Electrochemical Impedance of a Battery Electrode with Anisotropic Active Particles

TL;DR

This paper derives analytical models for the electrochemical impedance of anisotropic battery electrode particles, revealing how their directional properties influence impedance spectra and can inform material characterization.

Contribution

It introduces new analytical expressions for impedance considering anisotropic diffusivities and surface reactions, advancing understanding of modern crystalline electrode materials.

Findings

Impedance spectra reflect anisotropic material properties.

Signatures of particle aspect ratio are identifiable in spectra.

Statistical variations affect impedance signatures.

Abstract

Electrochemical impedance spectra for battery electrodes are usually interpreted using models that assume isotropic active particles, having uniform current density and symmetric diffusivities. While this can be reasonable for amorphous or polycrystalline materials with randomly oriented grains, modern electrode materials increasingly consist of highly anisotropic, single-crystalline, nanoparticles, with different impedance characteristics. In this paper, analytical expressions are derived for the impedance of anisotropic particles with tensorial diffusivities and orientation-dependent surface reaction rates and capacitances. The resulting impedance spectrum contains clear signatures of the anisotropic material properties and aspect ratio, as well as statistical variations in any of these parameters.