Cobalt Doping To Boost the Electrochemical Properties of Ni@Ni 3 S 2 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@Ni 3 S 2 core–sheath nanowire film electrodes for high‐performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni 3 S 2 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 730 C cm −3 at 0.25 A cm −3 ) and excellent rate capability are obtained after Co is doped into Ni@Ni 3 S 2 core–sheath nanowires. A hybrid asymmetric supercapacitor with Co‐doped Ni@Ni 3 S 2 as the positive electrode and graphene‐carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142 F cm −3 (based on the total volume of both electrodes) at 0.5 A cm −3 and excellent cycling stability (only 3 % capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5 mWh cm −3 , which is much larger than those of thin‐film lithium batteries (1–10 mWh cm −3 ). These results may provide useful insights for the fabrication of high ‐ performance film electrodes for energy‐storage applications.