Interphasial Pre‐lithiation and Reinforcement of Micro‐Si Anode through Fluorine‐free Electrolytes

Abstract Micro‐sized silicon (mSi) anodes offer advantages in cost and tap density over nanosized counterparts. However, its practical application still suffers from poor cyclability and low initial and later‐cycle coulombic efficiency (CE), caused by the unstable solid electrolyte interphase (SEI) and irreversible lithiation of the surface oxide layer. Herein, a bifunctional fluorine (F)‐free electrolyte was designed for the mSi anode to stabilize the interphase and improve the CE. A combined analysis revealed that this electrolyte can chemically pre‐lithiate the native oxide layer by the reductive LiBH 4 , and relieve SEI formation and accumulation to preserve the internal conductive network. The significance of this F‐free electrolyte brings unprecedented F‐free interphase that also enables the high‐performance mSi electrode (80 wt % mSi), including high specific capacity of 2900 mAh/g, high initial CE of 94.7 % and excellent cyclability capacity retention of 94.3 % after 100 cycles at 0.2 C. This work confirms the feasibility of F‐free interphase, thus opening up a new avenue toward cost‐advantaged and environmentally friendly electrolytes for more emerging battery systems.