Fe/Zr binary MOF-based separator for highly efficient polysulfide adsorption and conversion in Li-S batteries

Lithium-sulfur (Li-S) batteries are known as a next-generation energy storage technology due to their high theoretical energy density and low cost. However, the shuttling of soluble lithium polysulfides (LPS) between electrodes hinders the practical realization of Li-S batteries, resulting in short cycle life. To address this issue, this work discloses a highly efficient separator with Fe/Zr binary metal-organic framework (MOF) coated on a polypropylene (PP) separator. Fe³⁺ metal ions were integrated into the UiO-66(Zr)-NH₂ framework through a simple one-step hydrothermal method. The adsorption test confirmed the superior LPS adsorption capability of the UiO-66(Fe/Zr)-NH₂ than monometallic UiO-66(Zr)-NH₂, which provides not only uniform-sized nanochannels for effective LPS sorption and even Li⁺ ions transport but also Fe active sites for electrocatalytic conversion of the LPS. UiO-66(Fe/Zr)-NH₂-based Li symmetrical cells demonstrated a uniform stripping and plating of Li at exceptionally higher current densities (1–10 mA cm⁻²). CR2023 coin cell Li-S battery using a S-CNT/GO composite cathode and UiO-66(Fe/Zr)-NH₂/PP separator delivered an initial discharge capacity of 900 mAh/g at 0.3C and a long cycle life (820 cycles) with minimal capacity decay of merely 0.067 % per cycle. The significantly improved performance demonstrates the potential of binary MOF-based materials for metal-sulfur batteries.