Experimental lithium-ion batteries operate in extreme cold conditions

Few recent inventions have proven their worth more than the humble lithium-ion battery. It’s only been 30 years since they left the lab for the first time, but they are what power smartphones into 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 have become more and more powerful. But they are not perfect. For one, they struggle in the deep cold. At temperatures that would not be unfamiliar to anyone experiencing particularly severe winters, these batteries do not hold their charge, nor do they deliver it.

But scientists are trying to make more durable batteries. In an article published in the magazine Central Science ACS On June 8, chemical engineers from several Chinese universities worked together to build a better battery that can withstand down to minus 31 ° F.

From previous studies, scientists knew that most lithium-ion batteries start discharging at around -4 ° F. Below this point, they do not hold the same charge and are unable to transfer it, which means it is more difficult to use them for power. And the colder they go, the worse they behave.

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 freezing 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 drawback also means that lithium-ion batteries cannot work as engineers might hope in other places that commonly experience sub-zero cold: high in the mountains, in the air where commercial planes fly, or in the cold of outer space. illuminated.

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

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

And lithium ions are what makes the battery work, hence the name.

When a battery is running, those ions fall off the positive plate, pass through the electrolyte like a fish drifting down a river, and land on the negative plate, providing constant shocks of electricity in the process. When a battery is connected for charging, the electric current forces the ions to flee in the opposite direction. It works, without too much fuss, and lithium-ion on the go powers your phone or car for hours on end.

That is, it works until the battery cools below minus 4 ° F. In recent years, scientists have found that much of the problem has to do with the movement of the ions themselves, as they struggle to properly exit the electrolyte and land on the negative plate. Scientists have tried to alleviate this problem by producing stronger electrolytes that better resist cold.

These latter researchers, however, took a different approach: they tinkered with that carbon-based negative plate instead. They decided to replace graphite with a completely new material. They heated a cobalt-containing compound to very high temperatures, nearly 800 ° F, producing tiny, 12-sided dice-shaped nuggets made of carbon atoms. The researchers molded these carbon dodecahedra into a more bumpy plate than flat graphite, allowing it to better grasp lithium ions.

When they tested their battery, they found it worked in freezing temperatures down to minus 31 ° F. Even after over 200 discharge, recharge and recharge cycles, this battery has maintained its performance.

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

This is the trick. As with many materials, trying to actually create more of these tiny carbon spheres is a challenge. It doesn’t help matters is that the cobalt compound is quite expensive. On the other hand, Hu says, this research can be useful for very specific applications.

It is not the end of this research, therefore, but rather the next incremental step. But, with each passing day, scientists are pushing the limits of these crucial batteries further and further.

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