Local Structure and Lithium Diffusion Pathways in Li4Mn2O5 High Capacity Cathode Probed by Total Scattering and XANES

In the constant race for more efficient Li-ion batteries, extensive research has focused on the design of new, more competitive cathode materials, currently limiting the battery performance. The improvement of cathode materials demands the detailed understanding of the complex structural mechanisms at play during battery operation, that is, when Li+ ions are inserted and extracted from the cathode. Moreover, new cathode designs involve more and more disordered/nanosized materials for enhanced Li+ cation diffusion and larger specific surfaces. This trend poses new challenges for the structural investigation methods employed, which mostly rely on the periodic and long-range ordered nature of the compounds under study. This is specially the case of the recently discovered nanostructured Li4Mn2O5 high capacity cathode material, which shows record reversible capacities superior to the state-of-the-art Li-Mn-O electrodes and displays a strongly disordered rock salt-type structure. This last feature, mainly due to its synthetic route involving high energy milling, prevented from reaching a full understanding of the lithium exchange mechanism of particular interest in this 3D framework compound. Here, we demonstrate that a thorough description of such a disordered structure can be achieved by a combination of near-edge X-ray absorption spectroscopy and pair distribution function analysis of neutron and X-ray total scattering data, which ultimately lead to the elucidation of the Li cation diffusion pathways.