THE ELECTROCHEMICAL IMPEDANCE OF POROUS NICKEL ELECTRODES IN ALKALINE MEDIA .2. NONUNIFORM TRANSMISSION-LINE ANALYSIS

Nonuniform transmission line models have been developed to provide an accurate account of the impedance characteristics of sintered porous nickel electrodes when charging and discharging under stress and low earth orbit cycling regimes (described in Part I which is the preceding article). This model represents a single pore in a porous electrode by a nonuniform transmission line involving both the charged (NiOOH) and discharged [Ni(OH)2] phases. The most accurate description of the impedance characteristics was obtained by assuming a conical geometry and a chi-2 distribution for the penetration depth of Ni(OH)2 down the pore on discharge. The modeling results indicate that charging and discharging a sintered electrode over 596 cycles increases both the number of active pores and the fraction of pores that are more deeply reduced. These two trends account for the observed increase in capacity of the electrode with cycle number.