(600bt) Development of Heterogeneous Electrocatalysts for Reversible Li-Air Battery Cathodes

Nonaqueous lithium-air batteries are promising electrochemical storage devices with very high theoretical specific energy and energy density. Li-air batteries are comprised of an anode (pure metallic lithium), an O₂ electrode (cathode, commonly composed of porous carbon), and an aprotic electrolyte. The chemistry at the cathode of Li-air batteries is fairly complex and plays an important role in their performance. The cathode of Li-air batteries is responsible for a number of processes, including (i) the transport of Li⁺ throughout the electrode in order to facilitate the formation of Li₂O₂ (ii) the electrochemical reactions (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)) with low overpotential losses, (iii) storing of Li₂O₂ in the porous media to achieve high capacity, and (iv) conduction of electrons with high efficiency. The commonly used Li-air cathodes are composed of carbon with porous architecture. While carbon cathodes are very good electron conductors with tunable porosity, they suffer from (i) the ability to transporting Li⁺ and (ii) poor activity toward the oxygen evolution reaction.

            In this contribution, we show our efforts in designing robust heterogeneous electrocatalysts for Li-air cathodes.  We find that the incorporation of layered metal oxide electrocatalysts in Li-air cathodes significantly lowers the charging potential of the cells.  Our controlled electrochemical and electron microscopy studies show that the decrease in the charging potential is due to an impact in the formation of Li₂O₂ during discharge, and lowering of the activation barrier for the oxygen evolution reaction.  We have been able to link the electrocatalytic properties of these materials to their chemical and structural composition. These structure/activity relationships can pave the way for the design of optimal layered metal oxide electrocatalysts for Li-air cathodes.