Trace Diluent‐Like Polyoxometalate Modulated Localized High‐Concentration Electrolyte Enables Highly Reversible Zinc Metal Chemistry

Abstract Aqueous zinc (Zn)‐metal batteries hold promise for large‐scale energy storage, but face challenges such as the irreversibility of Zn anodes in aqueous electrolytes due to parasitic hydrogen evolution reaction (HER), corrosion, and dendrite growth. Here, the concept of using the salt—ammonium phosphotungstate trihydrate (APT)—as a model diluent in aqueous electrolytes is introduced. Its crucial role in constructing a localized high‐concentration electrolyte (LHCE) is showcased, which facilitates Zn ²⁺ desolvation, inhibits HER, and promotes the formation of a uniform anion‐derived solid–electrolyte interphase on the Zn anode. The resulting Zn//Zn cells show dendrite‐free cycling exceeding 1300 h (2 mA cm ⁻² , 2 mA h cm ⁻² ) at room temperature and stable performance at low temperatures. Moreover, the full batteries setup Zn//NaV ₃ O ₈ ∙1.5H ₂ O, supported by this diluent, exhibit enhanced reaction kinetics and sustains stable operation at 5 A g ⁻¹ for over 3750 cycles at room temperature and 750 cycles at −30 °C, respectively. This study offers valuable insights into the use of salt as an aqueous electrolyte diluent for enhancing the reversibility of Zn batteries.