Cathode electrochemistry in nonaqueous lithium air batteries

Abstract

This chapter summarizes the authors' results and opinions of the electrochemistry occurring at a principally C cathode during Li-O2 discharge and charge. Ideally this reaction is only 2(Li+ + e -) + O2 虠 Li2O2 that involves 2e -/O2 consumed during discharge and 2e -/O2 liberated during charge. Using quantitative DEMS and other spectroscopies, however, we find significant other chemistry/electrochemistry occurring as parasitic processes in Li-O2 discharge/charge. Much of this is related to electrolyte stability issues (and is electrolyte specific), while some is related to C stability as a cathode material. Much of the work presented in this chapter is an attempt to isolate and study the ideal Li-O2 electrochemistry in order to answer a fundamental question. Even if there are no parasitic chemical processes or practical cell-dependent limitations, is the Li-O2 electrochemistry sufficient to build a high-energy and high-power battery? In this regard, we report a wide variety of experiments and theory on the mechanism, kinetic overpotentials, and charge transport through Li2O2. We then combine our understanding of these fundamental aspects of the electrochemistry with what we know about limitations (parasitic chemistry and cell limiting properties) to understand observed galvanostatic discharges and charges. We describe origins of the current dependent loss of potential in discharge, the cell sudden death or capacity limitations, and the potential rise during charging. At present, the fundamental Li-O2 electrochemistry appears very promising for ultimate use in a high-energy battery. However, both electrolyte stability and the poor electrical conductivity through the Li2O2 remain as challenges to developing a practical lithium air battery.