# [EVDL] LiFePO4 compression?



## EVDL List (Jul 27, 2007)

No. The cylinder cells apply the compression from the round design of
the cell. The steel enclosure does it's job just perfecty.

Prismatic cells do require come additional pressure at the middel
section at the big side. Newest TS cell design does no need it anymore
(said little birds).

I would still do the pack design with the compression devices. It's
not that hard.

Electrodes swell in use. Normal effect. Also poor compression usually
adds internal resistance and generates additional and unwanted losses.

-Jukka



2009/12/21 m gol <[email protected]>:
> Hello,
>
> I was wondering why the TS LiFePO4 batteries required compression around the
> cells?
>
> Is this something I need to do to the cylinder cells from a123 -type cells
> as well?
>
> Thanks
>
> Mike Golub
> Fairbanks, AK
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## EVDL List (Jul 27, 2007)

> m gol wrote:
> >
> > why the TS LiFePO4 batteries required compression around the cells?
> >
> ...


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## EVDL List (Jul 27, 2007)

> Elithion wrote:
> 
> > When charging, past a certain SOC, Lithium cells generate gases,
> > which are
> ...


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## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> >
> > Also, the cells that I have seen that have swelled have all done so
> > after being over discharged. That kind of runs contrary to swelling
> ...


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## EVDL List (Jul 27, 2007)

> Willie McKemie wrote:
> 
> > On Tue, Dec 29, 2009 at 11:31:22AM -0500, Roger Heuckeroth wrote:
> >>
> ...


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## EVDL List (Jul 27, 2007)

The internal temperature ages the cell. With LiFePO4 cells it seems to
be more drastic than with LiNiCoO cells. Then again these cells need
higher end of charge voltage and more careful finishing.

Thou.. let's not make too general assumptions. There are very wide
selection of various chemistries, variations and mixtures of them and
then electrolyte mixtures add another multiplier.

There are Lithium cells for very different operating voltages.


Bill Dube wrote:
"I suspect that the TS cells need the external "help" to keep the case
from cracking or splitting a seam as the cells age."

 ....Bill.. that's funny.. wearing the A123 cap ? 

TS cells require compression since it reduces the internal resistance
and just to prevent the cells from failing on heavy use. They were
trying to make cells that can be given to EV hobbyists as is ... 

Also I feel the mechanics of the TS cells are just sooo nice. Tie them
together and you have already quite stiff pack. Simple covers and BMS
inside.. So lovely.

I have not yet got my 1st "non-compression-needed" cells from TS.
Hopefully soon. Will share my experiences then.

-Jukka



2009/12/29 Roger Heuckeroth <[email protected]>:
>
>


> Willie McKemie wrote:
> >
> >> On Tue, Dec 29, 2009 at 11:31:22AM -0500, Roger Heuckeroth wrote:
> >>>
> ...


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## EVDL List (Jul 27, 2007)

The compression specified does not change the dimensions of 
the case.The compression plates simply maintain the original 
dimension of the case. The plates _keep_ the sides of the case flat. 
They do not flatten the sides of the new cells, since they arrive 
already flat.

Since the thickness of the case is unaltered by the external 
plates, exactly how does this reduce internal resistance?

The compression plates are required to keep the case sides 
in their original shape and position. This _maintains_ the internal 
plate-to-plate pressure, and _maintains_ the original internal 
resistance if the case were to be deformed by high temperature or over-charge.

I can see why some folks might want cells that have the 
internal structure to take the place of the compression plates, but 
this means that you must pay for this on every cell in added 
material, size, and weight. You only need the added structure on one 
wall of each of the end cells in a stack. That is why it makes sense 
to add them on instead of making them internal to every cell.

Bill Dube'





> >Bill Dube wrote:
> >"I suspect that the TS cells need the external "help" to keep the case
> >from cracking or splitting a seam as the cells age."
> 
> ...


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## EVDL List (Jul 27, 2007)

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