Lithium polysulfide solvation and speciation in the aprotic lithium-sulfur batteries

Fingerprinting sulfur speciation in aprotic electrolytes is a key to understand fundamental chemistry and design well-performing lithium–sulfur (Li–S) batteries. Lithium polysulfide (LiPS) dissolution and deposition in ether-based electrolytes during redox reactions have been probed and established by spectroscopy and microscopy. However, detailed LiPS structure and solvation properties influenced by conventional and newly developed electrolytes remain elusive, which exert fundamental challenges and practical difficulties in decoupling battery performance from electrolyte volume. This perspective aims to provide timely information to uncover underlying mechanisms that rein in sulfur speciation by considering the charge density of LiPSs and the coordination strength of solvents/salts. The discussion starts with unlocking the baseline electrolyte formulation to investigate its role in LiPS formation and compatibility. After that, the term coordination strength is used instead of donor number and dielectric constant to describe interactions between solvents and LiPSs and to reveal LiPS structure evolution. This work is expected to encourage the discovery of new electrolyte working mechanisms to develop energy-dense and power-intensive Li–S batteries.