In-plane flexible solid-state microsupercapacitors for on-chip electronics

Small-scale supercapacitors or microsupercapacitors (MSCs) can be integrated with miniaturized electronics to work as stand-alone power sources, or as efficient energy storage units coupling with energy harvesters to realize self-powered microdevices. Despite many advances, research and development of MSCs are still in their infancy. In this work, in-plane flexible solid-state MSCs based on interdigital electrodes are developed through a facile, cost-effective, universal and industrially applicable protocol, i.e. screen printing technique. To verify the generality of such method, activated carbon (AC) nanospheres and molybdenum oxide (MoO3-x) nanorods as representative electrical double-layer capacitive material and intercalation pseudocapacitive material are used as the electrode active material, respectively. Using a highly viscous AC nanosphere or MoO3-x nanorod paste, shape-designable microelectrodes with an effective area of 0.415 cm2, and a spacing of 250 μm between the two electrode fingers are printed on flexible substrate in several seconds. The MSCs can deliver high areal capacitances and energy densities (5.04 mF cm−2 and 0.7 μWh cm−2 for the MSC with AC nanosphere electrodes, 41.7 mF cm−2 and 5.8 μWh cm−2 for the MSC with MoO3-x nanorod electrodes), own excellent rate capability and long cycle life for both the electric double-layer capacitive material and pseudocapacitive material. This work demonstrates the opportunity and practicability for developing MSCs for flexible on-chip electronic devices.