Biocompatible Polysaccharides Enable Sustainable Wearable Seawater-Based Zinc-Sulfur Pouch Cells

Seawater zinc-sulfur (Zn-S) batteries could support marine energy systems, but their development is hindered by sluggish sulfur redox kinetics, chloride-induced Zn corrosion, and poorly understood biological risks from electrolyte additives. Here, 4-formylphenyl β-D-allopyranoside, a saccharide-derived glycoside, is introduced as a biologically compatible electrolyte regulator for rechargeable seawater Zn-S batteries. The glycoside promotes reversible sulfur-ZnS conversion and suppresses hydrogen evolution, corrosion, and dendritic Zn deposition. This dual regulation enables an energy density of approximately 542 Wh/kg_sulfur and stable cycling over 6000 cycles, while supporting flexible pouch cells under mechanical deformation and low-temperature conditions. Zebrafish embryo, rat implantation, and human keratinocyte assays indicate that the glycoside-regulated electrolyte is less toxic than electrolytes containing conventional organic additives. By integrating molecular interfacial regulation with biosafety assessment, this work establishes a design strategy for durable and environmentally compatible seawater batteries, with potential applications in marine renewable-energy storage, distributed monitoring, and wearable technologies for ocean deployment.