Predicting the redox potentials of lithium polysulfides from first principles

Lithium-sulfur batteries are an attractive electrochemical option for electrochemical energy storage due to their high theoretical energy density, low toxicity, and moderate cost. Despite these interesting characteristics, lithium-sulfur batteries are limited by the loss of active cathode material (the shuttling effect), which causes self-discharge and reduces their Coulombic efficiency. In this work, we study polysulfide-electrolyte interactions from first principles to determine the charge-discharge response of lithium-sulfur batteries. Using semilocal density-functional theory with van der Waals correction and ab-initio molecular dynamics with explicit-implicit solvation models, the intrinsic charge-voltage response of polysulfide systems is calculated and compared to experimental data. This first-principles study reveals that the critical influence of solvation on the charge-voltage response and provides guiding principles for tuning the redox properties of solvated lithium polysulfides.