Influence of cathode chemistry and state of charge on flammability and explosion parameters of lithium-ion battery vent gas

The growing demand for energy storage systems highlights the need for safe and efficient lithium-ion batteries. A major safety concern is thermal runaway, which leads to the release of flammable battery vent gases (BVGs). This study systematically investigates the flammability characteristics of BVGs from LIBs with different cathode materials and state of charge levels through numerical simulations. Key combustion properties, including laminar flame speed, radical production and ignition delay time were evaluated under varying temperatures and equivalence ratios. Sensitivity analyses were also conducted to gain deeper insight into the roles of radical interactions in the combustion behaviours. Simulations were performed using CHEMKIN's Sandia PREMIX module for 1-D freely propagating flames and 0-D closed batch reactors using the San Diego mechanism. Results show that cathode chemistry significantly affects BVG flammability. NCA and NCM90505 produce vent gases with high H2 and CO content, leading to higher Su (65–70 cm/s) and shorter IDT. In contrast, NCM811 and NCM622 generate fewer flammable gases with lower Su (35–45 cm/s) and longer IDT due to their higher concentrations of CO2, CH4, and C2H4. LFP, despite its high H2 production, exhibits a balanced combustion profile. Laminar flame speed data for all BVG compositions are well described by a simple power-law correlation. SOC levels also strongly influence flammability. For SOC above 50 %, Su, IDT, and radical production remain relatively stable, as vent gas composition changes minimally impact combustion properties. However, below 50 % SOC, Su decreases, IDT increases, and radical production declines, with the strongest suppression at 0 % SOC. This effect is primarily due to the higher CO2 concentration, which acts as a thermal sink, absorbing heat and slowing flame propagation rather than affecting combustion kinetics.