Research on Thermal Runaway Characteristics of High-Capacity Lithium Iron Phosphate Batteries for Electric Vehicles

As the promotion of carbon peaking and carbon neutrality gains momentum, expediting the completion of technological upgrades in the new energy vehicle industry has emerged as an urgent issue for many countries. When it comes to reducing carbon emissions, pure electric vehicles offer unparalleled advantages over traditional fuel vehicles. In pure electric vehicles, batteries serve as the power source [1,2,3,4], playing a critical role in determining the driving range. However, in recent years, the safety concerns associated with battery thermal runaway incidents in pure electric vehicles have received widespread attention due to frequent occurrences of explosive combustion incidents. Consequently, preventing or mitigating the risk of lithium-ion battery thermal safety accidents has become a paramount concern for both the automotive and battery industries [5,6].

Currently, ternary lithium-ion batteries and lithium iron phosphate batteries are the commonly used types of batteries in electric vehicles. Lithium iron phosphate batteries are more widely used in public transportation. Although they exhibit slightly better thermal stability compared to ternary lithium-ion batteries, their thermal safety concerns cannot be ignored. Numerous scholars have conducted experiments and simulation studies to investigate the thermal safety of lithium-ion batteries. In a study by Zhou et al. [7], the thermal runaway (TR) of lithium iron phosphate batteries was investigated by comparing the effects of bottom heating and frontal heating. The results revealed that bottom heating accelerates the propagation speed of internal TR, resulting in higher peak temperatures and increased heat generation. Wang et al. [8] examined the impact of the charging rate on the TR of lithium iron phosphate batteries. They found that as the charging rate increases, the growth rate of lithium dendrites also accelerates, leading to microshort circuits and subsequently increasing the TR occurrence of lithium iron phosphate batteries. The effects of different heating positions, including large surface heating, side heating, and bottom heating, on the TR of lithium iron phosphate batteries were compared by Huang et al. [9]. It was observed that large surface heating produces the maximum smoke volume, jet velocity, and jet duration during the TR process. Zhao et al. [10] induced TR in ternary lithium-ion batteries through localized heating and studied the variation of internal thermal characteristics under different cooling conditions. When comparing the performance of lithium-ion batteries with different positive electrode materials during TR, Wang et al. [11] demonstrated that lithium iron phosphate batteries release a large amount of smoke during TR and exhibit poor overcharge tolerance. On the other hand, ternary lithium-ion batteries show better performance in terms of energy density and overcharge tolerance but may experience explosions during TR. Feng et al. [1,12,13] utilized EV-ARC to investigate the TR mechanism and characteristics of large-capacity ternary lithium-ion batteries. An adiabatic TR experiment with sudden cessation was designed, and the cooled batteries’ life decay mechanism was analyzed, revealing the thermo-electric coupling mechanism during the adiabatic TR test process of lithium-ion power batteries. Li et al. [14] conducted experiments by heating the surface and interior of lithium iron phosphate batteries using a heater to study the effects of different heating positions on the TR of lithium-ion batteries. The results showed that when the heater was external, there was a significant delay in the first stage of TR, but the maximum temperature and mass loss of the battery during TR were higher compared to when the heater was internally propagating inside the lithium-ion battery. Huang et al. [15] performed thermal chamber tests on ternary lithium-ion batteries at different states of charge, comprehensively studying characteristics such as the self-heat decomposition temperature and voltage change component transition of lithium-ion batteries during TR. The results indicated that as the state of charge increased from 0% to 100%, the critical temperature for lithium-ion battery TR decreased by 40 °C. During TR, the positive electrode material dissolved into small particles, and the surface became uneven. Liu et al. [16] investigated the effects of two different triggering methods, overheating and overcharging, on the TR of lithium iron phosphate batteries. Their findings demonstrated that under overcharge conditions, battery combustion is more severe, leading to higher fire risks.

Experimental studies on the thermal runaway (TR) of lithium-ion batteries have shown low repeatability and involve certain risks, requiring significant human and material resources. Furthermore, these studies are economically inefficient as they only provide limited observations of surface phenomena during the experimental process. In order to overcome these limitations, researchers have turned to numerical simulation software to simulate the thermal runaway process of lithium-ion batteries. This approach allows for accurate observations of temperature variations within the battery at different time intervals. As a result, an increasing number of scholars are engaging in in-depth research in this field. Ren et al. [17,18,19] conducted a study that combined an electrochemical–thermal coupled model with a thermal abuse model to predict the thermal behavior of lithium-ion batteries during overcharging. The results demonstrated that increasing the onset temperature of thermal runaway can effectively improve the performance of overcharging. Jin et al. [20] developed a three-dimensional simulation model to investigate the comprehensive effects of heating area and heating power on the thermal runaway of lithium-ion batteries. They found that smaller heating areas and higher heating powers result in faster triggering of thermal runaway. Zhang et al. [21], focusing on lithium iron phosphate batteries, analyzed the differences in data observed during thermal runaway under differential scanning calorimetry (DSC) and Accelerating Rate Calorimetry (ARC) testing conditions. Their analysis provided an effective dataset for thermal runaway modeling. Rojo et al. [22] replaced the battery failure location with a cylinder to study the spreading behavior of thermal runaway in lithium-ion batteries. They explored the influence of external laminar and turbulent flow conditions on thermal runaway by establishing a simulation model. Antonio et al. [23] compared thermal runaway models of batteries with different cathode materials and analyzed the differences in reaction mechanisms during the thermal runaway process. Xu et al. [24] proposed a thermal runaway propagation model that improves model-solving speed by coupling reduced-order thermal and thermal runaway models at the mini module, real module, and pack levels.

Some scholars have also conducted a certain amount of research on gas evolution, preventive measures, and other issues related to the TR process of lithium-ion batteries. Jin et al. [25], Koch et al. [26], and Wang et al. [27] analyzed thermal runaway, gas generation types, and contents under overheat and overcharge conditions for lithium iron phosphate batteries. Huang et al. [28] investigated the effect of series and parallel connections between batteries on thermal runaway. They found that the propagation speed of thermal runaway in lithium-ion batteries is accelerated under parallel conditions. Yu et al. [29] and Xiao et al. [30] studied the influence of different insulation materials and thicknesses on the propagation of thermal runaway using various thermal insulation materials between lithium iron phosphate batteries. Hang et al. [31] explored the inhibitory and delaying effects of liquid nitrogen on lithium-ion battery thermal runaway. Their research revealed that the delaying effect of liquid nitrogen on thermal runaway decreases as the battery surface temperature increases. Lie et al. [32,33] and others studied the inhibitory effects of immersion cooling on battery thermal runaway under different charge and discharge conditions.

Lithium-ion battery TR is primarily triggered by three types of abuse [1,34]: electrical abuse, thermal abuse, and mechanical abuse. Among these, thermal abuse is one of the primary methods for inducing TR in lithium-ion batteries and is widely applied in lithium-ion battery thermal safety research. This paper builds on previous studies by specifically focusing on exploring thermal abuse, using large-capacity lithium iron phosphate batteries as the subject of investigation. Through a combination of experimental simulation, an experimental platform for lithium-ion battery TR and a simulation model for lithium-ion battery TR are established, investigating the temperature characteristics and influencing factors during the battery’s TR process. The subsequent sections of this paper are organized as follows. In Section 2, the TR experiments of lithium-ion batteries are conducted, and the obtained conclusions are presented. In Section 3, the TR model is developed and validated, and numerical results are provided and discussed. In Section 4, some conclusions are summarized.