Study on the lithium power battery thermal runaway and prevention technology

Study on the lithium power battery thermal runaway and prevention technology | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Study on the lithium power battery thermal runaway and prevention technology Kai Wen, Xingfeng Fu, Hai Jiang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3966428/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract In order to the issue of preventing Thermal runaway of power battery, the thermal generation model of power battery was established, and the model was modified based on the experimental data. On the basis of simulation calculation, the scheme of preventing Thermal runaway of battery module and battery pack was designed, and samples were made for test. The results of test and simulation calculation were very consistent, which confirmed the accuracy of the simulation calculation model, the results of Thermal runaway test also prove that the measures designed to prevent Thermal runaway are effective and meet the design requirement. Thermal runaway Battery management system Simulation modeling Methods to prevent Thermal runaway Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction With the rapid development of electric vehicles, lithium-ion power battery systems as power sources have received more and more attention. With the continuous increase of battery specific energy, the range of electric vehicles has approached or exceeded the level of fuel vehicles, and the safety of power batteries has also received more and more attention. Since the power battery system of electric vehicles contains huge energy, once Thermal runaway or thermal diffusion occurs, serious fire and explosion accidents will be caused, posing a serious threat to the safety of vehicles and drivers. [ 1 ] Therefore, effective measures must be taken to prevent and suppress the occurrence and effect of thermal diffusion of power batteries, which is extremely important for protecting the safety of electric vehicles and drivers. [ 2 ] The thermal diffusion experiment of power batteries has become one of the most important projects in the safety experiment of power batteries. It is a mandatory project for regulatory inspections, an important development content for power battery system design, and an important evaluation indicator for evaluating the quality of a power battery system design. At present, the prevention and suppression technology of thermal diffusion in power batteries has become one of the most important development contents in power battery system design, and has attracted the attention of domestic and foreign researchers. [ 3 – 4 ] 2. Factors influencing the results of battery Thermal runaway The main factors that cause the Thermal runaway of electric vehicles are the abuse of the external battery and the internal short circuit caused by the internal battery., External abuse includes mechanical abuse, electrical abuse, and thermal abuse, while internal short circuits are mainly caused by battery damage caused by puncturing the battery separator or exceeding the allowed charging and discharging capacity of the battery. Generally, mechanical, electrochemical and thermal conditions will be combined, and the Thermal runaway of the battery is the result of multiple factors. [ 5 – 7 ] Mechanical abuse mainly refers to battery deformation caused by external forces, commonly seen in typical situations such as car collisions and battery compression. Whether the deformation of the battery caused by external force will lead to internal short circuit of the battery, and whether the internal short circuit will lead to Thermal runaway and explosion of the battery, which is the focus of researchers on mechanical abuse. Collision squeezing is a common form of mechanical abuse, which is generally studied at three levels: battery materials, battery cells, and battery systems. [ 8 ] The extrusion mechanical model of battery cells is generally based on the study of the mechanical properties of the materials that make up the battery cells. Researchers conducted quasi-static mechanical tests on batteries of different forms. The types of loading include compression, extrusion, bending, etc. This type of research is very meaningful for predicting internal short circuits in batteries under mechanical abuse. The research results indicate that the battery underwent significant deformation before the start of the internal short circuit. The mechanical abuse model at the module and package level is based on the mechanical model of the battery cell, and is closely related to the protective ability of the entire package against mechanical damage (collision, impact, etc.). [ 9 – 10 ] In the case of an external short circuit, the heating capacity of the power battery is generally not very high. The heat is mainly concentrated near the short circuit point, but if the battery is located near the short circuit point, it may be heated to the temperature where Thermal runaway occurs. In the design of the module, adding some external short circuit protection devices is of great significance for effectively suppressing the external short circuit of the battery. [ 11 ] For the internal short circuit of the power battery, improving the mass transfer efficiency of lithium ions in the negative electrode of the battery or increasing the negative electrode area of the battery can effectively improve the ability of the power battery to withstand external short circuit current impact. [ 12 ] Statistics show that overcharging is another common phenomenon of electricity abuse that induces Thermal runaway of power batteries, and it has also caused many Thermal runaway safety accidents in the actual use of electric vehicles. The direct cause of overcharging is the failure of BMS protection measures to cut off the charging current in a timely manner when the power battery is fully charged, and charging beyond the charging capacity of the power battery. Overcharging is usually accompanied by heating and gas generation, which mainly comes from Ohmic heat and side reaction heat. [ 13 – 14 ] Research has found that the heat generated by batteries is directly proportional to the charging current, indicating that ohmic heat is one of the main reasons for heat generation during the charging process. As shown in Fig. 1 . Overcharging can cause great damage to power batteries. Due to excessive lithium embedding in the negative electrode, lithium dendrites can form on the surface of the negative electrode. Excessive lithium detachment in the positive electrode can lead to structural collapse. With the generation of heat and central enterprises, the release of oxygen accelerates the decomposition of the electrolyte, producing a large amount of gas. After a sharp increase in internal pressure, the power battery may spray or explode. [ 15 ] Local excessive heating in the battery pack is a typical heat abuse condition. Local poor contact in the electrical connection may lead to excessive heating under the condition of high current, heating the nearby battery, causing Thermal runaway. For example, the defects of the battery system in the manufacturing process may lead to poor contact and increase of resistance. In addition, vibration, impact, and other conditions may also cause electrical connections to become loose, causing local heating. Due to the influence of preload and interface roughness on the contact resistance between connections. [ 16 ] When the internal separator of the battery is damaged and the positive and negative poles come into contact with each other, an internal short circuit occurs. Internal short circuit is one of the prominent characteristics of Thermal runaway. [ 17 ] After the occurrence of internal short circuit, the electric energy and electrochemical energy stored in the electrode plate will be released violently, and a large amount of heat will be generated in a short time, which will lead to runaway heating. In addition to the three types of external abuse mentioned above, the battery's own defects may also cause internal short circuits. 3. Research on suppression design of power battery Thermal runaway In the power battery system, when Thermal runaway occurs in one battery, Thermal runaway may spread to adjacent batteries. [ 18 ] An unexpected failure mode is that the spread of gas and flame can cause Thermal runaway diffusion. The reason why the first pathway is expected is mainly because it is relatively easy to block heat transfer. However, the reason why the second pathway is unexpected is mainly due to the uncertainty of gas and flame diffusion. These two failure pathways can be suppressed through the following methods: [ 19 ] (1) gas suppression; (2) Loss of integrity: (3) Flame ignition. In order to restrain the Thermal runaway diffusion at the power battery system level, researchers prefer to limit the failure diffusion caused by heat transfer. [ 20 ] Figure 2 is the Thermal runaway test process diagram of a square power battery. It can be seen from the figure that under the influence of the high temperature of the heating wire, the thermal runaway of the target battery caused a chain reaction of Thermal runaway of the two batteries around the module. In a short time, the two affected batteries caught fire first, and the maximum runaway temperature of the battery could reach more than 800 ℃, which has far exceeded the Thermal runaway control threshold of the battery, This caused internal damage to the battery and the ejection of high-temperature substances. With the ejection of polar materials inside the battery, the battery shell ruptured, and the vast majority of internal materials were ejected, causing heat energy to be directly released to the outside of the battery, resulting in a decrease in the internal temperature of the battery. Under the pressure of the gas inside the battery, the direction of the sprayed material inside the battery is relatively random and has great uncertainty. During the battery Thermal runaway test, the temperature sensor inside the battery module was damaged, so the battery temperature information disappeared after the second half of the battery Thermal runaway, i.e. 200 seconds. It can be seen from the test results in the figure that it is necessary to find a way to restrain the path and energy of external heat diffusion after a single cell Thermal runaway. In the initial module structure design, after the Thermal runaway battery is ignited, a large amount of heat and combustible materials inside the battery are sprayed onto the adjacent battery, resulting in the successive Thermal runaway of adjacent batteries, which is confirmed from the disassembly analysis of the cell. It is very important to study the associated failure methods of batteries during the process of battery runaway. 4. Heat generation simulation model of power battery 4.1 Simulation Calculation Model for Battery Heat Generation The actual heat production of the battery is complicated, the simulation calculation process of battery Thermal runaway is similar to the calculation model of battery heat generation, so some assumptions should be made about the physical properties of the battery itself in the simulation calculation: (1) The specific heat capacity and thermal conductivity of various materials inside the battery are not affected by the change of ambient temperature and state of charge; (2) The medium of various materials of the battery is evenly distributed, and the thermal physical parameters remain unchanged. For example, the thermal conductivity coefficient of the same material is equal in the same direction. (3) During charging and discharging of lithium-ion batteries, the current density is evenly distributed and the heat production rate is consistent at different temperatures. Through the above assumptions, the energy conservation equation of unsteady heat transfer is obtained. $$\rho {c}_{p}\frac{\partial T}{\partial t}={\lambda }_{x}\frac{{\partial }^{2}T}{{\partial x}^{2}}+{\lambda }_{xy}\frac{{\partial }^{2}T}{{\partial y}^{2}}+{\lambda }_{zx}\frac{{\partial }^{2}T}{{\partial z}^{2}}+q$$ 1 \({\rho }_{k}{c}_{p,k}\frac{\partial T}{\partial t}\) refers to the increase of the thermal mechanical energy of the battery unit within a unit time, \(\nabla \bullet \left({\lambda }_{k}\nabla T\right)\) refers to the heat added to the cells inside the battery due to convective heat transfer by the fluid around the battery, q is the rate of heat production per unit volume of a lithium-ion battery, ρk is refers to the average density of the cell, cp,kR is refers to the average specific heat capacity of lithium-ion battery cells, λk is refers to the thermal conductivity of the lithium-ion battery unit, T is thermal, t is time, \(\rho\) is the average density of the material inside a lithium-ion battery, \(q\) is heat production rate per unit volume of a lithium-ion battery, \({\lambda }_{x}\) , \({\lambda }_{y}\) and \({\lambda }_{zx}\) are thermal conductivity of lithium ion battery in three - dimensional orthogonal direction. Many parameters in the chemical reaction kinetics formula that need to be calibrated need to be measured by multiple groups of experimental equipment. The common test method is constant temperature scanning Calorimetry, and the common experimental equipment is differential scanning calorimetry (DSC). DSC can scan the sample at a constant temperature rise rate, and by comparing the difference between the heating amount of the sample and the reference heating amount, the heat release/absorption of the sample at this constant temperature rise rate can be obtained. If any battery inside the battery is used as a single battery, the formula for the temperature T of the battery as a function of time t is as follows: $$\text{T}\left(t\right)=T\left(0\right)+\underset{0}{\overset{t}{\int }}\frac{dT\left(\tau \right)}{d\tau }d\tau$$ 2 The temperature rise rate \(\frac{dT\left(t\right)}{dt}\) is determined by the net heat generating power \(\text{Q}\left(t\right) is\) inside the battery, where M is the battery mass and the Specific heat capacity of the battery is \({C}_{p}=1100J.{kg}^{-1}{K}^{-1}\) . $$Q\left(t\right)={Q}_{chem}\left(t\right)+{Q}_{e}\left(t\right)-{Q}_{h}\left(t\right)$$ 3 $${Q}_{chem}\left(t\right)={Q}_{SEI}\left(t\right)+{Q}_{anode}\left(t\right)+{Q}_{sep}\left(t\right)+{Q}_{e}\left(t\right)+{Q}_{cath}\left(t\right)$$ 4 $${Q}_{cath}\left(t\right)={Q}_{caht1}\left(t\right)+{Q}_{caht2}\left(t\right)$$ 5 \({Q}_{chem}\left(t\right)\) is chemical reaction heat generation power, \({Q}_{SEI}\left(t\right)\) is heat generating power of SEI membrane Chemical decomposition, \({Q}_{anode}\left(t\right)\) is the heat generation power of lithium metal embedded inside the negative electrode when it reacts with the electrolyte without the protection of the SEI film, \({Q}_{sep}\left(t\right)\) is the heat absorption power of the diaphragm during melting, \({Q}_{e}\left(t\right)\) is the exothermic power of the overall Chemical decomposition of electrolyte solution, \({Q}_{cath}\left(t\right)\) is thermal power generation during decomposition of ternary cathode materials. Since the reaction of ternary positive electrode has two exothermic peaks \({Q}_{caht1}\left(t\right)\) and \({Q}_{caht2}\left(t\right)\) , the two Exothermic reaction are only equal to \({Q}_{cath}\left(t\right)\) . $${Q}_{e}\left(t\right)=\frac{1}{\varDelta t}\left(\varDelta {H}_{e}-\underset{0}{\overset{t}{\int }}{Q}_{e}\left(\tau \right)d\tau \right)$$ 6 The calculation of Qe can be obtained from the following equation, \(\varDelta {H}_{e}\) represents the total electrical energy possessed by the battery when an internal short circuit occurs; ∆t represents the average time of electrical energy release. The adiabatic Thermal runaway model can simulate the dynamic characteristics of each chemical reaction, and it is calculated in the model。The maximum temperature of Thermal runaway should be consistent with the experimental results. Its main principle is the Conservation of energy, \(\varDelta \text{t}\) represents the total heat energy released in the process of Thermal runaway; M represents the quality of the battery; \({C}_{p}\) represents the Specific heat capacity of the battery; \(\varDelta T\) represents the maximum temperature rise of battery Thermal runaway, according to formula (2–6), ∆ T = T3-T1; \({\varDelta \text{H}}_{chem}\) represents the total amount of Chemical energy converted into heat energy in the process of Thermal runaway; \({\varDelta \text{H}}_{e}\) represents the total amount of electric energy converted into heat energy in the process of Thermal runaway. $$\varDelta \text{H}=\text{M}\bullet {C}_{p}\bullet \varDelta T={\varDelta \text{H}}_{chem}+{\varDelta \text{H}}_{e}$$ 7 $${\varDelta \text{H}}_{chem}=\sum _{x}\left({C}_{x,0}\bullet \varDelta {H}_{x}\bullet {m}_{x}\right)$$ 8 \({\varDelta \text{H}}_{chem}\) is determined by the properties of the material itself and can be calculated from the data in the formula, where \({\varDelta \text{H}}_{chem}\) is approximately 2.87 × 10 5 J. According to the energy conservation equation and the experimentally measured ∆ T, set \({\varDelta \text{H}}_{e}\) approximately 3.17 × 10 5 J. 4.2 Simulation calculation model of battery Thermal runaway Based on the above analysis results, in order to ensure an adiabatic testing environment and accurately test and obtain battery samples。The temperature rise rate dTS/dt of the product under adiabatic conditions should focus on eliminating the influence of sensor measurement errors, that is, the calorimeter EV-ARC should be calibrated before the experiment. During the calibration process, the heat dissipation environment of the calorimeter shall be as close as possible to the environment when the Thermal runaway test is actually conducted. The heat dissipation of the calorimeter chamber not only needs to consider the heat dissipation from its outer wall towards the environment of the experimental site, but also the impact caused by the heat absorption of the battery sample. The key points of using EV-ARC to conduct thermal insulation Thermal runaway test of large capacity power battery are: 1) thermal insulation environment maintenance; 2) Accurate detection of heat release rate dT/dt. In order to meet the above two points, the following work should be carried out during the experiment: 1) Before the formal experiment of thermal insulation Thermal runaway, reduce the impact of sensor measurement error through the calibration scheme of equal heat capacity replacement and sensor mechanical clamping; 2) Try to simulate the internal environment of the calorimetry chamber, including large capacity battery samples, during the calibration process to obtain better heat dissipation compensation calibration results; 3) During formal testing, pay attention to using the sensor mechanical clamping scheme to ensure that the sensor is tightly attached to the surface of the battery. It should also be noted that the temperature distribution inside the large capacity power battery is uneven, and when Thermal runaway occurs, the temperature, the unevenness of distribution is the greatest. In order to accurately evaluate the total energy released by the large capacity power battery in the process of Thermal runaway, the internal temperature of the large capacity power battery should also be measured, and attention should be paid to analyzing the change of the internal temperature difference during the experiment. Figure 3 shows the ARC experiment results obtained. From the results in Fig. 3 , it can be seen that T1 is the starting temperature of battery self-heating, T2 is the trigger temperature of Thermal runaway, about 200 ℃. At this point, the dT/dt value changes sharply, and T3 is the highest temperature when the battery Thermal runaway occurs. This temperature value is very high, which can be used as the reference temperature set by the battery system protection device. The results of this test are consistent with the simulation results of Thermal runaway of the battery before. It can be seen from the figure that when the temperature is about 60 ℃, the solid dielectric facial mask (SEI film) on the negative electrode surface begins to decompose. At this point, the negative electrode of the battery loses SEI film protection, and the lithium embedded inside the negative electrode comes into contact with the electrolyte, causing a reaction to release heat and generate a new SEI film. The loss of lithium in the negative electrode of the battery leads to an increase in the negative voltage. In addition, under high temperature conditions, metal ions inside the positive electrode of the battery dissolve in the electrolyte, causing the loss of active substances in the positive electrode and reducing the voltage of the positive electrode. Due to the fact that the voltage of lithium-ion power batteries is equal to the difference between the positive and negative voltage, the voltage of the battery also decreases. Figure 4 shows the comparison between the simulation calculation results and the experimental results of multiple battery center temperature points during the battery Thermal runaway test. These temperature sensors are embedded inside the battery to be measured. The internal center temperature of the battery is measured. See Table 1 for the simulation calculation values and measurement results inside the battery. It can be seen from the data in Fig. 4 and Table 1 that the simulation calculation results are very close to the measured results of the battery, with an accuracy of more than 90%, Therefore, the simulation calculation model of battery heat generation should be used to analyze the process of Thermal runaway of batteries. Table 1 Simulation and test results of battery inner temperature Cell1 Cell2 Cell3 Cell4 Simulation(℃) 1005.2 1005.1 1004.8 995.7 test(℃) 1055.0 998.8 957.6 940.3 Accuracy(%) 95.3 99.4 95.3 94.4 5. System design for preventing battery Thermal runaway There are many ways to improve the prevention of thermal diffusion in power batteries, and targeted design can be carried out from three aspects: battery cells, battery modules, and battery systems. From the cell level, on the premise of not affecting the basic performance of the battery, adding flame retardants in the battery electrolyte and selecting SEI films that are more resistant to high temperature are all effective measures to reduce the damage value of Thermal runaway. Due to limitations in the length of this article, measures to prevent thermal diffusion at the cell level will not be discussed in detail. The next research focus of this paper is the Thermal runaway prevention measures at the battery module and pack level. 5.1 Battery module thermal runaway prevention design On the target module for the Thermal runaway test, first, according to the design structure and size specifications of the actual module inside the battery pack, design a heating device with the same appearance size as the module for the battery Thermal runaway test, replace a module in the middle of the module, and embed temperature sensors outside and inside the heating device and the electric core inside the module, The control power supply of the heating plate is connected to the trigger power supply outside the battery pack through a wire, and the heating plate is installed together with the thermal conductive mica sheet. The design of the heating plate in the middle of the module is shown in Fig. 5 . Since the design size of the heating plate in the module is basically the same as the size of the battery cell in the original module, the introduction of the heating plate will not have too much impact on the structure of the battery module under test, thus affecting the deviation of the Thermal runaway experiment from the Thermal runaway effect of the actual battery module structure. Add a 1.0 mm thick Aerogel between the end plate and the PC plate, and the thermal conductivity of Aerogel is extremely low, about 0.025 W/(m · K), which is 12.5% of the PC plate. Added thermal resistance between the battery cells at both ends of the module and the module end plate, effectively blocking heat conduction on the end plate side. In order to better observe the heating target module of the heating plate, do not accidentally trigger the Thermal runaway of the surrounding modules. Therefore, on the other side of the heating plate, there is also a thermal insulation mica sheet. In this way, during the test, the heating plate only heats the target battery in the module, and does not heat the surrounding battery, so as not to affect the experimental effect. In the tested module, when the tested power battery leaves the factory, a temperature sensor will be added inside the battery and fluorescent substances will be added to the electrolyte, so that not only the temperature changes of the heating plate and battery shell can be observed during the experiment, but also the temperature changes inside the battery can be measured, providing favorable data support for the design of the scheme to restrain the Thermal runaway of the battery. At the same time, due to the addition of fluorescent substances in the electrolyte, the electrolyte eruption in the case of Thermal runaway of the power battery can be observed and measured after the experiment, which provides an excellent reference for improving the Thermal runaway suppression scheme of the power battery pack. 5.2 Battery system thermal runaway prevention design In the tested module, when the tested power battery leaves the factory, a temperature sensor will be added inside the battery and fluorescent substances will be added to the electrolyte, so that not only the temperature changes of the heating plate and battery shell can be observed during the experiment, but also the temperature changes inside the battery can be measured, providing favorable data support for the design of the scheme to restrain the Thermal runaway of the battery. At the same time, due to the addition of fluorescent substances in the electrolyte, the electrolyte eruption in the case of Thermal runaway of the power battery can be observed and measured after the experiment, which provides an excellent reference for improving the Thermal runaway suppression scheme of the power battery pack. As shown in Fig. 6 . 5.3 Battery system thermal runaway prevention software design According to the changes of battery temperature, internal resistance, voltage and insulation resistance values obtained during the experiment, the judgment conditions of battery Thermal runaway in the Battery management system are modified. For example, BMS judges the rate of cell voltage reduction, the temperature of the battery shell and the temperature changes on the mica chip for 10 consecutive times, which can find Thermal runaway faults earlier and report them truthfully, reducing the probability of false alarm and failure to report Thermal runaway faults. As shown in Fig. 7 , BMS needs to repeatedly confirm the Thermal runaway signal, compare the measured internal and external temperature of the battery, coolant temperature and flow information, battery insulation, explosion-proof valve pressure and other information, and make a final judgment by repeated comparison to avoid misjudgment of Thermal runaway. 5. Results of the experiment The Thermal runaway test of the entire battery pack will be arranged on the bench for testing. The left photo in Fig. 8 shows the modified Thermal runaway trigger module of the power battery. On this module, measures to prevent Thermal runaway have been added according to the previous design requirements. Thermocouples have been embedded inside the cell, and temperature sensors are arranged on the surface of the cell and at the ear of the cell. At the same time, it will monitor the individual voltage and insulation resistance of the battery. On the right is the photo of the battery pack being put into the explosion-proof temperature box for Thermal runaway test. The tested battery pack will be charged to full power in advance for testing to verify the most severe Thermal runaway situation, that is, the battery has the maximum energy during testing. The specific method is to charge to 4.2V with constant current and voltage, and calibrate it to 100% SOC. All temperature sensors are monitored and recorded in real time during the Thermal runaway experiment. Figure 9 is the photo of the battery module Thermal runaway test alone. It can be seen from the photo that during the whole Thermal runaway test process, high-temperature substances were ejected from the ignited battery, and the measured internal temperature of the battery cell has exceeded 1000 ℃. Under such high temperature, the SEI film and other substances have been decomposed and damaged. Within the same module, the temperature of the three surrounding batteries also rapidly increased, but no explosion or fire was found. The measured temperature values are shown in Fig. 10 . From the experimental results in Fig. 10 , it can be seen that the Thermal runaway prevention measures previously designed inside the module played a role. The heat of the Thermal runaway module was transferred to the cooling plate through the Thermally conductive pad, and the cooling plate conducted some of the heat out. At the same time, the fireproof materials between different electric cores in the same module also play a role in flame retardancy, leading to the surrounding electric cores not being ignited by the Thermal runaway battery. The experimental results are consistent with the simulation results, which also shows the accuracy of the simulation calculation model. At the same time, the protection measures inside the module have reached the design goal, playing a role in protecting the surrounding batteries. After completing the Thermal runaway test at the battery module level, install the designed Thermal runaway trigger module into the power battery box for Thermal runaway test of the whole package of batteries. This battery pack is internally composed of four large modules, 1 # is the Thermal runaway trigger module, and the temperature signals of the other three modules are collected by the temperature sensors embedded in the module. The temperature sensor settings are completely consistent with the mass production version structure of the battery pack. The distribution diagram of the module inside the battery pack is shown in Fig. 11 . Figure 12 shows the measured temperature information during the Thermal runaway experiment of different modules of the whole battery pack. It can be seen from the figure that the triggering process of 1 # Thermal runaway module met the design expectation, and the Thermal runaway was triggered quickly 200 seconds later, with the temperature rising sharply. The temperature of the three adjacent modules increased slowly, but all were below 200 ℃. According to the previous analysis, it can be considered that under the premise of the temperature below 200 ℃, Batteries will not cause dangerous accidents such as explosions and fires. During the whole test process, after the Thermal runaway was triggered, 1 # battery module released a large amount of heat and gas, which caused the upper cover of the battery pack to bulge and deform. However, since the four explosion-proof valves designed on the battery pack box were opened in time to release the air pressure, the whole battery box remained intact. In addition, during the experiment, the high-temperature gas and flame emitted by the 1 # battery module were isolated by the mica plate on the battery box cover, so the steel plate on the battery pack cover was not burned through and remained intact. The whole test process meets the passing conditions of battery pack Thermal runaway, which shows that the designed protective measures are effective and meet the design requirements. 6. Conclusion This paper studies the protection technology of Thermal runaway of power battery. By establishing the thermal simulation model of power battery and combining the experimental data to modify the battery thermal model, the established thermal model of power battery can accurately simulate the process of Thermal runaway of power battery. On this basis, targeted protection design is carried out to reduce the thermal damage of battery in the process of Thermal runaway, and only samples are made for real vehicle verification. The main achievements of this article are as follows: 1. The thermal diffusion simulation calculation model of the power battery is established, and the key parameters of the model are modified according to the experimental data. The model can well simulate the process of Thermal runaway of the battery. 2. Targeted design has been made for the power battery to prevent thermal runaway, and targeted changes have been made in the battery module design and pack design. The experimental results show that the designed protective measures meet the design requirements and have a good protective effect. The research results of this article can provide a certain reference for research in the same industry. Declarations Author Contribution Kai Wen provided experimental data.Xingfeng Fu design experiment plan , Data curation, Writing- Original draft preparation. Writing- Reviewing and Editing.Hai Jiang provided data analysis. References Wang Qingsong, Ping Ping, Zhao Xuejuan, et al. 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In Simultaneous estimation of thermal parameters for large-format laminated lithium-ion batteries [C]. Vehicle Power & Propulsion Conference, 2014, 106–116. Van R, Danilov D, Notten P, et al. Battery thermal management by boiling heat-transfer [J]. Energy conversion and management 2014, 79: 9-17. Wu B, Li Z, Zhang JB. Thermal design optimization of laminated lithium ion battery based on the analytical solution of planar temperature distribution [J].Scientia Sinica Technologica, 2014, 11: 1154-1172. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 18 Mar, 2024 Reviews received at journal 10 Mar, 2024 Reviewers agreed at journal 07 Mar, 2024 Reviewers invited by journal 07 Mar, 2024 Editor assigned by journal 07 Mar, 2024 Editor invited by journal 07 Mar, 2024 Submission checks completed at journal 07 Mar, 2024 First submitted to journal 18 Feb, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3966428","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":277346185,"identity":"aa8bea3d-4698-4190-b8ab-3b4d7ae08d7a","order_by":0,"name":"Kai Wen","email":"","orcid":"","institution":"（1.Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Kai","middleName":"","lastName":"Wen","suffix":""},{"id":277346186,"identity":"06221803-ae53-4b65-8032-66b9381a8fe2","order_by":1,"name":"Xingfeng Fu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAr0lEQVRIiWNgGAWjYBAC9gbGBwcSDCTk2NjbDxCnhecAs+GBDxU2xnw8ZxKI1mJ8cMaZtMR5Eg4GRGqRSGY4zNt2OL1NgiGB4UfFNiK08BwGa8ltk248wNhz5jZhLfbs/QcgWmQOJDAzthGhhYeZGeIwNokEAyK1sDczgLyfQIIWoF9AgWzYBgzkg0T5BRhizB+AUSkv395+8MGPCiK0oIADJKofBaNgFIyCUYALAABv2z2NQGBxXgAAAABJRU5ErkJggg==","orcid":"","institution":"GAC AION NEW ENERGY AUTOMOBILE CO.,LTD","correspondingAuthor":true,"prefix":"","firstName":"Xingfeng","middleName":"","lastName":"Fu","suffix":""},{"id":277346187,"identity":"7a51d085-7b12-4252-9d79-37fc2a269abc","order_by":2,"name":"Hai Jiang","email":"","orcid":"","institution":"（1.Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Hai","middleName":"","lastName":"Jiang","suffix":""}],"badges":[],"createdAt":"2024-02-18 08:53:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3966428/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3966428/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52460495,"identity":"8b815762-c294-4aaa-8141-67bc16be78b6","added_by":"auto","created_at":"2024-03-11 22:47:05","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":493367,"visible":true,"origin":"","legend":"\u003cp\u003eMorphology of lithium evolution and deposition of lithium metal on the negative electrode of power batteries under overcharging\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/2e33e723490c91056e89636d.png"},{"id":52460491,"identity":"f1877e07-29ce-4e22-ab0c-4a0cdf797503","added_by":"auto","created_at":"2024-03-11 22:47:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":26187,"visible":true,"origin":"","legend":"\u003cp\u003eExperiment result diagram of Thermal runaway of battery center temperature\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/c8190afa6b8e80ca17687c46.png"},{"id":52460493,"identity":"d8a7ef69-7fde-4516-838b-a7b44db9ab34","added_by":"auto","created_at":"2024-03-11 22:47:04","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":24966,"visible":true,"origin":"","legend":"\u003cp\u003eTest of ARC\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/f3d901d8d3520d5d81e64d5e.png"},{"id":52460490,"identity":"bfd977cf-05b0-4c70-8c05-076351ff79f3","added_by":"auto","created_at":"2024-03-11 22:47:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":34445,"visible":true,"origin":"","legend":"\u003cp\u003eExperiment and simulation diagram of Thermal runaway of battery center temperature\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/e3ab64dbb95d558a68b8d091.png"},{"id":52460492,"identity":"e2a7feb5-efa3-49a0-9603-81d37bf12139","added_by":"auto","created_at":"2024-03-11 22:47:04","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":59686,"visible":true,"origin":"","legend":"\u003cp\u003eBattery module thermal runaway prevention design\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/2d149bdbef6b8e555a7896e1.png"},{"id":52460575,"identity":"a1f2f3d4-80ae-4ab5-b36f-ccfb62473e18","added_by":"auto","created_at":"2024-03-11 22:55:05","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":748466,"visible":true,"origin":"","legend":"\u003cp\u003eBattery Pack thermal runaway prevention design\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/a2d92aeba8f25c9d957f1c35.png"},{"id":52460496,"identity":"743530be-5f52-4ca3-804e-7131fef47349","added_by":"auto","created_at":"2024-03-11 22:47:05","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":208955,"visible":true,"origin":"","legend":"\u003cp\u003eJudgment process of Thermal runaway\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/8f9d6014f5a581b774d52804.png"},{"id":52460498,"identity":"d6231043-8b0d-4958-b24d-1ece2c693796","added_by":"auto","created_at":"2024-03-11 22:47:05","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":295248,"visible":true,"origin":"","legend":"\u003cp\u003eThe battery module and battery pack of Thermal runaway\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/75535d2097b0c340e08fa5fa.png"},{"id":52460497,"identity":"d7ab30b7-6232-4fb6-a9e0-8b40ed89a2df","added_by":"auto","created_at":"2024-03-11 22:47:05","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":161822,"visible":true,"origin":"","legend":"\u003cp\u003eThe test picture of battery module thermal runaway\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/c750939fcd6b90f9bc5720fc.png"},{"id":52460494,"identity":"454f80d2-b9e2-4b64-9152-c09e70db78ad","added_by":"auto","created_at":"2024-03-11 22:47:04","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":66632,"visible":true,"origin":"","legend":"\u003cp\u003eExperiment and simulation diagram of Thermal runaway of battery module\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/414eea452ae76b0697b98331.png"},{"id":52460500,"identity":"e2e0d6ce-b97e-45e4-8c90-c65d47a3b6e9","added_by":"auto","created_at":"2024-03-11 22:47:05","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":121681,"visible":true,"origin":"","legend":"\u003cp\u003eThe module layout of battery pack\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/19c0d60aa97b79cfd190826c.png"},{"id":52460501,"identity":"47480d59-91cb-497b-9f31-209f35c0678b","added_by":"auto","created_at":"2024-03-11 22:47:05","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":43686,"visible":true,"origin":"","legend":"\u003cp\u003eThe test of battery pack thermal runaway\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/1e15df0d3968d977bd444475.png"},{"id":52460984,"identity":"61b2b3d1-a117-4017-8c92-55277abc07e3","added_by":"auto","created_at":"2024-03-11 23:03:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2989456,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3966428/v1/b8e0e7f5-4ee1-4ac5-8672-ad982e84658d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study on the lithium power battery thermal runaway and prevention technology","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the rapid development of electric vehicles, lithium-ion power battery systems as power sources have received more and more attention. With the continuous increase of battery specific energy, the range of electric vehicles has approached or exceeded the level of fuel vehicles, and the safety of power batteries has also received more and more attention. Since the power battery system of electric vehicles contains huge energy, once Thermal runaway or thermal diffusion occurs, serious fire and explosion accidents will be caused, posing a serious threat to the safety of vehicles and drivers. \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e Therefore, effective measures must be taken to prevent and suppress the occurrence and effect of thermal diffusion of power batteries, which is extremely important for protecting the safety of electric vehicles and drivers. \u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe thermal diffusion experiment of power batteries has become one of the most important projects in the safety experiment of power batteries. It is a mandatory project for regulatory inspections, an important development content for power battery system design, and an important evaluation indicator for evaluating the quality of a power battery system design. At present, the prevention and suppression technology of thermal diffusion in power batteries has become one of the most important development contents in power battery system design, and has attracted the attention of domestic and foreign researchers. \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e"},{"header":"2. Factors influencing the results of battery Thermal runaway","content":"\u003cp\u003eThe main factors that cause the Thermal runaway of electric vehicles are the abuse of the external battery and the internal short circuit caused by the internal battery., External abuse includes mechanical abuse, electrical abuse, and thermal abuse, while internal short circuits are mainly caused by battery damage caused by puncturing the battery separator or exceeding the allowed charging and discharging capacity of the battery. Generally, mechanical, electrochemical and thermal conditions will be combined, and the Thermal runaway of the battery is the result of multiple factors. \u003csup\u003e[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eMechanical abuse mainly refers to battery deformation caused by external forces, commonly seen in typical situations such as car collisions and battery compression. Whether the deformation of the battery caused by external force will lead to internal short circuit of the battery, and whether the internal short circuit will lead to Thermal runaway and explosion of the battery, which is the focus of researchers on mechanical abuse. Collision squeezing is a common form of mechanical abuse, which is generally studied at three levels: battery materials, battery cells, and battery systems. \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e The extrusion mechanical model of battery cells is generally based on the study of the mechanical properties of the materials that make up the battery cells. Researchers conducted quasi-static mechanical tests on batteries of different forms. The types of loading include compression, extrusion, bending, etc. This type of research is very meaningful for predicting internal short circuits in batteries under mechanical abuse. The research results indicate that the battery underwent significant deformation before the start of the internal short circuit. The mechanical abuse model at the module and package level is based on the mechanical model of the battery cell, and is closely related to the protective ability of the entire package against mechanical damage (collision, impact, etc.). \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn the case of an external short circuit, the heating capacity of the power battery is generally not very high. The heat is mainly concentrated near the short circuit point, but if the battery is located near the short circuit point, it may be heated to the temperature where Thermal runaway occurs. In the design of the module, adding some external short circuit protection devices is of great significance for effectively suppressing the external short circuit of the battery.\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e For the internal short circuit of the power battery, improving the mass transfer efficiency of lithium ions in the negative electrode of the battery or increasing the negative electrode area of the battery can effectively improve the ability of the power battery to withstand external short circuit current impact. \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStatistics show that overcharging is another common phenomenon of electricity abuse that induces Thermal runaway of power batteries, and it has also caused many Thermal runaway safety accidents in the actual use of electric vehicles. The direct cause of overcharging is the failure of BMS protection measures to cut off the charging current in a timely manner when the power battery is fully charged, and charging beyond the charging capacity of the power battery. Overcharging is usually accompanied by heating and gas generation, which mainly comes from Ohmic heat and side reaction heat. \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e Research has found that the heat generated by batteries is directly proportional to the charging current, indicating that ohmic heat is one of the main reasons for heat generation during the charging process. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eOvercharging can cause great damage to power batteries. Due to excessive lithium embedding in the negative electrode, lithium dendrites can form on the surface of the negative electrode. Excessive lithium detachment in the positive electrode can lead to structural collapse. With the generation of heat and central enterprises, the release of oxygen accelerates the decomposition of the electrolyte, producing a large amount of gas. After a sharp increase in internal pressure, the power battery may spray or explode. \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eLocal excessive heating in the battery pack is a typical heat abuse condition. Local poor contact in the electrical connection may lead to excessive heating under the condition of high current, heating the nearby battery, causing Thermal runaway. For example, the defects of the battery system in the manufacturing process may lead to poor contact and increase of resistance. In addition, vibration, impact, and other conditions may also cause electrical connections to become loose, causing local heating. Due to the influence of preload and interface roughness on the contact resistance between connections. \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eWhen the internal separator of the battery is damaged and the positive and negative poles come into contact with each other, an internal short circuit occurs. Internal short circuit is one of the prominent characteristics of Thermal runaway. \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e After the occurrence of internal short circuit, the electric energy and electrochemical energy stored in the electrode plate will be released violently, and a large amount of heat will be generated in a short time, which will lead to runaway heating. In addition to the three types of external abuse mentioned above, the battery's own defects may also cause internal short circuits.\u003c/p\u003e"},{"header":"3. Research on suppression design of power battery Thermal runaway","content":"\u003cp\u003eIn the power battery system, when Thermal runaway occurs in one battery, Thermal runaway may spread to adjacent batteries. \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e An unexpected failure mode is that the spread of gas and flame can cause Thermal runaway diffusion. The reason why the first pathway is expected is mainly because it is relatively easy to block heat transfer. However, the reason why the second pathway is unexpected is mainly due to the uncertainty of gas and flame diffusion. These two failure pathways can be suppressed through the following methods: \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(1) gas suppression;\u003c/p\u003e \u003cp\u003e(2) Loss of integrity:\u003c/p\u003e \u003cp\u003e(3) Flame ignition.\u003c/p\u003e \u003cp\u003eIn order to restrain the Thermal runaway diffusion at the power battery system level, researchers prefer to limit the failure diffusion caused by heat transfer. \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e is the Thermal runaway test process diagram of a square power battery. It can be seen from the figure that under the influence of the high temperature of the heating wire, the thermal runaway of the target battery caused a chain reaction of Thermal runaway of the two batteries around the module. In a short time, the two affected batteries caught fire first, and the maximum runaway temperature of the battery could reach more than 800 ℃, which has far exceeded the Thermal runaway control threshold of the battery, This caused internal damage to the battery and the ejection of high-temperature substances. With the ejection of polar materials inside the battery, the battery shell ruptured, and the vast majority of internal materials were ejected, causing heat energy to be directly released to the outside of the battery, resulting in a decrease in the internal temperature of the battery. Under the pressure of the gas inside the battery, the direction of the sprayed material inside the battery is relatively random and has great uncertainty. During the battery Thermal runaway test, the temperature sensor inside the battery module was damaged, so the battery temperature information disappeared after the second half of the battery Thermal runaway, i.e. 200 seconds.\u003c/p\u003e \u003cp\u003eIt can be seen from the test results in the figure that it is necessary to find a way to restrain the path and energy of external heat diffusion after a single cell Thermal runaway. In the initial module structure design, after the Thermal runaway battery is ignited, a large amount of heat and combustible materials inside the battery are sprayed onto the adjacent battery, resulting in the successive Thermal runaway of adjacent batteries, which is confirmed from the disassembly analysis of the cell. It is very important to study the associated failure methods of batteries during the process of battery runaway.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Heat generation simulation model of power battery","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Simulation Calculation Model for Battery Heat Generation\u003c/h2\u003e \u003cp\u003eThe actual heat production of the battery is complicated, the simulation calculation process of battery Thermal runaway is similar to the calculation model of battery heat generation, so some assumptions should be made about the physical properties of the battery itself in the simulation calculation:\u003c/p\u003e \u003cp\u003e(1) The specific heat capacity and thermal conductivity of various materials inside the battery are not affected by the change of ambient temperature and state of charge;\u003c/p\u003e \u003cp\u003e(2) The medium of various materials of the battery is evenly distributed, and the thermal physical parameters remain unchanged. For example, the thermal conductivity coefficient of the same material is equal in the same direction.\u003c/p\u003e \u003cp\u003e(3) During charging and discharging of lithium-ion batteries, the current density is evenly distributed and the heat production rate is consistent at different temperatures.\u003c/p\u003e \u003cp\u003eThrough the above assumptions, the energy conservation equation of unsteady heat transfer is obtained.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\rho {c}_{p}\\frac{\\partial T}{\\partial t}={\\lambda }_{x}\\frac{{\\partial }^{2}T}{{\\partial x}^{2}}+{\\lambda }_{xy}\\frac{{\\partial }^{2}T}{{\\partial y}^{2}}+{\\lambda }_{zx}\\frac{{\\partial }^{2}T}{{\\partial z}^{2}}+q$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\rho }_{k}{c}_{p,k}\\frac{\\partial T}{\\partial t}\\)\u003c/span\u003e \u003c/span\u003e refers to the increase of the thermal mechanical energy of the battery unit within a unit time,\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\nabla \\bullet \\left({\\lambda }_{k}\\nabla T\\right)\\)\u003c/span\u003e\u003c/span\u003e refers to the heat added to the cells inside the battery due to convective heat transfer by the fluid around the battery, q is the rate of heat production per unit volume of a lithium-ion battery, ρk is refers to the average density of the cell, cp,kR is refers to the average specific heat capacity of lithium-ion battery cells, λk is refers to the thermal conductivity of the lithium-ion battery unit, T is thermal, t is time, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rho\\)\u003c/span\u003e\u003c/span\u003e is the average density of the material inside a lithium-ion battery, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(q\\)\u003c/span\u003e\u003c/span\u003e is heat production rate per unit volume of a lithium-ion battery, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\lambda }_{x}\\)\u003c/span\u003e\u003c/span\u003e,\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\lambda }_{y}\\)\u003c/span\u003e\u003c/span\u003eand \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\lambda }_{zx}\\)\u003c/span\u003e\u003c/span\u003eare thermal conductivity of lithium ion battery in three - dimensional orthogonal direction.\u003c/p\u003e \u003cp\u003eMany parameters in the chemical reaction kinetics formula that need to be calibrated need to be measured by multiple groups of experimental equipment. The common test method is constant temperature scanning Calorimetry, and the common experimental equipment is differential scanning calorimetry (DSC). DSC can scan the sample at a constant temperature rise rate, and by comparing the difference between the heating amount of the sample and the reference heating amount, the heat release/absorption of the sample at this constant temperature rise rate can be obtained.\u003c/p\u003e \u003cp\u003eIf any battery inside the battery is used as a single battery, the formula for the temperature T of the battery as a function of time t is as follows:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\text{T}\\left(t\\right)=T\\left(0\\right)+\\underset{0}{\\overset{t}{\\int }}\\frac{dT\\left(\\tau \\right)}{d\\tau }d\\tau$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe temperature rise rate\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{dT\\left(t\\right)}{dt}\\)\u003c/span\u003e\u003c/span\u003eis determined by the net heat generating power\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{Q}\\left(t\\right) is\\)\u003c/span\u003e\u003c/span\u003einside the battery, where M is the battery mass and the Specific heat capacity of the battery is \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{p}=1100J.{kg}^{-1}{K}^{-1}\\)\u003c/span\u003e\u003c/span\u003e.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$Q\\left(t\\right)={Q}_{chem}\\left(t\\right)+{Q}_{e}\\left(t\\right)-{Q}_{h}\\left(t\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$${Q}_{chem}\\left(t\\right)={Q}_{SEI}\\left(t\\right)+{Q}_{anode}\\left(t\\right)+{Q}_{sep}\\left(t\\right)+{Q}_{e}\\left(t\\right)+{Q}_{cath}\\left(t\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$${Q}_{cath}\\left(t\\right)={Q}_{caht1}\\left(t\\right)+{Q}_{caht2}\\left(t\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({Q}_{chem}\\left(t\\right)\\)\u003c/span\u003e \u003c/span\u003e is chemical reaction heat generation power, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{SEI}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e is heat generating power of SEI membrane Chemical decomposition, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{anode}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e is the heat generation power of lithium metal embedded inside the negative electrode when it reacts with the electrolyte without the protection of the SEI film, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{sep}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e is the heat absorption power of the diaphragm during melting, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{e}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003eis the exothermic power of the overall Chemical decomposition of electrolyte solution, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{cath}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e is thermal power generation during decomposition of ternary cathode materials. Since the reaction of ternary positive electrode has two exothermic peaks\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{caht1}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{caht2}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e, the two Exothermic reaction are only equal to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Q}_{cath}\\left(t\\right)\\)\u003c/span\u003e\u003c/span\u003e.\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$${Q}_{e}\\left(t\\right)=\\frac{1}{\\varDelta t}\\left(\\varDelta {H}_{e}-\\underset{0}{\\overset{t}{\\int }}{Q}_{e}\\left(\\tau \\right)d\\tau \\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe calculation of Qe can be obtained from the following equation, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\varDelta {H}_{e}\\)\u003c/span\u003e\u003c/span\u003e represents the total electrical energy possessed by the battery when an internal short circuit occurs; ∆t represents the average time of electrical energy release. The adiabatic Thermal runaway model can simulate the dynamic characteristics of each chemical reaction, and it is calculated in the model。The maximum temperature of Thermal runaway should be consistent with the experimental results. Its main principle is the Conservation of energy, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\varDelta \\text{t}\\)\u003c/span\u003e\u003c/span\u003e represents the total heat energy released in the process of Thermal runaway; M represents the quality of the battery; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{p}\\)\u003c/span\u003e\u003c/span\u003e represents the Specific heat capacity of the battery; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\varDelta T\\)\u003c/span\u003e\u003c/span\u003e represents the maximum temperature rise of battery Thermal runaway, according to formula (2\u0026ndash;6), ∆ T\u0026thinsp;=\u0026thinsp;T3-T1; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\varDelta \\text{H}}_{chem}\\)\u003c/span\u003e\u003c/span\u003e represents the total amount of Chemical energy converted into heat energy in the process of Thermal runaway; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\varDelta \\text{H}}_{e}\\)\u003c/span\u003e\u003c/span\u003e represents the total amount of electric energy converted into heat energy in the process of Thermal runaway.\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\varDelta \\text{H}=\\text{M}\\bullet {C}_{p}\\bullet \\varDelta T={\\varDelta \\text{H}}_{chem}+{\\varDelta \\text{H}}_{e}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$${\\varDelta \\text{H}}_{chem}=\\sum _{x}\\left({C}_{x,0}\\bullet \\varDelta {H}_{x}\\bullet {m}_{x}\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\varDelta \\text{H}}_{chem}\\)\u003c/span\u003e \u003c/span\u003eis determined by the properties of the material itself and can be calculated from the data in the formula, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\varDelta \\text{H}}_{chem}\\)\u003c/span\u003e\u003c/span\u003eis approximately 2.87 \u0026times; 10\u003csup\u003e5\u003c/sup\u003eJ. According to the energy conservation equation and the experimentally measured ∆ T, set \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\varDelta \\text{H}}_{e}\\)\u003c/span\u003e\u003c/span\u003e approximately 3.17 \u0026times; 10\u003csup\u003e5\u003c/sup\u003eJ.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Simulation calculation model of battery Thermal runaway\u003c/h2\u003e \u003cp\u003eBased on the above analysis results, in order to ensure an adiabatic testing environment and accurately test and obtain battery samples。The temperature rise rate dTS/dt of the product under adiabatic conditions should focus on eliminating the influence of sensor measurement errors, that is, the calorimeter EV-ARC should be calibrated before the experiment. During the calibration process, the heat dissipation environment of the calorimeter shall be as close as possible to the environment when the Thermal runaway test is actually conducted. The heat dissipation of the calorimeter chamber not only needs to consider the heat dissipation from its outer wall towards the environment of the experimental site, but also the impact caused by the heat absorption of the battery sample.\u003c/p\u003e \u003cp\u003eThe key points of using EV-ARC to conduct thermal insulation Thermal runaway test of large capacity power battery are:\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e1) thermal insulation environment maintenance;\u003c/h3\u003e\n\n\u003ch3\u003e2) Accurate detection of heat release rate dT/dt.\u003c/h3\u003e\n\u003cp\u003eIn order to meet the above two points, the following work should be carried out during the experiment:\u003c/p\u003e \u003cp\u003e1) Before the formal experiment of thermal insulation Thermal runaway, reduce the impact of sensor measurement error through the calibration scheme of equal heat capacity replacement and sensor mechanical clamping;\u003c/p\u003e \u003cp\u003e2) Try to simulate the internal environment of the calorimetry chamber, including large capacity battery samples, during the calibration process to obtain better heat dissipation compensation calibration results;\u003c/p\u003e \u003cp\u003e3) During formal testing, pay attention to using the sensor mechanical clamping scheme to ensure that the sensor is tightly attached to the surface of the battery.\u003c/p\u003e \u003cp\u003eIt should also be noted that the temperature distribution inside the large capacity power battery is uneven, and when Thermal runaway occurs, the temperature, the unevenness of distribution is the greatest. In order to accurately evaluate the total energy released by the large capacity power battery in the process of Thermal runaway, the internal temperature of the large capacity power battery should also be measured, and attention should be paid to analyzing the change of the internal temperature difference during the experiment.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the ARC experiment results obtained. From the results in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, it can be seen that T1 is the starting temperature of battery self-heating, T2 is the trigger temperature of Thermal runaway, about 200 ℃. At this point, the dT/dt value changes sharply, and T3 is the highest temperature when the battery Thermal runaway occurs. This temperature value is very high, which can be used as the reference temperature set by the battery system protection device. The results of this test are consistent with the simulation results of Thermal runaway of the battery before.\u003c/p\u003e \u003cp\u003eIt can be seen from the figure that when the temperature is about 60 ℃, the solid dielectric facial mask (SEI film) on the negative electrode surface begins to decompose. At this point, the negative electrode of the battery loses SEI film protection, and the lithium embedded inside the negative electrode comes into contact with the electrolyte, causing a reaction to release heat and generate a new SEI film. The loss of lithium in the negative electrode of the battery leads to an increase in the negative voltage. In addition, under high temperature conditions, metal ions inside the positive electrode of the battery dissolve in the electrolyte, causing the loss of active substances in the positive electrode and reducing the voltage of the positive electrode. Due to the fact that the voltage of lithium-ion power batteries is equal to the difference between the positive and negative voltage, the voltage of the battery also decreases.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the comparison between the simulation calculation results and the experimental results of multiple battery center temperature points during the battery Thermal runaway test. These temperature sensors are embedded inside the battery to be measured. The internal center temperature of the battery is measured. See Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e for the simulation calculation values and measurement results inside the battery. It can be seen from the data in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e that the simulation calculation results are very close to the measured results of the battery, with an accuracy of more than 90%, Therefore, the simulation calculation model of battery heat generation should be used to analyze the process of Thermal runaway of batteries.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSimulation and test results of battery inner temperature\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCell1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCell2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCell3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCell4\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSimulation(℃)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1005.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1005.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1004.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e995.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etest(℃)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1055.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e998.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e957.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e940.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAccuracy(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e95.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e99.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e95.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e94.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003e5. System design for preventing battery Thermal runaway\u003c/h3\u003e\n\u003cp\u003eThere are many ways to improve the prevention of thermal diffusion in power batteries, and targeted design can be carried out from three aspects: battery cells, battery modules, and battery systems. From the cell level, on the premise of not affecting the basic performance of the battery, adding flame retardants in the battery electrolyte and selecting SEI films that are more resistant to high temperature are all effective measures to reduce the damage value of Thermal runaway. Due to limitations in the length of this article, measures to prevent thermal diffusion at the cell level will not be discussed in detail. The next research focus of this paper is the Thermal runaway prevention measures at the battery module and pack level.\u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Battery module thermal runaway prevention design\u003c/h2\u003e \u003cp\u003eOn the target module for the Thermal runaway test, first, according to the design structure and size specifications of the actual module inside the battery pack, design a heating device with the same appearance size as the module for the battery Thermal runaway test, replace a module in the middle of the module, and embed temperature sensors outside and inside the heating device and the electric core inside the module, The control power supply of the heating plate is connected to the trigger power supply outside the battery pack through a wire, and the heating plate is installed together with the thermal conductive mica sheet. The design of the heating plate in the middle of the module is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSince the design size of the heating plate in the module is basically the same as the size of the battery cell in the original module, the introduction of the heating plate will not have too much impact on the structure of the battery module under test, thus affecting the deviation of the Thermal runaway experiment from the Thermal runaway effect of the actual battery module structure. Add a 1.0 mm thick Aerogel between the end plate and the PC plate, and the thermal conductivity of Aerogel is extremely low, about 0.025 W/(m \u0026middot; K), which is 12.5% of the PC plate. Added thermal resistance between the battery cells at both ends of the module and the module end plate, effectively blocking heat conduction on the end plate side.\u003c/p\u003e \u003cp\u003eIn order to better observe the heating target module of the heating plate, do not accidentally trigger the Thermal runaway of the surrounding modules. Therefore, on the other side of the heating plate, there is also a thermal insulation mica sheet. In this way, during the test, the heating plate only heats the target battery in the module, and does not heat the surrounding battery, so as not to affect the experimental effect.\u003c/p\u003e \u003cp\u003eIn the tested module, when the tested power battery leaves the factory, a temperature sensor will be added inside the battery and fluorescent substances will be added to the electrolyte, so that not only the temperature changes of the heating plate and battery shell can be observed during the experiment, but also the temperature changes inside the battery can be measured, providing favorable data support for the design of the scheme to restrain the Thermal runaway of the battery. At the same time, due to the addition of fluorescent substances in the electrolyte, the electrolyte eruption in the case of Thermal runaway of the power battery can be observed and measured after the experiment, which provides an excellent reference for improving the Thermal runaway suppression scheme of the power battery pack.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Battery system thermal runaway prevention design\u003c/h2\u003e \u003cp\u003eIn the tested module, when the tested power battery leaves the factory, a temperature sensor will be added inside the battery and fluorescent substances will be added to the electrolyte, so that not only the temperature changes of the heating plate and battery shell can be observed during the experiment, but also the temperature changes inside the battery can be measured, providing favorable data support for the design of the scheme to restrain the Thermal runaway of the battery. At the same time, due to the addition of fluorescent substances in the electrolyte, the electrolyte eruption in the case of Thermal runaway of the power battery can be observed and measured after the experiment, which provides an excellent reference for improving the Thermal runaway suppression scheme of the power battery pack. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Battery system thermal runaway prevention software design\u003c/h2\u003e \u003cp\u003eAccording to the changes of battery temperature, internal resistance, voltage and insulation resistance values obtained during the experiment, the judgment conditions of battery Thermal runaway in the Battery management system are modified. For example, BMS judges the rate of cell voltage reduction, the temperature of the battery shell and the temperature changes on the mica chip for 10 consecutive times, which can find Thermal runaway faults earlier and report them truthfully, reducing the probability of false alarm and failure to report Thermal runaway faults.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, BMS needs to repeatedly confirm the Thermal runaway signal, compare the measured internal and external temperature of the battery, coolant temperature and flow information, battery insulation, explosion-proof valve pressure and other information, and make a final judgment by repeated comparison to avoid misjudgment of Thermal runaway.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Results of the experiment","content":"\u003cp\u003eThe Thermal runaway test of the entire battery pack will be arranged on the bench for testing. The left photo in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the modified Thermal runaway trigger module of the power battery. On this module, measures to prevent Thermal runaway have been added according to the previous design requirements. Thermocouples have been embedded inside the cell, and temperature sensors are arranged on the surface of the cell and at the ear of the cell. At the same time, it will monitor the individual voltage and insulation resistance of the battery. On the right is the photo of the battery pack being put into the explosion-proof temperature box for Thermal runaway test.\u003c/p\u003e \u003cp\u003eThe tested battery pack will be charged to full power in advance for testing to verify the most severe Thermal runaway situation, that is, the battery has the maximum energy during testing. The specific method is to charge to 4.2V with constant current and voltage, and calibrate it to 100% SOC. All temperature sensors are monitored and recorded in real time during the Thermal runaway experiment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e is the photo of the battery module Thermal runaway test alone. It can be seen from the photo that during the whole Thermal runaway test process, high-temperature substances were ejected from the ignited battery, and the measured internal temperature of the battery cell has exceeded 1000 ℃. Under such high temperature, the SEI film and other substances have been decomposed and damaged. Within the same module, the temperature of the three surrounding batteries also rapidly increased, but no explosion or fire was found. The measured temperature values are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFrom the experimental results in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, it can be seen that the Thermal runaway prevention measures previously designed inside the module played a role. The heat of the Thermal runaway module was transferred to the cooling plate through the Thermally conductive pad, and the cooling plate conducted some of the heat out. At the same time, the fireproof materials between different electric cores in the same module also play a role in flame retardancy, leading to the surrounding electric cores not being ignited by the Thermal runaway battery. The experimental results are consistent with the simulation results, which also shows the accuracy of the simulation calculation model. At the same time, the protection measures inside the module have reached the design goal, playing a role in protecting the surrounding batteries.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAfter completing the Thermal runaway test at the battery module level, install the designed Thermal runaway trigger module into the power battery box for Thermal runaway test of the whole package of batteries. This battery pack is internally composed of four large modules, 1 # is the Thermal runaway trigger module, and the temperature signals of the other three modules are collected by the temperature sensors embedded in the module. The temperature sensor settings are completely consistent with the mass production version structure of the battery pack. The distribution diagram of the module inside the battery pack is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows the measured temperature information during the Thermal runaway experiment of different modules of the whole battery pack. It can be seen from the figure that the triggering process of 1 # Thermal runaway module met the design expectation, and the Thermal runaway was triggered quickly 200 seconds later, with the temperature rising sharply. The temperature of the three adjacent modules increased slowly, but all were below 200 ℃. According to the previous analysis, it can be considered that under the premise of the temperature below 200 ℃, Batteries will not cause dangerous accidents such as explosions and fires. During the whole test process, after the Thermal runaway was triggered, 1 # battery module released a large amount of heat and gas, which caused the upper cover of the battery pack to bulge and deform. However, since the four explosion-proof valves designed on the battery pack box were opened in time to release the air pressure, the whole battery box remained intact.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition, during the experiment, the high-temperature gas and flame emitted by the 1 # battery module were isolated by the mica plate on the battery box cover, so the steel plate on the battery pack cover was not burned through and remained intact. The whole test process meets the passing conditions of battery pack Thermal runaway, which shows that the designed protective measures are effective and meet the design requirements.\u003c/p\u003e"},{"header":"6. Conclusion","content":"\u003cp\u003eThis paper studies the protection technology of Thermal runaway of power battery. By establishing the thermal simulation model of power battery and combining the experimental data to modify the battery thermal model, the established thermal model of power battery can accurately simulate the process of Thermal runaway of power battery. On this basis, targeted protection design is carried out to reduce the thermal damage of battery in the process of Thermal runaway, and only samples are made for real vehicle verification. The main achievements of this article are as follows:\u003c/p\u003e\n\u003cp\u003e\u003cspan\u003e1. The thermal diffusion simulation calculation model of the power battery is established, and the key parameters of the model are modified according to the experimental data. The model can well simulate the process of Thermal runaway of the battery.\u003cbr\u003e\u003c/span\u003e\u003cspan\u003e2. Targeted design has been made for the power battery to prevent thermal runaway, and targeted changes have been made in the battery module design and pack design. The experimental results show that the designed protective measures meet the design requirements and have a good protective effect.\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eThe research results of this article can provide a certain reference for research in the same industry.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eKai Wen provided experimental data.Xingfeng Fu design experiment plan , Data curation, Writing- Original draft preparation. Writing- Reviewing and Editing.Hai Jiang provided data analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWang Qingsong, Ping Ping, Zhao Xuejuan, et al. Thermal runaway caused fire and explosion of lithium ion battery [J]. Journal of Power Sources, 2012, 208: 210-224.\u003c/li\u003e\n\u003cli\u003eWilliard N, He Wei, Hendricks C, et al. Lessons learned from the 787 Dreamliner issue on lithium-ion battery reliability [J]. Energies, 2013, 6(9): 4682-4695.\u003c/li\u003e\n\u003cli\u003eABAZA A, FERRARI S, WONG HK, etal. 2018. Experimental study of internal and external short circuits of commercial automotive pouch lithiumion cells[J]. Journal of Energy Storage, 16: 211-217\u003c/li\u003e\n\u003cli\u003eALIM Y, LAI W J, PAN J. 2013. Computational models for simulations of lithium-ion battery cells under constrained compression tests[J]. Journal of Power Sources, 242:325-340.\u003c/li\u003e\n\u003cli\u003eQ. S Wang, Ping P, Zhao X J, et al. 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Vehicle Power \u0026amp; Propulsion Conference, 2014, 106\u0026ndash;116.\u003c/li\u003e\n\u003cli\u003eVan R, Danilov D, Notten P, et al. Battery thermal management by boiling heat-transfer [J]. Energy conversion and management 2014, 79: 9-17.\u003c/li\u003e\n\u003cli\u003eWu B, Li Z, Zhang JB. Thermal design optimization of laminated lithium ion battery based on the analytical solution of planar temperature distribution [J].Scientia Sinica Technologica, 2014, 11: 1154-1172.\u003c/li\u003e\n\u003c/ol\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Thermal runaway, Battery management system, Simulation modeling, Methods to prevent Thermal runaway","lastPublishedDoi":"10.21203/rs.3.rs-3966428/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3966428/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn order to the issue of preventing Thermal runaway of power battery, the thermal generation model of power battery was established, and the model was modified based on the experimental data. On the basis of simulation calculation, the scheme of preventing Thermal runaway of battery module and battery pack was designed, and samples were made for test. The results of test and simulation calculation were very consistent, which confirmed the accuracy of the simulation calculation model, the results of Thermal runaway test also prove that the measures designed to prevent Thermal runaway are effective and meet the design requirement.\u003c/p\u003e","manuscriptTitle":"Study on the lithium power battery thermal runaway and prevention technology","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-11 22:46:59","doi":"10.21203/rs.3.rs-3966428/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-03-18T04:38:11+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-03-11T01:12:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"b407ee6b-5ec3-4f01-9883-4cf7773dd69a","date":"2024-03-07T23:54:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-03-07T20:45:31+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-07T15:56:17+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-03-07T10:22:14+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-03-07T10:08:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-02-18T08:51:18+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4e26cb01-1277-4f97-8bb2-7039b45def2c","owner":[],"postedDate":"March 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-05-16T08:41:02+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-11 22:46:59","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3966428","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3966428","identity":"rs-3966428","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}