A method for evaluating safety state and grading safety failure of lithium ion battery

Abstract

The application provides a lithium ion battery safety state evaluation and safety fault grading method, which utilizes the abuse test of a lithium ion battery monomer, establishes a characteristic model relationship between the battery safety state under different abuse faults and corresponding parameters, and sets corresponding safety state threshold values, so that the real-time safety state and fault grade can be quickly and quantitatively analyzed by using each characteristic parameter of the lithium ion battery during work. The method has a simple process and extremely high real-time performance, is suitable for the rapid diagnosis of the battery safety state, and is beneficial to the early warning and elimination of risks.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery safety state diagnosis, and particularly relates to a lithium ion battery safety state evaluation and safety fault grading method. BACKGROUND

[0002] With the development of electric vehicles, the safety problems of lithium ion batteries used on vehicles are increasingly prominent, and the demand for timely evaluation of their safety state is extremely urgent. Lithium ion batteries are easily repaired in safety accidents during the working process, which is affected by overcharging, overdischarging, internal short circuit, high temperature thermal runaway, mechanical extrusion and other aspects. Therefore, it is necessary to establish a suitable grading diagnosis and safety state evaluation system for various fault causes to timely alarm and eliminate safety risks when faults occur. However, in the prior art, the fault and safety evaluation of lithium ion batteries are mostly only applicable to a single risk, lack comprehensive consideration of different fault causes, and cannot provide a more accurate and comprehensive quantitative grading evaluation method. SUMMARY

[0003] Therefore, in view of the technical problems in the art, the present application provides a lithium ion battery safety state evaluation and safety fault grading method, which specifically comprises the following steps:

[0004] S1, the following tests are carried out for lithium ion battery monomers respectively:

[0005] 1) overcharge abuse test, obtain the relationship curve between the battery monomer safety state value and the monomer voltage and monomer swelling force parameters, and determine the battery monomer voltage safety threshold and monomer swelling force safety state threshold respectively;

[0006] 2) high temperature abuse test, obtain the relationship curve between the battery monomer safety state and the temperature parameter, and determine the battery monomer temperature safety state threshold;

[0007] 3) monomer equivalent internal short circuit model simulation test, obtain the relationship curve between the battery monomer safety state value and the internal short circuit resistance parameter, and determine the battery monomer internal short circuit resistance safety state threshold;

[0008] 4) extrusion abuse test, obtain the relationship curve between the battery monomer safety state value and the extrusion deformation depth parameter, and determine the battery monomer extrusion deformation depth safety state threshold;

[0009] S2, according to the specific grouping form of the battery pack composed of lithium ion battery monomers and the safety state thresholds obtained from step S1, the relationship curves between the safety state values of the lithium ion battery pack and the parameters are calculated respectively, and the safety state thresholds of the battery pack are calculated; based on the safety state thresholds, a plurality of grades of different types of faults of the lithium ion battery pack are determined.

[0010] S3, collecting the voltage, current, temperature, internal short-circuit resistance, swelling force and extrusion deformation depth parameters of the lithium ion battery pack and the battery cells contained therein as evaluation objects in real time, determining the battery pack safety state values corresponding to each single parameter based on the relationship curves between the battery cell safety state values obtained in step S1 and each parameter, and determining the comprehensive safety state values and fault levels of the battery pack for the single or several parameters involved in the overcharge abuse failure, high temperature abuse failure, internal short-circuit failure and extrusion abuse failure.

[0011] Further, the relationship curves between the battery cell safety state values and each parameter and the safety state threshold values of each parameter in step S1 are specifically obtained by using different parameter values x and the statistical probability percentage f safety , and the following characteristic model function is obtained by fitting:

[0012]

[0013] In the formula, f safety (x) is a function of x, that is, the safety state value of the battery cell with respect to a single parameter, and m and d are coefficients to be fitted; a plurality of threshold values corresponding to different fault levels are set for the safety state value.

[0014] Further, in step S2, the fault level score of the battery pack with respect to a single parameter is determined according to the function f safety (x) corresponding to each parameter of the battery cell and each safety state threshold value.

[0015] Further, in step S3, for an abuse failure that occurs alone and involves several parameters, the product of the safety state values of the abuse failure with respect to each single parameter is specifically used to determine the comprehensive safety state and fault level score of the battery pack; and for different abuse failures that occur simultaneously, the safety state values of each abuse failure with respect to each single parameter are first calculated, and then the product of all safety state values is calculated as the comprehensive safety state and fault level score of the battery pack.

[0016] The lithium ion battery safety state evaluation and safety fault grading method provided by the present application uses the abuse test of the lithium ion battery cell to establish the characteristic model relationship between the battery safety state and the corresponding parameters under different abuse failures, and sets the corresponding safety state threshold values, so that the real-time safety state and fault level can be quickly and quantitatively analyzed using the characteristic parameters of the lithium ion battery during operation. The method has a simple process and high real-time performance, is suitable for rapid diagnosis of the battery safety state, and is conducive to early warning and elimination of risks. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A schematic diagram of the relationship between the battery safety state and the temperature parameter in the method provided by the present application;

[0018] Figure 2 A schematic diagram of the comprehensive failure level based on the temperature parameter in the example of the present application;

[0019] Figure 3 A schematic diagram of the comprehensive safety state and the failure level calculation for the abuse failure involving several parameters in the present application;

[0020] Figure 4 The comprehensive safety state and the failure level results based on the temperature and the internal short-circuit resistance in the example of the present application. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described clearly and completely in combination with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0022] The safety state evaluation and the safety failure grading method of the lithium ion battery provided by the present application specifically includes the following steps:

[0023] S1, the following tests are respectively carried out for the lithium ion battery monomer:

[0024] 1) overcharge abuse test, the relationship curves between the battery monomer safety state value and the monomer voltage and the monomer swelling force parameter are obtained, and the battery monomer voltage safety threshold and the monomer swelling force safety state threshold are respectively determined;

[0025] 2) high temperature abuse test, the relationship curve between the battery monomer safety state and the temperature parameter is obtained, and the battery monomer temperature safety state threshold is determined;

[0026] 3) monomer equivalent internal short-circuit model simulation test, the relationship curve between the battery monomer safety state value and the internal short-circuit resistance parameter is obtained, and the battery monomer internal short-circuit resistance safety state threshold is determined;

[0027] 4) extrusion abuse test, the relationship curves between the battery monomer safety state value and the extrusion deformation depth parameter are obtained, and the battery monomer extrusion deformation depth safety state threshold is determined;

[0028] S2. Based on the specific grouping form of the battery pack composed of lithium-ion battery cells and the safety state thresholds obtained in step S1, calculate the relationship curves between the safety state values ​​and parameters of the lithium-ion battery pack, as well as the safety state thresholds of the battery pack; and determine several levels of different types of faults in the lithium-ion battery pack based on the safety state thresholds.

[0029] S3. Real-time acquisition of parameters such as voltage, current, temperature, internal short-circuit resistance, expansion force, and extrusion deformation depth of the lithium-ion battery pack and its individual cells as the evaluation object during operation. Based on the relationship curve between the individual cell safety status values ​​obtained in step S1 and each parameter, determine the battery pack safety status value corresponding to each single parameter. For the single or several parameters specifically involved in overcharge abuse faults, high temperature abuse faults, internal short-circuit faults, and extrusion abuse faults, determine the comprehensive safety status value and fault level of the battery pack.

[0030] In a preferred embodiment of the present invention, step S1 selects a high-capacity lithium iron phosphate single cell as the object, conducts a high-temperature thermal runaway experiment in an adiabatic accelerated calorimeter, obtains relevant parameters of the lithium iron phosphate battery under high-temperature abuse conditions, and obtains the following parameters based on these parameters: Figure 1 The relationship between the safety state values ​​and temperature is shown. Through analysis of the self-generated heat initiation temperature and normal operating temperature range of the lithium iron phosphate battery during adiabatic thermal runaway, the temperature parameter corresponding to 100% safety state is 55℃, and the temperature parameter corresponding to 80% safety state is 90℃. The temperature parameter corresponding to 80% safety state can be used as the temperature safety threshold for the lithium iron phosphate battery. Therefore, different temperatures x and the statistical probability percentage f of a single battery cell being in a safe state at this value are used. safety And by fitting the following characterization model function, we obtain:

[0031]

[0032] In the formula, f safety (x) is a function of x, which is the safety state value of a single battery cell with respect to a single temperature parameter. m and d are the coefficients to be fitted. Several thresholds corresponding to different fault levels are set for the safety state value.

[0033] In step S2, the specific function f is based on the parameters of each battery cell. safety (x) and various safety state thresholds are used to determine the fault level score of the battery pack for a single parameter. Specifically, as follows... Figure 2 As shown, based on long-term statistical or empirical data of similar batteries, the probability f of a completely safe state is considered. safety If (x) = 1, then f safetyIf (x) > 0.8, the battery is considered safe. safety If (x) < 0.8, the battery is considered unsafe. When the temperature is below 60℃, the battery is considered to have no risk of thermal runaway. When the temperature reaches 90℃, self-heating begins to occur. When the temperature reaches 140℃, the separator melts, resulting in a large-area internal short circuit. Therefore, the safety state values ​​corresponding to 90℃ and 140℃ are selected as the standard for fault classification.

[0034] In a preferred embodiment of the present invention, in step S3, for a single abuse fault involving several parameters, the overall safety status and fault level score of the battery pack are determined by multiplying the safety status values ​​of the abuse fault with respect to each individual parameter. For different abuse faults occurring simultaneously, the safety status values ​​of each abuse fault with respect to each individual parameter are first calculated, and then the product of all safety status values ​​is calculated as the overall safety status and fault level score of the battery pack. When the overall safety status value is greater than 0.8, it indicates that the safety status represented by all parameters is likely above 0.8; when the overall safety status value is less than 0.8, it indicates that at least one parameter may represent a safety status below 0.8; when the overall safety status value is less than 0.8... n This indicates that the safety state represented by all parameters is likely below 0.8. Therefore, if... Figure 3 As shown, a comprehensive safety status evaluation score of 0.8 to 1 is defined as a Level 1 fault, and a score of 0.8 is defined as a Level 2 fault. n A value between ~0.8 indicates a level 2 fault; a value between 0 and 0.8 indicates a level 3 fault. n The fault is classified as a level three fault. Figure 4 The figure shows the safety fault level classification curve for lithium-ion batteries that have experienced both high-temperature abuse and internal short-circuit abuse.

[0035] It should be understood that the sequence number of each step in the embodiments of the present invention does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for lithium-ion battery safety state assessment and safety failure classification, characterized in that: Specifically comprising the following steps: S1, for lithium ion battery monomer, the following tests are carried out respectively: 1) overcharge abuse test, obtain the relationship curve between battery monomer safety state value and monomer voltage and monomer swelling force parameter respectively, and determine the battery monomer voltage safety threshold and monomer swelling force safety state threshold respectively; 2) high temperature abuse test, obtain the relationship curve between battery monomer safety state and temperature parameter, and determine the battery monomer temperature safety state threshold; 3) monomer equivalent internal short circuit model simulation test, obtain the relationship curve between battery monomer safety state value and internal short circuit resistance parameter, and determine the battery monomer internal short circuit resistance safety state threshold; 4) extrusion abuse test, obtain the relationship curve between battery monomer safety state value and extrusion deformation depth parameter respectively, and determine the battery monomer extrusion deformation depth safety state threshold; S2, according to the specific grouping form of the battery pack composed of lithium ion battery monomer and the safety state threshold obtained by step S1, the relationship curve between each safety state value of lithium ion battery pack and each parameter is calculated respectively, and the safety state threshold of battery pack is calculated respectively; Based on each safety state threshold, several levels of different types of faults of lithium ion battery pack are determined; S3, real-time acquisition of voltage, current, temperature, internal short circuit resistance, swelling force and extrusion deformation depth parameters of lithium ion battery pack and its contained battery monomer as evaluation object during work, respectively based on the relationship curve between battery monomer safety state value and each parameter obtained by step S1, determine the battery pack safety state value corresponding to each single parameter; For overcharge abuse fault, high temperature abuse fault, internal short circuit fault and extrusion abuse fault, determine the comprehensive safety state value and fault level of battery pack.

2. The method of claim 1, wherein: The relationship curve between the battery cell safety state value and each parameter in step S1 and the safety state threshold of each parameter are specifically obtained by using different parameter values x and the statistical probability percentage f of the battery cell being in a safe state at the value safety and fitting the following characteristic model function: where f safety (x) is a function of x, i.e. a safety state value of the battery cell with respect to a single parameter, m, d are coefficients to be fitted; a number of thresholds are set for the safety state value corresponding to different failure levels.

3. The method of claim 2, wherein: In step S2, the function f corresponding to each parameter of the battery cell is specifically used safety (x) and each safety state threshold, to determine the failure level score of the battery pack with respect to a single parameter.

4. The method of claim 3, wherein: In step S3, for the abuse fault which occurs alone and involves several parameters, the product of the safety state value of each single parameter about the abuse fault is used to determine the comprehensive safety state and fault level score of the battery pack; and for different abuse faults occurring at the same time, first calculate the safety state value of each single parameter about each abuse fault, then calculate the product of all safety state values as the comprehensive safety state and fault level score of the battery pack.

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