Mechanism for Limited 55°C Storage Performance of Li_1.05 Mn_1.95 O₄ 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 evidence for an acidic-induced Mn dissolution was confirmed, but more importantly we identified, by means of combined infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction measurements, the growth, upon storage of LiMn₂O₄ in the electrolyte at 100°C, of a protonated λ-MnO₂ phase partially in active with respect to lithiumintercalation.This result sheds light on how the mechanism of high temperature irreversible capacity loss proceeds. Mn dissolution first occurs, leading to a deficient spinel having all the Mninthe+4oxidationstate. Once this composition is reached, Mn cannot be oxidized further, and aprotonic ion-exchange reaction takes place at the expense of the delithiation reaction.The resulting protonated λ-Mn_2-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.