Solution-processed Nonstoichiometry NiOx Nanocrystal Aggregations for Supercapacitor Electrodes

Nickel oxide (NiOx) has been considered as one of the most promising electrode materials for electrochemical supercapacitors because of its exceptional redox and charge storage characteristic. Here, the nonstoichiometry NiOx nanocrystals were synthesized by a room-temperature chemical precipitation method with the following annealing process. The stoichiometric ratio and morphology of the NiOx nanocrystals were controlled by annealing Ni(OH)₂ nanoparticles under different temperatures. At 270 ^○C annealing process, the NiOx nanocrystals get together to aggregations, which not only have large specific surface area, but also have relatively long charge transfer channels. Meanwhile, with increasing temperature beyond 270 ^○C, Ni²⁺ active sites in the nonstoichiometry NiOx decrease. Furtherly, the NiOx nanocrystal aggregations show the superior electrochemical performance with a specific capacitance of 332 F · g^–1 at a current density of 1 A · g^–1. In addition, the stability of Coulombic efficiency can still retain 91.3 % after 500 cycle.