(An) investigation of electrochemical lithium intercalation into and deintercalation from porous $Li_{1+δ}[Ti_{2-y}Li_y]O_4$ (y=0; 1/3) electrodes by using current transient technique

Abstract

The present work is concerned with electrochemical lithium intercalation into and deintercalation from porous $Li_{1+δ}[Ti_{2-y}Li_y]O_4$ (y=0; 1/3) electrodes in the two-phase coexistence. For this purpose, the galvanostatic charge-discharge curves were obtained from both the porous $Li_{1+δ}[Ti_5/3Li_1/3]O_4$ electrode and $Li_{1+δ}Ti_2O_4$ electrode and the electrochemical impedance spectra were measured on the former electrode as a function of lithium content ($1+δ$). And the potentiostatic current transients were measured on the both electrodes as a function of the lithium injection potential during the lithium intercalation and deintercalation. The galvanostatic charge-discharge curves for the both electrodes showed a potential plateau, due to the coexistence of two pseudo-phases of a Li-diluted phase α and a Li-concentrated phase β. The potential plateau of the porous $Li_{1+δ}[Ti_5/3Li_1/3]O_4$ electrode was higher in value than that of the porous $Li_{1+δ}Ti_2O_4$ electrode. This is attributable to the transition 3.5 to 4 in average oxidation state of titanium in the electrode with change y = 0 to y = 1/3. The formation of β-phase in the porous $Li_{1+δ}[Ti_5/3Li_1/3] O_4$ electrode is more liable to occur in comparison with that in the porous $Li_{1+δ}Ti_2O_4$ electrode during the lithium intercalation, because of the stronger mutual attraction between the adjacent lithium ions in the former electrode than that in the latter electrode. Thus, the charge-discharge curves showed that the stable α-phase region of the former electrode appeared narrower than that of the latter electrode. The impedance spectra of porous $Li_{1+δ}[Ti_5/3Li_1/3]O_4$ electrode consist of two separated arcs in the high and intermediate frequency ranges and an inclined line in the low frequency range. In view of the fact that the high frequency arc representing the particle-to-particle contact resistance and capacitance was constant regardless of lithium content, it is expected t...