Hydrofluoroether-assisted dilution of Na-ion concentrated ionic liquid electrolyte for safe, stable cycling of high-voltage Na-metal batteries

Na metal anodes for liquid and solid-state Na batteries

“…Common cations employed in IL for NMBs include phosphonium [P nnn ] + , alkylmethylpyrrolidinium [C nm pyr] + , lkylmethylimidazolium [C nm im] + ; while common anions include bis(fluorosulfonyl)imide (FSI À ), bis(trifluoromethanesulfonyl)imide (TFI À ), fluorosulfonyl-(trifluoromethanesulfonyl)imide (TFA À ), hexafluorophosphate (PF 6 À ), and tetrafluoroborate BF 4 À . 181,222,223 Previously, Howlett and his coworkers evaluated the SEI layer composition and cycling stability of NMBs in a N-methyl-Npropylpyrrolidinium bis(fluorosulfonyl)imide (C 3 mpyrFSI) superconcentrated IL electrolyte with 50 mol% NaFSI containing different water concentrations (up to 5000 ppm). 224,225 In 2022, his team also made a comprehensive comparison between phosphonium IL (P 111i4 FSI) and C 3 mpyrFSI IL electrolytes at nearsaturated NaFSI salt concentrations in terms of the physicochemical properties, electrochemical performance, and post-cycling surface analysis.…”

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

“…Pal et al 162 achieved high reversibility with an ionic liquid electrolyte of [C 3 C 1 pyr][FSI] by adding 1,2-dimethoxyethane (DEM) and explained the decisive role of DEM in compact and stable SEI formation through molecular dynamics simulations. Similar ether addition methods also exist in sodium metal batteries, such as Lee et al 163 used hydrofluoroether to dilute [C 3 C 1 pyr]-[FSI]/[Tf 2 N], which promotes the formation of a stable NaFrich SEI with both anions on the anode surface and inhibits Na dendrites. In addition, Liu et al 164 form a more stable SEI to ensure a highly reversible plating/ stripping interface.…”

“…Pal et al 162 achieved high reversibility with an ionic liquid electrolyte of [C 3 C 1 pyr][FSI] by adding 1,2-dimethoxyethane (DEM) and explained the decisive role of DEM in compact and stable SEI formation through molecular dynamics simulations. Similar ether addition methods also exist in sodium metal batteries, such as Lee et al 163 used hydrofluoroether to dilute [C 3 C 1 pyr]-[FSI]/[Tf 2 N], which promotes the formation of a stable NaFrich SEI with both anions on the anode surface and inhibits Na dendrites. In addition, Liu et al 164 compared the electrochemical performance of locally concentrated ionic liquid electrolytes composed of two common cations [C 4 C 1 pyr] + and [EMIM] + ) and found that the electrolyte composed of [EMIM] + and [FSI] − had lower viscosity, a stronger ion transport ability, and relatively higher N content, which could form a more stable SEI to ensure a highly reversible plating/ stripping interface.…”

The Distance Between Phosphate‐Based Polyanionic Compounds and Their Practical Application For Sodium‐Ion Batteries

“…[170,171] Meanwhile, ionic liquids have also been used to realize the nonflammability of phosphate-based polyanionic cathodes or enhance the related sodium-storage capability, such as fast electrochemical kinetics, large reversible capacity, and long cycle life. [172][173][174]…”