Also, Honda's IMA Hybrid system will not gain much advantage
by going to Lithium battery. If Honda to stick with their integrated
motor assist low kilowatt electric motors of current, I see why Honda isn't going the Lithium Ion route..

But evidently lithium ion is okay for Honda's Clarity fuel cell vehicle available for lease this summer.

As we learned earlier this year, Toyota is not sure lithium is ready for prime-time either.....

http://priuschat.com/forums/prius-main-forum/41888-toyota-announce-plug-hybrid-launch.html

"for release" and "for sale" are quite different, aren't they?
Clarity is for closed-end lease only.

There are many "enthusiasts" eager for LiIon batteries.

Be aware there are few drawbacks to NiMH batteries.
They are easy to recycle.
They are very reliable.
They are well understood.
In a "standard hybrid" (not a plugin) they have enough capacity to give all the benefit needed for mileage improvement. Tests have shown even doubling the current cars battery capacity doesn't significantly improve mileage.

The only disadvantage compared to LiIon is weight. They weigh about twice what a LiIon of equivalent capacity does. So switching to LiIon in the current Prius would save about 30-50 lbs. Not enough to really matter.

LiIon batteries currently have several disadvantages.
They are -hard- to recycle currently.
They are not well understood (yet).

Now, if we're talking about a plugin hybrid, then LiIon would be preferable. Here you want maximum battery capacity possible at reasonable weight to extend EV range.

But as Honda and Toyota have both implied, LiIon batteries are not yet ready for "prime time".

I'm happy to see Honda state the facts, instead of burying them like GM!

100% of the power supplied to drive a hybrid comes from gasoline. It shouldn't make any difference (in mileage) if the battery chemistry is Lithium-ion or Nickel Metal Hydride. In this application, Nickel Metal Hydride is probably the better choice.

However, if one is thinking in terms of a plug-in hybrid, then a Lithium-ion battery has the advantage because better storage capacity to size/weight factor.

Keith

Emphasis mine.

I remember that when the first fellow (Wayne Green???) dropped a second battery into a Prius, he got significantly better mileage. This was not a PHEV. Just twice the battery. The reason apparently was that the battery serves to buffer the ICE's output (as well as to store regenerated energy) and a bigger buffer was an improvement. The down side was cost. Toyota had to balance FE against sticker price. But a battery with more capacity does give higher FE.

My guess is that Honda is looking at the cost difference.

Why is everybody still stuck on li-ion? Li-ion is an unstable chemistry which requires very careful monitoring and must be kept cool, at the risk of catching fire.

Lithium-Iron-Phosphate (LiFePO4, or LiFe for short) is a stable chemistry that can operate up to something like 500 degrees Fahrenheit, making it the clear choice for an automobile.

GM claims it will use LiFe in the Volt. Not li-ion (I say "claims" because I don't expect them ever to actually manufacture the car.) Tesla Motors uses li-ion because LiFe didn't exist when they designed the Roadster, and because cost was a critical factor.

I have LiFe in my Xebra. (One of only a small handful of Xebras so equipped.)

How easy and effective is it to recycle the LiFe?
I've of only a 20% recovery with Li-ion.

I was under the impression that lithium batteries were recyclable, but I have no actual information. It's a good question.

Lithium batteries are definitely environment friendly but I am not sure about their recycling technology. NiMh should be pretty well recycled nowadays since AA and AAA rechargeable types are used at customers in huge quantites.

I too, think that doubling the NiMh capacity gives better mileage. The efficiency of the regenerative braking should double, just to mention one thing.

I also very often run out of buffer, so extra capacity would come in handy in the following cases:

1) Mountain driving. You loose a lot of electricity on the way up and gain a lot down. Currently, the juice runs out at half the way up and the battery gets full halfway down.

2) Stop-and-go driving. Currently, the Prius looses its electricity in 5-10 minutes in a queue and then it has to switch the ICE on (and start getting bad mileage). With more battery, you could be in the queue for a longer time period before the ICE activates.