Precisely geometry controlled microsupercapacitors for ultrahigh areal capacitance, volumetric capacitance, and energy density

Microsupercapacitors are microscale rechargeable energy storage devices that can support or replace batteries in ultrasmall electronic devices. Although the use of high-capacitive, two-dimensional materials is promising, other methods are needed to reach a high capacitance and energy density, which cannot be achieved by fully utilizing the surface of electrode materials. Here, we introduce an effective strategy to control the geometry of interdigital microelectrodes for achieving an ultrahigh capacitance by utilizing the edge effect of in-plane structured graphene and improving ion transport. Theoretical calculations are employed to investigate the electrochemical enhancement at the edge of reduced graphene oxide in a KOH electrolyte. The presence of edges is predicted to enhance the capacitance by electronic redistribution. We report areal and volumetric stack capacitances (40 mF/cm² and 98 F/cm³, respectively) and energy densities (5.4 μWh/cm² and 13.7 mWh/cm³, respectively) that are much higher than those of any other microsupercapacitors containing micrometer-thick interdigital electrodes. This improvement is attributed to synergistic effects between numerous edge planes fabricated by a high-resolution laser-drilling process and a well-matched electrolyte as well as the in-plane structure of heat-treated graphene oxide, which provides minimal channel space for efficient ion transport. Our strategy provides a versatile method for designing high-performance microsupercapacitors and is promising for the development of microenergy storage devices for subminiature electronics that require a high energy density.