1.5.6 What If Current is Drawn from the Cell?
If current is drawn from the cell into an external circuit, the normal mode of operation
when chemical energy is converted into electrical energy, it flows through
the ionic impedance, Zi. This results in an additional voltage drop of Iout Zi, further
reducing the output voltage. If there were no electrochemical self-discharge, this
can be written as
Eout = Ethti−IoutZi (1.31)
The value of the ionic impedance of the system, Zi, may increase with the value
of the output current as the result of current-dependent impedances at the electrolyte/
electrode interfaces. The difference between Eth and Eout is also known as
polarization in electrochemical literature.
The result of the presence of current-dependent interfacial impedances to the
passage of ionic species that increase Zi is that the effective transference number of