Metal-Organic Frameworks with Axial Cobalt-Oxygen Coordination Modulate Polysulfide Redox for Lithium-Sulfur Batteries

Although the ultrahigh theoretical energy density and cost-effectiveness, lithium-sulfur (Li-S) batteries suffer from sluggish conversion kinetics and the shuttling effect of soluble lithium polysulfides (LiPSs). Herein, conductive hexagonal cobalt-organic framework (Co-HTP) nanosheets are anchored in situ on carboxyl graphene (CG) substrates and serve as host catalysts to modulate the polysulfide redox. Substantial characterizations identify that the local coordination environment of the quadrilateral Co-N4 units transforms into an asymmetric penta-coordinated O-Co-N4 with axial Co & horbar;O coordination, which triggers spin polarization and remarkable electron delocalization of Co 3d orbital. The higher spin state and lower local electron density of the O-Co-N4 sites induce more active electronic states in Co-HTP/CG and facilitate orbital hybridization with polysulfides to form more stable bond orders. Such optimized electronic structure significantly accelerates redox kinetics and enhances the adsorption strength of polysulfides. These merit the lithium-sulfur battery based on Co-HTP/CG with a high reversible capacity, impressive rate capability, and prolonged cycling performance over 500 cycles. This work will enrich the design philosophy of modulating the spintronic structure of electrocatalysts for advanced Li-S batteries and beyond. The Co-HTP/CG with axially oxygen-coordinated O-Co-N4 moiety are rationally constructed in situ on carboxyl graphene and serve as a multifunctional sulfur host for Li-S batteries. The axial Co-O coordination can induce spin polarization and Co 3d electron delocalization in Co-HTP/CG, which can firmly anchor the polysulfides and facilitate sulfur redox kinetics, thus offering high reversible capacity, impressive rate performance, and superior cycling stability. image