Preparation and electrochemical performance of an Fe_0.5Co_0.2Ni_0.3S₂ cathode material for thermal batteries

Transition metal sulphides have been widely studied in the field of thermal batteries, but their low decomposition temperature, low conductivity, and discharge capacity are still pressing issues hampering their practical application. Inspired by the strategy of entropy increase in sodium-ion and lithium-ion batteries, herein, we propose an Fe_0.5Co_0.2Ni_0.3S₂ cathode material possessing the advantages of electrochemically active elements Fe, Co, and Ni. Fe_0.5Co_0.2Ni_0.3S₂ exhibited a thermal decomposition temperature of 591 °C, which was significantly higher than that of FeS₂. Furthermore, the wettability of the LiCl-KCl molten salt on the surface of Fe_0.5Co_0.2Ni_0.3S₂ was improved and its contact area was 1.1 times that of FeS₂, providing more active sites for electrochemical reactions and effectively improving the electrochemical performance of the material. Moreover, it exhibited a specific capacity (cutoff voltage ≥1.5 V) of 584 mA h g^-1 at 500 °C with a discharge current of 100 mA cm^-2, representing an increase of approximately 96.5% compared to that of CoS₂. Thus, this work presents a new strategy for the design of high-performance cathode materials for thermal batteries.