Method for drying and purifying LiFSI
A method for drying and purifying a lithium bis(fluorosulfonyl)imide salt in solution in an organic solvent S1, the method including the following steps: a) adding deionised water to dissolve and extract the lithium bis(fluorosulfonyl)imide salt, forming an aqueous solution of the salt; b) extracting the lithium bis(fluorosulfonyl)imide salt from the aqueous solution, using an organic solvent S2, the step being repeated at least once; c) concentrating the lithium bis(fluorosulfonyl)imide salt by evaporating the organic solvent S2 and the water, in a short-path thin-film evaporator, under the following conditions: temperature of 30° C. to 95° C., pressure of 10 −3 mbar abs to 5 mbar abs, residence time no longer than 15 min; and d) optionally crystallising the lithium bis(fluorosulfonyl)imide salt. Also, a composition made of lithium bis(fluorosulfonyl)imide salt, and the uses thereof in Li-ion batteries.
1 . A process for drying and purifying a solution of a lithium bis(fluorosulfonyl)imide salt in an organic solvent S1, said process comprising the following steps:
a) addition of deionized water to said solution of the lithium bis(fluorosulfonyl)imide salt in the organic solvent S1 to dissolve and extract the lithium bis(fluorosulfonyl)imide salt, forming an aqueous solution of said salt, wherein the mass of the deionized water is greater than or equal to a third of the mass of said solution of the lithium bis(fluorosulfonyl)imide salt in the organic solvent S1;
a′) optional concentration of said aqueous solution of said salt;
b) extraction of the lithium bis(fluorosulfonyl)imide salt from said aqueous solution, with an organic solvent S2, this step being repeated at least once;
c) concentration of said lithium bis(fluorosulfonyl)imide salt by evaporation of said organic solvent S2 and of the water, in a short-path thin-film evaporator, under the following conditions:
temperature of between 30° C. and 95° C.;
pressure between 10-3 mbar abs and 5 mbar abs; and
residence time of less than or equal to 15 min;
d) optionally, crystallization of the lithium bis(fluorosulfonyl)imide salt.
2 . The process as claimed in claim 1 , comprising step a′) of concentration of said aqueous solution.
3 . The process as claimed in claim 1 , in which the organic solvent S2 is chosen from the group consisting of organic carbonates, ethers, esters, and mixtures thereof.
4 . The process as claimed in claim 1 , in which the organic solvent S1 is chosen from the group consisting of esters, nitriles, ethers, chlorinated solvents and aromatic solvents, and mixtures thereof.
5 . The process as claimed in claim 1 , in which the organic solvent S2/water mass ratio, during an extraction, ranges from 1/6 to 1/1.
6 . The process as claimed in claim 1 , in which the concentration step c) is performed at a pressure of between 10 −2 mbar abs and 5 mbar abs.
7 . The process as claimed in claim 1 , in which step c) is performed at a temperature of between 30° C. and 90° C.
8 . The process as claimed in claim 1 , in which step c) is performed with a residence time of less than or equal to 5 minutes.
9 . The process as claimed in claim 1 , in which the organic phase separated from the aqueous solution extracted in step a) is not reintroduced into the subsequent steps b) to d) of the process.
10 . The process as claimed in claim 1 , in which, during step d), the lithium bis(fluorosulfonyl)imide salt is crystallized under cold conditions at a temperature of less than or equal to 25° C., optionally in an organic solvent S3 chosen from chlorinated solvents, and aromatic solvents, said salt optionally being recovered by filtration.
11 . The process as claimed in claim 1 , wherein it leads to a lithium bis(fluorosulfonyl)imide salt comprising water in a content of less than or equal to 45 ppm relative to the total mass of said salt.
12 . A process for drying and purifying a solution of a lithium bis(fluorosulfonyl)imide salt in an organic solvent S1, said process comprising the following steps:
a) addition of deionized water to said solution of the lithium bis(fluorosulfonyl)imide salt in the organic solvent S1 to dissolve and extract the lithium bis(fluorosulfonyl)imide salt, forming an aqueous solution of said salt;
a′) concentration of said aqueous solution of said salt;
b) extraction of the lithium bis(fluorosulfonyl)imide salt from said aqueous solution with an organic solvent S2, forming an organic solution, this step being repeated at least once;
c′) concentration of the organic solution to obtain a concentrated organic solution with a mass content of the lithium bis(fluorosulfonyl)imide salt of between 20% and 60%;
c) concentration of said concentrated organic solution by evaporation of said organic solvent S2 and of the water, in a short-path thin-film evaporator, under the following conditions:
temperature of between 30° C. and 95° C.;
pressure between 10 −3 mbar abs and 5 mbar abs; and
residence time of less than or equal to 15 min;
d) optionally, crystallization of the lithium bis(fluorosulfonyl)imide salt.
13 . The process as claimed in claim 12 , in which the concentration step c′) is performed in a rotary evaporator.
14 . The process as claimed in claim 12 , in which the concentration step c′) is performed at a temperature of between 25° C. and 60° C.
15 . The process as claimed in claim 12 , in which the concentration step c′) is performed at a pressure below 50 mbar abs.