Abstract: Prior studies on lithium-ion battery thermal runaway often examine the gas generation characteristics under specific chemistries or single conditions, systematic sorting and in-depth exploration of the complex structure-activity relationship between the inherent characteristics of batteries (such as chemical composition, state of charge SOC) and gas hazards (flammability, toxicity) remains limited. Notably, inconsistent test conditions and methods hinder data standardization. This study integrates systematic analysis and multi-dimensional data to establish a framework for analyzing gas evolution during thermal runaway. Results show that for lithium iron phosphate (LFP) and nickel-manganese-cobalt oxide (NMC) batteries, there are significant differences in the difficulty of triggering thermal runaway and the characteristics of heat release, and the gas hazards are more complex. LFP generates less total gas, yet its mixtures have lower flammability limits and, under certain conditions, higher HF emissions than NMC. These findings underscore the need for safety evaluation from multiple dimensions such as thermodynamics, flammability, and toxicity.

Key words: electric vehicles, lithium-ion batteries, thermal runaway, gas hazards, state of charge