Lithium-ion batteries are the undisputed top dog of the battery world at the moment, but magnesium-ion devices have the potential to steal the crown – if scientists can crack the problem of finding an efficient electrolyte. Now a collaboration between Berkeley Lab, MIT and Argonne National Laboratory has developed a solid-state material that appears to be one of the fastest conductors of magnesium-ions, which could lead to safer and more efficient batteries.

Lithium-based batteries power everything from phones to electric cars, and while the metal does the job for now, there's plenty of room for improvement in terms of efficiency and price. Magnesium, on the other hand, has a higher energy density than lithium and is far more abundant in the natural world, meaning devices made with the stuff should be cheaper and easier to produce.

The stumbling block to using magnesium in batteries is often the electrolyte, the material that carries the charge between the cathode and anode. Recent research from Toyota and KIT has focused on developing better liquid electrolytes, but these have the tendency to corrode other parts of the battery. So, the scientists on the new study wanted to try something else.

"Magnesium is such a new technology, it doesn't have any good liquid electrolytes," says Gerbrand Ceder, co-author of a paper describing the new device. "We thought, why not leapfrog and make a solid-state electrolyte?"

The end result of their work is a material called magnesium scandium selenide spinel, a solid-state electrolyte that allows magnesium ions to easily move through the material. In fact, the team found that their electrolyte was as effective a conductor as the solid-state electrolytes used in some lithium batteries.

Theoretical studies initially predicted that the material would work this well, and to confirm that practically the team ran nuclear magnetic resonance (NMR) spectroscopy experiments. This instrument can be tuned to detect magnesium or lithium ions moving through a material, but because the material the team had developed was so new and complex, they had some trouble interpreting the data.

"Protocols are basically non-existent," says Pieremanuele Canepa, lead author of the study. "These findings were only possible by combining a multi-technique approach (solid-state NMR and synchrotron measurements at Argonne) in addition to conventional electrochemical characterization."

As encouraging as the find is, the team says a few kinks need to be ironed out before the magnesium material could be used in an actual battery. Currently, there's a small amount of electron leakage, but the improved ion mobility is encouraging for an eventual commercial solid-state battery, which is much safer than the conventional liquid-based devices.

"This probably has a long way to go before you can make a battery out of it, but it's the first demonstration you can make solid-state materials with really good magnesium mobility through it," says Ceder. "Magnesium is thought to move slowly in most solids, so nobody thought this would be possible."

The research was published in the journal Nature Communications.

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