​The revolution in mobile electronic technology has been made possible by high-performance batteries based on the movement of lithium ions in materials of the form Li_xCoO₂. Increasing demand for energy storage for renewable energy sources and the scarcity of lithium have led to intense interest in sodium-ion batteries, including the structurally-related Na_xCoO₂.

In work published in Scientific Reports, an international team of researchers used diffuse X-ray scattering, quasi-elastic neutron scattering (QENS) and ab-initio molecular dynamics simulations to determine the diffusion mechanism for Na_0.8CoO₂. The group performed QENS measurements of Na-ion diffusion on single-crystal and high-purity-powder samples using the OSIRIS spectrometer. Beforehand, they measured their samples using diffraction on SXD to determine which crystal to use in their experiment.

Using an approach that could also be used to understand the diffusion mechanism in other Na-ion, and Li-ion, battery materials, they found that the ordering of the sodium ions in the material structure is what determines the diffusion pathways and governs the diffusion rate. Their work uncovered factors that enhance the ionic conductivity for layered Na-ion cathode materials, and those which suppress diffusion. Their results are a step towards designing electrodes and solid electrolytes with better ionic conductivity.  

Related publication: “Diffusion mechanism in the sodium-ion battery material sodium cobaltate" Scientific Reports (2018) 8:3210, DOI: 10.1038/s41598-018-21354-5

Authors: T. J. Willis (Royal Holloway, ISIS), D. G. Porter (Diamond Light Source), D. J. Voneshen (ISIS), S.Uthayakumar (Royal Holloway), F. Demmel (ISIS), M. J. Gutmann (ISIS), M. Roger (Service de Physique de l’Etat Condensé), K. Refson (Royal Holloway, ISIS) & J. P. Goff (Royal Holloway)

​Instruments: OSIRIS, SXD