Highly-concentrated bis(fluorosulfonyl)imide-based ternary gel polymer electrolytes for high-voltage lithium metal batteries

Polymer electrolytes (PEs) have arisen as the most promising candidates for being used in rechargeable lithium metal batteries (LMBs). However, classic gel polymer electrolytes (GPEs) with volatile plasticizers show poor inherent safety, despite their higher ionic conductivities vs. dry PE systems, which largely hampers the practical deployment of GPE-based LMBs. Herein, we report the electrochemical performances of a highly-concentrated bis(fluorosulfonyl)imide (FSI)-based ternary gel polymer electrolyte (TGPE) comprising a plasticized polymerized ionic liquid as polymer scaffold. The as-prepared FSI-TGPEs show high lithium-ion conductivities at room temperature, wide electrochemical stability both at oxidative and reductive potentials, and superior compatibility with lithium metal electrode. These unique properties of FSI-TGPE enable stable Li plating and stripping processes, as well as high discharge capacity of a Li||Li(Ni0.6Mn0.2Co0.2)O2 cell at ambient temperatures. The present work offers not only safe and highly conductive PEs but also a better understanding on the determining role of FSI− anions in high-energy LMBs. [Display omitted] •Bis(fluorosulfonyl)imide (FSI)-based ternary gel polymer electrolytes are studied.•The FSI-based electrolytes enable reversible cycling of lithium metal electrode.•The FSI-based Li°||Li(Ni0.6Mn0.2Co0.2)O2 cells show high Coulombic efficiency