Core/shell Ni–P@Ni–Co composite with micro-/nanostructure for supercapacitor

In this paper, the core/shell Ni–P@Ni–Co composite with micro-/nanostructure, coating Ni–Co on the precursor Ni–P microspheres, has been synthesized successfully via facile two-step hydrothermal method. The chemical composition and microstructure of as-prepared samples were characterized by XRD, EDS, BET, XPS, SEM, and TEM. The results show that the core/shell composite Ni–P@Ni–Co, with a more rough surface and larger specific surface area (74.2 m2 g−1) than bare Ni–P, exhibits good charge storage performance (the specific capacitance reaches up to 1221.1 F g−1 at the current density of 1 A g−1, 1.8 times of Ni–P under the same conditions), and good cycling performance (the retention of specific capacitance is 95.8% after 5000 cycles at 2 A g−1 current density). To further evaluate the practical application property of Ni–P@Ni–Co, an asymmetric supercapacitor (Ni–P@Ni–Co//AC) was assembled, with the Ni–P@Ni–Co and activated carbon (AC) as the positive and negative electrodes, respectively. The electrochemical results reveal that Ni–P@Ni–Co//AC delivers a high energy density of 28.9 Wh kg−1 at a power density of 0.4 kW kg−1, along with a specific capacitance retention rate of 89.1% and nearly 100% Coulomb efficiency at a current density of 1 A g−1 after 5000 cycles.