Speakers
Description
Transition metal carbides and carbonitrides, MXenes, represent a unique class of 2D materials, where metallic electronic conductivity and redox-active surface coexist in a single material. This allows MXenes to function as "all-in-one" platforms for energy storage electrodes: the surface groups inherited from synthesis provide active redox centers. At the same time, the inherent electronic conductivity ensures efficient current flow throughout the electrode. The variety of atoms that can form MXenes, the control over flake stacking, and the ability to intercalate guest species provide three distinct degrees of freedom to tune this material family for specific applications.
Here, we showcase how engineering of the interlayer environment can be used through intercalation of a vast range of species, from $Li^+$ to CTAB. Because these processes occur in aqueous media, the solvation shell (rather than the bare ion) dictates the intercalation process. Consequently, the entrapment of structural water molecules together with the intercalant defines the local environment and the resulting material properties. We employ Raman spectroscopy to probe these interlayer interactions between $Ti_3C_2$ MXene and confined species.
To demonstrate how engineering of interlayer space affects material properties, we used the example of Li-S batteries. This chemistry is an attractive application as it allows for the use of a Li-metal anode—theoretically the electrode with the highest specific capacity (3860 mAh/g). In this system, the inherent challenges of the sulfur cathode require a conductive and structural host—a great task for MXenes. By varying the interlayer spacing and the affinity of intercalants to sulfur, we obtained various sulfur loadings and sulfur allotropic modification. By applying this material for cathodes in Li-S batteries, we demonstrate the power of interlayer engineering in 2D materials.