Interaction of CuS and sulfur in Li-S battery system

The Lithium-Sulfur (Li-S) battery has been a subject of intensive research in recent years due to its potential to provide much higher energy density and lower cost than the current state of the art lithium-ion battery technology. In this work, we have investigated Cupric Sulfide (CuS) as a capacity-contributing conductive additive to the sulfur electrode in a Li-S battery. Galvanostatic charge/discharge cycling has been used to compare the performance of both sulfur electrodes and S:CuS hybrid electrodes with various ratios. We found that the conductive CuS additive enhanced the utilization of the sulfur cathode under a 1C rate discharge. However, under a C/10 discharge rate, S:CuS hybrid electrodes exhibited lower sulfur utilization in the first discharge and faster capacity decay in later cycles than a pure sulfur electrode due to the dissolution of CuS. The CuS dissolution is found to be the result of strong interaction between the soluble low order polysulfide Li₂S₃ and CuS. We identified the presence of conductive copper-containing sulfides at the cycled lithium anode surface, which may degrade the effectiveness of the passivation function of the solid-electrolyte-interphase (SEI) layer, accounting for the poor cycling performance of the S:CuS hybrid cells at low rate.