"I’m not sure what you mean by this." I am comparing to the lead acid chemistry where the charged state has a competing lower thermodynamic state, so a charge lead acid cell always runs down even in the absence of any short circuit or load. One of the neat things about Li ion cells that this condition does not exist. This is the self discharge that I am talking about.
Well, Dahn says very clearly in his lecture "there is no redox shuttle" back to the positive electrode. It is in answer to a question in the last 10 minutes. He is talking mostly about Li Metal O2, like LiCOO2; not the LFP, usually. But I don't believe the activity at the negative, graphene electrode (as opposed to the LFP positive electrode) is any different in an LFP cell. The secret sauce of intercalation is the bistable nature it imparts to Li ion cells. The ions end up nestled with a circle of carbon atoms above and below that has no motivation for change (thermodynamically stable). In the Linden's Handbook of Batteries, Chapter 26, by Dr. Dahn is a nice discussion of how the negative electrode is manufactured, how and why it works. It is possible to make a negative electrode poorly. If the graphene is misaligned, poorly made, and so on, you can get ions into the electrode, but it would not be stable and the capacity would be low. "If a low enough resistance path for electrons to the cathode is provided, lithium will move back to the cathode to combine with electrons there and form LiFePO4 " I pretty much said the same thing. However, good cells don't have this. " No cells I know of are using graphene for one of the electrodes. People are experimenting with it, but no cells in production. " You are incorrect or maybe talking about LFP cells again. It is very hard to know everything that is going on, and lots of information becomes quickly dated. Check out the Linden's Handbook. On Mon, Jun 22, 2015 at 9:57 AM, tomw via EV <ev@lists.evdl.org> wrote: > /“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.”/ > > I’m not sure what you mean by this. > > Jay Whitacre (Materials Science, Carnegie Mellon): The phase change LiFePO4 > to FePO4 occurs at 3.4V, redox reaction. During charging all lithium > leaves > the cathode, now have 3.4V driving Li back to the cathode when the charger > is disconnected. > - that's from the video I posted a link to after I posted the link to the > video by Dahn. If a low enough resistance path for electrons to the cathode > is provided, lithium will move back to the cathode to combine with > electrons > there and form LiFePO4, driven by the 3.4V chemical potential, with no > external potential applied as during charging. Maybe by "stable" you mean > this won't happen unless a low enough resistance path is provided, such as > dendrites through the separator, conducting contamination on the cell > packaging surface between electrodes, or an external wire connection. > > /"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."/ > > No cells I know of are using graphene for one of the electrodes. People > are > experimenting with it, but no cells in production. Most use "specially > formulated" graphite. Maybe that's what you meant since the carbon atoms > bound in hexagons are arranged in sheets in graphite. Graphene is of course > one of those single sheets, famously lifted with tape from a pencil mark > when first studied, so I guess that is what you mean rather than an actual > graphene electrode which would have quite different properties than > graphite. > > > > > -- > View this message in context: > http://electric-vehicle-discussion-list.413529.n4.nabble.com/Bicycle-battery-tp4676242p4676429.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) > > -- 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/20150622/f77e09be/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)
