Lithiation of organic polysulfides: insight into embedding site preference and lithium storage capability from DFT calculations

Abstract

The lithium storage capability of organic polysulfides (OPSs) is strongly influenced by their geometric and electronic structures. Herein, several cyclic OPSs (I–IV) and their lithiation properties have been investigated by density functional theory (DFT) calculations. It was found that the lithium storage capacity of OPSs depends on the number of sulfur atoms, and Li atoms are preferentially embedded into the S–S bond in the lithiation process. Notably, the lithiation behaviors differ between the embedding of odd and even numbers of Li atoms, and the lithiation accommodating an even number of Li atoms is generally more favorable thermodynamically. Since each embedded Li atom almost has one net electron transfer to the linked S atoms, the system embedded with an even number of lithium atoms has higher thermodynamic stability than that with odd lithium atoms, due to the pairing bonding of transferred electrons. The relatively high lithium-storage capability and the high stability of the newly-generated lithiated polysulfides (LiPSs) suggest that OPSs can be used as potential cathode materials for lithium–sulfur batteries.