Ultrafine nanosulfur particles sandwiched in little oxygen-functionalized graphene layers as cathodes for high rate and long-life lithium-sulfur batteries

Although lithium-sulfur batteries are one of the promising candidates for next-generation energy storage systems, the practical applications are still hampered by the poor cycle life, which can be attributed to the insulating properties of sulfur and the shuttle effect of electrochemical intermediate polysulfides. To address these problems, we synthesize sandwich-like composites which consist of ultrafine nanosulfur particles enveloped by little oxygen-functionalized graphene layers (F-GS@S). In this structure, the little oxygen-functionalized graphene backbone can not only accelerate the redox kinetics of sulfur species, but also eliminate the shuttle effect of polysulfides by strong chemical interaction. Moreover, the sandwich confinement structures can further inhibit the dissolution of polysulfides by physical restraint and accommodate the volume contraction/expansion of sulfur during cycling. As a result, the F-GS@S composites used as cathodes for lithium-sulfur batteries display a superior rate capability with the high capacities of 1208 mAh g-1 at 0.1 C and 601.7 mAh g-1 at 2 C and high cycling stability with a capacity retention of 70.5% after 500 cycles at 2 C. In situ characterizations and real-time monitoring experiments during the charge-discharge process are carried out to elucidate the reaction mechanism of the F-GS@S composites as cathodes for high rate and long-life lithium-sulfur batteries.