Power Struggle

A 21st century electric-car revival is under way. But the first challenge—building a cheap, safe, powerful battery—is the hardest

By Seth Fletcher Posted 10.28.2008 at 5:15 pm 74 Comments

High Wire: General Motors is staking its future on building the Volt plug-in hybrid: Courtesy General Motors

Anointing the vendor that will develop the miracle-box powerpack that could determine the fate of an entire company is not a decision to be made lightly. And so, for two weeks beginning in February 2007, delegations from eight battery manufacturers filed one after another, props and proposals in hand, into the massive glass-walled Vehicle Engineering Center on General Motors's Warren Tech Center campus. Start-ups and multinational giants alike, these companies had survived the initial cut in the Volt battery-supplier derby, a baroque process in which some 20 employees across almost every GM division, from engineering to finance, spent two months scrutinizing 27 proposals. They graded each company's batteries on energy and power density, temperature performance, safety, life span and cost. They weighted each metric by importance and factored in what Volt vehicle-line executive Tony Posawatz diplomatically calls "qualitative factors," such as, Are we going to hate working with these guys? Next, 30 reviewers voted on which ones to bring in and grill in a marathon series of four-hour pitch sessions.

Each supplier was in Warren to prove that its battery could do the following: Store 16 kilowatt-hours of energy. Drive the Volt 40 miles on electricity alone. Launch the car from 0 to 60 in eight seconds. Run for at least 10 years. Withstand 5,000 full discharges and lose just 10 percent of its charge capacity along the way. Fit in a 64-by-33.5-inch box capable of sliding into the tunnel that houses a conventional car's driveshaft. Weigh no more than 400 pounds. Cost as little as possible. And never, ever explode.

This is not an easy order to fill.

That's because batteries are unruly pieces of technology. Each is a brew of billions of molecules that work together to store electrical energy as chemical energy. Ions (charged particles) swim back and forth between the positive and negative terminals through an electrolyte, a solution that acts as a bridge between the two terminals. During discharge, this process produces electricity by knocking electrons loose from the negative terminal. Those electrons then flow up a current collector, out of the battery and through an external circuit before traveling back down into the positive terminal, where they start the loop again. Problem is, those billions of molecules form an infinitely complex system in which all manner of chemical-reaction mischief can take place. And few battery technologies are more prone to mischief than the one that every single semifinalist was presenting to GM: lithium ion.

Lithium-ion batteries are far lighter and more energy-dense than the lead-acid and nickel-metal hydride that preceded them (and that powered the two generations of EV1 cars). They are the batteries behind the incredible shrinking of consumer electronics over the past decade. But when overheated, overcharged or otherwise abused, lithium-ion batteries -- particularly those found in cellphones and laptops, which generally use some form of lithium cobalt oxide for the positive terminal, or cathode -- have an unfortunate tendency to start a chain reaction that can end in what battery scientists call thermal runaway. Search for "exploding battery" on YouTube, and you'll get the idea.

So before a carmaker can even consider using lithium ion in a mass-produced moving vehicle (every hybrid on the road today uses nickel-metal hydride), it needs to move beyond lithium cobalt oxide. Hence GM's elaborate vendor-elimination process. Since Sony developed the first commercial lithium-ion battery in 1991, researchers have created dozens of variations on the technology, primarily by changing the makeup of the cathode. Sixteen years later, GM was on the hunt for substrains of lithium ion safe and powerful enough to put in the highest-profile car in the company's 100-year history.

On June 5, 2007, at GM's annual shareholder meeting, Bob Lutz, the vice chairman of global product development, announced the two finalists in the Chevy Volt battery race: Compact Power, Inc. (CPI), the auto-battery arm of the Korean consumer-electronics battery giant LG Chem; and A123 Systems, a Watertown, Massachusetts, start-up that would be partnering with the German auto-parts manufacturer Continental to package its cells into fully functional battery packs.

CPI had been working for five years on a cathode chemistry called lithium manganese oxide, which is cheaper and safer than lithium cobalt oxide and has one major advantage for automotive applications: excellent power. Think of a bottle of water. Energy is how much water fits in the bottle; power is how quickly you can pour it out. A lack of power isn't a big deal for a laptop, but in a car, power equals acceleration.

Cobalt chemistries are low on power because they form two-dimensional structures that restrict the number of ways lithium ions can enter and exit the cathode, placing fundamental limits on how quickly the battery can discharge electricity. In contrast, CPI's manganese-based cathode is a three-dimensional crystal lattice that makes it easy for lithium ions to come and go quickly. Faster exchange of ions means more electrons pumped out more quickly, which means more power.

But to mold this raw technology into a battery fit for the Volt would take much more work. "We had to have a cell that effectively doubled the energy capacity of a typical hybrid cell," says Prabakhar Patil, the CEO of Compact Power. CPI's 70 staffers worked late nights and weekends for four months after the shareholder meeting. They then surprised the engineers in GM's battery lab by actually delivering their first finished battery pack right on time (somewhat ominously, on Halloween day).

Meanwhile, A123's first pack was hung up in Customs. The U.S. Department of Transportation considers lithium-ion batteries hazardous material, which made it difficult to get the pack delivered from Continental's packaging facilities in Germany. (It probably didn't help that the stainless-steel casing wrapped around A123's cells looked like a nuclear weapon from a Jerry Bruckheimer movie.) Appearances aside, though, A123's lithium-iron-phosphate chemistry is probably the safest around. The covalent double bonds in the phosphate -- the strongest chemical bonds in nature -- make it nearly impossible for these cathodes to start the reactions that can lead to exploding batteries.

Finally, in January, Customs released the batteries, and GM learned that A123's product would arrive any day. Jon Lauckner was in Washington, D.C., sitting on a panel on plug-in hybrids at the Center for American Progress, and he insisted he be told the very minute the battery reached the lab. Lauckner took the stage and began to field questions from the audience. "Where are you with the second battery?" someone asked. Lauckner looked down at his BlackBerry and replied, "It arrived in our lab five minutes ago."

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