Cathode materials which store charge using the oxide ions could be implemented to increase the energy density of Li-ion batteries. In most cases, oxide oxidation results in the formation of trapped molecular O2 and undesirable voltage hysteresis. In a small handful of exceptional materials, however, such as Na0.6(Li0.2Mn0.8)O2, reversible high voltage oxygen redox is possible.
In this paper* published in Nature Energy, a collaborative team led by Dr Robert House, Professor Sir Peter Bruce and Professor Saiful Islam, including researchers from Oxford Materials, Oxford Chemistry, Bath University and Diamond Light Source, report the nature of oxidised oxygen in these high voltage cathodes.
Using SQUID magnetometry, 17O NMR, DFT and RIXS, they show that oxide oxidation leads to the formation of electron holes which are delocalised across the O sublattice. Furthermore, they follow this unusual and metastable material as it rearranges to form molecular O2 over a period of a few days, revealing the O-redox mechanism in unprecedented detail.
This work forms part of the Faraday Institution's CATMAT project, led by Professor Saiful Islam in Oxford Materials, which is focused on developing the next generation of high energy Li-ion battery cathode materials.
*'Delocalized electron holes on oxygen in a battery cathode'.