The electrochemical lithium intercalation reaction into amorphous and crystalline $Li_{1±δ}Mn_2O_4$ electrodes in 1M $LiClO_4$ propylene carbonate(PC) solution has been investigated as a function of lithium content (1±δ) in the oxide electrodes by using galvanostatic intermittent titration experiment, electrochemical impedance spectroscopy and cyclic voltammetry. Amorphous and crystalline powder specimens were prepared from solid state reaction and sol-gel process, and the crystal structure of crystalline phase was identified as a cubic spinel structure with space group Fd3m by X-ray diffractometry. Ac-impedance measurements were carried out by superimposing an ac voltage of 10mV amplitude ranging between 1mHz and 100kHz in a dc potential range of 3.0 to 4.4 $V_{Li}/Li_+$. The impedance spectra of both the amorphous and crystalline $Li_{1±δ}Mn_2O_4$ electrodes consist of two separated arcs, in the higher frequency range of 1Hz to 100kHz, and a line inclined at approximately 45° in the lower frequency range of 1mHz to 1Hz. The two arcs are due to the contact resistance among the oxide particles and the absorption reaction at the interface of electrolyte/oxide electrode. The fact that the absorption resistance remains constant with lithium content is due to the stability of 3-dimensional cubic structure of $LiMn_2O_4$ experiencing small volume change with lithium content. When lithium content (1±δ) exceeded 1, cubic spinel structure of $Li_{1±δ}Mn_2O_4$ was transformed into tetragonal spinel structure due to Jahn-Teller distortion, then the value of absorption resistance became very large. This occurred more predominantly at the crystalline electrode than the amorphous electrode. The charge-discharge curve shows a potential slopping with lithium content for amorphous electrode. In contrast, the crystalline electrode exhibits two distinct potential plateaus near 4$V_{Li}/Li_+$, indicating that two phases coexist within the oxide. From the experimental results, it was concluded that the amorphous electrode has higher diffusivity, better reversibility and better ability to relax strain than the crystalline electrode, which was discussed in terms of larger diffusion path and more open structure of the amorphous electrode.
