Physical and chemical dual-confinement of polysulfides within hierarchically meso-microporous nitrogen-doped carbon nanocages for advanced Li-S batteries

Lithium-sulfur (Li-S) batteries with high theoretical specific energy (1675 mA h g(-1)), environmental benignity and low cost are considered to be some of the most promising next-generation energy-storage systems compared with conventional lithium-ion batteries. However intrinsic large volume expansion and irreversible loss of activated materials seriously limit their commercial applications. To solve the problems, nitrogen-doped hierarchical carbon nanocages were synthesized and used as efficient sulfur hosts. The synthesized nitrogen doped hierarchically meso-microporous carbon (N-MMC) had large BET surface area and mesopore volumes, contributing to high sulfur loading and a reduced volume-change effect of sulfur during lithiation. Moreover, the strong physical adsorption in the micropores together with improved chemical adsorption caused by nitrogen doping lead to effective polysulfide trapping. The N-MMC/S exhibited high initial capacities of 1202.2 mA h g(-1) at 0.2C and 1024 mA h g(-1) at 0.5C. The capacity kept at as high as 780 mA h g(-1) after 60 cycles at 0.2C and 623.8 mA h g(-1) after 70 cycles at 0.5C.