Metrohm Autolab DuoCoin Cell Holder with EIS measurements on a commercial battery

Significance of the Topic

The accurate characterization of commercial coin cell batteries by electrochemical impedance spectroscopy (EIS) is critical for the development and quality control of lithium-ion energy storage devices. Minimizing measurement artifacts due to lead and contact impedance ensures reliable evaluation of cell internal resistance and enables meaningful comparisons across studies.

Objectives and Study Overview

This application note demonstrates the use of the Metrohm Autolab DuoCoin Cell Holder for EIS measurements on a Panasonic VL2330 rechargeable Li-ion coin cell. It compares impedance data obtained via a four-terminal (Kelvin) sensing configuration against traditional two-terminal setups to quantify the impact of lead impedance on the measured spectra.

Instrumentation

• Autolab PGSTAT204 potentiostat/galvanostat with FRA32M EIS module
• Autolab DuoCoin Cell Holder with gold-plated four-point Kelvin contacts
• Rechargeable Panasonic VL2330 Li-ion coin cell (30 mAh, 3 V nominal)
• NOVA software for instrument control and data analysis

Methodology

EIS measurements were performed at open circuit potential over a frequency range of 10 kHz to 100 mHz with a 10 mV amplitude and ten frequencies per decade. Three lead configurations were tested: a true four-terminal connection separating current and sense leads, and two distinct two-terminal arrangements pairing working/sense and counter/reference leads in different orders.

Main Results and Discussion

The Nyquist plots reveal that the four-terminal configuration yields consistently lower impedance values compared to two-terminal measurements. Key observations include:

• At high frequencies, the four-terminal spectrum is shifted by approximately 170 mΩ toward lower impedance.
• At the low-frequency end of the semicircle, the difference grows to about 2 Ω.
• Two tested two-terminal arrangements produce nearly identical spectra, indicating that the dominant error arises from the combined lead path rather than lead ordering.

These findings underline the significance of separating current and potential sensing paths when characterizing low-impedance devices to avoid overestimation of internal resistance.

Benefits and Practical Applications

• Enhanced accuracy in internal resistance measurement for coin cells and other low-impedance energy storage systems.
• Improved reproducibility by eliminating voltage drop contributions from wiring.
• Capability to test two cells in parallel, increasing throughput for comparative studies.
• Gold-plated contacts and stable mounting reduce contact corrosion and variability.

Future Trends and Potential Applications

Advances in EIS accessory design and automation will facilitate broader adoption in battery R&D and production QA/QC. Potential developments include scaled holders for pouch and cylindrical cells, integration with temperature control, coupling with in situ optical or spectroscopic probes, and enhanced data analytics with machine-learning models for rapid health diagnostics.

Conclusion

The Metrohm Autolab DuoCoin Cell Holder paired with a four-terminal EIS configuration provides a robust solution for precise low-impedance battery characterization. By isolating sensing leads from current paths, it significantly reduces measurement artifacts, ensuring reliable evaluation of coin cell performance.