Originally Posted by mizlplix
you are saying CALB's "resistance" test is worthless?
Then why was it even included?
It's not just CALB. Roughly, 70 % of Li-ion spec sheets
give the 1 kHz impedance, 5 % give true DC resistance, and the rest give nothing.
Why AC impedance? Because cell manufacturers have ready access to equipment that can measure AC impedance.
Why at 1 kHz? because the impedance of Li-ion cells has a 2-lobe shape, and there is a dip at around 1 kHz, so the numbers look better there. Also, at 1 kHz the impedance is more consistent than at other frequencies.
Why not DC resistance? Because it varies a lot, from cell to cell, as SOC changes, as temperature changes, and as the cell ages. And because they may not know how to measure it, or do not have access to equipment that does so.
Why does CALB publish each cell's AC impedance? Because it gives the user a sense that the manufacturer is thorough and therefore it imparts a sense confidence in the user.
Why does CALB ship cells with such a wide variance of AC impedance? Because those values are all well below their self-imposed cutoff threshold.
How do I know? I did a lot of research in the process of writing the Li-ion BMS book
. Still, there are some holes in my understanding, so please forgive me if I missed something.