Facile large-scale synthesis of core–shell structured sulfur@polypyrrole composite and its application in lithium–sulfur batteries with high energy density

In this context, we report a novel one-pot synthesis of S@Polypyrrole core–shell spheres as the cathode material in lithium–sulfur battery, designed by polypyrrole (PPy) wrapping on the formed nano-sulfur via the facile wet chemical strategy. The in-situ polymerized PPy layer in this special structure is helpful to inhibit aggregation of sulfur particles with small size, the polysulfide dissolution and shuttling, and offer fast and efficient transport of electron/lithium ion within the electrode. Besides, the flexible PPy layer effectively accommodates the volume expansion. PPy with partial PO43− doping was also employed to improve cycling stability and C-rate performance of S@PPy composite by exchanging Cl− with PO43−. Thus, the sulfur electrode with a high sulfur loading of 80% delivered an initial discharge capacity of 1142mAhg−1 and maintained a high capacity of 805mAhg−1 after 50 cycles at 0.1C. The corresponding capacity retention over 100 cycles was about 65%, with a limited decay of 0.3% per cycle. Even at a high current density of 1.5C, the composite still exhibited a high discharge capacity of about 700mAhg−1. This results mean that the designed electrode can achieve a high practical specific energy density of more than 400Wh/kg, far beyond the commercial LiCoO2 batteries. Due to low cost, facile large-scale synthesis and superior electrochemical performance of S@PPy cathode with high sulfur loading, this work will provide a very promising method to further promote the Li–S batteries in the practical application of portable electronic devices, electric devices and energy storage system.