Ofodike A. Ezekoye

ABSTRACT Thermochemical characterization of battery materials links intrinsic material properties to decomposition pathways, heat generation, and gas evolution that govern performance and safety. Despite extensive work on NMC811‐Graphite, variability across partial configurations and the limited adoption of micro‐cell architectures (cathode+anode+electrolyte+separator) hinder robust cell‐scale interpretation. Accordingly, this work establishes a bottom‐up, component‐resolved methodology integrating DSC/TGA, evolved gas analysis (EGA), and in situ XRD to link decomposition pathways and energy release across partial and micro‐cell configurations, providing a transferable assessment of safety and stability in emerging chemistries. In separator‐free configurations, the gas–solid reaction between cathode‐evolved and anode‐leached Li dominates the net heat release (1139 J ). In contrast, in the micro‐cell configuration, the separator hinders transport and alters the timing and pathways of other reactions, and reduces the net energy release to 618 J . Energy release was organized into defined temperature windows that provide a framework for a thermodynamic model combining quantified gas evolution with selected decomposition pathways and effective reaction enthalpies to estimate net specific energy release, with agreement between DSC and cell‐level tests. Ex situ XPS of heat‐treated samples extends post‐mortem analysis to thermal‐abuse regimes, supporting key pathway elements.

Lithium-ion batteries (LIBs) undergoing thermal runaway vent a complex mixture of particles alongside condensable and non-condensable gases. These emissions may ignite or remain unignited, potentially producing a broader range of species. This study presents experimental data and physical insights into the coupled behavior of vented gases and aerosol particles emitted from cylindrical 18650-format LIBs. Thermal abuse experiments were first conducted with near-source measurements of gases and aerosol particles, providing a benchmark for condensable gas characterization. The near-source sampling configuration featured short residence times and a high air change rate. The cell thermal abuse test was then conducted in a poorly ventilated, reduced-scale room, resulting in longer gas and particle residence times. These conditions more closely represent enclosed environments such as residences or aircraft cabins and enable investigation of aerosol particle growth dynamics under confinement. In both configurations, aerosol particles smaller than 0.5 µm dominate number concentrations. Following thermal runaway, the aerosol particle number size distribution broadens, with increases in geometric mean and mode diameters. The reduced-scale room experiments reveal aerosol particle growth driven by electrolyte solvent condensation and coagulation. Notably, an increase in aerosol particle number concentration after direct cell emissions ceased is observed only in the reduced-scale room configuration. To interpret these observations, a simplified moment-based general dynamic equation model for aerosol evolution is applied to experimental data. By linking observed size distribution changes to condensation, coagulation, and sedimentation processes, this work connects fundamental battery venting mechanisms to exposure, safety, and mitigation considerations in enclosed spaces. Copyright © 2026 American Association for Aerosol Research

Lithium-ion batteries (LIBs) undergoing thermal runaway vent a complex mixture of particles alongside condensable and non-condensable gases. These emissions may ignite or remain unignited, potentially producing a broader range of species. This study presents experimental data and physical insights into the coupled behavior of vented gases and aerosol particles emitted from cylindrical 18650-format LIBs. Thermal abuse experiments were first conducted with near-source measurements of gases and aerosol particles, providing a benchmark for condensable gas characterization. The near-source sampling configuration featured short residence times and a high air change rate. The cell thermal abuse test was then conducted in a poorly ventilated, reduced-scale room, resulting in longer gas and particle residence times. These conditions more closely represent enclosed environments such as residences or aircraft cabins and enable investigation of aerosol particle growth dynamics under confinement. In both configurations, aerosol particles smaller than 0.5 µm dominate number concentrations. Following thermal runaway, the aerosol particle number size distribution broadens, with increases in geometric mean and mode diameters. The reduced-scale room experiments reveal aerosol particle growth driven by electrolyte solvent condensation and coagulation. Notably, an increase in aerosol particle number concentration after direct cell emissions ceased is observed only in the reduced-scale room configuration. To interpret these observations, a simplified moment-based general dynamic equation model for aerosol evolution is applied to experimental data. By linking observed size distribution changes to condensation, coagulation, and sedimentation processes, this work connects fundamental battery venting mechanisms to exposure, safety, and mitigation considerations in enclosed spaces. Copyright © 2026 American Association for Aerosol Research

Lithium-ion batteries (LIBs) undergoing thermal runaway vent a complex mixture of particles alongside condensable and non-condensable gases. These emissions may ignite or remain unignited, potentially producing a broader range of species. This study presents experimental data and physical insights into the coupled behavior of vented gases and aerosol particles emitted from cylindrical 18650-format LIBs. Thermal abuse experiments were first conducted with near-source measurements of gases and aerosol particles, providing a benchmark for condensable gas characterization. The near-source sampling configuration featured short residence times and a high air change rate. The cell thermal abuse test was then conducted in a poorly ventilated, reduced-scale room, resulting in longer gas and particle residence times. These conditions more closely represent enclosed environments such as residences or aircraft cabins and enable investigation of aerosol particle growth dynamics under confinement. In both configurations, aerosol particles smaller than 0.5 µm dominate number concentrations. Following thermal runaway, the aerosol particle number size distribution broadens, with increases in geometric mean and mode diameters. The reduced-scale room experiments reveal aerosol particle growth driven by electrolyte solvent condensation and coagulation. Notably, an increase in aerosol particle number concentration after direct cell emissions ceased is observed only in the reduced-scale room configuration. To interpret these observations, a simplified moment-based general dynamic equation model for aerosol evolution is applied to experimental data. By linking observed size distribution changes to condensation, coagulation, and sedimentation processes, this work connects fundamental battery venting mechanisms to exposure, safety, and mitigation considerations in enclosed spaces.Copyright © 2026 American Association for Aerosol Research

Improvements in lithium-ion battery (LIB) safety rely on understanding the thermal runaway failure of the cells. Thermal abuse tests are done on LIBs to study their exothermic reaction kinetics and gaseous hazards. Typically, testing is conducted in either pressure vessels or accelerating rate calorimetry (ARC) systems. These experimental systems are often used with little cleaning between tests, raising questions about whether the accumulated or adhered vented products pose respiratory and other health concerns. Also, the guidelines on personal protective equipment (PPE) for researchers often do not specifically address hazards associated with LIB thermal abuse tests. There is a relative lack of data on what species might be re-emitted from these experimental systems and how standard PPE reduces exposure to any off-gassed species. To help answer some of these questions, this paper characterized gas emissions from a vessel containing LIB residue post-thermal runaway, detecting species including electrolyte solvents, dimethylcyclosiloxanes, and other low-volatility organic compounds. The most abundant species were ethylene carbonate (39 ppb) and propylene carbonate (34 ppb). None of the species concentrations from this well-ventilated vessel posed acute toxicity, but repeated exposure may result in chronic health impacts. Fabric samples from clothes exposed to the vessel headspace re-emit the adsorbed gases, which extends the duration of inhalation exposure for individuals. The low volatility of the species was further supported by partition coefficient values above one, indicating their persistence and dermal exposure risks. Respirator effectiveness against gases evolved from LIB residue was investigated. Suggestions on improving worker safety were given based on the results of this paper.

Improvements in lithium-ion battery (LIB) safety rely on understanding the thermal runaway failure of the cells. Thermal abuse tests are done on LIBs to study their exothermic reaction kinetics and gaseous hazards. Typically, testing is conducted in either pressure vessels or accelerating rate calorimetry (ARC) systems. These experimental systems are often used with little cleaning between tests, raising questions about whether the accumulated or adhered vented products pose respiratory and other health concerns. Also, the guidelines on personal protective equipment (PPE) for researchers often do not specifically address hazards associated with LIB thermal abuse tests. There is a relative lack of data on what species might be re-emitted from these experimental systems and how standard PPE reduces exposure to any off-gassed species. To help answer some of these questions, this paper characterized gas emissions from a vessel containing LIB residue post-thermal runaway, detecting species including electrolyte solvents, dimethylcyclosiloxanes, and other low-volatility organic compounds. The most abundant species were ethylene carbonate (39 ppb) and propylene carbonate (34 ppb). None of the species concentrations from this well-ventilated vessel posed acute toxicity, but repeated exposure may result in chronic health impacts. Fabric samples from clothes exposed to the vessel headspace re-emit the adsorbed gases, which extends the duration of inhalation exposure for individuals. The low volatility of the species was further supported by partition coefficient values above one, indicating their persistence and dermal exposure risks. Respirator effectiveness against gases evolved from LIB residue was investigated. Suggestions on improving worker safety were given based on the results of this paper.

Improvements in lithium-ion battery (LIB) safety rely on understanding the thermal runaway failure of the cells. Thermal abuse tests are done on LIBs to study their exothermic reaction kinetics and gaseous hazards. Typically, testing is conducted in either pressure vessels or accelerating rate calorimetry (ARC) systems. These experimental systems are often used with little cleaning between tests, raising questions about whether the accumulated or adhered vented products pose respiratory and other health concerns. Also, the guidelines on personal protective equipment (PPE) for researchers often do not specifically address hazards associated with LIB thermal abuse tests. There is a relative lack of data on what species might be re-emitted from these experimental systems and how standard PPE reduces exposure to any off-gassed species. To help answer some of these questions, this paper characterized gas emissions from a vessel containing LIB residue post-thermal runaway, detecting species including electrolyte solvents, dimethylcyclosiloxanes, and other low-volatility organic compounds. The most abundant species were ethylene carbonate (39 ppb) and propylene carbonate (34 ppb). None of the species concentrations from this well-ventilated vessel posed acute toxicity, but repeated exposure may result in chronic health impacts. Fabric samples from clothes exposed to the vessel headspace re-emit the adsorbed gases, which extends the duration of inhalation exposure for individuals. The low volatility of the species was further supported by partition coefficient values above one, indicating their persistence and dermal exposure risks. Respirator effectiveness against gases evolved from LIB residue was investigated. Suggestions on improving worker safety were given based on the results of this paper.

Characterizing thermal runaway propagation (TRP) within a module and racks of modules is critical for the design of compartment-level safety systems. However, there is a dearth of large-scale experimental data. This study investigated TRP in a 14-cell, 5.5 kWh prismatic nickel–manganese–cobalt oxide module in which 94-Ah cells were not in direct contact with each other. Unlike most TRP tests, in this cell arrangement radiation is the dominant heat transfer process driving TRP. Two types of experiments were conducted: (i) single-cell failure tests in a pressure vessel and open air to estimate the generated vent-gas volume and mass loss of the cells and (ii) whole-module tests performed either on a stand without confinement or in a confined rack with dummy modules. Interior compartment temperature and heat flux data were also obtained to assess TRP-driven compartment-level response. For the single-cell testing, the average vent-gas volume per cell was 238 L at a reference condition of 300 K and 1 atm, and the average mass loss was approximately 0.9 kg during intense venting. For the module tests, although per-cell TR-onset times differed across runs by up to $$\sim$$ 300 s due to variability in the test systems, the total propagation time converged to $$\sim$$ 1000 s in all module tests. The TRP rate accelerated progressively, as an increasing number of failed cells and the module housing fire convectively and radiatively preheated the remaining cells. Complementary diagnostics including temperature, video, acoustic, and gravimetric measurements were employed to enable robust characterization of TRP.

Lithium-ion batteries (LIBs) are the leading technology used in consumer electronics, electric vehicles, and grid-level electrochemical energy storage applications. The ever-increasing use of LIBs has highlighted a gap in understanding of their behavior throughout their life cycle. Current monitoring systems rely on electrical and sometimes temperature measurements to assess the internal state which limits information about complex electrochemical processes. In response, ultrasonic testing (UT) has shown promise for non-invasive assessment due to its ease of use and sensitivity to mechanical changes which are correlated with electrochemical changes within the battery. We summarize the research in UT methods applied to LIBs throughout their life cycle. We also discuss physics-based and data-driven modeling approaches used to interpret ultrasonic signals in the context of LIBs, with an emphasis on the existing challenge of establishing rigorous links between electrochemical behavior and elastic and poroelastic wave physics to gain insight regarding physical changes in the LIB that can be directly measured using UT. Finally, we discuss the challenges of implementing UT across the LIB life cycle and identify opportunities for further research. This review aims to provide helpful guidance to researchers and practitioners of UT in the growing field of UT for electrochemical battery systems.

Lithium-ion batteries (LIBs) are the leading technology used in consumer electronics, electric vehicles, and grid-level electrochemical energy storage applications. The ever-increasing use of LIBs has highlighted a gap in understanding of their behavior throughout their life cycle. Current monitoring systems rely on electrical and sometimes temperature measurements to assess the internal state which limits information about complex electrochemical processes. In response, ultrasonic testing (UT) has shown promise for non-invasive assessment due to its ease of use and sensitivity to mechanical changes which are correlated with electrochemical changes within the battery. We summarize the research in UT methods applied to LIBs throughout their life cycle. We also discuss physics-based and data-driven modeling approaches used to interpret ultrasonic signals in the context of LIBs, with an emphasis on the existing challenge of establishing rigorous links between electrochemical behavior and elastic and poroelastic wave physics to gain insight regarding physical changes in the LIB that can be directly measured using UT. Finally, we discuss the challenges of implementing UT across the LIB life cycle and identify opportunities for further research. This review aims to provide helpful guidance to researchers and practitioners of UT in the growing field of UT for electrochemical battery systems.

Anode–electrolyte reactivity and salt–solvent interactions govern low- and high-temperature thermal events, guiding the design of safer potassium-ion batteries.

ABSTRACT The rapid growth of lithium‐ion batteries (LIBs) applications drives the need for fast‐charging solutions ensuring speed, safety, durability, and performance. Such charging protocol design needs to be guided by mechanistic understanding of degradation pathways, ionic transport limitations, and thermal constraints. However, in practice, many charging protocols used in commercial electronics and electric vehicles (EVs) have limited mechanistic transparency. In this review, we adopt a reverse perspective by extracting mechanistic insights from practical charging protocols to inform future design. To this end, standardized fast‐charging protocols and those implemented in real‐world applications such as smartphones and EVs are analyzed to examine how their voltage–current profiles evolve with state‐of‐charge (SOC) and to reflect distinct design rationales. These features are further examined in terms of SOC‐dependent physical and chemical transformations in electrode materials, kinetic limitations such as polarization and reaction heterogeneity influenced by charging protocol design, and distinct heat generation patterns governed by protocol characteristics. Advanced characterization techniques are then highlighted for providing real‐time insights into structural transitions, diffusion kinetics, and heat evolution during fast charging. Finally, future protocol design may be informed by multiscale material modelling, real‐time sensing for adaptive control, and data‐driven optimization to support the development of advanced fast‐charging systems.

Electrification of transportation and grid-scale renewable energy storage are driving an unprecedented demand for energy storage solutions. Next-generation (next-gen) battery technologies, including the use of alternatives to commercial graphite anode materials and solid-state electrolytes, offer the potential for enhanced performance compared to conventional lithium-ion batteries (LIBs). Recent research has shown that ultrasonic inspection methods provide insightful understanding of mechanical property changes that occur in lithium-ion batteries with different lithiation and aging states. This work presents preliminary research that extends the use of ultrasonic methods for next-gen batteries and compares the observations with those in conventional LIBs. We investigate contact and immersion ultrasonic testing methods to monitor the evolution of time-domain characteristics (e.g., time of flight, amplitude) and frequency-domain metrics (e.g., spectral content, attenuation) under various cycling conditions and thermal loading. By tracking these metrics, we intend to get insights into changes in mechanical properties associated with electrochemical behavior unique to next-gen cells. Ultrasonic immersion imaging provides insights into spatial heterogeneities of the inspected cells subjected to the same loading processes. These experiments, paired with physical modeling of wave phenomena in these systems, provide a framework for comparing next-gen batteries to traditional LIBs and provide insight into their unique chemistries.

In lithium-ion battery manufacturing, following electrode preparation and cell assembly, electrolyte filling and wetting is a critical and throughput-determining step that often takes tens of hours due to the slow electrolyte infiltration of porous electrodes. This prolonged wetting process significantly limits production efficiency and increases manufacturing costs, highlighting the need for more effective electrolyte wetting strategies. In this study, we investigated the electrolyte wetting behavior of 2 Ah LiFePO 4 (LFP)–graphite (Gr) pouch cells using ultrasonic transmission imaging and electrochemical impedance spectroscopy. Although elevated temperature can moderately accelerate electrolyte wetting, the improvement remains insufficient for practical production. Inspired by the sponge-like absorption behavior in the densely packed, highly tortuous, and irregular porous structures, we developed a pulsed pressurizing strategy that applies intermittent mechanical pressure to promote electrolyte penetration, successfully reducing the impregnation time to within 1 h. Electrochemical cycling tests further confirm that applying pressure during wetting does not compromise battery performance. This work offers a practical and scalable solution to significantly shorten electrolyte wetting time and accelerate the overall production process of lithium-ion batteries.

The primary hazards associated with thermal runaway of batteries are related to thermal and pressure behaviors, as well as toxicity of emitted materials. Managing the thermal runaway event such that the temperatures and pressures do not pose uncontrollable hazardous conditions is paramount for designing safe battery systems and requires a detailed knowledge of heat and gas generation behaviors. Understanding the toxicity hazards of emitted materials from thermal runaway is also important for guiding first-responder preparedness and clean-up operations. Here, research on characterizing the thermal, gaseous, and toxicity hazards of thermal runaway of current and next generation batteries will be discussed. This will start with an overview of the Battery Failure Databank, the largest open-access resource of thermal and mass ejection behaviors of commercial Li-ion batteries. The presentation will then cover hazards that are not yet well characterized such as particulate emissions from thermal runaway events that are hazardous to human health. Finally, new risks and hazards presented by up-and-coming battery technologies like Na-ion and K-ion cells, will be discussed. Figure 1

The quality of lithium-ion battery (LIB) electrodes is critical to ensuring optimal performance, safety, and lifespan. Defects in graphite electrodes, such as cracks, agglomeration, and coating inhomogeneity, can severely impact battery performance by disrupting ion transport, promoting inactive lithium formation, and posing safety risks. In this study, we investigate coating defects in graphite electrodes and their influence on electrochemical performance. Among the observed defects, surface cracks were found to cause the most severe capacity degradation, likely due to local thickness variations and lithium accumulation at exposed copper sites. To enable comprehensive defect detection, we propose a multimodal characterization approach that integrates optical imaging, infrared thermography, and X-ray radiography. This strategy combines surface, thermal, and volumetric information, allowing for reliable, in-line assessment of coating uniformity and defect severity, and offering practical guidance for improving electrode manufacturing quality control.

Lithium-ion batteries are crucial for portable electronics, electromobility, and stationary energy storage, playing a critical role in global decarbonization goals. Tracking battery performance during their lifetime ensures reliability, as various degradation mechanisms affect their operation. These changes may alter mechanical properties and thus understanding the complex relationship between electrochemistry, heat transfer, and mechanical properties therefore remains a key research challenge. Elastodynamic inspection methods, such as ultrasonic and vibrational analysis, have shown promise in detecting mechanical changes under varying states of charge (SOC) and state of health (SOH). Recent research has demonstrated the shift in the fundamental resonance frequency is a reliable metric of the SOC and SOH of Nickel-Manganese-Cobalt (NMC) pouch cells. This study presents an analysis of flexural modes for NMC cells at 0% and 100% SOC over 80 charge–discharge cycles. We employ spatial filtering to extract and enhance the response of the first three modes. We observe a correlation between the resonance frequency and the SOC/SOH for all the modes explored. The trends in resonance frequency and quality factor versus cycle from the data are explored and we propose model-based methods to extract insights regarding the evolution of mechanical properties that exploit higher modes as a function of charge level and aging.

Lithium-ion batteries are indispensable power sources for a wide range of modern electronic devices. However, battery lifespan remains a critical limitation, directly affecting the sustainability and user experience. Conventional battery failure analysis in controlled lab settings may not capture the complex interactions and environmental factors encountered in real-world, in-device operating conditions. This study analyzes the failure of commercial wireless earbud batteries as a model system within their intended usage context. Through multiscale and multimodal characterizations, the degradations from the material level to the device level are correlated, elucidating a failure pattern that is closely tied to the specific device configuration and operating conditions. The findings indicate that the ultimate failure mode is determined by the interplay of battery materials, cell structural design, and the in-device microenvironment, such as temperature gradients and their fluctuations. This holistic, in-device perspective on environmental influences provides critical insights for battery integration design, enhancing the reliability of modern electronics.

Large-scale battery failures can lead to explosion and toxicity hazards. Mitigation of battery hazards requires accurate data of battery flammable and toxic gas composition and early indicators of failure. In this study, NMC and LFP cathode cylindrical format lithium-ion batteries were failed using external heating to characterize the time evolution of evolved gases as the current interrupt devices (CID) activated. Measurements included the cell surface temperature, voltage, and gas composition using a near-source gas sampling system with a Fourier-transform infrared spectrometer (FTIR). Three early indicators of cell failure venting, which releases toxic and flammable gases, were identified. First, dimethyl carbonate (DMC), ethylene carbonate (EC), and hydrogen fluoride (HF) were the first detected species once the cell vents. Second, the voltage drop due to CID activation correlates with cell venting. The time gap between CID activation and the burst disk rupture that allows gases to be released by the cell is 27 ± 9 s and 16 ± 6 s for LFP and NMC cells, respectively. Third, the cell surface temperature at which the CID activates is 208 ± 29 °C for the LFP cells and 212 ± 15 °C for the NMC cells. Using CO as an internal standard for quantitative analysis, the CO 2 /CO ratio verified that the near-source gas sampling system gives similar results compared to literature data. This serves as a method for quantitatively measuring the HF concentration using the HF/CO ratio. The DMC/CO ratio revealed that DMC is abundant and contributes to the overall gas flammability in addition to the more typically-reported dry vent gases. This study recommends that flammability models for battery systems include the vented electrolyte components to more accurately predict the explosion hazards.

Purpose The COVID-19 pandemic dramatically affected the fire service: stay-at-home orders and potential exposure hazards disrupted standard fire service operations and incident patterns. The ability to predict incident volume during such disruptions is crucial for dynamic and efficient staff allocation planning. This work proposes a model to quantify the relationship between the increase in “residential mobility” (i.e. time spent at home) due to COVID-19 and fire and emergency medical services (EMS) call volume at the onset of the pandemic (February – May 2020). Understanding this relationship is beneficial should mobility disruptions of this scale occur again. Design/methodology/approach The analysis was run on 56 fire departments that subscribe to the National Fire Operations Reporting System (NFORS). This platform enables fire departments to report and visualize operational data. The model consists of a Bayesian hierarchical model. Text comments reported by first responders were also analyzed to provide additional context for the types of incidents that drive the model’s results. Findings Overall, a 1% increase in residential mobility (i.e. time spent at home) was associated with a 1.43% and 0.46% drop in EMS and fire call volume, respectively. Around 89% and 21% of departments had a significant decrease in EMS and fire call volume, respectively, as time spent at home increased. Originality/value A few papers have investigated the impact of COVID-19 on fire incidents in a few locations, but none have covered an extensive number of fire departments. Additionally, no studies have investigated the relationship between mobility and fire department call volumes.

The lithium-ion batteries used in high-power applications require thousands of cells arranged in arrays where failure of an individual cell may lead to total system failure via thermal runaway. One cause of thermal runaway is high-temperature abuse. This work explores the viability of ultrasonic inspection to detect whether lithium-ion cells have been previously subjected to localized thermal abuse by comparing ultrasonic features recorded during the charge-discharge cycling before and after thermal abuse. We employ 1 MHz Gaussian pulses propagating through mechanically-confined NMC lithium-ion cells as they undergo charge-discharge cycling, localized heating between 50°C and 150°C, and post-abuse charge-discharge cycling. Metrics of the transmitted ultrasonic signal, the Time of Flight Shift (TOFS) and Signal Amplitude (SA), are analyzed to assess their utility in detecting pre-existing damage due to localized thermal abuse. Results indicate that the SA and TOFS trends are strongly affected by previous, localized thermal abuse in the following charge-discharge cycles, while the model provides insight about which cells components are contributing to the observed changes in ultrasonic signals.

Lithium-ion batteries are pivotal in various technological applications, from powering electric vehicles to supporting renewable energy storage systems. Understanding and monitoring the intricate chemo-mechanics within lithium-ion cells is imperative for ensuring their reliability and performance over time. Previous research has shown that both ultrasonic and vibrational measurements provide a measure of a cell’s state of charge (SOC) and state of health (SOH) and provide indications of existing or previous thermal or electrical abuse. Recent work suggests that ultrasonic and modal analysis may provide complementary insights into the evolution of layer interfaces during early-life aging due to charge-discharge cycling [J. Acoust. Soc. Am., 154, A284 (2023)]. This work presents the results of concurrent ultrasonic and modal measurements over multiple charge-discharge cycles. Namely, we monitor concurrent changes in the ultrasonic time-of-flight and signal amplitude and the resonance frequency of a clamped-clamped 10 Ah Nickel–Manganese–Cobalt pouch cell as a function of electrical cycling. The evolution of these metrics paired with analytical and numerical models of the cell will be used to understand changes in the material properties at layer interfaces and potential structural alterations within the battery which may be important indicators of SOC and early-life aging mechanisms.

The robustness and safety of battery-operated systems will become critically important as society transitions away from fossil fuels. In the foreseeable future, lithium-ion batteries will be used for high-power, high-capacity applications such as electric vehicles and renewable energy storage. In these applications, which require thousands of cells, existing battery management systems do not monitor the operating conditions of each cell. Variability in temperature and pressure can affect a cell’s state of charge (SOC) or state of health (SOH). This environmental loading coupled with cell-to-cell variability makes SOC/SOH estimation very difficult. Inaccurate measurements of SOC/SOH can reduce the lifespan of battery systems or lead to accidental overcharge and thermal runaway. We present modal analysis as a viable approach to estimate SOC/SOH for electrically cycled cells. Modal tests are performed using laser Doppler vibrometry on 10 Ah Nickel–Manganese–Cobalt pouch cells at 0% and 100% SOC across more than 30 cycles. Changes in the resonance frequencies of the cell are correlated with SOC/SOH to provide an understanding of how the mechanical properties of cell components change as a function of charge level and aging. This work demonstrates that modal analysis may be used as a tool for regular battery maintenance to improve battery safety.

Electric vehicles require nearly 1000 individual lithium-ion batteries to provide appropriate power and capacity. It has recently been shown that ultrasonic inspection can detect localized heating in a LIB cell with a combination of input frequencies and propagation paths [J. Acoust. Soc. Am. 152, A283 (2022)]. However, monitoring the thermal conditions of every cell in a battery pack is highly challenging to implement. This work explores the use of ultrasonic inspection to diagnose LIB cells with damage histories due to local, thermal abuse. LIBs were interrogated with ultrasonic waves while subjected to electrical and thermal loading, specifically, standard charge-dischargecycling followed by moderate localized thermal abuse and another phase of charge-discharge cycling. Ultrasonic signals from each portion of the test and data for the cycling before and after heating are directly compared for indicators of past abuse. Experimental data are compared to a transfer-matrix model to simulate the time-of-flight (TOF) through an individual cell using temperature-specific material properties for individual components to simulate the effect of heat on TOF. Experimental results indicate that deviations in time-domain features of the received signals can be used to detect previous thermal abuse via ultrasonic testing during charge-discharge cycling after thermal abuse.