Insights on transport performance, thermodynamic properties, and mechanical properties of Ruddlesden-Popper antiperovskite LiBr(Li2OHBr)2 and LiBr(Li3OBr)2.

Due to high ion conductivity, low cost, and adjustable composition, antiperovskite has attracted much attention as a potentially useful material in solid-state batteries. Compared with simple antiperovskite, Ruddlesden-Popper (R-P) antiperovskite is an updated material, which is not only more stable but also reported to significantly enhance conductivity when added to simple antiperovskite. However, systematic theoretical research on R-P antiperovskite is scarce, hindering its further development. In this study, the recently reported easily synthesized R-P antiperovskite LiBr(Li2OHBr)2 is calculated for the first time. Comparative calculations were conducted on the transport performance, thermodynamic properties, and mechanical properties of H-rich LiBr(Li2OHBr)2 and H-free LiBr(Li3OBr)2. Our results indicate that due to the presence of protons, LiBr(Li2OHBr)2 is more prone to defects, and synthesizing more LiBr Schottky defects can improve its Li-ion conductivity. Young's modulus of the LiBr(Li2OHBr)2 is as low as 30.61 GPa, which is beneficial for its application as a sintering aid. However, the calculated Pugh's ratio (B/G) of 1.28 and 1.50, respectively, indicates that R-P antiperovskites LiBr(Li2OHBr)2 and LiBr(Li3OBr)2 exhibit mechanical brittleness, which is not conducive to its application as solid electrolytes. Through quasi-harmonic approximation, we found that the linear thermal expansion coefficient of LiBr(Li2OHBr)2 is 2.07 × 10-5 K-1, which is more advantageous in matching electrodes than LiBr(Li3OBr)2 and even simple antiperovskites. Overall, our research provides comprehensive insights into the practical application of R-P antiperovskite in solid-state batteries.