Intra-layer ordering and inter-layer disordering of the Li2MnO3 phase in Li1.07Mn1.93O4-δ cathode materials: electron diffraction investigation and DIFFaX simulation of X-ray diffraction patterns

A previous transmission electron microscopy (TEM) analysis revealed the existence of monoclinic Li2MnO3 in the lithium‐rich and oxygen‐deficient Li1.07Mn1.93O4−δ powder. Interestingly, the monoclinic phase exhibits different nanoscale lamellar variants involving a rotation of the stacking direction by 120 or 240° along the pseudo‐threefold axis, i.e. the [103]M//[111]C (M and C denote the monoclinic and cubic phases, respectively) zone axis. Here, a theoretical X‐ray diffraction (XRD) study of Li2MnO3 employing the DIFFaX program is presented. It is found that, with the occurrence of different stacking configurations, the characteristic superstructure reflections with 2θ between 20 and 35° (Cu Kα) in the XRD pattern become more and more broadened with the increasing degree of stacking disorder, indicating that XRD may fall short in detecting the presence of the monoclinic Li2MnO3 phase. Moreover, selective peak asymmetry appears when the stacking sequence becomes extremely disordered. Further selected‐area electron diffraction and theoretical neutron diffraction investigation may clarify the similar ambiguity concerning the crystal phases of other structurally related compound cathode materials for lithium‐ion batteries (e.g. LiNi1/2Mn1/2O2, LiNi1/3Co1/3Mn1/3O2).