Graphene nanoribbon wrapped cobalt manganite nanocubes for high performance all-solid-state flexible supercapacitors

Nanocubes of cobalt manganite, CoMn2O4, were grown in situ over graphene nanoribbons (GNRs) to form a CoMn2O4/GNR composite during hydrothermal processing. The proposed all-solid-state supercapacitor (SC), CoMn2O4/GNR//CoMn2O4/GNR, with a polymer gel electrolyte showed an excellent electrochemical performance. It can be reversibly cycled over a large potential range of 3 V, resulting from the synergism of the pseudocapacitive and electrical double layer capacitor (EDLC) materials. The pseudocapacitance arises from the binary redox couple of the different cations in CoMn2O4, which, in combination with the GNRs, endows a high performance and long term stability. The SC demonstrates a high energy density of 44.6 W h kg(-1) and a power density of 11.3 kW kg(-1) with a short diffusion coefficient (D-a) of 1.02 x 10(-7) cm(2) s(-1) and a relaxation time constant (tau) of 5.6 mu s. It demonstrates similar to 95% capacitive retention with a steady coulombic efficiency even after 12 000 charge/discharge cycles. Moreover, a steady performance of the cell with good capacitive behaviour, even in the harsh environment of different bending states, encourages its commercial use in portable electronics.