Thermal Runaway Induced Casing Rupture: Formation Mechanism and Effect on Propagation in Cylindrical Lithium Ion Battery Module

Abstract

With the wide-ranging and ever-increasing applications of lithium-ion batteries in electric vehicles (EV), thermal runaway (TR)-induced safety issues, such as fires and explosions, are raising more and more concerns. In this work, cylindrical 21700 batteries were externally heated to conduct the TR experiment, and the casing rupture in the form of melting holes and tearing cracks was found to be one of the key factors that caused cell-to-cell TR propagation. The appearance and the cross-section microstructure of the ruptured casing showed that the melting hole is formed because of a large current short circuit and the tearing crack is due to a decrease in the mechanical strength at high temperatures. Experimental simulations were conducted to further demonstrate the casing rupture mechanism. In addition, new designs with increased casing thickness were implemented to inhibit the occurrence of casing rupture, and their effectiveness was analyzed by performing numerous TR experiments. The improved casing was used in a commercial battery pack, and no TR propagation occurred during operation. Thus, in this study, the casing rupture mechanism was first elucidated, and guidance for the design of lithium-ion batteries with improved safety was provided.

Extensive Experimental Thermal Runaway and Thermal Propagation Characterization of Large-Format Tabless Cylindrical Lithium-Ion Cells with Aluminum Housing and Laser Welded Endcaps

“…39 This introduces the additional risk of simply melting away the aluminum around the nail insertion area rather than bursting the housing due to internal overpressure. This failure mechanism was already reported by Lao et al 17 when investigating 21 700 steel cells. They concluded this was caused by extreme heat from short circuits between the housing and the jelly roll.…”

“…14 This increases the risk of side ruptures which are considered among the worst-case failure scenarios. [15][16][17] If a side rupture occurs, the cell behaves totally unpredictable and releases venting gas and solid ejecta in an uncontrolled way. These complex failure scenarios are impossible to predict with mathematical models and extensive experimental investigation is crucial to understand the resilience of large-format cells with aluminum housing against side ruptures.…”

Advances in Prevention of Thermal Runaway in Lithium‐Ion Batteries

“…It is also important to note that extreme events such as cell rupture and short circuit may cause a release of energy beyond which the cooling system can mitigate. [45] Therefore, it is crucial to constantly monitor the state of health of the cells in the battery pack using a BMS. This is discussed in the following section.…”

Analysis of the Thermal Behavior of a Lithium Cell Undergoing Thermal Runaway

“…(3) the polarization internal resistance caused by the electrochemical reaction of the electrode; (4) the concentrated polarization internal resistance caused by the lithium ion transport process [14]. Thus, the heat generated mainly consists of four parts: chemical reaction heat Q f , ohmic internal resistance heat Q n , polarization heat Q p and side reaction heat Q s .…”