Method for mass decoupling of battery thermal runaway polyphase ejecta

Abstract

This invention belongs to the field of lithium-ion battery safety technology and relates to a method for mass decoupling of multiphase ejections during battery thermal runaway. The method obtains the mass of non-condensable reactive gases through a gas analysis measuring tank, obtains the mass of the electrolyte droplets and solid particle mixture ejected during the safety valve opening phase by interrupting heating, and obtains the total mass of electrolyte vapor and non-condensable reactive gases discharged during the thermal runaway phase by continuous heating. Combining this with the total battery mass loss before and after thermal runaway, the method achieves staged mass separation of the multiphase ejections according to mass conservation, and further constructs the hydrodynamic simulation boundary conditions for the discrete phase model. This method can improve the accuracy of mass quantification of multiphase ejections during battery thermal runaway.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery safety technology, specifically relating to a method for staged measurement, mass separation, and simulation boundary condition construction of multiphase ejected materials during battery thermal runaway. Background Technology

[0002] Lithium-ion batteries are widely used in energy storage, electric vehicles, and other electrochemical energy applications due to their high energy density and long cycle life. However, under conditions of mechanical, electrical, and thermal abuse, batteries are prone to thermal runaway, releasing large amounts of heat, fumes, and ejected contaminants in a short period. Thermal runaway ejected contaminants are typically not a single gaseous phase but a multiphase mixture containing non-condensable reactive gases, electrolyte vapors, electrolyte droplets, and solid particles. The non-condensable reactive gases often include components such as H2, CO, CO2, CH4, C2H4, and C2H6; the liquid phase includes the liquid electrolyte and its vapors; and the solid phase may include electrode material fragments and decomposition residues. These ejected contaminants not only affect the propagation and diffusion of thermal runaway but are also closely related to the flammability, corrosiveness, conductivity, deposition behavior, and subsequent fire response within the energy storage space. Therefore, accurately understanding the mass distribution of ejected contaminants during battery thermal runaway is of practical significance for the safety design, risk assessment, and numerical simulation of energy storage systems.

[0003] In existing technologies, solutions employ closed containers combined with pressure and temperature changes and the ideal gas law to measure the gas production under thermal runaway conditions, and can further detect gas composition. For example, Chinese patent application CN114545248A discloses a method and detection device for characterizing the thermal runaway characteristics of lithium-ion batteries, which focuses on quantitatively characterizing the gas production rate and volume under thermal runaway conditions, and monitoring temperature, pressure, and gas composition. Another example is Chinese patent application CN110600817A, which discloses a pressure resistance test device for studying the thermal runaway hazard of lithium-ion batteries, capable of collecting the gas and solid products released after thermal runaway and analyzing parameters throughout the process. CN206236353U discloses a lithium-ion battery thermal runaway experimental device, which can test mass changes, gas concentration, pressure changes, etc. These schemes provide a technical foundation for thermal runaway experimental platforms, total gas production analysis, and overall hazard studies. However, their focus is mainly on the total gas production, overall experimental parameters, or the overall collection of gas / solid products. A complete methodological path has not yet been formed to measure the safety valve opening stage and the subsequent thermal runaway stage separately, and to perform mass-closed separation of non-condensable reactive gases, electrolyte vapors, electrolyte droplets, and solid particles.

[0004] Furthermore, existing solutions typically do not directly convert the experimentally measured phased mass data into fluid dynamics simulation boundary conditions that can be called upon by discrete phase models. Therefore, there is still a reliance on empirical proportions or simplified assumptions between experimental data and simulation inputs.

[0005] Therefore, it is still necessary to propose a new method that is centered on the methodology and can utilize conventional experimental equipment to complete the decoupling of multiphase ejecta mass in stages and support the construction of simulation boundaries. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a mass decoupling method for battery thermal runaway multiphase ejecta that can distinguish between the safety valve opening stage and the thermal runaway stage, and perform staged mass separation of non-condensable reactive gases, electrolyte droplets, electrolyte vapors and solid particles.

[0007] To address the aforementioned technical problems, this invention provides a method for mass decoupling of multiphase ejecta from battery thermal runaway, comprising the following steps:

[0008] S1. Place the battery under test in the gas analysis measurement container to trigger thermal runaway. After standing until the electrolyte vapor condenses, measure the gas pressure, temperature and composition information in the container, and calculate the mass of non-condensable reactive gas based on the ideal gas law.

[0009] S2. Place the batteries to be tested in the same batch in a heat-insulated vapor venting tank, and use the interrupted heating mode to trigger the heating until the battery safety valve opens and then stop heating. Capture the electrolyte droplets and solid particle mixture sprayed out during the safety valve opening stage, and obtain the mass of the droplet and particle mixture during this stage based on the mass changes of the heat-insulated vapor venting tank and the battery before and after the experiment.

[0010] S3. Place the batteries to be tested in the same batch in a thermally insulated vapor venting tank, and use a continuous heating mode to trigger thermal runaway. After the thermal runaway ends and the batteries inside are cooled, weigh the thermally insulated vapor venting tank and the batteries inside as the same control body to obtain the total mass of electrolyte vapor and non-condensable reactive gas discharged during the thermal runaway stage.

[0011] S4. Based on the measurement results of steps S1 to S3 and the total mass loss of the battery before and after thermal runaway, the multiphase ejection during the safety valve opening stage and the thermal runaway stage is separated by mass according to the law of conservation of mass to obtain the mass of non-condensable reactive gas, electrolyte droplets, electrolyte vapor and solid particles.

[0012] S5. Based on the mass separation results of step S4, construct time-varying mass flow rate curves and perform multiphase component allocation to form the fluid dynamics simulation boundary conditions for the discrete phase model.

[0013] Furthermore, the non-condensable reactive gas includes at least one of H2, CO, CO2, CH4, C2H4, and C2H6.

[0014] Furthermore, in step S1, the gas inside the analysis tank is collected through the gas sampling port, and the volume fraction of each gas component is analyzed. The mass of the non-condensable reactive gas is calculated based on the ideal gas law. It satisfies:

[0015] ;

[0016] in, R is the volume of the gas analysis measuring vessel, and R is the gas constant. This indicates the number of gas species involved in the summation calculation. and These are the initial pressure and the initial temperature, respectively. and These are the pressure and temperature after the system has been allowed to reach equilibrium. and denoted as volume fraction and molar mass of the i-th gas, respectively.

[0017] Furthermore, in step S2, the interrupted heating mode is: detecting the battery safety valve opening signal, and immediately cutting off the heating source when the safety valve opening signal is detected, so that the battery stops entering the subsequent thermal runaway stage.

[0018] Furthermore, after steps S2 and S3, the process further includes: separating the captured droplet and particle mixture using a drying method to obtain the mass of the electrolyte droplets. and solid particle mass And satisfy:

[0019] = + ;

[0020] in, The mass of the droplet and particle mixture is given.

[0021] Furthermore, the drying method is as follows: the mixture of droplets and particles is dried to constant weight at a preset temperature, the residue after drying is taken as solid particles, and the mass difference before and after drying is taken as the mass of electrolyte droplets.

[0022] Furthermore, in step S4, batteries of the same batch and the same state of charge are selected, and their initial mass and final mass after thermal runaway are measured respectively. The total mass loss of each battery is calculated and the average value is taken as the benchmark for the total mass loss of the battery before and after thermal runaway.

[0023] Mass of electrolyte vapor ejected during thermal runaway phase satisfy:

[0024] ;

[0025] in, This represents the total mass of electrolyte vapor and non-condensable reactive gases emitted during the thermal runaway phase. The mass of the non-condensable reactive gas calculated in step S1.

[0026] Furthermore, in step S5, a time-varying mass flow rate curve is constructed based on the safety valve opening time, thermal runaway initiation time, and thermal runaway termination time recorded during the experiment.

[0027] During the safety valve opening phase, if the duration of this phase is Δ The total ejected mass is Then the peak mass flow rate satisfies:

[0028] =2 / Δ ;

[0029] During the thermal runaway phase, if the duration of this phase is Δ The total ejected mass is Then the average mass flow rate satisfies:

[0030] = / Δ ;

[0031] The total mass flow rate is then allocated to the multiphase components based on the mass percentage of each phase.

[0032] Compared to existing technologies, this invention does not stop at obtaining the total gas production or overall experimental parameters during thermal runaway. Instead, it divides the battery thermal runaway ejection process into a safety valve opening stage and a thermal runaway stage, and obtains key mass information for each stage. Then, it achieves mass separation of multiphase ejected materials through mass conservation. Therefore, it is possible to simultaneously obtain the mass results of non-condensable reactive gases, electrolyte droplets, electrolyte vapor, and solid particles within the same methodological chain. The obtained results are further transformed into the hydrodynamic simulation boundary conditions of the discrete phase model, thereby improving the consistency between experimental measurements and simulation modeling. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0034] Figure 1 This is an overall operation flowchart of the battery thermal runaway multiphase ejection mass decoupling method provided in an embodiment of the present invention;

[0035] Figure 2 This is a bar chart of the mass decoupling results obtained in the experiment of this invention embodiment. Each bar corresponds to the mean value of different mass parameters. The black I-shaped lines above the bars represent error bars, which are used to characterize the dispersion or uncertainty range of the experimental data. The numbers marked near the error bars represent the mean value of the corresponding physical quantities.

[0036] Figure 3 The diagram shows the uncertainty analysis results obtained through multiple sets of experiments in the embodiments of the present invention, which is used to illustrate the measurement stability of each mass parameter obtained by the method of the present invention.

[0037] Figure 4 This is a comparison image of the high-speed camera experimental image at 1ms in an embodiment of the present invention and the corresponding CFD simulation image, wherein:

[0038] Figure 4 Image (a) in the image is a high-speed camera image taken at 1 ms.

[0039] Figure 4 (b) in the image is the corresponding CFD simulation image at 1ms.

[0040] Figure 5 This is a comparison image of the high-speed camera experimental image at 5ms in an embodiment of the present invention and the corresponding CFD simulation image, wherein:

[0041] Figure 5 Image (a) in the image is a high-speed camera image taken at 5ms.

[0042] Figure 5 (b) in the image is the corresponding CFD simulation image at 5ms.

[0043] Figure 6 This is a comparison image of the high-speed camera experimental image at 10ms in an embodiment of the present invention and the corresponding CFD simulation image, wherein:

[0044] Figure 6 (a) in the image is a high-speed camera experimental image at 10ms.

[0045] Figure 6 (b) in the image is the corresponding CFD simulation image at time 10ms;

[0046] Figure 7 This is a comparison image of the high-speed camera experimental image at 20ms in an embodiment of the present invention and the corresponding CFD simulation image, wherein:

[0047] Figure 7 Image (a) in the image is a high-speed camera image taken at 20ms.

[0048] Figure 7(b) in the image is the corresponding CFD simulation image at time 20ms;

[0049] Figure 8 This is a comparison image of the high-speed camera experimental image at 100ms in an embodiment of the present invention and the corresponding CFD simulation image, wherein:

[0050] Figure 8 (a) in the image is a high-speed camera experimental image at 100ms.

[0051] Figure 8 (b) in the image is the corresponding CFD simulation image at 100ms.

[0052] Figure 9 This is a comparison image of the high-speed camera experimental image at 200ms in an embodiment of the present invention and the corresponding CFD simulation image, wherein:

[0053] Figure 9 Image (a) in the image is a high-speed camera image taken at 200ms.

[0054] Figure 9 (b) in the image is the corresponding CFD simulation image at 200ms. Detailed Implementation

[0055] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described below with reference to the accompanying drawings. It should be understood that the following embodiments are mainly used to explain the methodological concept of this invention, and are not intended to limit this invention to a fixed equipment configuration, a specific container form, or a single experimental platform. After reading this specification, those skilled in the art can select from the prior art a sealed measuring container, an insulated venting container, a weighing device, a heating device, a sampling device, and a data acquisition device capable of achieving the corresponding functions to complete the method flow of this invention, based on the specifications of the battery to be tested, experimental conditions, and safety requirements.

[0056] like Figure 1 As shown, this embodiment provides a method for mass decoupling of multiphase ejecta from battery thermal runaway. This method primarily addresses the industry challenge of distinguishing the mass distribution of multiphase ejecta during the safety valve opening phase from the intense gas generation phase of thermal runaway, a problem present in existing technologies. The core theoretical basis of this invention lies in scientifically dividing the entire ejection process into two distinct physical stages based on the differences in the physical mechanisms of multiphase jets during battery thermal runaway:

[0057] In the first stage, as the internal temperature and pressure of the battery rise sharply, the safety valve is instantly forced open, and the high-pressure gas accumulated inside the battery, containing a large amount of electrolyte vapor, is ejected outward at high speed. During this high-speed ejection process, the high-pressure gas violently entrains and traps the liquid electrolyte inside the battery, forming a typical high-speed gas-liquid two-phase jet. Therefore, the physical characteristic of this safety valve opening stage is dominated by the atomization and spraying of electrolyte droplets.

[0058] As thermal runaway progresses into its second stage—the stage of intense gas production—the safety valve remains continuously open and depressurized. Inside the battery, various complex redox side reactions, the collapse of positive and negative electrode materials, and the decomposition of the electrolyte continue to occur intensely and continuously. In this stage, the jet's momentum primarily stems from the stable pressure difference maintained by the continuous gas production from the internal chemical reactions, rather than the extreme pressure surge caused by the instantaneous depressurization in the first stage. Because the jet's momentum distribution tends to be uniform, the strong high-speed airflow shearing effect of the moment the safety valve opens is absent, thus significantly reducing the entrainment effect of high-pressure gas on the liquid electrolyte. During this period, the remaining electrolyte inside the battery is mainly converted into a gaseous state through continuous evaporation under high-temperature conditions. Therefore, the jet material in this stage is primarily dominated by the mixed diffusion of non-condensable reactive gases and electrolyte vapors, with liquid droplets accounting for a very small proportion, which can be essentially ignored in engineering calculations and mass decoupling.

[0059] Based on the above analysis of the physical characteristics of the thermal runaway stage, the specific steps of this embodiment first proceed to step S1, namely, the mass measurement of the non-condensable reactive gas. In this step, the experimenter first needs to select the battery to be tested. To ensure the accuracy of the data, the surface of the battery to be tested should be thoroughly cleaned before placing it into the experimental container to remove any impurities that may affect the mass measurement. Subsequently, the battery to be tested can be initially weighed using a high-precision balance, and its initial mass can be accurately recorded. Next, the battery to be tested is placed in the gas analysis and measurement container. The gas analysis and measurement container used in this step can be a sealed container in the art that can withstand the corresponding experimental conditions, as long as its volume is known and pressure, temperature, and composition information can be measured after the experiment. In order to eliminate the interference of oxygen, nitrogen, and moisture in the ambient air on the thermal runaway reaction mechanism and the analysis of the gas-generating components, and also to ensure the safety of the entire high-temperature experimental process, the gas analysis and measurement container can be evacuated and filled with inert protective gas before triggering thermal runaway. For example, the inside of the gas analysis and measurement container can be evacuated by starting a vacuum pump. After achieving a certain vacuum level, a pure inert protective gas is introduced into the container. High-purity nitrogen or argon is typically used as the inert protective gas. To completely replace any residual air, this process of evacuating and introducing inert protective gas can be repeated multiple times, for example, up to four times, to ensure a completely pure inert environment is formed inside the container.

[0060] After all the replacement operations are completed, the experimenters need to accurately record the initial pressure inside the gas analysis and measurement tank. and initial temperature .

[0061] After preparation, optionally, the battery under test is fixedly attached to the heating plate, and then the heating plate is activated to continuously heat the battery inside the gas analysis measurement container at a constant power. During this process, the data acquisition system monitors the surface temperature, voltage, and pressure changes inside the container in real time. When a sudden rise in battery temperature is observed, accompanied by a sudden increase in pressure data inside the container, it can be determined that the battery has been successfully triggered and thermal runaway has occurred. At this point, the control system must immediately shut down the heating plate to stop the heat input. Because the thermal runaway reaction releases heat and a large amount of multiphase mixed ejecta, the inside of the container is under high temperature and high pressure.

[0062] To accurately separate the gaseous and condensed phases, the gas analysis container must be kept absolutely sealed and allowed to stand for a sufficient period of time. The ultimate goal of this standing period is to allow the temperature of the gas inside the container to reach a dynamic equilibrium with the external ambient temperature. Once the temperature drops and stabilizes, the electrolyte vapor, which was initially in a gaseous state at high temperatures, gradually loses its thermal energy and condenses completely into droplets, which adhere to the inner wall or bottom of the container due to gravity. After this thorough condensation process, only the non-condensable reactive gases that cannot be liquefied at room temperature and pressure remain free in the container space and contribute to the pressure. These non-condensable reactive gases are products of the complex chemical decomposition of the battery's internal materials, typically including, but not limited to, at least one of H2, CO, CO2, CH4, C2H4, and C2H6. At this point, the researchers record the precise pressure after the equilibrium is reached. and stable temperature .

[0063] Subsequently, the mixed gas inside the container can be collected using an airtight gas sampling bag, and the sample is immediately sent to a gas chromatograph for component analysis to obtain the types of each gas component and their corresponding volume fractions. Based on the ideal gas law, the total mass of the non-condensable reactive gases can be calculated using specific mathematical formulas. The formula satisfies: In this calculation formula, The free volume of the gas analysis and measurement vessel refers to the effective gas survival space after deducting the volume of the battery body and internal support frame; R represents the universal gas constant. Indicates the number of gas species involved in the summation calculation; and These correspond to the initial pressure and initial temperature recorded before the experiment began; and These correspond to the final pressure and final temperature after thermal runaway ends and the system is allowed to condense and reach equilibrium. This represents the volume fraction of the i-th gas as determined by gas chromatography. This represents the standard molar mass of the i-th gas. Through the derivation of this formula, the mass of the non-condensable reactive gas in a multiphase mixture can be independently decoupled.

[0064] Next, we proceed to step S2 of this method, namely, mass capture of the droplet-particle mixture. In this stage, a brand-new test cell from the same batch, model, and state of charge as those used in previous experiments is required. Similarly, its surface is cleaned and it is weighed before the experiment, and the initial mass of this cell is recorded. The battery was then carefully placed on a specialized fixture inside an insulated steam venting tank. Before the experiment officially began, the entire insulated steam venting tank, along with the battery inside, was weighed as a whole on a high-precision balance, and the initial total mass was recorded. .

[0065] To accurately capture the products at specific stages, this step employs an interrupted heating mode. Specifically, a heating plate is connected to begin heating the battery. Simultaneously, a highly sensitive safety valve opening detection device, such as an acoustic sensor, a micro-differential pressure sensor, or an optical displacement sensor, can be placed near the battery's safety valve. The data acquisition module is pre-programmed to immediately trigger a relay to cut off the power input to the heating plate once it detects a characteristic signal indicating the safety valve has ruptured and opened. The core purpose of this interrupted heating mode is to stop the battery from absorbing external heat the instant the safety valve is forced open by internal high pressure. This artificial intervention interrupts the process of heat accumulation in the battery, preventing it from entering the subsequent, more severe, and widespread thermal runaway phase.

[0066] In the extremely brief instant that the safety valve is ruptured by high pressure, the high-pressure gas accumulated inside the battery erupts out, carrying with it a large number of electrolyte droplets and possibly a small number of tiny solid particles. These high-speed ejected particles detach from the battery body and move violently upwards or in the intended exhaust direction. At this point, they will encounter the pre-set trapping structure inside the insulated vapor venting tank.

[0067] The entire heating experiment was interrupted at this point, and the entire tank was kept under insulation to ensure that the emitted electrolyte vapors and non-condensable reactive gases could completely escape to the external environment through the tank openings. After the internal reaction had completely subsided and the system had naturally cooled to a safe room temperature, the researchers weighed the entire insulated vapor venting tank, along with all trapped materials, as a single unit and recorded the mass at this point. Then, the can was carefully opened, the battery residue inside was removed, and the liquid droplets and particulate residue adhering to its surface were carefully cleaned before it was weighed again, and the mass of the battery residue at this time was recorded. Based on the law of conservation of mass, the total mass of electrolyte vapor and non-condensable gases ejected from the system during the safety valve opening phase and not captured is... This is equal to the overall mass difference of the insulated steam venting tank before and after the experiment, which satisfies the formula: = - .

[0068] At the same time, the total mass loss of the battery during the isolated phase when the safety valve opens can be calculated, which satisfies the formula: = - Furthermore, since the total mass lost by the battery minus the mass of vapor and gas escaping to the external environment equals the mass of the material retained and trapped inside the tank, it can be deduced that the mass of the mixture of droplets and solid particles discharged during the safety valve opening phase satisfies the following formula: - .

[0069] Following this, to further refine the decoupling of droplets and particles in the mixture, the collected droplet-particle mixture can be separated using a drying method. The specific procedure is as follows: the mixture adhering to the bottom of the container and the filter screen is scraped and collected, placed in an oven, and continuously dried at a constant preset temperature until the mass of two consecutive weighings remains constant, indicating a constant weight state. After drying, the solid matter remaining in the container is identified as solid particles, and its individual mass is recorded as _____. The difference between the total mass of the mixture before drying and the mass of the residual solids after drying is naturally the single mass of the electrolyte droplets that evaporated during the process, denoted as . .

[0070] In practical engineering processes, if no obvious free droplets or formed solid particles are found in the mixture collected during the safety valve opening stage or thermal runaway stage by visual inspection, the mass contribution of the corresponding phase can be ignored within the allowable engineering error range.

[0071] It should be noted that the insulated steam venting tank used in this step can be implemented using a container structure that can simultaneously perform insulation, venting, and collection functions, as is currently available in the art. Its basic requirements are: on the one hand, it should allow the timely discharge of steam and non-condensable reactive gases; on the other hand, it should collect as much of the droplet and particle mixture ejected during the safety valve opening phase as possible. Correspondingly, the collection structure used to achieve the collection function can also adopt any applicable solution in the art, such as inertial impaction, filtration interception, cyclone separation, or other equivalent techniques, as long as effective retention of droplets and particles can be achieved. To prevent steam condensation in the collection path, the corresponding path can be insulated or heated as needed; to reduce the retention of steam and non-condensable reactive gases in the container, openings can be provided or other existing discharge methods can be used. The above descriptions all pertain to conventional experimental configurations that can be freely selected by those skilled in the art to implement the method steps of this invention.

[0072] The process then proceeds to step S3, which involves acquiring the mass of the electrolyte vapor. This stage focuses on the second, violent reaction phase of thermal runaway. A brand-new test battery from the same batch and in the same condition is accurately weighed and its weight recorded before being placed in an insulated vapor venting container. The entire venting container and battery are then placed on a precision balance, and the initial total mass is recorded. .

[0073] Unlike the interrupted heating in step S2, this step uses a continuous heating mode to trigger the battery after connecting the heating plate. This means that even if the safety valve rupture signal occurs, the heating plate will continue to provide heat input until the battery completely enters a runaway state and violently erupts. In this stage, the safety valve is fully open, and the internal materials react violently to generate a large amount of heat, causing the remaining electrolyte to rapidly boil and vaporize, forming a large-scale electrolyte vapor, which is accompanied by a large amount of newly generated non-condensable reactive gases that gush out.

[0074] It should be noted that the insulated steam venting tank used to implement step S3 can also be implemented using structures that meet the insulation and venting requirements in the prior art. For example, heating can be achieved by wrapping the tank with silicone electric heating tape, or by covering it with a hot air convection circulation box, high-power infrared radiation heating, or any other existing industrial heating and insulation methods. For those skilled in the art, any alternative implementation method that can achieve the same function using other existing technologies is acceptable.

[0075] In practical applications, the temperature inside the tank can be flexibly set according to the physicochemical properties of the electrolyte used in the battery being tested, as long as the temperature inside the tank is maintained above the boiling point of the electrolyte.

[0076] After the thermal runaway reaction has completely ended, all the fumes have dissipated, and the container has cooled to room temperature, the entire insulated vapor venting tank is weighed again as a control volume, and the mass after the experiment is recorded. Since very few droplets and particles are ejected during the second stage, the mass reduction within the tank is primarily attributed to the escape of gaseous substances. Therefore, the total mass of electrolyte vapors and non-condensable reactive gases ejected and escaped during the thermal runaway phase is [not specified]. This is equal to the mass difference before and after the tank is emptied. Subtract the total mass of electrolyte vapor and non-condensable reactive gases that escape during the safety valve opening phase. , recorded as = .

[0077] After obtaining the basic mass data for each stage, the process proceeds to step S4, mass decoupling calculation. In this comprehensive calculation phase, to eliminate random errors caused by individual manufacturing variations in single batteries, multiple batteries from the same batch and with the same state of charge are selected, and their initial mass before thermal runaway is precisely measured using a precision balance. Then, these batteries were subjected to a complete thermal runaway experiment one by one. After the experiment was completely completed and the battery debris had completely cooled to room temperature, the external adhering substances on the surface were carefully removed, and the debris was weighed again to obtain the final mass of the debris. By calculating the mass difference of each battery before and after combustion, the total mass loss of each battery can be calculated. Then, the mathematical average of these data is calculated and used as the benchmark for the total mass loss of the battery before and after thermal runaway, denoted as . Based on all the measurement results obtained above, mathematical separation begins.

[0078] First, the mass of non-condensable reactive gases. It is obtained directly from step S1.

[0079] Secondly, mass decoupling is performed on the safety valve opening phase. Step S2 has already measured the total mass of electrolyte vapor and non-condensable reactive gas discharged during the safety valve opening phase. At the same time, the total mass loss of the battery during this stage was measured. Due to the mass loss of the battery during this stage, part of it is discharged through the opening in the form of electrolyte vapor and non-condensable reactive gases, while the other part is trapped by the trapping structure in the form of electrolyte droplets and solid particles. Therefore, the total mass of the droplet and particle mixture during the safety valve opening stage can be expressed as: Therefore, the overall mass of the non-gas phase ejected during the safety valve opening phase can be obtained.

[0080] If the mixture of droplets and particles captured in step S2 is further dried and separated, the mass difference before and after drying corresponds to the mass of the electrolyte droplets. The residual solids after drying correspond to the mass of solid particles. .

[0081] Next, mass decoupling is performed on the thermal runaway stage. Step S3 has already measured the total mass of electrolyte vapor and non-condensable reactive gases emitted during the thermal runaway stage. Since the total mass comprises two parts—the mass of electrolyte vapor and the mass of non-condensable reactive gases—and the mass of non-condensable reactive gases is... As obtained in step S1, the electrolyte vapor mass during the thermal runaway phase is... It can be represented as: - This allows for the differentiation between the vapor portion and the non-condensable reactive gas portion in the gas phase during thermal runaway.

[0082] Furthermore, the total mass loss of the battery before and after thermal runaway was measured. Because of the total mass loss of the battery before and after thermal runaway, there is already This portion is discharged as electrolyte vapor and non-condensable reactive gases; therefore, the total mass of the droplet and particle mixture during the thermal runaway phase... It can be represented as: .

[0083] If the mixture of droplets and particles collected during the thermal runaway stage is further dried and separated, the mass of the electrolyte droplets during the thermal runaway stage can be obtained similarly. and solid particle mass .

[0084] In summary, the mass decoupling results for different stages and phases in this embodiment can be summarized as follows:

[0085] The mass of the non-condensable reactive gas is ;

[0086] The total mass of electrolyte vapor and non-condensable reactive gases discharged during the safety valve opening phase is: The total mass of the mixture of droplets and particles during the safety valve opening phase is: The mass of the electrolyte droplets is The mass of the solid particles is ;

[0087] The total mass of electrolyte vapor and non-condensable reactive gases discharged during the thermal runaway phase is The mass of electrolyte vapor during the thermal runaway phase is The total mass of the droplet and particle mixture during the thermal runaway phase is The mass of the electrolyte droplets is The mass of the solid particles is .

[0088] Through the above-mentioned phase-by-phase decoupling, the mass separation of multiphase ejecta from battery thermal runaway is finally achieved.

[0089] like Figure 2 and Figure 3 As shown, this embodiment uses actual experimental data to interpret the feasibility and scientific validity of the method. For example... Figure 2 As shown, the mass of non-condensable gases The average value was 182.3g, representing the mass of the mixed gas phase discharged during the thermal runaway phase. The average value is 752.7g, and the total mass loss due to battery thermal runaway is... The total mass loss during the safety valve opening phase is as high as 1146.2g. The mass of the gas-phase mixture during the safety valve opening phase is 142.3g. The mass of the ejected droplets was only 23.9g. Comparison of these data reveals that during the extremely brief opening of the safety valve, the strong entrainment effect generated by the instantaneous release of high-speed internal airflow resulted in the droplets being the dominant mass of the ejected material at this stage. Since the battery had not yet entered a period of intense high-temperature side reactions, and the electrode materials such as the positive and negative electrode frames and current collectors had not undergone large-scale collapse and tearing, almost no macroscopic solid particles were carried out during this stage. In the subsequent second stage of intense thermal runaway, decoupling data suggests that the mass of the ejected droplets was negligible. This is because during this prolonged and intense gas production stage, the safety valve was fully open, and the driving force of the jet was solely the stable internal and external pressure difference maintained by continuous internal chemical gas production, rather than the explosive instantaneous pressure release at the moment the safety valve ruptured. This relatively gentle and uniform jet flow lacks the high-speed airflow shearing effect unique to the moment the safety valve opens, significantly reducing the entrainment effect of the airflow on the liquid. Simultaneously, because the internal temperature of the battery has already reached a high level, the remaining liquid electrolyte inside the battery rapidly and continuously transforms into high-energy electrolyte vapor through boiling and evaporation. Therefore, in this second-stage jet ejection, non-condensable chemical reaction gases and vaporized electrolyte vapor are the main components, while the mass of liquid droplets is extremely low and scientifically negligible. This summary of phenomena based on real experimental data also provides a data-theoretical basis for the simplification of subsequent complex computational fluid dynamics (CFD) models and the setting of boundary conditions.

[0090] To demonstrate the engineering feasibility and data reliability of this decoupling method, the inventors conducted uncertainty mathematical analysis using systematically performed multiple sets of comparative experimental data. For example... Figure 3 As shown, the total mass loss of the battery after thermal runaway The measurement performance was the most stable, with an extremely small combined uncertainty of only ±2.42g, representing the accuracy of conventional methods such as balance weighing. In contrast, the total mass loss during the safety valve opening phase... The combined uncertainty, as shown in the graph, reaches a maximum of ±19.2g. However, this relatively large fluctuation is entirely consistent with natural laws, confirming the inherent physical randomness of the instantaneous high-pressure release process due to the slight difference in the safety valve rupture threshold during this stage. Other parameters, such as the mixed gas phase uncertainty of ±5.1g, the non-condensable gas uncertainty of ±8.28g, and the average mass of the thermal runaway vapor reaching 570.4g with a corresponding uncertainty of ±25.66g, etc., are also considered and analyzed from a macroscopic relative error perspective. The relative expanded uncertainty of all key mass parameters is strictly controlled below the extremely low level of 5%. Therefore, the comprehensive experimental measurement system provided by this invention, which includes physical isolation and mathematical derivation, has an uncertainty level within a completely reasonable and sound scientific research engineering range, absolutely ensuring the authenticity, validity, and high reliability of the experimental data and scientific conclusions derived from it.

[0091] Finally, we proceed to step S5, which involves the construction and scientific correction of the CFD simulation boundary conditions. This step aims to transform the static mass data obtained through precise decoupling in the previous experiments into dynamic boundary input parameters that can be directly read and used by the CFD solver. First, it is necessary to construct the time-varying mass flow rate curve. This is based on the instantaneous opening time of the safety valve, precisely recorded by the data acquisition module throughout the experiment. The onset of the violent thermal runaway reaction and the moment when thermal runaway completely ends Based on the total quality values ​​of each stage obtained in the previous steps, a mathematical model is constructed.

[0092] In the first stage of the safety valve opening, because this process is extremely short, the duration is denoted as Δ. The total ejected physical mass during this stage was measured experimentally and denoted as . It includes the gas phase. and solid-liquid phase Since the depressurization process typically exhibits a rapid decay after an initial burst, it is scientifically hypothesized that the total mass flow rate during this phase follows a triangular distribution curve on the time axis, with its peak flow rate naturally occurring at... At time point 2 / 2, the peak mass flow rate satisfies the mathematical relationship: =2 / Δ .

[0093] In the second stage of thermal runaway and violent gas production, the reaction is relatively long and stable, and the duration is denoted as Δ. The total ejected mass at this time is It is mainly composed of gaseous products. = For this type of long-duration, stable injection, it is reasonable to assume that its mass flow rate exhibits an approximately uniform, gently sloping rectangular distribution along the time axis. Therefore, the average mass flow rate during this phase can be satisfied by a simple division formula: = / Δ .

[0094] After constructing the overall flow rate curve framework, the multiphase component weights must be assigned internally to the overall flow rate. During the safety valve opening phase, the mass percentage factor of the solid-liquid mixture is calculated based on the decoupling mass. = / and the mass percentage factor of the gas phase mixture = / .

[0095] Similarly, during the thermal runaway phase, the mass percentage factor of electrolyte vapor was calculated. = / The mass percentage factor of non-condensable reactive gases = / .

[0096] After completing these basic preparations, you can find the boundary feature surface representing the safety valve vent in the boundary settings interface of the commercial CFD solver software and set its type to mass flow inlet boundary.

[0097] In this embodiment, the insulated steam venting tank used in steps S2 and S3 can be placed on a precision balance throughout the experiment. The precision balance is connected to a data acquisition module to continuously record the real-time mass change data of the venting tank as a control body. Furthermore, the precision balance can output mass data according to a preset sampling period, for example, recording one mass sampling point every 1 second, thereby obtaining a real-time curve of mass change over time. Based on this real-time mass change curve, the total mass flow rate within a given time interval can be obtained by dividing the mass difference between adjacent sampling times by the corresponding time interval. .

[0098] When the simulation step time is in the safety valve opening phase, the total mass flow rate is adjusted using the software's built-in user-defined function (UDF) programming interface. Dynamic distribution interpolation is performed using the triangular function constructed above. Furthermore, based on the multiphase component weight allocation obtained from decoupling, independent mass flow rate inputs are subdivided: the mass flow rate assigned to the gas-phase mixture at this point... Satisfy the formula = × ; imparts mass flow rate to the solid-liquid mixture Satisfy the formula = × .

[0099] When the simulation time step reaches the second stage of thermal runaway, the total mass flow rate is expressed via UDF. Switch to constant average mass flow rate input Accordingly, the components are redistributed based on the component proportion parameters characteristic of this stage: the mass flow rate of the electrolyte vapor is then assigned... Satisfy the formula = × ; imparts a mass flow rate to the non-condensable reactive gas Satisfy the formula = × .

[0100] like Figures 4 to 9 As shown, this embodiment further compares and verifies the simulation results obtained from the CFD boundary conditions constructed based on the above-mentioned mass decoupling results with the high-speed camera experimental results at multiple typical time points. It can be seen that, in the jet initiation stage, rapid development stage, and continuous eruption stage, the simulation results obtained by constructing CFD boundary conditions using the mass decoupling results obtained by the method of this invention show good consistency with the high-speed camera experimental results in terms of the main jet initiation position, jet height development trend, overall diffusion profile, and continuous eruption morphology. This verifies the rationality and effectiveness of the multiphase ejecta mass decoupling method and its boundary condition construction method proposed in this invention.

[0101] In summary, this method successfully fills the technical gap in the field of battery safety testing where it is difficult to quantify the quality of multiphase ejecta in stages. Its significant technical effect is that, through scientific experimental isolation, the chaotic multiphase ejecta is decomposed into independently quantifiable basic data. This not only provides data support for exploring the microscopic mechanism of battery thermal runaway, but also creates and provides a high-precision boundary parameter generation tool for the formulation of fire prevention and control strategies for large-scale energy storage systems, the design of thermal propagation barrier materials, and system-level safety risk assessment and accurate numerical simulation.

Claims

1. A method for mass decoupling of multiphase ejecta from battery thermal runaway, characterized in that, Includes the following steps: S1. Place the battery under test in the gas analysis measurement container to trigger thermal runaway. After standing until the electrolyte vapor condenses, measure the gas pressure, temperature and composition information in the container, and calculate the mass of non-condensable reactive gas based on the ideal gas law. S2. Place the batteries to be tested in the same batch in a heat-insulated vapor venting tank, and use the interrupted heating mode to trigger the heating until the battery safety valve opens and then stop heating. Capture the electrolyte droplets and solid particle mixture sprayed out during the safety valve opening stage, and obtain the mass of the droplet and particle mixture during this stage based on the mass changes of the heat-insulated vapor venting tank and the battery before and after the experiment. S3. Place the batteries to be tested in the same batch in a thermally insulated vapor venting tank, and use a continuous heating mode to trigger thermal runaway. After the thermal runaway ends and the batteries inside are cooled, weigh the thermally insulated vapor venting tank and the batteries inside as the same control body to obtain the total mass of electrolyte vapor and non-condensable reactive gas discharged during the thermal runaway stage. S4. Based on the measurement results of steps S1 to S3 and the total mass loss of the battery before and after thermal runaway, the multiphase ejection during the safety valve opening stage and the thermal runaway stage is separated by mass according to the law of conservation of mass to obtain the mass of non-condensable reactive gas, electrolyte droplets, electrolyte vapor and solid particles. S5. Based on the mass separation results of step S4, construct time-varying mass flow rate curves and perform multiphase component allocation to form the fluid dynamics simulation boundary conditions for the discrete phase model.

2. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 1, characterized in that: In step S1, the non-condensable reactive gas includes at least one of H2, CO, CO2, CH4, C2H4, and C2H6.

3. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 1, characterized in that, In step S1, the gas inside the analysis tank is collected through the gas sampling port, and the volume fraction of each gas component is analyzed. The mass of the non-condensable reactive gas is calculated based on the ideal gas law. It satisfies: ； in, R is the volume of the gas analysis measuring vessel, and R is the gas constant. This indicates the number of gas species involved in the summation calculation. and These are the initial pressure and the initial temperature, respectively. and These are the pressure and temperature after the system has been allowed to reach equilibrium. and denoted as volume fraction and molar mass of the i-th gas, respectively.

4. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 1, characterized in that, In step S2, the interrupted heating mode is: detecting the battery safety valve opening signal, and immediately cutting off the heating source when the safety valve opening signal is detected, so that the battery stops entering the subsequent thermal runaway stage.

5. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 1, characterized in that, Following steps S2 and S3, the process further includes: separating the captured droplet and particle mixture using a drying method to obtain the mass of the electrolyte droplets. and solid particle mass And satisfy: = + ； in, The mass is the mixture of droplets and particles.

6. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 5, characterized in that, The drying method is as follows: the mixture of droplets and particles is dried to constant weight at a preset temperature, the residue after drying is taken as solid particles, and the mass difference before and after drying is taken as the mass of electrolyte droplets.

7. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 1, characterized in that, In step S4, select batteries from the same batch and with the same state of charge, measure their initial mass and final mass after thermal runaway, calculate the total mass loss of each battery, and take the average value as the benchmark for the total mass loss of the battery before and after thermal runaway. Mass of electrolyte vapor ejected during thermal runaway phase satisfy: ； in, This represents the total mass of electrolyte vapor and non-condensable reactive gases emitted during the thermal runaway phase. The mass of the non-condensable reactive gas calculated in step S1.

8. The mass decoupling method for multiphase ejecta from battery thermal runaway according to claim 1, characterized in that, In step S5, a time-varying mass flow rate curve is constructed based on the safety valve opening time, thermal runaway initiation time, and thermal runaway termination time recorded during the experiment. During the safety valve opening phase, if the duration of this phase is Δ The total ejected mass is Then the peak mass flow rate satisfies: =2 / D ; During the thermal runaway phase, if the duration of this phase is Δ The total ejected mass is Then the average mass flow rate satisfies: = / D ; The total mass flow rate is then allocated to the multiphase components based on the mass percentage of each phase.

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