American Scientist

Chris Paine's 2006 documentary film Who Killed the Electric Car examined the forces that cut short the brief electric-vehicle renaissance that took place in California at the turn of the 21st century. Various possible culprits were considered: consumers, oil companies, car companies, the government, the California Air Resources Board, the hydrogen fuel cell and batteries.

Paine let only one suspect off scot-free: the batteries available for use in electric vehicles. That omission was ironic; in truth, all of the other factors working against the electric car would have little traction if batteries were capable of powering such a vehicle for the distances one gets on a tank of gas and if they could be recharged as quickly as a conventional car fills up at the pump. Although batteries have yet to reach that watershed, there are now signs that the technology is getting pretty close.

The star of Paine's film is the EV1, an electric car that General Motors made and leased to a small number of California motorists between 1996 and 2004. Initially, the EV1 was outfitted with lead-acid batteries that could carry it about 65 miles in typical driving. Later versions of the EV1 had nickel-metal-hydride (NiMH) batteries and could go more than 100 miles between charges. NiMH batteries are widely used in various kinds of consumer electronic devices and in modern hybrid vehicles. The Toyota Prius, for example, contains a NiMH battery that holds a little less than 2 kilowatt-hours of energy.

Although larger NiMH packs have been used with considerable success in some fully electric cars, there is little activity in promoting this application for them now. Instead, electric-vehicle developers are keen to find out whether lithium-ion cells (the kind found most commonly in batteries for laptop computers) can serve even better. The key questions are whether large lithium-ion batteries will prove too costly or too dangerous—news stories of laptop batteries bursting into flames and of massive safety recalls being close to people's minds.

These batteries get their name from the lithium ions that pass from one electrode to the other. As the cell is being discharged, for example, lithium ions, which are positively charged, move from the negative electrode (the anode) to the positive electrode (the cathode). At the same time, electrons travel from the anode to the cathode through whatever load is placed in the external electrical circuit. During recharge, the lithium ions move in the opposite direction, from cathode to anode.

Standard lithium-ion cells use lithiated carbon (in the form of graphite) for the anode and lithium-cobalt-oxide for the cathode. Although this combination holds a great deal of energy, it has its downsides. For one, cobalt is expensive. Also, the cathode has a tendency to release oxygen at high temperatures, which is not good if, say, one of the cells overheats. The released oxygen increases the chances that the cell, its neighbors or perhaps even the whole pack could go up in flames. Such an event is problematic enough when it happens to a 30-watt-hour laptop battery; with a 30-kilowatt-hour vehicle battery, it could be catastrophic.

Battery makers are thus showing considerable interest in lithium-ion cathodes with better thermal stability. The most prominent example in the news is a Massachusetts company called A123Systems, an MIT spin-off that produces cells with lithium-iron-phosphate cathodes, a chemistry pioneered a decade ago by John Goodenough and his colleagues at the University of Texas, Austin.

Although the A123 cells look very promising for vehicular applications, there are drawbacks to using lithium-iron-phosphate cathodes, the most important being that the cell voltage (and hence the energy density) is reduced. The other problem is not so much technical as legal: A123 is embroiled in various lawsuits and countersuits over whether it infringed on patents on this form of cathode, which Goodenough and the University of Texas has licensed to a different company.

Another chemistry that appears to hold great promise is the use of lithium titanate to replace the carbon in the anodes. Although this switch also reduces the cell voltage (and hence its energy density), it provides a great measure of safety. "When you put lithium into carbon, it's like a bomb," says Michael Graetzel, a professor at the Swiss Federal Institute of Technology in Lausanne. More than a decade ago, he and his Swiss colleagues began promoting the use of lithium titanate anodes, especially ones using nanometer-sized particles of the material. This approach was followed by researchers at a New Jersey company called Telcordia Technologies who were putting together a hybrid battery-capacitor device. Aurelien Du Pasquier, a chemist who was with Telcordia and is now in the Department of Materials Science and Engineering at Rutgers, explains that he and his Telcordia colleagues had contacted Altair Nanotechnologies to obtain samples to use in constructing their hybrid battery-capacitor. These requests, along with similar ones coming from Graetzel, sparked interest at Altair in pursuing battery research, which it has been conducting in collaboration with these Swiss and New Jersey groups.

Altair has since developed a lithium-ion cell that uses nanometer-sized lithium titanate particles for its anode and is targeting the electric-vehicle market. With lithium titanate replacing carbon, safety is much less of an issue, and the small size of the particles allows rapid recharge times. "It's almost perfect, except that the energy density is lower," says Du Pasquier.

Charles Botsford of AeroVironment echoes this assessment. (AeroVironment, a California company, built the Impact, the prototype for GM's EV1, and, among other activities, sells specialized equipment to charge large lead-acid battery packs.) Botsford and his colleagues have been testing Altair's cells and in May demonstrated a vehicle-sized battery pack to the California Air Resources Board—the regulatory agency behind that state's zero-emissions-vehicle (ZEV) program.

Botsford reports that he and his colleagues were initially skeptical of what Altair was saying about its batteries. "They had some pretty outrageous claims," says Botsford, noting a familiar adage in his business: "There are liars, damn liars and battery suppliers." So when the technicians at AeroVironment went to test the ability of a large Altair battery to take a full charge in 10 minutes, they took appropriate precautions. Representatives from Altair were, however, confident. "They laughed at us when we had our fire extinguishers and safety glasses," says Botsford.

Designing a vehicle battery to take a full charge in only 10 minutes represents a strategic move on the part of Altair. That's because its batteries are slated to be used in a purely electric sport-utility truck being readied for market by Phoenix Motorcars, another California company. Its small trucks are said to be able to travel more than 100 miles on a single charge. If they can truly do that, and if they can be recharged in 10 minutes, they may qualify for the highest category of ZEV that the California Air Resources Board has established, one created ostensibly to spur the introduction of hydrogen fuel-cell vehicles. The consequences may be critical to Phoenix's bottom line: The credit earned for putting such vehicles on the road may be worth considerably more than the truck's $45,000 retail price.

This possibility suggests a second irony: that the amendments to the ZEV-credit system that were blamed for the death of the electric car in 2003, changes that were expected to foster the development of hydrogen fuel cells, might end up putting a lot of electric vehicles on the road over the next year or two.

Even if the rules are revised, there seems no doubt that California drivers will soon be seeing various kinds of electric cars on their highways. Apart from Phoenix, there are other electric-car companies in the state with business plans that don't include lucrative credit-trading revenues. Telsa Motors, for example, will shortly begin selling a sleek roadster, which uses 6,831 lithium-ion cells of the kind found in laptops to amazing effect, accelerating the company's sports car from zero to 60 in less than four seconds and providing more than 200 miles of driving range. Eventually, if battery technology allows, the major automakers might follow suit with electric cars of their own. If not, Tesla's roadster and other lithium-ion-powered vehicles will surely be leaving them in the dust.