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Li-Mg alloys are promising as positive electrodes (anodes) for Li-ion batteries due to the high Li storage capacity and the relatively lower volume change during the lithiation/delithiation process. They also present a unique opportunity to image the Li distribution through the electrode thickness at various delithiation states. In this work, spatial distributions of Li in electrochemically delithiated Li-Mg alloy electrodes have been quantitatively determined using neutron tomography. Specifically, the Li concentration profiles along thickness direction are determined. A rigorous analytical model to quantify the diffusion-controlled delithiation, accompanied by phase transition and boundary movement, has also been developed to explain the delithiation mechanism. The analytical modeling scheme successfully predicted the Li concentration profiles which agreed well with the experimental data. It is demonstrated that during discharge Li is removed by diffusion through the solid solution Li-Mg phases and this proceeds with β→α phase transition and the associated phase boundary movement through the thickness of the electrode. This is also accompanied by electrode thinning due to the change in molar volume during delithiation. Following the approaches developed here, one can develop a rigorous and quantitative understanding of electrochemical delithiation in electrodes of electrochemical cells, similar to that in the present Li-Mg electrodes. [ABSTRACT FROM AUTHOR]

Neutron radiography was used to investigate capillary uptake of water in Berea sandstone, which is widely used as a standard porous medium in flow and transport studies. The sorptivity and unsaturated diffusivity function were estimated from analyses of the neutron radiographs. These parameters have not been previously reported for this material. Neutron radiography is increasingly being used to study the dynamics of water movement in variably saturated porous media. It has been applied to visualize water imbibition in both natural and engineered materials, including soil, rock, brick, concrete, and glass. The sorptivity, S, and unsaturated diffusivity, D(θ), are important parameters for describing water movement under partially saturated conditions. Estimates of S and D(θ) have been obtained using a variety of techniques, including neutron imaging. However, we could find no previous reports of such measurements for the Berea sandstone, regardless of the method employed. Berea sandstone is a widespread, medium- to fine-grained terrestrial sandstone of Mississippian age that is used extensively as a standard porous medium in the geology and petroleum engineering fields. We used the CG-1D neutron imaging facility at the High Flux Isotope Reactor of Oak Ridge National Laboratory to estimate S and D(θ) from radiographs acquired every 26 s. A 25 -1/4m thick LiF/ZnS scintillator was employed in conjunction with a DW936 IkonL ANDOR charge coupled device (CCD) camera system, giving a spatial imaging resolution of -1/475-1/4m. Four replicate cores were investigated. The positions of the observed wetting fronts were linearly regressed against the square root of time. Sorptivity values calculated from the slopes of these relations ranged from 0.89 to 1.46 mm s-1/2. Further analysis yielded D(θ) functions. These functions were very reproducible and showed good agreement with independent D(θ) values calculated from relative permeability and capillary pressure-saturation data for Berea sandstone. To the best of our knowledge, these are the first published estimates of S and D(θ) for Berea sandstone. Our results clearly demonstrate the effectiveness of neutron imaging in providing high quality, quantitative data for the computation of unsaturated flow parameters [ABSTRACT FROM AUTHOR]