Dual protection of sulfur by carbon nanospheres and graphene sheets for lithium-sulfur batteries

Abstract

Well-confined elemental sulfur was implanted into a stacked block of carbon nanospheres and graphene sheets through a simple solution process to create a new type of composite cathode material for lithium-sulfur batteries. Transmission electron microscopy and elemental mapping analysis confirm that the as-prepared composite material consists of graphene-wrapped carbon nanospheres with sulfur uniformly distributed in between, where the carbon nanospheres act as the sulfur carriers. With this structural design, the graphene contributes to direct coverage of sulfur to inhibit the mobility of polysulfides, whereas the carbon nanospheres undertake the role of carrying the sulfur into the carbon network. This composite achieves a high loading of sulfur (64.2 wt %) and gives a stable electrochemical performance with a maximum discharge capacity of 1394 mAh g-1 at a current rate of 0.1 C as well as excellent rate capability at 1 C and 2 C. The improved electrochemical properties of this composite material are attributed to the dual functions of the carbon components, which effectively restrain the sulfur inside the carbon nano-network for use in lithium-sulfur rechargeable batteries. Sulfur sandwich: A new type of sandwiched carbon network, consisting of graphene-wrapped carbon nanospheres coated with sulfur (82.7 wt % sulfur) were designed as a cathode material for lithium-sulfur rechargeable batteries (see scheme, CS=carbon sphere, GO=graphene oxide). The composite material exhibits a high specific discharge capacity of 1394 mAh g-1 at 0.1 C, excellent cycling stability for 100 cycles, and high rate performance at 1 C and 2 C. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.