Lithium ion batteries like these will soon be powering more and more electric cars.

Argonne National Laboratory via Flickr/Creative Commons

This post, part of a series we're running all about electric cars, was written by Christopher Lampton from HowStuffWorks.com.

Most automobiles on the market today have lead-acid batteries under the hood. These batteries are popular for a couple of reasons. The first is that they are the oldest form of rechargeable battery still in common use, having been invented in the mid-19th century. Over the years, battery manufacturers have gotten very, very good at making them. The second is that they're relatively cheap to manufacture, especially in the small sizes needed in cars with internal combustion engines. Unfortunately, they also have a low energy density, which translated from tech-speak means that for a given amount of weight they don't have very much get up and go.

This is fine as long as all they have to do is provide the impulse that starts up an internal combustion engine and occasionally turn the car's lights on without the aid of a generator, but as a means of powering an electric car, lead-acid batteries don't have what it takes. In an electric car the battery has to provide all the power needed to make the car move at highway speeds for dozens if not hundreds of miles, but an electric car powered by lead-acid batteries needs such a heavy array of battery cells that it can barely move its own weight long enough to get you to work and back. (Worse, lead-acid batteries are slow to recharge, so you

That's why makers of electric cars like the Nissan Leaf and plug-in hybrids like the Chevy Volt (which only uses its internal combustion engine when the battery charge gets low) have decided to use lithium-ion (Li-ion) batteries, which pound for pound pack much more energy bang than either lead-acid or nickel-metal hydride (NiMH) batteries (the type of battery that runs the motor in hybrids like the Toyota Prius). As this Business Week article notes, "Lithium-ion cells can store up to three times more juice and generate twice the power of the nickel-metal hydride batteries used in today's hybrids." That means the array of battery cells can be lighter and still give the car a driving range comparable to that of a standard internal combustion engine.

Other advantages of Li-ion batteries is that they have a low self-discharge rate, which means they don't lose a lot of power if you leave them sitting in the garage for a few days without driving them. This is a distinct advantage over NiMH batteries (though lead-acid batteries have a self-discharge rate that's lower than either Li-ion or NiMH). And Li-ion batteries are made from less toxic materials than other types of car batteries. While both lead-acid and NiMH batteries become toxic waste when not recycled, the Environmental Defense and the Ecology Center of Ann Arbor, Michigan, has estimated that Li-ion batteries have the least potential of the three major battery types to do environmental damage. Combined with aggressive recycling programs from companies like Toyota and Honda, that's good news for the world we live in.