Imidazolium-based ionic liquid electrolytes for fluoride ion batteries

The fluoride ion battery (FIB) is a post-lithium anionic battery that utilizes the fluoride-ion shuttle, achieving high theoretical energy densities of up to 1393 Wh/L while eliminating the reliance on critical minerals. However, developing liquid elec- trolytes for FIBs has proven arduous due to a combination of low solubility of flu- oride salts and the chemical reactivity of the fluoride ion. By introducing a novel and chemically stable fluoride electrolyte based on 1,3-dimethylimidazolium [MMIm] bis(trifluoromethanesulfonyl)imide[TFSI]andtetramethylammoniumfluoride(TMAF), we achieve electrochemical stability window (ESW) of 4.65 V, ionic conductivity of 9.53 1 mS cm−1, and a TMAF solubility of 0.67 m. The origin of this high salt solubility and the solvation structure were investigated using both NMR spectroscopy and neutron total scattering, showing a fluoride solvation driven by strong electrostatic interactions and weak hydrogen bonding with no covalent H—F character. This indicates the chemical stability of 1,3-dimethylimidazolium towards the fluoride ion and its potential as an electrolyte for high-voltage FIBs.