N-Fluorobenzenesulfonimide as a multifunctional electrolyte additive for co-stabilizing dual-electrodes of lithium metal batteries with enhanced electrochemical performance

Lithium metal batteries (LMBs) hold great promise in the next-generation high energy density lithium battery system, yet excessive lithium dendrite growth induces poor cyclability and severe safety hazards of LMBs. Here, a novel bifunctional electrolyte additive, N-Fluorobenzenesulfonimide (NFSI), was developed to highly improve the cyclability and safety of LMBs. Benefiting from lower LUMO and higher HOMO energies, the NFSI additive preferentially reacts with the lithium anode to form stable solid electrolyte interphase (SEI) film to inhibit the electrolyte consumption and lithium dendrite growth upon cycling. Meanwhile, NFSI is also preferentially oxidized to generate a uniform and dense ultrathin cathode-electrolyte interphase (CEI) layer rich in conductive LiF and Li₃N on the cathode surface under high voltage. As a result, the Li||Li cells containing 0.1 M NFSI exhibit excellent cycle stability over 1000 h at 0.5 mA cm⁻², and the Li||Cu cells give a high Coulombic efficiency of over 94.5% after 100 cycles at 0.5 mA cm⁻² for 1 mAh cm⁻². Remarkably, the assembled LMBs including Li||LiFePO₄ and Li||NMC532 both demonstrate excellent long-term cyclability and high-rate performance when using NFSI-containing electrolyte, meaning that our developed NFSI bifunctional electrolyte additive will present promising potential in enhancing the cycle and rate performance of next-generation LMBs.