Materials chemistry and electrochemistry of O-redox cathode materials

This project falls within the EPSRC Physical Sciences and Energy research areas.
The invention of lithium ion batteries in the last century revolutionised portable electronics and they are now playing a key role in efforts to combat climate change. In addition to their use in consumer electronics, they are now supporting the integration of renewables into the electricity grid and the transition to electric vehicles. As dependence on batteries grows there is a demand for higher energy density, safer and cheaper materials. The cathode represents one of the greatest barriers to increasing the energy density of lithium ion batteries.
Currently most lithium batteries contain a transition metal oxide cathode, containing Ni, Mn and Co. There are supply and ethical issues surrounding the use of cobalt and there is a desire to reduce the amount of cobalt used in cathode materials. Another challenge is to increase the energy density by finding new cathode materials - this would increase the range of an electric vehicle. In recent years a new class of cathode materials have emerged that have the potential to significantly increase the energy density of lithium ion cells. These materials exhibit capacities beyond those expected based on transition metal redox and it has been shown that the additional capacity comes from the storage of charge on oxide ions. This has been termed anionic redox and has been observed in a number of materials. These materials are promising candidates for the next generation of cathode materials but there are number of challenges that must be addressed to realise their practical application, including oxygen loss, slow kinetics and structural instability.
This project will investigate the fundamental processes underlying anionic redox to tackle these problems and direct materials discovery. New materials which are expected to show anionic redox will be synthesised. These materials will ideally show limited voltage drop, hysteresis and capacity fade. Characterisation will be carried out to understand the structural changes taking place during cycling. This will involve the modification of existing and development of new tecnhiques. The knowledge of how and why these changes occur will be used to devise strategies for designing new materials, e.g. tuning composition.
The research methodology will involve a number of synthetic techniques, including co-precipitation, hydrothermal and solid-state. A wide range of characterisation techniques will be used to investigate the structural and electronic changes that occur during cycling. Techniques including diffraction, nuclear magnetic resonance spectroscopy and electron microscopy will be used to study structural changes. National and international facilities will be used to carry out ex-situ and operando measurements and techniques such as resonant inelastic X-ray scattering and X-ray absorption scattering will be used to investigate electronic changes.