The potentiostatic intermittent titration technique (PITT)[1] is, together with its galvanostatic counterpart, one of the most used techniques to retrieve insights on the diffusion coefficient of the electrodes’ active materials.
The experiment starts by recording the OCP of the battery (𝑉oc). Then, a step composed of 15 minutes pulse at 𝑉oc , followed by 15 minutes of relaxation with the cell switched off. Afterwards, a positive potential increment of 0.02 V is applied on 𝑉oc, and the signal is recorded for 15 minutes, followed by 15 minutes of relaxation time. The same potential increment is consecutively applied, starting from the voltage resulting from the previous step and the signal is recorded for 15 minutes. The potential pulses are applied until the upper limit of 4.2 V is reached. Each potential pulse is followed by 15 minutes of relaxation time. Afterwards, negative potential increments of -0.02 V are consecutively applied to the voltage resulting from the previous step, and the signal is recorded for 15 minutes. The potential pulses are repeated until the lower limit of 2.8 V is reached. Each potential pulse is followed by 15 minutes of relaxation time.
During the 0.02 V potential pulses, Li-ions are de-intercalated from the positive electrode and intercalated to the negative one. The reverse occurs during the negative discharging potential pulses, where the Li-ions are de-intercalated from the negative electrode and intercalated to the positive electrode. In both cases, the intercalation and de-intercalation processes result in current development, described in the following equation.
Where 𝐹 is the Faraday’s constant, 𝑆 is the surface area of the electrode. (Cs-C0) is the concentration difference of Li ions at the surface at time t and at the beginning of the potential pulse (𝑡= 0), 𝐷 is the diffusion coefficient and 𝐿 is the characteristic length of the electrode active material.
The diffusion coefficient 𝐷 of the active material present in one electrode is related to the current 𝑖 developed from the constant voltage pulses via the following formula
The above shows a plot of potential (blue line) and current (red line) vs. time. The D at different pulse can be calculated by re-plotting Ln(i) Vs t as the following
[1] https://www.ecochemie.nl/download/Applicationnotes/Autolab_Application_Note_BAT04.pdf