Development of the Aprotic Lithium-Oxygen Battery System

Abstract

With the increasing importance of electrified transport, the need for high energy density storage is also increasing. Possible candidates include Li-O2 batteries, which are the subject of rapidly increasing focus worldwide despite being in their infancy of understanding. This excitement owes to the high energy density of Li-O2 (up to 2-3 kWh kg-1), theoretically much higher compared to that of other rechargeable systems, and the open “semi-fuel” cell battery configuration that uses oxygen as the positive electrode material. To bring aprotic Li-O2 batteries closer to practical reality, and to attain suitable power delivery, understanding of the underlying chemistry based on the reversible reaction of O2 + Li ↔ Li2O2 is essential. In this thesis, the precise reactions (including side reactions) which occur during both discharge and charge are studied in detail. Light is shed on the true effect of heterogeneous electrocatalysis in this system. A trend is identified between the observed overpotential during charge and the stability of the electrode material to oxidation by lithium peroxide. Additionally, plausible mechanistic pathways for the decomposition of glyme electrolyte solvent molecules by superoxide attack are proposed along with the synthesis and characterization of a solvent with enhanced stability.