Structures and bonding properties of lithium polysulfide clusters LiS n -/0 ( n = 3-5) and Li 2 S 4 -/0 : size-selected anion photoelectron spectroscopy and theoretical calculations.

The structures and bonding properties of several lithium polysulfide clusters LiS n -/0 ( n = 3-5) and Li 2 S 4 -/0 were investigated by size-selected anion photoelectron spectroscopy coupled with quantum chemistry calculations. The vertical detachment energies of LiS 3 - , LiS 4 - , and LiS 5 - were estimated to be 2.17 ± 0.08, 3.30 ± 0.08 and 3.66 ± 0.08 eV, respectively, and that of Li 2 S 4 - was estimated to be 3.21 ± 0.08 eV. It is found that LiS 3 - and LiS 3 have planar quadrilateral structures, and LiS 4 - and LiS 4 have distorted five-membered ring structures. LiS 5 - has a distorted six-membered ring structure while neutral LiS 5 has a book-shaped structure. The lowest-lying structure of Li 2 S 4 - can be viewed as a S 2 unit connecting to the Li-Li edge of a Li 2 S 2 tetrahedron. The lowest-lying structure of neutral Li 2 S 4 can be viewed as a S 2 unit connecting to the S atoms of a Li 2 S 2 quadrilateral. The natural population analysis (NPA) and electron localization function (ELF) analyses show that the excess electron of LiS n - is mainly localized over the sulfur chains, especially on the S atoms interacting with Li, thus, the most stable structures of LiS n - can be regarded as a Li + cation interacting with a S n 2- dianion. The results may be useful for understanding the formation of lithium polysulfides in lithium sulfur batteries.