The only reason electric cars might one day compete with cars that rely on internal combustion is that gasoline engines are highly inefficient; nearly all of the energy stored in gasoline is lost to heat. But gasoline makes up for that flaw with another advantage: When your car's out of gas, you can refill it in a few minutes. With today's electrical infrastructure, batteries need many hours to recharge. There's some hope that we might one day install fast-charging stations across the country, but the researchers Fletcher interviews point out that this is a daunting challenge. The battery in today's Tesla roadster needs about four hours to charge. If you wanted to charge that battery in 15 minutes, you'd need a 200-kilowatt electric substation feeding the charging station. "Your house takes 1 kilowatt," one expert tells Fletcher. "If you want to have something like a gasoline fuel station that is all electrical, you're talking about multimegawatts of power at that station. And I just don't see that happening."
Neither do I. So what's the answer? Fletcher's book ends with a look at the most far-out research in the battery world—the lithium-air battery. In this design, lithium and carbon combine with oxygen from the air to form a system with a staggering potential to store energy. In theory, the lithium-air battery could store 11,000 watt-hours per kilogram, which makes it, Fletcher says, "the best chance battery scientists have to beat gasoline." A lithium-air battery could allow a car to drive 500 miles before recharging. With that range, you wouldn't need a nationwide system of quick-charging stations. You could drive pretty much wherever you wanted all day, and then recharge your car at night.
But lithium-air is the cold fusion of the battery world—a would-be game-changer that has the unfortunate downside of being impossible to achieve (probably). Researchers have been working at lithium-air for decades, but there are a number of challenges to overcome before such a battery might be commercially viable. For one thing, the system uses lithium metal, which is highly, explosively reactive with water. (In a lithium-ion battery, lithium is combined with another element in the cathode, and it is also present as a salt that's dissolved in a solution.) * Water, of course, is present in the air, so the very idea of a battery that mixes lithium metal with air has always seemed little more than a fantasy. Fletcher reports that the fantasy has become slightly more real lately. A company called PolyPlus has developed a way to coat lithium metal to protect it from moisture, and IBM has launched a research project aimed at building a lithium-air battery.
But with every advance, there's another hurdle. PolyPlus's innovation makes the lithium metal in a lithium-air battery easy to recharge, but nobody knows, yet, how to recharge such a battery. Figuring that out seems destined to take many more years. The chief technology officer of PolyPlus tells Fletcher that it will be "a long time before you see battery packs that are large enough and proven and tested enough that you would start thinking about transportation."
That's the paradox of battery research. Advanced batteries could well solve many of the problems that dog us today. But they'll only come about many, many years from now—and by then, it could be too late.
Correction, June 22, 2011: This article originally included an incorrect description of the components of lithium-ion batteries. The batteries include lithium both in the cathode and as part of a salt solution. (Return to the corrected sentence.)
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