Mechanistic insight into hierarchical nickel cobalt layered double hydroxide nanosheet-supported-nanowires arrays for high-performance hybrid supercapacitors

NiCo layered double hydroxide (NiCo LDH) nanosheet-supported-nanowire arrays are fabricated via a hydrothermal synthesis and subsequently alkali conversion. Some positive evolutions during alkali conversion, including the increasing content of Co3+ species via charge transfer and the change of surface morphology, are specified initially to enhance the capacitance of NiCo LDH. Moreover, the respective capacitive roles of nanowires and nanosheets are discussed. The free-standing nanosheet arrays guarantee sufficient adhesion for high cyclic stability, regulate the growth of nanowires with less lattice mismatch, and contribute most of the capacitance. Meanwhile, nanowires decorated on nanosheet promotes effectively the rate capability, and therefore, the electrode shows the capacitance of 832.5 C g−1 at 1 A g−1, and maintained 60.0% of the capacitance at 10 A g−1. However, the nanosheet-supported-nanowire arrays show poor cycling performance. Fortunately, the cyclic stability of NiCo LDH nanosheet-supported-nanowire arrays is improved in an all-solid-state asymmetric hybrid supercapacitors. When acted as positive electrode, the supercapacitor achieves a maximum working voltage of 1.8 V, and a specific energy of 63.3 Wh kg−1 at a specific power of 900 W kg−1 with 89.9% of capacitance retention after 10 000 cycles.