Capacity Fading Mechanisms on Cycling a High-Capacity Secondary Sulfur Cathode

Abstract

The cycle life and capacity fading mechanisms of secondary sulfur electrodes prepared by two different electrode fabrication methods were studied in an effort to improve the energy density of the cathode. Cycle life improved substantially when the uniformity of carbon distribution around the sulfur particles improved and electrode density increased, improving the overall structural integrity of the carbon matrix. Capacity fading in a high-energy-density cathode is mainly due to structural failure by physical crack propagations of the electrode structure and subsequent formation of the electrochemically irreversible Li2S layer at cracked surfaces of carbon particles or masses. The capacity fading due to these mechanisms appears to be reduced substantially and significantly by improved structural integrity with uniform pore structure of the carbon matrix. A Li/S cell containing a cathode fabricated by the improved technique cycled over 400 cycles without any severe structural damage of the electrode structure.