Probing mass transport processes in Li-ion batteries using electrochemical impedance spectroscopy

Electrochemical techniques, such as electrochemical impedance spectroscopy (EIS), are widely applied to probe dynamic processes across a range of systems including lithium-ion batteries (LIBs). Key questions remain on how different degradation phenomena effect the processes that allow LIB to function. One of the key processes that determines the response of batteries is the mass transport, particularly the transport of Lithium within the constituent electrode materials. This study considers mass transport within LIBs, and the extent to which electrochemical techniques, particularly EIS, can be used to meaningfully probe mass transport in LIBs with the aim to serve as a guide for future studies that wish to track changes in mass transport as batteries age and degrade. Herein, the benefits of using EIS compared to the Galvanostatic Intermittent Titration Technique (GITT) are demonstrated using well defined finite element method (FEM) simulations as the basis. Distribution of Relaxation Times was then applied to assign and map battery electrochemical processes to the EIS spectra based on their time constants. Effects such as electrode geometry, mass transport heterogeneities and the overlap between mass transport and other processes are considered and discussed with particular focus on how they affect the extraction of solid Lithium diffusion coefficients.