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 a molybdenum-doped tungsten oxide (Mo-WO₃) cathode and a hybrid water-in-salt electrolyte (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 revealed a significant increase in specific capacity from 21 mAh g⁻¹ (Mo-WO₃ in the salt-in-water electrolyte at 1 A g⁻¹) to 48 mAh g⁻¹ (Mo-WO₃ in the water-in-salt electrolyte at 1 A g⁻¹) and improved cyclic stability with 90% retention at 2 A g⁻¹ after 1200 cycles. Ex situ characterization elucidated the charge–discharge mechanism, while post-cycling analysis confirmed structural and morphological integrity after extensive cycling. The fabricated flexible device demonstrated exceptional stability over 3000 cycles at 2 A g⁻¹, retaining 72% of its initial capacity and exhibited 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.