High Output Voltage Aqueous Supercapacitors by Water Deactivated Electrolyte over Wide Temperature Range

Abstract Confined by factors such as low operating voltage, poor temperature resistance, and instability at high voltage, the energy density of conventional symmetric aqueous supercapacitors is undesirable over a wide temperature range. It is still challenging to develop aqueous flexible supercapacitors (AFSCs) that can provide stable and high voltage output (>2.0 V) at extreme ambient temperatures. Here, a strategy for constructing AFSC with ultrahigh output voltages over a wide temperature range is proposed through the development of organohydrogel electrolytes (OHEs) with excellent water deactivation, which achieve a notable output voltage of 3.0 V, and unprecedented energy densities of 23.16 µWh cm ⁻² at −40 °C (beyond 25 °C), surpassing the performance of all previously reported symmetric supercapacitors with aqueous electrolytes. Theoretical calculations and experimental analyses show that OHEs can deactivate water to increase the output voltage limit of AFSCs by enhancing intermolecular interactions and regulating inter Helmholtz plane. Meanwhile, it also shows excellent flexibility and cycling stability (80.5% after 20 000 cycles at 25 °C and 97.0% after 50 000 cycles at −40 °C). More importantly, OHEs enable AFSCs switchable output voltages (from 2.5 to 3.0 V), making it possible to operate supercapacitors with high energy density and stability at low temperatures.