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Thermal batteries are reserve batteries with molten salts as an electrolyte, which activates at high temperature. Due to their excellent reliability, long shelf life, and mechanical robustness, thermal batteries are used in military applications. A high-performance cathode for thermal batteries should be considered in terms of its high capacity, high voltage, and high thermal stability. Research progress on cathode materials from the recent decade is reviewed in this article. The major directions of research were surface modification, compounding of existing materials, fabrication of thin film cathode, and development of new materials. In order to develop a high-performance cathode, a proper combination of these research directions is required while considering mass production and cost.

FeS 2 -MWCNTs (Multi-Walled Carbon NanoTubes) composite without using an organic binder was used as a thin cathode for thermal batteries. A thin cathode with FeS 2 -MWCNTs composite exhibited good mechanical strength without an organic binder. A discharge evaluation of the thin cathode with FeS 2 -MWCNTs composite revealed a discharge capacity 2.3 times that of the pellet type cathode and 1.13 times that of a thin cathode with an organic binder. In addition, the single battery applying a thin cathode with FeS 2 -MWCNTs composite showed a lower total polarization than when applying an organic binder. These results showed that FeS 2 -MWCNTs composite is suitable as a thin cathode for thermal batteries. K E Y W O R D SFeS 2 -MWCNTs composite, organic binder-free, tape casting, thermal battery, thin cathode

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The polymer binder, poly(imide-co-siloxane) (PIS), was synthesized and applied to form a thin cathode layer of composites for a thermal battery that has an unusually high operating temperature of 450 °C. The PIS was prepared through cross-linking of the polyimide with polysiloxane. The morphology of FeS2/PIS composites showed that FeS2 particles was coated with the PIS cross-linked gel. The FeS2/PIS composites enabled to fabricate mechanically stable thin cathode layer that was 10–20% of the thickness of a conventional pellet-type cathode. The FeS2/PIS composites were stable up to 400 °C and maintained their morphology at this temperature. PIS coating layers decomposed at 450 °C, and a new residue was generated, which was observed by transmission electron microscopy, and the compositional change was analyzed. The FeS2/PIS composites showed enhanced thermal stability over that of FeS2 in thermogravimetric analysis. The thermal battery with the PIS polymer binder showed a 20% discharge capacity increase when compared to a conventional pellet-type cathode.

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In this study, we fabricated a cathode with lower amounts of additive materials and higher amounts of active materials than those of a conventional cathode. A thermal battery was fabricated using FeS 2 treated foam as the cathode frame, and its feasibility was verified. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy were used to analyze the effects of thermal sulfidation temperature (400 and 500 • C) on the structure and surface morphology of the FeS 2 foam. The optimal temperature for the fabrication of the FeS x treated foam was determined to be 500 • C. The FeS 2 treated foam reduced the interfacial resistance and improved the mechanical strength of the cathode. The discharge capacity of the thermal battery using the FeS 2 treated foam was about 1.3 times higher than that of a thermal battery using pure Fe metal foam.