CoS 2 Coatings for Improving Thermal Stability and Electrochemical Performance of FeS 2 Cathodes for Thermal Batteries

Abstract

The cathode material pyrite (FeS2) (core) was coated with 2.5, 5.0, 7.5, and 10.0 wt% CoS2 (shell) (denoted as FeS2@CoS2) by the hydrothermal method and a subsequent heat-treatment to form composites with enhanced thermal stability and electrochemical performance. Importantly, results indicate indicated that CoS2 particles with a complete crystal structure had been successfully coated on the FeS2 surface. The sample coated with the optimal amount of CoS2, which was determined to be 7.5 wt%, showed the highest thermal decomposition temperature (610.6◦C) and excellent specific capacity (as high as 320 mA h g−1 at 520◦C and 200 mA cm−2 at a cutoff voltage of 1.6 V), in compared to that of pure FeS2 (551.3◦C, 240 mA h g−1). Because CoS2 is an excellent electrical conductor, the surface of FeS2 is modified by CoS2, which leads to the change of the microstructure of FeS2 surface, which enhances the intercalation of ionic electrolyte and enhances the electrical conductivity of FeS2. In the meantime, CoS2 has high thermal stability and exhibits low solubility in the molten electrolyte, which reduces the elemental sulfur loss of FeS2 during discharge and thereby increases the electrochemical capacity. © The Author(s) 2018.