Flexible Quasi-Solid-State High-Performance Aqueous Zinc Ion Hybrid Supercapacitor with Water-in-Salt Hydrogel Electrolyte and N/P-Dual Doped Graphene Hydrogel Electrodes

Aqueous zinc ion hybrid supercapacitors (ZHSCs) have attracted considerable attention owing to the bivalent nature, high abundance, and stability in the water-based system of zinc. High energy density and superb power output can be achieved simultaneously by integrating a battery-type electrode and a capacitive-type electrode. However, there are still many issues that remain, including but not only hydrogen evolution reaction, dendrite growth, and dramatic capacity loss at low temperatures. Herein, a new type of hybrid “water-in-salt” hydrogel electrolyte based on 1 m Zn(CH 3 COO) 2 and 20 m CH 3 COOK to expand the voltage window of ZHSCs to 0–2.1 V by suppressing the decomposition of water molecules is developed. The aqueous ZHSC delivers maximum energy of 100.2 Wh kg −1 at a power density of 487.5 W kg −1 based on the active materials and displays excellent cycling stability with 99.5% capacitance retention after 4000 cycles. Meanwhile, it is found that the assembled flexible quasi-solid-state ZHSC using the potassium polyacrylate/sodium carboxymethyl cellulose hydrogel electrolyte (containing 1 m Zn(CH 3 COO) 2 and 20 m CH 3 COOK) also shows high-performance (energy density of 106.5 Wh kg −1 at a power density of 383.3 W kg −1 ) with temperature adaptability at low temperature and wearable application potential with excellent energy storage performance.