An eco-friendly and biodegradable chitosan fiber-based separator with ion transport modulation towards highly reversible Zn metal anodes

Abstract

The practical application of aqueous Zinc-ion batteries (ZIBs) as prospective substitutes to lithium-ion batteries is impeded by challenges associated with uncontrolled Zn dendrites growth and severe side reactions. Herein, an eco-friendly and biodegradable separator based on chitosan fiber (CF) is developed by a facile and scalable papermaking method. Compared to glass fiber separator, the CF separator exhibits high ionic conductivity and exceptional mechanical strength. More importantly, the CF separator can modulate ion transport by selectively binding with Zn²⁺ and protons and adsorbing water molecules attributed to the abundant functional groups present in chitosan molecules, including hydroxyl and amino groups. By facilitating the desolvation of hydrated Zn²⁺, accelerating the kinetics of Zn²⁺ deposition, and lowering Zn²⁺ nucleation barrier, the CF separator is effective in suppressing dendrites growth and mitigates side reactions. Consequently, the symmetric cell with CF separator exhibits an ultra-stable cycling performance over 4000 h at 5 mA cm⁻². The Zn||MnO₂ full cell with CF separator reveals an extended cycling life with outstanding capacity retention. Notably, the CF separator delivers superior biodegradation, fully aligning with the environmental prerequisites of modern energy storage systems. This work presents a simple yet effective strategy to enable highly reversible Zn metal anodes for promoting the practical application of ZIBs.