Interaction of TiS₂and Sulfur in Li-S Battery System

Abstract

With the ability to adsorb polysulfide, electronically conductive and electrochemically active TiS<sub>2</sub> is an effective multifunctional cathode additive to improve Li-S battery cycling performance. Furthermore, by using X-ray Photoelectron Spectroscopy (XPS), direct evidence is obtained to demonstrate the strong interaction between Li-polysulfide and TiS<sub>2</sub>. The observation of Li signature on Li<sub>2</sub>S<sub>8</sub> treated TiS<sub>2</sub> proves that the TiS<sub>2</sub> possesses the ability to adsorb Li-polysulfides species on its surface. An electron density transfer from Ti to Li and S is identified based on the positions of the peaks in the XPS spectrum before and after the interaction, which is consistent with the theoretically predicted polysulfide-TiS<sub>2</sub> interaction models in the literature. TiS<sub>2</sub> sample with 2.5x higher BET surface area is obtained by milling the raw TiS<sub>2</sub> particles and used as cathode additive in the sulfur electrode. Furthermore, in the presence of TiS<sub>2</sub> additive, long cycle life and improved sulfur utilization of Li-S cells under high rate discharge are demonstrated. In addition, we find that a uniform TiS<sub>2</sub> distribution in the sulfur-TiS<sub>2</sub> hybrid electrode is vital in determining its effectiveness in enhancing the performance of sulfur electrodes. Thus, by processing method and condition should be very important considerations in future development of sulfur electrodes with TiS<sub>2</sub> additive.