Operando X-ray imaging of battery electrodes

Doctoral thesis, 2026

Rechargeable batteries have become indispensable in modern society, enabling the widespread use of portable electronics and supporting emerging demands in transportation and grid energy storage. Increasing requirements for capacity, fast charging, and sustainability necessitate both a deeper understanding of existing technologies and the development of novel chemistries. At the heart of battery operation, complex electrochemical and structural transformations occur at the electrodes across multiple length and time scales, posing significant challenges for mechanistic insight and performance optimisation. This thesis addresses these challenges by employing operando X-ray imaging and scattering techniques to investigate key processes in lithium-ion, sodium-ion and lithium sulfur batteries (LiS). For Li-ion batteries, the focus was on lithium plating on graphite electrodes, a key degradation mechanism. Lithium plating was tracked using X-ray tomographic microscopy (XTM), and its interplay with the lithiation process of graphite was further investigated with scanning small- and wide-angle X-ray scattering (SWAXS). The results show that the use of electrolyte additives can delay the onset of lithium plating and that plating also occurs in the bulk of the electrode, and not only at the graphite/separator interface and that Li-plating is more localised with increasing current density. It was also found that lithium plating has an influence on intercalation by slowing down reaction kinetics. For Na-ion batteries, scanning S/WAXS was employed to follow the sodiation process in hard carbon electrodes. The results show that pore-filling is the dominant mechanism at low potentials (below 0.1 V), whereas intercalation between graphene layers occurs continuously during sodiation. Furthermore, SAXS tomography reveals increased heterogeneity in micropore filling at higher degrees of sodiation. For LiS batteries, XTM was used to track dissolution and precipitation of sulfur as a function of current rates. The results indicate that the sulfur conversion kinetics do not limit the cell’s final capacity. Instead, the capacity loss can be attributed to incomplete utilisation of sulfur due to diffusion of soluble polysulfides beyond the electrode, resulting in active material loss. These findings highlight the capability of operando X-ray imaging to elucidate degradation mechanisms and phase transformations in current and next generation batteries chemistries. The presented experimental and analysis routes will hopefully encourage a more widespread use of imaging techniques in the battery community.