Researchers from the Universities of Warwick and Dundee in the UK have published findings that challenge the conventional understanding of how lithium-ion battery cathodes store and release charge, providing new insights that could help guide the development of higher-energy battery materials.
The study, published in Nature Nanotechnology, was led by joint first authors Galo J. Páez Fajardo and Daniela Dogaru of Warwick Manufacturing Group (WMG), University of Warwick. The international research team also included Dr Hrishit Banerjee of the University of Dundee and the University of Birmingham, alongside collaborators from the Faraday Institution, University College Dublin, the Max Planck Institute for Solid State Research and Diamond Light Source.
The researchers investigated the electronic structure of lithium-ion battery cathodes during operation and found evidence that oxygen plays a much more active role in charge compensation than has traditionally been assumed.
For decades, the accepted model has been that electrons are removed primarily from transition metal ions such as nickel, cobalt and manganese as lithium ions leave the positive electrode during charging, while oxygen ions largely serve as a structural framework.
Using X-ray resonance photoemission spectroscopy, theoretical calculations and spectral simulations, the researchers examined two representative cathode materials: lithium manganese iron phosphate (LiMn₀.₆Fe₀.₄PO₄) and lithium nickel oxide (LiNiO₂). While the phosphate material was found to behave according to the conventional transition-metal redox model, the nickel-rich layered oxide cathode was shown to derive much of its charge compensation from oxygen-derived ligand-hole states.
Understanding charge compensation in lithium-ion cathodes
The researchers say the findings provide a unified framework for understanding charge compensation in lithium-ion cathodes, explaining how the charge-storage capacity of highly covalent nickel-rich materials is linked to oxygen-dominated electronic states without requiring oxygen dimerisation to explain the electrochemistry.
The work addresses one of the central questions in battery science – where the charge stored in lithium-ion cathodes originates – and could influence the design of future high-energy cathode materials for electric vehicles and stationary energy storage.
Professor Louis F. J. Piper, professor of battery innovation at WMG, University of Warwick, said: “Instead of treating metal and oxygen redox as separate, this work helps explain how they cooperate and identifies new ways to think about higher capacity cathode.”
The findings are particularly relevant as battery developers seek to increase the energy density of nickel-rich cathodes while reducing reliance on critical raw materials. Oxygen redox has long been recognised as a potential route to higher capacities but has also been associated with degradation mechanisms such as oxygen loss and voltage fade. By clarifying the underlying electronic processes, the researchers believe the new understanding provides a stronger foundation for engineering more stable, higher-capacity cathode materials.
