  Controlling nanostructure from molecular, crystal lattice to the electrode
level remains as arts in practice, where nucleation and growth of the crystals
still require more fundamental understanding and precise control to shape the
microstructure of metal deposits and their properties. This is vital to achieve
dendrite-free Li metal anodes with high electrochemical reversibility for
practical high-energy rechargeable Li batteries. Here, cryogenic-transmission
electron microscopy was used to capture the dynamic growth and atomic structure
of Li metal deposits at the early nucleation stage, in which a phase transition
from amorphous, disordered states to a crystalline, ordered one was revealed as
a function of current density and deposition time. The real-time atomic
interaction over wide spatial and temporal scales was depicted by the
reactive-molecular dynamics simulations. The results show that the condensation
accompanied with the amorphous-to-crystalline phase transition requires
sufficient exergy, mobility and time to carry out, contrary to what the
classical nucleation theory predicts. These variabilities give rise to
different kinetic pathways and temporal evolutions, resulting in various
degrees of order and disorder nanostructure in nano-sized domains that dominate
in the morphological evolution and reversibility of Li metal electrode.
Compared to crystalline Li, amorphous/glassy Li outperforms in cycle life in
high-energy rechargeable batteries and is the desired structure to achieve high
kinetic stability for long cycle life.
