Study of Solid-State Diffusion Impedance in Li-Ion Batteries Using Parallel-Diffusion Warburg Model

Anomalous diffusion impedance due to the solid-state Li+ diffusion in Li-ion batteries is often troublesome for the analysis. In this work, we propose a novel analytical Parallel-diffusion Warburg (PDW) model and couple it with the conventional equivalent electrical circuit model (EECM) analysis to tackle this long-standing challenge. The analytical expression of the PDW is derived from the classical Fickian diffusion framework, introducing non-unified diffusion coefficients that originate from the diverse crystalline conditions of Li+ diffusion paths, as theoretically demonstrated in the atomistic modeling results. The proposed approach (EECM + PDW) is successfully employed to study the diffusion impedance of thin-film LiNi0.5Mn1.5O2 (LNMO) electrodes and porous LiNi0.80Co0.15Al0.05O2 (NCA) electrodes, demonstrating the applicability and robustness of this method.