Cobalt Doping To Boost the Electrochemical Properties of Ni@Ni3S2 Nanowire Films for High-Performance Supercapacitors

Metal sulfides have aroused great interest for energy storage. However, their low specific capacities and inferior rate capabilities hinder their practical applications. In this work, a facile cobalt-doping process is used to boost the electrochemical performance of Ni@Ni3S2 core-sheath nanowire film electrodes for high-performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni3S2 nanosheets through a facile ion-exchange process. The electrochemical properties of film electrodes are improved greatly, and an ultrahigh volumetric capacity (increased from 105 to 730Ccm(-3) at 0.25Acm(-3)) and excellent rate capability are obtained after Co is doped into Ni@Ni3S2 core-sheath nanowires. A hybrid asymmetric supercapacitor with Co-doped Ni@Ni3S2 as the positive electrode and graphene-carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142Fcm(-3) (based on the total volume of both electrodes) at 0.5Acm(-3) and excellent cycling stability (only 3% capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5mWhcm(-3), which is much larger than those of thin-film lithium batteries (1-10mWhcm(-3)). These results may provide useful insights for the fabrication of high-performance film electrodes for energy-storage applications.