Achieving a highly safe supercapacitor via the combination of a temperature-responsive hydrogel-electrolyte and electrochromic electrodes

Abstract

Supercapacitors are promising electrochemical energy storage devices because of their high power density and long-life performance. However, thermal runaway is a critical obstacle to their safety and stable operation. Herein, an effective strategy combining a temperature-responsive hydrogel electrolyte and electrochromic pseudo-capacitance electrodes has been applied to address the thermal runaway issue, providing a smart supercapacitor (SSC) with monitoring, self-protection, and alarm functions. Specifically, the obtained SSC becomes almost transparent (fully discharged), turns to dark blue (fully charged), and displays a milky white pattern (heating up) in response to charging and temperature change, realizing the visual monitoring of multiple states of SSCs. Benefiting from the thermal gating behavior of the thermally responsive hydrogel electrolyte, the obtained SSC can achieve a reversible switch-off of capacitance upon heating/cooling, providing SSCs with self-protection at high temperatures. In addition, the SSC can shut itself off to stop further deterioration and send a signal to sound an alarm automatically for identifying the faulty SSC once the thermal runaway occurs. Such a combination of functions enables super safe and stable operation of SSCs under different conditions: it can indicate the capacitance value intuitively in regular operation, whereas in the case of thermal runaway, it rapidly shuts down and sounds an alarms automatically without compromising the performance. This work demonstrates a great reference for designing thermally responsive energy storage devices with enhanced safety.