Experimental and Reduced-Order Modeling Research of Thermal Runaway Propagation in 100 Ah Lithium Iron Phosphate Battery Module

He C.X., Liu Y.H., Huang X.Y., Wan S.B., Lin P.Z., Huang B.L., Sun J., Zhao T.S.

Wang Q., Wang H., Xu C., Jin C., Wang S., Xu L., Ouyang J., Feng X.

In electrochemical energy storage stations, battery modules are stacked layer by layer on the racks. During the thermal runaway process of the battery, combustible mixture gases are vented. Once ignited by high-temperature surfaces or arcing, the resulting intense jet fire can cause the spread of both the same-layer and upper-layer battery modules. The direction of thermal runaway propagation of the battery involves both horizontal and vertical dimensions. Currently, there is a lack of quantitative research on the multidimensional fire propagation mechanism and heat flow patterns of the "thermal runaway-spontaneous heating-flaming" process in lithium-ion phosphate batteries. This paper conducts multidimensional fire propagation experiments on lithium-ion phosphate batteries in a realistic electrochemical energy storage station scenario. It investigates the propagation characteristics of lithium-ion phosphate batteries in both horizontal and vertical directions, the heat flow patterns during multidimensional propagation, and elucidates the influence mechanism of flame radiation heat transfer on thermal runaway propagation. Research indicates that when the heat transfer reaches 56.6 kJ, it triggers the fire propagation of cell. The heat required to trigger the fire propagation of a battery module is 35.99 kJ. In vertical fire propagation, the thermal runaway propagation time of the upper module is shorter (reduced from 122.3 s to 62.3 s), the temperature is higher (increased from 610.6 °C to 645 °C), the heat release is greater (increased from 205.69 kJ to 221.05 kJ), and the combustion is more intense. The research results of this paper can provide a theoretical basis and technical guidance for the fire safety design of energy storage stations.

Liu J., Wang L., Wang J., Pan R., Zhou X.

The characteristics of 16Ah nickel-cobalt-manganese (523) square soft-pack lithium-ion battery (16Ah NCM523) during typical thermal runaway (TR) process under abusive conditions including heat, overcharge, and mechanical stress were studied. The heat TR experiment of lithium battery with heating plate as heat source shows that the temperature of 16Ah NCM523 escalates from 19.9 ℃ to 62 ℃. The TR of 16Ah NCM523 occurs violently, and the temperature of the soft package burst is 96.4 ℃. And the voltage sag time during this TR of 16Ah NCM523 obviously laged behind the heat production characteristics of the battery. The results of overcharged TR of 16Ah NCM523 shows that the temperature of 16Ah NCM523 rises andante with a rate not higher than 1℃/s and then reaches 98.5 ℃. Following, the temperature of battery increases rapidly to 481.2 ℃. During overcharged TR of 16Ah NCM523, the voltage begins to drop rapidly 2 s earlier than temperature change, which means that voltage and temperature can be used as early warning signals of overcharged TR. For the nail penetration TR of 16Ah NCM523, at the moment of mechanical abuse, the battery bulges and erupts gas. At the same time, the voltage of 16Ah NCM523 drops to zero in a very short time (

Schöberl J., Ank M., Schreiber M., Wassiliadis N., Lienkamp M.

Thermal runaway propagation mitigation is a prerequisite in battery development for electric vehicles to meet legal requirements and ensure vehicle occupants’ safety. Thermal runaway propagation depends on many factors, e.g., cell spacing, intermediate materials, and the entire cell stack setup. Furthermore, the choice of cell chemistry plays a decisive role in the safety design of a battery system. However, many studies considering cell chemistry only focus on the cell level or neglect the energetic impacts of safety measures on system integration. This leads to a neglect of the conflict of objectives between battery safety and energy density. In this article, a comprehensive analysis of the thermal runaway propagation in lithium-ion batteries with NMC-811 and LFP cathodes from a Mini Cooper SE and Tesla Model 3 SR+ is presented. The focus is set on the identification of differences in battery safety, the derivation of safety requirements, and the evaluation of their impact on system integration. A comparative analysis identified significantly higher safety requirements for Graphite|NMC-811 than for Graphite|LFP cell chemistries. Regarding cell energy, thermal runaway reaction speed is nine times faster in NMC-811 cells and five times faster considering the whole propagation interval than LFP cells. However, since LFP cell chemistries have significantly lower energy densities than ternary cell chemistries, it must be verified whether the disadvantages in energy density can be compensated by advanced system integration. An analysis of cell-to-pack ratios for both cell chemistries has revealed that, based on average values, the gravimetric disadvantages are reduced to 16%, and the volumetric disadvantages can be completely compensated for at the pack level. However, future research should further focus on this issue as an accurate safety-related design depending on cell chemistry could enable a cost-benefit evaluation under the constraints of safety standards in the development of batteries for electric vehicles.

Zhou G., Liu Y., Li Y., Yang S., Zhang Q., Wang J., Kong Y., Niklas K., Yu W.

NCM811 (Li(Ni0.8Co0.1Mn0.1)O2) lithium-ion battery (LIB) at 100 °C is in a critical state of internal chemical reaction and external thermal runaway (TR), and the coupled stimulations of nail penetration under such thermal load will accelerate TR, and coupled stimulations have hindered the development of LIBS. In this paper, an experimental platform for coupled stimulations of heat-penetration on LIBs was built, and revealed the thermal runaway acceleration mechanism, explored the influence of the SOC on the TR behavior of the cells when penetration under the critical thermal load condition. The results show that critical thermal load condition reduces the critical SOC for TR to occur, and 25% SOC NCM811 cell still produces a jet flame, elevating the fire risk of thermal runaway when compared to room temperature conditions. And the maximum temperature of 25% SOC cell was elevated by 76.1 °C, which was 18% higher than that of penetration at room temperature. Meanwhile, at critical 100 °C, as the SOC increases from 0% to 100%, the average temperature rise rate of the cell sharply increases from 1.992 °C/s to 93.033 °C/s, and the maximum temperature of cell increases from 125.9 °C to 652.9 °C, and the mass loss increases from 3.332 g to 31.180 g. The 0%SOC cell undergoes slighter TR, generating a lot of smoke but no flame. However, with the SOC increase of 25%–100%, the flame temperature increases from 437.8 °C to 918.5 °C, the flame area rise ratio reaching 281.77%. Combined with the microscopic performance characterization experiments, the dynamics behavior of particle eruption is mainly dominated by the anode graphite. The results of this study provide scientific guidance for the safety prevention of LIBs.

Wang G., Gao W., He X., Peng R., Zhang Y., Dai X., Ping P., Kong D.

The recently emerged cell-to-chassis (CTC) technology tremendously raises the energy density of the battery pack by directly integrating lithium-ion batteries into the chassis fame, while it also brings more safety concerns involving thermal runaway propagation (TRP). However, the TRP behavior and the relevant prevention measures for the CTC battery system have not been comprehensively studied yet. In this work, a three-dimensional model was developed within the framework of OpenFOAM to investigate the TRP behavior in CTC battery packs. The heat generation was described by the electrochemistry reaction kinetics fitted in stages and the heat balance was used to address the propagation of TR. This model captures the evolution process of TRP in CTC system and five typical heat transfer modes between the TR and normal cells are identified according to simulation results. The subsequent numerical study indicates that enhancing heat dissipation can reduce the demand on critical thickness of the thermal insulation layers to inhibit TRP. However, local failure of thermal insulation can initially lead to small-scale TR and further contribute to a larger heat accumulation, putting forward higher standards for critical parameters to cease TRP. As the thickness of insulting layers increases to 2 mm, TRP can be completely ceased even when local failure of insulation occurs. This work enhances the understanding of TRP mechanism and its prevention, which can serve as new guidelines for the safety protection of rapidly developing non-module battery pack technologies.

Yang M., Rong M., Ye Y., Yang A., Chu J., Yuan H., Wang X.

The failure and fires have increasingly become puzzles that may not be ignored for Li-ion batteries (LIBs). Overcharging is notoriously difficult to detect in the early stage. To address this problem, eight types of commercial LiFePO4 batteries are used to evaluate overcharge-thermal runaway (TR) properties in a sealed chamber, including surface temperature, voltage, pressure, and vent gas. And a gas-based fault diagnosis method is proposed based on the gas results. The results show that the Tmax and Pmax of the cells are between 121–150 °C and 132–144 kPa except for the battery type 3. The primary gases measured by the gas chromatograph are CO, H2, CO2, and alkanes, and the total amount of gases ranges from 12 to 45 mmol. Moreover, the proportions of H2 and CO2 both exceeded 30 %. Furthermore, the overcharge-warning experiment showed that H2 was outperformed by CO and CH4, and the capture time was 271 s and 579 s earlier than smoke and TR. Once the gases are detected, TR may be completely suppressed, and the battery neither smokes nor fires. The gas-based TR method is significantly superior to the traditional method in terms of reliability and rapidity. This study can provide a reference for the fault diagnosis of LIBs.

Zhu M., Zhang S., Chen Y., Zhao L., Chen M.

Thermal runaway (TR) has emerged as a critical challenge for the practical implementation of lithium-ion batteries (LIBs) in electric vehicles and energy storage systems. This paper examines thermal runaway propagation (TRP) in NCM pouch LIBs under two operating conditions: different state of charge (SOC) and spacing. Based on the results of various SOC experiments conducted without spacing, it is evident that the TRP time decreases significantly as the SOC increases. Additionally, there is a gradual increase in the maximum temperature and mass loss rate of the module and more intense flame ejection behavior. Furthermore, the TRP interval and duration gradually increase with increasing spacing. In comparison, different SOC has a more pronounced effect on maximum temperature, mass loss, and flame ejection behavior of the module than changes in spacing do. Heat transfer analysis shows that the main source of heat before TR is mainly contributed by the previous cell, which accounts for 35.3 %–72 % of the total heat absorbed by the cell. This study offers guidance for further characterization studies and safety measures of the LIBs TRP.

Wang G., Ping P., Peng R., Lv H., Zhao H., Gao W., Kong D.

Thermal runaway (TR) and the resulting fire propagation are still critical issues puzzling the application of lithium-ion batteries in energy storage system (ESS). A fire propagation model including accurate TR propagating process assists in understanding the battery failure mechanism and determining the safety-optimal design of ESS, while its development is hindered by the complexity of simulating large-scale spatial system and interactions between TR and fire. In this work, a coupled semi reduced-order model (SROM) toward real-scale ESS is developed to capture battery TR and fire propagation behavior. Wherein, meshless methods are implemented for battery cluster by constructing thermal resistance network to simulate heat generation and transfer, which simultaneously couples a mass flowing network to address gas generation and subsequent jet. Full-order CFD model is adopted to simulate burning behavior in external fluid with higher precision. This model can accurately capture cross-scale parameters, including temperature evolution at cell-level and heat release rates (HRR) at system-level, as confirmed by experiments. Simulation results elucidate the failure propagation mode and mechanism from cell-to-cell to module-to-module levels. The significant impact of triggering position on fire behavior is also revealed that TR originating from the cluster center causes rapider fire growth and larger peak HRR during fire propagation. The SROM covers entire phenomena chain from cell-level to system-level, which can serve as new guidelines for designing and running safer ESS.

Sun Y., Jin Y., Jiang Z., Li L.

With its high energy density and long lifespan, li-ion battery (LIB) is now dominating the power source market for portable electronics such as smartphones, laptops, and electric vehicles. However, LIB electrolyte is flammable, and the diaphragm has low stability, making it easy to cause thermal runaway (TR). This paper reviews the research progress on TR propagation characteristics and prevention strategies. The study reviewed the analysis of practical measures of battery management systems, safety devices, flame retardants, electrolyte additives, and thermal absorption materials. It also discusses accidents related to TR of LIBs to emphasise the significance of TR to the entire accident investigation and analysis process. This paper can provide useful information on how to avoid TR-related accidents.

Jia Z., Wang S., Qin P., Li C., Song L., Cheng Z., Jin K., Sun J., Wang Q.

With the large-scale application of LiFePO4 (LFP) batteries in the field of electrochemical energy storage (EES), more attention is being paid to the problem of thermal runaway (TR). This paper investigates the TR and gas venting behaviors of 86 Ah LFP batteries caused by overcharging and overheating. Compared with previous studies, the main contributions lie in the gas venting behavior analysis of the LFP batteries during the whole TR process and the causes of the safety venting under overcharging and overheating. Two significant results are obtained from the experiments: (I) the overcharging of the LFP battery promotes gas release inside the battery, resulting in advance of safety venting, but the safety venting under overheating is caused by electrolyte volatilization; (II) the total gas volume (including H2, CH4, C2H4, CO and CO2) during TR under overcharging and overheating is 62.1 and 101.3 L. Moreover, the results calculated by the fractional compelling dose model show that there is no toxicity before TR under overheating. However, the duration of toxicity under the overcharge is 1211 s before TR. This work provides a meaningful theoretical guide for EES systems' safety warning and fire protection.

Chen H., Yang K., Liu Y., Zhang M., Liu H., Liu J., Qu Z., Lai Y.

The thermal runaway (TR) behavior and combustion hazards of lithium-ion battery (LIB) packs directly determine the implementation of firefighting and flame-retardants in energy storage systems. This work studied the TR propagation process and dangers of large-scale LIB packs by experimental methods. The LIB pack consisted of twenty-four 60 Ah (192 Wh) LIBs with LiFePO4 (LFP) as the cathode material. Flame performance, temperature, smoke production, heat release rate (HRR), and mass loss were analyzed during the experiment. The results indicated that TR propagation of the LIB pack developed from the outside to the inside and from the middle to both sides. The development process could be divided into five stages corresponding to the combustion HRR peaks. In the initial stages, the main factor causing LFP battery TR under heating conditions was the external heat source. With the propagation of TR, heat conduction between batteries became the main factor. Hazard analysis found that the HRRmax of the LIB pack was 314 KW, more than eight times that of a single 60 Ah battery under heating conditions. The LIB pack had higher normalized mass loss and normalized THR (6.94 g/Ah and 187 KJ/Ah, respectively) than a single LFP battery. This study provides a reference for developing strategies to address TR propagation or firefighting in energy storage systems.

Xu C., Wang H., Jiang F., Feng X., Lu L., Jin C., Zhang F., Huang W., Zhang M., Ouyang M.

The study presents a thermal runaway propagation (TRP) model developed by coupling the reduced-order thermal and thermal runaway (TR) models at the mini-module, real-module, and pack levels. Comparing to the ANSYS thermal model, the maximum error of reduced-order model was less than 1.2%. Moreover, the speed is 12 times faster. Furthermore, the TRP models of the mini-module with 4 cells and real-module with 18 cells were validated experimentally. The simulation error of the mini-module test was less than 3.52%. The simulation of the real-module revealed different propagation modes. The TRP time though the whole module was 1906.2s. Finally, the model was extended to the pack level. The propagation characteristic on the triggered module was quite similar with that in the real module. The propagation time of the initiated module in the pack was 1069.4s, which is faster than the propagation time in the real-module. The TRP between the modules was found in the battery pack and accelerated by the cooling plate. The reduced order TRP model can well simulated the TRP of battery pack from mini-module level to the pack level, which is possible to guide the safety design method on the battery pack.

Liu X., Wang M., Cao R., Lyu M., Zhang C., Li S., Guo B., Zhang L., Zhang Z., Gao X., Cheng H., Ma B., Yang S.

Electric vehicles are developing prosperously in recent years. Lithium-ion batteries have become the dominant energy storage device in electric vehicle application because of its advantages such as high power density and long cycle life. To ensure safe and efficient battery operations and to enable timely battery system maintenance, accurate and reliable detection and diagnosis of battery faults are necessitated. In this paper, the state-of-the-art battery fault diagnosis methods are comprehensively reviewed. First, the degradation and fault mechanisms are analyzed and common abnormal behaviors are summarized. Then, the fault diagnosis methods are categorized into the statistical analysis-, model-, signal processing-, and data-driven methods. Their distinctive characteristics and applications are summarized and compared. Finally, the challenges facing the existing fault diagnosis methods are discussed and the future research directions are pointed out.

Song L., Huang Z., Mei W., Jia Z., Yu Y., Wang Q., Jin K.

Thermal runaway propagation (TRP) of lithium iron phosphate batteries (LFP) has become a key technical problem due to its risk of causing large-scale fire accidents. This work systematically investigates the TRP behavior of 280 Ah LFP batteries with different SOCs through experiments. Three different SOCs including 40 %, 80 %, and 100 % are chosen. In addition to key TRP characteristic parameters such as temperature, TRP time and speed are analyzed, more importantly, the energy flow distribution during the TRP of large-size LFP module is also revealed. The results indicate that among the three groups of modules, TRP occurs only in the module with 100 % SOC, which is attributed to the higher internal energy (666.11 kJ) and heat transfer power (264.07 W). For the module with 100 % SOC, the TRP time interval fluctuates from 667 s to 1305 s, and the TRP speed is in the range of 0.05–0.12 mm/s. Furthermore, the energy flow distribution indicates that more than 75 % of the energy is used to heat battery itself, and approximately 20 % is carried out by ejecta. Less than 10 % can trigger neighboring batteries into thermal runaway. This work may provide important guidance for the process safety design of energy storage power stations.