Gold-doped iron disulfide as cathode materials for enhanced electrochemical performance in thermal batteries

Abstract

Iron disulfide (FeS₂) has been widely used in thermal batteries because of its high theoretical specific capacity and voltage plateau. However, low thermal decomposition temperature, poor conductivity and inferior actual specific capacity limit its wide applications. Herein, we report a gold-doped FeS₂ (FeS₂-Au), which not only reduces the band gap of the FeS₂ crystals but also enriches the electron transport path of FeS₂ by the formation of Au nanoparticles. First-principles calculation shows that the diffusion energy barrier of lithium-ion is reduced after the Au-doped FeS₂. In addition, Au increases the electron cloud density around sulfur atoms, which helps to enhance the stability of Fe-S covalent bonds and thus results in better thermal stability of FeS₂. When the Au content is 130 μg·g⁻¹ (FeS₂-Au₄), the thermal decomposition temperature (TG_5%) of FeS₂-Au is 72.2 °C higher than that of pristine FeS₂. At a discharge temperature of 500 °C, a current density of 200 mA·cm⁻² and a cutoff voltage of 1.4 V, FeS₂-Au₄ demonstrates superior specific capacity and high specific energy compared to FeS₂. More precisely, the specific capacity of FeS₂-Au₄ attains a value of 379 mAh·g⁻¹, with a corresponding specific energy of 714 Wh·kg⁻¹. In contrast, the discharge specific capacity and specific energy of FeS₂ are lower, amounting to 348 mAh·g⁻¹ and 656 Wh·kg⁻¹, respectively. This study offers a novel approach to enhancing the electrochemical performance of FeS₂ in high-temperature molten salt electrochemical systems (thermal batteries), thereby laying a solid foundation for its potential practical application.

Graphic abstract