# [EVDL] Cold Lithium Cell Question



## EVDL List (Jul 27, 2007)

On Wed, Nov 2, 2011 at 8:03 PM, Mike Nickerson <[email protected]> wr=
ote:
> Hello everybody,
>
> I have a question about operation of ThunderSky LiFePo4 cells in the cold.
> I don't know how much experience people have with this situation, but I'm
> gathering opinions.
>

I've had some of the same questions. I noted that the TS spec sheet
said charging was to be above 0=B0C and discharge could be below that. I
hadn't been able to find what would happen to the batteries if they
were charged when below 0=B0C until I read technical paper on the
electrolytes used in various Lithium batteries including LiFePO4
cells. The paper is at
http://parts.digikey.com/1/parts/50903-cap-alum-3900uf-100v-20-snap-eco-s2a=
p392da.html

On page 4363, the first two full paragraphs summarize what happens.
"Thus, at temperatures lower than the liquidus temperature (usually
above -20 =B0C for most electrolyte compositions),50e,159,160 EC
precipitates and drastically reduces the conductivity of lithium ions
both in the bulk electrolyte and through the interfacial films in the
system. During discharge, this increase of cell impedance at low
temperature leads to lower capacity utilization, which is normally
recoverable when the temperature rises. However, permanent damage
occurs if the cell is being charged at low temperatures because
lithium deposition occurs, caused by the high interfacial impedance,
and results in irreversible loss of lithium ions. An even worse
possibility is the safety hazard if the lithium deposition continues
to accumulate on the carbonaceous surface.

At temperatures higher than 60 =B0C, various decompositions occur among
the electrolyte components, electrode materials, and SEI or surface
layers, while LiPF6 acts as a major initiator or catalyst for most of
these reactions.152,310,332,333 The damage caused by high-temperature
operation is permanent. Because gaseous products accumulate, a safety
hazard
is also likely. Therefore, the specified temperature range for the
normal operation of most commercial lithium ion cells is -20 =B0C to +50
=B0C. While sufficient for most consumer purposes, the above range
severely restricts the applications of lithium ion technology for
special areas such as military, space, and vehicle traction uses."

I wasn't able to determine if there is any damage by pulling the cell
voltages down into the 1-2V range with in spec currents. The batteries
will warm up as they are used. Of course the wind might be cooling
them off too fast for the temperature rise to be noticeable.

If it gets really cold here I'll still try to charge when my batteries
are over 0=B0C but it looks like no permanent damage will be done as
long as they are above -20=B0C. I do have 3/4" of insulation around my
batteries and a nearly sealed box.

-- =

David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com

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## EVDL List (Jul 27, 2007)

Here is the correct link: http://www.tinhoahoc.com/Battery/cr030203g.pdf



> David Nelson <[email protected]> wrote:
> > On Wed, Nov 2, 2011 at 8:03 PM, Mike Nickerson <[email protected]> =
> wrote:
> >> Hello everybody,
> ...


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## EVDL List (Jul 27, 2007)

> David Nelson wrote:
> 
> > If it gets really cold here I'll still try to charge when my batteries
> > are over 0=B0C but it looks like no permanent damage will be done as
> ...


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## EVDL List (Jul 27, 2007)

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## EVDL List (Jul 27, 2007)

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## EVDL List (Jul 27, 2007)

> Evan Tuer wrote:
> 
> > It's interesting, and something I've asked about before, but does it
> > apply to LiFePo4?
> ...


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## EVDL List (Jul 27, 2007)

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Zm8vZXYK


----------



## EVDL List (Jul 27, 2007)

> On 2 Nov 2011 at 21:28, David Nelson wrote:
> 
> > Therefore, the specified temperature range for the normal operation of
> > most commercial lithium ion cells is -20 =B0C to +50 =B0C. ... the above
> ...


----------



## EVDL List (Jul 27, 2007)

> David Nelson wrote:
> >> Therefore, the specified temperature range for the normal operation of
> >> most commercial lithium ion cells is -20 =B0C to +50 =B0C. ... the above
> >> range severely restricts the applications of lithium ion technology for
> ...


----------



## EVDL List (Jul 27, 2007)

I don't see why. My EV-95 NiMH are not particularly peppy on cold
morning and I live in LA so it doesn't really get cold here. On the
high end they won't take much of a charge over 40 degree C and they
have an exothermic charge reaction so active cooling is required. Self
discharge also becomes a noticeable problem on hot days.

Temperature wise I'd say Lithium is a step up from NiMH. Granted,
maybe NiMH could have been improved further if it hadn't been so
restricted by the patents.


Their longevity is their best attribute.





> EVDL Administrator <[email protected]> wrote:
> > On 2 Nov 2011 at 21:28, David Nelson wrote:
> >
> >> Therefore, the specified temperature range for the normal operation of
> ...


----------



## EVDL List (Jul 27, 2007)

> gottdi <[email protected]> wrote:
> >
> > http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Thanks everybody, for the very interesting discussion. I'm charging at .125C from 120V, so I need to be careful with the lithium plating. The weather has warmed up some here (above freezing at least), so I'm doing some temperature experiments to see what my battery temperature is compared to ambient. This evening, it looks like it is about 10F above ambient under the hood (some airflow) and 15F above ambient in the trunk. I blocked off the front grill, so I'm getting less airflow under the hood than I used to.

I'm most worried about charging at work since the car is outside. When I'm home, it's garaged and I could wait a while to charge after arriving home.

I'm not sure I want to go with battery boxes yet, but if I don't, I know the days I need to leave the car parked at home now!

Mike

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Evan Tuer
> Sent: Thursday, November 03, 2011 1:19 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Cold Lithium Cell Question
> 
> On Thu, Nov 3, 2011 at 5:26 PM, Roger Stockton <[email protected]>


> > wrote:
> > > Evan Tuer wrote:
> > >
> > >> It's interesting, and something I've asked about before, but does it
> ...


----------



## EVDL List (Jul 27, 2007)

Sent from my iPhone



> Roger Stockton <[email protected]> wrote:
> 
> > Evan Tuer wrote:
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Insulation and right sizing of the pack is everything when working
outside the cell operating temperature area.

We can do just fine even in -35C. Charging and discharging. But even
for the sake of the efficiencies it's reasonable to do everything to
keep the cells in the optimal operating condition.

A 600 kg battery pack just does not cool off. It has a lot of mass
that can maintain the heat in the active materials. This is why the
plastic insulator case is used with Winston-type cells. It helps to
maintain the operating conditions in the cell. And for some reason
we've been reading the bad words on the bad design how these cells do
not cool off as well as pouch and stainless casings. Change the cell
design and you'll do all kind of compromises on the way.

Now.. if you have cool but not yet cold cells (say -25C) the
electrolyte still remins liquid. By changing the electrolyte
composition you can keep it more viscose at even lower temps but then
you'll have to do a compromise again. Lithium plating occurs at some
conditions but it is not that black and white as the documents linked
to this thread may imply.

Have you guys (should I say persons ?) ever thought that how much mass
is in the electrolyte and how much energy it is requires to heat just
that component out in the cell ? Wy heat all external parts of it if
it is not really required ?

I'll refer to the patent later when it's out.

-akkuJukka

http://www.google.com/profiles/jarviju#about



2011/11/4 Mike Golub <[email protected]>:
>
>
> Sent from my iPhone
>
>


> Roger Stockton <[email protected]> wrote:
> >
> >> Evan Tuer wrote:
> >>
> ...


----------



## EVDL List (Jul 27, 2007)

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----------



## EVDL List (Jul 27, 2007)

I was just looking through the ThunderSky "datasheet" that I have for my
cells, and it specifies temperature range for both charge and discharge at
-25C to 75C. However, the document is VERY brief and doesn't list any other
information besides that range. =


That tends to corroborate Jukka's comments. I've been measuring the
external case temperatures of the cells with an infrared thermometer. I
realize the cell's internal temperature could be higher, but my 45 cells are
not arranged in a monolithic block. They are arranged in individual rows so
each cell has exposed sides. Therefore, I'm probably not being too
conservative with my external measurements.

I'm probably going to have to do something. It may be battery boxes and
insulation. It might also be leaving the car parked at home on the coldest
days.

Mike

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Jukka J=E4rvinen
> Sent: Friday, November 04, 2011 1:49 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Cold Lithium Cell Question
> =

> Insulation and right sizing of the pack is everything when working outside
the
> cell operating temperature area.
> =

> We can do just fine even in -35C. Charging and discharging. But even for
the
> sake of the efficiencies it's reasonable to do everything to keep the
cells in
> the optimal operating condition.
> =

> A 600 kg battery pack just does not cool off. It has a lot of mass that
can
> maintain the heat in the active materials. This is why the plastic
insulator case
> is used with Winston-type cells. It helps to maintain the operating
conditions
> in the cell. And for some reason we've been reading the bad words on the
> bad design how these cells do not cool off as well as pouch and stainless
> casings. Change the cell design and you'll do all kind of compromises on
the
> way.
> =

> Now.. if you have cool but not yet cold cells (say -25C) the electrolyte
still
> remins liquid. By changing the electrolyte composition you can keep it
more
> viscose at even lower temps but then you'll have to do a compromise again.
> Lithium plating occurs at some conditions but it is not that black and
white as
> the documents linked to this thread may imply.
> =

> Have you guys (should I say persons ?) ever thought that how much mass is
> in the electrolyte and how much energy it is requires to heat just that
> component out in the cell ? Wy heat all external parts of it if it is not
really
> required ?
> =

> I'll refer to the patent later when it's out.
> =

> -akkuJukka
> =

> http://www.google.com/profiles/jarviju#about
> =

> =

> =

> 2011/11/4 Mike Golub <[email protected]>:
> >
> >
> > Sent from my iPhone
> >
> > On Nov 3, 2011, at 9:26 AM, Roger Stockton <[email protected]>


> > wrote:
> > >
> > >> Evan Tuer wrote:
> > >>
> ...


----------



## EVDL List (Jul 27, 2007)

Hi Mike,

That is an unusual arrangement - do you have any pictures or diagrams =

of how your cells are mounted?

Don't forget this sort of insulation which worked very well for me...

http://www.screwfix.com/p/airtec-double-insulation-1-5-x-25m/50913

... and which I have mentioned before on the EVDL. It has max effect =

for min bulk.

I have not come across the idea of using the cells internal resistance =

as a built-in heater. Rather than use heating pads which, in your =

situation would get very expensive, has anyone experimented with the =

idea of continually charging and discharging (though a load resistor =

or whatever) the pack at a rate sufficiently high enough to just keep =

the cells at a constant temperature and in the top 5% or so of charge =

state? This might be more efficient than using heaters and might also =

be simpler to effect - no need for heater pads etc. Shame it can't be =

done 'in reverse' too for cooling.

In my experience, as long as you are not thrashing the cells (which =

will not bode well for longevity anyway) heat won't be a problem in =

most climates as the cells just don't have enough run time to get too =

hot. However, if you plan to avail yourself of fast chargers say, on =

long trips for example, then cooling will become essential.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk



> Mike Nickerson wrote:
> 
> > I was just looking through the ThunderSky "datasheet" that I have =
> 
> ...


----------



## EVDL List (Jul 27, 2007)

There are 20 cells in the trunk. There are 4 packs of 5 cells. These are
the most monolithic, but still all exposed to open air on 2 sides. Since
they are in the trunk, they do stay warmer. =


The cells under the hood are in two strings. One string is 10 cells (2
packs of 5 cells) just inside the front grille of the car. Behind them sits
the controller and electrical wiring boxes. Behind that sits the next
string. Again 10 cells (2 packs of 5 cells) along the firewall. There is
another set of 5 cells beside the charger and in front of the back row of
cells.

I've updated my evalbum page with photos of the trunk and hood area.
(www.evalbum.com/2778)

Mike

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Martin WINLOW
> Sent: Saturday, November 05, 2011 4:51 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Cold Lithium Cell Question
> =

> Hi Mike,
> =

> That is an unusual arrangement - do you have any pictures or diagrams of
> how your cells are mounted?
> =

> Don't forget this sort of insulation which worked very well for me...
> =

> http://www.screwfix.com/p/airtec-double-insulation-1-5-x-25m/50913
> =

> ... and which I have mentioned before on the EVDL. It has max effect for
min
> bulk.
> =

> I have not come across the idea of using the cells internal resistance as
a
> built-in heater. Rather than use heating pads which, in your situation
would
> get very expensive, has anyone experimented with the idea of continually
> charging and discharging (though a load resistor or whatever) the pack at
a
> rate sufficiently high enough to just keep the cells at a constant
temperature
> and in the top 5% or so of charge state? This might be more efficient
than
> using heaters and might also be simpler to effect - no need for heater
pads
> etc. Shame it can't be done 'in reverse' too for cooling.
> =

> In my experience, as long as you are not thrashing the cells (which will
not
> bode well for longevity anyway) heat won't be a problem in most climates
as
> the cells just don't have enough run time to get too hot. However, if you
> plan to avail yourself of fast chargers say, on long trips for example,
then
> cooling will become essential.
> =

> Regards, Martin Winlow
> Herts, UK
> http://www.evalbum.com/2092
> www.winlow.co.uk
> =

>


> Mike Nickerson wrote:
> > =
> 
> > > I was just looking through the ThunderSky "datasheet" that I have for
> ...


----------



## EVDL List (Jul 27, 2007)

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L2V2Cg==


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## EVDL List (Jul 27, 2007)

Cells tend to drift apart more when at significantly different temperatures
requiring more balancing. The CMU materials science prof mentioned this,
and a poster on diyelectriccar reported observing it on two groups of cells
he had at something like 10 to 20 F difference in temperature (don't recall
exact diff).

It would be a pain to have to re-install cells in new boxes with heaters,
but for anyone who lives in an area where it gets to those low temperatures
I think it is well worth just including heaters in the design up front. I
have 1/2" insulation lining 16 gauge steel aluminum boxes with Farnum heater
pads under each group of 4 to 5 cells, ten total, controlled with the
controller for these pads purchased with the pads from KTA-EV. It added
some cost but has worked well over two winters now, and starting into the
third. They only draw 350W total when on, but have kept the cells at set
point temperature at temperatures as low as 5 F (lowest we've had in that
time) in an unheated metal building. I plug in the car to heat while it is
parked in the garage with current set point of 65 F, but have used 55 to 60
F in the past. Last night for example, the cells were at 64 F when I left
home. I parked the car in an open lot for 5 hours in windy, snowy conditions
with temperature in the high 20's F. When I returned the cells were at 54
F. As Jukka said they have considerable heat capacity, and when in enclosed
in insulated boxes will hold their temperature without too much loss for
several hours.

I have 3 boxes, one in front behind the bumper exposed to air flow, which I
covered on the front and ends with 1" R-Max insulation, one completely
inside the car, and one through the floor several inches. The heaters seem
to keep the cells fairly close in temperature in winter, usually varying by
less than 5 F by IR measurement on terminals and cases (gives about same
reading) with an EXTECH EX830 DVM. These readings always agree with that of
a thermocouple on one of the cell clamps to within less than 2 degrees.

--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Cold-Lithium-Cell-Question-tp3984152p3995937.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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## EVDL List (Jul 27, 2007)

> Martin WINLOW wrote:
> > Don't forget this sort of insulation which worked very well for me...
> > http://www.screwfix.com/p/airtec-double-insulation-1-5-x-25m/50913
> > ... and which I have mentioned before on the EVDL. It has max effect
> ...


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## EVDL List (Jul 27, 2007)

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