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How to Build a Better Lithium Ion Battery

Researchers are still struggling to improve these ubiquitous batteries in a bid to make electric vehicles more viable
Argonne National Laboratory



Photo courtesy of Argonne National Laboratory.

DOWNERS GROVE TOWNSHIP, Ill. -- With current battery systems reaching their performance limits, researchers are scrutinizing every component of lithium-ion cells in order to develop energy storage mechanisms that can make electric vehicles better competitors to fossil-fueled engines.

Lithium-ion systems have made tremendous strides since they were invented in the 1970s. The cells have matured beyond expensive, fire-prone energy systems, becoming the go-to chemistry to power new mobile devices and electric vehicles. Still, prices need to drop further and the batteries themselves need be more durable to drive electric cars into more driveways and garages.

Researchers at Argonne National Laboratory outside Chicago are now tackling this problem, from designing batteries by the molecule in computers to postmortem battery analyses. In the process, the facility hopes to create innovations that will drive the industry, giving American manufacturers an edge over other countries as these energy storage systems find their way under the hood.

Khalil Amine, senior fellow scientist and manager for the Advanced Lithium Battery Program at Argonne, noted that historically, the United States led the world in energy storage research, but other countries like South Korea, Japan and China were better at commercializing these technologies.

But with high gasoline prices and increased global competition, the U.S. government has taken a renewed interest in developing and producing next-generation batteries within its borders. "Energy storage now is very strategic, not only for Argonne, but for the country," Amine said. "Whoever develops the technology will become the Saudi Arabia of batteries, so obviously it's very critical to get the technologies."

Under the American Recovery and Reinvestment Act of 2009, Argonne received $8.8 million to build new labs to design battery components, test them, scale up their production, build prototypes, run them through tests and analyze them.

The cheaper, more powerful battery starts with molecules
Though some other countries have more manpower devoted to researching energy storage, Amine said that Argonne has its own advantages. "Here, we use our advanced supercomputer to design molecules for validation," he said, allowing engineers to create suitable molecules from the ground up rather than testing various materials to see what sticks. "It's a very powerful tool that companies do not have."

Once researchers find a candidate molecule for a battery component, they produce it in small amounts to see if it works as predicted, usually in 100- to 500-gram batches. However, many promising materials languished in the past, failing to make the jump from the test tube to the assembly line and attract interest from industry.

"Great research is being done, great materials are being developed, but not a lot of them are making it out of the lab," explained Gregory Krumdick, a researcher at Argonne. "When you're scaling up technologies, what works at the bench will not work at the industrial scale."

To bridge this "Valley of Death," Argonne is building the Materials Engineering Research Facility. The laboratory takes processes that produce grams of compounds used in electrolytes, cathodes and anodes, and ramps up the output by an order of magnitude or more. Krumdick is the principal systems engineer at this scale-up facility.

Scientists tend to craft their chemicals like artisans, using specialized tools and forming the products in tiny quantities. This gives them precise control over their work and lets them tweak the process, validating their results through experiments and computer models. The material is often sufficient for a button cell like the ones that power wristwatches, but to get manufacturers really interested, you have to make enough for large batteries while using cheaper, off-the-self hardware.

The push for this service has been swift and strong: As the new scale-up facility is being constructed, Argonne has already brought two interim labs online -- one for cathode materials and one for electrolyte materials. The battery electrolyte setup is for research to "improve safety, lower flammability limits [and] prevent thermal runaways," according to Krumdick. "Cathode material is where you improve your energy density, improve your performance, improve your cycle life of your battery."

In an expansive warehouse-like building on Argonne's campus, over the din of compressors and fans, scientists working under fume and powder hoods mix solutions in glass co-precipitation reactors. The resulting blue-green liquid sits in large 20-liter containers, with brown cathode materials settling at the bottom. This material is washed, dried, mixed with lithium salts and heated.

Leaping from the bench to the Volt
The final black powder, weighing about a kilogram per batch, is placed into silver pouches to be made into test batteries, usually the standard 18650 cells, which are about the size of AA batteries, or pouch cells, like those used in mobile phones. "This size is what industry could really test and make substantial numbers of cells to determine 'Is this material good?'" said Krumdick. The material is also compared to the substances produced in small batches to make sure it still behaves the same way.

The interim electrolyte facility, which has been running for over a year, uses conventional equipment for mixing and processing organic substances. Researchers have already scaled up six electrolyte compounds. They began transferring equipment to the new scale-up facility last week, though parts of the site are still under construction. With the improved safety systems in the new lab, Krumdick expects to increase production throughput further with a 200-liter reactor.

The cathode facility proved more challenging. "Being able to make and scale up a cathode material is not a trivial task, and the equipment needed is not readily available," Krumdick said, noting that the hardware, like calcining furnaces with precise atmospheric controls, had to be purchased from South Korea, Japan and Germany.

The temporary lab has been operational for six months, and the team is still ironing out the process. "We've made material, but we don't feel it's been fully optimized, and we're still working on improving its properties," he said. Eventually, Krumdick anticipates making 100-kilogram batches of cathode compounds.

This quantity is an important threshold. "You could easily take it up to the ton quantity and your economic calculations would be linear, so you would be able to calculate out just what it would cost to make that material," said Krumdick. The lab is now negotiating licensing agreements for its materials with several companies. A cathode material developed at Argonne is already used in the 2011 Chevrolet Volt, General Motors Co.'s plug-in hybrid electric car.

With new materials, researchers can also build batteries for testing. At the Electrochemical Analysis and Diagnostics Laboratory, researchers put devices -- individual cells and full-size multicell modules, ranging from tall metal cylinders to flat boxes -- through tests that simulate a lifetime of use to see how things fail and how performance degrades.

The O'Hare/Palm Springs tests
Behind glass doors in beige cabinets, batteries are charged and discharged repeatedly under a spectrum of ordinary, not extraordinary, temperature and atmospheric conditions, to see how the batteries would respond if they were left in the long-term parking lot at Chicago's O'Hare Airport in the winter or if they would still function after a hot week in Palm Springs, Calif. The computer-controlled testing system runs 24 hours a day.

"What we do in this department is take material from discovery through pubescence and teenage years, exercise it and then take it to death and see what changed," said Ira Bloom, chemist and lab manager for the testing facility.

Once the batteries are put out of their misery, scientists conduct an autopsy in the Post-Test Facility. Lithium reacts with air and moisture, so the whole procedure is done in sealed glove boxes filled with inert gases, using tools like saws and ceramic scissors to prevent short circuits in what Bloom described as "a very inelegant process."

After cutting open the batteries, the researchers analyze what happened to the electrolytes, the cathodes, the anodes and other components. Using Raman spectroscopy, an X-ray photoelectron spectrometer, a gas chromatograph, a scanning electron microscope and a thermogravimetric analyzer, they can find out what happened to the battery as it grew old, what compounds it gave off, how its structure changed and what parts wore out. The team can then determine what led to the observed results and figure out ways to control these factors.

Bloom found that batteries are most significantly affected by temperature, followed by how intensely they are charged and discharged. Lithium-ion cells in particular don't like to sit idle, which can shorten their lifespans.

With information like this, battery and automobile manufacturers can figure out how to set up a warranty for their energy storage systems, while getting a handle on the limits of the technology in terms of performance and safety. "Right now, they're shooting for a 15-year life of the battery," Bloom said.

The facility's capacity is expected to double to cope with a large backlog of test materials, according to Bloom. The process is incremental, and he expects it will be five to 10 years before some of these designs hit the market. "It's been more of an evolution than a revolution," he said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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