<p>Zinc (Zn) metal anodes for aqueous batteries suffer from dendrite growth, hydrogen evolution and corrosion, limiting their stability and utilization rate. Here, a low-cost and highly soluble copolymer additive (poly(acrylamide-co-diallyldimethylammonium chloride), PAD) is introduced into the electrolyte to achieve long-term and highly reversible Zn²⁺ plating/stripping. Specifically, the zincophilic amide segments facilitate Zn²⁺ conduction via coordination interaction, while the zincophobic quaternary ammonium segments promote Zn²⁺ migration through electrostatic repulsion. Such synergistic interaction establishes fast ion transport channels in the electrolyte with a high Zn²⁺ transfer number of 0.72. Moreover, PAD spontaneously constructs a bilayer interphase at the electrode/electrolyte interface, including a protective outer layer rich in positive charges and amide groups, as well as an organic-inorganic hybrid inner layer. Such a dual structure accelerates the Zn²⁺ desolvation, homogenizes the Zn²⁺ flux, and hinders the direct contact between water molecules and the Zn metal anode. Consequently, the Zn//Zn cells with a trace amount (0.5 wt%) of PAD operate stably for 5400 h and withstand an ultrahigh depth-of-discharge of 85.6% for over 1300 h.</p>