Controllable graphene coated mesoporous carbon/sulfur composite for lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries are attractive for the next generation of rechargeable batteries due to their high energy density, but several problems have hindered their widespread practical realization. Mesoporous carbon/sulfur (CMK-3/S) composites, controllably coated with graphene sheets via the functionalization of the CMK-3 surface with the assistance of a bridging agent (L-lysine and PEG), are presented here. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that the graphene could be coated uniformly and tightly on the surface of mesoporous carbon/sulfur (RGO@CMK-3/S) particles in the presence of L-lysine. In this unique “double-carbon” structure, the abundant pore structure and graphene coating layers serve to accommodate the large volume expansion of the sulfur nanoparticles during discharge, preventing the dissolution of polysulfide intermediates from the cathode, and improving the sulfur nanoparticles’ electrical conductivity. Galvanostatic charge–discharge tests indicated that the RGO@CMK-3/S composite prepared using L-lysine exhibited high and stable specific capacities of up to ∼720 mA h g⁻¹ over more than 100 cycles at 0.5C, and an excellent rate capability of 660 mA h g⁻¹ at a rate of 2C, representing a promising cathode material for rechargeable lithium batteries.