2D Molybdenum Disulfide Nanosheets As Functional Electroactive Materials and Additives for Lithium and Lithium Sulfur Based Batteries

摘要

The 2D structured dichalcogenide molybdenum (IV) sulfide (MoS_2) has generated significant interest for Li ion batteries due to its high theoretical capacity, good rate capability, and minimal volume changes during cycling. To enable full realization of MoS_2 as an electroactive material, an important and continuing challenge is to understand the many polymorphs of MoS_2 that can be (de)stabilized by electrochemical lithiation and nanosizing. Characteriation of bulk MoS_2 and nanosheet-type MoS_2 as solids, both structurally (X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS)) and compositionally (X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES)) will be described to rationalize observed differences in capacity and efficiency in lithium based cells. X-ray analysis compatible lithium cells (in situ XRD and ex situ XAS) measurements of the specific phase changes to rationalize the significant difference in electrochemistry between the nanosheet and bulk materials upon (de)lithiation will also be discussed. The application of 2D MoS_2 nanosheets for lithium sulfur batteries (Li-S) will also be described. Significantly improved Li-S electrochemistry in an environmentally friendly electrolyte solvent is demonstrated through implementation of MoS_2 nanosheet materials as cathode additives, leading to improved capacity retention upon extended cycling in lithium sulfur cells. The findings will be discussed in light of the unique attributes of the MoS_2 atomic level (2D) and mesoscale (3D) heterostructure.