Unusual switching of ionic conductivity in ionogels enabled by water‐induced phase separation

Abstract Developing smart iontronic materials is highly desired for eradicating the widely occurring potential short‐circuit hazard and subsequent safety problems caused by high ambient humidity. In this work, a humidity‐responsive ionogel (HRIG) based on a poly(benzyl methacrylate) matrix swollen by hydrophobic ionic liquid and hygroscopic lithium salt is reported. The HRIG exhibits an anomalous decrease in ionic conductivity upon hydration by increased humidity, totally differing from traditional ionic conductors, which are usually more conductive due to the plasticizing effect of water molecules. This unique ionogel shows a dramatic decrease in ionic conductivity (as much as 10 2 ) when exposed to humidity. The conductive pathway within the HRIG would be shut down spontaneously above a critical relative humidity due to water‐induced phase separation. Moreover, this transition can be perfectly reversed when the ambient humidity drops. A humidity‐responsive smart supercapacitor that can be switched on and off by capturing humidity changes is designed for demonstration. It is believed that such unusual HRIG material will provide new insights into the development and applications of smart iontronics.