Co-N/KB porous hybrid derived from ZIF 67/KB as a separator modification material for lithium-sulfur batteries

•Co-N/KB composite is derived from ZIF67/KB precursor which is prepared by a facile water solution reaction.•Co-N/KB composite is coated on the PE separator of Li-S coin battery which served as the polysulfides barrier layer.•Co-N/KB barrier show both physical and chemical interactions with polysulfides based on its rich pore structure and Co-N active site doping.•Coin cells with sulfur areal density of 5 mg cm−2 can cycle with a high capacity retention 81.1% after 200 cycles. The commercialization of lithium sulfur battery is greatly impeded by the severe capacity decay induced by polysulfides shuttle during charge/discharge process. Herein, we propose a composite carbon material with Co-N doping and high conductivity for polysulfides barrier layer. ZIF67 and high conductivity Ketjen Black(KB) are combined by a facile water solution reaction at room temperature at first, afterwords the as-prepared ZIF67/KB precursor is calcined in nitrogen atmosphere to obtain a novel Co-N/KB nano structure. The Co-N/KB hybrid is then coated on the commercial PE separator to improve electrochemical properties of Li-S battery. The Co-N/KB coating layer apparently promote the redox kinetics and show chemisorption ability toward polysulfides. Furthermore, the coating layer with high conductivity can also be used as a second current collector to promote the electronic transmission, which will increase the use ratio of active substances and improve the cycle retention. By the use of Co-N/KB modified separator, the initial discharge capacity of sulfur cathode with a sulfur areal loading of 3 mg cm−2 reaches 888 mAh g−1 at 0.5 C and shows a slow capacity decay rate of 0.025%/cycle after 200 cycles. Even when the areal loading of active sulfur is added up to 5 mg cm−2, the battery can also show a stable cycle performance for more than 300 cycles.