Uniform MoS2 nanolayer with sulfur vacancy on carbon nanotube networks as binder-free electrodes for asymmetrical supercapacitor

Abstract

Molybdenum sulfide (MoS2) is regarded as a promising material for supercapacitor applications but the intrinsically low electrical conductivity greatly limits its high specific capacitances. Herein, we introduce sulfur vacancy on MoS2 nanolayer (MoS2−x) by a pulsed laser deposition (PLD) process. By further using the highly conductive carbon nanotube (CNT) networks as the current collector, the as-fabricated defect-rich MoS2@CNTs/Ni core/shell-structured electrode delivers an ultrahigh specific capacitance of 512F g−1 at 1 A g−1, excellent rate performance (342F g−1 at 30 A g−1) and long cycle life (no decay after 2000 cycles) in 1 M Na2SO4 electrolyte, which are among the best reported values for MoS2-based supercapacitors. Along with the experiment results, our DFT calculations further demonstrate that the S vacancy can create deep acceptor levels in the MoS2 monolayer, which can trap electrons and improve the electrons mobility. For practical application, we build an asymmetrical supercapacitor (ASC) with MoS2−x@CNTs/Ni as the positive electrode and CNT networks as the negative electrode, which exhibits a large energy density of 63 Wh kg−1 at 850 W kg−1 and an impressive power density of 25.5 kW kg−1 at 44.2 Wh kg−1. These results indicate that PLD is a very powerful technique to construct the binder-free film electrodes for energy storage applications.