LiFePO4 batteries
prof_braino
Posts: 4,313
I just discovered LiFePO4 batteries.
http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery
These have a lesser energy density, but are supposed to be more forgiving for over under charging, and can last longer than NiMH or other lithium battery types.
I checked a rechargeable battery pack from 2007, and to my surprise, it still works just fine. Compare this to all my Dell and HP laptop battery packs which have all died after 2 1/2 years whether I abuse them or not.
Anybody else use these? Insights?
http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery
These have a lesser energy density, but are supposed to be more forgiving for over under charging, and can last longer than NiMH or other lithium battery types.
I checked a rechargeable battery pack from 2007, and to my surprise, it still works just fine. Compare this to all my Dell and HP laptop battery packs which have all died after 2 1/2 years whether I abuse them or not.
Anybody else use these? Insights?
Comments
All sorts of claims that they are environmentally superior as the form of Lithium they use is found in a natural mineral state. But if they do burst and flame up at all, fluoride gases from the internal insulation seem a bit nasty to me.
Overall, they are generally considered the best choice going forward into the future for a lithium cell chemistry.
Meanwhile, we are having more electric car fires due to battery packs being ruptured by hitting objects on the roadway.
Chinese vendors often confuse LiFePO4 and LiPO (which is Lithium Polymer technology), so you really have to be careful when shopping. I thought the two were the same for quite awhile, and they just may be in some cases... but not always... and I am beginning to believe they never are.
You might buy an electric bicycle that touts LiFePO4 and get LiPO instead.
Interesting point in posts 14 & 15: The Dreamliner batteries were spec'd 8 years ago, before the LiFePO batteries were available. So they very easily passed all the safety checks -known-at-the-time-. Apparently it would have been nobody's job to go back and check, if that work was done by temporary contractors instead of full time employees. Makes more sense now.
The max voltage is 3.6 or so, which most 3.3V chips handle. One LiFePO4 cell can replace 2 alkaline rather well
too, 4 in series make a good 12V supply...
Generally I favour them.
Erlend
Why so? Look at the actual high voltage limit of charging the LiFePO4. 3.2volt represents the bulk of the power delivery, but if the device is being charged while in operation it is going to get 3.6 volts, and maybe a bit higher.
Since most chips limit over-voltage tolerance to about 10% and 110% of 3.3 volt ooperation 3.52 volts, there is a potential for problems.
Regarding Boeing and the Dreamliner's choice of Lithium chemistry...
It is all rather mysterious as to why Li Cobalt was selectied. Since the end of WWII, Japan and Germany have been paricipants in the Trilateral Commision that decides substantial issues of technology transfer between the USA, Germany, and Japan... behind closed doors. It may also negotiate why Japan buyings so much US debt in the form of bonds, and a lot of other issues that the public isn't aware of.
Boeing seems to have not backed off of the Li Cobalt cells, just reconfigured safety features. The actual available total energy may have favored Li Cobalt.
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The ever-expanding chemistry alternatives for Lithium still struggle with two core issues.
A. Lithium metal burns at low temperatures and in air if given a chance.
B. Batteries are being constructed from foils and coatings that are progressively thinner... physically easier to harm.
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I strongly suspect that Lithium cells and maybe all newer battery cells are much safer and simpler in single cell applications. Two cells in series requires more management. And when 3 or more cells are put into a series configuration, control of charging, discharging, damage, and thermal runaway are still nasty.
Yes, when they're good they're very good but when they're bad they're a big problem. Some of the motorcycle lithium battery mfgrs include the balancing circuitry and logic in the battery as they are also quite fragile and you're always one overcharge or full discharge from either fire or a permanently damaged battery that is $2-300 to replace. That said, I use them in the bikes as the weight savings is huge and I keep them on a proper trickle charger when not being ridden anyway.
It seems that the more you try to do, the more power you waste in the process, the more time you add to the recharge cycle, and that the results are often worse than minimal management.
3.3 x 1.1 = 3.63V, not 3.52V. Abs max are usually higher still.
Good inforrmation!
Okay.. my math was off. But some leeway in the the top end of charging these does exist... a charger may go to 3.7 volts instead of 3.6. The cell would then deliver 3.7 volts for awhile.
It is just important to be aware that the operating range is from about 3.0 to 3.6 or 3.7 and to make sure your project can adapt to the full range.