The thermal-gas coupling mechanism of lithium iron phosphate batteries during thermal runaway

Lithium iron phosphate batteries, renowned for their safety, low cost, and long lifespan, are widely used in large energy storage stations. However, recent studies indicate that their thermal runaway gases can cause severe accidents. Current research hasn't fully elucidated the thermal-gas coupling mechanism during thermal runaway. Our study explores the battery's thermal runaway characteristics and material reaction mechanisms, linking the battery to its constituent materials. Results show that a 23 Ah commercial battery has a low T3 of 607 °C. Hydrogen comprises 36.34 % of the gases released. The cathode exhibits exothermic peaks only near 540 °C and 740 °C, suggesting a reaction gap, a key factor in the low T3. The high hydrogen content is due to the cathode's stability, preventing oxygen release, leading to increased anode-HF reactions and hydrogen generation. This study offers guidance for the intrinsic safety design of lithium iron phosphate batteries, and isolating the reactions between the anode and HF, as well as between LiPF6 and H2O, can effectively reduce the flammability of gases generated during thermal runaway, representing a promising direction. •FePO4 has two exothermic peaks at 530 °C and 740 °C.•The presence of reaction gap reduces the peak temperature of thermal runaway.•Combustible gas results from anode-electrolyte reaction.•Stable cathode facilitates thorough anode-electrolyte reaction.