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.
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