First-principles and Continuum Modeling of Charge Transport in Li-O2 Batteries.

Abstract

Li-O2 batteries are a very attractive energy storage technology due to their high theoretical specific energy density. However, several critical challenges impede the development of a practical Li-O2 battery. One of these challenges is the sluggish transport of ions and/or electrons through the Li2O2 discharge product. The purpose of this work is to develop a physics-based picture of transport phenomena within the Li-O2 discharge product and to elucidate how different characteristics of the discharge product influence its apparent transport properties. To this end we employ density functional theory calculations in conjunction with continuum-scale transport models. Our calculations indicate that charge transport in bulk Li2O2 is mediated by hole polarons and Li-ion vacancies, and that a low concentration of these species results in poor intrinsic ionic and electronic conduction. However, structural disorder, the presence of impurities, and the formation of space-charge layers are predicted to significantly enhance charge transport. These results suggest several design strategies for improving Li-O2 cell performance: promoting the formation of amorphous Li2O2, introducing impurities into the discharge product, controlling crystallite orientation in the discharge product, and increasing the operating temperature.