Pressure induced structural phase of lithium disulfide with a close to intermediate product character of lithium-sulfur battery

• Published in: Journal of alloys and compounds 2019-03, Vol.778, p.588-592
• Main Authors: Li, Xiumei, Li, Hengtao, Chen, Jiao, Cai, Xinyong, Wang, Hongyan, Lao, Zebin, Sun, Bai, Tao, Li, Chen, Yuanzheng
• Format: Article
• Language: English
• Subjects: Diffusion barriers; Diffusion coefficient; First principles; High pressure; Li[sbnd]S battery; Lithium disulfide; Lithium sulfur batteries; Mathematical analysis; Molecular structure; Structure predictions
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.11.176

Recently spotlighting on lithium disulfide (Li2S2) as an intermediate product of a promising high capacity lithium–sulfur (LiS) battery, a structure of P42/mnm had been proposed for understanding the existence of Li2S2 in LiS battery. Here using first-principles unbiased CALYPSO structure searching calculations, we uncovered a new energetically favored structural phase (P21/c) of Li2S2, being more stable than the P42/mnm structure at above 2.78 GPa. This predicted P21/c structure possess a similar quasi-molecular S2 and Li atoms in the interstice of S2 with P42/mnm structure, but having a denser polyhedral packing (LiS6) with Li atoms six-fold coordination in contract to the four-fold coordinated LiS4 polyhedron of P42/mnm. Further, a calculated discharge voltage of 2.34 V was obtained for 2Li+ + 2e− + Li2S2 →2Li2S and comparable to that of P42/mnm. Adopting CI-NEB method, we calculated the diffusion barrier and diffusion coefficient of Li ions with a high diffusion coefficient of 5.98 × 10−2/cm2 s−1. This character reflects that it can acts as an intermediate product like as P42/mnm in a LiS battery. This work has a value in exposing the pressure–induced phase of Li2S2 and enriching the views for understanding in LiS batteries. •A new pressure–induced phase (P21/c) of Li2S2 is proposed and compared with P42/mnm.•The P21/c structure possesses quasi-molecular S2 and forms Li six-fold coordination.•The discharge voltage was obtained for 2Li+ + 2e− + Li2S2 .→2Li2S in P21/c structure.•A high diffusion coefficient of Li ions was revealed in the P21/c structure.•The P21/c structure exhibits close to intermediate product character of LiS battery.