Physicochemical synergistic interface optimization via natural eumelanin colloidal electrolyte enables highly reversible Zn anodes

Aqueous zinc-ion batteries (AZIBs) have gained significant attentions as a promising energy storage system due to their low cost, non-toxicity and intrinsic safety, but suffer from dendritic Zn growth, grievous hydrogen evolution reaction and corrosion. Here, a natural eumelanin (NE) colloidal electrolyte capable of physicochemical synergistic effect was proposed to realize highly reversible Zn anodes. The abundant polar functional groups of NE generate strong interaction with Zn²⁺ and further reconfigure the Zn²⁺ ions solvation structure to improve the Zn²⁺ transfer kinetics, while the nanostructured NE can physically fill the defects on Zn anode and redistribute the electric field for compact Zn deposition. Benefitting from the physicochemical synergistic strategy, the NE-based colloidal electrolyte enables Zn anodes with a high coulombic efficiency of 98.82 %, while the Zn//Zn symmetric cell exhibited highly reversible galvanostatic plating/stripping for >3800 h at 5 mA cm⁻²/1 mAh cm⁻² and an ultra-high cumulative plating capacity exceeding 9500 mAh cm⁻². This physicochemical synergistic interface optimization strategy provides a promising approach to achieving highly reversible Zn anodes.