CNFs/S 1-x Se x Composites as Promising Cathode Materials for High-Energy Lithium-Sulfur Batteries

High-energy lithium-sulfur (Li-S) batteries still suffer from poor rate capability and short cycle life caused by the polysulfides shuttle and insulating nature of S (and the discharge product, Li 2 S). Selenium disulfide (SeS 2 ), with a theoretical specific capacity of 1342 mAh g -1 , is a promising cathode material as it has better conductivity compared to sulfur. The electrochemical reaction kinetics of CNFs-S/SeS 2 composites (denoted as CNFs/S 1-x Se x , where x ≤ 0.1) are expected to be remarkably improved because of the better conductivity of SeS 2 compared to sulfur. Here, a high-performance composite cathode material of CNFs/S 1-x Se x for novel Li-S batteries is reported. The CNFs/S 1-x Se x composites combine the higher conductivity and higher density of SeS 2 with high specific capacity of sulfur. The CNFs/S 1-x Se x electrode shows good initial discharge capacity of ~1050 mAh g -1 at 0.05 C rate with high mass loading of materials (~6-7 mg cm -2 of composites) and > 97% initial coulombic efficiency. The CNFs/S 1-x Se x electrode shows more than 600 mAh g -1 specific capacity after 50 charge-discharge cycles at 0.5C rate, much higher compared to the CNFs/S cathodes.