Driving range and fast charge capability of electric vehicles are heavily dependent on the 3D microstructure of lithium-ion batteries (LiBs) and substantial fundamental research is required to ...optimise electrode design for specific operating conditions. Here we have developed a full microstructure-resolved 3D model using a novel X-ray nano-computed tomography (CT) dual-scan superimposition technique that captures features of the carbon-binder domain. This elucidates how LiB performance is markedly affected by microstructural heterogeneities, particularly under high rate conditions. The elongated shape and wide size distribution of the active particles not only affect the lithium-ion transport but also lead to a heterogeneous current distribution and non-uniform lithiation between particles and along the through-thickness direction. Building on these insights, we propose and compare potential graded-microstructure designs for next-generation battery electrodes. To guide manufacturing of electrode architectures, in-situ X-ray CT is shown to reliably reveal the porosity and tortuosity changes with incremental calendering steps.
The performance of lithium ion electrodes is hindered by unfavorable chemical heterogeneities that pre-exist or develop during operation. Time-resolved spatial descriptions are needed to understand ...the link between such heterogeneities and a cell's performance. Here, operando high-resolution X-ray diffraction-computed tomography is used to spatially and temporally quantify crystallographic heterogeneities within and between particles throughout both fresh and degraded Li
Mn
O
electrodes. This imaging technique facilitates identification of stoichiometric differences between particles and stoichiometric gradients and phase heterogeneities within particles. Through radial quantification of phase fractions, the response of distinct particles to lithiation is found to vary; most particles contain localized regions that transition to rock salt LiMnO
within the first cycle. Other particles contain monoclinic Li
MnO
near the surface and almost pure spinel Li
Mn
O
near the core. Following 150 cycles, concentrations of LiMnO
and Li
MnO
significantly increase and widely vary between particles.
Optimizing the chemical and morphological parameters of lithium-ion (Li-ion) electrodes is extremely challenging, due in part to the absence of techniques to construct spatial and temporal ...descriptions of chemical and morphological heterogeneities. We present the first demonstration of combined high-speed X-ray diffraction (XRD) and XRD computed tomography (XRD-CT) to probe, in 3D, crystallographic heterogeneities within Li-ion electrodes with a spatial resolution of 1 μm. The local charge-transfer mechanism within and between individual particles was investigated in a silicon(Si)−graphite composite electrode. High-speed XRD revealed charge balancing kinetics between the graphite and Si during the minutes following the transition from operation to open circuit. Subparticle lithiation heterogeneities in both Si and graphite were observed using XRD-CT, where the core and shell structures were segmented, and their respective diffraction patterns were characterized.
Calendering is a crucial manufacturing process in the optimization of battery performance and lifetime due to its significant effect on the 3D electrode microstructure. By conducting an in situ ...calendering experiment on lithium-ion battery cathodes using X-ray nano-computed tomography, here we show that the electrodes composed of large particles with a broad size distribution experience heterogeneous microstructural self-arrangement. At high C-rates, the performance is predominantly restricted by sluggish solid-state diffusion, which is exacerbated by calendering due to the increased microstructural and lithiation heterogeneity, leading to active material underutilization. In contrast, electrodes consisting of small particles are structurally stable with more homogeneous deformation and a lower tortuosity, showing a much higher rated capacity that is less sensitive to calendering densification. Finally, the dependence of performance on the dual variation of both porosity and electrode thickness is investigated to provide new insights into the microstructural optimization for different applications in electrode manufacturing.
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•Electrode with coarse architecture is prone to self-arrangement under calendering•Solid-state diffusion determines the performance of a large-particle electrode•Small-particle electrode maintains high power performance under calendering•Calendering exacerbates reaction heterogeneity and underutilization of capacity
The rapid evolution of electric vehicles market has inspired a major effort in the fundamental research of lithium-ion batteries (LiBs). A rationalized electrode-processing philosophy is critical to improve the rate capability, capacity, cycle life, and safety of LiBs. Calendering is one of the key production steps that tunes the energy and power performance for different applications by tailoring the 3D microstructure of the electrodes. Here, we conduct an in situ compression experiment to replicate the calendering process on LiB electrodes. Using X-ray nano-computed tomography, we track the electrode’s microstructural evolution and correlate it with the battery performance. The critical porosity and electrode thickness are suggested, beyond which a catastrophic drop is expected in battery performance. Knowledge gained from this study is anticipated to suggest a route to maximise the energy and power density of batteries via electrode design and manufacturing for demanding applications.
Calendering is a critical step in the production of the lithium-ion battery, as it reduces the electrode thickness compressively to achieve high energy density, which significantly determines the driving range of electric vehicles. This study conducts an in situ calendering experiment on lithium-ion battery cathodes using X-ray nano-computed tomography to correlate the microstructural evolution with the electrochemical performance so as to rationalize the manufacturing process. Distinct susceptibility of microstructure and performance is found for electrodes composed of large and small particles.
Lithium-based rechargeable batteries such as lithium-ion (Li-ion), lithium-sulfur (Li-S), and lithium-air (Li-air) cells typically consist of heterogenous porous electrodes. In recent years, there ...has been growing interest in the use of in-situ and operando micro-CT to capture their physical and chemical states in 3D. The development of in-situ electrochemical cells along with recent improvements in radiation sources have expanded the capabilities of micro-CT as a technique for longitudinal studies on operating mechanisms and degradation. In this paper, we present an overview of the capabilities of the current state of technology and demonstrate novel tomography cell designs we have developed to push the envelope of spatial and temporal resolution while maintaining good electrochemical performance. A bespoke PEEK in-situ cell was developed, which enabled imaging at a voxel resolution of ca. 230 nm and permitted the identification of sub-micron features within battery electrodes. To further improve the temporal resolution, future work will explore the use of iterative reconstruction algorithms, which require fewer angular projections for a comparable reconstruction.
Lithium sulfur (Li-S) batteries offer higher theoretical specific capacity, lower cost and enhanced safety compared to current Li-ion battery technology. However, the multiple reactions and phase ...changes in the sulfur conversion cathode result in highly complex phenomena that significantly impact cycling life. For the first time to the authors' knowledge, a multi-scale 3D in-situ tomography approach is used to characterize morphological parameters and track microstructural evolution of the sulfur cathode across multiple charge cycles. Here we show the uneven distribution of the sulfur phase fraction within the electrode thickness as a function of charge cycles, suggesting significant mass transport limitations within thick-film sulfur cathodes. Furthermore, we report a shift towards larger particle sizes and a decrease in volume specific surface area with cycling, suggesting sulfur agglomeration. Finally, we demonstrate the nano-scopic length-scale required for the features of the carbon binder domain to become discernible, confirming the need for future work on in-situ nano-tomography. We anticipate that X-ray tomography will be a powerful tool for optimization of electrode structures for Li-S batteries.
Among the aqueous redox flow battery systems, redox chemistries using a zinc negative electrode have a relatively high energy density, but the potential of achieving high power density and long cycle ...life is hindered by dendrite growth at the anode. In this study, a new cell design with a narrow gap between electrode and membrane was applied in a zinc-iodide flow battery. In this design, some of the electrolyte flows over the electrode surface and a fraction of the flow passes through the porous felt electrode in the direction of current flow. The flow battery was tested under constant current density over 40 cycles, and the efficiency, discharge energy density, and power density of the battery were significantly improved compared to conventional flow field designs. The power density obtained in this study is one of the highest power densities reported for the zinc-iodide battery. The morphology of the zinc deposition was studied using scanning electron microscopy and optical profilometry. It was found that the flow through the electrode led to a thinner zinc deposit with lower roughness on the surface of the electrode, in comparison to the case where there was no flow through the electrode. In addition, inhibition of dendrite formation enabled operation at a higher range of current density. Ex situ tomographic measurements were used to image the zinc deposited on the surface and inside the porous felt. Volume rendering of graphite felt from X-ray computed tomography images showed that in the presence of flow through the electrode, more zinc deposition occurred inside the porous felt, resulting in a compact and thinner surface deposit, which may enable higher battery capacity and improved performance.
Due to complex degradation mechanisms, disparities between the theoretical and practical capacities of lithium-ion battery cathode materials persist. Specifically, Ni-rich chemistries such as ...LiNi0.8Mn0.1Co0.1O2 (or NMC811) are one of the most promising choices for automotive applications; however, they continue to suffer severe degradation during operation that is poorly understood, thus challenging to mitigate. Here we use operando Bragg coherent diffraction imaging for 4D analysis of these mechanisms by inspecting the individual crystals within primary particles at various states of charge (SoC). Although some crystals were relatively homogeneous, we consistently observed non-uniform distributions of inter- and intracrystal strain at all measured SoC. Pristine structures may already possess heterogeneities capable of triggering crystal splitting and subsequently particle cracking. During low-voltage charging (2.7–3.5 V), crystal splitting may still occur even during minimal bulk deintercalation activity; and during discharging, rotational effects within parallel domains appear to be the precursor for the nucleation of screw dislocations at the crystal core. Ultimately, this discovery of the central role of crystal grain splitting in the charge/discharge dynamics may have ramifications across length scales that affect macroscopic performance loss during real-world battery operation.
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•Crack detection in lithium-ion battery electrodes.•Machine learning approach.•Development of classification model using stochastic 3D microstructure model.•Verification on ...hand-labelled tomography data from real electrode.
It is an open question how the particle microstructure of a lithium-ion electrode influences a potential thermal runaway. In order to investigate this, information on the structural changes, in particular cracked particles, caused by the failure are desirable. For a reliable analysis of these changes a reasonably large amount of data is necessary, which necessitates automatic extraction of particle cracks from tomographic 3D image data. In this paper, a classification model is proposed which is able to decide whether a pair of particles is the result of breakage, of the image segmentation, or neither. The classifier is developed using simulated data based on a 3D stochastic particle model. Its validity is tested by applying the methodology to hand-labelled data from a real electrode. For this dataset, an overall accuracy of 73% is achieved.
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