Designing safer, high performance sodium-ion battery materials with neutrons

The global push for more sustainable and affordable energy storage has driven interest in sodium-ion batteries (SIBs), a promising alternative to lithium-ion batteries thanks to the abundance and low cost of sodium. However, developing suitable negative electrodes for SIBs remains a major challenge—conventional graphite, which works well in lithium systems, performs poorly with sodium.

In this study, researchers from Yokohama National University (Japan) and their collaborators—including contributors from LEPMI (France) and the CROSS neutron facility (Japan)—developed a novel layered electrode material: P3-type Na₀.₅Cr₀.₅Ti₀.₅O₂. This compound was designed using an innovative ion-exchange method, where potassium ions in a parent structure were replaced with sodium at room temperature, yielding a sodium-deficient but highly conductive metastable phase.

Crucially, neutron diffraction played a pivotal role in elucidating the structure of the synthesized material, results are summaries in the figure below. Unlike X-rays, neutrons are highly sensitive to light elements and can distinguish between neighboring transition metals such as chromium (Cr) and titanium (Ti), thanks to their contrasting neutron scattering lengths.^1,2 This sensitivity allowed the team to precisely map the positions of potassium and the transition metals within the layered structure, confirming the disordering of cations, a key feature that facilitates fast ion movement and high electrical/ionic conductivity.

The result is a robust electrode material with exceptional performance: a high capacity of 125 mAh g⁻¹ and excellent rate capability (up to 80% capacity retention at a 20C rate), along with long-term cycling stability (70% after 1000 cycles). Its fast-charging ability and safer operating voltage (≈0.8 V) make it a strong candidate for next-generation batteries, especially for electric vehicle applications.