Freestanding Ion Gels for Flexible, Printed, Multifunctional Microsupercapacitors

Freestanding ion gels (FIGs) provide unique opportunities for scalable, low-cost fabrication of flexible microsupercapacitors (MSCs). While conventional MSCs employ a distinct electrolyte and substrate, FIGs perform both functions, offering new possibilities for device integration and multifunctionality while maintaining high performance. Here, a capillarity-driven printing method is demonstrated to manufacture high-precision graphene electrodes on FIGs for MSCs. This method achieves excellent self-alignment and resolution (width: 50 μm, interdigitated electrode footprint: <1 mm²) and 100% fabrication yield (48/48 devices) and is readily generalized to alternative electrode materials including multiwalled carbon nanotubes (MWCNTs). The devices demonstrate good performance, including high specific capacitance (graphene: 0.600 mF cm^-2; MWCNT: 6.64 mF cm^-2) and excellent stability against bending, folding, and electrical cycling. Moreover, this strategy offers unique opportunities for device design and integration, including a bifacial electrode structure with enhanced capacitance (graphene: 0.673 mF cm^-2; MWCNT: 7.53 mF cm^-2) and improved rate performance, print-and-place versatility for integration on diverse substrates, and multifunctionality for light emission and transistor gating. These compelling results demonstrate the potential of FIGs for scalable, low-cost fabrication of flexible, printed, and multifunctional energy storage devices.