Lithium iron phosphate battery thermal runaway gas production and fire explosion risk assessment method

Abstract

The invention discloses a lithium iron phosphate battery thermal runaway gas production and fire explosion risk assessment method, which comprises the following steps: acquiring a battery runaway full-period gas production characteristic by utilizing a thermal runaway gas production experimental device; acquiring a gas production rule according to the full-period gas production characteristic; analyzing a fire explosion risk according to the gas production rule to obtain an analysis result; and performing visualization processing on the analysis result by using a radar map to obtain a research result. Through staged gas production mechanism analysis, multi-parameter coupling evaluation and risk visualization technologies, the purposes of quantifying the thermal runaway fire explosion risk and optimizing the safety prevention and control strategy of the energy storage system are achieved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery safety technology, and particularly relates to a method for assessing the risk of thermal runaway gas generation and fire / explosion in lithium iron phosphate batteries. Background Technology

[0002] In new energy vehicles and energy storage systems, thermal runaway of lithium-ion batteries is a key hidden danger leading to fires and explosions. Specifically, the flammable gases such as hydrogen and carbon monoxide released during thermal runaway of lithium iron phosphate batteries accumulate continuously in confined spaces, becoming a core trigger for fires and explosions. Fires and explosions caused by thermal runaway gas production not only result in casualties and property damage, affecting the safe operation of energy storage systems, but also, due to the increased risk of flammable gas explosions and intensified combustion under high charge states, are prone to rapid fire spread and secondary disasters. Therefore, to quantify the fire and explosion risks, it is necessary to establish an assessment model based on a phased gas production dynamics mechanism. This model should incorporate the influence of state of charge on flammable gas composition, lower explosive limit, laminar flame velocity, and adiabatic flame temperature into a multi-parameter coupled analysis system to assess the probability and severity of fires and explosions. Currently, there is a lack of systematic research on the gas generation dynamics mechanism in the entire battery lifecycle, which means that existing methods have not clearly defined the gas generation laws in the three typical stages of the battery, making it difficult to accurately quantify the dynamic changes of gas components under different states of charge. At the same time, the risk level is not assessed by combining stage explosion parameters, resulting in a lack of targeted prevention and control strategies. In addition, the relationship between gas generation mechanism and combustion characteristics has not been revealed, which restricts the theoretical support for safety design. Summary of the Invention

[0003] To address the aforementioned technical issues, this invention proposes a risk assessment method for thermal runaway gas generation and fire / explosion risks in lithium iron phosphate batteries. This method can accurately quantify the probability and severity of risks, providing technical support for battery safety design, early warning, and accident prevention.

[0004] To achieve the above objectives, this invention provides a method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries, comprising:

[0005] Using a thermal runaway gas generation experimental device, the gas generation characteristics of the battery throughout the runaway cycle were obtained;

[0006] Based on the described full-cycle gas production characteristics, the gas production pattern is obtained;

[0007] Based on the gas production pattern, the fire and explosion risks are analyzed, and the analysis results are obtained.

[0008] The analysis results are visualized using radar charts to obtain the research findings.

[0009] Optionally, the thermal runaway gas generation experimental device can be used to obtain the gas generation characteristics of the battery throughout the entire runaway cycle, including:

[0010] Using a thermal runaway gas generation device, the thermal runaway gas generation of the battery is divided into three stages, and the gas generation amount and the proportion of each component in each stage are obtained.

[0011] Based on the gas production volume and component ratio at each stage, the gas production characteristics of the battery throughout the runaway cycle are obtained.

[0012] Optionally, the thermal runaway gas generation of the battery can be divided into three stages, including:

[0013] Based on the safety valve opening temperature, thermal runaway trigger temperature, and maximum thermal runaway temperature, the thermal runaway gas generation of the battery is divided into the safety valve venting stage, the thermal runaway gas generation stage, and the thermal runaway cooling stage.

[0014] Optionally, based on the gas production pattern, the fire and explosion risk can be analyzed, and the analysis results can include:

[0015] Based on the gas production law, the hazard index is obtained using an improved Le-Chatelier model. The Le-Chatelier model is improved by using a mathematical elimination method, which is used to calculate the upper explosive limit and lower explosive limit of the gas mixture.

[0016] Based on the aforementioned hazard index, the laminar flame velocity and adiabatic flame temperature of the mixed gas at different stages were obtained using the CHEMKIN model.

[0017] Based on the laminar flame velocity and adiabatic flame temperature, the fire and explosion risks are analyzed, and the analysis results are obtained.

[0018] Optionally, based on the aforementioned gas production patterns, the hazard index can be obtained using an improved Le-Chatelier model, including:

[0019] The combustible and inert components in the thermal runaway gas are paired to obtain a mixed gas.

[0020] Calculate the content and component ratio of the mixed gas to obtain the explosion limit of the mixed gas;

[0021] The danger index is obtained based on the stated explosion limits.

[0022] Optionally, the method for obtaining the explosion limits of the gas mixture is as follows:

[0023]

[0024] Among them, L m It is the explosion limit of the gas mixture, L i V is the explosion limit of each component in the gas mixture. iIt represents the volume fraction of each component in the gas mixture, where i is the serial number of each component in the gas mixture, and n is the total number of components in the gas mixture.

[0025] Optionally, the method for obtaining the hazard index based on the explosion limits is as follows:

[0026]

[0027] Among them, H E , where UEL is the upper explosive limit of the gas mixture and LEL is the lower explosive limit of the gas mixture.

[0028] Optionally, the analysis results can be visualized using radar charts to obtain the following research findings:

[0029] The data in the analysis results are normalized.

[0030] Construct a radar chart coordinate system;

[0031] Based on the radar chart coordinate system, coordinate transformation is performed on the normalized data to obtain rectangular coordinates;

[0032] Based on the rectangular coordinates, the risk area is calculated using the polygon area formula;

[0033] Based on the stated risk area, the research results were obtained.

[0034] Optionally, calculating the risk area using the polygon area formula includes:

[0035] The risk area is calculated using the polygon area formula, including:

[0036]

[0037] Where S is the risk area, m is the number of risk indicator dimensions, h is the h-th risk indicator, and x h Let x be the x-axis of the h-th risk indicator. h+1 Let y be the x-axis of the (h+1)th risk indicator. h Let y be the ordinate of the h-th risk indicator. h+1 The vertical axis represents the (h+1)th risk indicator.

[0038] Compared with the prior art, the present invention has the following advantages and technical effects:

[0039] The lithium-ion battery thermal runaway fire and explosion risk assessment method provided by this invention can divide thermal runaway gas production into three stages (safety valve venting, thermal runaway gas production, and thermal runaway cooling) through a self-designed closed experimental device and multi-dimensional parameter monitoring, clarifying the dynamic change law of gas components in each stage; it can dynamically quantify the lower explosive limit and explosion hazard index of the mixed gas in different stages through an improved Le-Chatelier model, identify the explosion risk surge characteristics under high charge state, and provide a theoretical basis for related risk level classification; it can simulate laminar flame velocity and adiabatic flame temperature through CHEMKIN software, revealing the positive correlation mechanism between combustion intensity and charge state, supporting the dynamic assessment of fire spread speed and destructive intensity; it can construct a risk radar chart by integrating explosion parameters and combustion characteristic parameters, realizing the visual mapping of risk probability and severity; and it can comprehensively quantify the superimposed risk level of each stage through normalization processing and closed polygon area calculation. This invention achieves the purpose of quantifying thermal runaway fire and explosion risk and optimizing the safety control strategy of energy storage system through staged gas production mechanism analysis, multi-parameter coupled assessment, and risk visualization technology. Attached Figure Description

[0040] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0041] Figure 1 This is a flowchart of a method for assessing the risk of thermal runaway gas production and fire / explosion from lithium iron phosphate batteries, according to an embodiment of the present invention.

[0042] Figure 2 This is a flowchart illustrating the calculation of the explosion limits of a gas mixture using the improved Le-Chatelier formula through mathematical elimination in this embodiment of the invention.

[0043] Figure 3 This is a flowchart of the visualization of fire and explosion risk parameters based on radar charts in an embodiment of the present invention;

[0044] Figure 4 This is a diagram showing the explosion limits of different combustible-inert gas combinations in embodiments of the present invention. Detailed Implementation

[0045] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0046] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0047] This invention proposes a method for assessing the risks of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries, such as... Figure 1 As shown, the specific steps include:

[0048] Using a thermal runaway gas generation experimental device, the gas generation characteristics of the battery throughout the runaway cycle were obtained;

[0049] Based on the full-cycle gas production characteristics, the gas production patterns are obtained;

[0050] Based on the gas production pattern, the fire and explosion risks are analyzed, and the analysis results are obtained.

[0051] The analysis results are visualized using radar charts to obtain the research findings.

[0052] Specifically, the risk radar chart construction focuses on the dynamic risk presentation of multi-parameter coupling. By integrating core parameters such as the lower explosive limit, explosion range, explosion hazard index, laminar flame velocity, and adiabatic flame temperature, a risk radar chart is constructed to achieve a visual mapping of risk levels at each stage of the entire thermal runaway cycle. The risk probability axis, using the lower explosive limit, explosion range, and explosion index as dimensions, quantifies the likelihood of a gas mixture reaching explosive concentrations, intuitively reflecting the relationship between flammable gas concentrations under different charge states and the lower explosive limit. The severity axis selects laminar flame velocity and adiabatic flame temperature as characterization parameters, corresponding to fire spread speed and combustion energy release intensity, respectively, revealing the evolution of flame propagation characteristics and destructive capabilities during thermal runaway. After normalization, the coupling effect of multi-dimensional risks is comprehensively represented by the area of ​​closed polygons. This indicates that the stronger the superposition effect of risk probability and severity, the more intuitively the comprehensive risk level at different stages can be quantified, providing a visual data carrier for risk difference analysis during the thermal runaway process.

[0053] Furthermore, using a thermal runaway gas generation experimental device, the gas generation characteristics throughout the entire battery runaway cycle were obtained, including:

[0054] Using a thermal runaway gas generation device, the thermal runaway gas generation of the battery is divided into three stages, and the gas generation amount and the proportion of each component in each stage are obtained.

[0055] Based on the gas production volume and component ratio at each stage, the gas production characteristics throughout the battery runaway cycle are obtained.

[0056] Specifically, in a self-designed experimental tank, the three-stage division of thermal runaway gas generation in lithium iron phosphate batteries and the amount and composition ratio of gas generated in each stage were determined. Based on three characteristic temperatures—safety valve opening temperature, thermal runaway trigger temperature, and maximum thermal runaway temperature—the gas generation process was divided into three stages: the safety valve venting stage, the thermal runaway gas generation stage, and the thermal runaway cooling stage.

[0057] Furthermore, the thermal runaway gas generation of the battery is divided into three stages, including:

[0058] Based on the safety valve opening temperature, thermal runaway trigger temperature, and maximum thermal runaway temperature, battery thermal runaway gas generation is divided into the safety valve venting stage, the thermal runaway gas generation stage, and the thermal runaway cooling stage.

[0059] Specifically, the phased gas generation kinetics method and experimental setup design employ a self-designed thermal runaway gas generation experimental device (including an explosive container, high-precision thermocouples, a gas collection system, and a gas chromatography-mass spectrometry system) to monitor temperature and pressure in real time during the battery's thermal runaway process under different states of charge. The phase division criteria are based on characteristic temperatures (safety valve exhaust temperature T). sv Thermal runaway trigger temperature T tr Maximum temperature T max The process of thermal runaway gas generation is divided into three stages: safety valve venting, thermal runaway gas generation, and thermal runaway cooling. The gas generation law formula is used to clarify the gas generation law in each stage.

[0060] Furthermore, based on the gas production patterns, the fire and explosion risks are analyzed, and the analysis results include:

[0061] Based on the gas production pattern, the hazard index was obtained using the improved Le-Chatelier model;

[0062] Based on the hazard index, the laminar flame velocity and adiabatic flame temperature of the mixed gas at different stages were obtained using the CHEMKIN model.

[0063] Fire and explosion risks are analyzed based on laminar flame velocity and adiabatic flame temperature, and the analysis results are obtained.

[0064] Specifically, (1) Dynamic assessment method for explosion limits and hazard index:

[0065] Based on an improved Le-Chatelier model, a quantitative analysis framework for the explosion limits of multi-component gas mixtures is constructed. First, combustible and inert components in the thermal runaway gas are paired. The lower explosion limit (LEL) and upper explosion limit (UEL) of the mixture are calculated by weighted summation of the component volume fractions and the explosion limits of individual gases. Furthermore, an explosion hazard index is introduced to quantify the risk, revealing that during the thermal runaway gas production stage, due to the concentration advantage of combustible gases and the low LEL characteristic, the explosion concentration range is wider and the trigger threshold is lower, forming a high-probability explosion risk condition. This method establishes a dynamic correlation between the state of charge and explosion characteristic parameters through real-time monitoring of gas components and model calculations, providing a fundamental theoretical tool for risk coupling analysis.

[0066] (2) Combustion characteristic simulation and mechanism coupling method:

[0067] Using CHEMKIN chemical kinetics software, the laminar flame velocity (LFS) and adiabatic flame temperature (AFT) of gas mixtures at different stages were simulated. This simulation method, by inputting the concentrations of each component in the gas mixture and combining them with a reaction kinetic model, performs precise calculations, systematically revealing the intrinsic coupling between combustion characteristic parameters and gas composition and state of charge. This provides quantitative support for in-depth analysis of combustion risk mechanisms.

[0068] Furthermore, based on gas production patterns, the hazard index, obtained using the improved Le-Chatelier model, includes:

[0069] The combustible and inert components in the thermal runaway gas are paired to obtain a mixed gas.

[0070] Calculate the content and component ratio of the gas mixture to obtain the explosion limits of the gas mixture;

[0071] Based on the explosion limits, obtain the danger index.

[0072] The explosion limit relationships for different combinations of combustible and inert gases are shown in the diagram below. Figure 4 As shown.

[0073] The following is a detailed description of this embodiment with reference to the accompanying drawings:

[0074] Step 1: In a self-designed experimental tank, the three-stage division of thermal runaway gas generation in lithium iron phosphate batteries and the amount and composition ratio of gas generated in each stage were determined. Based on three characteristic temperatures—safety valve opening temperature, thermal runaway trigger temperature, and thermal runaway maximum temperature—the gas generation process was divided into three stages: safety valve venting stage, thermal runaway gas generation stage, and thermal runaway cooling stage. The trigger temperature is defined by formula (1):

[0075] T(k+1)-T(k)≥1℃,k=1,2,3...#(1)

[0076] In the formula, T(k+1) and T(k) are adjacent recording points, in °C. The thermal runaway trigger temperature is defined as the temperature difference between adjacent points being greater than 1 °C / s.

[0077] The amount of gas produced in each stage is calculated using the ideal gas law, as shown in formulas (2), (3), and (4).

[0078] V a =V bao -V c +V void #(2)

[0079]

[0080] In the formula, V bao The volume of the experimental vessel is expressed in liters (L) and volumes (V). c This refers to the battery volume, measured in liters (L) and volts (V). void It is the gap in the battery (V) void =0.07V c (), unit L. T0 is the initial temperature T0 inside the tank, unit K. P0 is the initial temperature inside the tank, unit kPa. R is the ideal gas constant, unit J / (mol·K). Z g The compression factor is, typically, 1.

[0081] Gases from each stage were selected and their components were analyzed using gas chromatography-mass spectrometry.

[0082] Step 2: Calculate fire and explosion risk parameters:

[0083] Based on the gas ratio analysis of each stage, the fire and explosion risks of each stage are determined by the improved Le-Chatelier formula, the explosion index formula, and CHEMKIN software simulation.

[0084] The main gaseous components at each stage are: carbon dioxide, hydrogen, carbon monoxide, ethylene, methane, ethane, propylene, and propane. For example... Figure 2 As shown, using the improved Le-Chatelier formula, a mathematical elimination method is employed to pair a specific inert gas with a combustible gas, treating it as a "new" combustible gas to calculate its total content and component ratio. Then, formula (5) is used for calculation:

[0085]

[0086] Among them, L m It is the explosion limit of the gas mixture, L i V is the explosion limit of each component in the gas mixture. i It represents the volume fraction of each component in the gas mixture, where i is the serial number of each component in the gas mixture, and n is the total number of components in the gas mixture.

[0087] The explosion limit is calculated using the above equations, and the explosion index is calculated using formulas (6) and (7).

[0088] R E =UEL-LEL#(6)

[0089]

[0090] In the formula R E and H E , where UEL is the upper explosive limit of the gas mixture and LEL is the lower explosive limit of the gas mixture.

[0091] Then, the gas proportions for each stage are input into the CHEMKIN software to simulate the laminar flame velocity and adiabatic flame temperature.

[0092] Step 3: Visualize fire and explosion risk parameters, such as Figure 3 As shown:

[0093] Based on fire and explosion risk parameters such as upper and lower explosion limits, explosion range, explosion index, laminar flame velocity, and adiabatic flame temperature, the radar map area is calculated to visualize the risk.

[0094] The radar chart contains data points r1, r2, r3, r4, r5, and r6 corresponding to the above six dimensions (coordinate axes) for the upper and lower limits of explosion, explosion range, explosion index, laminar flame velocity, and adiabatic flame temperature. The above parameters are normalized as shown in formula (8) to eliminate differences in dimensions and ranges, so that the weights of each dimension are balanced.

[0095]

[0096] In the formula r i Let r be the radius of the risk parameter, min(r) be the minimum radius of the risk parameter, and max(r) be the maximum radius of the risk parameter.

[0097] The six coordinate axes are evenly distributed on the circumference, with adjacent axes forming an angle of 60°. Angle starting point: The positive x-axis is taken as 0 degrees, and counter-clockwise rotation is the positive direction. Closed polygon: To ensure the polygon is closed, the first point is repeated as the last point.

[0098] The 6-dimensional data points represent the value r' of each data point on the i-th coordinate axis. i The corresponding polar coordinates are (r') i ,iθ). The polar coordinates of each parameter are converted to coordinates in the rectangular coordinate system using formula (9).

[0099]

[0100] In the formula x i Calculate the x-value and y-value for the risk parameters. i Calculate the risk parameter y-value.

[0101] The risk area is calculated using formula (10). Half of the absolute value is taken to obtain the risk area. The larger the area presented on the radar chart, the higher the risk, thus realizing risk visualization.

[0102]

[0103] Where S is the risk area, m is the number of risk indicator dimensions, h is the h-th risk indicator, and x h Let x be the x-axis of the h-th risk indicator. h+1 Let y be the x-axis of the (h+1)th risk indicator. h Let y be the ordinate of the h-th risk indicator. h+1 The vertical axis represents the (h+1)th risk indicator.

[0104] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries, characterized in that, include: Using a thermal runaway gas generation experimental device, the gas generation characteristics of the battery throughout the runaway cycle were obtained; Based on the described full-cycle gas production characteristics, the gas production pattern is obtained; Based on the gas production pattern, the fire and explosion risks are analyzed, and the analysis results are obtained. The analysis results are visualized using radar charts to obtain the research findings.

2. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 1, characterized in that, Using a thermal runaway gas generation experimental setup, the full-cycle gas generation characteristics of a battery runaway were obtained, including: Using a thermal runaway gas generation device, the thermal runaway gas generation of the battery is divided into three stages, and the gas generation amount and the proportion of each component in each stage are obtained. Based on the gas production volume and component ratio at each stage, the gas production characteristics of the battery throughout the runaway cycle are obtained.

3. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 2, characterized in that, The thermal runaway gas generation of the battery is divided into three stages, including: Based on the safety valve opening temperature, thermal runaway trigger temperature, and maximum thermal runaway temperature, the thermal runaway gas generation of the battery is divided into the safety valve venting stage, the thermal runaway gas generation stage, and the thermal runaway cooling stage.

4. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 1, characterized in that, Based on the aforementioned gas production pattern, the fire and explosion risks are analyzed, and the analysis results include: Based on the gas production law, the hazard index is obtained using an improved Le-Chatelier model. The Le-Chatelier model is improved by using a mathematical elimination method, which is used to calculate the upper explosive limit and lower explosive limit of the gas mixture. Based on the aforementioned hazard index, the laminar flame velocity and adiabatic flame temperature of the mixed gas at different stages were obtained using the CHEMKIN model. Based on the laminar flame velocity and adiabatic flame temperature, the fire and explosion risks are analyzed, and the analysis results are obtained.

5. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 4, characterized in that, Based on the aforementioned gas production patterns, the hazard index, obtained using the improved Le-Chatelier model, includes: The combustible and inert components in the thermal runaway gas are paired to obtain a mixed gas. Calculate the content and component ratio of the mixed gas to obtain the explosion limit of the mixed gas; The danger index is obtained based on the stated explosion limits.

6. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 5, characterized in that, The method for obtaining the explosion limits of a gas mixture is as follows: Among them, L m It is the explosion limit of the gas mixture, L i V is the explosion limit of each component in the gas mixture. i It represents the volume fraction of each component in the gas mixture, where i is the serial number of each component in the gas mixture, and n is the total number of components in the gas mixture.

7. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 5, characterized in that, The method for obtaining the hazard index based on the explosion limits is as follows: Among them, H E , where UEL is the upper explosive limit of the gas mixture and LEL is the lower explosive limit of the gas mixture.

8. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 1, characterized in that, The analysis results are visualized using radar charts to obtain the following research findings: The data in the analysis results are normalized. Construct a radar chart coordinate system; Based on the radar chart coordinate system, coordinate transformation is performed on the normalized data to obtain rectangular coordinates; Based on the rectangular coordinates, the risk area is calculated using the polygon area formula; Based on the stated risk area, the research results were obtained.

9. The method for assessing the risk of thermal runaway gas production and fire / explosion in lithium iron phosphate batteries according to claim 8, characterized in that, The risk area is calculated using the polygon area formula, including: Where S is the risk area, m is the number of risk indicator dimensions, h is the h-th risk indicator, and x h Let x be the x-axis of the h-th risk indicator. h+1 Let y be the x-axis of the (h+1)th risk indicator. h Let y be the ordinate of the h-th risk indicator. h+1 The vertical axis represents the (h+1)th risk indicator.

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