Low Concentration Electrolyte Enabling Anti-Clustering of Lithium Polysulfides and 3D-Growth of Li₂S for Low Temperature Li-S Conversion Chemistry

The development of low-temperature lithium-sulfur batteries (LSB) has been suppressed by rather poor sulfur utilization and cycle performance, caused by planar Li2S growth, hindered lithium polysulfides (LiPSs) transformation, and poor stability of the anode. Recently, low-concentration electrolytes (LCE) have been employed as promising solutions to solve the above issues. However, aggregation and deposition behavior of polysulfides have been rarely studied. In this work, by comparing the performance of 0.1 and 1 m LiFSI electrolytes, LCEs are proven beneficial for low-temperature LSBs via new fundamental insights. According to growth pattern analyses by both morphology observation and theoretical models, Li2S nucleation in LCEs switch into progressive mode with less initial nuclei, which favors the vertical growth of Li2S, resulting in a more complete lithium-sulfur conversion reaction under cold conditions. Through visual experiments, computational simulation, and progressive electrochemical impedance spectroscopy, the ability of LCEs to suppress LiPSs clustering is supported and this anti-clustering ability effectively enhances the Li-S conversion reaction kinetics. Moreover, in LCEs a protective SEI with LiF and Li2S/Li2S2 is likely to form on and stabilize the anode. As a whole, the boosting effect and the mechanism of LCEs enlighten future designs on low-temperature electrolytes for high-performance cryogenic LSBs.