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.