A versatile non-graphene 2D material (MoS₂) has recently attracted great research attention owing to their novel structure-property relation for high performance energy storage devices. The unique hexagonal layered family of transition metal dichalcogenides (TMDs-MX₂) composed of X-M-X layers; are stacked together by van der Waals bonding. Different fabrication methods including mechanical/chemical exfoliation, chemical vapor deposition, co-evaporation, and hydrothermal reactions have been employed to fabricate different thickness of MoS₂. However, there is continuous pursuit to explore various novel methods for uniform and large-scale synthesis of MoS₂ on different substrate. Here in, we present two different applications of MoS₂for electrochemical energy storage devices:

Firstly, MoS₂ nanomaterials are very efficient supercapacitor electrode due to its sheet like structure providing high surface area for double layer charge storage and exhibits multiple oxidation states for pseudo capacitive charge transfer due to intercalation of H⁺ and Li⁺ into MoS₂ structure. We have synthesized large scale and flexible MoS₂ electrodes just by using direct magnetron sputtering technique. The novel three-dimensional (3D) porous structure of the MoS₂ on copper film exhibits an excellent capacitance of 330 F /cm³ along with a high volumetric power and energy density of 40–80 W/cm³ and 1.6–2.4 mWh/cm³, respectively. Additionally, it shows excellent cycling stability upto 5000 cycles with capacitance retention of 97%.

Secondly,a unique binder-free electrode of 3-dimensional carbon nanotubes (3D CNTs) coated by MoS₂ has been fabricated by a chemical vapor deposition (CVD) and direct magnetron sputtering method. The unique vertically oriented nanoflakes of MoS₂ are strongly bonded on 3D CNTs with diameter of 50-100nm. The 3D geometry for the accommodation of active material (MoS₂) provides high surface area with active electrochemical sites, enhances ion diffusivity, and compensates volumetric expansion of MoS₂. The electrochemical performance of the binder-free 3D CNTs-MoS₂ electrode shows very high areal capacity of ~1.65mAh/cm² with an areal density (of MoS₂) of ~0.35mg/cm² at 0.5C rate; it also shows capacity retention of ~82% after 50 cycles. The unique architecture of 3D CNTs-MoS₂ is suggestive to be a promising anode for next generation Li-ion batteries with high capacity and long cycle life.

References:

(a) N. Choudhary⁺, M. Patel⁺ (⁺ First Authors), Y.H. Ho, N.B. Dahotre, W.Lee, J.Y. Hwang, W.Choi, Directly deposited MoS₂ thin film electrodes for high performance supercapacitors, J. Mater. Chem. A 3 (2015) 24049-24054

(b) M.D. Patel, E. cha, N. Choudhary, C. Kang, W. Lee, J. Hwang, W. Choi, Vertically oriented MoS₂ nanoflakes coated on 3D carbon nanotubes for next generation Li-ion batteries, Nanotechnology 27 (2016) 495401-495410