Method for determining safety boundary of electric arc caused by thermal runaway injection of battery

Abstract

The invention provides a method for determining the safety boundary of an electric arc triggered by thermal runaway injection of a battery, and belongs to the technical field of battery safety. The method for determining the safety boundary of the electric arc triggered by thermal runaway injection of the battery comprises the steps of building an experimental platform of the electric arc triggered by thermal runaway injection of the battery; setting a working condition range, carrying out a battery thermal runaway injection arc experiment, and obtaining a critical condition; calculating the critical electric field intensity of arcing based on an electric field intensity calculation formula, and converting the critical electric field intensity into a voltage-electrode spacing relational expression to obtain a safety boundary; adjusting the placement height of the electrode, and circulating the steps to obtain the safety boundary of the electric arc caused by thermal runaway injection of the battery at different electrode heights; the invention provides a method for determining a safety boundary of an electric arc caused by thermal runaway injection of a battery, which can solve the problems that the assessment of electrical safety and the confirmation mode of danger caused by the electric arc in the thermal runaway process not only relate to high-risk operation under high-temperature and high-pressure conditions, but also consume a large amount of manpower and material resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery safety, and more specifically, relates to a method for determining the safety boundary of an arc caused by battery thermal runaway spraying. Background Art

[0002] Lithium-ion batteries have been widely used in fields such as electric vehicles and electrochemical energy storage. In practical applications, due to problems such as electrothermal abuse, lithium-ion batteries may experience thermal runaway, accompanied by a violent gas and solid spraying process. Existing research has pointed out that the spraying particles generated during the thermal runaway spraying process of ternary lithium-ion batteries can reduce the environmental breakdown voltage, leading to the occurrence of arcs and even multiple occurrences. As a common electrical fault, an arc can persist at a voltage of 30V and the central temperature can instantaneously exceed 2000°C. There are numerous electrical connection points in the battery pack, usually having the voltage conditions for arc initiation. If an arc fault is triggered by solid spray during the battery thermal runaway process, it may further exacerbate the thermal runaway process, posing a thermal threat to the normal batteries in the battery pack, and its harmfulness is more urgent.

[0003] Currently, there is little research on the arcs caused by the thermal runaway spraying process of lithium-ion batteries. Existing battery safety standards and testing methods usually focus on the basic performance indicators of batteries (such as capacity, charging rate, cycle life, etc.), while the evaluation of electrical safety during the thermal runaway process and the hazards caused by arcs have not received sufficient attention and research. Testing each working condition through experimental methods requires a large amount of manpower and material resources, and also involves high-risk operations under high-temperature and high-pressure conditions. Therefore, without relying on complex experiments, there is still a lack of a simple and effective method to determine the safety voltage and electrical distance for an arc breakdown caused by battery thermal runaway spraying. Summary of the Invention

[0004] In view of this, the present invention provides a method for determining the safety boundary of an arc caused by battery thermal runaway spraying, which can solve the problems that the methods for evaluating electrical safety during the thermal runaway process and confirming the hazards caused by arcs not only involve high-risk operations under high-temperature and high-pressure conditions but also consume a large amount of manpower and material resources.

[0005] The present invention is implemented as follows:

[0006] The present invention provides a method for determining the safety boundary of an arc caused by battery thermal runaway spraying, which includes the following specific steps:

[0007] S10: Build an experimental platform for an arc caused by battery thermal runaway spraying;

[0008] S20: Set the working condition range, and conduct an experimental study on an arc caused by battery thermal runaway spraying in the experimental platform for an arc caused by battery thermal runaway spraying to obtain the critical conditions;

[0009] S30: Calculate the critical electric field strength for arc initiation based on the electric field strength calculation formula, convert it into a voltage - electrode spacing relationship formula, and obtain the safety boundary.

[0010] S40: Adjust the height of the electrode placement, and loop through the above steps to obtain the safety boundaries of the arcs triggered by battery thermal runaway ejection at different electrode heights.

[0011] Based on the above technical solution, a method for determining the safety boundary of an arc triggered by battery thermal runaway ejection of the present invention can be further improved as follows:

[0012] Among them, the specific steps of building the experimental platform for battery thermal runaway ejection - triggered arc include:

[0013] The first step is to connect the components of the battery thermal runaway arc simulation experimental platform correspondingly.

[0014] The second step is to arrange the metal electrodes for arc initiation opposite to each other above the battery exhaust valve, fix them through a fixture, and connect them to the power supply line.

[0015] Further, for the electrical signal acquisition in the experimental platform for battery thermal runaway ejection - triggered arc, a high - frequency acquisition device with communication and data storage functions is used.

[0016] Further, the specific steps of setting the working condition range and conducting the battery thermal runaway ejection arc experiment in the experimental platform for battery thermal runaway ejection - triggered arc to obtain the critical conditions include:

[0017] The first step is to refer to the actual battery pack voltage and electrical component spacing data, set the research ranges of voltage and electrode spacing, and trigger battery thermal runaway through heating or overcharging.

[0018] The second step is to analyze the electrical signal data of the battery ejection process obtained by the high - frequency acquisition device, and judge whether an arc occurs by combining the instantaneous change rates of voltage and current signals and the time - window average value.

[0019] The third step is to repeat the above steps, obtain the arc occurrence situations at different voltages and electrode spacings, and extract the critical conditions for arc initiation.

[0020] Further, the thresholds of the instantaneous change rates of voltage and current signals are obtained through actual experiments.

[0021] Further, the time window is set to 1 - 2 times the sampling interval.

[0022] Further, the specific steps of calculating the critical electric field strength for arc initiation based on the electric field strength calculation formula, converting it into a voltage - electrode spacing relationship formula, and obtaining the safety boundary include:

[0023] First, establish a theoretical model for the arc initiation by battery ejecta, and analyze the boundary conditions of the electric field strength;

[0024] Second, based on the calculation formula of the electric field strength and the boundary conditions, combine the critical arc initiation conditions to obtain the voltage-electrode spacing relationship, and obtain the safety boundary.

[0025] Furthermore, in the step of oppositely arranging the metal electrodes for arc initiation above the battery exhaust valve, fixing them with a fixture and connecting them to the power supply line:

[0026] The metal electrodes are made of copper or tungsten with a high melting point, and the fixture is a rigid fixture with insulation isolation to prevent errors caused by the shaking or falling off of the electrodes due to the violent ejection of the battery.

[0027] Furthermore, the specific steps of setting the research range of voltage and electrode spacing with reference to the actual battery pack voltage and the spacing data of electrical components, and triggering the thermal runaway of the battery by heating or overcharging include:

[0028] The experimental conditions start from the lower limit of the set electrode spacing, and the dichotomy method is used to test from the upper limit of the set voltage to efficiently approach the most stringent arc initiation critical conditions and avoid missing working conditions that affect the accuracy of the safety boundary results.

[0029] Furthermore, the specific steps of establishing the theoretical model for the arc initiation by battery ejecta include:

[0030] Combined with the arc phenomena and the changes in arc signals recorded in the experiment, it is observed that there are obvious stage characteristics of the arc occurrence (the voltage drops from the reference value) - continuation (the voltage remains unchanged or changes slightly) - disappearance (the voltage rises to the reference value). Assuming that the high-speed ejecta for arc initiation is a uniform particle cluster passing through the middle of the electrode electric field, establish a theoretical model for the arc initiation by battery ejecta from the high-speed ejecta for arc initiation, and obtain the boundary conditions of the electric field strength during the displacement process of the particle cluster initiating the arc.

[0031] Compared with the prior art, the beneficial effects of a method for determining the safety boundary of arc initiation caused by the thermal runaway ejection of a battery provided by the present invention are:

[0032] (1) Obtain the critical arc initiation conditions through the experiment on the arc initiation caused by the thermal runaway ejection of the battery, obtain the boundary conditions based on the theoretical model of the arc initiation by ejecta, and then obtain the voltage-electrode spacing relationship through the calculation of the electric field strength, and obtain the safety boundary of the arc initiation caused by the thermal runaway ejection of the battery, filling the method blank in the field.

[0033] (2) This method effectively reduces the experimental test cost of the battery thermal runaway, and the obtained safety boundary can provide a reference for the electrical safety design of the battery pack, such as the setting of the electrical clearance at different voltage levels in the battery system. Description of the Drawings

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments of the present invention. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 It is an operation flowchart of a method for determining the safety boundary of an arc induced by battery thermal runaway ejection;

[0036] Figure 2 It is a schematic diagram of an experimental device for a method for determining the safety boundary of an arc induced by battery thermal runaway ejection;

[0037] Figure 3 It is the experimental data and theoretical model of an arc induced by battery thermal runaway ejection for a method for determining the safety boundary of an arc induced by battery thermal runaway ejection;

[0038] Figure 4 It is a safety boundary result diagram when the electrode height is 3 cm in an embodiment of a method for determining the safety boundary of an arc induced by battery thermal runaway ejection;

[0039] Figure 5 It is a safety boundary result diagram when the electrode height is 4 cm in an embodiment of a method for determining the safety boundary of an arc induced by battery thermal runaway ejection;

[0040] Figure 6 It is a safety boundary result diagram when the electrode height is 5 cm in an embodiment of a method for determining the safety boundary of an arc induced by battery thermal runaway ejection;

[0041] Figure 7 It is a diagram of the relationship between the critical arcing voltage and the electrode gap when the electrode heights are 3, 4, and 5 cm. Specific Embodiments

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

[0043] As Figure 1 shown, it is the first embodiment of a method for determining the safety boundary of an arc induced by battery thermal runaway ejection provided by the present invention. In this embodiment, the following specific steps are included:

[0044] S10: Build an experimental platform for an arc induced by battery thermal runaway ejection;

[0045] S20: Set the operating condition range, conduct the battery thermal runaway spray-induced arc experiment on the battery thermal runaway spray-induced arc experiment platform, and obtain the critical conditions;

[0046] S30: Based on the electric field strength calculation formula, calculate the critical electric field strength for arc initiation, convert it into a voltage-electrode spacing relationship formula, and obtain the safety boundary;

[0047] S40: Adjust the electrode placement height, and cycle through the above steps to obtain the safety boundaries of battery thermal runaway spray-induced arcs at different electrode heights.

[0048] Among them, in the above technical solution, the specific steps for building the battery thermal runaway spray-induced arc experiment platform include:

[0049] The first step is to connect the various components of the battery thermal runaway arc simulation experiment platform correspondingly;

[0050] The second step is to arrange the metal electrodes for initiating arcs oppositely above the battery exhaust valve, fix them with jigs, and connect them to the power supply line.

[0051] Furthermore, in the above technical solution, the electrical signal acquisition in the battery thermal runaway spray-induced arc experiment platform uses a high-frequency acquisition device with communication and data storage functions (above 10 kHz), such as an oscilloscope, high-frequency probe, etc.

[0052] Furthermore, in the above technical solution, the specific steps for setting the operating condition range and conducting the battery thermal runaway spray-induced arc experiment on the battery thermal runaway spray-induced arc experiment platform to obtain the critical conditions include:

[0053] The first step is to refer to the actual battery pack voltage and electrical component spacing data, set the research ranges of voltage and electrode spacing, and trigger battery thermal runaway through heating or overcharging;

[0054] The second step is to analyze the electrical signal data of the battery spray process obtained by the high-frequency acquisition device, and judge whether an arc occurs by combining the instantaneous change rates of voltage and current signals and the time window mean value;

[0055] The third step is to repeat the above steps, obtain the arc occurrence conditions at different voltages and electrode spacings, and extract the critical conditions for arc initiation.

[0056] Furthermore, in the above technical solution, the thresholds of the instantaneous change rates of voltage and current signals are obtained through experimental measurements.

[0057] Furthermore, in the above technical solution, the time window is set to 1 - 2 times the sampling interval.

[0058] Among them, when the instantaneous change rate or the time-window average value of the current and voltage signals satisfies the following conditions, it is determined that a breakdown arc event has occurred (either the instantaneous change rate or the average value condition is satisfied), otherwise it is determined that there is no arc or abnormal interference:

[0059]

[0060] is the instantaneous change rate of the voltage; is the instantaneous change rate of the current; U 平均 is the average value of the voltage; U 基准 is the reference value of the voltage;

[0061] Furthermore, in the above technical solution, based on the electric field strength calculation formula, calculating the critical electric field strength for arc initiation, and transforming it into a voltage-electrode spacing relationship, the specific steps to obtain the safety boundary include:

[0062] The first step is to establish a theoretical model of arc initiation caused by battery ejecta and analyze the boundary conditions of the electric field strength;

[0063] The second step is to obtain the voltage-electrode spacing relationship based on the electric field strength calculation formula and the boundary conditions, and combine with the critical arc initiation conditions to obtain the safety boundary.

[0064] Furthermore, in the above technical solution, in the step of arranging the metal electrodes for arc initiation opposite to each other above the battery exhaust valve, fixing them with a fixture and connecting them to the power supply line:

[0065] The metal electrodes are made of high-melting-point copper or tungsten, and the fixture is a rigid fixture with insulation isolation to prevent errors caused by electrode shaking, falling off, etc. due to violent battery ejection.

[0066] Furthermore, in the above technical solution, referring to the actual battery pack voltage and electrical component spacing data, setting the research range of voltage and electrode spacing, and the specific steps to trigger battery thermal runaway by heating or overcharging include:

[0067] The experimental conditions start from the lower limit of the set electrode spacing, and the dichotomy method is used to test from the upper limit of the set voltage to efficiently approach the strictest critical arc initiation conditions and avoid missing working conditions that affect the accuracy of the safety boundary results.

[0068] Furthermore, in the above technical solution, the specific steps to establish a theoretical model of arc initiation caused by battery ejecta include:

[0069] Combined with the arc phenomenon and arc signal changes recorded in the experiment, it was observed that the arc had obvious stage characteristics of occurrence (voltage dropped from the baseline value) - continuation (voltage remained unchanged or changed slightly) - disappearance (voltage rose to the baseline value). It was assumed that the high-speed ejecta that triggered the arc was a uniform particle cluster passing through the middle of the electrode electric field. A theoretical model of arc induced by battery ejecta was established based on the high-speed ejecta that triggered the arc, and the boundary conditions of the electric field intensity during the displacement process of the particle cluster induced arc were obtained.

[0070]

[0071] Where E is the electric field strength, E c is the critical arcing field strength;

[0072] The voltage-electrode spacing relationship is obtained based on the critical electric field strength and boundary conditions, including the following steps:

[0073] Calculate the maximum electric field strength E between the positive and negative electrodes max , since the electric field strength is the largest at the midpoint of the vertical midline, x is taken as 0, and the formula is as follows:

[0074]

[0075] For the electric field strength E that can generate an arc d ,satisfy:

[0076] E d ≥E c >E n ;

[0077] Among them, E n is the electric field strength under critical conditions where no arc is generated;

[0078] Since the voltage U is proportional to the charge Q:

[0079] Q ∝ U;

[0080] Combining the above formulas, we can get the voltage condition for the battery ejection to trigger an arc:

[0081]

[0082] Among them, U n , L n They are respectively the voltage and electrode distance under the critical condition where no arc is generated.

[0083] According to the voltage condition of the arc triggered by the battery spray, the safe voltage under different electrode spacing and the safe spacing under different voltage conditions can be obtained.

[0084] Among them, the safety boundaries for different electrode heights can be used for the height arrangement of the battery pack top plate, electrical and metal components, etc., to guide the electrical safety protection design of the battery system.

[0085] As Figure 1-4 shown, it is the second embodiment of a method for determining the safety boundary of an arc caused by battery thermal runaway injection provided by the present invention. In this embodiment, the following specific steps are included:

[0086] S10: Build an experimental platform for an arc caused by battery thermal runaway injection;

[0087] S20: Set the operating condition range, conduct a battery thermal runaway injection arc experiment on the experimental platform for an arc caused by battery thermal runaway injection, and obtain the critical conditions;

[0088] S30: Based on the electric field strength calculation formula, calculate the critical electric field strength for arc initiation, convert it into a voltage - electrode spacing relationship formula, and obtain the safety boundary;

[0089] S40: Adjust the electrode placement height, and cycle the above steps to obtain the safety boundaries of an arc caused by battery thermal runaway injection at different electrode heights.

[0090] Among them, in the above technical solution, the specific steps for building an experimental platform for an arc caused by battery thermal runaway injection include:

[0091] The first step is to connect the components of the battery thermal runaway arc simulation experimental platform correspondingly;

[0092] The second step is to arrange the metal electrodes for arc initiation oppositely above the battery exhaust valve. In this embodiment, the electrodes are arranged 3 cm above the exhaust valve; fix them through a fixture and connect them to the power supply line.

[0093] Furthermore, in the above technical solution, the electrical signal acquisition in the experimental platform for an arc caused by battery thermal runaway injection uses a high - frequency acquisition device with communication and data storage functions (above 10 kHz), such as an oscilloscope, a high - frequency probe, etc. In this embodiment, an oscilloscope with a sampling frequency of 12.5 kHz is used to collect arc signals, and a 400V / 20A DC regulated power supply is used to provide voltage conditions, and a resistor is connected in series to enhance the circuit load capacity;

[0094] Furthermore, in the above technical solution, the specific steps for setting the operating condition range, conducting a battery thermal runaway injection arc experiment on the experimental platform for an arc caused by battery thermal runaway injection, and obtaining the critical conditions include:

[0095] First step, set the research ranges of voltage and electrode spacing. Starting from the lower limit of the electrode spacing, different voltages are experimentally tested by the bisection method. In this embodiment, the set voltage is 100V - 400V, and the electrode spacing is 3mm - 7mm. Starting from the condition of 3mm and 400V, the tests are carried out in sequence; the battery thermal runaway is triggered by heating.

[0096] Second step, analyze the electrical signal data of the battery injection process obtained by the high-frequency acquisition device, and combine the instantaneous change rates and time window means of the voltage and current signals to judge whether there is an arc occurrence.

[0097] Among them, when the instantaneous change rate or the time window average value of the current and voltage signals meets the following conditions, it is determined that a breakdown arc event occurs (either the instantaneous change rate or the average value condition is satisfied), otherwise it is determined that there is no arc or abnormal interference:

[0098]

[0099] is the instantaneous change rate of the voltage; is the instantaneous change rate of the current; U 平均 is the average value of the voltage; U 基准 is the reference value of the voltage;

[0100] In this embodiment, the time window of the average value takes twice the sampling interval, that is, 0.16ms.

[0101] In this embodiment, the arc occurrence situations obtained through experiments are shown in Table 1.

[0102] Table 1: Arc occurrence situations obtained through experiments

[0103]

[0104] Third step, repeat the above steps to obtain the arc occurrence situations at different voltages and electrode spacings, and extract the critical conditions for triggering an arc. In this embodiment, through Table 1, it can be obtained that the critical arc occurrence conditions are between 200V / 7mm and 400V / 7mm.

[0105] Further, in the above technical solution, based on the electric field strength calculation formula, the critical electric field strength for arc initiation is calculated, and it is transformed into a voltage - electrode spacing relationship formula. The specific steps for obtaining the safety boundary include:

[0106] First step, establish a theoretical model for the arc initiated by the battery ejecta, and analyze the electric field strength boundary conditions;

[0107] Second step, based on the electric field strength calculation formula and the boundary conditions, combine the critical arc initiation conditions to obtain a voltage - electrode spacing relationship formula, and obtain the safety boundary.

[0108] Further, in the above technical solution, the metal electrodes for initiating the arc are arranged opposite to each other above the battery exhaust valve, fixed by a clamp and connected to the power supply line:

[0109] The metal electrode is made of copper or tungsten with a high melting point, and the fixture is a rigid fixture with insulation isolation to prevent errors caused by violent battery ejection, such as electrode shaking or falling off.

[0110] Furthermore, in the above technical solution, the specific steps of establishing a theoretical model of arc induced by battery injection include:

[0111] Combined with the arc phenomenon and arc signal changes recorded in the experiment, it is observed that the arc has obvious characteristics of occurrence (voltage drops from the baseline value)-continuation (voltage remains unchanged or changes slightly)-disappearance (voltage rises to the baseline value). It is assumed that the high-speed ejecta that triggers the arc is a uniform particle cluster passing through the middle of the electrode electric field. The theoretical model of battery ejecta-induced arc is established based on the high-speed ejecta that triggers the arc, such as Figure 3 As shown, the boundary conditions of the electric field intensity during the arc displacement induced by the particle cluster are obtained.

[0112]

[0113] Where E is the electric field strength, E c is the critical arcing field strength;

[0114] The voltage-electrode spacing relationship is obtained based on the critical electric field strength and boundary conditions, including the following steps:

[0115] Calculate the maximum electric field strength E between the positive and negative electrodes max , since the electric field strength is the largest at the midpoint of the vertical midline, x is taken as 0, and the formula is as follows:

[0116]

[0117] For the electric field strength E that can generate an arc d ,satisfy:

[0118] E d ≥E c >E n ;

[0119] Among them, E n is the electric field strength under critical conditions where no arc is generated;

[0120] Since the voltage U is proportional to the charge Q:

[0121] Q ∝ U;

[0122] Combining the above formulas, we can get the voltage condition for the battery ejection to trigger an arc:

[0123]

[0124] Among them, U n and L n are the voltage and electrode spacing under the critical condition without arc generation, respectively.

[0125] According to the voltage condition for the arc initiated by the battery ejecta, the voltage-electrode spacing safety boundary for the thermal runaway ejecta of the battery at 3 cm above the battery is obtained, as Figure 4 shown. The voltage safety boundary information at different electrode spacings and the change of the electrical clearance under different voltage conditions can be extracted from the figure. For example, when the voltage is 400 V, the electrical safety clearance at 3 cm above the battery cannot be lower than 9.9 mm.

[0126] As Figure 5 shown, it is the third embodiment of a method for determining the safety boundary of the arc initiated by the thermal runaway ejecta of the battery provided by the present invention. In this embodiment, the following specific steps are included:

[0127] S10: Build an experimental platform for the arc initiated by the thermal runaway ejecta of the battery;

[0128] S20: Set the working condition range, conduct an experiment on the thermal runaway ejecta arc of the battery in the experimental platform for the arc initiated by the thermal runaway ejecta of the battery, and obtain the critical conditions;

[0129] S30: Based on the electric field strength calculation formula, calculate the critical electric field strength for arc initiation, convert it into a voltage-electrode spacing relationship formula, and obtain the safety boundary;

[0130] S40: Adjust the placement height of the electrodes, and cycle the above steps to obtain the safety boundary of the arc initiated by the thermal runaway ejecta of the battery at different electrode heights.

[0131] Among them, in the above technical solution, the specific steps for building the experimental platform for the arc initiated by the thermal runaway ejecta of the battery include:

[0132] The first step is to connect the various components of the experimental platform for simulating the thermal runaway arc of the battery correspondingly;

[0133] The second step is to arrange the metal electrodes for initiating the arc oppositely above the battery exhaust valve. In this embodiment, the electrodes are arranged 4 cm above the exhaust valve; fix them through a fixture and connect them to the power supply line.

[0134] Further, in the above technical solution, for the acquisition of electrical signals in the experimental platform for battery thermal runaway ejection-induced arc, a high-frequency acquisition device with communication and data storage functions (above 10 kHz), such as an oscilloscope, a high-frequency probe, etc., is used. In this embodiment, an oscilloscope with a sampling frequency of 12.5 kHz is used to collect arc signals, and a 400V / 20A DC regulated power supply is used to provide voltage conditions. At the same time, a resistor is connected in series to enhance the load capacity of the circuit;

[0135] Further, in the above technical solution, a working condition range is set, and a battery thermal runaway ejection arc experiment is carried out in the experimental platform for battery thermal runaway ejection-induced arc. The specific steps for obtaining the critical conditions are as follows:

[0136] The first step is to set the research ranges of voltage and electrode spacing. Starting from the lower limit of the electrode spacing, different voltages are experimentally tested by the dichotomy method; in this embodiment, the set voltage is 100V - 400V, and the electrode spacing is 3mm - 7mm. Starting from the condition of 3mm and 400V, the tests are carried out in sequence; the battery thermal runaway is triggered by heating.

[0137] The second step is to analyze the electrical signal data of the battery ejection process obtained by the high-frequency acquisition device, and judge whether an arc occurs by combining the instantaneous change rates of voltage and current signals and the mean value of the time window;

[0138] Among them, when the instantaneous change rate or the average value of the current and voltage signals satisfies the following conditions, it is determined that a breakdown arc event occurs (either the instantaneous change rate or the average value condition is satisfied), otherwise it is determined that there is no arc or abnormal interference:

[0139]

[0140] is the instantaneous change rate of voltage; is the instantaneous change rate of current; U 平均 is the average value of voltage; U 基准 is the reference value of voltage;

[0141] In this embodiment, the average value time window is taken as twice the sampling interval, that is, 0.16 ms.

[0142] In this embodiment, the arc occurrence situation obtained through experiments is shown in Table 2.

[0143] Table 2: Arc occurrence situation obtained through experiments

[0144]

[0145] The third step is to repeat the above steps to obtain the arc occurrence situations at different voltages and electrode spacings, and extract the critical conditions for triggering an arc.

[0146] Further, in the above technical solution, based on the electric field strength calculation formula, calculating the critical electric field strength for arc ignition, and transforming it into a voltage - electrode spacing relationship, the specific steps for obtaining the safety boundary include:

[0147] First step, establish a theoretical model for the arc initiated by the battery ejecta, and analyze the electric field strength boundary conditions;

[0148] Second step, based on the electric field strength calculation formula and the boundary conditions, combine with the critical arc ignition condition to obtain the voltage - electrode spacing relationship and obtain the safety boundary.

[0149] Further, in the above technical solution, in the step of oppositely arranging the metal electrodes for initiating the arc above the battery exhaust valve, fixing them with a fixture and connecting them to the power supply line:

[0150] The metal electrode is copper or tungsten with a high melting point, and the fixture is a rigid fixture provided with insulation isolation to prevent errors caused by the shaking, falling off, etc. of the electrode due to the violent ejection of the battery.

[0151] Further, in the above technical solution, the specific steps for establishing a theoretical model for the arc initiated by the battery ejecta include:

[0152] Combined with the arc phenomenon and the change of the arc signal recorded in the experiment, it is observed that there are obvious stage characteristics of the occurrence (the voltage drops from the reference value) - continuation (the voltage remains unchanged or changes slightly) - disappearance (the voltage rises to the reference value) of the arc. Assuming that the high - speed ejecta for initiating the arc is a uniform particle cluster passing through the middle of the electrode electric field, establish a theoretical model for the arc initiated by the battery ejecta from the high - speed ejecta for initiating the arc, as Figure 3 shown, and obtain the electric field strength boundary conditions during the displacement of the particle cluster initiating the arc.

[0153]

[0154] Among them, E is the electric field strength, and E c is the critical arc ignition field strength;

[0155] Based on the critical electric field strength and the boundary conditions to obtain the voltage - electrode spacing relationship, including the following steps:

[0156] Calculate the maximum value E max of the electric field strength between the positive and negative electrodes. Since the electric field strength is the largest at the mid - point of the vertical center line, so x takes 0, and the formula is as follows:

[0157]

[0158] For the electric field strength E d that can generate an arc, it satisfies:

[0159] E d ≥Ec >E n ;

[0160] Among them, E n is the electric field strength under critical conditions where no arc is generated;

[0161] Since the voltage U is proportional to the charge Q:

[0162] Q ∝ U;

[0163] Combining the above formulas, we can get the voltage condition for the battery ejection to trigger an arc:

[0164]

[0165] Among them, U n , L n They are respectively the voltage and electrode distance under the critical condition where no arc is generated.

[0166] According to the voltage condition of arc induced by battery ejection, the voltage-electrode spacing safety margin of arc induced by thermal runaway ejection 4 cm above the battery is obtained, such as Figure 5 As shown in the figure, the voltage safety boundary information under different electrode spacing and the change of electrical clearance under different voltage conditions can be extracted from the figure. For example, when the voltage is 800V, the electrical safety clearance 4cm above the battery cannot be less than 10mm.

[0167] like Figure 6 FIG. 4 is a fourth embodiment of a method for determining a safety boundary of an arc caused by a battery thermal runaway ejection provided by the present invention. In this embodiment, the following specific steps are included:

[0168] S10: Build an experimental platform for battery thermal runaway jet-induced arcing;

[0169] S20: Setting the operating range, carrying out a battery thermal runaway jet arc experiment in a battery thermal runaway jet arc experiment platform, and obtaining critical conditions;

[0170] S30: Based on the electric field strength calculation formula, the critical electric field strength for arc initiation is calculated and converted into a voltage-electrode spacing relationship to obtain a safety margin;

[0171] S40: Adjust the electrode placement height, and repeat the above steps to obtain the safety margin of arc induced by battery thermal runaway ejection at different electrode heights.

[0172] Among them, in the above technical solution, the specific steps of building a battery thermal runaway jet-induced arc experimental platform include:

[0173] The first step is to connect the various components of the battery thermal runaway arc simulation experimental platform accordingly;

[0174] In the second step, metal electrodes for initiating an electric arc are arranged oppositely above the battery exhaust valve. In this embodiment, the electrodes are arranged 5 cm above the exhaust valve and fixed by a fixture and connected to the power supply line.

[0175] Furthermore, in the above technical solution, for the acquisition of electrical signals in the experimental platform for the electric arc initiated by the thermal runaway ejection of the battery, a high-frequency acquisition device with communication and data storage functions (above 10 kHz), such as an oscilloscope, a high-frequency probe, etc., is used. In this embodiment, an oscilloscope with a sampling frequency of 12.5 kHz is used to collect the electric arc signals, and a 400V / 20A DC regulated power supply is used to provide the voltage condition, and a resistor is connected in series to enhance the load capacity of the circuit.

[0176] Furthermore, in the above technical solution, a working condition range is set, and in the experimental platform for the electric arc initiated by the thermal runaway ejection of the battery, the specific steps for obtaining the critical conditions in the experiment on the electric arc initiated by the thermal runaway ejection of the battery include:

[0177] In the first step, the research ranges of voltage and electrode spacing are set. Starting from the lower limit of the electrode spacing, different voltages are experimentally tested by the dichotomy method. In this embodiment, the set voltage is 100V - 400V, and the electrode spacing is 3mm - 7mm. Starting from the condition of 3mm and 400V, the tests are carried out in sequence, and the battery thermal runaway is triggered by heating.

[0178] In the second step, the electrical signal data of the battery ejection process obtained by the high-frequency acquisition device is analyzed, and whether an electric arc occurs is judged by combining the instantaneous change rates of voltage and current signals and the mean value of the time window.

[0179] Among them, when the instantaneous change rate of current and voltage signals or the average value of the time window meets the following conditions, it is determined that a breakdown electric arc event occurs (either the instantaneous change rate or the average value condition is satisfied), otherwise it is determined that there is no electric arc or abnormal interference:

[0180]

[0181] is the instantaneous change rate of voltage; is the instantaneous change rate of current; U 平均 is the average value of voltage; U 基准 is the reference value of voltage;

[0182] In this embodiment, the time window of the average value is taken as twice the sampling interval, that is, 0.16 ms.

[0183] In this embodiment, the occurrence situation of the electric arc obtained through experiments is shown in Table 3.

[0184] Table 3: Occurrence situation of the electric arc obtained through experiments

[0185]

[0186] In the third step, repeat the above steps to obtain the arc generation conditions at different voltages and electrode spacings, and extract the critical conditions for arc initiation.

[0187] Further, in the above technical solution, based on the electric field strength calculation formula, calculating the critical electric field strength for arc initiation and converting it into a voltage-electrode spacing relationship, the specific steps for obtaining the safety boundary include:

[0188] In the first step, establish a theoretical model for arc initiation by battery ejecta, and analyze the electric field strength boundary conditions;

[0189] In the second step, based on the electric field strength calculation formula and boundary conditions, combine the critical arc initiation conditions to obtain a voltage-electrode spacing relationship and obtain the safety boundary.

[0190] Further, in the above technical solution, in the step of oppositely arranging the metal electrodes for arc initiation above the battery exhaust valve, fixing them with a fixture and connecting them to the power supply line:

[0191] The metal electrodes are made of high-melting-point copper or tungsten, and the fixture is a rigid fixture with insulation isolation to prevent errors caused by electrode shaking, falling off, etc. due to violent battery ejection.

[0192] Further, in the above technical solution, the specific steps for establishing a theoretical model for arc initiation by battery ejecta include:

[0193] Combined with the arc phenomena and arc signal changes recorded in the experiment, it is observed that the arc has obvious stage characteristics of occurrence (voltage drops from the reference value) - continuation (voltage remains unchanged or changes slightly) - disappearance (voltage rises to the reference value). Assuming that the high-speed ejecta causing the arc is a uniform particle cluster passing through the electrode electric field, establish a theoretical model for arc initiation by battery ejecta from the high-speed ejecta causing the arc, as Figure 3 shown, to obtain the electric field strength boundary conditions during the displacement of the particle cluster causing the arc.

[0194]

[0195] Among them, E is the electric field strength, and E c is the critical arc initiation field strength;

[0196] Based on the critical electric field strength and boundary conditions to obtain the voltage-electrode spacing relationship, including the following steps:

[0197] Calculate the maximum electric field strength E max between the positive and negative electrodes. Since the electric field strength is the maximum at the midpoint of the vertical center line, x is taken as 0, and the formula is as follows:

[0198]

[0199] For the electric field strength E that can generate an arc d ,satisfy:

[0200] E d ≥E c >E n ;

[0201] Among them, E n is the electric field strength under critical conditions where no arc is generated;

[0202] Since the voltage U is proportional to the charge Q:

[0203] Q ∝ U;

[0204] Combining the above formulas, we can get the voltage condition for the battery ejection to trigger an arc:

[0205]

[0206] Among them, U n , L n They are respectively the voltage and electrode distance under the critical condition where no arc is generated.

[0207] According to the voltage condition of arc induced by battery ejection, the voltage-electrode spacing safety margin of arc induced by thermal runaway ejection 5 cm above the battery is obtained, such as Figure 6 As shown in the figure, the voltage safety boundary information under different electrode spacing and the change of electrical clearance under different voltage conditions can be extracted from the figure. For example, when the voltage is 1500V, the electrical safety clearance 5cm above the battery cannot be less than 11.6mm.

[0208] like Figure 7 As shown, it is the fifth embodiment of the method for determining the safety boundary of the arc triggered by the injection of a battery thermal runaway provided by the present invention. In this embodiment, combined with the safety boundary relationship formula under different electrode heights obtained in the early stage, a relationship diagram between the arc starting critical voltage and the electrode gap when the electrode height is 3, 4, and 5 cm is drawn.

[0209] When the external voltage remains unchanged, the higher the electrode height, the smaller the electrode gap required for the battery thermal runaway jet to trigger an arc; when the electrode gap remains unchanged, the higher the electrode height, the higher the required external voltage. This is because the battery particle jet is in an inverted cone shape, and the farther away from the safety valve, the lower the concentration of the jet particles, and therefore the more stringent the requirements for forming a breakdown arc. According to the calculation results, it can be seen that when the voltage and electrode gap conditions are determined, the critical value of the electrode height can also be determined accordingly from the figure. Therefore, this method can be used for the height layout of the battery pack top plate, electrical and metal components, etc., to guide the design of electrical safety protection for the battery system.

[0210] Specifically, the principle of the present invention is as follows: during use, an experimental platform for battery thermal runaway jet-induced arc is built; the operating condition range is set, and battery thermal runaway jet arc experiments are carried out in the experimental platform for battery thermal runaway jet-induced arc to obtain the critical conditions; based on the electric field strength calculation formula, the critical electric field strength for arc initiation is calculated, which is converted into a voltage-electrode spacing relationship formula to obtain the safety boundary; the electrode placement height is adjusted, and the above steps are cycled to obtain the safety boundaries for battery thermal runaway jet-induced arc at different electrode heights.

Claims

1. A method for determining the safety boundary of arc induced by thermal runaway injection of a battery, characterized in that: The specific steps include: S10: Build an experimental platform for battery thermal runaway jet-induced arcing; S20: setting a working condition range, carrying out a battery thermal runaway jet arc experiment in the battery thermal runaway jet arc experiment platform, and obtaining critical conditions; S30: Based on the electric field strength calculation formula, the critical electric field strength for arc initiation is calculated and converted into a voltage-electrode spacing relationship to obtain a safety margin; S40: Adjust the electrode placement height, and repeat the above steps to obtain the safety margin of arc induced by battery thermal runaway ejection at different electrode heights.

2. The method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 1, characterized in that: The specific steps of building a battery thermal runaway jet-induced arc experimental platform include: The first step is to connect the various components of the battery thermal runaway arc simulation experimental platform accordingly; In the second step, the metal electrodes used to initiate the arc are arranged opposite to each other above the battery exhaust valve, fixed by a clamp and connected to the power supply line.

3. The method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 2, characterized in that: The electrical signal acquisition in the battery thermal runaway jet-induced arc experimental platform adopts a high-frequency acquisition device with communication and data storage functions.

4. The method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 3, characterized in that: The specific steps of setting the operating condition range, carrying out a battery thermal runaway jet arc experiment in the battery thermal runaway jet arc experiment platform, and obtaining critical conditions include: The first step is to set the voltage and electrode spacing research range by referring to the actual battery pack voltage and electrical component spacing data, and trigger battery thermal runaway by heating or overcharging; The second step is to analyze the electrical signal data of the battery injection process obtained by the high-frequency acquisition equipment, and combine the instantaneous change rate of the voltage and current signals and the time window mean to determine whether an arc occurs; The third step is to repeat the above steps to obtain the arc occurrence conditions at different voltages and electrode spacings and extract the critical conditions for arc initiation.

5. The method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 4, characterized in that: The instantaneous change rate thresholds of voltage and current signals are obtained through experimental measurements.

6. The method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 5, characterized in that: The time window is set to 1-2 times the sampling interval.

7. A method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 6, characterized in that: The specific steps of calculating the arc-starting critical electric field strength based on the electric field strength calculation formula, converting it into a voltage-electrode spacing relationship, and obtaining the safety margin include: The first step is to establish a theoretical model of arc induced by battery ejecta and analyze the boundary conditions of electric field intensity; In the second step, based on the electric field strength calculation formula and boundary conditions, combined with the critical arc starting conditions, the voltage-electrode spacing relationship is obtained to obtain the safety margin.

8. The method for determining the safety boundary of arc induced by thermal runaway injection of a battery according to claim 7, characterized in that: In the step of arranging the metal electrodes for initiating the arc opposite to each other above the battery exhaust valve, fixing them by a clamp and connecting them to the power supply line: The metal electrode is copper or tungsten with a high melting point, and the fixture is a rigid fixture provided with insulating isolation to prevent errors caused by violent battery spraying, such as electrode shaking and falling off.

9. The method for determining the safety boundary of arc induced by thermal runaway injection of a battery according to claim 8, characterized in that: The specific steps of setting the voltage and electrode spacing research range by referring to the actual battery pack voltage and electrical component spacing data, and triggering battery thermal runaway by heating or overcharging include: The experimental working condition starts from the lower limit of the electrode spacing setting, and uses the dichotomy method to test from the upper limit of the set voltage, so as to efficiently approach the most stringent arc starting critical condition and avoid the omission of working conditions that affects the accuracy of the safety boundary result.

10. The method for determining the safety boundary of a battery thermal runaway ejection arc according to claim 9, characterized in that: The specific steps of establishing a theoretical model of battery injection-induced arcs include: Combined with the arc phenomenon and arc signal changes recorded in the experiment, it was observed that the arc had obvious stage characteristics of occurrence (voltage dropped from the baseline value) - continuation (voltage remained unchanged or changed slightly) - disappearance (voltage rose to the baseline value). It was assumed that the high-speed ejecta that triggered the arc was a uniform particle cluster passing through the middle of the electrode electric field. A theoretical model of arc induced by battery ejecta was established based on the high-speed ejecta that triggered the arc, and the boundary conditions of the electric field intensity during the displacement process of the particle cluster induced arc were obtained.

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