EIS study on metal hydride electrodes using a porous model: Fitting methodology and SOC effects

• Published in: Journal of energy storage Vol. 27; p. 101067
• Main Authors: Martínez, Marcos, Teliz, Erika, Zinola, Carlos F., Díaz, Verónica
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-02-2020
• Subjects: Batteries; EIS; Electrochemical energy storage; Hydrides; Hydrides; Batteries; EIS; Electrochemical energy storage
• ISSN: 2352-152X; 2352-1538
• DOI: 10.1016/j.est.2019.101067

•A fitting methodology was designed to ease the process and to avoid arbitrariness.•Time constants τct, τx and τdif were found useful to interpret results.•Frequency range where porous effects are relevant was identified.•Ohmic resistance and double layer related parameters did not show dependence on SOC.•Rct decreases as SOC increases. τx diminishes and τdif increases towards SOC 100%.
In order to understand and improve the performance of Metal Hydride (MH) materials for Ni-MH battery's applications, Electrochemical Impedance Spectroscopy is used to provide interfacial information. However, it still offers significant challenges regarding methodology practices and results' interpretation due to the multiple interpretations arising from equivalent circuit fittings. The use of physicochemical models expresses in a better way the functionalities of charge/discharge mechanisms in MH. Moreover, for the impedance of MH porous electrodes there is little information from previous models, so the physical meaning of parametric figures and time constants is here emphasized. A complete fitting methodology is detailed and implemented via a specifically designed Octave program. An AB2 alloy of Zr0.3Ti0.7Cr0.7Mo0.3Ni composition is used to construct a porous electrode. Impedance spectra of the activated electrode are recorded and standard deviations of data are experimentally estimated. Validity of both the model and the methodology are thoroughly assessed. Changes in the system response when varying its state of charge are fully analyzed.