A polypyrrole-coated acetylene black/sulfur composite cathode material for lithium–sulfur batteries

Lithium–sulfur batteries are promising next-generation energy storage devices beyond conventional lithium ion batteries. However, it suffers from rapid capacity fading and poor cyclic stability. Here we report a facile in situ sulfur deposition and chemical oxidative polymerization method for preparing acetylene black/sulfur@polypyrrole(AB/S@PPy) composite as a cathode material for lithium–sulfur batteries. It is demonstrated that PPy is covered uniformly onto the surface of the AB/S composite forming a core–shell structure. In the structure, AB in the matrix and PPy on the surface acts as a combined conductive framework to provide ions and electrons transport pathways, and to inhibit the dissolution or diffusion of polysulfide into the electrolyte. The as-designed AB/S@PPy composite exhibits excellent rate capability and cyclic stability. The initial discharge specific capacity is as high as 1179.4 m Ah/g, and remains at769.3 m Ah/g after 80 cycles at 0.2 C. Even at a high rate(0.5 C), a maximum discharge capacity of 811.1 m Ah/g is still achieved for the AB/S@PPy composite after activation, and the capacity retention is over62.5% after 200 cycles.