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Re: [EVDL] Kokam / lithium "shelf life"

All lithiums currently have a limited calendar life. Well, technically
a nicad is affected by aging too but it could take decades to become
significant. Lead acid ages significantly too but some lead-acids have
a 10-yr service life in float.

Some lithium batts have substantially longer calendar lives than others.

Unlike lead-acids which degrade the least when stored fully charged
(they sulfate up), lithium ion and lithium polymer degrade substantially
less when stored at partial state of charge. Also lower temps vastly
increases calendar life.

http://en.wikipedia.org/wiki/Lithium_ion has a chart showing how temps
and charge state affect calendar life. At best, storing at 40% [email protected]
is only 2% per year so it would take 15 years to get below 70% of
original capacity. On the other hand storing at 100% SOC @ 140F this
same degradation will occur in just over 2 months! 140F is realistic to
see in some parts of a vehicle for several hours each day it is left in
an open parking lot in the Texas summer.

One can expect this damage to be cumulative, figure the % cap loss per
hour spent at that SOC at that temp and sum the time vs rate to get
total permanent capacity loss.

Danny

----- Original Message -----
From: "Osmo S." <[email protected]>
Date: Wednesday, November 7, 2007 11:14 am
Subject: Re: [EVDL] Kokam / lithium "shelf life"
To: Electric Vehicle Discussion List <[email protected]>

> I believe this information comes from Philippe Borges, who wrote in
>
> March 2006:
>
> "i think no company will answer you (trustfully) on calendar life
> of
> their
> lithium batteries, because it's their major drawback.
> It's a fact than once assembled, it start to "self-destruct", worst
>
> if not
> used...
>
> This said one people aswered me, it was Kokam CEO himself during
> EVS21 :^)
> I asked about calendar life of their li-ion cells
> He told me something like: our cells are near new but we think you can
> expect arround 4-5 years calendar life before real capacity loss.
> I asked if capacity loss was significative
> he told me: under usual target 80% capacity left.
> I asked if half capacity loss was possible
> He told me: yes it's possible."
>
> Terveisin,
> Osmo
>
> Lawrie, Robin kirjoitti 7.11.2007 kello 18.01:
>
> > Ive heard persistent rumours that the Kokam Cells have a restricted
> > shelf life regardless of usage... is this the case? I cant even
> > remember
> > where I heard it... is this an issue with li-po cells in general?
> >
> > Cliff? You seem to be the man to ask..
> >
> > Ive been quoted a nice (its all relative) price on some 40 ah
> > cells, but
> > don't want to blow my load on some 2000+ cycle cells that only
> last 5
> > years regardless...
> >
> > _______________________________________________
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>
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