Enabling High-Performance Lithium Metal Batteries by Stabilizing the Anode Interface with a Trace 6FDA Additive

The regulation of electrolyte additives represents a straightforward and highly effective strategy for mitigating interface instability in lithium metal anodes, with the core of this approach lying in the rational design of molecular structures. We introduce a fluorinated macromolecular additive, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), whose anhydride group and fluorine-rich characteristics enable the formation of a dense and robust LiF-rich solid electrolyte interphase (SEI). Remarkably, the addition of merely 0.02 wt % 6FDA significantly reduces the lithium nucleation overpotential from 234.6 mV to 80.5 mV, enabling uniform lithium deposition and suppressing side reactions. Intuitively, the Li||Li symmetric cells enable stable cycling for over 800 h at 0.5 mA cm^-2. Assembled with an NCM88 cathode, the full cell achieved an initial Coulombic efficiency of 90.4%, and a capacity retention of 80.17% after 150 cycles at 1 C, significantly higher than the 30.87% of the traditional electrolyte. The rate behavior was markedly improved from 128.65 mAh g^-1 to 170.22 mAh g^-1 at 5 C. This study demonstrates that the 6FDA additive, a fluorinated macromolecular structure, considerably improves the electrochemical performance and cycling stability of lithium metal batteries through in situ interface engineering. This approach provides a promising strategy for the development of low-cost, high-safety lithium metal batteries.