Enhancing the specific energy of lithium-oxygen batteries by using redox mediators

Lithium-oxygen batteries are a promising alternative to power future electric vehicles because, once fully developed, they could deliver a specific energy (i.e. energy per unit weight) around 10 times higher than modern Li-ion batteries. The incorporation of soluble redox mediators is one of the most promising approaches to develop lithium-oxygen batteries that can reach their full potential. Redox mediators can not only enhance the kinetics of the reactions but also overcome key issues such as electrode passivation, electrolyte degradation and electrode corrosion. This project aims to develop a fundamental understanding of the role of soluble redox mediators in lithium-oxygen batteries that will found the basis for the rational battery development. Enhancement in battery performance will also be sought by exploiting the synergistic effect between the redox mediator in solution and the composition and structure of the solid electrode.

The project aims to develop lithium-oxygen batteries capable to deliver 10 times higher energy than lithium-ion batteries of the same weight. Even though the commercialisation of lithium-oxygen batteries will probably require more than 10 years of research, the implications of such outstanding energy storage system in terms of climate change and energy sustainability targets makes this research topic worth the effort.
Lithium-oxygen batteries are specially promising to power pure electric vehicles, since they could potentially extend the driving range to >500 mi. This would overcome the problem of "range anxiety", which consumers cite as the main disadvantage of pure electric vehicles. Public policy could also be applied to further enhance the uptake of pure electric vehicles. Noteworthy, currently, a quarter of UK carbon emissions comes from transport, and therefore, increasing the number and use of pure electric vehicles is very important.
In addition to environmental and economic benefits, the transition to an electric transportation technology would also have other benefits for society, such as increasing the purity of air and decreasing noise. And in addition to transport applications, high energy batteries would also be beneficial for consumer portable devices such as mobile phones or laptops.
The demonstration that lithium-oxygen batteries can achieve in practice a high specific energy would be key in order to promote further involvement by the UK industry in this area of research. In addition, research on lithium-oxygen batteries is beneficial for the development of other energy storage systems:
-The mediators that will be developed in this project can also be used as for overcharge protection in Li-ion batteries. Overcharge of lithium-ion batteries induces degradation reactions that not only deteriorate the performance of the battery, but they also compromise the safety.
-The outcomes of this project in terms of understanding the reaction mechanism and development of novel techniques will also be largely applicable for the development of lithium-sulphur batteries. Many of the fundamental limitations of lithium-oxygen batteries are also present in lithium-sulphur batteries, which are specially promising because of their low cost and potential high specific energy.
-The mediators developed in this project will be also applicable to dye sensitised solar cells, since the requirements of a good mediator are the same in both types of devices. Compared to the more conventional silicon-based solar cells, the dye sensitised solar cells are cheaper and work better in low-light conditions.
The results of this project could therefore be of significant value to a large number of UK companies interested in the development of energy storage systems. Dr Garcia-Araez has already established relationships with several companies working in this field, including SHARP, Qinetiq, HMGCC, DSTL and Oxis. This has shown that the project would be relevant for industry and provides a platform for realising the potential economic benefits of the project.
In conclusion, developing high energy lithium-oxygen batteries will pave the way for the transition to a clean, safe and affordable energy system as well as strengthening the UK economic competitiveness.