Modeling early-stage solid-state crystallization of amorphous LiCoO2 under flash lamp annealing

The crystallinity of LiCoO2 (LCO) cathodes is essential for the performance of thin-film solid-state batteries. Flash-lamp annealing (FLA) can crystallize amorphous LCO within milliseconds, as a single 1.75 ms pulse heats the precursor to above 1000 K. Here we resolve the early stages of this rapid crystallization with isothermal molecular dynamics simulations at FLA-relevant temperatures using an Allegro machine-learning potential trained on stoichiometric LCO. The crystallization enthalpy is about -130 kJ/mol, negligible relative to the FLA pulse energy. Primary grains of the rock-salt-type host lattice nucleate at random orientations, and most retain a nearly random distribution of Li and Co cations. With increasing temperature the trajectories pass from a nucleation-and-growth regime to Ostwald-style coarsening. Importantly, nucleation and initial crystallization occur within nanoseconds, far shorter than the FLA pulse duration.