ZnMnCo-S nanoneedle arrays as battery-type eletrodes for high-performance hybrid supercapacitors

Abstract

Transition metal sulfides are used in the field of supercapacitors due to their remarkable electrical conductivity and superior energy density. However, few research has been conducted on how the sulfidation process affects the structure and electrochemical properties of electrodes. The nanoneedle array Zn-Mn-Co sulfide (ZMC-S/NF) electrode is prepared by directly growing on nickel foam (NF) via a two-step hydrothermal technique. During the first step, the Zn-Mn-Co carbonate hydroxide nanoneedle skeleton can be obtained. During the second step, the nanoneedle skeletons are etched, and rough nanoneedle arrays are created by the introduced sulfur ions,i.e., the sulfidation process. The ZMC-S/NF electrode exhibits a specific capacity of 1401.0 C g−1 at 2 A g−1. It still has excellent rate performance with a specific capacity of 1015.3 C g−1 at 20 A g−1. Moreover, it exhibits excellent cycling stability with 81.9% capacity retention after 10,000 cycles. ZMC-S/NF as the cathode and activated carbon (AC) as the anode are assembled to be a hybrid supercapacitor (HSC), which has an energy density of 43.4 Wh kg−1 at a power density of 700.4 W kg−1. The effect of adding Zn and Mn to the Co3S4 on energy band structure and density of states during the sulfidation process is calculated by the DFT. The HSC devices constructed by two series-connected ZMC-S/NF//AC can light a star made by ten 1.8 V-red Light Emitting Diodes (LEDs) for 10 minutes.