I would say that thermal cycling is a main culprit to degrade an Li cell. But, there are other significant failure modes. The Jeff Dahn video given at Waterloo Canada (find it on YouTube) is as go a discussion as you will find. I think it is called Why Lithium Ion Batteries Die.
To summarize the Li ions in the electrolyte get depleted by reactions at the positive electrode, the SEI gets too thick or coated with Li metal and ions can't pass, the structure of the negative electrode gets damages and the number of intercalation sites or paths to them are reduced. The electrolyte it self can get messed up. These modes are often related to too much heat and too great SOC%. On Feb 15, 2016 9:26 AM, "EVDL Administrator via EV" <[email protected]> wrote: > This piece claims to be a myth buster, but as a non-engineer and non- > electrochemist even I can identify some errors and myths in the article > itself. Am I wrong about any of these? What others have I missed? > > On 15 Feb 2016 at 3:22, brucedp5 via EV wrote: > > > A decade ago nicad (nickel cadmium) and nickel-metal hydride rechargeable > > batteries were pretty common in phones and laptops, > > I don't think this is true. I don't know about mobile phones, but lithium > batteries were already common in laptops 15-20 years ago. I owned a couple > of them, a 1996-vintage Thinkpad and a 1998-vintage Dell. > > NiCd and NiMH in portable computers date back more like 25-30 years. > Somewhere around 1986, '87, or '88, I got an NEC Multispeed with a NiCd > battery. (Also, two floppy drives and a monochrome lcd screen. Woohoo.) > > I can even remember a brief fad for lead batteries in portable computers > during the mid- to late-1980s. > > > Lithium owes its market dominance to being a lightweight. At number > > three in the periodic table, it's the lightest metal, which really > > helps it store more energy for the same weight and volume. > > Also its high electronegativity, no? > > > Back in the day, we all dutifully let our phones and seven-kilogram > > laptops go totally flat before recharging to avoid the dreaded battery > > 'memory' problem - where batteries held less and less charge over time > > if you recharged them before they were fully flat. > > Sigh. Here we go again. Nickel based battery memory effect is a very rare > phenomenon which happens only when a battery is repeatedly discharged to > exactly the same SOC every time before it's recharged. > > There is another phenomenon, voltage depression, which occurs with aging > and > can cause a nickel battery to SEEM like it has less capacity even though it > really doesn't. The voltage on discharge falls too far too fast. > > Most devices powered by batteries have circuitry that shuts them down when > the battery is nearly flat. This is partly to protect the battery and > partly to keep the user out of trouble. For example, a digital video > camera > might sense when its battery is close to flat, so it can write the data in > its buffer to permanent memory and carry out a clean shutdown, before it > loses all power. > > Voltage depression causes these devices to shut down before they need to, > while the battery still has usable capacity. This is a failure in the > design > of the device, not in the battery. > > > > > - Their chemistry doesn't work over about 45 degrees Celsius, and > operating > > at high temp shortens their life. > > I've never seen the claim that "Their chemistry doesn't work over about 45 > degrees" before. AFAIK modern lithium ion batteries will work fine up to > 70- > 100 deg C, though safety concerns kick in above around 100 deg C. In fact, > at those higher temperatures, they have higher specific power and energy. > > That doesn't mean that those temperatures are good for cycle life, however, > and they shouldn't be charged when they're hot (over 30 deg C, IIRC; > someone > correct me if that's wrong). They also shouldn't be stored for any length > of time at high temperatures, and definitely not when charged over about > 50- > 70%. > > For practical everyday use, sub-freezing temperatures are more of a > concern. > > > > > The memory problem ... was a real issue for nickel-based batteries, but > > with their different chemistry lithium ion batteries only show a very > minor > > effect [ (from Toyota) > > http://www.tytlabs.com/comp/history02/history02_2013.html > > Discovery of 'Memory Effect' in Li-ion Battery > > This is an interesting article, but again, what they're describing isn't > memory effect. > > > > > > > So recharge your devices whenever you like - but try to give them a full > > charge (let the battery go into the red) every now and then to > recalibrate > > your battery level reading. > > Good grief, when he says "(let the battery go into the red)," is he > actually > suggesting overcharging??? > > > The ageing is caused by chemical changes at the electrodes. The positive > > electrode isn't a solid lump - it's made of microscopic particles of a > > lithium-based material. Over time those particles coalesce together > forming > > bigger lumps, so there's less surface area for the lithium-releasing > > reaction when the battery is being used (discharging). > > > > And recharging doesn't send 100 per cent of the lithium ions back to the > > negative electrode - some ions always get permanently stuck to the > positive > > electrode. So over time there are fewer positive lithium ions 'in play' > in > > the battery. > > Is this really the degradation model for lithium ion batteries? I don't > know, I'm asking the experts. > > > > From a greenhouse emission standpoint, their energy-heavy manufacture > means > > lithium ion batteries take a long time to recoup the energy that went > into > > making them, so maximising the battery's lifespan - avoiding excess heat > and > > keeping the charge topped up - is important. > > I don't know how energy-intensive battery manufacture really is, but I do > know that "keeping the charge topped up" is NOT the way to maximize a > lithium ion battery's cycle life. > > I'm sure the writer of this piece, Bernie Hobbs, means well. Unlike many, > he at least tried to do his homework. However, I still see some > significant problems. Am I wrong about these? > > David Roden - Akron, Ohio, USA > EVDL Administrator > > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > EVDL Information: http://www.evdl.org/help/ > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > Note: mail sent to "evpost" and "etpost" addresses will not > reach me. To send a private message, please obtain my > email address from the webpage http://www.evdl.org/help/ . > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Read EVAngel's EV News at http://evdl.org/evln/ > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... 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