Multiscale Modeling of Phase Evolution and Li-Ion Transport Kinetics in Boron Nitride Membranes

Boron nitride (BN) has gained attention in the field of electrochemistry due to its controllable surface chemistry and adjustable bandgap, along with mechanical robustness, thermal stability, and chemical inertness. In this work, we examine Li-ion migration behavior in defected hexagonal BN (hBN) using first-principles methods, towards applications as a separator or protected membrane in Li batteries. By comparing the activation energies of Li-ion diffusion along in-plane (between the BN layers) and out-of-plane (across the BN layers) pathways, we find that pristine hBN permits in-plane Li-ion diffusion with a relatively low energy barrier of 0.34 eV, while prohibiting out-of-plane Li-ion diffusion due to a high energy barrier (6.68 eV). Introducing defects is found effective to unlock the out-of-plane diffusion pathway despite the fact that local vacancies can trap Li and influence its consequent in-plane diffusion near the vacancy sites. In addition to the investigation of Li-ion transport behavior in hBN, we evaluate its phase stability by directly extracting its phase evolution kinetics from large-scale molecular dynamics simulations enabled by a machine-learning interatomic potential. We further investigate the impact of microstructure on the BN phase evolution kinetics and link it to various experimentally relevant conditions, which can ultimately allow us to establish strategies to fabricate BN membranes with desired properties.<br/><br/>This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.