Electrochemical characteristics of orthorhombic LiMnO_2 with different degrees of stacking faults

摘要

Orthorhombic LiMnO_2 (o-LiMnO_2) is known to have stacking faults (local regions of monoclinic ordering) that are caused by structure disorder between Li and Mn sites. Previous research has indicated that this structural disorder, correlated with the full width at half maximum (FWHM) of the (110) X-ray diffraction (XRD) peak, might affect the electrochemical properties of o-LiMnO_2. In this study, o-LiMnO_2 powders are prepared by an emulsion drying method. Different degrees of stacking faults are induced by varying the heating rate. From electrochemical and ex situ XRD experiments, it is found that a sample with a high number of stacking faults undergoes easier phase transformation from the orthorhombic to the spinel structure on cycling. This form of o-LiMnO_2 displays no capacity fading in the 4 V (versus Li/Li~+) region, but suffers severe capacity fading in the 3-V region. By contrast, a sample with a low number of stacking faults experiences no capacity fading in either the 3- or 4-V regions and has good cycleability.