The search for a superbatteryBy Louise Lerner • July 1, 2012
How Research at Argonne will Help Power the Next Generation of Electric Vehicles
This story was originally published in volume 6, issue 1 of Argonne Now, the laboratory's biannual science magazine.
Imagine if you only had to plug in your phone once a week. Or your laptop lasted days between charges. Or an affordable electric car that ran for more than 200 miles on a single battery charge.
That wonderful battery is still a gleam in the eyes of scientists working in Argonne National Laboratory’s energy storage program, but their work is bringing that dream closer all the time.
Last year, more than a decade’s worth of battery R&D at Argonne made its way into the world’s first mass-produced plug-in hybrid electric car: GM’s Chevy Volt. Argonne’s material helps the battery—a lithium-ion design similar to those in your cell phone or laptop—last longer, run more safely and perform better at lower cost than other batteries currently on the market.
As demand grows for electric and hybrid cars, automakers are searching for the battery that will make those cars compete with gasoline. Almost fifteen years ago, GM’s short-lived EV1, star of Who Killed the Electric Car?, ran on a battery that weighed 1,175 pounds. The battery in the hybrid Volt weighs in at a svelte 435 pounds.
But the next generation of batteries, according to Argonne materials scientist Khalil Amine, will be 50% more energetic—so automakers could double the range or significantly drop the price and size of the battery. We’ll need a battery like this to make electric cars available to anyone who wants to buy one.
Lithium-ion is a relative newcomer to the battery scene: it wasn’t until 1991 that the first commercial Li-ion batteries went into electronics. They’re ideal for cars because they pack a bigger punch per ounce than any other kind of battery currently on the market.
What exactly happens inside Li-ion batteries? They are named for lithium ions, which shuttle back and forth between the two poles of the battery. When you charge a battery, you are using electric current from the outlet to drive all of the lithium ions over into one pole, called the anode. As soon as you unplug the battery and begin to use it, the lithium ions flow back to the cathode, which generates a current that powers your laptop.
About the same time that the EV1 hit roads, Argonne researchers Chris Johnson and Michael Thackeray set out to improve lithium-ion cathodes even further. Early commercial Li-ion batteries were still new and expensive, somewhat unstable when fully charged, and just couldn’t make the cut for a cheap all-electric car.
The scientists wanted to find a material to stabilize the battery that would also be cheap and safe—essential if you want to manufacture batteries for millions of cars and laptops.
In the cathode, atoms sit side by side in rows. When lithium ions are pulled out of the cathode during charging, they leave holes behind in the structure. The more lithium ions that can circulate during charge and discharge, the better the performance, but too many holes and you run the risk of ruining the structure.
“We tackled the problem in a unique fashion,” Thackeray said. “Our idea was to embed a sort of ‘skeleton’ into the cathode. It’s inactive, but it serves as bones that help keep the structure intact when lithium ions are pulled out.””
The resulting integrated structure is highly complex. “It’s very difficult to determine exactly how the atoms are arranged at the molecular level,” Thackeray said. “If we understand the routes that lithium ions take as they move in and out of the structure, and the damage that occurs when this happens, it will allow us to think of ways to stabilize the structure.”
The Advanced Photon Source (APS), Argonne’s large X-ray synchrotron, helped shine a light on the matter. Johnson paired with scientists at the APS who specialize in spectroscopy to use brilliant X-rays to come up with a picture of the materials at the atomic level. “We can even put the materials in a whole working battery and watch what happens while the battery cycles,” Johnson said.
To find the best mixture for the cathode, the team tested dozens of combinations—first creating the new materials, then checking performance in actual batteries. They also upped the charging voltage to 4.6 volts—considerably higher than the usual voltage—and saw the cathode’s capacity double.
“Having these large facilities like the APS helps us enormously to characterize the battery materials.” – Michael Thackeray, Argonne battery scientist
But it’s one thing to make a tiny sample for a lab test, and another to make that process work consistently at the huge scales required for factories to make cheap batteries.
This was Khalil Amine’s challenge: improve the synthesis process.
“When you’re manufacturing a battery, the way you synthesize it is absolutely key to how good the battery actually is,” Amine said. “You have to get the exact right temperature, starting chemicals, reaction times, and environment—all the parameters have to be right.”
He set up a lab to focus on identifying reactor processes to turn out materials more consistently. When battery companies became interested in the technology, they sent their staff to Argonne to learn how to make the materials.
"Seeing homegrown innovations going into a large-scale production car that’s helping electrify the American fleet—that's really exciting and good for the country. It's really the ultimate goal for a researcher." – Argonne battery chemist Chris Johnson
The next horizon
Amine, Thackeray, and others are already working on the next generation of Li-ion batteries. They are close to making significant advances. The next generation will allow more lithium to cycle freely through the battery, which will significantly boost the battery’s capacity — but there are still a few bugs to work out. “Advances come in cycles,” Amine said. “We find a problem, we fix it, we find another problem, we fix that problem too.”
Amine thinks this new generation will be a huge improvement on the last one. “We’re looking at increasing the energy by another 50 percent,” he said. “That means a huge reduction in the cost of the battery, or a huge jump in how far you can go on a single charge.”
But even the most perfect Li-ion battery wouldn’t be quite on a par with gasoline, which is one of the most energy-dense substances on Earth.
Further down the metaphorical road, the Argonne team has turned its sights on a new kind of battery chemistry called lithium-oxygen. In the Li-oxygen battery, oxygen at the cathode reacts with lithium ions from the anode; the battery gets its energy from breaking and forming these bonds over and over through an electrochemical reaction. In theory, this reaction offers up to 10 times more energy density than the reaction that powers Li-ion batteries.
In fact, based on early calculations, many scientists think this battery could be the “superbattery”—the one that pulls close to gasoline. It could take that imaginary electric car 500 miles on a single charge.
Right now, though, Li-oxygen technology has a lot of problems. For one, Li-oxygen batteries don’t recharge efficiently. What we need is a good catalyst to help make and break the lithium and oxygen bonds more easily. To tackle the challenge, Amine, Thackeray, and their teams are partnering up with scientists across Argonne and calling in the big guns—the Advanced Photon Source and Blue Gene Q supercomputer—to help them solve the materials challenges posed by lithium-oxygen batteries.
For now, though, the next big breakthrough might be just around the corner. “In science, you never really know quite how things are going to play out,” Thackeray said. “There’s an element of intuition, of knowing the direction you want to take, and a bit of luck. It’s a very exciting time to be a battery researcher.”