Controlled synthesis of transition metal disulfides (MoS2 and WS2) on carbon fibers: Effects of phase and morphology toward lithium–sulfur battery performance. (September 2019) - Eng, Alex Yong Sheng
Graphical abstract: Abstract: Group 6 transition metal disulfides (TMDs) are highly anisotropic 2D layered nanomaterials, which can adopt diverse phases and morphologies. While a large variety of "top-down" ( e.g. chemical intercalation/exfoliation) and "bottom-up" approaches ( e.g. colloidal synthesis, chemical vapour deposition) are available to produce different TMDs, it is difficult for a single procedure to access their various phases and morphologies from a common precursor. Herein, we present a unified synthetic scheme based on a solvothermal method, which can be achieved despite using just one common tetrathio-metallate precursor. TMD composition (Mo vs . W), phase (semiconducting vs . metallic), and morphology (edge vs . basal plane orientations) may thus be controlled and grown on supporting carbon fibers. Employing this controllable approach for the first time, we systematically study TMD structure–property relationships toward lithium sulfur battery (LSB) performance, based on their ability to act as polysulfide anchors in LSB cathodes. Using voltammetry, impedance spectroscopy, and galvanostatic cycling, we observed that the TMD phase plays the most important role influencing cell performance compared to morphology, for both MoS2 and WS2 . At high C-rates, 1T-phase edge-oriented polytypes outperformed others due to the combination of its metallic character and preferential edge adsorption. For long-term cycling however, 1T-phase basal-oriented polytypes had the highest capacity retention, attributed to its lower charge transfer resistances. An increased areal capacity of ∼4 mAh cm −2 was also demonstrated toward future application of LSBs. While other challenges of LSBs remain to be addressed, insights gained from our morphology and phase engineering study contribute toward better design of sulfur-host cathodes.