Vertically Oriented Graphene Nanoribbon Fibers for High-Volumetric Energy Density All-Solid-State Asymmetric Supercapacitors

Abstract

Graphene fiber based micro-supercapacitors (GF micro-SCs) have attracted great attention for their potential applications in portable and wearable electronics. However, due to strong π-π stacking of nanosheets for graphene fibers, the limited ion accessible surface area and slow ion diffusion rate leads to low specific capacitance and poor rate performance. Here, the authors report a strategy for the synthesis of a vertically oriented graphene nanoribbon fiber with highly exposed surface area through confined-hydrothermal treatment of interconnected graphene oxide nanoribbons and consequent laser irradiation process. As a result, the as-obtained fiber shows high length specific capacitance of 3.2 mF cm^-1 and volumetric capacitance of 234.8 F cm^-3 at 2 mV s^-1 , as well as excellent rate capability and outstanding cycling performance (96% capacitance retention after 10 000 cycles). Moreover, an all-solid-state asymmetric supercapacitor based on graphene nanoribbon fiber as negative electrode and MnO₂ coated graphene ribbon fiber as positive electrode, shows high volumetric capacitance and energy density of 12.8 F cm^-3 and 5.7 mWh cm^-3 (normalized to the device volume), respectively, much higher than those of previously reported GF micro-SCs, as well as a long cycle life with 88% of capacitance retention after 10 000 cycles.