Unveiling Mechanistic Material Manipulation in Functional Separators for Metal Sulfur Batteries: Progress and Prospects

Metal-sulfur batteries (MSBs) are emerging energy storage candidates due to their high energy density, cost-effective nature, and environmental compatibility. However, polysulfide shuttling, slow kinetics, and dendritic issues severely plague their nexus stage from academic to commercial applications. Inspired by the low cost and higher storage capacity of metal sulfur batteries, numerous strategies, from electrode design to separator modification, are developed to eliminate these challenges on practical grounds. Among them, functionalizing separators hold great promise to stabilize metal sulfur battery operation mechanistically in terms of safety, stability, and electrochemical benchmarks, as existing polyolefin separator designs cannot fully satisfy the complex chemistry of polysulfides. This review first discusses the critical challenges of metal sulfur batteries with associated mechanistic approaches to better describe the requirement for material manipulation in separator design. Furthermore, the role of modulated and functional materials is critically highlighted and screened to synergistically achieve an advanced and recent four-year plethora of metal sulfur battery separators. Finally, future directions in metal sulfur battery separators are outlined for academic and practical research. This review will offer a comprehensive reference and new paths for designing and modulating functional separators in advancing high-energy-density storage systems.