Preparation and Characterization of Li-Ion Graphite Anodes Using Synchrotron Tomography

Bridging nano- and microscale X-ray tomography for battery research by leveraging artificial intelligence

X-ray computed tomography (CT) is a non-destructive imaging technique in which contrast originates from the materials' absorption coefficient. The recent development of laboratory nanoscale CT (nano-CT) systems has pushed the spatial resolution for battery material imaging to voxel sizes of 50 nm, a limit previously achievable only with synchrotron facilities. Given the non-destructive nature of CT, in situ and operando studies have emerged as powerful methods to quantify morphological parameters, such as tortuosity factor, porosity, surface area and volume expansion, during battery operation or cycling. Combined with artificial intelligence and machine learning analysis techniques, nano-CT has enabled the development of predictive models to analyse the impact of the electrode microstructure on cell performances or the influence of material heterogeneities on electrochemical responses. In this Review, we discuss the role of X-ray CT and nano-CT experimentation in the battery field, discuss the incorporation of artificial intelligence and machine learning analyses and provide a perspective on how the combination of multiscale CT imaging techniques can expand the development of predictive multiscale battery behavioural models.

Synchrotron X-Ray Tomography for Rechargeable Battery Research: Fundamentals, Setups and Applications

Understanding the complicated interplay of the continuously evolving electrode materials in their inherent 3D states during the battery operating condition is of great importance for advancing rechargeable battery research. In this regard, the synchrotron X-ray tomography technique, which enables non-destructive, multi-scale, and 3D imaging of a variety of electrode components before/during/after battery operation, becomes an essential tool to deepen this understanding. The past few years have witnessed an increasingly growing interest in applying this technique in battery research. Hence, it is time to not only summarize the already obtained battery-related knowledge by using this technique, but also to present a fundamental elucidation of this technique to boost future studies in battery research. To this end, this review firstly introduces the fundamental principles and experimental setups of the synchrotron X-ray tomography technique. After that, a user guide to its application in battery research and examples of its applications in research of various types of batteries are presented. The current review ends with a discussion of the future opportunities of this technique for next-generation rechargeable batteries research. It is expected that this review can enhance the reader's understanding of the synchrotron X-ray tomography technique and stimulate new ideas and opportunities in battery research.

An X-ray Tomographic Study of Rechargeable Zn/MnO₂ Batteries

We present non-destructive and non-invasive in operando X-ray tomographic investigations of the charge and discharge behavior of rechargeable alkaline-manganese (RAM) batteries (Zn-MnO₂ batteries). Changes in the three-dimensional structure of the zinc anode and the MnO₂ cathode material after several charge/discharge cycles were analyzed. Battery discharge leads to a decrease in the zinc particle sizes, revealing a layer-by-layer dissolving behavior. During charging, the particles grow again to almost their initial size and shape. After several cycles, the particles sizes slowly decrease until most of the particles become smaller than the spatial resolution of the tomography. Furthermore, the number of cracks in the MnO₂ bulk continuously increases and the separator changes its shape. The results are compared to the behavior of a conventional primary cell that was also charged and discharged several times.

Multi-Scale Correlative Tomography of a Li-Ion Battery Composite Cathode

Focused ion beam/scanning electron microscopy tomography (FIB/SEMt) and synchrotron X-ray tomography (Xt) are used to investigate the same lithium manganese oxide composite cathode at the same specific spot. This correlative approach allows the investigation of three central issues in the tomographic analysis of composite battery electrodes: (i) Validation of state-of-the-art binary active material (AM) segmentation: Although threshold segmentation by standard algorithms leads to very good segmentation results, limited Xt resolution results in an AM underestimation of 6 vol% and severe overestimation of AM connectivity. (ii) Carbon binder domain (CBD) segmentation in Xt data: While threshold segmentation cannot be applied for this purpose, a suitable classification method is introduced. Based on correlative tomography, it allows for reliable ternary segmentation of Xt data into the pore space, CBD, and AM. (iii) Pore space analysis in the micrometer regime: This segmentation technique is applied to an Xt reconstruction with several hundred microns edge length, thus validating the segmentation of pores within the micrometer regime for the first time. The analyzed cathode volume exhibits a bimodal pore size distribution in the ranges between 0-1 μm and 1-12 μm. These ranges can be attributed to different pore formation mechanisms.

A new method for quantitative marking of deposited lithium by chemical treatment on graphite anodes in lithium-ion cells

A novel approach for the marking of deposited lithium on graphite anodes from large automotive lithium-ion cells (≥6 Ah) is presented. Graphite anode samples were extracted from two different formats (cylindrical and pouch cells) of pristine and differently aged lithium-ion cells. The samples present a variety of anodes with various states of lithium deposition (also known as plating). A chemical modification was performed to metallic lithium deposited on the anode surface due to previous plating with isopropanol (IPA). After this procedure an oxygenated species was detected by scanning electron microscopy (SEM), which later was confirmed as Li2 CO3 by Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRPD). A valuation of the covered area by Li2 CO3 was carried out with an image analysis using energy-dispersive X-ray spectroscopy (EDX) and quantitative Rietveld refinement.