Lithium transport through non-fractal and fractal transition metal oxide electrodes such as $ Li_δV_2O_5$ and $Li_{1-δ}Mn_2O_4$ using quasi-steady-state and transient electrochemical methods based upon fractal G

Abstract

The present work involves lithium transport through non-fractal and fractal transition metal oxide electrodes such as $Li_δV_2O_5$ and $Li_{1-δ}Mn_2O_4$ using quasi-steady-state and transient electrochemical methods based upon fractal geometry. Chapter III deals with the mechanism transition of cell-impedance-controlled lithium transport through non-fractal $Li_δV_2O_5$ and surface-modified$Li_{1-δ}Mn_2O_4$ film electrodes. In chapter III-1, lithium transport through vanadium pentoxide xerogel film electrode was investigated in a 1 M solution of $LiClO_4$ in propylene carbonate by employing potentiostatic current transient technique (PCTT) and electrochemical impedance spectroscopy (EIS). From the comparison of the initial current experimentally measured with those initial currents theoretically calculated from the Ohm’s law and the Cottrell equation, it was confirmed that the cell-impedance-controlled constraint at the electrode surface is changed to the diffusion-controlled constraint when the potential step exceeds a critical value over the whole range of the lithium content. It was also found that the slope of the logarithmic current transient obtained at the lithium contents above 0.4 positively deviates in absolute value from 0.5 even under the diffusion-controlled boundary condition, but the phase angle of the diffusion impedance under the semi-infinite diffusion condition negatively deviates in absolute value from $45^\circ$ with increasing lithium content. With the aid of the X-ray diffractometry, the anomalous behaviours of the current transient and the diffusion impedance were discussed in terms of lithium transport through the interlayers with widely distributed spacings across the quasi-ordered xerogel film electrode. Furthermore, the current transient theoretically determined by employing the concept of interlayer spacing distribution coincided fairly well in form with that current transient experimentally measured. In Chapter III-2, lithium t...