Tracking surface ionic movement of Ni3S2@CuS electrode materials with high electrochemical performance

Supercapacitors have overwhelming advantages in cycle life, charging time and power density. Metal sulfides involve reversible Faraday redox reactions, and chemical reactions occur during charge and discharge, resulting in high specific capacity of the electrode. Different from the traditional nickel foam as a current collector, in this work, vulcanized nickel foam (Ni3S2) is used to further grow CuS nanosheets by hydrothermal reaction to produce new cathode material. The results show that the electrochemical properties of the electrode material Ni3S2@CuS obtained at 190 °C for 4 h reach a mass specific capacity of 967.7F/g. When assembled as a supercapacitor device, it has an energy density of 103.7 Wh/kg and a power density of 15050.3 W/kg. The coulomb efficiency of the device remains 97.4 % after 10,000 cycles of constant current charge and discharge. To deeply understand the mechanism of the capacitance increase, we carry out a molecular dynamics (MD) simulation on pure Ni3S2 electrode and Ni3S2@CuS to investigate the influence of this unique structure on capacitance for the first time. We discover that the CuS tunnel on the Ni3S2 electrode surface will restrict the deintercalation of K+ ions and promote the intercalation of OH–, and this phenomenon will promote the reversible redox reaction on the surface of the metal sulfides and enhance the capacitance of this pseudocapacitor.