Electrochemistry and Transport Limitations of Non-Aqueous Li-Air Batteries From First-Principles

Li-air batteries have much higher gravimetric energy storage density compared to all other battery chemistries, and this has led to a strong interest in seeing if such batteries could be developed for powering EVs, enabling driving ranges comparable to gasoline powered automobiles.  However, many fundamental challenges exist in these batteries that need to be solved before these batteries can become practical. 

In this work, we will discuss a detailed electrochemical model describing the discharge process of the growth of Li₂O₂ on terraces, steps and kinks.  The different kinds of growth mode along the different kinds of sites have vastly different thermodynamic overpotential.   This leads to an explanation of the high Tafel slope observed in Li-air batteries.  We will also discuss the effect of deep discharge and the origin of ‘sudden death’ in these lithium-air batteries and we will show that the origin of this ‘sudden death’ in flat electrode cells is due to the limitation imposed by electron transport to support the required electrochemistry.  Using a simple metal-insulator-metal model, we show that discharge products beyond > 10 nm, have serious transport limitations and this leads to a bias rise across the film.  In addition, we also discuss the effects of the presence of a carbonate layer which has been recently identified experimentally.  We will also discuss the development of a model incorporating details from some of the recent experiments that show the presence of a carbonate layer.  We conclusively show that the origin of potential rise during recharge of the lithium-air batteries is due to a rising concentration of carbonate impurities at the Li₂O₂-electrolyte interface.  This rise in the overpotential leads ultimately to the decomposition of the electrolyte and limits the rechargability of lithium-air batteries.