Split-half-tubular polypyrrole@sulfur@polypyrrole composite with a novel three-layer-3D structure as cathode for lithium/sulfur batteries

Polypyrrole@Sulfur@Polypyrrole composite with a novel three-layer-3D-structure, which consists of an external polypyrrole coating layer, an intermediate sulfur filling layer, and an internal polypyrrole split-half-tube conducting matrix layer, has been synthesized by the oxidative chemical polymerization method and chemical precipitation method in this article. Due to this unique three-layer-structure, the discharge specific capacity of Polypyrrole@Sulfur@Polypyrrole composite cathode retained at 554mAh g-1 after 50 cycles, which represents 68.8% retention of the initial discharge specific capacity. In comparison, the Sulfur@Polypyrrole composite cathode, with the same components as Polypyrrole@Sulfur@Polypyrrole composite, but without the three-layer-structure, has the discharge specific capacity of 370mAh g-1 after 50 cycles, which is 32.3% retention of the initial discharge specific capacity. Therefore, it can be concluded that the unique three-layer-structure plays an essential role in improving the performance of the Lithium/Sulfur batteries. Moreover, the effects of LiNO3 additive in the electrolyte on coulombic efficiency are discussed to further confirm the containment function of the external layer of polypyrrole in the Polypyrrole@Sulfur@Polypyrrole composite, which is the evidence that the external layer of polypyrrole can effectively confine the dissolved polysulfides.