Enhanced Sulfur Transformation by Multifunctional FeS/FeS/S Composites for High-Volumetric Capacity Cathodes in Lithium-Sulfur Batteries.

Lithium-sulfur batteries are currently being explored as promising advanced energy storage systems due to the high theoretical specific capacity of sulfur. However, achieving a scalable synthesis for the sulfur electrode material whilst maintaining a high volumetric energy density remains a serious challenge. Here, a continuous ball-milling route is devised for synthesizing multifunctional FeS/FeS/S composites for use as high tap density electrodes. These composites demonstrate a maximum reversible capacity of 1044.7 mAh g and a peak volumetric capacity of 2131.1 Ah L after 30 cycles. The binding direction is also considered here for the first time between dissolved lithium polysulfides (LiPSs) and host materials (FeS and FeS in this work) as determined by density functional theory calculations. It is concluded that if only one lithium atom of the polysulfide bonds with the sulfur atoms of FeS or FeS, then any chemical interaction between these species is weak or negligible. In addition, FeS is shown to have a strong catalytic effect on the reduction reactions of LiPSs. This work demonstrates the limitations of a strategy based on chemical interactions to improve cycling stability and offers new insights into the development of high tap density and high-performance sulfur-based electrodes.