Intimately interconnected nickel carbonate hydroxide nanosheet‐wire structure for high‐performance asymmetric supercapacitors

Low-cost nickel-based hydroxides with multiple valence states are excellent alternative supercapacitor (SC) electrode materials. However, their practical application is severely restricted by poor conductivity and unstable reaction kinetics. In this study, a highly interconnected nickel carbonate hydroxide nanosheet-wire structure (Ni Ns-w) was prepared by carefully controlling the urea content used during reflux synthesis. Compared to nickel hydroxide nanosheets, Ni Ns-w has a high specific capacitance (1160.7 F g−1), high rate capability (611.9 F g−1 at 10 A g−1), and excellent cycling stability (80.43% capacitance retention after 5000 cycles) due to the intimate connection between the nanosheets and nanowires that provides an abundant carrier transport paths, high structural stability, and a large reaction area. At the same time, the carbonate ions further enhance the electrochemical properties by increasing the wettability of the electrode materials and reducing the polarization during charge-discharge process. The corresponding asymmetric SC realized a high power density and a high energy density (9.0 kW kg−1 and 24.0 Wh kg−1, respectively). As a result, Ni Ns-w is an excellent candidate material for use in energy storage cells.