Efficient synthesis of FeVO4 cathode materials in high specific energy thermal batteries

Abstract

Thermal batteries, which are essential for applications in extreme environments, require cathode materials with high specific energy and thermal stability. In this study, metal vanadates were synthesized via a chemical precipitation method followed by high-temperature sintering, offering a promising alternative for conventional transition metal sulfides. The synthesized FeVO₄ exhibits phase purity, while copper and nickel vanadates show secondary phases, indicating challenges in achieving pure-phase synthesis of metal vanadates. Electrochemical evaluations reveal that FeVO₄ cathode delivers an initial discharge voltage of 2.65 V and a specific capacity of 190 mAh/g. Whereas the FeVO₄/CNTs composite cathode demonstrates an enhanced specific capacity of 253.66 mAh/g, which is attributed to prolonged discharge plateaus. Phase evolution studies indicated that FeVO₄ reacts with molten salts during high-temperature discharge, leading to the formation of Fe₂O₃ and Li_0.3V₂O₅, which contribute to the observed stepwise discharge behavior. These results emphasize the importance of optimizing the interactions between cathode materials and molten salts to improve the performance of high-temperature thermal batteries.