High-performance binder-free flower-like (Ni0.66Co0.3Mn0.04)2(OH)2(CO3) array synthesized using ascorbic acid for supercapacitor applications

A binder-free electrode material composed of nickel-rich cobalt-manganese hydroxyl carbonate (Ni0.66Co0.3Mn0.04)2(OH)2(CO3) (NCMHC) flowers was grown directly on nickel foam in a facile hydrothermal reactor using L-ascorbic acid as a morphology-directing green reducing agent and carbonate source. The electrode material NCMHC exhibited an excellent specific capacitance of 4635 F g−1 (1854 C g−1) at a current density of 1 A g−1. Furthermore, the hybrid supercapacitor, which consisted of a NCMHC positive electrode and an activated carbon negative electrode, exhibited a good specific capacitance of 144.4 F g−1, high energy of 51.4 Wh kg−1, and high power density of 8000 W kg−1 as well as remarkable charge-discharge cycling stability (capacity retention) of 96% after 10,000 cycles, outperforming previously reported nickel-cobalt-manganese-based electrode materials. This exceptional capacitive performance of NCMHC was attributed to the synergistic combination of ternary metal ions with the optimal oxidation states to obtain ideal electrical conductivity and highly exposed active sites due to the array of a unique flower petal-like morphology with short ion-diffusion paths for efficient energy storage. The facile synthesis and excellent supercapacitive performance highlights the potential of the advanced electrode materials for the next generation hybrid supercapacitors. © 2019 Elsevier B.V.