Extensive characterization of new cell materials or changes in production methods can be a time-consuming process, often taking several months for well-established chemistries. Nevertheless, there is a growing interest among battery manufacturers in understanding the performance and impact of emerging cell materials and production methods in a more expedited manner to ensure safety and quality under various usage and resting conditions. It is, therefore, necessary to know the impact of stress factors on the aging rate of the cells, without introducing specific aging mechanisms while also emulating normal usage conditions.
In this work, we investigate how stress factor combinations affect the aging rate. We have methodically investigated the cyclic aging of over 40-1Ah-pouch cells (NMC622/Graphite Lithium-Ion cell) supplied without electrolyte. The cells were filled with 1M LiPF6, EC/EMC 3:7, 2wt% VC and formation was done at 25°C. Four different stress factors (charge rate, discharge rate, rest time, and temperature) were considered most relevant for the degradation of cells. By constructing a cycling aging matrix using these stress factors, we test the cells under normal usage conditions without exacerbating specific aging mechanisms. Before cycling, we applied quasi-static pressure using two pressure plates, with the cell at 50% SoC. A performance test protocol was used every 100 cycles to obtain performance indicators at 25°C for all the cells.
The result of this work will provide the basis for the analysis and ranking of stress factor combinations for cells of similar chemistry. The stress factor ranking will serve as a guide in the selection of testing conditions for future tests. Furthermore, the dominant aging mechanism induced by a test condition can be determined from post-mortem studies and correlated to non-destructive electrical measurement results.