Stabilizing Lithium Anodes with a Dual-Functional Oxonium-Based Additive via Electrostatic Shielding and SEI Regulation

In lithium metal batteries (LMBs), the uncontrolled growth of lithium dendrites not only poses safety risks by potentially piercing the separator and causing short circuits, but also consumes active lithium, significantly reducing the Coulombic efficiency (CE). Moreover, the naturally fragile solid electrolyte interphase (SEI) tends to break and reform repeatedly, leading to sustained electrolyte consumption. In this study, trimethyloxonium tetrafluoroborate (TMOBF 4 ) is introduced as a dual-functional additive to promote uniform lithium deposition and stabilize the SEI. The TMO + cation, possessing a lower reduction potential than Li +, preferentially adsorbs at dendrite protrusions, forming an electrostatic shielding layer that redistributes the Li + flux. This adsorption suppresses localized Li + accumulation and effectively mitigates dendritic growth. Simultaneously, the BF 4 – anion is involved in the Li + solvation structure, significantly reducing the desolvation energy barrier and decomposing during cycling to form LiF, a critical component of a robust SEI. With the additive, the electrochemical performance of lithium cells is remarkably improved. Li||Li symmetric cell exhibits stable cycling stability for 2000 h at 0.5 mA cm –2, and Li||LiFePO 4 cells retain 93.0% capacity retention after 300 cycles at 1 C. These results present a promising strategy for developing high-performance LMBs.