Multi-dimensional signal evolution and heat transfer for thermal runaway propagation of large-capacity lithium-ion battery under overheating

• Multi-dimensional signal evolution during TRP of 314 Ah LFP batteries is studied. • Higher heating power significantly shortens the onset time of TR • Lower power leads to more uniform heating and nearly simultaneous core TR. • Heating power mainly affects TR onset timing rather than maximum TR severity. Existing studies have mostly focused on thermal runaway (TR) of lithium iron phosphate (LFP) batteries under various abuse conditions such as overheating, overcharge, and puncturing, with insufficient attention on thermal runaway propagation (TRP) mechanism. To address this, this study has conducted experiments on TRP of 314 Ah LFP batteries under various heating powers (400, 600, 800, 1000 W), acquiring and analyzing parameters including temperature, voltage, heat transfer, gas production, mass loss, and expansion force. As revealed, the heating power significantly affects the occurrence and propagation of TR. Higher power leads to shorter TR onset time, faster TR rate, and more rapid voltage drop. Meanwhile, TRP speed decreases with the increasing of power. Heat from Battery 1# to 2# rises with heating power, yet low-power settings (e.g., 400 W) enable Battery 2# to pre-accumulate heat and lower its TR trigger threshold. In addition, lower power causes more uniform heating and nearly simultaneous TR of cores, leading to higher H 2 and CO yields. Heating power mainly impacts TR onset time rather than severity, as mass loss and expansion force peaks remain basically consistent, indicating the stable reaction intensity once TR initiates. This study clarifies the TRP mechanism of large-capacity LFP batteries under overheating, linking heating power to key TR characteristics. The obtained results will deepen the understanding towards TRP mechanism of large-capacity LFP batteries and support the design of fire prevention and emergency disposal for energy storage system.