CN117607718A - An analysis method for battery performance degradation mechanism due to internal short circuit fault - Google Patents

Abstract

The present invention proposes a mechanism for internal short circuit fault to cause performance degradation of lithium-ion batteries. Conduct a battery internal short-circuit fault test coupled with mechanical stress on normal batteries and short-circuit batteries with positive and negative electrodes in contact due to separator holes, and obtain voltage, current, and internal and external temperature data of normal batteries and batteries with internal short-circuit faults. Analyze the external comprehensive performance of the battery, observe the battery voltage and temperature changes during the cycle, and determine the impact of internal short-circuit faults on battery performance. In addition, the voltage and internal and external temperature differences between normal batteries and internally short-circuited batteries during the process of continuous pressurization to thermal runaway were compared to obtain the maximum mechanical stress when thermal runaway occurs in the battery, and the impact of internal short-circuit faults on battery safety performance was analyzed. The short-circuit experimental simulation method adopted by the present invention is closer to the actual internal short-circuit situation, and the electrical and thermal signals obtained are more accurate and effective.

Description

An analysis method for battery performance degradation mechanism due to internal short circuit fault

Technical field

The present invention relates to the field of battery performance evaluation, and in particular to a method for analyzing the performance degradation mechanism of internal short circuit fault batteries.

Background technique

In recent years, with the rapid growth and large-scale promotion and application of lithium-ion batteries, safety has become a key issue restricting the development of the industry. Short-circuit faults within the battery due to manufacturing defects or abuse pose great challenges to the safe and reliable operation of lithium-ion batteries. Understanding the mechanism of battery failure and performance degradation after operation with faults is crucial to reducing battery safety risks. Therefore, it is necessary to obtain an analysis method for the performance degradation mechanism of lithium-ion batteries caused by internal short-circuit faults.

The mechanism of performance degradation of lithium-ion batteries after internal short circuit failure and fault operation is unknown. Therefore, it is necessary to propose a performance degradation mechanism analysis method for internal short-circuit fault batteries based on the different performances of electrical, thermal, and force signals between normal batteries and internal short-circuit batteries. An analysis method of battery performance degradation mechanism due to internal short-circuit fault is exactly the method that meets the above requirements.

In the existing technical solution, in order to reveal the mechanical characteristics of the internal short circuit in the battery, a finite element model of the electrochemistry, heat production and thermal runaway of the internal short circuit battery is established. The model is used to study the voltage, internal resistance, temperature and other characteristics of Cu-Al type and An-Ca type internal short circuits, and the differences and connections between them and external short circuits are analyzed to obtain characteristics that can be used for internal short circuit detection. The relationship between heat generation power density and thermal runaway when internal short circuit occurs is also studied, as well as the impact of contact resistance on heat generation power density, and methods to reduce the risk of thermal runaway are analyzed.

In order to quantify the short-circuit current and the thermal runaway risk of premature short-circuit failure, a short-circuit current estimation method based on the average-difference model is proposed. First, the short-circuit battery equivalent circuit model and parameter identification method were analyzed, and the short-circuit battery parameters were obtained by joint estimation of least squares and Kalman filtering. Then, the short-circuit current estimation method is divided into different scales according to the characteristics of the voltage signal, and the short-circuit current in the series battery pack is estimated using the model parameters and terminal voltage. Finally, experiments were used to verify the method, and the results showed that short-circuit currents of different sizes can converge to the reference value, achieving rapid diagnosis of internal short circuits.

In order to identify and detect micro-short circuits in the early stage of internal short-circuit development, a micro-short circuit diagnosis method using the battery charging capacity increment curve and the charging capacity difference change rule is proposed. First, the corresponding relationship between the highest peak of the IC curve and the battery state of charge under different current rates and temperatures was analyzed in detail. Then the charging capacity difference is proposed to explain the SOC difference between the faulty battery and the normal battery when there is an internal short circuit, and based on this, a quantitative method for internal short circuit is derived.

The existing technology has the following shortcomings: the data used to analyze the mechanism is obtained through experiments using external resistors, there are differences between the method of simulating internal short circuits and actual internal short circuits, and the conclusions about the internal resistance temperature have not been verified.

Contents of the invention

In response to the above problems, the present invention proposes a mechanism for lithium-ion battery performance degradation caused by internal short circuit faults. Conduct a battery internal short-circuit fault test coupled with mechanical stress on normal batteries and short-circuit batteries with positive and negative electrodes in contact due to separator holes, and obtain voltage, current, and internal and external temperature data of normal batteries and batteries with internal short-circuit faults. Analyze the external comprehensive performance of the battery, observe the battery voltage and temperature changes during the cycle, and determine the impact of internal short-circuit faults on battery performance. In addition, by comparing the voltage and internal and external temperature differences between normal batteries and internally short-circuited batteries during the process of continuous pressurization to thermal runaway, the maximum mechanical stress when the battery undergoes thermal runaway is obtained, and the impact of internal short-circuit faults on battery safety performance is analyzed. The short-circuit experimental simulation method adopted by the present invention is closer to the actual internal short-circuit situation, and the electrical and thermal signals obtained are more accurate and effective. The method specifically includes the following steps:

Obtain the evolution of battery capacity, internal resistance and self-discharge characteristics of normal batteries and internal short-circuit batteries;

Obtain the battery voltage and temperature evolution of normal batteries and internal short-circuit batteries;

Based on the voltage and internal and external temperature differences between normal batteries and internally short-circuited batteries during the continuous pressurization process, the pressure boundaries required when thermal runaway occurs between normal batteries and internally short-circuited batteries are obtained.

Based on the above scheme, the battery capacity, internal resistance and self-discharge characteristics were obtained through experimental tests:

Battery internal short-circuit fault test includes reference performance test, internal short-circuit trigger test and cycle aging test;

The test sequence of normal batteries is reference performance test mode one, cycle aging test and reference performance test mode three;

The test sequence of internal short-circuit batteries is reference performance test mode one, internal short-circuit trigger test, reference performance test mode two, cycle aging test and reference performance test mode three;

Among them, the reference performance test mode 1 is a performance test conducted before the internal short circuit is triggered;

Reference performance test mode 2 is a performance test performed after the internal short circuit is triggered;

Reference performance test mode three is the performance test of the internal short-circuit battery after the cycle test.

Based on the above scheme, the cyclic aging test adopts constant current and constant voltage charging method, specifically:

When the charging voltage reaches the upper limit cut-off voltage, it switches to constant voltage charging until the current drops to a smaller value;

After standing for a period of time, it is discharged to the lower limit cut-off voltage with a constant current.

Based on the above solution, the reference performance test includes capacity test, pulse test and self-discharge test;

Evaluate the self-discharge characteristics of the battery through battery voltage changes during storage and battery charge and discharge efficiency before and after storage;

Record the charging capacity of the battery before and after it is left alone to determine whether the battery's self-discharge capacity is recoverable.

Based on the above solution, when performing a trigger test on an internally short-circuited battery, ensure direct contact between the positive and negative electrode materials of the battery.

Based on the above solution, a certain initial preload force is applied to the internally short-circuited battery at the short circuit position and the initial preload force is kept constant.

On the basis of the above solution, according to the change curve of the battery charging capacity retention rate with the number of cycles during the cycle aging test, the capacity attenuation of the normal battery and the short-circuit battery is obtained;

Based on the second-order equivalent circuit model, identify the ohmic internal resistance and polarization internal resistance of the battery at different performance test stages, and obtain the changes in the internal resistance of normal batteries and internal short-circuit batteries with SOC;

In the self-discharge test at different stages, after waiting for the voltage to stabilize, draw the change curve of the normal battery and the internal short-circuit battery relative to the initial value over a period of time;

The ratio of the battery's discharge capacity after shelving and the charging capacity before shelving is recorded as the first capacity retention rate, and the ratio of the charging capacity after shedding and the charging capacity before shelving is recorded as the second capacity retention rate. Through the change of battery voltage during the shelving period and the third The first capacity retention rate and the second capacity retention rate evaluate the self-discharge characteristics of the battery.

On the basis of the above scheme, the voltage curve of the battery in the constant current charging stage and the current curve of the constant voltage charging stage during the cycle aging test are extracted and differential operations are performed on them to obtain the internal short circuit battery as the number of cycles increases. Changes in voltage and current;

Extract the internal and external temperature change curves of the battery during the constant current charging stage during the cycle aging test, and obtain the difference between the internal and external temperatures of the normal battery and the short-circuit battery as the aging degree changes.

On the basis of the above solution, based on the voltage and internal and external temperature differences between normal batteries and internally short-circuited batteries during the continuous pressurization process, the pressure boundaries required when thermal runaway occurs between normal batteries and internally short-circuited batteries are specifically:

Continuously apply pressure to the internally short-circuited battery and the normal battery until the battery undergoes thermal runaway, and obtain the voltage and temperature evolution during the battery pressurization process;

Draw the voltage and internal and external temperature change curves of the internally short-circuited battery and the normal battery after being stressed;

By comparing the differences in voltage, internal and external temperature, and pressure changes between short-circuited batteries and normal batteries when thermal runaway occurs, the reasons why thermal runaway occurs between internally short-circuited batteries and normal batteries are proposed.

On the basis of the above solution, it also includes comparing the peak pressure of internal short-circuit batteries and normal batteries when thermal runaway occurs to obtain the impact of internal short-circuit faults on the safety margin of the battery.

Beneficial effects of the present invention:

The invention is based on the battery internal short-circuit fault test of coupled mechanical stress on a normal battery and an internal short-circuit fault battery, and obtains the voltage, current, and internal and external temperature data of the normal battery and the internal short-circuit fault battery. Obtain the comprehensive external performance of the battery and the changes in battery voltage and temperature during the cycle, and determine the impact of internal short-circuit faults on battery performance. In addition, based on the difference in voltage and internal and external temperatures between normal batteries and internally short-circuited batteries during the process of continuous pressurization to thermal runaway, the maximum mechanical stress when the battery undergoes thermal runaway is obtained, and the impact of internal short-circuit faults on battery safety performance is obtained. The short-circuit experimental simulation method adopted by the present invention is closer to the actual internal short-circuit situation, and the electrical and thermal signals obtained are more accurate and effective.

Description of drawings

The present invention has the following drawings:

Figure 1 is a flow chart of the analysis method of battery performance degradation mechanism due to internal short circuit fault;

Figure 2 shows the capacity and internal resistance characteristic curves of normal batteries and internal short-circuit batteries;

Figure 3 shows the self-discharge characteristic curves of normal batteries and internal short-circuit batteries;

Figure 4 shows the voltage and temperature signal curves during the cycle of normal batteries and internal short-circuit batteries;

Figure 5 shows the voltage and temperature signal curves during the pressurization process of normal batteries and internal short-circuit batteries.

Detailed ways

In order to make the purpose, advantages and features of the present invention more obvious, the present invention will be further described in detail below in conjunction with the accompanying drawings 1-5 and specific embodiments.

Referring to Figure 1, a specific embodiment of the present invention includes the following steps:

Conduct reference performance tests on normal batteries and internal short-circuit batteries to obtain the evolution of battery capacity, internal resistance and self-discharge characteristics of normal batteries and internal short-circuit batteries;

Conduct cycle aging tests on normal batteries and internal short-circuit batteries to obtain the battery voltage and temperature evolution of normal batteries and internal short-circuit batteries;

Based on the voltage and internal and external temperature differences between normal batteries and internally short-circuited batteries during the continuous pressurization process, the pressure boundaries required when thermal runaway occurs between normal batteries and internally short-circuited batteries are obtained to reveal the impact of internal short-circuit faults on safety performance.

In this example, a 3.95Ah ternary lithium-ion internal short-circuit fault battery was analyzed to determine the impact of the internal short-circuit fault between materials caused by the separator hole on the battery performance and safety performance, and revealed that the internal short-circuit fault caused lithium Mechanisms of ion battery performance degradation. The battery internal short-circuit fault experiment mainly includes cycle aging test, reference performance test and internal short-circuit trigger test. The cycle aging test adopts CCCV charging method. Reference performance tests include capacity test, small current balance potential test, pulse test, EIS test and self-discharge test. When performing a trigger test on an internally short-circuited battery, use the end of the short-circuit trigger device that extends to the outside of the battery to pull the device away from the separator opening to ensure direct contact between the positive and negative materials of the battery. In addition, consider that during actual operation, in addition to the initial preload force of the battery, that is, the interaction force when the battery cells are assembled, as the battery ages, whether the battery is in a normal temperature or high temperature environment, the SEI film thickens, etc. This will cause the internal gas production of each single cell in the battery pack to increase, causing the interaction force between the single cells in the battery pack to increase. Therefore, preferably, a die can be used on a partially shorted cell to apply pressure at the short circuit location.

This embodiment includes the electrothermal performance evolution characteristics of normal batteries and internal short-circuit batteries. During the cycle aging test, the change curve of the battery charging capacity retention rate with the cycle test is shown in Figure 2(a). Both normal batteries and internally short-circuited batteries show an approximately linear attenuation trend, and the attenuation speeds are similar. Based on the second-order equivalent circuit model, the battery ohmic internal resistance _Ro , polarization internal resistance R _p1 and R _p2 at different performance test stages are identified. Plot the changes in internal resistance of normal batteries and internal short-circuit batteries with SOC, as shown in Figure 2(b)(c)(d). Before and after internal short circuit triggering, R _o , R _p1 , and R _p2 of all batteries are basically the same. And after cyclic aging, the internal resistance of the internal short-circuit battery also did not change significantly. Regardless of capacity characteristics or internal resistance characteristics, internal short-circuit batteries have the same performance as normal batteries.

In the self-discharge test at different stages, after waiting for the voltage to stabilize, draw the change curves of the normal battery and the internal short-circuit battery relative to the initial value over a period of time, as shown in Figure 3(a)(c)(e). When an internal short circuit is triggered, in the second stage of the reference performance test, the speed of the voltage drop is that the internal short circuit battery under pressure is faster than the internal short circuit battery without pressure and the voltage drops faster than the normal battery. It can be seen that the internal short-circuit battery under pressure has a more serious degree of self-discharge than the internal short-circuit battery without pressure. When the cycle aging is completed, whether it is a normal battery or an internal short-circuit battery, the voltage drop rate in the reference performance test stage 3 decreases, but the internal short-circuit battery still has a faster voltage drop rate than the normal battery, and the pressure is applied The voltage of an internally short-circuited battery drops faster than that of an unstressed internally short-circuited battery. The changes in capacity retention rate 1 (RQ1) and capacity retention rate 2 (RQ2) of normal batteries and internal short-circuit batteries at different test stages are shown in Figure 3(b)(d)(f). Capacity retention 1 behaves the same as battery voltage changes during storage. Capacity retention rate 2 reflects the degree of recovery of battery capacity after self-discharge. In the reference performance test 1 and reference performance test 2 stages, the capacity retention rate 2 of the internal short-circuit battery is close to 100%, indicating that its self-discharge is recoverable. The changes in shelving voltage and capacity retention rate 1 confirm that short-circuit batteries have more severe self-discharge characteristics than normal batteries, and the degree of self-discharge of internally short-circuit batteries significantly deepens after being subjected to mechanical stress. After cyclic aging, the self-discharge of short-circuited batteries and normal batteries will be slightly weakened, and the internal short circuit of the battery will not be aggravated. In addition, the self-discharge of internally short-circuited batteries is recoverable before and after cycling.

Extract the voltage curve of the battery in the constant current charging stage and the current curve in the constant voltage charging stage during the cycle aging process, and perform differential operations on them. The curves of the normal battery and the internal short-circuit battery basically overlap. In order to make the display more concise and intuitive, this manual only provides the voltage, current and their differential curves of the internal short-circuit battery, as shown in Figure 4(a) and (b). It can be seen that as the number of cycles increases, the voltage and current of the internal short-circuit battery do not change significantly, and there are no sudden characteristics. In addition to the electrical signal, the internal and external temperature change curves of the battery in the constant current charging stage during the cycle aging process are extracted. The internal short-circuit battery has the same change pattern as the normal battery, and there are no sudden characteristics. During the charging process, the variation curves of the internal temperature and external temperature of the battery with the charging voltage are shown in Figure 4(c). The internal temperature and the external temperature have the same variation trend, but the internal temperature is significantly higher than the external temperature. Moreover, at different charging voltages, the difference between the internal temperature of the battery and the external temperature is different. The maximum temperature difference between the inside and outside of the normal battery and the internal short-circuit battery during the constant current charging process is plotted as a function of the number of cycles, as shown in Figure 4(d). As the number of cycles increases, the maximum temperature difference between the inside and outside of a normal battery remains basically unchanged, while the maximum temperature difference between the inside and outside of a short-circuit battery gradually increases. It can be seen that with the deepening of aging, the difference between the internal and external temperatures of the internal short-circuit battery gradually increases due to the cumulative effect, and is more significant under conditions of applied pressure.

By comparing the electrothermal performance evolution characteristics of normal batteries and internally short-circuited batteries, it can be seen that there is no obvious difference between the battery and the normal battery except for self-discharge when internal short-circuit occurs and after running with a fault. There are no sudden characteristics caused by cumulative effects. , but it will aggravate the internal and external temperature difference during battery charging. Based on this feature, internal short-circuit batteries can be diagnosed.

This invention continuously applies pressure to the short-circuit battery and the normal battery until the battery undergoes thermal runaway, obtains the evolution of the voltage and temperature of the battery during the pressurization process, and plots the voltage and internal and external temperature changes of the short-circuit battery and the normal battery after being pressurized. Curve, as shown in Figure 5(a)(b). Regardless of whether it is a short-circuited battery or a normal battery, after pressure is applied, the battery voltage eventually drops to zero, the temperature rises sharply, and thermal runaway occurs. In order to further compare the voltage and internal and external temperature differences between short-circuit batteries and normal batteries, the voltage and internal and external temperatures of internal short-circuit batteries and normal batteries when thermal runaway occurs are extracted, as shown in Figure 5(c)(d). Obviously, the voltage of a short-circuited battery is significantly different from that of a normal battery. The voltage of a short-circuited battery does not jitter significantly before it suddenly drops to zero, while a normal battery jitters violently before its voltage drops significantly. In addition, the moment when the temperature inside and outside of a short-circuited battery starts to rise sharply is different from that of a normal battery. The differential behavior of voltage and internal and external temperatures when thermal runaway occurs between normal batteries and internally short-circuited batteries indicates that the causes of thermal runaway are different. In addition to the significant differences in voltage and internal and external temperatures, pressure changes in short-circuited batteries and normal batteries also behave differently. When thermal runaway occurs, the pressure and voltage changes between the internally short-circuited battery and the normal battery are shown in Figure 5(e). For internally short-circuited batteries, the pressure of the internally short-circuited battery continues to increase before the voltage drops to zero. For a normal battery, while the voltage remains stable, the pressure suddenly begins to decrease. The battery voltage then began to jitter and eventually dropped significantly. The difference in the moment when the pressure drops between an internally short-circuited battery and a normal battery also shows that the causes of thermal runaway are different. In addition, the peak pressure of internal short-circuit batteries when thermal runaway occurs is lower than that of normal batteries, indicating that internal short-circuit faults in the battery cause the safety margin of the battery to decrease.

By analyzing the evolution of the safety performance of normal batteries and internally short-circuited batteries, it can be concluded that normal batteries cause thermal runaway due to puncture after the aluminum-plastic film ruptures. Internal short circuit of the positive and negative active materials of the battery. Due to the damage of the internal separator, the positive and negative active materials first rupture and form a serious internal short circuit. This causes thermal runaway before the aluminum plastic film is punctured, resulting in a drop in peak pressure and reduced safety performance. .

In summary, the present invention considers the mechanical stress existing in the actual battery use process, simulates the electrical, thermal, and mechanical characteristics of the internal short-circuit fault in the battery, and clarifies the operating conditions of the battery with faults in the early stage of internal short-circuit under the condition of considering mechanical stress. the following developments.

The above embodiments are only used to illustrate the patent of the present invention, but not to limit the patent of the present invention. Those of ordinary skill in the relevant technical fields can also make various changes and modifications without departing from the essence and scope of the patent of the present invention. , therefore all equivalent technical solutions also fall within the scope of the patent of the present invention, and the scope of patent protection of the patent of the present invention should be limited by the claims. Contents not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims (10)

1. A method for analyzing the performance degradation mechanism of batteries with internal short circuit faults, which is characterized by including the following steps: Obtain the evolution of battery capacity, internal resistance and self-discharge characteristics of normal batteries and internal short-circuit batteries; Obtain the battery voltage and temperature evolution of normal batteries and internal short-circuit batteries; Based on the voltage and internal and external temperature differences between normal batteries and internally short-circuited batteries during the continuous pressurization process, the pressure boundaries required when thermal runaway occurs between normal batteries and internally short-circuited batteries are obtained. 2. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery as claimed in claim 1, characterized in that the battery capacity, internal resistance and self-discharge characteristics are obtained through experimental testing: The internal short-circuit fault test of the battery includes multiple reference performance tests, internal short-circuit trigger test and cycle aging test; The test sequence of normal batteries is reference performance test mode one, cycle aging test and reference performance test mode three; The test sequence of internal short-circuit batteries is reference performance test mode one, internal short-circuit trigger test, reference performance test mode two, cycle aging test and reference performance test mode three; Among them, the reference performance test mode 1 is a performance test conducted before the internal short circuit is triggered; Reference performance test mode 2 is a performance test performed after the internal short circuit is triggered; Reference performance test mode three is the performance test of the internal short-circuit battery after the cycle test. 3. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery as claimed in claim 2, characterized in that the cyclic aging test adopts a constant current and constant voltage charging method, specifically: When the charging voltage reaches the upper limit cut-off voltage, it switches to constant voltage charging until the current drops to a smaller value; After standing for a period of time, it is discharged to the lower limit cut-off voltage with a constant current. 4. A method for analyzing the performance degradation mechanism of an 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; Evaluate the self-discharge characteristics of the battery through battery voltage changes during storage and battery charge and discharge efficiency before and after storage; Record the charging capacity of the battery before and after it is left alone to determine whether the battery's self-discharge capacity is recoverable. 5. An analysis method for the performance degradation mechanism of an internal short-circuit fault battery according to claim 2, characterized in that when performing a trigger test on an internal short-circuit battery, direct contact between the positive and negative electrode materials of the battery is ensured. 6. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery as claimed in claim 2, characterized in that 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. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery according to claim 2, characterized in that, according to the change curve of the battery charging capacity retention rate with the number of cycles during the cyclic aging test, the normal battery and the battery performance are obtained. Capacity fading of short-circuited batteries; Based on the second-order equivalent circuit model, identify the ohmic internal resistance and polarization internal resistance of the battery at different performance test stages, and obtain the changes in the internal resistance of normal batteries and internal short-circuit batteries with SOC; In the self-discharge test at different stages, after waiting for the voltage to stabilize, draw the change curve of the normal battery and the internal short-circuit battery relative to the initial value over a period of time; The ratio of the battery's discharge capacity after shelving and the charging capacity before shelving is recorded as the first capacity retention rate, and the ratio of the charging capacity after shedding and the charging capacity before shelving is recorded as the second capacity retention rate. Through the change of battery voltage during the shelving period and the third The first capacity retention rate and the second capacity retention rate evaluate the self-discharge characteristics of the battery. 8. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery as claimed in claim 2, characterized by extracting the voltage curve of the battery in the constant current charging stage and the current in the constant voltage charging stage during the cycle aging test. curve and perform differential operations on it to obtain the changes in internal short-circuit battery voltage and current as the number of cycles increases; Extract the internal and external temperature change curves of the battery during the constant current charging stage during the cycle aging test, and obtain the difference between the internal and external temperatures of the normal battery and the short-circuit battery as the aging degree changes. 9. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery as claimed in claim 1, characterized in that the normal battery is obtained based on the voltage and internal and external temperature differences between the normal battery and the internal short-circuit battery during the continuous pressurization process. The specific pressure boundary required when a thermal runaway occurs between a battery and an internally short-circuited battery is: Continuously apply pressure to the internally short-circuited battery and the normal battery until the battery undergoes thermal runaway, and obtain the voltage and temperature evolution during the battery pressurization process; Draw the voltage and internal and external temperature change curves of the internally short-circuited battery and the normal battery after being stressed; By comparing the differences in voltage, internal and external temperature, and pressure changes between short-circuited batteries and normal batteries when thermal runaway occurs, the reasons why thermal runaway occurs between internally short-circuited batteries and normal batteries are proposed. 10. A method for analyzing the performance degradation mechanism of an internal short-circuit fault battery as claimed in claim 9, further comprising: comparing the peak pressures of the internal short-circuit battery and the normal battery when thermal runaway occurs, to obtain the internal short-circuit fault response. The impact of battery safety margins.