A thermal runaway detection method for the whole life cycle of a lithium-ion battery pack

Abstract

The application relates to the technical field of battery pack thermal runaway detection, in particular to a thermal runaway detection method for the whole life cycle of a lithium ion battery pack, which comprises the following steps: determining the relative heat abnormality of each single body by comprehensively evaluating the aging degree, current temperature rise and relative state of each single body in the battery pack; determining the battery state abnormal threshold value based on the average value of the health state values of all single body batteries in the battery pack; determining the battery temperature abnormal threshold value based on the difference between the ambient temperature and the preset standard ambient temperature; and comparing the relative heat index of each single body in the battery pack with the battery state abnormal threshold value and the temperature with the battery temperature abnormal threshold value, respectively, to perform thermal runaway early warning on each single body in the battery pack. The application solves the false alarm and missed alarm problems caused by individual differences and environmental changes in the whole life cycle of the traditional fixed threshold method, and improves the accuracy of the battery pack thermal runaway risk detection.

Description

Technical Field

[0001] This application relates to the field of thermal runaway detection technology for battery packs, specifically to a thermal runaway detection method for the entire life cycle of lithium-ion battery packs. Background Technology

[0002] Thermal runaway refers to the process in which a lithium-ion battery experiences a chain reaction of exothermic reactions triggered by factors such as short circuits, overcharging, aging, or external damage. The rate of heat generation far exceeds the rate of heat dissipation, causing a surge in temperature and pressure, ultimately leading to combustion or even an explosion. Since lithium-ion battery packs are typically composed of multiple cells connected in series and parallel, once a cell experiences thermal runaway, the released heat can be rapidly transferred to adjacent cells through heat conduction, exhaust flames, etc., causing the entire battery system to experience thermal runaway within a very short time. Therefore, thermal runaway detection must be performed on lithium-ion battery packs throughout their entire service life, from manufacturing and installation to aging and eventual death. Continuously identifying early signs of thermal runaway is crucial for providing early warning throughout the continuous degradation of battery performance and preventing sudden safety accidents.

[0003] Existing thermal runaway detection methods primarily monitor the overall operating conditions of lithium-ion batteries, such as temperature detection, heating rate detection, and voltage anomaly detection. These methods typically assume that the thermal runaway characteristics of the battery remain unchanged throughout its entire lifespan and employ uniform detection thresholds and judgment logic. However, because the aging rates of individual cells within a battery pack are inconsistent, leading to significant differences in internal resistance, cells with higher internal resistance generate more heat during charging and discharging and have lower tolerance for abnormal heating. Therefore, fixed thresholds cannot distinguish between normal temperature differences caused by individual cell variations and abnormal temperature differences that are precursors to thermal runaway, thus reducing the accuracy of detecting thermal runaway risks in battery packs. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a thermal runaway detection method for the entire lifecycle of lithium-ion battery packs, thereby resolving existing issues.

[0005] This application presents a thermal runaway detection method for the entire lifecycle of lithium-ion battery packs, employing the following technical solution:

[0006] One embodiment of this application provides a thermal runaway detection method for the entire life cycle of a lithium-ion battery pack, the method comprising the following steps:

[0007] Real-time acquisition of the temperature, current, internal resistance of each cell after each charge, and ambient temperature of each cell during battery pack operation;

[0008] By comparing the difference between the cumulative current of each cell from the start of its use to the current moment and its rated capacity, the equivalent cycle number of each cell at the current moment is determined.

[0009] By analyzing the internal resistance of each cell after the most recent charging and the difference between the internal resistance and the initial internal resistance, as well as the difference between the preset life-end internal resistance and the initial internal resistance of each cell, and combining the difference between the equivalent cycle number and the rated cycle life of each cell, the battery health status value of each cell at the current moment is determined.

[0010] By comparing the difference between the current state of health value of each cell and the average state of health value of all cells in the battery pack, as well as the difference between the temperature of each cell and the ambient temperature, the relative heat generation anomaly of each cell at the current moment can be determined.

[0011] Based on the average health status value of all individual cells in the battery pack at the current moment, the abnormal battery status threshold at the current moment is determined; based on the difference between the current ambient temperature and the preset standard ambient temperature, the abnormal battery temperature threshold at the current moment is determined; the relative heat generation index of each cell in the battery pack and the abnormal battery status threshold, as well as the temperature and the abnormal battery temperature threshold, are compared respectively to provide an early warning of thermal runaway for each cell in the battery pack at the current moment.

[0012] Preferably, the expression for the equivalent number of cycles for each individual at the current moment is: In the formula, This represents the equivalent loop count for single entity i at the current moment; This represents the current signal of cell i; Indicates the current time; This indicates the rated capacity of monomer i.

[0013] Preferably, the expression for the battery health status value of each individual cell at the current moment is: In the formula, This represents the battery health status value of cell i at the current moment; , These represent the internal resistance of cell i after its most recent charging ended and the difference between the internal resistance and the initial internal resistance, respectively, and the difference between the preset end-of-life internal resistance of cell i and the initial internal resistance. , These represent the internal resistance of cell i after its most recent charging cycle ended and the initial internal resistance of cell i, respectively. , These represent the equivalent number of cycles and the rated cycle life of monomer i at the current moment, respectively.

[0014] Preferably, the method for determining the relative thermal anomaly of each individual at the current moment is as follows:

[0015] Based on the difference between the current state of health of each individual cell and the average state of health of all individual cells in the battery pack, the difference in the degradation state of each individual cell at the current moment is determined.

[0016] determining a heat generation difference value of each monomer at the current time based on the difference between the temperature of each monomer and the ambient temperature;

[0017] determining a relative heat abnormality degree of each monomer at the current time based on the attenuation state difference value and the heat generation difference value.

[0018] Preferably, the expression of the attenuation state difference value of each monomer at the current time is: ; wherein, represents the attenuation state difference value of monomer i at the current time; represents the mean value of the battery health state values of all monomers in the battery pack at the current time; represents the difference between the battery health state value of monomer i and the mean value of the battery health state values at the current time.

[0019] Preferably, the determination method of the heat generation difference value of each monomer at the current time is:

[0020] respectively calculating the difference between the temperature of each monomer and the ambient temperature at any time, denoted as the temperature difference value of each monomer at any time;

[0021] comparing the temperature difference value of each monomer at the current time with the difference between the temperature difference value of the corresponding monomer at the starting time of the preset time length before the current time and the length of the preset time length, and taking the result as the temperature change rate of each monomer at the current time;

[0022] comparing the temperature change rate of each monomer at the current time with the mean value of the temperature change rates of all monomers in the battery pack at the current time, and taking the result as the heat generation difference value of each monomer at the current time.

[0023] Preferably, the relative heat abnormality degree of each monomer at the current time is the product of the attenuation state difference value and the heat generation difference value of each monomer at the current time.

[0024] Preferably, the expression of the battery state abnormality threshold value at the current time is: ; wherein, represents the battery state abnormality threshold value at the current time; represents a preset reference abnormality degree threshold value; represents the battery health state value of all monomers in the battery pack at the current time.

[0025] Preferably, the expression of the battery temperature abnormality threshold value at the current time is: ; wherein, represents the battery temperature abnormality threshold value at the current time; represents the ambient temperature at the current time; represents a preset temperature limit value; represents a preset standard ambient temperature.

[0026] Preferably, the thermal runaway early warning of each single cell in the battery pack at the current time comprises:

[0027] At the current time, if the relative heat abnormality degree of the current single cell is greater than the battery state abnormality threshold or the temperature of the current single cell is greater than the battery temperature abnormality threshold, the thermal runaway early warning is triggered, otherwise, the thermal runaway early warning is not triggered.

[0028] The present application has at least the following beneficial effects:

[0029] The present application uses equivalent cycle number instead of traditional cumulative cycle count, integrates the total charge and discharge capacity of the single cell in the whole life cycle, and compares it with the rated capacity, so as to more truly reflect the battery loss under different use intensities, and provide more accurate basic data for subsequent state of health assessment; further, the present application determines the battery health state value of each single cell by analyzing the difference between the internal resistance of each single cell after the last charging and the initial internal resistance, and the difference between the preset end-of-life internal resistance of each single cell and the initial internal resistance, and combining the difference between the equivalent cycle number of each single cell and the rated cycle life, changes the traditional SOH from a pure performance degradation index to a dynamic risk assessment value that can comprehensively reflect the current health state and future thermal runaway sensitivity of the battery; further, the present application dynamically couples the instantaneous temperature rise behavior of the single cell with the long-term health state by constructing the relative heat abnormality degree, thereby improving the detection sensitivity of the aging single cell and avoiding false positives of the healthy single cell, and realizing accurate identification of the thermal runaway precursor; finally, the present application dynamically adjusts the abnormality threshold based on the overall health state of the battery pack, so that the detection sensitivity automatically improves with the aging of the battery; on the other hand, the absolute temperature upper limit is adjusted in real time combined with the ambient temperature to eliminate external interference; when the relative heat abnormality degree or the absolute temperature of any single cell exceeds the corresponding threshold, a graded early warning is triggered, and a 30-second continuous confirmation strategy is supplemented, thereby effectively filtering transient fluctuations in the whole life cycle of the battery and improving the accuracy of the battery pack thermal runaway risk detection. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0031] Figure 1A step flow chart of a thermal runaway detection method for a full life cycle of a lithium ion battery pack is provided for an embodiment of the present application.

[0032] Figure 2 A relative heat abnormality extraction process flow chart is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purposes, the specific embodiments, structures, features and effects of the thermal runaway detection method for a full life cycle of a lithium ion battery pack according to the present application are described in detail as follows in combination with the drawings and preferred embodiments. Different "one embodiment" or "another embodiment" in the following description do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0035] The specific scheme of the thermal runaway detection method for a full life cycle of a lithium ion battery pack provided by the present application is described in detail below in combination with the drawings.

[0036] The thermal runaway detection method for a full life cycle of a lithium ion battery pack provided by an embodiment of the present application specifically provides a thermal runaway detection method for a full life cycle of a lithium ion battery pack as follows. Please refer to Figure 1 The method includes the following steps:

[0037] Step S1: Real-time acquisition of the temperature, current, internal resistance of each monomer after each charging of each monomer, and environmental temperature during the operation of the battery pack.

[0038] Real-time acquisition of the operation data of the battery pack, including the temperature (unit: ℃), current (unit: A), internal resistance (unit: ) of each monomer after each charging of each monomer in the battery pack, and environmental temperature (unit: ℃), wherein the data acquisition frequency is set to f; the basic information of the battery pack includes the initial internal resistance (measured value when the battery monomer is factory-finished, unit: ), rated capacity (unit: Ah), and rated cycle life (unit: times) of each monomer in the battery pack.

[0039] It should be noted that the value of the data acquisition frequency f is artificially set, and in the present embodiment, the value of the data acquisition frequency f is 1 Hz. In actual application, as other implementation manners, the implementer can also set it by himself / herself according to the specific circumstances, and the present embodiment does not make special limitation.

[0040] Step S2: Determine the relative heat abnormality degree of each monomer at the current time by comprehensively evaluating the aging degree, current temperature rise and relative state of each monomer in the battery pack.

[0041] The internal resistance of lithium ion battery will increase nonlinearly due to aging in the whole life cycle, so the heat generation efficiency will increase significantly under the same working condition. Because the Joule heat is proportional to the internal resistance, if the fixed threshold preset by the new battery is used consistently, the heat generated by the normal work of the aging battery may be misjudged as a precursor of thermal runaway. In addition, the tolerance of the aging monomer to thermal disturbance decreases, so the risk of thermal runaway is much higher than that of the healthy monomer. If the overall threshold is used for judgment, it is difficult to distinguish the precursor of abnormal thermal runaway, which may cause false negatives.

[0042] Therefore, in the embodiment, the relative heat abnormality degree of each monomer at the current time is determined by comprehensively evaluating the aging degree, current temperature rise and relative state of each monomer in the battery pack, that is, by calculating the battery health state of the monomers in the battery pack in real time, the internal resistance growth and cycle aging are quantified as a risk weight that decreases with the life cycle, which is used to dynamically adjust the alarm threshold on one hand, so that the detection sensitivity can be synchronized with the aging; on the other hand, the deviation correction of the battery health state is introduced, so that the aging monomer with high risk can obtain a larger coefficient in the relative abnormality index, and the differential monitoring is realized, thereby significantly reducing false positives and false negatives in the whole life cycle. The relative heat abnormality degree extraction process flowchart provided by the embodiment is shown in Figure 2 The specific acquisition process of the relative heat abnormality diagram is as follows:

[0043] S2.1: Determine the equivalent cycle number of each monomer at the current time by comparing the difference between the cumulative amount of current of each monomer from the start of use to the current time and the rated capacity.

[0044] Since the cumulative cycle number is the count of full charge and full discharge events by the battery management system (BMS), shallow charging and shallow discharging, rate difference and temperature influence are ignored, so the equivalent cycle number obtained by comparing the difference between the cumulative amount of current of each monomer from the start of use to the current time and the rated capacity can more accurately reflect the actual use intensity of each monomer. Specifically:

[0045] In the embodiment, the equivalent cycle number of monomer i at the current time is expressed as: ; in the formula, represents the current signal of monomer i; represents the current time; represents the rated capacity of monomer i.

[0046] The principle of the formula is that the integral of the monomer current in the molecule obtains the total transmission electric quantity, and the absolute value is added to represent the charging current and the discharging current, the molecule is twice the rated capacity because a complete cycle contains charging and discharging once, the total electric quantity needs to be divided by twice the rated capacity to obtain the equivalent full charging and full discharging times, and then multiplied by 3600 to convert into .

[0047] So far, in order to accurately quantify the actual aging degree of the battery, the embodiment adopts the equivalent cycle number to replace the traditional cumulative cycle count, integrates the total charging and discharging electric quantity of the monomer in the whole life cycle, and compares it with the rated capacity, so that the battery loss under different use intensities can be more truly reflected, and more accurate basic data is provided for subsequent state of health assessment.

[0048] S2.2: Determine the battery state of health value of each monomer at the current time by analyzing the difference between the internal resistance of each monomer after the last charging before the current time and the initial internal resistance, and the difference between the preset end-of-life internal resistance of each monomer and the initial internal resistance, and combining the difference between the equivalent cycle number of each monomer and the rated cycle life.

[0049] The traditional battery state of health SOH only reflects the capacity or internal resistance decay, and does not consider the nonlinear growth characteristics of the thermal runaway risk with decay, so it cannot be directly applied to the whole life cycle thermal runaway detection of lithium ion battery pack. In the embodiment, the battery state of health value of each monomer at the current time is determined by analyzing the difference between the internal resistance of each monomer after the last charging before the current time and the initial internal resistance, and the difference between the preset end-of-life internal resistance of each monomer and the initial internal resistance, and combining the difference between the equivalent cycle number of each monomer and the rated cycle life, that is, the battery state is evaluated in two dimensions of internal resistance growth and thermal runaway sensitivity. Specifically:

[0050] In the embodiment, the battery state of health value of monomer i at the current time is expressed as: ; in the formula, , respectively represent the difference between the internal resistance of monomer i after the last charging before the current time and the initial internal resistance, and the difference between the preset end-of-life internal resistance of monomer i and the initial internal resistance; , respectively represent the internal resistance of monomer i after the last charging before the current time, and the initial internal resistance of monomer i; , respectively represent the equivalent cycle number of monomer i at the current time, and the rated cycle life.

[0051] It should be noted that the preset end-of-life internal resistance of monomer i in the embodiment is .

[0052] The principle of the formula is: is the basic health degree, which linearly reflects the attenuation of internal resistance based on the internal resistance growth rate; is the thermal runaway sensitivity correction factor, wherein represents the internal resistance ratio, which reflects the linear relationship between the heat generation power and the internal resistance growth. The more severe the battery attenuation, the greater the heat generation power, represents the cycle life ratio, which reflects the decrease in thermal stability caused by battery aging. The more the number of cycles, the thicker the SOHEI film inside the battery and the loss of active material, and the lower the thermal runaway threshold temperature. The capacity attenuation and thermal runaway risk growth of the battery are comprehensively considered, that is, under the same internal resistance growth, the battery with more cycle times has a higher risk of thermal runaway than the battery with fewer cycle times.

[0053] So far, by introducing the correction factor combining the internal resistance ratio and the cycle life ratio, the embodiment captures the nonlinear growth of the thermal runaway risk with aging, thereby converting the traditional SOH from a simple performance degradation indicator to a dynamic risk assessment value that can comprehensively reflect the current health status and future thermal runaway sensitivity of the battery.

[0054] S2.3: By comparing the difference between the battery health state value of each monomer at the current time and the average of all monomer battery health state values in the battery pack, and the difference between the temperature of each monomer and the ambient temperature, the relative heat abnormality of each monomer at the current time is determined.

[0055] Since the battery health state (SOH) can only represent the degree of aging, but thermal runaway often occurs locally and instantaneously under relative working conditions, therefore, monomers with the same degree of aging have a large difference in temperature rise rate under large current, high temperature or boundary failure. Therefore, by comparing the difference between the battery health state value of each monomer at the current time and the average of all monomer battery health state values in the battery pack, and the difference between the temperature of each monomer and the ambient temperature, the relative heat abnormality of each monomer at the current time is determined to avoid misjudgment of the normal high temperature rise of healthy monomers under large current, and to realize differentiated judgment throughout the life cycle. Specifically:

[0056] Firstly, the embodiment determines the attenuation state difference value of each monomer at the current time based on the difference between the battery health state value of each monomer at the current time and the average of all monomer battery health state values in the battery pack. Specifically:

[0057] In the embodiment, the attenuation state difference value of monomer i at the current time is expressed as: ; in the formula, represents the average of the battery health state values of all monomers in the battery pack at the current time; represents the difference between the battery health state value of the single battery i in the battery pack at the current time and the average value of the battery health state value.

[0058] The principle of the formula is: the greater the degree of aging of the single battery, the smaller the battery health state value, when the degree of aging of the single battery is greater than the average value, the risk of thermal runaway is greater than the average value, that is, , greater than 1, which amplifies the abnormality, because the single battery with low SOH is more sensitive to thermal runaway, and a slightly higher temperature rise rate than the average value also needs to be vigilant; when the degree of aging of the single battery is less than the average value, the risk of thermal runaway is less than the average value, that is, , less than 1, which reduces the abnormality, because the single battery with high SOH is more resistant to thermal runaway, and a slightly higher temperature rise may also be a normal situation, represents the greater the aging of the battery pack, the greater the influence of the difference between the single batteries, that is, the greater the degree of amplification or reduction of the abnormality.

[0059] Further, the embodiment is based on the difference between the temperature of each single battery and the ambient temperature to determine the heat difference value of each single battery at the current time, specifically:

[0060] The difference between the temperature of each single battery at any time and the ambient temperature is calculated, denoted as the temperature difference value of each single battery at any time;

[0061] The difference between the temperature difference value of each single battery at the current time and the temperature difference value of the corresponding single battery at the starting time of the preset time length before the current time is divided by the length of the preset time length, and the result is taken as the temperature change rate of each single battery at the current time.

[0062] The temperature change rate of each single battery at the current time is divided by the average value of the temperature change rate of all single batteries in the battery pack at the current time, and the result is taken as the heat difference value of each single battery at the current time.

[0063] It should be noted that the value of the preset time length is artificially set, and in the embodiment, the value of the preset time length is 60s. In actual application, as other implementation manners, the implementer can also set it himself according to the specific situation, and the embodiment does not make special restrictions.

[0064] According to the heat difference value of each monomer at the current time, it can be understood that the heat difference value is used to represent the deviation of the monomer heat behavior from the average level of the whole battery pack, which directly reflects the consistency of the heat behavior of the monomer in the group. If the proportion of the temperature change rate of the current monomer in the average of the temperature change rate of all monomers in the battery pack is larger, the heat difference value is larger, which means that the temperature rise rate of the current monomer is much higher than the average level of the battery pack, indicating that the current monomer may be experiencing an abnormal heat process caused by internal short circuit; on the contrary, if the proportion of the temperature change rate of the current monomer in the average of the temperature change rate of all monomers in the battery pack is smaller, the heat difference value is smaller, which means that the temperature rise rate of the current monomer is lower than or equal to the average level of the battery pack, indicating that the heat behavior of the monomer is normal or relatively conservative, and stable in the group.

[0065] Further, the embodiment determines the relative heat abnormality degree of each monomer at the current time based on the attenuation state difference value and the heat difference value, specifically:

[0066] In the embodiment, the product of the attenuation state difference value and the heat difference value of each monomer at the current time is taken as the relative heat abnormality degree of each monomer at the current time.

[0067] According to the relative heat abnormality degree of each monomer at the current time, it can be understood that the relative heat abnormality degree is used to represent the comprehensive risk after the abnormal behavior of the monomer and the long-term health state. If the attenuation state difference value of the current monomer is larger, and the heat difference value of the current monomer is larger, it means that the aging degree of the current monomer is more serious and the heat is more serious, and the corresponding relative heat abnormality degree is larger, so the high-risk monomer needs to be monitored and the timeliness of early warning is improved. On the contrary, if the attenuation state difference value of the current monomer is smaller, that is, the monomer is healthier, and the heat difference value of the current monomer is smaller, that is, the heat behavior is normal, then the corresponding relative heat abnormality degree is smaller, which means that the current state of the monomer is stable and the comprehensive risk is low, so there is no need for excessive intervention, thereby effectively reducing the false alarm rate.

[0068] So far, the embodiment dynamically couples the instantaneous temperature rise behavior and the long-term health state of the monomer by constructing the relative heat abnormality degree. This method first uses environmental normalization processing to obtain the relative temperature rise rate to represent the instantaneous heat abnormality, then combines the attenuation state difference value based on the health state deviation to quantify the tolerance of the monomer, and finally obtains the relative heat abnormality degree by the product of the two, so as to improve the detection sensitivity of the aging monomer and avoid false alarm of the healthy monomer, and realize the accurate identification of the precursor of thermal runaway.

[0069] Step S3: determining a battery state abnormality threshold at the current time based on the average of the health state values of all single batteries in the battery pack at the current time; determining a battery temperature abnormality threshold at the current time based on the difference between the ambient temperature at the current time and the preset standard ambient temperature; comparing the relative heat generation index of each single battery in the battery pack at the current time with the battery state abnormality threshold and the temperature with the battery temperature abnormality threshold, respectively, to perform thermal runaway early warning on each single battery in the battery pack at the current time.

[0070] The abnormality threshold is dynamically adjusted according to the overall thermal runaway risk level of the battery pack, and the upper limit of the temperature is dynamically adjusted according to the ambient temperature, specifically:

[0071] First, the battery state abnormality threshold at the current time is determined based on the average of the health state values of all single batteries in the battery pack at the current time, specifically:

[0072] In this embodiment, the battery state abnormality threshold at the current time is expressed as: ; in the formula, the preset reference abnormality threshold is 1.5 in this embodiment; the battery health state value of each single battery in the battery pack at the current time.

[0073] According to the battery state abnormality threshold, it can be understood that the battery state abnormality threshold is based on the temperature rise consistency statistical characteristics under the normal working condition of the battery pack, which can effectively identify abnormalities and will not be too sensitive to cause false positives. With the aging and attenuation of the battery, not only the heat generation increases, but also the thermal runaway threshold temperature decreases, so a more stringent alarm threshold is needed. At this time, the threshold gradually decreases, and the dynamic threshold ensures that the detection sensitivity matches the actual risk throughout the life cycle of the battery.

[0074] Further, the battery temperature abnormality threshold at the current time is determined based on the difference between the ambient temperature at the current time and the preset standard ambient temperature in this embodiment, specifically:

[0075] In this embodiment, the battery temperature abnormality threshold at the current time is expressed as: ; in the formula, the ambient temperature at the current time; the preset temperature limit value; the preset standard ambient temperature.

[0076] It should be noted that the preset temperature limit value in this embodiment is 60℃, and the preset standard ambient temperature is 25℃.

[0077] The principle of the formula is that in a high-temperature environment, the battery temperature reference itself is high, so the upper limit of the temperature should also be increased accordingly to avoid false positives; similarly, in a low-temperature environment, the battery temperature reference is low, and the upper limit of the temperature should also be decreased accordingly to improve sensitivity.

[0078] Further, the embodiment compares the relative heat generation index of each monomer in the battery pack at the current time and the battery state abnormal threshold, and the temperature and the battery temperature abnormal threshold, respectively, to perform thermal runaway early warning for each monomer in the battery pack at the current time. Specifically:

[0079] At the current time, if the relative heat generation abnormality degree of the current monomer is greater than the battery state abnormal threshold or the temperature of the current monomer is greater than the battery temperature abnormal threshold, a thermal runaway early warning is triggered, otherwise, no thermal runaway early warning is triggered.

[0080] When any monomer triggers an early warning, an early warning information is output, including: the abnormal monomer number, the relative heat generation abnormality degree of the monomer at the current time, the temperature of the monomer at the current time, the temperature rise rate at the current time, and the early warning level; the early warning level includes: a first-level early warning (mild abnormality): or ℃; a second-level early warning (moderate abnormality): or ℃; a third-level early warning (severe abnormality, high risk of thermal runaway): or ℃.

[0081] In order to avoid false positives caused by instantaneous fluctuations, a continuous monitoring strategy is adopted. Only when the abnormal state lasts more than 30 seconds, the early warning is confirmed and an alarm is triggered. If the abnormal state recovers to normal within 30 seconds, no alarm is triggered, only a log is recorded.

[0082] By now, the embodiment dynamically adjusts the abnormality threshold based on the overall health status of the battery pack, so that the detection sensitivity is automatically improved as the battery ages. On the other hand, the absolute temperature upper limit is adjusted in real time in combination with the ambient temperature to eliminate external interference. When the relative heat generation abnormality degree or the absolute temperature of any monomer exceeds the corresponding threshold, a graded early warning is triggered, and a 30-second continuous confirmation strategy is supplemented, so that instantaneous fluctuations are effectively filtered in the whole life cycle of the battery, and the accuracy of the battery pack thermal runaway risk detection is improved.

[0083] It should be noted that the above-mentioned order of the embodiments of the present application is only for description, and does not represent the advantages and disadvantages of the embodiments. Moreover, the specific embodiments of the present description are described above. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multi-task processing and parallel processing are also possible or can be advantageous.

[0084] ​The various embodiments in the specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the difference from other embodiments.

[0085] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; the technical solutions recorded in the foregoing embodiments are modified, or some technical features are replaced equivalently, and the essence of the corresponding technical solutions does not deviate from the scope of the technical solutions of the embodiments of the present application, which should be included in the protection scope of the present application.

Claims

1. A thermal runaway detection method for the full life cycle of a lithium-ion battery pack, characterized by, The method comprises the following steps: Real-time acquisition of the temperature, current, internal resistance of each single battery after each charging, and ambient temperature during the operation of the battery pack; Determination of the equivalent cycle number of each single battery at the current time by comparing the difference between the cumulative amount of current and the rated capacity of each single battery from the start of use to the current time; Determination of the battery health state value of each single battery at the current time by analyzing the difference between the internal resistance after the last charging and the initial internal resistance of each single battery before the current time, and the difference between the preset end-of-life internal resistance and the initial internal resistance of each single battery, and combining the difference between the equivalent cycle number and the rated cycle life of each single battery; Determination of the relative heat abnormality of each single battery at the current time by comparing the difference between the battery health state value of each single battery at the current time and the average value of the battery health state values of all single batteries in the battery pack, and the difference between the temperature of each single battery and the ambient temperature; Determination of the battery state abnormal threshold at the current time based on the average value of the battery health state values of all single batteries in the battery pack at the current time, and determination of the battery temperature abnormal threshold at the current time based on the difference between the ambient temperature at the current time and the preset standard ambient temperature; comparison of the relative heat index of each single battery in the battery pack at the current time with the battery state abnormal threshold, and comparison of the temperature with the battery temperature abnormal threshold, to perform thermal runaway early warning for each single battery in the battery pack at the current time; The expression of the battery health state value of each monomer at the current time is: ; In the formula, represents the battery health state value of monomer i at the current time; , respectively represent the internal resistance after the last charging of monomer i before the current time and the difference from the initial internal resistance, and the difference between the preset end-of-life internal resistance of monomer i and the initial internal resistance; , respectively represent the internal resistance after the last charging of monomer i before the current time, the initial internal resistance of monomer i; , respectively represent the equivalent cycle number of monomer i at the current time, and the rated cycle life.

2. The thermal runaway detection method for the full life cycle of a lithium-ion battery pack according to claim 1, wherein, The expression of the equivalent cycle number of each monomer at the current time is: ; in which, represents the equivalent cycle number of monomer i at the current time; represents the current signal of monomer i; represents the current time; represents the rated capacity of monomer i.

3. The thermal runaway detection method for the full life cycle of a lithium-ion battery pack of claim 1, wherein, The determination method of the relative heat abnormality of each single battery at the current time is: Determination of the attenuation state difference value of each single battery at the current time based on the difference between the battery health state value of each single battery at the current time and the average value of the battery health state values of all single batteries in the battery pack; Determination of the heat difference value of each single battery at the current time based on the difference between the temperature of each single battery and the ambient temperature; Determination of the relative heat abnormality of each single battery at the current time based on the attenuation state difference value and the heat difference value.

4. The thermal runaway detection method for lithium-ion battery pack full life cycle of claim 3, wherein, The expression of the difference value of the attenuation state of each monomer at the current time is: ; in the formula, represents the difference value of the attenuation state of monomer i at the current time; represents the average value of the battery health state values of all monomers in the battery pack at the current time; represents the difference between the battery health state value of monomer i and the average value of the battery health state values in the battery pack at the current time.

5. The thermal runaway detection method for lithium-ion battery pack full life cycle of claim 3, wherein, The determination method of the heat difference value of each single battery at the current time is: Respectively calculate the difference between the temperature of each single battery at any time and the ambient temperature, denoted as the temperature difference value of each single battery at any time; Take the result of dividing the difference between the temperature difference value of each single battery at the current time and the temperature difference value of the corresponding single battery at the starting time of the preset time length before the current time by the length of the preset time length as the temperature change rate of each single battery at the current time; Take the result of dividing the temperature change rate of each single battery at the current time by the average value of the temperature change rates of all single batteries in the battery pack at the current time as the heat difference value of each single battery at the current time.

6. The thermal runaway detection method for lithium-ion battery pack full life cycle of claim 3, wherein, The relative heat abnormality of each single battery at the current time is the product of the attenuation state difference value and the heat difference value of each single battery at the current time.

7. The thermal runaway detection method for lithium-ion battery pack full life cycle of claim 1, wherein, The expression of the battery state abnormality threshold at the current time is: wherein, represents the battery state abnormality threshold at the current time; represents the preset reference abnormality threshold; represents the battery health state value of all single bodies in the battery pack at the current time.

8. The thermal runaway detection method for lithium-ion battery pack full life cycle of claim 1, wherein, The expression of the battery temperature abnormal threshold at the current time is: ; wherein, represents the battery temperature abnormal threshold at the current time; represents the ambient temperature at the current time; represents the preset temperature limit; represents the preset standard ambient temperature.

9. The thermal runaway detection method for lithium-ion battery pack full life cycle of claim 1, wherein, The thermal runaway early warning for each single battery in the battery pack at the current time comprises: At the current time, if the relative heat abnormality of the current single battery is greater than the battery state abnormal threshold or the temperature of the current single battery is greater than the battery temperature abnormal threshold, trigger the thermal runaway early warning, otherwise, do not trigger the thermal runaway early warning.

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