Structural change of the LiMn2O4 spinel structure induced by extraction of lithium

Abstract

A structural change of the Li_xMn₂O₄ spinel induced by extraction of lithium was investigated using the Rietveld refinement method for its X-ray diffraction pattern change. Two cubic phases of the spinel Li_xMn₂O₄ were observed in the range 0.5> x >0.13 and their lattice parameters were found to decrease with decreasing x. If both phases were thermodynamically stable, the lattice parameters should not change during the extraction of lithium. Therefore, our X-ray diffraction (XRD) patterns suggest the destruction of the rigid Li_xMn₂O₄ spinel structure which provides a high reversibility for the insertion and extraction of lithium. The possible mechanisms corresponding to this structural degradation are the compositional change of Mn or O atoms in Li_xMn₂O₄ through the extraction of lithium. On the other hand, the separation of Mn²⁺ ions from Li_xMn₂O₄(0.5> x >0.13) was detected by electron paramagnetic resonance (EPR). From these results, it is concluded that Li_xMn₂O₄ decomposes through the extraction of lithium to form Mn²⁺ compounds as a separate phase.