The battery that is being held by the bronze medieval alchemist is nearly as useless as my knowledge of battery technology. A lithium ion Motorola BT50, it worked great in my cell phone when it was new, but over the past year or so, it deteriorated to the point where it will only hold a charge for a couple of hours (sometimes even less than that). No matter how long I charged it or how many times, it kept declining steadily.

But what a difference a brand-new battery makes! I just got one yesterday, charged it up, and 24 hours later, it hasn't registered the slightest drop in the phone's battery strength meter.

"Battery life sucks!" is an expression I hear bandied around a lot. But what does "battery life" mean? The battery life is fine if we're talking about a new battery. But the battery life is absolutely awful with an old one.

Battery life is relative to age, but what I want to know is why. The Wiki entries (for batteries and lithium ion batteries) really doesn't explain it, and I get the impression that the chemistry is either a trade secret, or else something the industry doesn't want to let the public know about; Wiki says it is not widely publicized:

A unique drawback of the Li-ion battery is that its life span is dependent upon aging from time of manufacturing (shelf life) regardless of whether it was charged, and not just on the number of charge/discharge cycles. So an older battery will not last as long as a new battery due solely to its age, unlike other batteries. This drawback is not widely publicised.

According to Wiki, this is what happens:

It is important to note that lithium ions themselves are not being oxidized; rather, in a lithium-ion battery the lithium ions are transported to and from the cathode or anode, with the transition metal, Co, in LixCoO2 being oxidized from Co3+ to Co4+ during charging, and reduced from Co4+ to Co3+ during discharge.

I'm wondering whether there are any readers with a background in electrical or chemical engineering (or just well-red geeks) who might be able to explain in lay terms precisely what is happening to these batteries as they age, as I'd love to know. Is there a steady chemical change, and is it irreversible? I've seen car batteries go bad from sulfur accumulation, and I know that they can be taken apart, the plates cleaned, and new acid poured in (a process called "rebuilding"). Is something similar at work inside a lithium ion battery?

Whatever the problem is, they better figure it out before the Prius converts to lithium ion, or there will be a lot of pissed off owners in 2009! A $10.00 cell phone battery is one thing, but the batteries in a car that costs $75,000 is quite another. Saving the world might be more expensive than imagined.

I realize my ignorance may be showing, but it seems to me that if today's alchemists can synthesize gold, they ought to be able to prevent lithium aging.

UPDATE (07/18/07): In today's Wall Street Journal, Lee Gomes discusses the battery tech bottleneck, and he says that Lithium ion batteries are the best to appear so far:

The famous Moore's Law has computer chips doubling in capacity every two years or so. The progress for batteries is more in the neighborhood of 10% a year, says Lawrence H. Dubois, who heads up physical-sciences research at SRI International, the Menlo Park, Calif., research outfit. Improvements, he said, tend to be incremental, even "mundane," like figuring out a thinner container for batteries and thus saving space.

Not surprising, device manufacturers regard every advance in batteries as something of a gift from heaven. "With even 20% more efficiency, you could make the phone slimmer or the display bigger and brighter," said Muzib Khan, a Samsung vice president working with mobile phones. "It opens up more opportunities."

The problem is that the basic design of batteries hasn't changed -- and really can't. One part gives up electrons for energy, one part accepts them and a third part keeps the two separated. Researchers scout for new materials that will provide the most chemical energy in the least weight and space; lithium-ion batteries, used in consumer electronics for the past 10 years, is the best anyone has come up with.

The biggest problem with Lithium ion technology appears to be lifespan. As the date of manufacture is more important than any other factor, I'm still not completely sure what accounts for the degradation, but I'm not convinced I'd want them in a car.

There's a fascinating discussion of Lithium ion batteries in cars here.