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

A survey of the chemical stability of high-surface area LiMn{sub 2}O{sub 4} 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 the authors identified, by means of combined infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction measurements, the growth, upon storage of LiMn{sub 2}O{sub 4} in the electrolyte at 100 C, of a protonated {lambda}-MnO{sub 2} phase partially inactive with respect to lithium intercalation. This results 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 Mn in the +4 oxidation state. Once this composition is reached, Mn cannot be oxidized further, and a protonic ion-exchange reaction takes place at the expense of the delithiation reaction. The resulting protonated {lambda}-Mn{sub 2{minus}y}O{sub 4} 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.