Cathode loading effect on sulfur utilization in lithium-sulfur battery

Abstract

The lithium-sulfur (Li-S) battery is under intensive research in recent years due to its potential to provide higher energy density and lower cost than the current state-of-the-art lithium-ion battery technology. To meet cost target for transportation application, high-sulfur loading up to 8 mAh cm 2 is predicted by modeling. In this work, we have investigated the sulfur loading effect on the galvanostatic charge/discharge cycling performance of Li-S cells with theoretical sulfur loading ranging from 0.5 to 7.5 mAh cm 2 . We found that the low sulfur utilization of electrodes with sulfur loading of > 3.0 mAh cm 2 is due to their inability to deliver capacities at the voltage plateau of 2.1 V, which corresponds to the conversion of soluble Li 2 S 4 to insoluble Li 2 S 2 /Li 2 S. This electrochemical conversion process recovers to deliver the expected sulfur utilization after several activation cycles for electrodes with sulfur loading up to 4.5 mAh cm 2 . For electrodes with 7.0 mAh cm 2 loading, no sulfur utilization recovery was observed for 100 cycles. The root cause of this phenomenon is elucidated by SEM/EDS and EIS investigation. Carbon-interlayer cell design and low-rate discharge activation are demonstrated to be effective mitigation methods.