The green transition depends not only on producing renewable energy, but also on storing it efficiently. One of the major scientific challenges is hidden inside batteries: in the solid electrode materials where ions migrate, redox processes occur, and atomic structures expand, distort, rearrange — or sometimes break down.

Dorthe Ravnsbæk’s research focuses on the link between atomic structure and their ability to reversibly transform and store energy. In her research group, they particularly focus on synthesizing and characterizing new electrode materials for rechargeable batteries and investigate how their structures affect the battery performance and how they change during charge and discharge. This knowledge is essential for developing more sustainable batteries based on abundant elements.

A central focus is sodium-ion batteries as a potential supplement to the present lithium-ion technology. Lithium and sodium are naturally closely related: both are alkali metals, form monovalent ions, and can take part in similar intercalation chemistries. However, important chemical differences remain. Something as seemingly simple as the larger ionic size of Na⁺ compared with Li⁺ changes how the ions migrate through electrode structures, which coordination environments they prefer, and which structural transformations are triggered during cycling. Design principles from lithium-ion batteries therefore cannot simply be transferred directly to sodium-ion systems.

As new potential Na-ion battery electrodes, Dorthe and her research group investigate sustainable sodium transition-metal oxides, for example materials based on iron and manganese. When sodium is removed from or inserted into a layered oxide, the atomic layers may glide, new phases may form, and metal ions may migrate to new positions in the structure. These processes determine the internal resistance in the battery and whether the electrode retains its capacity or gradually loses its ability to function.

To follow such changes, the group uses advanced characterization methods, including operando X-ray diffraction, total scattering with pair distribution function analysis, X-ray absorption spectroscopy and neutron scattering. These techniques make it possible to study the atomic scale structure of the electrodes while the battery is working. This is crucial because battery materials operate far from equilibrium, and the structures formed during cycling may be difficult or impossible to capture in conventional static experiments.

A recurring theme in the research is that the average crystal structure does not tell the whole story. Local distortions, short-range order, stacking faults and migration of individual metal ions can strongly influence ion transport, redox chemistry and structural stability. This approach brings new ideas towards rational design of new materials, where disorder is not a problem, but a property that can be understood, controlled, and used actively. At the Center for Sustainable Energy Materials, CENSEMAT, this idea is taken further: structural order and disorder are treated as key design parameters in future sustainable energy materials.