All-natural charge gradient interface for sustainable seawater zinc batteries

Paring seawater electrolyte with zinc metal electrode has emerged as one of the most sustainable alternative solutions for offshore stationary energy storages owing to the intrinsic safety, extremely low cost, and unlimited water source. However, it remains a substantial challenge to stabilize zinc metal negative electrode in seawater electrolyte, given the presence of chloride ions and complex cations in seawater. Here, we reveal that chloride pitting initiates negative electrode corrosion and aggravates dendritic deposition, causing rapid battery failure. We then report a charge gradient negative electrode interface design that eliminates chloride-induced corrosion and enables a sustainable zinc plating/stripping performance beyond 1300 h in natural seawater electrolyte at 1 mA cm-2/1 mAh cm-2. The gradually strengthened negative charges formed via diffusion-controlled electrostatic complexation of biomass-derived polysaccharides serve to repel the unfavorable accumulation of chloride ions while simultaneously accelerating the diffusion of zinc ions. The seawater-based Zn | |NaV3O8·7H2O cell delivers an initial areal discharge capacity of 5 mAh cm-2 and operates over 500 cycles at 500 mA g-1. Seawater electrolytes provide a sustainable option for aqueous zinc batteries but challenge the stability of zinc metal electrodes. Here, authors elucidate the zinc electrode failure mechanisms and propose a charge gradient interface strategy to stabilize the zinc electrode in seawater electrolytes.