I've been lurking here for a while and am building an electric canoe, with LiFePO4 cells. I've been playing with electric vehicles for a while and have been following the development of lithium-based battery technology.
What seems clear is that some lithium chemistries, like the LiCoO2 and LiMnO4 cells commonly used in laptops and other consumer applications (commonly referred to as Lithium Polymer or Lithium Ion) have a fairly limited life when compared to newer chemistries, like LiFePO4. Cycle life of LiCoO2 and LiMnO4 cells is typically around 500 cycles to 80% capacity loss, but this can be improved by careful charge/discharge management.
LiFePO4 chemistry cells, like those linked to, has a much better cycle life. Most users are getting around 1000 cycles plus, although the cells haven't been around long enough to see just how much more than 1000 cycles users will get. Some testing done by Sandia Labs has shown that LiFePO4 cells from BMI in Taiwan comfortably exceed 2000 cycles with limited charge/discharge depth, in fact they get to well over 10,000 cycles or so if charge/discharge depth is restricted to hybrid vehicle levels.
I've used some LiFePO4 cells in a couple of EV projects and they seem to live up the the claims made, but they do have some limitations and traps for the unwary. Energy density for LiFePO4 is lower that that for other Lithium Ion chemistry cells, due primarily to their lower terminal voltage (3.2V nominal Vs 3.7V nominal). Maximum discharge rate is also lower, few LiFePO4 cells are happy at more than about 5C and most work best at less than 2C. Finally, these cells are almost all made in either China or Taiwan and quality can be very variable. Although buying direct from the Far East can seem cheap, unless you buy from a reputable and well-known company you can easily end up with poor quality cells.
Headway are now just starting to make cells with consistent quality, Sky Energy are a bit of an unknown but may be OK, HiPower seem to be gaining a reasonable reputation, Thundersky had an awful initial reputation, but are reportedly improving their quality now. Best of the currently available LiFePO4 cells is undoubtedly A123, with BMI a reasonably close second, the latter often sold badged as "LifeBatt", with a big price hike over the BMI price). A123 cells aren't readily available and are small format.
Warranties are often quite limited, as cell life is very largely a direct function of battery management system effectiveness. One thing the early adopters (including me!) have found is that this cell chemistry is extremely intolerant of abuse; charge and discharge conditions have to be carefully managed, as cells will die from over voltage, under voltage or over current with surprising ease........
Jeremy
SALISBURY
UK
--- In electricboats@
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> I hear all the hype about long life of lithium ion batteries and am very very sceptical. I run a computer company and deal with laptops and other small devices that use lithium ion batteries on an every day basis and while they are much better than ni-cad or nimh batterys, I have never seen any get close to the cycle life that is advertised. I would estimate that in real use a good laptop battery might get 600 cycles before needing to be replaced in the average laptop and I'm being generous and assuming that whoever used the laptop has actually discharged the battery every day for two years. If someone has a two year old laptop with a battery that still gives even 50% of its rated capacity I am amazed.
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> My second area of skepticism is on average quality of the batteries. ie.. percent of weak or defective cells in lithium ion batteries. out of every 10 batteries I deal with 1 will be bad or go bad within a month of getting it and starting to use it. I have a tablet pc that the failure rate on the batteries has been more in the neighboorhood of 85%. With these type of real world experiences you wouldn't catch me spending the kind of money it would take to put a lithium ion battery pack in a boat. I think you could double or triple the projected cost of lithium ion in planning the real world cost including failures and dead cells.
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> For a product that claims such high cycle life the warranty periods are pretty low also.. that sets off my bullshit detector as well. The average lead acid battery has a 18 month free replacement and pro-rated 5 year warranty with a average cycle life of 300 to 500 cycles. Most of the warranties on lithium ion batteries are at most 1 year "period" that I have seen. This with a product that advertises a cycle life of up to 2000 cycles.
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> I will not be an early adopter of this technology till it has some years of track record behind it, at least for what it costs now for them.
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> I like the look of the new oddysey batteries with the thin lead plate technology.. they have incrementally higher capacity but given the correct charging technology you can bring a battery bank up to 100% charge in about 20 minutes flat. The average battery bank for a electrically power boat is capable of accepting 500 amps of charge.. The limiting point now is that there really isn't any existing chargers and generators for the market that are capable of putting out this much current. The decrease in lifetime charging costs using an engine or generator
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> just my opionion
> scott
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> --- In electricboats@
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> > Search eBay for "Lithium-Ion Battery 12V 40AH".
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> > Now granted...my (230AH) bank would run $6000. "Not cheap!" you say. But that's with a (reported) cycle time of 2000 cycles. I will generously credit my existing el-cheapo Walmart deep cycles batteries with 300 cycles. They cost $560 (8 x 12v). Good Trojan T-105's should be closer to 500 cycles - but would have cost $1200 (8 x 6v).
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> > $4800 (equivalent cycles) is still less than $6000. And BMS + chargers will bump it further. But - I save 300lbs in weight, can distribute it better, is (maybe) safer, and get probably 20% more range/charge (no Peukert). It's also easy to keep spare cells on hand in case of failure. The form-factor is intriguing - I can see 3.2V cells spread out against my hull in a couple of flat 48V strings and saving my limited storage space for more beer...
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> > We are not quite there...but so close. Being human, we tend not to factor in long-term costs very well - but maybe it's time.
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> > Anyone running lithium (in a boat, not a dragster) yet? I think when (the rest of) my Wallyworlds die in another year or 2 - it's time.
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> > -Keith
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