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 °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 × 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]O4 (x < 0.1) at higher temperature of > 600 °C.