Rational design of a zwitterionic porous organic framework loaded with Co(ii) ions to host sulfur and synergistically boost polysulfide redox kinetics for lithium sulfur batteries

Abstract

In the development of lithium–sulfur batteries (LiSBs), the irreversible volume changes, annoying shuttle effect and slow conversion kinetics of lithium polysulfides (LiPSs) are the main obstacles for further commercialization. Therefore, a rational design of a multifunctional sulfur cathode is essential to broaden the application of LiSBs, namely, using a squaraine-linked porous organic framework as the cathode by means of anchoring Co(II) ions into the polar site of the porous structure. The as-obtained Co-HUT4 material maintains an abundant pore structure to house sulfur and gives physical confinement to LiPSs. Besides, the well-dispersed cobalt(II) ions provide good chemical capture sites and catalytic activity, helping to suppress the shuttling effect and enhance the adsorption and conversion of LiPSs. Benefitting from these multifunctional characteristics, LiSBs based on the Co-HUT4 electrode exhibit an exceptional stability of 650 mA h g⁻¹ after 500 cycles at 1.0C, and a specific capacity of 740 mA h g⁻¹ can also be realized with a high sulfur loading (5.5 mg cm⁻²), which shows remarkable potential for LiSBs.