Heterostructure and carbon modification regulate FeF3/molten salt electrolyte interface in high-specific-energy thermal batteries

Abstract

FeF₃ is an ideal cathode material for high-specific-energy thermal batteries, but its low conductivity and severe dissolution reactions with molten salt causes active material loss, interfacial passivation, and increased resistance, degrading discharge performance. To address these challenges, this study proposes the in situ construction of FeF₂ on the FeF₃ surface to form the FeF₃/FeF₂ heterostructure, enhancing the conductivity and mitigating dissolution. And the conductive rGO and CNTs are introduced to further improve conductivity, regulate interfacial behavior, and suppress dissolution reactions, and reduce active material loss and passivation layer formation, thereby enhancing discharge performance. The FeF₃/FeF₂@CNTs cathodes achieve high specific capacity with 343.44 mAh g⁻¹ at 0.1 A cm⁻² and 566.68 mAh g⁻¹ at 0.05 A cm⁻², outperforming FeF₃/FeF₂@rGO cathodes with stronger suppression of dissolution by 27.5 % and 48.3 %, respectively. Pulse resistance testing and interfacial analysis reveal that rGO coating reduces cathode/electrolyte interfacial wettability, causing interface separation, increased resistance, and voltage decline. Thus, this study highlights the importance of not only improving conductivity but also regulating interfacial wettability, dissolution, and charge transfer coupling to enhance discharge performance of thermal batteries, offering a novel design strategy for high-specific-energy thermal batteries.