Stabilizing Water Molecules in Hydrogel Electrolytes Enables 2.8 V-Class Purely Aqueous Zn-Li Hybrid Batteries

Currently, reported high-voltage aqueous zinc batteries generally operate below 2.0 V. Achieving a discharge plateau/average operating voltage exceeding 2.0 V typically requires charging voltages above 2.5 V; however, the limited electrochemical stability of water molecules in has thus far prevented purely aqueous zinc batteries from reaching this threshold. Here, we report an extreme water-confinement strategy that elevates the oxygen evolution potential of water in a poly(acrylamide-co-hydroxypropyl acrylate) hydrogel electrolyte to 2.85 V versus Zn/Zn²⁺, far beyond the theoretical value (∼1.58 V versus Zn/Zn²⁺). This remarkable enhancement originates from the synergistic effects of strong cation-water coordination, TFSI^--induced water segregation, and extensive hydrogen bonding within the polymer network, which collectively suppress water activity. When coupled with a lithium nickel manganese oxide cathode, the hydrogel electrolyte enables a 2.8 V-class Zn-Li hybrid battery that delivers a record-breaking average operating voltage/discharge plateau of 2.35 V, far exceeding all previously reported purely aqueous zinc batteries. The battery further exhibits excellent mechanical robustness and directly powers a multifunctional wireless sensing monitoring of dynamic pressure, finger movement, muscle activity, speech, and full-body motion. This work provides a viable pathway toward ultrahigh-voltage aqueous zinc batteries for next-generation wearable and intelligent electronic systems.