Overcharge Conditions Research Articles

Explosion dynamics for thermal runaway gases of 314 Ah LiFePO4 lithium-ion batteries triggered by overheating and overcharging

Thermal runaway (TR) of LiFePO4 lithium-ion batteries (LFPs) can produce significant amounts of smoke, posing serious explosion hazards. This paper systematically investigated TR gas generation, explosion limits, explosion overpressure, and post-explosion gas compositions of 314 Ah LFPs under overcharging and overheating. Quantum chemical and explosion reaction kinetics calculations clarified the elementary reactions and compositional alterations occurring in gases and free radicals during the explosion process. The findings revealed that H2 constituted the primary component of TR gases, comprising 47.64 % and 53.12 % of the overcharging and overheating, respectively, followed by CO2 and CO. The ranges of explosion concentration for TR gases, when subjected to overheating and overcharging conditions, were 6.32–29.3 % and 6.83–26.91 %, respectively. At the point of maximum explosion overpressure (Pmax), the gas concentrations peaked at 15.86 % and 16.25 %. The elementary reaction R1 held a pivotal position in enhancing the explosion overpressure. As the TR gas concentration escalated, the Rate of Production (ROP) of R31 and R35 also surged, ultimately resulting in elevated concentrations of CO. The reactions R123, R250, and R279 facilitated the generation of H2 while simultaneously consuming hydrocarbon gases. This resulted in a risk of secondary explosion of the TR gas after the explosion. Post-explosion gas residual quantities followed the order: C2H6 < C2H4 < CH4 < H2 < CO. The results revealed crucial insights for developing explosion prevention and suppression in the process safety industry and Energy Storage Systems.

Comparison of NaNi1/3Fe1/3Mn1/3O2 and Na4Fe3(PO4)2(P2O7) cathode sodium-ion battery behavior under overcharging induced thermal runaway

It is expected that the safety characteristics of sodium-ion batteries are higher than that of lithium-ion batteries, but the response of sodium-ion batteries with different material systems under thermal runaway is still lacking in-depth analysis. In this study, the thermal runaway characteristics of NaNi1/3Fe1/3Mn1/3O2 and Na4Fe3(PO4)2(P2O7) cathode pouch sodium-ion batteries are compared. First, thermal runaway experiments analyze the electro-thermal–mechanical-gas response of the two kinds of sodium-ion batteries. Based on this, the sodium plating and gas generation process under overcharge conditions are analyzed using coin batteries and in-situ cells coupled with optical microscopy. By combining the macro and micro characteristics at different stages of thermal runaway, this study elucidates the thermal runaway characteristics and corresponding causes of the two kinds of cathode material sodium-ion batteries. The results provide a foundation for subsequent research on the materials of sodium-ion batteries and methods for monitoring thermal runaway.

Difluoroester solvent toward fast-rate anion-intercalation lithium metal batteries under extreme conditions

Anion-intercalation lithium metal batteries (AILMBs) are appealing due to their low cost and fast intercalation/de-intercalation kinetics of graphite cathodes. However, the safety and cycliability of existing AILMBs are constrained by the scarcity of compatible electrolytes. Herein, we showcase that a difluoroester can be applied as electrolyte solvent to realize high-performance AILMBs, which not only endows high oxidation resistance, but also efficiently tunes the solvation shell to enable highly reversible and kinetically fast cathode reaction beyond the trifluoro counterpart. The difluoroester-based electrolyte demonstrates nonflammability, high ionic conductivity, and electrochemical stability, along with excellent electrode compatibility. The Li| |graphite AILMBs reach a high durability of 10000 cycles with only a 0.00128% capacity loss per cycle under fast-cycling of 1 A g−1, and retain ~63% of room-temperature capacity when discharging at −65 °C, meanwhile supply stable power output under deformation and overcharge conditions. The electrolyte design paves a promising path toward fast-rate, low-temperature, durable, and safe AILMBs.

Effects of capacity on the thermal runaway and gas venting behaviors of large-format lithium iron phosphate batteries induced by overcharge

Large-capacity lithium iron phosphate (LFP) batteries are widely used in electric bicycles. However, while crucial, thermal runaway (TR) behaviors under overcharge conditions have rarely been studied, leading to frequent fire accidents. This paper investigates the overcharge behavior and TR characteristics of four LFP batteries with the same components and materials but varying capacities (86, 100, 120, and 140 Ah). Overcharge tests were conducted in a customized apparatus, and the surface temperature, mass loss, and gas venting phenomenon were recorded. The results revealed that under the same overcharge conditions, the TR early warning temperature can differ considerably with respect to battery capacity, highlighting the importance of selecting the appropriate early warning temperature in real-time temperature monitoring based on the capacity of the LFP battery. Three characteristic times were used to describe the thermal behavior of the batteries, namely, the time to reach the voltage plateau (tPV), the time when the safety valve opens (tSV), and the start time of TR (tTR). Analysis of critical heat accumulation indicated that the 86 Ah LFP battery has the lowest tolerance to overcharge and, thus, the highest TR risk. However, after TR, the 86 Ah LFP battery exhibited the smallest maximum temperature (Tmax), maximum temperature increase rate (Rmax), maximum total mass loss, and maximum mass loss rate (Mmax) among all the batteries, suggesting the least TR hazard. Consequently, a safety evaluation and scoring system using these six parameters was established considering the overcharge behavior and TR characteristics of LFP batteries. The results indicated that the TR risk ranking of LFP batteries with different capacities was 86 Ah LFP > 100 Ah LFP > 140 Ah LFP > 120 Ah LFP, while the TR hazard ranking was 140 Ah LFP > 120 Ah LFP > 100 Ah LFP > 86 Ah LFP. This comparative study of LFP batteries with varying capacities enhances our understanding of their overcharge behavior and TR characteristics, and a safety evaluation and scoring system can also be used for risk and hazard assessments of other types of batteries.

Influence Mechanism of Interfacial Oxidation of Li3YCl6 Solid Electrolyte on Reduction Potential.

Halide-based solid electrolytes are promising candidates for all solid-state lithium-ion batteries (ASSLBs) due to their high ionic conductivity, wide electrochemical window, and excellent chemical stability with cathode materials. However, when tested in practice, their intrinsic electrochemical stability windows do not well match the conditions for stable operation of ASSBs. Existing literature reports halide-based ASSBs that still operate well outside the electrochemical stability window, while ASSBs that do not operate within the window are not well studied or the studies are based on the cathode material interface. In this study, we aim to elucidate the mechanism behind all-solid-state battery failure by investigating how the reduction potential of Li3YCl6 solid-state electrolyte itself changes under overcharging conditions. Our findings demonstrate that in Li-In|Li3YCl6|Li3YCl6-C half-cells during the first state of charge, Cl ions participate in charge compensation, resulting in a depletion of ligands. This phenomenon significantly affects the reduction potential of Y3+, causing it to be reduced to Y2Cl3 and ultimately to Y0 at conditions far exceeding its actual reduction potential. Furthermore, we analyze the interfacial impedance induced by this process and propose a novel perspective on battery failure.

On the characterization of lithium-ion batteries under overtemperature and overcharge conditions: Identification of abuse areas and experimental validation

Although lithium-ion batteries have gained considerable popularity in renewable energy and electric vehicle applications, their safety still remains a concern under certain voltage, temperature, or state of charge conditions. This can lead to degradation and potential thermal runaway. In order to improve the safety assessment of LIBs based on their operating conditions, it is therefore essential to analyze not only their safe operating area but also their abuse region. This study focuses on the characterization of the abuse region of lithium-ion batteries by proposing a new methodology in which four areas of abuse are identified and experimentally validated using a commercial 3.6 Ah pouch cell. The cell is subjected to overtemperature and overcharge conditions, exploring various states of charge (0 to 200%) and ambient temperatures (25 to 100 °C). The influence of temperature and state of charge on the battery’s behavior is thoroughly analyzed to fully characterize the abuse region. Results reveal the limiting temperatures and states of charge that define the boundaries of the abuse areas. By extending the characterization of LIBs behavior beyond the safe operation area with the determination of four areas of abuse, this article contributes to a better understanding of the phenomena and abuse mechanisms produced by overtemperature and overcharge events with an eye to improving battery safety.

A systematic investigation of thermal runaway characteristics, inflame evolution and post-mortem analysis caused by overcharging for lithium-ion batteries with different cathode materials

In this work, three pouch batteries based on different cathode materials including LiCoO2 (LCO), Li(Ni0.6Mn0.2Co0.2)O2 (NMC622), and LiFePO4 (LFP) are studied. The thermal runaway (TR) characteristics, flame evolution, internal morphology and functional group changes during the TR process caused by overcharge are comprehensively compared for the first time. The LFP battery takes the shortest time to reach TR under overcharging conditions, followed by the LCO battery, and the NMC622 battery. However, the TR behaviour of LiFePO4 batteries is the safest, as they do not ignite but instead generate a large amount of smoke. The highest temperature reached is only about 310 °C. In contrast, LCO and NMC622 batteries undergo severe combustion processes with peak temperatures exceeding 1000 °C. Sparks and jet fires are the predominant flame forms, with jet fire in particular being a major factor in the propagation of TR. The dynamic changes of flame characteristic parameters are also quantitatively analysed, including maximum temperature, inflame height, inflame area and inflame probability map. With the increase of charging rate, the flame spread for the LCO and NMC622 batteries is bigger. Under the overcharge condition of 2 C, LCO batteries exhibit the highest flame height of 341.7 mm, while NMC622 batteries exhibit the largest flame area of 0.3 m2. After TR, drastic morphological and chemical changes are observed for the LCO and NMC622 cathodes, while the LFP cathode maintained a better dense structure with minor chemical changes.

Study on the thermal runaway characteristics and debris of lithium-ion batteries under overheating, overcharge, and extrusion

As the use of lithium-ion batteries (LIBs) becomes more widespread in various fields, incidents of combustion caused by thermal runaway (TR) of LIBs are increasing. However, identifying the causes of TR is challenging. To address this, we employ a method that combines TR characteristics and debris analysis to identify the causes of TR in this study. We investigate a commercial LiFePO4 (LFP) battery and trigger TR under overheating, overcharge, and extrusion conditions. Following TR, we observe that under the overheating and overcharge condition, numerous floccule attach to the anode debris; under the extrusion condition, the anode debris is covered by numerous small particles; and under the overcharge condition, a large number of flocculant and smooth balls attach to the anode debris, and the composition of these substances contains numerous metal oxides. Moreover, under the overheating condition, the heat release, and gas release rate of the debris are the minimum, while they are the maximum under the extrusion condition. Due to the different reaction processes and degrees of TR under different conditions, the properties of the LIB debris also differ. By analyzing the debris and data, we can distinguish the debris under different conditions. This enables us to quickly identify the trigger factors of battery TR after it occurs.

Irreversible Mechanical Deformations Associated with the Formation of Cathode-Electrolyte Interface on Lithium Iron Phosphate Cathodes

The demand for rechargeable batteries for energy storage in electrical automobiles is rising presently due to their key role in reducing carbon emissions. However, the increasing demands require improvement in batteries lifetime. interfacial instabilities associated with the formation of cathode-electrolyte interface and intercalation-induced volumetric expansions are the primary reasons behind the capacity fade. Although there have been great efforts to understand structural stress/strains in cathodes, there is a lack of knowledge about the formation mechanism of cathode-electrolyte interface (CEI) layers. To fill the gap, we investigate the role of electrolyte chemistry on the interfacial deformation of lithium iron phosphate (LFP) cathodes by employing digital image correlation (DIC), spectroscopy, and electrochemical techniques. DIC was utilized to study the dynamic physical behavior of the electrode materials and irreversible strains associated with the electrolyte decomposition on the electrode surface [1]. Therefore, the overall objective of this study is to elucidate the mechanical deformations in the LFP cathodes of battery electrodes by investigating the physical response of the electrode and dynamic changes on the electrode – electrolyte interface.To be able to understand the different effects of the electrolyte solution, electrolytes were made of either LiPF6, LiClO4, or LiTFSI salts dissolved in 1 M EC:DMC. When cycled in the LiClO4 and LiTFSI salts containing electrolytes, the volumetric contraction is observed in the electrode because of the extraction of lithium and associated phase transformations during the first delithiation. However, positive strain generation was observed only during the first cycle in LiPF6 containing electrolyte, although delithiation results in reducing the lattice parameters. Control experiments were conducted where the electrode was cycled in LiClO4-containing electrolyte for one cycle and electrolyte was changed to the LiPF6-containing electrolyte for the subsequent cycles. A similar irreversible mechanical behavior was also observed in the control experiments where positive strain generation is recorded during the subsequent first delithiation cycle in LiPF6-containing electrolyte. To further analysis, electrochemical impedance spectroscopy measurements were performed on each system to identify surface resistance of the electrodes in a voltage range between 3 - 4.4 V. Increasing in the surface resistance of the electrodes were associated with CEI layer formations [2, 3]. Chemical composition of the CEI layers were characterized by using x-ray photoelectron spectroscopy. Our study provides a pathway to investigate the formation of the cathode-electrolyte interface on the cathode electrodes by monitoring irreversible physical behavior of the electrode – electrolyte interface during cycling.This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (Award numberDE-SC0021251). References Çapraz, Ö. Ö., Rajput, S., Bassett, K. L., Gewirth, A. A., White, S. R., & Sottos, N. R. (2019). Controlling expansion in lithium manganese oxide composite electrodes via surface modification. Journal of The Electrochemical Society, 166(12), A2357.Liu, Y., & Xie, J. (2015). Failure study of commercial LiFePO4 cells in overcharge conditions using electrochemical impedance spectroscopy. Journal of The Electrochemical Society, 162(10), A2208.Bassett, K. L., Çapraz, Ö. Ö., Özdogru, B., Gewirth, A. A., & Sottos, N. R. (2019). Cathode/electrolyte interface-dependent changes in stress and strain in lithium iron phosphate composite cathodes. Journal of the Electrochemical Society, 166(12), A2707.

Safety and Quality Issues of Counterfeit Lithium-Ion Cells.

Lithium-ion batteries continue to transform consumer electronics, mobility, and energy storage sectors, and the applications and demands for batteries keep growing. Supply limitations and costs may lead to counterfeit cells in the supply chain that could affect quality, safety, and reliability of batteries. Our research included studies of counterfeit and low-quality lithium-ion cells, and our observations on the differences between these and original ones, as well as the significant safety implications, are discussed. The counterfeit cells did not include internal protective devices such as the positive temperature coefficient or current interrupt devices that typically offer protection against external short circuits and overcharge conditions, respectively, in cells from original manufacturers. Poor-quality materials and lack of engineering knowledge were also evident on analyses of the electrodes and separators from low-quality manufacturers. When the low-quality cells were subjected to off-nominal conditions, they experienced high temperature, electrolyte leakage, thermal runaway, and fire. In contrast, the authentic lithium-ion cells performed as expected. Recommendations are provided to identify and avoid counterfeit and low-quality lithium-ion cells and batteries.

Enhanced hazard characterization of lithium-ion batteries subject to destructive overcharge conditions

Enhanced hazard characterization of lithium-ion batteries subject to destructive overcharge conditions

Analysis of solid combustion products to establish a theoretical model of the causes of thermal runaway of ternary lithium-ion battery overcharge and heating

It is difficult to determine whether ternary lithium-ion batteries (t-LIBs) were the “source” of the actual fire scene because of the little available direct evidence left after thermal runaway combustion of lithium-ion batteries (LIBs) and the lack of relevant analytical methods for t-LIBs after complete combustion. As a result, a large number of fires involving t-LIBs are controversially identified as the cause every year. In this paper, we conducted experiments on the two most common thermal runaway types of t-LIBs to investigate the correlation model between their combustion products and thermal runaway types. In the case of overcharge, the combustion products (black powder) of t-LIBs contain aluminum elements, which may be due to the thermal reaction of aluminum. In contrast, in the case of heating, the combustion products of t-LIBs have almost no detectable elemental aluminum. The reason may be due to the ability of the electrode material to continuously decompose and precipitate a large amount of metal oxides under the overcharge condition, which constitutes the condition for the occurrence of the aluminum thermal reaction, making the presence of Al2O3 in the combustion products. However, the lack of continuous current action under the heating condition prevents the generation of the aluminum thermal reaction.

Unveil Overcharge Performances of Activated Carbon Cathode in Various Li-Ion Electrolytes

Typically, the practical lithium-ion capacitor (LIC) is composed of a capacitive cathode (activated carbon, AC) and a battery-type anode (graphite, soft carbon, hard carbon). There is a risk of the LIC cell overcharging to an unsafe voltage under electrical abuse conditions. Since the anode potential is usually quite low during the charging process and can be controlled by adjusting the amount of anode materials, the overcharge performances of LIC full-cell mainly depend on the AC cathode. Thus, it is necessary to independently investigate the overcharge behaviors of the AC cathode in nonaqueous Li-ion electrolytes without the interference of the anode electrode. In this work, the stable upper potential limits of the AC electrode in three types of lithium-ion electrolytes were determined to be 4.0−4.1 V via the energy efficiency method. Then, the AC//Li half-cells were charged to 5.0 V and 10.0 V, respectively, to investigate the overcharge behaviors. For the half-cells with propylene carbonate (PC)-based electrolytes, the voltage increased sharply to 10.0 V with a vertical straight line at the end of the overcharging process, indicating that the deposits of electrolyte decomposition had separated the AC electrode surface from the electrolytes, forming a self-protective passivation film with a dielectric capacitor behavior. The dense and compact passivation film is significant in separating the AC electrode surface from the electrolytes and preventing LIC cells from volume expansion and explosion risks under electrical abuse and overcharging conditions.

Self-shutdown function based on overcharge-triggered electrochemical nano-switch for safer Li-ion batteries

Overcharge abuse is one of the most common initiators of thermal runaway in lithium ion batteries (LIBs). Much efforts have been devoted to the developments of advanced Battery Management System (BMS) and redox shuttles to provide overcharge protection for LIBs. However, the current overcharge protection strategies are not able to permanently eliminate the safety hazards caused by overcharge abuse. Herein, we propose a new overcharge protection mechanism based on the overcharge-triggered electrochemical nano-switch (denoted as OTENS). The results demonstrate that the insertion of OTENS into between the current collector and the active mass has a little negative effect on the electrochemical performances of battery under normal and slight overcharge conditions. More importantly,the OTENS will be activated under deep overcharge condition, permanently shutting down the overcharged cell and consequently avoiding the continuous cell damage. Such a overcharge-triggered shutdown mechanism originates from the overoxidation of electrically conductive polymer that causes the loss of its electrochemical activity and electric conduction. This electrode design for constructing safer LIBs is simple and also fully compatible with the present industrial manufacture process.

Aging effect delays overcharge-induced thermal runaway of lithium-ion batteries

This research focuses on the effect of overcharging on aged batteries, and the experiments aim to show the thermal runaway (TR) behavior of batteries with different degrees of aging. In order to clarify the typical behavioral characteristics of overcharge-induced battery thermal runaway, commercial 18,650 type LiMn2O4 (LMO)/graphite batteries with different capacity retention rates (CRRs) were applied for overcharge testing operation. The changes of external characteristics, such as surface temperature, voltage and fire explosion phenomena of aged batteries during the whole process of thermal runaway under overcharge conditions were investigated. The results showed that the battery TR trigger time was negatively correlated with the CRR. The batteries having CRR of 86.7%, 80.8%, and 75.2% took 28.2%, 32.5%, and 52.0% longer than fresh battery to reach the TR triggering temperature. Besides, they took 54.1%, 91.8% and 115.1% longer than fresh battery to reach the lithium plating time point. The deposition of manganese oxide on the cathode surface and the phenomenon of lithium plating on the anode surface together lead to the reduction of reversible lithium. With the deepening of aging, the amount of reversible lithium inside the battery decreases, which is the main reason why the TR trigger time is delayed.

Sensitivities of lithium-ion batteries with different capacities to overcharge/over-discharge

A series of experiments were carried out in this study to investigate the sensitivity of lithium-ion batteries with different capacities to overcharge and over-discharge conditions; whereby, two nominal capacities (2100 and 3000 mAh) were included. It is observed that batteries experience a serious degradation in the process of overcharge cycling; moreover, the degradation behavior exacerbates with the increase of battery nominal capacity. That is, the battery with a higher nominal capacity is more sensitive to overcharge conditions, which may be ascribed to the more severe lithium inventory loss, electrolytes loss and anode materials loss along cycling. The worse polarization and heat generation for the higher capacity battery cause inhomogeneous lithium distribution and heat distribution, therefore battery aging is aggravated. The degradation behavior is further demonstrated through the evolution of battery charge/discharge voltage, battery surface temperature, battery resistance and battery internal morphology. Similar phenomenon is also illustrated under the over-discharge condition. Considering the serious damage of overcharge and over-discharge on batteries, it is critical to avoid overcharge and over-discharge especially for the high-capacity battery.

Investigation and Suppression of Oxygen Release by LiNi0.8Co0.1Mn0.1O2 Cathode under Overcharge Conditions

AbstractThe safety issue of lithium‐ion batteries is a crucial factor limiting their large‐scale application. Therefore, it is of practical significance to evaluate the impact of their overcharge behavior because of the severe levels of oxygen release of cathode materials during this process. Herein, by combining a variety of in situ techniques of spectroscopy and electron microscopy, this work studies the structural degradation of LiNi0.8Co0.1Mn0.1O2 (NCM811) accompanying the oxygen release in the overcharge process. It is observed that a small amount of O2 evolves from the initial surface at ≈4.7 V. When charging to a higher voltage (≈5.5 V), a large amount of O2 evolves on the newly formed surface due to the occurrence of microcracks. Based on experimental results and theoretical calculations, it is determined that the oxygen release mainly occurs in the near‐surface regions, where the remaining oxygen vacancies accumulate to create voids. To suppress the oxygen release, single‐crystalline NCM811 with integrated structure is introduced and serves as a cathode, which can effectively inhibit morphology destruction and reduce the activation of lattice oxygen in the surface region. These findings provide a theoretical basis and effective strategy for improving the safety performance of Ni‐rich cathode materials in practical applications.

An Electrothermal Model to Predict Thermal Characteristics of Lithium-Ion Battery under Overcharge Condition

Understanding the thermal characteristics of lithium-ion batteries (LIBs) under various operating situations is critical for improving battery safety. Although the application of LIBs in the real world is mostly transient, many previous models consider the phenomenon of the constant state. This study examines thermal behavior by developing a 2D electrothermal model to predict the thermal behavior of LIBs with overcharge abuse in high thermal conditions. The 18,650 cylindrical LiCoO2 graphite is investigated in a thermally controlled chamber at 35, 50, and 60 °C with a K-type thermocouple mounted on the LIB surface under charging rates of 1C, 2C, and 3C to acquire quantitative data regarding the thermal response of LIBs. Maximum critical temperatures are found at 62.6 to 78.9 °C, 66.4 to 83.5 °C, and 72.1 to 86.6 °C at 1C, 2C, and 3C, respectively. Comparing simulation analysis and experimental conditions, the highest relative error of 1.71% was obtained. It was found that relative errors increase as the charging rate increases. Moreover, increasing the charging current and surrounding temperature significantly increases the battery’s surface temperature. Furthermore, battery heat distribution appears almost uniform and tends to increase towards the positive terminal because cathode material is highly resistant. In addition, increasing the LIB heat transfer coefficient could positively improve the battery performance by eventually curbing the rise in battery temperature and reducing non-uniformity.

Study on Thermal Runaway Behavior of Lithium Ion Battery under Overcharge Using Numerical Detecting Method

In order to provide support for the early warning model of thermal runaway of lithium-ion battery, the thermal runaway behavior of power lithium battery is studied by analyzing the charging current, voltage and other parameters of lithium-ion power battery under overcharge condition. In addition, the morphological changes of battery before and after thermal runaway are compared. It is found that under the conditions of this study, overcharging for 58 minutes will lead to thermal runaway of full load lithium-ion battery. In the early stage of thermal runaway, the leakage gas in the battery box will continue to increase, which is 1339 ppm in the First Level early warning, 3405 ppm in the Second Level early warning and 8292 ppm in the Third Level early warning.

Structure and morphological changes of multilayer separators for lithium‐ion batteries under abuse/overcharge conditions

AbstractMost separators for lithium‐ion (Li‐ion) batteries are manufactured using polyolefins. However, such thermoplastic materials may undergo structural changes under high voltage or temperature. Thus, this study investigates the structural and morphological changes of separators during overcharge conditions. Unlike a single‐layer polypropylene (PP) separator, a composite separator with an interface, such as a PP/polyethylene (PE)/PP separator, exhibits a characteristic peak in voltage during the overcharging process before the occurrence of the shutdown mechanism by the PE layer. As the temperature rises, parts of the irregular crystalline structure of PE melt because of their lower melting temperature at the PP/PE interface. This results in local shrinkage and interfaces disturbance, and the Li‐ion channel becomes partially blocked. The Li‐ions follow alternative channels, and this causes the voltage to abruptly increase during overcharging. The experimental results clearly indicate that the microstructural changes of the separator are important in the above‐mentioned phenomenon.