Thermal runaway (TR), characterized by rapid exothermic reactions, presents a serious safety risk in lithium-ion batteries (LiBs). External triggers such as high temperatures, mechanical abuse, or internal short circuits (ISCs) can initiate TR, often resulting in sidewall rupture, which may escalate to catastrophic battery pack failure. In this study, we developed and applied high-speed synchrotron imaging techniques to investigate sidewall rupture mechanisms in LiBs subjected to different triggering scenarios. Using in situ 4D tomographic imaging, we visualized the dynamic evolution of sidewall rupture with high spatial and temporal resolution. The results revealed distinct failure behaviors linked to each trigger, underscoring the complex and condition-specific nature of sidewall breach and battery failure. These insights highlight the critical importance of implementing tailored safety strategies across diverse applications. Our findings demonstrate the powerful potential of synchrotron high-speed tomography as a diagnostic tool for advanced safety testing and cell qualification.

Understanding lithium-ion battery (LIB) degradation pathways and failure mechanisms is essential given the rare but potentially severe associated hazards. Recent regulations on thermal runaway prevention are driving the need for advanced early detection diagnostic techniques. Acoustic methods, including Acoustic Emission (AE) and Ultrasonic Testing (UT), are promising operando monitoring tools owing to their cost-effectiveness, non-invasive nature, and real-time capability to detect physical and electrochemical changes within cells. This study demonstrates the first use of AE as a diagnostic tool for monitoring stateof-health (SoH), state of safety, and early failure onset. AE measurements were correlated with high-speed synchrotron X-ray radiography, linking acoustic signals to real-time physical changes such as gas formation, cell-volume expansion, and cracking. Experiments across a range of SoC and SoH, covering pristine, aged, and cells cycled below 0 ºC, highlight the robustness of the approach. Machine learning algorithms trained across multiple chemistries and formats enabled real-time signal interpretation. AE reliably identified degradation mechanisms and issued failure alerts across a spectrum of severity, 2 including in lithium-plated cells, with synchrotron imaging confirming the physical origin of key signals. Integrating AE into battery management systems could significantly enhance LIB safety across automotive, grid storage, and manufacturing applications without compromising cost.

While supercapacitors are widely considered to be safer than current lithium-ion battery technologies, their reputation for safety, stability, and long cycling lifetimes is primarily based on their testing under highly favourable electrochemical and environmental conditions. However, the impact of extreme conditions on even the most common Electrochemical Double Layer Capacitors (EDLCs) remains unclear, limiting the understanding of their potential failure mechanisms and the risks they could present to individuals and systems into which they are increasingly being integrated. In this study, we investigate the effects of thermal abuse conditions, induced by overheating and overcharging, on a typical commercial EDLC. Our findings reveal that while EDLC cell failures are less extreme than the well-documented failures of Li-ion batteries, they still pose significant risks to the integrity of the cell itself and the direct environment. This is most evident from the fact that between the overheating and overcharging tests, more than half of all the cells tested in this study failed catastrophically, leading to an explosive event. The high cell temperatures induced by these abusive tests led to electrolyte vaporisation and cell gassing that was not effectively mitigated by cell vent designs. This study therefore challenges the perception of intrinsic supercapacitor safety and provides a foundation onto which safer system designs can be built.

The operation of lithium-ion cells at sub-zero temperatures can result in the deposition of metallic lithium onto the surface of the negative electrode. The resulting lithium deposits have substantial ramifications for the performance and safety of the cell, with rapid capacity fade and reduced thermal stability both exhibited in cells aged under these conditions. In this study, it is found that extending the cycling temperatures of these cells to sub-zero temperatures results in a change in plating behaviour, with cells cycled at-10 degrees C exhibiting reversible plating behaviour and cells cycled at-20 degrees C plating irreversibly instead. Additionally, the nature of the plating is observed to transition from reversible to irreversible with progressive ageing in the cells cycled at-10 degrees C. Using operando electrochemical analysis such as voltage relaxation and Coulombic efficiency (CE) measurement, characteristics of the degradation are revealed. Electrochemical impedance spectroscopy (EIS) is also employed between cycles to provide information on the changes in internal cell processes due to plating. Ex-situ investigations complement the analysis allowing images of electrode condition to be collected. In-situ X-ray computed tomography further highlights how lithium plating compromises the structural integrity of the internal cell architecture, leading to increased safety concerns. Testing the aged cells with accelerated rate calorimetry also shows that the presence of more strongly reductive metallic lithium within a cell results in lower onset temperatures for self-heating and thermal runaway, plus an increased potential for projectiles during failure.

Thermal Runaway (TR) in lithium-ion batteries (LIB) is a critical technological and social concern. Whilst such events are rare, TR is characterized by uncontrollable heating leading to catastrophic failures. To deepen the understanding of the failure process and subsequently develop more accurate TR prediction models and as a result safer battery systems, we present in this work high-speed X-ray tomography for in-depth investigations of the copper current collector melting and agglomeration during TR. The melting process presents valuable real-time internal information about heat evolution during TR, previously challenging to access but crucially important for validating TR models. In this work, controlled failure studies combined with high-speed X-ray tomography were performed on two different commercial LIB models, subjecting them to both external heating and nail penetration to induce TR. Through real-time observation via high-speed tomography, followed by segmentation, rendering, and analysis, the formation of copper agglomerates was qualitatively and quantitatively characterized and visualized for the first time. Agglomerates tended to form either from the battery’s outermost layers or centrally, depending on the method of TR initiation, and gives an indirect insight into the internal temperature evolution and distribution. Moreover, an initial comparative analysis between the battery models also revealed differences in agglomerate size, which has been linked to the thicker copper current collectors of one of the cell models. We further discuss the impact of larger copper agglomerates on heat distribution and safety. This study not only sheds light on the intricate dynamics of TR in LIBs but also underscores the pivotal role of ’gold-standard’ imaging techniques in advancing battery safety, crucial for the robust modeling of TR and the future design of electric vehicle safety systems.

The thermal response of Li-ion cells can greatly vary for identical cell designs tested under identical conditions, the distribution of which is costly to fully characterize experimentally. The open-source Battery Failure Databank presented here contains robust, high-quality data from hundreds of abuse tests spanning numerous commercial cell designs and testing conditions. Data was gathered using a fractional thermal runaway calorimeter and contains the fractional breakdown of heat and mass that was ejected, as well as high-speed synchrotron radiography of the internal dynamic response of cells during thermal runaway. The distribution of thermal output, mass ejection, and internal response of commercial cells are compared for different abuse-test conditions, which when normalized on a per amp-hour basis show a strong positive correlation between heat output from cells, the fraction of mass ejected from the cells, their energy- and power-density. Ejected mass was shown to contain 10× more heat per gram than non-ejected mass. The causes of ‘outlier’ thermal and ejection responses i.e., extreme cases, are elucidated by high-speed radiography which showed how occurrences such as vent clogging can create more hazardous conditions. High-speed radiography also demonstrated how the time-resolved interplay of thermal runaway propagation and mass ejection influences the total heat generated.

As the EV and battery market continues to grow, understanding and mitigating battery thermal runaway remains a critically important area of research. Under controlled experimental conditions, researchers have employed a range of different techniques to initiate battery fires and understand both how and why they occur. These tests give important information about how a battery cell catastrophically fails under abuse conditions. However, recognizing the changes in the internal structure of the cell is vital to understanding the mechanisms of thermal runaway which enables the development of effective mitigation strategies. During the last decade, X-ray imaging has emerged as an important diagnostic tool for battery degradation, electrochemical performance, and safety diagnostics. Researchers use X-ray imaging to directly observe the internal changes in the cell during all stages of thermal runaway. Depending on the initiation method, it can sometimes take minutes, hours, or days for a cell to undergo failure. However, the actual final reactions that cause thermal runaway occur over fractions of a second. High-speed cameras, operating at up to 40,000 frames per second, can capture the interactions between electrodes at the final moments of thermal runaway. In this article, the basics of high-speed X-ray imaging and how this technique has been applied to investigating battery thermal runaway are discussed.

Lithium-ion batteries are at the forefront of facilitating the modern-day industrial revolution: a transition from petrochemical energy storage to specialised carbon-free energy storage. Batteries hold a crucial role in storing energy generated by renewables outside of peak energy demands, whilst also enabling an extended portable energy supply for applications such as electronic devices, aerospace applications and electric vehicles. Increasing the energy densities of our batteries is one of the main avenues these technologies are taking to ensure the demands of the green transition are met. In recent years, numerous high-profile failures of lithium-ion batteries have been reported1, contributing to wider concerns about the safety of high energy density cells. Inadequate management of such systems can be costly for both human health and financial damages. To accommodate these more energy-dense cells, manufacturers need to provide better assurances in safe cell operations. Apprehensions in cell safety can mainly be attributed to a cell’s ability to enter thermal runaway, a process that is most often caused by an internal short circuit (ISC). Such an event can be triggered by three different modes of abuse: thermal, mechanical, and electrical. At the anode, metallic lithium can precipitate onto the surface via three main conditions: overcharge, high charging currents, and low charging temperatures. Each of which creates a saturation of intercalated lithium-ions in the crystallographic active sites near the anode surface. This lowers the anodes surface potential until it is sufficiently low enough for lithium plating to occur. This work investigates cell function at low temperatures and how the resulting degradation affects their response to abusive conditions. Various ageing regimes were applied to a set of commercial lithium-ion cells and, by monitoring their electrochemical behaviour, carrying out ex-situ characterisation of the aged negative electrodes, and employing X-ray computed tomography (CT), this work evaluates the decline in performance observed at low temperatures. Subsequent accelerated rate calorimetry (ARC) and operando ultra-high-speed synchrotron tomography studies highlight the diminished thermal stability these aged cells possess as the states of degradation become more advanced and reveal the mechanisms through which failure occurs. These findings demonstrate why improved cell architecture and real-time management systems are necessary to realise commercial success in future battery applications. Figure 1

Previous research on transistor gate oxides reveals a clear link between hydrogen content and oxide breakdown. This has implications for redox-based resistive random access memory (ReRAM) devices, which exploit soft, reversible, dielectric breakdown, as hydrogen is often not considered in modeling or measured experimentally. Here quantitative measurements, corroborated across multiple techniques are reported, that reveal ReRAM devices, whether manufactured in a university setting or research foundry, contain concentrations of hydrogen at levels likely to impact resistance switching behavior. To the knowledge this is the first empirical measurement depth profiling hydrogen concentration through a ReRAM device. Applying a recently-developed Secondary Ion Mass Spectrometry analysis technique enables to measure hydrogen diffusion across the interfaces of SiOx ReRAM devices as a result of operation. These techniques can be applied to a broad range of devices to further understand ReRAM operation. Careful control of temperatures, precursors, and exposure to ambient during fabrication should limit hydrogen concentration. Additionally, using thin oxynitride or TiO2 capping layers should prevent diffusion of hydrogen and other contaminants into devices during operation. Applying these principles to ReRAM devices will enable considerable, informed, improvements in performance.

Acoustic emission (AE) is a low-cost, non-invasive, and accessible diagnostic technique that uses a piezoelectric sensor to detect ultrasonic elastic waves generated by the rapid release of energy from a localised source. Despite the ubiquity of the cylindrical cell format, AE techniques applied to this cell type are rare in literature due to the complexity of acoustic wave propagation in cylindrical architectures alongside the challenges associated with sensor coupling. Here, we correlate the electrochemical performance of cells with their AE response, examining the differences during pristine and aged cell cycling. AE data was obtained and used to train various supervised binary classifiers in a supervised setting, differentiating pristine from aged cells. The highest accuracy was achieved by a deep neural network model. Unsupervised machine learning (ML) models, combining dimensionality reduction techniques with clustering, were also developed to group AE signals according to their form. The groups were then related to battery degradation phenomena such as electrode cracking, gas formation, and electrode expansion. There is the potential to integrate this novel ML-driven approach for widespread cylindrical cell testing in both academic and commercial settings to help improve the safety and performance of lithium-ion batteries.

The roadmap is organized into several thematic sections, outlining current computing challenges, discussing the neuromorphic computing approach, analyzing mature and currently utilized technologies, providing an overview of emerging technologies, addressing material challenges, exploring novel computing concepts, and finally examining the maturity level of emerging technologies while determining the next essential steps for their advancement.

Battery safety design is important to consider from the individual Li-ion cell to the level of the macro-system. On the macro-level, failure in one single cell can lead to propagation of the thermal runaway and rapidly set a whole battery pack on fire. Factors that can impact the propagation outcome, such as cell model/chemistry and electrical connection are here investigated using a combination of measurements. Several abusive tests were conducted, combining two different cell models (Molicel P42A and LG M50, both 21700s) in series and parallel connections (16 tests per configuration). Overall, a propagation outcome of 56% was measured from the 32 conducted tests, a minimum temperature of 150 °C was required to initiate propagation, and the fastest propagation occurred in 123 s. Temperature measurements were higher in series connected cells, initiating the discussion of cell chemistry and internal resistance on this effect. The difference in current-flow during thermal runaway in series and parallel connections, and how this can affect the temperature evolution is further discussed. Spatio-temporal mapping of X-ray radiography allowed us to derive the speed of thermal runaway evolution inside the battery and has shown that series connected cells, in particular P42A, occur faster. It was further observed that deviant sidewall behaviors such as temperature-induced breaches and pressure-induced ruptures occurred in P42As only respective nail-penetrated cells only.

The investigation of lithium-ion battery failures is a major challenge for personnel and equipment due to the associated hazards (thermal reaction, toxic gases and explosions). To perform such experiments safely, a battery abuse-test chamber has been developed and installed at the microtomography beamline ID19 of the European Synchrotron Radiation Facility (ESRF). The chamber provides the capability to robustly perform in situ abuse tests through the heat-resistant and gas-tight design for flexible battery geometries and configurations, including single-cell and multi-cell assemblies. High-speed X-ray imaging can be complemented by supplementary equipment, including additional probes (voltage, pressure and temperature) and thermal imaging. Together with the test chamber, a synchronization graphical user interface was developed, which allows an initial interpretation by time-synchronous visualization of the acquired data. Enabled by this setup, new meaningful insights can be gained into the internal processes of a thermal runaway of current and future energy-storage devices such as lithium-ion cells.

Lithium-ion battery safety continues to be an obstacle for electric vehicles and electrified aerospace. Cell failure must be studied in order to engineer improved cells, battery packs and management systems. In this work, the thermal runaway of commercially available, high-power cells is studied, to understand the optimal areas to develop mitigation strategies. Accelerating rate calorimetry is coupled with mass spectrometry to examine self-heating and the corresponding evolution of gases. A statistical analysis of cell failure is then conducted, combined with post-mortem examinations. The methodology forms a robust assessment of cell failure, including the expected worst- and best-cases, and the associated real-world hazards. Cells produce a highly flammable, toxic gas mixture which varies over the course of self-heating. Failure also produces particulate matter which poses a severe health hazard. Critically, the onset of self-heating is detectable more than a day in advance of full thermal runaway. Likewise, voltage drops and leaks are detectable prior to venting, highlighting the potential for highly effective early onset detection. Furthermore, the behaviour of the cap during thermal runaway indicates that ejection of material likely reduces the chance of thermal runaway propagation to neighbouring cells. These findings also emphasise that research must be conducted safely.

With the rapid deployment of Li-ion batteries (LiBs) in a range of applications, it is crucial to ensure their safe operation. Therefore, it is necessary to investigate the rapid thermal runaway failure that LiBs can undergo if improperly operated or subjected to abuse scenarios so that hazardous events can be avoided or mitigated. Sidewall breaches or ruptures of LiBs during thermal runaway are considered the most hazardous failure scenario, resulting in hot abrasive flare from the casing of the cell that can impinge on neighbouring cells and lead to the propagation of thermal runaway throughout a battery pack. Yet, the process leading up to the sidewall breach is not well understood due to the extreme difficulty in visualizing such a failure in commercially relevant cells. With the application of a newly developed chamber for remote-controlled abuse testing of batteries coupled with simultaneous X-ray imaging, we demonstrate here for the first time an in-situ visualization of a sidewall breach. By further applying spatiotemporal mapping techniques, the internal thermal runaway events leading up to the sidewall breach can be analyzed in detail. Subsequently, the speed of the electrode layer delamination could be calculated to a speed of 0.6 m/s. These new insights bring more clarity regarding this phenomenon, that in turn can help battery designers improve battery safety.

In recent years, the use of disposable electric (e)-cigarettes containing lithium-ion batteries in the UK has led to remarkable wastage, the full environmental impact of which is yet to be realized. This study investigates the suitability for reuse and safety aspects of cells found in disposable e-cigarettes. Through electrochemical and safety characterization techniques, the cells' performance and hazards were evaluated. Rate capability and long-term cycling experiments showed that cells sold as disposable were capable of completing 474 cycles at 1C charge/discharge before reaching 80% capacity fade. A nail penetration test revealed significant gas expulsion and a maximum temperature of 495 degrees C. However, the cell format prevented significant material ejection. This work out-lines the potential health hazards and highlights the possibility for second-life use of disposable e-cigarette cells, shedding light on the environmental impact and safety considerations.

Filamentary resistance switching, or ReRAM, devices based on oxides suffer from device-do-device and cycle-to-cycle variability of electrical characteristics (electroforming voltages, set and reset voltages, resistance levels and cycling endurance). These are largely materials issues related to the microstructure of the switching oxide. Here we outline strategies to engineer the electrical performance of silicon oxide ReRAM by controlling the oxide microstructure at the nanometre scale through approaches including engineered interfaces and ion implantation. We demonstrate control over the distribution of switching voltages, electroforming voltages, and stable multilevel resistance states.

Abuse testing of lithium-ion batteries is widely performed in order to develop new safety standards and strategies. However, testing methodologies are not standardised across the research community, especially with failure mechanisms being inherently difficult to reproduce. High-speed X-ray radiography is proven to be a valuable tool to capture events occurring during cell failure, but the observations made remain largely qualitative. We have therefore developed a robust image processing toolbox that can quantify, for the first time, the rate of propagation of battery failure mechanisms revealed by high-speed X-ray radiography. Using Gabor filter, the toolbox selectively tracks the electrode structure at the onset of failure. This facilitated the estimation of the displacement of electrodes undergoing abuse via nail penetration, and also the tracking of objects, such as the nail, as it propagates through a cell. Further, by cross-correlating the Gabor signals, we have produced practical, illustrative spatiotemporal maps of the failure events. From these, we can quantify the propagation rates of electrode displacement prior to the onset of thermal runaway. The highest recorded acceleration (≈ 514 mm s-2) was when a nail penetrated a cell radially (perpendicular to the electrodes) as opposed to axially (parallel to the electrodes). The initiation of thermal runaway was also resolved in combination with electrode displacement, which occurred at a lower acceleration (≈ 108 mm s-2). Our assistive toolbox can also be used to study other types of failure mechanisms, extracting otherwise unattainable kinetic data. Ultimately, this tool can be used to not only validate existing theoretical mechanical models, but also standardise battery failure testing procedures.