I am late to this discussion and have little to add, but this called me to comment:
"I did a bit of research. Some authors talk about "intercalation", which happens below freezing. Intercalation is when the anode becomes plated with lithium ions instead of the ions being absorbed into the anode." I don't know the authors referred to, but this is an incorrect definition of intercalation. Intercalation is the nestling of Li ions between sheets of graphene in the anode. It happens are all temperatures, not only below freezing. [Here is a hoard of images describing intercalation: <goog_1326516460> http://tinyurl.com/y46elflk] Intercalation has nothing to do with Li plating onto the anode. Intercalation of the ions is what makes Li ion cells so much better than PbSO4, and why there is little decrease in the state of charge if a cell sits for a long time. The ions sort of drop into little pockets of the hexagonal structure of carbon in graphene. It is a stable condition. I base this on the Waterloo lecture by Dr. Jeff Dahn,and other reference material. I am old enough to forget stuff, but I am pretty certain of this. The decrease in cell function due to plating is purely mechanical. The anode needs to be porous enough that ions pass from the electrolyte easily. he plating of the Li on the SEI (solid electrolyte interphase) of the anode simply blocks the passage of ions and reduces their ability to penetrate the anode. It clogs the screen so to speak. This is not intercalation it is simple plating. Clotting up the SEI of the anode nd degredation of the electrolyte are significant causes of cell dysfunction. the discharged cathode is highly reactive and mess with the electrolyte. A lot of improvements in Li ion cells is additives to make the electrolyte less easily damaged when the cell is fully charged. Heat is also a factor when the cell is fully charged. This is a good reason to mostly charge no more than 80% or 90% of 100% SOC. It keeps the positive electrode from becoming fully reactive and starting to tear up the electrolyte. Back the subject of cold performance. Part of the problem is simply increased viscosity of the electrolyte leading to lower mobility of the ions. I am not sure what is going on with electrolyte formulation, but lower viscosity was one of the main paths of interest 5 years ago. A little OT: some electrochemists are averse to talking about anodes and cathodes preferring to refer to the positive and negative electrodes. This is because the words anode and cathode apparently change meaning depending on whether a cell is charging or discharging. Referring to positive and negative electrodes eliminates confusion. The purchase and application of the graphene has a major effect on cell capacity. Definitely non-trivial. You don't just smear some carbon on a sheet of copper. (You could make a Li ion cell in your garage, but it would be limited by your ability to make a quality application of the graphene.) Cell capacity 5 years ago was limited by the ability of the graphene to make proper orientation in the manufactured electrode, and therefore the availability of sites for intercalation iwas limited. A cell with theoretically perfect graphene formation would be many times greater in capacity. Mike On Mon, Sep 9, 2019 at 8:12 PM paul dove via EV <[email protected]> wrote: > You are confusing electric current with a chemical process. > Ohms law does not apply in a chemical process. > Low temperatures slow the chemical reaction and charge transfer > velocity, which leads to the decrease of ionic conductivity in the > electrolytes and lithium-ion diffusion within the electrodes. Such decrease > will result in the reduction of energy and power capability, and sometimes > even performance failure. > > > Sent from my iPhone > On Sep 9, 2019, at 12:38 PM, Peri Hartman via EV <[email protected]> > wrote: > > > Hi, > > Does anyone have a more in-depth explanation why li ion cells perform > poorly in cold weather ? It's well known that your range goes down when the > battery is cold. Lots of writers talk about the phenomena and advise you > about it but fail to give any real explanations. I think this conversation > may have come up a long while ago but it's hard to search for. > > I did a bit of research. Some authors talk about "intercalation", which > happens below freezing. Intercalation is when the anode becomes plated with > lithium ions instead of the ions being absorbed into the anode. Obviously, > that permanently ruins the battery. So, this is irrelevant regarding poor > range in cold weather. > > I did find one article that might be relevant, though. > > > https://cen.acs.org/articles/96/i10/Rechargeable-battery-weathers-extreme-cold-conditions.html > > They claim the electrolyte becomes viscous, slowing down the ion movement. > That's about all they say. But, I'll add my thoughts. > > If the electrolyte is viscous, then I suspect the voltage potential drops. > Since watts-hours (energy) is V * Ah, you have less energy available, > assuming that the Ah is constant. But, what about internal resistance ? For > the same driving behavior, you'll need higher amps at a lower voltage. > Resistance loss is I^2 * R, so that loss should go up significantly. I'm > getting into a trap here: why doesn't the increased resistance loss heat up > the battery ? The nominal resistance is extremely low, so maybe even at an > elevated state there isn't enough heat to affect the electrolyte's > viscosity. Don't know. > > Here's another article that talks about electrolyte. They talk about > preventing decomposition of electrolyte. > > https://spectrum.ieee.org/energywise/green-tech/fuel-cells/lithium-additives > > Obviously, the other major factors are cabin heat and defrost. > > Peri > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20190909/fe1b9187/attachment.html > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -- Michael E. 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