Fast and High Resolution Expansion Measurement at an Audi e-tron Battery Cell

In this paper, an interferometric measurement method is described, which allows the measurement of the expansion of lithium-ion pouch cells with a temporal resolution of 40ms and a spatial resolution of 1.3 nm. An original Audi e-tron pouch cell with 12 mm thickness and 55 Ah capacity was measured at a charge current of 50 A.Within 60 seconds, an expansion of 2.57$\mu$m was measured, and within 6 seconds, an expansion of 195nm. The paper also includes cyclic aging with 200 cycles and expansion measurements by a scanning white light interferometer during charging from 0% to 100% SOC. Cyclic aging increases cell expansion at 100% SOC from 135.6 $\mu$m to 196.7 $\mu$m and reduces cell capacity from 55.1 Ah to 54.2 Ah.