Irradiation-Induced Phase-Separated Ionogels with High Ionic Liquid Content for Flexible Supercapacitors

Ionogels with high ionic liquid (IL) content often face a trade-off between achieving high ionic conductivity and maintaining structural integrity and tensile strength. To address this, polymerization-induced phase separation (PIPS) has gained popularity; however, it still suffers from relatively low ionic conductivity due to the increase in IL content, which may result in leakage or ion aggregation. In this work, we demonstrate that controlled irradiation, combined with PIPS, plays a critical role in increasing the IL content of the ionogel for the enhancement of ionic conductivity. By controlling the irradiation, the high IL content ionogel exhibits higher ionic conductivity via increased cross-link density and degree of phase separation, allowing better segregation of ions while also maintaining excellent structural integrity. Notably, the [EMIM][BF4] ionogel fabricated via PIPS exhibits among the highest ionic conductivities reported for [EMIM]-based PIPS ionogels for supercapacitors and sensors under comparable conditions, measuring 5.51 ± 0.31 mS/cm. Furthermore, the practical applicability of the ionogel as a flexible supercapacitor was demonstrated, as the integrated device delivered a high specific capacitance of 103 F/g at a current density of 0.5 A/g along with an energy density of 122 Wh/kg and a power density of 2928 W/kg. The device also exhibited a high capacitance retention (93%) after 30,000 charge-discharge cycles at 1 A/g and was able to maintain stable electrochemical performance even under repeated mechanical deformation. This study demonstrates that irradiation is an effective strategy to further increase the IL content incorporated for higher ionic conductivity and overall better electrochemical performance while maintaining excellent structural integrity under deformation, underscoring its suitability for flexible and wearable devices.