What have we learned by multiscale models on improving the cathode storage capacity of Li-air batteries? Recent advances and remaining challenges

This review article highlights the major breakthroughs achieved in the designing of novel cathodes with optimized discharge capacity of Li-air batteries by using multiscale modeling, which have provided comprehensive insights into the multiphysics/multi-scale phenomena occurring inside complex cathode structure. These models allowed to discover that the fundamental reasons of the low discharge capacity are attributed to pore-clogging, limited O2 transport, surface passivation, less accessible surface area (low reaction sites), and uneven distribution of electrolyte and solid discharge product inside the porous cathode. Numerous models were employed to uncover these challenges in Li-air batteries. For instance, Continuum models predicted the molecular transport (coupled with electrochemical kinetics) at macroscopic-microscopic level. Three-dimensional Kinetic Monte Carlo and Pore network techniques provided insight into the transport process, reaction kinetics, pores interconnectivity, and influence of pore size on surface passivation inside real cathode structures. Multiscale modelling approaches integrating Lattice Boltzmann, Density Functional Theory, Molecular Dynamics, and several other models predicted the relationship between Li2O2 layer thickness and the active surface area at nanoscale, Li2O2 average concentration (at mesoscale), and discharge curves (at cell level). Despite significant progress, the influence of stochastic nature of pore interconnectivity (tortuosity), electrode wettability, multicomponent transport (N2, CO2, H2O and O2, for Li-air battery), composite cathode structures, and transport limitations through electrocatalysts on enhancing cathode storage capacity still need further investigations.