Mechanically robust and water-trapping separators for zinc-ion batteries via hydrophilic surface engineering

Abstract

In aqueous zinc-ion batteries (ZIBs), the separator plays a critical role beyond merely acting as an ionic-conductive medium—it directly influences Zn2+ flux uniformity, desolvation characteristics, and overall electrochemical reversibility. Therefore, addressing the inherent limitations of conventional separator materials—such as non-uniform ion transport and structural deformation—and introducing surface functionalities are critical for enhancing electrochemical performance. In this study, a polyvinylidene fluoride (PVDF) layer was coated onto the surface of a glass fiber (GF) separator to suppress structural deformation caused by prolonged electrolyte exposure. Furthermore, plasma treatment introduced hydrophilic functional groups onto the PVDF surface, enabling hydrogen bonding with water molecules and suppressing H2O-induced side reactions. An MnO2||Zn full cell using the FP@GF separator retained ∼98 % of its initial capacity after 350 cycles. Even after extensive charge/discharge cycling, the interface between the separator and Zn anode remained clean. Moreover, the MnO2||Zn full cell maintained a capacity exceeding 101 mAh g−1 at 2.0 C after 30 days of storage, approximately twice that of its bare-GF-based counterpart. Thus, this study demonstrates a strategy to overcome the mechanical shortcomings of GF separators and suppress water-induced parasitic reactions in aqueous electrolytes, substantially enhancing the long-term stability of GF-based ZIBs.