Could ceramics make safer lithium batteries?

An international team of scientists have used Diamond to reveal how a phenomenon, known as geometric frustration, can be used to increase the way in which a ceramic material can conduct charge.

Today’s lithium-ion batteries rely on electrolytes – the component which allows current to flow between the positive to negative ends of the battery – which are often flammable liquids. Researchers are interested in how inflammable solid materials, such as ceramics, could be used as electrolytes to make these batteries safer. Furthermore, such batteries could be operated at higher temperatures.

Key to producing an effective solid electrolyte material is a property known as ionic conductivity, which relates to how easily current can flow through the crystalline structure of a material. The researchers used Diamond’s B18 beamline to study how the ionic conductivity of a ceramic material can be increased by a property known as geometric frustration.

“The absorption spectroscopy measurements obtained at B18 were key to measure the disorder at a microscopic level,” commented Dr Silvia Ramos. “This allowed us to unequivocally link the increased geometric frustration to the increased conductivity.” The researchers were able to show that geometric frustration results in structural and dynamic attributes within the ceramic that were typically associated with heating.

“The disorder created by geometric frustration is analogous to handing out two differently-sized umbrellas to an orderly parade of people, and then asking them to put them up and come as close together as the umbrellas allow,” explain Dr Andre Düvel and Dr Dean Sayle, lead researcher on the project, from the University of Kent. “This would naturally lead to a disordered formation featuring a large number of gaps. Similarly, we used two different sized atoms to induce geometric frustration and hence structural disorder of the ceramic, increasing its charge transport properties by 100,000.”

The research demonstrates the potential for controlling the structure and hence conductivity of a material. Increasing the conductivity in ceramics is also desirable because they could be used to manufacture fuel cells that operate at lower temperatures.

One of the techniques the B18 beamline offers is extended X-Ray absorption fine structure (EXAFS) a highly sensitive elemental mapping technique under real conditions. Requiring tuneable X-rays unique to a light source like Diamond, the technique allows researchers to determine what elements are within a crystal and their chemical states.

“We’re seeing increased access by researchers who are looking for a detailed characterisation of novel compounds in the energy field here at Diamond,” adds Giannantonio Cibin, Principal Beamline Scientist on the B18 beamline. “This work is an excellent example of how the techniques we offer on the beamline can bring essential understanding of the complex structures characteristic of these advanced materials.”  

Thumbnail image reprinted (adapted) from: Is Geometric Frustration-Induced Disorder a Recipe for High Ionic Conductivity? Andre Düvel, Paul Heitjans, Pavel Fedorov, Gudrun Scholz, Giannantonio Cibin, Alan V. Chadwick, David M. Pickup, Silvia Ramos, Lewis W. L. Sayle, Emma K. L. Sayle, Thi X. T. Sayle, and Dean C. Sayle Journal of the American Chemical Society 2017 139 (16), 5842-5848 DOI: 10.1021/jacs.7b00502.

Copyright 2017 American Chemical Society.

The paper can be accessed at the ACS Publications website.