Thermal runaway risk assessment of pouch cells with modified current collectors under mechanical abuse

Thermal runaway risk assessment of pouch cells with modified current collectors under mechanical abuse | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermal runaway risk assessment of pouch cells with modified current collectors under mechanical abuse MD ABUL KASHEM, Haodong Chen, Sadia Tasnim Mowri, Mushfiqur Rahman, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8296559/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract This work presents an experimental study to evaluate the thermal runaway (TR) risk of pouch cells with modified current collectors (MCCs), which incorporate polyethylene terephthalate (PET) for mitigating internal short circuits and further preventing TR. Two types of cells, with capacities of 5 Ah and 10 Ah, were adopted and subjected to nail penetration tests. The results showed that the 5 Ah MCC cells exhibited improved safety, with only one out of four undergoing TR, compared to both control cells without MCCs experiencing TR. In contrast, all 10 Ah cells, including those with MCCs, experienced TR, indicating that the MCC's protective benefits may not apply to higher-capacity cells under similar test conditions. Comprehensive post-mortem analyses, including computed tomography (CT) scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), were performed to assess the internal structural and compositional changes. The findings indicate that MCC technology significantly reduces TR risk in lower-capacity cells, while additional safety measures may be requited for the higher-capacity cells . This study highlights the potential of MCC technology to enhance battery safety and underscores the need for further research to address safety challenges in emerging battery technologies. Battery Safety Pouch Cell Modified Current Collector Nail Penetration Test Thermal Runaway Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Highlights Modified current collector lowers Thermal Runaway risk in 5 Ah pouch cells Only 1 of 4 modified 5 Ah cells had Thermal Runaway All 10 Ah cells had Thermal Runaway, showing limits of modified current collector CT and SEM revealed internal changes after nail penetration PET-based current collector helps safety, needs work for larger cells 1. Introduction The widespread adoption of lithium-ion batteries (LIBs) in portable electronic devices and electric vehicles (EVs) highlights their pivotal role in contemporary technology. Noted for their remarkable energy density, extended cycle longevity, and comparatively minimal self-discharge rates, these batteries play a crucial role in powering a diverse range of electronic devices and EVs [1, 2]. Over the past three decades, significant advancements in electrode engineering and ongoing developments in new chemistries have led to remarkable improvements in the energy density of LIBs [3, 4]. However, the increasing energy density of LIBs necessitates innovative designs to ensure safety. Safety concerns, such as thermal runaway (TR), remain a significant challenge. TR, characterized by an uncontrollable increase in temperature and potential cell rupture, poses severe risks, especially under abusive conditions such as mechanical abuse [5, 6]. The safety of LIBs has relied on components such as separators, current interrupt devices (CIDs), positive temperature coefficient (PTC) device, safety vents, and stringent control of operating conditions conventionally [7, 8]. Additionally, robust packaging is essential to protect LIBs from mechanical impacts, which inadvertently adds extra weight and volume, thereby reducing the overall energy density [9, 10]. The current collector (CC) in a battery cell provides an electronic conduction pathway for both the anode electrode and the cathode electrode, typically using aluminum or copper for their electrochemical stability [11, 12]. While these metals efficiently conduct electricity and prevent degradation, conventional CCs can facilitate high current flow, potentially triggering TR. Numerous researchers have investigated the factors leading to TR by examining the characteristics and behavior of battery cells prior to its occurrence [13, 14]. TR has also been extensively studied and reviewed in the existing literature, with many studies focusing on mitigation techniques and risk reduction strategies [15-17]. But research on modifying these CCs to mitigate TR risks is limited. Some efforts to redesign them, along with electrodes, have been pursued [18, 19]. With these modified current collectors (MCCs), battery safety can be enhanced through thermally conductive and flame-retardant coatings [20, 21]. In related studies, metalized polymer films have been used as MCCs to improve thermal stability and reduce internal short circuits [8, 22]. Recent research also suggests that these metal-coated polymer CCs can retract from heat sources during thermal events, potentially preventing TR and significantly enhancing battery safety [23]. A rigorous evaluation of the performance of MCC-equipped cells under mechanical abuse conditions is required to determine their potential to prevent TR and enhance overall battery safety. This investigation is critical in advancing the understanding of the safety mechanisms in high-energy-density batteries and contributing to the development of safer and more reliable energy storage solutions. The findings will offer valuable insights into the effectiveness of the MCC in real-world applications, guiding future innovations in battery design and safety. 2. Experiment Setup Four types of pouch cells were used in this study, two types of control cells and two types of MCC cells where current collectors were coated with polyethylene terephthalate (PET). The cell parameters are listed in Table 1. The cathode and the anode are lithium nickel cobalt manganese oxide (NMC) and graphite, respectively. Nail penetration tests (NPTs) were conducted on a total of twelve pouch cells, which were divided into two groups based on their capacities. Table 1. Pouch cell information. Item Control Cell Modified Cell Control Cell Modified cell Nominal capacity (Ah) 5 5 10 10 Mass (g) 85 83 154 148 Specific energy (Wh/kg) 214.7 219.9 237.0 246.6 Dimension (mm) 100*60*6 100*60*6 100*60*10 100*60*10 Nominal voltage (V) 3.65 Charge cut-off voltage (V) 4.2 Discharge cut-off voltage (V) 2.5 Cathode Lithium Nickel Cobalt Manganese Oxide (LiNi x Co y Mn z O 2 ) Anode Graphite (C) Number 2 4 2 4 The first group consisted of six cells, each with a capacity of 5 Ah, while the second group comprised six cells with a higher capacity of 10 Ah. Within each capacity group, four cells were fabricated using MCC technology, and the remaining two cells served as control samples to facilitate comparative analysis. The 5 Ah and 10 Ah rated capacity cells were identical in dimensions, differing only in thickness. The 10 Ah cell had an increased number of anode and cathode layers compared to the 5 Ah cell. Control cells without the MCCs were adopted to benchmark the improved safety MCC offers. To comprehensively assess the effectiveness of MCC, we conducted a series of NPTs. During tests, thermal behaviour was monitored with thermocouples, voltage sensors, and a high-resolution thermal infrared camera. Furthermore, we employed advanced forensic techniques including computed tomography (CT), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to analyse the post-abuse internal state of the cells. CT scans provide detailed visualizations of the internal structure, allowing us to identify any structural damages and deformations that occurred as a result of the abuse conditions. This 3D imaging helps us to assess whether the MCCs effectively mitigated damage propagation within the cell, thereby contributing to safety. SEM was utilized to reveal microstructural changes. This high-resolution imaging technique enables us to examine the surface morphology and detect any micro-cracks, voids, or phase separations that might compromise the integrity of the cell. By comparing the microstructures of electrodes adjacent to the nail-penetrated area with those located slightly further away, we aim to highlight how MCC cells prevent short circuits between the electrodes. EDS was used to identify elemental composition changes within the cells. This technique allows us to detect any migration or segregation of elements that could indicate thermal degradation or chemical reactions due to the CC’s properties. By analyzing these changes, we could determine whether the MCCs contributed to maintaining the chemical stability of the cells under abusive conditions. These multidimensional analyses offer a robust understanding of the safety enhancements provided by the MCC because they collectively provide a comprehensive assessment of the cell's structural integrity, microstructural stability, and chemical consistency. This holistic approach not only highlights the advantages of MCCs in mitigating various failure modes but also guides the development of safer energy storage solutions by identifying key areas for further improvement. The experimental setup, as depicted in Fig. 1(a), comprises several key components designed to assess the safety and thermal performance of pouch cells. Twelve K-type thermocouples were strategically positioned to monitor the thermal behavior of the cell during tests, as illustrated in Fig. 1(b). These thermocouples were arranged to capture temperature variations across critical locations, including areas near the nail penetration site on both the cell surface and near the edge of the cell, midpoints between the nail penetration site and the edge of the cell, and regions proximal to the positive terminal. This arrangement ensures comprehensive thermal data acquisition, facilitating a detailed comparison of the cell's thermal response at various points. L and W denotes length and width on the figure. The tests were conducted inside a European Council for Automotive R&D (EUCAR) level 7 Chamber, specifically designed to withstand explosions caused by battery abuse conditions. During testing, the pouch cell was securely held in place by a custom jig featuring a motor-driven linear actuator. To ensure consistent pressure, a steel plate, measuring 149 mm in length, 69 mm in width, and 10 mm in thickness, was positioned above the pouch cell. A 3 mm thick calcium-magnesium silicate sheet, capable of maintaining uniform temperature distribution up to 1260°C, was placed between the cell and the steel plate to minimise the heat transfer from the cell to the steel plate during testing. The nail penetration occurred at the side center of the pouch cell, a critical point vulnerable to external impacts. The nail used was made of steel and had a diameter of 4 mm, a length of 107 mm, and a conical angle of 40°. Initially, the insertion speed was set at 6 mm/s, but it was later adjusted to 14 mm/s to ensure that the nail penetrated through the cell. The cell's state of charge (SOC) was set to 100%. To achieve this, all cells were fully charged using Maccor cyclers inside a climatic chamber before the tests. During the tests, the ambient temperature for all cells ranged between 15 to 20 ℃. To capture TR events during the tests, two web cameras (4K Pro, Logitech) and one infrared camera (VarioCam HD, InfraTech) were used. Gas analysis was performed using a Gasmet gas analyzer, as depicted in Fig. 1 (a). The gas analyzer's purpose in the test was to monitor and quantify gas emissions, providing insights into the thermal degradation behavior, chemical reactions, and safety characteristics of the tested pouch cells. 3. Test And Results 3.1 Nail penetration test Table 2 summarises the test conditions and results. The results for the 5 Ah MCC cells indicated that only one out of the four tested cells exhibited TR, whereas the remaining three cells did not experience TR. In contrast, both control cells within the 5 Ah group underwent TR, suggesting a potential enhancement in safety performance attributed to the MCC technology. The 5Ah cells with MCC can still undergo charging and discharging after NPT, but they no longer exhibit the same capacity as they did before tests. In the 10 Ah group, the results were significantly different. All six cells, regardless of whether they incorporated MCC technology or were control cells, experienced TR. This outcome highlights that, at higher capacities, the cells were uniformly prone to TR, indicating that the benefits of MCC observed in the 5 Ah cells did not extend to the 10 Ah cells under the similar test conditions. Probable reasons for such behaviour are discussed further in Section IV. Photographs of 5 Ah cells (Tests 2, 7, and 12) and 10 Ah cells post-TR are illustrated in Fig. 2 and 3, respectively. Table 2. NPT Test Summary Item Test no. Test conditions (nail speed) Thermal Runaway Maximum temperature (°C) loss ratio (residual mass/initial mass) Control cell (5 Ah) 1 6 mm/s Yes -- 29.1% 2 Yes 860.6 27.9% MCC Cell (5 Ah) 3 14 mm/s No N/A 0.0% 5 No N/A 0.0% 7 Yes 798.2 37.3% 12 No N/A 0.0% Control Cell (10 Ah) 8 Yes 867.1 38.3% 10 Yes 891.2 37.7% MCC Cell (10 Ah) 4 Yes 851.1 34.5% 6 Yes 845.9 37.2% 9 Yes 827.2 40.5% 11 Yes 810.4 39.7% All 4 MCC cells and 2 control cells experienced TR. Condition of these cells was significantly worse compared to the 5 Ah cells that underwent TR. Side ruptures were observed in most cells between the two tabs, indicating the primary point of flame or explosion release alongside the nail penetrating point. In terms of weight loss listed in Table 2, MCC cells generally had higher loss ratios during TR compared to control cells for 5 Ah. However, for 10 Ah cells, MCC cells had comparable loss ratios to control cells. 3.1.1 Temperature and Voltage Analysis As previously mentioned, among the four 5 Ah MCC cells, three of them did not undergo TR, while one cell did. The detailed temperature and voltage profiles for each sample are discussed below. During Test 3, the nail was initially blocked when its speed was 6 mm/s. The nail penetrated both 5 Ah control cells in Tests 1 and 2 at that speed. However, when we conducted the same test at 6 mm/s in Test 3, the nail did not penetrate the cell. After increasing the speed to 14 mm/s, the nail eventually penetrated the cell, with no TR occurring. This blockage of the nail was likely due to the greater mechanical strength of the current collector in the MCC cell. Following penetration, the voltage dropped from 4.16 V to 4.05 V, and the temperature increased by approximately 1.5 °C. After three minutes, the nail was removed, resulting in a decrease in temperature and recovery of the voltage. Subsequently, the test was repeated at 14 mm/s with the same cell. During this test, the nail completely penetrated the cell, causing a slight increase in temperature and an immediate voltage drop. Thereafter, the cell temperature slightly decreased, and the voltage recovered to a nearly steady value as depicted in Fig. 4(a). No smoke, sparks, or gases were observed during the test. The voltage and temperature profiles during NPT at test 5 revealed an initial temperature increase of approximately 2 °C upon nail insertion. This was followed by a gradual, marginal rise of 1 °C over the next hour. Simultaneously, the voltage gradually decreased from an initial value of approximately 4.2 V to 4.1 V. After one hour, upon the removal of the nail, the voltage exhibited a slight recovery. Concurrently, the cell’s temperature decreases, returning to its initial level of 18 °C within 5 minutes, as depicted in Fig. 4(b). During test 7, NPT resulted in TR, characterized by a rapid temperature increase to approximately 800 °C. A subsequent cooldown to ambient levels followed this. Simultaneously, the cell voltage dropped precipitously from its initial value of 4.15 V to 0 V, as illustrated in Fig. 4(c). At test 12, initial temperature increase of approximately 2 °C was observed upon nail insertion, followed by stabilization at ambient levels. However, the cell voltage continued to decline steadily over 17 hours, reaching approximately 3.75 V. Remarkably, upon nail removal, the voltage instantaneously increased above 3.9 V, as shown in Fig. 4(d). For both test 5 and test 12, cell exhibited a consistent trend of voltage reduction while the nail remained inserted. Although the possibility of a soft short due to nail penetration exists, it did not TR in either sample. On the other hand, both 5 Ah control cells experienced TR. For both cells, the temperature exceeded slightly more than 800 °C during TR. The peak temperature for the control cells was marginally higher than that observed in the 5 Ah MCC cell (during Test 7). Additionally, the voltage for the control cells dropped to 0 V immediately at the onset of TR. Voltage and temperature profiles are depicted in Fig. 4(e) for the Test 2. For the 10 Ah cells, NPTs were conducted on six cells: four MCC cells (test 4, 6,9, and 11) and two control cells (test 8 and 10). All six cells experienced TR. The universal occurrence of TR in the 10 Ah cells could be attributed to their increased thickness and capacity. The nail was inserted at the same speed and with the same dimensions across all tests. Likely, the jelly roll of the anode and cathode inside the 10 Ah cells was compressed to a greater extent than in the 5 Ah cells, compromising the control mechanism and leading to TR [23]. The increased thickness and capacity of the 10 Ah cells likely influenced the formation of short circuit paths, as the greater compression and denser packing of the electrodes increased the probability of internal contact between the anode and cathode layers. This increased the likelihood of multiple short circuits, which, in turn, generated more heat and exacerbated thermal runaway. The four MCC cells that experienced TR exhibited lower peak temperatures during TR compared to the control cells, as depicted in Fig. 5. The peak temperature for all four MCC cells remained around 800 °C. In contrast, the two control cells reached peak temperatures close to 850 °C. 3.1.2. Fire Behaviour Fig. 6. Test 9 section, illustrates the fire behavior during and immediately after the triggering of thermal runaway (TR) for test 9 of the 10 Ah MCC cell. It is shown that a jet flame emerged from the bottom of the cell where the nail was inserted, with no jet flame observed from the top of the cell initially. Following the initial thrust, a transient fireball erupted from the side of the cell along the tab, as depicted in Fig. 6-Test 9 (c, d). This combined jet flame and explosive activity persisted for approximately three seconds during the TR event. Along with the transient fireball, there were sparks during the test, as well as smoke and gases observed. On the other hand, the 5 Ah MCC cell that underwent TR exhibited less explosive fire behaviour compared to the 10 Ah MCC cell. When TR was triggered, a jet flame emerged from both the bottom and top surfaces of the cell, as depicted in Fig. 6-Test 7(a). This behaviour may be attributed to the smaller width of the 5 Ah MCC cell compared to the 10 Ah MCC cell, allowing the fire to escape from the top penetration point as well. Following the initial thrust, there was a short moment with only smoke and no jet flame or fire, as shown in Fig. 6 Test 7 (b). Subsequently, another jet flame occurred from both the top and bottom of the cell Fig. 6 Test 7 (c,d). Unlike the 10 Ah MCC cell, no fireball was observed from the side of the 5 Ah MCC cell. The overall fire duration was shorter than that of the 10 Ah MCC cell, lasting less than two seconds. Fig. 7 shows the thermal images captured during the thermal runaway (TR) event at the triggering point and at the peak of fire intensity. Panels (a) and (b) display thermal images of a 10 Ah MCC cell, while panels (c) and (d) show thermal images of a 5 Ah MCC cell. During the testing, the 5 Ah control cell exhibited minimal sparking upon nail penetration initially. When TR occurred in Test 2, there was almost no visible fire, but the entire test chamber filled with smoke shown in Fig. 8. 5 Ah Control Cell. Test 2 also showed high smoke levels with minimal fire for the that cell. Fig. 8. 10 Ah Control cell depicts the fire behavior of 10 Ah control cells during test 10, where a significant fire emerged similarly to the pattern observed in the 10 Ah MCC cells. Subsequently, an explosion occurred from the side of the cell between the tabs. This trend was consistent for both 10 Ah control cells. 3.1.3. Gas Emission During the tests, gas emissions were captured using a gas analyser. Figure 9 shows the emitted gases for the 10 Ah cell. Figure 9 (a) contained the 10 Ah MCC cell emitted gas data for test 6, and Figure 9 (b) displayed the data for the 10 Ah control cell from test 10. From the plot, it was observed that carbon monoxide (CO) was the dominant gas emitted. For the MCC cell, CO emission was around 800 ppm, while for the control cell, it was approximately 600 ppm. This difference in CO levels could be due to the material composition and reaction pathways of the MCC, which might produce more CO due to incomplete combustion or localized hotspots. The control cell, lacking these modifications, might undergo more uniform heat distribution and combustion, leading to lower CO emissions. Other emitted gases, such as nitrogen monoxide (NO), ethylene (C₂H₄), diethyl carbonate (C₅H₁₀O₃), dimethyl carbonate (C₃H₆O₃), ethyl methyl carbonate (C₄H₈O₃), and propylene carbonate (C₄H₆O₃), all had emissions in the range of 200 ppm or below for the MCC cell. For the control cell, these emissions were around 150 ppm. Again this difference in emission levels may be due to the material composition and thermal stability of the MCC cells, which could lead to the formation of more volatile organic compounds and nitrogen compounds during thermal degradation. The modified design of MCC cells might also create different thermal environments and gas retention dynamics that promote higher emissions of these gases. There was no significant emission of water vapor or carbon dioxide (CO₂). 3.2. Computed Tomography (CT) Scan A CT scan was conducted on the cell after the nail penetration test, following a discharge to a 0% state of charge (SOC). This scan was performed on the 5 Ah MCC cell from test 3. We did two CT scan, one with nail still inside and another after removal of nail from the cell. Figure 10 displays the CT scan image with the nail still embedded inside the cell. It was observed that while some cathode layers retracted from the nail, others did not, which potentially explains the occurrence of micro-shorts and the gradual voltage drop when the nail was present. Captured lateral, side and top views of CT scan over the cell can be found in Figure 11. This CT scan image is taken when the nail was not inside. This is taken to understand the internal structure, particularly around the nail penetration area. According to some researchers, upon nail penetration, the cathode layers retreat below the anode layers for MCC cell, preventing short circuits through the nail [25]. However, our experiment did not show this behaviour for most of the cathode layers. Specifically, as seen in the CT scan images, the bright cathode layers near the penetration site do not uniformly retreat beneath the light-grey anode layers. Instead, in the lateral and side views, the cathode layers appear to split apart in some regions, resembling a crocodile jaw, while maintaining contact in others. This incomplete retraction of cathode layers suggests the possibility of persistent micro-shorts, which likely contributed to the gradual voltage drop observed during the test. Additionally, the top view highlights a concentric pattern of structural deformation around the penetration site, further supporting the occurrence of localized disruptions in layer alignment without a consistent retreat of cathode layers beneath the anode. This phenomenon, where the light cathode layers did not retreat into the grey anode layers for all the layers, is evident in both lateral and side views of the nail-penetrated cell. The voltage profile of the nail-penetrated cell (described in section 3.1.1) showed a continuous drop in cell voltage upon nail penetration, with recovery over time after nail removal, which aligns with the CT scan results. The CT scan here indicates that a short circuit through the nail is possible. 3.3. SEM and EDS SEM and EDS analyses were performed on both the anode and cathode over the 5 Ah MCC cell from test 3. EDS analysis was specifically conducted at the electrode's edge, directly at the site of nail penetration, and at regions slightly removed from the penetration site. Additionally, cross-sectional SEM imaging was utilized to elucidate the structural composition of the cathode. This detailed investigation aimed to observe any morphological and compositional variations induced by mechanical penetration. The primary objective of this test was to determine whether an insulating layer had formed at the edge of the electrode adjacent to the nail penetration point. By comparing samples from near the edge and slightly away from the penetration site, we sought to identify and confirm the presence of any insulating layer, which could have significant implications for understanding the electrical and thermal behaviour of the electrode after NPT. A TASCAN Clara (Libusina, Czech Republic) ultra-high-resolution scanning electron microscope (UHR-SEM) with a field emission gun electron source was utilized to capture SEM images. Standard stubs were prepared with double-sided conductive carbon tape, and each sample was meticulously positioned on the stubs. These stubs were then mounted on an SEM pin mount specimen holder, which was placed in the vacuum chamber. E-T detectors were employed during the image collection process. 3.3.1. Cathode EDS Analysis The primary differences observed between the samples are the elevated presence of aluminium in the edge sample, contrasted with higher percentages of nickel, carbon, fluorine, manganese, and cobalt in the surface sample. Figure 12 shows, that the aluminium concentration was significantly higher at the edge (23.1%) compared to the surface (0.1%). This disparity is anticipated, as the nail penetration exposes the current collector. However, this analysis does not reveal any insulating layer at the edge that could prevent short-circuiting through the nail. This absence of an insulating layer could be due to the limitations of the analytical techniques employed. The methods used, such as SEM and EDS, might not be sensitive enough to detect very thin or discontinuous polymeric insulating layers. Alternatively, it is also possible that no insulating layer exists at the edge, indicating that the conditions during the nail penetration did not favor the formation of such a layer. 3.3.2. Anode SEM and EDS Analysis Fig. 13 presents EDS analysis of the anode. Similar to the observations made for the cathode, a substantial amount of copper (11.3%) was detected at the edge where nail penetration occurred. This presence of copper likely results from the exposure of the current collector due to the nail penetration. However, as with the anode, the EDS analysis did not detect any insulation layer at the edge of the nail penetration point. The SEM image (Figure 14) revealed a notable presence of a white substance at the edge where nail penetration occurred. This white substance was absent on the surface, as shown in Figure 14 (b). For the cathode, we also did not detect any hypothesized insulating layer. And this could be again due to the limitations of the analytical techniques used. Jus like the case of anode, it is also possible that there is no insulating layer present at the edge of the ail penetration point. 3.3.3. Cross Sectional SEM Image A cross-sectional SEM image of the anode was obtained, revealing two layers of copper instead of a single, solid layer typically observed in current collectors. It is likely that an additional layer, possibly a polymer, is present between these two Cu layers. Figure 15 illustrates this configuration. 4. Discussion The study conducted on the TR risk of pouch cells equipped with MCC under mechanical abuse conditions provided valuable insights into the safety enhancements offered by the MCC technology. The NPTs revealed significant differences in the behaviour of 5 Ah and 10 Ah capacity cells. For the 5 Ah cells, the incorporation of MCC technology showed a marked improvement in safety performance. Only one out of the four MCC-equipped cells experienced TR, while all control cells without MCC underwent TR. This indicates that MCC technology has the capability of mitigating the risk of TR in lower-capacity cells. The MCC's ability to prevent internal short circuits, likely due to its design incorporating PET demonstrates its effectiveness in enhancing cell safety under mechanical abuse. The 10 Ah cells presented a contrasting scenario. All tested cells, irrespective of MCC technology, experienced TR. This outcome suggests that the MCC's protective benefits observed in the 5 Ah cells do not apply to higher-capacity cells under similar testing conditions. The uniform TR occurrence in 10 Ah cells indicates that additional factors, such as increased energy density and associated thermal risks, may overshadow the MCC's effectiveness. The CT scans conducted on a 5 Ah MCC cell following a nail penetration test revealed that while some cathode layers receded from the nail, others did not, potentially leading to micro-shorts and a gradual voltage drop. Contrary to previous results, most cathode layers did not recede below the anode layers upon penetration, aimed at preventing short circuits [17]. The voltage profile of the cell exhibited a continuous drop during nail penetration, followed by recovery upon nail removal, aligning with the CT scan findings suggesting a possible short circuit. SEM and EDS analyses were performed on the cathode and anode surfaces of a battery cell after mechanical penetration, particularly nail penetration. Results showed increased aluminum concentration near the penetration site on the cathode and copper concentration on the anode, indicating current collector exposure. However, no insulating layer was detected at the penetration points. SEM imaging revealed a white substance at the anode penetration site, suggesting a reaction. Cross-sectional SEM imagery of the anode showed a complex structure with two copper layers, possibly indicating the presence of a polymer layer. These findings underscore the need for further investigation into safety and performance implications of mechanical penetration on battery cells. 5. Conclusion The experimental study demonstrated that MCC technology significantly enhances the safety of 5 Ah lithium-ion pouch cells by reducing the incidence of thermal runaway under mechanical abuse conditions. The MCC's integration with PET effectively mitigates internal short circuits, preventing thermal runaway in lower-capacity cells. However, this benefit may not apply to higher-capacity 10 Ah cells, indicating a need for additional safety measures in larger energy storage systems. Further research is necessary to address the safety challenges in higher-capacity cells, which may involve modifications to both MCC technology and the separator. Understanding the factors contributing to these inconsistencies should be a priority for future research. Declarations Acknowledgements This project provided an excellent opportunity to deepen our understanding and expertise in assessing the safety performance of emerging technologies. The project was executed by the JLR Catapult project, and we extend our sincere gratitude to the JLR Catapult project for their invaluable support and for offering this wonderful research opportunity. 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DOI 10.1149/2.0701906jes Naguib, M., et al., Limiting internal short-circuit damage by electrode partition for impact-tolerant Li-ion batteries. Joule, 2018. 2(1): p. 155-167. https://doi.org/10.1016/j.joule.2017.11.003 Adamson, A., et al., Improving lithium-ion cells by replacing polyethylene terephthalate jellyroll tape. Nature Materials, 2023. 22(11): p. 1380-1386. https://doi.org/10.1038/s41563-023-01673-3 Niu, J., et al., Experimental study on low thermal conductive and flame retardant phase change composite material for mitigating battery thermal runaway propagation. Journal of Energy Storage, 2022. 47: p. 103557. https://doi.org/10.1016/j.est.2021.103557 Li, H., et al., Thermal‐responsive and fire‐resistant materials for high‐safety lithium‐ion batteries. Small, 2021. 17(43): p. 2103679. https://doi.org/10.1002/smll.202103679 Li, J., et al., Lithium-Ion Batteries with Safer Current Collectors. 2022, Oak Ridge National Lab.(ORNL), Oak Ridge, TN (United States); Soteria …. https://doi.org/10.2172/1895226 Pham, M.T., et al., Prevention of lithium-ion battery thermal runaway using polymer-substrate current collectors. Cell Reports Physical Science, 2021. 2(3). https://doi.org/10.1016/j.xcrp.2021.100360 Spielbauer, M., et al., Experimental study of the impedance behavior of 18650 lithium-ion battery cells under deforming mechanical abuse. Journal of Energy Storage, 2019. 26: p. 101039. Darcy, E. Investigating the Ability of Plastic Current Collectors to Isolate Internal Shorts in High Energy Cells. in 4th International Battery Safety Workshop (IBSW). 2023. Hu, W., Y. Peng, Y. Wei, and Y. Yang, Application of electrochemical impedance spectroscopy to degradation and aging research of lithium-ion batteries. The Journal of Physical Chemistry C, 2023. 127(9): p. 4465-4495. https://doi.org/10.1021/acs.jpcc.3c00033 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 20 Feb, 2026 Reviewers agreed at journal 30 Jan, 2026 Reviewers agreed at journal 30 Jan, 2026 Reviewers invited by journal 29 Dec, 2025 Editor assigned by journal 26 Dec, 2025 Submission checks completed at journal 11 Dec, 2025 First submitted to journal 06 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8296559","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":566771661,"identity":"bdf3fcfc-7b5e-47e1-b09d-7b62af5a76e9","order_by":0,"name":"MD ABUL KASHEM","email":"data:image/png;base64,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","orcid":"","institution":"University of Warwick","correspondingAuthor":true,"prefix":"","firstName":"MD","middleName":"ABUL","lastName":"KASHEM","suffix":""},{"id":566771662,"identity":"d0ab5147-2c6b-4809-b55a-80c3c4810035","order_by":1,"name":"Haodong Chen","email":"","orcid":"","institution":"University of Warwick","correspondingAuthor":false,"prefix":"","firstName":"Haodong","middleName":"","lastName":"Chen","suffix":""},{"id":566771663,"identity":"d982e07f-14bf-42d4-8a0f-9832dea44be1","order_by":2,"name":"Sadia Tasnim Mowri","email":"","orcid":"","institution":"University of Warwick","correspondingAuthor":false,"prefix":"","firstName":"Sadia","middleName":"Tasnim","lastName":"Mowri","suffix":""},{"id":566771664,"identity":"e5bed78e-2398-4bbc-a317-0d16c61037a2","order_by":3,"name":"Mushfiqur Rahman","email":"","orcid":"","institution":"University of Warwick","correspondingAuthor":false,"prefix":"","firstName":"Mushfiqur","middleName":"","lastName":"Rahman","suffix":""},{"id":566771665,"identity":"ffe1bf3b-b2ad-4f8b-9199-d2fb06ec2d36","order_by":4,"name":"Anup Barai","email":"","orcid":"","institution":"University of Warwick","correspondingAuthor":false,"prefix":"","firstName":"Anup","middleName":"","lastName":"Barai","suffix":""}],"badges":[],"createdAt":"2025-12-06 19:23:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8296559/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8296559/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":99320729,"identity":"0086c1ce-397e-477f-9be9-d7d6ab5cb2d6","added_by":"auto","created_at":"2025-12-31 16:38:53","extension":"doc","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":9890537,"visible":true,"origin":"","legend":"","description":"","filename":"THERMA1.doc","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/c858412deec26268d46932f3.doc"},{"id":99319765,"identity":"1a90c336-dbe9-4cee-a40c-e00f020b4cc2","added_by":"auto","created_at":"2025-12-31 16:37:48","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6971,"visible":true,"origin":"","legend":"","description":"","filename":"e4e5a7a821f24ecd9c6188f50858eafa.json","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/b1c3918e7ce9ded1d4912960.json"},{"id":99287208,"identity":"719c5f55-7f53-4860-b06b-960c149cb1ed","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":447057,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic of overall test setup, (b) Thermocouple location.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/50b6686dc26b85aba3b2c541.png"},{"id":99287217,"identity":"a22ea103-a4bc-4dd6-86c3-524993ee8408","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":290302,"visible":true,"origin":"","legend":"\u003cp\u003eCondition of 5 Ah cells after NPT testing: (a) 5 Ah MCC in test 12 with no TR, (b) 5 Ah MCC in test 7 with TR, (c) 5 Ah control with TR\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/bbeb7fb71a4d8ec285378b8c.png"},{"id":99287212,"identity":"6e7b4f11-f7a1-434a-8d31-d00bfa8416dd","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":694081,"visible":true,"origin":"","legend":"\u003cp\u003eCell condition for 10 Ah cell post TR. (a) 10 Ah MCC-test 4, (b) 10 Ah MCC-test 6, (c) 10 Ah control-test 8, (d) 10 Ah MCC-test 9, (e) 10 Ah control-test 10, (f) 10 Ah MCC-test 11\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/76ffcfc73295ffc001108d8b.png"},{"id":99287211,"identity":"95e924e8-e73a-4a88-9685-6ee58ed25c4c","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":811873,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage and Temperature Profile of 5 Ah Pouch cell during Nail Penetration test (a) Sample 1 (No TR), (b) Sample 2 (No TR), (c) Sample 3 (TR), (d) Sample 4 (No TR). (e) 5 Ah control cell.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/3871fa82830b9d31ce1152e3.png"},{"id":99287209,"identity":"dd3b2dc2-101c-4d38-9e54-0f1fc1f024f4","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":51546,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature and voltage profile 10 Ah cell (a) MCC cell, (b) Control cell.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/22bc23138a17df1822169de9.png"},{"id":99319616,"identity":"9369f706-b6e5-4990-acbf-6f65f248fded","added_by":"auto","created_at":"2025-12-31 16:37:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1241177,"visible":true,"origin":"","legend":"\u003cp\u003eFire behaviour of 10 Ah MCC cell (Test 9) and 5 Ah MCC cell undergoing TR (Test 7).\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/947edace9229c9e17e650959.png"},{"id":99320745,"identity":"f8a93c26-7874-40bb-8637-53f669f14b09","added_by":"auto","created_at":"2025-12-31 16:38:53","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":709239,"visible":true,"origin":"","legend":"\u003cp\u003eThermal image capture of both 10 Ah \u0026amp; 5 Ah MCC cell during TR.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/8b01c99e8e8948081a374fce.png"},{"id":99287224,"identity":"639a6331-672d-4e02-a600-0cde799eb264","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":931010,"visible":true,"origin":"","legend":"\u003cp\u003eFire behaviour of 5 Ah (Test 2) and 10 Ah Control Cell undergoing TR (Test 10).\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/49cd344b49b5b7b1bac85cd2.png"},{"id":99287214,"identity":"1eb1d49b-cfbf-4b82-ad65-d4a3ca398316","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1808444,"visible":true,"origin":"","legend":"\u003cp\u003eEmitted Gas (a) 10 Ah MCC cell, (b) 10 Ah control cell\u003c/p\u003e","description":"","filename":"image9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/85d357768a055263158f60df.jpeg"},{"id":99321012,"identity":"3c58fa31-dc3e-4b61-9e61-f1e87ff964ac","added_by":"auto","created_at":"2025-12-31 16:39:02","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":260160,"visible":true,"origin":"","legend":"\u003cp\u003eCT Scan of cell (with nail inside the cell)\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/1e5f182d62bd49db7ccd3684.png"},{"id":99321041,"identity":"e9b10062-5843-49e2-925e-7fc6fd7dbf8c","added_by":"auto","created_at":"2025-12-31 16:39:07","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":199435,"visible":true,"origin":"","legend":"\u003cp\u003eCT Scan of Nail Penetrated 5 Ah pouch cell. (a) Lateral, (b) Side, (c) Top View.\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/a5eb045aba88e10d234f68c2.png"},{"id":99320784,"identity":"4a0d6c16-735c-4820-a2ff-a380732f9f7c","added_by":"auto","created_at":"2025-12-31 16:38:54","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":267070,"visible":true,"origin":"","legend":"\u003cp\u003eEDS analysis of Cathode. (a) edge near the nail penetration, (b) surface away from nail penetration.\u003c/p\u003e","description":"","filename":"image12.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/f67112c5984f0bc3516f87cd.png"},{"id":99287219,"identity":"8d79f3b9-5b79-4b53-9f19-546c88e74f79","added_by":"auto","created_at":"2025-12-31 09:35:25","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":326331,"visible":true,"origin":"","legend":"\u003cp\u003eEDS Analysis of Anode (a) edge near nail-penetration, (b) surface away from nail penetrated area\u003c/p\u003e","description":"","filename":"image13.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/1b86cadad5a9c56c78ef4705.png"},{"id":99320150,"identity":"27fb6141-3229-40b4-974d-6d62109aee0e","added_by":"auto","created_at":"2025-12-31 16:38:18","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":152666,"visible":true,"origin":"","legend":"\u003cp\u003eSEM analysis of Anode. (a) edge near the nail penetration, (b) at the surface.\u003c/p\u003e","description":"","filename":"image14.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/2c3fb426b7bf2a7a0b737c97.png"},{"id":99320669,"identity":"db7bbb89-50b9-4b59-b7a1-17de1b226515","added_by":"auto","created_at":"2025-12-31 16:38:51","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":190751,"visible":true,"origin":"","legend":"\u003cp\u003eCross Sectional SEM image of Anode\u003c/p\u003e","description":"","filename":"image15.png","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/af8c6036a455d890de5a3e68.png"},{"id":99324266,"identity":"a92e6a84-a508-4794-9e70-c5ffb1aa6e12","added_by":"auto","created_at":"2025-12-31 16:47:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":10036453,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8296559/v1/616170a9-64a2-4e90-aab7-982af04b605b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermal runaway risk assessment of pouch cells with modified current collectors under mechanical abuse","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eModified current collector lowers Thermal Runaway risk in 5 Ah pouch cells\u003c/li\u003e\n \u003cli\u003eOnly 1 of 4 modified 5 Ah cells had Thermal Runaway\u003c/li\u003e\n \u003cli\u003eAll 10 Ah cells had Thermal Runaway, showing limits of modified current collector\u003c/li\u003e\n \u003cli\u003eCT and SEM revealed internal changes after nail penetration\u003c/li\u003e\n \u003cli\u003ePET-based current collector helps safety, needs work for larger cells\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eThe widespread adoption of lithium-ion batteries (LIBs) in portable electronic devices and electric vehicles (EVs) highlights their pivotal role in contemporary technology. Noted for their remarkable energy density, extended cycle longevity, and comparatively minimal self-discharge rates, these batteries play a crucial role in powering a diverse range of electronic devices and EVs [1, 2]. Over the past three decades, significant advancements in electrode engineering and ongoing developments in new chemistries have led to remarkable improvements in the energy density of LIBs [3, 4]. However, the increasing energy density of LIBs necessitates innovative designs to ensure safety. Safety concerns, such as thermal runaway (TR), remain a significant challenge. TR, characterized by an uncontrollable increase in temperature and potential cell rupture, poses severe risks, especially under abusive conditions such as mechanical abuse [5, 6]. The safety of LIBs has relied on components such as separators, current interrupt devices (CIDs), positive temperature coefficient (PTC) device, safety vents, and stringent control of operating conditions conventionally [7, 8]. Additionally, robust packaging is essential to protect LIBs from mechanical impacts, which inadvertently adds extra weight and volume, thereby reducing the overall energy density [9, 10].\u003c/p\u003e\n\u003cp\u003eThe current collector (CC) in a battery cell provides an electronic conduction pathway for both the anode electrode and the cathode electrode, typically using aluminum or copper for their electrochemical stability [11, 12]. While these metals efficiently conduct electricity and prevent degradation, conventional CCs can facilitate high current flow, potentially triggering TR. \u0026nbsp;Numerous researchers have investigated the factors leading to TR by examining the characteristics and behavior of battery cells prior to its occurrence [13, 14]. TR has also been extensively studied and reviewed in the existing literature, with many studies focusing on mitigation techniques and risk reduction strategies [15-17]. But research on modifying these CCs to mitigate TR risks is limited. Some efforts to redesign them, along with electrodes, have been pursued [18, 19]. With these modified current collectors (MCCs), battery safety can be enhanced through thermally conductive \u0026nbsp;and flame-retardant coatings [20, 21]. In related studies, metalized polymer films have been used as MCCs to improve thermal stability and reduce internal short circuits [8, 22]. Recent research also suggests that these metal-coated polymer CCs can retract from heat sources during thermal events, potentially preventing TR and significantly enhancing battery safety [23].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA rigorous evaluation of the performance of MCC-equipped cells under mechanical abuse conditions is required to determine their potential to prevent TR and enhance overall battery safety. \u0026nbsp;This investigation is critical in advancing the understanding of the safety mechanisms in high-energy-density batteries and contributing to the development of safer and more reliable energy storage solutions. The findings will offer valuable insights into the effectiveness of the MCC in real-world applications, guiding future innovations in battery design and safety.\u003c/p\u003e"},{"header":"2. Experiment Setup","content":"\u003cp\u003eFour types of pouch cells were used in this study, two types of control cells and two types of MCC cells where current collectors were coated with polyethylene terephthalate (PET). The cell parameters are listed in\u0026nbsp;Table 1. The cathode and the anode are lithium nickel cobalt manganese oxide (NMC) and graphite, respectively. Nail penetration tests (NPTs) were conducted on a total of twelve pouch cells, which were divided into two groups based on their capacities.\u003c/p\u003e\n\u003cp\u003eTable 1. Pouch cell information.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"627\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eItem\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eControl Cell\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eModified Cell\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eControl Cell\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3844%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eModified cell\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eNominal capacity (Ah)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3844%;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eMass (g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e154\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3844%;\"\u003e\n \u003cp\u003e148\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eSpecific energy (Wh/kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e214.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e219.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e237.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3844%;\"\u003e\n \u003cp\u003e246.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eDimension (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e100*60*6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e100*60*6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e100*60*10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3844%;\"\u003e\n \u003cp\u003e100*60*10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eNominal voltage (V)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 68.5805%;\"\u003e\n \u003cp\u003e3.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eCharge cut-off voltage (V)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 68.5805%;\"\u003e\n \u003cp\u003e4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eDischarge cut-off voltage (V)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 68.5805%;\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eCathode\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 68.5805%;\"\u003e\n \u003cp\u003eLithium Nickel Cobalt Manganese Oxide (LiNi\u003cem\u003e\u003csub\u003ex\u003c/sub\u003e\u003c/em\u003eCo\u003cem\u003e\u003csub\u003ey\u003c/sub\u003e\u003c/em\u003eMn\u003cem\u003e\u003csub\u003ez\u003c/sub\u003e\u003c/em\u003eO\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eAnode\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 68.5805%;\"\u003e\n \u003cp\u003eGraphite (C)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 31.4195%;\"\u003e\n \u003cp\u003eNumber\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.0654%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17.3844%;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe first group consisted of six cells, each with a capacity of 5 Ah, while the second group comprised six cells with a higher capacity of 10 Ah. Within each capacity group, four cells were fabricated using MCC technology, and the remaining two cells served as control samples to facilitate comparative analysis. The 5 Ah and 10 Ah rated capacity cells were identical in dimensions, differing only in thickness. The 10 Ah cell had an increased number of anode and cathode layers compared to the 5 Ah cell. Control cells without the MCCs were adopted to benchmark the improved safety MCC offers.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo comprehensively assess the effectiveness of MCC, we conducted a series of \u0026nbsp;NPTs. During tests, thermal behaviour was monitored with thermocouples, voltage sensors, and a high-resolution thermal infrared camera.\u003c/p\u003e\n\u003cp\u003eFurthermore, we employed advanced forensic techniques including computed tomography (CT), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to analyse the post-abuse internal state of the cells. CT scans provide detailed visualizations of the internal structure, allowing us to identify any structural damages and deformations that occurred as a result of the abuse conditions. This 3D imaging helps us to assess whether the MCCs effectively mitigated damage propagation within the cell, thereby contributing to safety. SEM was utilized to reveal microstructural changes. This high-resolution imaging technique enables us to examine the surface morphology and detect any micro-cracks, voids, or phase separations that might compromise the integrity of the cell. By comparing the microstructures of electrodes adjacent to the nail-penetrated area with those located slightly further away, we aim to highlight how MCC cells prevent short circuits between the electrodes. EDS was used to identify elemental composition changes within the cells. This technique allows us to detect any migration or segregation of elements that could indicate thermal degradation or chemical reactions due to the CC\u0026rsquo;s properties.\u003c/p\u003e\n\u003cp\u003eBy analyzing these changes, we could determine whether the MCCs contributed to maintaining the chemical stability of the cells under abusive conditions. These multidimensional analyses offer a robust understanding of the safety enhancements provided by the MCC because they collectively provide a comprehensive assessment of the cell\u0026apos;s structural integrity, microstructural stability, and chemical consistency. This holistic approach not only highlights the advantages of MCCs in mitigating various failure modes but also guides the development of safer energy storage solutions by identifying key areas for further improvement.\u003c/p\u003e\n\u003cp\u003eThe experimental setup, as depicted in Fig. 1(a), comprises several key components designed to assess the safety and thermal performance of pouch cells.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTwelve K-type thermocouples were strategically positioned to monitor the thermal behavior of the cell during tests, as illustrated in Fig. 1(b). These thermocouples were arranged to capture temperature variations across critical locations, including areas near the nail penetration site on both the cell surface and near the edge of the cell, midpoints between the nail penetration site and the edge of the cell, and regions proximal to the positive terminal. This arrangement ensures comprehensive thermal data acquisition, facilitating a detailed comparison of the cell\u0026apos;s thermal response at various points. L and W denotes length and width on the figure.\u003c/p\u003e\n\u003cp\u003eThe tests were conducted inside a European Council for Automotive R\u0026amp;D (EUCAR) level 7 Chamber, specifically designed to withstand explosions caused by battery abuse conditions. During testing, the pouch cell was securely held in place by a custom jig featuring a motor-driven linear actuator. To ensure consistent pressure, a steel plate, measuring 149 mm in length, 69 mm in width, and 10 mm in thickness, was positioned above the pouch cell. A 3 mm thick calcium-magnesium silicate sheet, capable of maintaining uniform temperature distribution up to 1260\u0026deg;C, was placed between the cell and the steel plate to minimise the heat transfer from the cell to the steel plate during testing.\u003c/p\u003e\n\u003cp\u003eThe nail penetration occurred at the side center of the pouch cell, a critical point vulnerable to external impacts. The nail used was made of steel and had a diameter of 4 mm, a length of 107 mm, and a conical angle of 40\u0026deg;. Initially, the insertion speed was set at 6 mm/s, but it was later adjusted to 14 mm/s to ensure that the nail penetrated through the cell. The cell\u0026apos;s state of charge (SOC) was set to 100%. To achieve this, all cells were fully charged using Maccor cyclers inside a climatic chamber before the tests. During the tests, the ambient temperature for all cells ranged between 15 to 20 ℃. To capture TR events during the tests, two web cameras (4K Pro, Logitech) and one infrared camera (VarioCam HD, InfraTech) were used. Gas analysis was performed using a Gasmet gas analyzer, as depicted in Fig. 1 (a). The gas analyzer\u0026apos;s purpose in the test was to monitor and quantify gas emissions, providing insights into the thermal degradation behavior, chemical reactions, and safety characteristics of the tested pouch cells.\u003c/p\u003e"},{"header":"3. Test And Results","content":"\u003cp\u003e\u003cstrong\u003e3.1\u0026nbsp;\u003c/strong\u003eNail penetration test\u003c/p\u003e\n\u003cp\u003eTable 2 summarises the test conditions and results. The results for the 5 Ah MCC cells indicated that only one out of the four tested cells exhibited TR, whereas the remaining three cells did not experience TR. In contrast, both control cells within the 5 Ah group underwent TR, suggesting a potential enhancement in safety performance attributed to the MCC technology. The 5Ah cells with MCC can still undergo charging and discharging after NPT, but they no longer exhibit the same capacity as they did before tests.\u003c/p\u003e\n\u003cp\u003eIn the 10 Ah group, the results were significantly different. All six cells, regardless of whether they incorporated MCC technology or were control cells, experienced TR. This outcome highlights that, at higher capacities, the cells were uniformly prone to TR, indicating that the benefits of MCC observed in the 5 Ah cells did not extend to the 10 Ah cells under the similar test conditions. Probable reasons for such behaviour are discussed further in Section IV. Photographs of 5 Ah cells (Tests 2, 7, and 12) and 10 Ah cells post-TR are illustrated in Fig. 2 and 3, respectively.\u003c/p\u003e\n\u003cp\u003eTable 2. NPT Test Summary\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eItem\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTest no.\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTest conditions (nail speed)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eThermal Runaway\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMaximum temperature (\u0026deg;C)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eloss ratio (residual mass/initial mass)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003eControl cell (5 Ah)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e6 mm/s\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e29.1%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e860.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e27.9%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003eMCC Cell (5 Ah)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"10\" valign=\"top\" style=\"width: 18px;\"\u003e\n \u003cp\u003e14 mm/s\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e0.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e0.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e798.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e37.3%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e0.0%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003eControl Cell (10 Ah)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e867.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e38.3%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e891.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e37.7%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003eMCC Cell (10 Ah)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e851.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e34.5%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e845.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e37.2%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e827.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e40.5%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 17px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 21px;\"\u003e\n \u003cp\u003e810.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19px;\"\u003e\n \u003cp\u003e39.7%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAll 4 MCC cells and 2 control cells experienced TR. Condition of these cells was significantly worse compared to the 5 Ah cells that underwent TR. Side ruptures were observed in most cells between the two tabs, indicating the primary point of flame or explosion release alongside the nail penetrating point.\u003c/p\u003e\n\u003cp\u003eIn terms of weight loss listed in Table 2, MCC cells generally had higher loss ratios during TR compared to control cells for 5 Ah. However, for 10 Ah cells, MCC cells had comparable loss ratios to control cells.\u003c/p\u003e\n\u003ch3\u003e3.1.1 Temperature and Voltage Analysis\u003c/h3\u003e\n\u003cp\u003eAs previously mentioned, among the four 5 Ah MCC cells, three of them did not undergo TR, while one cell did. The detailed temperature and voltage profiles for each sample are discussed below.\u003c/p\u003e\n\u003cp\u003eDuring Test 3, the nail was initially blocked when its speed was 6 mm/s. The nail penetrated both 5 Ah control cells in Tests 1 and 2 at that speed. However, when we conducted the same test at 6 mm/s in Test 3, the nail did not penetrate the cell. After increasing the speed to 14 mm/s, the nail eventually penetrated the cell, with no TR occurring. This blockage of the nail was likely due to the greater mechanical strength of the current collector in the MCC cell. Following penetration, the voltage dropped from 4.16 V to 4.05 V, and the temperature increased by approximately 1.5 \u0026deg;C. After three minutes, the nail was removed, resulting in a decrease in temperature and recovery of the voltage. Subsequently, the test was repeated at 14 mm/s with the same cell. During this test, the nail completely penetrated the cell, causing a slight increase in temperature and an immediate voltage drop. Thereafter, the cell temperature slightly decreased, and the voltage recovered to a nearly steady value as depicted in Fig. 4(a). No smoke, sparks, or gases were observed during the test.\u003c/p\u003e\n\u003cp\u003eThe voltage and temperature profiles during NPT at test 5 revealed an initial temperature increase of approximately 2 \u0026deg;C upon nail insertion. This was followed by a gradual, marginal rise of 1 \u0026deg;C over the next hour. Simultaneously, the voltage gradually decreased from an initial value of approximately 4.2 V to 4.1 V. After one hour, upon the removal of the nail, the voltage exhibited a slight recovery. Concurrently, the cell\u0026rsquo;s temperature decreases, returning to its initial level of 18 \u0026deg;C within 5 minutes, as depicted in Fig. 4(b).\u003c/p\u003e\n\u003cp\u003eDuring test 7, NPT resulted in TR, characterized by a rapid temperature increase to approximately 800 \u0026deg;C. A subsequent cooldown to ambient levels followed this. Simultaneously, the cell voltage dropped precipitously from its initial value of 4.15 V to 0 V, as illustrated in Fig. 4(c).\u003c/p\u003e\n\u003cp\u003eAt test 12, initial temperature increase of approximately 2 \u0026deg;C was observed upon nail insertion, followed by stabilization at ambient levels. However, the cell voltage continued to decline steadily over 17 hours, reaching approximately 3.75 V. Remarkably, upon nail removal, the voltage instantaneously increased above 3.9 V, as shown in Fig. 4(d). For both test 5 and test 12, cell exhibited a consistent trend of voltage reduction while the nail remained inserted. Although the possibility of a soft short due to nail penetration exists, it did not TR in either sample.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOn the other hand, both 5 Ah control cells experienced TR. For both cells, the temperature exceeded slightly more than 800 \u0026deg;C during TR. The peak temperature for the control cells was marginally higher than that observed in the 5 Ah MCC cell (during Test 7). Additionally, the voltage for the control cells dropped to 0 V immediately at the onset of TR. Voltage and temperature profiles are depicted in Fig. 4(e) for the Test 2.\u003c/p\u003e\n\u003cp\u003eFor the 10 Ah cells, NPTs were conducted on six cells: four MCC cells (test 4, 6,9, and 11) and two control cells (test 8 and 10). All six cells experienced TR. The universal occurrence of TR in the 10 Ah cells could be attributed to their increased thickness and capacity. The nail was inserted at the same speed and with the same dimensions across all tests. Likely, the jelly roll of the anode and cathode inside the 10 Ah cells was compressed to a greater extent than in the 5 Ah cells, compromising the control mechanism and leading to TR [23].\u003c/p\u003e\n\u003cp\u003eThe increased thickness and capacity of the 10 Ah cells likely influenced the formation of short circuit paths, as the greater compression and denser packing of the electrodes increased the probability of internal contact between the anode and cathode layers. This increased the likelihood of multiple short circuits, which, in turn, generated more heat and exacerbated thermal runaway.\u003c/p\u003e\n\u003cp\u003eThe four MCC cells that experienced TR exhibited lower peak temperatures during TR compared to the control cells, as depicted in Fig. 5. The peak temperature for all four MCC cells remained around 800 \u0026deg;C. In contrast, the two control cells reached peak temperatures close to 850 \u0026deg;C.\u003c/p\u003e\n\u003ch3\u003e3.1.2. Fire Behaviour\u003c/h3\u003e\n\u003cp\u003eFig. 6. Test 9 section, illustrates the fire behavior during and immediately after the triggering of thermal runaway (TR) for test 9 of the 10 Ah MCC cell. It is shown that a jet flame emerged from the bottom of the cell where the nail was inserted, with no jet flame observed from the top of the cell initially. Following the initial thrust, a transient fireball erupted from the side of the cell along the tab, as depicted in Fig. 6-Test 9 (c, d). This combined jet flame and explosive activity persisted for approximately three seconds during the TR event. Along with the transient fireball, there were sparks during the test, as well as smoke and gases observed.\u003c/p\u003e\n\u003cp\u003eOn the other hand, the 5 Ah MCC cell that underwent TR exhibited less explosive fire behaviour compared to the 10 Ah MCC cell. When TR was triggered, a jet flame emerged from both the bottom and top surfaces of the cell, as depicted in Fig. 6-Test 7(a). This behaviour may be attributed to the smaller width of the 5 Ah MCC cell compared to the 10 Ah MCC cell, allowing the fire to\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eescape from the top penetration point as well. Following the initial thrust, there was a short moment with only smoke and no jet flame or fire, as shown in Fig. 6 Test 7 (b). Subsequently, another jet flame occurred from both the top and bottom of the cell Fig. 6 Test 7 (c,d). Unlike the 10 Ah MCC cell, no fireball was observed from the side of the 5 Ah MCC cell. The overall fire duration was shorter than that of the 10 Ah MCC cell, lasting less than two seconds.\u003c/p\u003e\n\u003cp\u003eFig. 7 shows the thermal images captured during the thermal runaway (TR) event at the triggering point and at the peak of fire intensity. Panels (a) and (b) display thermal images of a 10 Ah MCC cell, while panels (c) and (d) show thermal images of a 5 Ah MCC cell.\u003c/p\u003e\n\u003cp\u003eDuring the testing, the 5 Ah control cell exhibited minimal sparking upon nail penetration initially. When TR occurred in Test 2, there was almost no visible fire, but the entire test chamber filled with smoke shown in Fig. 8. 5 Ah Control Cell. Test 2 also showed high smoke levels with minimal fire for the that cell. Fig. 8. 10 Ah Control cell depicts the fire behavior of 10 Ah control cells during test 10, where a significant fire emerged similarly to the pattern observed in the 10 Ah MCC cells. Subsequently, an explosion occurred from the side of the cell between the tabs. This trend was consistent for both 10 Ah control cells.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.3. Gas Emission\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDuring the tests, gas emissions were captured using a gas analyser. Figure 9 shows the emitted gases for the 10 Ah cell. Figure 9 (a) contained the 10 Ah MCC cell emitted gas data for test 6, and Figure 9 (b) displayed the data for the 10 Ah control cell from test 10. From the plot, it was observed that carbon monoxide (CO) was the dominant gas emitted. For the MCC cell, CO emission was around 800 ppm, while for the control cell, it was approximately 600 ppm. This difference in CO levels could be due to the material composition and reaction pathways of the MCC, which might produce more CO due to incomplete combustion or localized hotspots. The control cell, lacking these modifications, might undergo more uniform heat distribution and combustion, leading to lower CO emissions. Other emitted gases, such as nitrogen monoxide (NO), ethylene (C₂H₄), diethyl carbonate (C₅H₁₀O₃), dimethyl carbonate (C₃H₆O₃), ethyl methyl carbonate (C₄H₈O₃), and propylene carbonate (C₄H₆O₃), all had emissions in the range of 200 ppm or below for the MCC cell. For the control cell, these emissions were around 150 ppm. Again this difference in emission levels may be due to the material composition and thermal stability of the MCC cells, which could lead to the formation of more volatile organic compounds and nitrogen compounds during thermal degradation. The modified design of MCC cells might also create different thermal environments and gas retention dynamics that promote higher emissions of these gases. There was no significant emission of water vapor or carbon dioxide (CO₂).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2. Computed Tomography (CT) Scan\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA CT scan was conducted on the cell after the nail penetration test, following a discharge to a 0% state of charge (SOC). This scan was performed on the \u0026nbsp;5 Ah MCC cell from test 3. We did two CT scan, one with nail still inside and another after removal of nail from the cell. Figure 10 displays the CT scan image with the nail still embedded inside the cell. It was observed that while some cathode layers retracted from the nail, others did not, which potentially explains the occurrence of micro-shorts and the gradual voltage drop when the nail was present.\u003c/p\u003e\n\u003cp\u003eCaptured lateral, side and top views of CT scan over the cell can be found in Figure 11. This CT scan image is taken when the nail was not inside. This is taken to understand the internal structure, particularly around the nail penetration area. According to some researchers, upon nail penetration, the cathode layers retreat below the anode layers for MCC cell, preventing short circuits through the nail [25]. However, our experiment did not show this behaviour for most of the cathode layers. Specifically, as seen in the CT scan images, the bright cathode layers near the penetration site do not uniformly retreat beneath the light-grey anode layers. Instead, in the lateral and side views, the cathode layers appear to split apart in some regions, resembling a crocodile jaw, while maintaining contact in others. This incomplete retraction of cathode layers suggests the possibility of persistent micro-shorts, which likely contributed to the gradual voltage drop observed during the test. Additionally, the top view highlights a concentric pattern of structural deformation around the penetration site, further supporting the occurrence of localized disruptions in layer alignment without a consistent retreat of cathode layers beneath the anode.\u003c/p\u003e\n\u003cp\u003eThis phenomenon, where the light cathode layers did not retreat into the grey anode layers for all the layers, is evident in both lateral and side views of the nail-penetrated cell. The voltage profile of the nail-penetrated cell (described in section 3.1.1) showed a continuous drop in cell voltage upon nail penetration, with recovery over time after nail removal, which aligns with the CT scan results. The CT scan here indicates that a short circuit through the nail is possible.\u003c/p\u003e\n\u003ch2\u003e3.3. SEM and EDS\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eSEM and EDS analyses were performed on both the anode and cathode over the 5 Ah MCC cell from test 3. EDS analysis was specifically conducted at the electrode\u0026apos;s edge, directly at the site of\u0026nbsp;\u003c/p\u003e\n\u003cp\u003enail penetration, and at regions slightly removed from the penetration site. Additionally, cross-sectional SEM imaging was utilized to elucidate the structural composition of the cathode. This detailed investigation aimed to observe any morphological and compositional variations induced by mechanical penetration. The primary objective of this test was to determine whether an insulating layer had formed at the edge of the electrode adjacent to the nail penetration point. By comparing samples from near the edge and slightly away from the penetration site, we sought to identify and confirm the presence of any insulating layer, which could have significant implications for understanding the electrical and thermal behaviour of the electrode after NPT.\u003c/p\u003e\n\u003cp\u003eA TASCAN Clara (Libusina, Czech Republic) ultra-high-resolution scanning electron microscope (UHR-SEM) with a field emission gun electron source was utilized to capture SEM images. Standard stubs were prepared with double-sided conductive carbon tape, and each sample was meticulously positioned on the stubs. These stubs were then mounted on an SEM pin mount specimen holder, which was placed in the vacuum chamber. E-T detectors were employed during the image collection process.\u003c/p\u003e\n\u003ch3\u003e3.3.1. Cathode EDS Analysis\u003c/h3\u003e\n\u003cp\u003eThe primary differences observed between the samples are the elevated presence of aluminium in the edge sample, contrasted with higher percentages of nickel, carbon, fluorine, manganese, and cobalt in the surface sample. Figure 12 shows, that the aluminium concentration was significantly higher at the edge (23.1%) compared to the surface (0.1%). This disparity is anticipated, as the nail penetration exposes the current collector. However, this analysis does not reveal any insulating layer at the edge that could prevent short-circuiting through the nail. This absence of an insulating layer could be due to the limitations of the analytical techniques employed. The methods used, such as SEM and EDS, might not be sensitive enough to detect very thin or discontinuous polymeric insulating layers. Alternatively, it is also possible that no insulating layer exists at the edge, indicating that the conditions during the nail penetration did not favor the formation of such a layer.\u003c/p\u003e\n\u003ch3\u003e3.3.2. Anode SEM and EDS Analysis\u003c/h3\u003e\n\u003cp\u003eFig. 13 presents EDS analysis of the anode. Similar to the observations made for the cathode, a substantial amount of copper (11.3%) was detected at the edge where nail penetration occurred. This presence of copper likely results from the exposure of the current collector due to the nail\u0026nbsp;\u003c/p\u003e\n\u003cp\u003epenetration. However, as with the anode, the EDS analysis did not detect any insulation layer at the edge of the nail penetration point.\u003c/p\u003e\n\u003cp\u003eThe SEM image (Figure 14) revealed a notable presence of a white substance at the edge where nail penetration occurred. This white substance was absent on the surface, as shown in Figure 14 (b). For the cathode, we also did not detect any hypothesized insulating layer. And this could be again due to the limitations of the analytical techniques used. Jus like the case of anode, it is also possible that there is no insulating layer present at the edge of the ail penetration point.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3.3. Cross Sectional SEM Image\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA cross-sectional SEM image of the anode was obtained, revealing two layers of copper instead of a single, solid layer typically observed in current collectors. It is likely that an additional layer, possibly a polymer, is present between these two Cu layers. Figure 15 illustrates this configuration.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe study conducted on the TR risk of pouch cells equipped with MCC under mechanical abuse conditions provided valuable insights into the safety enhancements offered by the MCC technology. The NPTs revealed significant differences in the behaviour of 5 Ah and 10 Ah capacity cells.\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eFor the 5 Ah cells, the incorporation of MCC technology showed a marked improvement in safety performance. Only one out of the four MCC-equipped cells experienced TR, while all control cells without MCC underwent TR. This indicates that MCC technology has the capability of mitigating the risk of TR in lower-capacity cells. The MCC\u0026apos;s ability to prevent internal short circuits, likely due to its design incorporating PET demonstrates its effectiveness in enhancing cell safety under mechanical abuse.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eThe 10 Ah cells presented a contrasting scenario. All tested cells, irrespective of MCC technology, experienced TR. This outcome suggests that the MCC\u0026apos;s protective benefits observed in the 5 Ah cells do not apply to higher-capacity cells under similar testing conditions. The uniform TR occurrence in 10 Ah cells indicates that additional factors, such as increased energy density and associated thermal risks, may overshadow the MCC\u0026apos;s effectiveness.\u003c/li\u003e\n \u003cli\u003eThe CT scans conducted on a 5 Ah MCC cell following a nail penetration test revealed that while some cathode layers receded from the nail, others did not, potentially leading to micro-shorts and a gradual voltage drop. Contrary to previous results, most cathode layers did not recede below the anode layers upon penetration, aimed at preventing short circuits [17]. The voltage profile of the cell exhibited a continuous drop during nail penetration, followed by recovery upon nail removal, aligning with the CT scan findings suggesting a possible short circuit.\u003c/li\u003e\n \u003cli\u003eSEM and EDS analyses were performed on the cathode and anode surfaces of a battery cell after mechanical penetration, particularly nail penetration. Results showed increased aluminum concentration near the penetration site on the cathode and copper concentration on the anode, indicating current collector exposure. However, no insulating layer was detected at the penetration points. SEM imaging revealed a white substance at the anode penetration site, suggesting a reaction. Cross-sectional SEM imagery of the anode showed a complex structure with two copper layers, possibly indicating the presence of a polymer layer. These findings underscore the need for further investigation into safety and performance implications of mechanical penetration on battery cells.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThe experimental study demonstrated that MCC technology significantly enhances the safety of 5 Ah lithium-ion pouch cells by reducing the incidence of thermal runaway under mechanical abuse conditions. The MCC\u0026apos;s integration with PET effectively mitigates internal short circuits, preventing thermal runaway in lower-capacity cells. However, this benefit may not apply to higher-capacity 10 Ah cells, indicating a need for additional safety measures in larger energy storage systems. Further research is necessary to address the safety challenges in higher-capacity cells, which may involve modifications to both MCC technology and the separator. Understanding the factors contributing to these inconsistencies should be a priority for future research.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis project provided an excellent opportunity to deepen our understanding and expertise in assessing the safety performance of emerging technologies. The project was executed by the JLR Catapult project, and we extend our sincere gratitude to the JLR Catapult project for their invaluable support and for offering this wonderful research opportunity.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKim, T., et al., Lithium-ion batteries: outlook on present, future, and hybridized technologies. Journal of materials chemistry A, 2019. 7(7): p. 2942-2964. \u003cstrong\u003ehttps://doi.org/10.1039/C8TA10513H\u003c/strong\u003e\u003c/li\u003e\n\u003cli\u003eLu, Y.,Q.Zhang, and J.Chen, Recent progress on lithium-ion batteries with high electrochemical performance. Science China Chemistry, 2019. 62:p. 533-548.https://doi.org/10.1007/s11426-018-9410-0\u003c/li\u003e\n\u003cli\u003eSahana, M.B. and R. Gopalan, Recent developments in electrode materials for lithium-ion batteries for energy storage application. Handbook of Advanced Ceramics and Composites: Defense, Security, Aerospace and Energy Applications, 2020: p. 1297-1333. https://doi.org/10.1007/978-3-030-16347-1_44\u003c/li\u003e\n\u003cli\u003eZhang, H., C. Mao, J. Li, and R. Chen, Advances in electrode materials for Li-based rechargeable batteries. RSC advances, 2017. 7(54): p. 33789-33811. 10.1039/C7RA04370H\u003c/li\u003e\n\u003cli\u003eHu, X., et al., Advancements in the safety of Lithium-Ion Battery: The Trigger, consequence and mitigation method of thermal runaway. Chemical Engineering Journal, 2024: p. 148450. https://doi.org/10.1016/j.cej.2023.148450\u003c/li\u003e\n\u003cli\u003eXiao, Y., et al., Staged thermal runaway behaviours of three typical lithium-ion batteries for hazard prevention. Journal of Thermal Analysis and Calorimetry, 2024: p. 1-13. https://doi.org/10.1007/s10973-024-13080-0\u003c/li\u003e\n\u003cli\u003eLiu, K., et al., Materials for lithium-ion battery safety. Science advances, 2018. 4(6): p. eaas9820. https://doi.org/10.1126/sciadv.aas9820\u003c/li\u003e\n\u003cli\u003eXu, B., et al., Mitigation strategies for Li-ion battery thermal runaway: A review. Renewable and Sustainable Energy Reviews, 2021. 150: p. 111437. https://doi.org/10.1016/j.rser.2021.111437\u003c/li\u003e\n\u003cli\u003eArora, S. and A. Kapoor, Mechanical design and packaging of battery packs for electric vehicles. Behaviour of Lithium-Ion Batteries in Electric Vehicles: Battery Health, Performance, Safety, and Cost, 2018: p. 175-200. https://doi.org/10.1007/978-3-319-69950-9_8\u003c/li\u003e\n\u003cli\u003eWidyantara, R.D., et al., Review on battery packing design strategies for superior thermal management in electric vehicles. Batteries, 2022. 8(12): p. 287. https://doi.org/10.3390/batteries8120287\u003c/li\u003e\n\u003cli\u003eMyung, S.-T., Y. Hitoshi, and Y.-K. Sun, Electrochemical behavior and passivation of current collectors in lithium-ion batteries. Journal of Materials Chemistry, 2011. 21(27): p. 9891-9911. \u003cstrong\u003ehttps://doi.org/10.1039/C0JM04353B\u003c/strong\u003e\u003c/li\u003e\n\u003cli\u003eLu, L.-L., et al., Free-standing copper nanowire network current collector for improving lithium anode performance. Nano letters, 2016. 16(7): p. 4431-4437. https://doi.org/10.1021/acs.nanolett.6b01581\u003c/li\u003e\n\u003cli\u003eLopez, C.F., J.A. Jeevarajan, and P.P. Mukherjee, Experimental analysis of thermal runaway and propagation in lithium-ion battery modules. Journal of the electrochemical society, 2015. 162(9): p. A1905. \u003cstrong\u003eDOI\u003c/strong\u003e 10.1149/2.0921509jes\u003c/li\u003e\n\u003cli\u003eZheng, S., L. Wang, X. Feng, and X. He, Probing the heat sources during thermal runaway process by thermal analysis of different battery chemistries. 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Investigating the Ability of Plastic Current Collectors to Isolate Internal Shorts in High Energy Cells. in 4th International Battery Safety Workshop (IBSW). 2023.\u003c/li\u003e\n\u003cli\u003eHu, W., Y. Peng, Y. Wei, and Y. Yang, Application of electrochemical impedance spectroscopy to degradation and aging research of lithium-ion batteries. The Journal of Physical Chemistry C, 2023. 127(9): p. 4465-4495. https://doi.org/10.1021/acs.jpcc.3c00033\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"fire-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"fire","sideBox":"Learn more about [Fire Technology](http://link.springer.com/journal/10694)","snPcode":"10694","submissionUrl":"https://submission.springernature.com/new-submission/10694/3","title":"Fire Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Battery Safety, Pouch Cell, Modified Current Collector, Nail Penetration Test, Thermal Runaway","lastPublishedDoi":"10.21203/rs.3.rs-8296559/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8296559/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"This work presents an experimental study to evaluate the thermal runaway (TR) risk of pouch cells with modified current collectors (MCCs), which incorporate polyethylene terephthalate (PET) for mitigating internal short circuits and further preventing TR. Two types of cells, with capacities of 5 Ah and 10 Ah, were adopted and subjected to nail penetration tests. The results showed that the 5 Ah MCC cells exhibited improved safety, with only one out of four undergoing TR, compared to both control cells without MCCs experiencing TR. In contrast, all 10 Ah cells, including those with MCCs, experienced TR, indicating that the MCC's protective benefits may not apply to higher-capacity cells under similar test conditions. Comprehensive post-mortem analyses, including computed tomography (CT) scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), were performed to assess the internal structural and compositional changes. The findings indicate that MCC technology significantly reduces TR risk in lower-capacity cells, while additional safety measures may be requited for the higher-capacity cells . This study highlights the potential of MCC technology to enhance battery safety and underscores the need for further research to address safety challenges in emerging battery technologies.","manuscriptTitle":"Thermal runaway risk assessment of pouch cells with modified current collectors under mechanical abuse","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-31 09:35:17","doi":"10.21203/rs.3.rs-8296559/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-02-21T02:07:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"312022763461105853963000836601823997601","date":"2026-01-30T08:09:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"120651785892724053120427912527877023969","date":"2026-01-30T06:16:45+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-29T10:38:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-26T15:59:38+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-11T11:41:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Fire Technology","date":"2025-12-06T19:17:29+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"fire-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"fire","sideBox":"Learn more about [Fire Technology](http://link.springer.com/journal/10694)","snPcode":"10694","submissionUrl":"https://submission.springernature.com/new-submission/10694/3","title":"Fire Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4e26103d-837a-4deb-b1be-ad5c70ab2d51","owner":[],"postedDate":"December 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-12-31T09:35:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-31 09:35:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8296559","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8296559","identity":"rs-8296559","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}