Quantum-mechanics-based molecular dynamics simulations of the structure and performance of sulfur-enriched Li3PS4 cathodes

Sulfur-enriched Li3PS4 is a promising cathode for lithium-sulfur batteries, but there is not yet clear structural information about this material. Here, we use quantum-mechanics-based molecular dynamics to predict the structures of the fully charged Li3PS4+5 and various stages of discharge to nearly discharged Li3+9PS4+5 at 298 K. We predict that the fully charged cathode has a distorted orthorhombic structure similar to Li3PS4, but with additional S4 and S8 chains each linked to an S atom of a PS4 anion. This leads to a density of 2.19 g/cm3 for this material. For the nearly discharged cathode, we find that the lithium atoms insert into all S−S bonds, with none of the aforementioned chains remaining, leading to a density of 1.71 g/cm3. We examined the discharge process as lithium ions from the electrolyte diffuse into the cathode and react with the S−S chains to form Li2S. The predicted discharge curve agrees well with the experiment.