Effective bipyridine and pyrazine‐based polysulfide dissolution resistant complex framework materials (CFM) systems for high capacity rechargeable Lithium – Sulfur battery

Lithium-sulfur (Li-S) batteries with high theoretical capacity (approximate to 1650 mAh g(-1)) and specific energy density (approximate to 2567 Wh g(-1)) have not achieved commercialization status due to low cycling stability arising from lithium polysulfide dissolution. Herein, sulfur infiltrated noncarbonized noncarbonate containing metal organic complex framework material (CFM) systems; sulfur-copper-bipyridine-CFM (S-Cu-bpy-CFM) and sulfur-copper-pyrazine-CFM (S-Cu-pyz-CFM) are developed as sulfur cathodes for the first time. The S-Cu-bpy-CFM and S-Cu-pyz-CFM show an initial capacity of 1626 and 1565 mAh g(-1) with stable capacities of 1063 and 1025 mAh g(-1), respectively, after 150 cycles. An X-ray photoelectron spectroscopy (XPS) analysis after sulfur infiltration reveals the presence of -C-S- bonds arising from the Lewis acid-base interaction of the CFMs with sulfur. The battery separators cycled with the CMF cathodes display complete absence of polysulfides after 150 cycles. These CFM cathodes exhibit an initial fade in capacity during the first approximate to 25 cycles attributed to the irreversible reaction of nitrogen with sulfur (-N-S-) during cycling. A clear understanding of this chemical interaction between sulfur and nitrogen present in the sulfur-infiltrated CFMs is essential for engineering nitrogen containing hosts for trapping polysulfides effectively. Understanding reported here will lead to new materials for achieving the high specific energy densities characteristic to Li-S batteries.