Kinetic Study of Li-Ion Extraction and Insertion at LiMn[sub 2]O[sub 4] Single Particle Electrodes Using Potential Step and Impedance Methods

Abstract

The kinetics of Li-ion extraction and insertion at single particles (8-21 μm diam) were investigated by cyclic voltammetry, potential step chronoamperometry (PSCA), and electrochemical impedance spectroscopy (EIS) methods using a microelectrode technique. The EIS measurements in a frequency range from 110 kHz to 11 mHz were conducted successfully on a single particle resulting in the magnitude of MΩ orders. The impedance spectra exhibited (i) a single semicircle in the high frequency region, (ii) a Warburg impedance in the low frequency region, and (iii) a limiting capacitance in the very low frequency region. The EIS spectra were fitted to a modified Randles-Ershler circuit, so that the reaction kinetics could be evaluated precisely. The dependences of the charge transfer resistance and the apparent diffusion coefficient of Li within the particle on the electrode potential were evaluated. Obtained values for were in the range of to from EIS measurements, in fair agreement with those from PSCA results. Finally, the apparent chemical diffusion coefficients of Li-ion in the single crystal, thin-film, and single particle of are compared. © 2003 The Electrochemical Society. All rights reserved.