Ternary transition metal chalcogenides Ti2PX2 (X = S, Se, Te) anodes for high performance metal-ion batteries: A DFT study

Two-dimensional (2D) materials display special interest as for metal-ion batteries (MIBs) due to they have high specific surface area and unique electrochemical activity. Here, interactions between ternary transition metal chalcogenides Ti2PX2 (X = S, Se, Te) and metal-ion (Li, Na, K and Ca) are theoretically studied via density functional theory (DFT) calculations. Their metal-ion storage capabilities are systematically explored and compared with available experimental and theoretical information. Ti2PX2Li2 and Ti2PX2K2 exhibit the same storage capacity (281 mAhg−1), however K shows lower diffusion barrier (~0.07 eV) than Li (~0.17–0.21 eV). Although Ca shows significant large capacity (842–1685 mAhg−1), its diffusion barrier is higher than other ions. The small change in lattice parameter (Ti2PX2Na6: <1.2%), high capacity (842 mAhg−1 up to Ti2PX2Na6), low open circuit voltage (0.4–0.6 V) and low diffusion barrier energy (~0.1 eV) are found in Ti2PX2 for sodium-ion adsorption. These properties are superior as compared to other available 2D materials, such as graphene, MXenes (Ti3C2), MoS2 and so on. Our results indicate that Ti2PX2 monolayers may be promising for MIBs anode materials, especially for sodium-ion batteries (SIBs) applications.