Transition Metal Sulfide Based Cathode Materials for Efficient Hybrid Supercapacitors

Abstract

Supercapacitors (SCs) have been widely recognized in a wide range of energy storage applications over the past decade, such as hybrid electric vehicles, mobile electronic devices, large industrial equipments, memory backup systems, and military devices, due to their unique properties including higher specific power density (10 kW kg-1) than batteries, and higher specific energy density (5-10Wh kg-1) than conventional dielectric capacitors without sacrificing cycle life (>100,000 cycles). In recent years, nanostructured metal sulfides have been intensively investigated as SCs electroactive materials. In this study, nickel and cobalt binary sulfide nanoparticles decorated on the surface of multi-walled carbon nanotubes (designated as Ni-CoS/MWCNT composite) and Ni3S2 thin films directly deposited onto Ni foam is successfully prepared by a facile glucose-assisted hydrothermal method and pulse-reversal (PR) deposition approach. On the basis of tuning the Ni/Co molar ratio of the Ni-CoS/MWCNT composites, the optimized Ni-CoS/MWCNT composite was employed as the cathode and a reduced graphene oxide was used as the anode to fabricate a hybrid supercapacitor (HSC). As-fabricated HCS is able to be operated reversibly in a full voltage region of 0–1.6 V and achieves a high specific capacity of 33 mAh g−1 at 1 A g−1. Moreover, it can still deliver a maximum energy density of 23 Wh kg−1 at a power density of 684 W kg−1. Furthermore, the HSC still retains 90% of its initial discharge capacity after 2000-cycle charge/discharge test at a fair high current density of 4 A g−1. Additionally, another HSC is then assembled by using the optimized PR-Ni3S2 electrode as cathode and carbon fiber cloth (CFC) as anode, respectively. The HSCs can be operated with a potential window between 0 and 1.8 V and deliver a high specific capacity value of 25.5 mAh g-1 at 0.5 A g-1. Moreover, the energy density and power density of the HCS can be achieved up to 28.8 Wh kg-1and 564 W kg-1, respectively. The most important thing is that the HSC displays excellent cycling stability with only 20% capacity loss after 5000 cycles. As a result, the highly efficient HSCs can be achieved based on the transition metal sulfide based materials as cathodes