Metal-Organic Framework-Based Separators for Enhancing Li-S Battery Stability: Mechanism of Mitigating Polysulfide Diffusion

The shuttling effect of polysulfides severely hinders the cycle performance and commercialization of Li-S batteries, and significant efforts have been devoted to searching for feasible solutions to mitigate the effect in the past two decades. Recently, metal-organic frameworks (MOFs) with rich porosity, nanometer cavity sizes, and high surface areas have been claimed to be effective in suppressing polysulfide migration. However, the formation of large-scale and grain boundary-free MOFs is still very challenging, where a large number of grain boundaries of MOF particles may also allow the diffusion of polysulfides. Hence, it is still controversial whether the pores in MOFs or the grain boundaries play the critical role. In this study, we perform a comparative study for several commonly used MOFs, and our experimental results and analysis prove that a layer of MOFs on a separator did enhance the capacity stability. Our results suggest that the chemical stability and the aggregation (packing) morphology of MOF particles play more important roles than the internal cavity size in MOFs.