Lithium-ion transfer at LiMn2O4 thin film electrode prepared by pulsed laser deposition

LiMn2O4 thin film electrode was prepared by pulsed laser deposition for fabrication of structurally ordered electrode/electrolyte interface. Li-ion transfer at the LiMn2O4 electrode was studied by AC impedance spectroscopy. At potentials below 3.70 V (vs. Li/Li+), no semi-circle was observed on Nyquist plot. No oxidation and reduction currents were observed in cyclic voltammogram of LiMn2O4 thin film electrode at the potential range of 3.50-3.70 V, showing blocking electrode behaviors. Nyquist plots gave one semi-circle in the higher frequency region and a linear Warburg impedance in the lower frequency region at potential region above 3.80 V. The resistance of semi-circle was dependent on electrode potential and practical electrical resistance of LiMn2O4 along the thickness was negligible because of its small thickness. Hence, the semi-circle was identified as resistance for interfacial lithium-ion transfer. The resistance decreased with increasing electrode potentials up to 4.0 V and then increased with increasing electrode potentials. Temperature dependency of the resistance gave activation energy of 50 +/- 2.4 kJ mol(-1), indicating that high activation barrier exists at electrode/electrolyte interface for lithium-ion transfer. (C) 2003 Elsevier Science B.V. All rights reserved.