Thermal Runaway Characteristics of LMFP Hybrid Batteries at Different State of Charge

Lithium-ion batteries (LIBs) have drawn substantial scientific interest because of their impressive energy storage capabilities and long-term operational stability. In recent years, new battery material systems have emerged, among which LMFP (LiMn_xFe_1−xPO₄) is regarded as a promising candidate for future battery development, combining high energy density with enhanced safety. However, research on the thermal runaway (TR) behavior of LMFP-based batteries remains scarce, leaving their cell-level safety unverified. This study modifies the conventional state of charge (SOC) classification method by measuring the oxidation state of cathode materials at specific voltages. By testing the thermal runaway (TR) temperature and gas release characteristics of LMFP hybrid batteries under different voltage states, it reveals the influence of cathode oxidation state on TR behavior. The results demonstrate that when the NCM (LiNi₀.₅Co₀.₂Mn₀.₃O₂) component remains unoxidized, the battery does not undergo complete TR. The self-heating temperature (T₁) increases as the voltage decreases. However, comparative analysis of 3.9 V and 4.2 V batteries indicates that the oxidation state of NCM has the most significant impact on peak TR temperature. Furthermore, the severity of TR weakens with decreasing voltage, whereas the explosion hazard from vented gases intensifies, peaking at 3.5 V. This work fills a critical research gap in understanding the cell-level TR behavior of LMFP-based batteries, providing a theoretical foundation for their further optimization.