LiMn2O4-based Li-ion cells suffer from a limited cycle-life and a poor storage performance at 55 degrees C, both in their charged and discharged states. From 3-electrode type electrochemical measurements, the non-stability of LiMn2O4 in electrolytes containing traces of HF was identified as being the source of such a poor performance. To gel some insight in the mechanism by which the high-temperature ageing proceeds, a survey of the chemical stability of high surface area LiMn2O4 in various Li-based electrolytes was performed as a function of temperature. The growth of a protonated lambda-MnO2 phase was identified when LiMn2O4 powders were stored into the electrolyte at 100 degrees C for several hours. Such a protonated phase is partially inactive with respect to lithium intercalation, thereby accounting for same of the irreversible capacity loss experienced at 55 degrees C far LiMn2O4-based Li-ion cells.