[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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