Mn(OH)2-containing Co(OH)2/Ni(OH)2 Core-shelled structure for ultrahigh energy density asymmetric supercapacitor

In this work, a facile hydrothermal method is used to grow ternary metal hydroxide nanorods on Ni foam for use as a novel electrode in pseudocapacitor. The nanorods exhibit a unique core-shelled structure that has an Mn(OH)2-containing Co(OH)2 core and a Ni(OH)2 shell. The resulting core–shell structured electrode shows an excellent specific capacitance (Csp), high retention, and great cycling stability up to 2000 cycles. The excellent electrochemical performance is ascribed to the unique synergistic effect of Co(OH)2, Mn(OH)2, and Ni(OH)2. The Csp is optimized to be 2286F g−1 with 0.9 mg of active mass. The Mn(OH)2-containing Co(OH)2/Ni(OH)2 core-shelled structure is also evaluated as an positive electrode in asymmetric supercapacitor cell with N-doped graphene as an negative electrode. The asymmetric supercapacitor cell exhibits an ultrahigh energy density of 92 Wh kg−1 at a power density of 1.7 kW kg−1. Furthermore, the asymmetric supercapacitor cell shows an excellent cycling stability with a capacitance retention of 91.7% over 5,000 cycles. The diffusion-controlled charge storage and surface-charge controlled storage mechanisms in the core and shell, respectively, lead to these outstanding electrochemical performances.