Cell-level hazard evaluation of 18650 form-factor Lithium-ion battery with different cathode materials

The thermal runaway process was studied in a Fire Propagation Apparatus (FPA) for three types of Lithium-ion batteries (LIB) of 18650 form-factor. Cathode materials are lithium cobalt oxide (LiCoO2, or LCO), lithium nickel manganese cobalt oxide (LiNi1/3Mn1/3Co1/3O2, or NMC), and lithium iron phosphate (LiFePO4, or LFP). All batteries have a graphite anode and were at a 100% state-of-charge. Each LIB was externally heated to a thermal runaway event, with the heat input at constant values of 20.4 or 34.1 W, which yielded heating rates on the order of 1 K/s, representative of the thermal runaway propagation process. The mass loss fraction before the thermal runaway events and the maximum values are similar under different heat inputs for a given type of LIB. For different types of LIBs, the maximum mass loss fraction shows the trend of LCO>NMC>LFP. Under the same heating condition, NMC has the highest maximum surface temperature followed by LCO then LFP. A lumped heat transfer thermal runaway model is developed using two decomposition reactions and one internal short circuit reaction to model the internal heat generation. The effective model parameters are optimized using the measured surface temperature and mass loss fraction. The model is able to simulate the thermal runaway behavior of LIB under external heating conditions and reasonably matches the experimental data of LIBs with different cathodes. The model predicts that under the same heat input condition, the thermal runaway time of LCO is shorter than NMC and LFP; the effective average internal heat generations are 22.6, 20.2, and 11.5 kJ for LCO, NMC, and LFP, respectively. The thermal runaway model will be used to predict the thermal runaway propagation in a LIB module.