Evolving Structural Pathways in Next-Generation Lithium- and Sodium-Ion Battery Materials Revealed by Pair Distribution Function Analysis

The need for battery technologies with higher energy densities and improved sustainability has motivated a large body of research into new potential electrode materials for rechargeable lithium- and sodium-ion batteries. However, in many cases, characterising the lithium/sodium-ion (de)insertion mechanisms of these new materials presents significant challenges to conventional crystallographic analysis, as disordered or nano-sized phases may form, some of which may be metastable and exist only within the battery. Here, I will present our recent work detailing how pair distribution function (PDF) analysis - a total scattering technique which is sensitive to both local and long-range structure – has been applied in situ to give highly consistent data sets from which subtle changes to local structure during electrochemical cycling can be resolved. PDF data is analysed alongside complementary methods such as x-ray diffraction, solid-state nuclear magnetic resonance, x-ray absorption spectroscopy and theoretical calculations to gain insight into a range of potential new electrode materials, including disordered rock salt cathodes, lithium-ion conversion anodes and alloying anodes for sodium-ion batteries. In particular, my focus will be on systems where the lithiation/sodiation mechanisms evolve upon electrochemical cycling, forming nanostructures which differ significantly from the initial electrode structure. I will discuss the impact of these evolving structural pathways on the physical properties and how these structural insights may aid future electrode material discovery and design.