From Thermal Runaway to Fire Hazard: A Multi-parameter Evaluation of State of Charge Effects in 280 Ah Lithium Iron Phosphate Battery

Abstract

Safety concerns surrounding thermal runaway (TR) pose a significant challenge to the large-scale deployment of lithium-ion batteries (LIBs) in energy storage systems. Although lithium iron phosphate (LFP) batteries exhibit relatively high intrinsic safety, they can still present fire risks when used in large-scale, highly integrated energy storage applications. This study systematically investigates the TR behavior and multi-parameter evolution of large capacity LFP batteries at different states of charge (SOCs) under external heating abuse and post-ignition conditions in a standard combustion test platform. Experimental results show that both TR kinetics and thermodynamic characteristics strongly depend on SOC. High-SOC cells show the most rapid internal TR propagation rate of approximately 0.841 mm·s⁻¹ and exhibit a peak heat-release rate exceeding 90 kW after ignition. In contrast, low-SOC cells display the highest apparent pressure-rise-rate indicator upon safety vent activation, reaching 3585 Pa·s⁻¹. Additionally, estimation of cell normalized HRR relative to common fuels demonstrates that LFP batteries can still exhibit significant fire hazards. A TR multi-parameter comparative visualization framework, developed using radar-chart visualization and key TR characteristic parameters, further indicates that lowering SOC effectively mitigates overall TR hazards. This work elucidates the relationships among TR behavior, fire hazards, and SOC in LFP batteries, and the proposed multi-parameter visualization framework offers a basis for enhancing the safety design and practical deployment of energy storage systems.