Tackling the challenges of aqueous Zn-ion batteries via functional separator design

Aqueous Zn-ion batteries (ZIBs) are attractive complements to Li-ion batteries for large-scale energy storage due to their high safety, cost-effectiveness, and environmental benignity. In the past decade, great progress has been achieved by exploiting advanced electrode materials and functional electrolytes to resolve the critical issues of ZIBs, including Zn dendrites, anode corrosion, hydrogen revolution reactions, and cathode dissolution. Recently, the synthesis of functional separators has proved to be another effective approach to overcome these challenges. Herein, we summarize the leading separator fabrication, design strategies, and their corresponding roles in electrode stabilization. The performance-boosting through advanced coating has also been reviewed. The specific functions of the advanced separators, including dendrites inhibition and anode protection through homogenizing the electric field, regulating Zn ion distribution, and introducing zincophilic sites, are outlined. The separator could also ameliorate the cathode by adsorbing active materials to re-utilize them. We also discuss the remaining issues and perspectives to guide the future explorations of novel separators.