Electrochemical Modeling of GITT Measurements for Improved Solid-State Diffusion Coefficient Evaluation

TL;DR

This paper introduces a direct pulse fitting method for GITT data analysis that employs a coupled electrochemical model to independently validate diffusion coefficients, significantly improving accuracy over conventional methods.

Contribution

The study develops a novel direct pulse fitting approach for GITT data that enhances diffusion coefficient accuracy and validates the single-particle model for polydisperse systems.

Findings

Non-ideal diffusion coefficients are two orders of magnitude more accurate.

The coupled electrochemical model effectively predicts discharge behavior.

Single-particle approach is valid for polydisperse particles when scaled appropriately.

Abstract

Galvanostatic Intermittent Titration Technique (GITT) is widely used to evaluate solid-state diffusion coefficients in electrochemical systems. However, the existing analysis methods for GITT data require numerous assumptions, and the derived diffusion coefficients typically are not independently validated. To investigate the validity of the assumptions and derived diffusion coefficients, we employ a direct pulse fitting method for interpreting GITT data that involves numerically fitting an electrochemical pulse and subsequent relaxation to a one-dimensional, single-particle, electrochemical model coupled with non-ideal transport to directly evaluate diffusion coefficients that are independently verified through cycling predictions. Extracted from GITT measurements of the intercalation regime of FeS2 and used to predict the discharge behavior, our non-ideal diffusion coefficients prove to be two orders of magnitude more accurate than ideal diffusion coefficients extracted using conventional methods. We further extend our model to a polydisperse set of particles to show the validity of a single-particle approach when the modeled radius is proportional to the total volume-to-surface-area ratio of the system.