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 (WO 3 ) is both of fundamental interest and relevant for potential applications. One of the most important features of WO 3 lithiation is the formation of the chemically flexible, nonstoichiometric Li x WO 3 , known as tungsten bronze. Herein, we achieved the real‐time observation of the deep electrochemical lithiation process of single‐crystal WO 3 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 WO 3 nanowires leads to the formation of highly disordered and near‐amorphous Li x WO 3 phases, but with no detectable traces of elemental W and segregated Li 2 O phase formation. These results highlight the remarkable chemical and structural flexibility of the Li x WO 3 phases in accommodating the rapid and deep lithiation reaction.