Ultrathin cellulosic gel electrolytes with a gradient hydropenic interface for stable, high-energy and flexible zinc batteries†

Abstract

The increasing demand for personalized health monitoring has driven the development of wearable electronics. Flexible zinc-ion batteries (FZIBs) are ideal power sources for wearable devices, but their low volumetric energy densities have been a limitation for practical application. We present an ultrathin cellulose-based electrolyte (DCG) with a gradient hydropenic interface designed for stable and high-energy FZIBs to address this. The gradient hydropenic interface composed of deep eutectic solvent (DES) residuals effectively mitigates moisture-induced side reactions and guides planar zinc deposition. The resulting zinc anode with the ultrathin DCG shows 99.9% coulombic efficiency (CE) and a cycle life exceeding 4000 hours in symmetrical configuration. Under stringent conditions, including a 66% depth of discharge (DOD) and reduced DCG thickness (10 μm), the flexible zinc battery demonstrates stable cycling with energy densities of 222 W h kg⁻¹ and 214.3 W h L⁻¹ and successfully applied in wearable watches, offering performance comparable to lithium-ion batteries and outperforming previously reported zinc batteries.