So far most li-ion chemistries with organic electrolytes start dying right after the formation process in the factory. What ever you do by using the cells is just killing them faster.
Elevated heat is the most biggest issue with the laptops. Not the voltage. If it would be the voltage *all* the laptops would be dying flat on the 1st year. But 95% of them keep working just fine several years. My cells in MBP now are sitting on 4.16Vpc and all is fine. They are in the hysteresis state and no current is pushed to the cells. No explosions or near death escapes expected. When LFP came and replaced LCP (NMC) we saw better cyclic life and due lower nominal voltage a much longer calendar life. Much less specific energy in the weight and in the volume. Also added BMS cost due added cell count. I was sceptic and felt that we are just taking steps backwards. Now I think differently since the proven stability of this certain chemistry is extraordinary. Track record is impressive. We can finally get the numbers right which we have been chasing for a decade. (referring to specific energy and cost) I got from Winston in 2004 some 30Ah LFP cells in white cases with shaved labels. These were the 1st zero-series ever made. I still have few dozen of these cells. Most of them have been stored in various conditions and I test them once a year. This year I had to skip the tests due more important battery related things. Some cells are still on the same charge they came from the factory. And showing over 2v. Some are completely dead (corrosion inside). Packs that have BMS set on top balancing to 3.7v with less than 0.,3C charge and about 1C peak discharge are showing some interesting things. Pack regains capacity and performance if pulled to 4.25Vpc. The effect remains for next dozens of cycles. Few cells have unevenly heating terminals. The connections are tight and near to same torque (read: very tight). The interconnect bolts have lost too much material and the connections inside the cells are coming loose. Even the cells are installed poles upwards. In EV application about 80% (~261Ah of 325Ah (350Ah nominal was never there)) of the original usable capacity was available few weeks ago. About 8 years on daily use. Cold weather performance is weaker. Pack needs to be 'hot' before it provides original power. Pack is still very usable (but I'm worried about the unavoidable death from mechanical failure inside the cells) In short: The temperature and calendar life are more significant factor than peak voltages. At least as long as they are in the realm of the electrolyte specifications. Lower operation voltage lessens the electrolyte stress. -Jukka Disclaimer: Reader can choose if one believes the observations I have told above. Facts behind the observations are 'IP' that is being used to create better battery products. These observations do not apply on pouch or cylinder cells or to any other chemistry that has not been mentioned (and *every* manufacturer has a different one). 2013/10/9 Ben Apollonio <e...@bapollo.com> > Indeed! I believe low charging voltages are, at least in part, > responsible for LiFePO4's amazing calendar/cycle life. Also, I am told > Tesla's Model S gives owners the option to charge conservatively, for life > at the expense of range, or aggressively for a long trip. Another part of > Tesla's secret is that the pack is so large that C rates are kept low, as > is DoD for most drives. That, and you don't need many cycles at 265 miles > each to hit 100k miles... > > I am curious, though: what do the real world results say from people > driving homemade EVs? ThunderSky has been around for a while now; even > CALB has been around a few years. I haven't noticed many posts about > people replacing lithium packs and it's hard to get a feel browsing the EV > album how many miles people are putting on their lithiums. So, how many > miles have people gotten out of their packs? Are any outright dying? > Maybe we could compile a database and make some graphs like that excellent > pluginamerica link? I don't have significant data yet, but I'll go first, > as an example: > > Pack: 54 ThunderSky 100Ah > Age: 3yrs (bought June 2010), in service since March 2012 > Miles Driven: 5000 > Capacity remaining: unknown* but have hit 80% DoD several times without > issue > Top charge voltage: 3.6V > BMS used: yes, custom > Temperature Management: no > Location: Massachusetts > > *one cell was over-discharged last winter after ~2000 miles. During > recovery, it accepted 103Ah to 3.6V @ 5A (+/- maybe 5%?). It has sat idle > since... > > Cheers! > -Ben > > On Oct 8, 2013, at 7:25 PM, Cor van de Water wrote: > > > I posted in the past a spec how end charge voltage affects cycle life. > > There are numerous complaints from laptop owners whose battery failed > > just after the 1-year warranty, so most likely they never got more than > > 100-200 cycles (which is marginal lead-acid type performance) > > and it appears that laptops tend to charge their cells to 4.2-4.3V wich > > indeed significantly reduces their life, but giving highest capacity. > > Lowering the final charge voltage to 4.1 alone will sacrifice some > > capacity > > but multiply (!) the cycle life by 2 or 3. > > So, I am quite sure that EV manufacturers do not charge their packs > > to the brim and by staying well away from that bleeding edge, give their > > packs a much longer and much happier life - even if they use the same > > technology as consumer cells... > > (but since we have been able to read here how Tesla deviates from > > standard cells, we know that they get special variants and they have the > > volume to make demands...) > > > > Regards, > > > > Cor van de Water > > Chief Scientist > > Proxim Wireless Corporation http://www.proxim.com > > Email: cwa...@proxim.com Private: http://www.cvandewater.info > > Skype: cor_van_de_water Tel: +1 408 383 7626 > > _______________________________________________ > 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) > > -------------- next part -------------- An HTML attachment was scrubbed... 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