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Published on October 17th, 2014 | by Tina Casey

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What’s Next For Magnesium-Ion Batteries: Molecular Foundry Coughs Up A Clue

October 17th, 2014 by  


If you thought you knew everything there is to know about magnesium-ion batteries, guess again. Some folks over at the Lawrence Berkeley National Laboratory’s “Molecular Foundry” supercomputer have gotten to the bottom of a problem that has stalled the development of this promising energy storage technology, and they have discovered that there isn’t much of anything there after all.

Wasn’t somebody just getting on our case for getting too excited about computer simulations? Well, we’ll just have to try and contain ourselves from now on, but if Mg-ion batteries can deliver on their promise, the gold standard of lithium-ion batteries will have to step aside for something much more efficient, and cheaper, too. Now excuse me for a minute, I have to go find my pom-poms.

LBNL breakthrough for Mg-ion batteries

Mg ions (orange) surrounded by four “nearest neighbors” (brown). Image courtesy of LBNL.

My Magnesium-Ion Batteries Beat Your Lithium-Ion Batteries…

For those of you new to the topic, lithium-ion is currently the gold standard for electric vehicle batteries among many other applications (lithium is a soft metal, and ion refers to a charged atom or molecule). Just ask our good friends over at Tesla Motors, they’ll tell you how good Li-ion batteries are.

However, we’ve been catching wind of some new developments in Mg-ion batteries here and there, and Toyota, for one, has been in hot pursuit of the technology for electric vehicle batteries.

As described in the Berkeley Lab’s breakdown of its Mg-ion battery supercomputer simulation, the advantage of Mg-ion batteries over Li-ion is threefold: they offer greater energy density, at lower cost, while minimizing safety issues.

The secret sauce in Mg-ion batteries is an extra electron, giving it a +2 charge. Compared to Li-ion’s +1 charge, that extra electron means that Mg-ions could deliver double the current of Li-ions under the same energy density conditions.

…Or Maybe Not…

That’s the theory. In practice, researchers have bumped up against a wall that we’re going to call the Multivalent Mosh Pit.

 

The extra electron puts Mg-ions in the class of multivalent ions, and therein lies the catch. Since opposites attract, Mg-ions are extra attractive to oppositely charged ions moshing around in the electrolyte of the battery. They get swarmed, which slows down their motion, making them less efficient.

…Or Maybe Not Not.

However, according to the Berkeley team, that turns out to be less of a problem than conventional wisdom has it.

On a molecular level, it was previously assumed that Mg-ions were dragging along their six nearest neighbors. If you were happily free-forming in the pit and all of a sudden six other guys piled on to you that would slow you down, too, so that explains why the research was stalling out.

That assumption was based on studies of magnesium chloride and other magnesium-containing solids using X-ray absorption.

The Berkeley team switched things up and ran molecular dynamics simulations on supercomputers at the Molecular Foundry and at the lab’s National Energy Research Scientific Computing Center.

The results showed that at room temperature, only four other ions were involved. That still sounds like a lot, but it does provide a pathway for moving forward. Here’s the money quote:

Our hypothesis is that the dissolved magnesium chloride salt may be precipitating out of solution, or at least forming the seeds of magnesium chloride crystals in cases where the initial salt concentration is high and approaching its solubility limit. Local fluctuations in concentrations near electrode surfaces may be enough to drive this switch to solid-phase coordination and create problems in working cells by trapping active material in an insoluble form.

In other words, the problem isn’t within the electrolyte itself, it’s occurring at the interface between the electrodes and the electrolyte.

The team suggests that steering clear of high-concentration electrolytes could be one way to improve efficiency in Mg-ion batteries.

They are also anticipating the next level of experimentation, which would be to go back to X-ray absorption methodology to dig a little deeper into the difference between four-neighbor and six-neighbor coordination.

If you want to check it out for yourself, look them up in the Journal of the American Chemical Society under “The Solvation Structure of Mg Ions in Dichloro Complex Solutions from First-Principles Molecular Dynamics and Simulated X‑ray Absorption Spectra.”

Also don’t forget the group hug thing, all you taxpayers out there. Berkeley Lab is part of the JCESR Energy Innovation Hub, one of several new high tech research centers launched by the Obama Administration.

But What About Tesla Motors?

If you’re thinking that this whole Mg-ion thing is making things a little hairy for Tesla Motors, given the company’s thisclose relationship with Li-ion technology, put away the fainting salts for now. CEO and co-founder Elon Musk is already on record stating that the new Tesla Gigafactory could be retooled to accommodate changes in battery technology with relative ease.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



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