Pre‐Coverage of Side Reaction Sites Enables Quasi‐Anode‐Free Rechargeable Aqueous Zinc Batteries

Abstract Rechargeable aqueous zinc metal batteries (RAZMBs) have garnered significant attention owing to their low cost and safety. Enhancing the energy density of RAZMBs is crucial for their rapid adoption in the energy market, and anode‐free configurations offer the greatest potential to maximize this metric. However, such designs require exceptionally high Zn plating/stripping reversibility at the anode side. Here, a simple pre‐Zn‐plating/stripping‐cycling treatment of carbon substrates is applied, which induces preferential in situ formation of zinc hydroxy sulfate at hydrogen evolution reaction (HER)‐active sites, thereby suppressing parasitic reactions at the anode and achieving Coulombic efficiencies exceeding 99.9%. When employed as the anode current collector in a quasi‐anode‐free (QAF) cell combined with a nanosized ZnMn 2 O 4 cathode, this substrate enables an energy density of 520 Wh kg −1 with stable cycling over 50 cycles, offering a straightforward and reliable pathway toward high‐energy‐density RAZMBs.