A study carried out by researchers at UCL and the University of Chicago Illinois has found that tiny particles of magnesium chromium oxide may hold the key to new magnesium batteries with better storage than conventional lithium-ion batteries.
The research, published in the Royal Society of Chemistry’s journal Nanoscale, reports a new, scalable method for making a material that can reversibly store magnesium ions at high-voltage, the defining feature of a cathode.
The group claims that this represents a significant step towards magnesium-based batteries. To date, very few inorganic materials have shown reversible magnesium removal and insertion, which is key for the magnesium battery to function.
“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,” said co-lead author, UCL’s Dr Ian Johnson.
“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.”
One factor limiting lithium-ion batteries is the anode. Low-capacity carbon anodes have to be used in lithium-ion batteries for safety reasons, as the use of pure lithium metal anodes can cause dangerous short circuits and fires.
In contrast, magnesium metal anodes are much safer, so partnering magnesium metal with a functioning cathode material would make a battery smaller and store more energy.
Previous research using computational models predicted that magnesium chromium oxide (MgCr2O4) could be a promising candidate for Mg battery cathodes.
Inspired by this work, UCL researchers produced a ~5nm, disordered magnesium chromium oxide material in a very rapid and relatively low temperature reaction.
Collaborators at the University of Illinois at Chicago then compared its magnesium activity with a conventional, ordered magnesium chromium oxide material ~7nm wide.
They used a range of different techniques including X-ray diffraction, X-ray absorption spectroscopy and cutting-edge electrochemical methods to see the structural and chemical changes when the two materials were tested for magnesium activity in a cell.
The two types of crystals behaved very differently, with the disordered particles displaying reversible magnesium extraction and insertion, compared to the absence of such activity in larger, ordered crystals.
“This suggests the future of batteries might lie in disordered and unconventional structures… It highlights the importance of seeing if other structurally defective materials might give further opportunities for reversible battery chemistry” explained UCL’s Professor Jawwad Darr.
The group now plans to expand its studies to other disordered, high surface area materials, to enable further gains in magnesium storage capability and develop a practical magnesium battery.
Funding for the project was provided by 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.