Lewis‐Base Electrolyte Additive Mediates Interfacial Chemistry for Stable Lithium Metal Batteries

Electrolytes play a crucial role in regulating interfacial chemistry, which is essential for the development of high‐energy‐density lithium metal batteries. Herein, we present an ether‐based electrolyte system incorporating the simplest Grignard reagent, CH3MgCl, as an additive. This additive, endowed with Lewis‐base characteristics, enhances the stability of the anode‐electrolyte interface through bifunctional effects. During Li deposition, CH3Mg+ preferentially adsorbs onto the electrode surface, attracting more anions into the Helmholtz layer. Concurrently, CH3– creates an electron‐rich environment, facilitating nucleophilic attacks on anions and promoting its reduction to form an inorganic‐rich solid‐electrolyte interphase (SEI). Additionally, Mg2+ undergoes electrodeposition prior to Li+, forming a Li‐Mg alloy with subsequently deposited Li. This process lowers the nucleation barrier for Li deposition, resulting in improved deposition uniformity. Accordingly, the designed electrolyte demonstrates excellent cycling stability for Li anodes in both Li||Cu half‐cells and full‐cells paired with LiFePO4 cathodes. Notably, Li||LiFePO4 batteries using a thin‐film Li anode pre‐deposited on Cu retain ~92.84% of their initial capacity after 300 cycles with an average Coulombic efficiency of ~99.74%. These findings highlight the critical role of additives in engineering interfacial chemistry and provide a promising strategy for designing advanced electrolytes to improve the cycling performance of Li metal batteries.