Rechargeable lithium-air batteries using mathematical modelling

Abstract

Throughout the years numerous studies for non-aqueous Li-air or Li-oxygen batteries have been investigated to elucidate their reactions and mechanisms. However, there have been only a few models developed for Li-air batteries. Therefore, the main objective of this work was to develop mathematical models for non-aqueous Li-air battery to increase understanding of the air cathode behaviour as well as predict the battery performance during cycling. A micro-macro homogeneous mathematical model was developed for a rechargeable Li-air battery using a concentrated binary electrolyte theory, and validated against experimental data. The dynamic behaviour of the porous cathode was determined by a numerical solution of the combined continuity, transport and kinetics equations. The microscopic behaviour included the local mass transfer between lithium peroxide (Li2O2) layer inside the cathode and active surface morphology changing with the Li2O2 solid precipitate growth. The model predicted that the capacity and discharge potential were sensitive to the solubility of oxygen and also the cathode porosity, the cathode structure and kinetic parameters. In addition, the charging behaviour was simulated by modelling the dissolution of solid Li2O2 product. The model suggested that the charging voltage can be decreased depending on capability of electrolyte to dissolve the Li2O2 discharge products. To improve the battery performance, the promising structure of a Li-air flow battery system with a electrolyte recycling unit continuously delivered the discharge capacity and provided high power density.