(298c) Cathode/Electrolyte Interface in Lithium-Sulfur Batteries Under Lean Electrolyte Condition

A low electrolyte/sulfur (E/S) ratio is essential to achieving high specific energy for lithium-sulfur (Li-S) batteries. Comparing to flooded Li-S cells, lean electrolyte condition results in significantly different mass transfer and charge transfer dynamics that closely related to the cathode/electrolyte interfacial properties. We probe the interfacial processes on the sulfur cathode under the lean electrolyte condition using operando electrochemical impedance spectroscopy (EIS) and a galvanostatic intermittent titration technique (GITT). The operando EIS reveals a significant and rapid increase in the charge-transfer resistance during the transition from high-order polysulfides to low-order ones at a low E/S ratio, which is induced by a kinetic bottleneck at the interphase due to Li-ion mass transfer limitation. The GITT results confirm the kinetic bottleneck by revealing a large discharge overpotential during the transition phase. We demonstrate that improving the adsorption of dissolved high-order polysulfides, a key step in the interfacial processes, can alleviate the kinetic limitation, thus enhancing the achievable capacity under the lean electrolyte condition. We further study the effects of ion solvation properties at the interface on the dissolution and reduction of high-order polysulfides.