Titanium-Containing Metal–Organic Framework\nModified Separator for Advanced Lithium–Sulfur Batteries

Abstract

The shuttling of\npolysulfide intermediates (Li₂S<i>_n</i>, 2 < <i>n</i> ≤ 8) and\nthe dendrite growth on the Li-metal surface have blocked the practical\napplications of lithium–sulfur (Li–S) batteries. Functionalizing\nthe separator provides a straightforward approach to address these\nissues. Herein, we demonstrate a multifunctional MIL-125­(Ti)-modified\npolypropylene/polyethylene separator for advanced Li–S batteries.\nThe MIL-125­(Ti), a Ti-containing metal–organic framework (MOF),\nfeatures an open-skeleton construction, a high intrinsic microporosity\nand a Lewis acid characteristic. Compared with pristine separator,\nthat with MIL-125­(Ti) coating shows better electrolyte wettability\nand less resistance. The unique coating layer acts as an effective\nphysical and chemical barrier region to capture polysulfide species\nwithout affecting the smooth transport of Li⁺. Meanwhile,\nthe highly ordered micropores with a diameter of ∼1.5 nm in\nthe MOFs guide in a homogeneous Li⁺ plating and thereby\ninhibit lithium dendrites. Consequently, the MOF-modified separator\nenables a significantly improved cycling stability and rate capability\nof the Li–S battery. The capacity retention of over 60% at\n0.2 C (1 C = 1675 mA g^–1) upon 200 cycles and a\nspecific capacity of 612 mAh g^–1 at 2 C is realized.\nThe facile approach offers an effective pathway toward high-performance\nLi–S batteries.