Neutron Spectroscopy and Computational Methods in investigation of Na ion Battery Materials: A Perspective

Abstract: Adoption of renewable energy is essential to address the challenge of climate change, but that necessitates energy storage technologies. Lithium-ion batteries, the most ubiquitous solution, are insufficient for large-scale applications, so sodium-ion batteries (SIBs), an alternative, are of great current interest. To design and synthesise a commercially viable SIB with required performance, a fundamental understanding of the materials is imperative. Neutron diffraction and spectroscopy provide a unique insight of atomistic understanding of structure and dynamics in materials, therefore in this perspective we have explored how these techniques have been used in SIB research. As neutrons have high penetrability in materials and neutron-matter interaction probabilities are independent of the atomic number, they can provide unique information about motion of particles in bulk materials in the pico- to nanosecond time scales. This makes neutron scattering techniques important tools in battery research. Sodium has a low neutron cross section, which makes computational simulations essential for analysing neutron scattering data of SIB materials. With the availability of high flux neutron sources, high resolution instruments and high performance computers and simulations tools, neutron spectroscopy has been an emerging technique in the last decade for SIB research. In this perspective, we have shown that neutron diffraction is the most popular, while neutron spectroscopies, are just emerging. Computational simulation methods, both force field based and from first principles, are common but still are mostly used independent of neutron experiments. We have identified that suitable improvements of instrumentation, sample environments and simulations methodology will allow these techniques to be more accessible in future.