Super SEI‐Forming Anion for Enhanced Interfacial Stability in Solid‐State Lithium Metal Batteries

The extremely high chemical reactivity of lithium metal (Li°) electrodes and its enormous volume change during repetitive cycles cause continuous interfacial degradations in prevailing organic electrolytes, thus deteriorating the cycling performances of rechargeable lithium metal batteries (LMBs). Herein, departing from traditional wisdom on the design of electrolyte components, a super SEI-forming anion (SSA), as an efficient percussor for building stable interphases on Li° electrode, is proposed. Comprehensive investigations related to the unique anion chemistry of SSA reveal that the sulfonate and polyfluoroalkyl functionalities synergistically contribute to uniform spatial distributions of designer interfacial species, greatly improving the surface coverage property and conformal ability of the resulting interphases. Consequently, the incorporation of SSA leads to significant improvements in the cyclability of Li° electrode (exceeding 575 mAh cm^-2 before failure) and the corresponding rechargeable Li°||LiFePO₄ cells [a five-time increase in lifespan as compared to the benchmark cell with the popular SEI-forming anion bis(fluorosulfonyl)imide (FSI)]. The present work offers a paradigm shift to tame the notorious interfacial issues via upgraded anion chemistry, which can promote the practical development of rechargeable LMBs and other kinds of metal batteries.