Impedance modeling of nickel fiber/carbon fiber composite electrodes for electrochemical capacitors

Abstract

A process for producing composite materials from metal fibers and carbon fibers was developed in our laboratory. This process allows for independent adjustment of void volume and macro porosities not attainable by other processes or electrode structures. Contact resistance in the sintered metal fiber-carbon fiber composites is low due to the sintered metal structure which entraps carbon fibers in the finished electrode. Extensive mechanistic discrimination and model testing has yielded an equivalent circuit model which successfully predicts impedance performance from 10/sup -2/ to 10/sup 5/ Hz. An equivalent circuit model for a nickel fiber mesh, represented by a constant phase element (CPE) in parallel with a mesh resistance, is combined with a model developed specifically to describe the impedance of activated carbons. The five parameters in the model circuit were successfully correlated with variations in temperature and electrolyte conductivity, also variations in the equivalent circuit parameters with sintering conditions are also presented. The above noted model is applicable for the simulation and design of electrochemical capacitors for specialized used in various pulse power systems.