Ida Nielsen

What inspired you to pursue this research topic, and how has your understanding of it evolved throughout your PhD journey?

My research is about Prussian blue analogue (PBA) cathode materials for sodium-ion batteries. My interest in materials for a greener transition began during my Master’s studies, and therefore, I wanted to work in this field for my PhD. Batteries play a crucial role in this transition, so when I saw the project, I was intrigued. The PBA I work with contains water, which is detrimental to the battery’s performance and is therefore removed before building the battery. However, the water helps stabilize the structure by keeping it enlarged, which facilitates open channels for ion transport. By utilizing this effect and by replacing water with a battery-compatible molecule, the battery's performance can be further enhanced. To do this, we need to know where in the atomic structure the water is and how the water moves around within the structure. At the beginning, we had a very simplified understanding of this system, but it has proven to be much more complicated. It has been challenging but also very rewarding to dive deeper into and obtain a new understanding of this material.

Can you describe a key finding or insight from your research that you’re especially proud of—and why it matters in your field?

The movement of water within the material is vital for understanding what other guest molecules we can implement instead. We used quasi-elastic neutron scattering to gain insight into the local diffusion and found that water is trapped inside small cavities within the structure. Water moves around randomly within these cavities, thereby stabilizing the structure. This means that another guest molecule should be able to fulfill the same role. What we also found is that a small fraction of the water is coordinated to sodium. This is not ideal in a battery since we risk that the water leaves the structure during cycling (sodium extraction and insertion), thereby losing the stabilizing effect over time. This is the first time we have an understanding of the movement of water, and it actually gives clear requirements for what other guest molecule we want instead of water. It was also super fun to do the experiments at SINQ in Switzerland.

How do you hope your research will be used or built upon after your defense—whether in academia, industry, or society at large?

I hope I have shown that even though a material is fully commercialized, we still need to be careful with our characterization and open to new interpretations of the system when provided with new data. My research has demonstrated the level of rigor needed to characterize sodium-based PBAs, and that a lot of fundamental knowledge is still missing for a compound that is being thrown into applications. In addition, neutron scattering is not widely used by industry, and hopefully, they would be more open to such methods due to the highly valuable information you can get from these techniques. There are still a lot of unanswered questions about PBAs that need to be answered to be able to design new, improved PBAs for battery applications and also for other applications.

What role has SwedNess played in your journey?

SwedNess has given me many opportunities throughout my PhD, such as great training in neutron scattering, as well as opening the door to a fantastic community of researchers. Their support for all my travels to different facilities and conferences has been crucial for both my PhD research and my future career. One of my favorite times during my PhD has been to visit Matt Tucker at the Spallation Neutron Source in Oak Ridge, USA (Neutrons at ORNL) during my SwedNess extended stay. I learned a lot from being at a world-class facility surrounded by neutron experts. SwedNess has also provided the knowledge foundation for my upcoming postdoc position at PSI Paul Scherrer Institute in collaboration with DanScatt, where I will continue doing research in energy materials using neutron scattering and also take part in the daily work on a neutron instrument. I look forward to expanding my knowledge and network in my new role!

Thesis: Water in Prussian Blue Analogues: A Blessing or a Curse?