Many drivers who consider buying an electric car ask a key question: How long will it take to charge the battery? During a long-distance trip, a pit stop can take more than 30 minutes, depending on the charger. Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are working on technology to speed up charging — an important step in hastening the widespread adoption of electric vehicles (EV) and reducing greenhouse gas emissions.
The ability to travel efficiently over long distances isn’t just important to commuters and road-trippers. The American economy relies heavily on trucking to move goods, and that sector also will need fast charging times for a future electrified fleet. Improved energy storage options will make that possible.
“We are reaching a stage where electric cars and trucks must charge fast — it’s not a nice-to-have.” — Venkat Srinivasan, XCEL lead
Today, Argonne leads an effort to troubleshoot the hurdles to fast charging, targeting a recharging window of 15 minutes or less. The initiative, called eXtreme Fast Charge Cell Evaluation of Lithium-ion Batteries (XCEL), also involves DOE’s Idaho National Laboratory, Lawrence Berkeley National Laboratory, Oak Ridge National Laboratory, SLAC National Accelerator Laboratory and the National Renewable Energy Laboratory.
Swift charging: a must for the clean energy future
“I think it’s fair to say that every car company views fast charging as the ‘killer app,’” said Venkat Srinivasan, director of the Argonne Collaborative Center for Energy Storage Science (ACCESS) and leader of XCEL, referring to the concept of an essential, game-changing computer application. “We are reaching a stage where electric cars and trucks must charge fast — it’s not a nice-to-have.” He added that fast charging will also be essential for sustainable aviation as planes become more dependent on electric power.
Research through the XCEL initiative, which began in 2017, has already demonstrated in laboratory tests an increase by 50% the energy density — or the driving range packed into a battery — that is possible with fast charging. The next phase of work seeks a similar gain by 2026. In practice, this would mean a 10-minute charge for an EV that delivers 90 miles of travel with current technology would, in the future, keep you on the road for 180 miles.
Speed bumps on the road to fast charging
Current lithium-ion batteries run into three main challenges with fast charging. One is that parts of the battery can crack under the stress. Another is that they generate too much heat too quickly, which slashes their lifetimes.
The third and biggest challenge is a phenomenon called lithium plating. When the battery charges, lithium ions (atoms or molecules with an electric charge) move across a liquid medium called an electrolyte from the positive to the negative electrode. Fast charging can cause a sort of ion traffic jam, where lithium piles up permanently outside the negative electrode. That leads to a shorter battery life, and it can also be a safety hazard.
Before it’s possible to start solving these challenges, they need to be detected first — another big obstacle in battery research. It’s simple enough to open up a battery and see what went wrong after it fails, but that can take hundreds of charging cycles. When and where did the problem start happening? How long will the battery last afterward? These questions are more difficult to answer without being able to watch the battery in action over a long time.
XCEL scientists have an extraordinary tool to do exactly that. They use the intense X-ray beams at the Advanced Photon Source (APS), a DOE Office of Science user facility located at Argonne. At 11-ID-B, one of many experiment stations at the APS, researchers have watched a series of battery cells charge under varying conditions. The high energy of the X-ray beam allows researchers to penetrate the whole battery, while the flux of the x-ray beam speeds up data collection, allowing scientists to follow the rate of the energy transfer during charging.
“You could perform aspects of this type of experiment elsewhere, but the high beam intensity at the APS reduces measurement time from days to minutes, making it possible to track uneven battery performance related to fast charging,” said Kamila Magdalena Wiaderek, an Argonne electrochemist.
Wiaderek is studying battery cell heterogeneity, a phenomenon where some parts of lithium-ion batteries operate more efficiently than other parts. She and colleagues have used the APS to inspect cells as they charge and discharge, documenting causes of heterogeneity — including issues that occur during faster charging. And they are detailing through experiments the how, where and when of lithium plating and other changes on the atomic scale.
The coming APS Upgrade, which will allow the facility to generate X-ray beams up to 500 times brighter than ones generated today, will further strengthen XCEL research and reduce data collection time even further.
“The improved quality of the beam will allow us to observe with much finer detail the fast processes taking place within batteries while they operate,” Wiaderek said. “The faster data collection times will also allow us to use techniques that are currently out of our reach for experiments observing batteries in action.”
Building cells at CAMP
To test and examine batteries one after another, researchers need a supply of consistently made cells — the basic units of a battery. They get them from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility, which builds prototype battery electrodes and cells that meet industry requirements. These prototypes have about 100 times the capacity of a little coin cell you might find in a bathroom scale, but they’re also many times smaller than what would go into a vehicle. That helps to bridge a gap between lab inventions and commercial-scale production.
“It’s a major investment for a company to take a research idea you might read about in an academic paper and scale it up to a point where they can run it through their production line,” said Andrew Jansen, a senior chemical engineer who runs the CAMP Facility. “Here at CAMP, we use equipment and components that are very similar to what the industry would use.”
The facility’s production tools sit in a dry room that maintains less than 100 parts-per-million moisture levels at all times. (For comparison, a typical indoor room at a comfortable 30% relative humidity would have readings near 10,000 parts per million.) The extremely low humidity is needed because water in the air can react with salt in the battery electrolyte to produce damaging acid. Jansen added that CAMP’s trained, dedicated staff have unique skills and techniques that help move batteries from prototypes to products.
“CAMP is an opportunity for new battery chemistries to move further toward commercial production here in the United States,” he said.
Lithium-ion batteries aren’t necessarily the only type of energy storage that will accelerate fast charging, but they are the dominant one. Some research at Argonne and across the DOE laboratory network focuses on solid-state batteries and other innovations that could eventually replace conventional lithium-ion with earth-abundant ions. “While we’re going to be driving lithium-ion battery cars for the next decade, we want to have a portfolio of technologies that we are pursuing simultaneously,” Srinivasan said.
In addition to strides in energy density and battery monitoring, XCEL researchers have been able to reduce the cracking that happens in cathode materials during fast charging. They have also developed promising new electrolytes that help ferry lithium ions across the battery more efficiently and prevent lithium plating.
This kind of progress happens because of a multidisciplinary research loop among Argonne’s teams and facilities: the ability to inspect batteries at minute scales, develop prototypes, test them and then start the cycle again.
“We take a fundamental approach to fast charging problems in XCEL by saying ‘let’s understand what happened with the battery’”, Srinivasan said. “That understanding will give us some ideas of what to do next, and we can try to find a way to solve it.”
About the Advanced Photon Source
The U. S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory is one of the world’s most productive X-ray light source facilities. The APS provides high-brightness X-ray beams to a diverse community of researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. These X-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being. Each year, more than 5,000 researchers use the APS to produce over 2,000 publications detailing impactful discoveries, and solve more vital biological protein structures than users of any other X-ray light source research facility. APS scientists and engineers innovate technology that is at the heart of advancing accelerator and light-source operations. This includes the insertion devices that produce extreme-brightness X-rays prized by researchers, lenses that focus the X-rays down to a few nanometers, instrumentation that maximizes the way the X-rays interact with samples being studied, and software that gathers and manages the massive quantity of data resulting from discovery research at the APS.
This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
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