Heat Treatment Effect on Microstrain and Electrochemical Performance of Nano-sized FeS2 Cathode for Thermal Batteries

Abstract

Iron pyrite (FeS2) is the most widely used material for cathodes in thermal batteries, attributed to its high specific energy density and natural abundance as well as low cost. In this study, nano-sized FeS2 powders were synthesized by high-energy milling to improve electrochemical performance Li(Si)/FeS2 thermal battery, and their particle sizes, microstrain, and thermal stabilities were investigated by particle size analysis (PSA), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Electrochemical performance was evaluated by single-cell discharge tests. The average particle size decreased from 107 mu m to 261 nm after 10 h of dry milling, resulting in microstrain on FeS2. This microstrain led to the thermal instability of the FeS2 powder, causing an increase of the open-circuit voltage of Li(Si)/FeS2 single cells. The voltage was stabilized from 2.45 V to 1.93 V, and thermal instability was mitigated by the heat treatment of the FeS2 powder up to 400 degrees C. The electrochemical performance of the single cells fabricated with nano-sized FeS2 thermally annealed at 400 degrees C improved by 57% as compared with that of untreated ones at a cut-off voltage of 1.4 V.