Electrochemical Impedance Spectroscopy

Electrochemical Impedance Spectroscopy (EIS) offers a non-destructive route to in-situ analysis of the dynamic processes occurring inside a battery by measuring the complex impedance.

idealised Nyquist plot
Idealised Nyquist Plot of a Lithium Ion Battery

Looking at the idealised Nyquist Plot is a good way of understanding the fundamentals:

  1. The Axes and Flow
  2. The Inductive Artefact (Highest Frequency)
  3. Internal Ohmic Resistance (Rohmic)
  4. Solid Electrolyte Interphase (SEI) Layer (Mid-High Frequency)
  5. Charge Transfer Resistance (Mid Frequency)
  6. Warburg Diffusion (Low Frequency)

Meddings et al [1] look at and describe an idealised Nyquist plot of an EIS measurement:

  • The inductive behaviour observed in the upper frequency range (blue background) of the spectrum can be an artefact of the measurement system and the cell:
    • wires connecting the cell to the measuring device
    • geometry of the cell
    • cell windings
  • The high-frequency intercept with the real axis, when the inductance effect is properly subtracted, corresponds to the sum of internal ohmic resistances, including:
    • electrolyte
    • active material
    • current collectors
    • electrical (metallic) contacts
  • The arcs appearing in the mid-frequency range (green background) are primarily due to the electrochemical processes occurring at the electrode/electrolyte interfaces inside the cell, which combine resistive and capacitive effects. At each electrode, lithium transport through the solid electrolyte interphase (SEI) occurs in parallel with dielectric polarisation, and lithium (de-)intercalation occurs in parallel with double layer (dis)charging. Thus there are contributions from at least four different processes
    • anode charge transfer
    • anode SEI
    • cathode charge transfer
    • cathode SEI
    • However, some research works suggest a possible additional contribution of the current collector/active material contacts in commercial cells.
  • The low-frequency tail mainly reflects solid state lithium ion diffusion in the active material of the cell electrodes, although other diffusion aspects (e.g., diffusion in electrolyte-filled pores within the electrodes and concentration gradients within the separator) have been considered.

The Alexandros Ch. Lazanas and Mamas I. Prodromidis EIS Tutorial [2] gives a detailed overview of Electrochemical Impedance Spectroscopy from the theoretical background through the principles of measurement and interpretation to applications of it’s use.

Meddings et al [1] look at how the EIS spectra change based on four parameters:

  1. different potentiostatic or galvanostatic excitation signal amplitudes in the 1 kHz – 10 mHz frequency range at 23 °C.
  2. Variation with SOC of the impedance spectrum.
  3. Variation with temperature of the impedance spectrum.
  4. EIS spectra at SOC 50 % and 25 °C in the 1 kHz – 100 mHz frequency range, after selected cycles at 1C.

Note: these spectra are from different studies and included here as an indication of how the spectra change under different input parameters.

The EIS measurement is particularly difficult in terms of repeatability and hence it is worth reading the work of Anup Barai et all [3]. Hallemans et al [4] take the technique to the next level by looking at the information that can be extracted from measurements of EIS of a cell in use.

How well can an LLM Interpret Electrochemical Impedance Spectroscopy (EIS) Data?

The analysis of EIS data involves basically three stages/steps:

  1. Check for data quality or KK using tools such as Boukamp’s linKK [2]
  2. Fit of an equivalent circuit model (ECM) model to the data by means of complex non-linear least squares (CNLS)
  3. Analysis of the distribution of relaxation times (DRT)

We know that there are existing tools and algorithms for these analyses. This package uses an LLM workflow to automate the analysis.

EIS data for a supercapacitor
EIS for Supercapacitor Electrodes

A powerful electrochemical technique used to analyse resistance, charge transfer processes, and ion diffusion in supercapacitor electrodes.

  • Small Rs → good electrical conductivity
  • Small semicircle → low charge transfer resistance
  • Steep low-frequency line → fast ion diffusion
  • Nearly vertical line → ideal capacitive behaviour
temperature estimation from EIS data
Estimating Battery Internal Temperature Through Electrochemical Impedance Spectroscopy

These findings establish quantitative design criteria for battery management systems:

  • Target frequency range: 100 Hz – 1 kHz for optimal temperature sensitivity
  • Required precision: Sub-4 μΩ measurement uncertainty for both real and imaginary impedance

References

  1. Nina Meddings, Marco Heinrich, Frédéric Overney, Jong-Sook Lee, Vanesa Ruiz, Emilio Napolitano, Steffen Seitz, Gareth Hinds, Rinaldo Raccichini, Miran Gaberšček, Juyeon Park, Application of electrochemical impedance spectroscopy to commercial Li-ion cells: A review, Journal of Power Sources, Volume 480, 2020
  2. Alexandros Ch. Lazanas and Mamas I. Prodromidis, Electrochemical Impedance Spectroscopy─A Tutorial, American Chemical Society, 2023
  3. Barai, Anup, Chouchelamane, Gael H., Guo, Yue, McGordon, Andrew and Jennings, P. A. (Paul A.) (2015) A study on the impact of lithium-ion cell relaxation on electrochemical impedance spectroscopy. Journal of Power Sources, Volume 280 . pp. 74-80
  4. Hallemans, Noël, Widanage, Widanalage Dhammika, Zhu, Xinhua, Moharana, Sanghamitra, Rashid, Muhammad, Hubin, Annick and Lataire, John (2022) Operando electrochemical impedance spectroscopy and its application to commercial Li-ion batteries. Journal of Power Sources, 547 . 232005
cell resistance vs temperature

DCIR of a Cell

The DCIR of a cell is the Direct Current Internal Resistance. This is the resistance in charge and discharge to a direct current demand applied across the terminals.

See also: Cell Measurement Parameters, Reference Electrode