(110a) Investigating Fundamental Electrochemical Processes In a Li-O2 Battery

Li-air batteries have received significant attention as a potential high specific energy alternative to current state-of-the-art rechargeable Li-ion batteries.  Nevertheless, published Li-air embodiments have only achieved a small fraction of their enormous theoretical specific energy (11,700 Wh/kg of Li) with limited rechargeability, and many operational aspects, including lithium-oxygen electrochemistry, appear to be poorly understood.  This presentation will outline our initial efforts to understand some fundamental properties of non-aqueous Li-O₂ electrochemistry.     

Among the many important challenges facing the development of Li-air batteries, our research has focused on processes occurring at the porous carbon cathode. To better understand the electrolyte solvent’s role in producing the desired rechargeable cathode reaction (i.e., Li⁺ + O₂ + 2e^- → Li₂O₂), quantitative Differential Electrochemical Mass Spectrometry (DEMS), coupled with ex-situ chemical analysis of cell cathodes, was used to study the applicability of carbonates and dimethoxyethane in Li-O₂ cells.

Our studies have revealed that carbonate-based electrolyte solvents, similar to those used in Li-ion batteries, irreversibly decompose upon Li-O₂ cell discharge to form undesired electrodeposits composed mainly of lithium carbonate and lithium alkyl carbonates.  Employing dimethoxyethane (DME) as a solvent, however, mainly produces lithium peroxide on discharge, but both Li₂O₂ decomposition (the desired electrochemistry) and DME oxidation (a parasitic side reaction) occur during cell charging.  These results clearly indicate that oxidative and reductive electrolyte stability in the presence of Li₂O₂ is critically important to produce a truly rechargeable Li-air battery.