Determination of the diffusion coefficient of an inserted species in a host electrode with EIS, PITT and GITT techniques

Importance of the topic

The mobility of guest species inserted into intercalation electrodes governs the rate capability, cyclability and overall performance of electrochemical energy storage devices. Precise measurement of diffusion coefficients is vital for the design and optimization of Li-ion batteries and related systems.

Objectives and overview

This work compares three electrochemical techniques—Electrochemical Impedance Spectroscopy (EIS), Potentiostatic Intermittent Titration Technique (PITT) and Galvanostatic Intermittent Titration Technique (GITT)—for determination of diffusion coefficients under restricted linear diffusion conditions in thin film electrodes. Experimental validation employs a Tokin 1 F supercapacitor and a custom AC dummy cell simulating a two-electrode Li-ion cell.

Methodology and instrumentation

EIS characterization uses a finite Warburg (M) element to model restricted linear diffusion, extracting diffusion resistance (R_d) and time constant (τ_d) via Nyquist plot fitting or the knee-frequency method. PITT applies small potential steps and analyses current decay in short-time (Cottrell) and long-time (exponential) regimes to derive τ_d. GITT imposes current pulses, measuring the voltage transient slope at long times to calculate τ_d and D. Experiments were conducted with BioLogic VMP3 and SP-300 potentiostats, a BCS series cycler, a Tokin 1 F/5.5 V supercapacitor and a three-RC AC dummy cell.

Key results and discussion

EIS yielded consistent τ_d ≈ 22 s for both the supercapacitor and dummy cell. PITT without IR compensation overestimated τ_d (≈ 41 s and 97 s); IR compensation improved values (≈ 27 s and 86 s) but remained above EIS. GITT gave τ_d ≈ 36 s and 110 s, while IR compensation reduced them to ≈ 26 s and 92 s. Only EIS reliably determined diffusion kinetics in systems with significant series resistance, interfacial capacitances and charge-transfer resistances. PITT/GITT deliver accurate results only for ideal single-electrode, reversible systems with negligible ohmic and kinetic limitations; compensation techniques partially mitigate errors in complex assemblies.

Benefits and practical applications

• Rapid screening of electrode materials for diffusion kinetics.
• Support of battery performance modeling and design.
• Quality control in cell manufacturing.
• Characterization of supercapacitor and Li-ion cell prototypes.

Future trends and opportunities

Integration of advanced numerical fitting routines for PITT/GITT under non-ideal conditions; development of high-frequency IR compensation methods; extension to solid-state and composite electrodes; coupling with in-situ/operando spectroscopy; application of machine-learning algorithms for automated parameter extraction and anomaly detection.

Conclusion

EIS with restricted diffusion modeling offers robust extraction of diffusion time constants and coefficients in real-world electrodes. PITT and GITT remain useful for ideal systems but require careful IR compensation and are limited by kinetic and ohmic contributions. Technique selection should match system complexity and desired accuracy.

Instrumentation

• BioLogic VMP3 potentiostat (EIS, PITT, GITT)
• BioLogic SP-300 potentiostat (high-resolution IR compensation)
• BCS-805/810/815 battery cycler with AC dummy cell
• Tokin 1 F, 5.5 V supercapacitor

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