In Situ Synchrotron X-Ray Diffraction Studies of the Phase Transitions in Li[sub x]Mn[sub 2]O[sub 4] Cathode Materials

Abstract

In situ X‐ray diffraction studies of spinel cathode materials during charge‐discharge cycling were carried out using a synchrotron as the X‐ray source. Lithium‐rich 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 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 litium‐richel cathode materials proceeds through a series of phase transitions from a lithium‐rich to a phase lithuim‐poor phase and finally to a cubic phase, rather than through a continuous lattice constant contraction in a single phase. ©1999 The Electrochemical Society