Discharging pulls lithium off of the cathode side SEI (solid electrolyte interface) if it has been plated there, but according to the electrochemists other bad stuff goes on so the capacity lost to plating the cathode is not reversible even if the plating itself is reversible.
I wish I understood this better, but the science of it may be uncertain beyond knowing that it is bad. So when you charge, the ions move towards the cathode, and when it is cold the motion into the cathode is too slow and the lithium piles up on the SEI as a metallic lithium - it is plated. When you discharge the metallic lithium diffuses into the electrolyte and the motion of ions is towards the anode. I am not aware that discharging is a problem, I have seen nothing in the literature about it; and high currents will generate heat right where the action is. On Mon, Feb 23, 2015 at 2:11 PM, Rick Beebe via EV <[email protected]> wrote: > That was one of my big concerns when I built my truck so I tried to fix it > from the beginning. I put 1" of foam insulation in all my battery boxes. I > installed battery warmers under the batteries. I used 35 watt Farnum > heaters I got from KTA-EV. And I built a controller to turn the heaters on > below 15C and to disable charging below 3C. All of that runs only when the > truck is plugged in. > > I've been leaving the truck plugged in at home and it's keeping the > batteries at 15C (60F) despite temps to -20C. CALB allows the cells to be > discharged at a much lower temperature than charging so I'm less worried > about the cells cooling off with the truck unplugged at work. That said, > the insulation really helps slow down that process. I've found that on a > 20F day the cells have dropped to about 45F after 8 hours at work. The > other advantage to the cells being warmer, of course, is much better > performance. > > My understanding is that temperature of the anode is the critical piece. I > don't know if your BMS is measuring that or simply the air above the cell. > > --Rick > > On 02/20/2015 03:25 PM, Danpatgal via EV wrote: > >> Reviving this thread as we're having another very cold stretch here in the >> Eastern US. >> >> My batteries (SE130 CALBs) are still going, but boy do they sag when it's >> cold like this. It's annoying. >> >> I've been charging when my BMS sensors (atop each cell) are over 0C, which >> they have generally remained over the past few weeks despite the cold >> (thankfully my garage generally stays above 0C). >> >> But, my follow-up question on all this is if the BMS measurement is good >> enough. For example, I guess there is resistive heat that gets generated >> upon charge/discharge/shunting that probably make the sensors read higher >> than the cells themselves. How much, I don't know. >> >> Does anybody have any thoughts, experience on this? We've gotten down to >> -20C with a HIGH today of only -10C ... yet I'm charging. I didn't really >> want to do it, but I was dragging so much on the road with low SOC%, I had >> to, or risk having to really limp home. >> >> _______________________________________________ > 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) > > -- To invent, you need a good imagination and a pile of junk. Thomas A. Edison <http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150223/52534a0f/attachment.htm> _______________________________________________ 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)
