Stable Na/K–S Batteries with Conductive Organosulfur Polymer Microcages as Cathodes

Na–S and K–S batteries, with high-energy density, using naturally more abundant and affordable metals compared with rare resources like Li, Co, and Ni elements, have inspired intense research interest. However, the sulfur cathodes for Na/K storage are plagued by soluble polysulfide shuttling, larger volumetric deformation, and sluggish redox kinetics. Here, we report that a conductive organosulfur polymer microcage, fabricated facilely with the microbe and elemental sulfur as precursors, can effectively address these issues for stable high-capacity Na–S and K–S batteries. The covalently bonded short-chain sulfur species enable superior reaction kinetics and avoid soluble polysulfide formation. The microcage architecture with built-in cavities buffers the volume deformation to ensure a resilient electrode. The resultant conductive organosulfur polymer can promise a combination of high capacity and extraordinary cyclability with a promising rate and Coulombic efficiency. Especially, as a K–S battery cathode, it could deliver a high capacity of 1206.5 mAh g–1 together with an extraordinary cyclability (>99% capacity retention over 1100 cycles), which is much better than that of state-of-the-art sulfur cathodes. This work envisions new perspectives on building conductive organosulfur cathode materials with high performance via a simple and feasible protocol.