Question from me to anyone that knows: What are the benefits of Lithium-ion over NiMH, as far as battery capacity and discharge rate (performance). Why is everyone making it sound like Li-Ion is the key to the future?
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it wil hold more energy for the same wieght and size

but not sure about the lifetime and heat etc.

There are lots & lots of new lithium chemestries. In other words, besides being more energy dense ... it's continuing improvements mean it may even get better and better as these new chemestries keep coming on line. Another issue: Often the "misuse" issue is smaller with lithium chemestries. Fail to charge nickel batteries properly (short charges ... long periods w/ no charges, etc) and failures are more frequent. Ever worked for a large corporation w/ 100's of company cars? Disney had a fleet of the Chevy EV pickups. The untrained employees destroyed 'em in record time ... simply from battery neglect. Then of course the industry says, "see? ... EV's don't work!". Lithium has a greater chance to deal with the ignorant factor. There's other considerations too. Nickel is becoming way more expensive ... not that lithium sourcing is slam dunk ... but not as big an issue is nickel costs.


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They're somewhat overblown - Lithium Ion (manganese/phosphate) may achieve maybe 20% better capacity than NiMH. Cobalt is generally higher but can't deliver high currents.

Are the Hybrid Cars here to stay?

The main reason that everyone's concentrating on Lithium is that Cobasys (a subsidiary of Chevron) owns a patent on large-format NiMH batteries and won't license to anyone. No auto manufacturer can cross-license because Chevron doesn't need patented car technology. Toyota and Panasonic EV Energy were sued and eventually settled, with terms restricting the manufacture and sale of NiMH batteries. See SEC filing [PDF] and press release.

Prius NiMH modules are on the low side of energy density at 46Wh/kg - another page at BatteryUniversity gives a range of 60-120Wh/kg as typical for NiMH.

FYI, some of the stories regarding the fleet testing of the Prius plug-in have expressly stated Toyota would be testing various lithium battery chemistries (as a part of the testing).

Lithium batteries are capable of significantly higher energy densities than NiMH cells. Cells are available now that have 2-3 times the energy to weight ratio of NiMH cells.

In addition, you can also get Lithium cells with a significantly higher power to weight ratio.

Now, you can't get both characteristics optimized at the same time, but luckily, that's not too much of a problem because if you need high capacity, you also tend to need a lot more cells so the power that you need per cell is lower.

The Prius batteries have a relatively low energy density because for a hybrid application, you don't need a lot of energy storage (see how energy capacity has actually gone down over the years in the Prius), what you need is high power. And lower energy density cells tend to capable of higher power.

A good example are A123 batteries. Their energy density isn't much to write about (their latest prismatic cells are probably somewhere between 100-150 Wh/kg), but they can pump out around 5,000 W/kg. So the 3rd gen Prius with about 100kW of motor in it, could be powered with a 50 lb battery (about half the weight of the NiMH cells) and have double the capacity.

For a plug-in or EV, you'd want a higher energy density battery than the A123 batteries, unless you were looking to build a car to go 0-60 faster than the Tesla!

Great responses. Thank you.

Mike Dimmick, I would definitely look up the standard reduction potentials, but the problem (as was mentioned) is that for Li-Ion there are numerous different chemical combinations, all of which are complex ions.

Hill, I definitely know what you mean about Li-Ion being more forgiving. Over the past decade, I have definitely learned that with cell phone batteries. Although I have to admit the discharge rate and power of my NiMH DeWalt power drill is awesome! (I wish Mercedes AMG made an hybrid that was 250hp from V6 and 250hp from a 300pound plug-in NiMH battery ). My current cell phone, an iPhone3G has Li-Ion battery life that "keeps going and going and going." The battery capacity is significantly greater than any NiMH battery that I've ever had in the past.

A little off-topic, but I'm considering upgrading my power tools to Li-Ion. Anyone with experience with them? Especially lawn mowers?