Light and powerful lithium-ion batteries have allowed automakers to make electric and plug-in hybrid vehicles with ample acceleration and reasonable range and life. But lithium is expensive—the battery pack of the Nissan Leaf costs about $12,000—and the range of electric vehicles is still limited—about 138 miles per charge in ideal conditions for the Leaf—making the technology a tough sell for many drivers.
Toyota researchers are making steady progress in developing a battery that uses magnesium instead of lithium, and which could someday offer a cheaper and more energy-dense alternative.
Earlier this month, researchers at the Toyota Research Institute of North America (TRINA) in Michigan published a paper in the journal Chemical Communications that describes experiments involving a magnesium-ion battery with a new kind of anode, made of tin, and the same type of electrolytes used in lithium-ion batteries.
The tests showed promising performance and open the path for further research, says Nikhilendra Singh, the lead author of the paper.
“The potential is definitely there,” Singh says. “There are some improvements we need to make to its performance, which we’ve addressed in the paper as well. But overall, we’re very excited.”
Magnesium is an abundant material, so magnesium-ion batteries promise to be cheap. Such batteries should also have a higher storage capacity than lithium-ion ones because magnesium ions have a positive charge of two, rather than one for lithium ions. A magnesium-ion battery could store more charge per gram, and that would translate into a longer driving range in a car or running time for consumer electronics. But the chemistry involved in making a magnesium-ion battery work efficiently has yet to be perfected.
There are two primary routes of exploration, says Yuyan Shao, a senior scientist at the Pacific Northwest National Laboratory.
One is focused on making batteries with a magnesium metal anode. This type of anode transfers charge efficiently but is incompatible with conventional electrolytes. When these are used, a “blocking layer” forms on the magnesium anodes that effectively shuts a battery down, Singh says. So some researchers are searching for new electrolytes that work well with magnesium metal.
Another potential solution is to use a different type of anode, one that works with familiar, conventional electrolytes. This approach has also had limited success previously, but Toyota’s paper demonstrates that it is worth further research, specifically aimed at finding a high-capacity, high-voltage cathode, Shao says.
There is a great deal of work in academia and industry aimed at improving battery performance and lowering materials costs, either by advancing lithium-ion technology or by exploring new chemistries, such as lithium air, sodium air, and lithium sulfur. The work at TRINA is focused exclusively on magnesium, but Toyota scientists elsewhere are exploring other new battery types, including lithium-air and sodium-ion batteries, which are also considered candidates to replace lithium-ion batteries in autos and consumer electronics.
A company that is also actively pursuing magnesium-ion batteries is Pellion Technologies, which was spun out of MIT. The company is using computerized screening to rapidly test the performance of the active materials in magnesium-ion batteries. Two of Pellion’s cofounders declined to comment on the Toyota work.
In the 1970s and 1980s, lithium-ion battery researchers attempted to build batteries with a lithium metal anode because, as with magnesium, it promised a higher voltage, and thus better energy density. Eventually, though, different anode materials were used, which paved the way for today’s lithium-ion industry, says Venkat Srinivasan, researcher and manager at Lawrence Berkeley Laboratory’s Batteries for Advanced Transportation Technologies program.
When it comes to magnesium batteries, it’s far too early to declare which route—a magnesium anode or tin insertion type anode—holds the most promise, Srinivasan says.
Indeed, researchers at TRINA continue to pursue both paths.
“It’s a little bit early for us to decide on only one system,” says Takashi Kuzuya, the general manager at TRINA. “That’s why we are investigating many, many possibilities.” He expects magnesium batteries to first be used in consumer electronics and then in cars, the same way that lithium-ion batteries were adopted.
The impact of Toyota’s paper will be felt primarily within the research community, says Srinivasan. Commercialization of magnesium batteries is more than 10 years away: “Once you have a breakthrough, meaning you have an anode, a cathode, and electrolyte, it takes maybe five years to reach the commercialization stage, and we don’t have all that with magnesium, so it’s going to take a while,” he says.