LiFePO4 Impedance Measurement

Hello,

I'm trying to measure the impedance of a LiFePO4 cell.To get the impedance i'm implementing the EIS technique (Electrochemical impedance spectroscopy). For that i managed to produce an AC variable frequency voltage source with 10mV of amplitude at the terminals of the cell. After that, i have to divide my 10mV ac voltage by the current i'm acquiring and i get the battery impedance.
I'm facing problems in reading a phase displacement between the two signs(voltage and current). The cell impedance will be very low(10-50 mOhm). My question is: I'm reading both signs with external ADC's (AD7680), one for voltage and the other for current(through an Hall sensor), i was expecting to see some phase displacement between voltage and current, will their(ADC) internal resistance affect the voltage sign at the terminals of the cell? (One of the AD7680 is reading the voltage, in parallel with the battery).

With no circuit diagram, no clear description of the problem you are facing, and no example data, you expect an intelligent suggestion that solves your problem?

Why are you doing this experiment and what do you expect to learn?

EISs is a labororatory type procedure, many here are very experienced electronicaly but you will have to define your question or problem carefully to get a useful response.

Circuit diagram and a description of what/how you are trying to measuer something.

Pictures are always nice too.

Bota:
Hello,

My question is: I'm reading both signs with external ADC's (AD7680), one for voltage and the other for current(through an Hall sensor), i was expecting to see some phase displacement between voltage and current,

HOW

The impedance of the source is much lower than the impedance of the ADC, so there won't be any
inaccuracy from that.

The capacitance of the cell may be appreciable but the internal resistance is extremely small
and will dominate unless you go to high frequencies. There are other effects too, such as
polarisation, which make things complicated (I presume this is what electrochemical impedance
spectroscopy is all about).

You haven't said what frequency range you've been looking at.

Bota:
Hello,

I'm trying to measure the impedance of a LiFePO4 cell.To get the impedance i'm implementing the EIS technique (Electrochemical impedance spectroscopy). For that i managed to produce an AC variable frequency voltage source with 10mV of amplitude at the terminals of the cell. After that, i have to divide my 10mV ac voltage by the current i'm acquiring and i get the battery impedance.
I'm facing problems in reading a phase displacement between the two signs(voltage and current). The cell impedance will be very low(10-50 mOhm). My question is: I'm reading both signs with external ADC's (AD7680), one for voltage and the other for current(through an Hall sensor), i was expecting to see some phase displacement between voltage and current, will their(ADC) internal resistance affect the voltage sign at the terminals of the cell? (One of the AD7680 is reading the voltage, in parallel with the battery).

The one method measure battery impedance by feed it 1 kHz, 100 mA constant current source.
No measure current is needed, measure voltage only.

Sample 1 kHz constant current source (Howland current pump) by OPA547 high-voltage/high-current op amplifier: