Asma Medjahed | Searcharxiv

arXiv2025

Dead, Slow and Overworked Graphite: Operando X-ray Microdiffraction Mapping of Aged Electrodes

Aging limits lithium-ion battery lifetime and must be understood to improve durability and performance, requiring a detailed understanding of how aging alters the availability of cyclable lithium and the integrity of active particles. In this work, (de)lithiation mechanisms are examined and spatially-resolved at the microscale in aged graphite electrodes dismounted from a large format graphite/LiFePO4-Li(NiCoAl)O2 cell at 70% remaining capacity. A multi-technique workflow is employed, combining electrochemical methods with post-mortem structural and morphological analyses, and introducing synchrotron microX-ray 2D diffraction imaging as a technique to probe aged graphite, applied at C-rates from C/5 to C. In-plane and through-plane heterogeneities in graphite dynamics are evidenced, showing the presence of inactive regions localized in two dimensions. In these areas, particles are either disconnected (irreversibly lost) or kinetically limited (reactivated at a slow C-rate), with dead or slow particles exhibiting a wide range of compositions, from x = 0 to x = 1 in LixC6. These inactivated graphite particles are found to be heterogeneously distributed throughout the depth of the aged negative electrode. In particular, the most inactivated region localizes at the negative electrode-separator interface, correlating to overworking graphite near the separator.

cond-mat.mtrl-sci↗

arXiv2025

The crystalline properties of silica biomorphs vary within and between morphologies

Silica-witherite biomorphs are a class of emergent materials, i.e. composite microstructures made of nanometric barium carbonate surrounded by amorphous silica. They form via co-precipitation of barium carbonate and siliceous species, and self-organize into a multitude of shapes with a distinct long-range order of the carbonate nanocrystals. However, the internal structural organization within and across different morphologies remains insufficiently resolved. Here, we use X-ray texture and diffraction tomography to create three-dimensional, spatially resolved maps of crystallographic orientation and structural parameters in silica-witherite biomorphs. At the sub-micron voxel level, all morphologies exhibit a crystallographic order consistent with a fiber texture around the c-axis. At larger length scales, however, the orientation field as well as crystallite size, crystallite shape anisotropy and the unit cell volume show systematic spatial variations. Leaf-like and helical morphologies contain defined directions along which structural parameters change systematically. Furthermore, we find recurring structural regimes with strong similarities between these morphologies. Conversely, coral-like morphologies are overall less textured and outside of the nucleation region we do not find clear structural regimes in the crystalline properties. These results provide a three-dimensional description of the internal organization of crystallites in silica-witherite biomorphs and establish a basis for systematically relating crystallographic organization to morphology.

cond-mat.mtrl-sci↗