Catalytic Metal-Organic Framework-Functionalized Inverse-Opal Architectured Polymeric Separator for High-Performance Li-S Batteries

Separators are crucial in lithium-sulfur batteries (LiSBs) to ensure optimal ion transport and prevent internal short circuits. High-performance separators with excellent thermal stability, electrolyte wettability, porosity, and Li⁺ selectivity are essential for the safety and enhancing the energy density of LiSBs. This is particularly important for mitigating polysulfide (LiPS) shuttling, which degrades both the capacity and cycling stability of LiSBs. In this work, a novel separator design for high-performance LiSBs is introduced that combines a poly(ether ether ketone) (PEEK)-based inverse opal (PIO) architecture with an in situ grown cobalt-imidazole metal-organic framework of ZIF-67 on the polymeric surface. The PIO provides improved Li⁺ conductivity due to the unique structural characteristics of inverse opal and the excellent thermal/mechanical properties of the PEEK. Additionally, ZIF-67 imparts an enhanced electrochemical system through its selective permittivity to LiPS. The unique chemical configuration of ZIF-67 significantly suppresses the LiPS shuttling; its negative imidazole sites accelerate Li⁺ mobility while the Lewis acidic Co²⁺ centers strongly interact with S_x²⁻base. Consequently, the LiSBs with the developed separator exhibits remarkable inhibition of LiPS shuttling due to synergistic effects from both Lewis acid-base interactions and the physical characteristics of the separator. It also demonstrates effective regulation of Li-dendrite growth, leading to enhanced cycling stability of LiSBs. With its greatly enhanced cycling performance, rate capability, and electrochemical stability, the ZIF-PIO separator presented in this work provides a promising solution for practical LiSBs applications.