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Ed And Bob:<br>
<br>
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.<br>
<br>
Chris Moon<br>
<br>
On 12/6/2010 9:00 AM, Ed White wrote:
<blockquote cite="mid:675848.13702.qm@web83501.mail.sp1.yahoo.com"
type="cite">
<style type="text/css"><!-- DIV {margin:0px;} --></style>
<div style="font-family: arial,helvetica,sans-serif; font-size:
10pt;">Never mind. Found it.<br>
<br>
<span><a moz-do-not-send="true" target="_blank"
href="http://barnson.org/node/1842">http://barnson.org/node/1842</a></span><br>
<div><br>
</div>
<div style="font-family: arial,helvetica,sans-serif; font-size:
10pt;"><br>
<div style="font-family: times new roman,new york,times,serif;
font-size: 12pt;"><font face="Tahoma" size="2">
<hr size="1"><b><span style="font-weight: bold;">From:</span></b>
Ed White <a class="moz-txt-link-rfc2396E" href="mailto:edvwhite@yahoo.com"><edvwhite@yahoo.com></a><br>
<b><span style="font-weight: bold;">To:</span></b> General
pattern discussion
<a class="moz-txt-link-rfc2396E" href="mailto:nsrca-discussion@lists.nsrca.org"><nsrca-discussion@lists.nsrca.org></a><br>
<b><span style="font-weight: bold;">Sent:</span></b> Mon,
December 6, 2010 7:56:41 AM<br>
<b><span style="font-weight: bold;">Subject:</span></b>
Re: [NSRCA-discussion] Swelling Lipo<br>
</font><br>
<div style="font-family: arial,helvetica,sans-serif;
font-size: 10pt;">I'd like to use this also. Anybody know
at least who the author is?<br>
<br>
Ed<br>
<div><br>
</div>
<div style="font-family: arial,helvetica,sans-serif;
font-size: 10pt;"><br>
<div style="font-family: times new roman,new
york,times,serif; font-size: 12pt;"><font
face="Tahoma" size="2">
<hr size="1"><b><span style="font-weight: bold;">From:</span></b>
Bob Kane <a class="moz-txt-link-rfc2396E" href="mailto:getterflash@yahoo.com"><getterflash@yahoo.com></a><br>
<b><span style="font-weight: bold;">To:</span></b>
General pattern discussion
<a class="moz-txt-link-rfc2396E" href="mailto:nsrca-discussion@lists.nsrca.org"><nsrca-discussion@lists.nsrca.org></a><br>
<b><span style="font-weight: bold;">Sent:</span></b>
Sun, December 5, 2010 1:14:00 PM<br>
<b><span style="font-weight: bold;">Subject:</span></b>
Re: [NSRCA-discussion] Swelling Lipo<br>
</font><br>
<table border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td style="font: inherit;" valign="top">Can I
use this in a club newsletter ?<br>
<br>
Bob Kane<br>
<a class="moz-txt-link-abbreviated" href="mailto:getterflash@yahoo.com">getterflash@yahoo.com</a><br>
<br>
--- On <b>Sun, 12/5/10, Chris <i><a class="moz-txt-link-rfc2396E" href="mailto:cjm767driver@hotmail.com"><cjm767driver@hotmail.com></a></i></b>
wrote:<br>
<blockquote style="border-left: 2px solid
rgb(16, 16, 255); margin-left: 5px;
padding-left: 5px;"><br>
From: Chris <a class="moz-txt-link-rfc2396E" href="mailto:cjm767driver@hotmail.com"><cjm767driver@hotmail.com></a><br>
Subject: [NSRCA-discussion] Swelling Lipo<br>
To: "NSRCA Mailing List"
<a class="moz-txt-link-rfc2396E" href="mailto:nsrca-discussion@lists.nsrca.org"><nsrca-discussion@lists.nsrca.org></a><br>
Date: Sunday, December 5, 2010, 9:30 AM<br>
<br>
<div id="yiv1906141060"> Here is the full
article with much more detail. <br>
Chris<br>
<h2>What's Really Going On Inside A Dying
Lithium Battery</h2>
<p class="yiv1906141060MsoNormal"> </p>
<p class="yiv1906141060MsoNormal"><span
class="yiv1906141060submitted">Thu, </span><span
class="yiv1906141060submitted">07/08/2010</span><span
class="yiv1906141060submitted"> </span></p>
<p class="yiv1906141060MsoNormal"><span
class="yiv1906141060submitted"> </span></p>
<p class="yiv1906141060MsoNormal">Warning:
Science ahead! Close your eyes and turn
away, you've been warned!</p>
<p>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.</p>
<p>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.</p>
<p>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!</p>
<h2>Cause #1: WATER in the mix.</h2>
<p><i>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.</i></p>
<p>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.</p>
<p>Here's the science. You have three
ingredients that are functional in a
LiPo battery. The rest is wrapping and
wiring attachments.</p>
<ul type="disc">
<li class="yiv1906141060MsoNormal"
style="">Cathode: LiCoO2 or LiMn2O4</li>
<li class="yiv1906141060MsoNormal"
style="">Separator: Conducting polymer
electrolyte</li>
<li class="yiv1906141060MsoNormal"
style="">Anode: Li or carbon-Li
intercalation compound</li>
</ul>
<p>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.</p>
<p>Remember your chemistry class? Note the
absolute <strong>lack of any hydrogen
atoms in the reaction</strong>. None,
zero, zip, nada. If you have <strong>water
inside your battery</strong> -- 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.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<h2>Cause #2: Formula degradation from
over-charge/over-discharge</h2>
<p>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.</p>
<p>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...</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
<h2>Cause #3: Poor separator construction</h2>
<p>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.</p>
<p>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).</p>
<h2>Exacerbating factor: HEAT.</h2>
<p>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.</p>
<p>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.</p>
<h2>Conclusion</h2>
<p>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.</p>
<p>And now you know the answer to today's
geeky topic. Why lithium polymer
batteries often puff up.</p>
<p class="yiv1906141060MsoNormal"> </p>
<br>
</div>
<br>
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