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

Abstract

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.

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