A flexible, high-voltage and safe zwitterionic natural polymer hydrogel electrolyte for high-energy-density zinc-ion hybrid supercapacitor

Abstract With the development of flexible wearable electronic devices, energy storage equipment like supercapacitor with high energy density, good mechanical properties and safety has attracted more and more attention. However, the currently existing energy storage materials normally suffer from several drawbacks, such as poor flexibility, hidden danger, toxicity and especially low energy density, limiting their practical applications. Expanding the voltage window by employing the hydrogel electrolyte is regarded as an effective method to improve the energy density of supercapacitor. Herein, we employ a zwitterionic natural polymer hydrogel with excellent mechanical strength and flexibility as electrolyte to assemble a solid-state zinc-ion hybrid supercapacitor (H-ZHS) with Zn foil and activated carbon electrode. The H-ZHS exhibits an amazingly wide and stable voltage window of 2.4 V, high maximum energy density of 286.6 Wh kg−1 at the power density of 220 W kg−1 and superior capacity retention of 95.4% after 2000 cycles at 2 A g−1 calculated based on mass of activated carbon electrode. The strategy in this work should provide a new insight in exploring zinc-ion hybrid supercapacitor with high energy density for flexible wearable electronic devices.