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Over the last century, X-ray imaging instruments and their accompanying tomographic reconstruction algorithms have developed considerably. With improved tomogram quality and resolution, voxel sizes down to tens of nanometers can now be achieved. Moreover, recent advancements in readily accessible lab-based X-ray computed tomography (X-ray CT) instruments have produced spatial resolutions comparable to specialist synchrotron facilities. Electrochemical energy conversion devices, such as fuel cells and batteries, have inherently complex electrode microstructures to achieve competitive power delivery for consideration as replacements for conventional sources. With resolution capabilities spanning tens of microns to tens of nanometers, X-ray CT has become widely employed in the three-dimensional (3D) characterization of electrochemical materials. The ability to perform multiscale imaging has enabled characterization from system-down to particle-level, with the ability to resolve critical features within device microstructures. X-ray characterization presents a favorable alternative to other 3D methods, such as focused ion beam scanning electron microscopy, due to its non-destructive nature, which allows four-dimensional (4D) studies, three spatial dimensions plus time, linking structural dynamics to device performance and lifetime. X-ray CT has accelerated research from fundamental understanding of the links between cell structure and performance, to the improvement in manufacturing and scale-up of full electrochemical cells. Furthermore, this has aided in the mitigation of degradation and cell-level failures, such as thermal runaway. This review presents recent developments in the use of X-ray CT as a characterization method and its role in the advancement of electrochemical materials engineering. [ABSTRACT FROM AUTHOR]

Abstract In recent years, the ability to examine the processes that cause the catastrophic failure of batteries as a result of thermal runaway has improved substantially. In this work, the effect of thermal runaway on the microstructure of the electrodes of a Na-ion battery is examined using X-ray computed tomography for the first time. The thermal failure induced via accelerating rate calorimetry enabled the examination of failed electrodes, which were subsequently compared with fresh samples. Pre- and post-mortem microstructural analysis shows changes in both electrodes as a result of the thermal runaway process at the micrometre length-scale. It is seen that the cathode shows the largest changes in structure, with the anode remaining morphologically similar post-failure at the sub-micron length-scale. The formation of a highly X-ray attenuating layer, which is proposed to be a metallic product of the thermal runaway reaction, is observed, indicating that the thermal runaway mechanisms which occur in Na-ion batteries may be similar to those reported for Li-ion systems. Graphical abstract Image 1 Highlights • Na-ion electrodes examined after undergoing thermal runaway at two length scales. • Bulk changes in both electrodes observed at micro-scale. • Nano-scale analysis highlights similar anode morphology post failure. • Cathode observed to be fundamentally degraded due to the runaway reaction. • Reduction of cathode and crossover of anode material detailed after thermal failure. [ABSTRACT FROM AUTHOR]

Fracture of lithium-ion battery electrodes is found to contribute to capacity fade and reduce the lifespan of a battery. Traditional fracture models for batteries are restricted to consideration of a single, idealised particle; here, advanced X-ray computed tomography (CT) imaging, an electro-chemo-mechanical model and a phase field fracture framework are combined to predict the void-driven fracture in the electrode particles of a realistic battery electrode microstructure. The electrode is shown to exhibit a highly heterogeneous electrochemical and fracture response that depends on the particle size and distance from the separator/current collector. The model enables prediction of increased cracking due to enlarged cycling voltage windows, cracking susceptibility as a function of electrode thickness, and damage sensitivity to discharge rate. This framework provides a platform that facilitates a deeper understanding of electrode fracture and enables the design of next-generation electrodes with higher capacities and improved degradation characteristics. [Display omitted] • Realistic fracture predictions in an entire electrode microstructure. • Highly heterogeneous electrochemical and fracture response is predicted. • Prediction of elevated cracking due to enlarged cycling voltage windows. • Cracking shown to occur as a function of electrode thickness. • Increasing damage as the rate of discharge is increased. [ABSTRACT FROM AUTHOR]

Diagnostic systems for Li-ion batteries have become increasingly important due to the larger size, and cost of the batteries being deployed in increasingly demanding applications, including electric vehicles. Here, ultrasound acoustic time-of-flight (ToF) analysis is conducted under a range of operating conditions. Measurements are performed on a commercial pouch cell during varying discharge rates to identify a range of effects that influence the acoustic ToF measurements. The cell was examined using X-ray computed tomography to ensure no significant defects were present and to confirm the layered structure in the region being investigated, validating the signal pattern observed. Analyses of the acoustic signals obtained suggest that stresses are generated in the electrodes during both the charge and discharge of the cell with the magnitude of Young's modulus for the component materials being both a function of the state-of-charge and applied current. Characteristic responses for both electrodes during the charge/discharge cycle highlight the potential application of the technique as a real-time diagnostic tool. • Ultrasound measurement demonstrated as a potential operando diagnostic for Li-ion batteries. • Response of batteries shown to be highly rate dependent at large C-rates. • Time-of-flight measurement shown to identify electrochemical stiffness in cells. [ABSTRACT FROM AUTHOR]