Thermal runaway and fire behavior investigation of lithium ion batteries using modified cone calorimeter

The lithium ion battery has been widely used, but it has high fire risk due to its flammable materials. In this study, a series of combustion tests are conducted on the 18650-type lithium ion batteries using the modified cone calorimeter. The temperature and voltage variation of the battery, heat release rate and gas generation during combustion are measured in this study. The battery is heated evenly by the self-made heater, and the reliable trigger temperatures of thermal runaway are obtained for different states of charge (SOCs) batteries in this study. The fire behavior of the 100% SOC batteries is shown in this paper. The net heat absorption by the battery before thermal runaway is calculated based on the heat transfer theory. It ranges from 56.81 to 64.05 kJ for 0 to 100% SOC batteries, which shows a decreasing trend as SOC increases. The peak combustion heat release rate of 100% SOC batteries is 3.747?±?0.858 kW. CH₄ and CO gases are detected before and after thermal runaway. The generation of CO shows an increasing trend as SOC increases. Some suggestions on the early warning system of battery thermal runaway are proposed based on this study.

     

Evaluation of thermal hazard for commercial 14500 lithium-ion batteries

Commercial lithium-ion batteries ranged from different sizes, shapes, capacities, electrolytes, anode and cathode materials, etc. have recently caused many incidents under abusive or normal operating conditions worldwide. Inherently safer designs with active or passive protections have became the captious issues that need more attentions paid to. In this study, the worst scenarios on thermal runaway of four commercial batteries were conducted and compared. A customized-made closed testing instrument was utilized to measure and track thermal behaviors of four brands of cylindrical lithium-ion batteries under maximum open circuit voltage condition. Characteristics on thermal hazards of lithium-ion batteries such as onset temperature, maximum temperature, maximum self-heat rate, maximum pressures, battery mass loss, etc. were measured and evaluated. Results point out that one brand of cells reached the maximum temperature and maximum self-heat rate of 590.9 K and 1,130.4 K min^?1, respectively. In conclusion, in case of thermal runaway all the lithium-ion batteries will rupture the cell and catch fire automatically owing to the maximum temperatures over the auto-ignition temperature of electrolytes and the maximum pressure higher than four times of maximum allowable working pressure, respectively. In addition, Lithium-ion battery with cathode material of LiFePO₄ was verified to be more stable than the lithium-ion battery with cathode material of LiMn₂O₄ or LiCoO₂.     

金属锂电池的热失控与安全性研究进展

锂离子电池在便携式储能器件及电动汽车领域得到了广泛应用,然而频繁发生的电池起火爆炸事故,使热失控和热安全问题备受人们关注,目前已有多篇综述报道了缓解锂离子电池热失控的措施。相比于已经接近理论比能极限的锂离子电池,金属锂负极具有更高的比容量、更低的电势和高反应活性,但是不可控的锂枝晶生长,使得金属锂电池的热失控问题更为复杂和严重。针对金属锂电池的热失控问题,本文首先介绍了热失控的诱因及基本过程和阶段,其次从材料层面综述了提高电池热安全性的多种策略,包括使用阻燃性电解质、离子液体电解质、高浓电解质和局域高浓电解质等不易燃液态电解质体系,开发高热稳定性隔膜、热响应隔膜、阻燃性隔膜和具有枝晶检测预警与枝晶消除功能的新型智能隔膜,以及研究热响应聚合物电解质,最后对金属锂电池热失控在未来的进一步研究进行了展望。     

A unique control strategy to improve the life cycle of the battery and to reduce the thermal runaway for electric vehicle applications

This paper presents a unique thermal control strategy to improve the ageing of the battery and to maintain the internal temperature of the battery within the optimum limit of 20 °C–40 °C for electric vehicle (EV) applications. The hybrid EV system encompasses photovoltaic (PV) module, high power density device supercapacitor (SC) and high energy density Li-ion battery (LIB) as an energy storage element. The vehicle dynamics encounter frequent voltage fluctuations in the direct current (DC) bus, which ultimately reduces the lifecycle of the battery and also the heat is generated inside the battery when it is connected in parallel to the DC bus. The frequent charging/discharging of LIB is controlled by the unique thermal control strategy of the hybrid EV system. The DC bus voltage is controlled by the SC bi-directional converter (BDC) where, the battery BDC delivers the essential constant current from the main source (PV) to the DC bus. This unique thermal control strategy supports the distribution of power from the PV/LIB/SC hybrid source system to the EV and also improves the battery life cycle. Due to constant charging/discharging of battery the thermal runaway (TR) problem such as leak, smoke, gas venting, rapid disassembly, flames etc., can be eliminated. Decoupling of load power and battery power comprises the growth in the battery lifecycle and to maintain the optimum internal temperature of the LIB by conditional flow of current through hybrid thermal management system (HTMS). To certify the thermal control strategy and to estimate the performance of HTMS, a simulation of a hybrid source system with vehicle dynamics is performed in MATLAB/Simulink. Numerical analysis of the LIB during constant charging/discharging is performed using ANSYS fluent software to validate the temperature effect of HTMS.

     

Thermal hazard evaluations of 18650 lithium-ion batteries by an adiabatic calorimeter

In this study, the thermal hazard features of various lithium-ion batteries, such as LiCoO₂ and LiFePO₄, were assessed properly by calorimetric techniques. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was used to measure the thermal hazards and runaway characteristics of the 18650 lithium-ion batteries under an adiabatic condition. The thermal behaviors of the lithium-ion batteries were obtained at normal and abnormal conditions in this study. The critical parameters for thermal hazardous behavior of lithium-ion batteries were obtained including the exothermic onset temperature (T ₀), heat of decomposition (ΔH), maximum temperature (T _max), maximum pressure (P _max), self-heating rate (dT/dt), and pressure rise rate (dP/dt). Therefore, the result indicates the thermal runaway situation of the lithium-ion battery with different materials and voltages in view the of TNT-equivalent method by VSP2. The hazard gets greater with higher voltage. Without the consideration of other anti-pressure measurements, different voltages involving 3.3, 3.6, 3.7, and 4.2 V are evaluated to 0.11, 0.23, 0.88, and 1.77 g of TNT. Further estimation of thermal runaway reaction and decomposition reaction of lithium-ion battery can also be confirmed by VSP2. It shows that the battery of a fully charged state is more dangerous than that of a storage state. The technique results showed that VSP2 can be used to strictly evaluate thermal runaway reaction and thermal decomposition behaviors of lithium-ion batteries. The loss prevention and thermal hazard assessment are very important for development of electric vehicles as well as other appliances in the future. Therefore, our results could be applied to define important safety indices of lithium-ion batteries for safety concerns.     

In-situ Study of Charge and Discharge of Ni-MH Battery Using the Combined Method of Electrochemistry and Microcalorimetry

An apparatus to study the battery system has been set up. The thermal effects of charge and discharge of Ni-MH batteries have been studied. The calorimetric measurements indicate that the net heat dissipation during charging is larger than that during discharging. It is observed that the ratio of heat dissipation to charging energy varies with charging capacity, and almost 90 percent of charging energy is lost as heat dissipation near the end of the charging process at 97.7 mA. A jump of thermal curve near the end of discharge due to a secondary electrode reaction has been observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Computational study of a latent heat thermal energy storage system enhanced by highly conductive metal foams and heat pipes

Numerical simulations are performed to analyze the thermal characteristics of a latent heat thermal energy storage system with phase change material embedded in highly conductive porous media. A network of finned heat pipes is also employed to enhance the heat transfer within the system. ANSYS-FLUENT 19.0 is used to create a transient multiphase computational model to simulate the thermal behavior of the storage unit. Copper foam is the porous medium used to enhance the heat transfer and is impregnated with the phase change material, potassium nitrate (KNO₃). The effects of the porosity of the metal foam and the quantity of heat pipes on the thermal characteristics of storage unit have been investigated. The results indicated that increasing the quantity of the embedded heat pipes leads to drastic acceleration of both charging and discharging process. Impregnating the copper foam with potassium nitrate phase change material significantly affects the total charging and discharging times of the storage unit. It was shown that the porosity of the metal foam plays a key role in the thermal behavior of the system during the charging and discharging processes.

     

Evaluate the flammability of a PU foam with double-scale analysis

Two-scale tests, microscale and bench scale, are conducted to analyze the flammability of a flexible polyurethane foam. Microscale tests include simultaneous thermal analysis coupled to Fourier transform infrared spectroscopy, and microscale combustion calorimeter (MCC). Evolved gas components, heat release rate per unit mass, total heat release, derived heat release capacity, and minimum ignition temperature are obtained. Bench scale tests are performed on cone calorimeter. Peak heat release rate per unit area, effective heat of combustion, minimum incident heat flux for ignition, and total heat release per unit area of different incident heat fluxes are obtained. FO-category of the PU foam is estimated by multiple discriminant function analysis based on the results of cone calorimeter test. The relationship between the two-scale tests is analyzed. The minimum ignition temperatures derived from multi heating rate MCC tests are used to predict the time to ignition and compared with the results from cone calorimeter tests. This PU foam is evaluated as a high fire hazard polymer having low heat release capacity, low ignition temperature, and short ignition time.

     

Characterization of ignition and combustion characteristics of phenolic fiber-reinforced plastic with different thicknesses

The present study focuses on ignition and combustion characteristics of phenolic fiber-reinforced plastic (FRP) with different thicknesses under different external heat fluxes using cone calorimeter, which receives little attention to date. A series of parameters including ignition time, thermal thickness, mass loss factor, mass loss rate (MLR), heat release rate (HRR), total heat release (THR), fire performance index (FPI) and fire growth index (FGI) are measured or calculated. Results indicate that the ignition time increases with the thickness, but decreases with the external heat flux. Phenolic FRP with thickness of 3 mm may be considered as thermally thin material. However, phenolic FRP with thickness of 5 and 8 mm is prone to be thermally thick material. The critical heat flux, minimum heat flux and ignition temperature are deduced and validated. The thermal thickness increases with the external heat flux. Linear correlations of the thermal thickness with the ratio of specimen density and external heat flux are demonstrated and presented. The mass loss factor decreases with the thickness. Three and two peak MLRs occur in the cases of low and high external heat fluxes, respectively. The average MLR increases with the external heat flux and thickness. The average and maximum HRR increases with the external heat flux. The FGI for the maximum HRR increases with the external heat flux. Linear correlations of the average MLR, the average and maximum HRR and the FGI for the maximum HRR with the external heat flux are demonstrated and presented.

     

3, 4-乙烯二氧噻吩单体用作锂离子电池安全性改善添加剂的研究

安全性是制约锂离子电池向电动汽车领域应用拓展的主要障碍. 本工作提出了一种能够有效改善锂离子电池安全性的电解液添加剂-3,4-乙烯二氧噻吩单体（EDOT）,研究了其在有机电解液中的电氧化聚合行为,以及对LiCoO₂电极高温热行为和电池安全性、电化学性能的影响. 循环伏安（CV）和透射电镜（TEM）表征结果表明,单体添加剂能够在电池充电过程发生电氧化聚合,在正极表面形成一层聚（3,4-乙烯二氧噻吩）（PEDOT）导电聚合物膜;差示扫描量热（DSC）分析结果显示,PEDOT隔离了电解液与正极表面的直接接触,减少了过热条件下电解液在正极表面的分解放热. 安全性测试结果表明,在电解液中仅添加0.1%的EDOT单体,即可将电池在150 ^oC高温热冲击下发生热失控的时间推迟13.8分钟. 电化学性能测试结果表明,聚合产物良好的电子导电性能有效改善正极的电子传导能力,在一定程度上提高电池的倍率性能和循环稳定性,而容量、低温性能等基本不受影响,展示出良好的应用前景.     

A multifunctional separator with Mg(OH)_2 nanoflake coatings for safe lithium-metal batteries

Dendrite growth and thermal runaway induce serious safety hazards,impeding the practical applications of lithium metal batteries(LMBs).Although extensive advances have been attained in terms of LMB safety,most work only focus on a single aspect at a time.This paper reports a multifunctional separator coated by Mg(OH)2 nanoflakes with various excellent properties including electrolyte wettability,ionic conductivity,Li+ transference number,puncture strength,thermal stability and flame retardance.When used in LMBs,the Mg(OH)2 nanoflake coatings enable uniform Li+ distributing,which makes it homogeneous to deposit lithium,realizing effective dendrite suppression and less volume expansion.Meanwhile,Mg(OH)2 coatings can ensure LMBs are in normal conditions without thermal runaway until 140 ℃.A part of lithium can be converted into Li+ ions by Mg(OH)2 during repeated charge/discharge cycles,not only reducing the risk of separator damage and consequent short circuit,but also replenishing the capacity loss of LMBs.The Mg(OH)2 nanoflakes can coat on all kinds of commercial separators to improve their performances,which offers a facile but effective strategy for fabricating multifunctional separators and a comprehensive insight into enhancing LMB safety.     

A study on the fire behaviors of 18650 battery and batteries pack under discharge

Journal of Thermal Analysis and Calorimetry - In order to have a better understanding of the fire behaviors of lithium-ion battery (LIB) and batteries pack under discharge, a series of fire tests...     

Safety properties of liquid state soft pack high power batteries with carbon-coated LiFePO4/graphite electrodes

The carbon-coated LiFePO₄ materials were synthesized, and their structure and morphology were characterized by X-ray diffraction and transmission electron microscopy. The safety and heating mechanism of the 066094-type liquid state soft pack high power batteries with carbon-coated LiFePO₄/graphite electrodes under abusive conditions, such as overcharge, overdischarge, and short current were extensively investigated. It was found that the increase in the temperature of the LiFePO₄/graphite high power batteries during overcharge was attributed to the reaction of the electrolyte decomposition and the Joule heat. The batteries were heated rapidly by the irreversible heat generated from the current passing through the electrodes during short current. The temperature rise of the batteries which were overdischarged to 0 V was mainly due to the Joule heat. The overdischarge at 1 C/0 V almost did not influence the cycling performance of the batteries. The batteries did not fire, smoke, and explode under the above-mentioned abusive conditions. Therefore, the 066094-type liquid state soft film pack high power batteries with carbon-coated LiFePO₄/graphite electrodes showed excellent safety performance.     

Incompatible reaction for (3-4-epoxycyclohexane) methyl-3′-4′-epoxycyclohexyl-carboxylate (EEC) by calorimetric technology and theoretical kinetic model

(3-4-Epoxycyclohexane) methyl-3′-4′-epoxycyclohexyl-carboxylate (EEC) is a typical epoxy resin (EP). In Asia, due to the unstable reactive natures of EP, various thermal hazard and runaway reaction incidents have been occasioned by EP in the manufacturing process, such as fire, explosion, and toxic release, resulting in loss of life as well financial catastrophes and social outcries. Certain catalysis substances, H₂SO₄, acetic acid, or NaOH, may accelerate the reaction or curing rate for EP. However, an incompatible reaction with these chemical substances may induce a thermal hazard, causing a runaway excursion during the last stage. We employed thermogravimetry (TG) to obtain thermal stability parameters under non-isothermal conditions to evaluate the runaway reactions for EEC. The experimental data were compared with kinetics-based curve fitting to assess thermally hazardous phenomena by optimizing curve fitting on the kinetic parameters. The aim of this study was to estimate the incompatible hazards for EEC, provide thermal hazard information in order to determine the optimum operation conditions, and diminish the likelihood of fire and explosion accidents incurred by EP.     

Numerical investigation on cooling performance of PCM/cooling plate hybrid system for power battery with variable discharging conditions

To solve the cooling problems of power battery with variable discharging conditions, a hybrid thermal management system combined with phase change materials (PCM) and cooling plate is designed. Moreover, the ANSYS FLUENT is adopted to simulate the three-dimensional model. As a result, the effects of water flow direction and variable discharging conditions are discussed on the maximum temperature and maximum temperature difference inside the battery as well as the liquid fraction of PCM. The numerical results indicate that the maximum temperature is governed by the physical parameters of PCM, whereas the water flow direction in the cooling plate plays a dominant role on the maximum temperature difference. Moreover, the flow direction scheme of case 5 is benefit to reduce the maximum temperature and temperature difference simultaneously. Although the cooling performance of hybrid thermal management system can be deteriorated by increasing the pulse duration and heat flux, the melting of PCM dramatically suppresses the increase in maximum temperature and temperature difference. Considering the limited quality of PCM, enhancing the thermal conductivity of PCM and employing cooling scheme with staggered flow direction are recommendable ways to extend the applicability of the hybrid thermal management system for power battery with complex discharging conditions.

     

固定型阀控式铅酸蓄电池失效模式研究

研究了由于水损耗、热失控而引起固定型阀控式铅酸蓄电池失效的原因．认为通过提高电池内部氧再复合效率、采用合适的电池槽盖材料及减少正极板腐蚀,可解决水损耗问题;热失控问题可通过改善电池外部条件解决．     

Measurement of lithium diffusion coefficient in thin metallic multilayer by neutron depth profiling

Diffusion of Li ions in thin sandwich films with copper or lead encompassing layers (obtained by ion beam sputtering deposition technique) has been studied. These metals are promising candidates for electrodes in lithium-ion batteries. It is because they exhibit an ability to store and release Li ions during charging and discharging processes. Lithium diffusion was induced in samples by thermal annealing cycles. The lithium depth profile was measured using a nondestructive neutron depth profiling technique after each thermal annealing step. The analysis of experimental data allowed to evaluate the lithium depth profiles and directly calculate the diffusion coefficients.     

Thermal runaway hazards of <Emphasis Type="Italic">tert</Emphasis>-butyl hydroperoxide by calorimetric studies

Thermal runaway reactions associated with exothermic behaviors of tert-butyl hydroperoxide (TBHP) solutions and TBHP reacting with alkaline contaminants were studied. A differential scanning calorimetry (DSC) was used to characterize these inherent behaviors of TBHP solutions with KOH, NaOH, LiOH and NH₄OH. The exothermic peak in thermal curves of TBHP solutions with different alkali were detected by DSC thermal analysis. By thermal analysis, we compared various heats of decomposition of TBHP solutions with alkaline impurities, and determined the incompatible hazards of various TBHP solutions with alkaline contaminants. Comparing with TBHP in various diluents, the adiabatic runaway reaction via vent sizing package 2 (VSP2) indicated that aqueous TBHP intrinsically possesses the phenomena of thermal explosion with dramatic self-reactive rate and pressure rise under adiabatic conditions. Many commercial organic peroxides may have different hazard behaviors. Therefore, using thermal method to classify the hazards is an important subject.     

锂硫电池及关键材料研究进展

锂硫电池因具有远高于传统锂离子电池的理论比容量和质量能量密度,而受到人们的广泛关注,近年来一直是高能锂金属电池领域的研究热点之一. 然而这一体系的一些固有特性问题依然没有得到解决,无法实现稳定理论容量输出,严重阻碍了锂硫电池的实际应用. 其中,比较突出的问题是电池充放电过程中生成可溶性中间产物-多硫化物-对硫基正极、锂基负极和电解液等电池关键组成部分具有深刻的影响. 本综述从多硫化物的热力学和动力学等性质入手,详细介绍了锂硫电池中关键材料的功能化设计和优化策略,并对未来的发展做出展望.     

Screening defective lithium ion batteries of 0?V open-circuit voltage by a high current charge process in combination with in situ infrared thermal imaging technology

How to screen defective lithium ion batteries is of great importance to the producers and consumers, which has been a challenging problem, since some lithium ion batteries will not present evident different electrochemical behaviors at the initial use stage. Here, we found that defective lithium ion batteries of zero open-voltage could be differentiated from the good ones by charging at 1,800 mA (corresponding to 3 C) in combination with in situ infrared thermal imaging technology. During the charge process, the surface temperatures of the defective lithium ion batteries of zero open-voltage showed at least 10 °C higher than that of the good one. Results of the charge voltage, charge current, temperature rise, and the analysis of the cathode strip, separator, and anode strip after full-discharge process showed that this method was effective.