Tom Rüther

My PhD involved me dealing with the characterisation of processes within lithium-ion batteries. Electrochemical impedance spectroscopy, coupled with an analytical methodology such as the distribution of time constants, is a common approach used to investigate the likes of new materials or to better comprehend ageing effects and performance properties.

It facilitates the development of long-life batteries, for example, or of algorithms that curtail charging time. One problem associated with this is the interpretation of some more complex properties within the distribution function. This research issue was investigated during my stay.

The group under Professor Plett and Professor Trimboli at the University of Colorado Colorado Springs deals with the physics-based modelling of lithium-ion batteries. Both professors are pioneers in the field of modelling and have published key fundamental works in this domain. They are currently in particular using reduced order methods, which can be used to directly analyse input-output relationships.

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Hiking on the snowy Seven Bridges Trail near Cheyenne Mountain

This procedure is novel and is at present only being applied by a few groups worldwide. It radically reduces the effort required for parametrisation of the models. Precisely this input-output relationship is relevant to analysing the distribution of time constants, so the models can be optimally used for deducing interpretations.

During my research stay, I applied sensitivity analysis methods in relation to the model to analyse individual processes within the distribution of time constants. I moreover investigated the influence of distributed processes on the distribution function and adapted the model to also scrutinise various measurement concepts relating to lithium-ion batteries with respect to their interpretation.

The start of my research stay involved me getting to know the research group and familiarising myself with the university. I cultivated a close direct exchange with both the professors and the other researchers in the group to enable me to better understand the models in particular. I had the opportunity to meet with both professors on a weekly basis during my entire stay, which substantially consolidated our collaboration.

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Exploring the Rocky Mountain National Park near Estes Park

Intensive exchange with other researchers at the university also gave me the opportunity to discuss additional aspects relating to battery technology. This specifically enabled me to arouse my interest in alternative topics such as lithium-metal batteries. In general, I greatly appreciated the regular and detailed exchange of ideas with my local colleagues from different nations. Indeed the different perspectives given our varied research training were extremely enriching. In comparison with Germany, I didn’t perceive any disparity in terms of working environment or social interaction with my colleagues or surroundings.

I had the opportunity at the end of my research stay to summarise my findings in an article for a peer review journal. (Addition by Mr. Rüther: The article was published in the Journal of The Electrochemical Society.) The experience of my colleagues in Colorado was a great benefit to me during the drafting process.

I was also able to take advantage of a number of services provided by the university. The sports opportunities in particular were something I exploited, which above all included hiking and use of the university’s large recreation centre. This provided the option of using a fitness studio, a climbing park and a swimming pool. Colorado sits directly at the foot of Pikes Peak, so I was especially able to enjoy the mountains and their associated snow. Indeed the Garden of the Gods Visitor and Nature Centre located in Colorado Springs was a place I loved to visit in my free time.

In addition to the landscape, the Saint Patrick´s Day Parade was another highlight of my stay. The parade was very reminiscent of our German Carnival. There are many cultural parallels to Germany to be found, yet also some differences. Especially the fact that almost all activities involve using a car nevertheless came as a surprise to me, despite familiar stereotypes.

I can say in summary that my stay was not only professionally and academically enriching, it also contributed to improvements in my command of English and gave me a better understanding of US culture. I still remain in touch with our group at the University of Colorado Colorado Springs and am extremely grateful to the DAAD-Stiftung for this unique opportunity.