Zn–Co–S coatings with a rough and porous nano-dendrite structure for high-performance asymmetric supercapacitors without binder

Abstract

Transition metal sulfides (TMSs) are one kind of peculiarly attractive electrode materials for supercapacitors (SCs) due to their high specific capacity and various structures. However, an irreversible structural damage leads to a significant decline of the electrochemical properties during a long period of the redox reactions. A suitable structure may improve the long stability. A rough and porous nano-dendrite Zn-Co-S directly grown on nickel foam (Zn-Co-S/NF) based on the nano-dendritic Zn-Co hydroxide was prepared by a rapid ion-exchange reaction, and its microstructure and electrochemical properties were observed through SEM, TEM, XRD, XPS, and electrochemical tests. It is shown that the Zn-Co-S with the rough and porous nano-dendritic structure was due to the etching effect of S2− during the ion exchange reaction process. The size of these nano-dendrites was about 150 nm. The rough and porous nano-dendritic structure had a good ability in resisting collapse caused by the solution erosion. The nano-dendrite of Zn-Co-S exhibited an outstanding rate capability, relatively low charge transfer resistance, and an excellent cycling stability, which originated from facilitated transportation of the electrolyte ions, good electrical conductivity, and buffered the volume changes due to the unique rough and porous structure. An asymmetric supercapacitor was assembled with the Zn-Co-S/NF as the cathode and the RuO2-ZnO electrode as the anode in 3M KOH solution. The energy densities of 46.9 W h kg−1 and 24.1 W h kg−1 could be obtained when the power density was 1006.6 W kg−1 and 8204.2 W kg−1.