Untangling Cation Ordering in Complex Lithium Battery Cathode Materials – Simultaneous Refinementof X-ray, Neutron and Resonant Scattering Data

The presence of multiple, neighbouring transition metals presents a challenge for powder diffraction when trying to locate individual elements in a structure. Combining the information in X-ray and neutron data in simultaneous refinements has historically been a powerful tool. However, increasingly complex compositions require more information and element contrast than two datasets can provide. This paper presents results demonstrating the application of resonant powder diffraction as additional datasets in simultaneous X-ray and neutron Rietveld refinements. Final results are presented for a simple layered R-3m structure with four cations, and preliminary results for a more complex monoclinic C2/m structure, again with four different cations. The more complex structure presents challenges with respect to the occupational constraints across sites with different multiplicities whilst allowing the lithium-to-transition metal ratio to refine. INTRODUCTION Lithium-ion batteries have largely replaced nickel-cadmium and nickel-metal hydride batteries for consumer electronics applications. This is due to their increased energy density, where increased functionality is being demanded from ever smaller devices. The lithium-ion cell relies on the ability of lithium ions to shuttle backwards and forwards between a cathode (usually a lithiated transition metal oxide) and anode (usually graphite). One of the more costly components of a lithium-ion battery is the cathode material, the conventional material being 328