Lithium-ion batteries are widely used in electrochemical energy storage and other fields due to their superior performance. However, the fire accident of energy storage power station has become a hot topic of concern in recent years. The main reason for the accident of the energy storage power station is the instability of the internal materials of the lithium-ion battery, which further induces the thermal runaway of the battery to produce a large amount of gas, and even ignite. Although there are many studies on the thermal runaway gas production and flame characteristics of lithium-ion batteries, the research objects are concentrated on small and medium-sized batteries, and the thermal runaway characteristics of lithium iron phosphate batteries for energy storage are relatively rare. Therefore, the purpose of this study is to analyze the characteristics of thermal runaway gas production and flame behavior of lithium iron phosphate batteries, clarify the danger of thermal runaway behavior, and provide a theoretical basis for the preparation of emergency plans and fire protection design of electrochemical energy storage power stations.
Wang Qingsong's research group from the State Key Laboratory of Fire Science of the University of Science and Technology of China and the Anhui Electric Power Research Institute took the 280ah lithium iron phosphate battery as the research object, and used experimental methods to study the thermal runaway behavior characteristics of the lithium iron phosphate battery for energy storage under overheating conditions. The thermal runaway hazards of thermal runaway are obtained from two aspects: gas production behavior and flame behavior, and the manifestations of the danger of thermal runaway gas production and flame behavior of lithium iron phosphate battery for energy storage are revealed.
1) The four stages of the battery thermal runaway process were quantified. According to the relationship between the surface temperature and the temperature rise rate, the thermal runaway process of the battery is divided into four stages: heating stage, thermal runaway gestation stage, thermal runaway stage and cooling and cooling stage, as shown in Figure 1. The surface temperature of the battery is mainly affected by the state of charge, and the gas or flame radiation generated has little influence on the temperature of the battery itself.
Fig.1 Curves of surface temperature rise rate during thermal runaway of batteries under different states of charge.
2) Reveal the dangerous manifestations of gas-producing and flame-producing behaviors.
By analyzing the gas temperature at different heights above the battery, it can be seen that with the increase of altitude, the gas temperature gradually decreases, and the maximum gas production temperature for 50% and 100% SoC batteries is respectively. 7, as shown in Figure 2;Through real-time measurement of gas composition, a large amount of carbon dioxide and alkane combustible gases are produced in the process of thermal runaway, and there are also a large number of hydrogen and toxic and harmful gases, so the danger of thermal runaway gas production behavior is mainly manifested in the toxicity, suffocation and deflagration characteristics of gases.
In the energy storage power station, if there is an electric spark, a large number of combustible gases will be ignited, and due to the presence of flames, high-temperature flue gas and thermal radiation will be generated. According to the flame temperature of different heights above the battery, the maximum temperature can reach 750 -900, as shown in Figure 3, at the same time, a large amount of electrolyte and combustible gas combustion releases a large amount of heat, which produces a strong thermal radiation effect on the surrounding items, so the danger of thermal runaway flame behavior is mainly manifested in high temperature flame and strong thermal radiation.
Fig.2 The temperature, composition and proportion of the gas production in the thermal runaway process (except H2).
Fig.3 Flame temperature and thermothermal runaway rate variation curves during thermal runaway.
3) Large-capacity lithium iron phosphate batteries have internal thermal runaway and diffusion phenomenon. There are multiple spikes in the rate of mass loss during the thermal runaway of the battery, as shown in Figure 4. After disassembling the thermal runaway battery, it is found that there are four cores inside, and the thermal runaway of the four cores in turn constitutes the whole process of the whole battery thermal runaway, which corresponds to multiple peak mass loss rates, as shown in Figure 5, so there is an obvious internal thermal runaway diffusion phenomenon in the thermal runaway process of large-capacity lithium iron phosphate batteries.
Fig.4 Variation curve of mass loss during thermal runaway of 100% SoC lithium iron phosphate battery.
Figure 5Schematic diagram of the internal propagation process of thermal runaway of lithium iron phosphate battery.
Brief introduction of the results.The above research results were published in the journal Journal of Energy Storage, with Wang Shuping as the first author, Song Laifeng and others as collaborators, and Duan Qiangling and Wang Qingsong as co-corresponding authors.
shuping wang, laifeng song, changhao li, jiamin tian, kaiqiang jin, qiangling duan*, qingsong wang*. experimental study of gas production and flame beh**ior induced by the thermal runaway of 280 ah lithium iron phosphate battery, journal of energy storage 74 (2023) 109368.