Highly Stable Three-Dimensional Nickel-Cobalt Hydroxide Hierarchical Heterostructures Hybridized with Carbon Nanotubes for High-Performance Energy Storage Devices.

A three-dimensional (3D) composite consisting of nickel-cobalt (Ni-Co) dual hydroxide nanoneedles (NCDHNs) grown on a carbon nanotube (CNT) material, denoted as CNTs@NCDHNs, was designed using a facile one-step hydrothermal method. This composite was further fabricated into electrodes, which exhibited high rate capability and long cycle life. Comparative analysis of the electrochemical performance between 3D CNTs@NCDHNs electrodes and Ni-Co hydroxide electrodes revealed that the high rate capability and long cycle life of the CNTs@NCDHNs are due to a synergistic effect. The CNTs@NCDHNs exhibited a high specific capacitance of 1823 F g-1 at a current density of 1 A g-1, and more than 77.6% of the capacitance was retained at a charge-discharge rate of 20 A g-1. To evaluate the functional behavior of the CNTs@NCDHNs, quasi-solid-state cells using CNTs@NCDHNs as the positive electrode and rGO-Fe2O3 as the negative electrode were assembled and tested. These devices presented ultrafast charge-discharge rates of up to 20 A g-1 with high rate capabilities and excellent long-term cyclic stability. The corresponding quasi-solid-state device presented a high energy density of up to 54.6 Wh kg-1 at a power density of 1.13 kW kg-1 and an energy density of 35.8 Wh kg-1 at 12.4 kW kg-1 when a voltage in the range 0-1.6 V was applied. Moreover, the device exhibited optimal flexibility, stability, and safety under different extreme conditions.