Theoretical Exploration of Stable and Meta-Stable Li-Sn Compounds for Understanding the Reaction Mechanism of Sn Anode in Li-ion Batteries

It is already been shown that at high pressure several exotic and unusual stoichiometries can be obtained, that may even survive decompression from high-to-ambient pressure with improved mechanical properties. With a belief that hydrostatic pressure may also help in realizing Li-richer (x > 4.25) Li-Sn compounds, we performed extensive calculations using the evolutionary algorithm and density functional theory to explore all stable and possible low energy metastable Li-Sn compositions at a pressure ranging from 1 atm to 20 GPa. Besides the experimentally known Li-Sn compounds, our study reveals the existence of five unreported stoichiometries (Li₈Sn₃, Li₃Sn₁, Li₄Sn₁, Li₅Sn₁, and Li₇Sn₁). While Li₈Sn₃ has been identified as one of the most stable Li-Sn compounds in the considered pressure range with R-3m symmetry, the Li-rich compounds are predicted to be metastable at ambient pressure and found to get thermodynamically stable at high pressure. Here, the discovery of Li₅Sn₁ and Li₇Sn₁ opens up the possibility to integrate them as a prelithiated anode as compared to known Li_4.25Sn, as void-space engineering by using a Li_xSn phase as a pre-lithiated anode, with an optimal value for x, may help in improving mechanical integrity and reducing pulverization in Li-ion batteries.