In Situ Colloidal Electrolyte via Anion–Polycation Interaction Enables Stable Zn Metal Batteries

Aqueous zinc (Zn) metal batteries (AZMBs) are a promising candidate for large-scale energy storage, but the issues of Zn anodes involving nonuniform Zn plating/stripping, H₂ evolution, and low Zn utilization rate (ZUR) in aqueous electrolytes hinder their practical application. Herein, we report an <i>in situ</i> colloidal electrolyte via SO₄^2--polycation electrostatic interaction to circumvent these challenges. Mechanistic studies reveal that the polycation-confined SO₄^2- diffusion significantly elevates the Zn²⁺ transference number to 0.82, which can suppress anion-induced side reactions and minimize interfacial concentration gradients. Moreover, the polycations can form dynamic adsorption on Zn, disrupt the water's original H-bond network, and create an H₂O-poor electrical double layer, which homogenizes the electric field distribution and suppresses H₂ evolution on Zn. Consequently, the optimized electrolyte (Colloid-6) enables highly compact and (100)-plane-oriented Zn electrodeposits and uniform Zn stripping behavior even at 25 mAh cm^-2, corresponding to 85.4% ZUR. The Zn electrodes in Colloid-6 achieve a long-term cycling life over 4200 h under 2 mAh cm^-2, deep-cycling stability over 300 h under 25 mAh cm^-2, and high-temperature adaptability (80 °C). Moreover, Colloid-6 with low water reactivity can inhibit the vanadium oxide cathode dissolution, thus supporting the stable operation of Zn//V₂O₅·<i>n</i>H₂O full batteries under harsh conditions.