Innards of thundersky cells + a bit of info on lithium ion cells

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reikiman
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Innards of thundersky cells + a bit of info on lithium ion cells

This is an interesting video by Jack Rickard (evtv.me). The point of the video was to cut open a thundersky cell and see what makes it tick. But he spends a half hour talking before doing so. It's very interesting though I did wish he'd have gotten to the point a little more quickly.

The video is mpeg-4 so should be playable everywhere.

The video is very large so you'll have to wait a long while for it to download all the way, even on a fast connection.

http://web.me.com/mjrickard/movies/thunderskybat-desktop.m4v

The bit about the thundersky battery innards .. he cut apart a 90ah cell that had gone dead and found a bunch of foil plates separated by a polymer film. The plates fall into two groups, copper and aluminum, and each are coated with specific extra stuff including graphite and lithium paste.

There is very little liquid, most if it is pastes applied to these foil plates.

One thing I take from it is these cells can be mounted any which way because there's no liquid sloshing around ...

frodus
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Re: Innards of thundersky cells + a bit of info on lithium ...

all of the manufacturers of the prismatics recomend having the vents faced upwards.

The reason being, when they DO vent, if the cell goes bad, they want it to spew mostly gas, and not particulate matter.

____________

Travis Gintz
1986 Honda VFR Conversion
www.evfr.net

PJD
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Re: Innards of thundersky cells + a bit of info on lithium ...

My 40AH cells, before being put into service, DO have audible liquid sloshing in them. But after a few cycles (ideally a proper conditioning cycle) the liquid can no longer be heard.

Then, while testing a suspect cell I got distracted and over-discharged it at about a 5 amp rate completely flat (near zero volts, recovering to about 1.5 volts). This over discharged cell has slightly bulging sides, had a hollow sound when tapped, and once again had free liquid. I assumed the cell was ruined, but decided to re-charge it anyway. It charged normally, and the "hollowness" went away. It seem to be holding a charge normally, and discharging normally at up to 20 amps. I'll try a higher discharge rate soon, but the cell seems to have withstood a complete discharge.

The appearance and disappearance of the liquid may be related to expansion and contraction of the porous active materials as the lithium ions migrate in or out. Also, some liquid may be lost through the formation of the "solid electrolyte interphase" during the first charge/discharge.

I think keeping the cells vertical is a good idea, but at least one EV builder, CuMoCo, plans, to mount their cells (after a conditioning cycle) on their sides, long edge-down.

antiscab
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Re: Innards of thundersky cells + a bit of info on lithium ...

a car conversion i know of has had a bunch of 200AH cells on their sides (long side down) for more than a year now.

I'll see how they're fairing tomorrow (hopefuly).

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km

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