Graphene and its derivatives in lithium–sulfur batteries

On the edge of impending energy and environmental crisis, electrochemical energy storage has rapidly gained momentum. Among all the candidates in the “beyond lithium-ion battery” arena, lithium–sulfur (Li–S) battery has attracted extensive attention due to its ultrahigh theoretical capacity and the abundance of sulfur. However, the development of Li–S battery is hindered by its quick capacity decay and short lifespan because of the insulating nature of sulfur/Li₂S and the high solubility of lithium polysulfides. Under this scenario, graphene and its derivatives have been explored to overcome the shortcomings of Li–S batteries. Graphene is mechanically robust, highly flexible, and exceptionally conductive, enabling abundant porosity for high sulfur loading, expeditious electron/ion transfer, and effective polysulfide encapsulation. Graphene oxide (GO), on the other hand, is often attached with various functional groups which are able to chemically bond with polysulfides, rendering GO a strong polysulfide entrapping ability. The graphene/GO enabled physical confinements and chemical interactions can be further enhanced via constructing graphene-sulfur configurations and doping functional groups or heteroatoms. In addition to the intrinsic advantages, graphene and GO are highly compatible with many engineering materials, making graphene-based composite electrodes promising for low-cost, high-performance Li–S batteries. This review article sequentially illustrates the interaction between sulfur/polysulfides and graphene, sulfur infiltration methods, sulfur/graphene configurations, applications of graphene and its derivatives in Li–S batteries, and presents state of the art and future outlook.