New Energy-Dense Battery Could Enable Long-Distance Electric Cars

NOVEL ELECTRODE: By adding silicon to the anode, pictured here, among other improvements, Envia has more than doubled the energy density of current lithium-ion batteries. Image: Courtesy of Envia

NATIONAL HARBOR, Md.?A company founded in the Palo Alto public library has taken a dose of government money and technology and turned it into the most energy-dense battery ever. Envia System's new lithium-ion battery packs roughly twice as much energy per gram as present batteries, the company will announce here at the third annual summit of the Advanced Research Projects Agency?Energy (ARPA?e).

"We achieved 400 watt-hours per kilogram," explains materials scientist Sujeet Kumar, Envia co-founder and chief technology officer. "We have made a 40 ampere cell in a large format that automakers can recognize and use," and one that has been validated by independent energy density tests at the Naval Surface Warfare Center in Crane, Ind.

With a $4 million grant from ARPA?e, the Envia technology builds on work done at Argonne National Laboratory that found that including manganese in a mix of materials for the cathode?the electrode to which the lithium ions flock?better energy densities could be achieved. The team then switched focus to the anode?the electrode from which lithium ions flow to produce the electric current?and boosted its performance by incorporating silicon along with the typical graphite.

By blending silicon with carbon, the researchers claim to have gotten around the problems of silicon anodes that have disabled other batteries ability to charge and discharge time and time again. Simply put, silicon swells. "It will hardly last 10 cycles because of the high volumetric changes," admits Kumar. But by encasing it in a carbon coating?as well as interlacing carbon fibers?the Envia team argues it has surmounted that problem and its battery has cycled 400 times?and counting. "Even if the silicon pulverizes in the first cycle, connectivity is maintained through the carbon fibers," Kumar adds.

That leaves so-called "thermal runaway," an engineering euphemism for batteries bursting into flame?a persistent problem with energy-dense storage devices based on lithium-ion technology. This is particularly true in cars where batteries must undergo a test in which an 8-millimeter nail penetrates the battery at speed. Envia claims its batteries pass that test. "It's mainly that the cells are much thinner," Kumar says. "It's very easy to remove the heat," though it will be up to each individual automaker whether they want to employ air or liquid cooling of battery packs.

The slim, energy-dense batteries developed at an Envia center in China could reduce the number needed per car by half. And the batteries are cheap at $125 per kilowatt-hour, less than half what current batteries cost, an expense that contributes some 65 percent of the cost of an electric car. But, in addition to further independent testing, the Envia battery must now embark on the multi-year process of testing by actual car-makers. GM is an investor, but Envia declines to identify who is interested. "We are working with all the brand name [carmakers] around the world," says Atul Kapadia, Envia chairman and CEO. The idea is to either form joint ventures to produce the batteries in tandem or to license the technology to pre-existing partners.

But, assuming a single nail doesn't bring down the new technology, the battery could boost the range of electric vehicles, such as GM's Chevy Volt. The more watt-hours per kilogram, the farther an electric car can travel. That means a Nissan LEAF boasting Envia's batteries might be able to travel the 300 miles between St. Louis and Chicago on a single $10 charge, rather than the roughly 80 it can travel today. "We expect Envia's next generation lithium-ion battery will revolutionize the [electric vehicle] industry by eliminating the three remaining barriers to mass adoption: cost, range and safety," Kumar said in a statement announcing the breakthrough. "The ability to drive up to 300 miles on a single charge will eliminate 'range anxiety.'"

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