Short-Range Ordering in Battery Electrode, the ‘Cation-Disordered’ Rocksalt Li1.25Nb0.25Mn0.5O2

We show the occurrence of local cation ordering in Li-ion battery material Li_1.25Nb_0.25Mn_0.5O₂, previously thought to be disordered. We deduce this ordering from X-ray diffraction, and test it against neutron diffraction & PDF, magnetic susceptibility and solid state NMR evidence. We identify the nature of the ordering as having a local structure related to that of gamma-LiFeO₂, determine the correlation length of such ordering, and demonstrate its significant consequences for the material's electrochemistry.