In Situ Reactive Synthesis of Polypyrrole-MnO₂ Coaxial Nanotubes as Sulfur Hosts for High-Performance Lithium-Sulfur Battery.

Abstract

Lithium-sulfur batteries are considered as a promising candidate for high energy density storage applications. However, their specific capacity and cyclic stability are hindered by poor conductivity of sulfur and the dissolution of redox intermediates. Here, we design polypyrrole-MnO₂ coaxial nanotubes to encapsulate sulfur, in which MnO₂ restrains the shuttle effect of polysulfides greatly through chemisorption and polypyrrole serves as conductive frameworks. The polypyrrole-MnO₂ nanotubes are synthesized through in situ polymerization of pyrrole using MnO₂ nanowires as both template and oxidization initiator. A stable Coulombic efficiency of ∼98.6% and a decay rate of 0.07% per cycle along with 500 cycles at 1C-rate are achieved for S/PPy-MnO₂ ternary electrodes with 70 wt % of S and 5 wt % of MnO₂. The excellent trapping ability of MnO₂ to polysulfides and tubular structure of polypyrrole with good flexibility and conductivity are responsible for the significantly improved cyclic stability and rate capability.