LAUSR

The poor Zn reversibility has been criticized for limiting applications of aqueous Zn‐ion batteries (ZIBs); however, its behavior in aqueous media is not fully uncovered yet. Here, this knowledge gap is addressed, indicating that Zn electrodes face a O2‐involving corrosion, besides H2 evolution and dendrite growth. Differing from aqueous Li/Na batteries, removing O2 cannot enhance ZIB performance because of the aggravated competing H2 evolution. To address Zn issues, a one‐off electrolyte strategy is reported by introducing the triple‐function C3H7Na2O6P, which can take effects during the shelf time of battery. It regulates H+ concentration and reduces free‐water activity, inhibiting H2 evolution. A self‐healing solid/electrolyte interphase (SEI) can be triggered before battery operation, which suppresses O2 adsorption corrosion and dendritic deposition. Consequently, a high Zn reversibility of 99.6% is achieved under a high discharge depth of 85%. The pouch full‐cell with a lean electrolyte displays a record lifespan with capacity retention of 95.5% after 500 cycles. This study not only looks deeply into Zn behavior in aqueous media but also underscores rules for the design of active metal anodes, including Zn and Li metals, during shelf time toward real applications.