[NSRCA-discussion] Swelling Lipo
Ed White
edvwhite at yahoo.com
Mon Dec 6 04:56:58 AKST 2010
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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>
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