New insights into the limiting parameters of the Li/S rechargeable cell

The lithium/sulfur (Li/S) battery is a promising electrochemical system that has high theoretical capacity of 1675 mAh g−1. However, the system suffers from several drawbacks: poor active material conductivity, active material dissolution, and use of the highly reactive lithium metal electrode. This study was aimed at understanding the most important limiting parameters of a Li/S cell. Different sulfur material pre-treatments were experimented to increase the practical capacity, and various morphologies were obtained. But none of these treatments led to improvements in electrochemical performance. Electrolyte additives were also used to increase cell discharge capacity, but again without success. Finally, it was concluded that the cell capacity limitation may be linked to dissolution of sulfur material and to passivation of the positive electrode. As the final discharge products are insulating and poorly soluble, they precipitate and induce passivation of the positive electrode surface, leading to incomplete active material utilization. EIS measurements confirmed this passivation problem.

► Elemental sulfur positive electrode for lithium secondary batteries.
► Elemental sulfur pre-treatment and composite electrode preparation.
► No pre-treatments enable the electrochemical performances to be efficiently improved.
► Main limitations linked to positive electrode passivation and electrolyte composition.