Theoretical prediction of MXene-like structured Ti3C4 as a high capacity electrode material for Na ion batteries

Abstract

MXenes are attracting much attention as electrode materials due to their excellent energy storage properties and good electrical conductivity. Here a carbonized derivative of Ti<inf>3</inf>C<inf>2</inf> (one representative MXene material), a Ti<inf>3</inf>C<inf>4</inf> monolayer, is designed. Density functional theory (DFT) calculations were performed to investigate the geometric and electronic properties, dynamic stability, and Li/Na storage capability of Ti<inf>3</inf>C<inf>4</inf>. The Ti<inf>3</inf>C<inf>4</inf> monolayer is proved to be a structurally stable material showing the nature of the metal with C<inf>2</inf> dimers rather than the individual C atom. Moreover, the Ti<inf>3</inf>C<inf>4</inf> monolayer exhibits a low diffusion barrier and high storage capacity (up to Ti<inf>3</inf>C<inf>4</inf>Na<inf>4</inf> stoichiometry) in Na ion batteries (NIBs) compared with Li ion batteries (LIBs). Its superior properties, such as good electronic conductivity, fast Na diffusion, low open circuit voltage (OCV), and high theoretical Na storage capacity, make the Ti<inf>3</inf>C<inf>4</inf> monolayer a promising anode material for NIBs. More importantly, similar to MXene Ti<inf>3</inf>C<inf>2</inf>, new M<inf>3</inf>C<inf>4</inf> monolayers with C<inf>2</inf> dimers can be formed by replacing M with other transition metal elements, and the properties of these monolayers are worthy of further study.