# Coulombic Efficiency



## theclay333 (Sep 10, 2011)

I am trying to find information on the CE of LiFePO4 cells at high C charge/discharge. I have been trying to contact manufacturers but it has been a challenge to find the information so far. Has anyone here had luck finding this information?


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## Yabert (Feb 7, 2010)

Hi

About the discharge, why don't just use the ohm law???

For example, if a small 10Ah cell have an internal impedance of 0.005 ohm:
Discharge at 15C the lost will be: 150 x 0.005 = 112.5w

I'm not sure if this law can be good in charge!
Do you need something more specific?


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## Semper Vivus (Apr 13, 2011)

Hello,
you mix the coulomb efficiency with the energy efficiency. Your example faces the energy efficiency. Coulomb Efficiency is only the current that flows in and out. In theory it should be 100%. In reality I think it is something about 95 to 100 percent.

Kind Regards
Tom



Yabert said:


> Hi
> 
> About the discharge, why don't just use the ohm law???
> 
> ...


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## Yabert (Feb 7, 2010)

_*Coulombic Efficiency* _
_Coulomb counting is also subject to errors since all the Coulombs pumped into the battery during charging can not be converted into available charge. Some of the energy is inevitably lost in the chemical conversion process usually as heat. Similarly on the return trip, for the same reasons, some of the available charge is lost and only part of the stored charge is available for doing work. The round trip energy loss is about 3% for a Lithium battery. The Coulombic efficiency is the ratio between the discharge energy and the charging energy._


So, I continuous to learn. I will keep an eye on this thread!


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## major (Apr 4, 2008)

Yabert said:


> _*Coulombic Efficiency* _
> _Coulomb counting is also subject to errors since all the Coulombs pumped into the battery during charging can not be converted into available charge. Some of the energy is inevitably lost in the chemical conversion process usually as heat. Similarly on the return trip, for the same reasons, some of the available charge is lost and only part of the stored charge is available for doing work. The round trip energy loss is about 3% for a Lithium battery. The Coulombic efficiency is the ratio between the discharge energy and the charging energy._
> 
> 
> So, I continuous to learn. I will keep an eye on this thread!


Hi Yab,

I saw that also. From: http://www.mpoweruk.com/soc.htm And that definition differs from what I was taught. They claim it is the ratio of energy between discharge and charge. I think it is the ratio of charge out over charge in. In other words, AH(out)/AH(in)*100%. And I thought this figure was near 100% for Lithium cells.

Let's see if we can get some others to chime in here 

major


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## dougingraham (Jul 26, 2011)

major said:


> Hi Yab,
> 
> I saw that also. From: http://www.mpoweruk.com/soc.htm And that definition differs from what I was taught. They claim it is the ratio of energy between discharge and charge. I think it is the ratio of charge out over charge in. In other words, AH(out)/AH(in)*100%. And I thought this figure was near 100% for Lithium cells.
> 
> ...


Yes, AH(out)/AH(in)*100 % is very close to 100% for LiFePo4 and LiCo type cells. Quite a lot worse for NiCd and NiMH and dismal for Lead Acid.

WH(out)/WH(in)*100 % is still quite good but is dependent on the internal resistance of the cells. So very good at low charge/discharge currents but much less good at high charge/discharge rates because of the voltage differential. I always thought coulombic efficiency is energy in and out.


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## azdeltawye (Dec 30, 2008)

major said:


> ....
> Let's see if we can get some others to chime in here
> major


Battery efficiency is also dependant on temperature. Here is a plot of energy out / energy in vs. ambient temp. 

This data is compiled from over 15k miles of driving and almost 400 charge/discharge cycles.

Battery pack consists of 45 Thundersky 180 Ah batteries. Check the following link for more details. http://www.evalbum.com/3531


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