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

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.