Development of operando NMR methods for the characterisation of next generation battery technologies'

This project falls within the EPSRC Physical Sciences and Energy research areas.
The demand for energy storage devices has never been greater. Lithium ion batteries have played key role in the development of consumer electronics, due to their high energy densities, and they are a key technology in enabling the transition to greener energy sources, in particular the electrification of transport. Unfortunately a single technology is not suitable for all applications and current lithium ion batteries will not be able to meet the demands of other forms of transport, such as aviation and maritime applications - beyond lithium ion technologies are needed alongside new materials for lithium ion cells. The lithium-air battery offers the highest theoretical specific energy of any battery technology making it well suited to demanding applications. New technology that enables electrification of other parts of the transport network and supports the transition to renewables which will reduce carbon emissions and help meet climate change targets.
To realise this potential we need to understand the chemistry and electrochemistry that underpins the operation of lithium-air cells and factors affecting performance. The Li-air battery consists of a lithium metal negative electrode and a porous positive electrode, separated by an organic electrolyte. On discharge, at the positive electrode, lithium peroxide is formed, which is oxidised on subsequent charging. The lithium air battery is known to undergo detrimental decomposition reactions during cycling, leading to unwanted side-products. Preventing the formation of these species is vital to realise the full potential.
The project will involve developing an in-operando multinuclear benchtop nuclear magnetic resonance (NMR) methodology to understand the electrochemistry and parasitic reactions taking place in the lithium-air battery. Our understanding is limited due to lack of knowledge on how electrolytes change as a cell is cycled. Electrolytes will also play an important role in enabling the next generation of cathode materials for lithium ion cells. These anionic redox materials operate at high voltages, where electrolyte degradation is significant. Understanding the changes in battery materials as the cell is cycled is crucial to devise strategies to prevent decomposition and improve performance. Current techniques require cells to be dissembled before analysis. Benchtop NMR is a relatively new technique in the field and offers the chance to develop a new range of operando experiments to directly probe components as the cell is cycled. Other experimental techniques, such as electrochemistry, UV-Vis spectroscopy, diffraction and differential electrochemical mass spectrometry will be used to provide complementary data. The methodology developed in this project will be relevant to other storage technologies.
The project is co-funded by Oxford Instruments as part of an iCASE studentship.