Polarization, overpotential, Difference between OCV and CCV

・In Japanese
Prerequisite knowledge
・Standard electrode potential
・Activation energy

Polarization has different meanings depending on the field, but here I will explain battery polarization.

■What is polarization and overpotential?

Polarization is the reduction of the battery's original electromotive force (standard electrode potential). The voltage when no current is flowing is called OCV (Open Circuit Voltage), and the voltage when current is flowing is called CCV (Closed circuit voltage). Overpotential is the potential difference between the potential when current flows and the standard electrode potential, so it is the potential difference between OCV and CCV. A battery can be expressed by the equivalent circuit shown below.

■Polarization factors

① Resistance polarization
Polarization caused by the electrical resistance of electrolytes and electrodes.

② Activation polarization
Polarization caused by the activation energy spent when an electrode reaction occurs.

③ Concentration polarization
Polarization occurs when the concentration of reactants on the electrode surface decreases as the electrode reaction progresses. This tends to occur when charging and discharging rapidly. After a while, the concentration becomes uniform and disappears.

■How to calculate CCV

OCV depends on the electromotive force of the battery. CCV is also determined by the flowing current value and internal resistance value, and can be expressed by the following formula.



In the above equation, CCV is determined by the current value, but the current value flowing through the circuit is determined by CCV, so the calculation loops. If you know the external load resistance, you can calculate the CCV from the partial voltage with the internal resistance, but in some cases the external load resistance is unknown, so by repeatedly calculating the relationship between the current and CCV and finding the convergence point, Calculate CCV.

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