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.