Side reaction rates increase with temperature, but that is only part of the story. The rates are even more dependent on cell voltage, and Dahn mentions this: *• The biggest factor is time spent at highest voltage. o Longer is worse o Most of the parasitic reactions happen above 4v.*
This was mentioned by Jay Whitacre who made this video for the guys at Charged Car at Carnegie-Mellon which was widely discussed several years ago by diyers: http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387 He now has founded a storage battery company: Energy Storage Technology | Energy Storage Technologies | Aquion That’s one reason that many of us decided years ago to charge LiFePO4 cells to only the beginning of the exponential part of the charge (V versus Ah) curve, ~3.45 for those not using a bms with shunts, ~ 3.50V to 3.55V for those using shunts, even though at that time some of the LiFePO4 manufacturers specs stated full charge to 4 V. CALB has since lowered this to 3.6 V. Also Venkat of LBL at his This Week In Batteries blog stated that the main cause of premature death of laptop batteries was leaving them plugged in all the time. This holds the cells above 4V to maximize the amount of stored charge – since customers rate laptops on how long the batteries last on a charge. http://thisweekinbatteries.blogspot.com/2010/02/pull-plug-your-battery-will-thank-you.html As Dahn points out, additives can make a large difference in cell life, so general comments on relative lifetimes of different cell formulations – LFP, LCO, etc – aren’t very instructive since the lifetime of each formulation may vary widely with additives used,and we don't know which additives various manufacturers are using, nor their relative effects. The LiFePO4 cells in my car have been over 104 F a number of times during each of the last 5 summers, and as high as 115 F. You can’t really avoid it without active cooling when driving on 100 F days. A couple cells were accidently charged to ~3.95V, but none have been over 4 V. The pack has about 850 cycles on it now, 5 ¼ years old, 40k ev miles. No noticeable decrease in range, but it could have decreased by 5% or so and I likely wouldn’t notice, since the only test I do is drive it to about 28% SoC (of the nominal 180Ah, or ~130 Ah used) once in a while, then floor it (pulling ~3C) and see if the bms LVC alarms. Hasn’t so far. Coming years are going to be hotter. The positive cycle of the Pacific Decadal Oscillation and what seems to be a beginning El Nino this year are predicted to make this a record hot year, and the PDO typically lasts for around a decade. Going to be tough on batteries in Phoenix AZ, as well as some other areas. http://thinkprogress.org/climate/2015/04/02/3640842/global-warming-jump-imminent/ -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/ENERDEL-Battery-Experiences-tp4674615p4674752.html Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
