ZIF-8/Ketjen Black derived ZnO/N/KB composite for separator modification of lithium sulfur batteries

Abstract

Lithium-sulfur batteries have the advantages of high specific capacity, high energy density, environmental friendliness, and low price, and have become one of the most promising new electrochemical technologies. However, during the charge-discharge reaction, the shuttle effect of the reaction intermediate polysulfides leads to a decrease in battery activity, which limits its development and commercialization. In this paper, we prepared a novel ZnO/N/Ketjen Black (KB) composite to act as a separator barrier to reduce the influence of polysulfides shuttle effects. A simple aqueous solution reaction was used to mix Zn(NO3)2∙6H2O with KB and ZIF-8/KB was obtained by adding dimethylimidazole, and then ZIF-8/KB precursor was carbonized at high temperature in inert gas atmosphere to obtain ZnO/N/KB composite. Finally, the prepared ZnO/N/KB composite was coated on commercial PE separator. Through the dual effects of adsorption and catalysis, the shuttle effect of polysulfides is sufficiently inhibited by the ZnO/N/KB layer, therefore the electrochemical performances of lithium-sulfur batteries are largely improved. The results show that when the sulfur cathode of Li-S battery contains 3 mg cm−2 active material, the specific discharge capacity can be as high as 1284.5 mAh g−1 at 0.05 C. Furthermore, at a higher rate of 0.5 C, the initial discharge specific capacity also reaches 868.3 mAh g−1. After 400 cycles of the charge/discharge process, it still remains 495.9 mAh g−1, which means a capacity retention rate of 57.1%.