Starting this thread on the advice of blake to have a thread dedicated for LiFePO4, shed some light and answer questions (to the best of my ability) on Li-ion batteries and in particular, LiFePO4. Do some testing with LiFePO4, put my results up here, charge and discharge curves, all the geeky nerdy stuff placed here for your entertainment!
Was reading the thread "Baby steps in reducing lead" and one of the posts was concerning the actual real dangers of Li-ion cells, but then a little misconception in stating that those dangers are for all Li-ion cell. It is true, Li-ion if abused by overcharging can "cause injury and/or damage to person(s) or property", but can't all rechargeable batteries to some extent cause injury and/or damage to person(s) or property, even Lead-Acid (LA)? I am not making light of the accidents, injuries and other horrible events that investigators have determined were caused by Li-ion batteries, but just trying to put things in a little perspective here. It would be like saying that is a basket of fruit, but in that basket there are apples, oranges, and the odd ball avocado, all fruit, but different make-ups. Here is something I found with concerns to LA, makes me not want to purchase any type of SLA (Sealed Lead Acid)!
"Accidentally overcharging a battery will boil the sulfuric acid and distilled water mix. The casing of the battery can become hot to the touch, and begin to melt or swell. Flammable hydrogen can build up inside the sealed cells of the battery, causing swelling of the casing under pressure and seepage through small vents. Once the hydrogen is introduced to oxygen, it becomes a sitting time bomb. A small electrical spark can ignite the gas and cause the battery to explode, sending plastic and lead shrapnel flying around, in addition to a caustic sulfuric acid spray. Obviously, this is the most dangerous side-effect of an overcharged battery."
WOW! No way am I going to have that around me and my family! Possibly can have a sitting time bomb? Gases? Caustic sulfuric acid spray? If proper care is taken of the LA battery then this situation most likely won't happen, agreed? The same is for Li-ion chemistry. Yes, the Li-ion (depending on the cathode chemistry) can burst into flames like a Roman Candle on the 4th of July if not properly taken care of, but if proper care is taken, then they are a great investment. Any driving force behind an electric motor is the power source, in LEV’s (Light Electric Vehicles) the power source is the batteries and they should be an “investment” that you take care of. Not have to baby, but like with any investment, proper care should be taken with them, and do your "pros and cons" homework on the type of Li-ion chemistry you are planning to purchase.
Heat is one of the biggest issues with Li-ion chemistries. Many Li-ion cells are excellent for the power to weight ratios, but many cannot withstand high temperatures. LiPo (Lithium Polymer) has some great power to weight ratios, but many of the packs come pre-assembled (primarily for the RC crowd) which means the anodes and cathodes of the individual cells are already connected and the possibility for a short circuit is there, which means heat, which means some potential problems, unless of course you are a pyro! This is the reason why 49 CFR, IATA and IMDG regulations are so strict in transporting Li-ion batteries. Remember, I am not here to bash any chemistry, just giving some information and answer some questions on Li-ion cells. Like I stated before, as with any battery, as long as care is taken, then the possibility of any potential risk is reduced dramatically. The hub-bub about LiFePO4 (Lithium Iron Phosphate) is that although the power to weight ratio may not be as high as LiPO or LiCoO2 (Lithium Colbalt Oxide), they still have a decent power to weight ratio plus the chemistry is more stable at higher temperatures (cells do heat up when they are being used!) along with a higher cycle life. The LiMn2O4 (Lithium Maganese Oxide) is up there with the safety of LiFePO4 compared to the other Li-ion chemistries, but they deteriorate at a fast pace at temperatures above 50*C or 122*F. Compared to the LiFePO4 chemistry, whose operating temperatures are -20*C~70*C or -4*F~158*F.
As far as power capabilities of LiFePO4, here is a short YouTube video of two electric vehicles in a street race. One a Tesla, the other a BMW conversion with Headway LiFePO4 cells, enjoy! http://www.youtube.com/watch?v=-gGn4smzBcM
So if you are thinking of Li-ion cells, do your homework, do some comparison. Figure out which cathode chemistry is best suited for your application. I am ready to be bombarded by questions, so fire away!