Analysis method for main failure mechanism of battery with electrolyte leakage fault

Abstract

The invention provides a method for analyzing a main failure mechanism of a battery with an electrolyte leakage fault. The method comprises the following steps of: performing calendar aging, cyclic aging and reference performance test on a normal battery and a leakage battery; comparing the external characteristics of the normal battery and the leakage battery, and obtaining the difference between the leakage battery and the normal battery in the aspect of external characteristic performance; carrying out deep analysis on the dynamic degradation mechanism of the liquid leakage battery by utilizing an in-situ analysis means; obtaining a normal battery pole piece and a fault battery pole piece, and characterizing the battery pole pieces by using an electrochemical characterization means; battery regeneration is realized by using a battery pole piece, re-supplementing electrolyte and manufacturing a button battery; performance testing and aging testing are performed on the regenerated battery; the performance of the regenerated battery is evaluated; and a failure mechanism of the battery with liquid leakage is disclosed. And comparing the performance difference between the regenerative battery and the normal battery, and determining the irreversible influence of the fault on the battery. According to the invention, the main way of failure of the battery with liquid leakage and the irreversible influence of the liquid leakage fault on the battery can be revealed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to an analysis method for main failure mechanism of electrolyte leakage fault battery. BACKGROUND

[0002] With the large-scale application of lithium ion batteries in electric vehicles and energy storage fields, the safety of lithium ion batteries has become the focus of the industry and scientific research. Among them, electrolyte leakage is one of the common fault types of lithium ion batteries. Poor sealing, welding defects in the manufacturing process, and mechanical damage leading to shell damage or external extreme temperature changes causing shell expansion or shrinkage and cracks, etc. will all cause electrolyte leakage. Some of the gases produced by leakage are flammable, which will reduce the safety of battery use, and in severe cases may even cause safety accidents.

[0003] Because after the electrolyte of the battery leaks, there are various complex side reactions, and their influence on the fault battery is not clear. Therefore, it is necessary to clarify the key factors of the failure of the leakage battery, which is of great significance for accurately identifying the fault mode and effectively improving the reliability and safety of battery operation.

[0004] Current research on electrolyte leakage faults is very limited. Some studies only focus on a single abnormal phenomenon during electrolyte leakage, including the decrease of electrolyte content or the degradation of battery internal pollution on the performance of normal batteries. Among them, Fang et al. further found that the main mechanism of life attenuation is that when the electrolyte of the normal battery is consumed to be insufficient to fill the pores of the active material, the electrode active material area will decrease, promote the growth of SEI film, and form a positive feedback between SEI film growth and electrolyte consumption, eventually leading to nonlinear capacity attenuation of the battery. Zhou et al. analyzed the performance evolution of lithium ion batteries under different water content, and proposed that the SEI film will overgrow with the increase of water content, thereby causing the decline of battery rate performance and cycle performance. Stich et al. also showed that higher water content in lithium iron phosphate batteries would cause a significant increase in the mid-frequency impedance of the battery, indicating the formation of a high-resistance surface film, and the capacity attenuation rate accelerated during the cycle process.

[0005] Another part, although it relates to the research of electrolyte leakage failure, mainly focuses on the description of the leakage phenomenon that occurs under extreme conditions, and the attention to the failure mechanism of the leakage battery is limited. Among them, Maddipatla et al. found that the battery leaked electrolyte in the study of the influence of abnormally high temperature on the safety of the battery, and determined that the difference in the thermal expansion coefficient between the various parts of the battery top cover was the main reason for the electrolyte leakage of the battery under high temperature conditions. Zhang et al. found that the arc failure would damage the battery safety valve and cause the battery seal to be damaged, which would cause the electrolyte to leak, in the study of the influence of different arc energies on the battery safety valve and the electrochemical characteristics of the failed battery. These research results all show that the battery with electrolyte leakage has more serious performance degradation compared with the normal battery. However, they did not design an analysis method to decouple the influence of the failure factor on the battery performance, and further analyze the failure mechanism of the leakage battery.

[0006] The prior art analyzes the rules of the leakage battery in the external characteristics, and obtains the difference between the leakage battery and the normal battery, but does not analyze the dominant factor in the leakage failure mechanism. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide an analysis method for the main failure mechanism of the electrolyte leakage failure battery, so as to reveal the main failure path in the complex failure mechanism of the electrolyte leakage failure battery.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: An analysis method for the main failure mechanism of an electrolyte leakage failure battery, comprising: S1: performing calendar aging test, cycle aging test and reference performance test on normal battery and leakage battery; S2: comparing the external characteristics of the normal battery and the leakage battery, obtaining the difference in the external characteristic performance between the leakage battery and the normal battery; S3: using in-situ analysis means, deeply analyzing the kinetic degradation mechanism of the leakage battery, and determining the influence of the failure on the impedance of each part of the battery; S4: obtaining the normal battery and the failure battery pole piece, using the electrochemical characterization means to characterize the battery pole piece; using the battery pole piece, replenishing the electrolyte, making a button cell to realize the regeneration of the battery, and testing the performance and aging of the regenerated battery, evaluating the performance of the regenerated battery, and revealing the failure mechanism of the leakage battery; S5: comparing the performance difference between the regenerated battery and the normal battery, determining the irreversible influence of the failure on the battery.

[0009] Further, the calendar aging test is to place the battery at different SOCs in the early and late stages of electrolyte leakage.

[0010] Furthermore, the cyclic aging test adopts a CCCV constant current and constant voltage charging method.

[0011] Furthermore, the reference performance test includes capacity testing, equilibrium potential testing, HPPC pulse testing, and EIS testing; reference performance tests are performed on normal batteries and leaking batteries after early and late calendar aging tests; and reference performance tests are performed at specific capacity retention intervals during cycle aging tests.

[0012] Furthermore, the cycle aging test adopts the CCCV constant current and constant voltage charging method, which specifically includes switching to constant voltage charging when the charging voltage reaches the cutoff voltage, until the current drops to a small value, and then discharging the battery with a constant current after resting.

[0013] Furthermore, the external characteristics include capacity, internal resistance, resting curve, and charging curve.

[0014] Furthermore, the comparison of the external characteristics of normal batteries and leaking batteries specifically includes: obtaining the capacity decay of normal batteries and leaking batteries based on the capacity test and cycle test in the calendar aging test; identifying the ohmic internal resistance and polarization internal resistance of normal batteries and leaking batteries based on the second-order equivalent circuit model; analyzing the change of internal resistance with SOC; analyzing the voltage curves of the battery during the depolarization plateau process after charging to different SOCs; plotting the voltage, current and temperature during the charging process of normal batteries and faulty batteries; and evaluating the charging performance of faulty batteries.

[0015] Furthermore, the in-situ analysis method specifically includes: analyzing the kinetic decay process of the leaking battery based on the in-situ kinetic analysis methods EIS and DRT; analyzing the EIS curves of normal and faulty batteries at different performance stages, and transforming the EIS curves to obtain DRT curves to separate the kinetic processes; determining the electrochemical processes corresponding to each peak of the DRT curve, and determining the degree of influence of the fault on each kinetic process of the battery based on the changes in the peak values ​​of the DRT curve.

[0016] Furthermore, S4 specifically includes: when the battery life ends, disassembling the faulty battery, obtaining the battery electrodes, characterizing different positions of the electrodes using electrochemical characterization methods, and evaluating the material loss of the fresh and faulty batteries; fabricating button cells from the faulty and fresh battery electrodes, replenishing the electrolyte during the process to regenerate the battery electrodes; simultaneously, fabricating button half cells using the same method, performing reference performance tests and cycle tests on the button cells, performing reference performance tests on the half cells, evaluating battery performance, and revealing the main mechanism of battery failure due to leakage.

[0017] Furthermore, S5 specifically includes: analyzing the external characteristic parameters of the regenerated button cell based on performance testing, determining the difference between the faulty cell and the normal cell after adding electrolyte; identifying the DC internal resistance of the cell based on a second-order equivalent circuit model, measuring the EIS curve of the cell using an electrochemical workstation, and obtaining the AC impedance of the cell; comparing the differences in DC impedance and AC impedance between the faulty cell and the normal cell, and assessing the irreversible impact of the fault on the cell.

[0018] The beneficial effects of this invention are: This invention obtains the evolution patterns of external characteristics of normal and leaking batteries under different aging conditions, and determines the changes in external characteristic parameters of the leaking batteries. Furthermore, based on battery regeneration technology and electrochemical characterization methods, it reveals the main failure pathways of leaking batteries and the irreversible effects of leakage. Revealing the main failure paths of leaking batteries is of great significance for accurate fault mode diagnosis. Attached Figure Description

[0019] The present invention includes the following figures: Figure 1 is a flowchart of the analysis method for the main failure mechanism of the electrolyte leakage fault battery of the present invention; Figure 2 shows the evolution curve of the external comprehensive performance of the faulty battery; Figure 3 shows the battery regeneration process; Figure 4 shows the analysis curves of the dominant failure mechanism of the faulty battery; Figure 5 shows the analysis curve of the irreversible damage mechanism of the faulty battery; Figure 6 shows the irreversible kinetic degradation of the faulty battery. Detailed Implementation

[0020] To make the objectives, advantages and features of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 As shown, this invention analyzes leaking batteries, determines the main impact paths of leakage faults on batteries, and reveals the main failure mechanisms of leaking batteries.

[0022] This invention utilizes a small electric drill to drill a hole in the battery top cover to simulate electrolyte leakage. Subsequently, the battery undergoes various aging tests and reference performance tests to analyze the evolution of its external characteristics. Aging tests include cycle aging and calendar aging experiments. The cycle aging experiment uses CCCV charging. The calendar aging test involves prolonged static placement of the battery at low, medium, and high SOC points during the early and late stages of leakage, respectively. Reference performance tests include capacity testing, equilibrium potential testing, HPPC pulse testing, and EIS testing.

[0023] This invention includes the evolution of external characteristics of leaking batteries and normal batteries. Since calendar aging and cycle aging conditions exhibit similar evolution patterns of external characteristics, a faulty battery under cycle aging is used as an example for illustration. The capacity retention rate of the battery during cycling is shown in the curve below. Figure 2 As shown in (a), normal batteries exhibit linear degradation, while faulty batteries fall into two stages. The first stage is essentially linear degradation, but the degradation rate is much higher than that of normal batteries. The second stage exhibits non-linear degradation, with the degradation rate accelerating. Additionally, some faulty batteries show abnormal charging capacity. Based on a second-order equivalent circuit model, the battery's DC internal resistance is identified, and the variation of internal resistance with SOC is plotted, as shown below. Figure 2 As shown in (b), (c), and (d), the internal resistance of the faulty battery is significantly greater than that of the normal battery, and the polarization internal resistance of the faulty battery increases exponentially with the decrease in capacity retention. Voltage differential curves during battery depolarization after charging to different SOCs are plotted, as shown below. Figure 2 As shown in (e) and (f), the faulty battery exhibits a voltage peak during depolarization, while the normal battery does not. To determine the cause of the abnormal charging in the faulty battery, charging curves for the normal and faulty batteries were plotted, as follows. Figure 2 As shown in (g) and (h), all faulty batteries exhibited a prolonged voltage plateau during the constant current charging phase, while batteries with abnormal charging capacity showed an abnormal increase in current accompanied by an abnormal increase in temperature during the constant voltage phase. Furthermore, under the same conditions, the impact of the fault varied among different individual cells.

[0024] This invention includes analyzing the impact of faults on the impedance of various parts of the battery based on in-situ dynamic analysis methods. Figure 3 (a) The EIS curves of a faulty battery and a normal battery under calendar aging conditions are described using 30% as an example. Intuitively, in the late stage of leakage, the total impedance of the faulty battery increases, while the impedance of the normal battery decreases slightly. The DRT curves of the battery at different SOCs are shown below. Figure 3 As shown in (b), the three peaks are named P1, P2, and P3 sequentially from high to low frequency. Based on the time constant and the relationship between the peaks and SOC, it can be determined that P1 is the electrochemical process dominated by SEI film impedance. P3 is the diffusion process. Peak P2 represents the charge transfer process. The DRT curves of the faulty battery and the normal battery are shown in Figure [image missing]. Figure 3 As shown in (c), all peak values ​​of the faulty battery increased, while P1 and P3 of the normal battery decreased slightly, and P2 remained essentially unchanged. To determine the increase in internal resistance of each component, their average changes were further calculated, as shown in... Figure 3 As shown in (d), the R of the faulty battery... SEI The increase is greatest at all SOC points. Batteries under cycle aging conditions show similar results, such as...Figure 3 As shown in (e) and (f), the increase in impedance of each part of the faulty battery under cyclic conditions is greater than that under calendar conditions. The time experienced by the faulty battery under calendar aging conditions is greater than that under cyclic conditions. Therefore, it can be concluded that the severity of the kinetic degradation of the leaking battery is closely related to the leakage time, but not so much to the operating conditions.

[0025] This invention includes using electrochemical characterization techniques to perform microscopic characterization of disassembled electrode sheets, and refilling the battery electrode sheets with electrolyte to achieve battery regeneration. After the battery reaches the end of its lifespan, the battery is disassembled... Figure 4 The battery regeneration process was demonstrated. Based on the delamination of the negative electrode after disassembly, the electrode sheets were divided into two regions. Electrode sheets from different regions were extracted to fabricate coin cells, thus achieving battery regeneration. After fabrication, the coin cells underwent cycle testing and reference performance testing, including equilibrium potential testing, HPPC pulse testing, and EIS testing. After activation, the coin half-cells underwent equilibrium potential testing to assess the damage to the battery materials.

[0026] This invention includes analyzing the performance of regenerated batteries to reveal the main failure paths of leaking batteries. After refilling, multiple coin cells from different regions did not exhibit the charging anomalies found in commercial batteries, including voltage plateaus during constant current charging and current rises during constant voltage charging. Figure 5 As shown in (a-1) and (a-2), further analysis of the impact of leakage on battery materials is presented in Figure 5(b-1). The capacity decay rate of batteries in different regions is basically the same as that of fresh batteries. Furthermore, the average maximum usable capacity of different types of negative and positive electrode half-cells is basically the same as that of fresh batteries, such as... Figure 5 As shown in (b-2) and (b-3), based on the electrochemical characterization results, the electron microscopy images of the fresh battery and the faulty battery are as follows. Figure 5 As shown in (c-1)-(c-4), the morphology of the faulty battery is not significantly different from that of the fresh battery. Meanwhile, Figure 5The EDS results in (d) also show that the elemental content of the faulty battery did not change significantly compared to the fresh battery. Therefore, combining the evolution of the external characteristics of commercial batteries, the disappearance of the phenomenon after electrolyte injection in regenerated batteries, and the test results of electrochemical characterization methods, it can be confirmed that the impact of electrolyte leakage on battery materials is relatively small. The main reason for battery failure is the severe degradation of battery kinetics caused by electrolyte loss, which in turn leads to battery failure. Specifically, the evaporation of electrolyte solvent leads to a reduction in electrolyte volume, resulting in a local increase in lithium-ion concentration, exacerbating concentration polarization, and thus significantly increasing diffusion resistance. At the same time, the reduction in electrolyte volume directly reduces ionic conductivity, causing a significant increase in ohmic resistance. In addition, oxygen and moisture in the air react with components in the electrolyte to generate acidic corrosive substances, which on the one hand damage the integrity of the SEI film, and on the other hand promote the deposition of by-reaction products on the electrode surface to form a passivation layer. The passivation layer causes a sharp increase in various battery impedances. Among them, the SEI film impedance increases the most. Ultimately, when the electrolyte is depleted to the point where it can no longer adequately wet the electrodes, the reduction in active surface area leads to an increase in the current density of the side reaction, which accelerates the rate of the side reaction, forming a self-reinforcing cycle of "electrolyte consumption - intensified side reaction" until the battery fails.

[0027] Furthermore, after battery regeneration, no voltage plateau appeared in the relaxation process of batteries in different regions at all SOC levels, such as Figure 5 As shown in (e). Furthermore, XRD analysis revealed no lithium plating inside the faulty battery, as indicated. Figure 5 As shown in (f), the changes in battery phenomena before and after electrolyte injection indicate that the abnormal voltage plateau is due to the extremely uneven distribution of electrolyte after an electrolyte leak. During relaxation, the electrolyte undergoes significant redistribution, and a voltage plateau appears when the battery reaches local equilibrium. In contrast, although a battery with sufficient electrolyte also experiences electrolyte redistribution during relaxation, this process is not reflected in the external characteristics of the battery due to its smaller concentration gradient. Therefore, the voltage plateau disappears after electrolyte refilling.

[0028] This invention includes quantifying the irreversible effects of electrolyte leakage on batteries. The recovery of battery performance after electrolyte refilling indicates that some of the effects of electrolyte failure on the battery are reversible. However, to further confirm whether electrolyte failure causes irreversible damage to the battery, a detailed analysis of the performance test data of button batteries was conducted. For example... Figure 6 As shown in (a), there are significant differences in the initial charge / discharge efficiency, constant capacity, and maximum usable capacity of different types of coin cells, with the parameter relationship being: Region I < Region II < Fresh Cell. This indicates that electrolyte failure may lead to irreversible kinetic degradation of the battery, and the degree of degradation is related to the battery's location relative to the leakage hole. To further verify this conclusion, the DC internal resistance variation of the coin cell was identified based on a second-order equivalent circuit model. Figure 6(b) shows the changes in the average values ​​of Ro, Rp1, and Rp2 of the coin cells in Regions I and II relative to fresh cells. The relative DC impedance is: Region I > Region II > Fresh Cell. Similarly, as Figure 6 As shown in (c), the AC impedance test results also exhibit a similar trend, indicating that electrolyte failure does indeed lead to irreversible kinetic degradation of the battery. Furthermore, the impact of leakage faults on battery performance varies, and the degree of impact is closely related to the distance from the leak hole. The closer to the hole, the more severe the impact. This is because after electrolyte leakage, air enters the battery interior, reacts with the battery components to generate byproducts, and covers the battery surface, forming a passivation layer. Although refilling the electrolyte can restore some battery performance, the deposits cannot be completely removed. Therefore, the kinetic performance of the faulty battery cannot be restored to the level of a normal battery. Moreover, the closer to the leak hole, the more intense the reaction may be, leading to a more severe degree of kinetic degradation.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing the main failure mechanisms of batteries with electrolyte leakage, characterized in that, include: S1: Perform calendar aging tests, cycle aging tests, and reference performance tests on normal and leaking batteries; S2: Compare the external characteristics of normal batteries and leaking batteries to obtain the differences in external performance between leaking batteries and normal batteries; S3: Using in-situ analysis, we can conduct an in-depth analysis of the dynamic degradation mechanism of leaking batteries and clarify the impact of faults on the impedance of various parts of the battery. S4: Obtain normal and faulty battery electrodes, characterize the battery electrodes using electrochemical characterization methods; use the battery electrodes to replenish the electrolyte, fabricate button batteries to achieve battery regeneration, conduct performance and aging tests on the regenerated batteries, evaluate the performance of the regenerated batteries, and reveal the mechanism of leakage battery failure. S5: Compare the performance differences between regenerated batteries and normal batteries to determine the irreversible impact of the fault on the battery.

2. The method as described in claim 1, characterized in that, The calendar aging test involves placing the battery at different SOC levels during the early and late stages of leakage.

3. The method as described in claim 2, characterized in that, The cyclic aging test uses a CCCV constant current and constant voltage charging method.

4. The method as described in claim 3, characterized in that, The reference performance tests include capacity testing, equilibrium potential testing, HPPC pulse testing, and EIS testing; reference performance tests are performed on normal batteries and leaking batteries after early and late calendar aging tests; and reference performance tests are performed at specific capacity retention intervals during cycle aging tests.

5. The method as described in claim 3, characterized in that, The cycle aging test adopts the CCCV constant current and constant voltage charging method, which specifically includes switching to constant voltage charging when the charging voltage reaches the cutoff voltage, until the current drops to a small value, and then discharging the battery with a constant current after resting.

6. The method as described in claim 1, characterized in that, The external characteristics include capacity, internal resistance, resting curve, and charging curve.

7. The method as described in claim 1, characterized in that, The comparison of the external characteristics of normal and leaking batteries specifically includes: obtaining the capacity decay of normal and leaking batteries based on capacity testing and cycle testing in the calendar aging test; identifying the ohmic internal resistance and polarization internal resistance of normal and leaking batteries based on a second-order equivalent circuit model; analyzing the change of internal resistance with SOC; analyzing the voltage curves of the battery during the depolarization plateau process after charging to different SOCs; plotting the voltage, current, and temperature during the charging process of normal and faulty batteries; and evaluating the charging performance of faulty batteries.

8. The method as described in claim 1, characterized in that, The in-situ analysis method specifically includes: analyzing the kinetic decay process of the leaking battery based on the in-situ kinetic analysis methods EIS and DRT; analyzing the EIS curves of normal and faulty batteries at different performance stages, and transforming the EIS curves to obtain DRT curves to separate the kinetic processes; determining the electrochemical processes corresponding to each peak of the DRT curve, and determining the degree of influence of the fault on each kinetic process of the battery based on the changes in the peak values ​​of the DRT curve.

9. The method as described in claim 1, characterized in that, S4 specifically includes: when the battery life ends, disassembling the faulty battery, obtaining the battery electrodes, characterizing different positions of the electrodes using electrochemical characterization methods, and evaluating the material loss of the fresh and faulty batteries; fabricating button full cells from the faulty and fresh battery electrodes, replenishing the electrolyte during the process to regenerate the battery electrodes; simultaneously, fabricating button half cells using the same method, performing reference performance tests and cycle tests on the button full cells, and performing reference performance tests on the half cells to evaluate battery performance and reveal the main mechanism of battery failure due to leakage.

10. The method as described in claim 9, characterized in that, S5 specifically includes: analyzing the external characteristic parameters of the regenerated button cell based on performance testing, determining the difference between the faulty cell and the normal cell after adding electrolyte; identifying the DC internal resistance of the cell based on a second-order equivalent circuit model, measuring the EIS curve of the cell using an electrochemical workstation, and obtaining the AC impedance of the cell; comparing the differences in DC impedance and AC impedance between the faulty cell and the normal cell to assess the irreversible impact of the fault on the cell.

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