Oxygen holes: The new frontier in EV battery technology

Scientists crack the code on nickel-rich batteries.

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In the quest for more efficient and powerful electric vehicle (EV) batteries, researchers have recently turned their attention to a promising avenue: oxygen’ holes.’ These microscopic features within battery materials have shown the potential to unlock higher performance levels in EV batteries. By delving into the significance of these oxygen ‘holes,’ we may be on the brink of a groundbreaking advancement in electric transportation.

Researchers from the University of Cambridge and the University of Birmingham have achieved a significant breakthrough in pursuing high-energy-density lithium-ion batteries for electric vehicles and grid-scale storage. Energy density can be significantly improved by increasing the proportion of nickel in these batteries. However, the practical applications of such materials have been limited by structural instability and the loss of oxygen atoms, which cause battery degradation and failure.

In their investigation, the team focused on ‘oxygen holes,’ where an oxygen ion loses an electron, within nickel-rich battery materials, discovering that these oxygen holes play a critical role in degradation by accelerating oxygen release, further damaging the battery’s cathode. Published in the journal Joule, these research findings offer valuable insights into this phenomenon.

Utilizing advanced computational techniques on powerful UK regional supercomputers, the researchers observed intriguing changes in the oxygen within the material during the charging process. At the same time, the nickel charge remained essentially unchanged. This groundbreaking discovery holds the potential to pave the way for more durable and efficient nickel-rich cathodes, bringing us closer to advanced battery technologies for a sustainable future.

Professor Andrew J Morris, from the University of Birmingham, who co-led the research, said, “We found that the charge of the nickel ions remains around +2, regardless of whether it’s in its charged or discharged form. At the same time, the charge of the oxygen varies from -1.5 to about -1. This is unusual. The conventional model assumes that the oxygen remains at -2 throughout charging. However, these changes show that the oxygen is not very stable, and we have found a pathway for it to leave the nickel-rich cathode.”

The researchers successfully compared their calculations with experimental data, validating their findings. They proposed a mechanism involving oxygen radicals combining to form a peroxide ion, eventually transforming into oxygen gas, leading to material vacancies. This process releases energy and produces highly reactive singlet oxygen.

To improve battery stability and longevity, the researchers suggest adding compounds that shift electrochemical reactions away from oxygen and towards transition metals on the battery material’s surface. This breakthrough could pave the way for more efficient and reliable energy storage systems using lithium-ion batteries, which have faced challenges related to cathode material stability affecting overall performance and lifespan. The research received support from the Faraday Institution, the UK’s flagship battery research program.

The study on oxygen ‘holes’ in nickel-rich battery materials represents a significant advancement in pursuing higher-performing EV batteries. By understanding the underlying mechanism of oxygen loss and its impact on battery degradation, researchers can work towards developing more durable and efficient nickel-rich cathodes. This research, supported in part by the Faraday Institution, promises to unlock higher energy density and stability for lithium-ion batteries, opening up new possibilities for electric vehicles and grid-scale energy storage systems in a sustainable future.

Journal Reference:

  1. Annalena R Genreith-Schriever et al. ‘Oxygen Hole Formation Controls Stability in LiNiO2 Cathodes: DFT Studies of Oxygen Loss and Singlet Oxygen Formation in Li-Ion Batteries.’ Joule. DOI: 10.1016/j.joule.2023.06.017.
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