A hydrophobic and fluorophilic coating layer for stable and reversible aqueous zinc metal anodes

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising solutions for large-scale energy storage applications due to their low-cost, high safety and relatively high energy densities. However, they still suffer from poor reversibility and cycling stability that is primarily caused by the instability of the zinc anode in aqueous electrolytes, leading to detrimental side reactions and Zn dendrite accumulation. Herein, we propose a simple, cost-effective, yet promising strategy to stabilize the Zn anode in an aqueous electrolyte by interposing a hydrophobic perfluoropolyether (PFPE) liquid. This PFPE interlayer suppresses deleterious side reactions by limiting H2O exposure on the Zn surface and facilitates the in-situ formation of a ZnF2 interfacial layer. Accordingly, the PFPE-modified cell has a low nucleation overpotential and voltage polarization of 42 and 39 mV, respectively at 1 mA cm−2 current density. The PFPE-coated Zn|Cu half-cell achieves a high coulombic efficiency of 99.2% over 500 cycles. The rechargeability of the PFPE-Zn|ε-MnO2 full cell demonstrates an improved performance, with a capacity retention after 300 cycles of 74%, at a high rate of 2.4 A g−1 (≈7.8C). This work demonstrates new opportunities for using hydrophobic perfluorinated compounds in Zn-based battery research, providing a promising and practical strategy to improve the cycling stability of the metal anodes in large-scale applications.