The first big hurdle in GM's quest to make the Volt concept a reality was choosing the right battery chemistry and battery supplier. The lithium battery in the Volt is not the same as those in the burning laptop computers on view on YouTube. Standard lithium-ion batteries—technically, lithium–cobalt oxide—power most consumer electronics. Instead, the newer, safer lithium batteries for vehicle applications typically substitute manganese oxide or iron phosphate electrodes for the more costly and less stable cobalt oxide ones, reports professor M. Stanley Whittingham, a researcher at Binghamton University in New York State who many call the "father of the lithium-ion battery."
"Selecting the battery supplier is also important because you cannot assume that the supplier can deliver a 'drop-in' battery," Weber tells ScientificAmerican.com. Because the battery's operating characteristics are so crucial to how the car runs, "the battery must be integrated into the entire system right from the start." This means that the carmaker and supplier must work closely to fine-tune the battery as it is being developed.
"You need a nearly perfect manufacturing process that employs strict quality-assurance methods, because a single cell failure will cause the entire [250-cell] battery pack to fail," he says. "I'd rather have an 80 percent–capable cell chemistry with a perfect production process than a perfect chemistry with 80 percent–effective manufacturing process."
GM considered two battery makers for the Volt. One, A123 Systems in Watertown, Mass., is a three-year-old firm that builds batteries that use electrodes made from nanostructured iron phosphates, an innovation developed at the Massachusetts Institute of Technology (M.I.T.), according to Whittingham. (A123 is teamed with German auto components–maker, Continental, to package its cells into battery packs.) The other, LG Chem, the largest chemical company in Korea and corporate sister of giant LG Electronics Worldwide, uses manganese oxide–based electrodes.
The car company has not publicly announced the winner, but according to Reuters, it's settled on LG Chem to build the Volt's battery. If true, it is a good bet that the Korean firm's six-year effort to beef up its production of lithium ion batteries—mostly used in mobile devices—figured strongly in the decision. Some longtime observers, such as Felix Kramer, the hybrid car proponent and founder of the California Cars Initiative, wonder if GM might also contract with A123 for Volt batteries to expand the supplier base.
Keeping the Volt's "diva" happy was the next big issue that its engineers had to address. In particular, Weber says, "You have to avoid letting the battery get exposed to high temperatures, which threatens its operating life." Too much heat drives the cell's electrochemical reactions faster, leading to accelerated aging. "There's a big difference between 70 degrees Fahrenheit (21 degrees C) and 90 or 100 degrees F (32 to 38 degrees C)," he says, so the car's thermal management system has to keep the diva within her comfort zone.
The other major piece of the Volt equation is the control system and associated power electronics. The operation of every modern automobile is determined by a set of computerized control functions—a hierarchy of rules that govern when each subsystem should activate, to what degree, and for how long. Each control function "constantly talks to and affects each other," Weber says and, so, they must work together in a finely coordinated manner to ensure smooth sailing. Because the Volt constitutes a "whole new propulsion category," he notes, "hundreds of control functions that have never before been implemented must be integrated so they operate seamlessly and flawlessly." Usually this process takes several years of progressive iteration, but Weber's engineering team must rethink all these basic interactions in the relatively short time remaining until the new model is rolled out.