Advanced materials for reversible air electrodes of high energy density metal-air batteries – E-AIR

This 42 month project will be carried out in close collaboration between three academic laboratories (UCCS University of Lille, IC2MP University of Poitiers and LCMCP at the Collège de France) and one private company (EDF). In the past decade, advances in lithium ion batteries enabled the commercialization of long-life mobile power systems supplying portable electric devices (cellular phones, digital cameras,…) or electric vehicles. This technology attracted much attention because of its high energy efficiency (> 90%) and long-cycling life (5000 cycles). However, only incremental improvements in lithium-ion batteries are henceforward expected both in terms of performance and cost (currently in the range of 600 $/kWh). The next breakthrough in batteries could come from metal-air batteries. Metal-air batteries using aqueous electrolytes are more environmentally friendly, safer and recyclable, and have the potential to reach high energy densities. Two electrochemical couples have great promises: the lithium-air and the zinc-air batteries. Battery costs below 100 €/kWh with energy densities equivalent to, or higher than, lithium-ion batteries are possible with zinc-air batteries. Energy densities above 500 Wh/kg are achievable with lithium-air batteries. However, the air electrode is still a weak point in this technology. By using a bi-electrode in which charge and discharge is performed on separate electrodes, long lifetimes have been obtained (>3000 cycles), but an even better solution would be a truly reversible, stable, air electrode. It would open the way to even more compact and lighter metal-air batteries (i.e. higher energy densities) and a simpler battery management system. It would also have important applications in reversible fuel cells. In this context, the present proposal aims at providing major advances in the development of metal-air batteries with high energy density (typically in the range 600 Wh/kg for Li-air batteries and in the range of 250 Wh/kg for Zn-air batteries), high cycle life (> 3000 cycles), high energy efficiency (up to 75%) and low cost. The focus of the project will be to develop a novel highly stable oxygen reduction/evolution electrode for aqueous alkaline electrolytes. This will be achieved by the engineering of cheap and novel high surface area transition metal oxide (TMO) nanocatalysts which will be grown directly onto heteroatom doped reduced graphene oxide (HDRGO). Recent publications have shown that graphene and N- and S-doped graphenes are considerably more electrochemically stable than classical carbon-based materials possessing a low graphitization degree, and could provide a great development pathway to highly stable reversible air electrodes. The project therefore aims to use these more stable forms of carbon with spinel-type TMO materials with controlled size and morphology (MxM’3-xO4 where M is a transition metal and M’= Co, Mn).The novel nanostructured composites will be tested as catalysts for oxygen evolution and reduction reactions. These engineered composite catalysts should exhibit increased activity and stability of the catalyst towards oxygen reduction and evolution reactions as a consequence of:
- A decrease of the charge transfer resistance
- A modification of the electron density on surface metallic sites.
- An increase of HDRGO graphitic materials stability toward corrosion because of electronic modifications of carbon by doping and of strong electron coupling with TMO.

The activity and stability of composite catalysts under electrochemical conditions in half cells and full Zn-air or Li-air batteries will be analysed and optimised. Lithium based electrolytes have been observed to have a significant negative impact on the activity of traditional OER and ORR catalysts, which is why different in-situ spectroscopic techniques will be used such in-situ Fourier transform infra-red measurements to analyse this effect. The results will then be used to develop better catalysts.