Lithium sulfonate-rich MOF modified separator enables high performance lithium–sulfur batteries

Lithium–sulfur (Li–S) battery is regarded as a desirable energy storage device due to its ultrahigh energy density, but the shuttle effect and lithium dendrite growth largely impede its widespread application. Herein, a lithium sulfonate-rich UiO-66-type MOF (UiO-66(SO3Li)4) was synthesized from postsynthetic oxidation of thiol-rich UiO-66 framework (UiO-66(SH)4) followed by lithiation and adopted as a separator modifier to address the aforementioned issues. After grafting dense –SO3Li groups in the ordered pores, the resultant UiO-66(SO3Li)4 features stronger electronegativity, larger lithium-ion conductivity, and higher transference number than primitive UiO-66 and MOF with each linker bearing two –SO3Li (UiO-66(SO3Li)2). Moreover, the UiO-66(SO3Li)4 modified separator can inhibit the polysulfide shuttling by strong electrostatic repulsion and provide abundant pathways for rapid lithium ion transport as well as protect lithium anode simultaneously. Based on these merits, the Li–S coin cells assembled with resultant UiO-66(SO3Li)4 modified separators deliver a prominent discharge capacity of 1493.3 mAh g–1 at 0.1 C, enhanced rate capability with a capacity of 730.1 mAh g–1 at 2 C and exceptional cyclability with an average attenuation rate as low as 0.053% during 1000 cycles at 1 C. With a higher sulfur loading of 4.83 mg cm–2, the cell is still able to achieve a capacity of 838.6 mAh g–1. Overall, this work offers new opportunities for the design of functionalized MOFs and multifunctional separators for advanced Li–S batteries.