Investigation of the Li–S Battery Mechanism by Real-Time Monitoring of the Changes of Sulfur and Polysulfide Species during the Discharge and Charge

The mechanism of the sulfur cathode in Li–S batteries has been proposed. It was revealed by the real-time quantitative determination of polysulfide species and elemental sulfur by means of high-performance liquid chromatography in the course of the discharge and recharge of a Li–S battery. A three-step reduction mechanism including two chemical equilibrium reactions was proposed for the sulfur cathode discharge. The typical two-plateau discharge curve for the sulfur cathode can be explained. A two-step oxidation mechanism for Li 2 S and Li 2 S 2 with a single chemical equilibrium among soluble polysulfide ions was proposed. The chemical equilibrium among S 5 2–, S 6 2–, S 7 2–, and S 8 2– throughout the entire oxidation process resulted for a single flat recharge curve in Li–S batteries.