Enabling rapid polysulfide conversion kinetics by using functionalized carbon nanosheets as metal-free electrocatalysts in durable lithium-sulfur batteries

Propelling polysulfide conversion and regulating the precipitation of lithium sulfides by introducing electrocatalysts has been proven as an effective strategy to enhance the durability of the lithium-sulfur (Li-S) batteries. Herein, the two-dimensional N-doped carbon nanosheets with appropriate distribution of micro/mesopores are proposed as a novel barrier to modify the commercial polypropylene separator, which significantly reduce the shuttle effect of soluble polysulfides via physical confinement and chemical bonding and immobilize them as active materials within the cathode side. In addition, the efficient electrocatalysis of the functionalized carbon nanosheets on improving sulfur redox electrochemistry is revealed by systematic characterization, leading to rapid polysulfide conversion kinetics and uniform deposition of lithium sulfides. Due to the smooth trappingadsorption-conversion process of polysulfides by applying the modified separator, the Li-S batteries with the simple carbon black/S cathodes exhibit outstanding lithium storage capacity (1338 mAh g(-1) at 0.1 C) and satisfactory cycling stability (0.029% capacity decreasing per cycle over 700 cycles at 3 C). More importantly, a high reversible areal capacity of 4.3 mAh cm(-2) could be maintained at high sulfur loading (5.8 mg cm(-2)), showing the striking commercial potential. These findings not only provide a feasible method to enhance electrochemical performance of Li-S batteries, but also open up a new sight on developing carbon nanomaterials as metal-free electrocatalysts for multistep reactions in battery electrochemistry.