Quinones as redox mediators for the lithium-oxygen battery

Abstract

Increasing demand for lighter and more powerful batteries has driven research beyond lithium-ion batteries. One system that has received significant attention is lithium-oxygen. This system exploits the reduction of oxygen to lithium peroxide, to provide a theoretical specific energy of 3500 Wh kg-1. One of the major problems facing the lithium-oxygen battery is the passivation of the air electrode caused by insoluble lithium oxides and lithium carbonate formed from unstable electrolytes. These products are not fully oxidized during the charge step and accumulate within the electrode, causing the capacity to fade with each cycle.

This work focuses on the use of quinones as solution based catalysts in non-aqueous electrolytes to facilitate the electron transfer of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The required overpotential for the ORR is shown to decrease by 400 mV and the discharge capacity increase by 100% by incorporating quinones into the electrolyte. Analysis of the carbon electrode by X-ray diffraction confirms lithium peroxide as the discharge product. Furthermore the evolution and consumption of oxygen during cycling has been demonstrated to require only two electrons per mole of oxygen using on-line mass spectrometry indicating that the dominant reaction is the formation of lithium peroxide.

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ORCID for Nuria Garcia-Araez: orcid.org/0000-0001-9095-2379

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