Acetonitrile-Mediated Decomposition Competition for Dendrite-Free Lithium Metal Anodes

Lithium metal batteries (LMBs) have attracted tremendous attention due to their ultrahigh energy density. However, fluoroethylene carbonate (FEC), a commonly used additive in traditional ester-based electrolytes, is usually over-reduced during cycling, leading to form an extra-thick solid electrolyte interphase (SEI) which hinders the transport of Li⁺ and deteriorates fast charging performance. Herein, we propose a decomposition-competition-driven strategy to control the growth of SEI. Acetonitrile (AN) preferentially decompose to form a nitrogen-containing SEI due to low Lowest Unoccupied Molecular Orbital (LUMO) energy level (-2.96 eV), high polarity, and favorable wettability, which exhibits a capacity of inhibiting the decomposition of FEC. As a result, the polarization voltage of the cell is remarkably stable. Furthermore, AN reconstructs the solvation structure, accelerates Li⁺ desolvation and increases the Li⁺ transference number and diffusion coefficient. Benefiting from the optimized electrolyte system, Li||Li cells demonstrate stable cycling over 3300 h at 1 mA cm^{- 2}, and Li||LFP cells retain 155 mAh g^{- 1} after 500 cycles at 1 C with 91.57% capacity retention. Additionally, excellent rate and long-cycle performance can also be achieved in high-voltage Li||NCM811 cells. This work provides new insights into enhancing interfacial and transport properties of electrolytes for practical LMBs.