A method for modularly quantifying the heat flux of lithium-ion battery thermal runaway exhaust

Abstract

The application provides a kind of modular quantitative test lithium ion battery thermal runaway exhaust heat flux method, belong to lithium ion battery test technical field, the skeleton of the modular quantitative test lithium ion battery thermal runaway exhaust heat flux device is built by high-strength aluminum alloy section, the limited space in the interior of battery package is formed by adjustable height roof and peripheral baffle space restraint simulation, heating trigger device is arranged in it, distributed temperature measurement plate array is fixed by slot positioning around the top of test battery in the heating trigger device, it can adapt to the arrangement requirement of different experimental conditions, realize the real-time monitoring and quantitative analysis of the heat flux of thermal runaway exhaust in the limited space;The application provides a kind of modular quantitative test lithium ion battery thermal runaway exhaust heat flux method, can realize the experimental reduction and heat quantization of the heating process of thermal runaway exhaust on adjacent area.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery testing technology, and specifically relates to a modular quantitative testing method for the thermal runaway exhaust heat flux of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, grid energy storage, and other fields. However, during operation, batteries may experience thermal runaway events due to mechanical, electrical, or thermal abuse. Thermal runaway causes a rapid rise in battery temperature, and the internal chain reaction generates a large amount of flammable gas and vapor cloud. These gases increase the internal pressure of the battery until it reaches the threshold of the battery safety valve, causing it to erupt. The released high-temperature flammable multiphase flow will diffuse and flow within the battery module, further heating other batteries and increasing their risk of thermal runaway. Existing research focuses on the ignition behavior and flame propagation process of thermal runaway. However, in many real-world cases (especially for lithium iron phosphate batteries), thermal runaway often manifests as a prolonged high-temperature exhaust phase without open flame. During this phase, the released flammable gases, electrolyte vapors and droplets, and solid particles flow, rebound, and deposit within the battery pack's encapsulation structure. The heat transfer process in this event involves complex mechanisms, including jet impact, vapor condensation, particle deposition, and radiative heating of nearby structures, resulting in a significant heating effect on other batteries. This multiphase flow exhaust thermal coupling behavior represents the hidden heat propagating in thermal runaway, and these heat fluxes are difficult to capture through numerical simulation alone. Therefore, quantitatively characterizing the spatiotemporal heat transfer distribution induced by multiphase flow in thermally runaway batteries within the confined space of a battery pack is of great significance for assessing the safety performance of large battery packs. However, current technologies lack effective devices and methods for spatial reproduction and heat quantification, greatly limiting the scientific basis for thermal safety design. Summary of the Invention

[0003] In view of this, the present invention provides a modular quantitative method for testing the thermal runaway exhaust heat flux of lithium-ion batteries, which can realize the experimental reconstruction and heat quantification of the heating process of thermal runaway exhaust on adjacent cells.

[0004] This invention is implemented as follows:

[0005] The first aspect of this invention provides a modular quantitative testing device for the thermal runaway exhaust heat flux of a lithium-ion battery. The device's frame is constructed of high-strength aluminum alloy profiles. An adjustable-height top plate and peripheral baffles form a spatial constraint that simulates the restricted space inside the battery pack. A heating triggering device is installed inside the device. A distributed temperature measuring plate array is positioned and fixed around the top of the test battery in the heating triggering device via slots. This arrangement can adapt to different experimental conditions and realize the experimental reproduction and heat quantification of the thermal runaway exhaust's effect on the adjacent area.

[0006] Based on the above technical solution, the modular quantitative testing device for thermal runaway exhaust heat flux of lithium-ion batteries of the present invention can be further improved as follows:

[0007] The top plate is an adjustable-height flat plate structure made of high-strength stainless steel with a thickness of 5 mm. It is used to simulate the upper boundary of the battery pack. Its height can be adjusted according to experimental needs to change the size of the top gap of the confined space. The side of the top plate away from the battery is covered with an aerogel insulation layer of the same area and a thickness of 5 mm. The edge of the top plate that contacts the surrounding baffle is filled with aerogel material to insulate heat and prevent heat from being conducted away through the top plate.

[0008] Furthermore, the peripheral baffle is a stainless steel plate with a thickness of 5 mm surrounding the experimental battery. It is made of the same material as the top plate and can be flexibly installed or removed as needed to form a restrictive sidewall structure similar to the battery module housing. The baffle is used to constrain the flow path of the high-speed ejected gas when thermal runaway exhaust occurs, limiting it to mainly flow horizontally inside the device to avoid direct and rapid escape, thereby more realistically reproducing the exhaust environment inside the battery pack.

[0009] Furthermore, the temperature measuring plate is composed of an aluminum plate, thermocouples, and a heat-insulating substrate. The top surface dimension of each temperature measuring plate is the same as that of the top of the battery. The aluminum plate is made of aluminum alloy with high thermal conductivity as the heating surface. A K-type thermocouple is attached to the bottom surface of the aluminum plate, one at the front and one at the back of the bottom of each aluminum plate, with a sampling frequency of 1. The system achieves real-time recording of temperature changes at Hz. A mica-based heat-insulating base is tightly attached beneath the aluminum plate, supporting the aluminum plate and thermocouple from below and reducing heat transfer to the bottom frame. The aluminum plate and heat-insulating base are bonded together using high-temperature adhesive. Each temperature measuring plate is quickly fixed to the test device frame via grooves on both sides of the heat-insulating base. Its top height is flush with the top surface of the trigger battery, simulating the situation where adjacent batteries in a real battery module have their top surfaces at the same level. When the trigger battery experiences thermal runaway and exhaust, each temperature measuring plate, like the upper surface of an adjacent battery, will be directly heated by the high-temperature exhaust. By distributing several temperature measuring plates around the test battery according to the actual arrangement of the battery module, a distributed temperature measuring plate array is formed, enabling multi-point capture of regional temperature responses and providing basic data for subsequent heat flow distribution calculations.

[0010] Furthermore, a 500 W heating plate is installed close to one side of the trigger battery as a heating trigger device. The battery and the heating plate are tightly attached by a clamp, and a 1 kN preload is applied to the clamp bolts to ensure that the battery and the heating plate are in full contact for heat transfer during the heating process. The other sides of the trigger battery are covered with a 3 mm thick aerogel insulation layer to reduce the heat conduction from the battery casing to the surrounding temperature measuring plate during the heating process and to isolate unexpected heat conduction paths.

[0011] Furthermore, the heating plate is slightly lower than the top surface of the trigger battery, and is covered with a 3 mm thick aerogel pad and a mica plate of the same size as the temperature measuring plate. This minimizes the direct heat conduction and radiation impact of the heating plate on the surrounding temperature measuring plates during the thermal runaway of the trigger battery.

[0012] The beneficial effects of adopting the above-mentioned improved scheme are as follows: The modular confined space testing device constructed by this invention fills the gap in existing testing methods. Traditional battery thermal runaway experiments are mostly conducted in open environments, failing to truly reflect the heating effect of high-temperature exhaust gas on adjacent batteries within the confined space of the battery pack. However, this invention, through the combination of an adjustable top plate and baffles, enables the experiment to reproduce the exhaust gas constraint conditions and flow characteristics inside the battery pack, and quantitatively measure the impact of exhaust gas on the surrounding heat transfer. Its testing capabilities allow for the capture and evaluation of some phenomena that were previously difficult to observe and measure (such as the implicit heating of adjacent batteries by high-temperature unburned gas), greatly deepening the understanding of the thermal runaway propagation mechanism within lithium battery modules.

[0013] This invention achieves a quantitative description of the thermal runaway exhaust heating process through a distributed temperature sensing plate array and its thermal resistance network modeling and analysis method. In contrast, traditional technologies often only rely on a few thermocouples or overall temperature rise to roughly determine the impact of exhaust on other batteries in the module. This solution can provide high-resolution spatial temperature and heat flow distribution data, clearly showing the intensity differences of exhaust heating at different locations. The empirical heat flow model established thereby can be used to predict the risk of thermal runaway propagation under different battery pack designs, guiding the optimization of battery module structure. For example, the test results of this invention show that shortening the gap between the battery and the top of the battery pack significantly enhances the heating effect of exhaust on surrounding batteries. Therefore, it is recommended to leave sufficient exhaust space or channels in the battery pack design. These safety design recommendations based on experimental data are the practical application value of this invention, demonstrating its role in promoting battery safety technology.

[0014] The device provided by this invention offers excellent flexibility and safety. Its modular and adjustable structure facilitates the combination of various experimental conditions, improving research efficiency. In a laboratory environment, the device can simulate complex thermal runaway gas dynamics and heat transfer behavior without requiring large, expensive testing equipment, resulting in lower costs and relatively simple operation. This means that the device and method are not only suitable for scientific research but can also provide battery manufacturers and safety regulatory authorities with a new tool for assessing battery thermal runaway risks, helping to identify and address safety hazards in a timely manner during product development.

[0015] A second aspect of the present invention provides a modular quantitative method for testing the thermal runaway exhaust heat flux of a lithium-ion battery, comprising the following specific steps:

[0016] S10: Based on the battery type, capacity, and battery pack structure to be tested, adjust the device structural parameters, arrange the distributed temperature measuring plate array range, and set the initial state of charge (SOC) of the trigger battery. For example, adjust the installation height of the top plate on the frame to set the distance between the top of the battery and the top plate (e.g., 15 mm, 25 mm, 50 mm, or 100 mm), and decide whether to install peripheral baffles and the range of the baffles (complete enclosure to form a restricted space or partial removal to form an open boundary). Simultaneously, select the location type of the trigger battery in the simulated battery pack, such as placing it in the center of the array (simulating the central cell of the module) or near the side / corner (simulating the edge cell), to examine the differences in the impact of exhaust on the surroundings under different locations. The initial SOC of the trigger battery is set as needed, such as 100%, 75%, or 50%, to study the effect of SOC on the thermal runaway exhaust heat release characteristics. After completing the above settings, install the trigger battery and heating trigger device in place, connect the thermocouple sensor and data acquisition system, and confirm that the temperature measuring plate array and instrument are working properly.

[0017] S20: The heating trigger device is activated, applying thermal abuse to the trigger battery according to the predetermined heating power. During heating, the battery surface temperature is monitored in real time. When the battery temperature approaches its thermal runaway trigger threshold (typically the temperature at which severe internal side reactions occur), the battery safety valve opens, releasing high-temperature, high-pressure flammable exhaust gas. Once thermal runaway is detected (the center temperature on the opposite side of the battery's contact surface with the heating plate exceeds 1°C / s, indicating the battery has entered the thermal runaway stage), the heating plate power is immediately cut off, stopping external heating of the battery. At this point, the trigger battery enters the autonomous thermal runaway stage, releasing a large amount of heat and gas through the internal reaction. The high-temperature multiphase flow is ejected at high speed into the surrounding space through the safety valve at the top of the battery. Due to the presence of the top plate and baffle of this device, the ejected gas is restricted vertically, mainly diffusing horizontally near the top of the trigger battery. In the case of complete enclosure, the exhaust gas can only escape through limited gaps at the edge of the device; in the case of partial enclosure, the airflow will also be guided to some extent and will not immediately dissipate to a distant location. Thus, the device successfully reproduced the process by which thermally runaway gas is ejected from an actual battery module, flows within a confined space, and interacts with the surface of adjacent batteries.

[0018] S30: Throughout the thermal runaway exhaust process, the temperature sensing plates distributed around the trigger battery are subjected to high-temperature multiphase flow impact heating. Thermocouples embedded inside these plates monitor the temperature rise, and the data acquisition system records the temperature change curve of each sensing plate over time at 1 Hz. This real-time temperature data provides a clear picture of the heating status of the "batteries" at different locations. For example, the sensing plates closer to the trigger battery may experience rapid and high temperature rise peaks, while the temperature rise is relatively moderate at locations farther from the trigger battery. These differences provide fundamental data for quantitatively assessing the exhaust heating effect.

[0019] S40: Through in-depth processing of temperature rise data, the temperature response of each temperature measuring plate is transformed into heat flow distribution information of the exhaust gas heating it, and a method for deconstructing the heat balance equation of the temperature measuring plate array and extracting and analyzing multiphase flow heat flow is established.

[0020] Based on the above technical solution, the modular quantitative testing method for thermal runaway exhaust heat flux of lithium-ion batteries of the present invention can be further improved as follows:

[0021] Furthermore, the specific steps of establishing the thermal balance equation deconstruction and multiphase flow heat flux extraction and analysis method for the temperature measuring plate array include:

[0022] The first step is to establish a heat balance equation for each temperature measuring plate based on the principle of energy conservation.

[0023] The second step involves constructing a two-dimensional thermal resistance network model for the temperature sensing plate array and the test battery / heating plate. Each temperature sensing plate is considered as a separate node, and contact thermal resistance exists between nodes and at the contact interfaces between nodes and the trigger battery / heating plate. The calibration test was conducted in an open environment (generally in an open space where there are no top plates or baffles to restrain the thermal runaway exhaust, which can be considered as a direct thermal shock to the temperature measuring plate). The relationship between the temperature difference and thermal conductivity between the temperature measuring plates (≈0) is used to calibrate the contact thermal resistance of each contact interface. Additionally, the total thermal resistance at the bottom of the temperature measuring plates is also considered. Alternatively, the temperature can be measured by directly heating the measuring plate with a heating plate and then measuring the steady-state temperature difference (the actual measured value is approximately 42.589 m). 2 By substituting the calibrated thermal resistance parameters into the thermal resistance network model under the constrained space test of the simulated battery pack, the heat flux exchanged between each temperature measuring plate and its neighboring nodes through heat conduction during the experiment can be quantitatively calculated. ;

[0024] Thirdly, in the confined space exhaust experiment, the temperature rise recorded by the temperature measuring plates includes both the direct heating contribution from the exhaust and a certain degree of conduction between the plates. Using the aforementioned thermal resistance network model, for any time t, the heat flux lost at the bottom of each temperature measuring plate node is first calculated, combined with the conduction heat flux obtained from adjacent nodes. The total heat absorption power corresponding to the temperature rise of the temperature measuring plate. minus By considering the bottom loss, the net heat flux power obtained by the temperature measuring plate from the multiphase flow of thermal runaway exhaust gas can be obtained. For each temperature measuring plate throughout the entire event... Analysis revealed the transient heating intensity distribution of the exhaust gas on different surrounding locations. Based on this heat flux distribution data, characteristic parameters of the exhaust gas heating effect can be further extracted. For example, the peak heat flux density experienced by each temperature measuring plate (…). The heat flux includes the occurrence time, cumulative heat absorbed per unit area, duration of high heat flux, and gradient of heat flux distribution in space.

[0025] The fourth step involves extracting characteristic parameters of the exhaust heating effect based on heat flow distribution data, constructing an exhaust heat flux correlation based on experimental data fitting, and calculating the heat flux per unit area of ​​thermal runaway exhaust at any given distance and time under the test battery and simulated battery pack structures.

[0026] Furthermore, in the process of establishing a heat balance equation for each temperature measuring plate based on the principle of energy conservation, the total heat absorbed by the temperature measuring plate is equal to the superposition of heat transfer from various sources, including: convective heat transfer from the high-speed jet of thermal runaway exhaust, heat transfer from electrolyte liquefaction, and heat transfer from ejected material deposition, denoted as... The heat conducted through the edge of the temperature measuring plate to adjacent structures (adjacent temperature measuring plates, trigger battery casing, etc.) is denoted as... ; and a small amount of heat loss through conduction from the bottom of the temperature measuring plate to the supporting structure, denoted as Because the bottom of the temperature measuring plate uses a high thermal resistance mica insulation base, The heat exchange is relatively small and slow, and can be approximated as constant or ignored in the early stages of transient analysis. Thus, the main dynamic heat exchange of the temperature measuring plate is in the two aspects of top heating and horizontal conduction.

[0027] Furthermore, the total heat flux corresponding to the temperature rise of the temperature measuring plate is obtained by multiplying the rate of temperature change by the heat capacity and mass of the temperature measuring plate.

[0028] Compared with existing technologies, the advantages of the modular quantitative testing method for thermal runaway exhaust heat flux of lithium-ion batteries provided by this invention are:

[0029] This invention employs a modular structure with adjustable top plate height and variable baffle position, enabling flexible changes to the geometry and opening degree of the test space. This allows for simulation of thermal runaway exhaust environments under different battery pack packaging conditions, overcoming the limitations of traditional fixed structures. The same device can adapt to various test scenarios, significantly improving the applicability and practicality of the experimental setup. The multi-point temperature measuring plate array utilizes high thermal conductivity aluminum plates and built-in thermocouples to synchronously monitor temperature changes at various locations. This comprehensively captures the thermal shock effects of thermal runaway exhaust on adjacent directions, greatly improving the spatial resolution of data acquisition and ensuring complete recording and accurate quantification of the exhaust heating effects on each area within the module. A thermal balance modeling calculation method based on thermal resistance networks combines the temperature rise data of the measuring plates with the contact thermal resistance parameters calculated from the control test group in an open environment, allowing for the calculation of the dynamic heat flow distribution experienced by each measuring plate under thermal runaway exhaust. This method can quantitatively extract the heating power and energy indicators of the exhaust multiphase flow on adjacent batteries, thereby forming an empirical model of the thermal runaway heating effect. Attached Figure Description

[0030] Figure 1 A schematic diagram of a modular device for quantitatively testing the thermal runaway exhaust heat flux of a lithium-ion battery.

[0031] Figure 2 This is a schematic diagram of the heating triggering device;

[0032] Figure 3 This is a schematic diagram of the temperature measuring plate.

[0033] Figure 4 A flowchart of a modular quantitative method for testing the thermal runaway exhaust heat flux of lithium-ion batteries;

[0034] Figure 5 The images show the arrangement of the temperature measuring plate and the test battery on the test platform under four different operating conditions.

[0035] Figure 6 The figures (a) show the temperature rise curves of the temperature measuring plate at some coordinate points in the CC scenario. (b) and (c) Heat map, temperature rise curves of the thermometer plate at some coordinate points in the SC scenario (d). (e) and (f) Heat map;

[0036] Figure 7 The figures (a) show the temperature rise curves of the temperature measuring plate at some coordinate points in the CS scenario. (b) and (c) Heat map, temperature rise curves of the thermometer plate at some coordinate points in the SS scenario (d). (e) and (f) Heat map;

[0037] Figure 8 Photographs (a)-(d) of the test platform and top plate after battery thermal runaway experiments were triggered at different locations, respectively. and Comparison at different levels of impact;

[0038] Figure 9 These are schematic diagrams of the thermal resistance network formed by the region near the trigger battery in the temperature measuring plane;

[0039] Figure 10 Different trigger locations (a)-(d), and The changing trend (e) and the fitted f(τ) curve (f);

[0040] The attached diagram lists the components represented by each number as follows:

[0041] 11. Heating-triggered battery thermal runaway device; 111. Thermocouple; 112. Heating plate; 113. Trigger battery; 114. Mica interlayer; 115. Temperature measuring plate; 1151. Aluminum plate; 1152. Mica plate; 1153. Support frame; 1154. Thermal insulation substrate; 1155. High-temperature resistant adhesive; 116. Fixture; 12. Top plate; 13. Aerogel insulation layer; 14. Peripheral baffle. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0043] like Figure 1-3 The figure shows a schematic diagram of a modular quantitative testing device for the thermal runaway exhaust heat flux of a lithium-ion battery provided by the present invention. In the figure, the frame of the device is constructed of high-strength aluminum alloy profiles. An adjustable top plate 12 and peripheral baffles 14 form a confined space simulating the inside of a battery pack. A heating-triggered battery thermal runaway device 11 is installed inside. Around the top of the test battery of the heating-triggered battery thermal runaway device 11, an array of temperature measuring plates 115 are fixedly distributed by slots, which can adapt to the arrangement requirements of different experimental conditions and realize the experimental reproduction and heat quantification of the thermal runaway exhaust on the adjacent area.

[0044] In the above technical solution, the top plate 12 is an adjustable height flat plate structure made of high-strength stainless steel with a thickness of 5 mm. It is used to simulate the upper boundary of the battery pack. Its height position can be adjusted according to experimental needs, thereby changing the size of the top gap of the confined space. The side of the top plate 12 away from the battery is covered with an aerogel insulation layer 13 with the same area and a thickness of 5 mm. The edge where the top plate contacts the surrounding baffle is filled with aerogel material to insulate heat and prevent heat from being conducted away through the top plate.

[0045] Furthermore, in the above technical solution, the peripheral baffle 14 is a stainless steel plate with a thickness of 5 mm surrounding the experimental battery. It is made of the same material as the top plate and can be flexibly installed or removed as needed to form a restrictive sidewall structure similar to the battery module housing. The baffle is used to constrain the flow path of the high-speed ejected gas when thermal runaway exhaust occurs, limiting it to mainly flow horizontally inside the device to avoid direct and rapid escape, thereby more realistically reproducing the exhaust environment inside the battery pack.

[0046] Furthermore, in the above technical solution, the temperature measuring plate 115 is composed of an aluminum plate 1151, a thermocouple 111, and a heat-insulating substrate 1154. The top surface dimension of each temperature measuring plate 115 is the same as that of the top of the battery. The aluminum plate 1151 is made of aluminum alloy with high thermal conductivity as the heating surface. A K-type thermocouple is attached to the bottom surface of the aluminum plate 1151, with one thermocouple at the front and one at the bottom of each aluminum plate 1151, and the sampling frequency is 1. The system achieves real-time recording of temperature changes at Hz. A mica plate 1152 is attached tightly to the bottom of the aluminum plate, supporting the aluminum plate 1151 and thermocouple 111 from below and reducing the efficiency of heat conduction to the bottom frame. The aluminum plate and the heat insulation base are bonded and fixed together by high-temperature resistant adhesive 1155. Each temperature measuring plate is quickly fixed to the support frame 1153 of the test device through the grooves on both sides of the heat insulation base. Its top height is flush with the top surface of the trigger battery, simulating the situation where the top surfaces of adjacent batteries in a real battery module are at the same level. When the trigger battery experiences thermal runaway and exhaust, each temperature measuring plate, like the upper surface of an adjacent battery, will be directly heated by the impact of the high-temperature exhaust. By distributing several temperature measuring plates around the test battery according to the actual arrangement of the battery module, a distributed temperature measuring plate array is formed, realizing multi-point capture of regional temperature response and providing basic data for subsequent heat flow distribution calculation.

[0047] Furthermore, in the above technical solution, a 500 W heating plate 112 is installed close to one side of the trigger battery as a heating trigger device. The battery and the heating plate are tightly attached by a clamp 116, and a pre-tightening force of 1 kN is applied to the clamp bolts to ensure that the battery and the heating plate are in full contact for heat transfer during the heating process. The other sides of the trigger battery are covered with an aerogel insulation layer of about 3 mm thick to reduce the heat conduction effect from the battery casing to the surrounding temperature measuring plate during the heating process and to isolate unexpected heat conduction paths.

[0048] Furthermore, in the above technical solution, the heating plate is slightly lower than the top surface of the trigger battery, and is covered with a 3 mm thick aerogel pad and a mica interlayer 114 of the same size as the temperature measuring plate, so as to minimize the direct heat conduction and radiation impact of the heating plate on the surrounding temperature measuring plates during the thermal runaway of the trigger battery 113.

[0049] like Figure 4 The diagram shows a flowchart of a modular quantitative method for testing the thermal runaway exhaust heat flux of a lithium-ion battery, provided by this invention. The method includes the following specific steps:

[0050] S10: Based on the operating conditions to be studied, set the device structural parameters and battery status, and set the initial state of charge (SOC) of the trigger battery as needed. For example, adjust the installation height of the top plate on the frame to set the distance between the top of the battery and the top plate (e.g., 15 mm, 25 mm, 50 mm, or 100 mm), and determine whether to install peripheral baffles and the range of the baffles (complete enclosure to form a restricted space or partial removal to form an open boundary). Simultaneously, select the location type of the trigger battery in the simulated battery pack, such as placing it in the center of the array (simulating the central cell of the module) or near the side / corner (simulating the edge cell), to examine the differences in the impact of exhaust on the surroundings under different locations. The initial SOC of the trigger battery is set as needed, such as 100%, 75%, or 50%, to study the effect of SOC on the heat release characteristics of thermal runaway exhaust. After completing the above settings, install the trigger battery and heating trigger device in place, connect the thermocouple sensor and data acquisition system, and confirm that the temperature measuring plate array and instrument are working properly.

[0051] S20: The heating trigger device is activated, applying thermal abuse to the trigger battery according to the predetermined heating power. During heating, the battery surface temperature is monitored in real time. When the battery temperature approaches its thermal runaway trigger threshold (typically the temperature at which severe internal side reactions occur), the battery safety valve opens, releasing high-temperature, high-pressure flammable exhaust gas. Once thermal runaway is detected (the center temperature on the opposite side of the battery's contact surface with the heating plate exceeds 1°C / s, indicating the battery has entered the thermal runaway stage), the heating plate power is immediately cut off, stopping external heating of the battery. At this point, the trigger battery enters the autonomous thermal runaway stage, releasing a large amount of heat and gas through the internal reaction. The high-temperature multiphase flow is ejected at high speed into the surrounding space through the safety valve at the top of the battery. Due to the presence of the top plate and baffle of this device, the ejected gas is restricted vertically, mainly diffusing horizontally near the top of the trigger battery. In the case of complete enclosure, the exhaust gas can only escape through limited gaps at the edge of the device; in the case of partial enclosure, the airflow will also be guided to some extent and will not immediately dissipate to a distant location. Thus, the device successfully reproduced the process by which thermally runaway gas is ejected from an actual battery module, flows within a confined space, and interacts with the surface of adjacent batteries.

[0052] S30: Throughout the thermal runaway exhaust process, the temperature sensing plates distributed around the trigger battery are subjected to high-temperature multiphase flow impact heating. Thermocouples embedded inside these plates monitor the temperature rise, and the data acquisition system records the temperature change curve of each sensing plate over time at 1 Hz. This real-time temperature data provides a clear picture of the heating status of the "batteries" at different locations. For example, the sensing plates closer to the trigger battery may experience rapid and high temperature rise peaks, while the temperature rise is relatively moderate at locations farther from the trigger battery. These differences provide fundamental data for quantitatively assessing the exhaust heating effect.

[0053] S40: Through in-depth processing of temperature rise data, the temperature response of each temperature measuring plate is transformed into heat flow distribution information of the exhaust gas heating it, and a thermal balance modeling and multiphase flow heat flow extraction and analysis method for the temperature measuring plate array is established.

[0054] Furthermore, in the above technical solution, the specific steps for establishing the thermal balance modeling and multiphase flow heat flux extraction and analysis method for the temperature measuring plate array include:

[0055] The first step is to establish a heat balance equation for each temperature measuring plate based on the principle of energy conservation.

[0056] The second step is to simplify the temperature sensor array and adjacent batteries / heating plates into a node-thermal resistance network model. Each temperature sensor is considered a node, and the contact interfaces between nodes and between nodes and trigger batteries / heating plates have a certain contact thermal resistance. Through independent calibration tests (generally conducted in open space conditions, where there are no top plates or baffles to restrain the thermal runaway exhaust, which can be considered as a direct thermal shock to the temperature measuring plate), ≈0) and using the relationship between the temperature difference between the temperature measuring plates and the thermal conductivity, the contact thermal resistance of each contact interface is calibrated. In addition, the total thermal resistance at the bottom of the temperature measuring plate is also calibrated. Alternatively, the temperature can be measured by directly heating the temperature measuring plate with a heating plate and measuring the steady-state temperature difference (measured at approximately 42.589 m²K / W). By substituting the calibrated thermal resistance parameters into the thermal resistance network model, the heat power exchanged between each temperature measuring plate and neighboring nodes through heat conduction during the experiment can be quantitatively calculated. ;

[0057] Thirdly, in the confined space exhaust experiment, the temperature rise recorded by the temperature measuring plates includes both the direct heating contribution from the exhaust and a certain degree of conduction between the plates. Using the aforementioned thermal resistance network model, for any time t, the heat power gained or lost by each temperature measuring plate from its neighbor through conduction is first calculated. The total heat absorption power corresponding to the temperature rise of the temperature measuring plate. minus By considering the bottom loss, the net heat flux power obtained by the temperature measuring plate from the multiphase flow of thermal runaway exhaust gas can be obtained. For each temperature measuring plate throughout the entire event... Analysis revealed the transient heating intensity distribution of the exhaust gas on different surrounding locations. Based on this heat flux distribution data, characteristic parameters of the exhaust gas heating effect can be further extracted. For example, the peak heat flux density experienced by each temperature measuring plate (…). The heat flux includes the occurrence time, cumulative heat absorbed per unit area, duration of high heat flux, and gradient of heat flux distribution in space.

[0058] The fourth step involves extracting characteristic parameters of the exhaust heating effect based on heat flow distribution data. By comparing parameters under different experimental conditions, the influence of factors such as top plate height, trigger battery position, and SOC on the exhaust secondary heating effect is quantitatively evaluated.

[0059] Furthermore, in the process of establishing a heat balance equation for each temperature measuring plate based on the principle of energy conservation, the total heat absorbed by the temperature measuring plate is equal to the superposition of heat transfer from various sources, including: convective heat transfer from the high-speed jet of thermal runaway exhaust, heat transfer from electrolyte liquefaction, and heat transfer from ejected material deposition, denoted as... The heat conducted through the edge of the temperature measuring plate to adjacent structures (adjacent temperature measuring plates, trigger battery casing, etc.) is denoted as... ; and a small amount of heat loss through conduction from the bottom of the temperature measuring plate to the supporting structure, denoted as Because the bottom of the temperature measuring plate uses a high thermal resistance mica insulation base, The heat exchange is relatively small and slow, and can be approximated as constant or ignored in the early stages of transient analysis. Thus, the main dynamic heat exchange of the temperature measuring plate is in the two aspects of top heating and horizontal conduction.

[0060] Furthermore, in the above technical solution, the total heat flux corresponding to the temperature rise of the temperature measuring plate is obtained by multiplying the temperature change rate by the heat capacity and mass of the temperature measuring plate.

[0061] Example:

[0062] The location of the thermal runaway trigger battery within the battery pack affects the thermal runaway propagation mode; therefore, investigating the impact of changes in trigger battery location on the heating effect is of great significance. Experiments were conducted at four typical locations: center-centre (CC), center-side (CS), side-centre (SC), and side-side (SS). The arrangement of the battery and temperature sensor was as follows: Figure 5 As shown, areas without temperature measuring plates were replaced with mica panels of the same size. Peripheral baffles were placed around the entire test platform to simulate the packaging structure of an actual battery pack, creating a confined space between the top plate and the test platform. When the test battery activates the safety valve to release gas, the gas will spread within this confined space and slowly exit through the gaps at the edges, thus prolonging the residence time of the multiphase flow in the test platform. To improve the reliability of the results, each operating condition was repeated at least three times. The experiment was conducted at an ambient temperature of 16℃ (±1℃). The heating plate was turned on after the experiment began, and turned off when the temperature rise rate on the back of the battery exceeded 1℃ / s to ensure the battery underwent a complete thermal runaway process.

[0063] like Figure 6-7 As shown, the rapidly rising intervals in the temperature rise curves of the temperature measuring plate under the four scenarios correspond to the thermal runaway stage of the test battery. At this point, the test battery rapidly generates heat and gas due to a violent thermal runaway chain reaction. To more comprehensively characterize the temperature rise of the temperature measuring plate under different scenarios, peak temperature differences (TDI) were further plotted. A heatmap of thermal exposure integral (TEI) values. and The calculation method is as follows:

[0064] ;

[0065] ;

[0066] in, This is the highest temperature monitored by the temperature measuring plate during the experiment. This is the time it takes to test the battery's activation of the safety valve. It is the temperature measuring plate. The temperature at that time.

[0067] Drawing Similar to the TEI thermogram, a significant exhaust heating effect was observed. Most electrolyte droplets and solid particles remained on the test platform, while electrolyte vapor fully exchanged heat with the temperature measuring plate surface and ultimately liquefied and deposited on the plate. For example... Figure 8 As shown in (a)-(d), obvious electrolyte residues were found on the test platform and top plate in all four scenarios, and electrolyte deposits were even found in the edge areas.

[0068] Taking into account the distance between the temperature measuring plate and the trigger battery, ΔT and Factors such as these can lead to the influence of the trigger battery on each temperature sensor plate, which can be broadly categorized into four levels from extremely high to low, corresponding to areas such as... Figure 6-7 In As shown in the heat map. Figure 8 (e) and (f) provide four scenarios. and The curves show how the impact level varies. Each data point is accompanied by an error bar, representing the dispersion of the results in repeated experiments for the corresponding impact level. First, we can see that, under all impact levels, the CC scenario... and All are minimum values. Additionally, the error bar for the CC scenario is relatively longer. The speculated reason is that when triggered at the center, the exhaust diffuses outwards, and differences in jet angles between different tests significantly affect the exhaust flow direction, leading to large fluctuations in the heating of the temperature measuring plate; while when the trigger battery is at the edge, the exhaust is constrained by the surrounding baffles, and the jet angle has a relatively smaller impact on the flow path. The SS scenario has the highest ΔTpeak and TEI among influence levels ① to ③. However, if... Figure 8 As shown in (f), the heat received by the temperature sensing plates decreases significantly with increasing distance from the trigger battery. This indicates that the SS scenario exhibits a more pronounced local hotspot effect compared to other scenarios, meaning that most of the heat accumulates near the trigger battery. The different locations of the trigger battery illustrate that when the trigger battery is in the center, the exhaust diffuses outwards, causing multiple peripheral temperature sensing plates to heat up, resulting in a wider impact range. However, when the trigger battery is at the edge, the constraint of the side baffles causes heat to concentrate in a localized area. The temperature sensing plates near the trigger battery generally absorb more heat than in the CC scenario, while the heat received by temperature sensing plates further away may decay faster compared to the CC scenario. These phenomena indicate that the location of the thermal runaway trigger battery has a significant impact on the diffusion path and impact range of the exhaust within the module.

[0069] Based on the temperature rise data of the temperature measuring plates at four trigger positions obtained from the experiments, the heat flow analysis of the exhaust heating effect is further conducted below. First, the test platform is simplified into a thermal resistance network, with each temperature measuring plate considered as a node, such as... Figure 9As shown, for any temperature measuring plate, its heat balance equation can be written according to the law of conservation of energy.

[0070] ;

[0071] In the formula, This indicates the total heat corresponding to the temperature rise of the temperature measuring plate. This indicates the heat transfer between the temperature measuring plate and other supporting components (including adjacent temperature measuring plates, battery cells, etc.) in the horizontal direction. The heat exchange between the aluminum plate on top of the temperature measuring plate and the environment typically includes convection and radiation. However, during the thermal runaway exhaust phase, due to the high-speed airflow and electrolyte / particle deposition, this heat transfer mechanism far exceeds the norm. Therefore, it is not considered separately during the thermal runaway phase, but its impact is attributed to... . Heat is conducted through the bottom of the temperature measuring plate (aluminum plate, high-temperature resistant adhesive, and mica plate connected in series). Based on material parameters, the thermal resistance of the aluminum plate (2 mm thick, thermal conductivity λ≈150 Wm⁻¹K⁻¹) is negligible; the thermal resistance of the high-temperature resistant adhesive layer (0.5 mm thick, λ≈0.25 Wm⁻¹K⁻¹) is approximately 2 m²K / W; and the thermal resistance of the mica plate (10 mm thick, λ≈0.23 Wm⁻¹K⁻¹) is approximately 25 m²K / W. In total... ≈27 m² K / W. A verification experiment was conducted by directly heating the surface of the aluminum thermometer plate with a heating plate and measuring the temperature of the bottom of the plate. The experimental results were calculated to be approximately 27 m² K / W. The measured value was 42.589 m² K / W, significantly higher than the theoretical estimate. This is presumably because the theoretical estimate neglected the interfacial contact thermal resistance. Therefore, subsequent calculations used actual measurements. value. This includes the additional heat input generated by multiphase flow coupling effects such as high-temperature exhaust jetting, solid particle deposition, and baffle radiation. The governing equations for each are listed in Table 1.

[0072] Table 1. Governing equations for each variable in the heat balance equation:

[0073]

[0074] It is important to note that, In the governing equations, This is the instantaneous temperature of the current temperature measuring plate (node). This represents the instantaneous temperature of the temperature measuring plate or solid (battery, heating plate, etc.) adjacent to this node and in contact along direction k, and the thermal resistance. Let k be the contact thermal resistance of the contact interface along direction k. Further determination is needed. This part can be calibrated by combining tests in an open environment to determine the contact thermal resistance of the temperature measuring plates at each location. In an open environment, the multiphase coupling effect is very weak and can be approximated as... ≈0. Therefore, the total heat flux of the temperature measuring plate can be expressed as:

[0075] ;

[0076] right After linear regression fitting with ΔTk, the thermal resistance values ​​of five types of contact interfaces were obtained, as shown in Table 2.

[0077] Table 2. Calculation results of thermal resistance at each contact interface of the temperature measuring plate:

[0078]

[0079] After determining the five types of contact thermal resistances mentioned above, they were incorporated into the experimental data processing within the confined space. Based on... The governing equations can be used to calculate the values ​​at each temperature sensor node. Further obtained The heat flux curve is calculated by introducing the distance *r* from each temperature sensor to the trigger battery safety valve. In data processing, the instantaneous multiphase flow heat flux power of temperature sensors with similar or equal distances (≤5 mm) is used. The curves are averaged. Although this ignores the stronger heating effect in some local areas caused by changes in the jet angle, this process helps to obtain a comprehensive heat flux profile. In this way, instantaneous multiphase flow heat flux profiles at different distances under different triggering scenarios are obtained.

[0080] ;

[0081] Figure 10 (a)-(d) show four trigger positions for r=40 mm (i.e., the temperature measuring plate at position (1,0)). The curve shows that the temperature sensor received the most heat during the stage that triggered battery thermal runaway. The peak value mainly appears in the early stages of thermal runaway, and then gradually decreases as thermal runaway progresses. After the thermal runaway phase ends, although... There are still some tail sections with values ​​above 0, but this is mainly due to the continued release of a small amount of gas after the thermal runaway ends, as well as the radiative heating of the temperature measuring plate by the heated top plate. Since the duration of thermal runaway varies in different experiments, a dimensionless time τ is introduced for comparison. Within τ∈[0,1], it indicates that the battery thermal runaway is currently triggered; once τ is greater than 1, it indicates that the battery thermal runaway has ended. Then, for repeated test groups under different scenarios, within τ∈[0,5]... Integral, to obtain ,like Figure 10 As shown in (e), The effect decreases with increasing distance. The closer to the trigger battery, the more significant the exhaust heating effect on the temperature sensor plate under the SS scenario. However, compared to the CC scenario, the SS scenario... The decay rate increases faster with distance; beyond 150 mm, the SS scenario... It is lower than the other three scenarios.

[0082] To further fit a general comprehensive heat flux function, the multiphase flow heat flux curves for each scenario are decomposed into two parts: scenario-distance separation coefficient and time evolution function.

[0083] ;

[0084] ;

[0085] ;

[0086] In the formula, To average for different scenarios The amplitude is obtained by exponential fitting of the curve, where α is the corresponding spatial attenuation coefficient. A larger α indicates that the energy decays faster with distance, while a smaller α indicates that the multiphase flow has a wider range of influence. The fitting results are shown in Table 3.

[0087] Table 3. Spatial coefficient fitting results:

[0088]

[0089] Based on the fitting results of the scene-distance separation coefficient, the following steps can be taken to obtain the integrated heat flow model: First, in a single experiment, the spatial attenuation coefficient is used to separate the scene-distance at each distance. Equivalent at the minimum distance and for different distances The arithmetic mean was used to obtain the average heat flux curve of the experiment. Then, for multiple repeated trials of the same scenario, the results of each trial will be... Time normalization (dimensionless) is performed, and the average is taken to obtain the average dimensionless heat flux curve for this scenario. Finally, for different scenarios Amplitude normalization is performed to achieve cross-scenario fitting of fi(τ).

[0090] ;

[0091] ;

[0092] ;

[0093] ;

[0094] ;

[0095] The polynomial coefficients ak and bk obtained through fitting calculations are listed in Table 4, and the fitting curve is shown in Figure 4. Figure 10 As shown in (f), this yields the comprehensive heat flux function. This function can estimate the thermal runaway multiphase flow heat flux per unit area at a given battery type, scene type, target distance, and time.

[0096] ;

[0097] Table 4. Fitting results of polynomial coefficients for the time evolution function:

[0098]

[0099] In summary, this invention provides an experimental method that enables the quantitative expression of the heating effect of non-combustible exhaust gases in lithium battery modules. It is applicable to testing batteries of various types, SOCs, and structures, providing a quantifiable and verifiable experimental support platform for battery module thermal design, thermal runaway mitigation path design, and thermal protection material selection.

[0100] Specifically, the principle of this invention is as follows: Based on the working condition to be studied, the device structural parameters and battery state are set, and the initial state of charge of the trigger battery is set as needed; the heating trigger device is activated, and thermal abuse is applied to the trigger battery according to a predetermined heating power; throughout the entire process of thermal runaway exhaust, each temperature measuring plate distributed around the trigger battery will be subjected to impact heating by high-temperature multiphase flow, and the thermocouples embedded inside will monitor the temperature rise; the data acquisition system records the temperature change curve of each temperature measuring plate over time at 1 Hz; through in-depth processing of the temperature rise data, the temperature response of each temperature measuring plate is converted into heat flow distribution information of the exhaust heating it, and a thermal balance modeling and multiphase flow heat flow extraction and analysis method for the temperature measuring plate array is established.

[0101] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A modular quantitative method for testing the thermal runaway exhaust heat flux of a lithium-ion battery, characterized in that, The frame of the modular quantitative test device for thermal runaway exhaust heat flux of lithium-ion batteries is constructed with high-strength aluminum alloy profiles. The space constraint formed by the adjustable height top plate and surrounding baffles simulates the restricted space inside the battery pack. A heating trigger device is set inside. In the heating trigger device, a distributed temperature measuring plate array is fixed around the top of the test battery through slots. It can adapt to the arrangement requirements of different experimental conditions and realize the experimental reproduction and heat quantification of the thermal runaway exhaust heating process of the adjacent area. The temperature measuring plate consists of an aluminum plate, thermocouples, and a heat-insulating substrate. The top surface dimension of each temperature measuring plate is the same as that of the top of the battery. The aluminum plate is made of high thermal conductivity aluminum alloy as the heating surface. A K-type thermocouple is attached to the bottom surface of the aluminum plate, one at the front and one at the back of the bottom of each aluminum plate, with a sampling frequency of 1. The system achieves real-time recording of temperature changes at Hz. A mica-based heat-insulating base is tightly attached beneath the aluminum plate, supporting the aluminum plate and thermocouples from below and reducing heat transfer to the bottom frame. The aluminum plate and heat-insulating base are bonded together using high-temperature adhesive. Each temperature sensor plate is quickly fixed to the test device frame via grooves on both sides of the heat-insulating base. Its top height is flush with the top surface of the trigger battery, simulating the situation where adjacent batteries in a real battery module have their top surfaces at the same level. When the trigger battery experiences thermal runaway and exhaust, each temperature sensor plate, like the upper surface of an adjacent battery, will be directly heated by the high-temperature exhaust. By distributing several temperature sensor plates around the test battery according to the actual arrangement of the battery module, a distributed temperature sensor array is formed, enabling multi-point capture of regional temperature responses and providing basic data for subsequent heat flow distribution calculations. The method includes the following specific steps: S10: Adjust the device structure parameters, arrange the range of the distributed temperature measuring plate array, and set the initial state of charge of the trigger battery according to the battery type, capacity and battery pack structure to be tested. S20: Activate the heating trigger device to apply thermal abuse to the trigger battery according to the predetermined heating power; S30: During the entire process of thermal runaway exhaust, the temperature measuring plates distributed around the trigger battery will be heated by the impact of high temperature multiphase flow. The thermocouples embedded inside will monitor the temperature rise. The data acquisition system records the temperature change curve of each temperature measuring plate over time at 1 Hz. S40: Through in-depth processing of temperature rise data, the temperature response of each temperature measuring plate is transformed into heat flow distribution information of the exhaust gas heating it, and a method for deconstructing the heat balance equation of the temperature measuring plate array and extracting and analyzing multiphase flow heat flow is established. The specific steps of the method for establishing the thermal balance equation deconstruction and multiphase flow heat flux extraction and analysis of the temperature measuring plate array include: The first step is to establish a heat balance equation for each temperature measuring plate based on the principle of energy conservation. The second step involves constructing a two-dimensional thermal resistance network model for the temperature measuring plate array and the test battery / heating plate. Each temperature measuring plate is considered as a separate node. There is contact thermal resistance between nodes and between nodes and the trigger battery / heating plate. By calibrating the temperature difference and thermal conductivity relationship between temperature measuring plates in an open environment, the contact thermal resistance of each contact interface is calibrated. The calibrated thermal resistance parameters are then substituted into the thermal resistance network model under the constrained space test of the simulated battery pack, so that the heat flux exchanged between each temperature measuring plate and the adjacent nodes through heat conduction during the experiment can be quantitatively calculated. The third step is to calculate the heat flux lost at the bottom of each temperature plate node, and combine it with the conduction heat flux obtained from the adjacent nodes. The sum of the two is processed to obtain the total heat received corresponding to the temperature rise measured by the temperature plate, so as to obtain the heat flux obtained by the temperature plate from the multiphase flow of the thermal runaway exhaust. By analyzing the exhaust heat flux of each temperature plate during the entire event, the transient heating intensity distribution of the exhaust to different locations around it can be obtained. The fourth step is to further extract the characteristic parameters of the exhaust heating effect based on the heat flow distribution data, construct the exhaust heat flux correlation based on the experimental data fitting, and realize the heat flux per unit area of ​​the thermal runaway exhaust at any given distance and time under the test battery and simulated battery pack structure. Based on the principle of energy conservation, in the process of establishing a heat balance equation for each temperature measuring plate, the total heat absorbed by the temperature measuring plate is equal to the superposition of heat transfer from various aspects, including: convective heat transfer from the high-speed jet of thermal runaway exhaust, heat transfer from electrolyte liquefaction, and heat transfer from ejected material deposition; conductive heat through the edge of the temperature measuring plate and adjacent structures; and a small amount of heat loss through conduction to the supporting structure through the bottom of the temperature measuring plate. Since the bottom of the temperature measuring plate uses a high thermal resistance mica insulation base, the heat loss is relatively small and slow, and can be approximately regarded as constant or ignored in the early stage of transient analysis. The total heat flux corresponding to the temperature rise of the temperature measuring plate is obtained by multiplying the rate of temperature change by the heat capacity and mass of the temperature measuring plate.

2. The method for modularly and quantitatively testing the thermal runaway exhaust heat flux of a lithium-ion battery according to claim 1, characterized in that, The top plate is an adjustable-height flat plate structure made of high-strength stainless steel with a thickness of 5 mm. It is used to simulate the upper boundary of the battery pack. Its height position can be adjusted according to experimental needs to change the size of the top gap of the confined space. The side of the top plate away from the battery is covered with an aerogel insulation layer of the same area and a thickness of 5 mm. The edge of the top plate that contacts the surrounding baffle is filled with aerogel material to insulate heat and prevent heat from being conducted away through the top plate. The peripheral baffle is a stainless steel plate with a thickness of 5 mm surrounding the experimental battery. It is made of the same material as the top plate and can be flexibly installed or removed as needed to form a restrictive sidewall structure similar to the battery module housing. The baffle is used to constrain the flow path of the high-speed ejected gas when thermal runaway occurs, limiting it to mainly flow horizontally inside the device to avoid direct and rapid escape, thereby more realistically reproducing the exhaust environment inside the battery pack.

3. The method for modularly and quantitatively testing the thermal runaway exhaust heat flux of a lithium-ion battery according to claim 2, characterized in that, A 500 W heating plate is mounted on one side of the trigger battery as a heating trigger device. The battery and the heating plate are tightly attached by a clamp, and a 1 kN preload is applied to the clamp bolts to ensure that the battery and the heating plate are in full contact and heat transfer during the heating process. The other sides of the trigger battery are covered with a 3 mm thick aerogel insulation layer to reduce the heat conduction from the battery casing to the surrounding temperature measuring plate during the heating process and to isolate unexpected heat conduction paths. The heating plate is slightly lower than the top surface of the trigger battery, and is covered with a 3 mm thick aerogel pad and a mica plate of the same size as the temperature measuring plate. This minimizes the direct heat conduction and radiation impact of the heating plate on the surrounding temperature measuring plates during the thermal runaway of the trigger battery.

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