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Disordered Particles of Magnesium Chromium Oxide Hold Potential for Future Battery Technology

New magnesium battery energy storage technologies can possibly be realized through disordered and tiny particles of magnesium chromium oxide.

According to researchers from the University College London (UCL) and the University of Illinois at Chicago, such technologies can have more capacity when compared to traditional lithium-ion batteries.

Published in Nanoscale, the study reveals a novel scalable technique for creating a material that has the ability to reversibly store magnesium ions at an extreme voltage, which happens to be the defining aspect of a cathode.

Although the concept is still at an initial phase, the scientists believe that it represents a major advancement in shifting towards batteries based on magnesium. So far, only a few inorganic materials have demonstrated reversible removal and insertion of magnesium, which is important for the operation of the magnesium battery.

Lithium-ion technology is reaching the boundary of its capability, so it’s important to look for other chemistries that will allow us to build batteries with a bigger storage capacity and a slimmer design,” stated co-lead author Dr Ian Johnson (UCL Chemistry). “Magnesium battery technology has been championed as a possible solution to provide longer-lasting phone and electric car batteries, but getting a practical material to use as a cathode has been a challenge.”

Anode is one factor that limits lithium-ion batteries. For the sake of safety reasons, low-capacity carbon anodes have to be utilized in lithium-ion batteries because the application of pure lithium metal anodes can result in hazardous short circuits and fires. On the other hand, magnesium metal anodes are relatively safer, therefore combining a functioning cathode material with magnesium metal would not only help in storing more energy but would also aid in making a battery smaller.

Earlier studies using computational models estimated that magnesium chromium oxide (MgCr2O4) could be a potential option for Mg battery cathodes.

Taking a cue from the study, UCL scientists created a disordered magnesium chromium oxide material of ~5 nm in an extremely rapid and comparatively low temperature reaction. Next, collaborators at the University of Illinois at Chicago compared the magnesium activity of this material with a ~7 nm-wide traditional and ordered magnesium chromium oxide material.

The research team applied a wide range of methods such as advanced electrochemical methods, X-ray absorption spectroscopy, and X-ray diffraction to view the chemical and structural variations when both the materials were tested for magnesium activity within a cell.

The behavior of the two types of crystals was found to be quite different, with the disordered particles showing reversible extraction and insertion of magnesium, in comparison to the lack of such an activity in larger, ordered crystals.

This suggests the future of batteries might lie in disordered and unconventional structures, which is an exciting prospect and one we've not explored before as usually disorder gives rise to issues in battery materials. It highlights the importance of seeing if other structurally defective materials might give further opportunities for reversible battery chemistry.

Jawwad Darr, Professor, Chemistry, University College London.

We see increasing the surface area and including disorder in the crystal structure offers novel avenues for important chemistry to take place compared to ordered crystals. Conventionally, order is desired to provide clear diffusion pathways, allowing cells to be charged and discharged easily - but what we've seen suggests that a disordered structure introduces new, accessible diffusion pathways that need to be further investigated.

Jordi Cabana, Professor, University of Illinois at Chicago.

These results are the culmination of a new, exciting partnership between US and UK scientists. The University of Illinois at Chicago and UCL are now planning to further expand their studies to other high surface-area, disordered materials to allow additional gains in the storage capability of magnesium and thus create a feasible magnesium battery.

The Joint Center for Energy Storage Research, a US Department of Energy Innovation Hub, and the JUICED Energy Hub by the Engineering and Physical Sciences Research Council supported the study.

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