3D Porous Spherical Sulfur/Carbon Cathode Materials with in Situ Vapor-Phase Polymerized Polypyrrole Coating Layer for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are promising candidates for high-energy-density battery systems, but their practical application is hindered by low S loading and polysulfide shuttling. Here, we design a composite material of porous spherical ketjen black (KB)-carbon nanotubes (CNTs) (PSKC) with a three-dimensional structure via a spray-drying method. The PSKC material possesses a large pore volume and high specific surface area and is an excellent carbon skeleton for loading high-content S. The S/PSKC cathode with a high S loading of 80 wt % displays an initial capacity of approximately 1226 mAh g(-1) with a rapidly decreasing Coulombic efficiency. To solve the polysulfide shuttling issue, the S/PSKC material is encapsulated by a polymer protective layer via in situ vapor-phase pyrrole polymerization. The elemental mappings of a S/PSKC@polypyrrole microsphere cross section reveal that S is uniformly distributed in the microsphere and the polypyrrole (PPy) coating layer is simultaneously formed outside and inside the microsphere during the vapor-phase polymerization process. The S/PSKC@PPy cathode with 72.8 wt % S shows a specific capacity of 1109.2 mAh g(-1) at 0.15 C, and the reversible capacity remains 931.6 mAh g(-1) after 100 cycles. The S/PSKC@PPy cathode exhibits superior cyclic stability and improved Coulombic efficiency, demonstrating the PPy layer effectively suppresses polysulfide shuttling.