Crumpled graphene microspheres anchored on NiCo2O4 nanoparticles as an advanced composite electrode for asymmetric supercapacitors with ultralong cycling life

The rational design of composite electrodes that may take full advantage of pseudocapacitive metal oxides and graphene is still challenging. Herein, nickel cobaltate (NiCo2O4) nanoparticle-anchored crumpled graphene microspheres (CGMs) were fabricated through a simple spray-assisted self-assembly process and used as a composite electrode for aqueous supercapacitors. Due to the porous spherical architecture and well-dispersed NiCo2O4 nanoparticles on graphene, the NiCo2O4/CGM electrode displays ideal electrochemical performance, including a specific capacitance of 369.8 F g-1 (at 1 A g-1), good rate performance of 85% capacitance retention even at 10 A g-1 and intriguing cycling stability. An aqueous asymmetric supercapacitor (ASC) with an operating voltage of 1.6 V was then assembled using the NiCo2O4/CGM composite and nitrogen-doped CGM (N-CGM) as the positive and negative electrodes in KOH electrolyte, respectively. The ASC device exhibited an excellent energy density of 24.7 W h kg-1 at a power density of 799.6 W kg-1, and an ultralong cycling life with a capacitance retention of 85% after 50 000 cycles. The satisfactory electrochemical performance and ultralong cycling stability indicate that the NiCo2O4/CGM electrode has promising applications in advanced supercapacitors.