Mapping of Spatial Inhomogeneities with Laboratory X-Ray Diffraction

Abstract

We have developed a new laboratory X-ray diffraction technique to probe meso-scale inhomogeneities in battery cathode materials. Conventional diffraction uses an X-ray beam that covers most of the cathode surface, giving average properties over all locations. In contrast, our technique uses a laboratory diffractometer with a sub-millimeter beam to extract location-specific structure information. Up until now, this has only been reported with synchrotron radiation. We have used this technique to uncover inhomgeneities related to a variety of factors, such as preparation technique, the size and position of the anode, and the charge rate of the cell. For example, in one experiment, sections of an LiMn₂O₄ cathode were found to lag behind the global state in areas of poor contact with the current collector. This effect was not seen at slow rates (C/10), however, suggesting that alternate electrical pathways are still available, though kinetically less viable. This technique can also be used to map an electrode's cross-section to find effects occuring along the direction of charge flow.