CN117607718A - Analysis method for performance degradation mechanism of internal short circuit fault battery - Google Patents
Analysis method for performance degradation mechanism of internal short circuit fault battery Download PDFInfo
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- 230000007246 mechanism Effects 0.000 title claims abstract description 23
- 230000015556 catabolic process Effects 0.000 title claims abstract description 21
- 238000006731 degradation reaction Methods 0.000 title claims abstract description 21
- 238000004458 analytical method Methods 0.000 title claims description 8
- 238000012360 testing method Methods 0.000 claims abstract description 55
- 238000000034 method Methods 0.000 claims abstract description 47
- 230000008859 change Effects 0.000 claims abstract description 32
- 125000004122 cyclic group Chemical group 0.000 claims abstract description 29
- 230000008569 process Effects 0.000 claims abstract description 26
- 238000011056 performance test Methods 0.000 claims description 33
- 230000032683 aging Effects 0.000 claims description 27
- 230000014759 maintenance of location Effects 0.000 claims description 17
- 238000007600 charging Methods 0.000 claims description 9
- 238000010277 constant-current charging Methods 0.000 claims description 7
- 238000010280 constant potential charging Methods 0.000 claims description 5
- 238000002474 experimental method Methods 0.000 claims description 5
- 238000003825 pressing Methods 0.000 claims description 4
- 239000010405 anode material Substances 0.000 claims description 3
- 239000010406 cathode material Substances 0.000 claims description 3
- 238000010281 constant-current constant-voltage charging Methods 0.000 claims description 3
- 238000007599 discharging Methods 0.000 claims description 2
- 230000000694 effects Effects 0.000 claims description 2
- 230000006641 stabilisation Effects 0.000 claims description 2
- 238000011105 stabilization Methods 0.000 claims description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 8
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 8
- 230000008878 coupling Effects 0.000 abstract description 3
- 238000010168 coupling process Methods 0.000 abstract description 3
- 238000005859 coupling reaction Methods 0.000 abstract description 3
- 238000004088 simulation Methods 0.000 abstract description 3
- 230000035882 stress Effects 0.000 description 7
- 238000011161 development Methods 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 238000003745 diagnosis Methods 0.000 description 3
- 229910017767 Cu—Al Inorganic materials 0.000 description 2
- 208000032953 Device battery issue Diseases 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000007773 negative electrode material Substances 0.000 description 2
- 239000002985 plastic film Substances 0.000 description 2
- 229920006255 plastic film Polymers 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
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- 230000010287 polarization Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/389—Measuring internal impedance, internal conductance or related variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
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Abstract
The invention provides a mechanism for causing performance degradation of a lithium ion battery by internal short circuit fault. And carrying out a battery internal short-circuit fault test of coupling mechanical stress on the short-circuit battery with positive and negative electrodes in contact caused by the normal battery and the diaphragm perforation, and obtaining voltage, current and internal and external temperature data of the normal battery and the internal short-circuit fault battery. And analyzing the external comprehensive performance of the battery, observing the voltage and temperature change of the battery in the cyclic process, and determining the influence of the internal short circuit fault on the service performance of the battery. In addition, the voltage and internal and external temperature differences of the normal battery and the internal short-circuit battery in the process of continuously pressurizing to thermal runaway are compared, the maximum mechanical stress of the battery when the thermal runaway occurs is obtained, and the influence of the internal short-circuit fault on the safety performance of the battery is analyzed. The short circuit experimental simulation mode adopted by the invention is closer to the actual internal short circuit condition, and the acquired electric and thermal signals are more accurate and effective.
Description
Technical Field
The invention relates to the field of battery performance evaluation, in particular to an analysis method of a performance degradation mechanism of an internal short circuit fault battery.
Background
In recent years, along with the rapid increase of the number of lithium ion batteries and large-scale popularization and application, the safety has become a key problem for restricting the development of the industry. The safe and reliable operation of lithium ion batteries is greatly challenged by short-circuit faults in the battery caused by manufacturing defects or abuse. The definition of the mechanism of performance degradation after battery failure generation and operation with failure is critical to reducing battery safety risks. Therefore, it is necessary to obtain an analysis method of the internal short circuit fault-induced lithium ion battery performance degradation mechanism.
The internal short circuit fault and the performance degradation mechanism after the operation with the fault of the lithium ion battery are unknown. Therefore, it is necessary to propose a method for analyzing the performance degradation mechanism of the internal short-circuit fault battery according to the different performances of the normal battery and the internal short-circuit battery on the electric, thermal and force signals. An analysis method of the performance degradation mechanism of an internal short circuit fault battery is a method which meets the requirements.
In the prior art, in order to reveal the mechanism characteristics of the internal short circuit of the battery, an internal short circuit battery electrochemical, heat generation and thermal runaway finite element model is established. The characteristics of the Cu-Al type and the An-Ca type internal short circuit such as voltage, internal resistance, temperature and the like are researched by using the model, and the distinction and the connection between the Cu-Al type and the An-Ca type internal short circuit and the external short circuit are analyzed, so that the characteristics which can be used for detecting the internal short circuit are obtained. And the relation between the heat-generating power density and the thermal runaway when the internal short circuit occurs and the influence of the contact resistance on the heat-generating power density are studied, and a method for reducing the thermal runaway risk is analyzed.
In order to quantify short-circuit current and thermal runaway risk of early short-circuit evidence, a short-circuit current estimation method based on an average-difference model is provided. Firstly, a short-circuit battery equivalent circuit model and a parameter identification method are analyzed, and parameters of the short-circuit battery are obtained through least square and Kalman filtering combined estimation. And then dividing the short-circuit current estimation method into different scales according to the characteristics of the voltage signals, and estimating the short-circuit current in the series battery pack by using the model parameters and the terminal voltage. Finally, the method is verified by using an experiment, and the result shows that short-circuit currents with different scales can be converged to a reference value, so that the rapid diagnosis of the internal short circuit is realized.
In order to identify and detect the micro-short circuit in the early stage of the internal short circuit development, a micro-short circuit diagnosis method utilizing the increment curve of the battery charging capacity and the change rule of the charging capacity difference is provided. First, the corresponding relation between the highest peak of the IC curve and the charge state of the battery under different current multiplying powers and temperatures is analyzed in detail. And then, providing a charge capacity difference to illustrate the SOC difference between the fault battery and the normal battery when the internal short circuit exists, and accordingly obtaining a quantification method of the internal short circuit.
The prior art has the following disadvantages: the data used by the analysis mechanism is obtained through experiments conducted in a mode of externally connecting resistors, the mode of simulating the internal short circuit is different from the actual internal short circuit, and the conclusion about internal resistance temperature and the like is not verified.
Disclosure of Invention
In view of the above problems, the present invention proposes a mechanism for causing degradation of performance of a lithium ion battery by internal short circuit failure. And carrying out a battery internal short-circuit fault test of coupling mechanical stress on the short-circuit battery with positive and negative electrodes in contact caused by the normal battery and the diaphragm perforation, and obtaining voltage, current and internal and external temperature data of the normal battery and the internal short-circuit fault battery. And analyzing the external comprehensive performance of the battery, observing the voltage and temperature change of the battery in the cyclic process, and determining the influence of the internal short circuit fault on the service performance of the battery. In addition, the voltage and internal and external temperature differences of the normal battery and the internal short-circuit battery in the process of continuously pressurizing to thermal runaway are compared, the maximum mechanical stress of the battery when the thermal runaway occurs is obtained, and the influence of the internal short-circuit fault on the safety performance of the battery is analyzed. The short circuit experimental simulation mode adopted by the invention is closer to the actual internal short circuit condition, and the acquired electric and thermal signals are more accurate and effective. The method specifically comprises the following steps:
acquiring the battery capacity, internal resistance and self-discharge characteristic evolution conditions of a normal battery and an internal short-circuit battery;
acquiring the battery voltage and temperature evolution conditions of a normal battery and an internal short-circuit battery;
and obtaining the pressure boundary required when the normal battery and the internal short-circuit battery are out of control in a thermal manner according to the voltage and the internal and external temperature difference of the normal battery and the internal short-circuit battery in the continuous pressurization process.
Based on the scheme, the battery capacity, the internal resistance and the self-discharge characteristic are obtained through experimental tests:
the battery internal short circuit fault test comprises a reference performance test, an internal short circuit trigger test and a cyclic aging test;
the test sequence of the normal battery is a reference performance test mode I, a cyclic aging test and a reference performance test mode III in sequence;
the test sequence of the internal short-circuit battery is sequentially a first reference performance test mode, an internal short-circuit trigger test, a second reference performance test mode, a cyclic aging test and a third reference performance test mode;
the first reference performance test mode is one-time performance test performed before internal short circuit triggering;
the second reference performance test mode is a one-time performance test performed after internal short circuit triggering;
and the third reference performance test mode is the performance test of the internal short-circuit battery after the cyclic experiment.
Based on the scheme, the cyclic aging test adopts a constant-current constant-voltage charging mode, and is specifically as follows:
when the charging voltage reaches the upper limit cutoff voltage, the constant voltage charging is converted until the current drops to a smaller value;
after standing for a period of time, discharging to a lower limit cut-off voltage with constant current.
On the basis of the scheme, the reference performance test comprises a capacity test, a pulse test and a self-discharge test;
evaluating self-discharge characteristics of the battery by battery voltage variation during rest and battery charge-discharge efficiency before and after rest;
the charge capacity before and after the battery was set aside was recorded, and it was determined whether the self-discharge capacity of the battery was restorable.
On the basis of the scheme, when the trigger test is carried out on the internal short-circuit battery, the direct contact between the anode material and the cathode material of the battery is ensured.
On the basis of the scheme, certain initial pretightening force is applied to the internal short-circuit battery at the short-circuit position, and the initial pretightening force is kept constant.
Based on the scheme, according to the change curve of the battery charge capacity retention rate along with the cycle times in the cyclic aging test process, the capacity attenuation conditions of a normal battery and a short-circuit battery are obtained;
based on a second-order equivalent circuit model, identifying the ohmic internal resistance and the polarized internal resistance of the battery in different performance testing stages, and obtaining the change condition of the internal resistances of the normal battery and the internal short-circuit battery along with the SOC;
in the self-discharge test of different stages, after waiting for voltage stabilization, drawing a change curve of a normal battery and an internal short-circuit battery relative to initial values in a period of time;
the ratio of the discharge capacity after the battery was set aside to the charge capacity before the battery was set aside was designated as a first capacity retention rate, the ratio of the charge capacity after the battery was set aside to the charge capacity before the battery was set aside was designated as a second capacity retention rate, and the self-discharge characteristics of the battery were evaluated by the change in the battery voltage during the setting aside and the first capacity retention rate and the second capacity retention rate.
On the basis of the scheme, the voltage curve of the battery in the constant-current charging stage and the current curve of the battery in the constant-voltage charging stage in the cyclic aging test process are extracted, and differential operation is carried out on the voltage curve and the current curve to obtain the change of the voltage and the current of the internal short-circuit battery along with the increase of the cyclic times;
and extracting an internal and external temperature change curve of the battery in a constant current charging stage in a cyclic aging test process to obtain the change condition of the difference between the internal temperature and the external temperature of the normal battery and the short-circuit battery along with the aging degree.
Based on the above scheme, the method for obtaining the pressure boundary required by the thermal runaway of the normal battery and the internal short-circuit battery according to the voltage and the internal and external temperature difference of the normal battery and the internal short-circuit battery in the continuous pressurization process specifically comprises the following steps:
respectively and continuously applying pressure to the internal short-circuit battery and the normal battery until the battery is in thermal runaway, so as to obtain the voltage and temperature evolution condition in the pressurizing process of the battery;
drawing voltage and internal and external temperature change curves of the internal short-circuit battery and the normal battery after being pressed;
the cause of thermal runaway of the internal short-circuited battery and the normal battery is proposed by comparing the differences in voltage, internal and external temperature and pressure changes of the short-circuited battery and the normal battery when thermal runaway occurs.
On the basis of the scheme, the method further comprises the step of obtaining the influence of the internal short circuit fault on the safety boundary of the battery by comparing the peak pressure of the internal short circuit battery with the peak pressure of the normal battery when thermal runaway occurs.
The invention has the beneficial effects that:
the invention obtains voltage, current and internal and external temperature data of the normal battery and the internal short-circuit fault battery based on a battery internal short-circuit fault test of coupling mechanical stress of the normal battery and the internal short-circuit fault battery. And obtaining the external comprehensive performance of the battery and the change of the voltage and the temperature of the battery in the cyclic process, and determining the influence of the internal short circuit fault on the service performance of the battery. In addition, based on the voltage and internal and external temperature difference of the normal battery and the internal short-circuit battery in the process of continuously pressurizing to thermal runaway, the maximum mechanical stress of the battery when the thermal runaway occurs is obtained, and the influence of the internal short-circuit fault on the safety performance of the battery is obtained. The short circuit experimental simulation mode adopted by the invention is closer to the actual internal short circuit condition, and the acquired electric and thermal signals are more accurate and effective.
Drawings
The invention has the following drawings:
FIG. 1 is a flow chart of an analysis method of a degradation mechanism of internal short circuit fault battery performance;
FIG. 2 is a graph showing the capacity versus internal resistance characteristics of a normal cell and an internal short cell;
FIG. 3 is a graph showing the self-discharge characteristics of a normal cell and an internal short cell;
FIG. 4 is a graph of voltage versus temperature signal during a cycle of a normal cell and an internal short cell;
fig. 5 is a graph showing voltage versus temperature signals during the voltage application process of a normal battery and an internal short-circuit battery.
Detailed Description
The present invention will be described in further detail with reference to fig. 1-5 and the detailed description of the invention, in order to make the objects, advantages and features of the invention more apparent.
Referring to fig. 1, one embodiment of the present invention includes the following steps:
performing reference performance test on the normal battery and the internal short-circuit battery to obtain battery capacity, internal resistance and self-discharge characteristic evolution conditions of the normal battery and the internal short-circuit battery;
performing cyclic aging test on the normal battery and the internal short-circuit battery to obtain the battery voltage and temperature evolution conditions of the normal battery and the internal short-circuit battery;
and obtaining a pressure boundary required when the normal battery and the internal short-circuit battery are in thermal runaway according to the voltage and the internal and external temperature difference of the normal battery and the internal short-circuit battery in the continuous pressurizing process so as to reveal the influence of the internal short-circuit fault on the safety performance.
In the embodiment, the 3.95Ah ternary lithium ion internal short-circuit fault battery is analyzed, the influence condition of internal short-circuit faults among materials caused by diaphragm perforation on the service performance and the safety performance of the battery is determined, and a lithium ion battery performance degradation mechanism caused by the internal short-circuit faults is disclosed. The battery internal short circuit fault experiment mainly comprises a cyclic aging test, a reference performance test and an internal short circuit triggering test. The cyclic aging test adopts a CCCV charging mode. The reference performance tests include capacity tests, low current balance potential tests, pulse tests, EIS tests, and self-discharge tests. When the internal short-circuit battery is triggered and tested, the device is pulled away from the position of the diaphragm opening by utilizing the tail end of the short-circuit triggering device extending to the outside of the battery, so that the direct contact between the anode material and the cathode material of the battery is ensured. In addition, in the actual operation process, besides the initial pretightening force of the battery, namely the interaction force when the battery cells are grouped, as the aging degree of the battery deepens, no matter the battery is in a normal temperature or high temperature environment, the SEI film thickens and the like, the internal gas production amount of each single battery in the battery pack can be increased, so that the interaction force between the single batteries in the battery pack is increased. Thus, it is preferable that pressure be applied to the partially shorted cell at the location of the short circuit using a die.
The embodiment comprises the evolution characteristics of the electrothermal performance of a normal battery and an internal short-circuit battery. The change curve of the battery charge capacity retention rate with the cyclic test during the cyclic aging test is shown in fig. 2 (a). The normal battery and the internal short-circuit battery have approximately linear attenuation trend, and the attenuation speeds are similar. Based on second-order equivalent circuit model, battery ohm internal resistance R in different performance testing stages is identified o Internal resistance of polarization R p1 And R is R p2 . And drawing the change condition of the internal resistances of the normal battery and the internal short-circuit battery along with the SOC, as shown in fig. 2 (b) (c) (d). R of all cells before and after internal short-circuit triggering o 、R p1 、R p2 Substantially identical. And after cyclic aging, the internal resistance of the internal short-circuit battery is not obviously changed. The internal short-circuited battery has the same performance as a normal battery, regardless of the capacity characteristic or the internal resistance characteristic.
In the self-discharge test at different stages, after the voltage is stabilized, a change curve of the normal battery and the internal short-circuit battery with respect to initial values is drawn for a period of time, as shown in fig. 3 (a) (c) (e). After triggering the internal short circuit, in the stage 2 of the reference performance test, the voltage drop speed is that the internal short circuit battery applying pressure is faster than the non-pressure internal short circuit battery and is faster than the normal battery. It can be seen that the pressure-applied internal short circuit cell has a more severe degree of self-discharge than the non-pressure internal short circuit cell. When the cycle aging is completed, the voltage drop rate at the reference performance test 3 stage is reduced, either for a normal cell or for an internal short-circuited cell, but the internal short-circuited cell still has a faster voltage drop rate than for a normal cell, and the internal short-circuited cell with applied pressure has a faster voltage drop rate than for an internal short-circuited cell without pressure. The capacity retention rate 1 (RQ 1) and capacity retention rate 2 (RQ 2) of the normal cell and the internal short cell at different test stages are changed as shown in fig. 3 (b) (d) (f). The capacity retention rate 1 has the same behavior as the battery voltage variation during rest. The capacity retention rate 2 reflects the degree of restorability of the battery capacity after self-discharge. In both the reference performance test 1 and the reference performance test 2, the capacity retention rate 2 of the internal short-circuited battery was close to 100%, indicating that the self-discharge thereof was restorable. The change in the rest voltage and the capacity retention rate 1 confirms that the short-circuited battery has more severe self-discharge characteristics than the normal battery, and that the self-discharge degree of the internal short-circuited battery is significantly deepened after being subjected to mechanical stress. After cyclic aging, the self discharge of the short-circuited battery and the normal battery is slightly weakened, and the internal short-circuited degree of the battery is not increased. In addition, the self-discharge of the internal short-circuit battery has restorability before and after the cycle.
And extracting a voltage curve of the battery in a constant-current charging stage and a current curve of the battery in a constant-voltage charging stage in a cyclic aging process, and performing differential operation on the voltage curve and the current curve, wherein the curves of the normal battery and the internal short-circuit battery are basically overlapped. For simplicity and visual presentation, the present description provides only the voltage, current and differential curves of the internal short-circuit battery, as shown in fig. 4 (a) and (b). It can be seen that with the increase of the cycle times, the voltage and current of the internal short-circuit battery do not change significantly, and there is no abrupt feature. Besides the electric signal, the internal and external temperature change curves of the battery in the constant current charging stage in the cyclic aging process are extracted, the internal short-circuit battery has the same change rule as the normal battery, and the burst characteristic does not exist. In the charging process, the change curve of the internal temperature and the external temperature of the battery with the charging voltage is shown in fig. 4 (c), and the internal temperature and the external temperature have the same change trend, but the internal temperature is significantly higher than the external temperature. Also, at different charging voltages, the difference between the internal temperature of the battery and the external temperature is different. The variation curve of the maximum temperature difference between the inside and outside of the normal battery and the internal short-circuit battery with the cycle number in the constant current charging process is drawn as shown in fig. 4 (d). With the increase of the cycle times, the maximum temperature difference inside and outside the normal battery is basically kept unchanged, and the maximum temperature difference inside and outside the short-circuited battery is gradually increased. It can be seen that as the degree of aging increases, the difference between the internal and external temperatures of the internal short-circuited battery gradually increases due to the cumulative effect, and is more remarkable under the condition of applying pressure.
By comparing the evolution characteristics of the electric heating performance of the normal battery and the internal short-circuit battery, the battery has no obvious difference from the normal battery except for self-discharge when internal short-circuit occurs and after operation with faults, has no sudden characteristics caused by accumulation effect, but can aggravate the internal and external temperature difference in the battery charging process. According to this feature, the diagnosis of the internal short-circuited battery can be performed.
According to the invention, pressure is continuously applied to the short-circuit battery and the normal battery respectively until the battery is in thermal runaway, the evolution condition of the voltage and the temperature of the battery in the pressurizing process is obtained, and the voltage and the internal and external temperature change curves of the short-circuit battery and the normal battery after being pressurized are drawn, as shown in fig. 5 (a) and (b). Whether the battery is short-circuited or normal, the final battery voltage drops to zero after the pressure is applied, the temperature rises sharply, and thermal runaway occurs. To further compare the voltage and internal and external temperature differences between the short-circuited battery and the normal battery, the voltage and internal and external temperatures at which thermal runaway occurs between the internal short-circuited battery and the normal battery are extracted as shown in fig. 5 (c) (d). Obviously, the voltage of the shorted cell is significantly different from that of the normal cell. The voltage of the short-circuited battery does not shake significantly before suddenly dropping to zero, while the normal battery shakes drastically before the voltage drops significantly. Further, the short-circuited battery is different from the normal battery in the time when the internal and external temperatures start to rise sharply. The differential behavior of the voltage and the internal and external temperatures when the normal battery and the internal short-circuit battery are in thermal runaway shows that the reasons for the thermal runaway are different. In addition to the significant difference in voltage and internal and external temperatures, the pressure change of the shorted cell also has a different behavior than that of the normal cell. When thermal runaway occurs, the pressure and voltage change of the internal short-circuited battery and the normal battery are as shown in fig. 5 (e). For an internal short-circuited battery, the pressure in the internal short-circuited battery continues to increase until the voltage drop is zero. For a normal cell, the pressure suddenly begins to decrease during the time the voltage remains stable. The battery voltage is dithered and finally drops greatly. The difference in the times of the pressure drop of the internal short-circuited battery from that of the normal battery also indicates that the cause of thermal runaway thereof is different. In addition, the peak pressure of the internal short-circuited battery is lower when thermal runaway occurs compared to the normal battery, indicating that the internal short-circuited battery failure causes the safety margin of the battery to be lowered.
By analyzing the safety performance evolution conditions of the normal battery and the internal short-circuit battery, the normal battery can be obtained to cause thermal runaway due to puncture after the aluminum plastic film is broken. The internal short-circuit battery of the positive and negative electrode active materials is broken by the internal diaphragm, so that the positive and negative electrode active materials are broken to form serious internal short circuit, and thermal runaway is caused before the aluminum plastic film is pierced, so that the peak pressure of the internal short-circuit battery is reduced, and the safety performance of the internal short-circuit battery is reduced.
In summary, the invention considers the mechanical stress existing in the practical battery using process, simulates the electric, thermal and force characteristics of the short-circuit fault in the battery, and defines the development condition of the battery under the condition of considering the mechanical stress and the operation condition of early-stage short-circuit fault in the battery.
The above embodiments are only for illustrating the present invention and not for limiting the present invention, and various changes and modifications may be made by one skilled in the relevant art without departing from the spirit and scope of the present invention, so that all equivalent technical solutions fall within the scope of the present invention, which is defined by the claims. What is not described in detail in this specification is prior art known to those skilled in the art.
Claims (10)
1. An analysis method of a degradation mechanism of internal short circuit fault battery performance is characterized by comprising the following steps:
acquiring the battery capacity, internal resistance and self-discharge characteristic evolution conditions of a normal battery and an internal short-circuit battery;
acquiring the battery voltage and temperature evolution conditions of a normal battery and an internal short-circuit battery;
and obtaining the pressure boundary required when the normal battery and the internal short-circuit battery are out of control in a thermal manner according to the voltage and the internal and external temperature difference of the normal battery and the internal short-circuit battery in the continuous pressurization process.
2. The method for analyzing the degradation mechanism of the internal short-circuit fault battery performance according to claim 1, wherein the battery capacity, the internal resistance and the self-discharge characteristics are obtained by experimental tests:
the battery internal short circuit fault test comprises a plurality of reference performance tests, an internal short circuit triggering test and a cyclic aging test;
the test sequence of the normal battery is a reference performance test mode I, a cyclic aging test and a reference performance test mode III in sequence;
the test sequence of the internal short-circuit battery is sequentially a first reference performance test mode, an internal short-circuit trigger test, a second reference performance test mode, a cyclic aging test and a third reference performance test mode;
the first reference performance test mode is one-time performance test performed before internal short circuit triggering;
the second reference performance test mode is a one-time performance test performed after internal short circuit triggering;
and the third reference performance test mode is the performance test of the internal short-circuit battery after the cyclic experiment.
3. The method for analyzing a degradation mechanism of an internal short-circuit fault battery according to claim 2, wherein the cyclic aging test adopts a constant-current constant-voltage charging mode, specifically:
when the charging voltage reaches the upper limit cutoff voltage, the constant voltage charging is converted until the current drops to a smaller value;
after standing for a period of time, discharging to a lower limit cut-off voltage with constant current.
4. The method for analyzing the degradation mechanism of the internal short-circuit fault battery according to claim 2, wherein the reference performance test includes a capacity test, a pulse test and a self-discharge test;
evaluating self-discharge characteristics of the battery by battery voltage variation during rest and battery charge-discharge efficiency before and after rest;
the charge capacity before and after the battery was set aside was recorded, and it was determined whether the self-discharge capacity of the battery was restorable.
5. The method for analyzing the performance degradation mechanism of the internal short-circuit fault battery according to claim 2, wherein when the internal short-circuit battery is subjected to a trigger test, direct contact between the anode material and the cathode material of the battery is ensured.
6. The method for analyzing the performance degradation mechanism of the internal short-circuit fault battery according to claim 2, wherein a certain initial pre-tightening force is applied to the internal short-circuit battery at the short-circuit position and the initial pre-tightening force is kept constant.
7. The method for analyzing a degradation mechanism of internal short-circuit fault battery performance according to claim 2, wherein the capacity attenuation conditions of a normal battery and a short-circuit battery are obtained according to a change curve of a battery charge capacity retention rate with the number of cycles in the cyclic aging test process;
based on a second-order equivalent circuit model, identifying the ohmic internal resistance and the polarized internal resistance of the battery in different performance testing stages, and obtaining the change condition of the internal resistances of the normal battery and the internal short-circuit battery along with the SOC;
in the self-discharge test of different stages, after waiting for voltage stabilization, drawing a change curve of a normal battery and an internal short-circuit battery relative to initial values in a period of time;
the ratio of the discharge capacity after the battery was set aside to the charge capacity before the battery was set aside was designated as a first capacity retention rate, the ratio of the charge capacity after the battery was set aside to the charge capacity before the battery was set aside was designated as a second capacity retention rate, and the self-discharge characteristics of the battery were evaluated by the change in the battery voltage during the setting aside and the first capacity retention rate and the second capacity retention rate.
8. The method for analyzing the performance degradation mechanism of the internal short-circuit fault battery according to claim 2, wherein the voltage curve of the battery in the constant-current charging stage and the current curve in the constant-voltage charging stage in the cyclic aging test process are extracted and subjected to differential operation, and the change of the voltage and the current of the internal short-circuit battery along with the increase of the cycle times is obtained;
and extracting an internal and external temperature change curve of the battery in a constant current charging stage in a cyclic aging test process to obtain the change condition of the difference between the internal temperature and the external temperature of the normal battery and the short-circuit battery along with the aging degree.
9. The method for analyzing a performance degradation mechanism of an internal short-circuit fault battery according to claim 1, wherein the obtaining a pressure boundary required when thermal runaway occurs between the normal battery and the internal short-circuit battery according to a voltage and an internal and external temperature difference between the normal battery and the internal short-circuit battery in a continuous pressurization process is specifically:
respectively and continuously applying pressure to the internal short-circuit battery and the normal battery until the battery is in thermal runaway, so as to obtain the voltage and temperature evolution condition in the pressurizing process of the battery;
drawing voltage and internal and external temperature change curves of the internal short-circuit battery and the normal battery after being pressed;
the cause of thermal runaway of the internal short-circuited battery and the normal battery is proposed by comparing the differences in voltage, internal and external temperature and pressure changes of the short-circuited battery and the normal battery when thermal runaway occurs.
10. The method of claim 9, further comprising obtaining an effect of the internal short circuit fault on a safety margin of the battery by comparing peak pressures of the internal short circuit battery with peak pressures of the normal battery when thermal runaway occurs.
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