Promoted rate and cycling capability of Li-S batteries enabled by targeted selection of co-solvent for the electrolyte

Lithium sulfur (Li–S) batteries are considered as promising candidates for high-energy-density battery systems owing to the high theoretical capacity of sulfur (1675 mAh g−1) and low cost of raw materials. However, their practical application is hampered by low rate capability and rapid degradation of capacity, arising from the passivation of the cathode by lithium sulfides (Li2S2/Li2S) deposited during discharge and low interfacial stability of the Li anode. Herein, we report on a comprehensive strategy to select co-solvent to the electrolyte to regulate the deposition of lithium sulfides during charge-discharge process. We show that addition of a co-solvent with high solubility, and strong interaction with Li2S to a conventional electrolyte effectively mitigates the formation of a passivating layer on the sulfur cathode and dramatically improves the interfacial stability of the Li anode. We demonstrate that Sulfolane (SL) has these properties and that a Li–S cell with an electrolyte containing 6 vol% SL exhibits outstanding cyclic performance (0.083% decay per cycle) and rate capability (capacity density of 765 mAh g−1 at rate of 1.0C). Thus, we provide a facile strategy for the selection of co-solvent for improved performance of Li–S batteries, realizing their practical application for high-energy-density battery systems.