For the preliminary evaluation of new active materials, separators, and electrolytes, coin cells are commonly used, as they require only small amounts of material and allow for easier and faster assembly than larger cell formats. However, industrial applications require larger cell formats, such as pouch cells. Interestingly, several studies report a worse performance of coins cells compared to larger pouch cells, yet the underlying reasons for this discrepancy remain under discussion. A deeper understanding of the aging mechanisms responsible for the inferior performance of coin cells is necessary to further improve their performance. Moreover, achieving a comparable performance between coin and pouch cells are beneficial for an efficient scale-up, saving time and cost.
This study, therefore compares calendaric (40°C) and cyclic (20°C, 40°C and 60°C) aging of commercially available 1 Ah pouch cells (LiFun Company) and coin cells. To ensure identical material in both formats, the electrodes and separator used in coin cells were directly punched from the commercial pouch cells. At 20°C, the coin cells exhibit a slightly faster capacity loss compared to pouch cells. However, at 40°C and especially at 60°C, the coin cells show a significant faster linear capacity fade. This resulted in a doubling of the capacity loss after 700 cycles at 40°C for the coin cells compared to the pouch cells. Calendaric aging tests conducted at state of charge of 0% and 100% at 40°C showed again increased capacity loss for coin cells. This suggests that there is an additional ageing mechanism in coin cells which is temperature-dependent but voltage-independent.
These findings provide new insights into the origin of the performance differences between coin and pouch cells. Coin cells have an additional temperature-dependent aging mechanism that causes faster capacity loss, particularly at increased temperatures.