[Elithion]

Note that the bottom cell is bloated, and the separators have a burned color.

 

[kennybobby]

Thanks for posting the picture.
Can you determine how they are constructed? Are those cells composed of stacks of pouch cells, or are those the individual exposed foils with the tabs welded together?

It looks like about 40 separator sheets in each +/- terminal pair or 80 sheets per cell--so wonder if that's 80 individual foil sets, or 2 big pouches (40 foil pouch), or 80 small pouches, to make up a cell.

 

[Siwastaja]

AFAIK they are not pouch cells. Pouch cells have polymer separator; hence they are called LiPo. Because of the rigidity of the polymer separator, LiPo doesn't need the extra casing. (LiPo is NOT a battery chemistry, but a type. LiFePO4 can be LiPo).

So the prismatics should have "liquid" electrolyte, just like the cylindrical cells, and hence they need the case.

Correct me if wrong.

 

[Elithion]

LiPo is NOT a battery chemistry, but a type. LiFePO4 can be LiPo).

Bless you for saying that!

• LiPo not necessarily pouch (prismatic cells can be LiPo)
• Pouch not necessarily LiPo (pouch can use a standard separator)
• LiPo not necessarily LiCoO2 (LiPo can be LiFePO4)
• LiCoO2 not necessarily LiPo (LiCoO2 can be any format)
• LiPo not necessarily 3.6 V (LiFePO4 LiPo is 3.2 V)
• 3.6 V not necessarily LiPo (Laptop cells are 3.6 V)

LiPo is an arcane technology inside some cells, and whether or not that technology happens to be used in a given cell has no effect to us users.


So, why use the term LiPo at all? Beats me.

 

[Elithion]

Can you determine how they are constructed?

Same as all other prismatic cells: many sets of cells in a bag, many bags in a case. The positive tabs from each cell are pressed together, and clamped to the case positive terminal. Same for the negative terminal.

While the guts of a prismatic cell are somewhat similar to a pouch cell, they are different in at least one major point: each bag is not sealed (pouch cells are sealed), so they share the gaseous portion of the electrolyte. The electrolyte is poured into the case through the plug at the top, at the end of construction.

 

[kennybobby]

hard to pour peanut butter...

... The electrolyte is poured into the case through the plug at the top, at the end of construction.

Huh? What Li cell uses a pourable liquid electrolyte? In the cells that i have seen it is only a liquid in the sense of not being a solid or a gas--it has the viscosity of grease and is spread on the foils like peanut butter.

 

[Elithion]

Re: hard to pour peanut butter...

electrolyte... has the viscosity of grease and is spread on the foils like peanut butter.

Actually, I am not so sure. I do know of solid electrolytes for pouch cells. I do believe that many (all?) cylindrical cells use liquid electrolyte. But you're making me doubt what I understood about prismatic cells.

reference?

Could someone with more direct know-how chime in?

 

[major]

Re: hard to pour peanut butter...

Could someone with more direct know-how chime in?

Well, I don't know-how But I have had liquid come out of damaged pouch cells. (lithium nickel manganese cobalt)

 

[swoozle]

The Rickard thundersky dissection video shows essentially no free liquid and the anodes/cathodes barely wet with electrolyte.

 

[Elithion]

The Rickard thundersky dissection video shows essentially no free liquid and the anodes/cathodes barely wet with electrolyte.

Correct: as my reference (above) says, the electrolyte is very precisely metered.
Only the exact amount of electrolyte is poured in that will be completely absorbed by the cell, leaving no unabsorbed electrolyte. If indeed it is poured in a prismatic cell (as I remember being told). If is "spread like peanut butter", then no. We're looking for someone who actually knows the answer. I am not an expert in Li-ion chemistry and manufacture.

And, indeed, no liquid poured from any of the 4 GBS cells we just opened.

 

[onegreenev]

The LiFePO4 Prismatic cells don't have thick electrolyte and many actually have more than one encasement per plastic case. Like my Hi-Power 100 AH cells actually have two fully wrapped 50 Ah sections per plastic case and clearly no pourable liquid but there was some moisture. Not enough to pour by any means and doubtful if the electrolyte is poured in after they are put in. Can't see that happening with the Hi-Power because the inner pouches are wrapped. Don't see it with the others either. The TS do have a bit more liquid in them than the HI-Powers. I got to see the cells that Rickard had apart at the First EV convention.

Pete

http://greenev.zapto.org/GreenEV/Gr...ons_Photo_Albums/Pages/Hi-Power_Photos.html#0

I'll leave my server on so you can view the images.

 

[evmetro]

Is this a gen 3? I am guessing that this bloating is why they need the clamping and banding.

 

[kennybobby]

Davide,

Would you be able probe down between the plastic separators to see if the electrode foils and electrolyte are actually visible or if these might be separately sealed pouches?

 

[Elithion]

see if the electrode foils and electrolyte are actually visible,,,

They are visible: you can see them clearly in the picture. The white sheets are the separators.

... or if these might be separately sealed pouches?

They are not separate pouches. That is, they are not a bunch of individually sealed bags.