In situ synchrotron X-ray diffraction studies of the phase transitions in LixMn2O4 cathode materials

In situ X-ray diffraction studies of LixMn2O4 spinel cathode materials during charge- discharge cycling were carried out using a synchrotron as the X-ray source. Lithium-rich (x = 1.03- 1.06) spinel materials, obtained from two different sources, were studied. Three cubic phases with different lattice constants were observed during charge-discharge cycles in all of the samples when a sufficiently low charge-discharge rate (less than or equal to C/10) was used. There were two regions of two-phase coexistence, which indicates that both phase transitions are first order. The separation of the Bragg peaks representing these three phases varied from sample to sample and also depended on the charge-discharge rate. These results show that the deintercalation of lithium in lithium-rich spinel cathode materials proceeds through a series of phase transitions from a lithium-rich phase to a lithium-poor phase and finally to a lambda-MnO2-like cubic phase, rather than through a continuous lattice constant contraction in a single phase. (C) 1999 The Electrochemical Society. S1099- 0062( 98) 11- 078- 7. All rights reserved.