Self-assembled layer-by-layer partially reduced graphene oxide-sulfur composites as lithium-sulfur battery cathodes.

Abstract

Constructing a reliable conductive carbon matrix is essential for the sulfur-containing cathode materials of lithium–sulfur batteries. A ready-made conductive matrix infiltrated with sulfur as the cathode is the usual solution. Here, a partially reduced graphene oxide–sulfur composite (prGO/S) with an ordered self-assembled layer-by-layer structure is introduced as a Li–S battery cathode. The prGO/S composites are synthesized through a facile one-step self-assembly liquid route. An appropriate amount of sulfur is in situ deposited on the surface of the prGO nanosheets by adjusting the reduction degree of the GO nanosheets. The combined effect of the electrostatic repulsions and surface energy makes the sulfur wrapped prGO nanosheets self-assemble to form an ordered layer-by-layer structure, which not only ensures the uniform distribution of sulfur but also accommodates the volume change of the sulfur species during cycling. Moreover, the conductivity of the prGO/S composites improves when the reduction time increases. XPS spectra confirm that sulfur is still chemically bonded to the prGO. After applying the prGO coating of the prGO/S composite particle and as an interlayer in a lithium–sulfur battery configuration, a high initial discharge capacity of 1275.8 mA h g−1 is achieved and the discharge capacity of the 100th cycle is 1013.8 mA h g−1 at 0.1C rate.