lithium ion graphic
Graphic from the published paper.

Lithium-ion batteries are a key technology that enable portable electronic devices and electric vehicles.  

The time it takes for a battery to charge is determined by the speed at which the lithium ions can move through the materials that make up the battery.  Faster charging batteries are highly desired; electric vehicles that can be filled up as quickly as petrol powered cars are one possible application.

The research group of Dr Andrew J. Morris in the School of Metallurgy and Materials uses computational modelling techniques to simulate atomic processes that occur inside batteries as they charged and discharged.

In a new article in the journal Chemistry of Materials, they looked at how lithium moves in a new class of materials called Wadsley-Roth phases. Dr Morris’ group has been studying these materials in collaboration with the group of Professor Clare Grey, who discovered them in 2018.

“They are a very interesting class of materials, and are still relatively unexplored,” Dr Morris says “, we have made a great deal of progress in terms of our understanding, at the atomistic level, of how these materials work and why they are so good.”

In the new article they explore the motion of lithium ions within the crystal structure of these materials. “It is essentially like rolling balls over hilly landscapes”, the balls being the lithium ions and the hills being the barrier they need to surmount. “The key is to explore the shape of the landscape, and relate it to the properties of the material.” By using quantum mechanical modelling techniques, Can Koçer in Dr Morris group showed that lithium motion occurs within one dimensional tunnels in the structures, with lithium ions being able to jump between the tunnels.

“This idea of a 'multi-lane highway’ was proposed in the original paper, and now we were able to out these ideas on a more quantitative footing. We showed that the energy required to surmount these barriers is very low, leading to fast motion.”

“In addition, we were able to identify other types of processes that occur in the structure, for example certain types of positions that act like parking spots for lithium, with them being tucked away from the tunnels."

By studying how these materials work we are gaining insight into how they might be improved, but are also making observations that potentially describe the whole class of materials.

The article has been chosen as an American Chemical Society’s “Editor’s choice”, an honour awarded to only one new article each day out of over 60 ACS journal, highlighting the importance of the work.