Bis(fluorosulfonyl)imide-based electrolyte for rechargeable lithium batteries: A perspective

The inherent properties of non-aqueous electrolytes are highly associated with the identity of salt anions. To build highly conductive and chemically/electrochemically robust electrolytes for lithium-ion batteries (LIBs) and rechargeable lithium metal batteries (RLMBs), various kinds of weakly coordinating anions have been proposed as counterparts of lithium salts and ionic liquids. Among them, bis(fluorosulfonyl)imide anion ([N(SO2F)2]−, FSI−) has aroused special attention in battery field due to the unique physical, chemical, and electrochemical properties of the FSI-based electrolytes. Herein, an overview on the synthetic methodologies of the FSI-based salts (e.g., alkali metal salts, ionic liquids) is provided, and their applications in LIBs and RLMBs are also updated. Future directions on developing FSI-based and/or FSI-derived electrolytes are presented. The present work is anticipated to inspire the design and screening of new anions for battery use, particularly, those stemming from sulfonimide anions.