(An) investigation of the electrochemical reactions and electrostatic interactions at the interfaces between nanoporous fractal carbon electrodes and non-aqueous/aqueous electrolytes

Abstract

The present work involves an investigation of the electrochemical reactions and electrostatic interactions at the interfaces between nanoporous fractal carbon electrodes and non-aqueous/aqueous electrolytes. In chapter III, electrochemical reactions at the interface between mesoporous carbon electrode and $SOCl_2$ electrolyte in $Li-SOCl_2$ battery were investigated using galvanostatic discharge experiment and ac-impedance spectroscopy. From the analysis of the high frequency arc in a Nyquist plot of the ac-impedance spectra, it was observed that, as discharge progressed, there appeared a low to high transition in the average growth rate of the primary film over a narrow range of depth of discharge, regardless of discharge current. The inclined line in the intermediate frequency range associated with the secondary layer revealed that there existed also a transition of the straight line with a phase angle higher than 4˚ to the convex line with a phase angle lower than 45˚ with progressing depth of discharge, regardless of discharge current. A conventional transmission line model was modified in order to numerically analyse the ac-impedance spectra for the non-cylindrical pores comprising the porous secondary layer based upon a series combination of the position-dependent resistance and capacitance in value. From the coincidence in shape of the impedance spectra experimentally measured with those theoretically calculated in the intermediate frequency range, it was concluded that there occurred a transformation of the conically shaped pores to the warhead-shaped pores comprising the secondary layer with progressing depth of discharge. The compactness of the secondary layer increased with progressing depth of discharge below and above the transition depth of discharge. The transition cathodic overpotential at which both the transition depth of discharge for the primary layer and the secondary layer just appeared was measured to be about between 360 and 400 mV, re...