Electrochemical Patterns of Phase Transforming Intercalation Materials: Diagnostic Criteria for the Case of Slow Nucleation Rate Control

Abstract

In this paper we implement and test a new approach for the description of the electrochemical data (cyclic voltammetry and chronoamperometry) for phase transforming intercalation electrode materials. This approach assumes the rate-limiting step being associated with the slow nucleation of a new phase in the material particles. As a test model system, we used LiFePO4 material. It is shown that all the electrochemical data for LiFePO4 can be self-consistently described assuming a slow nucleation step with only minor influence of ionic diffusion and interfacial charge transfer kinetics on the intercalation rates. The developed formalism allows for a reliable diagnostics of the reaction rate control regime as well as for the extraction of information on the pre-exponential factor and activation energy values. The electrochemical diagnostic criteria for the slow nucleation step are formulated based on the shapes of the cyclic voltammetry peaks, current transients registered under potentiostatic conditions and specific features in the impedance spectra of phase-transforming electrodes.