Lithium transport in carbonaceous electrodes and electrochemical reactions at electrode/electrolyte interfaces with emphasis of fractal approach to the morphology of surface groups

Abstract

The present work involves the lithium transport in carbonaceous electrode and electrochemical reactions at electrode/electrolyte interfaces with emphasis of fractal approach to the morphology of surface groups. In chapter III, the effect of electrolyte temperature on the passivity of solid electrolyte interphase (SEI) was investigated using galvanostatic charge-discharge experiment, and ac-impedance spectroscopy combined with Fourier transform infra-red (FTIR) spectroscopy, and high resolution transmission electron microscopy (HRTEM). The galvanostatic charge-discharge curves at 20℃ evidenced that the irreversible capacity loss during electrochemical cycling was markedly increased with rising SEI formation temperature 0˚ to 40℃. This implies that the higher the SEI formation temperature, the more were the graphite electrodes exposed to the structural damages. From both the increase of the relative amount of the $Li_2CO_3$ to $ROCO_2Li$, and the decrease of the resistance to the lithium transport through the SEI layer with increasing SEI formation temperature, it is reasonable to claim that due to the enhanced gas evolution reactions during the transformation of $ROCO_2Li$ to $Li_2CO_3$, the rising SEI formation temperature increased the number of defect sites in the SEI layer. From the analysis of HRTEM images, no significant structural destruction in bulk graphite layer was observed after charge-discharge cycles. This means that solvated lithium ions were intercalated through the defect sites in the SEI, at most, into the surface region of the graphite layer. In chapter IV, this article critically evaluates the characteristics of a new in situ spectroelectrochemical cell with an optimised path of IR beam designed at our laboratory for the study on the SEI layer formed between the porous graphite anode and alkyl carbonate solution for lithium ion batteries. The in situ cell was designed in view of the optical principles underlying the way the in situ cell ...