Glassy Li Metal Anode for High-Performance Rechargeable Li Batteries

TL;DR

This study uses advanced microscopy and simulations to understand the nucleation and growth of lithium metal deposits, revealing phase transitions that influence the morphology and stability of Li anodes for high-performance batteries.

Contribution

It uncovers the atomic-scale dynamics of Li nucleation, demonstrating the importance of amorphous structures for improved battery cycle life.

Findings

Amorphous-to-crystalline transition depends on exergy, mobility, and time.

Amorphous Li outperforms crystalline Li in cycle life.

Kinetic pathways influence nanostructure and reversibility.

Abstract

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.