Thermal runaway of a lithium ion cell occurs when the heat-output of the cell is greater than the heat loss. The heat output of a cell’s decomposition can be measured using an adiabatic calorimeter as long as the sample sizes are on the order of a 26650 cell or smaller.
In this example we have three 18650 cells with different chemistries and different SOC. It is clear that the LiFePO4 cells show smaller reactions starting at higher temperatures. However the initial voltage and the total charge also play a role in the decomposition and these can be tested independently.