First-principles calculations on LaX3 (X: Sb, Sn) as electrode material for lithium-ion batteries

Using first-principle calculations, we investigate the rare-earth intermetallic compound LaX₃ (X = Sb and Sn) as a cathode material for rechargeable lithium-ion batteries (LIBs). The calculations have been performed to look into the stability of the structure and the electronic properties of host LaX₃ as well as its lithiated phases, Li_xLa_1−xX₃ (0 < x ≤ 1). In this study, we have observed a structural phase transformation of these intermetallic compounds from a cubic to a tetragonal structure upon lithiation to host structure. The ground state energy is calculated using the WIEN2k package to determine the structure stability and volume change due to lithium addition, which is further used to calculate the formation energy, open circuit voltage (OCV), and lithium-ion storage capacity. The equilibrium structural parameters for all the phases are determined by achieving a total energy convergence of 10⁻⁴ Ry. The estimated band structure along high-symmetry lines in the first Brillouin zone and the total as well as partial density of states demonstrate unequivocally that the addition of lithium does not change the metallic nature of these electrode materials. We have also calculated the theoretical lithium-ion storage capacity and OCV for all the compounds. Despite a higher value for OCV larger than 5 V, many of the investigated materials could not be found suitable from a synthesis point of view due to positive formation energies. The formation energy calculation shows that LaSb₃, with a 50% concentration of Li, is the most stable compound out of those investigated here. The calculated OCV for Li_0.5La_0.5Sb₃ is 4.27 V. This is substantially higher than the value obtained up to this point for LIBs, which ranges from 3.20 to 3.65 V/cell. These improved results related to the most stable alloy (Li_0.5La_0.5Sb₃) investigated in this work indicate that it is necessary to check the experimental feasibility of its synthesis and actual device performance.