Materials chemistry and electrochemistry of the lithium-air battery

Energy storage represents one of the greatest scientific challenges of our time. The development of the lithium-ion battery led to the revolution of the portable electronics industry and the subsequent improvement of this technology has found application in electric vehicles. However, due to the mass of the cell components, the specific energy of the lithium-ion battery is intrinsically limited. Few technologies are able to exceed the performance of lithium-ion batteries, but of these the lithium-air battery promises the highest theoretical specific energy and may produce a driving range to compete with that of the internal combustion engine. The lithium-air battery normally consists of a lithium metal anode, an organic electrolyte and a porous carbon cathode. On discharge, oxygen from the atmosphere is reduced at the cathode and combines with lithium cations from the anode forming lithium peroxide in a two electron charge transfer. The discharge product, lithium peroxide, poses several problems for the lithium-air battery. It's formation on the cathode surface leads to polarisation issues on cycling due to its poor electronic conductivity. As well as this, the build-up of lithium peroxide in the porous electrode can block gas diffusion pathways leading to reduced capacity and early cell death.

The project aims to improve the longevity and efficiency of the lithium-air battery. This will be achieved by building on our fundamental understanding of oxygen redox electrochemistry in lithium containing organic electrolytes to form lithium peroxide, and its reversal on charging. An investigation into novel chemical mediators to facilitate the oxygen reduction and evolution will be carried out. Mediators that enhance battery reaction kinetics are needed to improve the cycling life of the lithium-air battery.

The lithium-air battery differs from lithium-ion systems as it contains solid, liquid and gaseous phases. Hence mass transport limitations in both liquid and gaseous phases within the battery presents a unique problem that needs to be investigated. New battery architectures will be designed specifically for the lithium-air system to optimise mass transport and realise practical gains in battery capacity.

This project will use a range of electrochemical (cycling and electrochemical impedance spectroscopy), spectroscopic (Raman, FTIR, XPS and in situ mass spectrometry) and microscopic techniques such as SEM and AFM to study the oxygen redox electrochemistry. Such techniques are well-suited to the study of the presence and nature of reaction intermediates and products.

This work aims to develop new science and intellectual property in the field of lithium-air batteries and as such is in line with EPSRC's theme of Energy Storage. The Bruce group is world-leading in the field of lithium-air research and solid state materials, and is well placed to contribute further fundamental knowledge for development of this technology.