In situ TEM observation of lithium nanoparticle growth and morphological cycling.

Lithium fluoride crystals were subjected to electron beam irradiation at 200 and 300 keV using transmission electron microscopy in order to study in situ fabrication of Li nanostructures. We observed that LiF crystals decompose in a unique way different to all other metal halides: Fluorine ablation and salt-to-metal conversion is non-local and due to a rapid lateral diffusion of Li, the life cycle from nucleation to annihilation of fresh Li nano-crystals can be observed at a distance from the Li-source, the irradiated salt. Growth, shape transition and annihilation of Li nanostructures follow at slow enough speed for live video recording with resolution of 25 frames per second. The equilibrium shapes of pure Li nano-crystals range from cubic to rod-shaped and ball-shaped and up to 300 nm size. By varying the e-beam flux of irradiation, transitions from cube to spherical shape can be induced cyclically.