Comparison of the Electrochemical Impedance Spectroscopy Characteristics of Insertion Electrode Materials Used in Secondary Metal Hydride and Lithium-Ion Electrodes

and graphite powder disk electrodes sandwiched between two nickel screens were used as working electrodes in 6.0 M KOH and in 1.0 M in propylene carbonate-ethylene carbonate-dimethyl carbonate (1:1:3) solution, respectively. Different electrochemical impedance spectroscopy protocols were used for analysis of the kinetics of insertion and extraction of hydrogen and lithium into these materials and accompanying changes in intrinsic electrode resistance. The imaginary vs. real impedance plots for both electrodes show a high frequency depressed semicircle, a midfrequency charge transfer semicircle, then an inclined line for reactant diffusion in the host structure. In both cases, the first semicircle was not a result of particle-to-current collector and particle-to-particle contact impedance, although part of the contact impedance is shown to be in series with the kinetic impedance.