Pore-scale simulation of reactive transport processes in lithium-oxygen batteries

The achievable energy density of lithium-oxygen batteries is modest despite their superior theoretical energy density. This issue can be alleviated by optimizing electrode microstructures, but the implementation of this strategy requires a thorough understanding of how electrode microstructure affects batteries' discharge performance. In this paper, a three-dimensional pore-scale lattice Boltzmann model is developed to investigate the reactive transport processes in reconstructed electrodes of lithium-oxygen batteries. Detailed characterizations of the reconstructed electrode microstructures and their impacts on the battery discharge performance are investigated. The results reveal that discharge capacity decreases as the current density increases, and significantly increases with the porosity. Electrodes with a large average pore size are preferred at high current densities, while electrodes with a small average pore size are favored at low current densities. Compared to electrodes with uniform pore size along its thickness, electrodes with graded microstructures, in which the pore size near the oxygen inlet is larger, generally offer better discharge performance. Introducing small secondary pores in electrodes can significantly increase their available surface area, but not necessarily enhance their discharge capacity much due to severe pore blocking. The implications of the pore-scale simulation results on the application of porous electrode theories are discussed.