In situ TEM investigation of hexagonal WO3 irreversible transformation to Li2WO4.

Lithium-ion migration at the WO 3 /electrolyte interface is governed by the phase transformation mechanism by which metastable states are replaced from one phase to another. Herein, an in situ single nanowire-based cell is constructed to investigate the dynamic phase transformation and morphology evolution of h-WO 3 nanowire in real-time during its deep lithiation. One of the most significant features of h-WO 3 lithiation is the irreversible transformation from h-WO 3 to Li 2 WO 4. There are a large number of deep ion-trapping sites composed of 4 O atoms in Li 2 WO 4 crystal structure, that is, inserted lithium ions are irreversibly bound in these traps and nearly cannot be deintercalated. A mechanism on irreversible WO 3 -to-Li 2 WO 4 transformation in deep lithiation reaction is demonstrated. With the aid of in situ transmission electron microscopy, we controllably triggered lithium-ion migration at the WO 3 /electrolyte interface and directly visualized the nanoscale lithium-ion migration as a stop motion movie. Hexagonal WO 3 irreversible transformation to Li 2 WO 4 can be experimentally demonstrated via in situ HRTEM in the deep lithiation process including the initial activation of the lithium metal, the wetting of a single WO 3 nanowire and the migration of lithium ions into WO 3 , and the restructuring of hexagonal WO 3. [Display omitted] [ABSTRACT FROM AUTHOR]