Comparison on Thermal Runaway and Critical Characteristics of Cylindrical Lithium-Ion Batteries: A Review

The thermal hazard results of commercial cylindrical lithium-ion batteries (LIBs) of different sizes from international laboratories are reviewed and discussed. The four types discussed encompass 14500, 18650, 21700, and 26650 ones. Characteristic data from the calorimeter include onset temperature, critical temperature, maximum temperature, maximum self-heat rate, enthalpy change, and quantity of noncondensable gases. By integrating thermal hazard data, a box-plot was established and hazard ranking was clearly evaluated as 21700 > 18650 non-LiFePO₄ (LFP) ≫ 26650 LFP > 14500 non-LFP > 18650 LFP > 14500 LFP. Among all types of cylindrical lithium-ion batteries, the 21700 exhibits the worst consequence, which is attributed to the adoption of high energy density LiNi_0.8Co_0.15Al_0.05O₂ (NCA) and LiNi_xMn_yCo_zO₂ (NMC) cathode materials. It was found that the critical temperature T_cr and maximum temperature broadly scattered; besides, most of the maximum self-heat rate (dT/dt) and pressure data were absent in literature. Definitions of onset temperature, critical temperature, trigger temperature, and possible heat sources to stimulate the severe thermal runaway were collected and found to be unimaginably divergent. A thermal analysis database was established to classify critical temperatures into high T_cr (above 180 °C), low T_cr (130–180 °C), and no T_cr. The low T_cr inducement is speculated to be caused by gas shock or electron breakdown after the separator melted, while the intrinsic characteristics of T_cr require further investigation. Thermal runaway features of cylindrical LIBs can be concisely classified as lowest T_onset of 88.0 °C (21700 NMC) vs highest T_onset of 220.0 °C (18650 LFP), highest (dT/dt)_max of 64536.0 °C min^–1 (21700 NCA) vs lowest (dT/dt)_max of 3.0 °C min^–1 (18650 LFP), highest T_max of 1257.9 °C (21700 NCA) vs lowest T_max of 243.2 °C (18650 LFP), highest Δn of 314.0 mmol (18650 NCA) vs lowest Δn of 23.3 mmol (14500 LFP), lowest T_cr of 145.5 °C (21700 NCA) vs (no T_cr) (14500 and 18650 LFP), and highest ΔH of 70.5 kJ (21700 NCA) vs lowest ΔH of 0.8 kJ (14500 LFP). In this work, the present research is reviewed in detail and future perspectives are proposed. This review on the critical characteristics of cylindrical batteries under thermal failure and thermal abuse provides a reference for solving intrinsic safety issues for lithium-ion batteries of the next generation.