Method and device for monitoring gas release of battery pack

Abstract

The invention provides a method and device for monitoring gas release of a battery pack, and the method comprises the following steps: a to-be-detected battery pack is placed in a high-pressure or low-pressure airtight cabin, and the pressure intensity of the high-pressure or low-pressure airtight cabin is the external pressure intensity of the battery pack in actual use. A piezoelectric excitation piece is attached to the high-pressure or low-pressure airtight cabin, the airtight cabin is subjected to frequency sweeping excitation to obtain the initial frequency f0 of the standing high-pressure or low-pressure airtight cabin, and the initial quality factor Q (0) is calculated. And continuously starting the piezoelectric excitation sheet by taking each second as a period to obtain a real-time frequency f (t) of the airtight cabin, and calculating a real-time quality factor Q (t) of the airtight cabin based on the initial frequency f0 and the real-time frequency f (t). And obtaining a threshold value A of a quality factor between electrolyte decomposition and diaphragm decomposition of the battery pack according to the capacity and the type of the battery pack and the volume of the airtight cabin. And comparing the real-time quality factor Q (t) with a threshold value A, and if Q (t) is less than A, stopping the pressurization or negative pressure device. Through the method, the explosion risk caused by continuous leakage of the battery pack is prevented.

Description

Technical Field

[0001] The present application relates to the field of airtightness detection, and in particular to a method and device for monitoring gas release from a battery pack. Background Art

[0002] A typical soft-pack lithium battery consists of an internal cell and an external hard shell. The lithium battery industry places high demands on sealing and explosion-proofing. Battery packs are highly susceptible to explosion in extreme environments, such as high or low pressure. The battery pack's explosion process involves the decomposition of the SEI membrane, the electrolyte, the diaphragm, and finally the explosion. Once the diaphragm decomposes during the battery pack reaction phase, the explosion can occur within seconds. This means that once the diaphragm inside the cell ruptures, the positive and negative electrodes come into contact, creating a short circuit. This can quickly lead to rapid heating and expansion, ultimately leading to explosion.

[0003] Existing battery air-tightness testing methods involve placing various sensors with different detection orientations within the negative pressure zone of the air-tightness test. During the air-tightness test, the battery pack is prone to continuous leakage. If the air-tightness test system fails to respond due to contaminated sensors, the continued leakage and inability to terminate the air-tightness test can lead to explosion accidents. Therefore, a method and device for monitoring battery pack gas release is needed to prevent the risk of explosion caused by continuous battery pack leakage during testing. Summary of the Invention

[0004] In view of this, it is necessary to provide a method for reducing costs and accurately detecting gas released from battery packs to solve the above problems.

[0005] An embodiment of the present application provides a method for monitoring gas release from a battery pack, wherein the volume of the airtight compartment is 300 L, and the battery pack is a 48 V, 50 Ah ternary lithium battery.

[0006] In at least one embodiment of the present application, when 30≤Q(t)≤40, the battery pack is in electrolyte decomposition;

[0007] When Q(t)<30, the battery pack is in the process of diaphragm decomposition;

[0008] Set the threshold A, A=35.

[0009] In at least one embodiment of the present application, the step of “deriving a threshold value A of the quality factor of the battery pack between electrolyte decomposition and diaphragm decomposition based on the capacity and type of the battery pack and the volume of the airtight compartment” includes the following steps:

[0010] Based on the capacity and type of the battery pack, the volume of the airtight compartment, and the reaction formula of the battery pack, the content ratio of the gas components generated in the battery pack reaction stage is calculated;

[0011] Injecting gas components with matching content ratios into the airtight compartment respectively. The pressure of the high-pressure or low-pressure airtight compartment is the amount of gas generated by the battery pack during actual use, so as to collect the gas content frequency F1 generated by the corresponding gas component and calculate the quality factor of the corresponding gas component;

[0012] Based on the initial quality factor Q(0) and the quality factor Q(h) of the gas component, the rate of decrease A0 of the quality factor of the gas component is calculated;

[0013] A gas release prediction model is constructed using the decline rate of the quality factor of the gas component as an indicator;

[0014] Based on the initial quality factor Q(0) and the real-time quality factor Q(t), the real-time quality factor decrease rate A1 is calculated. The real-time quality factor decrease rate A1 is used to match the gas release prediction model to determine the reaction stage of the battery pack.

[0015] Set the quality factor drop rate threshold B between electrolyte decomposition and diaphragm decomposition. If A1 ≥ B, stop the pressurization or negative pressure device.

[0016] In at least one embodiment of the present application, a judgment structure for stopping the pressurization or negative pressure device is implemented by cross-verification using threshold value A and threshold value B.

[0017] In at least one embodiment of the present application, when the decrease rate A1 of the real-time quality factor decreases by 5%–10%, it indicates that the SEI film is decomposed, and a pressurization or negative pressure device is performed;

[0018] When the real-time quality factor decrease rate A1 drops by 10–35%, the electrolyte is decomposed and a pressurization or negative pressure device is used;

[0019] When the decrease rate A1 of the real-time quality factor decreases by 30%, the pressurization or negative pressure device is stopped.

[0020] In at least one embodiment of the present application, a piezoelectric piece PZT vibration excitation is used as an excitation method;

[0021] Install the piezoelectric accelerometer on the airtight chamber opposite to the piezoelectric excitation piece;

[0022] The FFT module of the piezoelectric accelerometer responds to the excitation signal, and the FFT module extracts the main peak of the spectrum in real time.

[0023] In at least one embodiment of the present application, the FFT curve and Q value trajectory acquired in real time are derived based on the frequency spectrum;

[0024] Save the judgment conditions for stopping the pressurization or negative pressure device;

[0025] Archive the capacity, type, and volume of the battery pack's airtight compartment, and generate a battery pack explosion assessment report.

[0026] In at least one embodiment of the present application, the initial frequency of the airtight cabin obtained by frequency sweeping is 2900 Hz, and the resonance peak bandwidth obtained is 50 Hz;

[0027] Calculation shows that Q(0)=58.

[0028] A device for monitoring gas release from a battery pack includes the above-mentioned method steps for monitoring gas release from a battery pack.

[0029] The beneficial effects of the above-mentioned method for monitoring gas release from a battery pack are as follows:

[0030] 1. By directly attaching the piezoelectric excitation plate and piezoelectric accelerometer to the airtight compartment instead of directly contacting the battery pack, the electric excitation plate and the piezoelectric accelerometer are prevented from directly contacting the heat source of the battery pack. This forms a physical isolation area between the electric excitation plate and the heat generating area of ​​the battery pack, and between the piezoelectric accelerometer and the heat generating area of ​​the battery pack, thereby preventing the high temperature generated by the battery pack from causing device aging or data drift.

[0031] 2. The battery pack's reaction releases gas, which is trapped inside the airtight chamber due to its tight seal. As the battery pack reacts, the gas density inside the chamber increases, and the resonance bandwidth widens, causing the quality factor inside the chamber to decrease. Therefore, by sweeping the frequency of the chamber to excite it, the quality factor can be obtained and the battery pack's reaction process can be monitored. This method solves the problem of multiple sensors in airtight testing, thereby reducing costs.

[0032] 3. By setting a threshold for the quality factor, the test can be terminated before the diaphragm decomposes, avoiding thermal runaway explosion of the battery pack a few seconds after entering the diaphragm decomposition, which cannot guarantee the personal safety of the test personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of the method for monitoring gas release from a battery pack described in this application;

[0034] Figure 2 A real-time quality factor Q(t) curve and a frequency curve are shown in the embodiment of the present application.

[0035] Figure 3 This is a graph showing a decreasing trend of the quality factor of Example 1 of the present application;

[0036] Figure 4 A schematic diagram of the internal structure of the battery pack described in this application;

[0037] 100. Battery pack; 1. Battery cell; 10. SEI membrane; 20. Positive electrode sheet; 30. Negative electrode sheet; 40. Current collector; 50. Separator; 60. Electrolyte; 2. Hard shell. DETAILED DESCRIPTION

[0038] The embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0039] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component. The terms "top", "bottom", "upper", "lower", "left", "right", "front", "back", and similar expressions used herein are for illustrative purposes only.

[0040] An embodiment of the present application provides a method for monitoring gas released from a battery pack, comprising the following steps:

[0041] S1: Place the battery pack to be tested in a high-pressure or low-pressure airtight chamber, where the pressure of the high-pressure or low-pressure airtight chamber is the external pressure of the battery pack during actual use.

[0042] S2: Attach the piezoelectric excitation plate to the high-pressure or low-pressure airtight chamber, sweep the frequency to excite the airtight chamber to obtain the initial frequency f0 of the static high-pressure or low-pressure airtight chamber, and calculate the initial quality factor Q(0)

[0043] Among them, S2 also includes the steps:

[0044] S21: Set the excitation frequency band of the piezoelectric excitation piece to 5 kHz to 25 kHz, and use the piezoelectric piece PZT vibration excitation as the excitation method.

[0045] S22: Install the piezoelectric accelerometer on the airtight chamber opposite to the piezoelectric excitation piece.

[0046] S23: an FFT module of the piezoelectric accelerometer responding to the excitation signal, and the FFT module extracts the main peak of the spectrum in real time.

[0047] S3: The piezoelectric excitation plate is continuously turned on at a rate of one second to obtain the real-time frequency f(t) of the airtight chamber. The real-time quality factor Q(t) of the airtight chamber is calculated based on the initial frequency f0 and the real-time frequency f(t).

[0048] S4: Determine the threshold value A of the quality factor of the battery pack between electrolyte decomposition and diaphragm decomposition based on the capacity, type and volume of the airtight compartment of the battery pack.

[0049] Among them, S4 also includes the steps of:

[0050] S41: Calculate the content ratio of gas components generated in the battery pack reaction stage based on the capacity and type of the battery pack, the volume of the airtight compartment, and the reaction formula of the battery pack;

[0051] S42: Injecting gas components with matching content ratios into the airtight chamber respectively, and using a piezoelectric excitation piece to sweep the frequency of the airtight chamber to collect the gas content frequency F1 generated by the corresponding gas component, and calculate the quality factor of the corresponding gas component;

[0052] S43: Calculate the decrease rate A0 of the reference quality factor based on the initial quality factor Q(0) and the quality factor Q(h) of the gas component;

[0053] S44: Constructing a gas release prediction model using the decrease rate A0 of the reference quality factor as an indicator;

[0054] S45: Calculate the real-time quality factor decrease rate A1 based on the initial quality factor Q(0) and the real-time quality factor Q(t), and use the real-time quality factor decrease rate A1 to match the gas release prediction model to determine the reaction stage of the battery pack;

[0055] S5: Compare the real-time quality factor Q(t) with the threshold A. If Q(t) < A, stop the pressurization or negative pressure device.

[0056] S6: deriving the real-time acquired FFT curve and Q value trajectory according to the spectrum;

[0057] S7: Save the judgment condition for stopping the pressurization or negative pressure device;

[0058] S8: Archive the capacity, type, and volume of the battery pack and generate an assessment report on the battery pack explosion.

[0059] The following embodiments of the present application are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features therein may be combined with each other.

[0060] In order to better understand the technical solution of this application, it is necessary to explain here that:

[0061] The battery pack consists of an internal cell and an external hard shell. The cell includes an SEI film, a positive electrode sheet, a negative electrode sheet, a current collector, a separator, and an electrolyte. The SEI film is a layer of film formed on the surface of the negative electrode sheet during the first charge of the battery pack due to the reduction reaction.

[0062] Each positive electrode sheet is connected to a current collector, and each negative electrode sheet is connected to a current collector. The current collector is the heat source of the battery pack. The electrolyte is the material filling the battery cell, that is, the electrolyte envelops the positive and negative electrode sheets, the separator, and the SEI film. The separator is located between the positive and negative electrodes. If the separator ruptures, the positive and negative electrodes will contact and short-circuit, causing the battery pack to explode.

[0063] When a battery pack is abnormally heated, the current collector first heats up and transfers heat to the connected negative electrode surface, causing the SEI film to decompose first, releasing gas and heat. Second, the large amount of heat and gas generated by the SEI film decomposition further heats the interior of the battery cell, causing the electrolyte temperature to rise. The electrolyte decomposes as the temperature rises, further releasing large amounts of flammable gas and exacerbating the temperature rise. Finally, the temperature rises to the heat resistance limit of the separator, causing it to melt and rupture, short-circuiting the positive and negative electrodes and causing an explosion. Therefore, the battery pack explosion reaction stages include the sequential decomposition of the SEI film, electrolyte, and separator.

[0064] The main components and reaction chemical formulas of the SEI film are as follows:

[0065] (CH2OCO2Li)2→Li2CO3+C2H4+CO2

[0066] Li2CO3→Li2O+CO2

[0067] The SEI film also includes trace components and generates other trace gases, which have little impact on the technical solution of this application and are therefore ignored and will not be described in detail.

[0068] The SEI film is only a layer of film generated on the surface of the negative electrode. Its content is very small compared to the electrolyte, resulting in a small amount of carbon dioxide and ethylene gas generated by the decomposition reaction of the SEI film and a slow reaction.

[0069] The electrolyte is the fluid that fills the space between the porous positive and negative electrode sheets. The main function of the electrolyte is to direct the movement of lithium ions to generate charge.

[0070] The main components and reaction chemical formulas of the electrolyte are as follows:

[0071] LiPF6→PF5+LiF

[0072] PF5+H2O→POF3+2HF

[0073]

[0074] The electrolyte also includes trace components and generates other trace gases. Here, in order to facilitate understanding of the technical solution of the present application, they are ignored and will not be described in detail.

[0075] The content of the electrolyte is much greater than that of the SEI film in the previous stage, so the gas content of hydrofluoric acid, hydrogen and carbon monoxide generated is high.

[0076] The amount of gas generated by the battery pack in the airtight cavity affects the resonance frequency in the airtight cavity, and as the explosion reaction stage continues, the amount of gas generated by the battery pack will gradually increase.

[0077] In this application, the main gases released by the battery pack are carbon dioxide, ethylene, hydrofluoric acid, hydrogen and carbon monoxide. The content of other trace gases is too small to have a negligible impact on the detection experiment.

[0078] See also Figure 1-4 , embodiments of the present application provide a method for monitoring gas released from a battery pack,

[0079] In step S1, the battery pack is placed in either a high-pressure airtight cabin or a low-pressure airtight cabin, and the pressure of either airtight cabin is used to simulate the battery pack in an extreme environment, that is, a high-pressure environment or a low-pressure environment.

[0080] The airtight chamber is equipped with a fixing slot that matches the shape of the battery pack's bottom slot. When the battery pack is placed in the airtight chamber, the bottom slot of the battery pack is placed in the fixing slot and connected to the fixing slot. This prevents the battery pack from moving during monitoring due to chemical reactions. This displacement vibration can affect the accuracy of the real-time frequency.

[0081] In step S2, the electro-active sheet is attached to the wall of any airtight compartment, and is located in the external environment to avoid direct contact between the electro-active sheet and the heat source of the battery pack, which may cause aging of the electro-active sheet.

[0082] Both the electro-active plate and the piezoelectric accelerometer can be attached to the airtight cabin using thermal insulation adhesive to prevent the heat source of the battery pack from being transferred through the airtight cabin to the electro-active plate and the piezoelectric accelerometer connected to the airtight cabin.

[0083] Insulation adhesives such as aerogel insulation adhesive, silicone insulation adhesive, polyurethane insulation adhesive, etc. will not be given examples one by one.

[0084] A static high-pressure airtight cabin or a static high-pressure airtight cabin or a static low-pressure airtight cabin is a state in which the battery pack is placed in the airtight cabin, and the battery pack is not started and does not release gas. The airtight cabin is initially excited by a sweep frequency using an electric excitation plate, and the initial frequency f0 and the resonance peak bandwidth Δf0 are recorded. The initial quality factor Q(0) is obtained based on the calculation. Here, the quality factor Q refers to the vibration quality factor (Quality Factor, referred to as Q value) of the airtight cabin as an excited vibration system. This is an important parameter that describes the energy loss capacity of a vibration system. It originates from the fields of acoustics and mechanical vibration, and its essential meaning is:

[0085] Q = 2π × (system stored energy / energy lost per cycle)

[0086] The interior of the airtight cabin is a completely enclosed space in which the gas will not leak or flow. This closed state allows the vibration energy under piezoelectric excitation to be reflected and stored multiple times inside the cabin, and the energy is not easily dissipated. Therefore, because the battery pack in the system is in a state where the battery pack is not started and no gas is released, the damping in the airtight cabin system is small, that is, the energy loss in each vibration cycle is very small. Because of this, the system has good vibration retention ability, which is reflected in a higher quality factor (Q value). Therefore, the better the airtightness, the slower the system energy decays and the higher the Q value.

[0087] On the contrary, if the battery pack leaks to produce gas, the SEI membrane decomposes or the diaphragm ruptures, resulting in internal leakage or external leakage, the air pressure in the cabin will fluctuate, causing the damping of the vibration system in the airtight cabin to increase, resulting in large energy loss of the airtight cabin system, and thus a decrease in the Q value.

[0088] Q(0) satisfies the relationship:

[0089] Q(0)=f0 / Δf0.

[0090] In step S3, after the battery pack starts to release gas, the piezoelectric actuator is activated once per second to sweep the airtight chamber. Each time, the real-time main peak frequency f(t) and bandwidth Δf(t) are obtained, and the real-time quality factor Q(t) is calculated.

[0091] Q(t)=f(t) / Δf(t)

[0092] Δf(t)=f(t)-f0

[0093] Among them, the piezoelectric excitation piece can be a piezoelectric piece PZT vibration excitation, which generates vibration through the piezoelectric effect to excite the airtight cabin. And a piezoelectric accelerometer is used to receive the excitation signal generated by the piezoelectric excitation piece. The excitation signal is the resonant frequency generated by the swept frequency excitation of the airtight cabin by the electric excitation piece. The piezoelectric accelerometer is installed on the airtight cabin and is arranged opposite to the piezoelectric excitation piece. The piezoelectric excitation piece generates vibration through the piezoelectric effect, and the vibration energy propagates in the airtight cabin in the form of waves. If the accelerometer is arranged relative to the excitation piece, such as being located on the opposite side or symmetrically of the excitation piece, it can ensure that the vibration signal received by the accelerometer is a direct response to the excitation signal, rather than a reflected or attenuated signal.

[0094] The FFT module of the piezoelectric piece PZT vibration excitation receives the excitation signal generated by the piezoelectric excitation piece. The FFT module extracts the main peak of the spectrum in real time and calculates the resonant frequency f(t) and bandwidth Δf.

[0095] After stopping the pressurization or negative pressure device, the FFT curve of the real-time frequency response curve and the Q value trajectory of the Q(t) change over time are exported. The judgment conditions for stopping the pressurization or negative pressure device are saved. The battery pack capacity, type, and airtight compartment volume are then archived, and a battery pack explosion assessment report is generated.

[0096] The excitation frequency band of the piezoelectric excitation plate is 5kHz to 25kHz, and according to the Q(t) trajectory of the curve graph showing the change of quality factor over time, as the amount of gas released from the battery pack increases, the gas density in the airtight compartment increases, which will cause the quality factor to decrease.

[0097] And through step S4, the capacity and type of the battery pack are obtained, and the content ratio of the electrolyte and the SEI film in the battery pack is obtained.

[0098] According to the reaction formula of the battery pack and the content ratio of the electrolyte and SEI film in the battery pack, the ratio of the gas content released by the battery pack during the reaction process is calculated.

[0099] The ratio of the gas content released during the battery pack explosion reaction affects the quality factor, which in turn determines the threshold A of the quality factor between electrolyte decomposition and diaphragm decomposition.

[0100] By comparing A and the real-time quality factor Q(t), the monitoring experiment is judged as the condition for whether to proceed. When Q(t) < A, the pressurization or negative pressure device is stopped. When Q(t) ≥ A, the pressurization or negative pressure device is continued.

[0101] Because the larger the battery capacity, the more chemical substances inside, resulting in a greater amount of gas released once a reaction occurs. Under the same cabin, batteries with large capacity are more likely to cause significant structural frequency changes. And because of the same battery state changes, the larger the airtight cabin, the lower the stiffness distribution and resonant frequency distribution of the airtight cabin, and the "much" vibration. Therefore, in order to avoid the influence of battery pack capacity, type and airtight cabin volume on real-time quality factors, this embodiment uses a 48V, 50Ah ternary lithium battery pack to be tested and places it in a 300L low-pressure airtight cabin or a high-pressure airtight cabin. This is used as an example for Example 1 to facilitate understanding of the technical solution of this application. The next step is to:

[0102] The piezoelectric excitation plate attached to the airtight cabin performs sweep frequency excitation on the unactivated ternary lithium battery. When the ternary lithium battery is not activated and no gas is released, the initial frequency of the airtight cabin is 2900Hz, the resonance peak bandwidth is 50Hz, and the initial quality factor Q(0) is calculated to be 58.

[0103] After the battery pack starts to release gas, the piezoelectric excitation plate is turned on once per second to sweep the airtight chamber.

[0104] According to the 48V, 50Ah ternary lithium battery, the conventional standard includes 18.2% electrolyte and 0.11% SEI film.

[0105] Given a 48V, 50Ah ternary lithium battery, monitor the frequency and quality factor curves over time in a 300L low-pressure airtight chamber, and analyze the Q(t) trajectory of the curves.

[0106] The real-time quality factor Q(t) curve and frequency curve are shown in the attached figure of the specification. Figure 2 .

[0107] The Q(t) quality factor graph shows a slow decline from 0 to 20 seconds, corresponding to the slow decomposition of the SEI film, releasing small amounts of CO2 and C2H4. The graph shows that when 40 < Q(t) ≤ 58, the battery pack is in the process of SEI film decomposition. When Q(t) > 40, the disturbance is small, the system energy loss is low, and the curve is stable.

[0108] The rapid decline phase between 20 and 40 seconds corresponds to the rapid decomposition of the electrolyte, releasing multiple components such as CO, HF, and H2. As shown in the figure, when 30 ≤ Q(t) ≤ 40, the battery pack is in the electrolyte decomposition stage. The gas in the airtight chamber gradually increases, exacerbating the resonance imbalance. The mid-to-late stage of electrolyte decomposition serves as the critical explosion protection judgment zone.

[0109] After 40 seconds, the severe disturbance phase begins, corresponding to diaphragm rupture, rapid structural changes, and increased short-circuit risk. When Q(t) < 30, testing must be stopped immediately and pressure relief must be implemented.

[0110] The frequency curve shows that the frequency jitter amplitude increases as the explosion phase approaches, indicating intensified modal mixing and bubble disturbances. By combining the frequency curve with Q(t), we can conclude that slowly varying frequency shifts indicate SEI film decomposition, frequency jumps indicate electrolyte decomposition, and disordered frequency jitter indicates diaphragm decomposition.

[0111] The criteria for determining whether to stop the pressurization or negative pressure device are set as the quality factor between electrolyte decomposition and diaphragm decomposition, with the threshold value A of the quality factor set as a prerequisite. Threshold A is the middle value of the electrolyte stage. The main factor in selecting the middle value is that the middle value has two-way fault tolerance. If A is set to > 38, it is in the early stage of electrolyte decomposition, and some electrolytes are not fully released, which can easily lead to misjudgment, frequent test terminations, and reduced efficiency. It is also premature protection, but not a real danger. However, if A is set to < 32, this is close to the diaphragm decomposition stage, with a clear risk of explosion, and stopping the pressurization or negative pressure device is too late. It is a delayed protection, but the safety margin is approaching. Therefore, the middle value A = 35 is the optimal critical point that takes into account detection stability, response adequacy, and safety lead time.

[0112] The gas content generated by the electrolyte decomposition reaction and the gas content generated by the SEI film reaction are calculated based on the mass conservation law and stoichiometric relationship of the chemical reaction formula. The specific method steps and the calculation formula involving existing foundations are as follows:

[0113] The industry standard quality of ternary lithium batteries is:

[0114] 43.2g / Ah×50Ah=2160g.

[0115] The mass of the electrolyte is 393 g and the mass of the SEI film is 2.38 g.

[0116] First, balance the chemical equation and calculate the molar mass of each substance.

[0117] The amount of reactant substance is calculated based on the molar mass available from the periodic table, satisfying the formula:

[0118]

[0119] n is the amount of substance (mol), m is the mass (g), and the molar mass M (g / mol). The molar mass is calculated based on the atomic number and relative atomic mass (g / mol) of the elements in the periodic table, and will not be described in detail here.

[0120] The calculated amount of the reactant (CH2OCO2Li)2 in the SEI film is 0.01266 mol.

[0121] According to the stoichiometric conversion of the amount of substance of the product, the amount of substance of Li2CO3, C2H4 and CO2 is 0.01266 mol.

[0122] Based on the amount of substance and molar mass, calculate the mass of each product. The mass of Li2CO3 is 0.937g, the mass of C2H4 is 0.354g, and the mass of CO2 is 0.557g.

[0123] As time goes by, the SEI film decomposes and gradually generates a main reaction formula with the reactant being (CH2OCO2Li)2 and a side reaction formula with the reactant being Li2CO3.

[0124] As time goes by, the electrolyte decomposes into the main reaction of reactant LiPF6 and the first side reaction of PF5 and water. After the main reaction and negative reaction occur, accompanied by the heating of the battery pack, EC / DMC will quickly decompose into the second side reaction of CH4, CO, and H2 only after the internal temperature of the battery pack reaches 90°C. However, it hardly reacts at room temperature.

[0125] The mass of HF, the first side reaction, and the mass of CH4, CO, and H2, the second side reaction, are calculated using the above method. When EC / DMC decomposes, a large number of bubbles, such as CH4, CO, and H2, are instantly formed. These bubbles quickly fill the insulation layer and the gaps in the cell cavity, causing a local pressure rise and a violent phase transition from boiling liquid to gas. The large number of bubbles reduces the effective acoustic impedance of the battery pack, increasing sound absorption and reducing reflections, resulting in increased system damping and accelerated energy attenuation. This in turn causes frequency jump disturbances in the acquisition of the swept frequency excitation, until frequency jitter disorder occurs, reaching the diaphragm decomposition.

[0126] The first injection of C2H4 and CO2 gases, generated by the primary reaction of SEI membrane decomposition, into the airtight chamber. Simultaneously, the piezoelectric actuator is activated once per second to sweep the chamber's frequency. The final resonant frequency of the chamber after the injection of C2H4 and CO2 gases is acquired. The trend of the quality factor within the chamber after the primary reaction of SEI membrane decomposition is obtained.

[0127] Next, the airtight chamber is injected with the amount of CO2 generated by the side reaction of the SEI membrane decomposition. Simultaneously, the piezoelectric excitation plate is activated once per second to sweep the airtight chamber. The resonant frequency of the airtight chamber, obtained after the CO2 gas injection, is collected. The change trend of the quality factor within the airtight chamber after the main and side reactions of the SEI membrane decomposition are obtained. The rate of decrease of the quality factor within the airtight chamber relative to the initial quality factor of the airtight chamber after the SEI membrane decomposition is completed is obtained.

[0128] Next, the amount of HF gas generated by the primary reaction of electrolyte decomposition is injected into the airlock for the third time. Simultaneously, the piezoelectric excitation plate is activated once per second to sweep the airlock. The resonant frequency of the airlock is acquired after the HF gas injection is complete. The quality factor trend within the airlock is obtained after the primary reaction and the first secondary reaction of electrolyte decomposition are completed.

[0129] Next, the amount of CH4, CO, and H2 gases generated by the main reaction of electrolyte decomposition is continuously injected into the airtight chamber for the fourth time. Simultaneously, the piezoelectric excitation plate is activated once per second to sweep the airtight chamber. The resonant frequency of the airtight chamber, obtained after the injection of CH4, CO, and H gases, is collected. The trend of the quality factor change within the airtight chamber after the main reaction, the first side reaction, and the second side reaction of electrolyte decomposition are obtained. The rate of decrease of the quality factor within the airtight chamber relative to the initial quality factor of the airtight chamber after the electrolyte decomposition is completed is obtained.

[0130] The degradation rates of the quality factors obtained four times are integrated to construct the stage of the battery pack reaction formula corresponding to the degradation rate generated in each reaction stage, determine the reaction stage of the battery pack, and construct a gas release prediction model including the degradation rate of the quality factor of the gas component.

[0131] Based on the above content, the quality factor decrease trend curve of the 48V, 50Ah ternary lithium battery pack placed in a 300L low-pressure airtight cabin or a high-pressure airtight cabin is shown in the attached figure of the specification. Figure 3 .

[0132] The decrease rate A1 of the real-time quality factor is matched with the decrease rate of the real-time quality factor of the gas release prediction model.

[0133] As shown in the figure, when the real-time QF decrease rate A1 drops by 5%–10%, it indicates SEI membrane decomposition, the disturbance is mild, and the reaction continues. Pressurization or negative pressure devices should be used. When the real-time QF decrease rate A1 drops by 10–35%, it indicates electrolyte decomposition. Pressurization or negative pressure devices should be used and dynamically monitored. When the real-time QF decrease rate A1 drops by 30%, it reaches the critical point before membrane disturbance and instability, and pressurization or negative pressure devices should be stopped.

[0134] Furthermore, the pressurization or negative pressure device is stopped based on the absolute value and the drop rate of Q(t). That is, if Q(t) < 35 or the drop rate ≥ 30%, the pressurization or negative pressure device is stopped.

[0135] A device for monitoring gas release from a battery pack includes the steps of the method for monitoring gas release from a battery pack described above. Detailed descriptions are omitted here.

[0136] The above method for monitoring gas release from a battery pack has the following beneficial effects:

[0137] 1. By directly attaching the piezoelectric excitation plate and piezoelectric accelerometer to the airtight compartment instead of directly contacting the battery pack, the electric excitation plate and the piezoelectric accelerometer are prevented from directly contacting the heat source of the battery pack. This forms a physical isolation area between the electric excitation plate and the heat generating area of ​​the battery pack, and between the piezoelectric accelerometer and the heat generating area of ​​the battery pack, thereby preventing the high temperature generated by the battery pack from causing device aging or data drift.

[0138] 2. The battery pack's reaction releases gas, which is trapped inside the airtight chamber due to its tight seal. As the battery pack reacts, the gas density inside the chamber increases, and the resonance bandwidth widens, causing the quality factor inside the chamber to decrease. Therefore, by sweeping the frequency of the chamber to excite it, the quality factor can be obtained and the battery pack's reaction process can be monitored. This method solves the problem of multiple sensors in airtight testing, thereby reducing costs.

[0139] 3. By setting a threshold for the quality factor, the test can be terminated before the diaphragm decomposes, avoiding thermal runaway explosion of the battery pack within a few seconds after the diaphragm decomposes, which cannot guarantee the personal safety of the test personnel.

[0140] The above is only an implementation method of the present application. It should be pointed out that for ordinary technicians in this field, improvements can be made without departing from the creative concept of the present application, but these all fall within the scope of protection of the present application.

Claims

1. A method for monitoring gas release from a battery pack, characterized in that: The method comprises the following steps: Place the battery pack to be tested in a high-pressure or low-pressure airtight chamber, where the pressure of the high-pressure or low-pressure airtight chamber is the external pressure of the battery pack during actual use; Attach the piezoelectric excitation plate to the high-pressure or low-pressure airtight chamber, sweep the frequency to excite the airtight chamber to obtain the initial frequency f0 of the static high-pressure or low-pressure airtight chamber, and calculate the initial quality factor Q(0); The piezoelectric excitation plate is continuously turned on at a cycle of one second to obtain the real-time frequency f(t) of the airtight cabin, and the real-time quality factor Q(t) of the airtight cabin is calculated based on the initial frequency f0 and the real-time frequency f(t); The quality factor threshold A of the battery pack between electrolyte decomposition and diaphragm decomposition is obtained based on the capacity, type and volume of the airtight compartment of the battery pack; Compare the real-time quality factor Q(t) with the threshold A. If Q(t) < A, stop the pressurization or negative pressure device.

2. The method for monitoring gas released from a battery pack according to claim 1, wherein: The volume of the airtight cabin is 300L, and the battery pack is a 48V, 50Ah ternary lithium battery.

3. The method for monitoring gas released from a battery pack according to claim 2, wherein: When 30≤Q(t)≤40, the battery pack is in electrolyte decomposition; When Q(t)<30, the battery pack is in the process of diaphragm decomposition; Set the threshold A, A=35.

4. The method for monitoring gas released from a battery pack according to claim 1, wherein: The method of “deriving a threshold value A of the quality factor of the battery pack between electrolyte decomposition and diaphragm decomposition based on the capacity and type of the battery pack and the volume of the airtight compartment” includes the following steps: Based on the capacity and type of the battery pack, the volume of the airtight compartment, and the reaction formula of the battery pack, the content ratio of the gas components generated in the battery pack reaction stage is calculated; Injecting gas components with matching content ratios into the airtight compartment respectively. The pressure of the high-pressure or low-pressure airtight compartment is the amount of gas generated by the battery pack during actual use, so as to collect the gas content frequency F1 generated by the corresponding gas component and calculate the quality factor of the corresponding gas component; Based on the initial quality factor Q(0) and the quality factor Q(h) of the gas component, the rate of decrease A0 of the quality factor of the gas component is calculated; A gas release prediction model is constructed using the decline rate of the quality factor of the gas component as an indicator; Based on the initial quality factor Q(0) and the real-time quality factor Q(t), the real-time quality factor decrease rate A1 is calculated. The real-time quality factor decrease rate A1 is used to match the gas release prediction model to determine the reaction stage of the battery pack. Set the quality factor drop rate threshold B between electrolyte decomposition and diaphragm decomposition. If A1 ≥ B, stop the pressurization or negative pressure device.

5. The method for monitoring gas released from a battery pack according to claim 4, wherein: Use threshold A and threshold B for cross-validation to stop the judgment structure of the pressurization or negative pressure device.

6. The method for monitoring gas released from a battery pack according to claim 2, wherein: When the real-time quality factor decrease rate A1 drops by 5%–10%, it indicates that the SEI film is decomposed and a pressurization or negative pressure device is used; When the real-time quality factor decrease rate A1 drops by 10–35%, the electrolyte is decomposed and a pressurization or negative pressure device is used; When the decrease rate A1 of the real-time quality factor decreases by 30%, the pressurization or negative pressure device is stopped.

7. The method for monitoring gas released from a battery pack according to claim 1, wherein: The method of "attaching a piezoelectric excitation sheet to a high-pressure or low-pressure airtight capsule, sweeping the frequency to excite the airtight capsule to obtain the initial frequency f0 of the static high-pressure or low-pressure airtight capsule, and calculating the initial quality factor Q(0)" comprises the following steps: Use piezoelectric PZT vibration excitation as the excitation method; Install the piezoelectric accelerometer on the airtight chamber opposite to the piezoelectric excitation piece; The FFT module of the piezoelectric accelerometer responds to the excitation signal, and the FFT module extracts the main peak of the spectrum in real time.

8. The method for monitoring gas released from a battery pack according to claim 1, wherein: The method of "stopping the pressurization or negative pressure device" further comprises the following steps: Export the real-time FFT curve and Q value trajectory based on the spectrum; Save the judgment conditions for stopping the pressurization or negative pressure device; Archive the capacity, type, and volume of the battery pack's airtight compartment, and generate a battery pack explosion assessment report.

9. The method for monitoring gas released from a battery pack according to claim 2, wherein: The initial frequency of the airtight cabin obtained by frequency sweep is 2900 Hz, and the resonance peak bandwidth is 50 Hz; Calculation shows that Q(0)=58.

10. A device for monitoring gas release from a battery pack, characterized in that: A method for monitoring gas released from a battery pack according to any one of claims 1 to 9.

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