Galvanostatic Intermittent Titration Technique

The Galvanostatic Intermittent Titration Technique or GITT as most know it in the world of battery chemistry and modelling as it is used to estimate diffusion coefficients, OCV, over-potentials and resistance. First described by Weppner and R. A. Huggins [5].

The GITT measures the transient voltage change and open circuit voltage (OCV) change during the charging and discharging processes using only a constant current supply and specified cut-off intervals.

When a constant current pulse (I_p) is applied at time t₀, a sudden voltage step occurs, ΔV₁ owing to the current flux in the form of an IR drop (the voltage increases or decreases when the current is positive or negative, respectively).

During the current duration time (Δt_p), the mobile ions (lithium ions, Li+) are deintercalated from the host material, and the voltage changes to ΔV₁+ΔV₂ After the constant current pulse, the voltage recovers owing to an IR drop.

During the relaxation period, the composition of the electrode becomes homogeneous by Li+ diffusion in the material, and the voltage reaches a new equilibrium state.

This step is applied and after each pulse a relaxation period is required to reach equilibrium. Hence this measurement can take weeks to perform a complete sweep against state of charge and temperature.

As shown [1, 2] this measurement allows the diffusion coefficient to be estimated for small currents and short time pulses:

E₀ is the starting potential difference between the electrodes and E₄ is the ending potential after relaxation. r_p is the radius of the particles and t_p is the pulse duration. E(t) is the potential progression during the current pulse.

The open circuit voltage and internal resistance can also be calculated from this data.

This post has been built based on the support and sponsorship from: Thermo Fisher Scientific, Eatron Technologies, About:Energy, Quarto Technical Services and Alvatek.

The GITT procedure is usually performed in a half cell, i.e., made of the electrode with the active material under investigation, which will become the positive electrode, and a negative electrode made of metallic lithium, plus the electrolyte. If possible, a three-electrode setup is preferable, with a small metallic lithium crumb as pseudo-reference electrode. In this way, knowing the composition of the material under investigation and the working electrode’s surface area, it is possible to calculate the chemical diffusion coefficient per potential step dE and/or per coulometric titration step d𝛿.

GITT , Metrohm

The Biologic application note [4] shows how this measurement can be applied to understand if the battery is limited by the cathode or anode.

Parameterisation of OCV and Diffusion Coefficient

• To simulate a battery, the open circuit voltage (OCV) and diffusion coefficient of its active materials must be determined.
• The established methodology is the Galvanostatic Intermittent Titration Technique (GITT). However, its significant limitation is the large experimental duration, requiring multiple days.
• Here, Intermittent Current Interruption (ICI) was used as a fast alternative. The rest durations were varied to optimise between accuracy and test duration.

References

1. Jaeyoung Kim, Sangbin Park, Sunhyun Hwang, Won-Sub Yoo, Principles and Applications of Galvanostatic Intermittent Titration Technique for Lithium-ion Batteries, J. Electrochem. Sci. Technol., 2022, 13(1), 19-31
2. T. Schied, A. Nickol, C. Heubner, M. Schneider, A. Michaelis, M. Bobeth, G. Cuniberti, Determining the Diffusion Coefficient of Lithium Insertion Cathodes from GITT measurements: Theoretical Analysis for low Temperatures, ChemPhysChem 2021, 22, 885.
3. Galvanostatic Intermittent Titration Technique (GITT), Metrohm
4. Protocols for studying intercalation electrodes materials- I: Galvanostatic cycling/potential limitations (GCPL) GITT Battery – Application Note 1, Biologic
5. W. Weppner, R. A. Huggins, Determination of the Kinetic Parameters of Mixed‐Conducting Electrodes and Application to the System Li₃Sb, 1977 J. Electrochem. Soc. 124 1569

See also: Cell Measurement Techniques, Chemistry Analysis