds with aprotic nonpolar solvents to obtain a byproduct LiBF 4 Better dissolves, but the target lithium salt LiODFB is insoluble, thus realizing LiODFB products and LiBF 4 But the method needs slow reaction by heating, and the process is complex. Further purification methods for converting by-product impurities into target salts, e.g. Chinese patentDocument CN109734735B will contain LiBF 4 And LiODFB solution of LiF impurity, filtering to remove LiF, adding ammonium oxalate and trimethylchlorosilane into filtrate, and adding LiBF 4 Further converted into LiODFB, and then distilled and recrystallized, but the method introduces new impurity elements such as silicon, chlorine and the like.
Therefore, there is a need to develop a simple and efficient purification method of lithium difluorooxalato borate.
Disclosure of Invention
The invention aims to provide a purification method of lithium difluoro oxalate borate, which can solve the problem of complex operation in the current purification of lithium difluoro oxalate borate.
In order to achieve the above purpose, the purification method of the lithium difluorooxalate borate adopts the following technical scheme:
a purification method of lithium difluorooxalato borate comprises the following steps:
(1) Mixing lithium difluorooxalato borate and liquid hydrogen fluoride until the lithium difluorooxalato borate is completely dissolved, and enabling the mass fraction of the lithium bisoxalato borate in the dissolved liquid to be not more than 0.005%, so as to obtain a first mixed liquid; the impurities in the lithium difluoroborate comprise lithium tetrafluoroborate;
(2) Mixing the first mixed solution with lithium oxalate to remove lithium tetrafluoroborate in the first mixed solution to obtain a second mixed solution, and removing liquid hydrogen fluoride in the second mixed solution to obtain a solid product;
(3) Mixing the solid product and an organic solvent until lithium difluoroborate in the solid product is completely dissolved, carrying out solid-liquid separation, and crystallizing the liquid obtained by the solid-liquid separation to obtain a purified product of lithium difluoroborate; the organic solvent is a benign solvent for lithium difluorooxalato borate and is a poor solvent for lithium fluoride and lithium oxalate.
The method for purifying lithium difluorooxalato borate of the invention comprises the steps of adding lithium bisoxalato borate (LiBOB) and lithium tetrafluoroborate (LiBF) 4 ) The impurity lithium difluorooxalate borate is dissolved in liquid hydrogen fluoride, and the hydrogen fluoride is used as a solvent and a catalyst to promote LiBF 4 Reaction with LiBOBLithium difluorooxalato borate (LiODFB) was generated, and LiBF 4 And LiBOB has a relatively high reaction speed in a liquid phase, and the reaction formula is as follows: liBF 4 +LiB(C 2 O 4 ) 2 →2LiBF 2 C 2 O 4 Because the molar ratio of the lithium tetrafluoroborate to the lithium bisoxalato borate in the lithium difluorooxalato borate is greater than 1:1, and the lithium tetrafluoroborate and the lithium bisoxalato borate are both dissolved in liquid hydrogen fluoride, the reaction speed is high and the reaction is thorough in a liquid phase, so that the impurities of the lithium bisoxalato borate in the lithium difluorooxalato borate can be completely removed in the step (1); then adding excessive lithium oxalate to enable the lithium oxalate to react with the residual lithium tetrafluoroborate to obtain lithium difluorooxalate borate and lithium fluoride, wherein the reaction formula is as follows: liBF 4 +Li 2 C 2 O 4 →LiBF 2 C 2 O 4 +2LiF; through the operation of the step (1) and the step (2), the impurities of the lithium bisoxalato borate and the lithium tetrafluoroborate in the lithium difluorooxalato borate are converted into lithium difluorooxalato borate, lithium fluoride and lithium oxalate, and finally the lithium difluorooxalato borate is further purified by utilizing the solubility difference of the lithium difluorooxalato borate, the lithium fluoride and the lithium oxalate in an organic solvent to obtain a purified product of the lithium difluorooxalato borate. The purification method of the lithium difluorooxalate borate is simple to operate, and the purity of the purified lithium difluorooxalate borate product is high, so that the use requirement of the electrolyte can be met.
Preferably, the impurities in the lithium difluorooxalato borate further comprise lithium bisoxalato borate, and the molar ratio of the lithium bisoxalato borate to the lithium tetrafluoroborate is less than 1:1.
It is understood that when the impurity in the lithium difluorooxalato borate contains lithium bisoxalato borate, the lithium bisoxalato borate and lithium tetrafluoroborate are converted into lithium difluorooxalato borate by reaction in the process of dissolving the lithium difluorooxalato borate in liquid hydrogen fluoride; when the impurities in the lithium difluorooxalato borate do not contain lithium bisoxalato borate, the reaction of converting the lithium bisoxalato borate into lithium difluorooxalato borate does not occur in the process of dissolving the lithium difluorooxalato borate in liquid hydrogen fluoride.
When the impurities in the lithium difluorooxalato borate contain lithium bisoxalato borate, if the lithium difluorooxalato borate, the lithium oxalate and the liquid hydrogen fluoride are mixed together, the lithium tetrafluoroborate impurities in the lithium difluorooxalato borate preferentially react, and after the lithium tetrafluoroborate is consumed, the lithium bisoxalato borate in the lithium difluorooxalato borate cannot be effectively removed, so that the purity of a purified product is reduced.
It can be understood that in the step (1), the concentration of the lithium bis (oxalato) borate in the first mixed solution can be monitored in real time, so as to determine whether the lithium bis (oxalato) borate is completely removed (whether the lithium bis (oxalato) borate is completely reacted with lithium tetrafluoroborate); in the step (2), the concentration of the lithium tetrafluoroborate in the first mixed solution can be monitored in real time to further determine whether the lithium tetrafluoroborate is completely removed (whether the lithium tetrafluoroborate is completely reacted with the lithium oxalate).
Preferably, the temperature of the mixing in step (1) and step (2) is independently not less than 0 ℃. In the step (1) and the step (2), the temperature of the mixing is lower than 0 ℃, so that the solubility of the lithium difluorooxalato borate in the liquid hydrogen fluoride is too low, the consumption of the liquid hydrogen fluoride is too high, and the productivity is reduced.
Preferably, the temperature of the mixing in step (1) and step (2) is independently from 0 to 15 ℃. The temperature of the mixture is slightly lower than the boiling point of the liquid hydrogen fluoride, so that the liquid hydrogen fluoride is prevented from being gasified in a large amount during operation, the liquid hydrogen fluoride is lost, the lithium difluoro oxalate borate and impurities in the lithium difluoro oxalate borate are separated out prematurely, and the yield and the purity of the product are reduced.
Preferably, in step (1), the temperature of the mixing is 0 to 15 ℃.
Preferably, the operation in step (1) is carried out at 0 to 15 ℃.
Preferably, in step (2), the temperature of the mixing is not lower than 0 ℃.
Preferably, in step (2), the temperature of the mixing is 0 to 15 ℃.
Preferably, the operations in step (1) and step (2) are performed under closed conditions. The operation in the step (1) and the step (2) is carried out under a closed condition, so that the hydrogen fluoride can be recycled, and no waste gas and waste liquid are generated.
Preferably, in the step (1), the mass ratio of the lithium difluorooxalato borate to the liquid hydrogen fluoride is (80-100) to 500. Excessive use of liquid hydrogen fluoride can lead to complex post-treatment procedures, reduce productivity, enrich impurities in the liquid hydrogen fluoride and reduce purity of a purified product of lithium difluorooxalato borate. The use amount of the liquid hydrogen fluoride is too small, so that insufficient dissolution of the lithium difluorooxalate borate can be caused, the lithium bisoxalato borate in the lithium difluorooxalate borate can not fully react with the lithium tetrafluoroborate, the lithium bisoxalato borate can not be completely removed, and the product purity is reduced; experiments show that even a small amount of liquid hydrogen fluoride can completely dissolve lithium difluorooxalato borate, but still can lead to a higher impurity content in the product.
In order to ensure complete removal of lithium tetrafluoroborate in the first mixed solution, preferably, in the step (2), the molar ratio of lithium oxalate to lithium tetrafluoroborate in the first mixed solution is not less than 1:1.
Preferably, in the step (2), the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed solution is (1.02 to 1.2): 1. The lithium oxalate consumption is too little, can cause the lithium tetrafluoroborate in the first mixed solution to be fully removed, and the lithium oxalate consumption is too much, can introduce new impurity, increases the follow-up edulcoration degree of difficulty to reduce the purity of the purification product of lithium difluorooxalate borate.
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 for use, the impurity removing effect is poor, and lithium difluorooxalato borate, lithium fluoride and lithium oxalate cannot be effectively separated.
Preferably, in the step (3), the mass ratio of the solid product to the organic solvent is 1 (5-7.5). Excessive organic solvent consumption not only causes complex post-treatment procedures, but also causes the purity reduction of the purified product; the excessive use of the organic solvent can cause incomplete dissolution of the lithium difluoro oxalate borate, and reduce the product yield.
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 comprises the following steps: heating or placing the liquid obtained by solid-liquid separation in a vacuum environment to evaporate diethyl ether in the liquid obtained by solid-liquid separation to obtain concentrated solution, and cooling the concentrated solution to-20 to-15 ℃ 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, and the mass ratio of the solid product to the organic solvent is 1 (7-7.5); the temperature for mixing in the step (3) is 50-55 ℃; the crystallization method comprises the following steps: cooling the liquid obtained by solid-liquid separation to 15-25 ℃ for crystallization. The too high temperature of mixing in the step (3) can cause product decomposition, so that the purity of the product is reduced, and the too low temperature of mixing in the step (3) can cause poor separation effect and influence the quality of the product.
It is understood that when the organic solvent is dimethyl carbonate or propylene carbonate, the temperature of the liquid obtained by the solid-liquid separation is 50-55 ℃, and the temperature of the liquid obtained by the solid-liquid separation is reduced from 50-55 ℃ to 15-25 ℃ during crystallization.
Detailed Description
The technical scheme of the invention is further described below with reference to specific embodiments.
Example 1
The purification method of the lithium difluoroborate of the embodiment specifically comprises the following steps:
(1) Adding 100g of lithium difluoroborate crude product and 500g of anhydrous hydrogen fluoride into a sealed container lined with polytetrafluoroethylene at 15 ℃, stirring until the lithium difluoroborate crude product is completely dissolved (in the dissolving process, a small amount of lithium bisoxalato borate contained in the lithium difluoroborate crude product is converted into lithium difluorooxalato borate through reaction), and enabling the mass fraction of the lithium bisoxalato borate in the dissolved liquid to be 0.002%, thus obtaining a first mixed liquid;
then adding anhydrous lithium oxalate (the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed solution is 1.02:1) into the first mixed solution, and stirring for 30min to obtain a second mixed solution; the mass fraction of lithium tetrafluoroborate in the second mixed solution is detected to be less than 0.005%;
(2) Then heating and concentrating the second mixed solution under vacuum to remove hydrogen fluoride in the second mixed solution, so as to obtain a solid product;
(3) Adding the solid product into diethyl ether (the mass ratio of the solid product to the diethyl ether is 1:5), stirring to fully dissolve the solid product, filtering (the solid obtained by filtering is lithium fluoride and lithium oxalate), placing the liquid obtained by filtering in a vacuum environment (vacuumizing) to evaporate diethyl ether in the liquid, obtaining concentrated solution, cooling the concentrated solution to-20 ℃ for crystallization, and finally drying the precipitated crystal at 120 ℃ for 2 hours to obtain 87.2g of purified product.
Example 2
The purification method of the lithium difluoroborate of the embodiment specifically comprises the following steps:
(1) Adding 80g of lithium difluoroborate crude product and 500g of anhydrous hydrogen fluoride into a sealed container lined with polytetrafluoroethylene at the temperature of 0 ℃, stirring until the lithium difluoroborate crude product is completely dissolved (in the dissolving process, a small amount of lithium bisoxalato borate contained in the lithium difluoroborate crude product is converted into lithium difluorooxalato borate through reaction), and enabling the mass fraction of the lithium bisoxalato borate in the dissolved liquid to be 0.002%, thus obtaining a first mixed liquid;
then adding anhydrous lithium oxalate (the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed solution is 1.2:1) into the first mixed solution, and stirring for 30min to obtain a second mixed solution; the mass fraction of lithium tetrafluoroborate in the second mixed solution is detected to be less than 0.005%;
(2) Then heating and concentrating the second mixed solution under vacuum to remove hydrogen fluoride in the second mixed solution, so as to obtain a solid product;
(3) Adding the solid product into dimethyl carbonate at 55 ℃ (the mass ratio of the solid product to the dimethyl carbonate is 1:7.5), stirring to fully dissolve the solid product, filtering to remove solid impurities such as lithium fluoride, lithium oxalate and the like, cooling the liquid obtained by filtering to 25 ℃ for crystallization, and finally drying the precipitated crystals at 120 ℃ for 2 hours to obtain 66.4g of purified product.
Example 3
(1) Adding 100g of lithium difluoro oxalate borate crude product and 500g of anhydrous hydrogen fluoride into a sealed container lined with polytetrafluoroethylene at 15 ℃, and stirring until the lithium difluoro oxalate borate crude product is completely dissolved to obtain a first mixed solution;
then adding anhydrous lithium oxalate (the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed solution is 1.02:1) into the first mixed solution, and stirring for 30min to obtain a second mixed solution; through detection, the mass fraction of lithium tetrafluoroborate in the second mixed solution is 0.005%;
(2) Then heating and concentrating the second mixed solution under vacuum to remove hydrogen fluoride in the second mixed solution, so as to obtain a solid product;
(3) The solid product was added to propylene carbonate at 55 ℃ (mass ratio of the solid product to the propylene carbonate is 1:7.5), stirred to make the solid product fully dissolved, then filtered, the liquid obtained by the filtration was cooled to 15 ℃ for crystallization, and finally the precipitated crystals were dried at 120 ℃ for 2 hours to obtain 85.6g of purified product.
Experimental example
In order to evaluate the purification effect of the purification method of lithium difluorooxalato borate of the present invention, the mass fraction of lithium difluorooxalato borate in the crude lithium difluorooxalato borate used in examples 1 to 3 and the purified product of lithium difluorooxalato borate obtained by the purification of each example, and the mass fraction of each impurity are shown in table 1. In Table 1, examples 1, 2 and 3 show the purified products of lithium difluorooxalato borate obtained by purification in examples 1 to 3, respectively.
TABLE 1 lithium difluorooxalato borate crude product and purified product obtained by purification of examples mass fraction of lithium difluorooxalato borate and mass fraction of impurities
Claims (10)
1. The purification method of the lithium difluoroborate is characterized by comprising the following steps of:
(1) Mixing lithium difluorooxalato borate and liquid hydrogen fluoride until the lithium difluorooxalato borate is completely dissolved, and enabling the mass fraction of the lithium bisoxalato borate in the dissolved liquid to be not more than 0.005%, so as to obtain a first mixed liquid; the impurities in the lithium difluoroborate comprise lithium tetrafluoroborate;
(2) Mixing the first mixed solution with lithium oxalate to remove lithium tetrafluoroborate in the first mixed solution to obtain a second mixed solution, and removing liquid hydrogen fluoride in the second mixed solution to obtain a solid product;
(3) Mixing the solid product and an organic solvent until lithium difluoroborate in the solid product is completely dissolved, carrying out solid-liquid separation, and crystallizing the liquid obtained by the solid-liquid separation to obtain a purified product of lithium difluoroborate; the organic solvent is a benign solvent for lithium difluorooxalato borate and is a poor solvent for lithium fluoride and lithium oxalate.
2. The method of purifying lithium difluoroborate as claimed in claim 1, wherein the impurities in the lithium difluoroborate further comprise lithium bis (oxalato) borate, and the molar ratio of the lithium bis (oxalato) borate to the lithium tetrafluoroborate is less than 1:1.
3. The method for purifying lithium difluorooxalato borate as claimed in claim 1, wherein the temperature of the mixing in step (1) and step (2) is independently not lower than 0 ℃.
4. The method for purifying lithium difluorooxalato borate as claimed in claim 2, wherein the temperature of the mixing in step (1) and step (2) is independently 0 to 15 ℃.
5. The method for purifying lithium difluoroborate as claimed in any one of claims 1 to 4, wherein in the step (1), the mass ratio of the lithium difluoroborate to the liquid hydrogen fluoride is (80 to 100): 500.
6. The method of purifying lithium difluoroborate according to any one of claims 1 to 4, wherein in the step (2), the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed solution is not less than 1:1.
7. The method of purifying lithium difluoroborate as claimed in claim 6, wherein in the step (2), the molar ratio of the lithium oxalate to the lithium tetrafluoroborate in the first mixed solution is 1.02 to 1.2.
8. The method for purifying lithium difluoroborate as claimed in any one of claims 1 to 4, wherein the organic solvent is one selected from diethyl ether, acetonitrile, dimethyl carbonate, propylene carbonate.
9. The method for purifying lithium difluorooxalato borate as claimed in claim 8, wherein in the step (3), the mass ratio of the solid product to the organic solvent is 1 (5 to 7.5).
10. The method for purifying lithium difluoroborate as claimed in any one of claims 1 to 4, wherein the organic solvent is diethyl ether, and the mass ratio of the solid product to the organic solvent is 1 (5 to 5.5); the crystallization method comprises the following steps: heating or placing the liquid obtained by solid-liquid separation in a vacuum environment to evaporate diethyl ether in the liquid obtained by solid-liquid separation to obtain concentrated solution, and cooling the concentrated solution to-20 to-15 ℃ 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, and the mass ratio of the solid product to the organic solvent is 1 (7-7.5); the temperature for mixing in the step (3) is 50-55 ℃; the crystallization method comprises the following steps: cooling the liquid obtained by solid-liquid separation to 15-25 ℃ for crystallization.
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