Mechanism for limited 55 degrees C storage performance of Li1.05Mn1.95O4 electrodes

A survey of the chemical stability of high-surface area LiMn2O4 in various Li-based electrolytes was performed as a function of temperature. The evide nce for an acidic-indued Mn dissolution was confirmed, hut more importantly we identified, by means of combined infrared spectroscopy, thermogravimetr ic analysis, and X-ray diffraction measurements, the growth, upon storage o f LiMn2O4 in the electrolyte at 100 degrees C, of a protonated lambda-MnO2 phase partially inactive with respect to Lithium intercalation. This result sheds light on bow the mechanism of high temperature irreversible capacity loss proceeds. Mn dissolution first occurs, leading to a deficient spinel having all the Mn in the +4 oxidation state. Once this composition is reach ed, Mn cannot he oxidized further, and a protonic ion-exchange reaction tak es place at the expense of the delithiation reaction. The resulting protona ted lambda-Mn2-yO4 phase has a reduced capacity with respect to lithium, th ereby accounting for some of the irreversible capacity loss experienced at 55 degrees C for such a material (C) 1999 The Electrochemical Society. S001 3-4651(98)01-081-7. All rights reserved.