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

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 conducive 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.