Accelerated Defluorination Kinetics for an Ultrathin Solid–Electrolyte Interphase in Durable Lithium Metal Batteries

The cycle life of lithium (Li) metal batteries is plagued by the rapid depletion of electrolyte and Li inventory due to the continuous formation of a massive, thick solid–electrolyte interphase (SEI). Here, in situ generation of an ultrathin SEI is proposed by accelerating defluorination kinetics of the electrolyte to retrench the amount of electrolyte and Li inventory in SEI formation for durable batteries. The ultrathin SEI is generated in a dimethoxy(dimethyl)silane (DMDMS)-based electrolyte. Compared with the dispersed contact ion pairs in routine electrolytes, DMDMS, with both ultrahigh solubility of Li salts and weak solvating power, is favorable for the formation of joint aggregates in the electrolyte. The joint aggregates exhibit a fast defluorination rate, inducing uniform and compact nucleation sites on the Li metal surface. The compact nucleation sites grow simultaneously and subsequently come into contact with each other. This process rapidly passivates the exposed anode surface and facilitates the formation of an ultrathin SEI. The prototype pouch cell (≥500 Wh kg^–1) with the ultrathin SEI achieves 190 cycles and can operate at −30 °C with 66% energy retention. This work reveals the formation mechanism of the SEI and demonstrates the potential of meticulous SEI engineering in the development of durable Li metal batteries.