Rational Solvent Fluorination Design for Solvation Regulation Enabling Stable Interfaces in High‐Voltage Li‐Ion Batteries

Fluorinating electrolyte solvents is an effective strategy to enhance the interfacial stability of lithium‐ion batteries (LIBs) under high‐voltage conditions, where severe interfacial side reactions typically undermine the long‐term performance. However, the influence of both the number and positional arrangement of fluorinated groups on solvation structure remains poorly understood. In this work, we systematically investigate how trifluoromethyl group number and substitution position in diethyl carbonate (DEC) derivatives affect Li + solvation behavior. It is revealed that the introduction of a DEC‐based solvent with symmetric two trifluoromethyl groups tends to regulate the solvation structure enriched with anions and fluoroethylene carbonate (FEC). This optimized solvation structure facilitates the formation of a robust cathode‐electrolyte interphase derived from both anions and FEC. Consequently, Ni‐rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathodes with a high loading mass of 10.5 mg cm −2 achieve stable cycling at 4.6 V, retaining 80% of their capacity after 300 cycles. These findings provide fresh insights into the rational design of fluorinated solvents for high‐voltage LIBs.