The fundamental process in lithium ion cells is the intercalation of ions into the negative electrode's graphene structure. Intercalated ions are a stable condition, and it takes an electric potential to undo the intercalation - to de-lithiate the negative electrode. If there is no reversed potential there is no de-lithiation. This is why the basic lithium ion battery is totally bistable.
If you take a cell, unconnected from a circuit or parasitic load, it can be modeled as a cell with a very high resistance across the two poles. At some low resistance electrons could pass from the negative to positive electrode outside the cell and then an ion would leave the graphene, enter the electrolyte and an ion would pop out of the electrolyte into the positive lithium metal oxide electrode. That is about it. You could short out the pack internally, but for obvious reason that is not done in manufacturing, and it won't happen sitting on a shelf, dendritic filament growth aside, or the external poles could be too close together and electrons could migrate by creepage over smut and graddoo. On a given cell the pressure to travel is only 4 volts or so which means creepage is very unlikely. Here is a quotation from Chapter 16 of Linden's Handbook of Batteries about lead acid cells by Alvin Salkind and George Zguris (they define self discharge in a sub head on page 16.13). The equilibria of electrode reactions are normally in the discharge direction since, thermodynamically, the discharged state is more stable. The rate of self-discharge (loss of capacity [charge] when no external load is applied) of the lead acid cell is fairly rapid, but it can be reduced significantly by incorporating certain design features. The rate of self discharge depends on several factors. Lead and lead dioxide are thermodynamically unstable in sulphuric acid solutions, and on open circuit, they react with the electrolyte. Oxygen is evolved at the positive electorde and hydrogen at the negative, at a rate dependent on temperature and acid concentration (the gassing rate increases with increasing acid concentration) as follows: [a chemical reaction equation] And so on, describing how to reduce self-discharge. Low antimony in the grids is one way. This is the difference. A lithium cell has no thermodynamic forcing function to move the ions back to the positive electrode. Stating this in the terms above - neither of the discharged or charge states are more stable than the other. In the charged state the ions are sort of cradled between many carbon atoms when the carbons are geometrically disposed correctly. You can pop the the lithium ions in and out, but they are happy to stay put. A lot of the effort that goes into forming the negative electrode has to do with physically arranging little plates of graphene so that there is a large percentage of the volume in this fortuitous geometry. This is one of the things that makes a bad, better, good or excellent cell. The garage DIY guy can do it, but not producing an electrode that efficiently uses the materials. Believe what you like, I am going with the thermodynamics. On Sun, Jun 21, 2015 at 4:30 PM, David Nelson via EV <ev@lists.evdl.org> wrote: > Cor, > > Remember that there is a demand from people for some self discharge > number. What easier way than just to make up a number? Maybe that is > what they did and maybe that isn't. Lets not confuse capacity loss > with self discharge. Also, a voltage measurement on a cell left to sit > with no load doesn't prove self discharge either. Your analogy of an > ideal circuit can't be used to size wiring doesn't apply because the > theory does include resistance. I know what you are trying to say, > however. It is just that so many people believe that self discharge > exists and keep speaking it that many, including those who should know > better, ignore things to justify their position. IIRC, you were one > who told me that my battery pack would be way out of balance in a > short period of time if I took my BMS boards off. Well, 4 years later > and it hasn't happened. I say this, not to imply you don't know > anything, but to show that we always need to be open to the fact that > we might have missed something. > > Watch https://youtu.be/9qi03QawZEk. From the description: > > 'Published on Sep 6, 2013 > > On July 30th, 2013, Professor Jeff Dahn of Dalhousie University > delivered a lecture entitled "Why do Li-ion batteries die and can they > be immortal?".' > > If you don't want to watch all 1:13:30 of it, which everyone on this > list really should, skip to 1:09 where he directly answers the > question about a charge shuttle reaction. He clearly said that no Li > battery has one built in. Watch to the whole lecture where other > things about Li cells are addressed. > > > On Fri, Jun 19, 2015 at 5:11 PM, Cor van de Water via EV > <ev@lists.evdl.org> wrote: > > David, > > > > Why do all manufacturers of Li-Ion batteries specify the amount of > self-discharge > > and why do people like me who monitor Li-Ion batteries over time, see > and measure > > the self-discharge? > > I understand that you say "theoretical" the pure Li-Ion cell may not > have a > > self discharge mechanism and thus the actual present self-discharge > appears to be > > a spurious effect, possibly caused by contamination, so the amount of > self-discharge > > is a quality indicator of the (lack of) contamination in the cell... > > > > However, saying that the ideal (theoretical) cell does not have any > self-discharge is as valuable > > as saying that the ideal (theoretical) connection does not have any > resistance. > > In practice however you better take that resistance into account when > sizing your wiring and connections. > > Similar to taking self-discharge (and especially the difference in > self-discharge between cells) into account > > when designing a battery pack. > > > > Cor van de Water > > Chief Scientist > > Proxim Wireless > > > > office +1 408 383 7626 Skype: cor_van_de_water > > XoIP +31 87 784 1130 private: cvandewater.info > > www.proxim.com > > > > > > This email message (including any attachments) contains confidential and > proprietary information of Proxim Wireless Corporation. If you received > this message in error, please delete it and notify the sender. Any > unauthorized use, disclosure, distribution, or copying of any part of this > message is prohibited. > > > > > > -----Original Message----- > > From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of David Nelson > via EV > > Sent: Friday, June 19, 2015 4:37 PM > > To: Bill Dube; Electric Vehicle Discussion List > > Subject: Re: [EVDL] "Zero self-discharge" (was: Bicycle battery) > > > > Bill, > > > > I have dug through many scientific papers on Li batteries and how they > work and I haven't been able to find anything about a theoretical > self-discharge mechanism. I have found some explicitly talking about the > lack of a charge shuttle mechanism like in lead-acid batteries, however. > > > > One paper I read has a section devoted to figuring out a charge shuttle > mechanism to add to a Li cell. It isn't a paper for the faint of heart, > however. It is "Nonaqueous Liquid Electrolytes for Lithium-Based > Rechargeable Batteries" by Kang Xu published in the Chemical Review, 2004, > Vol. 104, No. 10, pp. 4303-4417 and published on the web 09/16/2004. > > > > While I'm sure I don't get it 100% of the time I try to make sure I say, > "LiFePO4 cells have no theoretical self discharge mechanism." > > This, according to all I have been able to find on the cells, is true. > > Also, the most ardent anti-BMS people I have found have in fact done a > lot of searching of the scientific literature and came to the same > conclusion. It was not just something they made up to support their > anti-BMS position. > > > > If you have other literature showing what the self-discharge mechanism > is please share it. > > > > On Fri, Jun 19, 2015 at 11:46 AM, Bill Dube via EV <ev@lists.evdl.org> > wrote: > >> This "zero self-discharge" myth seems to be a common thread with the > >> "anti-BMS" crowd. I don't know where this misinformation comes from. > >> > >> All cells have self-discharge. It is just a matter of degree. > >> Also, the self-discharge varies from cell to cell. That's why you need > a BMS. > >> These are well-documented facts for all those that care to > >> investigate, either through the scientific literature or by simply > >> systematically testing cells for themselves (as Lee Hart has done.) > >> > >> I strongly suspect the "zero self-discharge" myth comes from > >> the same unscientific source that the anti-BMS myth has sprung from. > >> > >> Bill D. > >> > >> _______________________________________________ > >> 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) > >> > > > > > > > > -- > > David D. Nelson > > http://evalbum.com/1328 > > http://www.levforum.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) > > > > _______________________________________________ > > 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) > > > > > > -- > David D. Nelson > http://evalbum.com/1328 > http://www.levforum.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) > > -- 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) 585-6737 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell michael.e.r...@gmail.com <michael.e.r...@gmail.com> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150621/db85e60a/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)
