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Lithium ion batteries

Discussion in 'Gen II Prius Accessories & Modifications' started by derlmiller, Jan 13, 2006.

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  1. derlmiller

    derlmiller New Member

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    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
  2. Jerry P

    Jerry P Member

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    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!
  3. windstrings

    windstrings Certified Prius Breeder

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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.
  4. priusenvy

    priusenvy Senior Member

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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.
  5. benighted

    benighted New Member

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    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.
  6. priusenvy

    priusenvy Senior Member

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    That wouldn't address the lower maximum discharge current.
  7. EricGo

    EricGo New Member

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    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.
  8. jdenenberg

    jdenenberg EE Professor

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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
  9. windstrings

    windstrings Certified Prius Breeder

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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.
  10. windstrings

    windstrings Certified Prius Breeder

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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!
  11. windstrings

    windstrings Certified Prius Breeder

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    True, but they added "alot" more batteries so that all combined could still take the 50KW... thats what I was saying...

    They have alot more total capacitance.

    For example.. if you just run in EV mode with the current NiMH batteries, you may get 5 miles if your lucky before you are dead... but they have enough stored energy to do a 40 mile round trip.... got 12 grand extra lying around, you too can do it!
  12. windstrings

    windstrings Certified Prius Breeder

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    It would be complex... you cannot mix different type of batteries.
  13. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    there is already AER (all electric range) hybrids on the road now. one that gives AER of 30 miles (this satisfies 90% of all driving needs for commuters in the US). can be had for a projected $5000 over current pricing. (that is estimated cost for initial production using current supply lines. est cost after establishment would be up to 75% less) one of the vehicles modified is a 2004 Prius. it can be recharged to full in 8 hours and runs on battery until it reaches its discharge rate, then it goes to gas power. for the researcher at UC-Davis, this literally meant never using gas. he later experimented with taking road trips on weekends and said the average driver would get about 150 mpg, drive 1500-2000 miles before having to fill up and the "non-gas powered" mileage can be had for less than a buck a gallon at $.065 KWh. (cheap i know...but he was in Wa State when he made that statement and that is about what we pay here)
  14. derlmiller

    derlmiller New Member

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    I read through the info at calcars and edrive. Thanks for the references. The gears in my head will need some oil soon! My initial question isn't answered yet however. If you add more battery capacity (through LiIon or additional NiMH, whatever) can Toyota's ECU take advantage of it?

    Thanks
  15. windstrings

    windstrings Certified Prius Breeder

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    It has to be reprogrammed.... only a few outside of Toyota know how....

    If you read Calcars... they had to also......
  16. EricGo

    EricGo New Member

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    In case others find these numbers a bit confusing --

    The Prius can travel one mile on about 200 - 250 Wh of electricity, depending on speed, etc. Or 4 to 5 miles at your local Kwh cost. If you can recharge at night at a lower rate, many utilities offer 6 - 7 cents/Kwh, getting costs to well under two pennies/mile.
  17. EricGo

    EricGo New Member

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    Yep.

    Not ready for my kind of prime time, but I am very optimistic that in five years or so, attractive upgrade solutions will be available. In regards to price -- I currently spend 5 cents/mile for petrol, and electricity would cost me 1.5 cents/mile. If the upgraded battery is good for 100K miles, the breakeven point for the upgrade would be $3,500 US. Petrol prices are going nowhere but up IMO, and battery prices/capacity have been dropping about 50% annualy.

    As I said, I am optimistic :)
  18. McShemp

    McShemp New Member

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    The power density for Li-Ion is lower because the cell voltage is anywhere from 3.2V - 4.5V depending upon the chemistry. The cell voltage for NiMH is 1.2V. Hence, it takes 3 NiMH cells to produce the same voltage as 1 Li-Ion cell, and those 3 cells weigh more than the one cell.

    Also, capacity for Li-Ions can equal that of the NiMH cells in use today (PEVE prismatic modules in the Prius, Lexus, and Highlander). The NiMH is an established chemistry with potential for small improvements (due to advances in production and anode/cathode design). Conversely, the Li-ion market can make tremendous gains due to its infancy. Investors, scientists, and engineers see the differences in potential gains for relatively equal outlays. Thus, the remaining NiMH advances could evaporate and all focus could be placed upon Li-ion development.

    The issue has always been the Li-ion chemistry. The oxide-based cells can suffer from thermal runaway due to damage (crash or puncture), wear (expanding internal parts and chaffing), or over-voltage/over-current. These conditions typically lead to fire/explosion in a thermal runaway.

    The phosphate-base Li-ion cells produced by Valence (used in the CalCar plug-in Prius) and others don't explode or catch fire during an over-voltage/over-current event. Still, charging - especially during regen braking - must be well controlled to avoid damaging the cells. Over-voltage is more critical to Li-ion than NiMH. There will probably be a Li-ion hybrid in production by the end of 2008.


    Lastly, since the cell voltages and charging characteristics between the two chemistries is different. There would be no future "exchange" of the NiMH battery pack in a current car with a Li-ion one ... ever.
  19. EricGo

    EricGo New Member

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    What did CalCars do ?
  20. benighted

    benighted New Member

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    They exchanged the NiMH batteries for Li-Ion...
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