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An experimental and analytical study of thermal runaway propagation in a large format lithium ion battery module with NCM pouch-cells in parallel

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... 3,4 As shown in Figure 1a, a cell is triggered into TR by exposing to a heater, and the TR starts first in the layer close to the heater and then proceeds to the entire cell. Inside a module, if the thermal management system fails to function properly, the heat can trigger TR in the adjacent cells, resulting in a cell-tocell TR-propagation, 5,6 as sketched in Figure 1b. A module adjacent to the module in TR-propagation may undergo the TR-propagation as well causing module-to-module TR-propagation, as shown in Figure 1c. ...
... heat flow in modules made of prismatic cells and also the occurrence of TR-propagation is determined by the temperature at the front surface of the prismatic cell. Shang et al. 6 investigated the heating-triggered TR-propagation of a 4-NCM-battery module in parallel. They reported that the heat transfer in a module with cells in parallel includes both a thermal path and an electric path. ...
... Several researches investigating the cell-to-cell TR-propagation phenomena reported that the heat conduction and electrical connection are the key elements during cell-to-cell TR-propagation. 5,6,17,[20][21][22][23][24][25][26][27] ...
... Early studies of TR propagation mainly focus on the small format LIB [7][8][9][10]. In recent years, with the rapid development of LIB technology and its wide application in the field of electric vehicles and energy storage, the safety issues from large format LIB TR propagation have attracted more researchers' attention [11][12][13][14][15][16][17][18][19][20][21][22]. ...
... Previous studies have systematically summarized the effect of numerous objective factors on TR propagation behaviors in battery modules or packs, such as the cathode material [17], state of charge (SOC) [12], electrical mode [7,11,14,20], battery shape [7], space environment [23], venting location [8,24], TR trigger cell's location [15], TR trigger method [18,19,22] and the preventive or blocking method [21], etc. In the aspect of cathode materials, it is generally considered that LFP batteries have a lower thermal risk of TR than NCM material systems, due to the reduction of available oxygen produced by the decomposition of the cathode material limits the amount of electrolyte that can be ignited during TR [25]. ...
... As for the SOC, it is easy to understand that a lower SOC of LIB can mitigate the combustion and TR propagation behaviors in modules, due to a lower level [4] of energy storage [12]. Some researchers have also investigated the TR propagation at various electrical connection modes, and the results show that the TR of LIB modules in series spreads faster than in an unconnected mode, and the TR propagation of LIB modules in parallel is the most aggressive condition [7,11,14]. This is due to the series connection between batteries results in additional thermal conduction paths, and the connection in a parallel mode not only provides a new thermal transfer path but also a circuit that allows other batteries to convert electrical energy into joule heat. ...
Article
Currently, the horizontal ceiling structure is widely adopted in large format battery systems. Thus systematically investigating the thermal runaway (TR) propagation behaviors features of large format lithium ion battery modules under different inclined ceilings is of importance for the safety design and protection of battery systems. This work focuses on the experimental phenomenon elucidation and theoretical analysis of the single cell TR and its propagation. Firstly, a single cell test is carried out to investigate the TR behavior features of target battery. Then, four sets of TR propagation tests with different ceiling angles (0°, 10°, 30°, 90°) are performed to explore the effect of inclined ceiling angle on TR propagation. Besides, a set of 0° ceiling angle experiment with fireproof barriers is conducted to study the blocking effect of barriers. Results show that a larger ceiling angle provides a better heat dissipation condition for modules, and the threshold value of ceiling angle at which TR stops propagating is between 10 and 30°. The barriers cannot block the TR propagation but great delay and weaken the propagation process. This study helps to enhance the insight of TR propagation behaviors and provides valuable guidance for the relative researchers and engineers.
... Heat transfer by conduction through tabs in a parallel connected module was found to contribute a significant part of the total heat transfer [15]. Meanwhile, Feng et al [11] and Gao et al [16] proposed examining the influence of discharge/charge on TR propagation behaviors during tests. Batteries that experienced TR acted as loads in the electric circuit, and they were transferred current by the unaffected adjacent batteries, leading to a higher state of charge (SOC) and severer TR hazard. ...
... Hence, fast discharge to a lower SOC can be a potential hazard control strategy [35]. In a parallel connected module, a discharge process occurs during the TR propagation [16], which could decrease the thermal hazard of the latter batteries. Conversely, the TR propagation could be intensified in the initial stage. ...
Article
Water mist (WM) is an efficient cooling control strategy for thermal runaway (TR) propagation in lithium ion battery (LIB) modules, presenting potential for application in real systems. To comprehensively understand the cooling effect, WM is experimentally tested under significantly severe conditions, where LIB modules are connected in parallel and experience intensified TR propagation. Results show that 18650-type LIBs in the parallel connected module experience intensified TR hazard with higher propagation speeds. An extremely small voltage variation is detected during TR propagation, which leads to the negligible charge capacity. The enhanced heat transfer through pole connectors is demonstrated to be the major cause of the intensified TR propagation hazard. Batteries in the parallel connected module present much lower TR onset temperature, leading to a decreased critical control temperature. Once the critical control temperature reaches below 100 °C, the cooling process mainly depends on the sensible heat of water, and thus, the cooling efficiency of the WM is significantly weakened. The control mechanism is interpreted by qualitatively comparing the relationship between the battery heating rate and the WM cooling rate. The decreased critical control temperature and the enhanced heat transfer are identified as the main causes of the poor control effect.
... More seriously, lithium plating brings about the formation of dendrite which may pierce the separator and induce the cell to an internal short circuit ( Kasnatscheew et al., 2017) and catastrophic TR. Many researchers devoting to evaluate and predict the risk of Li plating risk by analyzing voltage plateau signals ( Gao et al., 2019), measuring the cell thickness (Feng et al., 2014), and simulation models ( Parhizi et al., 2017). However, the internal short circuit due to Li plating which can result in serious problems in reliability and safety of LIBs, is difficult to predict, making cell safety design more complex. ...
... Overcharge on cathode caused by high potential of the positive electrode will also seriously affect the safety performance. More lithium ions are extracting from the cathode materials in overcharge, aggravating the instability of cathode material ( Gao et al., 2019), which further reduces TR temperature, resulting in the deterioration of battery stability. Once the cathode materials decompose and release a large amount of oxygen, the heat release rate rises sharply due to the strong reactions between oxygen and electrode materials. ...
Article
Full-text available
As the most widely used energy storage device in consumer electronic and electric vehicle fields, lithium ion battery (LIB) is closely related to our daily lives, on which its safety is of paramount importance. LIB is a typical multidisciplinary product. A tiny single cell is composed of both organic and inorganic materials in multi scale. In addition, its relatively closure property made it difficult to be studied on line, let alone in the battery pack or system level. Safety, often manifested by stability on abuse, including mechanical, electrical, and thermal abuses, is a quite complicated issue of LIB. Safety has to be guaranteed in large scale application. Here, safety issues related to key materials and cell design techniques will be reviewed. Key materials, including cathode, anode, electrolyte, and separator, are the fundamental of the battery. Cell design and fabrication techniques also have significant influence on the cell's electrochemical and safety performances. Here, we will summarize the thermal runaway process in single cell level, and some recent advances on battery materials and cell design.
... And propose that the transfer of electric energy between LIBs in parallel modules when TR occurs. Gao et al. [22] [][][] investigated the TR propagation within a large format pouch LIB modules in parallel and used an equivalent circuit model to the electric current transferred during TR propagation. However, there has been little research on TR propagation in large format LIB modules with different electrical connection. ...
... 15. The equivalent circuit model of the TR propagation of the LIBs in parallel [22]. ...
Article
This paper experimentally investigated the thermal runaway (TR) characteristics of lithium ion batteries (LIBs) with different state of charges (SOC) and its propagation in the large format module with different electrical connection. Some critical parameters of LIBs with different SOCs such as temperature, voltage, mass loss, heat release rate, released gas during TR were analyzed. The results indicated that the TR severity of LIB with 100% is much higher than that of LIB with 50% SOC. The generations of combustible and toxic gases for LIB with 100% SOC are much higher than those of 50% SOC. Based on the experiment results, the modules consisting of four LIBs with 100%SOC were built to investigate the effect of electrical connection on TR propagation characteristics. It was found TR propagates faster in parallel module than in series and unconnected modules, and TR spreads faster in series modules than in unconnected module. Moreover, the average maximum temperature of the module in parallel is about 30 °C higher than that of module in series. A significant time delay of TR propagation time between the last two LIBs in parallel module was observed. Finally, the heat transfer between LIBs was calculated.
... Electrochemical reac- * Corresponding author. tions are dependent on the operating temperature, and thus a significant increase in temperature can cause thermal runaway and possible explosion [9] . Since maintaining the lithium-ion battery operating temperature range within 25 °C to 40 °C and temperature uniformity below 5 °C are critical parameters for safety, longevity and overall performance, an efficient thermal management is highly required for electric vehicles [10] . ...
... The turbulent kinetic energy and eddy viscosity equations are given in Eqs. (9) and (10) , respectively. ...
... Most of the LIBs accidents are caused by thermal runaway (TR), a violent electrochemical reaction inside the battery accompanied by the phenomenon of violent jet fire, gas production and intense heat release. LIBs can easily be triggered to thermal runaway under abuse conditions such as overheating [4][5][6][7][8][9] , mechanical damage [10][11][12][13][14][15][16][17] , overcharging [ 16 , 18 ], etc. In practice, the battery system for EVs and energy storage power station are composed of numerous single LIB, in order to meet the voltage and capacity demands. ...
... Besides, the harmful effects will be increased due to the inhalation of CO 2 . Irritating effects is evaluated by calculating the Fractional Effective Concentration( FEC ) as described in Eq. (8) . F is the critical concentration of each irritant gas that is expected to seriously compromise occupants' tenability, which is provided by Standard [30] . ...
Article
LiNixCoyMnzO2 (NCM) and LiFePO4 (LFP) batteries are the two most widely employed in vehicles and energy storage stations, however, fire accidents related to them occurs frequently. A comparative analysis on the thermal runaway (TR) propagation behavior of NCM and LFP module are conducted in this work. Results indicate that intense jet fire and combustion behavior occurs in the NCM module, only a considerable amount of white smoke is observed in the LFP module. Generally, the duration time (td) of TR and the maximum temperature (Tmax) of the NCM LIB are significantly higher than those of the LFP LIB. Compared with NCM modules, LFP modules are significantly less likely to suffer from TR propagation. Once TR propagation occurs in LFP module, the TR propagation in a single LFP LIB and LFP module is less aggressive and risk than in the NCM LIB and NCM module, respectively. And the TR propagation mechanism of the LFP and NCM modules are comparatively analyzed. Besides, the comparative analysis of gas production and gas toxicity of large format NCM and LFP module during TR propagation is revealed for the first time, which is very meaningful for the further evacuation and rescue of large-format LIB fires. It is found that the total mass of ejected combustible gases (including H2, CH4, C2H4, C3H6, CO) per failed cell number of the NCM module are much higher than that of the LFP module, which is determined to be 21.09 g and 4.17 g for the NCM and LFP module, respectively. Besides, the results calculated by the FED and FEC models demonstrate that the toxicity of ejected gases from NCM module is greater than that of the LFP module. This work present in detail the TR propagation characteristics of large-format NCM and LFP modules, which can provide valuable information for the safety design of lithium-ion batteries.
... Nevertheless, the propagation of thermal runaway within tightly packed LIB modules was not guaranteed, as observed for series-connected modules in [17][18][19][20]. The large heat dissipation to the environment contributes to the failed propagation, which could prevent LIB cells from reaching the critical thermal-runaway temperature [3]. ...
... Moreover, methods of connecting LIBs or the circuit arrangement also influence the thermal-runaway propagation process, because of the possible short circuit. Gao et al. [18] showed that for a close-circuit pouch-cell module, the cell temperature was 10 ℃ higher than the reference opencircuit module. Joshua et al. [19] showed that an intense thermal-runaway propagation occurred in the cylindrical-cell module with the parallel connection, while the propagation did not occur with the series connection. ...
Article
Full-text available
Thermal-runaway propagation in battery systems can escalate the battery fire hazard and pose a severe threat to global users. In this work, the thermal-runaway propagation over 18650 cylindrical lithium-ion battery was tested in the linear-arranged module with a 3-mm gap. State of charge (SOCs) from 30% to 100%, ambient temperatures from 20°C to 70°C, and three tab-connection methods were investigated. Results indicate that the battery thermal-runaway propagation speed was about 0.35 ± 0.15 #/min, which increased with SOC and ambient temperature. The critical surface temperature of thermal runaway ranged from 209°C to 245°C, which increased with ambient temperature while decreased with SOC. Compared to the open-circuit module, the flat tab connection could cause an external short circuit to accelerate the thermal-runaway propagation, and the non-flat tab connection was more likely to trigger an explosion. A heat transfer analysis was proposed to qualitatively explain the speed and limiting conditions of thermal-runaway propagation, as well as the influence of SOC, ambient temperature, and tab connection. This work reveals the thermal-runaway propagation characteristics under well-controlled environments, which could provide scientific guidelines to improve the safety of the battery module and reduce battery fire hazards.
... And the LIB with a higher SOC level always has higher fire propagation hazards [10]. In terms of system configuration, factors such as connection modes [12], cell arrangements [13], and thermal management strategies [14] have significant impacts on thermal runaway propagation. For instance, LIBs connected in parallel have a strong thermal runaway propagation due to the enhanced heat transfer through tabs [12]. ...
... In terms of system configuration, factors such as connection modes [12], cell arrangements [13], and thermal management strategies [14] have significant impacts on thermal runaway propagation. For instance, LIBs connected in parallel have a strong thermal runaway propagation due to the enhanced heat transfer through tabs [12]. But introducing air gaps between cells can effectively prolong the time for thermal runaway propagation [13]. ...
... Moreover, the cells connected in series are prone to over-discharge, which results in an internal short circuit [20]. The sudden propagation of the thermal runaway heat by the failed cell(s) to the neighbouring cells leads to the complete destruction of the battery module [21]. Hence, the module-level study of thermal Abbreviations: PCM, Phase change material; EV, Electric Vehicle; RMN, Runaway Mitigation Number; SEI, Solid electrolyte interphase; TMS, Thermal management system; TR, Thermal runaway; SoC, State of Charge. ...
... The module-level thermal runaway experiments are often limited to small modules due to poor scalability and prohibitive cost for larger ones [21,33,34]. Therefore, characterization and, more importantly, prediction of the heat propagation in a module through appropriate multi-physics models are crucial. ...
Article
Safe and reliable design of lithium-ion battery packs necessitates prevention of thermal runaway and its propagation. To characterize the propagation behaviour in a battery module, a three-mode heat transfer model coupled with electrochemical and abuse-reaction-kinetics models is developed here. The efficacy of an active thermal management system in preventing damage-cascade for a standard EV module geometry (as used in Tesla) is elucidated. The model effectively captures the temperature profile, heat generation rate, and the extent of resulting decomposition of cell-components as validated against the literature. A temperature spike is applied to a cell within a standard battery module to emulate abuse driven runaway. The propagation of damage to other cells due to the temperature-spike in the triggered cell is simulated through the model as developed. A counter-intuitive non-monotonic trend (increasing first, decreasing later) is observed for the damage-severity as a function of coolant flow rate. Through a unified analysis of cumulative heat generation and heat dissipation through coolant, a mitigation strategy for runaway propagation is obtained in terms of a generalized non-dimensional parameter, Runway Mitigation Number (RMN), which predicts runaway propagation beyond a value of ~1.8 for similar module designs.
... Zhu et al. [19] investigated the overcharge-induced thermal runaway features of pouch Li-ion batteries under different current rates and concluded the higher current rate is easier to cause the thermal runaway because of the dramatic side reactions. Gao et al. [20] recently showed that the voltage waving can be utilized to determine the thermal runaway propagation time and the pouch battery module in parallel has poor safety than module in series. Most of the past studies focused on battery fires initiated or 'self-ignited' under extreme operating conditions such as external heating, short circuit, fast-charging, and over-discharging (e.g. during the fast acceleration of EV). ...
Article
Full-text available
The fire safety issue of Lithium-ion (Li-ion) batteries is an important obstacle for its market growth and applications. Although the open-circuit condition (e.g. storage, transport and disposal) accounts for the major part of battery lifespan, little research has investigated its self-ignition hazard during non-operating periods. In this work, we experimentally study the self-heating behavior of piled pouch Li-ion battery cells through the classical hot-plate experiments. Results show that the self-ignition of battery occurs under a hot plate temperature ranging from 199 °C to 262 °C, depending on the number of cells and environmental cooling. Thermal runaway always first occurs to the cell next to the hot plate and then propagates to upper cells. This critical temperature is increased by 20 °C under a good environmental cooling condition whereas it is reduced by 40 °C as the state of charge increases from 30% to 80%. Moreover, the critical plate temperature for self-ignition increases slightly with the height of battery pile, which is opposite to both hot-plate experiments of hydrocarbon materials and the oven experiments of battery. Therefore, the classical self-ignition theory may not be applicable for Li-ion batteries next to a hot boundary. This research reveals new self-ignition phenomena and helps understand the fire safety of Li-ion batteries in storage and transport.
... In Feng's review, TR mechanisms of the commercial lithium ion batteries are comprehensively summarized, containing three abuse conditions -mechanical abuse, electrical abuse and thermal abuse [182] . In recent years, Feng and coworkers have undertaken significant research to investigate the TR of batteries [ [89] , [183][184][185][186][187] ]. In most cases, the catastrophic outcomes of TR originates from a cell level where ISC happens inside a single cell due to the penetration of the separator. ...
Article
Lithium-ion batteries (LIBs) have been widely recognized as the most promising energy storage technology due to their favorable power and energy densities for applications in electric vehicles (EVs) and other related functions. However, further improvements are needed which are underpinned by advances in conventional electrode designs. This paper reviews conventional and emerging electrode designs, including conventional LIB electrode modification techniques and electrode design for next-generation energy devices. Thick electrode designs with low tortuosity are the most conventional approach for energy density improvement. Chemistries such as lithium-sulfur, lithium-air and solid-state batteries show great potential, yet many challenges remain. Microscale structural modelling and macroscale functional modelling methods underpin much of the electrode design work and these efforts are summarized here. More importantly, this paper presents a novel framework for next-generation electrode design termed: Cyber Hierarchy And Interactional Network based Multiscale Electrode Design (CHAIN-MED), a hybrid solution combining model-based and data-driven techniques for optimal electrode design, which significantly shortens the development cycle. This review, therefore, provides novel insights into combining existing design approaches with multiscale models and machine learning techniques for next-generation LIB electrodes.
... Several investigations have been conducted with NMC lithium-ion batteries (e.g., [1][2][3]), but only a few studies have been conducted on the characteristic behavior and gaseous release at variable state of charge (SOC) levels [4]. The findings from an investigation with an 18-battery module with 24 Ah (≈100 Wh) pouch cells at 100% SOC revealed that during thermal propagation, the unaffected adjacent cells transferred current to the cells in a thermal runaway (TR) [5]. This resulted in an increase in temperature by 10 K. Other studies by a number of researchers have mainly concentrated on pouch LIBs with 100% SOC [6][7][8]. ...
Article
Full-text available
In this study, 19 experiments were conducted with 25 pouch cells of NMC cathode to investigate thermal runaway and the release of gases from lithium-ion batteries (LIBs). Single cells, double cells, and a four-cell battery stack were forced to undergo thermal runaway inside an air-tight reactor vessel with a volume of 100 dm3. The study involved two series of tests with two types of ignition sources. In the Series 1 tests, a heating plug was used to initiate thermal runaway in LIBs in the ranges of 80–89% and 90–100% SOC. In the Series 2 tests, a heating plate was used to trigger thermal runaway in LIBs in the ranges of 30–50%, 80–89%, and 90–100% SOC. Thermal runaway started at an onset temperature of 344 ± 5 K and 345 K for the Series 1 tests and from 393 ± 36 K to 487 ± 10 K for the Series 2 tests. Peak reaction temperatures ranged between 642 K and 1184 K, while the maximum pressures observed were between 1.2 bar and 7.28 bar. Thermal runaway induced explosion of the cells and lead to a rate of temperature increase greater than 10 K/s. The amounts of gases released from the LIBs were calculated from pressures and temperatures measured in the reactor. Then, the gas composition was analyzed using a Fourier transform infrared (FTIR) spectrometer. The highest gaseous production was achieved at a range of 90–100% SOC and higher battery capacities 72 L, 1.8 L/Ah (Series 1, battery stack) and 103 L, 3.2 L/Ah (Series 2, 32 Ah cell)). Among the gases analyzed, the concentration of gaseous emissions such as C2H4, CH4, and C2H6 increased at a higher cell capacity in both series of tests. The study results revealed characteristic variations of thermal behavior with respect to the type of ignition source used.
... The purpose of the TRP test in new GB is to give 5-min of escape time before the passengers get into danger caused by single cell TR. Generally speaking, the GB standard chooses to trigger one cell to TR to examine if the TR sensor could provide an alarm signal before the pack cannot withstand the jet flame [27,28]. It is recommended to use the nail penetration or external heating to trigger the TR of target cell. ...
Article
Thermal runaway tests with different heating schemes are conducted. • The combined effect of heating power and heating area on thermal runaway triggering is investigated. • Thermal runaway prediction and recommended heating scheme selection map is proposed. • Thermal runaway mechanism of lithium-ion battery induced by external heating is investigated. A R T I C L E I N F O Keywords: Lithium ion battery Safety Heating trigger thermal runaway Thermal runaway model Thermal runaway mechanism Heating scheme selection A B S T R A C T Intentionally inducing worst-case thermal runaway scenarios in Lithium-ion batteries on-demand is a definitive way to test the efficacy of battery systems in safely mitigating the consequences of catastrophic failure. This study investigates the combined impact of heating power and heating area on thermal runaway triggering. Two different heating powers and four incremental heating areas constitute eight heating schemes in the experimental test. A 3D model is built in Comsol to satisfy the experimental result and investigate the heat transfer thermal runaway mechanism induced by external heating. The results indicate that when the heating power is the same, the smaller heating area that has higher heating power density can trigger TR quicker. The heater produces less heating energy, and less flux energy will be introduced into the battery. Thermal runaway prediction and recommended heating scheme map is proposed based on simulation result. The heating scheme with both high heating power and the small heating area has the greatest ability on shortening the heating time. The flux energy and its equivalent flux power pass through the interface between heater and battery is used to construct a comprehensive description of thermal runaway mechanism induced by heating method.
... TR propagation is affected by electrical connection configuration. TR propagation of parallel modules was more aggressive and risk than that of series and unconnected modules due to the transfer of electrical energy through the electrical path [4,9,21]. Besides, increasing the battery spacing can effectively mitigate the TR propagation between batteries [5]. ...
Article
Overcharge and overheating are two common safety issues for the large-scale application of lithium-ion batteries (LIBs), and in-depth understanding of the thermal runaway (TR) and its propagation of LIBs induced by overcharging and overheating are strongly required to guide the safety design of battery system. In this paper, investigation on characteristics and mechanism of TR and its propagation of LIBs induced by overcharging and overheating are conducted experimentally. Besides, critical thermal energy triggering TR and chemical thermal contribution are identified. The normalized critical energy triggered by overcharging and overheating to TR are also determined. The results show compared with TR induced by overheating, TR induced by overcharging exhibits a more severe and catastrophic result due to their higher heat release, more combustible gases and mass loss. In addition, critical thermal energy triggering TR may be constant for fully charged batteries under the overheating of 300 W and 400 W, which is slightly affected by heating power (Ph). Moreover, Critical chemical heat shows a certain upward trend with increasing Ph. Critical electric energy triggering TR and critical self-generated heat slightly decrease with increasing overcharge rate. In open environment, TR induced by overheating propagates faster than that induced by overcharging.
... The research conducted by Lamb et al. (Lamb et al., 2015) also shows that thermal runaway did not propagate in the module in series, but propagation happened in the module in parallel. Gao et al. (Gao et al., 2019) demonstrated that the reason why the temperature rise of the battery module in parallel after TR is higher than that in the module in series is a short circuit appeared in the cell in TR of the module in parallel, and other cells released electric energy to the cell in TR. Xu et al. (Xu et al., 2021) have investigated the TR propagation behaviours in modules with different electrical connections; the results show that the transferred electricity led to a temperature increase of approximately 28.2 • C in the most severe condition. ...
Article
Full-text available
This study presents a mathematical model and experimental verification of factors influencing thermal runaway propagation of NCM811/C lithium-ion battery module after fast charging operation. The key factors considered for the thermal runaway propagation include charging C-rate, battery spacing, triggering temperature, speed, and interval of the thermal runaway propagation. The analysis of the 3D model shows that increasing the spacing and triggering temperature of the battery will reduce the risk of thermal runaway propagation of the battery module and change the order of thermal runaway propagation. Further, the thermal runaway propagation speed increases gradually with the propagation process; however, it is inhibited by increasing triggering temperature and battery spacing and the decrease of charging C-rate. These observations play a critical role in the lithium-ion battery pack design.
... The research conducted by Lamb et al. [54] also shows that thermal runaway did not propagate in the module in series, but propagation happened in module in parallel. Gao et al. [55] demonstrated that the reason why temperature rise of the battery module in parallel after TR is higher than that in the module in series is a short circuit appeared in the cell in TR of the module in parallel, and other cells released electric energy to the cell in TR. Xu et al. [56] have investigated the TR propagation behaviours in modules with different electrical connections, the results shows that the transferred electricity led to a temperature increase of approximately 28.2 • C in the most severe condition. ...
Article
The growing use of electric vehicles has made it imperative to use safe battery packs. Severe accidents may occur even due to minor faults in battery packs. One such issue is thermal runaway (TR) propagation in lithium-ion batteries (LIBs). In this study, cylindrical 18650 LIBs were employed to determine the factors responsible for TR propagation in battery packs. The main parameters studied were cycle aging, connection mode, arrangement, and state-of-charge (SOC). The results indicate that cyclic aging have little influence on the propagation process. When the positive of the battery are placed in the same direction, it is easier to cause the thermal runaway propagation of the battery pack than when the positive and negative are placed in the same direction. Meanwhile, parallel connections increased the probability of TR propagation. In addition, the SOC of the battery pack significantly affected TR propagation, with the highest probability at SOC values in the range of 40% to 60%. However, the probability of TR reduced at 80% and 100% SOC. Finally, our results indicate that the probability of TR propagation increased when the rate of increase in the temperature of adjacent cells was greater than 0.36 °C/s.
... Meanwhile, the front surface temperature of the cell measured by TC1-3 exhibited the same trend. The temperature response of TC1-3 lagged behind TC4 due to the furthest distance from the heater, the thermal runaway propagated from the electrode layer closest to the heat source to the layer at the other side [27], as shown in Fig. 6. The temperature of TC2 increased obviously when the voltage experienced a sharp drop, indicating that large-scale inner short circuit occurred inside the cell. ...
Article
Currently, effective suppression methods are still required to deal with lithium-ion battery (LIB) fires. In this paper, a novel synergistic fire extinguishing method of gas extinguishing agent (C6F12O, CO2 and HFC-227ea) and water mist is designed to evaluate the effect of their combination. A 243 Ah large-scale LIB with LiFePO4 as cathode is used in this work. Several cell parameters are measured to evaluate the suppression effect of fire extinguishing method, such as extinguishing time, maximum temperature, mass loss and heat release rate. Meanwhile, the cooling effect, fire extinguishing effect and economic benefit of different fire extinguishing methods are all considered. Results show that the suppression effect of synergistic fire extinguishing method is better than that of the single agent. Single application of water mist can hardly extinguish the flame, while the combination of gas extinguishing agents and water mist can extinguish the flame finally. However, the C6F12O extinguishes the flame immediately, while CO2 has a longer extinguishing time, and HFC-227ea cannot extinguish the flame. So in these experiments, the C6F12O combined with water mist exhibits the best extinguishing and cooling effect. The CO2 combined with water mist has good economic benefit, better fire extinguishing effect and cooling effect in these experiments, which can also be considered in suppressing LiFePO4 LIB fires.
... The transferred electric energy causes the temperature increment in the TR cell. This phenomenon is significant in the battery pack with parallel structure [20]. However, the battery pack structure in this study is different from parallel structure. ...
Article
High-power lithium-ion batteries (LIBs) suffer from thermal runaway (TR) under unusual forces and misuse. Consequent TR propagation can cause battery pack breakdown and even dangerous fires or explosions. In this study, a four-step TR propagation prediction method is proposed for large-scale battery packs with series and parallel connection. To investigate the TR propagation behavior in battery packs, a lumped thermal resistance network was constructed based on the heat transfer characteristics of LIB packs. The energy balance equation for each cell and heat exchange between cells were solved via electrical circuit analogy. TR propagation features are discussed with different TR trigger locations, and the TR prevention effect of phase change materials (PCMs) is evaluated. The proposed prediction method exhibits high computational efficiency and adequate accuracy in resolving TR propagation. The prediction of battery core temperature and the experimental results are good in agreement. The TR propagation includes three stages: initial stage, rapid expanding stage and burst stage. The TR propagates preferentially along the thermal path with lower thermal resistance. When a PCM is applied to prevent TR, the critical behavior of TR propagation prevention is discovered. If the trigger cell of TR is prevented with the PCM, TR propagation in the entire pack can be avoided. The proposed method fulfils the fast prediction of TR propagation, which can provide insights into the on-board thermal safety design of electric vehicles.
... short circuit after separator collapse [15][16][17] , oxygen being released by the decomposition of the cathode [18] , and interactions between the lithiated anode and electrolyte [ 19 , 20 ]. The TR propagates from one cell to its neighbors after a failure is triggered [21][22][23][24] . During TR propagation (TRP), a large temperature variance is observed within the jelly-roll/cell-core for largeformat batteries. ...
Article
Long, large-format lithium-ion batteries have become prominent in recent years in high-power application scenarios, such as in electrochemical energy storage stations, electric vehicles, and electric ships. In these batteries, failure is always initiated from a local point and then propagates to the full cell, requiring countermeasures to quench the in-cell thermal runaway propagation. This study investigates the thermal runaway propagation behaviors of long, large-format lithium-ion batteries. A thermal runaway front exists during the propagation of thermal runaway; it separates the failure zone and normal zone and carries significant information regarding the thermal runaway reactions. The characteristics of the thermal runaway front are investigated through experiments and simulations. The thermal runaway front moves forward with an average velocity of approximately 24.14 mm·s⁻¹, driven by the large temperature gradient between the failure and intact zones. The velocity of the thermal runaway front is correlated with the thermophysical properties of the battery. A modeling analysis indicates that the velocity of the thermal runaway front in propagation has a square root correlation with the thermal conductivity and heat generation rate. This square root correlation links the failure process and the thermophysical properties of the battery and can contribute to the future safety design of large-format batteries.
... The start of voltage drop reflects that the separator of jelly-roll 1 collapses and induces micro internal short circuits (ISC) owing to the parallel connection. Afterwards, the voltage begins to rise back and a rebound point can be observed, corresponding to complete failure of jelly-roll 1 (Feng et al., 2015;Gao et al., 2019). The phenomenon may not be obvious in the LiNi 0.8 Co 0.1 Mn 0.1 O 2 LIBs owing to the quite fast propagation speed, but this phenomenon can be reflected in LFP cells, as shown in Fig. 11. ...
Article
With the increasing deployment of large-scale lithium ion batteries (LIBs), thermal runaway (TR) and fire behavior are significant potential risks, especially for high energy density cells. A series of thermal abuse tests and hazard analysis on 117 Ah LiNi0.8Co0.1Mn0.1O2/graphite LIBs were performed under two conditions, “open space” and “confined space”. In open space tests, the fire behavior of LIBs was characterized with respect to the TR process, temperature characteristics, mass variation, voltage, heat release rate and gas release. To simulate the application scenarios in electric vehicles, a confined cabinet was introduced. The effects of state of charge and confined cabinet on the fire behavior of individual cell were analyzed. Furthermore, a real-scale scenario was considered for the evaluation of fire-induced toxicity using Fractional Effective Dose (FED) and Fractional Effective Concentration (FEC) models. The obtained results show that the effects of asphyxiant gases are more significant than those of irritant gases. The maximum FEC and FED values are greater than the critical threshold of 1, indicating the catastrophic toxicity in such fire scenarios. The minimum fresh air renewal rate required is computed to provide quantitative guides for ventilation management, firefighting and rescue.
... In electric vehicles, the power battery system consists of a large number of single batteries connected to form a pack, which should meet the required voltage and capacity. The batteries are tightly bonded within the pack to reduce the bulk with the aim of improving the energy density [4]. In the event of a TR in a single battery, the generated heat is easily transferred to the adjacent ones, leading to the TR propagation in the pack. ...
Article
Thermal runaway (TR) of an lithium-ion battery pack is investigated under laboratory conditions. The experimental battery pack consists of 10 18,650-type lithium-ion batteries connected in parallel and with a serpentine channel liquid-cooling thermal management system (TMS). The effect of the applied liquid-cooling TMS with different coolant flow rates (0 L/h, 32 L/h, 64 L/h and 96 L/h) on the TR propagation in the battery pack is analyzed , and the results indicate that the TMS is capable of preventing TR propagation. It is examined the eventual relation between TR prevention and the flow rate. The rate of TR in the batteries is almost random for lower values of the coolant flow rate (0 L/h, 32 L/h and 64 L/h), but for the coolant flow rate of 96 L/h, TR propagation can be effectively prevented. It is also found that the high-temperature electrolyte ejected from the positive side of the TR battery can rapidly spread to the adjacent batteries and trigger instantly their own TR. This is the leading mechanism yielding the TR propagation in the battery pack. Heat conduction and radiation, especially when the positive sides of the batteries are largely covered by the current connectors, play a minor role in the TR propagation. These findings may prove useful in designing lithium-ion battery packs with appropriate TMS strategies.
... Besides, the impact of electrical connections on TR propagation have also been studied extensively. Electricity can be transferred from the adjacent cells to the TR cell during TR propagation [20], and the transferred electricity led to a temperature increase of approximately 28.2 ℃ of TR cell in the pouch cells module [21]. Therefore, it is common to use blocking and discharge diodes within large parallel battery packs to prevent self-discharge of the battery through a shorted cell [22]. ...
Article
Thermal runaway (TR) is the most critical safety issue of lithium ion battery (LIB), and more uncertain hazard factors may be introduced under working state. In this study, TR propagation in LIB modules during charging was investigated firstly. A shorter TR propagation time is observed with increasing charging rate, and the average TR propagation time at 3 C charging rate is only 12.1 % of that at 0.5 C. Besides, the TR propagation exhibited an obvious acceleration effect and the TR onset temperature decreased with TR propagation at high charging rates, the lowest TR onset temperature is only 127.4 ℃. Redistributed current led to rapid heat generation of the remaining cells, and the side reaction heat gradually replaced the heat absorbed from surroundings and became the main source of heat accumulation. Coupled with the heat generation of charging, the TR propagation accelerated. In addition, the heat conduction through air accounts for 67 % of the total heat transfer, so reducing the thermal conductivity between cells can be considered as a means of mitigating TR propagation. This study delivers an underlying analysis of TR propagation during charging, and which is expected to contribute references for the safety of LIB application.
Article
Lithium-ion batteries are now becoming the primary energy storage device for electric vehicles. However, thermal runaway caused by the internal short circuit in lithium-ion batteries draws attention to the safety issues. The dramatic temperature change of lithium-ion batteries can lead to fatal accidents. This paper aims to find a better way to estimate the lithium-ion batteries' temperature distribution under the nail penetration condition. Then a semi-analytical solution based on Green's function is derived at three different punching positions. A three-dimensional battery model is constructed by utilizing COMSOL Multiphysics software to simulate the characteristics of temperature distribution’s variation. The results show that the temperature distribution is related to the nail penetration position. When the punching position is near to the positive electrode of the battery, the temperature can reach the highest value compared with the other two nail penetration positions, the middle of the battery and the position that is far from the positive electrode. In addition, the simulation results are compared with the temperature curve drawn by solving the semi-analytical solution. It shows that these temperature curves follow a similar trend, and the difference between the simulation results and the semi-analytical solution is small with an error less than 5%.
Article
Ternary power batteries, as the mainstream power sources of electric vehicles, are liable to inducing thermal runaway (TR) with respect to their sensitivity to abusive conditions. Among various abuse conditions, the overcharge of a battery has been considered as the most common and severe case giving rise to thermal safety accidents. In this study, an overcharged battery and a normal battery, both using ternary/graphite electrodes, were investigated and analyzed synergistically through thermal behaviors and electrochemical characteristics. Initially, a series of electrochemical parameters including charge and discharge voltage plateaus, discharged capacity and time at different discharge rates, and internal resistances were carried out. Then, the heat generation behaviors between normal and overcharged batteries were evaluated. Furtherly, the interconnectedness with the electrochemical capacity degradation and heat generation aggravation of the ternary battery after overcharge was analyzed. Besides, the essential causes of the deterioration of electrochemical properties and severe heat behaviors resulting from overcharge were intensively analyzed via microscopic perspectives. In addition, the electrochemical characteristics fading of abused ternary battery triggered by overcharge were investigated, especially under higher temperature (55°C) and ultralow temperature (−20°C) conditions. Therefore, for an overcharged battery, this research not only elaborates the essential causa of the degraded electrochemical and anabatic thermal performance from a materials and thermal science perspective but also provides a foundation for further promoting the safety properties of commercialized power batteries with ternary chemical systems.
Article
Thermal management plays an important role in battery modules, especially under extreme operating conditions. Phase change materials (PCMs)-based cooling has been recognized as a promising approach that can prolong the life span of batteries and endure the passive thermal accumulation in the module. In this study, various mass fractions (0 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) of aluminum nitride (AlN) were added to composite PCMs to serve as heat-transfer promoters. The effect of the AlN additives on the thermal conductivity, mechanical properties, and volume resistivity were analyzed, and the root causes originating from the morphologies and structures of the composite PCMs were further examined. The results indicated that adding 20 wt% of the AlN in the composite PCMs was an optimal strategy. In addition, an AlN/paraffin (PA)/expanded graphite (EG)/epoxy resin composite PCMs-based 18650 LiFePO4 battery module was designed for thermal management. This battery module exhibited much better heat dissipation and temperature uniformity than an air-cooled battery module, leading to a 19.4% decrease of the maximum temperature and a less than 1 °C temperature difference at a high discharge rate of 3C. Thus, it could be concluded that the AlN-enhanced composite PCMs thermal management system exhibited a prominent controlling temperature and balancing temperature capacity for the battery module.
Article
The effect of phase change material (PCM) on thermal runaway (TR) and failure propagation in cell modules is investigated. Two PCMs, paraffin (PPCM) and graphene-enhanced hybrid (GHPCM) are considered. Each module is composed of three fully charged 50 Ah LiNixCoyMn1-x-yO2/graphite cells isolated by air or PCM. The onset TR times of cell 1 are around 812, 801, and 942 s in modules without PCM, with PPCM and with GHPCM, respectively. The propagation time from cell 1 (cell 2) to cell 2 (cell 3) is reduced (delayed) from 638 s (168 s) in modules without PCM to 394 s (178 s) in GHPCM modules and 536 s (493 s) in PPCM modules. The PPCM module accompanied by a considerable amount of gas can relieve TR propagation because of less heat feedback from the flame, while the GHPCM module is prone to facilitating propagation due to strong heat transfer between adjacent cells. The module without PCM may delay TR propagation owing to limited heat transfer through contact walls. Compared to modules without PCM and with PPCM, the GHPCM module presents a higher maximum surface temperature (885 °C) and more heat release (7614 kJ). Finally, residue and physical damage are also examined.
Article
This paper presents a method of internal temperature detection of thermal runaway in lithium-ion cells during extended-volume accelerating rate calorimetry (EV-ARC) tests. Thermocouples were inserted into pouch, prismatic, and cylindrical cell samples with only moderate breakage of the cell packages. The temperatures measured at cell surface were compared with the internal temperatures. And for the pouch and prismatic cell samples, a common alternative method of simulating internal temperature by measuring the temperature between two identical cells was also evaluated for comparison. The results demonstrate that the surface measurements can be used to investigate the mild side reactions from the onset temperature, where the rate of temperature increase is slow enough to allow equilibration, to the triggering temperature, beyond which thermal runaway cannot be arrested. However, after the triggering temperature, the internal temperature detection is the most accurate for evaluating the maximum temperature and rate of increase. For the pouch cell, the simulated internal temperature detection method was sufficiently accurate, whereas for the prismatic and cylindrical cells, the simulated temperatures were inaccurate.
Article
Thermal runaway of lithium-ion batteries is a risk that is magnified when stacks of lithium-ion cells are used for large scale energy storage. When limits of propagation can be identified so that systems can be designed to prevent large scale cascading failure even if a failure does occur, these systems will be safer. This work addresses the prediction of cell-to-cell failure propagation and the propagation limits in lithium-ion cell stacks to better understand and identify safe designs. A thermal-runaway model is presented based on recent developments in thermochemical source terms. It is noted that propagating failure is characterized by temperatures above which calorimetry data is available. Results show high temperature propagating failure predictions are too rapid unless an intra-particle diffusion limit is included, introducing a Damköhler number limiter into the rate expression. This new model form is evaluated against cell-to-cell failure propagation where the end cell of a stack is forced into thermal runaway through a nail-induced short circuit. Limits of propagation for this configuration are identified. Results show cell-to-cell propagation predictions are consistent with measurements over a range of cell states of charge and with the introduction of metal plates between cells to add system heat capacity representative of structural members. This consistency extends from scenarios where propagation occurs through scenarios where propagation is prevented.
Article
An efficient battery thermal management system (BTMS) will undoubtedly promote the performance and lifespan of battery packs. In this study, a novel flame-retarded composite PCMs composed by paraffin (PA), expanded graphite (EG), ammonium polyphosphate (APP), red phosphorus (RP) and epoxy resin (ER) has been proposed for battery module. The thermophysical and flame retardant properties are investigated at both macro and micro levels. The results show that the proposed composite PCMs with an APP/RP ratio of 23/10 exhibit the optimum flame retardant performance. Besides, the APP/RP-based composite PCMs for 18,650 ternary battery module has also been researched comparing with air cooled and PCM with pure PA modes. The experimental results indicated that the fire retardant PCMs shown significant cooling and temperature balancing advantages for battery module, leading to a 44.7% and 30.1% reduction rate of the peak temperature and the maintenance of the maximum temperature difference within 1.36 °C at a 3 C discharge rate for 25 °C. Even at 45 °C, the temperature uniformity can still be controlled within 5 °C. Thus, this research indicates the composite PCM had good flame retardant and form stable properties, it would be utilized in BTMS, energy storage and other fields.
Article
Thermal runaway (TR) propagation significantly affects the safety of lithium-ion battery systems. In this study, the TR propagation behaviours in modules with different electrical connections were investigated. In detail, three different kind of modules were studied: 12 cells having no electrical connections, four cells in parallel and three in series, as well as three cells in parallel and four in series. Considering the maximum temperature and propagation time, the parallel-series connection types of the battery module appeared to have no significant influence on the TR propagation behaviour. An equivalent circuit model was built to calculate the transfer of electricity from the adjacent cells to the runaway cell. According to calculations, the transferred electricity led to a temperature increase of approximately 28.2 °C in the most severe condition. By integrating thermocouples inside the cells, the internal temperatures of the cells in the modules during TR propagation were measured and compared. The internal temperature was 160 °C higher (on average) than that on the cell surface. The significance of the temperature differences requires attention for the further modelling of TR propagation.
Article
Deviations between batteries in series appear gradually and increase with the number of cycles. This inconsistency reduces the lifetime of battery packs, increases the cost of using them, and may lead to security issues. Equalization is an important means of reducing battery differences. The relevant research has focused on the design of equalization circuits and the improvement of equalizer efficiency while neglecting a comparative analysis of methods of equalization on the performance of battery packs, which hinders technicians from making the correct choice during application. A quantitative analysis is provided in this paper to compare the effects of methods of equalization on reducing the differences among batteries. Multiple parameters are introduced to describe differences among equalization methods, and the results indicated that equalization worked only at appropriate current rates and failed at large ones. With the same current rate in charging and discharging, the relative equalization time of active equalization was shorter than that of hybrid equalization. Active equalization was better than passive equalization in reducing battery capacity differences. The maximum difference in state of charges among batteries with active equalization at a current rate of 0.25 C decreased from 10% to 9.207% in discharging, while that with passive equalization dropped from 10% to 9.492%. Therefore, active equalization was suitable for short period charge and discharge. Moreover, the values of the equalization current of the equalization methods were similar, but the effect of hybrid equalization on reducing the differences among batteries was more significant. The average hybrid equalization current was 0.073 A larger than the average active equalization current. However, the capacity of the battery pack with hybrid equalization was 0.369 Ah higher than that with active equalization. Hybrid equalization was more conducive to the regular maintenance of the battery pack. In the life cycle of the battery pack, an equalization management mode of “single‐cycle active equalization + hybrid equalization regular maintenance” could be introduced. On this basis, fast equalization within a single cycle could be achieved and consistency among cells during long‐term cycling could be guaranteed. This study provides a scientific basis for engineering practice and helps choose an appropriate method of equalization.
Article
Thermal runaway (TR) may propagate in a lithium-ion battery (LIB) pack in confined and semi-confined spaces, because of insufficient heat dissipation. This may induce accidents and lead to significant losses. However, the heat transfer modes between cells when TR propagates in an LIB pack have not been revealed. In this work, aluminium foil (AF), which has low emissivity and high thermal conductivity, and refractory ceramic fibre (RCF), which has low thermal conductivity, were employed to reduce the heat transferred between two cells through conduction and radiation via the air, respectively. Therefore, the differences in heat transfer properties in these two materials were used to quantitatively analyse the heat transfer modes in the process of TR propagation in an LIB pack under confined and semi-confined spaces. The TR propagation process was roughly divided into three stages, and the maximum temperature of the cell experiencing TR in a confined space was lower than that in a semi-confined space. TR propagation speed decreased from 7.84×10⁻³ s⁻¹ to 6.14×10⁻³ s⁻¹ and from 11.9×10⁻³ s⁻¹ to 9.62×10⁻³ s⁻¹ owing to the use of RCF in confined and semi-confined spaces, respectively. Furthermore, the TR propagation speed decreased from 7.84×10⁻³ s⁻¹ to 5.1×10⁻³ s⁻¹ and from 10.87×10⁻³ s⁻¹ to 7.46×10⁻³ s⁻¹ owing to the use of AF. In the LIB pack, the heat was mainly transferred through conduction via the air between two neighbouring cells, in a proportion of approximately 50–83.8%. Then, the main heat transfer mode changed to radiation when the neighbouring cell underwent TR. However, when one cell was wrapped with AF on its surface to decrease the radiation heat absorbed from the neighbouring cell, the main heat transfer mode was conduction, and it did not change even though the neighbouring cell underwent TR. This is different from the aforementioned phenomenon. Therefore, the radiation heat influences the TR propagation more significantly than the conduction heat. A detailed analysis of the main heat transfer mode can provide valuable guidelines for the safety design and prevention of TR propagation in LIB packs.
Article
Overheat is one of the common safety issues for the large-scale application of lithium-ion batteries (LIBs), and is a potential risk that triggers thermal runaway (TR). In this work, the effects of the heating power and state of charge (SOC) on TR characteristics of large-format (Ni1/3Co1/3Mn1/3)O2 LIBs under overheat are investigated experimentally. The relationship between heating power, critical input thermal energy (Einput) and TR are identified firstly. The results show the Einput, critical internal energy, chemical heat and joule heat of batteries in critical TR state all decrease with increasing SOC. The heating power exhibits more significant impact on TR behavior than SOC dues to the rapid deterioration of TR as heating power ascends. The peak heat release rate of TR rises from 7.5 to 95.2 kW when heating power increases from 400 to 700 W. And the law the severity of TR deteriorates sharply with increasing heating power is more prominent in the TR propagation process. Besides, TR induced by higher heating power requires lower Einput. Einput decreases from 477.08 to 329.23 kJ as heating power ascends from 400 to 700 W. Furthermore, the relationship between internal short circuit and TR under different SOC and heating power are analyzed.
Article
This work introduces a method for measuring the main physical quantities, such as short-circuit current and capacity loss, in the thermal runaway process of the parallel battery module and presents detailed analysis and discussion on a 25 Ah commercial prismatic lithium-ion ferrous phosphate (LFP) battery. By establishing a basic circuit model of the thermal runaway process of the parallel battery module, experiments were conducted to observe the thermal runaway process of the parallel battery module. The parameters related to the electrothermal effect in the thermal runaway process were obtained by either direct measurement or calculation. The results showed that the short-circuit resistance of the cell, which was triggered to thermal runaway changed dramatically. The minimum resistance was about 0.5 mΩ, and the peak current of discharge was more than 1100 A. During the stable discharge process of the other parallel cells to the thermal runaway cell, the short-circuit resistance was about 10 mΩ. In the stable discharge stage, the electric heating power was about 600 to 900 W. However, the power of thermal runaway reaction from the cell itself was still more than 30 times the heating power of the electrothermal effect, exceeding 21 kW. The accuracy of the measurement method and analysis method was also verified by comparing the same parametric data obtained using different methods. The results showed that the method is feasible for studies on the mechanism and simulation of thermal runaway of parallel battery modules.
Article
Thermal runaway (TR) is a primary safety problem on the application of lithium-ion batteries (LIBs), while TR characteristics and mechanism of LIBs under varied heating positions are still unclear. In this study, the impact of heating position on TR is investigated employing an experimental approach. Due to the prismatic battery shape, the heated positions of LIBs are selected as the front, bottom and side surfaces. The results indicate the maximum temperature, peak temperature increase rate and mass loss rate of LIBs are significantly affected by heating position. The onset times of safety valve opening, internal short circuit and TR are almost consistent when the battery bottom and side surfaces are heated. The maximum jet flow velocity occurs at the instant of the safety valve opening, and the values are 74.79 m/s and 77.26 m/s for bottom and side surface heating, which are about three times that of front surface heating. Compared with front surface heating, bottom and side surface heating modes cause more significant damage on LIBs owing to higher mean thermal conductivities and more intense exothermic reactions. This study can provide guidance for the safe design of LIBs and the prevention of TR propagation between LIB modules.
Article
Thermal runaway propagation in battery systems seriously hinders the rapid development of electric vehicles. Side plates are commonly employed to ensure the rigidity of the battery system, which can considerably affect the propagation behaviors. However, little attention has been focused on optimizing the design of side plates to mitigate the failure propagation from the perspective of weakening heat transfer. In this study, an orthogonal experimental design was applied to investigate the effects of the thickness, height and convective heat transfer coefficient of side plates, and the thickness of thermal insulating slices on regulating propagation behaviors. The results show that the height of the side plates is the most significant factor in the propagation process. Furthermore, a multi-objective optimization method based on a verified approximate model was proposed to design lightweight side plates with thermal safety. The Pareto frontier among the optimal objectives was obtained by using Non-dominated Sorting Genetic Algorithm II. The average propagation time interval is effectively prolonged by 46.0% after multi-objective optimization. Moreover, the mass of the side plates is decreased by 59.6%, resulting in a lightweight battery module. The local hot pot (battery failure point) first reaching the triggering temperature of the thermal runaway moves from both sides of the battery module to the center of the batteries. This study creatively presents the multi-objective optimization of side plates in a battery module to mitigate thermal runaway propagation. The results can provide valuable guidelines for the safety design of battery modules.
Article
Insights into thermal behaviors of thermal runaway (TR) and propagation in a battery enclosure are significant for the safe application of lithium-ion batteries. In this study, the thermal behaviors of TR and its propagation over a lithium-ion battery module in a battery enclosure are investigated via thermal abuse experiments. The conduction heat flux between adjacent cells is measured for the first time. The results show that the onset time of the TR with the enclosure is later than that without the enclosure. However, the cells in the enclosure have a higher maximum TR temperature, and their temperature distribution is more uniform. Moreover, the duration of the TR propagation to adjacent cells in the enclosure is significantly shorter. And the occurrence of a jet fire further increases the maximum temperature of the cell in the enclosure. The measurement of the heat flux shows that the heat conduction intensity between the cells in the enclosure is greater than that without the enclosure. This work is beneficial for understanding the mechanism of TR and its propagation in practical applications and provides valuable references for the safety management of lithium-ion batteries.
Article
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External heating was considered the best repeatable triggering method in thermal runaway propagation test. This paper investigates the effects of heating power and heating energy on the thermal runaway propagation characteristics of lithium-ion battery modules through both experiments and simulations. Thermal propagation tests were conducted with seven different heating powers, and the correlated models were built and calibrated by the test results. For both the simulations and experiments, propagation time intervals between adjacent batteries under thermal runaway sequence are extracted and compared. The energy flow of four critical heat transfer interfaces in a battery module was analyzed, the mechanism of thermal runaway triggered by external heating is revealed: the accumulation of heat energy. Through the analysis of 3D temperature distributions of the module before the first battery thermal runaway, the pre-heating effect, was discovered and was regarded as the primary cause of acceleration of TRP time interval. The pre-heating effect can help to reveal the other circumstances that lead to TRP acceleration. The energy flow under higher heating powers is compared with battery’s TR, allowing the selection of the appropriate triggering heating power for the thermal runaway propagation test. The model-based tool of battery safety saves time and cost during research and development, supporting the technical issues for making reasonable tests. And it is important to understand the model-based tool in predicting the thermal runaway behavior of the battery module.
Article
The thermal abuse of high specific energy NCM811 lithium-ion power battery in the process of use or safety test was simulated by winding resistance wire heating method, and local heating and uniform heating were carried out to trigger a thermal runaway. When thermal runaway triggered by uniform heating, the safety valve is opened timely and only open flame occurred without explosion, it did not cause the internal short circuit, and the safety valve was not damaged. However, when thermal runaway triggered by the local heating method, it caused a serious internal short circuit, the released electrolyte and other material burned violently and exploded, and the safety valve was completely damaged. In this process, a thin film heat flux sensor is also used to quantify the surface heat flux during thermal runaway, which could provide the test method and calculation basis for the thermal management design. The experimental results were also compared with those of NCM111, NCM 532 and NCM 622 batteries, the results revealed that increase of nickel content in positive electrode would also increase the degree of damage when a TR triggered by local heating method.
Article
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This paper presents a novel model for analyzing thermal runaway in Li-ion battery cells with an internal short circuit device implanted in the cell. The model is constructed using Arrhenius formulations for representing the self-heating chemical reactions and the State of Charge. The model accounts for a local short-circuit, which is triggered by the device embedded in the cell windings (jelly roll). The short circuit is modeled by calculating the total available electrical energy and adding an efficiency factor for the conversion of electric energy into thermal energy. The efficiency factor also accounts for the energy vented from the cell. The results show good agreement with the experimental data for two cases – a 0D model and a 3D model of a single cell. Introducing the efficiency factor and simplifying the short-circuit modeling by using an Arrhenius formulation reduces the calculation time and the computational complexity, while providing relevant results about the temperature dynamics. It was found that for an 18650 NCA/graphite cell with a 2.4 Ah capacity, 28% of the electrical energy leaves with the effluent.
Article
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This paper presents a mathematical model built for analyzing the intricate thermal behavior of a 18650 LCO (Lithium Cobalt Oxide) battery cell during thermal runaway when venting of the electrolyte and contents of the jelly roll (ejecta) is considered. The model consists of different ODEs (Ordinary Differential Equations) describing reaction rates and electrochemical reactions, as well as the isentropic flow equations for describing electrolyte venting. The results are validated against experimental findings from Golubkov et al. [1] [Andrey W. Golubkov, David Fuchs, Julian Wagner, Helmar Wiltsche, Christoph Stangl, Gisela Fauler, Gernot Voitice Alexander Thaler and Viktor Hacker, RSC Advances, 4:3633e3642, 2014] for two cases - with flow and without flow. The results show that if the isentropic flow equations are not included in the model, the thermal runaway is triggered prematurely at the point where venting should occur. This shows that the heat dissipation due to ejection of electrolyte and jelly roll contents has a significant contribution. When the flow equations are included, the model shows good agreement with the experiment and therefore proving the importance of including venting.
Article
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Thermal runaway characteristics of two types of commercially available 18650 cells, based on LixFePO4 and Lix(Ni0.80Co0.15Al0.05)O2 were investigated in detail. The cells were preconditioned to state of charge (SOC) values in the range of 0% to 143%; this ensured that the working SOC window as well as overcharge conditions were covered in the experiments. Subsequently a series of temperature-ramp tests was performed with the preconditioned cells. Charged cells went into a thermal runaway, when heated above a critical temperature. The following thermal runaway parameters are provided for each experiment with the two cell types: temperature of a first detected exothermic reaction, maximum cell temperature, amount of produced ventgas and the composition of the ventgas. The dependence of those parameters with respect to the SOC is presented and a model of the major reactions during the thermal runaway is made.
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Based on the electrochemical and thermal model, a coupled electro-thermal runaway model was developed and implemented using finite element methods. The thermal decomposition reactions when the battery temperature exceeds the material decomposition temperature were embedded into the model. The temperature variations of a lithium titanate battery during a series of charge-discharge cycles under different current rates were simulated. The results of temperature and heat generation rate demonstrate that the greater the current, the faster the battery temperature is rising. Furthermore, the thermal influence of the overheated cell on surrounding batteries in the module was simulated, and the variation of temperature and heat generation during thermal runaway was obtained. It was found that the overheated cell can induce thermal runaway in other adjacent cells within 3 mm distance in the battery module if the accumulated heat is not dissipated rapidly.
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Technologies for storage of electric energy are central to a range of applications—from transportation systems, including electric and hybrid vehicles, to portable electronics. Lithium-ion batteries have emerged as the most promising technology for such applications, thanks to their high energy density, lack of hysteresis, and low self-discharge currents. One of the most important problems in battery technology is achieving safe and reliable operation at low cost. Large packs of batteries, required in high-power applications such as submarines, satellites, and electric automobiles, are prone to thermal runaways which can result in damage on a large scale. Safety is typically ensured by over-design, which amounts to packaging and passive cooling techniques designed for worst-case scenarios. Both the weight and the cost of the batteries can be con-siderably lowered by developing models of thermal dynamics in battery packs and model-based estimators and control laws. At present, only detailed numerically-oriented models (often referred to as CFD or FEM models) exist, which are used for computationally intensive off-line tests of operating scenarios, but are unsuitable for real-time implementation. In this paper, we develop a model of the thermal dynamics in large battery packs in the form of two-dimensional partial differential equations (2D PDEs). The model is a considerable simplification of the full CFD/FEM model and therefore offers the advantage of being tractable for model-based state estima-tion, parameter estimation, and control design. The simulations show that our model matches the CFD model reasonably well while taking much less time to compute, which shows the viability of our approach.
Article
An overcharge model of lithium ion battery pack was built by coupling the electrochemical model with thermal abuse model. The pack consists of three fully-charged batteries, each of which has a capacity of 10 Ah, using Li[Ni1/3Co1/3Mn1/3]O2 as the positive electrode. The three batteries in the pack were juxtaposed, and only the middle one was overcharged. The influences of current, convection coefficient and gap between batteries on the thermal runaway propagation were studied. The results of temperature and voltage obtained from the models were validated experimentally, and they were agreed well with the experimental data with the relative error within 6%. The results showed that the onset temperature of thermal runaway of the charged battery increased with an increase in the current, while the temperatures for the other two decreased. The temperature rate of the charged battery changed little when the convection coefficient was greater than 40 W/m² K. The clamp of lithium ion battery pack had an important effect on the thermal runaway propagation. The occurrence of thermal runaway propagation was depended on whether there was the existence of clamp when the battery gap exceeded 5 mm.
Article
A series of reproducible and repeatable experiments on thermal runaway propagation are conducted in this work. The impact of parameters on the process of thermal runaway propagation is explored, including the heating power, the state of the charge (SOC) and the cell spacing in the module, respectively. The cylindrical heaters with varying heating power are used to trigger thermal runaway in this work. The shape and size of the heater are designed to be the same as the sample cells. Therefore, the heat transfer mode between the heater and the cell is similar to that of the cells, where the heater is regarded as a thermal runaway cell. The results show that the module with 50% SOC releases more gases while the dramatic jet flame occurs in the module with 100% SOC. Besides, it takes around 240–280 seconds to propagate the thermal runaway event between the different layers in the battery modules. It is expected that the results of this experiment can provide the deep understanding and basic data for the module safety design.
Article
Effects of using microchannels on the wettability of the porous electrodes and preventing the battery cell from thermal runaway have been studied. Two-dimensional Lattice Boltzmann Method (LBM) simulation was carried out to simulate the effects of embedded microchannels inside the electrodes on the elec-trolyte transport in the porous electrodes as well as their effects to lead the generated gases during thermal runaway out of the battery cell. The two-phase intermolecular potential model was utilized to investigate the microscopic behavior of the electrolyte flow in the porous electrodes. The results showed that embedding microchannels inside the electrodes significantly improves the wettability of the electrodes , especially for the electrodes with lower porosities. Furthermore, the use of microchannels inside the electrodes could considerably reduce possibility of occurrence of the thermal runaway. During thermal runaway, the electrodes with higher number of smaller microchannels could drive the generated gases out of the battery cell much quicker than the electrodes with lower number of larger microchannels.
Article
Insight of thermal behaviour of lithium-ion batteries under various operating conditions is crucial for the development of battery management system (BMS). Although battery thermal behaviour has been studied by published models, the reported modelling normally addresses either normal operation or thermal runaway condition. A comprehensive electro-thermal model which can capture heat generation, voltage and current variation during the whole process from normal cycling to thermal runaway should be of benefit for BMS by evaluating critical factors influencing potential transition to thermal runaway and investigating the evolution process under different cooling and environment conditions. In this study, such a three-dimensional model has been developed within the frame of open source computational fluid dynamics (CFD) code OpenFOAM to study the electrical and thermal behaviour of lithium-ion batteries (LIBs). The equations governing the electric conduction are coupled with heat transfer and energy balance within the cell. Published and new laboratory data for LiNi0.33Co0.33Mn0.33O2/Li1.33Ti1.67O4 (LNCMO/LTO) cells from normal cycling to thermal runaway have been used to provide input parameters as well as model validation. The model has well captured the evolution process of a cell from normal cycling to abnormal behaviour until thermal runaway and achieved reasonably good agreement with the measurements. The validated model has then been used to conduct parametric studies of this particular type of LIB by evaluating the effects of discharging current rates, airflow quantities, ambient temperatures and thickness of airflow channel on the response of the cell. Faster function losses, earlier thermal runaway and higher extreme temperatures were found when cells were discharged under higher current rates. The airflow with specific velocity was found to provide effective mitigation against over-heating when the ambient temperature was below 370 K but less effective when the ambient temperature was higher than the critical value of 425 K. The thickness of airflow channel was also found to have critical influence on the cell tolerance to elevated temperatures. These parametric studies demonstrate that the model can be used to predict potential LIB transition to thermal runaway under various conditions and aid BMS.
Article
This paper presents an electrochemical-thermal coupled overcharge-to-thermal-runaway (TR) model to predict the highly interactive electrochemical and thermal behaviors of lithium ion battery under the overcharge conditions. In this model, the battery voltage equals the difference between the cathode potential and the anode potential, whereas the temperature is predicted by modeling the combined heat generations, including joule heat, thermal runaway reactions and internal short circuit. The model can fit well with the adiabatic overcharge tests results at 0.33C, 0.5C and 1C, indicating a good capture of the overcharge-to-TR mechanism. The modeling analysis based on the validated model helps to quantify the heat generation rates of each heat sources during the overcharge-to-TR process. And the two thermal runaway reactions including the electrolyte oxidation reaction and the reaction between deposited lithium and electrolyte are found to contribute most to the heat generations during the overcharge process. Further modeling analysis on the critical parameters is performed to find possible solutions for the overcharge problem of lithium ion battery. The result shows that increasing the oxidation potential of the electrolyte, and increasing the onset temperature of thermal runaway are the two effective ways to improve the overcharge performance of lithium ion battery.
Article
This paper presents a numerical model used for analyzing heat propagation as a safety feature in a custom-made battery pack. The pack uses a novel technology consisting of an internal short circuit device implanted in a cell to trigger thermal runaway. The goal of the study is to investigate the importance of wrapping cylindrical battery cells (18650 type) in a thermally and electrically insulating mica sleeve, to fix the cells in a thermally conductive aluminum heat sink. By modeling the full-scale pack using a 2D model and coupling the thermal model with an electrochemical model, good agreement with a 3D model and experimental data was found (less than 6%). The 2D modeling approach also reduces the computation time considerably (from 11 h to 25 min) compared to using a 3D model. The results showed that the air trapped between the cell and the boreholes of the heat sink provides a good insulation which reduces the temperature of the adjacent cells during thermal runaway. At the same time, a highly conductive matrix dissipates the heat throughout its thermal mass, reducing the temperature even further. It was found that for designing a safe battery pack which mitigates thermal runaway propagation, a combination of small insulating layers wrapped around the cells, and a conductive heat sink is beneficial.
Article
The safety concern is the main obstacle that hinders the large-scale applications of lithium ion batteries in electric vehicles. With continuous improvement of lithium ion batteries in energy density, enhancing their safety is becoming increasingly urgent for the electric vehicle development. Thermal runaway is the key scientific problem in battery safety research. Therefore, this paper provides a comprehensive review on the thermal runaway mechanism of the commercial lithium ion battery for electric vehicles. Learning from typical accidents, the abuse conditions that may lead to thermal runaway have been summarized. The abuse conditions include mechanical abuse, electrical abuse, and thermal abuse. Internal short circuit is the most common feature for all the abuse conditions. The thermal runaway follows a mechanism of chain reactions, during which the decomposition reaction of the battery component materials occurs one after another. A novel energy release diagram, which can quantify the reaction kinetics for all the battery component materials, is proposed to interpret the mechanisms of the chain reactions during thermal runaway. The relationship between the internal short circuit and the thermal runaway is further clarified using the energy release diagram with two cases. Finally, a three-level protection concept is proposed to help reduce the thermal runaway hazard. The three-level protection can be fulfilled by providing passive defense and early warning before the occurrence of thermal runaway, by enhancing the intrinsic thermal stability of the materials, and by reducing the secondary hazard like thermal runaway propagation.
Article
The safety issues of lithium ion batteries pose ongoing challenges as the market for Li-ion technology continues to grow in personal electronics, electric mobility, and stationary energy storage. The severe risks posed by battery thermal runaway necessitate safeguards at every design level – from materials, to cell construction, to module and pack assembly. One promising approach to pack thermal management is the use of phase change composite materials (PCC™), which offer passive protection at low weight and cost while minimizing system complexity. We present experimental nail penetration studies on a Li-ion pack for small electric vehicles, designed with and without PCC, to investigate the effectiveness of PCC thermal management for preventing propagation when a single cell enters thermal runaway. The results show that when parallel cells short-circuit through the penetrated cell, the packs without PCC propagate fully while those equipped with PCC show no propagation. In cases where no external short circuits occur, packs without PCC sometimes propagate, but not consistently. In all test conditions, the use of PCC lowers the maximum temperature experienced by neighboring cells by 60 °C or more. We also elucidate the propagation sequence and aspects of pack failure based on cell temperature, voltage, and post-mortem data.
Article
Insight of the thermal characteristics and potential flame spread over lithium-ion battery (LIB) modules is important for designing battery thermal management system and fire protection measures. Such thermal characteristics and potential flame spread are also dependent on the different anode and cathode materials as well as the electrolyte. In the present study, thermal behavior and flame propagation over seven 50 A h Li(Ni1/3Mn1/3Co1/3)O2/Li4Ti5O12 large format LIBs arranged in rhombus and parallel layouts were investigated by directly heating one of the battery units. Such batteries have already been used commercially for energy storage while relatively little is known about its safety features in connection with potential runaway caused fire and explosion hazards. It was found in the present heating tests that fire-impingement resulted in elevated temperatures in the immediate vicinity of the LIBs that were in the range of between 200 °C and 900 °C. Such temperature aggravated thermal runaway (TR) propagation, resulting in rapid temperature rise within the battery module and even explosions after 20 min of “smoldering period”. The thermal runaway and subsequent fire and explosion observed in the heating test was attributed to the violent reduction of the cathode material which coexisted with the electrolyte when the temperature exceeded 260 °C. Separate laboratory tests, which measured the heat and gases generation from samples of the anode and cathode materials using C80 calorimeter, provided insight of the physical-chemistry processes inside the battery when the temperature reaches between 30 °C and 300 °C. The self-accelerating decomposition temperature of the cell, regarded as the critical temperature to trigger TR propagation, was calculated as 126.1 and 139.2 °C using the classical Semenov and Frank-Kamenetskii models and the measurements of the calorimeter with the samples. These are consistent with the measured values in the heating tests in which TR propagated. The events leading to the explosions in the test for the rhombus layout was further analyzed and two possible explanations were postulated and analyzed based on either internal catalytic reactions or Boiling Liquid Expansion Vapor Explosion (BLEVE).
Article
In this paper, a 3D thermal runaway (TR) propagation model is built for a large format lithium ion battery module. The 3D TR propagation model is built based on the energy balance equation. Empirical equations are utilized to simplify the calculation of the chemical kinetics for TR, whereas equivalent thermal resistant layer is employed to simplify the heat transfer through the thin thermal layer. The 3D TR propagation model is validated by experiment and can provide beneficial discussions on the mechanisms of TR propagation. According to the modeling analysis of the 3D model, the TR propagation can be delayed or prevented through: 1) increasing the TR triggering temperature; 2) reducing the total electric energy released during TR; 3) enhancing the heat dissipation level; 4) adding extra thermal resistant layer between adjacent batteries. The TR propagation is successfully prevented in the model and validated by experiment. The model with 3D temperature distribution provides a beneficial tool for researchers to study the TR propagation mechanisms and for engineers to design a safer battery pack.
Article
Thermal management is critical for large-scale, shipboard energy storage systems utilizing lithium-ion batteries. In recent years, there has been growing research in thermal management of lithium-ion battery modules. However, there is little information available on the minimum cell-to-cell spacing limits for indirect, liquid cooled modules when considering heat release during a single cell failure. For this purpose, a generic four-cell module was modeled using finite element analysis to determine the sensitivity of module temperatures to cell spacing. Additionally, the effects of different heat sink materials and interface qualities were investigated. Two materials were considered, a solid aluminum block and a metal/wax composite block. Simulations were run for three different transient load profiles. The first profile simulates sustained high rate operation where the system begins at rest and generates heat continuously until it reaches steady state. And, two failure mode simulations were conducted to investigate block performance during a slow and a fast exothermic reaction, respectively. Results indicate that composite materials can perform well under normal operation and provide some protection against single cell failure; although, for very compact designs, the amount of wax available to absorb heat is reduced and the effectiveness of the phase change material is diminished. The aluminum block design performed well under all conditions, and showed that heat generated during a failure is quickly dissipated to the coolant, even under the closest cell spacing configuration.
Article
In order to study the thermal safety of cylindrical battery deeply, based on the theory of heat transfer, thermal explosion and nonlinear modeling, a three-dimensional non-steady state thermal explosion mathematical model of cylindrical fireworks with non-uniform heat dissipation of the lateral surface was established for the first time (three-dimensional partial differential equation group). Combining seven point difference method and Newton-homotopy algorithm, the numerical calculation method of the three-dimensional non-steady state thermal explosion partial differential equation was established and the numerical calculation program was written base on Matlab. The validity of calculation program has been demonstrated by comparison of numerical solutions and classical solutions. The accuracy of model has been validated by example computation and analysis. The critical parameters describing non-steady state model of cylindrical fireworks when stored individually and stored in combination form were calculated in this paper, including temperature distribution, temperature-time history, thermal explosion time to ignition, etc. The results show that when the ambient temperature is 450 K, the fireworks stored individually do not have thermal explosion, but the fireworks stored in combination form will explode finally and the thermal explosion time to ignition is 19013.53 s. When the ambient temperature is 460 K, thermal explosion will occur in both the fireworks stored individually and stored in combination form, and the thermal explosion time to ignition are 3187.07 s and 3066.60 s respectively. It shows a more exact analytical methods and solutions of thermal safety evaluation of fireworks was established in this paper. Thus, it is need to strengthen the safety monitoring and management of cylindrical battery (combined fireworks) because of the higher thermal hazard.
Article
While the energy and power density of lithium-ion batteries (LIBs) are steadily improving, thermal safety continues to remain a critical challenge. Under abuse conditions, exothermic reactions may lead to the release of heat that can trigger subsequent unsafe reactions. The situation worsens in a module configuration, as the released heat from an abused cell can activate a chain of reactions in the neighboring cells, causing catastrophic thermal runaway. This work focuses on experimental elucidation and analysis of different LIB module configurations to characterize the thermal behavior and determine safe practices. The abuse test consists of a heat-to-vent setting where a single cell in a module is triggered into thermal runaway via a heating element. The cell-to-cell thermal runaway propagation behavior has been characterized. Results have shown that increasing the inter-cell spacing in a module containing cylindrical cells significantly decreases the probability of thermal runaway propagation. Additionally, it was determined that appropriate tab configuration combined with cell form factors exhibit a major influence on thermal runaway propagation. Different thermal insulation materials have been analyzed to determine their ability to ameliorate and/or potentially mitigate propagation effects.
Article
The results of the tests conducted at NASA-JSC indicate that lithium-ion cells, when used in high voltage and high capacity configurations, have to be designed with stringent monitoring and control. The limitations with cell-level controls are described in detail in this paper.
Article
The efficiency of cooling plates for electric vehicle batteries can be improved by optimizing the geometry of internal fluid channels. In practical operation, a cooling plate is exposed to a range of operating conditions dictated by the battery, environment, and driving behaviour. To formulate an efficient cooling plate design process, the optimum design sensitivity with respect to each boundary condition is desired. This determines which operating conditions must be represented in the design process, and therefore the complexity of designing for multiple operating conditions. The objective of this study is to determine the influence of different operating conditions on the optimum cooling plate design. Three important performance measures were considered: temperature uniformity, mean temperature, and pressure drop. It was found that of these three, temperature uniformity was most sensitive to the operating conditions, especially with respect to the distribution of the input heat flux, and also to the coolant flow rate. An additional focus of the study was the distribution of heat generated by the battery cell: while it is easier to assume that heat is generated uniformly, by using an accurate distribution for design optimization, this study found that cooling plate performance could be significantly improved.
Article
Lithium-ion cells are being used in an increasing number of electric and hybrid vehicles. Both of these vehicle types contain many cells. Despite various safety measures, however, there are still reports of accidents involving abnormal heat, smoke, and fire caused by thermal runaway in the cells. If thermal runaway in one cell triggers that of another and thus causes thermal runaway propagation, this can lead to rupture of the battery pack, car fire, or other serious accidents. This study is aimed to ensure the safety of vehicles with lithium-ion cells by clarifying such accident risks, and so we investigated the process of thermal runaway propagation. In the experiment, we created a battery module made of seven laminate-type cells tightly stacked one on another. Then, we induced thermal runaway in one of the cells, measured the surface temperatures of the cells, and collected video data as the process developed. As a result, all of the seven cells underwent thermal runaway. We clarified the timing at which gas and flame eruptions occurred and the process of thermal runaway propagation. This experiment clarified one of the phenomena that occur during such propagation.
Article
Traditionally, safety and impact of failure concerns of lithium ion batteries have dealt with the field failure of single cells. However, large and complex battery systems require the consideration of how a single cell failure will impact the system as a whole. Initial failure that leads to the thermal runaway of other cells within the system creates a much more serious condition than the failure of a single cell. This work examines the behavior of small modules of cylindrical and stacked pouch cells after thermal runaway is induced in a single cell. Cylindrical cells are observed to be less prone to propagate owing to the limited contact between neighboring cells. The electrical connectivity is found to be impactful as the 10S1P cylindrical cell module did not show failure propagation through the module, while the 1S10P module had an energetic thermal runaway consuming the module minutes after the initiation failure trigger. Modules built using pouch cells conversely showed the impact of strong heat transfer between cells. In this case, a large surface area of the cells was in direct contact with its neighbors, allowing failure to propagate through the entire battery within 60–80 s for all configurations (parallel or series) tested.
Article
In this paper, the use of flat heat pipe as an effective and low-energy device to mitigate the temperature of a battery module designed for a HEV application was investigated. For this purpose, nominal heat flux generated by a battery module was reproduced and applied to a flat heat pipe cooling system. The thermal performance of the flat heat pipe cooling system was compared with that of a conventional heat sink under various cooling conditions and under several inclined positions. The results show that adding heat pipe reduced the thermal resistance of a common heat sink of 30% under natural convection and 20% under low air velocity cooling. Consequently, the cell temperature was kept below 50 °C, which cannot be achieved using heat sink. According to the space allocated for the battery pack in the vehicle, flat heat pipe can be used in vertical or horizontal position. Furthermore, flat heat pipe works efficiently under different grade road conditions. The transient behaviour of the flat heat pipe was also studied under high frequency and large amplitude variable input power. The flat heat pipe was found to handle more efficiently instant increases of the heat flux than the conventional heat sink.
Article
Thermal runaway hazards related to adiabatic runaway reactions in various 18650 Li-ion batteries were studied in an adiabatic calorimeter with vent sizing package 2 (VSP2). We selected two cathode types, LiCoO2 and Li(Ni1/3Co1/3Mn1/3)O2, and tested Li-ion batteries to determine the thermal runaway features. The charged 18650 Li-ion batteries were tested to evaluate the thermal hazard characteristics, such as the initial exothermic temperature (T0), self-heating rate (dT/dt), pressure rise rate (dP/dt), pressure–temperature profiles, maximum temperature (Tmax) and pressure (Pmax), which are measured by VSP2 with a customized stainless steel test can. The thermal reaction behaviors of the Li-ion battery packs were shown to be an important safety concern for energy storage systems for power supply applications. The thermal abuse trials of the adiabatic calorimetry methodology used to classify the self-reactive ratings of the various cathodes for Li-ion batteries provided the safety design considerations.
Article
A simple approach for using accelerating rate calorimetry data to simulate the thermal abuse resistance of battery packs is described. The thermal abuse tolerance of battery packs is estimated based on the exothermic behavior of a single cell and an energy balance than accounts for radiative, conductive, and convective heat transfer modes of the pack. For the specific example of a notebook computer pack containing eight 18650-size cells, the effects of cell position, heat of reaction, and heat-transfer coefficient are explored. Thermal runaway of the pack is more likely to be induced by thermal runaway of a single cell when that cell is in good contact with other cells and is close to the pack wall.
Article
A passive thermal management system is evaluated for high-power Li-ion packs under stressful or abusive conditions, and compared with a purely air-cooling mode under normal and abuse conditions. A compact and properly designed passive thermal management system utilizing phase change material (PCM) provides faster heat dissipation than active cooling during high pulse power discharges while preserving sufficiently uniform cell temperature to ensure the desirable cycle life for the pack. This study investigates how passive cooling with PCM contributes to preventing the propagation of thermal runaway in a single cell or adjacent cells due to a cell catastrophic failure. Its effectiveness is compared with that of active cooling by forced air flow or natural convection using the same compact module and pack configuration corresponding to the PCM matrix technology. The effects of nickel tabs and spacing between the cells were also studied.