Selectively "size-excluding" water molecules to enable a highly reversible zinc metal anode

Significant water-related side reactions hinder the development of highly safe, low-cost aqueous zinc metal batteries (AZMBs) for grid-scale energy storage. Herein, by regulating the length of alkyl chains, we successfully adjust interstitial voids between the polymer chains of a metal soap interface between 1.48 Å (size of a zinc ion) and 4.0 Å (size of a water molecule). Therefore, water molecules are selectively "size-excluded," while smaller zinc ions are permitted to pass through. Consequently, water-related side reactions (including hydrogen evolution and corrosion) could be effectively inhibited. Furthermore, abundant zinc ion tunnels accompanied with zincophilic components facilitate the homogenization of the Zn²⁺ flux, thus preventing dendrite growth. Therefore, the Zn symmetric cell shows a lifespan of approximately 10 000 cycles at 20 mA cm^-2 and 1 mA h cm^-2, and the Zn//Na₅V₁₂O₃₂ (NVO) full cell delivers much better cycling stability with much higher capacity retention of around 93% after 2000 cycles at 2 A g^-1 compared to its bare Zn counterpart (19%). This work provides valuable insights for the utilization of metal soap interfaces and regulation of their channel size between perpendicular alkyl chains to realize precise water shielding, which is not only applicable in ZMBs but also in other aqueous batteries.