X-ray diffraction microscopy of lithiated silicon microstructures

Optically patterned silicon microstructures show great promise as lithium ion battery electrodes as they can balance the high intrinsic charge capacity of silicon with its large volume changes during repeated cycling. Previous scanning electron microscopy showed that lithiation initially occurs at (110)-oriented facets, but was not directly sensitive to the amount of crystalline silicon within the core of each microstructure. Here, we image the extent of the lithiation and the degree of residual crystallinity in individual silicon micro-posts directly using full-field x-ray reflection interfacial microscopy (XRIM). Images of the silicon posts are interpreted using a straightforward model relevant for XRIM images obtained from large scale topological features. This approach should be widely applicable to a broad range of battery materials and for probing the liquid/solid interfaces of complex heterostructures during lithiation reactions.