Effect of Titanium Disulfide Cathode Additive in the Performance of Li-S Batteries

Abstract

Lithium-sulfur (Li-S) batteries have attracted considerable attention as one of the most promising next-generation energy storage system owing to the high theoretical specific capacity (1675 mAh g-1), low cost, natural abundance and environmentally benign nature of sulfur. However, the poor electrical conductivity of elemental S results in low utilization of S specific capacity, and hence, insufficient specific energy of Li-S batteries. Development of Li-S batteries is hindered by sluggish kinetics resulting from the intrinsic poor conductivity of sulfur and capacity degradation due to solubility of polysulfides intermediate. One strategy to overcome with these issues is to use of titanium disulfide (TiS2) as an additive to sulfur electrodes as it is a good electrical conductor and electrochemically active and also has the ability to adsorb polysulfide. Herein, we investigated TiS2 as additive with sulfur using hierarchical architectures of carbon as effective hosts for S/TiS2. By a facile one-step melting diffusion method, we synthesized S/TiS2@carbon nanofibers (CNFs) composites in which TiS2 was uniformly distributed over the S-CNFs. The hierarchical S/TiS2@CNFs (TiS2, 20 wt%) electrodes shows good initial discharge capacity of 1085 mAh g−1 at 0.05 C rate with high mass loading of material (~6-6.5 mg/cm2 of composite) and ~99% initial coulombic efficiency. The composite electrode shows stable cycling performance for more than 100 charge-discharge cycles with specific capacity of ~750 mAh g-1 at a rate of C/3 and coulombic efficiency over 99%. Thus, in the presence of TiS2 additive, long cycle life and improved sulfur utilization of Li-S cells under high current rate (C/3) are demonstrated with high sulfur mass-loading.