Oxygen discovery sparks Li-ion battery storage capacity gains
The dsicovery will help to improve the development of new materials for future batteries to provide higher storage capacity than up to now.
Working with researchers from the Universities of Oxford and Kent in England and from the USA, Uppsala University team have looked into special kinds of Li-ion battery materials which can provide batteries with higher energy levels those in use today.
“We discovered for the first time that oxygen in the electrodes behaved in an unexpected manner. Usually, oxygen takes up two electrons as fast as it can. In this material, it released one of them again and this is what provides the higher capacity seen in the charging process,” said Laurent Duda, university lecturer in physics at Uppsala University.
The study, published in Nature Chemistry on 21 March, was produced by scientists from a number of different fields of research and was carried out using a synchrotron light source called Advanced Light Source, ALS. Advanced X-ray spectroscopy was necessary to understand how the materials work.
“It has been mostly oxide materials with a combination of metals such as nickel, cobalt and manganese which have seemed the most promising storage electrodes for high energy in lithium batteries. But certain combinations of metals give an unexpectedly high storage capacity and the reason for this has been argued about for a long time,” said Kristina Edström, professor of chemistry at Uppsala University.
Researchers previously thought that the extra storage capacity depended only upon unwanted side effects which produce oxygen in the electrolyte when lithium batteries are charged to their limit. Another possible explanation has been that so-called peroxides have been formed which break down the electrode material.
For the study, researchers used advanced X-ray spectroscopy to examine a variant of a so-called Li-rich material. Other methods provide summary information on the battery material but with X-ray spectroscopy it is possible to follow how every kind of atom behaves when a battery is being charged.
According to the study, only some oxygen atoms in the material act this way, namely those close to manganese and lithium, where they form a ‘localized island’ until the battery is discharged again.
“This discovery will enable us to research into ways to customize materials combinations with appropriate manganese content levels,” said Duda.
Reference
Charge-compensation in 3d-transition-metaloxide intercalation cathodes through the generation of localized electron holes on oxygen; Kun Luo, Matthew R. Roberts, Rong Hao, Niccoló Guerrini, David M. Pickup, Yi-Sheng Liu, Kristina Edström, Jinghua Guo, Alan V. Chadwick, Laurent C. Duda and Peter G. Bruce, doi:10.1038/nchem.2471
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