A physics-based impedance response model of a graphite| LiNMC cell is developed to investigate the effect of high-temperature calendar aging on electrode microstructure. Experimental data indicate unique contributions to aging from each electrode. The model relaxes the constraints placed by the Bruggeman relation, instead using a free parameter to relate the porosity and tortuosity. The incorporation of a two-layered cathode particle and adjustment of the Bruggeman relation produce mid- and low-frequency responses that quantitatively agree with the experimental data. The significance of the model modifications toward measuring the effects of high-temperature aging is discussed. (c) The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License.