Rationally Engineering Interfaces at Cathodes and Anodes in Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries have received increasing attention due to the high theoretical capacity and low cost of the naturally abundant sulfur cathode.However, its practical application suffers formidable challenges due to instable solid electrolyte interphases (SEIs) on Li metal anode, shuttle caused by the dissolution of intermediate polysulfides into the electrolyte and sluggish kinetics of the sulfur redox reaction, etc. In order to address the above issues, in our presentation, we will propose the novel approaches to rationally engineer the interfaces at both cathode and anode sides to improve Li-S performances. On the one hand, a modified Pechini method is developed to synthesize nanoporous carbon host decorated with Ni3S2@Ni particles. Such cathode delivers enhanced specific capacities with extended cycling life in lean electrolytes, due to the dual functions of Ni3S2 shell, which can both facilitate reaction kinetics and promote electrolyte wetting. On the other hand, we demonstrated a bi-layer structure, constructed of an interconnected, tortuous, porous LiF-rich layer in contact with lithium and a dense in-situ formed inorganic-rich layer on top of the porous structure, showing enhanced anode stability. The porous layer increases the number of Li/LiF interfaces, which reduces local volume fluctuations and improves Li+ diffusion along these interfaces. Additionally, the tortuous porous structure guides uniform Li+ flux distribution and mechanically suppresses dendrite propagation. The dense upper layer of the SEI accomplishes a closed-host design, preventing continuous consumption of active materials. The duality of a dense top layer with porous bottom layer led to extended cycle life and improved rate performance, evidenced with symmetric cell testing, as well as full cell testing paired with sulfur cathodes.