List of publications
Peter Bugryniec & Solomon Brown
ECS Meeting Abstracts (2024) MA2024-02 365; https://doi.org/10.1149/MA2024-023365mtgabs
Lithium-ion batteries (LIBs) are now an integral part of our energy system. Their high-performance characteristics make them suitable for automotive, marine and stationary applications. However, safety concerns exist for LIBs related to thermal runaway (TR) which presents significant fire, explosion and toxicity hazards. Computational modelling has been used to predict cell TR [1] and thermal runaway propagation (TRP) in battery modules [2]. However, our previous work [3] has shown that it is important to consider the variation in kinetic parameters of the model to predict the probability, as well as the severity, of cell TR under an abuse scenario. Our previous work is extended herein to consider the effects of cell variations on the predictions of module TRP behaviour. From this, we aim to determine the value and confidence in predicted TRP prevention methods. A 0-dimensional thermal resistive network model for a battery stack of 6 prismatic cells was studied to evaluate the value of heat transfer that is required to prevent TRP. The cells are assumed to be electrically connected, with heat transfer between cell surfaces and tab connections, and heat loss to the environment by convection and radiation. TR heat generation in each cell is modelled by Arrhenius equations for the four major decomposition reactions. The initiation of TR is modelled by a large internal short circuit in the first cell. The TRP behaviour of NMC and LFP cell battery stacks are compared. Uncertainty analysis is performed via Monte Carlo analysis. The model, not considering parameter uncertainty, is validated against NMC data and shown to predict TR behaviour accurately. Both the NMC and LFP cell stack undergo TRP at ambient conditions. Considering parameter uncertainty, it is shown that the predictions of maximum temperature, time to TR and time to TRP become more uncertain as TRP progresses. Further, while the uncertainty in maximum cell temperatures is similar between chemistries, for time to TRP and TRP it is greater for the LFP stack. Considering a lumped heat dissipation coefficient to account for radiation and convection, it is found that TRP is completely prevented in the NMC and LFP stacks at values of 344W/m2K and 150W/m2K, respectively (see Figure 1). However, when considering parameter uncertainty, TRP is only prevented 40% and 45% of the time for the NMC and LFP stack, respectively. To reach a median probability of 99% for the prevention of TRP the heat dissipation coefficient has to be increased to 950W/m2K and 300W/m2K for the NMC and LFP stack, respectively (see Figure 1). As such, with a heat dissipation coefficient up to 500W/m2K and 1000W/m2K for heat pipe cooling and liquid immersion cooling, respectively, LFP cell stack TR can be mitigated by thermal management systems discussed in the literature. However, NMC cell stacks requiring a heat dissipation coefficient over 950W/m2K would entail more complex forced convection or condensing vapour technique. Using a thermal resistive network model of a LIB stack to evaluate TRP, it is shown that the predicted heat transfer coefficient to prevent TRP is 2-3 times larger (depending on cell chemistry) when considering parameter uncertainty compared to typical modelling techniques. This highlights the importance of considering uncertainty in TR modelling when determining safety-critical parameters.
Kinetic modelling of thermal decomposition in lithium-ion battery components during thermal runaway
Hosein Sadeghi and Francesco Restuccia
Journal of Power Sources 629 (2025) 236026; https://doi.org/10.1016/j.jpowsour.2024.236026
This study presents kinetic models for the thermal decomposition of 18650-type lithium-ion battery components during thermal runaway, including the SEI layer, anode, separator, cathode, electrolyte, and binder. The decomposition kinetics were sourced from the literature. The approach used inverse modelling, employing a Genetic Algorithm to estimate kinetic and stoichiometric parameters. Experimental thermogravimetry data from the literature served as the reference benchmarks. The optimisation errors ranged from 0.039% to 1.531%, and the algorithm performed well in terms of reaction temperatures, with errors between 0.51% and 11.07%. The models were validated for calculating the mass loss of a full cell at 100% state of charge during thermal runaway. The early stages of thermal runaway, including the decomposition of the anode and separator, were considered in an electrochemical-thermal simulation of charge/discharge cycling using PyBaMM solver. The results showed that these decompositions could advance temperature and voltage profiles by 0.07 C over 20 cycles, aiding early prediction of thermal runaway in battery management systems. This work introduces novel models to calculate mass losses, identify reactions, quantify heat release, and estimate thickness or volume reductions in battery components during thermal runaway.
Elliott Read, Simon Jones and James Marco
Journal of Power Sources Advances 30 (2024) 100162; https://doi.org/10.1016/j.powera.2024.100162
Six thermal runaway propagation tests were performed on small modules consisting of seven 21700 lithium-ion cells in a hexagonal configuration with 3 mm spacing between adjacent cells. One cell in the centre of the module was triggered into thermal runaway using an 8 mm diameter nail penetrated through the positive terminal of the cell. For half of the tests, sidewall rupture was initiated in the trigger cell using a 35 mm penetration depth. For the other half of the tests, sidewall rupture was not initiated in the trigger cell using a 10 mm penetration depth. In all tests where the trigger cell experienced sidewall rupture, there was thermal runaway propagation to the remaining six cells in the module; in all tests where the trigger cell did not experience sidewall rupture, there was no thermal runaway propagation to any other cells in the module. These results are explained by the directionality and magnitude of heat transfer for sidewall rupture failures relative to nominal failure. These results highlight the increased propensity for thermal runaway propagation when a sidewall rupture failure occurs in a battery module and emphasise the importance of methods to mitigate this failure in battery systems.
Peter J. Bugryniec, Erik G. Resendiz, Solomon M. Nwophoke, Simran Khanna, Charles James and Solomon F. Brown
Journal of Energy Storage 87 (2024) 111288; https://doi.org/10.1016/j.est.2024.111288
Lithium-ion batteries (LIBs) present fire, explosion and toxicity hazards through the release of flammable and noxious gases during rare thermal runaway (TR) events. This off-gas is the subject of active research within academia, however, there has been no comprehensive review on the topic. Hence, this work analyses the available literature data to determine how battery parameters affect the variation in off-gas volume and composition, to determine the flammability and toxicity hazards of different battery chemistries. It is found on average that: (1) NMC LIBs generate larger specific off-gas volumes than other chemistries; (2) prismatic cells tend to generate larger specific off-gas volumes than offer cell forms; (3) generally a higher SOC leads to greater specific gas volume generation; (4) LFP batteries show greater toxicity than NMC; (5) LFP is more toxic at lower SOC, while NMC is more toxic at higher SOC (respective to themselves); and (6) LFP off-gas has a greater flammability hazard. Further, recommendations are presented so that significant improvements in research can be made to advance the understanding of LIB off-gas further. Finally, this work is a critical resource to the battery community to aid the risk assessment of LIB TR fire, explosion and toxicity hazards.
Predictive Hazard Level Assessment of Li-ion Cell Thermal Runaway Failure
Peter J Bugryniec and Solomon F Brown
Energy Storage Conference 2023 (ESC 2023) Glasgow, UK 15–16 November 2023; https://doi.org/10.1049/icp.2023.3096
Li-ion batteries (LIBs) are a widely adopted energy storage device that are increasingly used in transportation and stationary applications. However, LIBs come with the risk of thermal runaway (TR) which is known to be unpredictable. Previous computational work has assessed the sensitivity of TR to model inputs, while some experimental work has quantified the distribution of TR behaviour. However, no work is known to have used computational simulations of cell abuse to predict the probability of cell failure under typical abuse test standards. This work applies an abuse model to achieve this, as well as using key TR output variables to calculate the magnitude of cell failure according to the redefined EUCAR hazard level assessment. Abuse simulations of Underwriter Laboratory’s oven test are simulated thousands of times considering parameter distributions with two different coefficient of variance sets. This work shows that it is possible to predict the change in the probability of failure against the change in oven temperature and the probability of different hazard levels. However, there is a need to better understand and refine the variance in cell parameters, specifically those related the kinetic behaviour, to allow for analysis that is more suitable for risk assessment purposes
Justin Holloway, Muinuddin Maharun, Irma Houmadi, Guillaume Remy, Louis Piper, Mark A. Williams and Melanie J. Loveridge
Batteries 10 (2024), 104; https://doi.org/10.3390/batteries10030104
The ubiquitous deployment of Li-ion batteries (LIBs) in more demanding applications has reinforced the need to understand the root causes of thermal runaway. Herein, we perform a forensic simulation of a real-case failure scenario, using localised heating of Li(Ni0.5Mn0.3Co0.2)O2 versus graphite 18650 cylindrical cells. This study determined the localised temperatures that would lead to venting and thermal runaway of these cells, as well as correlating the gases produced as a function of the degradation pathway. Catastrophic failure, involving melting (with internal cell temperatures exceeding 1085 ◦C), deformation and ejection of the cell componentry, was induced by locally applying 200 ◦C and 250 ◦C to a fully charged cell. Conversely, catastrophic failure was not observed when the same temperatures were applied to the cells at a lower state of charge (SOC). This work highlights the importance of SOC, chemistry and heat in driving the thermal failure mode of Ni-rich LIB cells, allowing for a better understanding of battery safety and the associated design improvements.
First Cycle Cracking Behaviour Within Ni-Rich Cathodes During High-Voltage Charging
A. Wade, A. V. Llewellyn, T. M. M. Heenan, C. Tan, D. J. L. Brett, Rhodri Jervis and P. R. Shearing
Journal of The Electrochemical Society (2023) 170 070513; https://doi.org/10.1149/1945-7111/ace130
Increasing the operating voltage of lithium-ion batteries unlocks access to a higher charge capacity and therefore increases the driving range in electric vehicles, but doing so results in accelerated degradation via various mechanisms. A mechanism of particular interest is particle cracking in the positive electrode, resulting in losses in capacity, disconnection of active material, electrolyte side reactions, and gas formation. In this study, NMC811 (LiNi 0.8Mn0.1Co 0.1O 2 ) half-cells are charged to increasing cut-off voltages, and ex situ X-ray diffraction and X-ray computed tomography are used to conduct post-mortem analysis of electrodes after their first charge in the delithiated state. In doing so, the lattice changes and extent of cracking that occur in early operation are uncovered. The reversibility of these effects is assessed through comparison to discharged cathodes undergoing a full cycle and have been relithiated. Comparisons to pristine lithiated electrodes show an increase in cracking for all electrodes as the voltage increases during delithiation, with the majority of cracks then closing upon lithiation.
Galo J. Páez Fajardo, Meltiani Belekoukia, Satish Bolloju, Eleni Fiamegkou, Ashok S. Menon, Zachary Ruff, Zonghao Shen, Nickil Shah, Erik Björklund, Mateusz Jan Zuba, Tien-Lin Lee, Pardeep K. Thakur, Robert S. Weatherup, Ainara Aguadero, Melanie J. Loveridge, Clare P. Grey and Louis F. J. Piper
RSC Appl. Interfaces (2024) 1, 133–146; https://doi.org/10.1039/d3lf00093a
The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants.
E. Read, J. Mathew, S. Charmer, M. Dowson, D. Lorincz, I. Örökös-Tóth, M. Dobson and J. Marco
Journal of Energy Storage 95 (2024) 112491; https://doi.org/10.1016/j.est.2024.112491
Containing thermal runaway propagation in lithium-ion battery packs is a pertinent problem that is exacerbated when considering high energy density batteries and severe battery failure modes, such as sidewall rupture. This work investigates five different passive thermal barrier materials for their performance with respect to containing sidewall rupture and mitigating thermal runaway propagation between high energy density 21,700 cells. Along with propagation rate and total count of sidewall rupture failures, two new key performance indicators are introduced, the temperature reduction value and the sidewall rupture ratio, to quantify a material’s performance. Overall, a stainless steel thermal barrier coated with an intumescent flame-retardant fabric performs best out of the five materials investigated. Evidence is given for the count of sidewall ruptures being linearly correlated to the propagation rate. It is shown that cells that fail with sidewall rupture have an average maximum surface temperature of 919 ◦C compared to 653 ◦C for cells that fail with top cap rupture. Evidence is also presented that sidewall rupture propagates to adjacent cells in a module. This work aims to provide battery pack designers with information to aid them in determining a strategy for containing thermal runaway propagation and sidewall rupture, including a method to evaluate the performance of thermal barrier materials against this objective.
D. P. Finegan, J. Billman, J. Darst, P. Hughes, J. Trillo, M. Sharp, A. Benson, M. Pham, I. Kesuma, M. Buckwell, H.T. Reid, C. Kirchner-Burles, M. Fransson, D. Petrushenko, T.M.M. Heenan, R. Jervis, R. Owen, D. Patel, L. Broche, A. Rack, O. Magdysyuk, M. Keyser, W. Walker, P.R. Shearing and E. Darcy
Journal of Power Sources 597 (2024) 234106; https://doi.org/10.1016/j.jpowsour.2024.234106
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.
B. Gulsoy, H. Chen, C. Briggs, T.A. Vincent, J.E.H. Sansom and J. Marco
Journal of Power Sources 617 (2024) 235147; https://doi.org/10.1016/j.jpowsour.2024.235147
Real-time monitoring of temperature and pressure in lithium-ion batteries provides a comprehensive insight into several failure mechanisms that collectively are associated with thermal runaway. These are characterised by elevated temperatures that triggers heat-generating decomposition processes and the release of flammable gases that rapidly degrade the battery. This study presents a new methodology that for the first-time facilities the simultaneous real-time monitoring of internal temperature and gas pressure in high-capacity 21700-format cylindrical cells. This includes the assessment of severity of thermal runaway events. The method uses a bespoke sensing system with integrated thermocouples and pressure sensors. After investigating the instrumented cells’ performance and verifying sensor functionality, thermal runaway characteristics are investigated further with cell failure triggered by external heating. Results highlight the accumulation of gas pressure inside the cell, the elevation of internal cell temperature and variations in cell voltage during the different phases of cell failure: prevent, soft-vent, and flame generation. This study underpins developing early detection or mitigation strategies against safety hazards in lithium-ion battery systems. Moreover, the availability of unmeasured datasets supports creating mathematical models to optimise battery performance, safety and longevity.
A. Fordham, S.-B. Joo, R.E. Owen, E. Galiounas, M. Buckwell, D.J.L. Brett, P.R. Shearing, R. Jervis and J.B. Robinson
Journal of The Electrochemical Society 171 (2024) 070521; https://doi.org/10.1149/1945-7111/ad59c9
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.
R.E. Owen, E. Wiśniewska, M. Braglia, R. Stocker, P.R. Shearing, D.J.L. Brett and J.B. Robinson
Journal of The Electrochemical Society 171 (2024) 040525; https://doi.org/10.1149/1945-7111/ad3beb
Lithium-ion batteries (LIBs) play an integral role in powering various applications, from consumer electronics to stationary storage, and notably in the accelerating domain of electric vehicles (EVs). Despite their widespread adoption and numerous benefits, safety issues are of major concern, especially with the surge in their utilization and increasing proliferation of second-life cells, particularly in domestic energy storage applications. A critical concern revolves around susceptibility to thermal runaway, leading to highly hazardous and challenging-to-contain fires. Addressing these concerns necessitates effective methods to monitor internal temperature dynamics within lithium-ion cells swiftly and cost-effectively, alongside a need to develop prognostic techniques to pre-empt thermal runaway occurrences. This study presents an innovative approach that uses ultrasound analysis to track intricate internal temperature fluctuations and gradients within cells. Moreover, an efficient multi-stage warning system is proposed that is designed to proactively prevent thermal runaway events. The findings offer promising avenues for enhancing the safety and reliability of lithium-ion battery systems.
Investigations into the Dynamic Acoustic Response of Lithium-Ion Batteries During Lifetime Testing
E. Galiounas, F. Iacoviello, M. Mirza, L. Rasha, R.E. Owen, J.B. Robinson and R. Jervis
Journal of The Electrochemical Society 171 (2024) 070514; https://doi.org/10.1149/1945-7111/ad5d21
Techniques using acoustic waves to interrogate batteries are increasingly investigated in the literature due to the appeal of three main properties: they are non-destructive, relatively low cost and have acquisition rates enabling operando testing. Popular demonstrations attempt to extract degradation markers from acoustic data, by continuous monitoring, and to attribute them to degradation modes. This is founded on the premise that the speed of sound depends on mechanical properties, such as the density and stiffness. Nevertheless, additional sensitivities of an acoustic time-of-flight analysis are often neglected, leading to incomplete experiments that can overstate the capabilities of the technique. In this work, such sensitivities are quantified and the use of pulse tests instead of CCCV protocols is recommended to elucidate the concurrent dynamic evolution of temperature, voltage and acoustic signals. A degradation experiment is performed, with pulse sequences incorporated in periodic reference performance tests. Dynamic parameters are extracted from each pulse; specifically, the dynamic rise of the time-of-flight (ΔToFrise) and temperature (ΔTemprise) signals. Their evolution with degradation is traced and a statistical comparison of the main effects is performed. It is concluded that markers of degradation in the dynamic acoustic response are very subtle, masked by the effects of temperature.
A. Jnawali, M.D.R. Kok, M. Krishna, M.A. Varnosfaderani, D.J.L. Brett and P.R. Shearing
Journal of The Electrochemical Society 170 (2023) 090540; https://doi.org/10.1149/1945-7111/acf883
Lithium-ion (Li-ion) batteries have undergone a multitude of improvements and achieved a high level of technological maturity. To further optimise cell performance, an understanding of the failure mechanisms is important. Forty-eight state-of-the-art cylindrical cells in the 21700 format, suitable for electric vehicles, are studied at the beginning-of-life (BOL) and end-of-life (EOL) by X-ray computed tomography (X-ray CT) and image analysis. The results indicate that shifting current collecting tabs closer to the centre of the cell and including a mandrel is likely to supress the propagation of capacity depleting deformations. It is recommended that manufacturers also try to improve cell assembly processes to form a more uniformly circular jelly roll and use tapered electrodes to minimise the nucleation of deformations.
Matilda Fransson, Ludovic Broche, Hamish T. Reid, Drasti Patel, Alexander Rack and Paul R. Shearing
Applied Energy 369 (2024) 123070; https://doi.org/10.1016/j.apenergy.2024.123070
Prevention and mitigation of hazardous battery failure scenarios can be achieved through the integration of different safety systems. These mechanisms are routinely evaluated post-testing in a static fashion but lack insights to their dynamic behavior. However, thanks to fast X-ray imaging one can assess the function of these safety mechanisms in-situ. In this work, micro batteries equipped with a combined venting and current interruption mechanism have been subjected to abuse testing in combination with synchrotron high-speed X-ray imaging. Acquired radiography reveals that the current interrupting system was not always activated as described by the manufacturer, and thus provides insights into potential improvements of the system. In addition, the cell was tested in a different configuration where this mechanism was impeded and we conclude that in-situ visualization with X-ray imaging is a crucial tool for validation of safety mechanisms integrated into batteries.
Unveiling aqueous lithium-ion batteries via advanced modelling and characterisation: A review
Xiaoxia Guo , Hongzhen He , Siyu Zhao , Haobo Dong , Paul R. Shearing , Rhodri Jervis and Jie Lin
Energy Storage Materials 70 (2024) 103505; https://doi.org/10.1016/j.ensm.2024.103505
Aqueous lithium-ion batteries (ALIBs) are promising candidates for sustainable energy storage, offering great advantages in safety, cost, and environmental impact over the conventional nonaqueous LIBs. This paper delves into the forefront of ALIB research in electrolyte formulations, electrode materials, and design strategies of ALIBs that have stemmed from the integration of advanced modelling and characterisation techniques. A detailed examination of multiscale modelling approaches, e.g., density functional theory (DFT), molecular dynamics (MD), microscopic and spectroscopic techniques, e.g., X-ray, Raman, and particularly in situ and in operando methods that provide real-time observations of battery processes, is carried out. We note that the synergy between modelling and characterisation techniques have offered unprecedented insights into the fundamental processes governing ALIB performance, however, more methods that have been demonstrated effective in commercial LIBs, can be employed and contribute to resolving the current bottlenecks of ALIBs. The models at mesoscale, continuum-scale and even larger scales can supplement DFT and MD to investigate the electrochemical processes in electrode-electrolyte interface, bulk electrolyte, porous electrodes, and prototype cells, and cooperate with essential measurements to characterise physicochemical properties of aqueous electrolytes, which are not widely discussed. Other microscopic, structural, and multi-physical characterisations, such as scanning transmission electron microscopy, computed tomography, thermography, and acoustic techniques can provide more insights into lithium intercalation, phase change and degradation, inspiring the theory and model development of ALIBs. By amalgamating the current state-of-the-art and existing challenges, this paper paves the way for future prospects in ALIBs.
Hosein Sadeghi and Francesco Restuccia
Journal of Power Sources 603 (2024) 234480; https://doi.org/10.1016/j.jpowsour.2024.234480
This study presents a modelling approach for simulating fires in thermal runaway and here, it is applied to 18650-type batteries with LCO, NMC, and LFP cathodes at 100% SOC. The model assumes a single-step pyrolysis, where a solid lumped substance, representing the battery components, degrades into volatiles which are vent gases here. Coupling an in-house MATLAB code and FDS solver, a parameter estimation using Bayesian optimization was performed to fit the simulated mass loss and heat release rate to the experimental measurements. One-step kinetics are used for vent gas combustion, with CO yield obtained from literature and soot yield determined via 1-D diffusion flame simulations with CRECK kinetic mechanism in Cantera solver. 3-D simulations using the obtained models yielded maximum values of flame temperature, CO2 and H2O mole fractions, velocity, radiative heat flux, and flame height as 2520 K, 0.47, 0.15, 10.08 m/s, 13.29 kW/m2, and 0.62 m, respectively. The novelties associated with this approach are that, unlike the past studies, there is no need to model the thermal runaway process prior to flaming and, the resulting heat release rate is experimentally verified which makes further analyses, such as flame temperature, height and heat emissions possible.
The Influence of Cathode Degradation Products on the Anode Interface in Lithium-Ion Batteries
Zhenyu Zhang, Samia Said, Adam J. Lovett, Rhodri Jervis, Paul R. Shearing, Daniel J. L. Brett and Thomas S. Miller
ACS Nano 18 (2024), 9389−9402; https://doi.org/10.1021/acsnano.3c10208
Degradation of cathode materials in lithium-ion batteries results in the presence of transition metal ions in the electrolyte, and these ions are known to play a major role in capacity fade and cell failure. Yet, while it is known that transition metal ions migrate from the metal oxide cathode and deposit on the graphite anode, their specific influence on anode reactions and structures, such as the solid electrolyte interphase (SEI), is still quite poorly understood due to the complexity in studying this interface in operational cells. In this work we combine operando electrochemical atomic force microscopy (EC-AFM), electrochemical quartz crystal microbalance (EQCM), and electrochemical impedance spectroscopy (EIS) measurements to probe the influence of a range of transition metal ions on the morphological, mechanical, chemical, and electrical properties of the SEI. By adding representative concentrations of Ni2+, Mn2+, and Co2+ ions into a commercially relevant battery electrolyte, the impacts of each on the formation and stability of the anode interface layer is revealed; all are shown to pose a threat to battery performance and stability. Mn2+, in particular, is shown to induce a thick, soft, and unstable SEI layer, which is known to cause severe degradation of batteries, while Co2+ and Ni2+ significantly impact interfacial conductivity. When transition metal ions are mixed, SEI degradation is amplified, suggesting a synergistic effect on the cell stability. Hence, by uncovering the roles these cathode degradation products play in operational batteries, we have provided a foundation upon which strategies to mitigate or eliminate these degradation products can be developed.
Up in smoke: Considerations for lithium-ion batteries in disposable e-cigarettes
Hamish T. Reid, Arthur Fordham, Lara Rasha, Mark Buckwell, Daniel J.L. Brett, Rhodri Jervis & Paul R. Shearing
Joule (2023); https://doi.org/10.1016/j.joule.2023.11.008
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 495C. However, the cell format prevented significant material ejection. This work outlines 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.
Correlative non-destructive techniques to investigate aging and orientation effects in automotive Li-ion pouch cells
Arthur Fordham, Zoran Milojevic, Emily Giles, Wenjia Du, Rhodri E. Owen, Stefan Michalik, Philip A. Chater, Prodip K. Das, Pierrot S. Attidekou, Simon M. Lambert, Phoebe K. Allan, Peter R. Slater, Paul A. Anderson, Rhodri Jervis, Paul R. Shearing & Dan J.L. Brett
Joule (2023); https://doi.org/10.1016/j.joule.2023.10.011
The growing demand for electric vehicles (EVs) continues to raise concern for the disposal of lithium-ion batteries reaching their end of life (EoL). The cells inside EVs age differently depending on multiple factors. Yet, following extraction, there are significant challenges with characterizing degradation in cells that have been aged from real-world EV usage. We employed four non-destructive techniques —infrared thermography, ultrasonic mapping, X-ray tomography, and synchrotron X-ray diffraction—to analyze the aging of Nissan Leaf large-format pouch cells that were arranged in different orientations and locations within the pack. The combination of these methods provided complementary insights into cell degradation, with rotated/vertically aligned cells exhibiting distinct aging patterns compared with flat/horizontally aligned cells. These findings offer valuable information for pack design and demonstrate how cost-effective non-destructive techniques can provide practical assessment capabilities comparable to synchrotron studies. This approach enables decision support during EoL, enhancing battery production efficiency and minimizing material waste.
A review of ultrasonic monitoring: Assessing current approaches to Li-ion battery monitoring and their relevance to thermal runaway
Daniel Williams, Royce Copley, Peter Bugryniec, Rob Dwyer-Joyce & Solomon Brown
Journal of Power Sources (2023); https://doi.org/10.1016/j.jpowsour.2023.233777
Li-ion batteries (LIBs) are increasingly used in applications from personal electronics to electric vehicles (EVs) and grid scale storage. Research into LIB monitoring, such as state-of-charge (SOC) and state-of-health (SOH), and the effects of abuse on LIBs has received increased attention to allow for better battery performance and safety. To improve LIB safety better detection of thermal runaway (TR) is required for the mitigation of the associated consequences or to prevent it entirely. This paper reviews the growing field of ultrasound (US) sensing of LIBs for state monitoring and thermal runaway detection, with an additional perspective on of advancements made in thermal runaway testing. In this work, US is categorised by: hardware used in research; application for SOC and SOH monitoring. Further, TR is categorised by abuse scenario: overheating; penetration; overcharging; and gas generation. This review summarises the development of US to detect changes within a LIB. However, it is found that further developments are required to (1) isolate and characterise the various abuse/failure mechanisms using US and (2) decouple temperature and charge effects on the US signal. It is shown that decoupling the temperature-charge relationship within the US signal is necessary for accurate SOC and SOH monitoring.
Calculating Heat Release Rates from Lithium-Ion Battery Fires: A Methodology Using Digital Imaging
Malcom S. Wise, Paul A. Christensen, Neville Dickman, Joe McDonald, Wojciech Mrozik, Simon M. Lambert & Francesco Restuccia
Fire Technology (2023); https://doi.org/10.1007/s10694-023-01484-7
Measuring flame lengths and areas from turbulent flame flares developing from lithium-ion battery failures is complex due to the varying directions of the flares, the thin flame zone, the spatially and temporally rapid changes of the thermal runaway event, as well as the hazardous nature of the event. This paper reports a novel methodology for measuring heat release rate from flame flares resulting from thermal runaway of electric vehicle lithium-ion modules comprising eight 56.3Ah lithium nickel manganese cobalt (NMC) pouch cells using digital cameras and a newly developed numerical code to process the distortion of the flame size based on distance, direction, and shape. The model is tested with a set of experiments using lithium-ion battery packs and validated with a reference set of measurements using calibration boxes, a method commonly used in the reconstruction of flame areas. The experiments showed that the effect of calibration is large, and thus digital imaging without the appropriate calibration can give very large errors in measurement of flames. The combined imaging and processing method proposed in this work allows the determination of heat release rates from lithium-ion battery packs, one of the most challenging variables to quantify during the failure of a battery pack outside the laboratory. In the example experiment that this method was applied to, almost double the heat released was accounted for, meaning 50% of the total heat released would not have been accounted for without this image processing method.
Multiscale dynamics of charging and plating in graphite electrodes coupling operando microscopy and phase-field modelling
Xuekun Lu, Marco Lagnoni, Antonio Bertei, Supratim Das, Rhodri E. Owen, Qi Li, Kieran O’Regan, Aaron Wade, Donal P. Finegan, Emma Kendrick, Martin Z. Bazant, Dan J. L. Brett & Paul R. Shearing
Nature Communications (2023) 14, 5127; https://doi.org/10.1038/s41467-023-40574-6
The phase separation dynamics in graphitic anodes significantly affects lithium plating propensity, which is the major degradation mechanism that impairs the safety and fast charge capabilities of automotive lithium-ion batteries. In this study, we present comprehensive investigation employing operando high-resolution optical microscopy combined with non-equilibrium thermodynamics implemented in a multi-dimensional (1D+1D to 3D) phase-field modeling framework to reveal the rate-dependent spatial dynamics of phase separation and plating in graphite electrodes. Here we visualize and provide mechanistic understanding of the multistage phase separation, plating, inter/intra-particle lithium exchange and plated lithium back-intercalation phenomena. A strong dependence of intra-particle lithiation heterogeneity on the particle size, shape, orientation, surface condition and C-rate at the particle level is observed, which leads to early onset of plating spatially resolved by a 3D image-based phase-field model. Moreover, we highlight the distinct relaxation processes at different state-of-charges (SOCs), wherein thermodynamically unstable graphite particles undergo a drastic intra-particle lithium redistribution and inter-particle lithium exchange at intermediate SOCs, whereas the electrode equilibrates much slower at low and high SOCs. These physics-based insights into the distinct SOC-dependent relaxation efficiency provide new perspective towards developing advanced fast charge protocols to suppress plating and shorten the constant voltage regime.
Mapping internal temperatures during high-rate battery applications
T. M. M. Heenan, I. Mombrini, A. Llewellyn, S. Checchia, C. Tan, M. J. Johnson, A. Jnawali, G. Garbarino, R. Jervis, D. J. L. Brett, M. Di Michiel, P. R. Shearing
Nature (2023) 617, 507–512; https://doi.org/10.1038/s41586-023-05913-z
Electric vehicles demand high charge and discharge rates creating potentially dangerous temperature rises. Lithium-ion cells are sealed during their manufacture, making internal temperatures challenging to probe1. Tracking current collector expansion using X-ray diffraction (XRD) permits non-destructive internal temperature measurements2; however, cylindrical cells are known to experience complex internal strain3,4. Here, we characterize the state of charge, mechanical strain and temperature within lithium-ion 18650 cells operated at high rates (above 3C) by means of two advanced synchrotron XRD methods: first, as entire cross-sectional temperature maps during open-circuit cooling and second, single-point temperatures during charge–discharge cycling. We observed that a 20-minute discharge on an energy-optimized cell (3.5 Ah) resulted in internal temperatures above 70 °C, whereas a faster 12-minute discharge on a power-optimized cell (1.5 Ah) resulted in substantially lower temperatures (below 50 °C). However, when comparing the two cells under the same electrical current, the peak temperatures were similar, for example, a 6 A discharge resulted in 40 °C peak temperatures for both cell types. We observe that the operando temperature rise is due to heat accumulation, strongly influenced by the charging protocol, for example, constant current and/or constant voltage; mechanisms that worsen with cycling because degradation increases the cell resistance. Design mitigations for temperature-related battery issues should now be explored using this new methodology to provide opportunities for improved thermal management during high-rate electric vehicle applications.
Comprehensive analysis of thermal runaway and rupture of lithium-ion batteries under mechanical abuse conditions
Haodong Chen, Evangelos Kalamaras, Ahmed Abaza, Yashraj Tripathy, Jason Page, Anup Barai
Applied Energy (2023) 349 121610; https://doi.org/10.1016/j.apenergy.2023.121610
Sidewall rupture of lithium-ion batteries plays an important role in thermal runaway (TR) propagation because flame burst from the side of cell can directly heat adjacent cells. However, the understanding of sidewall rupture in high specific energy cells under mechanical abuse conditions remains limited. In this work, nail penetration is adopted as a trigger method of TR of 21700-format cylindrical cells with high specific energy (257.0 W∙h/kg). The effects of test parameters including nail diameter, nail speed, penetrating location, penetrating depth, and state of charge on likelihood and severity of thermal runaway and sidewall rupture behaviour were investigated. A series of equipment including high-definition cameras, thermal imaging camera, X-ray computed tomography (CT), cycler and electronic balance were adopted to reveal the behaviour and the mechanism of TR and sidewall rupture. Discussion on CT scan and fire behaviour provides new perspectives for understanding sidewall rupture and TR mechanisms in high specific energy cells. The results show that the mean mass loss ratio of the cell with 100% SoC is greater than 45% under each test condition, and the maximum of them is as high as 62.5% when penetrating off-centre from the cell bottom and with a penetrating depth of 10 mm. The likelihood of sidewall rupture increases with the increasing nail speed, nail diameter, penetrating depth and state of charge when penetrating from the top cover of the cell, but it is little affected by the penetrating depth and nail diameter for penetrating from the bottom of the cell. For the first time such a relationship is presented. The root-cause analysis for the sidewall rupture of the cell has been discussed, which highlights the three key factors, including the casing strength, the internal pressure, and the opening area of the venting disk.
Towards a micro-kinetic model of Li-ion battery thermal runaway — Reaction network analysis of dimethyl carbonate thermal decomposition
P. Bugryniec, S. Vernuccio, S. Brown
Journal of Power Sources, (2023) 580 23339; https://doi.org/10.1016/j.jpowsour.2023.233394
Thermal runaway (TR), a major safety concern for Li-ion batteries (LIBs), involves a complex network of chemical reactions leading to the production of flammable and toxic gases. Computational modelling of LIB TR continues to aid safer battery design. But to improve the capability of TR simulations, here we apply micro-kinetic modelling to describe the kinetics of LIB TR at a mechanistic level. We focused on developing a micro-kinetic model for the thermal decomposition of dimethyl carbonate, an important electrolyte component. Comparing two reaction networks for this process, (1) not involving radical pathways and (2) involving radical pathways, we show that radical reaction pathways are important for the decomposition of DMC at low temperatures in the region of TR onset. Further, this second network is important for the accurate prediction of off-gas species. This work forms the basis of being able to predict hazardous species production. With further work to develop a reaction network for the decomposition of the entire electrolyte and electrode-electrolyte reactions, predictive capabilities can be extended to allow for detailed risk assessment of LIBs.
Predicting the Evolution of Flammable Gases During Li-ion Battery Thermal Runaway Using Micro-Kinetic Modelling
P. Bugryniec, S. Vernuccio, S. Brown
Computer Aided Chemical Engineering (2023) 52 1077-1082; http://dx.doi.org/10.1016/B978-0-443-15274-0.50172-4
Li-ion batteries are a widely used electrochemical energy storage device. But, catastrophic failure via thermal runaway leads to great flammability and toxicity hazards. As such, there is a need to better understand the thermal runaway process. In doing so, reducing its occurrence and improving predictions of its hazards. To achieve this, we aim to develop a more detailed model of thermal runaway. This is based on fundamental reaction theory. Micro-kinetic modelling techniques are applied to predict the kinetic evolution of the reacting systems on a mechanistic level, based on a detailed analysis of the elementary reaction steps. Using this methodology, we simulate the thermal decomposition of dimethyl carbonate, as a model electrolyte solvent, and predict the product species present in the off-gas. We also investigate the impact of the temperature on the composition of the off-gas and the lower flammability limit. This demonstrates a method for predictive hazard assessments of Li-ion battery failure. For the DMC case study, we show that the LFL increases with increasing the operating temperature due to the large proportion of CO2 generated. This effectively makes the off-gas safer in terms of explosion hazards. Further work will extend this methodology to construct the reaction systems for a complete Li-ion cell.
Sidewall breach during lithium-ion battery thermal runaway triggered by cell-to-cell propagation visualized using high-speed X-ray imaginG
Matilda Fransson, Ludovic Broche, Mark Buckwell , Jonas Pfaff, Hamish Reid, Charlie Kirchner-Burles, Martin Pham, Stefan Moser, Alexander Rack, Siegfried Nau, Sebastian Schopferer, Donal P. Finegan, Paul Shearing
Journal of Energy Storage (2023) 71 108088; https://doi.org/10.1016/j.est.2023.108088
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.
Improving the Safety of Lithium-ion Battery Cells
Paul Christensen, Wojciech Mrozik, Julia Weaving.
Faraday Insights - Issue 17: July 2023; The Faraday Institution
Lithium-ion battery cells in electric vehicles are already safe and failure incidents are very rare. But with increasing use across automotive, stationary storage, aerospace and other sectors, there is a need to make them even safer. Whilst lithium-ion cell fires are extremely infrequent, they can occur under conditions of mechanical, thermal or electrical stress or abuse. Building safer and more reliable lithium-ion battery packs, as well as improving the design and optimisation of safety systems, will help to decrease the risks associated with rising lithium-ion battery usage.
Failure and hazard characterisation of high-power lithium-ion cells via coupling accelerating rate calorimetry with in-line mass spectrometry, statistical and post-mortem analyses.
Mark Buckwell, Charlie Kirchner-Burles, Rhodri E. Owen, Tobias P. Neville, Julia S. Weaving, Daniel J.L. Brett & Paul R. Shearing.
Journal of Energy Storage (2023) 65, 10706. DOI: 10.1016/j.est.2023.107069
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.
Experimental Study of Sidewall Rupture of Cylindrical Lithium-Ion Batteries under Radial Nail Penetration.
Haodong Chen, Evangelos Kalamaras, Ahmed Abaza, Yashraj Tripathy, Jason Page & Anup Barai.
Journal of the Electrochemical Society (2022) 169 (12), 120528. DOI: 10.1149/1945-7111/acadac
To understand the relationship of the sidewall rupture at different states of charge (SOCs) of cylindrical cells with high specific
energy, this work presents the results of radial nail penetration tests of 21700-format cylindrical cells at different SOCs. The
thermal runaway and sidewall rupture behaviours were characterised by key performance indicators such as temperature, mass, fire
behaviour, and voltage change. In addition, released gases from a subset of tests were measured using the Fourier transform
infrared spectroscopy. The change in the internal structure of another subset of cells after the test was observed by X-ray computed
tomography. The results show that the sidewall rupture still exists for tests at low SOC (< 30% SOC), but the outcome of thermal
runaway and sidewall rupture is milder than those at high SOC (⩾ 50% SOC). The average mass loss of cells increases with the
increment of SOC. The cell casing thickness is reduced by 12.7% ± 0.3% of the fresh cell, which in combination with the reduction
in the strength of the casing material at high temperatures could contribute to sidewall rupture.
In situ chamber for studying battery failure using high-speed synchrotron radiography.
J. Pfaff, M. Fransson, L. Broche, M. Buckwell, D. P. Finegan, S. Moser, S. Schopferer, S. Nau, P. R. Shearing & A. Rack.
Journal of Synchrotron Radiation (2023) 30, 192-199. DOI: 10.1107/S1600577522010244
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.
Surface Analysis of Pristine and Cycled NMC/Graphite Lithium-Ion Battery Electrodes: Addressing the Measurement Challenges.
Sofia Marchesini, Benjamen P. Reed, Helen Jones, Lidija Matjacic, Timothy E. Rosser, Yundong Zhou, Barry Brennan, Mariavitalia Tiddia, Rhodri Jervis, Melanie. J. Loveridge, Rinaldo Raccichini, Juyeon Park, Andrew J. Wain, Gareth Hinds, Ian S. Gilmore, Alexander G. Shard & Andrew J. Pollard.
ACS Applied Materials & Interfaces (2022) 14, 52779−52793. DOI: 10.1021/acsami.2c13636
Lithium-ion batteries are the most ubiquitous energy storage devices in our everyday lives. However, their energy storage capacity fades over time due to chemical and structural changes in their components, via different degradation mechanisms. Understanding and mitigating these degradation mechanisms is key to reducing capacity fade, thereby enabling improvement in the performance and lifetime of Li-ion batteries, supporting the energy transition to renewables and electrification. In this endeavor, surface analysis techniques are commonly employed to characterize the chemistry and structure at reactive interfaces, where most changes are observed as batteries age. However, battery electrodes are complex systems containing unstable compounds, with large heterogeneities in material properties. Moreover, different degradation mechanisms can affect multiple material properties and occur simultaneously, meaning that a range of complementary techniques must be utilized to obtain a complete picture of electrode degradation. The combination of these issues and the lack of standard measurement protocols and guidelines for data interpretation can lead to a lack of trust in data. Herein, we discuss measurement challenges that affect several key surface analysis techniques being used for Li-ion battery degradation studies: focused ion beam scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry. We provide recommendations for each technique to improve reproducibility and reduce uncertainty in the analysis of NMC/graphite Li-ion battery electrodes. We also highlight some key measurement issues that should be addressed in future investigations.
Gaussian-Process based inference of electrolyte decomposition reaction networks in Li-ion battery failure.
Peter J. Bugryniec, Aaron Yeardley, Aarjav Jain, Nicholas Price, Sergio Vernuccio & Solomon F. Brown.
Computer Aided Chemical Engineering (2022) 51, 157-162. DOI: 10.1016/B978-0-323-95879-0.50027-8
Li-ion batteries (LIBs) are widely adopted in EVs and stationary battery energy storage due to their superior performance over other battery chemistries. But LIBs come with the risk of thermal runaway (TR) which can lead to fire and explosion of the LIB. Hence, improving our understanding of TR is key to improving LIB safety. To achieve this, we aim to develop a detailed model of LIB TR, as existing models are oversimplified and often lead to inaccuracies when compared to experiments. To build a realistic representation of the reaction network (RN) for LIB TR, we present a case study on the ethylene carbonate (EC) solvent component of the LIB electrolyte. We use a RN for EC identified from literature to build a micro-kinetic model and optimize it against experimental data. Parameters optimisation and sensitivity analysis for a complex RN is made possible by using Gaussian Processes (GPs). It is found that the only four of the 14 parameters influence the simulation output significantly. Also, this work highlights areas of GP development for improved surrogate modelling of this type of problem. From this the methodology can be scaled to larger networks and can be applied LIB TR models to improve their accuracy, which in turn will help the development of safer LIBs.
Asphericity Can Cause Nonuniform Lithium Intercalation in Battery Active Particles.
Aashutosh Mistry, Thomas Heenan, Kandler Smith, Paul Shearing & Partha P. Mukherjee
ACS Energy Letters (2022) 7, 5, 1871–1879. DOI: 10.1021/acsenergylett.2c00870
Uniform intercalation is desired to enable next-generation Li-ion batteries. While we expect nonuniformity in materials undergoing a phase change, single-phase intercalation materials such as nickel manganese cobalt oxide are believed to lithiate uniformly at the particle/electrolyte interface. However, recent imaging reveals nonuniform lithiation. Motivated by this discrepancy, we examine if aspherical particle shape can cause such nonuniformity since the conventional belief is based on spherical particle theory. We obtain real particle geometries using rapid lab-based X-ray computed tomography and subsequently perform physics-based calculations accounting for electrochemical reactions at the particle/electrolyte interface and lithium transport inside the particle bulk. The aspherical geometry breaks the symmetry and causes nonuniform reaction distribution. Such nonuniformity is exacerbated as the particle becomes more aspherical. The proposed mechanism represents a fundamental limit on achievable lithiation uniformity in aspherical particles in the absence of other mechanisms causing inhomogeneity, such as grain structure, nonuniform carbon-binder coating, etc.
In-situ X-ray tomographic imaging study of gas and structural evolution in a commercial Li-ion pouch cell.
Wenjia Du, Rhodri E. Owen, Anmol Jnawali, Tobias P. Neville, Francesco Iacoviello, Zhenyu Zhang, Sebastien Liatard, Daniel J. L. Brett & Paul R. Shearing
Journal of Power Sources (2022) 520, 230818. DOI: 10.1016/j.jpowsour.2021.230818
Gas generation within Li-ion batteries (LIB) can lead to an increase in resistance, thereby, reducing their cycle lifetime. The chance of catastrophic failure via internal gas evolution may increase as a function of cell size and capacity. However, in-situ studies of gas evolution at the cell level are very limited due to limited number of techniques that can effectively probe this. Hence, for the first time, we employed high-energy X-ray tomography to non-destructively observe the structural evolution (gas and electrodes) as a function of cycle numbers for a 400 mAh commercial Li-ion pouch cell. Gas agglomeration led to cell deformation in different areas were observed in 4D (3D + time), the subsequent quantification including the volume fraction, surface area and thickness showed a heterogeneous gas distribution, revealing the degradation mechanism involving the coalescence of gas. This study demonstrates a feasible case of the use of lab-based X-ray to investigate the cell degradation and monitor state of health (SOH) by tracking the thickness in-situ, providing practical guidance for designing safer pouch cells.
Spatially Resolved Operando Synchrotron-Based X-Ray Diffraction Measurements of Ni-Rich Cathodes for Li-Ion Batteries.
Andrew Stephen Leach, Alice V. Llewellyn, Chao Xu, Chun Tan, Thomas M. M. Heenan, Alex Dimitrijevic, Karin Kleiner, Clare P. Grey, Dan J. L. Brett, Chiu C. Tang, Paul R. Shearing & Rhodri Jervis
Frontiers in Chemical Engineering (2022) 3, 794194. DOI: 10.3389/fceng.2021.794194
Understanding the performance of commercially relevant cathode materials for lithium-ion (Li-ion) batteries is vital to realize the potential of high-capacity materials for automotive applications. Of particular interest is the spatial variation of crystallographic behavior across (what can be) highly inhomogeneous electrodes. In this work, a high-resolution X-ray diffraction technique was used to obtain operando transmission measurements of Li-ion pouch cells to measure the spatial variances in the cell during electrochemical cycling. Through spatially resolved investigations of the crystallographic structures, the distribution of states of charge has been elucidated. A larger portion of the charging is accounted for by the central parts, with the edges and corners delithiating to a lesser extent for a given average electrode voltage. The cells were cycled to different upper cutoff voltages (4.2 and 4.3 V vs. graphite) and C-rates (0.5, 1, and 3C) to study the effect on the structure of the NMC811 cathode. By combining this rapid data collection method with a detailed Rietveld refinement of degraded NMC811, the spatial dependence of the degradation caused by long-term cycling (900 cycles) has also been shown. The variance shown in the pristine measurements is exaggerated in the aged cells with the edges and corners offering an even lower percentage of the charge. Measurements collected at the very edge of the cell have also highlighted the importance of electrode alignment, with a misalignment of less than 0.5 mm leading to significantly reduced electrochemical activity in that area.
Thermal Runaway of Li-Ion Cells: How Internal Dynamics, Mass Ejection, and Heat Vary with Cell Geometry and Abuse Type.
Matthew Sharp, John Jacob Darst, Peter Hughes, Julia Billman, Martin Pham, David Petrushenko, Thomas M. M. Heenan, Rhodri Jervis, Rhodri Owen, Drasti Patel, Du Wenjia, Harry Michael, Alexander Rack, Oxana V. Magdysyuk, Thomas Connolley, Dan J. L. Brett, Gareth Hinds, Matt Keyser, Eric Darcy, Paul R. Shearing, William Walker & Donal P. Finegan
Journal of The Electrochemical Society (2022) 169(2), 020526. DOI: 10.1149/1945-7111/ac4fef
Thermal runaway of lithium-ion batteries can involve various types of failure mechanisms each with their own unique characteristics. Using fractional thermal runaway calorimetry and high-speed radiography, the response of three different geometries of cylindrical cell (18650, 21700, and D-cell) to different abuse mechanisms (thermal, internal short circuiting, and nail penetration) are quantified and statistically examined. Correlations between the geometry of cells and their thermal behavior are identified, such as increasing heat output per amp-hour (kJ Ah−1) of cells with increasing cell diameter during nail penetration. High-speed radiography reveals that the rate of thermal runaway propagation within cells is generally highest for nail penetration where there is a relative increase in rate of propagation with increasing diameter, compared to thermal or internal short-circuiting abuse. For a given cell model tested under the same conditions, a distribution of heat output is observed with a trend of increasing heat output with increased mass ejection. Finally, internal temperature measurements using thermocouples embedded in the penetrating nail are shown to be unreliable thus demonstrating the need for care when using thermocouples where the temperature is rapidly changing. All data used in this manuscript are open access through the NREL and NASA Battery Failure Databank.
Quantitative spatiotemporal mapping of thermal runaway propagation rates in lithium-ion cells using cross-correlated Gabor filtering.
Anand N. P. Radhakrishnan, Mark Buckwell, Martin Pham, Donal P. Finegan, Alexander Rack, Gareth Hinds, Dan J. L. Brett & Paul R. Shearing
Energy & Environmental Science (2022) 15, 3503-3518. DOI: 10.1039/D1EE03430H
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.
Environmental impacts, pollution sources and pathways of spent lithium-ion batteries.
Wojciech Mrozik, Mohammad Ali Rajaeifar, Oliver Heidrich & Paul Christensen
Energy & Environmental Science (2021) 14, 6099-6121. DOI: 10.1039/D1EE00691F
There is a growing demand for lithium-ion batteries (LIBs) for electric transportation and to support the application of renewable energies by auxiliary energy storage systems. This surge in demand requires a concomitant increase in production and, down the line, leads to large numbers of spent LIBs. The ever-increasing battery waste needs to be managed accordingly. Currently, there are no universal or unified standards for waste disposal of LIBs around the globe. Each country uses one or a combination of practices such as landfilling, incineration and full or partial recycling depending on the number of batteries leaving the market, current legislation and infrastructures. Informal disposal or reprocessing is not a rare activity. This review records, identifies and categorises the environmental impacts, sources and pollution pathways of spent LIBs. The drawbacks of the disposal practices are highlighted and the threats associated with them are discussed. The evidence presented here is taken from real-life incidents and it shows that improper or careless processing and disposal of spent batteries leads to contamination of the soil, water and air. The toxicity of the battery material is a direct threat to organisms on various trophic levels as well as direct threats to human health. Identified pollution pathways are via leaching, disintegration and degradation of the batteries, however violent incidents such as fires and explosions are also significant. Finally, the paper discusses some of the main knowledge gaps for future assessments. The current study offers a comprehensive overview of the threats and hazards that need to be managed in order to ensure the design and implementation of safe disposal and processing options for spent LIBs.
Operando Ultrasonic Monitoring of Lithium-Ion Battery Temperature and Behaviour at Different Cycling Rates and under Drive Cycle Conditions.
Rhodri E. Owen, James B. Robinson, Julia S. Weaving, Martin T. M. Pham, Thomas G. Tranter, Tobias P. Neville, Duncan Billson, Michele Braglia, Richard Stocker, Annika Ahlberg Tidblad, Paul R. Shearing & Dan J. L. Brett
Journal of The Electrochemical Society (2022) 169(4), 040563. DOI: 10.1149/1945-7111/ac6833
Effective diagnostic techniques for Li-ion batteries are vital to ensure that they operate in the required voltage and temperature window to prevent premature degradation and failure. Ultrasonic analysis has been gaining significant attention as a low cost, fast, non-destructive, operando technique for assessing the state-of-charge and state-of-health of Li-ion batteries. Thus far, the majority of studies have focused on a single C-rate at relatively low charge and discharge currents, and as such the relationship between the changing acoustic signal and C-rate is not well understood. In this work, the effect of cell temperature on the acoustic signal is studied and shown to have a strong correlation with the signal's time-of-flight. This correlation allows for the cell temperature to be inferred using ultrasound and to compensate for these effects to accurately predict the state-of-charge regardless of the C-rate at which the cell is being cycled. Ultrasonic state-of-charge monitoring of a cell during a drive cycle illustrates the suitability of this technique to be applied in real-world situations, an important step in the implementation of this technique in battery management systems with the potential to improve pack safety, performance, and efficiency.
Nanoscale state-of-charge heterogeneities within polycrystalline nickel-rich layered oxide cathode materials.
Chun Tan, Andrew S. Leach, Thomas M. M. Heenan, Huw Parks, Rhodri Jervis, Johanna Nelson Weker, Daniel J. L. Brett & Paul R. Shearing
Cell Reports Physical Science (2021) 2(12), 100647. DOI: 10.1016/j.xcrp.2021.100647
Nickel-rich cathodes (LiNixMnyCo1-x-yO2, x > 0.6) permit higher energy in lithium-ion rechargeable batteries but suffer from accelerated degradation at potentials above 4.1 V versus Li/Li+. Here, we present a proof-of-concept in situ pouch cell and methodology for correlative 2D synchrotron transmission X-ray microscopy with 3D lab-based micro-CT. XANES analysis of the TXM data enables tracking of Ni edge energy within and between the polycrystalline NMC811 particles embedded in the operating electrode through its initial delithiation. By using edge energy as a proxy, state-of-charge heterogeneities can be tracked at the nanoscale, revealing the role of cracked particles as potential nucleation points for failure and highlighting the challenges in achieving uniform (de-)lithiation. We propose, in future work, to leverage the pouch cell design presented here for longitudinal TXM-XANES studies of nickel-rich cathodes across multiple cycles and operating variables and investigate the effect of dopants and microstructural optimization in mitigating degradation.
Motion-enhancement Assisted Digital Image Correlation of Lithium-ion Batteries during Lithiation.
Anmol Jnawali, Anand N. P. Radhakrishnan, Matt D. R. Kok, Francesco Iacoviello, Dan J. L. Brett & Paul R. Shearing
Journal of Power Sources (2022) 527, 231150. DOI: 10.1016/j.jpowsour.2022.231150
For the first time, a motion enhancement and registration technique (MERt) – an advanced phase based motion enhancement method combined with an optical flow based digital image correlation process is used to investigate batteries. This, in combination with the non-invasive investigative nature of X-ray computed tomography, makes for a powerful tool to examine the mechanism behind (de)lithiation of Li-ion cells. Through MERt, which magnifies the displacement of electrodes and tracks any internal changes, it is generally observed that the electrode expands outwards, but once encountering the solid barrier that is the cell casing, the electrode has nowhere to expand but inwards, which is why the electrode deformations initiate at the cell core. The technique clearly affirms that the greatest movement of electrodes during lithiation occurs at pre-existing inflection points in the jelly roll, which are a result of the manufacturing process, and eventually leads to the large deformations observed in this and previous works. MERt also indicates a contortion of the cell casings during lithiation which may be caused by the uneven expansion of the electrodes, but requires further studies to confirm.
Controlling Li dendritic growth in graphite anodes by potassium electrolyte additives for Li-ion batteries.
Sanghamitra Moharana, Geoff West, Marc Walker, Xinjie S. Yan & Melanie Loveridge
ACS Applied Materials & Interfaces (2022) 14, 42078–42092, DOI: 10.1021/acsami.2c11175
Fast charging promotes Li dendrite formation and its growth on graphite anodes, which affects cell performance in Li-ion batteries (LIBs). This work reports the formation of a robust SEI layer by introducing a KPF6 inorganic additive into the electrolyte. An optimal concentration of 0.001 M KPF6 effectively inhibits the growth of Li dendrites at 2C charging rates, compared with a commercial electrolyte. Electrolytes containing a KPF6 additive are shown here to deliver dual effects to mitigate the growth of dendrites. A thin LiF-rich SEI layer is formed on graphite, which blocks the electron leakage pathways. Additionally, K+ resides at defect sites (such as particle boundaries) due to its faster diffusion rate and blocks the incoming Li+ and restricts the growth of Li dendrites. The electrolyte with optimum concentration of KPF6, i.e., 0.001 M, effectively directs Li+ transport through the thin, durable, and low resistance LiF-rich SEI layer. This has implications for fast charging through optimization of the electrode/electrolyte interphase by controlling additive concentrations.
