Experimental lithium-ion batteries work in extreme cold

Few recent inventions have proven their worth more than a modest lithium-ion battery. It’s only been 30 years since they first left the lab, but they are the ones who power smartphones in the palms of the world and put electric cars on the road. They will only become more important as critical components of renewable energy networks.

Since the early 1990s, the prices of these batteries have fallen more than thirty times, although they are becoming more powerful. But they are not perfect. On the one hand, they are fighting in the deep cold. At temperatures that would not be unfamiliar to anyone experiencing particularly harsh winters, these batteries do not hold or charge.

But scientists are trying to make batteries more durable. In an article published in the journal ACS Central Science on June 8, chemical engineers from several universities in China worked together to create a better battery that lasted up to minus 31 ° F.

From past research, scientists knew that most lithium-ion batteries begin to equalize at about minus 4 ° F. Below this point, they don’t hold as much charge and aren’t as good as transferring it – which means it’s harder to use for power. And the colder they are, the worse they perform.

For most of the world, sub-zero temperatures are not a problem. But if you live in, say, the American Midwest, your electric car may have less range in January than you’d like. And if you’ve ever been caught outside in the frozen winter, you may have noticed that your phone’s battery tends to drain faster.

[Related: We need safer ways to recycle electric car and cellphone batteries]

This disadvantage also means that lithium-ion batteries may not work as well as engineers can expect in other places that typically experience sub-zero frosts: on top of mountains, in the air where commercial aircraft fly, or outside in the cold of unlit space.

So there is plenty of research dealing with the problem, according to Enyuan Hu, a battery chemist at the Brookhaven National Laboratory who was not involved in the article. And to do that, engineers and chemists have to deal with the insides of the battery.

Basically, the lithium-ion battery consists of two electrically charged plates, one negative, the other positive. The middle space is filled with electrolyte, which is an electrically conductive suspension containing dissolved ions. The negative plate is usually carbon-based, such as graphite; the positive plate usually contains metal and oxygen atoms.

And lithium ions are what make the battery tick – hence the name.

While the battery is running, these ions fall from the positive plate, cross the electrolyte like a fish floating on a river, and land on the negative plate, delivering constant shocks of electricity in the process. When you turn on a rechargeable battery, the electric current causes the ions to run in the opposite direction. It works without any problems and these moving lithium ions charge your phone or car for hours.

That is, it works until the battery cools to below minus 4 ° F. In the last few years, scientists have found that much of the problem is with the movement of the ions themselves, which struggle to get out of the electrolyte properly and land on the negative plate. Scientists have tried to alleviate this problem by making harder, cold-resistant electrolytes better.

However, these latest researchers have taken a different approach: they have dealt with this negative carbon-based plate. They decided to replace the graphite with a completely new material. They heat a cobalt-containing compound to very high temperatures – almost 800 ° F – producing small nuggets shaped like 12-sided dice made of carbon atoms. Researchers have formed these carbon dodecahedrons into a plate that is more uneven than flat graphite, which allows it to better trap lithium ions.

When they tested their battery, they found that it operated at temperatures as low as minus 31 ° F. Even after more than 200 cycles of discharge, charging and recharging, this battery maintains its performance.

“The material is scientifically interesting,” says Hu. “But its practical application can be limited, as required [a] a complex path of synthesis. “

This is the trick. As with many materials, trying to create more of these little carbon orbs is a challenge. It does not matter that the cobalt compound is quite expensive. On the other hand, Hu says, this research could be useful for very specific applications.

Then this is not the end of this search, but rather the next step. But with each passing day, scientists are expanding the boundaries of these important batteries.

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