Material changes enable a new battery to store more electricity--and could boost the driving range of electric vehicles "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." 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).

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, though that impacts the voltage.

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