Orchestrating dual-interface stabilization via a threefold mechanistic synergy of aluminum dihydrogen phosphate for ultrastable aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are plagued by dendrite proliferation, parasitic hydrogen evolution, and cathode degradation, which stem intrinsically from high water activity and the inherent instabilities of the electrode interfaces. Herein, we demonstrate a trace aluminum dihydrogen phosphate (Al(H₂PO₄)₃, ADP) additive to enable coordinated “liquid-field-interface” regulation in aqueous Zn-ion batteries. Rather than relying on a single protective pathway, ADP integrates H₂PO₄⁻-mediated solvation/interphase chemistry with Al-containing cationic field regulation, thereby simultaneously decreasing water activity, homogenizing interfacial Zn²⁺ flux, and stabilizing both electrode/electrolyte interfaces. In the bulk electrolyte, H₂PO₄⁻ anions reconstruct the Zn²⁺ solvation sheath, suppressing free water activity and lowering the desolvation energy barrier. Across the interfacial electric field, hydrated Al-containing species are proposed to preferentially accumulate near high-field protrusions, thereby helping homogenize Zn²⁺ flux, reduce localized tip growth, and regulate the electric double layer to facilitate charge transfer kinetics. At the dual interfaces, the additive contributes to the formation of a phosphate-rich Al/P-containing interphase on the Zn anode and mitigates Mn dissolution at the MnO₂ cathode. Enabled by this multi-level regulation, Zn‖Zn symmetric cells exhibit an ultralong lifespan of 6000 h at 1 mA cm⁻² (0.5 mAh cm⁻²), and Zn‖MnO₂ full cells demonstrate superior cycling stability with 94.1% capacity retention after 1000 cycles. This work highlights a low-concentration inorganic additive strategy that integrates established solvation, field-regulation, and interphase-stabilization concepts into a coordinated dual-interface protection framework for long-duration AZIBs.