Agar and Chitosan Hydrogel Electrolytes with Solvation Sheath Enabling High Ionic Conductivity for High-Performance...

Rechargeable aqueous zinc-iodine (Zn-I₂) batteries are promising due to their eco-friendliness and low cost. However, challenges such as Zn dendrite growth, anode corrosion, and polyiodide shuttling in electrolytes persist. Here, chitosan and agar hydrogel has been prepared as electrolyte, in which the hydrophilic groups in polymers form solvation structure of Zn²⁺. Due to the minimal water content in the system, ClO₄ ^- also participates in the Zn²⁺ solvation structure, further reducing the number of solvated water molecules. Notably, the resulting hydrogel exhibits low water content yet achieves higher ionic conductivity (26.62 mS cm^-1) than typical water-poor gels. The reduced activity of H₂O suppresses Zn dendrite growth and corrosion, significantly extending the electrochemical window to 3.02 V. The assembled Zn||Zn symmetric cells demonstrate exceptional electrochemical stability, operating for over 4000 h at 1 mA cm^-2. For the iodine cathode, elemental iodine is fully adsorbed onto the carbon host. The layered porous structure of the electrode considerably increases its surface area, providing more active sites to facilitate electron transfer and ion diffusion. This, along with uniform iodine dispersion, enhances the practical iodine reaction ratio, yielding a high specific capacity of 186.5 mAh g^-1 at 5 A g^-1.