State of charge-capacity-pressure coupled effects on combustion characteristics and suppression of thermal runaway gases in lithium iron phosphate batteries

Against the backdrop of global energy transition and rapid development of energy storage systems, thermal safety and combustion-explosion risks of Lithium iron phosphate (LFP) batteries in confined high-pressure environments have become key bottlenecks; however, gas-generation combustion kinetics and suppression mechanisms under coupled state of charge (SOC), capacity, and pressure remain unclear. In this study, prismatic LFP batteries with varying SOCs (50%, 75%, 100%) and capacities (25, 52, 100 Ah) were tested under 1 and 2 atm conditions. Thermal runaway (TR) gases were analyzed by GC–MS. Four electrolyte systems with 25% and 50% fractions (EC:DMC:EMC = 1:1:1, EC:DMC:3:7, EC:DMC:1:1, EC:EMC:DEC = 3:5:2) and suppressants (TMP, DMMP, water vapor) were investigated. Combustion kinetics were simulated using CHEMKIN-Pro. Results show that lower SOC reduces peak temperature and delays TR, while higher capacity and pressure increase gas generation, pressure accumulation, and H₂ formation, intensifying thermal runaway risk. Combustion behavior is primarily governed by H₂ content and jointly influenced by pressure and capacity. High-SOC small cells (25 Ah, 100% SOC) exhibit the highest H₂ fraction, flame speed, and temperature (64.7%, 129.75 cm/s, 2386.68 K). LFS increases with H₂ content but decreases significantly with pressure. Elevated pressure suppresses flame propagation and heat release while shifting the risk from instantaneous deflagration to delayed accumulation. Electrolyte vapor dilution reduces combustion intensity, while composition sensitivity becomes more significant under high-capacity and high-pressure conditions. At 50% fraction, EC:EMC:DEC = 3:5:2 shows the highest hazard, with NHG difference reaching 32.62 (100 Ah, 2 atm). At 25% fraction, EC:DMC = 1:1 is most hazardous under 25 Ah and 100% SOC conditions. Under this condition, TMP and DMMP strongly suppress combustion through O/OH radical scavenging, significantly outperforming water vapor, with TMP showing slightly higher inhibition efficiency. These findings provide useful guidance for combustion suppression and battery safety design in confined high-pressure environments.