Polyacrylonitrile/graphene composite as a precursor to a sulfur-based cathode material for high-rate rechargeable Li-S batteries

Polyacrylonitrile/graphene (PAN/GNS) composites have been synthesized via an in situ polymerization method for the first time, which serve as a precursor to prepare a cathode material for high-rate rechargeable Li-S batteries. It is observed from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the PAN nanoparticles, less than 100 nm in size, are anchored on the surface of the GNS and this unique structure is maintained in the sulfur composite cathode material. The electrochemical properties of the pyrolyzed PAN-S/GNS (pPAN-S/GNS) composite cathode have been evaluated by cyclic voltammograms, galvanostatic discharge-charge cycling and electrochemical impedance spectroscopy. The results show that the pPAN-S/GNS nanocomposite, with a GNS content of ca. 4 wt.%, exhibits a reversible capacity of ca. 1500 mA hg(sulfur)(-1) or 700 mA hg(-1) composite in the first cycle, corresponding to a sulfur utilization of ca. 90%. The capacity retention is relatively stable at 0.1 C. Even up to 6 C, a competitive capacity of ca. 800 mA hg(sulfur)(-1) is obtained. The superior performance of pPAN-S/GNS is attributed to the introduction of the GNS and the even composite structure. The GNS in the composite materials works as a three-dimensional (3-D) nano current collector, which could act not only as an electronically conductive matrix, but also as a framework to improve the electrochemical performance.