Mechanism for Limited 55°C Storage Performance of Li1.05Mn1.95 O 4 Electrodes

Abstract

A survey of the chemical stability of high-surface area LiMn2O4 in various Li-based electrolytes was performed as a function of tem- perature. The evidence for an acidic-induced Mn dissolution was confirmed, but more importantly we identified, by means of com- bined infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction measurements, the growth, upon storage of LiMn2O4 in the electrolyte at 100C, of a protonated -MnO2 phase partially inactive with respect to lithium intercalation. This result sheds light on how the mechanism of high temperature irreversible capacity loss proceeds. Mn dissolution first occurs, leading to a defi- cient spinel having all the Mn in the 4 oxidation state. Once this composition is reached, Mn cannot be oxidized further, and a pro- tonic ion-exchange reaction takes place at the expense of the delithiation reaction. The resulting protonated -Mn2yO4 phase has a reduced capacity with respect to lithium, thereby accounting for some of the irreversible capacity loss experienced at 55C for such a material.