Enhanced performance on capacity retention of hierarchical NiS hexagonal nanoplate for highly stable asymmetric supercapacitor

Low energy density of the supercapacitors is considered as a roadblock for its application in or as a primary power source. While, utilization of high energy density battery-type electrode materials in an asymmetrical configuration was expected to resolve this hurdle, however, its inferior rate performance and poor cycling stability hinder the overall device performance. Incomplete utilization of active material at elevated current density was identified as the root for poor rate performance. Herein, we developed a hierarchical NiS microspheres build by the self-assembly of hexagonal nanoplates via trimethylamine (TEA) assisted hydrothermal method. The optimized sample exhibited a superior specific capacitance of 606 C/g at 0.5 A/g. More interestingly, the electrode was able to retain 50% (302 C/g at 20 A/g) of its maximum capacity even when the current density was multiplied 40-fold relative to 18% (50 C/g at 20 A/ g) shown by control sample prepared without TEA. Excellent rate performance of the electrode could be attributed to the increment in the electrolyte-accessible surface area by morphological modifications. Owing to its porous nature, optimized sample was able to retain 93% of its original capacity at the end of 2000 continuous cycles of charge-discharge. Furthermore, an asymmetric supercapacitor with NiS-C as the positive electrode and activated carbon as the negative electrode delivered a high energy density of 35.07 Wh/kg at a power density of 0.420 kW/kg within an operating voltage window of 1.5 V. (C) 2018 Elsevier Ltd. All rights reserved.