High-Performance Lithium Sulfide Cathode Made by Using Molten Lithium Polysulfides and ZIF-67

Lithium-sulfur batteries (LSBs) are among the most promising systems beyond lithium-ion batteries. For assembling LSBs, compared with the sulfur (S) cathodes, the lithium sulfide (Li 2 S) cathodes are disadvantageous in their incapability of using the melting-impregnation technique due to the high melting-point of Li 2 S. This paper reports a special melting-impregnation method for preparing Li 2 S cathodes, by utilizing the fluidic property of dimethoxyethane-adducted lithium polysulfides (Li 2 S n ) at 110°C. After the tannic-acid etched cobalt-organic-framework ZIF-67 is impregnated with such fluid and further calcined, the obtained h-Li 2 S@C67 materials present a 34% better performance vs. the commercial Li 2 S-derived c-Li 2 S@C67 cathode. Moreover, its capacity can be increased by 10%, when soaked in pyrrolidine and then heated to carbonize pyrrolidine. Major factors for the performance improvement include the catalytic effect of Co atoms on the charging/discharging kinetics between Li 2 S and S, the increased surface area via tannic acid etching, the enhanced conductivity from the ZIF- and pyrrolidine-derived carbon, and the self-catalytic Li 2 S@Li 2 S 2 @Li 2 S 6 double-shell structures derived from the calcined Li 2 S n .