Hierarchical NiCo2O4 nanosheets@hollow microrod arrays for high-performance asymmetric supercapacitors

Abstract

Novel hierarchical NiCo₂O₄ nanosheets@hollow microrod arrays (NSs@HMRAs) are fabricated by a simple and environmental friendly template-assisted electrodeposition followed by thermal annealing. Due to their unique nanostructures, the NiCo₂O₄ NSs@HMRAs, as electrodes, exhibited a high specific capacitance (C_sp) (678 F g⁻¹ at 6 A g⁻¹) and outstanding cycle stability (C_sp retention of 96.06% after 1500 cycles). The desirable superior capacitive performance of the NiCo₂O₄ NSs@HMRAs can be attributed to the large specific surface area, fast ion diffusion, and perfect charge transmission in the hierarchical NSs@HMRAs. The asymmetric supercapacitor (ASC) based on the NiCo₂O₄ NSs@HMRAs as a positive electrode and active carbon (AC) as a negative electrode was assembled and it exhibited a C_sp of 70.04 F g⁻¹ at 5 mV s⁻¹ and a high energy density of 15.42 W h kg⁻¹. Moreover, the NiCo₂O₄ NSs@HMRAs//AC ASC has an outstanding cycle stability (almost no C_sp loss after 2500 cycles), making it promising as one of the most attractive candidates for electrochemical energy storage.