In Situ Chemical Construction of Ultrathin Zn²⁺-Conductive Interphase for Dendrite-Free Zinc Metal Batteries

Aqueous zinc (Zn) interfacial chemistry is inherently safe but encounters significant challenges with irreversibility, as exemplified by low Coulombic efficiency (CE) and uncontrollable deposition. Here, an ultra-thin electrode skin, merely ∼100 nm thick and composed of zinc-polyphosphate and graphitic carbon nitride (g-C₃N₄) (denoted as PPAG) has been in situ constructed on the Zn anode surface through an ultrafast chemical synthesis. The PPAG layer integrates chain-like polyphosphate architectures with a ring-shaped negative microelectric field generated by g-C₃N₄, synergistically enabling Zn²⁺-dominated charge transport. This unique configuration facilitates long-range and rapid movement of cations, thereby increasing the Zn²⁺ transference number from 0.34 (bare Zn) to 0.70, ensuring high-current operation of the Zn anode. Moreover, the homogeneous dispersion of g-C₃N₄ within PPAG provides abundant nucleation sites, simultaneously enabling smooth Zn²⁺ deposition and suppressing parasitic reactions. Consequently, the Zn@PPAG||Cu half-cell achieves exceptional cyclability with a CE of 99.67% over 2900 cycles. Furthermore, symmetric cells demonstrate a superior cycling lifespan exceeding 3800 and 1500 h at current densities of 5.0 and 20 mA cm^-2, respectively. This work establishes a universal ultrafast strategy for Zn anode engineering, accelerating practical applications of Zn-based energy storage systems.