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

MXenes are attracting much attention as electrode materials due to their excellent energy storage properties and good electrical conductivity. Here a carbonized derivative of Ti₃C₂ (one representative MXene material), a Ti₃C₄ 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 Ti₃C₄. The Ti₃C₄ monolayer is proved to be a structurally stable material showing the nature of the metal with C₂ dimers rather than the individual C atom. Moreover, the Ti₃C₄ monolayer exhibits a low diffusion barrier and high storage capacity (up to Ti₃C₄Na₄ 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 Ti₃C₄ monolayer a promising anode material for NIBs. More importantly, similar to MXene Ti₃C₂, new M₃C₄ monolayers with C₂ dimers can be formed by replacing M with other transition metal elements, and the properties of these monolayers are worthy of further study.