Mechanism transition of cell-impedance-controlled lithium transport through Li1−δMn2O4 composite electrode caused by surface-modification and temperature variation

The mechanism transition of lithium transport through a Li_1−δMn₂O₄ composite electrode caused by the surface-modification and temperature variation was investigated using the galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS) and the potentiostatic current transient technique. From the analyses of the ac-impedance spectra, experimentally measured from unmodified Li_1−δMn₂O₄ and surface-modified Li_1−δMn₂O₄ with MgO composite electrodes, the internal cell resistance of the MgO-modified Li_1−δMn₂O₄ electrode was determined to be much smaller in value than that of the unmodified electrode over the whole potential range. Moreover, from the analysis of the anodic current transients measured on the MgO-modified Li_1−δMn₂O₄ electrode, it was found that the cell-impedance-controlled constraint at the electrode surface is changed to a diffusion-controlled constraint, which is characterised by a large potential step and simultaneously by a small amount of lithium transferred during lithium transport. This strongly suggests that the internal cell resistance plays a significant role in determining the cell-impedance-controlled lithium transport through the MgO-modified Li_1−δMn₂O₄ electrode. Furthermore, from the temperature dependence of the internal cell resistance and diffusion resistance in the unmodified Li_1−δMn₂O₄ composite electrode measured by GITT and EIS, it was concluded that which mechanism of lithium transport will be operative strongly depends on the diffusion resistance as well as on the internal cell resistance.