Inherently uncontrollable Li electrodeposition has significantly hindered the practical application of Li metal batteries largely due to a dendritic deposition which can initiate an internal short ...circuit and gives rise to severe safety issues. The understanding of the fundamental electrodeposition mechanism is, however, elusive and limited due to a lack of feasible in situ characterization techniques. Here synchrotron X-ray tomography was employed to noninvasively visualize Li deposition at the lithium/separator and lithium/carbon matrix interregion. A higher concentration of widely distributed deposition sites was observed under an increased current density. The 3D morphology and distribution of deposited Li within the widely used Celgard® 2325 polyolefin separator are, for the first time, visualized in situ, thus promoting the understanding of the short-circuiting process of Li metal batteries. In addition, we also visualized and quantified the spatial distribution of Li depositions inside a porous carbon host to unravel the deposition behavior that can hardly be probed by surface imaging techniques. The Li electrodeposition behavior found here could help to promote the understanding and development of surface modifications related to Li anodes, separators as well as novel 3D geometry electrode designs for accommodation of Li depositions and alleviation of volumetric changes.
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•The 3D morphology and distribution of Li deposition within Celgard® 2325 separator are visualized in situ.•An increased current density was found to bring about a higher concentration Li deposition sites.•The spatial distribution of Li depositions inside a porous carbon host is visualized and quantified.
Water dynamics in the membrane electrode assembly (MEA) and flow channels of polymer electrolyte fuel cells (PEFCs) is governed by the complex interplay of many physical and operational factors. The ...chemical nature and structure of the gas diffusion layer (GDL) plays a large part in this and is affected by the extent to which is mechanically compressed. Here, X-ray computed tomography shows the effect of cell compression on the MEA, and how it differs under the land and channel regions. Multi-orientation neutron radiography reveals the effect of compression on the way in which water accumulates and is transported between land and channel and between cathode and anode. By performing neutron imaging in both the in-plane and through-plane directions, it is possible to determine what constitutes a given ‘thickness’ of water mapped across the extent of an MEA. Changing MEA compression from 25% to 35% has a significant effect on water distribution and dynamics in operational cells. The effect of compression on performance is most marked in the mass transport region, and there are consequences for liquid accumulation in channels and back-diffusion of water from the cathode to the anode.
•Neutron radiography and X-ray CT study of PEFC compression.•Effect of compression and channel/land arrangement on the water dynamics.•Combined analysis through the in-plane and the through-plane radiographs.•Effect of compression on water removal efficiency and back-diffusion of water.
Innovative solutions have been designed to meet the global demand for energy and environmental sustainability, such as enhanced hydrocarbon recovery and geo-sequestration of CO
. These processes ...involve the movement of immiscible fluids through permeable rocks, which is affected by the interfacial properties of rocks at the pore scale. Overcoming major challenges in these processes relies on a deeper understanding about the fundamental factors that control the rock wettability. In particular, the efficiency of oil recovery strategies depends largely on the 3D wetting pattern of reservoir rocks, which is in turn affected by the adsorption and deposition of 'contaminant' molecules on the pores' surface. Here, we combined high-resolution neutron tomography (NT) and synchrotron X-ray tomography (XRT) to probe the previously unobserved 3D distribution of molecular and mineralogical heterogeneity of oil reservoir rocks at the pore scale. Retrieving the distribution of neutron attenuation coefficients by Monte Carlo simulations, 3D molecular chemical mappings with micrometer dimensions could be provided. This approach allows us to identify co-localization of mineral phases with chemically distinct hydrogen-containing molecules, providing a solid foundation for the understanding of the interfacial phenomena involved in multiphase fluid flow in permeable media.
Using phase-contracted synchrotron X-ray tomography, this study investigates the water distribution within the microporous layer (MPL) of polymer electrolyte membrane fuel cells (PEMFCs). Synchrotron ...X-ray tomography used to analyze the water distribution in the whole gas diffusion medium (GDM), which comprises the microporous layer (MPL) and the gas diffusion layer (GDL). The MPL has already been identified. In the future, the development of GDMs could be employed to enhance the performance and operating conditions of PEMFCs.
We present the first high-resolution synchrotron X-ray study on high temperature polymer electrolyte fuel cells (HT-PEFCs) in through-plane mode. Distribution and evolution of the phosphoric acid in ...the membrane electrode assembly was monitored in situ/in-operando under different operating conditions at steady states. At current densities of 350 mA cm super(-2) and 600 mA cm super(-2) significant changes in local media distribution were detected mainly beneath the channels of the flow field. We assign this effect to a varying degree of acid doping over the active region. Furthermore it was found that parts of the electrode structure were moved and partly irreversibly displaced after cell operation at load conditions. This effect might contribute to structural aging of the electrodes.
The influence of gradients in hardness and elastic properties at interfaces of dissimilar materials in laminated metallic composites (LMCs) on fatigue crack propagation is investigated experimentally ...for three different LMC systems: Al/Al-LMCs with dissimilar yield stress and Al/Steel-LMCs as well as Al/Ti/Steel-LMCs with dissimilar yield stress and Young’s modulus, respectively. The damage tolerant fatigue behavior in Al/Al-LMCs with an alternating layer structure is enhanced significantly compared to constituent monolithic materials. The prevalent toughening mechanisms at the interfaces are identified by microscopical methods and synchrotron X-ray computed tomography. For the soft/hard transition, crack deflection mechanisms at the vicinity of the interface are observed, whereas crack bifurcation mechanisms can be seen for the hard/soft transition. The crack propagation in Al/Steel-LMCs was studied conducting in-situ scanning electron microscope (SEM) experiments in the respective low cycle fatigue (LCF) and high cycle fatigue (HCF) regimes of the laminate. The enhanced resistance against crack propagation in the LCF regime is attributed to the prevalent stress redistribution, crack deflection, and crack bridging mechanisms. The fatigue properties of different Al/Ti/Steel-LMC systems show the potential of LMCs in terms of an appropriate selection of constituents in combination with an optimized architecture. The results are also discussed under the aspect of tailored lightweight applications subjected to cyclic loading.
We present an approach for multi-layer preparation to perform microstructure analysis of a Li-ion cell anode active material using synchrotron tomography. All necessary steps, from the disassembly of ...differently-housed cells (pouch and cylindrical), via selection of interesting layer regions, to the separation of the graphite-compound and current collector, are described in detail. The proposed stacking method improves the efficiency of synchrotron tomography by measuring up to ten layers in parallel, without the loss of image resolution nor quality, resulting in a maximization of acquired data. Additionally, we perform an analysis of the obtained 3D volumes by calculating microstructural characteristics, like porosity, tortuosity and specific surface area. Due to a large amount of measurable layers within one stacked sample, differences between aged and pristine material (e.g., significant differences in tortuosity and specific surface area, while porosity remains constant), as well as the homogeneity of the material within one cell could be recognized.
In order for electrolysis cells to operate optimally, mass transport must be improved. The key initial component for optimal operation is the current collector, which is also essential for mass ...transport. Water as an educt of the reaction must be evenly distributed by the current collector to the membrane electrode assembly. As products of the reaction, hydrogen and oxygen must also be directed quickly and efficiently through the current collector into the channel and removed from the cell. The second key component is the stoichiometry, which includes the current density and water volume flow rate and represents the ratio between the water supplied and water consumed. This study presents the correlation of the stoichiometry, two-phase flow in the channel and gas fraction in the porous transport layer for the first time. The gas-water ratio in the channel and porous transport layer during cell operation with various stoichiometries was investigated by means of a model in the form of an ex situ cell without electrochemical processes. Bubble formation in the channel was observed using a transparent cell. The gas-water exchange in the porous transport layer was then investigated using neutron radiography.
Li dendrites penetration through solid electrolytes (SEs) challenges the development of solid‐state Li batteries (SSLBs). To date, significant efforts are devoted to understand the mechanistic ...dynamics of Li dendrites nucleation, growth, and propagation in SEs, and various strategies that aim to alleviate and even inhibit Li dendrite formation have been proposed. Nevertheless, most of these conventional strategies require either additional material processing steps or new materials/layers that eventually increase battery cost and complexity. In contrast, using external fields, such as mechanical force, temperature physical field, electric field, pulse current, and even magnetic field to regulate Li dendrites penetration through SEs, seems to be one of the most cost‐effective strategies. This review focuses on the current research progress of utilizing external physical fields in regulating Li dendrites growth in SSLBs. For this purpose, the mechanical properties of Li and SEs, as well as the experimental results that visually track Li penetration dynamics, are reviewed. Finally, the review ends with remaining open questions in future studies of Li dendrites growth and penetration in SEs. It is hoped this review can shed some light on understanding the complex Li dendrite issues in SSLBs and potentially guide their rational design for further development.
This review focuses on the current research progress of utilizing a variety of external physical fields to regulate lithium dendrites penetration in all solid‐state batteries. To this end, the mechanical properties of lithium and solid electrolytes as well as the experimental results that visually track lithium penetration dynamics are also reviewed.
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