Development of flame-retardant ion-gel electrolytes for safe and flexible supercapacitors

The presence of organic electrolytes in typical liquid supercapacitors ultimately results in inadequate safety and poor flexibility, which limits the development and application of supercapacitors. Thus, we developed an easy-to-prepare ion-gel supercapacitor with strong flame-retardant properties, thermal stability, flexibility, and good electrochemical characteristics. Specifically, this ion-gel supercapacitor provides excellent performance by using the in situ cross-linking of ion-gel electrolytes on electrodes. The introduction of ether-containing flexible chain segments to the ion-gel electrolyte results in a high ionic conductivity (6.5 × 10−3 S cm−1) at an ambient temperature, and the in situ cross-linking results in a tight interfacial contact between the electrolyte and electrode. The ion-gel supercapacitor retains a stable electrochemical performance while bending due to the tight interfacial contact and excellent mechanical characteristics. Furthermore, incorporating the diazonaphthone structure in the cross-linked electrolyte renders the ion-gel electrolyte excellent flame-retardant properties and thermal stability, allowing it to sustain dimensional stability at 150°C for 30 min. The supercapacitor with the optimized ion-gel electrolyte has a specific capacity of 105 F g−1 and an energy density of 41.6 W h kg−1. The results of this study provide a practical method for preparing and optimizing ion-gel cross-linked electrolytes.