Charging lithium and ENDOTHERMIC reaction

[Doctorbass]

I dont know if i'm the only one to observe that fact, but i percrived that often, when i charge my lipo pack, most of the time when they are empty, they tend to cool down

This is so observable that i suggets you to try that by yourself!

and after 10 sec of search on internet i found a document that is explaning and confirming this fact

CHARGING LITHIUM CELL MAKE THEM TO COOL DOWN ( ENDOTHERMIC REACTION) ( they absorb heat due to chemical reaction)
DISCHARGING THEM MAKE THEM TO WARM UP ( EXOTHERMIC REACTION) but in this case it is also because of resistive loss)

See page 3 of this document: http://www.micro-power.com/userfiles/file/mp_tempcharge-1250026530.pdf

Almost completely ignored is the chemical reaction
in the cell. The chemical reaction that takes place during
charging of Lithium chemistry cell is endothermic (the
reaction absorbs heat). Since there is no free lunch in
thermodynamics, the discharge reaction is exothermic and
produces heat. The Central Research Institute of Electric
Power Industry (CRIEPI) did a classic study in 1995 that
characterized this in a calorimeter. The plot below was taken
from a report on that research

Doc

 

[Lebowski]

who's going to be the first to build a LiPo charging station / beercooler in 1 ?

 

[bearing]

This is also true for NiCd and NiMh.


In Nicad batteries, charging is an endothermic process, so a Nicad battery pack will either remain at the same
temperature or cool slightly during charging. When the battery becomes overcharged, its temperature will begin
to rise quickly, indicating that the charging current should be turned off.

http://www.ee.ryerson.ca/~phiscock/papers/nicad-battery.pdf


For NiMH cells, the process of moving or transporting hydrogen from the negative electrode to the positive
electrode absorbs heat and is therefore endothermic. Heat continues to be absorbed until the cell reaches a
state of over discharge, where a secondary reaction occurs within the cell resulting in a rise in temperature.

http://www.hardingenergy.com/pdfs/3%20Nickel%20Metal%20Hydride.pdf

 

[neptronix]

Pretty normal for them to warm up, particularly at the bottom of the discharge.. if you're pushing them at half their C rate or more. NOT normal for them to cool down, lol..

Notice here.. that the 2 cells on the bottom sagged more.
Higher internal resistance at the low point is what makes the heat of course..

Yup.. cells have both an internal resistance curve, and a voltage curve..

This is an interesting document, Doctor bass.. most battery docs are written in some combination of hebrew, yiddish, and 'greek to me'... but this calculates.. thanks

 

[whatever]

found an interesting paper on what gases are produced in lithium cells, its very detailed paper,
it seems to suggest that gases are produced over time when cells are cycled, theres also a graph of exothermic temp during discharge ( just to keep it a bit relevant to the thread)

 

[bearing]

You couldn't maybe perhaps give a link to that paper? =)

 

[nechaus]

I have had this happen as well not only that.. but if i abuse them and they are warm and jelly like.. they become firm once charging.. but if i charge it to fast they tend to heat up

 

[neptronix]

I have had this happen as well not only that.. but if i abuse them and they are warm and jelly like.. they become firm once charging.. but if i charge it to fast they tend to heat up

That's not good, run more in parallel to spread out the amp draw. You won't have a big ol' pack of trashed saggy puffy lipos in under 100 cycles that way.

Charging them too fast is another way to reduce their lifespan to 1/3rd or less.

1C charge rate unless you have nanotech.. and discharge at 1/4th the C rate of your total pack size.. you'll have a long life that way.

 

[nechaus]

neptronix..
my lipos are for abuse purpose only... i have much nicer life batts that i take extreme care of and have a much higher c rating then my turnigy's
i get alot more than 100 cycles using them the way i do... i never over or under charge them..
i just charge them fast and drain them fast.. the package on my turnigy's claim to take charge at 2c anyway

Nano's are great for regen braking imo.. if you have a good controller you can really stuff power back into the packs fast..

but it will never beat my lifep04 batteries.. only in weight



I remember when i first starting using lipo's.. i was kind scared to even hold them..
i was having dreams about my packs blowing up randomly while riding my ebike..
burning my house down and all sorts of nightmares..
I remember some guy came on this forum and was like
" what are you gonna say to the judge when your lipos burn down the house and kill people ?"

I feel my a123's are more dangerous than lipos... only because of the crazy discharge current.

 

[neptronix]

Hey, as long as you know what's up and aren't aiming for 600 cycles by playing nice with them like i am.

A lot of people don't. So i'll stop nagging ya

 

[whatever]

link to paper on gases evolved in lithiums
http://abcd.engin.umich.edu/publications/10ESLSeo.pdf

 

[nechaus]

I enjoyed reading that paper. thanks