Battery-like supercapacitive behavior of urchin-shaped NiCo <sub>2</sub> O <sub>4</sub> and comparison with NiCo <sub>2</sub> X <sub>4</sub> (X = S, Se, Te)
M.L. Aparna, Tiju Thomas, G. Ranga Rao
Abstract
Bimetallic chalcogenides are promising as potential electrode materials for supercapacitors on account of their multiple oxidation states and better electroactivity. Anion effect on the electrochemical performance of urchin-shaped NiCo 2 X 4, (X = O, S, Se, Te) is reported here. These materials crystallize in spinel cubic and monoclinic phases. Electron micrographs show that the materials possess a nanorod-like morphology that protrude from surfaces of microspheres. This gives it urchin-like appearance. Their structure enables ion permeability allowing for improved charge-discharge kinetics. The specific capacities obtained from 3-electrode electrochemical cell measurements are 137 mAh g −1 (492 C g −1 ), 108 mAh g −1 (390 C g −1 ), 76 mAh g −1 (272 C g −1 ) and 72 mAh g −1 (258 C g −1 ), respectively, for NiCo 2 O 4 , NiCo 2 S 4 , NiCo 2 Se 4 , and NiCo 2 Te 4 at 2 A g −1 . An asymmetric Swagelok device is fabricated for each chalcogenide material. Due to well-defined morphology and sufficient specific surface area, NiCo 2 O 4 proved to be the best material delivering a maximum energy density of 34 Wh kg −1 and power density of 6 kW kg −1 followed by NiCo 2 Te 4 delivering 22 Wh kg −1 and 11.25 kW kg −1 . Higher electrical conductivity of the telluride-based materials makes them efficient supercapacitor electrodes. Selenium-based materials display better cyclic stability owing to the monoclinic phase.