Hydrogels with highly concentrated salt solution as electrolytes for solid-state supercapacitors with a suppressed self-discharge rate

Abstract

Solid-state supercapacitors (SSSCs) using hydrogel electrolytes have attracted great interest in recent years due to their potential for powering flexible and wearable electronics. But the application of SSSCs has been severely restricted by self-discharge, which is an inevitable issue that causes fast decay of cell voltage and loss of stored energy. In this work, we demonstrate that suppressed self-discharge of SSSCs can be achieved by using polyacrylamide (PAAm) hydrogels containing highly concentrated LiCl as electrolytes. Specifically, for cells with 14 M LiCl-PAAm hydrogel electrolytes charged to 0.8 V, a low OCV decay rate of 6.7 × 10⁻⁵ V mF⁻¹ h⁻¹ and a small leakage current of 0.003 μA mF⁻¹ V⁻¹ are obtained. Notably, the leakage current is much smaller than that of currently reported supercapacitors using hydrogel electrolytes. In addition, when SSSCs are employed for storing energy harvested by using a triboelectric nanogenerator (TENG) that has a characteristic of pulsed output current at the μA scale, a much enhanced charging efficiency is attained.