Characterization on thermal runaway of commercial 18650 lithium-ion batteries used in electric vehicles: A review

A review summarizes and characterizes the calorimetric results of commercial 18650 lithium-ion batteries under thermal runaway. The cathode materials of 18650 batteries include LiCoO2, LiMn2O4, LiNixMnyCozO2, LiNi0.8Co0.15Al0.05O2, and LiFePO4. Characterization data obtained from calorimetry encompass the exothermic onset temperature, crucial temperature, maximum temperature, maximum self-heat rate, quantity of non-condensable gas, and enthalpy change. Maximum pressure and pressure-rising rate are not taken account of consideration because of the significant dependence on volume of the test system. A hexagonal radar plot is newly proposed for the presentation of runaway hazards aforementioned and associated with respective cathode chemistries. By integrating all the hazard data in the literature into hexagonal plots, the ranking of the hazard potential of commercial 18650 batteries is clearly assessed as follows: LiNi0.8Co0.15Al0.05O2 > LiCoO2 > LiNixMnyCozO2 > LiMn2O4 >> LiFePO4. The LiNi0.8Co0.15Al0.05O2 battery displays the worst case scenario among all the 18650 batteries owing to these highest maximum temperature, maximum self-heat rate, maximum pressure, quantity of non-condensable gas, and enthalpy change under thermal runaway. Differential characteristics of thermal runaway among LiCoO2, LiNixMnyCozO2, and LiNi0.8Co0.15Al0.05O2 batteries are discriminated and discussed. All the non-LiFePO4 batteries act similarly with a maximum self-heat rate exceeding 10000°C min−1 and a crucial temperature occurring at approximately 200°C. The 18650 LiFePO4 battery holds the highest exothermic onset temperature, lowest maximum temperature, lowest maximum self-heat rate, least non-condensable gases and lowest enthalpy change, indicating that the 18650 LiFePO4 battery is relatively safer than others. On the state of the art, a review is detailed herein and future perspectives are propounded as well. This integrated review of 18650 batteries under thermal failures provides a systematic database for extensive experimental investigations, theoretical studies and designs of safer batteries.