Lithium battery thermal runaway early warning method based on multi-parameter fusion analysis

Abstract

The invention discloses a lithium battery thermal runaway early warning method based on multi-parameter fusion analysis, and the method comprises the steps: collecting the real-time state parameters of a lithium battery, and the state parameters comprise the battery voltage, the surface temperature, the dependent variable and the environment gas concentration; each parameter in the state parameters is substituted into a corresponding safety state function to obtain a battery safety state corresponding to each parameter, and the safety state function corresponding to each parameter is obtained by fitting state parameters acquired in a battery thermal runaway process in advance; calculating a comprehensive safety state value of the battery based on the battery safety state corresponding to each parameter and the weight corresponding to each parameter; judging the current risk level of the battery according to the comprehensive safety state value, and performing early warning based on the risk level; according to the method, the problem of fusion of multiple parameters in the thermal runaway early warning process and the problem of lack of quantitative description for the safety state of the battery are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and in particular to a lithium battery thermal runaway early warning method based on multi-parameter fusion analysis. Background Art

[0002] As global environmental problems become increasingly serious, my country has proposed a "dual carbon" goal. Guided by this goal, my country will accelerate the green and low-carbon transformation of energy and rapidly develop a variety of technologies, mainly lithium-ion batteries.

[0003] However, the frequent battery fire and explosion accidents in recent years have threatened the healthy development of the new energy industry, and the safety of lithium batteries has become the biggest problem restricting the development of the industry. The safety of lithium batteries is closely related to their thermal runaway. There are many factors that induce thermal runaway of lithium batteries. In summary, there are electrical abuse, thermal abuse and mechanical abuse. These abuses will cause short circuits in lithium batteries, resulting in internal temperature rise, a series of side reactions, and ultimately thermal runaway. At the same time, the national standard stipulates that the occurrence of thermal runaway should be warned at least five minutes in advance to leave enough time for people to escape.

[0004] So far, there are many methods for thermal runaway warning of lithium batteries, most of which are based on various signals of various batteries, such as voltage, temperature, current and other signals. The collected signals are processed by the battery management system, and the threshold is set. When the corresponding data, such as temperature or the rate of temperature rise, reaches the threshold, an alarm is issued and fed back to the driver. In addition, there are warning methods based on other signals, such as gas signals. Current research has shown that lithium batteries will release a large amount of gas during thermal runaway, such as CO, CO2 and H2. Therefore, related research on thermal runaway warning based on gas signals has also been conducted.

[0005] At present, the thermal runaway detection methods of lithium batteries focus on the use of voltage and temperature data, and mainly divide the thermal runaway into different stages based on the different intervals of these data. The problem with this is that it focuses on the analysis of a single signal and ignores the interaction between different signals in the thermal runaway process. The thresholds of its various parameters will also change with the changes in the battery. In addition, there is a lack of quantitative description of the battery safety status. The current mainstream thermal runaway warning methods only make a qualitative description of the thermal runaway process, which results in insufficient accuracy.

[0006] In the related art, the patent application document with publication number CN116520153A proposes to improve the accuracy of thermal runaway prediction of cascade lithium batteries by comprehensive evaluation through multi-angle parameters such as voltage, temperature, air pressure, and heat generation. However, this scheme is essentially a multi-level early warning method, in which three detection data groups represent each level of the three-level early warning in turn, and does not achieve quantitative evaluation of the battery safety status. The document "Multi-parameter characteristic analysis and thermal runaway suppression technology of overcharge thermal runaway of lithium iron phosphate energy storage batteries, Tang Jia et al., High Voltage Technology, 2023-12-06" proposes to build an in-situ test platform for multi-parameter characteristics of battery overcharge thermal runaway, and place the battery inside the module shell for testing to simulate the static closed environment of the actual battery. The designed gas in-situ monitoring system is used to monitor the concentrations of three gases, CO, CO2, and H2, and high-temperature resistance strain gauges are used to measure the battery overcharge expansion deformation; the overcharge thermal runaway phenomenon and voltage, temperature, gas production, and deformation characteristics of batteries with different charging rates and different capacities are studied. In order to suppress the battery thermal runaway, a self-triggered battery thermal runaway suppression device based on thermosensitive insulating materials is designed, but this scheme does not study how to provide thermal runaway warning based on voltage, temperature, gas production, deformation and other characteristics.

[0007] Therefore, it is extremely meaningful to find a method that can integrate multiple parameters in thermal runaway warning and make a quantitative description of thermal runaway warning to improve the precision and accuracy of thermal runaway warning. Summary of the invention

[0008] The technical problem to be solved by the present invention is how to solve the problem of fusing multiple parameters in the thermal runaway warning process and the problem of lack of quantitative description of the battery safety status.

[0009] The present invention solves the above technical problems by the following technical means:

[0010] The present invention proposes a lithium battery thermal runaway early warning method based on multi-parameter fusion analysis, the method comprising:

[0011] Collecting real-time state parameters of the lithium battery, including battery voltage, surface temperature, strain and ambient gas concentration;

[0012] Substituting each parameter in the state parameters into the corresponding safety state function to obtain the battery safety state corresponding to each parameter, wherein the safety state function corresponding to each parameter is obtained by fitting the state parameters collected in advance during the battery thermal runaway process;

[0013] Based on the battery safety status corresponding to each parameter and the weight corresponding to each parameter, calculate the comprehensive safety status value of the battery;

[0014] The current risk level of the battery is determined according to the comprehensive safety status value, and an early warning is issued based on the risk level.

[0015] Furthermore, the fitting process of the safety state function corresponding to each parameter includes:

[0016] Use the experimental device to conduct thermal runaway experiments on lithium batteries and collect state parameters during the thermal runaway experiments of lithium batteries;

[0017] Processing the state parameters collected during the experiment, and using an entropy weight method to determine the weights corresponding to each of the state parameters in the safety state assessment;

[0018] The safety state function and safety margin of each parameter in the state parameters are determined, and the state parameters of the experimental process are used for fitting to obtain the safety state function corresponding to each parameter.

[0019] Furthermore, the state parameters of the collected experimental process are processed, and the weights corresponding to each parameter in the state parameters in the safety state assessment are determined by using an entropy weight method, including:

[0020] The decision matrix D is constructed by using each parameter in the state parameters of the experimental process. ij ) m*n , where q ij It represents the evaluation value of the i-th evaluation object on the j-th indicator, m is the number of warning parameters, and n is the number of types of warning parameters;

[0021] Normalizing the indicator elements in the decision matrix to obtain normalized indicator element values;

[0022] Calculate the indicator risk weight based on the normalized indicator element value;

[0023] Calculate the entropy value according to the risk weight of the indicator;

[0024] According to the entropy value, the weight corresponding to the parameter is determined.

[0025] Furthermore, the first safety state function corresponding to the battery voltage is:

[0026]

[0027] In the formula, x is the selected parameter, x min 、x max are the lower and upper limits of the battery's safe working state, respectively; m1, d1, m2, and d2 are the safety state function parameter values ​​under undervoltage and overvoltage conditions, respectively.

[0028] Furthermore, the second safety state functions corresponding to the surface temperature, strain and ambient gas concentration are all:

[0029]

[0030] In the formula, x is the selected parameter, x limit is the safety margin obtained by the experiment, and m and d are the safety state function parameters.

[0031] Furthermore, the determining of the safety state function and safety margin of each parameter in the state parameters, and fitting using the state parameters of the experimental process to obtain the safety state function corresponding to each parameter, includes:

[0032] Determine the safety margin according to the thermal runaway test conditions of the lithium battery, wherein the safety margin includes an absolutely safe range of the battery and a relatively safe range of the battery;

[0033] Substitute the absolute safety interval and the relative safety interval of the battery into the safety state function of each parameter, determine the fitting coefficient in the safety state function, and obtain the safety state function corresponding to each parameter.

[0034] Furthermore, the safety state function corresponding to the battery voltage is:

[0035]

[0036] In the formula, f volt (v) is the safety state function corresponding to the battery voltage, and v is the battery voltage collected in real time.

[0037] Furthermore, the safety state function corresponding to the surface temperature is:

[0038]

[0039] In the formula, f tem (t) is the safety state function corresponding to the surface temperature, and t is the surface temperature collected in real time;

[0040] The safety state function corresponding to the strain variable is:

[0041]

[0042] In the formula, f strain (s) is the safety state function corresponding to the strain variable, and s is the strain variable collected in real time;

[0043] The safety state function corresponding to the ambient gas concentration is:

[0044]

[0045] In the formula, f gas (g) is the safety state function corresponding to the ambient gas concentration, and g is the ambient gas concentration collected in real time.

[0046] Furthermore, based on the battery safety status corresponding to each parameter and the weight corresponding to each parameter, the comprehensive safety status value of the battery is calculated, and the formula is expressed as:

[0047] f safety =W1f volt (v)+W2f tem (t)+W3f strain (s)+W4f gas (g)

[0048] In the formula, f safety is the comprehensive safety status value of the battery, f volt (v) is the safety state function corresponding to the battery voltage, f tem (t) is the safety state function corresponding to the surface temperature, f strain (s) is the safety state function corresponding to the strain variable, f gas (g) is the safety state function corresponding to the ambient gas concentration, v, t, s, g are respectively the battery voltage, surface temperature, strain and ambient gas concentration collected in real time, W1, W2, W3, W4 are respectively the weights corresponding to the battery voltage, surface temperature, strain and ambient gas concentration.

[0049] Further, determining the current risk level of the battery according to the comprehensive safety status value and issuing an early warning based on the risk level includes:

[0050] At 0.95 ≤ f safety When ≤1, it is determined that the lithium battery is currently at level 1 risk and a level 1 warning is issued;

[0051] At 0.9 ≤ f safety When <0.95, the lithium battery is determined to be at level 2 risk and a level 2 warning is issued;

[0052] At 0.8 ≤ f safety When <0.9, it is determined that the lithium battery is currently at level 3 risk and a level 3 warning is issued;

[0053] In f safety When <0.8, the lithium battery is determined to be in a dangerous state and a thermal runaway warning is issued;

[0054] Among them, f safety is the comprehensive safety status value.

[0055] The advantages of the present invention are:

[0056] (1) The present invention uses battery voltage, surface temperature, strain, and gas data signals as thermal runaway warning signals, pre-fits the experimental data collected during the battery thermal runaway process to obtain the safety state function corresponding to each parameter signal, and calculates the weight corresponding to each parameter in the safety state assessment. When performing thermal runaway warning on the lithium battery to be tested, the parameter signals collected in real time are substituted into the corresponding safety state function to obtain the battery safety state corresponding to each parameter, and then the comprehensive safety state value of the battery is calculated based on the battery safety state corresponding to each parameter and the weight corresponding to each parameter, and the comprehensive safety state value of the battery is used as the judgment basis for the warning; the present invention calculates the safety state of the battery by introducing the concept of safety state, and uses it as the judgment basis, thereby solving the problems of the existing thermal runaway warning focusing on a single parameter and the resulting late reporting and missed reporting, and significantly improving the accuracy and effectiveness of the battery thermal runaway warning; in addition, it also solves the existing problem of lack of quantitative evaluation of battery safety state. At the same time, this method can be applied to online evaluation and can be integrated in a battery management system, and has broad application prospects.

[0057] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a flow chart of a lithium battery thermal runaway early warning method based on multi-parameter fusion analysis proposed in one embodiment of the present invention;

[0059] Figure 2 is a schematic diagram of voltage variation over time of a lithium-ion battery during thermal runaway in one embodiment of the present invention;

[0060] Figure 3 is a schematic diagram of the change of the surface temperature of a lithium-ion battery with time during its thermal runaway process in one embodiment of the present invention;

[0061] Figure 4 is a schematic diagram of the change of strain over time of a lithium-ion battery during its thermal runaway process in one embodiment of the present invention;

[0062] Figure 5 is a schematic diagram of changes in ambient gas concentration over time during thermal runaway of a lithium-ion battery in one embodiment of the present invention, wherein the gas includes CO, CO2, and H2;

[0063] Figure 6 It is a schematic diagram of the weights of various parameters in the safety state calculation obtained by calculating according to the entropy weight method in one embodiment of the present invention;

[0064] Figure 7is a schematic diagram of the change in shape of a lithium-ion battery over time during its thermal runaway process in one embodiment of the present invention;

[0065] Figure 8 is a schematic diagram of the change of the safety state of a lithium-ion battery over time during its thermal runaway process in one embodiment of the present invention;

[0066] Fig. 9 is a diagram of the position distribution of each sensor and an experimental device in one embodiment of the present invention;

[0067] Fig.10 It is a schematic diagram of a process of performing quantitative early warning evaluation based on battery safety status in one embodiment of the present invention. DETAILED DESCRIPTION

[0068] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] like Figure 1 As shown, a lithium battery thermal runaway early warning method based on multi-parameter fusion analysis is proposed in one embodiment of the present invention, and the method comprises the following steps:

[0070] S10, collecting real-time state parameters of the lithium battery, wherein the state parameters include battery voltage, surface temperature, strain and ambient gas concentration;

[0071] S20, substituting each parameter in the state parameters into a corresponding safety state function to obtain a battery safety state corresponding to each parameter, wherein the safety state function corresponding to each parameter is obtained by fitting the state parameters collected in advance during the battery thermal runaway process;

[0072] S30, calculating a comprehensive safety status value of the battery based on the battery safety status corresponding to each parameter and the weight corresponding to each parameter;

[0073] S40: Determine the current risk level of the battery according to the comprehensive safety status value, and issue an early warning based on the risk level.

[0074] This embodiment introduces the concept of safety status to calculate the safety status of the battery, and uses this as the basis for judgment, thereby solving the problems of existing thermal runaway warnings focusing on a single parameter and the resulting late reporting and missed reporting, and significantly improving the accuracy and effectiveness of battery thermal runaway warnings. In addition, a quantitative assessment is made on the safety status of the battery itself, and a thermal runaway warning method is proposed, thereby solving the existing problem of lack of quantitative assessment of the battery safety status. At the same time, this method can be applied to online evaluation and can be integrated in a battery management system, and has broad application prospects.

[0075] As a further preferred technical solution, the fitting process of the safety state function corresponding to each parameter in step S20 includes the following steps:

[0076] S1. Use the experimental platform to conduct a thermal runaway experiment on the lithium battery and collect state parameters during the thermal runaway experiment of the lithium battery;

[0077] Specifically, this embodiment uses relevant devices to conduct experiments and collect values ​​of various parameters during battery thermal runaway, including battery voltage, temperature, strain, and concentrations of gases such as CO, CO2, and H2 released by the battery.

[0078] like Figure 2 As shown, the experimental platform includes an experimental device, a signal acquisition element, and a data acquisition device; the experimental device includes a battery charging and discharging cabinet and an explosion-proof box; the signal acquisition element includes a thermocouple, a strain gauge, and a gas sensor, wherein the gas sensor used is an SGP30 sensor; the data acquisition device includes a temperature measuring instrument, a strain measuring instrument, a single-chip microcomputer connected to the gas sensor, and a host computer connecting the charging and discharging cabinet and the above instruments. The strain gauge is attached to the center of the experimental battery, and four thermocouples are attached to the bottom, middle, and bottom of the positive and negative poles of the battery.

[0079] It should be noted that the thermal runaway experiment specifically refers to first discharging the battery at a 1C rate to reduce the SOC of the battery to 0, and then overcharging at the same charging rate until the battery exhibits thermal runaway.

[0080] It should be understood that in some specific embodiments, the staff may perform sampling at different sampling rates according to actual conditions, which will not be elaborated here.

[0081] Specifically, the measured data are as follows: Figure 3 This is a schematic diagram of the voltage change over time of a specific lithium-ion battery during its thermal runaway process. Figure 4 A schematic diagram showing the change of surface temperature of a specific lithium-ion battery over time during its thermal runaway process; Figure 5 For a specific lithium-ion battery, the strain variation over time during its thermal runaway process is attempted. Figure 6The following is a schematic diagram of the change of ambient gas concentration over time during the thermal runaway process of a specific lithium-ion battery. Figure 3 It can be clearly seen that during the battery thermal runaway process, the voltage first increases slowly and then drops sharply. When the voltage drops sharply, thermal runaway is about to occur. Figure 4 It can be clearly seen that during the battery thermal runaway process, the temperature first rises slowly and then rises sharply; Figure 5 It can be clearly seen that during the battery thermal runaway process, the strain first increases slowly and then increases sharply. Figure 6 It can be clearly seen that during the battery thermal runaway process, the ambient gas concentration shows a characteristic of first changing slightly and then changing dramatically.

[0082] The safety function can be calculated based on the experimental data, the characteristics of the experimental data and the safety-related parameters for normal operation of the battery as shown in Table 1. It can be seen that the strain variable is the first to change among the above parameters.

[0083] Table 1 Safety related parameters for normal battery operation

[0084] parameter Lithium iron phosphate battery Standard voltage 3.4V Operating temperature 0-55℃ Overcharge voltage 3.7V Over discharge voltage 2.5V

[0085] S2. Processing the state parameters collected during the experiment, and using an entropy weight method to determine the weight corresponding to each parameter in the state parameters in the safety state assessment;

[0086] S3. Determine the safety state function and safety margin of each parameter in the state parameters, and use the state parameters of the experimental process to perform fitting to obtain the safety state function corresponding to each parameter.

[0087] It should be noted that the four parameters of battery voltage, surface temperature, strain and ambient gas concentration are specifically selected in this embodiment because these four parameters can characterize the entire stage of battery thermal runaway. The earliest change in the strain in the process of thermal runaway is the change in the battery. The corresponding battery state may have bulging and other phenomena at this time. As the thermal runaway continues, the battery voltage and surface temperature will increase in turn. As the thermal runaway further occurs, the battery will eventually rupture, and a large amount of internally accumulated gas will be released, which is also a precursor to thermal runaway. Therefore, these four parameters can run through the entire process of battery thermal runaway. Even for batteries of different models, their materials, surface hardness and packaging methods are not exactly the same, but the above parameters can describe the entire process of thermal runaway.

[0088] As a further preferred technical solution, the step S2: processing the state parameters of the collected experimental process, and using the entropy weight method to determine the corresponding weight of each parameter in the state parameter in the safety state assessment, specifically includes the following steps:

[0089] S21, construct a decision matrix D=(q ij ) m*n , where q ij It represents the evaluation value of the i-th evaluation object on the j-th indicator, m is the number of warning parameters, and n is the number of types of warning parameters;

[0090] S22, normalizing the indicator elements in the decision matrix to obtain normalized indicator element values;

[0091] Specifically, the formula for normalizing the indicator elements is:

[0092]

[0093] In the formula, q ij ' is the normalized value, q ij is the unnormalized value, minq j 、maxq j Respectively represent the maximum and minimum values ​​of the current parameter.

[0094] S23. Calculate the indicator risk weight based on the normalized indicator element value;

[0095] Specifically, the calculation formula for the indicator risk weight is:

[0096]

[0097] In the formula, r ij is the indicator risk weight, q ij ' is the normalized parameter value, and m is the number of warning parameters.

[0098] S24. Calculate the entropy value according to the risk weight of the indicator;

[0099] Specifically, the calculation formula of entropy value is:

[0100]

[0101] In the formula, E j is the entropy value.

[0102] S25. Determine the weight corresponding to the parameter according to the entropy value.

[0103] Specifically, the weight calculation formula is:

[0104]

[0105] Where W j is the weight corresponding to the jth parameter.

[0106] It should be noted that the entropy weight method is used to calculate the weights corresponding to each parameter. Figure 7 shown.

[0107] The reason why the entropy weight method is adopted in this embodiment is that the entropy weight method uses the information entropy of the data itself to determine the weight, reduces the interference of human factors, can objectively reflect the differences and importance between the indicators, and the calculation process is relatively simple, mainly including the calculation of the information entropy and entropy weight of each indicator, which is easy to implement and operate.

[0108] As a further preferred technical solution, for the battery voltage signal, it belongs to the first type of safety state function, and for the gas, temperature, and strain signals, it belongs to the second type of safety function, where:

[0109] The first safety state function indicates that the safe working state is in an interval where the lower limit is not 0, and the formula is:

[0110]

[0111] In the formula, x is the selected parameter, x min 、x max are the lower and upper limits of the safe working state of the battery, respectively; m1, d1, m2, and d2 are the safety state function parameter values ​​under undervoltage and overvoltage conditions, respectively.

[0112] The second safety state function indicates that the safe working state is in an interval with a lower limit of 0, and the formula is expressed as:

[0113]

[0114] In the formula, x is the selected parameter, x limit The safety margin obtained by the experiment, m and d are the safety state function parameters respectively.

[0115] As a further preferred technical solution, the step S3: determining the safety state function and safety boundary of each parameter in the state parameters, and fitting the state parameters in the experimental process to obtain the safety state function corresponding to each parameter, includes the following steps:

[0116] Determine the safety margin according to the thermal runaway test conditions of the lithium battery, wherein the safety margin includes an absolutely safe range of the battery and a relatively safe range of the battery;

[0117] Substitute the absolute safety interval and the relative safety interval of the battery into the safety state function of each parameter, determine the fitting coefficient in the safety state function, and obtain the safety state function corresponding to each parameter.

[0118] Specifically, this embodiment determines the safety boundary according to the experimental conditions, and the specific steps are as follows:

[0119] (1) According to the experimental conditions, the battery safety interval is determined, and each parameter is substituted into the corresponding first safety state function or second safety state function so that it satisfies the following formula to obtain the function parameter d value:

[0120] f safety (x) = 1

[0121] In the preferred embodiment, for voltage and temperature signals, their normal working range is as shown in Table 1 above, and their d value can be determined according to Table 1. For strain and gas concentration, their safe range is confirmed according to experimental data and literature reports. In this experiment, the experimental measurement values ​​of strain and ambient gas concentration are as follows: Figure 5 , Figure 6 The strain shown varies in the range of 0-6000, and the ambient gas concentration, taking CO2 as an example, is 500-2000PPM. When the battery is working normally, the strain change is generally less than 200, and the ambient gas concentration, taking CO2 as an example, is generally stable at around 500PPM. Therefore, the selected strain and ambient gas concentration, taking CO2 as an example, are 200 and 510PPM respectively. The reason for choosing 510PPM is that the ambient gas concentration, taking CO2 as an example, will fluctuate within a small range, so choosing 5100PPM is a reasonable threshold with a certain fault tolerance.

[0122] (2) According to the experimental conditions, the battery is judged to be relatively safe. Usually, according to international standards, it is considered unusable when it degrades to about 80%. Substitute the first safety state function or the second safety state function to satisfy the following formula to obtain the function parameter m value:

[0123] f safety (x) = 0.8

[0124] In the preferred embodiment, for voltage, surface temperature, strain, and ambient gas data, the out-of-control thresholds are determined based on experimental data and literature reports. Similarly, for voltage data, the experimental measured values ​​are as follows: Figure 3 As shown, the specific range is about 1.6-20V, that is, during the thermal runaway process, the battery voltage reaches a maximum of 20V, and then drops sharply to about 1.6V. Combining the normal operating voltage range of the battery and the threshold value reported in the literature, it is believed that when the battery is less than 2.2V, that is, over-discharge occurs, the safety of the battery will decrease, and the m value of the voltage safety state function during undervoltage is obtained. When the battery voltage exceeds 5V, the battery is overcharged and the safety decreases at this time. Using this as the threshold, the m value of the voltage safety state function during overvoltage is obtained.

[0125] As for the surface temperature data, experimental data show that the value is between 18-85°C. It is generally believed that when the battery surface temperature is greater than 55 degrees Celsius, the SEI film will decompose and the battery will have irreversible damage. Therefore, the threshold is taken as 55 degrees Celsius. It is believed that when the surface temperature of the battery reaches 55 degrees Celsius, the battery is no longer usable. The corresponding m value of the temperature safety state function is obtained in this way.

[0126] For strain data, experimental data show that its value is between -250 and 7000. Figure 8 The change in shape of a specific lithium-ion battery over time during its thermal runaway process, as well as reports in related literature, show that when the battery has obvious bulging and is obviously outside the normal working range, the strain change is usually greater than 200. Therefore, 200 is used as the threshold to obtain the corresponding strain safety state function m value.

[0127] As for the ambient gas concentration, CO2 is usually the first gas to change. Therefore, taking CO2 as an example, experimental data shows that its value is between 500-2000PPM. During the thermal runaway of the battery, its value is stable at around 500PPM. As the thermal runaway progresses, cracks appear on the surface of the battery and a large amount of gas is ejected. At this time, the concentration of CO2 rises sharply, so 510PPM is taken. It is believed that when the CO2 value of the battery environmental concentration is greater than this range, the safety state of the battery has significantly decreased, and the corresponding gas safety function m value is calculated based on this.

[0128] As a further preferred technical solution, the safety state function corresponding to the battery voltage is:

[0129]

[0130] In the formula, f volt (v) is the safety state function corresponding to the battery voltage, and v is the battery voltage collected in real time.

[0131] The safety state function corresponding to the surface temperature is:

[0132]

[0133] In the formula, f tem (t) is the safety state function corresponding to the surface temperature, and t is the surface temperature collected in real time;

[0134] The safety state function corresponding to the strain variable is:

[0135]

[0136] In the formula, f strain (s) is the safety state function corresponding to the strain variable, and s is the strain variable collected in real time;

[0137] The safety state function corresponding to the ambient gas concentration is:

[0138]

[0139] In the formula, f gas (g) is the safety state function corresponding to the ambient gas concentration, and g is the ambient gas concentration collected in real time.

[0140] As a further preferred technical solution, the calculation formula of the comprehensive safety status value of the battery is:

[0141] f safety =W1f volt (v)+W2f tem (t)+W3f strain (s)+W4f gas (g)

[0142] In the formula, f safety is the comprehensive safety status value of the battery, f volt (v) is the safety state function corresponding to the battery voltage, f tem (t) is the safety state function corresponding to the surface temperature, f strain (s) is the safety state function corresponding to the strain variable, f gas (g) is the safety state function corresponding to the ambient gas concentration, v, t, s, g are respectively the battery voltage, surface temperature, strain and ambient gas concentration collected in real time, W1, W2, W3, W4 are respectively the weights corresponding to the battery voltage, surface temperature, strain and ambient gas concentration.

[0143] Specifically, according to the above calculation, the current comprehensive safety status value of the battery is calculated, and the calculated battery safety status is specifically as follows: Fig. 9 As shown, when the battery safety state is less than 0.8, it is considered that the battery is in an extremely unsafe state and thermal runaway is about to occur.

[0144] As a further preferred technical solution, the step S40: determining the current risk level of the battery according to the comprehensive safety status value, and issuing an early warning based on the risk level, includes the following steps:

[0145] At 0.95 ≤ f safety When ≤1, it is determined that the lithium battery is currently at level 1 risk and a level 1 warning is issued;

[0146] At 0.9 ≤ f safety When <0.95, the lithium battery is determined to be at level 2 risk and a level 2 warning is issued;

[0147] At 0.8 ≤ fsafety When <0.9, it is determined that the lithium battery is currently at level 3 risk and a level 3 warning is issued;

[0148] In f safety When <0.8, the lithium battery is determined to be in a dangerous state and a thermal runaway warning is issued;

[0149] Among them, f safety is the comprehensive safety status value.

[0150] Specifically, Fig.10 As shown, in the early stage of thermal runaway, all battery parameters are within the normal working range, and the battery is in a safe state. As the thermal runaway progresses, various battery parameters change successively. When the comprehensive safety state value is between 0.95-1, the battery enters the first-level warning. As the battery thermal runaway progresses, the battery safety state continues to decline. When the comprehensive safety state value is between 0.9-0.95, the battery enters the second-level warning. The battery safety state continues to decline. When the comprehensive safety state value is between 0.8-0.9, the battery enters the third-level warning. As the battery thermal runaway continues, when the battery safety state is less than 0.8, it is considered that the battery is in the most dangerous state.

[0151] Obviously, for different types of batteries, we can use the above process to complete the early warning of battery thermal runaway, and we can also modify the selected parameters based on the above process. We only need to recalculate the weights of each parameter according to the experimental data, calculate the safety state function of each parameter, calculate the safety state of the battery and set the threshold at the same time.

[0152] Table 2 shows the results of a specific battery thermal runaway warning experiment, the battery status when each parameter reaches the corresponding warning level:

[0153] Table 2 Battery status at warning level

[0154] Thermal runaway warning level Voltage Surface temperature strain CO2 concentration Time to thermal runaway Level 1 warning 4.97V 21.59℃ 167 489PPM 63min Second level warning 5.62V 35.64℃ 184 496PPM 51min Level 3 warning 5.06V 57.25℃ 566 492PPM 33min

[0155] It can be seen from Table 2 that the first-level warning, second-level warning, and third-level warning can effectively avoid the occurrence of thermal runaway. When the battery is in the first-level warning moment, the battery state has not yet suffered irreversible damage. When the battery is in the second-level warning moment, the battery surface has obvious bulges. At this time, continuing to use it will have obvious safety hazards. When the battery reaches the third-level warning moment, it must be stopped immediately. At this time, the battery is in an extremely dangerous state. International standards usually require a warning five minutes before thermal runaway. This method uses a more stringent judgment method. The third-level warning is still 33 minutes away from the occurrence of thermal runaway. It not only takes into account the national standard requirements, but also leaves more redundancy for the safety of drivers and passengers. This result also proves the effectiveness and necessity of graded warnings.

[0156] Therefore, the thermal runaway warning scheme proposed in this embodiment is different from the existing multi-parameter comprehensive warning method in that, on the one hand, there are differences in the selection of parameters. Some methods use temperature, voltage, air pressure, heat generation and other parameters for warning, while the strain change is more sensitive and has higher sensitivity, and the strain monitoring technology is more mature and can work in harsh environments. In addition, this method aims to solve the problem of quantitatively evaluating the safety status of the battery. At the same time, the weight calculation method based on the entropy weight method is used to effectively eliminate the interference of human factors and objectively reflect the weights between the various indicators. Finally, the battery safety status function is obtained based on the experimental data, the safety performance of the battery is quantitatively evaluated, and the thermal runaway warning is completed in turn.

[0157] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0158] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0159] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A lithium battery thermal runaway early warning method based on multi-parameter fusion analysis, characterized in that: The method comprises: Collecting real-time state parameters of the lithium battery, including battery voltage, surface temperature, strain and ambient gas concentration; Substituting each parameter in the state parameters into the corresponding safety state function to obtain the battery safety state corresponding to each parameter, wherein the safety state function corresponding to each parameter is obtained by fitting the state parameters collected in advance during the battery thermal runaway process; Based on the battery safety status corresponding to each parameter and the weight corresponding to each parameter, calculate the comprehensive safety status value of the battery; The current risk level of the battery is determined according to the comprehensive safety status value, and an early warning is issued based on the risk level.

2. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 1, characterized in that: The fitting process of the safety state function corresponding to each parameter includes: Use the experimental device to conduct thermal runaway experiments on lithium batteries and collect state parameters during the thermal runaway experiments of lithium batteries; Processing the state parameters collected during the experiment, and using an entropy weight method to determine the weights corresponding to each of the state parameters in the safety state assessment; The safety state function and safety margin of each parameter in the state parameters are determined, and the state parameters of the experimental process are used for fitting to obtain the safety state function corresponding to each parameter.

3. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 2, characterized in that: The state parameters of the collected experimental process are processed, and the weights corresponding to each parameter in the state parameters in the safety state assessment are determined by using an entropy weight method, including: The decision matrix D is constructed by using each parameter in the state parameters of the experimental process. ij ) m*n , where q ij It represents the evaluation value of the i-th evaluation object on the j-th indicator, m is the number of warning parameters, and n is the number of warning parameters; Normalizing the indicator elements in the decision matrix to obtain normalized indicator element values; Calculate the indicator risk weight based on the normalized indicator element value; Calculate the entropy value according to the risk weight of the indicator; According to the entropy value, the weight corresponding to the parameter is determined.

4. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 2, characterized in that: The first safety state function corresponding to the battery voltage is: In the formula, x is the selected parameter, x min 、x max are the lower and upper limits of the safe working state of the battery, respectively; m1, d1, m2, and d2 are the safety state function parameter values ​​under undervoltage and overvoltage conditions, respectively.

5. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 2, characterized in that: The second safety state functions corresponding to the surface temperature, strain and ambient gas concentration are: In the formula, x is the selected parameter, x limit is the safety margin obtained by the experiment, and m and d are the safety state function parameters.

6. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 2, characterized in that: The step of determining the safety state function and safety boundary of each parameter in the state parameters, and fitting the state parameters in the experimental process to obtain the safety state function corresponding to each parameter includes: Determine the safety margin according to the thermal runaway test conditions of the lithium battery, wherein the safety margin includes an absolutely safe range of the battery and a relatively safe range of the battery; Substitute the absolute safety interval and the relative safety interval of the battery into the safety state function of each parameter respectively, determine the fitting coefficient in the safety state function, and obtain the safety state function corresponding to each parameter.

7. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 1 or 6, characterized in that: The safety state function corresponding to the battery voltage is: In the formula, f volt (v) is the safety state function corresponding to the battery voltage, and v is the voltage collected in real time.

8. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 1 or 6, characterized in that: The safety state function corresponding to the surface temperature is: In the formula, f tem (t) is the safety state function corresponding to the surface temperature, and t is the surface temperature collected in real time; The safety state function corresponding to the strain variable is: In the formula, f strain (s) is the safety state function corresponding to the strain variable, and s is the strain variable collected in real time; The safety state function corresponding to the ambient gas concentration is: In the formula, f gas (g) is the safety state function corresponding to the ambient gas concentration, and g is the ambient gas concentration collected in real time.

9. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 1, characterized in that: The comprehensive safety status value of the battery is calculated based on the battery safety status corresponding to each parameter and the weight corresponding to each parameter. The formula is expressed as: f safety =W1f volt (v)+W2f tem (t)+W3f strain (s)+W4f gas (g) In the formula, f safety is the comprehensive safety status value of the battery, f volt (v) is the safety state function corresponding to the battery voltage, f tem (t) is the safety state function corresponding to the surface temperature, f strain (s) is the safety state function corresponding to the strain variable, f gas (g) is the safety state function corresponding to the ambient gas concentration, v, t, s, g are respectively the battery voltage, surface temperature, strain and ambient gas concentration collected in real time, W1, W2, W3, W4 are respectively the weights corresponding to the battery voltage, surface temperature, strain and ambient gas concentration.

10. The lithium battery thermal runaway early warning method based on multi-parameter fusion analysis as claimed in claim 1, characterized in that: The determining the current risk level of the battery according to the comprehensive safety status value and issuing an early warning based on the risk level includes: At 0.95 ≤ f safety When ≤1, it is determined that the lithium battery is currently at level 1 risk and a level 1 warning is issued; At 0.9 ≤ f safety When <0.95, the lithium battery is determined to be at level 2 risk and a level 2 warning is issued; At 0.8 ≤ f safety When <0.9, the lithium battery is determined to be at level 3 risk and a level 3 warning is issued; In f safety When <0.8, the lithium battery is determined to be in a dangerous state and a thermal runaway warning is issued; Among them, f safety is the comprehensive safety status value.

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