[NSRCA-discussion] Swelling Lipo
Chris
cjm767driver at hotmail.com
Mon Dec 6 05:56:07 AKST 2010
Ed And Bob:
Sorry for not answering right away, I'm traveling and not fast with the
emails. That is of course the correct link that Ed posted and is the
easiest explanation that I have read from all of the technical papers
and manufacturers' technical dept explanations. So even though it's from
a blog, I think it is very accurate.
Chris Moon
On 12/6/2010 9:00 AM, Ed White wrote:
> Never mind. Found it.
>
> http://barnson.org/node/1842
>
>
> ------------------------------------------------------------------------
> *From:* Ed White <edvwhite at yahoo.com>
> *To:* General pattern discussion <nsrca-discussion at lists.nsrca.org>
> *Sent:* Mon, December 6, 2010 7:56:41 AM
> *Subject:* Re: [NSRCA-discussion] Swelling Lipo
>
> I'd like to use this also. Anybody know at least who the author is?
>
> Ed
>
>
> ------------------------------------------------------------------------
> *From:* Bob Kane <getterflash at yahoo.com>
> *To:* General pattern discussion <nsrca-discussion at lists.nsrca.org>
> *Sent:* Sun, December 5, 2010 1:14:00 PM
> *Subject:* Re: [NSRCA-discussion] Swelling Lipo
>
> Can I use this in a club newsletter ?
>
> Bob Kane
> getterflash at yahoo.com
>
> --- On *Sun, 12/5/10, Chris /<cjm767driver at hotmail.com>/* wrote:
>
>
> From: Chris <cjm767driver at hotmail.com>
> Subject: [NSRCA-discussion] Swelling Lipo
> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
> Date: Sunday, December 5, 2010, 9:30 AM
>
> Here is the full article with much more detail.
> Chris
>
>
> What's Really Going On Inside A Dying Lithium Battery
>
> Thu, 07/08/2010
>
> Warning: Science ahead! Close your eyes and turn away, you've been
> warned!
>
> Many radio-control enthusiasts experience disappointment with the
> cycle life of their Lithium-based batteries in electric aircraft.
> Often this is because they're not entirely sure what's going on
> inside the battery, and choose a capacity or voltage that's
> inappropriate for their application. Ultimately, this manifests
> itself in "swelling" or "ballooning" of a Lithium battery. This
> editorial attempts to explain what's actually going on when this
> happens.
>
> Chemically, there can be three causes for the swelling of a LiPo
> battery, and one exacerbating condition that makes it worse across
> the board. These occur in hard-shell Lithium Ion batteries, too,
> but the hard shell can withstand several atmospheres of pressure
> before expanding.
>
> Note: This is MY understanding of the chemistry involved. I may be
> off-base, after all, I'm a college dropout. But I did love
> chemistry class!
>
>
> Cause #1: WATER in the mix.
>
> /EDIT: Lithium manufacturers who's products are implicated in this
> assertion (read: Hextronik et al, circa 2006-2007, Thunder Power
> circa 2008) will dispute the assertion of contaminated Lithium.
> The most common contaminant is water, but there are many others
> that will cause lithium oxidation in the cell. Basically, any
> other substance containing oxygen that can be freed by
> electrolysis or heat will become a contaminant, and any substance
> that isn't the expected anode, cathode, or separator is a
> contaminant that will reduce the performance of the cell and cause
> swelling in other ways. Manufacturers have a fiduciary
> responsibility to claim that there was no product defect,
> otherwise they're responsible for a recall. I'll talk about the
> science and let you draw your own conclusions./
>
> This was the common problem with many cheap Chinese LiPos of
> around 2005-2008. Most are better now, but it's the #1 cause of
> premature LiPo failure: water contamination in the plant. Many of
> China's LiPo factories are on the coast, where the altitude is
> very low and the humidity is high. You can't run the humidity too
> low on the assembly floor, because you're working with volatile
> chemicals that could explode in the presence of a spark, and you
> can't run it too high because then you end up with a worthless
> LiPo that swells on first use.
>
> Here's the science. You have three ingredients that are functional
> in a LiPo battery. The rest is wrapping and wiring attachments.
>
> * Cathode: LiCoO2 or LiMn2O4
> * Separator: Conducting polymer electrolyte
> * Anode: Li or carbon-Li intercalation compound
>
> I'm going to be a little vague in my language here. The chemicals
> involved vary according to manufacturers, so I don't want to make
> any assumptions.
>
> Remember your chemistry class? Note the absolute *lack of any
> hydrogen atoms in the reaction*. None, zero, zip, nada. If you
> have *water inside your battery* -- and virtually all batteries
> have a little bit -- you've got problems. When the chemical bond
> of H20 is broken by electrolysis and heat, you end up with free
> oxygen. You also have free-roaming hydrogen that typically ends up
> bound to your anode or cathode, whichever side of the reaction
> it's on and depending on the state of charge of your battery.
>
> Now, this is a pretty unstable situation that's exacerbated by any
> over-discharge or over-charge condition creating metallic lithium
> in your cell. The end result is Lithium Hydroxide: 1 atom of
> lithium, one atom of hydrogen, and one atom of oxygen.
>
> But you still have a free oxygen atom floating around inside the
> battery casing, that typically combines with one other oxygen atom
> -- O2, or what we sometimes think of as "air" -- or two other
> oxygen atoms, to form a characteristic tangy, metallic-smelling
> substance called "ozone", or O3. Gases expand with heat and
> contract with cold. Chuck a swollen battery in the freezer and it
> might come out rock-hard again... until it heats up. It's not
> frozen, it just got cold enough that the gases inside didn't take
> up much space at all.
>
> And that free O2 or ozone is just waiting to pounce and oxidize
> some lithium on the slightest miscalculation on your part. The
> modest over-discharge during a punch-out, or running the battery a
> little too low or letting it get a little too hot, or running the
> voltage up to 4.235v/cell on a cold day when the actual voltage
> limit per cell is more like 4.1v. All of these create the perfect
> storm for a puffy battery to quickly turn itself into a ruined
> battery or an in-flight fire.
>
> Understanding the role of free oxygen in your battery, from water
> and other causes, is CRUCIAL to understanding why batteries fail,
> and why sometimes you can get by with flying a puffy battery, and
> sometimes you can't.
>
>
> Cause #2: Formula degradation from over-charge/over-discharge
>
> If a Lithium battery is overcharged or charged too quickly, you
> end up with LOTS of excess free lithium on the anode (metallic
> lithium plating), and free oxygen on the cathode. A free oxygen
> atom is small enough to freely traverse the separator without
> carrying an electric charge, resulting in lithium OXIDE on the
> anode. Lithium "rust", in reality. Useless to us at this point,
> just dead weight being carted around inside your battery's wrapper.
>
> But lithium oxide uses fewer oxygen atoms than existed in the
> ionized state, so you end up with, again, FREE OXYGEN. And people
> wonder why if you over-charge a LiPo underwater, it still ignites
> despite the lack of open air...
>
> If it's over-discharged or discharged too quickly, the reverse is
> true, but you end up with Lithium Oxide on the cathode, but at a
> lower rate because there's simply less there. Basically, an abused
> battery quickly develops corrosion on both poles of the battery
> inside the wrapper. And the more it's abused, the worse it gets as
> the resistance goes up and it still gets driven hard.
>
> This, by the way, is the most common cause of swelling today for
> our aircraft when flown with a high-quality pack (not knock-off
> eBay leftovers from expensive Chinese mistakes of 2004-2009). The
> reality is, these kinds of cells, regardless of their 'C' rating,
> are built for use where they last for several hours... not several
> minutes. While the chemistry if used as designed is good for
> thousands of cycles, we're driving them so far out of spec that
> we're lucky to get hundreds of cycles out of them.
>
> In most cases, too, our batteries are under-specced. If
> slow-charged and slow-discharged, many of these packs would often
> hold considerably more mAh than we think they do. That's one of
> the reasons we get the performance we do from them. Higher-C-rated
> packs also often introduce gelled electrolyte into the separator,
> and carbon or phosphorous nano-structures on the anode and cathode
> mixtures rather than the "pound it out thin and hope it's mixed
> right" approach used with sheets of anodes & cathodes today.
>
>
> Cause #3: Poor separator construction
>
> A number of cheap LiPos also use a bad separator formulation.
> Ultimately, it often boils down to using a dry separator with way
> too high of an internal resistance to hold up to manufacturer
> "C"-rating claims. The internal resistance grows over time because
> a higher and higher percentage of the LiPo is simple Lithium
> Oxide, and the balloon grows bigger as more oxygen atoms are freed.
>
> I'd also lump "poor anode or cathode chemistry" into this
> category, too. Ever get a bad battery out of a batch of good ones?
> Often it's because the mixture of chemicals was inconsistent, and
> you end up with too much or too little lithium on one side of the
> battery (well, in certain plates, you get my drift).
>
>
> Exacerbating factor: HEAT.
>
> A little heat makes everything work better for a Lipo. If you
> could fly your battery right at 140 Fahrenheit all the time, it
> would make fantastic power and be operating right in its happy
> zone. But it generates heat when charging, and when discharging.
> Hitting 150 results in significant metallic lithium generation,
> which as we can see from above is a major cause of puffing and
> cell destruction.
>
> Similarly, the maximum 4.235v/cell limit is only at that mythical
> 140F. It goes down steadily from there, to about 4.2v/cell at room
> temperatures, and around 4.0v/cell below 50F, beyond which the
> over-abundance of electrons will again break chemical bonds and
> free lithium to bond with oxygen and create lithium oxide... which
> is just a disaster waiting to bond with humidity in the air if the
> LiPo ruptures, to create Lithium Hydroxide.
>
>
> Conclusion
>
> Chemically, there are no LiPos that will not puff under certain
> circumstances. But tightly-controlled humidity, a superb gel
> separator, nano-structured anode and cathode, and careful charging
> and discharging within manufacturer limits should also prevent
> puffing. Similarly, putting a pack that has been abused into a
> lower-discharge aircraft, even when puffed, often serves the
> purpose of stopping the puffing in its tracks because no more
> metallic lithium is being created in the cell by abuse.
>
> And now you know the answer to today's geeky topic. Why lithium
> polymer batteries often puff up.
>
>
>
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