Toward a Molecular Understanding of Energetics in Li–S Batteries Using Nonaqueous Electrolytes: A High-Level Quantum Chemical Study

The Li–S battery (secondary cell or redox flow) technology is a promising future alternative to the present lithium intercalation-based energy storage, and, therefore, a molecular level understanding of the chemical processes and properties such as stability of intermediates, reactivity of polysulfides, and reactivity toward the nonaqueous electrolytes in the Li–S batteries is of great interest. In this paper, quantum chemical methods (G4MP2, MP2, and B3LYP) were utilized to compute reduction potentials of lithium polysulfides and polysulfide molecular clusters, energetics of disproportionation and association reactions of likely intermediates, and their reactions with ether-based electrolytes. Based on the computed reaction energetics in solution, a probable mechanism during the discharge process for polysulfide anions and lithium polysulfides in solution is proposed and likely intermediates such as S42–, S32–, S22–, and S31– radical were identified. Additionally, the stability and reactivity of propylen...