A high-energy, long cycle-life hybrid supercapacitor based on graphene composite electrodes

The energy density of a hybrid supercapacitor consisting of a battery-type electrode and a capacitive electrode could be significantly higher than that of an electrical double-layer capacitor (EDLC) due to the broadened voltage window and the high capacity of the battery-type electrode. However, the commercialization of hybrid supercapacitors is still hampered by lacking of proper electrode materials of desired nanostructures. Here we report a class of nanocomposite electrodes composed of CoxNi1-x(OH)(2) and reduced graphene oxide (rGO), derived from a facile process at room temperature using hydrous hydrazine and proper ratios of Co(II) to Ni(II) to tune the composition and morphology. In particular, an architectural composite electrode consisting of porous CoxNi1-x(OH)(2) disks wrapped by rGO achieves large capacity, high rate capability (743 and 545 C g(-1) at 1 and 20 A g(-1), respectively), and long cycling life. When coupled with a p-phenylenediamine (PPD)-modified rGO, the resulting hybrid supercapacitor exhibits superior energy densities of 72 and 44 W h Kg(-1) at power densities of 797 W Kg(-1) and 16.7 kW Kg(-1), respectively, and excellent cycling stability for 20,000 cycles at 20 A g(-1), implying that it is a very promising device for portable power and next-generation energy storage.