High specific surface area bimodal porous carbon derived from biomass reed flowers for high performance lithium-sulfur batteries.

With the advantages of excellent theoretical specific capacity and specific energy, lithium-sulfur (Li-S) battery is regarded as one of promising energy storage systems. However, poor conductivity and shuttle effect of intermediate electrochemical reaction products limit its application. As good sulfur carriers, porous carbon materials can effectively remit these shortcomings. In this paper, a combination of a hydrothermal KOH activation and successive pyrolysis of biomass reed flowers is proposed to prepare a bimodal porous carbon (BPC) material with high specific surface area (1712.6 m2 g-1). The as-obtained low-cost BPC/S cathodes exhibit excellent cycling performance (908 mAh g-1 at 0.1 C after 100 cycles), good rate capability and cyclability (663 mAh g-1 at 1 C after 1000 cycles), as well as a high areal capacity (6.6 mAh cm-2 at 0.1 C after 50 cycles with a sulfur loading of 8.3 mg cm-2). Such excellent electrochemical performance was mainly ascribed to a specific bimodal porous structure with high specific surface area and plenty spaces for sulfur impregnating, which significantly reduces the escape of polysulfides during cycling and guarantees a good cycling stability. Moreover, the secondary class pores (mesopores and micropores) of the material offer plenty of small channels to improve the electronic and ionic transfer rate and, consequently, to enhance the rate capability. The as-synthesized BPC material presents a great potential as a sulfur carrier material for Li-S battery applications. In this work, we also demonstrate a simple route to develop low-cost carbon materials derived from renewable biomass which may expand and promote their use in energy storage applications.