Thermal characteristics of LiMn_xFe_1-xPO₄ (x = 0, 0.6) cathode materials for safe lithium-ion batteries

Lithium-ion batteries have recently gained attention as energy storage devices due to their high energy densities and various applications. Layered Ni-Mn-Co-based cathode materials are widely used for their high energy density; however, their high cost necessitates the exploration of alternatives. Consequently, olivine-type LiMn_xFe_1-xPO₄ materials are gaining popularity and are being increasingly adopted. While the synthesis methods and electrochemical properties of these materials have been extensively studied, thermal analyses remain limited. In this study, we investigated the thermal properties of olivine-type LiMn_xFe_1-xPO₄ by combining thermal analysis, structural analysis, and computational calculations to evaluate the safety of lithium-ion batteries. Our results show that the formation energy of LiMn_0.6Fe_0.4PO₄ is more stable than that of LiFePO₄. As temperature increases, LiFePO₄ decomposes at 350 °C, whereas LiMn_0.6Fe_0.4PO₄ begins to decompose at 450 °C. The P-O bond plays a crucial role in the thermal stability of these materials; as the temperature rises, the thermal stability of the PO₄ group diminishes, leading to structural decomposition. To enhance thermal stability, it is recommended to experiment with doping small amounts of various elements at the P site. This paper provides valuable insights for the design and development of thermally stable olivine-structured cathodes for lithium-ion batteries.