Crown Ether COF-Phosphomolybdic Acid Composite Separator for High-Performance Lithium–Sulfur Batteries

Abstract In this work, a composite separator was fabricated by integrating a crown ether-based covalent organic framework (CE-COF) with phosphomolybdic acid (PMo12) for lithium–sulfur batteries (LSBs). The CE-TG-PMo12 modified separator endowed LSBs with a high initial specific capacity of 800 mAh g–1 at 1 C and maintained a reversible capacity of 592 mAh g–1 after 500 cycles, with an average capacity decay rate as low as 0.052% per cycle. The superior performance is attributed to the synergistic effect between the crown ether-based COF (CE-TG) and PMo12 components. The CE-TG framework provides well-ordered ion transport channels that facilitate rapid Li+ migration and acts as a physical barrier that sieves lithium polysulfides (LiPSs), thereby mitigating their dissolution and diffusion. On the other hand, the PMo12 component exhibits strong chemisorption ability toward LiPSs and high electrocatalytic activity for accelerating the conversion of LiPSs to insoluble Li2S2/Li2S. Consequently, the CE-TG-PMo12 modified separator enhances the Coulombic efficiency and cycling stability of LSBs. This work provides a promising strategy for constructing high-performance LSB separators through the synergistic coupling of functional COFs and polyoxometalates.