Proton-selective coating enables fast-kinetics high-mass-loading cathodes for sustainable zinc batteries.

The pressing demand for sustainable energy storage solutions has spurred the burgeoning development of aqueous zinc batteries. However, kinetics-sluggish Zn 2+ as the dominant charge carriers in cathodes leads to suboptimal charge-storage capacity and durability of aqueous zinc batteries. Here, we discover that an ultrathin two-dimensional polyimine membrane, featured by dual ion-transport nanochannels and rich proton-conduction groups, facilitates rapid and selective proton passing. Subsequently, a distinctive electrochemistry transition shifting from sluggish Zn 2+ -dominated to fast-kinetics H + -dominated Faradic reactions is achieved for high-mass-loading cathodes by using the polyimine membrane as an interfacial coating. Notably, the NaV 3 O 8 ·1.5H 2 O cathode (10 mg cm -2 ) with this interfacial coating exhibits an ultrahigh areal capacity of 4.5 mAh cm -2 and a state-of-the-art energy density of 33.8 Wh m -2 , along with apparently enhanced cycling stability. Additionally, we showcase the applicability of the interfacial proton-selective coating to different cathodes and aqueous electrolytes, validating its universality for developing reliable aqueous batteries.