Method and device for evaluating the thermal stability of a diaphragm

Abstract

The application discloses a method and device for evaluating the thermal stability of a diaphragm. The method comprises: selecting multiple experimental temperatures to perform multiple thermal shrinkage experiments on the diaphragm, obtaining multiple thermal shrinkage rates corresponding to each experimental temperature; using the thermal shrinkage rates corresponding to each experimental temperature to fit a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm; using the function of the temperature acceleration coefficient to calculate multiple thermal shrinkage rates corresponding to the highest working temperature of the diaphragm based on each experimental temperature and the corresponding thermal shrinkage rate; determining the final thermal shrinkage rate of the highest working temperature according to the thermal shrinkage rates corresponding to the highest working temperature of the diaphragm; using the final thermal shrinkage rate of the highest working temperature and the full life cycle of the diaphragm to calculate the thermal shrinkage rate of the full life cycle of the diaphragm; and determining the thermal shrinkage evaluation result of the diaphragm by comparing the thermal shrinkage rate of the full life cycle of the diaphragm with the shrinkage rate threshold of the diaphragm.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a method and apparatus for evaluating the thermal stability of a separator. Background Technology

[0002] Lithium-ion batteries have become one of the most widely used and technologically mature electrochemical energy storage devices due to their excellent performance. A separator is incorporated into lithium-ion batteries to physically separate the positive and negative electrode materials, preventing short circuits caused by electrode contact. However, high temperatures can cause the separator to shrink, increasing the risk of internal short circuits. Therefore, it is necessary to evaluate the separator's shrinkage rate.

[0003] Because higher temperatures result in greater membrane shrinkage and more accurate experimental results, while battery operation occurs at relatively low temperatures, leading to smaller membrane shrinkage and larger errors in experimental shrinkage measurements, current methods for evaluating membrane shrinkage rate primarily employ constant-temperature heating or stepped-temperature multi-stage heating methods. These methods involve heating the membrane at a single high temperature or multiple varying high temperatures for a given period. The thermal shrinkage rate is then calculated based on the dimensional changes before and after heating.

[0004] However, existing methods are all short-term tests, which tend to test the inherent thermal shrinkage rate of the separator itself. Therefore, they cannot assess the shrinkage of the separator throughout the entire life cycle of the battery cell. As a result, there is still a risk that the separator may shrink to a size smaller than the design size, leading to a short circuit in the battery. In other words, it cannot be accurately assessed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, this application provides a method and apparatus for evaluating the thermal stability of a diaphragm, so as to solve the problem that the prior art cannot accurately evaluate the shrinkage rate of the diaphragm throughout its entire life cycle.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] The first aspect of this application provides a method for evaluating the thermal stability of a diaphragm, comprising:

[0008] Multiple thermal shrinkage experiments were conducted on the diaphragm at various experimental temperatures to obtain multiple thermal shrinkage rates corresponding to each experimental temperature.

[0009] Using the thermal shrinkage rates corresponding to each of the experimental temperatures, a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm is fitted; wherein, the temperature acceleration coefficient is the ratio of the thermal shrinkage rates of the diaphragm at two different temperatures;

[0010] Based on each of the experimental temperatures and their corresponding thermal shrinkage rates, multiple thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm are calculated using a function of the temperature acceleration coefficient.

[0011] The final heat shrinkage rate at the highest operating temperature is determined based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0012] The thermal shrinkage rate of the diaphragm over its entire lifespan is calculated using the final thermal shrinkage rate at the highest operating temperature and the entire lifespan of the diaphragm.

[0013] The thermal shrinkage assessment result of the diaphragm is determined by comparing the thermal shrinkage rate of the diaphragm over its entire life cycle with the shrinkage rate threshold of the diaphragm.

[0014] Optionally, in the above-described method for evaluating the thermal stability of the diaphragm, the step of fitting a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm using the thermal shrinkage rates corresponding to each of the experimental temperatures includes:

[0015] Using the experimental temperatures and their corresponding thermal shrinkage rates, the relational parameters in the original function of the temperature acceleration coefficient are fitted; wherein, the original function of the temperature acceleration coefficient is the ratio expressed by the Arrhenius formula for the diaphragm at the two temperatures;

[0016] Substituting the fitted relationship parameters into the original function of the temperature acceleration coefficient, the function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm is obtained.

[0017] Optionally, in the above-described method for evaluating the thermal stability of the diaphragm, the step of fitting a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm using the thermal shrinkage rates corresponding to each of the experimental temperatures includes:

[0018] The heat shrinkage rates corresponding to each of the experimental temperatures are randomly combined to obtain multiple heat shrinkage rate groups; wherein each heat shrinkage rate group includes one heat shrinkage rate corresponding to each of the experimental temperatures;

[0019] By using each heat shrinkage rate in each heat shrinkage rate group and its corresponding experimental temperature, a function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group is fitted.

[0020] Optionally, in the above-described method for evaluating the thermal stability of the diaphragm, the step of calculating multiple thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm based on each of the experimental temperatures and their corresponding thermal shrinkage rates using a function of the temperature acceleration coefficient includes:

[0021] For each heat shrinkage rate group, each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest operating temperature of the diaphragm are substituted into the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group for calculation, so as to obtain multiple heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0022] Optionally, in the above-described method for evaluating the thermal stability of the diaphragm, determining the final thermal shrinkage rate at the highest operating temperature based on the various thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm includes:

[0023] Calculate the standard deviation of each thermal shrinkage rate corresponding to the highest operating temperature of the diaphragm;

[0024] Select the maximum heat shrinkage rate among the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm;

[0025] The maximum heat shrinkage rate is added to the standard deviation by a preset multiple to obtain the maximum heat shrinkage rate corresponding to the highest operating temperature of the diaphragm, and the maximum heat shrinkage rate is determined as the final heat shrinkage rate at the highest operating temperature.

[0026] Optionally, the shrinkage threshold of the separator is determined based on the minimum size of the separator exceeding the negative electrode of the battery.

[0027] A second aspect of this application provides an apparatus for evaluating the thermal stability of a diaphragm, comprising:

[0028] The experimental unit is used to select multiple experimental temperatures to conduct multiple heat shrinkage experiments on the diaphragm, and obtain multiple heat shrinkage rates corresponding to each experimental temperature.

[0029] The fitting unit is used to fit a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm using the thermal shrinkage rates corresponding to each of the experimental temperatures; wherein the temperature acceleration coefficient is the ratio of the thermal shrinkage rates of the diaphragm at two different temperatures.

[0030] The first calculation unit is used to calculate multiple thermal shrinkage rates corresponding to the highest working temperature of the diaphragm based on each of the experimental temperatures and their corresponding thermal shrinkage rates, using a function of the temperature acceleration coefficient.

[0031] The second calculation unit is used to determine the final heat shrinkage rate at the highest operating temperature based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0032] The third calculation unit is used to calculate the thermal shrinkage rate of the diaphragm over its entire life cycle using the final thermal shrinkage rate at the highest operating temperature and the entire life cycle of the diaphragm.

[0033] An evaluation unit is used to determine the thermal shrinkage evaluation result of the diaphragm by comparing the thermal shrinkage rate of the diaphragm over its entire life cycle with the shrinkage rate threshold of the diaphragm.

[0034] Optionally, in the above-described diaphragm thermal stability evaluation apparatus, the fitting unit includes:

[0035] The parameter fitting unit is used to fit the relational parameters in the original function of the temperature acceleration coefficient using each of the experimental temperatures and their corresponding thermal shrinkage rates; wherein the original function of the temperature acceleration coefficient is the ratio expressed by the Arrhenius formula for the diaphragm at the two temperatures.

[0036] The substitution unit is used to substitute the fitted relationship parameters into the original function of the temperature acceleration coefficient to obtain the function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm.

[0037] Optionally, in the above-described diaphragm thermal stability evaluation apparatus, the fitting unit includes:

[0038] A combination unit is used to randomly combine the heat shrinkage rates corresponding to each of the experimental temperatures to obtain multiple heat shrinkage rate groups; wherein each heat shrinkage rate group includes a heat shrinkage rate corresponding to each of the experimental temperatures;

[0039] The function fitting unit is used to fit a function of the temperature acceleration coefficient corresponding to each heat shrinkage rate group using each heat shrinkage rate in each heat shrinkage rate group and its corresponding experimental temperature.

[0040] Optionally, in the above-described diaphragm thermal stability evaluation device, the first calculation unit includes:

[0041] The first calculation subunit is used to calculate, for each heat shrinkage rate group, each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest working temperature of the diaphragm, by substituting each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest working temperature of the diaphragm into the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group, so as to obtain multiple heat shrinkage rates corresponding to the highest working temperature of the diaphragm.

[0042] The second computing unit includes:

[0043] The standard deviation calculation unit is used to calculate the standard deviation of each heat shrinkage rate corresponding to the highest operating temperature of the diaphragm.

[0044] The selection unit is used to select the maximum heat shrinkage rate among the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0045] The maximum value calculation unit is used to add the standard deviation of a preset multiple to the maximum heat shrinkage rate to obtain the maximum heat shrinkage rate corresponding to the highest operating temperature of the diaphragm, and to determine the maximum heat shrinkage rate as the final heat shrinkage rate at the highest operating temperature.

[0046] This application provides a method for evaluating the thermal stability of a diaphragm. Multiple thermal shrinkage experiments are conducted on the diaphragm at various experimental temperatures to obtain multiple thermal shrinkage rates corresponding to each experimental temperature. Then, using these thermal shrinkage rates at each experimental temperature, a function of the temperature acceleration factor of the diaphragm's thermal shrinkage rate is fitted. The temperature acceleration factor is the ratio of the thermal shrinkage rates of the diaphragm at two different temperatures. Next, based on each experimental temperature and its corresponding thermal shrinkage rate, multiple thermal shrinkage rates corresponding to the diaphragm's maximum operating temperature are calculated using the function of the temperature acceleration factor. Thus, by understanding the relationship between the ratio of the diaphragm's thermal shrinkage rates at different temperatures and temperature, a more accurate maximum operating temperature can be calculated. Then, based on the thermal shrinkage rates corresponding to the diaphragm's maximum operating temperature, the final thermal shrinkage rate at the maximum operating temperature is determined. By using the calculated multiple thermal shrinkage rates, any existing problems are eliminated, and an accurate thermal shrinkage rate for the maximum operating temperature is obtained. Therefore, obtaining accurate experimental data through higher experimental temperatures allows for the calculation of an accurate shrinkage rate at the maximum operating temperature. Then, using the final thermal shrinkage rate at the highest operating temperature and the entire life cycle of the separator, the thermal shrinkage rate of the separator throughout its entire life cycle is calculated, thereby analyzing the thermal shrinkage rate of the separator throughout its entire life cycle. Finally, by comparing the thermal shrinkage rate of the separator throughout its entire life cycle with the separator shrinkage rate threshold, the thermal shrinkage assessment result of the separator is determined, thus realizing an accurate assessment of the thermal shrinkage of the separator throughout the entire working life cycle of the battery. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0048] Figure 1 A flowchart illustrating a method for evaluating the thermal stability of a diaphragm, as provided in an embodiment of this application;

[0049] Figure 2 A schematic diagram of a DSC experimental curve of a diaphragm provided in an embodiment of this application;

[0050] Figure 3 A flowchart illustrating a method for fitting a function of the temperature acceleration coefficient, as provided in an embodiment of this application;

[0051] Figure 4 A flowchart illustrating a method for calculating the final thermal shrinkage rate at the highest operating temperature, provided for embodiments of this application;

[0052] Figure 5 This is a schematic diagram of the architecture of a diaphragm thermal stability evaluation device provided in an embodiment of this application. Detailed Implementation

[0053] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] This application provides a method for evaluating the thermal stability of a diaphragm, such as... Figure 1 As shown, it includes the following steps:

[0056] S101. Select multiple experimental temperatures to conduct multiple heat shrinkage experiments on the diaphragm, and obtain multiple heat shrinkage rates corresponding to each experimental temperature.

[0057] The temperatures in each experiment were below the thermal failure temperature of the diaphragm.

[0058] It should be noted that, since this embodiment requires analyzing the ratio of heat shrinkage rates at different temperatures, and the analysis is based solely on experimental data from individual temperatures, the accuracy of the results cannot be guaranteed. Therefore, in this embodiment, multiple experimental temperatures are selected for heat shrinkage experiments, and to eliminate errors and avoid randomness, multiple heat shrinkage experiments are performed at each experimental temperature.

[0059] Specifically, in each heat shrinkage test, the diaphragm is heated in an environment with the test temperature for a set time, and then the corresponding heat shrinkage rate is calculated based on the shrinkage before and after heating.

[0060] Optionally, because the maximum operating temperature of the battery is relatively low, the amount of shrinkage that can occur is small, making accurate measurement difficult and potentially leading to lower accuracy in the analysis results. Therefore, several different experimental temperatures were selected, each higher than the maximum operating temperature of the battery. Furthermore, to ensure that the separator shrinks normally, the selected experimental temperature should be lower than the separator's thermal fusion failure temperature. The thermal fusion failure temperature of the separator is primarily determined by its base material.

[0061] In practical applications, DSC (Digital Subtraction Angiography) curves of the separator can be obtained. Then, multiple temperatures from the initial temperature range on the ordinate (before the ordinate decreased) can be used as the experimental temperatures. Since a decrease in the ordinate indicates thermal failure, the temperature corresponding to this decrease can be considered the thermal failure temperature. Furthermore, these experimental temperatures must be higher than the highest operating temperature throughout the entire lifespan of the battery cell. In other words, the experimental temperatures are determined based on the separator material and the type of battery cell to match different cell models and application scenarios, thereby improving the reliability of the separator's thermal stability assessment.

[0062] For example, such as Figure 2 As shown, the DSC experimental curve of a separator made of PP material was obtained. The temperature before the vertical axis decreased was 130℃, therefore its thermal failure temperature is 130℃. Therefore, multiple experimental temperatures were obtained before this temperature, meaning the obtained temperatures need to be lower than 130℃. Taking lithium iron phosphate batteries as an example, the highest operating temperature of the cell throughout its entire lifespan is 50℃. Therefore, the obtained experimental temperatures should not be lower than 50℃. For example, three experimental temperatures were obtained: 90℃, 105℃, and 130℃. Then, three experiments were conducted at each of these three experimental temperatures to obtain three thermal shrinkage rates corresponding to the three experimental temperatures. For example, the specific data obtained are shown in Table 1 below.

[0063] Table 1

[0064]

[0065] S102. Using the thermal shrinkage rates corresponding to each experimental temperature, fit a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm.

[0066] The temperature acceleration coefficient is the ratio of the thermal shrinkage rate of the diaphragm at two different temperatures.

[0067] It should be noted that conducting experiments directly based on the maximum operating temperature will result in a large error. Therefore, the experimental temperature is higher than the maximum operating temperature of the battery cell. Furthermore, it is necessary to determine the thermal shrinkage rate at the maximum operating temperature by using the relationship between temperature and the thermal shrinkage rate of the separator.

[0068] Since thermal shrinkage is caused by a specific temperature, there is a relationship between the experimental temperature and the thermal shrinkage rate. That is, the higher the battery temperature and the longer the usage time, the greater the thermal shrinkage of the separator. Therefore, the thermal shrinkage rate at that temperature can be calculated. Specifically, based on two temperatures, the ratio of the separator's thermal shrinkage rate at those two temperatures can be calculated. Therefore, by using the thermal shrinkage rates corresponding to each experimental temperature, a function is fitted to calculate the ratio of the thermal shrinkage rates at each pair of experimental temperatures, resulting in a function representing the temperature acceleration factor of the separator's thermal shrinkage rate.

[0069] Optionally, in another embodiment of this application, one specific implementation of step S102 includes:

[0070] By fitting the relational parameters in the original function of the temperature acceleration coefficient using various experimental temperatures and their corresponding thermal shrinkage rates, and substituting the fitted relational parameters into the original function of the temperature acceleration coefficient, the function of the temperature acceleration coefficient of the diaphragm's thermal shrinkage rate is obtained.

[0071] The original function of the temperature acceleration coefficient is the ratio expressed by the Arrhenius equation for the diaphragm at the two temperatures.

[0072] It should be noted that the effect of temperature on the rate of a chemical reaction conforms to the Arrhenius equation, and the shrinkage rate of the diaphragm is precisely the effect of temperature on the shrinkage rate. Therefore, the relationship between the thermal shrinkage rate of the diaphragm and temperature can be expressed as follows:

[0073]

[0074] Where k is the thermal shrinkage rate of the diaphragm, which can be obtained by dividing the shrinkage of the diaphragm by the initial size of the diaphragm and then dividing the result by the experimental time; A is the pre-exponential factor; e is the base of the natural logarithm, approximately equal to 2.718; R is the gas constant, which is 8.314 J / mol*K; T is the temperature of the thermal test, i.e., the test temperature or experimental temperature, in K; and Ea is the activation energy of the reaction, in kJ / mol.

[0075] Therefore, the ratio of the thermal shrinkage rates k1 and k2 of the diaphragm at two temperatures T1 and T2 is the ratio of the above expression for the two temperatures. Thus, the simplified original function of the temperature acceleration coefficient can be expressed as:

[0076]

[0077] Where 'a' is A1 / A2, and since the pre-exponential factor is fixed, their ratio is 1; 'b' is -Ea / R. Therefore, 'b' is the relational parameter in the original function of the temperature acceleration coefficient, i.e., the parameter that needs to be fitted. Thus, by using each experimental temperature and its corresponding thermal shrinkage rate, 'b' can be fitted.

[0078] For example, in the above example, the relationship parameter b can be fitted as -19659 using the data in Table 1. Specifically, the relationship parameter b can be obtained by fitting the thermal shrinkage rate at two experimental temperatures. Alternatively, multiple relationship parameters can be obtained by fitting the thermal shrinkage rate at multiple experimental temperatures. The average value of these multiple relationship parameters is then used to determine the final relationship parameter b. For example, by fitting the thermal shrinkage rates of T1 and T2, T2 and T3, and T1 and T3 respectively, three relationship parameters can be obtained. The average value of these relationship parameters is then calculated to improve accuracy. Furthermore, the thermal shrinkage rate at each experimental temperature can be the average of multiple experiments, reducing the large fluctuations caused by a single experimental data point and further improving the reliability and accuracy of the data. In summary, by taking the average value twice, random errors can be reduced, reflecting the true condition of the diaphragm, while also reducing fitting bias and improving the reliability of the fitting results.

[0079] S103. Based on each experimental temperature and its corresponding thermal shrinkage rate, calculate multiple thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm using a function of the temperature acceleration coefficient.

[0080] In one embodiment of this application, since the temperature acceleration coefficient is a function of the ratio of two thermal shrinkage rates at two temperatures, a thermal shrinkage rate corresponding to the highest operating temperature can be calculated using the experimental temperature and its corresponding thermal shrinkage rate, and the highest operating temperature of the diaphragm.

[0081] Alternatively, based on the original function of the temperature acceleration coefficient, the thermal shrinkage rate corresponding to the highest operating temperature can be expressed as:

[0082]

[0083] Where T1 is the maximum operating temperature. T1 represents the thermal shrinkage rate corresponding to the highest operating temperature, and T2 represents the experimental temperature. This represents the thermal shrinkage rate corresponding to the experimental temperature. To ensure accuracy, it is necessary to calculate the thermal shrinkage rate corresponding to the highest operating temperature of the diaphragm using a function of the temperature acceleration coefficient, based on each experimental temperature and its corresponding thermal shrinkage rate, thereby calculating multiple thermal shrinkage rates.

[0084] For example, regarding the experimental temperature and data selected in the above example, if the maximum operating temperature is 50 degrees Celsius and the total lifespan is 25 years, then when calculating using the data in the first row of Table 1, the specific steps are as follows:

[0085] 1. When T1 = 50℃ and T2 = 90℃:

[0086]

[0087] Therefore, the thermal shrinkage rate of the diaphragm over 25 years is:

[0088]

[0089] 2. When T1 = 50℃ and T2 = 105℃:

[0090]

[0091] Therefore, the thermal shrinkage rate of the diaphragm over 25 years is:

[0092]

[0093] 3. When T1 = 50℃ and T2 = 130℃:

[0094]

[0095] Therefore, the thermal shrinkage rate of the diaphragm over 25 years is:

[0096]

[0097] As can be seen, different thermal shrinkage rates corresponding to different maximum operating temperatures can be obtained by using different experimental temperatures.

[0098] The inventors discovered through research that although a corresponding calculation function could be fitted by directly utilizing the relationship between the thermal shrinkage rate of the diaphragm and temperature to calculate the thermal shrinkage rate at the highest temperature, the calculated result was too small, and it was impossible to calculate multiple thermal shrinkage rates for further analysis, resulting in poor accuracy.

[0099] For example, using the same parameters as above, the following calculation function for the thermal shrinkage rate can be obtained:

[0100]

[0101] Therefore, when the temperature is 50℃, its thermal shrinkage rate is:

[0102]

[0103] Therefore, the thermal shrinkage rate of the diaphragm over 25 years is:

[0104]

[0105] Therefore, it can be seen that this method only calculates the thermal shrinkage rate of one diaphragm, and this value is only the middle of the three values ​​in the previous method. This results in an underestimation of the thermal shrinkage rate, which increases the risk of short circuit in the battery cell.

[0106] Based on this, alternatively, in another embodiment of this application, a specific implementation of step S102 is as follows: Figure 3 As shown, it includes the following steps:

[0107] S301. Randomly combine the heat shrinkage rates corresponding to each experimental temperature to obtain multiple heat shrinkage rate groups.

[0108] Each heat shrinkage rate group includes a heat shrinkage rate corresponding to each experimental temperature.

[0109] It should be noted that, as seen in the calculations in the examples above, the calculated thermal shrinkage rate of the diaphragm at 50℃ will differ when calculated at 90℃, 105℃, and 130℃ respectively. Clearly, the results will also differ when calculated at other temperatures. Therefore, this leads to an inability to effectively assess the true thermal shrinkage rate of the diaphragm. This is mainly because the physical properties of the diaphragm (such as thickness and porosity) vary during the diaphragm manufacturing process, resulting in different experimental results when diaphragms are taken from different locations. Furthermore, the experimental results are subject to fluctuations, such as measurement errors, uneven shrinkage, and differences between the test temperature and the actual temperature.

[0110] To eliminate errors and accurately assess the thermal shrinkage rate of the diaphragm, a large amount of data is needed for analysis and calculation to improve the reliability of the assessment. However, to reduce the number of tests and improve testing efficiency, in this embodiment, the thermal shrinkage rates corresponding to each experimental temperature are randomly combined to obtain multiple thermal shrinkage rate groups. In practical applications, the existing number of thermal shrinkage rates corresponding to each experimental temperature can be expanded into a large number of thermal shrinkage rate groups through permutation and combination. If the number of experimental temperatures is m, and each experimental temperature corresponds to w thermal shrinkage rate data, then a maximum of w can be randomly permuted and combined. m To improve testing efficiency, a maximum of 3 heat shrinkage rate groups can be created. For example, if there are 3 known experimental temperatures, and each experimental temperature corresponds to 3 heat shrinkage rates, then it can be expanded to a maximum of 3... 3 =27 heat shrinkage rate groups. Each heat shrinkage rate group includes heat shrinkage rates corresponding to multiple experimental temperatures.

[0111] By using random combinations, more possible experimental scenarios can be covered, thus more comprehensively reflecting the thermal shrinkage characteristics of the diaphragm at different temperatures. This increases data diversity, reduces randomness, and by generating a large number of thermal shrinkage rate groups, analysis can be conducted based on more data, thereby improving the reliability of the evaluation results.

[0112] S302. Using each heat shrinkage rate in each heat shrinkage rate group and its corresponding experimental temperature, fit the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group.

[0113] Since each heat shrinkage rate group contains heat shrinkage rates under different experimental temperatures, and the data are different, different functions of the temperature acceleration coefficient can be fitted using the data from each heat shrinkage rate group. The relationship parameter 'b' of the function of the temperature acceleration coefficient corresponding to each heat shrinkage rate group is different. The specific fitting method is described above and will not be repeated here.

[0114] Accordingly, in one embodiment of this application, step S103 includes:

[0115] For each heat shrinkage rate group, each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest working temperature of the diaphragm are substituted into the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group for calculation, so as to obtain multiple heat shrinkage rates corresponding to the highest working temperature of the diaphragm.

[0116] Specifically, since a function with a corresponding temperature acceleration coefficient is fitted for each heat shrinkage rate group, the function with the temperature acceleration coefficient corresponding to each heat shrinkage rate group can be used to calculate each data in each heat shrinkage rate group, thereby obtaining the heat shrinkage rate corresponding to the highest working temperature of each heat shrinkage rate group.

[0117] For example, as shown in Table 2 below, randomly combining the data in Table 1 yields 27 heat shrinkage rate groups. Then, for each data point in each heat shrinkage rate group, a heat shrinkage rate at 50℃ can be calculated, resulting in 81 heat shrinkage rates.

[0118] Table 2

[0119]

[0120] S104. Determine the final heat shrinkage rate at the highest operating temperature based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0121] It should be noted that since the heat shrinkage rates corresponding to the highest operating temperature calculated using various experimental data are different, there will be certain differences. Therefore, in order to ensure the accuracy of the evaluation, it is necessary to analyze the heat shrinkage rate of the highest operating temperature to ensure accuracy, based on the heat shrinkage rates corresponding to the highest operating temperature of the diaphragm, and use this as the final heat shrinkage rate of the highest operating temperature.

[0122] Optionally, in another embodiment of this application, step S104 is specifically implemented as follows: Figure 4 As shown, it includes the following steps:

[0123] S401. Calculate the standard deviation of each heat shrinkage rate corresponding to the highest operating temperature of the diaphragm.

[0124] It should be noted that due to differences in diaphragm properties and experimental errors, the obtained diaphragm shrinkage rate should be a range of data. Therefore, in this embodiment, a mathematical statistical method is used to analyze and select the data with high confidence as the final heat shrinkage rate. Thus, by calculating the standard deviation of each heat shrinkage rate corresponding to the highest operating temperature of the diaphragm, the deviation of the calculated heat shrinkage rate can be determined.

[0125] S402. Select the maximum heat shrinkage rate among all heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0126] To prevent the diaphragm from shrinking due to heat, resulting in its size being smaller than the design size and posing a short-circuit risk, the maximum heat shrinkage rate should not exceed the design value. Therefore, the maximum heat shrinkage rate among various heat shrinkage rates corresponding to the diaphragm's highest operating temperature is selected.

[0127] S403. Add the standard deviation of the maximum heat shrinkage rate to the maximum heat shrinkage rate corresponding to the highest working temperature of the diaphragm, and determine the maximum heat shrinkage rate as the final heat shrinkage rate at the highest working temperature.

[0128] To ensure safety, the maximum heat shrinkage rate needs to be added to the possible deviation, i.e., the standard deviation. To ensure accuracy, the standard deviation of a certain confidence interval is considered. Therefore, a certain multiple is preset, and then the maximum heat shrinkage rate is added to the standard deviation of the preset multiple to obtain the maximum heat shrinkage rate that is most likely to occur within the confidence interval.

[0129] The preset multiplier can be set to 3. Since the calculated data follows a σ distribution, 3σ can represent a 99.7% confidence interval, meaning that considering the σ distribution can display 99.7% of the test data, ensuring the reliability of the results.

[0130] For example, among the 81 values ​​calculated in Table 2 above, the maximum value is 0.0000158%, and the standard deviation of the 81 values ​​is s=0.0000018%. Therefore, the maximum value of the thermal shrinkage rate corresponding to the highest working temperature of the diaphragm is: θ=0.0000158%+3*s=0.0000212%.

[0131] By calculating the standard deviation, the dispersion of the data can be quantified, i.e. the difference between various heat shrinkage rates. This allows for a more comprehensive assessment of the diaphragm's heat shrinkage at the highest operating temperature, rather than relying solely on a single heat shrinkage rate value. This better reflects the differences caused by the diaphragm's physical properties and the fluctuations in the experiment, thus providing a more realistic assessment of the diaphragm's heat shrinkage performance. At the same time, more comprehensive data can be obtained with fewer tests, thereby improving testing efficiency.

[0132] To verify the feasibility of the preset multiplier and the effectiveness of the proposed solution, a higher temperature was selected to replace the maximum operating temperature for calculation. Experimental data for this higher temperature was then obtained. Finally, the calculated data was compared with the experimental data for verification.

[0133] For example, using experimental data at 90℃, 105℃, and 130℃, the thermal shrinkage rate of the diaphragm at 140℃ is calculated, and this data is compared with the experimental data at 140℃. The reason for choosing 140℃ is that, as can be seen from the DSC curve of the diaphragm, the vertical axis begins to decrease above 130℃, indicating that the enthalpy change of the diaphragm is different before and after 130℃. Therefore, the thermal shrinkage rates at 140℃ calculated using the experimental data at 90℃, 105℃, and 130℃ according to the aforementioned embodiment are definitely greater than the thermal shrinkage rates obtained from the 140℃ experiment. In this embodiment, by using the experimental data at 90℃, 105℃, and 130℃ and selecting an appropriate preset multiple, the calculated thermal shrinkage rate at 140℃ can cover the thermal shrinkage rate obtained from the 140℃ experiment. That is, the calculated thermal shrinkage rates at 140℃ include the thermal shrinkage rate obtained from the 140℃ experiment, thus covering the range from 50℃ to 130℃, i.e., the thermal shrinkage rate at 50℃ calculated by arbitrarily selecting an experimental temperature.

[0134] The specific calculation of the diaphragm heat shrinkage rate at 140℃ based on experimental data at 90℃, 105℃, and 130℃ is shown in Table 3.

[0135] Table 3

[0136]

[0137] Therefore, it can be seen that there are 81 calculated shrinkage rates of the diaphragm at 140℃, with the maximum value MAX being 9.56% and the standard deviation of the 81 values ​​s=0.97%. Therefore, the final heat shrinkage rates calculated using 3 times and 2 times are: θ1=MAX+3*s=12.46% and θ2=MAX+2*s=11.49%.

[0138] The experimental results at 140℃ are shown in Table 4 below:

[0139] Table 4

[0140]

[0141] Therefore, it can be seen that the average measured data of the diaphragm heat shrinkage rate at 140℃ is between θ1 and θ2. This indicates that when the multiplier is set to 3, the heat shrinkage rate calculated based on the experimental data at 90℃, 105℃, and 130℃ can cover the experimental results at 140℃. That is, the heat shrinkage rates calculated based on the experimental data at 90℃, 105℃, and 130℃ include the experimental results at 140℃. However, the results calculated using the preset multiplier of 2 cannot cover the experimental results at 140℃. Therefore, setting the multiplier to 3 is preferable. In other words, by selecting an appropriate preset multiplier, the heat shrinkage rate when the working temperature exceeds the heat-melting temperature can be corrected to conform to the actual situation, thereby improving overall applicability.

[0142] Optionally, in another optional embodiment of step 104, multiple heat shrinkage rates corresponding to different experimental temperatures and their corresponding heat shrinkage rates, as well as the highest working temperature of the diaphragm, can be calculated. The average value of the multiple heat shrinkage rates is then calculated to obtain the final heat shrinkage rate corresponding to the highest working temperature, i.e., the final heat shrinkage rate at the highest working temperature, in order to simplify the method and reduce the amount of calculation.

[0143] S105. Calculate the thermal shrinkage rate of the diaphragm over its entire lifespan using the final thermal shrinkage rate at the highest operating temperature and the diaphragm's total lifespan.

[0144] Since the final thermal shrinkage rate at the highest operating temperature is calculated using experimental data per unit time, it represents the shrinkage rate of the diaphragm per unit time at the highest operating temperature. Therefore, the thermal shrinkage rate of the diaphragm over its entire life cycle must be calculated using the diaphragm's entire life cycle.

[0145] Specifically, the entire lifespan of the diaphragm can be converted to the same unit of time as the experiment, and then the final thermal shrinkage rate at the highest operating temperature can be multiplied by the entire lifespan of the diaphragm to obtain the thermal shrinkage rate of the diaphragm over its entire lifespan.

[0146] For example, if the final heat shrinkage rate at the highest operating temperature calculated for the above example is 0.0000212%, then the heat shrinkage rate over the entire lifespan of the diaphragm is: .

[0147] S106. The thermal shrinkage assessment result of the diaphragm is determined by comparing the thermal shrinkage rate of the diaphragm throughout its entire life cycle with the shrinkage rate threshold of the diaphragm.

[0148] Specifically, compare whether the thermal shrinkage rate of the diaphragm over its entire lifespan exceeds the diaphragm's shrinkage rate threshold. If the thermal shrinkage rate over the diaphragm's entire lifespan exceeds the threshold, it indicates a risk. If the thermal shrinkage rate over the diaphragm's entire lifespan does not exceed the threshold, it indicates no risk.

[0149] Optionally, the separator shrinkage threshold is determined based on the minimum dimension by which the separator extends beyond the negative electrode of the battery. Further, the shrinkage threshold can be determined by multiplying the minimum value of the separator's width extension beyond the negative electrode by 2. In practical applications, the battery shrinkage threshold can be determined by the cell's overhang design dimensions, i.e., determining the limit value of the shrinkage dimension and calculating the limit value of the shrinkage rate. For example, a lithium iron phosphate cell uses PP as the separator material, and its core design dimensions are: the separator width dimension is 100mm. The cell bottom overhang design dimensions are: the separator extends beyond the negative electrode in the width direction by 2.5mm; the cell top overhang design dimensions are: the separator extends beyond the negative electrode in the width direction by 4mm. Therefore, to ensure that the separator is wider than the negative electrode, the limit value of the separator's thermal shrinkage is 2.5mm. If the separator shrinks by 5%, the top and bottom will shrink by 2.5%, resulting in a 2.5mm reduction in the top and bottom dimensions. Therefore, it is necessary to ensure that the separator's thermal shrinkage rate is less than 5% throughout its entire lifespan.

[0150] Therefore, the calculated thermal shrinkage rate of the separator over its entire lifespan, based on the above example, is 4.64%, which is less than the shrinkage rate threshold of 5%. This indicates that even if the separator is continuously exposed to 50°C for 25 years, the maximum thermal shrinkage rate will be 4.64%, which is less than 5%, posing no risk. Furthermore, in actual use, the battery cell only reaches 50°C for certain periods, while the temperature remains below 50°C at other times. Therefore, the thermal shrinkage rate of the separator will be far less than 5%, meaning that the battery cell will not experience a short circuit between its positive and negative terminals due to separator thermal shrinkage within 25 years.

[0151] This application provides a method for evaluating the thermal stability of a diaphragm. Multiple heat shrinkage experiments are conducted on the diaphragm at various experimental temperatures to obtain multiple heat shrinkage rates corresponding to each experimental temperature. Then, using these heat shrinkage rates at each experimental temperature, a function of the temperature acceleration factor of the diaphragm's heat shrinkage rate is fitted. The temperature acceleration factor is the ratio of the diaphragm's heat shrinkage rates at two different temperatures. Next, based on each experimental temperature and its corresponding heat shrinkage rate, multiple heat shrinkage rates corresponding to the diaphragm's highest operating temperature are calculated using the function of the temperature acceleration factor. Thus, by understanding the relationship between the ratio of the diaphragm's heat shrinkage rates at different temperatures and temperature, a more accurate highest operating temperature can be calculated. Then, based on the heat shrinkage rates corresponding to the diaphragm's highest operating temperature, the final heat shrinkage rate at the highest operating temperature is determined. By using the calculated multiple heat shrinkage rates, any existing problems are eliminated, and an accurate heat shrinkage rate for the highest operating temperature is obtained. Therefore, obtaining accurate experimental data through higher experimental temperatures allows for the calculation of an accurate shrinkage rate at the highest operating temperature. Then, using the final thermal shrinkage rate at the highest operating temperature and the entire life cycle of the separator, the thermal shrinkage rate of the separator throughout its entire life cycle is calculated, thereby analyzing the thermal shrinkage rate of the separator throughout its entire life cycle. Finally, by comparing the thermal shrinkage rate of the separator throughout its entire life cycle with the separator shrinkage rate threshold, the thermal shrinkage assessment result of the separator is determined, thus realizing an accurate assessment of the thermal shrinkage of the separator throughout the entire working life cycle of the battery.

[0152] Another embodiment of this application provides a device for evaluating the thermal stability of a diaphragm, such as... Figure 5 As shown, it includes:

[0153] Experimental unit 501 is used to select multiple experimental temperatures to conduct multiple heat shrinkage experiments on the diaphragm, and obtain multiple heat shrinkage rates corresponding to each experimental temperature.

[0154] Fitting unit 502 is used to fit a function of the temperature acceleration factor of the diaphragm's thermal shrinkage rate using the thermal shrinkage rates corresponding to each experimental temperature. The temperature acceleration factor is the ratio of the thermal shrinkage rates of the diaphragm at two different temperatures.

[0155] The first calculation unit 503 is used to calculate multiple thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm based on each experimental temperature and its corresponding thermal shrinkage rate, using a function of the temperature acceleration coefficient.

[0156] The second calculation unit 504 is used to determine the final heat shrinkage rate at the highest operating temperature based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0157] The third calculation unit 505 is used to calculate the thermal shrinkage rate of the diaphragm over its entire life cycle by using the final thermal shrinkage rate at the highest operating temperature and the entire life cycle of the diaphragm.

[0158] Evaluation unit 506 is used to determine the thermal shrinkage evaluation result of the diaphragm by comparing the thermal shrinkage rate of the diaphragm throughout its entire life cycle with the shrinkage rate threshold of the diaphragm.

[0159] Optionally, in another embodiment of the diaphragm thermal stability evaluation apparatus provided in this application, the fitting unit includes:

[0160] The parameter fitting unit is used to fit the relational parameters in the original function of the temperature acceleration coefficient using various experimental temperatures and their corresponding thermal shrinkage rates. The original function of the temperature acceleration coefficient is the ratio expressed by the Arrhenius formula for the diaphragm at the two temperatures.

[0161] The substituting unit is used to substitute the fitted relational parameters into the original function of the temperature acceleration coefficient to obtain the function of the temperature acceleration coefficient of the diaphragm's thermal shrinkage rate.

[0162] Optionally, in another embodiment of the diaphragm thermal stability evaluation device provided in this application, the fitting unit includes:

[0163] The combination unit is used to randomly combine the various heat shrinkage rates corresponding to different experimental temperatures to obtain multiple heat shrinkage rate groups. Each heat shrinkage rate group includes one heat shrinkage rate corresponding to each experimental temperature.

[0164] The function fitting unit is used to fit a function of the temperature acceleration coefficient corresponding to each heat shrinkage rate group using each heat shrinkage rate and its corresponding experimental temperature.

[0165] Optionally, in another embodiment of the diaphragm thermal stability evaluation device provided in this application, the first calculation unit includes:

[0166] The first calculation subunit is used to calculate, for each heat shrinkage rate group, each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest working temperature of the diaphragm are substituted into the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group, so as to obtain multiple heat shrinkage rates corresponding to the highest working temperature of the diaphragm.

[0167] In this embodiment of the application, the second computing unit includes:

[0168] The standard deviation calculation unit is used to calculate the standard deviation of each heat shrinkage rate corresponding to the highest operating temperature of the diaphragm.

[0169] The selection unit is used to select the maximum heat shrinkage rate among the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

[0170] The maximum value calculation unit is used to add the standard deviation of a preset multiple to the maximum heat shrinkage rate to obtain the maximum heat shrinkage rate corresponding to the highest operating temperature of the diaphragm, and to determine the maximum heat shrinkage rate as the final heat shrinkage rate at the highest operating temperature.

[0171] It should be noted that the specific working process of each unit provided in the above embodiments of this application can be referred to the implementation process of the corresponding steps in the above method embodiments, and will not be repeated here.

[0172] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0173] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the thermal stability of a diaphragm, characterized in that, include: Multiple thermal shrinkage experiments were conducted on the diaphragm at various experimental temperatures to obtain multiple thermal shrinkage rates corresponding to each experimental temperature. Using the thermal shrinkage rates corresponding to each of the experimental temperatures, a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm is fitted; wherein, the temperature acceleration coefficient is the ratio of the thermal shrinkage rates of the diaphragm at two different temperatures; Based on each of the experimental temperatures and their corresponding thermal shrinkage rates, multiple thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm are calculated using a function of the temperature acceleration coefficient. Based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm, determine the final heat shrinkage rate at the highest operating temperature; The thermal shrinkage rate of the diaphragm over its entire lifespan is calculated using the final thermal shrinkage rate at the highest operating temperature and the entire lifespan of the diaphragm. The thermal shrinkage assessment result of the diaphragm is determined by comparing the thermal shrinkage rate of the diaphragm over its entire life cycle with the shrinkage rate threshold of the diaphragm. The function that fits the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm using the thermal shrinkage rates corresponding to each of the experimental temperatures includes: Using the experimental temperatures and their corresponding thermal shrinkage rates, the relational parameters in the original function of the temperature acceleration coefficient are fitted; wherein, the original function of the temperature acceleration coefficient is the ratio expressed by the Arrhenius formula for the diaphragm at the two temperatures; Substituting the fitted relationship parameters into the original function of the temperature acceleration coefficient, the function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm is obtained; The step of determining the final heat shrinkage rate at the highest operating temperature based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm includes: Calculate the standard deviation of each thermal shrinkage rate corresponding to the highest operating temperature of the diaphragm; Select the maximum heat shrinkage rate among the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm; The maximum heat shrinkage rate is added to the standard deviation by a preset multiple to obtain the maximum heat shrinkage rate corresponding to the highest operating temperature of the diaphragm, and the maximum heat shrinkage rate is determined as the final heat shrinkage rate at the highest operating temperature.

2. The method according to claim 1, characterized in that, The function that fits the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm using the thermal shrinkage rates corresponding to each of the experimental temperatures includes: The heat shrinkage rates corresponding to each of the experimental temperatures are randomly combined to obtain multiple heat shrinkage rate groups; wherein each heat shrinkage rate group includes one heat shrinkage rate corresponding to each of the experimental temperatures; By using each heat shrinkage rate in each heat shrinkage rate group and its corresponding experimental temperature, a function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group is fitted.

3. The method according to claim 2, characterized in that, The calculation of multiple thermal shrinkage rates corresponding to the highest operating temperature of the diaphragm, based on each of the experimental temperatures and their corresponding thermal shrinkage rates, using a function of the temperature acceleration coefficient, includes: For each heat shrinkage rate group, each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest operating temperature of the diaphragm are substituted into the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group for calculation, so as to obtain multiple heat shrinkage rates corresponding to the highest operating temperature of the diaphragm.

4. The method according to claim 1, characterized in that, The shrinkage threshold of the separator is determined based on the minimum size of the separator that exceeds the negative electrode of the battery.

5. A device for evaluating the thermal stability of a diaphragm, characterized in that, include: The experimental unit is used to select multiple experimental temperatures to conduct multiple heat shrinkage experiments on the diaphragm, and obtain multiple heat shrinkage rates corresponding to each experimental temperature. The fitting unit is used to fit a function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm using the thermal shrinkage rates corresponding to each of the experimental temperatures; wherein the temperature acceleration coefficient is the ratio of the thermal shrinkage rates of the diaphragm at two different temperatures. The first calculation unit is used to calculate multiple thermal shrinkage rates corresponding to the highest working temperature of the diaphragm based on each of the experimental temperatures and their corresponding thermal shrinkage rates, using a function of the temperature acceleration coefficient. The second calculation unit is used to determine the final heat shrinkage rate at the highest operating temperature based on the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm. The third calculation unit is used to calculate the thermal shrinkage rate of the diaphragm over its entire life cycle using the final thermal shrinkage rate at the highest operating temperature and the entire life cycle of the diaphragm. An evaluation unit is used to determine the thermal shrinkage evaluation result of the diaphragm by comparing the thermal shrinkage rate of the diaphragm over its entire life cycle with a shrinkage rate threshold of the diaphragm. The fitting unit includes: The parameter fitting unit is used to fit the relational parameters in the original function of the temperature acceleration coefficient using each of the experimental temperatures and their corresponding thermal shrinkage rates; wherein the original function of the temperature acceleration coefficient is the ratio expressed by the Arrhenius formula for the diaphragm at the two temperatures. The substitution unit is used to substitute the fitted relationship parameters into the original function of the temperature acceleration coefficient to obtain the function of the temperature acceleration coefficient of the thermal shrinkage rate of the diaphragm. The second computing unit includes: The standard deviation calculation unit is used to calculate the standard deviation of each heat shrinkage rate corresponding to the highest operating temperature of the diaphragm. The selection unit is used to select the maximum heat shrinkage rate among the various heat shrinkage rates corresponding to the highest operating temperature of the diaphragm. The maximum value calculation unit is used to add the standard deviation of a preset multiple to the maximum heat shrinkage rate to obtain the maximum heat shrinkage rate corresponding to the highest operating temperature of the diaphragm, and to determine the maximum heat shrinkage rate as the final heat shrinkage rate at the highest operating temperature.

6. The apparatus according to claim 5, characterized in that, The fitting unit includes: A combination unit is used to randomly combine the heat shrinkage rates corresponding to each of the experimental temperatures to obtain multiple heat shrinkage rate groups; wherein each heat shrinkage rate group includes a heat shrinkage rate corresponding to each of the experimental temperatures; The function fitting unit is used to fit a function of the temperature acceleration coefficient corresponding to each heat shrinkage rate group using each heat shrinkage rate in each heat shrinkage rate group and its corresponding experimental temperature.

7. The apparatus according to claim 6, characterized in that, The first computing unit includes: The first calculation subunit is used to calculate, for each heat shrinkage rate group, each heat shrinkage rate in the heat shrinkage rate group and its corresponding experimental temperature and the highest working temperature of the diaphragm, by substituting them into the function of the temperature acceleration coefficient corresponding to the heat shrinkage rate group, so as to obtain multiple heat shrinkage rates corresponding to the highest working temperature of the diaphragm.

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