Influence of conductive additive and binder domain distribution and its structural properties on macroscopic impedances

Abstract

The conductive additive and binder domain (CBD) is an essential component of Lithium-ion battery electrodes. It enhances the electrical connectivity and mechanical stability within an electrode matrix. Migration of the binder during electrode drying leads to an inhomogeneous distribution of the CBD, impeding transport of lithium ions in the electrolyte, and diminishing the electronic pathways between solid particles[1]. The effect of this migration on the electrochemical performance of NMC622 electrodes is quantitatively investigated via microstructure-resolved 3D simulations and compared with experimental results. The virtual electrode microstructures are based on tomographic data. The valuable information derived from combining microstructure-resolved models[2] with electrochemical impedance spectroscopy (EIS) simulations on symmetric cells is used to characterize the lithium ion transport in the electrode pore space, including the contributions of the CBD. Additionally, half-cell discharge simulations are conducted to quantify the effect on performance.

In the above simulations, the CBD is treated as a homogenized phase with effective transport parameters, not resolving its internal nano-structure. A key aspect for predictively determining the physical and chemical processes occurring are the intrinsic properties of the CBD. To develop a more predictive model, we need to characterize and understand the properties of the CBD on the nano-scale. In the present contribution, high-resolution 3D FIB-SEM data is used to obtain further geometric information on the porous networks within the CBD, shedding light on its effective ionic conductivity. This information is then fed back to the model, allowing us to account for the tortuosity on the nano-scale in the CBD domain.