Lithium ion batteries

[derlmiller]

Would it make sense to replace the NiMH batteries with Li ion batteries? Looking into the near future (~8 years) when a currently new Prius may need new batteries, Li ion batteries should be more affordable. As I understand it, the capacity difference isn't that great but a Li ion battery can be discharged ~90% while a NiMH will only discharge to ~50% before the output drops off. Would the ECU in the Prius be able to take advantage of this?

thanks,
Derl

[Jerry P]

Great question, but I think the answer lies some years away. I honestly belive that the ICE in the Prius will last forever. Why? It is the coolest running engine I have ever seen. Drove home from work Wednesday and planned to drain and replace the engine oil and filter. Pulled in the garage, put the car on the ramps and flipped the Fumoto valve. The oil was just slightly warm after a 20 mile drive. I reached up and put my hand against the engine and it was only slightly warm also. I have always been told that hot running engines wear out quickly so....this bodes well for the 1NZ-FXE.
We will all probably face that battery replacement question, maybe after 200,000 miles or so. I have 45,000 on my 2004 already so I have maybe 6 or 7 years left to worry about it. I think lithium ion will be the thing then, or maybe graphite. Hopefully we will be able to take advantage of the new technology at a reasonable price. Of course, if we can get another 200k out of a new NiMH, it might be good enough!

[windstrings]

Originally posted by derlmiller@Jan 13 2006, 05:11 PM
Would it make sense to replace the NiMH batteries with Li ion batteries?  Looking into the near future (~8 years) when a currently new Prius may need new batteries, Li ion batteries should be more affordable.  As I understand it, the capacity difference isn't that great but a Li ion battery can be discharged ~90% while a NiMH will only discharge to ~50% before the output drops off.  Would the ECU in the Prius be able to take advantage of this?

thanks,
Derl

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There are extensive threads on this.. from what I remember.. the conclusion in my mind is that LiIon cannot take the intense amperage transfers efficiently. They get too hot. They can last forever and deeply discharge, but equivant size and Amp/Hour capacity size cannot handle 50KW transfers like the NiMH batteries can.

The way around it is to have "more" LiIon batteries! I haven't studied extensively because I don't have access to them,

but lets say the same size LiIon battery can only handle 1/5 the current without overheating. Then all you would need is a LiIon battery bank 5 times the size of the current NiMh to do the job! Plus you would have the added benifit of being able to drive much further in EV mode since you have 5 times the capacity and you can discharge much deeper with LiIon.

Of course you will have to also consider that the computer in the prius would have to be reworked to deal with the different capacitance, etc of the LiIon batteries.

There are also lubrication issues to consider, but Toyota could easily solve those problems.

Yes the technology is here today right now, but it is not cost effective yet. Once the batteries come down, we will have much more options.

BTW... getting stock in companies that make those batteries will do well!... check out ENER for instance.

[priusenvy]

Originally posted by windstrings@Jan 13 2006, 11:01 PM
There are extensive threads on this.. from what I remember.. the conclusion in my mind is that LiIon cannot take the intense amperage transfers efficiently.

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Maximum charge and discharge current for a Lithium Ion cell is between 1.0 and 2.0C. For a Prius, with 6500mAh cells, 2.0C would be 13 amps. 13 amps times 273 volts is what, around 3500 watts. 3500 watts is less than 5hp. So using current Li-Ion battery technology, the battery could only supply 5hp. In contrast, the Prius NiMh battery can supply 21kW (28 hp). Li-Ion has higher power density than NiMh, but not 6x higher.

[benighted]

Perhaps you could keep the NiMH battery for the quick charging and add Li-Ion batteries for extra capacity. If you are plugging your car in overnight this would probably work well.

[priusenvy]

Originally posted by benighted@Jan 14 2006, 02:36 AM
Perhaps you could keep the NiMH battery for the quick charging and add Li-Ion batteries for extra capacity.  If you are plugging your car in overnight this would probably work well.

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That wouldn't address the lower maximum discharge current.

[EricGo]

The newest Calcars.org PHEV Prius uses Lilon that has replaced NiMhydride. So even today, solutions are possible. In five years, who knows what our choices for upgrades will be.

[jdenenberg]

Originally posted by EricGo@Jan 14 2006, 10:29 AM
The newest Calcars.org PHEV Prius uses Lilon that has replaced NiMhydride. So even today, solutions are possible. In five years, who knows what our choices for upgrades will be.

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Check out the new Li hobby batteries for RC planes. They are just becoming available and claim extreme current capabilities (eg. one minute recharge times). I was told this by a hobby shop owner in Paraguay on a flight back from Brazil on Thursday. He raved about their high current capabilities (said 50C, but I'll wait to see the specs)

This bodes well for future battery systems for hybrids, but he said they are very expensive at this time.

JeffD

[windstrings]

Originally posted by priusenvy@Jan 14 2006, 02:58 AM
Maximum charge and discharge current for a Lithium Ion cell is between 1.0 and 2.0C.  For a Prius, with 6500mAh cells, 2.0C would be 13 amps.  13 amps times 273 volts is what, around 3500 watts.  3500 watts is less than 5hp.  So using current Li-Ion battery technology, the battery could only supply 5hp.  In contrast, the Prius NiMh battery can supply 21kW (28 hp).  Li-Ion has higher power density than NiMh, but not 6x higher.

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If thats true, then you would need 6 of those LiIon banks wired in parallel just to equal the current NiMH.

They really need to make the LiIon in "bigger" sizes to avoid such problems.... similiar to what they are doing with NiMH.

[windstrings]

Originally posted by jdenenberg@Jan 14 2006, 08:44 AM
Check out the new Li hobby batteries for RC planes.  They are just becoming available and claim extreme current capabilities (eg. one minute recharge times).  I was told this by a hobby shop owner in Paraguay on a flight back from Brazil on Thursday.  He raved about their high current capabilities (said 50C, but I'll wait to see the specs)

This bodes well for future battery systems for hybrids, but he said they are very expensive at this time.

JeffD

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Its all relative to what your comparing too when you say "extreme current" 50KW is a bit more than what an RX plane uses!