Acceptable internal resistance

[clay64]

I just received 16* "brand new B grade LF280k" cells. Only voltage and internal resistance measured. All voltages around 3.265V. Internal resistance most around 0.5mOhms but a couple around 1.0 mOhms and one 1.2mOhms. Spec for new cells is <=0.25mOhms. Are these cells acceptable? Or should I try to return them? Or test further?

 

[timselectric]

Internal resistance changes with SOC.
Until you top balance them, you can't compare them.

 

[RV10flyer]

Of the 200+kWh’s, none of mine were above .25mOhm upon receipt.

 

[RCinFLA]

I just received 16* "brand new B grade LF280k" cells. Only voltage and internal resistance measured. All voltages around 3.265V. Internal resistance most around 0.5mOhms but a couple around 1.0 mOhms and one 1.2mOhms. Spec for new cells is <=0.25mOhms. Are these cells acceptable? Or should I try to return them? Or test further?

How are you measuring internal resistance.

It should not be anywhere near that high even down to 10% SoC. If they are that high they are bad batteries.

There is internal conduction resistance that is primarily metal foil, terminal interconnection conductive resistance and electrolyte conductivity. This is what is measured with a four-point 1 kHz battery impedance meter like YR1035+.

Then there is overpotential voltage slump which is due to load current through cell. This is not actually internal resistance. It is voltage overhead to drive the lithium-ion migration to supply demanded electrode cell current. It also has an exponential time decay with a decay period of a few minutes. It is no-load rested open circuit terminal voltage minus the terminal voltage after several minutes of load current.

You can check the calibration on a battery impedance meter by measuring the resistance of a 500A/50mV current shunt which should measure 0.10 milliohms.

 

[clay64]

Thankyou for your reply. I am using the RC3563 battery tester. It has 4 point, 1kHz impedance testing. The measurements seem to be accurate and repeatable.