Theoretical prediction and characterization of novel two-dimensional ternary tetradymite compounds La2X2Y (X = I, Br, Cl; Y = Ge, Te) as anode materials for metal-ion batteries

Abstract

Tetradymite compounds, such as Bi₂Te₃, crystallizing in rhombohedral structures have triggered tremendous research interest from the scientific community because of their intriguing properties. Herein, using the state-of-the-art first-principles calculations, we identify that La₂X₂Y (X = I, Br, Cl; Y = Ge, Te) nanosheets exhibit a ternary tetradymite-type structure with extraordinary electrical and electrochemical properties. It is first demonstrated that the layered La₂X₂Y compounds exhibit weak interlayer coupling with cleavage energies in the range of ∼0.28–0.38 J m⁻², allowing the ready separation of monolayers that can be synthesized by mechanical exfoliation from their bulk counterparts. Next, we predict that La₂X₂Ge nanosheets exhibit a semiconducting nature, and upon physical realistic strain, a Dirac cone can be realized. These findings can be exploited in the transport properties. Furthermore, we comprehensively investigated the electrochemical properties of the predicted systems to evaluate their potential use in metal-ion (Li/Na) batteries. Our detailed analyses reveal that the Li (Na) adatoms are sufficiently mobile on the surface of the studied systems. For instance, the binding energy for the Li (Na) adatom on La₂I₂Ge is −2.24(−1.79) eV with a diffusion barrier of as small as ∼0.31(0.20) eV. Subsequently, the maximum theoretical specific capacity for Li (Na) reaches as high as 887(1064) mA h g⁻¹, which can be attributed to a much higher storage capacity compared to previously identified 2D anode materials. These findings substantiate that the predicted nanosheets could be synthesized to explore their potential applications in future metal-ion batteries.