Improving the electrochemical performance of Lithium-Sulfur batteries using an Nb-Doped TiO2 additive layer for the chemisorption of lithium polysulfides

This study presents a method to suppress the migration of lithium polysulfides in lithium-sulfur batteries by introducing a dual-layer electrode structure. Herein, unlike conventional methods of mixing the polar additives with sulfur/carbon composites, melted sulfur mixed with mesocarbon microbeads are used as the electrode and covered with an additive layer of Nb-doped TiO2/graphite composite via two-step blade coating. By doping TiO2 with Nb, electrical and lithium ion conductivity of TiO2 can be increased, thereby enhancing the redox reaction kinetics. Most importantly, chemisorption of lithium polysulfides to Nb-TiO2 can effectively mitigate the shuttle effect, resulting in higher capacity and longer cycle life. The electrode with the Nb-TiO2 additive layer results in a 1st and 100th cycle specific capacity of 1883 mAh g−1 and 894 mAh g−1, respectively, at 0.1 C (1 C = 1675 mAh), indicating enhanced electrochemical performance as compared with that of bare lithium-sulfur batteries. X-ray photoelectron spectroscopy (XPS) study was conducted to investigate the interaction between polysulfides and Nb-TiO2. The results indicate that the Nb-TiO2-layered electrode efficiently traps polysulfides on the cathode and improves the rate capability, cycle performance, and specific capacity.