Lithium battery thermal runaway radiant heat flux testing method based on patch thermocouple temperature measurement

Abstract

The invention discloses a lithium battery thermal runaway radiant heat flux testing method based on temperature measurement of a patch thermocouple, and relates to the technical field of lithium battery testing methods. Mounting a patch thermocouple on the surface of the lithium battery; the patch thermocouple is calibrated; the arranged patch thermocouples are preliminarily calibrated to ensure that the patch thermocouples can accurately measure the temperature, and measurement errors caused by environmental changes and battery surface material differences are reduced; collecting temperature data in real time; in the thermal runaway process of the lithium battery, continuously collecting temperature data of the patch thermocouple; the radiant heat flux is calculated through the Stefan-Boltzmann law; according to the collected temperature data, the thermocouple is directly fixed on the surface of the lithium battery, so that the response time is effectively shortened, and the real-time collection of the temperature change data is ensured; noise interference is eliminated through a low-pass filtering algorithm, and the purity and credibility of measured data are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery testing methods, and in particular to a lithium battery thermal runaway radiation heat flux testing method based on temperature measurement using a patch thermocouple. Background Art

[0002] Lithium-ion batteries have shown a wide range of application prospects and important roles. From providing power for new energy vehicles, to supporting energy storage systems for renewable energy, to meeting the needs of consumer electronics, the technological innovation and application expansion of lithium batteries are comprehensively promoting all walks of life to move towards a greener, more efficient and sustainable development.

[0003] As the number of lithium batteries used surges, their safety protection issues are becoming increasingly prominent. Since battery packs are usually densely arranged, once a battery cell experiences thermal runaway due to improper operation or failure, it may trigger a chain reaction, leading to combustion or even explosion, posing a huge threat to personal safety and property.

[0004] In the study of thermal runaway of lithium batteries, thermocouples are a key measurement tool, which is mainly used to accurately measure the temperature changes on the surface or inside the battery. Since thermocouples can directly contact the surface of the battery, they can provide real-time temperature data, which is essential for understanding the thermal behavior of the battery under normal working conditions and abnormal conditions. However, thermocouples are limited to measuring temperature and cannot provide information about heat flow. In current research, heat flow meters are usually used to obtain data such as heat flux, through the heat energy of a certain cross section, so as to evaluate the heat release of the battery in the case of thermal runaway. However, the heat flow meter usually needs to be placed at a certain distance between the surface of the lithium battery and the measuring instrument, which may cause a delay in the response time of the measurement and affect the real-time nature of the data. At the same time, the cost of the heat flow meter is relatively high, which increases the economic burden of the experiment, especially when large-scale or multiple tests are required. In addition, the installation and maintenance of the heat flow meter are also more complicated than thermocouples, and the technical requirements of the operator are higher.

[0005] Different from traditional thermocouples, the present invention uses a thin-film calorimeter made of patch thermocouples, which can be closely attached to the surface of the lithium battery and can quickly respond to temperature fluctuations on the battery surface caused by thermal runaway. In addition, the design of the patch thermocouple allows it to not only measure conductive heat, but also capture the radiant heat emitted from the battery surface, and further calculate the radiant heat flux on the lithium battery surface in combination with temperature changes. Therefore, a lithium battery thermal runaway radiant heat flux test method based on patch thermocouple temperature measurement is proposed to solve the above problems.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute the prior art that is already known to one of ordinary skill in the art. Summary of the invention

[0007] The purpose of the present invention is to provide a thermal runaway radiation heat flux test method for lithium batteries based on patch thermocouple temperature measurement, by arranging patch thermocouples on the surface of lithium batteries to monitor the temperature in real time, and using a specific algorithm to calculate the radiation heat flux on the surface of lithium batteries. The present invention integrates temperature monitoring and heat flux calculation functions, simplifies the traditional test process, reduces the complexity of equipment layout, and significantly improves the real-time and accuracy of lithium battery thermal runaway testing. The present invention effectively shortens the response time by directly fixing the thermocouple on the surface of the lithium battery, ensuring the real-time collection of temperature change data. Combined with the use of a thin-film calorimeter, the heat flux data of each surface of the battery can be fully collected, avoiding the problem of insufficient coverage of traditional test equipment. The present invention utilizes the Stefan-Boltzmann law and dynamically adjusts the emissivity to ensure the accuracy of heat flux calculation. The present invention also eliminates noise interference through a low-pass filtering algorithm to ensure the purity and credibility of the measured data. At the same time, the present invention is superior to traditional heat flow meter systems in terms of equipment cost and maintenance cost, and has good economy.

[0008] In order to achieve the above object, the present invention provides the following technical solution: a lithium battery thermal runaway radiation heat flux test method based on patch thermocouple temperature measurement, comprising the following steps:

[0009] Arrange the patch thermocouple on the surface of the lithium battery: install the patch thermocouple on the surface of the lithium battery;

[0010] Calibrate the patch thermocouples; perform preliminary calibration on the arranged patch thermocouples to ensure that they can accurately measure the temperature and reduce the measurement errors caused by environmental changes and differences in battery surface materials;

[0011] Real-time temperature data collection: During the thermal runaway of lithium batteries, the temperature data of the patch thermocouple is continuously collected, and the collection frequency is set to at least 2 times per second to ensure real-time and continuous acquisition of temperature change data;

[0012] Calculate the radiation heat flux using the Stefan-Boltzmann law: Based on the collected temperature data, the radiation heat flux on the surface of the lithium battery is calculated using the Stefan-Boltzmann law to ensure the accuracy of the calculation results;

[0013] Error correction of measurement data: Error correction of temperature data is performed, and the measurement data is corrected in combination with factors such as ambient temperature, humidity and material emissivity to improve the accuracy and reliability of calculations;

[0014] Output radiation heat flux results: After completing data collection and error correction, the calculated radiation heat flux generated during the thermal runaway process of the lithium battery is output as a basis for evaluating the degree of thermal runaway.

[0015] Preferably, when arranging a patch thermocouple on the surface of a lithium battery, a K-type thermocouple with a thickness of 0.25 mm is preferably used. The thermocouple is made of nickel-chromium alloy material, has high-strength thermal fatigue resistance, and can withstand a melting temperature of up to 1290°C. In order to ensure a close connection between the thermocouple and the calorimeter, the HOTSPOTTC technology is used to weld the thermocouple wire to the back of the calorimeter so that it can effectively sense temperature changes. According to the ASTME459 standard, the wire spacing is set to 1.6 mm during welding, and the effective sensing area of ​​the calorimeter is 1 cm 2 Since the thin sheet structure of the patch thermocouple needs to be consistent with the thermal design of the integrated capacitor, the dependence on the surface thickness of the thermocouple is reduced in the design, so that the thickness of the thermocouple is controlled at 0.508mm, and according to the provisions of the ASTME459 standard, an optimized thickness calculation formula is used to ensure its stability and effectiveness during the test process:

[0016]

[0017] Where k is the thermal conductivity of the sheet thermocouple material in W / mK, Tmax is the maximum temperature of the sheet calorimeter in K, T0 is the initial temperature, and q is the heat flux in W / m2; the average thermal conductivity value is obtained by averaging the k values ​​at the maximum and initial temperatures; a maximum temperature of 760°C was chosen as a typical average maximum value for large pile tests, and an initial temperature of room temperature, 21°C, was used; the k values ​​at these temperatures were 20.8 W / m°C and 9.8 W / m°C, respectively; the test results using a water-cooled heat flux meter found a maximum heat flux of approximately 60 kW / m2; substituting these values ​​into the above formula yields a δopt value of 0.113 m; the δopt value is based on an optimization of the maximum exposure time; since the sensor continuously measures the same heat flux as the water-cooled manometer throughout the experiment, it is assumed that the exposure time is sufficient for this application;

[0018] Since it is difficult to find the optimal thickness parameter in small-scale experiments, three different thicknesses of metal sheets were compared and analyzed, namely 1.2mm, 0.8mm and 0.5mm. The effects of different thicknesses of metal sheets on the accuracy and response time of heat flux measurement were observed experimentally. These thicknesses were selected for experiments in precision calorimeters, and the heat flux values ​​recorded by the calorimeters in all experiments were basically the same. In contrast, thinner calorimeters have faster response times and can provide more sensitive heat flux readings; although the 0.5mm thick calorimeter has the fastest response time, its thickness is close to the diameter of the thermocouple wire, which is prone to additional potential errors in the welding process. During the manufacturing process, thin sheet calorimeters are exposed to high temperatures of about 1000℃, and the metal surface may produce slight oxidation or gloss changes due to heat exposure. During flame baking exposure, the exposure time of thin sheets is short, and the gloss of the metal surface may disappear completely as the combustion process progresses. Since the emissivity of the metal sheet will change after the luster is lost, the emissivity change needs to be monitored regularly throughout the experimental period to ensure the accuracy and consistency of the test data. Because the metal will naturally lose its luster when the thin sheet calorimeter is located below the burn pile; Since the emissivity of the metal is expected to change when it loses its luster, the metal is exposed before testing to keep the emissivity the same constant between early and late tests;

[0019] At this time, the patch thermocouple should be installed on the positive electrode surface of the lithium battery, which is the area where the temperature rises fastest when the battery is in thermal runaway. By using a high-temperature heat-resistant adhesive, the thermocouple is tightly fixed to the battery surface to ensure that the thermocouple remains in place throughout the test and avoid the influence of external mechanical disturbances and electrical interference on the measurement.

[0020] Preferably, the specific steps of calibrating the patch thermocouple are as follows: ASTM E459 standard describes the use of thin-sheet calorimeters in radiation and convection environments; to ensure that the calorimeter produces accurate heat flux; the heat transfer of the thin-sheet calorimeter is performed under the assumption of concentrated capacitance, one-dimensional heat transfer, known material properties and constant emissivity; and the thin-sheet calorimeter is calibrated using a radiant propane heater; a cone calorimeter is used as a comparison;

[0021] Calibration using radiant heaters requires the thin slice calorimeter to be positioned vertically; the thin slice calorimeters in the test array were oriented horizontally; an additional calibration was performed using a cone calorimeter; two thin slice calorimeters were calibrated using this method; in this calibration, a reference water-cooled heat flux meter and the thin slice calorimeter to be calibrated were placed adjacent to each other below the center of the cone;

[0022] For one calibration, a thin-sheet calorimeter was calibrated at two heat flux densities; for the other calibration, a thin-sheet calorimeter was calibrated to seven heat fluxes, from 3-53kW / m2, chosen to cover the expected heat flux range; in the first calibration, a painted thin-sheet calorimeter was used; however, the second calibration was on a damaged thin-sheet calorimeter, similar to the one used in the tests; the use of radiant heaters allowed for the calibration of more gauges, providing a larger sample size for comparison.

[0023] Preferably, the specific steps of collecting temperature data in real time are as follows: by arranging a patch thermocouple on the surface of the lithium battery, collecting temperature data in real time at a sampling frequency of at least 100 times per second, the thermocouple is close to the key thermal runaway area of ​​the lithium battery and fixed by a high-temperature heat-resistant adhesive to ensure that the thermocouple maintains a stable position during the test; the data acquisition system pre-processes the collected temperature data in combination with a filtering algorithm during the acquisition process to eliminate the influence of electromagnetic interference and random noise, and ensure the stability and accuracy of the collected data, and the filtering algorithm is a low-pass filter to filter out noise interference with a frequency higher than a set value;

[0024] The data acquisition system has a built-in anomaly detection algorithm to monitor the fluctuation of temperature data in real time, detect and eliminate abnormal values ​​to ensure data continuity and credibility. The anomaly detection algorithm is based on the Z-score method to perform standardized calculations on each temperature data point and eliminate abnormal data that exceeds the preset threshold. The collected temperature data is transmitted to the remote data processing terminal in real time through the wireless communication module and is synchronously saved in the local storage device. The data transmission process is encrypted to ensure the integrity and security of the data. During the data processing process, the output value T of the temperature data T(t) after passing through the filter is 滤波 (t) can be calculated by the following expression:

[0025] Where T(t) represents the temperature data at time t, T 滤波 (t) is the filtered temperature data, and N is the window size of the filter, which is used to smooth the data and reduce the influence of noise;

[0026] During the anomaly detection process, each collected temperature value T(t) is calculated as the standardized value Z(T(t)) according to the Z-score algorithm. The calculation formula is:

[0027]

[0028] Among them, μ T is the average temperature of the collected data, σ T is the standard deviation of the temperature data; when |Z(T(t))| is greater than the preset threshold, the data point is determined to be an outlier and is removed from the data set.

[0029] Preferably, the energy from the fire can be obtained by performing an energy balance on the control volume of the thin film calorimeter.

[0030] The equation for the total heat flux from the stack to the thin-film calorimeter is: E stor =E in -E out , where Ein represents the energy flux entering the control volume and Eout represents the energy flux leaving the control volume. Using the general energy balance of the above equation with the heat transfer term for the heat flux, we obtain the heat transfer balance: in, The net heat is the net heat transferred from the combustion pile to the thin film calorimeter, Heat conversion is the energy transferred from the thin film calorimeter by natural convection cooling. Heat transfer is the heat reradiated from the thin film calorimeter to the environment. The heat meter stores heat and Thermal representation is heat conduction through the thin-film calorimeters to the wires and insulation, all quantities are measured in W / m2; convection cooling occurs from the thin-film calorimeter array to the environment: Where h is the convective heat transfer coefficient in W / m2K, TTS is the temperature of the thin-film calorimeter in K, and T∞ is the ambient air temperature in K;

[0031] Next, the specific steps for calculating the radiation heat flux using the Stefan-Boltzmann law are as follows: The sheet calorimeter radiates heat according to the Stefan-Boltzmann law: Where ε is the emissivity of the Inconel alloy, σ is the Stefan-Boltzmann constant; the heat storage rate is defined as:

[0032]

[0033] where ρ and cp are the density and specific heat of the Inconel metal, respectively, both are functions of the slice calorimeter temperature, and δ is the slice calorimeter thickness; a correction term is calculated to replace the conductive heat transfer rate to the surrounding insulation; this correction term is assumed to be a fraction of the incident radiative heat flux, and both are assumed to be temperature dependent.

[0034] Preferably, the specific steps of performing error correction on the measurement data are as follows: The error correction formula for the measurement data is: Where C is the C coefficient obtained through calibration as a function of temperature and αTS is the absorptivity of the Inconel metal.

[0035] Preferably, the specific steps of outputting the radiation heat flux result are as follows: The purpose of calibration is to find a correction factor that can be applied to the heat flux calculation in the experimental use of the thin film calorimeter; the C described above is found according to the method of Hildalgo et al., where:

[0036]

[0037] in, Heat flux is the incident heat flux measured by a reference water-cooled heat flux meter; It is the result measured by the reference water-cooled heat flow meter during the calibration process;

[0038]

[0039] The correction factor is applied to The second term, described as a correction term, takes into account the uncertainties associated with the emissivity of Inconel when tarnished and with conduction into the insulation and into the wires of the foil calorimeter; the corrected net heat flux is and Comparisons were made to determine the validity of the correction factors; the correction factors were plotted as a function of temperature and fitted to obtain C as a function of temperature for application during calculation of heat flux in experiments.

[0040] In the above technical scheme, the technical effects and advantages provided by the present invention are as follows: the present invention significantly improves the efficiency, accuracy and economy of thermal runaway testing of lithium batteries by arranging patch thermocouples on the surface of lithium batteries to monitor the temperature in real time, and calculating the radiation heat flux in combination with a specific algorithm. Compared with traditional heat flow meters and temperature sensors, the present invention has the characteristics of high integration, and combines the temperature measurement and heat flux calculation functions in one system, which greatly simplifies the test process. By arranging patch thermocouples in different areas of the battery surface and fixing them with high-temperature heat-resistant adhesives, the stability of the equipment is ensured, while avoiding the safety hazards caused by contact with the charged components inside the battery. This integrated design not only reduces the complexity of equipment layout, but also simplifies the operation process and reduces the workload of the operator. Compared with the complicated installation and operation requirements of traditional heat flow meter systems, the system design of the present invention makes the test work more efficient and convenient, especially in batch testing. It shows great advantages and can significantly shorten the experimental preparation time and equipment debugging time. In addition, during the monitoring process of traditional heat flow meter systems, due to the distance between the sensor and the battery surface, data acquisition is often delayed, and the temperature changes at the moment of thermal runaway of lithium batteries cannot be quickly captured. The present invention significantly reduces the response time by attaching the thermocouple directly to the battery surface, and can capture the most representative temperature data at the moment of thermal runaway, ensuring the real-time nature of the test. This makes the present invention extremely sensitive in capturing temperature data, laying an accurate foundation for subsequent heat flux calculations.

[0041] In addition, the present invention can collect data on each surface of the lithium battery through the combined use of a thin-sheet calorimeter and a patch thermocouple, thereby achieving comprehensive and comprehensive data collection. In a complex battery structure, a traditional heat flow meter system can usually only capture the heat flux changes in a local area and cannot comprehensively monitor the thermal behavior of the entire battery. The present invention arranges sensors on different surfaces to ensure that the temperature data of each surface can be accurately obtained, so that the heat flux changes of each surface can be comprehensively calculated. This comprehensive collection method of multi-surface data enables the heat released by the lithium battery during thermal runaway to be accurately evaluated, providing a scientific basis for battery heat dissipation design. At the same time, the specific algorithm used in the present invention can convert the collected temperature data into radiation heat flux, especially through the Stefan-Boltzmann law, combined with the emissivity of the material for dynamic adjustment, to ensure the accuracy of the heat flux calculation. In addition, the present invention also uses algorithms such as low-pass filtering to remove noise from the data, ensuring the purity and credibility of the measurement data. Compared with traditional equipment, the price of the patch thermocouple and thin-sheet calorimeter used in the present invention is much lower than that of traditional heat flow meters, which not only greatly reduces the test cost, but also greatly shortens the equipment maintenance and replacement time due to its simple structure and convenient maintenance. This cost-effective solution makes the present invention have obvious advantages in cost-effectiveness and is suitable for large-scale lithium battery thermal runaway testing and research. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present application and the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0043] Figure 1 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0044] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these example embodiments are provided so that the description of the present disclosure will be more comprehensive and complete, and the concept of the example embodiments will be fully conveyed to those skilled in the art.

[0045] The present invention provides Figure 1 The lithium battery thermal runaway radiation heat flux test method based on patch thermocouple temperature measurement shown includes the following steps: arranging patch thermocouples on the surface of the lithium battery: installing the patch thermocouples on the surface of the lithium battery;

[0046] Calibrate the patch thermocouples; perform preliminary calibration on the arranged patch thermocouples to ensure that they can accurately measure the temperature and reduce the measurement errors caused by environmental changes and differences in battery surface materials;

[0047] Real-time temperature data collection: During the thermal runaway of lithium batteries, the temperature data of the patch thermocouple is continuously collected, and the collection frequency is set to at least 2 times per second to ensure real-time and continuous acquisition of temperature change data;

[0048] Calculate the radiation heat flux using the Stefan-Boltzmann law: Based on the collected temperature data, the radiation heat flux on the surface of the lithium battery is calculated using the Stefan-Boltzmann law to ensure the accuracy of the calculation results;

[0049] Error correction of measurement data: Error correction of temperature data is performed, and the measurement data is corrected in combination with factors such as ambient temperature, humidity and material emissivity to improve the accuracy and reliability of calculations;

[0050] Output radiation heat flux results: After completing data collection and error correction, output the calculated radiation heat flux generated during the thermal runaway of the lithium battery as a basis for evaluating the degree of thermal runaway; when arranging patch thermocouples on the surface of the lithium battery, it is preferred to use a K-type thermocouple with a thickness of 0.25 mm. The thermocouple is made of nickel-chromium alloy material, has high strength resistance to thermal fatigue, and can withstand a melting temperature of up to 1290°C. In order to ensure a close connection between the thermocouple and the calorimeter, the HOTSPOTTC technology is used to weld the thermocouple wire to the back of the calorimeter so that it can effectively sense temperature changes. According to the ASTME459 standard, the wire spacing is set to 1.6 mm during welding, and the effective sensing area of ​​the calorimeter is 1 cm 2 Since the thin sheet structure of the patch thermocouple needs to be consistent with the thermal design of the integrated capacitor, the dependence on the surface thickness of the thermocouple is reduced in the design, so that the thickness of the thermocouple is controlled at 0.508mm, and according to the provisions of the ASTME459 standard, an optimized thickness calculation formula is used to ensure its stability and effectiveness during the test process:

[0051]

[0052] Where k is the thermal conductivity of the sheet thermocouple material in W / mK, Tmax is the maximum temperature of the sheet calorimeter in K, T0 is the initial temperature, and q is the heat flux in W / m2; the average thermal conductivity value is obtained by averaging the k values ​​at the maximum and initial temperatures; a maximum temperature of 760°C was chosen as a typical average maximum value for large pile tests, and an initial temperature of room temperature, 21°C, was used; the k values ​​at these temperatures were 20.8 W / m°C and 9.8 W / m°C, respectively; the test results using a water-cooled heat flux meter found a maximum heat flux of approximately 60 kW / m2; substituting these values ​​into the above formula yields a δopt value of 0.113 m; the δopt value is based on an optimization of the maximum exposure time; since the sensor continuously measures the same heat flux as the water-cooled manometer throughout the experiment, it is assumed that the exposure time is sufficient for this application;

[0053] Since it is difficult to find the optimal thickness parameter in small-scale experiments, three different thicknesses of metal sheets were compared and analyzed, namely 1.2mm, 0.8mm and 0.5mm. The effects of different thicknesses of metal sheets on the accuracy and response time of heat flux measurement were observed experimentally. These thicknesses were selected for experiments in precision calorimeters, and the heat flux values ​​recorded by the calorimeters in all experiments were basically the same. In contrast, thinner calorimeters have faster response times and can provide more sensitive heat flux readings; although the 0.5mm thick calorimeter has the fastest response time, its thickness is close to the diameter of the thermocouple wire, which is prone to additional potential errors in the welding process. During the manufacturing process, thin sheet calorimeters are exposed to high temperatures of about 1000℃, and the metal surface may produce slight oxidation or gloss changes due to heat exposure. During flame baking exposure, the exposure time of thin sheets is short, and the gloss of the metal surface may disappear completely as the combustion process progresses. Since the emissivity of the metal sheet will change after the luster is lost, the emissivity change needs to be monitored regularly throughout the experimental period to ensure the accuracy and consistency of the test data. Because the metal will naturally lose its luster when the thin sheet calorimeter is located below the burn pile; Since the emissivity of the metal is expected to change when it loses its luster, the metal is exposed before testing to keep the emissivity the same constant between early and late tests;

[0054] At this time, the patch thermocouple should be installed on the positive electrode surface of the lithium battery, which is the area where the temperature rises fastest when the battery is in thermal runaway. By using high-temperature heat-resistant adhesive, the thermocouple is tightly fixed to the battery surface to ensure that the thermocouple remains in position throughout the test and avoid the influence of external mechanical disturbances and electrical interference on the measurement;

[0055] When implementing the present invention, it is first necessary to arrange patch thermocouples on the surface of the lithium battery, select a suitable surface position, and ensure that the thermocouples can closely contact the battery surface. It is recommended to arrange the thermocouples in the positive electrode area of ​​the battery, because the temperature of this area usually rises faster during the thermal runaway of the battery, and can effectively capture temperature changes. The installation of the patch thermocouple needs to be fixed with a high-temperature heat-resistant adhesive to prevent the position from moving due to vibration or external interference during the test. After the thermocouple is fixed, it must be preliminarily calibrated. The calibration process includes testing the thermocouple at a known temperature, adjusting its sensing accuracy, and making necessary adjustments to the measurement system in combination with the material emissivity of the lithium battery surface to ensure that the temperature data can accurately reflect the temperature changes on the battery surface. During calibration, changes in external ambient temperature and humidity should also be considered to avoid external factors from interfering with the measurement results. After the thermocouple is calibrated, its measurement accuracy needs to be checked regularly to ensure efficient and accurate temperature monitoring throughout the test process;

[0056] The specific steps for calibrating the patch thermocouple are as follows: ASTM E459 standard describes the use of thin-sheet calorimeters in radiation and convection environments; to ensure that the calorimeter produces accurate heat flux; the heat transfer of the thin-sheet calorimeter is carried out under the assumption of concentrated capacitance, one-dimensional heat transfer, known material properties and constant emissivity; and the thin-sheet calorimeter is calibrated using a radiant propane heater; a cone calorimeter is used as a comparison;

[0057] Calibration using radiant heaters requires the thin slice calorimeter to be positioned vertically; the thin slice calorimeters in the test array were oriented horizontally; an additional calibration was performed using a cone calorimeter; two thin slice calorimeters were calibrated using this method; in this calibration, a reference water-cooled heat flux meter and the thin slice calorimeter to be calibrated were placed adjacent to each other below the center of the cone;

[0058] For one calibration, a thin-sheet calorimeter was calibrated at two heat fluxes; for the other calibration, a thin-sheet calorimeter was calibrated at seven heat fluxes, from 3-53kW / m2, chosen to cover the expected heat flux range; in the first calibration, a painted thin-sheet calorimeter was used; however, the second calibration was on a damaged thin-sheet calorimeter, similar to the one used in the tests; the use of a radiant heater allowed for the calibration of more gauges, thus providing a larger sample size for comparison;

[0059] The specific steps of real-time temperature data collection are as follows: by arranging patch thermocouples on the surface of lithium batteries, real-time temperature data is collected at a sampling frequency of at least 100 times per second. The thermocouples are close to the key thermal runaway area of ​​the lithium battery and fixed by high-temperature heat-resistant adhesives to ensure that the thermocouples maintain a stable position during the test; the data acquisition system pre-processes the collected temperature data in combination with the filtering algorithm during the acquisition process to eliminate the influence of electromagnetic interference and random noise, and ensure the stability and accuracy of the collected data. The filtering algorithm is a low-pass filter to filter out noise interference with a frequency higher than the set value; when collecting temperature data, the patch thermocouple will monitor the temperature of the lithium battery surface in real time at a sampling frequency of at least 100 times per second to ensure that the rapidly changing temperature fluctuations during the battery thermal runaway process can be captured. The collected temperature data will be processed by a low-pass filter to filter out data deviations caused by electromagnetic interference or other high-frequency noise, and ensure the purity and continuity of the collected data. During the entire acquisition process, the system will use anomaly detection algorithms (such as Z-score algorithms) to monitor the data in real time to automatically identify and eliminate abnormal temperature points to avoid sudden temperature fluctuations or external interference from affecting the test results. In order to ensure the security and real-time nature of the data, the collected data will not only be automatically stored in the local storage device, but will also be sent to the remote data processing terminal in real time through the wireless transmission module for subsequent analysis and processing. The entire temperature data collection process will be carried out synchronously to ensure that the temperature changes at every moment can be accurately recorded and seamlessly transmitted, thereby providing reliable basic data support for subsequent heat flux calculations;

[0060] The data acquisition system has a built-in anomaly detection algorithm to monitor the fluctuation of temperature data in real time, detect and eliminate abnormal values ​​to ensure data continuity and credibility. The anomaly detection algorithm is based on the Z-score method to perform standardized calculations on each temperature data point and eliminate abnormal data that exceeds the preset threshold. The collected temperature data is transmitted to the remote data processing terminal in real time through the wireless communication module and is synchronously saved in the local storage device. The data transmission process is encrypted to ensure the integrity and security of the data. During the data processing process, the output value T of the temperature data T(t) after passing through the filter is 滤波 (t) can be calculated by the following expression:

[0061]

[0062] Where T(t) represents the temperature data at time t, T 滤波 (t) is the filtered temperature data, and N is the window size of the filter, which is used to smooth the data and reduce the influence of noise;

[0063] During the anomaly detection process, each collected temperature value T(t) is calculated as the standardized value Z(T(t)) according to the Z-score algorithm. The calculation formula is:

[0064]

[0065] Among them, μ T is the average temperature of the collected data, σ T is the standard deviation of the temperature data; when |Z(T(t))| is greater than the preset threshold, the data point is determined to be an outlier and is removed from the data set;

[0066] By performing an energy balance on the control volume of the thin-film calorimeter, the equation for the total heat flux from the torch pile to the thin-film calorimeter is obtained: where Ein represents the energy flux entering the control volume and Eout represents the energy flux leaving the control volume. Using the general energy balance of the above equation with the heat transfer term for the heat flux, the heat transfer balance is obtained: in, The net heat is the net heat transferred from the combustion pile to the thin film calorimeter, Heat conversion is the energy transferred from the thin film calorimeter by natural convection cooling. Heat transfer is the heat reradiated from the thin film calorimeter to the environment. The heat meter stores heat and Thermal representation is heat conduction through the thin-film calorimeters to the wires and insulation, all quantities are measured in W / m2; convection cooling occurs from the thin-film calorimeter array to the environment: Where h is the convective heat transfer coefficient in W / m2K, TTS is the temperature of the thin-film calorimeter in K, and T∞ is the ambient air temperature in K;

[0067] Next, the specific steps for calculating the radiation heat flux using the Stefan-Boltzmann law are as follows: The sheet calorimeter radiates heat according to the Stefan-Boltzmann law: Where ε is the emissivity of the Inconel alloy, σ is the Stefan-Boltzmann constant; the heat storage rate is defined as:

[0068]

[0069] Where ρ and cp are the density and specific heat of the Inconel alloy metal, respectively, both of which are functions of the temperature of the thin-sheet calorimeter, and δ is the thickness of the thin-sheet calorimeter; a correction term is calculated to replace the conductive heat transfer rate to the surrounding insulation; the correction term is assumed to be part of the incident radiation heat flux, and both are assumed to be temperature-dependent; after the temperature data is collected, the system will immediately use the Stefan-Boltzmann law to calculate the radiation heat flux on the surface of the lithium battery. First, the system will dynamically adjust the emissivity according to the material type and emissivity characteristics of the lithium battery surface to ensure that the emissivity of different materials is accurately reflected in the heat flux calculation. During the specific operation, the calculation module will automatically calculate the instantaneous radiation heat flux value on the surface of the lithium battery based on the temperature data collected at each moment, combined with the material properties of the lithium battery and the ambient temperature. When calculating, the system will ensure the accuracy of the calculation results through multiple iterations, especially in the stage of rapid temperature change, through multiple data verification and emissivity correction to ensure the calculation accuracy of the radiation heat flux. All calculation processes will be performed automatically and synchronized with temperature acquisition to ensure that the heat flux data at each moment can correspond to the temperature change. The final calculation results will directly serve as an important basis for evaluating the heat release during the thermal runaway process of lithium batteries;

[0070] The specific steps for error correction of measurement data are as follows: The error correction formula for measurement data is: In the formula, C is the C coefficient obtained through calibration as a function of temperature, and αTS is the absorption rate of chromium-nickel-iron alloy metal; during the temperature data collection and heat flux calculation process, the system will perform real-time error correction on the measured data according to environmental conditions. First, the system will monitor the external temperature and humidity changes in real time through the built-in environmental monitoring module, and combine it with the collected temperature data to generate a correction factor. Secondly, the system will also adjust the emissivity values ​​of different materials according to the specific material properties of the lithium battery surface to ensure that the thermal radiation characteristics of different materials can be fully considered when calculating the radiant heat flux. During the entire data processing process, the error correction algorithm will automatically compensate for data deviations caused by environmental changes, material property differences, etc., and repeatedly calculate the correction factor and apply it to the temperature data, thereby reducing the impact of external interference on the measurement results. When performing error correction, the system will also compare with historical data to further verify whether the current correction result is reasonable, and dynamically adjust the correction range to ensure high accuracy and consistency of the measurement data;

[0071] The specific steps for outputting the radiation heat flux results are as follows: The purpose of calibration is to find a correction factor that can be applied to the heat flux calculations in experimental use of the thin-sheet calorimeter; the C described above was found according to the method of Hildalgo et al., where:

[0072]

[0073] in, Heat flux is the incident heat flux measured by a reference water-cooled heat flux meter; It is the result measured by the reference water-cooled heat flow meter during the calibration process;

[0074]

[0075] The correction factor is applied to The second term, described as a correction term, takes into account the uncertainties associated with the emissivity of Inconel when tarnished and with conduction into the insulation and into the wires of the foil calorimeter; the corrected net heat flux is and Compare to determine the validity of the correction factor; plot the correction factor as a function of temperature and fit it to obtain C as a function of temperature for application during the calculation of heat flux in the experiment; after completing temperature data acquisition, heat flux calculation and error correction, the system will output the final radiation heat flux result. The output results include not only the instantaneous heat flux value at each moment, but also a curve chart of the radiation heat flux changing with time during the thermal runaway of the lithium battery. This curve chart can intuitively show the dynamic changes of heat release during the thermal runaway of the lithium battery, which is convenient for researchers to conduct a comprehensive analysis of the thermal management performance of the lithium battery. When the system generates the curve chart, it automatically calls the data processing algorithm to format the collected raw data to ensure the smoothness and continuity of the curve. After the curve chart is generated, the system will store it together with other experimental data. Researchers can view the curve changes in real time through the remote data terminal, or export the data for subsequent analysis. In order to improve the applicability of the output results, the system supports multiple output formats. Researchers can customize the data output according to their needs to ensure that the final output results meet different experimental conditions and requirements.

[0076] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A lithium battery thermal runaway radiation heat flux test method based on temperature measurement by a patch thermocouple, characterized in that: The following steps are involved: Arrange a patch thermocouple on the surface of the lithium battery; install the patch thermocouple on the surface of the lithium battery; Calibrate the patch thermocouples; perform preliminary calibration on the arranged patch thermocouples to ensure that they can accurately measure the temperature and reduce the measurement errors caused by environmental changes and differences in battery surface materials; Collect temperature data in real time; During the thermal runaway of lithium batteries, the temperature data of the patch thermocouple is continuously collected, and the collection frequency is set to at least 2 times per second to ensure the real-time and continuous acquisition of temperature change data; Calculate the radiation heat flux using the Stefan-Boltzmann law: Based on the collected temperature data, calculate the radiation heat flux on the surface of the lithium battery using the Stefan-Boltzmann law to ensure the accuracy of the calculation results; Correct the error of the measured data; Correct the error of the temperature data, and correct the measured data by combining the factors of ambient temperature, humidity and material emissivity to improve the accuracy and reliability of the calculation; Output the radiation heat flux result; after completing data collection and error correction, output the calculated radiation heat flux generated during the thermal runaway process of the lithium battery as a basis for evaluating the degree of thermal runaway.

2. The method for testing the thermal runaway radiation heat flux of a lithium battery based on temperature measurement by a patch thermocouple according to claim 1, characterized in that: When arranging the patch thermocouple on the surface of the lithium battery, it is preferred to use a K-type thermocouple with a thickness of 0.25 mm. The thermocouple is made of nickel-chromium alloy material, has high strength and thermal fatigue resistance, and can withstand a melting temperature of up to 1290°C. In order to ensure a tight connection between the thermocouple and the calorimeter, the HOTSPOTTC technology is used to weld the thermocouple wire to the back of the calorimeter so that it can effectively sense temperature changes. According to ASTM E459 standard, the wire spacing is set to 1.6 mm during welding, and the effective sensing area of ​​the calorimeter is 1 cm 2 Since the thin sheet structure of the patch thermocouple needs to be consistent with the thermal design of the integrated capacitor, the dependence on the surface thickness of the thermocouple is reduced in the design, so that the thickness of the thermocouple is controlled at 0.508mm, and according to the provisions of the ASTME459 standard, an optimized thickness calculation formula is used to ensure its stability and effectiveness during the test process; ASTME459 provides a formula for calculating the optimal thickness of the calorimeter: Where k is the thermal conductivity of the sheet thermocouple material in W / mK, Tmax is the maximum temperature of the sheet calorimeter in K, T0 is the initial temperature, and q is the heat flux in W / m2; the average thermal conductivity value is obtained by averaging the k values ​​at the maximum and initial temperatures; a maximum temperature of 760°C was chosen as a typical average maximum value for large pile tests, and an initial temperature of room temperature, 21°C, was used; the k values ​​at these temperatures were 20.8 W / m°C and 9.8 W / m°C, respectively; the test results using a water-cooled heat flux meter found a maximum heat flux of approximately 60 kW / m2; substituting these values ​​into the above formula yields a δopt value of 0.113 m; the δopt value is based on an optimization of the maximum exposure time; since the sensor continuously measures the same heat flux as the water-cooled manometer throughout the experiment, it is assumed that the exposure time is sufficient for this application; Since it is difficult to find the optimal thickness parameters in small-scale experiments, three different thicknesses of metal sheets were compared and analyzed, namely 1.2mm, 0.8mm and 0.5mm. The effects of different thicknesses of metal sheets on the accuracy and response time of heat flux measurement were observed experimentally. These thicknesses were selected for experiments in precision calorimeters, and the heat flux values ​​recorded by the calorimeters in all experiments were basically the same. In contrast, thinner calorimeters have faster response times and can provide more sensitive heat flux readings; although the calorimeter with a thickness of 0.5mm has the fastest response time, its thickness is close to the diameter of the thermocouple wire, which is prone to additional potential errors in the welding process. During the manufacturing process, thin sheet calorimeters are exposed to high temperatures of about 1000℃, and the metal surface may produce slight oxidation or gloss changes due to heat exposure. When performing flame baking exposure, the exposure time of the thin sheet is short, and the gloss of the metal surface may completely disappear as the burning process progresses. Since the emissivity of the metal sheet will change after the gloss is lost, the change in emissivity needs to be monitored regularly throughout the experimental cycle to ensure the accuracy and consistency of the test data. Because the metal will naturally lose its gloss when the thin sheet calorimeter is located under the burning pile; since the emissivity of the metal is expected to change when it loses its gloss, the metal is exposed before testing, and the emissivity is kept constant between early and late tests; At this time, the patch thermocouple should be installed on the positive electrode surface of the lithium battery, which is the area where the temperature rises fastest when the battery is in thermal runaway. By using a high-temperature heat-resistant adhesive, the thermocouple is tightly fixed to the battery surface to ensure that the thermocouple remains in place throughout the test and avoid the influence of external mechanical disturbances and electrical interference on the measurement.

3. The method for testing the thermal runaway radiation heat flux of a lithium battery based on temperature measurement by a patch thermocouple according to claim 1, characterized in that: The specific steps for calibrating the patch thermocouple are as follows: ASTM E459 standard describes the use of thin-sheet calorimeters in radiation and convection environments; to ensure that the calorimeter produces accurate heat flux; the heat transfer of the thin-sheet calorimeter is carried out under the assumption of concentrated capacitance, one-dimensional heat transfer, known material properties and constant emissivity; and the thin-sheet calorimeter is calibrated using a radiant propane heater; a cone calorimeter is used as a comparison; Calibration using a radiant heater requires the thin slice calorimeter to be positioned vertically; the thin slice calorimeters in the test array were oriented horizontally; an additional calibration was performed using a cone calorimeter; two thin slice calorimeters were calibrated using this method; In this calibration, a reference water-cooled heat flow meter and the thin-sheet calorimeter to be calibrated are placed adjacent to each other below the center of the cone; For one calibration, a thin-sheet calorimeter was calibrated at two heat flux densities; for the other calibration, a thin-sheet calorimeter was calibrated to seven heat fluxes, from 3-53kW / m2, chosen to cover the expected heat flux range; in the first calibration, a painted thin-sheet calorimeter was used; however, the second calibration was on a damaged thin-sheet calorimeter, similar to the one used in the tests; the use of radiant heaters allowed for the calibration of more gauges, providing a larger sample size for comparison.

4. The method for testing the thermal runaway radiation heat flux of a lithium battery based on temperature measurement by a patch thermocouple according to claim 1, characterized in that: The specific steps of real-time temperature data collection are as follows: by arranging a patch thermocouple on the surface of the lithium battery, collecting temperature data in real time at a sampling frequency of at least 100 times per second, the thermocouple is close to the key thermal runaway area of ​​the lithium battery and fixed by a high-temperature heat-resistant adhesive to ensure that the thermocouple remains in a stable position during the test; The data acquisition system pre-processes the collected temperature data in combination with a filtering algorithm during the acquisition process to eliminate the influence of electromagnetic interference and random noise and ensure the stability and accuracy of the collected data. The filtering algorithm is a low-pass filter that filters out noise interference with a frequency higher than a set value. The data collection system has a built-in anomaly detection algorithm to monitor the fluctuation of temperature data in real time, detect and remove abnormal values ​​to ensure data continuity and credibility. The anomaly detection algorithm is based on the Z-score method to perform standardized calculations on each temperature data point and remove abnormal data that exceeds the preset threshold. The collected temperature data is transmitted to the remote data processing terminal in real time through the wireless communication module and is synchronously saved in the local storage device. The data transmission process is encrypted to ensure the integrity and security of the data. During the data processing process, the output value T of the temperature data T(t) after the filter is 滤波 (t) can be calculated by the following expression: Where T(t) represents the temperature data at time t, T 滤波 (t) is the filtered temperature data, and N is the window size of the filter, which is used to smooth the data and reduce the influence of noise; During the anomaly detection process, each collected temperature value T(t) is calculated as the standardized value Z(T(t)) according to the Z-score algorithm. The calculation formula is: Among them, μ T is the average temperature of the collected data, σ T is the standard deviation of the temperature data; when |Z(T(t))| is greater than the preset threshold, the data point is determined to be an outlier and is removed from the data set.

5. The method for testing the thermal runaway radiation heat flux of a lithium battery based on temperature measurement by a patch thermocouple according to claim 1, characterized in that: By performing an energy balance on the control volume of the thin-film calorimeter, the equation for the total heat flux from the torch pile to the thin-film calorimeter is obtained: E stor =E in -E out , where Ein represents the energy flux entering the control volume and Eout represents the energy flux leaving the control volume. Using the general energy balance of the above equation with the heat transfer term for the heat flux, we obtain the heat transfer balance: in, The net heat is the net heat transferred from the combustion pile to the thin film calorimeter, Heat conversion is the energy transferred from the thin film calorimeter by natural convection cooling. Heat transfer is the heat reradiated from the thin film calorimeter to the environment. The heat meter stores heat and Thermal representation is heat conduction through the thin-film calorimeters to the wires and insulation, all quantities are measured in W / m2; convection cooling occurs from the thin-film calorimeter array to the environment: Where h is the convective heat transfer coefficient in W / m2K, TTS is the temperature of the thin-film calorimeter in K, and T∞ is the ambient air temperature in K; Next, the specific steps for calculating the radiation heat flux using the Stefan-Boltzmann law are as follows: The sheet calorimeter radiates heat according to the Stefan-Boltzmann law: Where ε is the emissivity of the Inconel alloy, σ is the Stefan-Boltzmann constant; the heat storage rate is defined as: where ρ and cp are the density and specific heat of the Inconel metal, respectively, both are functions of the slice calorimeter temperature, and δ is the slice calorimeter thickness; a correction term is calculated to replace the conductive heat transfer rate to the surrounding insulation; this correction term is assumed to be a fraction of the incident radiative heat flux, and both are assumed to be temperature dependent.

6. The method for testing the thermal runaway radiation heat flux of a lithium battery based on temperature measurement by a patch thermocouple according to claim 1, characterized in that: The specific steps for error correction of measurement data are as follows: The error correction formula for measurement data is: Where C is the C coefficient obtained through calibration as a function of temperature and αTS is the absorptivity of the Inconel metal.

7. The method for testing the thermal runaway radiation heat flux of a lithium battery based on temperature measurement by a patch thermocouple according to claim 1, characterized in that: The specific steps for outputting the radiation heat flux results are as follows: The purpose of calibration is to find a correction factor that can be applied to the heat flux calculations in experimental use of the thin-sheet calorimeter; the C described above was found according to the method of Hildalgo et al., where: in, Heat flux is the incident heat flux measured by a reference water-cooled heat flux meter; It is the result measured by the reference water-cooled heat flow meter during the calibration process; The correction factor is applied to The second term, described as a correction term, takes into account the uncertainties associated with the emissivity of Inconel when tarnished and with conduction into the insulation and into the wires of the foil calorimeter; the corrected net heat flux is and Comparisons were made to determine the validity of the correction factors; the correction factors were plotted as a function of temperature and fitted to obtain C as a function of temperature for application during calculation of heat flux in experiments.

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