Pore-Scale Transport Resolved Model Incorporating Cathode Microstructure and Peroxide Growth in Lithium-Air Batteries

Abstract

The electrode microstructure plays an integral role in the performance of the non-aqueous Li-air battery. Computational modeling has proven to be an indispensible tool in the analysis of battery systems, but previous macroscale, volume-averaged models that consider the porous electrode as a homogenous medium of uniform geometric properties are insufficient to probe the effect of precise electrode microstructures. Utilizing a pore-scale transport-resolved model of the Li-air battery, the complex electrode and Li2O2 morphologies can be directly incorporated and their effects on the system-level performance can be evaluated. A thickness-dependent electrical conductivity of Li2O2 is considered in the model based on inputs from the density functional theory. Model validation is presented along with a sensitivity study of the applied current density and the reaction rate coefficient. The effect of electrode geometry (e.g., nanostructure spacing and height) on cell performance, including its influence on pore blocking compared against electrical insulation, is investigated. Pore blocking is observed for cathodes with nanostructure spacing less than twice a critical insulating thickness of Li2O2, suggesting the loss of active surface area as the mechanism for decreased cell performance. While for cathodes with larger nanostructure spacing, the discharge capacity is dictated by the electrical insulation of Li2O2.