Multi-Model Simulation of Li-Ion Dynamics in Battery Materials with Applied Electric Field

摘要

The possibility of combining multiple atomistic models within one single calculation allows one to achieve elaborate computational workflows. Here, we demonstrate the use of a multi-model approach, as implemented in the atomistic simulation platform QuantumATK, to investigate Li-ion diffusion in cathode materials, A multi-model approach can be used to study diffusion processes and mclude temperature effects by performing classical molecular dynamics (MD) simulations - in the presence of an external electric field, in which the time-dependent fluctuation of the atomic charges is described by density functional theory (DFT) calculations. Diffusion of ion species increases with temperature, as a natural consequence of the increase of hopping probability favoured by Brownian motion. However, in an electrochemical cell under operating conditions, the motion of the Li+ ions can also be expected to have a non-negligible drift component, due to the displacement field resulting from the voltage difference applied between the anode and the cathode. The combination of these two effects has seldom been considered in atomistic simulations and normally such atomistic simulations consider only one of the two. Here, we have applied the multi-model approach combining classical potentials with DFT to investigate the different components of the diffusion of Li+ ions along the [010] channels of LiFeP04 in the presence of an applied displacement field We demonstrate that the overall diffusion process is strongly dependent not only on the temperature itself, but also on the probability of collision events between the Li+ ions and the FeP04 lattice. This proves the importance of considering the combined effect of both the Brownian and drift contributions to the hopping for properly understanding and improving Li ion diffusions in cathode materials.