Real-time Observation of Deep Lithiation of Tungsten Oxide Nanowires by In Situ Electron Microscopy.

An in-depth mechanistic understanding of the electrochemical lithiation process of tungsten oxide (WO3 ) is both of fundamental interest and relevant for potential applications. One of the most important features of WO3 lithiation is the formation of the chemically flexible, nonstoichiometric Lix WO3 , known as tungsten bronze. Herein, we achieved the real-time observation of the deep electrochemical lithiation process of single-crystal WO3 nanowires by constructing in situ transmission electron microscopy (TEM) electrochemical cells. As revealed by nanoscale imaging, diffraction, and spectroscopy, it is shown that the rapid and deep lithiation of WO3 nanowires leads to the formation of highly disordered and near-amorphous Lix WO3 phases, but with no detectable traces of elemental W and segregated Li2 O phase formation. These results highlight the remarkable chemical and structural flexibility of the Lix WO3 phases in accommodating the rapid and deep lithiation reaction.