Investigation of the distribution of relaxation times of a porous electrode using a physics-based impedance model

Recently, the analysis of the distribution of relaxation times (DRT) has drawn wide attention in battery engineering due to its nondestructive nature and the ability to separate the electrochemical processes with different time constants. Since proposed, the DRT is only interpreted using the equivalent circuit model (ECM), and an interpretation based on physicochemical model is still missing. To characterize the cell parameters and extract the valuable information more effectively, a new theory is developed based on the deep understanding of the physics-based impedance model and the DRT method. Particularly, a closed-form analytical expression for the DRT spectrum is derived, therefore the DRT spectrum can be explained and interpreted with a clear physical meaning. In addition, it is found that the relaxation time dispersion of EIS may have multiple origins: the porous structure of the electrode, the regularization technique used to calculate the DRT and the constant phase element type behavior of the active material particles. Based on the theory developed in this work, an optimized data analysis framework is created to better interpret the DRT spectrum. Finally, the developed DRT analysis framework is applied to the impedance data of a commercial LIB to demonstrate its advantages and effectiveness.