PITT – Electrochemistry & Battery – Application Note 2Latest updated: May 6, 2020
One way of obtaining differential capacity plots (DCA) is via constant current techniques and analyzing the charge passed (dQ) between consecutive voltage markers (dE or dV). This provides steady-state data and can be obstructed by any kinetic limitations in the material under study. Conversely, PITT allows to apply predefined voltage steps and integrate the current (calculate charge passed) until user-specified equilibrium conditions are achieved. When performed in a three-electrode configuration, this experiment can provide information about both the positive and negative electrodes of the battery.
In general, this technique allows the discrimination of solid-solution vs. two- (or multi-) phase mechanism of intercalation, as well as look at transients during each voltage step, nucleation and growth kinetics, voltage hysteresis, as well as, the density of states of the intercalation materials. More on DCA in Application note #40.
The basic characteristic of an electroactive intercalation compound is the thermodynamic voltage-composition rela-tion, which corresponds to the equilibrium phase diagram of the system. See for example Armand  for a detailed description of the various behaviors that can be encountered, which depend upon the changes in electronic and structural properties upon intercalation/deintercalation.
In short, continuous dependence of the potential vs. composition corresponds to a solid-solution single-phase domain, whereas a potential plateau corresponds to a two-phase domain.
Other properties of interest, particularly in view of possible applications as active electrodes in a battery are the potential windows of electrochemical stability, kinetics and reversibility of the intercalation process.
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