Diffraction-based energy-resolved neutron imaging of rechargeable batteries under operation

The constant increase in renewable energy sources used around the world is making energy storage an increasingly important topic. To store energy produced from intermittent sources, large-scale grid storage devices are needed. Sodium-ion-batteries are a promising option, due to their cost, safety, and environmental sustainability. To employ them in this field, further investigations into their properties and failure mechanisms are needed. The work described in this PhD thesis focuses on applying new types of characterization techniques to this technology, to individually investigate the main components of such devices, as well as the cells in their entirety. One of the main objectives of this project was to characterize the cells in operando and in situ, using cell geometries comparable to commercial cells, and electrode materials that are currently considered promising candidates as components for commercial sodium-ion batteries. For this reason, extensive in-house testing has been performed on electrode materials, to test the performance and properties of the custom-built cells, and the most optimal preparation routes for optimal samples. Neutrons and X-rays are highly complementary and their combined use allows us to obtain more information on the sample under examination. Throughout this project, neutron and X-ray imaging were employed in 2D and 3D to monitor processes such as electrolyte degradation and electrode disconnection, two processes highly involved in the failure mechanisms of rechargeable batteries. Energy-resolved neutron imaging combined with neutron powder diffraction was applied in operando to measure the operation of a sodium half-cell, determine the active areas of the cell under investigation, and describe the cycling and degradation processes in detail. Finally, the crystallographic properties of Prussian white-based electrode materials were investigated by X-ray powder diffraction, both in operando and ex-situ, to gain more insights into the role of crystallized water in the functioning of this material, as well as to learn more about the phase transition processes involved in the cycling process of this material.