Aqueous zinc‐ion battery (AZB) is a promising candidate for next‐generation energy storage owing to inherent safety and low cost. However, AZBs are currently plagued by Zn dendrite growth and undesirable side‐reactions, leading to poor cycling stability and premature failure. To restrain the uncontrollable Zn growth, a unique separator is developed based on polyacrylonitrile/graphene oxide (abbreviated as PG) composite nanofibers, which contain abundance of zincophilicity functional groups to regulate the migration and distribution of Zn2+ ions in the separator. It is demonstrated that the cyano ligands on PG not only facilitate the dehydration of solvated Zn2+ ions prior to deposition, but also form fast lanes to enable homogenous scattering of deposition spots. Benefiting from these features, the PG separator offers a high ionic conductivity of 7.69 mS cm‐1 and a transference number of 0.74 for Zn2+. The Zn||Zn symmetrical cells with PG separators achieve an ultra‐stable cycle life over 13 000 h. Zn||Zn0.27V2O5 full batteries with PG separators retain 71.5% of the original capacity after 2800 cycles at a high current density of 2 A g‐1. This study offers future research directions toward the design of multifunctional separators to overcome the limits of Zn metal anode in AZBs.

The intercalation of protons represents a notable component for energy storage in aqueous zinc‐ion batteries. However, the mechanism of proton transport in metal oxide cathodes, especially related to how the cation distribution modulates the proton‐conducting lanes, remains far from consensus due to the lack of suitable model materials. Here, taking spinel ZnMn2O4 cathode as a prototype, it is disclosed that a deficiency of one half of lattice Zn ions can triple its specific capacity at high rates, which is predominantly contributed by proton storage. This promotion can be rationalized by the emergence of facile concerted proton transport in the Zn‐deficient sample, contrasting with the stoichiometric one, where proton intercalation undergoes a slow consecutive process. Furthermore, the restricted Zn motion in spinel phase causes high structural stability during cycling, preventing the recombination of external Zn ions with Zn vacant sites that readily accommodate protons. This work highlights the key role of controlled off‐stoichiometry in optimizing proton transport and storage for aqueous batteries.