Influence of M/A substitution on material properties of intermetallic compounds MSn 2 (M = Fe, and Co; A = Li, and Na): a first-principles study

Iron and cobalt distannides MSn 2 (M = Fe, and Co) are regarded as a promising conversion-type anode material for lithium- and sodium-ion batteries, but their properties are not well understood. In this work, we report a first-principles study of alkali metal (A = Li, and Na) substitutional effect on the structural, mechanical, lattice vibrational, electronic and defect properties of these distannides. Special attention is paid to systematic comparison between FeSn 2 and CoSn 2 . Our calculations reveal that M/A substitution induces a lattice expansion and decrease of elastic constants, which is more pronounced with Na substitution than with Li, and moreover changes the elastic properties of FeSn 2 from ductile to brittle, but preserves the ductility of CoSn 2 . An imaginary phonon frequency mode appears only for FeSn 2 and FeNaSn 2 , and M/A substitution provokes a definite gap between high and low frequency regions. We perform a careful analysis of electronic density of states, band structures and Fermi surface, providing an insight into differences of electronic structures between FeSn 2 and CoSn 2 . With further calculation of defect formation energies and alkali ion diffusion barriers, we believe this work can be useful to design conversion-type anode materials for alkali-ion batteries.