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Cross-section microstructures of the (a) the melting hole and (b) tearing crack samples in simulative experiments.
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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...
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Owing to increasing applications of lithium-ion batteries (LIBs), it is worth investigating the thermal runaway (TR) behaviors of LIBs under extreme conditions such as flash freezing, which has been proposed as a feasible way for LIB transportation or storage. In this study, a series of experiments was conducted to explore and compare the TR behavi...
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In this paper, tests and analysis of thermal runaway propagation for commercial modules consisting of four 41 Ah Li-ion pouch cells are presented. Module samples were tested at 100% state-of-charge and mechanically constrained between two steel plates to provide thermal and mechanical contact between the parts. Voltage and temperature of each cell...
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... For safety considerations, aluminum has low tensile strength, especially at elevated temperatures [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. ...
... 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 21700 steel cells. They concluded this was caused by extreme heat from short circuits 4 A c c e p t e d M a n u s c r i p t ...
Large-format tabless cylindrical lithium-ion cells are expected to enhance performance and reduce cost of next generation vehicles. However, he influence of innovative new tab designs, increased dimensions, and new housing materials are still unexplored and must be revealed to unlock safe future battery systems. Here, the thermal runaway and thermal propagation characteristics of sophisticated state-of-the-art large-format tabless cylindrical cells with aluminum housing and laser welded endcaps are extensively characterized. Multiple abuse test setups on cell and battery level are custom designed close to the true boundary conditions in real world applications. Results show cells with aluminum housing require careful choice of trigger methods as the low melting point and lesser mechanical strength compared to conventional nickel-plated steel housings introduce additional challenges. The tabless design was found to act as a strong mechanical connection that prevents shifting of the electrode assembly. Instead, axial ruptures of the jellyroll may occur. The leftover high density material conglomeration that is in tight contact with the inner housing wall transfers heat into the surroundings and is critical for thermal propagation safety. Strong interstitial potting compound with low thermal conductivity successfully prevented any major convective heat transfer into the neighboring cells by venting
... Abuse testing, followed by various post-mortem investigations has shown that some TR events can cause a sidewall breach where the flare of hot abrasive materials stems from the casing of the cell, but the cause remains unclear [2,5,6,9,10]. It has previously been elaborated by Finegan et al. that unsuccessful gas release due to material blocking the vent is more likely to lead to a sidewall rupture [6]. ...
... It has previously been elaborated by Finegan et al. that unsuccessful gas release due to material blocking the vent is more likely to lead to a sidewall rupture [6]. Further on, a higher casing temperature, leads to sidewall weakening and has been demonstrated by Lao et al. to impact the likelihood of sidewall breaching [10]. In a recent study by Chen et al., the relationship between state of charge (SoC) and sidewall breaches was investigated, showing that breaches occurs at SoC even below 30 % [2]. ...
With the rapid deployment of Li-ion batteries (LiBs) in a range of applications, it is crucial to ensure their safe operation. Therefore, it is necessary to investigate the rapid thermal runaway failure that LiBs can undergo if improperly operated or subjected to abuse scenarios so that hazardous events can be avoided or mitigated. Sidewall breaches or ruptures of LiBs during thermal runaway are considered the most hazardous failure scenario, resulting in hot abrasive flare from the casing of the cell that can impinge on neighbouring cells and lead to the propagation of thermal runaway throughout a battery pack. Yet, the process leading up to the sidewall breach is not well understood due to the extreme difficulty in visualizing such a failure in commercially relevant cells. With the application of a newly developed chamber for remote-controlled abuse testing of batteries coupled with simultaneous X-ray imaging, we demonstrate here for the first time an in-situ visualization of a sidewall breach. By further applying spatiotemporal mapping techniques, the internal thermal runaway events leading up to the sidewall breach can be analyzed in detail. Subsequently, the speed of the electrode layer delamination could be calculated to a speed of 0.6 m/s. These new insights bring more clarity regarding this phenomenon, that in turn can help battery designers improve battery safety.
... Eq. (10) yields 3.75 mm core diameter for 21700 cells and 5.0 mm core diameter for 46xxx cells. Diameters of the hollow cores for commercial 18650 and 21700 cells range from 3.0 mm to 4.65 mm [26,27]. ...
... Their research has shown that for 0.22 mm wall thickness the cells repeatedly experienced side-wall breaches during abuse testing. After increasing the wall thickness to 0.30 mm no more side-wall breaches were observed within a large sample size of 100 cells [27]. This leaves the assumption that the minimum wall thickness for 21xxx cells ranges between the investigated values. ...
... Based on our testing results 0.25 mm wall thickness for cells with 21 mm diameter and steel housing and 0.425 mm for aluminum housings were identified as reasonable values, which lays well within the middle of the values reported by Lao et al. [27]. For the assumption of constant burst pressure the wall thickness t wall is therefore calculated as ...
... Typical forms of energy release during thermal runaway of LIBs are as follows: venting/jetting, fire and explosion [23]. When thermal runaway occurs, a series of chemical reactions will be triggered and produce a large amount of gases [24]. Then the internal pressure of the battery rises sharply until the gases were released when the battery case or relief valve cannot withstand the high pressure, which is called venting/jetting [25]. ...
... 2,3 Energy released from a cell TR may damage adjacent cells or even cause the adjacent cells to TR, known as TR propagation. [4][5][6][7][8][9][10][11][12][13][14][15] Many kinds of battery abuse conditions, categorised as electrical, mechanical, thermal, and environmental can lead to cell TR. 16 The outcome of cell TR ranges from the release of toxic and non-toxic gases, smoke, spark, fire, rupture or explosion. ...
... Once one or more cells have sidewall rupture, sparks, hot gases, and flames coming out from the opening of the cell side can promote cascading failure of adjacent cells. 8,12,13 To prevent rupture or explosion, the vent disk is designed to relieve internal pressure caused by generated gases inside the cell when reaching its critical pressure. 8,17 However, the vent disk is sometimes partly or completely blocked by the electrode assembly or not activated due to malfunction even when the internal pressure has exceeded its critical pressure. ...
... 8,12,13 To prevent rupture or explosion, the vent disk is designed to relieve internal pressure caused by generated gases inside the cell when reaching its critical pressure. 8,17 However, the vent disk is sometimes partly or completely blocked by the electrode assembly or not activated due to malfunction even when the internal pressure has exceeded its critical pressure. 17,18 The sidewall rupture behaviour of LIBs under abuse conditions has been reported recently. ...
To understand the relationship of the sidewall rupture at different state of charge (SOC) of cylindrical cells with high specific energy, this work presents the results of radial nail penetration tests of 21700 cylindrical cells at different SOC. The thermal runaway and sidewall rupture behaviours were characterised by key performance indicators such as temperature, mass, fire behaviour, and voltage change. In addition, released gases from a subset of tests were measured using the Fourier transform infrared spectroscopy. The change in the internal structure of another subset of cells after the test was observed by X-ray computed tomography. The results show that the sidewall rupture still exists for tests at low SOC (< 30% SOC), but the outcome of thermal runaway and sidewall rupture is milder than those at high SOC (≥ 50% SOC). The average mass loss of cells increases with the increment of SOC. The cell casing thickness is reduced by 12.7% ± 0.3% of the fresh cell, which in combination with the reduction in the strength of the casing material at high temperatures could contribute to sidewall rupture
... The increased cell size leads to larger capacity and energy density in comparison with the 18650 format [3] . However, relatively few studies have addressed the thermal behavior of 21700 cells [4][5][6][7] . [13][14][15][16][17][18] and patch elements [19][20][21] . ...
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.
... The test has been conducted by heating a cell in module 3 (Fig. 10c) to trigger TR to observe whether the TR propagation would occur in the module or block [33]. The test result shows that except for TR of the triggering cell (No. 1 cell in Fig. 11a), no TR propagation occurs in the adjacent six cells (Nos. 2 to 7 cells in Fig. 11a). ...
We design and fabricate a novel lithium-ion battery system based on direct contact liquid cooling to fulfill the application requirement for the high-safety and long-range of electric vehicles. By the immersion in the flowing silicone oil to achieve the highly efficient heat exchange, the NCM811 cells can be grouped without gap, and thereby the battery system achieves maximum volume efficiency. The mass and volume integration ratio of the battery system are 91% and 72%, respectively, which are 1.1 and 1.5 times that of the tube-based indirect liquid contact cooling system, respectively. Specifically, the temperature increment of the cells during 1C discharge does not exceed 13 ℃, and the dynamic temperature difference is less than 8.8 ℃. The results from simulation show that the maximum temperature rise and maximum temperature difference of the direct contact liquid cooling system are only 20%–30% of the indirect contact liquid cooling system. Particularly, the system can effectively prevent the thermal runaway propagation without any additional measures, owing to the high heat dissipation rate and oxygen isolation. The research has led to the successful construction of an oil-immersed battery system with high integration ratio and excellent safety, which provides a feasible solution for the demand of the high safety and high specific energy of the electric vehicle battery system.
... 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. ...
The prevention of thermal runaway in lithium‐ion batteries is vital as the technology is pushed to its limit of power and energy delivery in applications such as electric vehicles. Thermal runaway and the resulting fire and explosion have been responsible for several high‐profile accidents and product recalls over the past decade. This review paper describes the causes of thermal runaway and examines novel preventative methods, approaching the problem from different angles by altering the internal structure of the battery to undergo thermal shutdown, or by developing the battery and thermal management systems so that they can detect and prevent thermal runaway. Ultimately, a variety of different technologies will be needed to address the emerging market of highly‐specialised lithium‐ion batteries. Key innovations discussed include positive temperature coefficient (PTC) materials, self‐healing polymer electrolytes, and hybrid liquid‐solid state electrolytes. Mist cooling could achieve a highly uniform temperature inside the battery pack without the need for pumps to circulate a coolant. The development of battery management systems which can model the internal temperature of the cell from real‐time data and prevent the cell reaching a critical temperature are an essential area for further research.
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... (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 . ...
This study examines the thermal runaway of a lithium ion battery caused by poor heat dissipation performances. The heat transfer process is analyzed on the basis of standard theoretical concepts. Water mist additives are considered as a tool to suppress the thermal runaway process. The ensuing behaviour of the battery in terms of surface temperature and heat generation is analyzed for different charge and discharge rates. It is found that when the remaining charge is 100%, the heat generation rate of the battery is the lowest, and the surface temperature with a 2C charge rate is higher than that obtained for a 0.5C charge rate. The experimental results show that when the additive concentration is 20% NaCl, its ability to inhibit the thermal runaway is the strongest.
... Typical forms of energy release during thermal runaway of LIBs are as follows: venting/jetting, fire and explosion [23]. When thermal runaway occurs, a series of chemical reactions will be triggered and produce a large amount of gases [24]. Then the internal pressure of the battery rises sharply until the gases were released when the battery case or relief valve cannot withstand the high pressure, which is called venting/jetting [25]. ...
