The EV batteries of today are pretty good, but apparently you ain’t seen nothing yet. Researchers are eyeballing magnesium to take over from lithium, which so far has been the workhorse of the EV revolution. There’s just one little problem, or two, or a bunch of them.
Why EV Batteries Need To Do Better
Lithium-ion technology is the gold standard for rechargeable EV batteries and other devices, and it just keeps getting better. However, that doesn’t mean some other materials could do even better. It’s just a matter of working out the kinks.
Also, battery performance is just one element in the sustainable mobility field. With millions of EVs set to take the roads, waterways, and airways in the coming years, the many-headed Hydra of the lithium supply chain has been catching attention, and not always in a good way.
Environmental and social justice concerns also factor in. The global supply of lithium seems ample enough, but securing a domestic supply in the US is fraught with pitfalls and impacts, as it is in other parts of the world.
There is no such thing as impact-free clean tech, but subbing in magnesium for lithium could result in better-performing EV batteries while also opening up a broader range of domestic supply options in the US and other parts of the world, helping to avoid sensitive environmental, cultural, and social issues.
Here, let’s have the US Geological Survey explain:
“Magnesium (Mg) is the eighth most abundant element and constitutes about 2% of the Earth’s crust, and it is the third most plentiful element dissolved in seawater…Magnesium and other magnesium compounds are also produced from seawater, well and lake brines and bitterns.”
Bitterns, now that’s interesting. Bitterns are small marsh-dwelling birds known for their ability to keep a secret, and apparently magnesium is one of them, though USGS is probably referring to the solution left over from evaporating brines and seawater.
Where were we? Oh right, domestic supply of magnesium for EV batteries. If US policy makers want to build up the magnesium supply chain in the US, they better start cracking. Only a handful of companies currently produce magnesium from brine in the US, and back in 2018 the Elko Daily published a long form story about the only magnesium mine operating in the US, which is even more interesting than the mystery of the bitterns.
Obstacles On The Road To Better EV Batteries
Assuming an ample supply of magnesium in hand, the next thing to worry about is performance. Magnesium does sound good for EV batteries in terms of energy density, at least on paper. According to our friends over that the US Department of Energy, magnesium-based anodes can store 5 times more energy than the graphite anodes typically used in lithium-ion batteries. However, it’s complicated.
“Rechargeable batteries based on magnesium, rather than lithium, have the potential to extend electric vehicle range by packing more energy into smaller batteries. But unforeseen chemical roadblocks have slowed scientific progress,” the Energy Department explained back in 2017.
They don’t mean small obstacles. They mean big ones. Magnesium ions can’t move easily through solid material, which is the key trick that lithium ions perform. Back in the day, magnesium was not considered a good candidate for EV batteries because of its mobility issues.
In addition, a 2017 study also revealed that magnesium battery degradation can occur even before the battery gets its first charge-up.
Ouch!
Solving The Magnesium Battery Problem
All the way back in 2010, the Energy Department’s newly hatched ARPA-E funding office pitched $3.2 million in funding to the MIT spinoff Pellion Technologies to develop magnesium EV batteries with twice the capacity of lithium-ion batteries.
According to a 2018 report in Quartz, other investors eventually lost interest, but the research has continued apace.
One key development occurred in 2018, when a study funded by the Energy Department described nanocrystal formation on the anode. That helped to lay the groundwork for future research into the precise mechanism by which magnesium could result in superior battery performance.
“Magnesium anodes…have a unique operating mechanism,” the Energy Department wrote “This mechanism enables batteries to charge and discharge quickly at freezing temperatures (0 °C). This characteristic is important for using these types of batteries in cars and other transportation applications.”
The Energy Department also looked at magnesium batteries from another angle in 2018, and came up with a more thorough understanding of the way magnesium ions can move through crystalline solids.
That brings us up to the latest magnesium battery research, from the Tohoku University in Japan.
The Tohoku research team took a close look at mobility issues relating to the cathode, and proposed using sulfur instead of the transition metal oxides used in lithium-ion batteries.
Other researchers have been pursuing the sulfur approach. That is a tough row to hoe as Tohoku University explains:
“…sulfur-based cathodes for MRBs have severe limitations: low electronic conductivity, sluggish Mg diffusion in solid Mg-S compounds, and dissolubility of polysulfides into electrolytes, which results in low-rate capability and poor cyclability.”
That did not dissuade the research team. They came up with cathodes based on a liquid sulfur/sulfide composite, which seems to have solved the problem.
“The researchers achieved the discharge capacity of ~900 mAh/g at a high current density of 1246 mA/g based on the mass of active sulfur. In addition, they revealed that the discharge potential was enhanced by utilizing non-equilibrium sulfur formed by fast charging processes,” Tohoku explains, adding that “this material allowed for a stable cathode performance at 150 for more than 50 cycles.
Not The End Of The Road For Magnesium EV Batteries
If you think 50 cycles is not much to write home about, you are partly right. The new Tohoku research is a significant development but obstacles remain, as the research team explains.
“We need electrolytes that are compatible with both the cathode and anode materials because the ionic liquid used in this work passivates the Mg-metal anode,” said lead researcher Dr. Kohei Shimokawa. “In the future, it is important to develop new electrochemically stable electrolytes to make MRBs more practical for widespread use.”
For more details, look up “Electrochemically synthesized liquid-sulfur/sulfide composite materials for high-rate magnesium battery cathodes” in the Journal of Materials Chemistry A.
Meanwhile, a state-of-the-research review published last March in the journal Advances in Mechanical Engineering finds that “sulfur-based cathodes coupled with a (HMDS)2Mg-based electrolyte shows substantial promise,” though the authors also indicate that other materials for magnesium EV batteries could perform even better.
Either way, if all goes according to plan it looks like a win for fans of global economic decarbonization.
“When overcoming these challenges, magnesium-ion batteries are posed to be a groundbreaking technology potentially revolutionizing the vehicle industry,” the authors conclude.
Follow me on Twitter @TinaMCasey.
Image: Magnesium batteries for electric vehicles courtesy of Tohoku University.
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