Physical Interpretations of Electrochemical Impedance Spectroscopy of Redox Active Electrodes for Electrical Energy Storage

Abstract

This study aims to provide physical interpretations of electrochemical impedance spectroscopy (EIS) measurements for redox active electrodes in a three-electrode configuration. To do so, a physicochemical transport model was used accounting for (i) reversible redox reactions at the electrode/electrolyte interface, (ii) charge transport in the electrode, (iii) ion intercalation into the pseudocapacitive electrode, (iv) electric double layer formation, and (v) ion electrodiffusion in binary and symmetric electrolytes. Typical Nyquist plots generated by EIS of redox active electrodes were reproduced numerically for a wide range of electrode electrical conductivity, electrolyte thickness, redox reaction rate constant, and bias potential. The electrode, bulk electrolyte, charge transfer, and mass transfer resistances could be unequivocally identified from the Nyquist plots. The electrode and bulk electrolyte resistances were independent of the bias potential, while the sum of the charge and mass transfer resistances increased with increasing bias potential. Finally, these results and interpretation were confirmed experimentally for LiNi0.6Co0.2Mn0.2O2 and MoS2 electrodes in organic electrolytes.

How to measure and report the capacity of electrochemical double layers, supercapacitors, and their electrode materials

“…Unfortunately there seems to be no overview of methodological aspects of impedance measurements available. Even a report apparently answering the question asked here does not provide a single equivalent circuit or a description of it possibly useful in a practical application [102]. The electrode studied here closely resembles an electrode composed of an intrinsically conducting polymer deposited on an electronically conducting substrate.…”

Fullerene C76: An Unexplored Superior Electrode Material with Wide Operating Potential Window for High‐Performance Supercapacitors

“…This can be attributed to the charge storage mechanism as can be interpreted via electrochemical impedance spectroscopy (EIS) analysis. In the EIS analysis, the x‐intercept represents the electrode resistance (R E ) whereas the slope indicates the charging process . Generally, the 45° linear spectrum in the low frequency regime of the Nyquist plot signifies a balanced charging process between the EDL and diffusion processes.…”

Metal‐Ion Coupled Electron Transfer Kinetics in Intercalation‐Based Transition Metal Oxides

“…However, the available justification seems incomplete and the origin of the high frequency semicircle is still debated. [ 60 ] Furthermore, the medium frequency semicircle for a significant number of systems does not demonstrate the expected Butler–Volmer‐like dependence on the potential, which allows attribution to the impedance of a preceding slow chemical step (desolvation/adsorption). [ 56 ]…”