threshold. Fraction of the initial amount of active material
consumed upon reaching the percolation threshold will be referred
to as critical fractional conversion. At the point of critical fractional
conversion, electrode behaves like an insulator since a conducting
path does not exist, and battery stops discharging. Metzendorf[1]
suggests this to be the explanation for the well known difference
between the theoretical capacity of an electrode, Qtheo, and its
nominal capacity,Qnom, i.e., the observed maximum capacity that it
can deliver. All these effects of variation in the resistance of an
electrode caused by change in its composition have been ignored in
mathematical models so far, and are investigated here. In view of
the percolative nature of electrical conductivity, the effect of
changing resistance of an electrode will be important only when
the critical fractional conversion of active materials is approached.
This can occur only under deep discharge conditions, and when
electrodes are the limiting reactants. When electrodes are the
limiting reactants, a sharp decline in voltage (a ‘knee’) is observed
towards the end of discharge. Successful modeling of this has not
been possible without the use of empirical expressions. It will be
shown that such non-mechanistic approaches can be avoided by
introduction of effect of the composition of an electrode on its
resistance and a justifiable expression for changes in the area of
active materials.