A California company called Envia Systems is developing a battery that promises to store twice the energy of lithium-ion batteries—the kind typically used in electric cars.
Envia has received investment from General Motors, which could be one of the biggest buyers of lithium-ion batteries for cars in coming years thanks to a planned lineup of plug-in cars including the Chevy Volt. The automaker's venture capital arm, GM Ventures, announced a $7 million investment in the startup last month.
Envia says its batteries could lower the cost of plug-in vehicles by reducing the need for costly metals, and by cutting the number of cells needed to store a given amount of energy in a vehicle's battery pack. In current batteries, an imbalance exists between the two electrodes: the anodes are equipped to accept far more charge than cathodes are able to supply. Envia's batteries use a cathode that is rich in manganese, which allows it to hold more charge.
Elton Cairns, a professor of chemical engineering at the University of California, Berkeley, says a manganese-based cathode should indeed help to reduce battery costs. "Most other oxide cells have cobalt in them, which is expensive," he says. There are, however, already some batteries that little or no cobalt.
Envia's recipe involves high-capacity, manganese-rich cathodes with a layered-layered composite structure (made with two different layered components) based on technology licensed from Argonne National Laboratory.
According to GM Ventures president Jon Lauckner, GM, Envia, and other companies have licensed different patents from one "family" of intellectual property related to manganese-rich layered-layered composite-cathode technology.
The current version of GM's Volt uses lithium-ion batteries made with lithium-manganese spinel cathodes ("spinel" refers to the three-dimensional arrangement of atoms in the material). The cathode material has active components, through which lithium ions move when the battery is charged or discharged, and inactive ones, which help stabilize the active material and extend the life of the battery—a vital quality in electric-car batteries.
Envia's cathode uses relatively inexpensive materials. Although the "cost is in the same ballpark as what cell makers use today," says Lauckner, the material could deliver a one-third improvement in energy density at the cell level compared to what's on the market today. This figure is based on data from a prototype that Envia designed for a specific GM vehicle application.
Envia has also begun working on more higher energy density anodes, with a $4 million grant from the U.S. Department of Energy's Advanced Research Projects Agency-Energy. Last year, in partnership with Argonne, Envia set out to develop silicon-carbon nanocomposite anodes with the idea of integrating them with high-capacity cathodes, and devising processes for scaling up production to high volumes.
Over the next three years, Envia hopes to develop a battery for all-electric vehicles. "We'll push the energy density as high as we can" by tweaking variables like coatings, porosity, and composition of the material, says Envia co-founder and business development chief Michael Sinkula. Envia was awarded a $3.65 million contract in December by the United States Advanced Battery Consortium (a coalition between Chrysler, Ford, and General Motors) to undertake this initiative.
Ultimately Envia's goal is to build a battery that has a capacity of more than 400 watt-hours per kilogram—triple that of current vehicle batteries, according to Sinkula. Currently, he says, Envia's best lab results are showing over 300 watt-hours per kilogram. But Sinkula believes that with a new anode material to match the potential of the company's cathode, the higher target will be achieved.
"If that 300 is real," says Cairns, "that would be a significant improvement." But he says this performance needs to be demonstrated and verified by a third party. Even after independent verification, a big question mark will hang over Envia's promise to deliver a better battery until it starts cranking out cells in larger volumes. Cairns says that until you have "some level of industrial production—many thousands of cells a year—you don't really have a chance to test under the range of conditions," such as high and low temperatures, and fast charging, that a commercial product will need to withstand.
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