Ultra-robust Zinc-Ion Batteries with Co-solvent Water-in-Salt Electrolytes for Enhanced Stability and Capacity

Abstract

This study presents highly durable and flexible zinc-ion energy storage devices utilizing molybdenum-doped tungsten oxide (Mo-WO₃) cathodes and hybrid water-in-salt electrolytes (WISE). Mo doping into WO₃ enhances its charge transfer properties, leading to improved electrochemical performance. The hybrid WISE, which incorporates dimethylformamide (DMF) as a co-solvent in a high-concentration ZnCl₂ aqueous solution, addresses the limitations of conventional aqueous electrolytes by suppressing parasitic reactions and enhancing stability. Electrochemical analysis reveals a significant increase in specific capacity from 21 mAh/g (WO₃ at 1 A/g) to 48 mAh/g (Mo-WO₃ at 1 A/g) and improved cyclic stability with 90% retention at 2 A/g after 1200 cycles. Ex-situ characterization elucidates the charge-discharge mechanism while post-cycling analysis confirms structural and morphological integrity after extensive cycling. A fabricated flexible device demonstrates exceptional stability over 3000 cycles at 2 A/g, retaining 72% of its initial capacity, and exhibits robust performance under bending, flammability, and mechanical stress tests. This study highlights the potential of Mo-doped WO₃ and hybrid WISE for developing ultra-robust, flexible zinc-ion batteries (ZIBs), paving the way for sustainable energy storage solutions in diverse applications.