Attacking Bridging Sulfur by a Soft Cation to Disrupt Lithium Polysulfide Clusters for Low-Temperature Lithium-Sulfur Batteries.

Low-temperature-induced rigid and cage-like lithium polysulfide clusters impede the kinetics of sulfur (S) conversion. Electronic analysis reveals a charge density contrast within these structures, in which terminal S with high charge density serves as a "hard base" to tightly bind with Li+, while the bridging S featuring low charge density acts as a "soft base". This soft base would be the ideal site for lithiation-incurred bond cleavage due to low bond energy. How to further loosen the bridging S-S bond and facilitate Li attack in these sites has not been studied. Guided by hard-soft-acid-base (HSAB) principles, this work proposes large-radius Cs+ as a "soft Lewis acid" (with respect to Li+) to selectively target soft bridging S sites, aiming at disrupting LiPS cluster symmetry and reducing the Mulliken bond order of bridging S-S, effectively lowering the rate-determining lithiation barrier. This work highlights large-cation-mediated structural disruption as a unique strategy to regulate specific S bond cleavage for expediting lithium-sulfur battery conversion kinetics at low temperature.