Synergistic Polysulfide Regulation by Nanodiamond and Sulfur Iodide on Cathode for Achieving Long-Cycling Na-S...

Despite delivering high theoretical capacity and cost-effectiveness advantages, sodium-sulfur (Na-S) batteries are plagued by rapid capacity degradation stemming from sulfur's inadequate electrical conductivity, substantial volume expansion, and polysulfide shuttle effects. The problems can be addressed by designing cathode with special architecture. In this work, we design a sulfur-iodine-carbon nanotube/nanodiamond (SIC/ND) cathode, where sulfur iodide (S_xI) uniformly coats on a carbon nanotube (CNT) framework incorporating nanodiamonds (NDs). The SIC/ND cathode exhibits exceptional electrochemical performance and consistently achieves high-capacity retention and outstanding cycling stability. Ex situ X-ray diffraction confirms suppression of the shuttle effect by inhibiting irreversible conversion and loss of polysulfides. Density functional theory calculations prove the adsorption and rapid ion transport on CNT and catalytic activity on ND. The improved performance is attributed to synergistic mechanisms from mechanical/electrical support and absorption of CNT, boosted kinetics by S_xI, as well as catalysis of NDs. Hence, this work presents a rationally designed strategy for advanced Na-S batteries.