A functional carbon layer-coated separator for high performance lithium sulfur batteries

A composite separator consisting of a functional layer of conductive carbon on the cathode-side of a Celgard separator has been investigated to improve the electrochemical performance of lithium sulfur batteries. The cell with functional carbon layer-coated separator can reach a high initial capacity of 1070 mAh g− 1 at the rate of 0.5 C, and maintain a high capacity retention ratio with the capacity of 778 mAh g− 1 after 100th charge/discharge cycle. Besides, the coulombic efficiency of the cell with functional carbon layer-coated separator rises from 80% to nearly 90% without the addition of LiNO3 additive, which indicates the reduction of shuttle effect. The improved cell performance is attributed to the functional carbon-coating layer, which serves as an upper current collector to facilitate electron transport for high active-material utilization and a conductive network for trapping and depositing dissolved sulfur-containing active materials, as confirmed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).