Recent progress of functional separators with catalytic effects for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage systems owing to their high specific capacity, high energy density, and environmental benignity. However, Li-S batteries still suffer from severe polysulfide shuttle effect and sluggish reaction kinetics, which are the intrinsic bottlenecks for their practical applications. Multifarious strategies have been adopted to overcome these bottlenecks and achieve high sulfur utilization and capacity retention for Li-S batteries. Among them, functionalizing separators with catalytic materials can not only effectively inhibit polysulfides shuttle effect but also greatly accelerate sulfur redox reaction kinetics, which could be of great significance for the realization of Li-S batteries with high energy density and long cycle life. Here, we have comprehensively reviewed the recent progress of functional separators for Li-S batteries using various catalytic materials, including metals, metal compounds, metal-organic frameworks, covalent-organic frameworks, heterostructures, and metal-free materials. The preparations, characterizations, advantages, and limitations of these catalytic materials are summarized, aiming to shed fresh light on fundamental understanding of catalytic effects for the improved electrochemical performance. Furthermore, engineering of functional separators and prospects of future design for high-performance Li-S batteries are discussed.