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.