Tailored 3-Alkoxy-N,N,N,2,2-Pentamethylpropan-1-Ammonium Bis(trifluoromethylsulfonyl)Imide Ionic Liquids for Room-Temperature Fluoride-Ion Batteries

Abstract

Two novel liquid electrolytes for room-temperature fluoride ion batteries are presented. These electrolytes are based on ionic liquids with quaternary ammonium cations 3-methoxy-N, N, N, 2, 2-pentamethylpropan-1-aminium (MNPA) and N, N, N, 2, 2-pentamethyl-3-(2, 2, 2-trifluoroethoxy)propane-1-aminium (NPPA) combined with a bis(trifluoromethylsulfonyl)-imide (TFSI) counterion. Quaternary ammonium fluorides can be added at concentrations up to 0.7 M to a functional fluoride electrolyte with a total diffusivity of 4.99 × 10⁻¹² m² s⁻¹, a viscosity of 260 mP⋅s and a wide operational voltage range exceeding 5.4 V. The liquid ion electrolyte with the MNPA cation supports stable fluoride ion shuttling for up to 100 h.