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Li-ion cell construction

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 04 August, 2014 » Li-ion cell construction « Previous Next »

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bruce
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Username: bruce

Post Number: 1043
Registered: 04-2008

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Posted on Tuesday, 08 July, 2014 - 12:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I have a stash of Li-ion cells pulled from laptop batteries which have been discarded ( as we all have, I suspect ). Some seem to be OK, some are dud.
Recharging these things usually requires a home-made device since it depends on what you're trying to do. But I heard an ugly rumour that the cells ( it's the ubiquitous 18650 ) have some electronics jiggery-pokery inside the can.
To check, it would be necessary to open the can, which I was somewhat nervous about, because of all the scare stories you hear.
Eventually, I did . I used an angle grinder to remove top and bottom and to split the cylinder lengthwise. Out popped a very tightly wound roll. The were 3 sheets rolled up just like a tubular capacitor. One was a very thin sheet of copper; one a plasticky sheet. Sandwiched in between was a very strange black material; very friable.

No idea. Theres no obvious electrolyte so I wonder how the little electrons move about.

You heard it here first. Oh, and I took a pic.

Answers on a post-card.

bruceLithium cell pulled apart
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bowden_p
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Username: bowden_p

Post Number: 329
Registered: 01-2006

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Posted on Tuesday, 08 July, 2014 - 06:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Bruce,
Looks like a "safe" variety of lithium cell - I didn't know there was such a thing however. I though that they all caught fire if opened!

No sign of any electronics then?

With regards, Paul.
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phonoplug
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Username: phonoplug

Post Number: 405
Registered: 08-2009


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Posted on Tuesday, 08 July, 2014 - 11:08 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

You have some electronics when you have a multi-cell battery. This is the charge balancer which makes sure all cells are charged to the same voltage, and that none are overcharged even when they have slightly different capacities.

Never heard of the individual cells having a circuit each. Think its confusion between cells and batteries.

Nice work dis-assembling the cell by the way. Not something I'd fancy having a go at, though if I did I'd make sure it was completely... completely... discharged
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pebe
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Username: pebe

Post Number: 160
Registered: 05-2005

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Posted on Wednesday, 09 July, 2014 - 12:14 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Individual cells with built-in electronics to control charge and discharge are known as 'Protected Cells'. This link gives an excellent explanation:

http://www.lygte-info.dk/info/battery%20protection%20UK.html
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tandy
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Username: tandy

Post Number: 39
Registered: 12-2012

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Posted on Thursday, 10 July, 2014 - 01:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The cells that catch fire are charged cells due to the large energy capacity. When a cell gets shorted all that energy is released rapidly and a lot of heat is generated up to the point where it is hot enough to ignite itself.
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bruce
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Username: bruce

Post Number: 1044
Registered: 04-2008

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Posted on Thursday, 10 July, 2014 - 05:54 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Well,
That explains why I heard that some cells had internal electronics. The cells from laptops obviously wouldn't have protection because there is an external controller. But not a Fat Controller. Incidentally, since you cant call people 'fat' any more, what's he called now? The 'Gastronomically-challenged' controller?
It's called progress.
So, now we know what a 18650 cell looks like. It wont change the World as we know it, but every little helps.
Bruce

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