Facile synthesis of Al-doped NiO nanosheet arrays for high-performance supercapacitors

Electrode material design is the key to the development of asymmetric supercapacitors with high electrochemical performances and stability. In this work, Al-doped NiO nanosheet arrays were synthesized using a facile hydrothermal method followed by a calcination process, and the synthesized arrays exhibited a superior pseudocapacitive performance, including a favourable specific capacitance of 2253 ± 105 F g^-1 at a current density of 1 A g^-1, larger than that of an undoped NiO electrode (1538 ± 80 F g^-1). More importantly, the arrays showed a high-rate capability (75% capacitance retention at 20 A g^-1) and a high cycling stability (approx. 99% maintained after 5000 cycles). The above efficient capacitive performance benefits from the large electrochemically active area and enhanced conductivity of the arrays. Furthermore, an assembled asymmetric supercapacitor based on the Al-doped NiO arrays and N-doped multiwalled carbon nanotube ones delivered a high specific capacitance of 192 ± 23 F g^-1 at 0.4 A g^-1 with a high-energy density of 215 ± 15 Wh kg^-1 and power density of 21.6 kW kg^-1. Additionally, the asymmetric device exhibited a durable cyclic stability (approx. 100% retention after 5000 cycles). This work with the proposed doping method will be beneficial to the construction of high-performance supercapacitor systems.