A Polyaniline-Coated Sulfur/Carbon Composite with an Enhanced High-Rate Capability as a Cathode Material for Lithium/Sulfur Batteries

Polyaniline-coated sulfur/conductive-carbon-black (PANI@S/C) composites with different contents of sulfur are prepared via two facile processes including ball-milling and thermal treatment of the conductive carbon black and sublimed sulfur, followed by an in situ chemical oxidative polymerization of the aniline monomer in the presence of the S/C composite and ammonium persulfate. The microstructure and electrochemical performance of the as-prepared composites are investigated systematically. It is demonstrated that the polyaniline, with a thickness of approximate to 510 nm, is coated uniformly onto the surface of the S/C composite forming a core/shell structure. The PANI@S/C composite with 43.7 wt% sulfur presents the optimum electrochemical performance, including a large reversible capacity, a good coulombic efficiency, and a high active-sulfur utilization. The formation of the unique core/shell structure in the PANI@S/C composites is responsible for the improvement of the electrochemical performance. In particular, the high-rate charge/discharge capability of the PANI @S/C composites is excellent due to a synergistic effect on the high electrical conductivity from both the conductive carbon black in the matrix and the PANI on the surface. Even at an ultrahigh rate (10C), a maximum discharge capacity of 635.5 mA h per g of sulfur is still retained for the PANI@S/C composite after activation, and the discharge capacity retention is over 60% after 200 cycles.