Exfoliated transition metal dichalcogenide (TMD) nanosheets for supercapacitor and sodium ion battery applications
Jonathan Turley, Santanu Mukherjee, Elisabeth Mansfield, Jason D. Holm, Lamuel David, Gurpreet Singh
The growing concerns regarding the safety, flammability and hazards posed by Li-ion systems has led to the research of alternative rechargeable metal-ion electrochemical storage technologies. Among the most notable of these are the Na-ion supercapacitors and batteries, motivated in part because of the similar nature and electrochemistry of Li and Na ions. However, due to the large size of the Na ions, developing novel materials and appropriate electrode architecture is of absolute significance. One of the most promising materials to this regard are the transition metal dichalcogenides (TMDs), they provide diverse morphologies and architectures that can be readily tailored. This manuscript looks at using a family of Mo based two dimensional (2D) layered TMDs e.g. MoS2, MoSe2 and MoTe2 for battery and supercapacitor applications for sodium ion systems. A novel superacid based technique has been used for fabricating the exfoliated TMD flakes. Hummers method was used to prepare reduced graphene oxide (rGO) which were combined with the TMD electrodes to be used as composites. Structural characterization results have indicated the successful formation of 2D layered TMD materials. Supercapacitor applications in aqueous media have indicated the predominance of the sulfide (MoS2), both in terms of providing specific capacitance and cycling stability. For battery applications, all the composite TMDs exhibited significantly large charge capacities than just the pristine rGO electrode. In this case, MoS2 was the best performing electrode with an initial charging (desodiation) capacity of 338.52 mAh g-1 and a coulombic efficiency of ∼100 % after 10 cycles.