The Coulombic efficiency measurement (CE) is a promising method to quickly determine the potential lifetime of a cell. It will be demonstrated that high precision measurements are required to determine the CE of modern cells. For this purpose, a comparison of our in-house developed precision hardware and two commercially available hardwares is performed. Furthermore, it is shown by means of a model that the CE can be misleading when it comes to the determination of cell aging. As a better alternative, the (conventional) differential capacity analysis ( $\Delta$ C) is presented and the difference compared to CE is demonstrated by a precision measurement.

Due to the long life of lithium ion cells, it is difficult to measure their low capacity degradation from cycle to cycle. In order to accelerate the measurements, cells are often exposed to extreme stress conditions, which usually means elevated temperatures and high charging currents. This raises doubts as to whether the results obtained in this way are representative for real world applications. This work shows that, with the help of very precise capacity measurements, it is possible to determine cell aging in a few days even under normal operating conditions from cycle to cycle. To verify this, a self-built measurement system is used. After demonstrating the capabilities of the system, two different cycling schemes are used simultaneously to determine the various causes of aging—namely cycle aging, calendrical aging and self-discharge due to leakage currents.