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

Abstract

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.