Trigger for Format Dependent Aging Identified
New battery materials are typically first tested in coin cells before being validated in more application-oriented pouch cells. The advantage of coin cells is that they can be assembled quickly, inexpensively, and with minimal material consumption. However, they age considerably faster than pouch cells. This complicates the transferability of research findings and carries the risk of ruling out promising materials too early. To identify the causes of this format dependent aging, a team from MEET Battery Research Center at the University of Münster subjected coin cells and pouch cells containing identical materials to cyclic and calendar aging and compared the results.
Coin Cell Housing Identified as a Potential Cause
In contrast to pouch cells, coin cells consistently lose capacity more rapidly during both cyclic and calendar aging. The discrepancy increases with rising temperature. “This makes it difficult to transfer results from one format to the other,” explains MEET PhD student Kai Büscher.
The researchers then systematically investigated possible triggers. They excluded factors such as pressure, electrolyte and additive amounts, lithium plating, and resistance as the primary causes. “Our findings suggest that the coin cell housing is not completely sealed. This may allow moisture to enter the cell, promoting decomposition reactions and accelerating aging,” explains Büscher. Furthermore, additional sealing of the coin cells with pouch film substantially reduced the aging effect.
Dr Philip Niehoff, deputy head of the MEET research division “Cell System”, adds: “To ensure that the results can be transferred as accurately as possible, coin cells should be studied at low temperatures and with shorter test durations, or they should be additionally sealed.” These findings could help researchers evaluate battery materials more reliably and reduce the need for time-consuming tests in larger cell formats. The research team intends to investigate the remaining differences between the two cell formats in more detail in future studies.
Entire Study Available
The detailed results have been published in the “Journal of The Electrochemical Society” by Kai Büscher, Bastian Vetter, Dr Sascha Nowak and Dr Philip Niehoff, MEET Battery Research Center, as well as Prof. Dr Martin Winter, MEET Battery Research Center and Helmholtz Institute Münster of Forschungszentrum Jülich.