Theoretical understanding for anchoring effect of MOFs for lithium-sulfur batteries

Abstract Metal organic framework materials (MOFs) ZIF-8, ZIF-67 and MOF-5 have been widely used to solve the shuttle effect of lithium-sulfur batteries based on the great anchoring effect. Elucidating the anchoring effect has important implications for the MOFs design. The first-principles calculation shows that the adsorption of polysulfides intermediates occurs through the Li-heteroatom (N/O) bonding with the capacity order of MOF-5> ZIF-8> ZIF-67. The electronegativity of Zn in ZIF-8 is lower than that of Co in ZIF-67, leading to a higher charge density of N atoms in the ligand, which results in greater adsorption. The electronegativity of O in the ligand of MOF-5 is higher than that of N in ZIF-8, which contributes to closer Li-O interaction. Besides, MOF-5 provides enough space for both Li atoms to bond with O atoms of the ligand. Accordingly, MOFs with low electronegativity metal center, high electronegativity ligand heteroatom, and sufficient ligand framework space would have great anchoring effect.