Salts for multivalent ion batteries
Methods for preparing electrolyte salts for alkaline earth metal-ion batteries (e.g., calcium and magnesium ion batteries) are described. The electrolyte salts comprise alkaline earth metal (e.g., Mg or Ca) salts of bis(fluorosulfonyl)imide (FSI) and 3,4-dicyano-2-trifluoromethylimidazole (TDI). The methods comprise contacting FSI or TDI with an alkaline earth metal bis(trifluoroacetate) salt in trifluoroacetic acid.
1. A method for preparing an alkaline earth metal salt of bis(fluorosulfonyl)imide (FSI) useful as an electrolyte salt for an alkaline earth metal-ion battery, the method comprising:
contacting FSI with a solution containing at least 0.5 molar equivalents of an alkaline earth metal bis-trifluoroacetate salt of the formula (CF 3 CO 2 ) 2 M, dissolved in trifluoroacetic acid to form an FSI salt of formula:
wherein M is an alkaline earth metal; and
recovering the FSI salt.
2. The method of claim 1 , wherein M is Mg.
3. The method of claim 1 , wherein M is Ca.
4. The method of claim 1 , wherein FSI is contacted with about 0.45 to about 0.75 molar equivalents of the salt of the formula (CF 3 CO 2 ) 2 M.
5. The method of claim 4 , wherein M is Mg.
6. The method of claim 4 , wherein M is Ca.
7. The method of claim 1 , wherein salt of the formula (CF 3 CO 2 ) 2 M, is dissolved in trifluoroacetic acid at a concentration in the range of about 0.05 to about 2 molar.
8. The method of claim 7 , wherein M is Mg.
9. The method of claim 7 , wherein M is Ca.
10. The method of claim 1 , wherein the step of recovering the FSI salt comprises filtration or evaporation of trifluoroacetic acid solvent.