Lewis acid-base interactions between polysulfides and metal organic framework in lithium sulfur batteries

Lithium-sulfur (Li-S) battery is one of the most promising energy storage systems because of its high specific capacity of 1675 mAh g(-1) based on sulfur. However, the rapid capacity degradation, mainly caused by polysulfide dissolution, remains a significant challenge prior to practical applications. This work demonstrates that a novel Ni-based metal organic framework (Ni-MOF), Ni6(BTB)4(BP)3 (BTB = benzene-1,3,5-tribenzoate and BP = 4,4'-bipyridyl), can remarkably immobilize polysulfides within the cathode structure through physical and chemical interactions at molecular level. The capacity retention achieves up to 89% after 100 cycles at 0.1 C. The excellent performance is attributed to the synergistic effects of the interwoven mesopores (∼2.8 nm) and micropores (∼1.4 nm) of Ni-MOF, which first provide an ideal matrix to confine polysulfides, and the strong interactions between Lewis acidic Ni(II) center and the polysulfide base, which significantly slow down the migration of soluble polysulfides out of the pores, leading to the excellent cycling performance of Ni-MOF/S composite.