Michael, I think you are starting to get it, even though you express it in a peculiar way.
In real life, nothing is 100% pure. Every material and every surface has *some* contamination, even in a clean room. They just make sure that what is still there is small enough or in low enough numbers that it does not really hurt their yield, but they still need to test every circuit since it still may be unacceptably damaged by the unavoidable contamination. Same in battery manufacturing - it only needs to be clean enough that the effect introduced by contamination is low enough not to harm the operation of the cell and for example the self-discharge is within specification. Have you ever seen a modern cell manufacturing facility? It is almost as good as a clean room just as all modern electronics production is done in very clean environment just to avoid failures. I do not know enough about the chemistry of the battery physics to judge if there is an inherent mechanism of self-discharge. I do know that a lot of battery parameters are a trade-off, for example you can buy batteries with higher power but with lower capacity or you can buy higher capacity with lower power (in the same form factor). Similar trade-offs exist between high and low temp operation. It may be that the basic chemical reaction does not have a self-discharge mechanism and that a theoretical perfect Li-Ion cell has no self-discharge. But that is the same as saying that a theoretical perfectly sealed ICE engine does not need new motor oil ever, because it does not leak. Still I check my oil level from time to time, even though I know that it does not leak now, I could be losing oil and damage the engine if I do not keep an eye on the level once in a while. The well-documented laptop Lithium battery fires were actually attributed to excessive contamination of battery cells during production, which could even cause short circuits in the cells and thermal runaway around those (large) contaminations. So - the result of this is that no matter how good manufactured, any Li-Ion cell will have some self-discharge. High quality cells will have lower numbers than more sloppy produced cells and variation of self-discharge will also be an indication of quality and consistency of the manufacturing process, but saying that there is no such thing while everyone who is working with batteries tells you that it does exist is, well, denying reality. Hope this clarifies, 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:[email protected]] On Behalf Of Michael Ross via EV Sent: Friday, June 19, 2015 11:34 AM To: Willie2; Electric Vehicle Discussion List Subject: Re: [EVDL] Bicycle battery I said it, because it has come up in papers and journal articles I have read. Paul agreed with me I think. The basic Li ion cell does not self discharge - none of them. Once charged they will just sit there and remain asis until something creates a circuit for the ions to migrate back to the positive electrode. I don't understand the mechanism for PbSO4, but they do discharge just sitting unattached to any circuit - all of them. What this says is if a cell is having ions migrate back to the positive electrode that something is wrong. There are all sorts of manufacturing defects that can cause it, or BMS deficiencies, etc. No amount of correction to a lead acid will stop it from discharging. If you tell me that your Thundersky cells shows a loss over time, I don't disbelieve that - I say instead, they needed more and better design work and some manufacturing improvement. There is some sort of fault causing an internal or external parasitic load. The prismatic, folded page cells, like CALB and TS are not very good in many respects, Some (all?) bolt the conductive plates onto an aluminum post with a threaded fastener. Bleh. Notice that folks like Tesla did not choose that form - even though the alternative was to make individual connections to 7000 smalls to accomplish the task. Those little cylindrical cells have some advantages. They lend themselves to very automated, read consistent, construction. Consistency is very important at the pack level. The cylindrical form is much more stable when subjected to the volumetric changes that Li ion cells undergo when charging and discharging. They can't be packed too close that they cannot convect heat well (with some extra gear to puch air (or other fluids around them). Internally the cylindrical cells are simpler with less opportunity for failure. The connection to a pack by welding is as good as it gets. And so on. I am pretty sure in that video by Jeff Dahn I keep alluding to (and linking) he mentions this characteristic of Li ion cells. Did you all notice that article Bruce linked to about Tesla funding research at the Dahn Lab? I am hoing the Tesla will make these results open to all as they have so many other things in the interest of furthering the use of EVs. Look forward for new information, rather than back to the old and less well done research. Stuff we read from 2009 is quite stale WRT Li cells. Mike On Fri, Jun 19, 2015 at 1:15 PM, Willie2 via EV <[email protected]> wrote: > On 06/19/2015 11:58 AM, Ben Goren wrote: > >> On Jun 19, 2015, at 9:33 AM, Willie2 via EV <[email protected]> wrote: >> >> I am curious as to how Paul came to his belief. >>> >> His methodology is inadequate to the task -- rather like using a >> roadside truck scale to weigh the first four people to pass by and >> concluding that all humans weigh exactly 200 pounds. >> > You may be implying that Paul attempted to deduce self discharge from > cell voltage? > > When my first lithium pack was new, I was frequently amazed that > NUMEROUS EV folks with extensive lead experience would put a volt > meter to my cells and proclaim: "Why these cells are PERFECTLY > balanced!" I don't know how many times I've attempted to explain that > it is almost impossible to determine state of charge from voltage on > lithium cells. Other than at the tails, of course. > > Though I don't know that Paul made that mistake. > > > _______________________________________________ > 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 [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... 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