Atypical Properties of FIB-Patterned RuO_<i>x</i> Nanosupercapacitors

Small-scale electrochemical capacitors, also called microsupercapacitors, have been the subject of intense research in the past few years as miniaturized energy storage components for modern electronics. Although numerous microfabrication processes have been successfully assessed to achieve low-profile supercapacitors with submillimeter-scale features, several advances still need to be made in their performance characteristics to become industrially viable components. Here we report the occurrence of unexpected properties of on-chip supercapacitors when reducing interelectrode spacing down to the nanometer scale. An ultrahigh power concomitant with a high capacitance and energy density, an unforeseeable extended cell voltage, and an impressive lifetime were obtained at such small dimensions with a focused ion beam (FIB)-patterned nanosupercapacitor based on RuOx pseudocapacitive material. The scaling relationship between miniaturized supercapacitors and electrochemical responses leads to valuable understanding of electrode reactions and rate-limiting steps. This finding offers new opportunities in the design of integrated energy storage devices with improved properties.