The Effects of Carbon Type and Cathode Loading on Lithium-Sulfur Battery Performance

Better electrical energy storage allows for the improved utilization of renewable energy and less dependence on fossil fuels.  Lithium-sulfur (Li-S) batteries are promising; however, many challenges accompany the development of Li-S batteries. The insulating effect of sulfur necessitates the use of conductive carbon additives which reduce energy density, and the formation of polysulfide intermediates during the conversion of sulfur to Li₂S causes undesirable side reactions which consume active material. The design of Li-S batteries must consider both of these factors in order to create a battery with higher discharge capacity, better cycle stability and longer cycle life. This study looks at the effects of different conductive carbon additives and cathode thicknesses on battery performance in order to develop a practical Li-S battery methodology. Two carbon microstructures, carbon black and mesoporous carbon, and active sulfur loadings from 0.28 to 4.4 mg/cm² were studied. While carbon type had no observable effect on coin cell performance, sulfur loading had significant impact on cell performance. Under sulfur loadings of 1.5 mg/cm², the delivered capacity linearly increased with loading. Over sulfur loadings of 1.8 mg/cm², lower capacities than were projected from the linear relationship were delivered at first, but after 30 cycles recovered and stabilized at approximately 400mAh/g. This activation process in high-loading cells could potentially be optimized for better-performing cells in future investigations.