Addressing Passivation of a Sulfur Electrode in Li-S Pouch Cells for Dramatically Improving Their Cyclic Stability.

The effective passivation of a sulfur electrode in Li-S pouch cells is addressed by increasing the discharging cutoff voltage from 1.6 to 2.0 V. This simple method can effectively suppress the generation of solid and insulated Li2S deposition while reserves the majority of capacity and improves the cyclic stability of Li-S pouch cells. Upon increasing the discharging cutoff voltage from 1.6 to 2.0 V, the Li-S pouch cell loses only 8% of the initial discharge capacity and remarkably promotes the capacity retention rate from 62.4 to 91.6% within 40 cycles at 0.05C. The analysis of electrochemistry and physics of a sulfur cathode demonstrates that the less Li2S deposition under the discharging cutoff voltage of 2.0 V can ensure fast reaction kinetics in Li-S pouch cells with high areal sulfur loadings and lean electrolyte. The mechanism of the passivation of a sulfur electrode is studied and discussed in detail. This brand new methodology may provide an effective approach to enhance the cyclic stability of a Li-S battery.