Purified lithium bis(fluorosulfonyl)imide (LiFSI) products, methods of purifying crude LiFSI, and uses of purified LiFSI products
Methods of removing target impurities from a crude lithium bis(fluorosulfonyl)imide (LiFSI) to make a purified LiFSI product. In some embodiments, a purification method includes contacting crude LiFSI with a first anhydrous organic solvent to create a solution containing LiFSI and the target impurity(ies), wherein the LiFSI is soluble and the impurity(ies) is/are substantially insoluble. In some embodiments, a second anhydrous organic solvent is added to the solution to precipitate the target impurity(ies), which is then filtered to obtain a filtrate. In some embodiments, solvent is removed from the filtrate to obtain a solid mass containing LiFSI, which may then be contacted with a third anhydrous organic solvent in which the LiFSI is insoluble. The LiFSI may then be isolated from the third anhydrous organic solvent to obtain the purified LiFSI product. Also disclosed are purified LiFSI products and electrochemical devices utilizing purified LiFSI products, among other things.
1. A method of removing one or more target impurities from crude lithium bis(fluorosulfonyl)-imide (LiFSI) containing LiFSI and the one or more target impurities so as to make a purified LiFSI product, the method comprising:
contacting the crude LiFSI, in solid form, with a first amount of at least one first anhydrous organic solvent under inert conditions to create a solution containing LiFSI and the one or more target impurities, wherein the LiFSI has a higher solubility in the at least one first anhydrous organic solvent at room temperature than each of the one or more target impurities, wherein the at least one first anhydrous organic solvent includes at least one solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propyl methyl carbonate (PMC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), trans butylene carbonate, acetonitrile, malononitrile, adiponitrile, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate (MP), ethyl propionate (EP), methanol, ethanol, propanol, and isopropanol;
following contacting the crude LiFSI with the first amount of the at least one first anhydrous organic solvent, adding to the solution at least one second anhydrous organic solvent in which each of the LiFSI and the one or more target impurities is substantially insoluble, wherein the at least one second anhydrous organic solvent is added in a minimum amount so as to precipitate the at least one target impurity, wherein the at least one second anhydrous organic solvent includes at least one solvent selected from the group consisting of dichloromethane, dichloroethane, chloroform, pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane;
following adding at least one second anhydrous organic solvent, filtering from the solution an insoluble portion of each of the one or more target impurities so as to produce a filtrate;
removing solvents from the filtrate so as to obtain a solid mass;
contacting the solid mass with at least one third anhydrous organic solvent in which the LiFSI is substantially insoluble so as to solvate a portion of the one or more target impurities, wherein the at least one third anhydrous organic solvent includes at least one solvent selected from the group consisting of dichloromethane, dichloroethane, chloroform, pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane; and
isolating the LiFSI from the at least one third anhydrous organic solvent to obtain the purified LiFSI product.
2. The method of claim 1 , wherein the crude LiFSI has a solubility in the at least one first anhydrous organic solvent of at least about 50% at room temperature, and each of the one or more target impurities has a solubility in the at least one first anhydrous organic solvent that is no more than about 20 parts per million (ppm) at room temperature.
3. The method of claim 1 , wherein the contacting of the crude LiFSI with the at least one first anhydrous organic solvent is performed at a temperature below about 25° C.
4. The method of claim 1 , further comprising controlling a temperature of the solution during the contacting of the crude LiFSI with the at least one first anhydrous organic solvent so as to maintain the temperature within about 2° C. of a target temperature.
5. The method of claim 1 , wherein the filtering is performed in an inert atmosphere.
6. The method of claim 5 , wherein the inert atmosphere comprises argon gas.
7. The method of claim 1 , wherein removing solvents is performed in vacuo.
8. The method of claim 7 , wherein removing solvents is performed at a pressure of about 0.1 Torr or less.
9. The method of claim 7 , wherein removing solvents is performed at a temperature of less than about 40° C.
10. The method of claim 1 , wherein isolating the LiFSI includes filtering the LiFSI in solid form from the at least one third anhydrous organic solvent.
11. The method of claim 10 , wherein isolating the LiFSI includes drying the solid LiFSI in vacuo.
12. The method of claim 11 , wherein drying the solid LiFSI in vacuo includes drying the solid LiFSI at a pressure of about 0.1 Torr or less.
13. The method of claim 1 , wherein the one or more target impurities includes one or more target impurities from the group consisting of lithium chloride (LiCl), lithium fluoride (LiF), lithium sulfate (Li 2 SO 4 ), lithium fluorosulfate (LiSO 3 F), hydrogen fluoride (HF), and fluorosulfonic acid (FSO 3 H).
14. The method of claim 1 , wherein:
the one or more target impurities include lithium sulfate (Li 2 SO 4 ); and
filtering an insoluble portion of each of the one or more target impurities includes simultaneously filtering an insoluble portion of the Li 2 SO 4.
15. The method of claim 1 , wherein contacting the crude LiFSI with at least one first anhydrous organic solvent includes contacting the crude LiFSI with an amount of the at least one first anhydrous organic solvent that is about 50 wt. % to about 75 wt. % of the solution.
16. The method of claim 15 , wherein adding at least one second anhydrous organic solvent to the first solution includes adding the at least one second anhydrous organic solvent in an amount that is no more than about 10 wt. % of the solution.
17. The method of claim 1 , wherein adding at least one second anhydrous organic solvent to the first solution includes adding the at least one second anhydrous organic solvent in an amount that is no more than about 10 wt. % of the solution.
18. The method of claim 1 , further comprising placing the purified LiFSI product in a dry atmosphere within a container that is substantially non-reactive with free fluorine and storing the container at a temperature of less than about 25° C.
19. The method of claim 1 , wherein the one or more target impurities are byproducts of a process of synthesizing the LiFSI in the crude LiFSI.
20. The method of claim 1 , wherein the purified LiFSI product contains 10 parts per million (ppm) or less of LiCl.
21. The method of claim 20 , wherein the purified LiFSI product contains less than 1 ppm of LiCl.
22. The method of claim 1 , wherein the purified LiFSI product contains about 500 parts per million (ppm) or less of FSO 3 Li, about 100 ppm or less of LiCl, and about 150 ppm or less of LiF.