Solvent‐derived Fluorinated Secondary Interphase for Reversible Zn‐graphite Dual‐ion Batteries

The irreversibility of anion intercalation‐deintercalation is a fundamental issue in determining the cycling stability of a dual‐ion battery (DIB). In this work, we demonstrate that using a partially fluorinated carbonate solvent can drive a beneficial fluorinated secondary interphase layer formation. Such layer facilitates reversible anion (de−)intercalation processes by impeding solvent molecule co‐intercalation and the associated graphite exfoliation. The enhanced reversibility of anion transport contributes to the overall cycling stability for a Zn‐graphite DIB—a high Coulombic efficiency of 98.5 % after 800 cycles, with an attractive discharge capacity of 156 mAh g−1 and a mid‐point discharge voltage of ≈1.7 V (at 0.1 A g−1). In addition, the formed fluorinated secondary interphase suppresses the self‐discharge behavior, preserving 29 times of the capacity retention rate compared to the battery with a commonly used carbonate solvent, after standing for 24 hours. This work provides a simple and effective strategy for addressing the critical challenges in graphite‐based DIBs and contributes to fundamental understanding to help accelerate their practical application. A fluorinated cathode‐electrolyte interphase layer that facilitates reversible anion intercalation and de‐intercalation processes in dual‐ion batteries (DIB) by preventing graphite exfoliation and suppressing solvent molecule co‐intercalation is demonstrated. The enhanced reversibility of anion transport contributes to the overall cycling stability for a Zn‐graphite DIB with high Coulombic efficiency and an attractive discharge capacity.