Dual core–shell structured sulfur cathode composite synthesized by a one-pot route for lithium sulfur batteries

Lithium–sulfur batteries are promising electrochemical devices for future energy conversion and storage. Its theoretical capacity is 1675 mA h g−1, much higher than that of conventional lithium-ion batteries. However, it suffers from rapid capacity decay and low energy efficiency. In this work, we introduce a novel dual core–shell structured sulfur composite with multi-walled carbon nanotubes (MWCNTs) and polypyrrole (PPy), MWCNTs@S@PPy, as a cathode material for Li–S batteries. The composite is synthesized via a facile one-pot method. In the structure, MWCNTs and PPy work as a combined conductive framework to provide access to Li+ ingress and egress for reaction with sulfur, and to inhibit the diffusion of polysulfide out of the cathode, and hence reduce the capacity decay. Meanwhile, LiNO3 additive is added into the electrolyte to improve the coulombic efficiency. The as-designed MWCNTs@S@PPy composite shows excellent rate capability and cyclability. The initial discharge specific capacity is as high as 1517 mA h g−1, and remains at 917 mA h g−1 after 60 cycles at a current density of 200 mA g−1. Even at a high current density of 1500 mA g−1, the composite still shows a good cycle performance with a capacity of 560 mA h g−1 after 200 cycles.