Moderately Fluorinated Additive Regulated Solvation Chemistry for 4.6 V Polymer Lithium Metal Batteries

ABSTRACT Lithium metal batteries (LMBs) paired with polymer electrolytes and high‐voltage cathodes are highly promising candidates for safe, high‐energy‐density energy storage. However, their practical application is limited by sluggish Li + transport and unstable electrode‐electrolyte interfaces, which accelerate capacity fading. Here we report a solvation‐ regulation strategy using moderately fluorinated diethyl carbonate derivatives as functional additives to tune interactions among Li + , poly( ε ‐caprolactone) (PCL) chains and anions. This design balances ionic conductivity with interfacial stability. Systematic molecular engineering reveals that both the fluorination site and fluorination degree determine electrolyte performance. The optimal additive, bis(2‐fluoroethyl) carbonate, competitively coordinates Li + , weakens its association with PCL chains, enriches anions in the primary solvation sheath, and promotes the in situ formation of a robust, inorganic‐rich cathode electrolyte interphase containing LiF. As a result, 4.4 V Li||NCM811 and 4.6 V Li||LCO cells retain 80% and 82% of their capacities after 400 and 250 cycles, respectively. Stable operation is also achieved at 80°C and in 0.672 Ah pouch cells. These findings clarify how fluorination modulates Li + solvation and interphase chemistry, and provide a molecular design strategy for high‐voltage LMBs.