Elaboration of Aggregated Polysulfide Phases: From Molecules to Large Clusters and Solid Phases.

With the increasing strategies aimed at repressing shuttle problems in the lithium-sulfur battery, dissolved contents of polysulfides are significantly reduced. Except for solid-state Li2S2 and Li2S, aggregated phases of polysulfides remain unexplored, especially in well confined cathode material systems. Here, we report a series of nanosize polysulfide clusters and solid phases from an atomic perspective. The calculated phase diagram and formation energy evolution process demonstrate their stabilities and cohesive tendency. It is interesting to find that Li2S6 can stay in the solid state and contains short S3 chains, further leading to the unique stability and dense structure. Simulated electronic properties indicate reduced band gaps when polysulfides are aggregated, especially for solid phase Li2S6 with a band gap as low as 0.47 eV. Their dissolution behavior and conversion process are also investigated, which provides a more realistic model and gives further suggestions on the future design of the lithium-sulfur battery.