Multiscale reaction modeling via a subgrid approach for the lattice Boltzmann method

Abstract

Many electrochemical effects impact processes of interest over multiple length scales. Examples in the field of batteries and fuel cells are for instance nucleation and growth, occurring in lithium-sulfur batteries, or (electro)-chemical reactions at platinum nano-particles in fuel cells. Understanding the impacts across length scales is vital to understanding a system at a whole. For that, computational simulations can provide detailed insight. For mesoscopic problems, lattice Boltzmann methods (LBM) have seen increasing usage due to their sound physical basis and efficient computational parallelization.

However, accurate simulation of multiple length scales requires spatial resolution at the smallest scale, which quickly becomes too expensive to compute the relevant meso- or macroscopic processes. A solution is to develop subgrid models for the smallest scales, while fully resolving the larger scales. Despite the relevance for multiple applications, this approach has been implemented in only a simplified manner to reactive boundaries in LBM.

In this contribution, we present a novel composite dynamics framework developed within the lattice Boltzmann method. This enables the simulation of multiple scales, making LBM more versatile in simulating mesoscopic phenomena while including nanoscopic effects. Our model has been applied to simulate and study nucleation and growth in porous cathodes of lithium-sulfur batteries. The simulation results successfully capture the nucleation phenomena, simulating subgrid nucleation and growth, and subsequent grid scale growth. This study elucidates effects such as surface passivation, and thus aids in developing better battery systems in the future.