Within hours of the unveiling of the Chevy Volt concept car in January, public interest in the vehicle skyrocketed. At the North American International Auto Show, crowds formed and media requests poured in. The Volt quickly became the belle of the ball there, reportedly attracting twice as much media coverage as the next closest vehicle, says GM. Its rollout generated articles in every major news venue, from The New York Times to Newsweek, and the buzz accelerated days later when President Bush mentioned plug-in hybrids during a State of the Union address. Moreover, consumers were weighing in. More than 250,000 of them responded to a GM.com Web survey, with 99 percent saying they would consider buying a Volt.
“We continue to get calls about it on a daily basis,” says a GM spokesman in a comment bordering on understatement.
Clearly, the Volt’s buzz is electric, and for good reason. Addressing an audience at the Auto Show, GM vice chairman Robert Lutz declared that the Volt could nearly eliminate trips to the gas station. “If you lived 30 miles from work and charged your vehicle every night when you came home or during the day at work, you could get 150 miles per gallon,” Lutz told Auto Show attendees.
Using its electric drive train and its engine-generator backup, the Volt reportedly features a 640-mile driving range. It offers the potential to take drivers to and from work without ever firing up its internal combustion engine and, at the same time, has the ability to traverse long distances. Significantly, it can do all that without any “inductive chargers” (a staple of GM’s EV1) or 220V re-charging stations. Rather, GM engineers say the Volt’s lithium-ion battery can be recharged in six to seven hours on a 110V, 15A household electrical current.
“The challenge was coming up with the right balance of energy in the battery and the right driving range, so it doesn’t take longer than overnight to charge it,” says Nick Zielinski, Volt’s chief engineer. “But we believe we’ve got it. We could serve three-quarters of the U.S. population with the electric-only driving range, and still have the engine and generator for back-up.”
No Timetable Yet
Indeed, General Motors may have tapped into a river of public interest with the Volt’s announcement, but its engineers warn that much work remains. The Volt is, after all, a concept car. And while GM says its vehicle engineering program has been launched, it simultaneously warns that there are no public timetables. The company has mentioned 2010 and 2012, but some experts believe that even that may be optimistic.
“The critical path for the introduction of this car goes through the development of the lithium-ion battery,” Zielinski says. “There are a number of issues with the battery that still need to be worked out.”
To be sure, all of the other propulsion technologies on the vehicle are capable now. Those technologies include a three-cylinder internal combustion engine, generator, power electronics, control systems, and the electric drive and motor that turns the Volt’s wheels.
During operation, the Volt’s method of propulsion will be far simpler than that of so-called mild hybrids (like the Toyota Prius), which drive the wheels with a combination of power from a gasoline-burning engine and electric motors. In contrast to those vehicles, the Volt will employ a single, three-phase, synchronous permanent magnet ac motor to drive the front wheels. Mounted transversely, the motor is oriented so that a coaxial drive shaft passes through its center, sending power to both front wheels. A planetary gear set on one end of the motor acts as a differential and power step-down, sending torque to the front right wheel through a linkage. A separate linkage connects the motor to the drive axle that delivers power to the left front. The motor, designed by engineers at General Motors’ Advanced Technology Center in Torrance, CA, delivers up to 120 kW of peak power.
Under all conditions, the battery-powered motor will serve as the Volt’s driving force. The question is, however, where will the battery get its charge? For daily commuting, GM engineers hope the battery will get its power exclusively from the owner’s electrical wall outlet. Zielinski says commuters who live within a 40-mile roundtrip commute can expect to get to their destination and back without ever running the internal combustion engine and generator.
Still, the beauty of the Volt is that, unlike GM’s EV1, commuters aren’t stuck if they exceed the limit of the six-hour charge and the battery runs out of juice. GM engineers are designing the Volt’s powertrain to employ a controller that monitors the state of charge of each of the battery’s individual cells. Using software algorithms to measure battery voltages, the controller determines when the state of charge has dropped below 30 percent, and then sends a signal to turn on the engine-generator set.
“It’s trickier to monitor the state of charge of a lithium-ion battery than it is to monitor a lead-acid battery,” Zielinski says. “The chemistry of the lithium-ion battery is more sophisticated, but it can be done.”
Waiting for ‘Discovery’
Still, the really tricky part of the Volt’s development lies in the creation of the lithium-ion battery pack.
Battery manufacturers say they’re confident they can develop a vehicle battery that offers the combination of features – power, specific energy, life, safety and cost – and do it on a timetable that would satisfy GM.
“We’ve got a lot of work to do, but there’s no silver bullet needed,” says Al Mumby, vice president and general manager of the Hybrid Battery Business Unit for Johnson Controls.
Johnson Controls has teamed with French battery maker, Saft, in a new venture, Johnson Controls-Saft Advanced Power Solutions, in an effort to develop a lithium-ion battery that could be used by GM. The new joint venture will go head-to-head with a separate team, Cobasys and A123Systems, in an effort to develop a lithium-ion battery for GM’s Saturn Vue plug-in hybrid. If a suitable battery emerges from the competition, it would power the Chevy Volt, as well.
Experts believe the battery makers can succeed in the key areas of battery life and power, and even in the key area of specific power (measured in W-hr/kg), but some question whether they can deliver those characteristics at a reasonable cost. The problem, they say, is that cobalt, commonly used in the cathode of lithium-ion batteries, is costly.
To be sure, there are alternatives to cobalt.
“There’s a lot of excitement over the use of lithium-iron-phosphate, instead of cobalt, because iron is the cheapest element on the periodic table,” says Donald Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT, and a nationally-renowned battery expert. “But iron phosphate hasn’t proven itself to be good enough in all respects.”
Sadoway contends that almost all aspects of lithium-ion battery chemistry problems are “resource-limited,” meaning they can be solved with enough cash. But the cost issue, he says, is “knowledge-limited” and therefore won’t necessarily topple if more money is made available.
“On the cathode side, we’re still looking for ‘discovery,’” he says. “The problem can’t be solved until more discoveries are made.”
The United State Advanced Battery Consortium (USABC), a government-sponsored agency that has provided money to battery makers to solve the problems, says it has set a near-term target goal of $150/kW-hr and a long-term goal of $100/kW-hr for electric vehicle batteries. Battery experts estimate that the current crop of lithium ion batteries are closer to $300/kW-hr, and maybe as high as $500/kW-hr.
For autos, the problem is particularly sticky because the cost and specific energy goals are far more daunting than they are for, say, laptop computers or cell phones. Autos can’t afford to give up a high percentage of their weight to a battery pack, so an auto battery’s specific energy must be very high. Moreover, the auto’s $100/kW-hr cost target is far more to difficult to reach than those of laptops and cell phones, which may cost more than $1,000 kW-hr.
“Lithium-ion batteries have a lot higher specific energy than the batteries now used in hybrids, and that’s important,” says Elton Cairns, emeritus professor of chemical engineering at the University of California-Berkeley, and a developer of EV batteries going back to the 1960s. “But they’re very expensive – too expensive for consumers.”
Still, battery experts are far more optimistic about the Volt and other so-called plug-in hybrids than they were about the pure battery-powered EVs of a decade ago. The addition of an on-board internal combustion engine brings the possibility of consumer demand much closer, because it dramatically extends the range of the vehicles, they say.
“As the batteries get better, we’ll kind of sneak up on the goals,” Cairns says. “Maybe we’ll see a plug-in hybrid because some big company wants to get good public relations, and they’re willing to sell the vehicles for little or no profit in the beginning.”
“There’s definitely going to be risk,” adds Zielinski of GM. “But we’re not going to make any progress unless we face up to those risks.”