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Lower explosion limit of the vented gases from Li-ion batteries thermal runaway in high temperature condition
Journal of Loss Prevention in the Process Industries 63 (2020) 103992
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Lower explosion limit of the vented gases from Li-ion batteries thermal runaway in high temperature condition Shichen Chen, Zhirong Wang *, Jinghong Wang **, Xuan Tong, Wei Yan Jiangsu Key Laboratory of Hazardous Chemicals Safety and Control, College of Safety Science and Engineering, Nanjing Tech University, Nanjing, 21009, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Explosive danger Collector device Theoretical calculation Comprehensive analysis approach
The thermal runaway of lithium-ion battery (or Li-ion battery, LIB) results in scrap of battery and fire, with the toxic and flammable gases generated. In this work, a self-made device was to collect gases from LIB thermal runaway, when the batteries were under different states of charge (SOC), temperatures of the environment and powers of external heating. Three samples of the collected gases were analyzed to get the results of the composition and content by chromatography-mass spectrometry system (GC-MS). The lower explosion limits (LELs) of the gases was tested by FRTA explosion limit instrument. And then the LEL of three analyzed samples whose composition and content were known by GC-MS were calculated via theoretical formulas. The calculated LELs were compared with those of the instrument test. The errors of the two results of three samples are 2.1%, 1.9%, and 0.4%. The Le Chatelier Formula and empirical formula provide a way to evaluate the LEL of the battery runaway gas more quickly.
1. Introduction With the development of technology, Li-ion battery (LIB) has been widely used in cameras, computers, mobile phones, electric vehicles, etc. due to its recharge ability, low cost, and large energy density (Guo et al., 2017). LIBs, however, contain considerable energetic materials in contact with the flammable chemical electrolyte as well as organic sol vents. Any abuse, including disposing of fire, overcharging, external short circuiting or crushing, can trigger spontaneous self-heating re actions, and lead to fire and explosion eventually (Armand and Tar ascon, 2008; Chen et al., 2017). The thermal runaway inside the battery mainly originates from decomposition of active electrolyte, and other parts such as solid electrolyte interphase (SEI), anode material, cathode material, polymer separator etc. also contribute to the runaway process. A large amount of toxic and flammable gases will generate and accu mulate inside the battery when subjected to the extreme conditions, resulting in a constantly increasing pressure. Once the difference be tween internal and external pressures reaches the threshold value, the battery ruptures, with the ejection of combustible gases. To begin with, we provide a brief background on the internal flam mable materials in the LIB. Electrolyte, as a kind of organic solvents, will
be unstable when its temperature reaches 80–100 � C (Campion et al., 2005). With the increasing of temperature, it starts reactions with anode and cathode of LIB, making the runaway decomposition products more complex (Fu et al., 2016; Zhang, 2006). In general, because of the flammable electrolytes and other active materials (Zhang et al., 2015) in LIB, the thermal runaway triggered tremendous consequences according to news reports in recent years (Wang et al., 2012). Flammable and toxic gas caused by thermal runaway is one of the hazardous factors to the human death and injury. The components of the main gas that came from the thermal runaway process, when the 18,650 type LIB was in different states of charge, could be tested by using gas-chromatography (Golubkov et al., 2013; Koch et al., 2018; Lammer et al., 2018). The results were analyzed to examine the composition and amount of the gas, which were orga nized systematically to show the possible damage from thermal runaway. A fire test chamber was used to get dynamic and visual per formance of the LIB runaway process and analyzed the species of pro duced gas (Spinner et al., 2015). Results manifested that carbon monoxide (CO) and methane (CH4), which came from the runaway phase, highlighted the toxicity and danger of a LIB failure. The safety performance of the common components of the gas from LIB with
* Corresponding author.Jiangsu Key Laboratory of Hazardous Chemicals Safety and Control, College of Safety Science and Engineering, Nanjing Tech University, Nanjing, 210009, China. ** Corresponding author. E-mail addresses: [email protected] (Z. Wang), [email protected] (J. Wang). https://doi.org/10.1016/j.jlp.2019.103992 Received 5 December 2018; Received in revised form 11 September 2019; Accepted 24 October 2019 Available online 28 October 2019 0950-4230/© 2019 Elsevier Ltd. All rights reserved.
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different kinds of electrolyte (Lamb et al., 2015) was evaluated by researching both the quantity and composition of gas and the hazard of different electrolytes. The quantitative heat release could be measured and the fluoride gas emissions also could be studied when the battery caught a fire or was in an external heating environment, while delayed ignition of the vented gases was also conducted after the gas vented. Seven different types of commercial LIBs fire tests showed that large amounts of hydrogen fluoride (HF) might be produced, and another potentially poison gas, phosphoryl fluoride (POF3), was found in some tests (Larsson et al., 2017). During the external heating tests, batteries underwent gas explosion as a result of delayed ignition of vented runaway gases mixed with the air in five of eleven cases (Larsson et al., 2018). Nevertheless, the composition of the thermal runaway gas concentrated on a limited kind of gas. All components of the vented gases are not clear. Meanwhile, the quantitative risk analysis of the gas was not conducted. Regardless of the rapid and mature test technology of LIBs, the dangers of toxicity, flammability and explosibility associated with gas emissions had this far not been feasible to take into consider ation due to the lack of data, and, especially the works on the explosion danger of the flammable gas was insufficient. From the above, previous work mainly concentrated on the effects of temperature and voltage change on the risks of LIBs, while scarce work concerning the whole gas components and explosion risk vented from the battery can be found in the literature. In consideration of the risk of thermal runaway, relevant work must be conducted to examine the performance of gas ejection, gas components, fire/explosion risks, etc. Lower explosive limit (LEL) is one of the important parameters in evaluating the flammability and explosibility of flammable gases. It is a basic threshold that guarantees the safety of the LIBs in the process of production, storage, transportation and usage, against the explosive gases. Our work focused on the LEL test of the gases from LIBs thermal runaway, which was collected by a self-made device, while the batteries were under different states of charge, temperatures of the environment and powers of external heating. The SOC gives users an indication of how much longer a battery will last before it needs recharging. The SOC estimates the amount of energy remaining in a cell compared with the energy it had when it was fully charged (Rezvanizaniani et al., 2014). Different SOC values represent different energy states and they are in ternal factors of batteries (Jiang et al., 2018). Whilst in actual use, batteries are sometimes at high environment temperature due to fire or poor heat dissipation conditions, or undergo intense high temperature heat radiation that makes a battery quickly rise to high temperature. Different environment temperatures and heating rates represent different heating processes. Therefore, in this work, the experiments were tested in three states: different SOC of LIB, heating temperatures of the heater, and heating rate (heating power of the device). According to the actual situation in industry, even though the battery and vented gas is in a confined space, the amount of the thermal runaway gas is relatively low, relative to the ambient space. Conse quently, this study focused on the LEL of the emission gas. Whilst, three samples were collected to conduct component analyses, aimed to get a result of the composition and content of the vented gas. Then the composition and content data were used to calculate the LEL by theo retical formulas and LEL data of pure substances. The calculated LEL was compared to the tested one and analyzed at last.
hexafluorophosphate salt. The separator material is two-layer structure made from polyethylene (PE). The experiment simulated the thermal runaway process of batteries during actual use in atmospheric air. The safety valve opened when the battery was heated to a surface temper ature of 132 � C–167 � C (Ping et al., 2018), then it released the pre-runaway phase gas (white smoke). With the heating of the battery, there was dramatic runaway and deflagration as its temperature rose to 199 � C–225 � C (Ping et al., 2018), with the gas venting radially from the air leaking holes (six as a circle) on top of the battery. 2.2. Vented gas collection The self-made vented gas collector device was made up of heater, trays, pedestal, glass cover, pressure gage and gas holes et al. (Fig. 1). This device can realize the functions of temperature control, power adjusting, atmosphere (air, inert gas and vacuum) control. In the experiment, an LIB (18650 type, diameter of 18 mm, height of 65 mm, cylindrical) was put into the heater which was connected to a close-loop temperature-controlling system, adopting Proportional-IntegralDerivative (PID) control system with successive approximation method to control the heating program. A type K thermocouple was positioned on side surface of the cylindrical battery. The thermocouple would not be affected by the vented gas and could measure the tem perature of the battery. The vented gases reacted with the air in the collector to produce combustion and explosion products. One of the gas holes on the top of the collector was open and the other two are closed. The open gas hole and a gasbag were connected together via a polyethylene gas tube. The gases products were collected into the gasbag from the gas hole and tube by gas pressure. The gas in the gasbag could be used in next tests directly (See Fig. 2). The thermal runaway process was recorded with a highspeed camera (100 frames per second (FPS)). 2.3. Gas component analysis The gas component analysis was conducted by using gas chromatography-mass spectrometry system, which is illustrated in Fig. 3. The types of two instruments are Agilent 7890 A (1 mL for sam ple) and Agilent 7890 B 7000C (1 mL for sample) made by Agilent Technologies in USA. Typical LIB thermal runaway situation was simulated, and the component and content of the vented gases were analyzed by using the
2. Experimental 2.1. Samples battery The Samsung ICR18650-26H M type 18,650 LIB has a capacity of 2600 mAh, a voltage of 3.6 V, and a weight of 44 g. The battery is composed of an intercalation graphite anode, lithiated metal oxide (Cobalt, Nickel, and Manganese) cathode, and an electrolyte consisting of ethylene carbonate and diethyl carbonate with lithium
Fig. 1. The experimental setup diagram. 2
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kettle was vacuumized. Then the kettle can be filled up by the air outside. The concentration of the gas in the air could be calculated by Dalton’s Law of Partial Pressure and the pressure data on the device’s screen. The ambient temperature was 20 � C. The purpose of explosion limit test is to obtain the LELs of the LIBs under different conditions directly by the tests. The scheme for the LEL tests is shown in Table 2. 3. Results and discussion
Fig. 2. A flow diagram of the gas-collection and follow-up tests.
3.1. Composition, content and toxicity of the thermal runaway gas Fig. 5 shows the thermal runaway process, which is a typical configuration, in atmospheric air at 300 � C of environment temperature, 400 W of heating rate and 100SOC. At the macro level, the thermal runaway of LIB can be divided into four stages. First, the LIB is contin uously heated and surface temperature gradually rises. Secondly, the safety valve cracks with a little bang at 2200 s and 165 � C. The tem perature has a small decline and then keeps increasing with producing smoke constantly. The runaway process goes to phase three when the smoke gets extremely thick. The intense burning of the vented gas starts with spark of dazzling, then emits strong light of flame and spew a large amount of gas. The flame fades away gradually and the temperature of LIB surface peaks at 629 � C. Last is the decay stage that the gas emission becomes lower and the light lessens, with the drop of temperature. Gas chromatography-mass spectrometry system can obtain the components via testing the mass spectrometer of different materials. The composition and content of three samples of the vented gas from the battery under three conditions are shown in Table 3, along with the LEL of every chemical (room temperature and atmospheric pressure). Three times experiments in one group were conducted and the data in the table are average values. The GC-MS exports the initial precise data directly. The errors of each data in one group are less than 0.5%. The gas is made up mainly of carbon dioxide, nitrogen, hydrogen, carbon monoxide and other organic chemicals (Table 3). The composi tion and volume fraction of each component is different from those of the works of Roth et al. (2004) and Somandepalli et al. (2014). By contrast, the composition of the vented gases is similar and the main components are carbon dioxide, hydrogen, carbon monoxide, hydro carbon and nitrogen, but the volume fraction of each component is different. This difference may be related to the battery types, battery SOCs, temperatures of environment, heating rates and atmospheres. The SEI layer tends to yield gaseous products, such as carbon monoxide and ethylene when at high temperatures (Spotnitz and Franklin, 2003). The decomposition of the electrolyte solvent, such as the reactions for diethyl carbonate with lithium hexafluorophosphate salt may be also the source of the carbon dioxide and ethylene (Kawamura et al., 2002). The hydrogen, methane and other hydrocarbon may come from the com bustion (Quintiere, 2006) of the internal and external materials of the LIB in the thermal runaway. The battery gives off flame, light, heat and a large amount of smoke when it undergoes thermal runaway, which is similar to a fire. The content of carbon monoxide in vented gas is between 2.0% and 9.9% and there is still a belief that it is the major lethal toxic agent in fires, which can lead to asphyxia, narcosis tissue hypoxia, loss of consciousness, organ failure and death (Giebułtowicz et al., 2017). Large quantities of carbon dioxide and nitrogen reduce the oxygen concentration of air and give people anoxia. The content of organic chemicals in the vented gas is not very high (5.1%–19.0%), but some of the chemicals are highly toxic, such as Benzene. It is carcinogenic to human by sufficient evidence and is placed in the Group 1 Human Carcinogen Category in International Agency for Research on Cancer (IARC) classification system (Zhang et al., 2010). Thermal runaway of LIB also releases a lot of smoke and dust that result in damage to individuals in the working environment of battery.
Fig. 3. Actual picture of gas chromatography–mass spectrometry system and the flow diagram of the component analysis.
gas chromatography-mass spectrometry system. The results can be used to predict the risk of the LIB danger. The parameters in this situation are shown in Table 1. The aim of gas component analysis is to obtain the composition and content of the vented gas. The composition and content data can be used to analyze the risk of the vented gas and calculate the LEL of it. 2.4. Explosion limit test In current work, the FRTA explosion limit instrument was employed to determine the LEL of flammable gases released by LIB, which was made by Idea Sciences Inc. in USA (as shown in Fig. 4). The instrument used ASTME681-2009 to determine the explosive limit of flammable gases at room temperature and atmospheric pressure. The sample gas, collected in a gas bag before, was transferred into the kettle for explosive in the device via the connecting pipe after the Table 1 The experimental scheme of LIB thermal runaway gas composition and content. Group of experimental A B C
SOC, % 100 60 100
Heating power, W 400 400 200
Heating temperature, � C 200 300 300
Atmosphere Air Air Air
3
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Journal of Loss Prevention in the Process Industries 63 (2020) 103992
Fig. 4. The experimental instrument of FRTA.
can explode when leaking to the ambient. In this situation, concentra tion of the gas is the main factor to decide the explosive intensity. When at lower concentration, there is not enough flammable gas to have an explosion, while at higher concentrations, the lack of oxygen cannot maintain combustion. Only between the explosive limits, can the air-fuel mixture have an explosion. The explosive limits can be tested by ex periments. Our studies focused on the LEL of gas generally as mentioned in Introduction. The security of the use and storage of LIB can be assessed according to LEL data, and the thermal runaway accidents that could happen can be warned early and evaluated, aiming to reduce the loss of gas explosion and improve the safety level. As illustrated in Fig. 6, the LEL of the vented gas increases in initial stage and then declines with the increase of the batteries SOCs. In initial stage, the LEL increases when the SOC is at a low level, which is the result of less violent thermal runaway and battery electrolyte can react with the air adequately. This combustion reaction produces a large amount of carbon dioxide (CO2), which makes the LEL higher as a kind of non-flammable gas. The thermal runaway takes place dramatically when it comes to a high SOC stage, while the internal materials in the battery cannot react with the air timely and adequately, producing much CO. The CO makes the LEL lower as a kind of flammable gas. As can be seen in Fig. 6, the highest LEL is at 60% SOC. The batteries should be stored as 60% SOC and stored in a not extremely dry environment, where the explosion risk of LIB is lower. It is better not to keep the SOC as 100%, which has a lowest LEL and a high risk of danger when a thermal runaway happens. As shown in Fig. 7, the LEL of the vented gas declines with the in crease of heating temperature in general. The higher temperature when
Table 2 The scheme for the LEL tests of vented gases produced from LIB thermal runaway. Group
I
Different SOC
II
Different heating temperature
III
Different heating power
No.
SOC, %
Heating power, W
Heating temperature, � C
Atmosphere
1 2 3 4 5 1 2 3 4 5 6 7 1 2 3 4 5
100 80 60 40 20 100 100 100 100 100 100 100 100 100 100 100 100
400 400 400 400 400 400 400 400 400 400 400 400 100 200 300 400 500
300 300 300 300 300 180 200 220 240 260 280 300 300 300 300 300 300
Air Air Air Air Air Air Air Air Air Air Air Air Air Air Air Air Air
3.2. Combustion and explosion hazards of the vented gases Whether a mixture of air and gas is combustible depends on the airto-fuel ratio. For each type of flammable gas or vapor, ignition occurs only within the explosive range (i.e. the lower and upper explosive limits, LEL and UEL). The vented gases from the LIB are flammable, and
Fig. 5. Thermal runaway process (100SOC, 300 � C, 400 W). 4
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Journal of Loss Prevention in the Process Industries 63 (2020) 103992
Table 3 Composition and volume fraction of the vented gases. LEL, %a
Chemical
Carbon dioxide Nitrogen Hydrogen Carbon monoxide Methane Ethylene Propylene Benzene Ethane Amyl acetate Oxygen 1,3-butadiene Methylbenzene N-pentane Acetylene N-butene Isobutene Propane 2-methyl-2-butene Allylene Allene Amylene Trans -2-butene N-butane Trans-2-pentene Other inflammable gas (C6þ) a b
b
non-inflammable non-inflammable 4.0 12.5 5.0 2.7 2.4 1.3 3.0 1.0 combustion-supporting 2.0 1.2 1.4 2.5 1.6 1.8 2.1 1.4 1.7 2.2 1.4 1.6 1.8 1.4 1.1
Volume fraction, % A 100SOC,200 � C,400 W
B 60SOC,300 � C,400 W
C 100SOC,300 � C,200 W
29.8571 33.1320 15.2542 7.2646 5.7084 4.3276 0.8950 0.7838 0.5403 0.4184 0.2440 0.1623 0.1315 0.0960 0.0847 0.0846 0.0790 0.0564 0.0252 0.0238 0.0204 0.0122 0.0118 0.0087 0.0060 1.8036
42.7524 44.8651 5.0337 2.0030 1.1064 1.3859 0.5245 0.2436 0.4691 0.1746 0.2018 0.1218 0.0710 0.0373 0.0724 0.0414 0.0080 0.0019 0.0029 0.0086 0.0050 0.0045 0.0026 0.0077 0.0041 0.8508
24.9487 25.4680 22.4154 9.8951 7.5091 6.0386 0.7950 0.4770 0.7743 0.4633 0.1505 0.1775 0.0707 0.0970 0.1021 0.1011 0.0353 0.0646 0.0325 0.0299 0.0134 0.0031 0.0145 0.0112 0.0069 0.3052
LEL data: Zabetakis (1964). LEL value of n-Hexane.
Fig. 6. LELs of flammable gases under different states of charge.
Fig. 7. LELs of flammable gases under different environmental temperature of heating.
the thermal runaway happens makes the runaway more violent, and the proportion of flammable gas is higher. Because of the poor stability of LIB, temperature monitoring is necessary to prevent it from thermal runaway at high temperature. Once the temperature goes to 120 � C, the inside of the battery will undergo an irreversible chemical change and the risk of runaway and explosion increases greatly. As presented in Fig. 8, the LEL of the vented gas declines with the increase of heating power obviously. Higher heating power leads to easier explosion risk. In the experiment, the heating power simulates the heating rate of temperature. When the heating rate of LIB is higher, the LEL of the vented gas goes lower, which makes the explosion easier. So
that the temperature change rate is also important. The possibility of the LIB explosion will reduce as long as the battery at a high increasing rate of temperature can be detected in time. The SOC is the basic property of the battery. The anode of the LIB stores lithium ions during charging process. The higher the SOC is, the more lithium ions the anode stores. The lithium ions in the anode react with the electrolyte, etc. when the battery undergoes a thermal runaway and the anode collapses. The reactions of the lithium ions decide the result of the venting of the thermal runaway gas. Heating temperature and heating power are the external factors to the thermal runaway on 5
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LEL’mix ¼ LELmix �
the heat absorption of the battery. The lowest LEL is 4.80% in this work, which can provide guidance for design of explosion-proof electric apparatus and setting alarm parameter of flammable gas detectors in a LIB container or warehouse. 3.3. Theoretical calculation on LEL of vented gas from LIB The LEL data of pure gas can be obtained from the database (Zabe takis, 1964) (room temperature and atmospheric pressure). The LEL of gaseous mixture can be predicted by Le Chatelier Formula (Cai et al., 2001) theoretically. When the components of the gaseous mixture are known, the LEL could be calculated by Eq. (1):
i¼1
4. Conclusions The aim of this study is to put forward a comprehensive analysis approach. It use three curves of the LEL with SOC, heating temperature and heating power to describe the LEL change trend of the vented gas from LIB thermal runaway and a kind of theoretic calculation method to validate the Le Chatelier Formula and empirical formula in LEL calcu lation & prediction of the battery runaway gas. A self-made vented gas collector device collected the vented gas from the LIBs thermal runaway. The batteries with different SOCs underwent thermal runaway at 300 � C of heating environment temperature and 400 W of heating power. The batteries with 100% SOC underwent thermal runaway at different heating environment and heating power. The composition and content of three samples of the vented gas were tested. The FRTA explosion limit instrument is used to test the lower explosion limit of all samples of the vented gas. The LEL of the vented gas increases in initial stage and then declines with the increase of the batteries SOCs. When the heating temperature increases, it declines in general. It declines with the increase of heating power obviously. Combined with the definition of lower explosion limit, the Le Chatelier Formula and the empirical formula, the prediction of the LEL of the gaseous mixture was carried out. The LELs of three samples of the vented gas, whose composition and content were tested before, were calculated
(1)
xi LELi
LELmix—LEL of gaseous mixture; LELi—LEL of one component in the gaseous mixture; xi—mole fraction or volume fraction of one component in the gaseous mixture; n—number of the components. When there are inert gases in the gaseous mixture, the LEL can be predicted by empirical formula Eq. (2): � � 1 þ 1 BB � 100 LEL’mix ¼ LELmix � % (2) 100 þ LELmix � 1 BB LEL0 mix——LEL of the gaseous mixture within inert gases; B——volume fraction of the inert gases. We use the data from group A as an example. From the Le Chatelier Formula: LELmix ¼
x H2 LELH2
xCO þ LEL þ CO
xCH4 LELCH4
% ¼ 8:68% 100 þ LELmix � 1 0:620 0:620
As a result, the LEL of the vented gas from the battery (100% of SOC, 400 W of heating power, 200 � C of heating temperature, atmospheric air) is 8.68% by components test and theoretical calculation. According to the LEL test experiment, the LEL of the vented gas from the battery (100% of SOC, 400 W of heating power, 200 � C of heating temperature, atmospheric air), is 8.50% by experimental test. The error of the two results is 2.1%, which is less than 5.0%. The complicated components may be the reason behind the error. Theoretical calculation results of all the three groups of experimental are shown in Table 4. The errors are all less than 5%. There are maybe three major reasons for the errors. Firstly, the composition and volume fraction of the vented gas from LIB thermal runaway is extremely complicated due to the violent reaction of battery materials. On the one hand, some less common chemical does not have an LEL datum in the database. On the other hand, because of instrument and chromatogram restrictions, some hydrocarbon cannot be identified and be labeled as C6þ chemicals. These cause the lack of data of the flammable chemicals in the calculation, which leads to the errors, despite the low volume fraction. Secondly, only the composition and volume fraction of the flammable gases are considered in the theoretical calculation equations. However, the influences of the bond energy, incomplete combustion and decomposition of the combustion products are neglected in the calculation. The last possible reason is the different test instruments. The LEL measurement is indirect by using a flammable gas container, which could have an impact on the explosive limits because of the surface area of the container, thermal conductivity co efficient of the container wall material, etc. As a result of the coaction of abovementioned factors, there are errors between theoretical calcula tion result and test data, which are smaller than 5.0% and acceptable.
Fig. 8. LELs of flammable gases under different power of heating device.
1 LELmix ¼ P n
� � 1 þ 1 0:620 � 100 0:620
Table 4 Composition and ratio table of the gas specimen.
1 ¼ 3:49% x xother þ LELC2CH4H þ LEL þ ⋅⋅⋅ other 2 4
From the empirical formula:
6
Group of experimental
LEL value of theoretical calculation result
LEL value of LEL test result
Error
A B C
8.68% 20.69% 7.80%
8.50% 21.10% 7.75%
2.1% 1.9% 0.6%
100SOC,200 � C,400 W 60SOC,300 � C,400 W 100SOC,300 � C,200 W
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theoretically. The errors of the three calculated results were less than 5 percentage points. The regularity of the LEL of the vented gas, that the battery is at different SOC, heating power and heating temperature, is acquired to apply to the industry for the safe use and storage of LIBs. The experimental method of LEL test needs to collect the vented gas more than twice with more than two batteries in one group, to get enough gas for the next explosion limit test. The test also needs to be done for many times in one set to get an accurate result of the LEL. Therefore, the method of Le Chatelier Formula and the empirical for mula can do an approximate calculation of the LEL with once collection process and once GC-MS analysis of the vented gas. This method pro vides a way to evaluate the explosion risk of the vented gas more quickly. The internal chemical reactions in the battery and external chemicals reactions of the released product from thermal runaway are the bridge between the LIB conditions and hazard risk.
batteries during the charge-discharge process. J. Loss Prev. Process. Ind. 49, 953–960. https://doi.org/10.1016/j.jlp.2017.05.029. Jiang, F.W., Liu, K., Wang, Z.R., Tong, X., Guo, L.S., 2018. Theoretical analysis of lithium-ion battery failure characteristics under different states of charge. Fire Mater. 42 (6), 680–686. https://doi.org/10.1002/fam.2522. Kawamura, T., Kimura, A., Egashira, M., Okada, S., Yamaki, J.-I., 2002. Thermal stability of alkyl carbonate mixed-solvent electrolytes for lithium ion cells. J. Power Sources 104 (2), 260–264. https://doi.org/10.1016/S0378-7753(01)00960-0. Koch, S., Fill, A., Birke, K.P., 2018. Comprehensive gas analysis on large scale automotive lithium-ion cells in thermal runaway. J. Power Sources 398, 106–112. https://doi. org/10.1016/j.jpowsour.2018.07.051. Lamb, J., Orendorff, C.J., Roth, E.P., Langendorf, J., 2015. Studies on the thermal breakdown of common Li-ion battery electrolyte components. J. Electrochem. Soc. 162 (10), A2131–A2135. https://doi.org/10.1149/2.0651510jes. Lammer, M., K€ onigseder, A., Gluschitz, P., Hacker, V., 2018. Influence of aging on the heat and gas emissions from commercial lithium ion cells in case of thermal failure. J. Electrochem. Sci. Eng. 8 (1), 101–110. https://doi.org/10.5599/jese.476. Larsson, F., Andersson, P., Blomqvist, P., Mellander, B.-E., 2017. Toxic fluoride gas emissions from lithium-ion battery fires. Sci. Rep. 7 (10018), 1–14. https://doi.org/ 10.1038/s41598-017-09784-z. Larsson, F., Bertilsson, S., Furlani, M., Albinsson, I., Mellander, B.-E., 2018. Gas explosions and thermal runaways during external heating abuse of commercial lithium-ion graphite-LiCoO2 cells at different levels of ageing. J. Power Sources 373, 220–231. https://doi.org/10.1016/j.jpowsour.2017.10.085. Ping, P., Kong, D.P., Zhang, J.Q., Wen, R.X., Wen, J., 2018. Characterization of behaviour and hazards of fire and deflagration for high-energy Li-ion cells by overheating. J. Power Sources 398, 55–66. https://doi.org/10.1016/j. jpowsour.2018.07.044. Quintiere, J.G., 2006. Fundamentals of Fire Phenomena. John Wiley & Sons, Chichester (UK), p. 35. Rezvanizaniani, S.M., Liu, Z.C., Chen, Y., Lee, J., 2014. Review and recent advances in battery health monitoring and prognostics technologies for electric vehicle (EV) safety and mobility. J. Power Sources 256, 110–124. https://doi.org/10.1016/j. jpowsour.2014.01.085. Roth, E.P., Crafts, C.C., Doughty, D.H., Mcbreen, J., 2004. Advanced Technology Development Program for Lithium-Ion Batteries: Thermal Abuse Performance of 18650 Li-Ion Cells. Office of Scientific & Technical Information Technical Reports. Somandepalli, V., Marr, K., Horn, Q., 2014. Quantification of combustion hazards of thermal runaway failures in lithium-ion batteries. SAE Int. J. Altern. Powertrains. 3 (1), 98–104. https://doi.org/10.4271/2014-01-1857. Spinner, N.S., Field, C.R., Hammond, M.H., Williams, B.A., Myers, K.M., Lubrano, A.L., Rose-Pehrsson, S.L., Tuttle, S.G., 2015. Physical and chemical analysis of lithium-ion battery cell-to-cell failure events inside custom fire chamber. J. Power Sources 279, 713–721. https://doi.org/10.1016/j.jpowsour.2015.01.068. Spotnitz, R., Franklin, J., 2003. Abuse behavior of high-power, lithium-ion cells. J. Power Sources 113 (1), 81–100. https://doi.org/10.1016/S0378-7753(02)00488-3. Wang, Q.S., Ping, P., Zhao, X.J., Chu, G.Q., Sun, J.H., Chen, C.H., 2012. Thermal runaway caused fire and explosion of lithium ion battery. J. Power Sources 208, 210–224. https://doi.org/10.1016/j.jpowsour.2012.02.038. Zabetakis, M.G., 1964. Flammability Characteristics of Combustible Gases and Vapors. Bureau of Mines, Pittsburgh, PA (United States), pp. 114–116. Zhang, S.S., 2006. A review on electrolyte additives for lithium-ion batteries. J. Power Sources 162 (2), 1379–1394. https://doi.org/10.1016/j.jpowsour.2006.07.074. Zhang, L.P., McHale, C.M., Rothman, N., Li, G., Ji, Z.Y., Vermeulen, R., Hubbard, A.E., Ren, X.F., Shen, M., Rappaport, S.M., North, M., Skibola, C.F., Yin, S.N., Vulpe, C., Chanock, S.J., Smith, M.T., Lan, Q., 2010. Systems biology of human benzene exposure. Chem. Biol. Interact. 184 (1–2), 86–93. https://doi.org/10.1016/j. cbi.2009.12.011. Zhang, W.X., Chen, X., Chen, Q.P., Ding, C., Liu, J.H., Chen, M.Y., Wang, J., 2015. Combustion calorimetry of carbonate electrolytes used in lithium ion batteries. J. Fire Sci. 33 (1), 22–36. https://doi.org/10.1177/0734904114550789.
Acknowledgements The authors are grateful for the support given by National Natural Science Foundation of China [grant number 51874184], the Key R & D programs (Social Development) in Jiangsu Province [grant number BE2016771], the Key Natural Science Foundation in Jiangsu Province [grant number 18KJA620003], the Jiangsu Project Plan for Outstanding Talents Team in Six Research Fields [grant number TD-XNYQC-002], and the Postgraduate Research & Practice Innovation Program of Jiangsu Province [grant number KYCX18_1051]. The authors also thank Yang Hongqi with Nanjing Tech University for much help to this manuscript. References Armand, M., Tarascon, J.-M., 2008. Building better batteries. Nature 451 (7179), 652–657. https://doi.org/10.1038/451652a. Cai, F.Y., Tan, Z.S., Meng, H., Cai, R.L., 2001. Chemical Process Safety Engineering. Science Press, Beijing (China), pp. 44–45. Campion, C.L., Li, W.T., Lucht, B.L., 2005. Thermal decomposition of LiPF6-based electrolytes for lithium-ion batteries. J. Electrochem. Soc. 152 (12) https://doi.org/ 10.1149/1.2083267. A2327–A2327. Chen, M.Y., Liu, J.H., He, Y.P., Yuen, R., Wang, J., 2017. Study of the fire hazards of lithium-ion batteries at different pressures. Appl. Therm. Eng. 125, 1061–1074. https://doi.org/10.1016/j.applthermaleng.2017.06.131. Fu, Y.Y., Lu, S., Shi, L., Chen, X.D., Zhang, H.P., 2016. Combustion characteristics of electrolyte pool fires for lithium ion batteries. J. Electrochem. Soc. 163 (9), A2022–A2028. https://doi.org/10.1149/2.0721609jes. Giebułtowicz, J., Ru_zycka, M., Wroczy� nski, P., Purser, D.A., Stec, A.A., 2017. Analysis of fire deaths in Poland and influence of smoke toxicity. Forensic Sci. Int. 277, 77–87. https://doi.org/10.1016/j.forsciint.2017.05.018. Golubkov, A.W., Fuchs, D., Wagner, J., Wiltsche, H., Stangl, C., Fauler, G., Voitic, G., Thaler, A., Hacker, V., 2013. Thermal-runaway experiments on consumer Li-ion batteries with metal-oxide and olivin-type cathodes. RSC Adv. 4 (7), 3633–3642. https://doi.org/10.1039/C3RA45748F. Guo, L.S., Wang, Z.R., Wang, J.H., Luo, Q.K., Liu, J.J., 2017. Effects of the environmental temperature and heat dissipation condition on the thermal runaway of lithium ion
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Journal of Loss Prevention in the Process Industries journal homepage: http://www.elsevier.com/locate/jlp
Lower explosion limit of the vented gases from Li-ion batteries thermal runaway in high temperature condition Shichen Chen, Zhirong Wang *, Jinghong Wang **, Xuan Tong, Wei Yan Jiangsu Key Laboratory of Hazardous Chemicals Safety and Control, College of Safety Science and Engineering, Nanjing Tech University, Nanjing, 21009, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Explosive danger Collector device Theoretical calculation Comprehensive analysis approach
The thermal runaway of lithium-ion battery (or Li-ion battery, LIB) results in scrap of battery and fire, with the toxic and flammable gases generated. In this work, a self-made device was to collect gases from LIB thermal runaway, when the batteries were under different states of charge (SOC), temperatures of the environment and powers of external heating. Three samples of the collected gases were analyzed to get the results of the composition and content by chromatography-mass spectrometry system (GC-MS). The lower explosion limits (LELs) of the gases was tested by FRTA explosion limit instrument. And then the LEL of three analyzed samples whose composition and content were known by GC-MS were calculated via theoretical formulas. The calculated LELs were compared with those of the instrument test. The errors of the two results of three samples are 2.1%, 1.9%, and 0.4%. The Le Chatelier Formula and empirical formula provide a way to evaluate the LEL of the battery runaway gas more quickly.
1. Introduction With the development of technology, Li-ion battery (LIB) has been widely used in cameras, computers, mobile phones, electric vehicles, etc. due to its recharge ability, low cost, and large energy density (Guo et al., 2017). LIBs, however, contain considerable energetic materials in contact with the flammable chemical electrolyte as well as organic sol vents. Any abuse, including disposing of fire, overcharging, external short circuiting or crushing, can trigger spontaneous self-heating re actions, and lead to fire and explosion eventually (Armand and Tar ascon, 2008; Chen et al., 2017). The thermal runaway inside the battery mainly originates from decomposition of active electrolyte, and other parts such as solid electrolyte interphase (SEI), anode material, cathode material, polymer separator etc. also contribute to the runaway process. A large amount of toxic and flammable gases will generate and accu mulate inside the battery when subjected to the extreme conditions, resulting in a constantly increasing pressure. Once the difference be tween internal and external pressures reaches the threshold value, the battery ruptures, with the ejection of combustible gases. To begin with, we provide a brief background on the internal flam mable materials in the LIB. Electrolyte, as a kind of organic solvents, will
be unstable when its temperature reaches 80–100 � C (Campion et al., 2005). With the increasing of temperature, it starts reactions with anode and cathode of LIB, making the runaway decomposition products more complex (Fu et al., 2016; Zhang, 2006). In general, because of the flammable electrolytes and other active materials (Zhang et al., 2015) in LIB, the thermal runaway triggered tremendous consequences according to news reports in recent years (Wang et al., 2012). Flammable and toxic gas caused by thermal runaway is one of the hazardous factors to the human death and injury. The components of the main gas that came from the thermal runaway process, when the 18,650 type LIB was in different states of charge, could be tested by using gas-chromatography (Golubkov et al., 2013; Koch et al., 2018; Lammer et al., 2018). The results were analyzed to examine the composition and amount of the gas, which were orga nized systematically to show the possible damage from thermal runaway. A fire test chamber was used to get dynamic and visual per formance of the LIB runaway process and analyzed the species of pro duced gas (Spinner et al., 2015). Results manifested that carbon monoxide (CO) and methane (CH4), which came from the runaway phase, highlighted the toxicity and danger of a LIB failure. The safety performance of the common components of the gas from LIB with
* Corresponding author.Jiangsu Key Laboratory of Hazardous Chemicals Safety and Control, College of Safety Science and Engineering, Nanjing Tech University, Nanjing, 210009, China. ** Corresponding author. E-mail addresses: [email protected] (Z. Wang), [email protected] (J. Wang). https://doi.org/10.1016/j.jlp.2019.103992 Received 5 December 2018; Received in revised form 11 September 2019; Accepted 24 October 2019 Available online 28 October 2019 0950-4230/© 2019 Elsevier Ltd. All rights reserved.
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different kinds of electrolyte (Lamb et al., 2015) was evaluated by researching both the quantity and composition of gas and the hazard of different electrolytes. The quantitative heat release could be measured and the fluoride gas emissions also could be studied when the battery caught a fire or was in an external heating environment, while delayed ignition of the vented gases was also conducted after the gas vented. Seven different types of commercial LIBs fire tests showed that large amounts of hydrogen fluoride (HF) might be produced, and another potentially poison gas, phosphoryl fluoride (POF3), was found in some tests (Larsson et al., 2017). During the external heating tests, batteries underwent gas explosion as a result of delayed ignition of vented runaway gases mixed with the air in five of eleven cases (Larsson et al., 2018). Nevertheless, the composition of the thermal runaway gas concentrated on a limited kind of gas. All components of the vented gases are not clear. Meanwhile, the quantitative risk analysis of the gas was not conducted. Regardless of the rapid and mature test technology of LIBs, the dangers of toxicity, flammability and explosibility associated with gas emissions had this far not been feasible to take into consider ation due to the lack of data, and, especially the works on the explosion danger of the flammable gas was insufficient. From the above, previous work mainly concentrated on the effects of temperature and voltage change on the risks of LIBs, while scarce work concerning the whole gas components and explosion risk vented from the battery can be found in the literature. In consideration of the risk of thermal runaway, relevant work must be conducted to examine the performance of gas ejection, gas components, fire/explosion risks, etc. Lower explosive limit (LEL) is one of the important parameters in evaluating the flammability and explosibility of flammable gases. It is a basic threshold that guarantees the safety of the LIBs in the process of production, storage, transportation and usage, against the explosive gases. Our work focused on the LEL test of the gases from LIBs thermal runaway, which was collected by a self-made device, while the batteries were under different states of charge, temperatures of the environment and powers of external heating. The SOC gives users an indication of how much longer a battery will last before it needs recharging. The SOC estimates the amount of energy remaining in a cell compared with the energy it had when it was fully charged (Rezvanizaniani et al., 2014). Different SOC values represent different energy states and they are in ternal factors of batteries (Jiang et al., 2018). Whilst in actual use, batteries are sometimes at high environment temperature due to fire or poor heat dissipation conditions, or undergo intense high temperature heat radiation that makes a battery quickly rise to high temperature. Different environment temperatures and heating rates represent different heating processes. Therefore, in this work, the experiments were tested in three states: different SOC of LIB, heating temperatures of the heater, and heating rate (heating power of the device). According to the actual situation in industry, even though the battery and vented gas is in a confined space, the amount of the thermal runaway gas is relatively low, relative to the ambient space. Conse quently, this study focused on the LEL of the emission gas. Whilst, three samples were collected to conduct component analyses, aimed to get a result of the composition and content of the vented gas. Then the composition and content data were used to calculate the LEL by theo retical formulas and LEL data of pure substances. The calculated LEL was compared to the tested one and analyzed at last.
hexafluorophosphate salt. The separator material is two-layer structure made from polyethylene (PE). The experiment simulated the thermal runaway process of batteries during actual use in atmospheric air. The safety valve opened when the battery was heated to a surface temper ature of 132 � C–167 � C (Ping et al., 2018), then it released the pre-runaway phase gas (white smoke). With the heating of the battery, there was dramatic runaway and deflagration as its temperature rose to 199 � C–225 � C (Ping et al., 2018), with the gas venting radially from the air leaking holes (six as a circle) on top of the battery. 2.2. Vented gas collection The self-made vented gas collector device was made up of heater, trays, pedestal, glass cover, pressure gage and gas holes et al. (Fig. 1). This device can realize the functions of temperature control, power adjusting, atmosphere (air, inert gas and vacuum) control. In the experiment, an LIB (18650 type, diameter of 18 mm, height of 65 mm, cylindrical) was put into the heater which was connected to a close-loop temperature-controlling system, adopting Proportional-IntegralDerivative (PID) control system with successive approximation method to control the heating program. A type K thermocouple was positioned on side surface of the cylindrical battery. The thermocouple would not be affected by the vented gas and could measure the tem perature of the battery. The vented gases reacted with the air in the collector to produce combustion and explosion products. One of the gas holes on the top of the collector was open and the other two are closed. The open gas hole and a gasbag were connected together via a polyethylene gas tube. The gases products were collected into the gasbag from the gas hole and tube by gas pressure. The gas in the gasbag could be used in next tests directly (See Fig. 2). The thermal runaway process was recorded with a highspeed camera (100 frames per second (FPS)). 2.3. Gas component analysis The gas component analysis was conducted by using gas chromatography-mass spectrometry system, which is illustrated in Fig. 3. The types of two instruments are Agilent 7890 A (1 mL for sam ple) and Agilent 7890 B 7000C (1 mL for sample) made by Agilent Technologies in USA. Typical LIB thermal runaway situation was simulated, and the component and content of the vented gases were analyzed by using the
2. Experimental 2.1. Samples battery The Samsung ICR18650-26H M type 18,650 LIB has a capacity of 2600 mAh, a voltage of 3.6 V, and a weight of 44 g. The battery is composed of an intercalation graphite anode, lithiated metal oxide (Cobalt, Nickel, and Manganese) cathode, and an electrolyte consisting of ethylene carbonate and diethyl carbonate with lithium
Fig. 1. The experimental setup diagram. 2
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kettle was vacuumized. Then the kettle can be filled up by the air outside. The concentration of the gas in the air could be calculated by Dalton’s Law of Partial Pressure and the pressure data on the device’s screen. The ambient temperature was 20 � C. The purpose of explosion limit test is to obtain the LELs of the LIBs under different conditions directly by the tests. The scheme for the LEL tests is shown in Table 2. 3. Results and discussion
Fig. 2. A flow diagram of the gas-collection and follow-up tests.
3.1. Composition, content and toxicity of the thermal runaway gas Fig. 5 shows the thermal runaway process, which is a typical configuration, in atmospheric air at 300 � C of environment temperature, 400 W of heating rate and 100SOC. At the macro level, the thermal runaway of LIB can be divided into four stages. First, the LIB is contin uously heated and surface temperature gradually rises. Secondly, the safety valve cracks with a little bang at 2200 s and 165 � C. The tem perature has a small decline and then keeps increasing with producing smoke constantly. The runaway process goes to phase three when the smoke gets extremely thick. The intense burning of the vented gas starts with spark of dazzling, then emits strong light of flame and spew a large amount of gas. The flame fades away gradually and the temperature of LIB surface peaks at 629 � C. Last is the decay stage that the gas emission becomes lower and the light lessens, with the drop of temperature. Gas chromatography-mass spectrometry system can obtain the components via testing the mass spectrometer of different materials. The composition and content of three samples of the vented gas from the battery under three conditions are shown in Table 3, along with the LEL of every chemical (room temperature and atmospheric pressure). Three times experiments in one group were conducted and the data in the table are average values. The GC-MS exports the initial precise data directly. The errors of each data in one group are less than 0.5%. The gas is made up mainly of carbon dioxide, nitrogen, hydrogen, carbon monoxide and other organic chemicals (Table 3). The composi tion and volume fraction of each component is different from those of the works of Roth et al. (2004) and Somandepalli et al. (2014). By contrast, the composition of the vented gases is similar and the main components are carbon dioxide, hydrogen, carbon monoxide, hydro carbon and nitrogen, but the volume fraction of each component is different. This difference may be related to the battery types, battery SOCs, temperatures of environment, heating rates and atmospheres. The SEI layer tends to yield gaseous products, such as carbon monoxide and ethylene when at high temperatures (Spotnitz and Franklin, 2003). The decomposition of the electrolyte solvent, such as the reactions for diethyl carbonate with lithium hexafluorophosphate salt may be also the source of the carbon dioxide and ethylene (Kawamura et al., 2002). The hydrogen, methane and other hydrocarbon may come from the com bustion (Quintiere, 2006) of the internal and external materials of the LIB in the thermal runaway. The battery gives off flame, light, heat and a large amount of smoke when it undergoes thermal runaway, which is similar to a fire. The content of carbon monoxide in vented gas is between 2.0% and 9.9% and there is still a belief that it is the major lethal toxic agent in fires, which can lead to asphyxia, narcosis tissue hypoxia, loss of consciousness, organ failure and death (Giebułtowicz et al., 2017). Large quantities of carbon dioxide and nitrogen reduce the oxygen concentration of air and give people anoxia. The content of organic chemicals in the vented gas is not very high (5.1%–19.0%), but some of the chemicals are highly toxic, such as Benzene. It is carcinogenic to human by sufficient evidence and is placed in the Group 1 Human Carcinogen Category in International Agency for Research on Cancer (IARC) classification system (Zhang et al., 2010). Thermal runaway of LIB also releases a lot of smoke and dust that result in damage to individuals in the working environment of battery.
Fig. 3. Actual picture of gas chromatography–mass spectrometry system and the flow diagram of the component analysis.
gas chromatography-mass spectrometry system. The results can be used to predict the risk of the LIB danger. The parameters in this situation are shown in Table 1. The aim of gas component analysis is to obtain the composition and content of the vented gas. The composition and content data can be used to analyze the risk of the vented gas and calculate the LEL of it. 2.4. Explosion limit test In current work, the FRTA explosion limit instrument was employed to determine the LEL of flammable gases released by LIB, which was made by Idea Sciences Inc. in USA (as shown in Fig. 4). The instrument used ASTME681-2009 to determine the explosive limit of flammable gases at room temperature and atmospheric pressure. The sample gas, collected in a gas bag before, was transferred into the kettle for explosive in the device via the connecting pipe after the Table 1 The experimental scheme of LIB thermal runaway gas composition and content. Group of experimental A B C
SOC, % 100 60 100
Heating power, W 400 400 200
Heating temperature, � C 200 300 300
Atmosphere Air Air Air
3
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Fig. 4. The experimental instrument of FRTA.
can explode when leaking to the ambient. In this situation, concentra tion of the gas is the main factor to decide the explosive intensity. When at lower concentration, there is not enough flammable gas to have an explosion, while at higher concentrations, the lack of oxygen cannot maintain combustion. Only between the explosive limits, can the air-fuel mixture have an explosion. The explosive limits can be tested by ex periments. Our studies focused on the LEL of gas generally as mentioned in Introduction. The security of the use and storage of LIB can be assessed according to LEL data, and the thermal runaway accidents that could happen can be warned early and evaluated, aiming to reduce the loss of gas explosion and improve the safety level. As illustrated in Fig. 6, the LEL of the vented gas increases in initial stage and then declines with the increase of the batteries SOCs. In initial stage, the LEL increases when the SOC is at a low level, which is the result of less violent thermal runaway and battery electrolyte can react with the air adequately. This combustion reaction produces a large amount of carbon dioxide (CO2), which makes the LEL higher as a kind of non-flammable gas. The thermal runaway takes place dramatically when it comes to a high SOC stage, while the internal materials in the battery cannot react with the air timely and adequately, producing much CO. The CO makes the LEL lower as a kind of flammable gas. As can be seen in Fig. 6, the highest LEL is at 60% SOC. The batteries should be stored as 60% SOC and stored in a not extremely dry environment, where the explosion risk of LIB is lower. It is better not to keep the SOC as 100%, which has a lowest LEL and a high risk of danger when a thermal runaway happens. As shown in Fig. 7, the LEL of the vented gas declines with the in crease of heating temperature in general. The higher temperature when
Table 2 The scheme for the LEL tests of vented gases produced from LIB thermal runaway. Group
I
Different SOC
II
Different heating temperature
III
Different heating power
No.
SOC, %
Heating power, W
Heating temperature, � C
Atmosphere
1 2 3 4 5 1 2 3 4 5 6 7 1 2 3 4 5
100 80 60 40 20 100 100 100 100 100 100 100 100 100 100 100 100
400 400 400 400 400 400 400 400 400 400 400 400 100 200 300 400 500
300 300 300 300 300 180 200 220 240 260 280 300 300 300 300 300 300
Air Air Air Air Air Air Air Air Air Air Air Air Air Air Air Air Air
3.2. Combustion and explosion hazards of the vented gases Whether a mixture of air and gas is combustible depends on the airto-fuel ratio. For each type of flammable gas or vapor, ignition occurs only within the explosive range (i.e. the lower and upper explosive limits, LEL and UEL). The vented gases from the LIB are flammable, and
Fig. 5. Thermal runaway process (100SOC, 300 � C, 400 W). 4
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Table 3 Composition and volume fraction of the vented gases. LEL, %a
Chemical
Carbon dioxide Nitrogen Hydrogen Carbon monoxide Methane Ethylene Propylene Benzene Ethane Amyl acetate Oxygen 1,3-butadiene Methylbenzene N-pentane Acetylene N-butene Isobutene Propane 2-methyl-2-butene Allylene Allene Amylene Trans -2-butene N-butane Trans-2-pentene Other inflammable gas (C6þ) a b
b
non-inflammable non-inflammable 4.0 12.5 5.0 2.7 2.4 1.3 3.0 1.0 combustion-supporting 2.0 1.2 1.4 2.5 1.6 1.8 2.1 1.4 1.7 2.2 1.4 1.6 1.8 1.4 1.1
Volume fraction, % A 100SOC,200 � C,400 W
B 60SOC,300 � C,400 W
C 100SOC,300 � C,200 W
29.8571 33.1320 15.2542 7.2646 5.7084 4.3276 0.8950 0.7838 0.5403 0.4184 0.2440 0.1623 0.1315 0.0960 0.0847 0.0846 0.0790 0.0564 0.0252 0.0238 0.0204 0.0122 0.0118 0.0087 0.0060 1.8036
42.7524 44.8651 5.0337 2.0030 1.1064 1.3859 0.5245 0.2436 0.4691 0.1746 0.2018 0.1218 0.0710 0.0373 0.0724 0.0414 0.0080 0.0019 0.0029 0.0086 0.0050 0.0045 0.0026 0.0077 0.0041 0.8508
24.9487 25.4680 22.4154 9.8951 7.5091 6.0386 0.7950 0.4770 0.7743 0.4633 0.1505 0.1775 0.0707 0.0970 0.1021 0.1011 0.0353 0.0646 0.0325 0.0299 0.0134 0.0031 0.0145 0.0112 0.0069 0.3052
LEL data: Zabetakis (1964). LEL value of n-Hexane.
Fig. 6. LELs of flammable gases under different states of charge.
Fig. 7. LELs of flammable gases under different environmental temperature of heating.
the thermal runaway happens makes the runaway more violent, and the proportion of flammable gas is higher. Because of the poor stability of LIB, temperature monitoring is necessary to prevent it from thermal runaway at high temperature. Once the temperature goes to 120 � C, the inside of the battery will undergo an irreversible chemical change and the risk of runaway and explosion increases greatly. As presented in Fig. 8, the LEL of the vented gas declines with the increase of heating power obviously. Higher heating power leads to easier explosion risk. In the experiment, the heating power simulates the heating rate of temperature. When the heating rate of LIB is higher, the LEL of the vented gas goes lower, which makes the explosion easier. So
that the temperature change rate is also important. The possibility of the LIB explosion will reduce as long as the battery at a high increasing rate of temperature can be detected in time. The SOC is the basic property of the battery. The anode of the LIB stores lithium ions during charging process. The higher the SOC is, the more lithium ions the anode stores. The lithium ions in the anode react with the electrolyte, etc. when the battery undergoes a thermal runaway and the anode collapses. The reactions of the lithium ions decide the result of the venting of the thermal runaway gas. Heating temperature and heating power are the external factors to the thermal runaway on 5
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LEL’mix ¼ LELmix �
the heat absorption of the battery. The lowest LEL is 4.80% in this work, which can provide guidance for design of explosion-proof electric apparatus and setting alarm parameter of flammable gas detectors in a LIB container or warehouse. 3.3. Theoretical calculation on LEL of vented gas from LIB The LEL data of pure gas can be obtained from the database (Zabe takis, 1964) (room temperature and atmospheric pressure). The LEL of gaseous mixture can be predicted by Le Chatelier Formula (Cai et al., 2001) theoretically. When the components of the gaseous mixture are known, the LEL could be calculated by Eq. (1):
i¼1
4. Conclusions The aim of this study is to put forward a comprehensive analysis approach. It use three curves of the LEL with SOC, heating temperature and heating power to describe the LEL change trend of the vented gas from LIB thermal runaway and a kind of theoretic calculation method to validate the Le Chatelier Formula and empirical formula in LEL calcu lation & prediction of the battery runaway gas. A self-made vented gas collector device collected the vented gas from the LIBs thermal runaway. The batteries with different SOCs underwent thermal runaway at 300 � C of heating environment temperature and 400 W of heating power. The batteries with 100% SOC underwent thermal runaway at different heating environment and heating power. The composition and content of three samples of the vented gas were tested. The FRTA explosion limit instrument is used to test the lower explosion limit of all samples of the vented gas. The LEL of the vented gas increases in initial stage and then declines with the increase of the batteries SOCs. When the heating temperature increases, it declines in general. It declines with the increase of heating power obviously. Combined with the definition of lower explosion limit, the Le Chatelier Formula and the empirical formula, the prediction of the LEL of the gaseous mixture was carried out. The LELs of three samples of the vented gas, whose composition and content were tested before, were calculated
(1)
xi LELi
LELmix—LEL of gaseous mixture; LELi—LEL of one component in the gaseous mixture; xi—mole fraction or volume fraction of one component in the gaseous mixture; n—number of the components. When there are inert gases in the gaseous mixture, the LEL can be predicted by empirical formula Eq. (2): � � 1 þ 1 BB � 100 LEL’mix ¼ LELmix � % (2) 100 þ LELmix � 1 BB LEL0 mix——LEL of the gaseous mixture within inert gases; B——volume fraction of the inert gases. We use the data from group A as an example. From the Le Chatelier Formula: LELmix ¼
x H2 LELH2
xCO þ LEL þ CO
xCH4 LELCH4
% ¼ 8:68% 100 þ LELmix � 1 0:620 0:620
As a result, the LEL of the vented gas from the battery (100% of SOC, 400 W of heating power, 200 � C of heating temperature, atmospheric air) is 8.68% by components test and theoretical calculation. According to the LEL test experiment, the LEL of the vented gas from the battery (100% of SOC, 400 W of heating power, 200 � C of heating temperature, atmospheric air), is 8.50% by experimental test. The error of the two results is 2.1%, which is less than 5.0%. The complicated components may be the reason behind the error. Theoretical calculation results of all the three groups of experimental are shown in Table 4. The errors are all less than 5%. There are maybe three major reasons for the errors. Firstly, the composition and volume fraction of the vented gas from LIB thermal runaway is extremely complicated due to the violent reaction of battery materials. On the one hand, some less common chemical does not have an LEL datum in the database. On the other hand, because of instrument and chromatogram restrictions, some hydrocarbon cannot be identified and be labeled as C6þ chemicals. These cause the lack of data of the flammable chemicals in the calculation, which leads to the errors, despite the low volume fraction. Secondly, only the composition and volume fraction of the flammable gases are considered in the theoretical calculation equations. However, the influences of the bond energy, incomplete combustion and decomposition of the combustion products are neglected in the calculation. The last possible reason is the different test instruments. The LEL measurement is indirect by using a flammable gas container, which could have an impact on the explosive limits because of the surface area of the container, thermal conductivity co efficient of the container wall material, etc. As a result of the coaction of abovementioned factors, there are errors between theoretical calcula tion result and test data, which are smaller than 5.0% and acceptable.
Fig. 8. LELs of flammable gases under different power of heating device.
1 LELmix ¼ P n
� � 1 þ 1 0:620 � 100 0:620
Table 4 Composition and ratio table of the gas specimen.
1 ¼ 3:49% x xother þ LELC2CH4H þ LEL þ ⋅⋅⋅ other 2 4
From the empirical formula:
6
Group of experimental
LEL value of theoretical calculation result
LEL value of LEL test result
Error
A B C
8.68% 20.69% 7.80%
8.50% 21.10% 7.75%
2.1% 1.9% 0.6%
100SOC,200 � C,400 W 60SOC,300 � C,400 W 100SOC,300 � C,200 W
S. Chen et al.
Journal of Loss Prevention in the Process Industries 63 (2020) 103992
theoretically. The errors of the three calculated results were less than 5 percentage points. The regularity of the LEL of the vented gas, that the battery is at different SOC, heating power and heating temperature, is acquired to apply to the industry for the safe use and storage of LIBs. The experimental method of LEL test needs to collect the vented gas more than twice with more than two batteries in one group, to get enough gas for the next explosion limit test. The test also needs to be done for many times in one set to get an accurate result of the LEL. Therefore, the method of Le Chatelier Formula and the empirical for mula can do an approximate calculation of the LEL with once collection process and once GC-MS analysis of the vented gas. This method pro vides a way to evaluate the explosion risk of the vented gas more quickly. The internal chemical reactions in the battery and external chemicals reactions of the released product from thermal runaway are the bridge between the LIB conditions and hazard risk.
batteries during the charge-discharge process. J. Loss Prev. Process. Ind. 49, 953–960. https://doi.org/10.1016/j.jlp.2017.05.029. Jiang, F.W., Liu, K., Wang, Z.R., Tong, X., Guo, L.S., 2018. Theoretical analysis of lithium-ion battery failure characteristics under different states of charge. Fire Mater. 42 (6), 680–686. https://doi.org/10.1002/fam.2522. Kawamura, T., Kimura, A., Egashira, M., Okada, S., Yamaki, J.-I., 2002. Thermal stability of alkyl carbonate mixed-solvent electrolytes for lithium ion cells. J. Power Sources 104 (2), 260–264. https://doi.org/10.1016/S0378-7753(01)00960-0. Koch, S., Fill, A., Birke, K.P., 2018. Comprehensive gas analysis on large scale automotive lithium-ion cells in thermal runaway. J. Power Sources 398, 106–112. https://doi. org/10.1016/j.jpowsour.2018.07.051. Lamb, J., Orendorff, C.J., Roth, E.P., Langendorf, J., 2015. Studies on the thermal breakdown of common Li-ion battery electrolyte components. J. Electrochem. Soc. 162 (10), A2131–A2135. https://doi.org/10.1149/2.0651510jes. Lammer, M., K€ onigseder, A., Gluschitz, P., Hacker, V., 2018. Influence of aging on the heat and gas emissions from commercial lithium ion cells in case of thermal failure. J. Electrochem. Sci. Eng. 8 (1), 101–110. https://doi.org/10.5599/jese.476. Larsson, F., Andersson, P., Blomqvist, P., Mellander, B.-E., 2017. Toxic fluoride gas emissions from lithium-ion battery fires. Sci. Rep. 7 (10018), 1–14. https://doi.org/ 10.1038/s41598-017-09784-z. Larsson, F., Bertilsson, S., Furlani, M., Albinsson, I., Mellander, B.-E., 2018. Gas explosions and thermal runaways during external heating abuse of commercial lithium-ion graphite-LiCoO2 cells at different levels of ageing. J. Power Sources 373, 220–231. https://doi.org/10.1016/j.jpowsour.2017.10.085. Ping, P., Kong, D.P., Zhang, J.Q., Wen, R.X., Wen, J., 2018. Characterization of behaviour and hazards of fire and deflagration for high-energy Li-ion cells by overheating. J. Power Sources 398, 55–66. https://doi.org/10.1016/j. jpowsour.2018.07.044. Quintiere, J.G., 2006. Fundamentals of Fire Phenomena. John Wiley & Sons, Chichester (UK), p. 35. Rezvanizaniani, S.M., Liu, Z.C., Chen, Y., Lee, J., 2014. Review and recent advances in battery health monitoring and prognostics technologies for electric vehicle (EV) safety and mobility. J. Power Sources 256, 110–124. https://doi.org/10.1016/j. jpowsour.2014.01.085. Roth, E.P., Crafts, C.C., Doughty, D.H., Mcbreen, J., 2004. Advanced Technology Development Program for Lithium-Ion Batteries: Thermal Abuse Performance of 18650 Li-Ion Cells. Office of Scientific & Technical Information Technical Reports. Somandepalli, V., Marr, K., Horn, Q., 2014. Quantification of combustion hazards of thermal runaway failures in lithium-ion batteries. SAE Int. J. Altern. Powertrains. 3 (1), 98–104. https://doi.org/10.4271/2014-01-1857. Spinner, N.S., Field, C.R., Hammond, M.H., Williams, B.A., Myers, K.M., Lubrano, A.L., Rose-Pehrsson, S.L., Tuttle, S.G., 2015. Physical and chemical analysis of lithium-ion battery cell-to-cell failure events inside custom fire chamber. J. Power Sources 279, 713–721. https://doi.org/10.1016/j.jpowsour.2015.01.068. Spotnitz, R., Franklin, J., 2003. Abuse behavior of high-power, lithium-ion cells. J. Power Sources 113 (1), 81–100. https://doi.org/10.1016/S0378-7753(02)00488-3. Wang, Q.S., Ping, P., Zhao, X.J., Chu, G.Q., Sun, J.H., Chen, C.H., 2012. Thermal runaway caused fire and explosion of lithium ion battery. J. Power Sources 208, 210–224. https://doi.org/10.1016/j.jpowsour.2012.02.038. Zabetakis, M.G., 1964. Flammability Characteristics of Combustible Gases and Vapors. Bureau of Mines, Pittsburgh, PA (United States), pp. 114–116. Zhang, S.S., 2006. A review on electrolyte additives for lithium-ion batteries. J. Power Sources 162 (2), 1379–1394. https://doi.org/10.1016/j.jpowsour.2006.07.074. Zhang, L.P., McHale, C.M., Rothman, N., Li, G., Ji, Z.Y., Vermeulen, R., Hubbard, A.E., Ren, X.F., Shen, M., Rappaport, S.M., North, M., Skibola, C.F., Yin, S.N., Vulpe, C., Chanock, S.J., Smith, M.T., Lan, Q., 2010. Systems biology of human benzene exposure. Chem. Biol. Interact. 184 (1–2), 86–93. https://doi.org/10.1016/j. cbi.2009.12.011. Zhang, W.X., Chen, X., Chen, Q.P., Ding, C., Liu, J.H., Chen, M.Y., Wang, J., 2015. Combustion calorimetry of carbonate electrolytes used in lithium ion batteries. J. Fire Sci. 33 (1), 22–36. https://doi.org/10.1177/0734904114550789.
Acknowledgements The authors are grateful for the support given by National Natural Science Foundation of China [grant number 51874184], the Key R & D programs (Social Development) in Jiangsu Province [grant number BE2016771], the Key Natural Science Foundation in Jiangsu Province [grant number 18KJA620003], the Jiangsu Project Plan for Outstanding Talents Team in Six Research Fields [grant number TD-XNYQC-002], and the Postgraduate Research & Practice Innovation Program of Jiangsu Province [grant number KYCX18_1051]. The authors also thank Yang Hongqi with Nanjing Tech University for much help to this manuscript. References Armand, M., Tarascon, J.-M., 2008. Building better batteries. Nature 451 (7179), 652–657. https://doi.org/10.1038/451652a. Cai, F.Y., Tan, Z.S., Meng, H., Cai, R.L., 2001. Chemical Process Safety Engineering. Science Press, Beijing (China), pp. 44–45. Campion, C.L., Li, W.T., Lucht, B.L., 2005. Thermal decomposition of LiPF6-based electrolytes for lithium-ion batteries. J. Electrochem. Soc. 152 (12) https://doi.org/ 10.1149/1.2083267. A2327–A2327. Chen, M.Y., Liu, J.H., He, Y.P., Yuen, R., Wang, J., 2017. Study of the fire hazards of lithium-ion batteries at different pressures. Appl. Therm. Eng. 125, 1061–1074. https://doi.org/10.1016/j.applthermaleng.2017.06.131. Fu, Y.Y., Lu, S., Shi, L., Chen, X.D., Zhang, H.P., 2016. Combustion characteristics of electrolyte pool fires for lithium ion batteries. J. Electrochem. Soc. 163 (9), A2022–A2028. https://doi.org/10.1149/2.0721609jes. Giebułtowicz, J., Ru_zycka, M., Wroczy� nski, P., Purser, D.A., Stec, A.A., 2017. Analysis of fire deaths in Poland and influence of smoke toxicity. Forensic Sci. Int. 277, 77–87. https://doi.org/10.1016/j.forsciint.2017.05.018. Golubkov, A.W., Fuchs, D., Wagner, J., Wiltsche, H., Stangl, C., Fauler, G., Voitic, G., Thaler, A., Hacker, V., 2013. Thermal-runaway experiments on consumer Li-ion batteries with metal-oxide and olivin-type cathodes. RSC Adv. 4 (7), 3633–3642. https://doi.org/10.1039/C3RA45748F. Guo, L.S., Wang, Z.R., Wang, J.H., Luo, Q.K., Liu, J.J., 2017. Effects of the environmental temperature and heat dissipation condition on the thermal runaway of lithium ion
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