Kristoffer is working towards his PhD at DTU Energy. In a nutshell, he used X-rays and Neutrons to characterise batteries. He grew up in Brussels, but moved to Copenhagen in 2013 to study Physics and Nanotechnology at DTU, and stayed on afterwards to conduct a Masters degree and then a PhD student. Alongside his research work, he competes professionally in triathlon, and enjoys the challenge of juggling two very different careers.

In his work at DTU, Kristoffer's aim is to increase our understanding of degradation mechanisms in batteries. This ranges from fundamental mechanisms related to a specific electrode material and its crystal structure, to degradation in commercial battery cells related to the build of the cell as a whole.

He does this using hard synchrotron X-ray radiation, and neutron diffraction and scattering, to perform in situ and operando studies. The complementarity of neutrons and X-rays is utilised to obtain more information about the processes taking place inside a battery during operation. With neutron radiation, it is possible to penetrate large samples, e.g. batteries encased in steel containers, while being very sensitive to lithium, due to its comparatively large neutron scattering cross section. This means that it is possible to get information about the structural environment of lithium during operation, as well as directly obtain information about lithium occupancy, which is not easily achievable by in situ X-ray diffraction, where the lattice parameters of the observed crystalline phase is used to estimate the lithium content. Using synchrotron X-ray radiation, it is possible to obtain extremely good angular resolution, which makes it possible to determine small changes in unit cell parameters and symmetry. Using focused synchrotron X-ray radiation it is also possible to obtain good spatial resolution, so that phase distribution and redistribution as a function of time can be determined.

At DTU, they are working on three distinct battery systems. The first is primary and secondary zinc-air batteries, where we have collected in situ XRD data mapping, in space and time, the phase transition between Zn and ZnO in the anode during operation. The second is commercial 18650 (a cell format) LiNiMnCoO based Li-ion cells, where we with the help of two bachelor students have done an ex-situ investigation of spatial inhomogeneities in degradation rates. These experiments will serve as a prelude to synchrotron based in situ experiments later on. Our third project is on the novel battery cathode material LiNiMnO where, in collaboration with Haldor Topsøe A/S, they are investigating structural degradation in the spinel material related to different electrochemical charge/discharge regimes confining activity to specific Ni oxidation steps.