A sandwich-structure composite carbon layer coated on separator to trap polysulfides for high-performance lithium sulfur batteries

Lithium sulfur battery with a high energy density holds great potential to be the next-generation storage device. However, the extensive commercial applications of Lithium sulfur batteries still have many obstacles, such as the most serious "shuttle effect". Here, we synthesize a novel nitrogen-doped mesoporous carbon only by simple calcination and acid treatment processes to effectively adsorb the diffused polysulfides. Then, the nitrogen-doped mesoporous carbon is sandwiched between two carbon nanotube layers to form a sandwich-structure composite carbon layer on the separator, which effectively synergizes the advantages of sp(3)-hybridized nitrogen-doped mesoporous carbon and sp(2)-hybridized carbon nanotube. The results indicate that the sandwich-structure composite carbon layer not only can well block the shuttle of polysulfides, but also has good conductive and mechanical properties. Therefore, the cells with the sandwich-structure composite carbon layers exhibit excellent long cycling performance at a high rate (422.9 mAh g(-1) after 400 cycles at 4C with a capacity decay of 0.081% per cycle) and outstanding rate capability (1279.4 mA h g(-1) at 0.2C and 644.3 mA h g(-1) at 4C). This work has certain practical value for Lithium sulfur batteries with its excellent electrochemical performances and simple synthesis processes. (C) 2019 Elsevier B.V. All rights reserved.