4D-resolved physical model for Electrochemical Impedance Spectroscopy of Li(Ni1-x-yMnxCoy)O2-based cathodes in symmetric cells: Consequences in tortuosity calculations

Electrochemical impedance spectroscopy (EIS) constitutes an experimental technique used for the characterization of Lithium Ion Battery (LIB) porous electrodes tortuosities. For the first time, a 4D (3D in space + time) physical model is proposed to simulate EIS carried out on NMC porous cathodes, derived from the simulation of their manufacturing process, in symmetric cells. EIS is simulated by explicitly considering the NMC active material, carbon-binder domains (CBD) and pores as spatially-resolved separated phases and assuming different physics for each of them. The calculated impedance responses are compared with in house experimental results coming from NMC-based cathodes prepared in a similar way. We investigate the influence of the physics assumed to describe the CBD behavior, the conductivity of the different solid phases and electrolyte, the relative amount of NMC and CBD and the impact of calendering on the EI spectra, and we compare the results with the experimental EIS measurements. This methodology allows to understand the limitations of using EIS, electric circuit models and homogenized physical models for the determination of the tortuosity factor of NMC-based cathodes, revealing a complex interplay between the conductivity of the solid phases, the electrolyte properties and the cathode meso/microstructure.