Sulfur functions as the activity centers for high-capacity lithium ion batteries in S- and O-bifunctionalized MXenes: A density functional theory (DFT) study

MXenes materials, a new family of two-dimensional carbides or nitrides, are promising electrode materials with high capacity and high charging rate. Its electrochemical performance depends strongly on the surface functions. A series of bifunctionalized Ti3C2 MXenes with different coverages of sulfur and oxygen functions were designed in this study, and the electrochemical properties and lithium (Li) storage performance of these bifunctionalized MXenes in different solvents were investigated based on the density functional theory. Ti3C2O4/3S2/3 possessed the best performance with relatively low barrier and high capacity. Single sulfur function surrounded by oxygen functions was activated as an adsorption center under the combined influence by the Li adsorption layer and the MXenes surface. Simulations in this study revealed the mechanism of sulfur substitution to Li storage, as well as provided a solid theoretical support to the modification of MXene materials.