Dense batteries are in our future

January 16, 2009

Dear Tom and Ray: Guys, what's the big deal about plug-in hybrid cars? I've read that various automakers plan to come out with plug-in hybrids in the next two to five years. Isn't a plug-in hybrid just a current hybrid (like a Prius) with a battery charger? Is there some additional technology here that I'm missing? -- Bob

RAY: Well, I guess you COULD put it that way, Bob.

TOM: But if I were to simplify it, I'd say that today's gasoline-electric hybrids use electricity to supplement a gasoline engine, whereas tomorrow's plug-in hybrids will use a gasoline engine to supplement electric power.

RAY: Cars like the Prius have enough battery power on board to power the cars up to 15 to 20 miles per hour and, after that, to assist the gasoline engine when necessary. That improves gas mileage significantly. You get twice as many miles per gallon as the average car, which is great.


TOM: But the Prius's batteries regularly need to be recharged by the engine (they never get plugged in), so the gasoline engine still has to run pretty frequently.

RAY: Plug-in hybrids alter the balance. They carry a lot more battery power, and use the batteries to do much more of the work of moving the car. And instead of constantly needing to be recharged by the engine, they get most of their recharging by being plugged in at night.

TOM: So, it's not just the rechargeability; it's that plug-in hybrids will store a lot more energy on board. That's also why they're not available yet. We're waiting for a new generation of batteries to be ready.

RAY: Current hybrids use nickel metal hydride batteries (NMh). That was an improvement over the first hybrids, which used a boatload of Eveready D-cells. But NMh batteries are still too big and heavy for practical plug-in hybrids.

TOM: Within the next few years, carmakers are anticipating the mass production of lithium ion batteries (Li), which are far more dense. Sort of like my brother.

RAY: I'm a different kind of dense.

TOM: In the case of batteries, "more dense" means they store more energy in a smaller package. So, with lithium ion, instead of having to fill the entire back seat of a Prius with batteries, they can make a plug-in hybrid that maintains the interior room people expect in a family car without weighing the thing so far down that's it's too heavy to be moved by its own batteries!

RAY: Perhaps the greatest advantage of plug-in hybrids, however, is that they'll allow us to address our oil use and pollution by focusing on a relatively small number of power plants, rather than on 100 million individual cars.

TOM: Right. So, once cars run primarily off the electric grid, we could add wind power, solar power, nuclear power, cow flatulence or anything we want to our power grid, while retiring dirtier, less-efficient plants. If we follow through with that, plug-in hybrids would be a great step toward energy independence and reducing pollution.

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