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Plotting the Aging Path of Batteries

Dr. Frieder Herb, longstanding ExtraEnergy associate and member, concluded his doctoral studies on the aging of batteries and fuel cells at the university of Ulm in 2010. Thanks to his research it is now possible to predict the lifespan of pedelec and e-bike batteries.

Dr. Herb invested several years in a systematic analysis of how batteries and fuel cells age. Among others, he studied the aging process and the types of problems which arise as batteries get older.

By simulating aging, Herb was able to speed up his investigation of what happened in real-world applications. From his investigations he was able to construct and verify aging models for lithium-ion batteries and Polymer electrolyte membrane (PEM) fuel cells.

"One problem that occurs with aging is, for instance, that the electrode surface mutate. High temperatures alter the material quicker and close up the pores, which, in turn, leads to increased resistances," said Herb.

Both models were integrated in a vehicle simulation and the impact of the value changes occurring in a battery and fuel cell monitored as they age. By reducing the dynamic of the fuel cell the aging process of the cell could be slowed. The lowest aging activity was measured in a big battery and a big fuel cell.

In the simulation Herb used so-called Raff tests to put batteries under additional stress, by exposing them to high temperatures and higher charge-turnarounds. The excessive stress levels were then calculated back to levels experienced in actual, real-world applications. In combination with the statistics collected on the measured test rides conducted by ExtraEnergy, a trip in the city could, for instance, be simulated over many years.

The outcome of the simulation: a prediction for the speed at which a battery of a pedelec ages when used in the city, without having to expose it to a long-term test.

With the Herb research as foundation, ExtraEnergy should now be able to integrate the aging of pedelec batteries and e-bikes in its tests.

Click here to download the entire thesis (in German only).

Copy: Dr. Frieder Herb
Translated by: Christoffel Volschenk
Photo: Susanne Brüsch

17 February 2011



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