High temperature X-ray diffractive study of spinel-type lithium manganese oxides

The thermal crystallization of spinel-type LiMn2O4 phases from a stoichiometric mixture of Li2CO3 and various manganese compounds has been investigated by means of a high temperature X-ray diffraction (HT-XRD) technique, and we obtained stoichiometric and oxygen-deficient LiMn2O4 oxides from different manganese compounds evaluated from the discharge capacities at 3.2 V in Li cells. The thermal behaviors of the stoichiometric and oxygen-deficient spinels were investigated in the temperature range between 25 and 700 degrees C in air by HT-XRD. The cubic spinel-type phase was maintained without any phase transitions, and the unit cell reversibly expanded/contracted. Their linear thermal expansion coefficients were 1.1-1.2 x 10(-5) K-1 and were independent of the oxygen deficiency. Furthermore, HT-XRD proved that Li-rich spinel, Li1.1Mn1.9O4, thermally underwent reversible phase separation into Li2MnO3 and spinel Li[LixMn1-(x),]O-4 (x<0.1)at higher temperature of >600 degrees C. (C) 2008 Elsevier B.V. All tights reserved.