An experimental study on thermal runaway characteristics of lithium-ion batteries with high specific energy and prediction of heat release rate

Understanding the potential thermal hazards of lithium-ion batteries (LIBs) during thermal runaway (TR) is helpful to assess the safety of LIB during storage, transport and use. This paper presents a comprehensive analysis of the thermal runaway (TR) characteristics of type 21700 cylindrical LIBs with a specific energy of 266 W∙h/kg. The batteries with both 30% state of charge (SOC) and 100% SOC were triggered to TR by uniform heating using a flexible heater in a laboratory environment. Three high definition cameras and one high-speed camera were placed to capture TR behavior and flame evolution from different viewpoints. Correlation between the heat release rate (HRR) and the mean flame height of turbulent jet diffusion flame were used to estimate the HRRs of LIBs. Additional characteristics of cell failure (for cells with 100% and 30% SOC) were also noted for comparison, including: number of objects ejected from the cell; sparks and subsequent jet fires. An approach has been developed to estimate the HRRs from TR triggered fires and results compared with previous HRR measurements for type 18650 cylindrical cells with a similar cathode composition

A simplified mathematical model for heating-induced thermal runaway of lithium-ion batteries

The present study aims to develop a simplified mathematical model for the evolution of heating-induced thermal runaway (TR) of lithium-ion batteries (LIBs). This model only requires a minimum number of input parameters, and some of these unknown parameters can be obtained from accelerating rate calorimeter (ARC) tests and previous studies, removing the need for detailed measurements of heat flow of cell components by differential scanning calorimetry. The model was firstly verified by ARC tests for a commercial cylindrical 21700 cell for the prediction of the cell surface temperature evolution with time. It was further validated by uniform heating tests of 21700 cells conducted with flexible and nichrome-wire heaters, respectively. The validated model was finally used to investigate the critical ambient temperature that triggers battery TR. The predicted critical ambient temperature is between 127 °C and 128 °C. The model has been formulated as lumped 0D, axisymmetric 2D and full 3D to suit different heating and geometric arrangements and can be easily extended to predict the TR evolution of other LIBs with different geometric configurations and cathode materials. It can also be easily implemented into other computational fluid dynamics (CFD) code

Combined numerical and experimental studies of 21700 lithium-ion battery thermal runaway induced by different thermal abuse

Combined numerical and experimental studies have been carried out to investigate thermal runaway (TR) of large format 21700 cylindrical lithium-ion battery (LIB) induced by different thermal abuse. Experiments were firstly conducted with the Extend Volume Accelerating Calorimetry (EV-ARC) using both the heat-wait-seek (HWS) protocol and under isothermal conditions. The kinetic parameters were derived from one of the HWS EV-ARC tests and implemented in the in-house modified computational fluid dynamics (CFD) code OpenFOAM. For the subsequent CFD simulations, the cell was treated as a 3-D block with anisotropic thermal conductivities. The model was verified by the remaining two HWS tests not used in the derivation of the kinetic parameters and validated with newly conducted isothermal EV-ARC tests. Further laboratory tests and model validation were also subsequently conducted using Kanthal wire heaters. The validated model was also used to fill the experimental gaps by predicting the onset temperature for TR in simulated EV-ARC environment, heat generation rate due to different abuse reactions, the influence of heating power and heating arrangement as well as the effect of heat dissipation on TR evolution and the implications for battery thermal management. The present study has identified the TR onset temperature of the considered 21700 LIB to be between 131 and 132 °C. The predicted heat generation rate due to the decompositions of SEI and anode were found to follow similar patterns while that from cathode increase sharply near the maximum cell surface temperature, indicating the possibility of delaying TR onset temperature by optimising the cathode material. The time to maximum cell surface temperature decreases rapidly with the increase of the heating power