Hand-in-Hand Reinforced rGO Film Used as an Auxiliary Functional Layer for High-Performance Li–S Batteries

For lithium–sulfur (Li–S) batteries, a promising candidate for future high-energy storage devices, several prominent problems still need to be solved urgently, such as limited rate capability and poor cycle life caused by the insulating nature of sulfur and the shuttle of soluble polysulfides produced during battery operation. In this work, a facile vacuum filtration method is employed to graft polyethyleneimine to reduced graphene oxide (rGO) in a "hand-in-hand" way using the amino and catechol groups from polydopamine. The resulting polymer-reinforced rGO (PPG) film is applied as a free-standing auxiliary functional layer for Li–S batteries. It has been confirmed by both theoretical calculations and experimental methods that, benefiting from the rich amine groups and oxygen-containing functional groups, the as-prepared PPG composite film shows great ability to capture polysulfides. Moreover, its high conductivity enables itself to function as a polysulfide reservoir, thus facilitating the successive reutilization of the trapped active materials and improving sulfur utilization. For this reason, the PPG film can also be regarded as a cathode material, serving as a novel "SPPG cathode" together with the pure sulfur cathode. The cell assembled with the pure sulfur cathode and the PPG auxiliary functional layer displays high reversible capacity, excellent Coulombic efficiency, and good cycling stability, suggesting that the rational auxiliary functional layer design ensures a good match with pure sulfur cathodes and shows the potential to achieve energy-dense Li–S batteries.