The understanding of the role of lithium sulfide clusters in lithium-sulfur battery
Lithium sulfide (Li2S) as an electrode material not only has high capacity but also overcomes many problems caused by the pure sulfur electrode. In particular, the battery performance of nanoscale, i.e. (Li2S)n clusters, is much better than that of bulk sized Li2S. However, the structures, stability, and properties of (Li2S)n clusters have still been unexplored, which is very important to the performance improvement. Here, the most stable structures of (Li2S)n (n = 1 - 10) were reliably determined by using the advanced swarm-intelligence structure prediction method. (Li2S)n (n ≥ 4) clusters exhibit intriguing cage-like structures, which are in favorable for eliminating the dangling bonds and enhancing the structural stability. Compared to Li2S monomer, each sulfur atom in clusters is coordinated with more lithium atoms, lengthening Li-S bond length and decreasing Li-S bond activation energy. Notably, adsorption energy gradually increases on the considered anchoring materials (AMs) as the cluster size increases. Moreover, N-doped graphene is a good AM in comparison with graphene or B-doped graphene. The predicted characteristic peaks of the infrared and electronic absorption spectra provide useful information for in-situ experimental investigation. Our work represents a significant step forward towards understanding (Li2S)n clusters, and improving the performance of Li-S battery.