Reversible self-discharge behavior and its intrinsic mechanism in supercapacitors based on bilayer heterogeneous hydrogel electrolytes.

Rapid self-discharge is a major challenge for the widespread application of supercapacitors. They are limited by their intrinsic energy storage mechanisms and structures, and it is difficult to suppress supercapacitor self-discharge through modification of the electrode or electrolyte materials. Herein, we discover a reversible self-discharge behavior in supercapacitors based on bilayer heterogeneous hydrogel electrolytes with different water contents. For the hydrogel electrolytes with high water contents (≥73 wt%), the self-discharge time of the supercapacitor when the electrode on the polycation side is positively charged is longer than that when the electrode on the polycation side is negatively charged. In contrast, for the hydrogel electrolytes with low water contents (≤54 wt%), the self-discharge time of the supercapacitor when the electrode on the polycation side is negatively charged is longer than that when the electrode on the polycation side is positively charged. The experimental and simulation results reveal that the reversible self-discharge behavior in this supercapacitor is governed by the competing effects of the built-in electric field at the interface between the two hydrogel electrolytes and the electrode/electrolyte interfaces. This reversible self-discharge behavior is also found in supercapacitors based on pseudocapacitive materials, which can be exploited to regulate the self-discharge of high-performance flexible supercapacitors.