CoC/CoC heterostructure towards polysulfide capture/conversion for advanced lithium-sulfur batteries.

The slow redox kinetics and intractable shuttle effect of lithium polysulfides (LiPSs) significantly hinder the practical usage of lithium-sulfur batteries (LSBs). Here, the nanostructured material combining doped nitrogen, cobalt carbides with high intrinsic activity, and electronically conductive carbon black (CoC/CoC/NEC) is prepared by a hydrothermal method and subsequent heat treatment. CoC/CoC heterostructure is comprised of CoC exhibiting a high adsorption capacity for LiPSs and CoC electrocatalyst demonstrating a mighty catalytic activity on LiPSs. The nitrogen doping generates the defects to increase the number of active sites and achieve the proper tuning of electronic structure. Specifically, the combined action of CoC/CoC and nitrogen doping enhances the trapping of LiPSs and achieves the efficient catalytic conversion of sulfur species. EC improves the electroconductibility of active sulfur. Density functional theory (DFT) calculations further prove that CoC and CoC play the unique roles in different mechanisms. Therefore, CoC/CoC/NEC electrocatalyst-based lithium-sulfur (Li-S) battery, equipped with CoC/CoC/NEC-PP separator and S-CoC/CoC/NEC cathode, possesses an original discharge capacity of 1131 mAh g at 0.5 C, retaining a discharge capacity of 977 mAh g after 300 cycles with a capacity retention of 86 %. Li-S battery shows a starting discharge capacity of 982 mAh g at 1 C, accompanied by a slight capacity decay rate of 0.023 % each cycle for 1500 cycles. Even in an areal sulfur loading of 5.6 mg cm and a lean electrolyte/sulfur (E/S) ratio of 4.5 μL mg, a good electrochemical behavior is still kept at 0.2 C during 100 cycles. This work pioneers the novel idea into the role of transition metal carbides (TMCs) in the design of high-performance LSBs, which would be extended to other secondary batteries.