A high-performance tellurium-sulfur cathode in carbonate-based electrolytes

The current technology of lithium-sulfur (Li-S) batteries is hindered by the sluggish kinetics and low utilization of sulfur (S) due to its electronic insulating nature. Herein, tellurium (Te) is introduced into S by forming TexSy solid solutions to reshape Li-S chemistry and facilitate the solid-state conversion of the cathode in carbonate-based electrolytes. Numerical calculations suggest a more delocalized charge-density difference around the Te atoms in Li16Te1S7 compared to site-equivalent S atoms in Li2S, thus enabling lower energy barriers throughout the Li migration pathway. Mesoporous carbon Ketjenblack (KB) is employed to confine TexSy materials via a melt diffusion method. By tuning the molar ratio of Te/S, it is found that the Te1S7/KB cathode delivers the highest reversible capacity of 1306.7 mAh g−1 at 0.1 A g−1 and maintains a capacity of 959.8 mAh g−1 after 400 cycles at 1 A g−1. Kinetics analysis reveals that the introduction of Te accelerates Li-ion diffusion and decreases reaction resistance during the charge/discharge process, thus enabling fast and reversible redox conversion. Moreover, the Te-containing solid electrolyte layer on the electrode surface is generated to prevent the loss of Te1S7 active materials. These encouraging findings suggest that the heteroatomic Te1S7/KB is a promising cathode to achieve long cycle life and high energy density for Li-S batteries.