Carbon Nanotube-Templated Covalent Organic Framework Nanosheets as an Efficient Sulfur Host for Room-Temperature Metal-Sulfur Batteries

We report here a versatile sulfur host, triazine-functionalized crystalline covalent organic framework nanosheets over end-opened multiwalled carbon nanotubes (CNT-CON), for room-temperature metal (viz., Li and Na)-sulfur rechargeable batteries. The CNT-CON, designed using strategies at a molecular level, accommodates nearly 78% sulfur (CNT-CON/S: cathode) and exhibits stable high capacities when cycled against lithium as well as sodium at room temperature. The battery cycling performance of CNT-CON/S is observed to be far superior compared to the bare covalent organic framework with sulfur (COF/S) and bare CNT loaded with sulfur (CNT/S). Systematic experimental and theoretical studies highlight the importance of the chemical design of the host and its influence on the battery performance. The superior battery performance of CNT-CON is a synergistic effect of the trapping mechanisms of CNT and CON. The CNT predominantly confines the nonpolar sulfur, whereas the polar polysulfides are chemically trapped by specific chemical entities in the CON framework.