Consistent battery cell quality is crucial for the high-volume production of lithium-ion battery systems. A single weak cell can be the limiting factor for the performance, lifetime, and safety of the overall battery system. However, even for mass-produced cell types, quality differences within and between production batches exist due to production process variations and environmental factors during storage as well as shipping. In this presentation, therefore at first the existing technical methods for cell quality assessment during incoming goods inspection are discussed in terms of practicability, capital expense and correlation with application relevant cell parameters.
Afterwards, a new quality assessment method and a high-throughput cell testing system, based on fast electrochemical impedance spectroscopy (EIS), for lithium-ion battery cells is presented. With this technique, an individual cell’s EIS measurement can be performed within seconds for a selected frequency range. This technique enables to perform semi- or even fully automated mass-screenings of large numbers of battery cells.
The talk will show real-life results of the impedance spectra of 4000 commercial cells, which have been measured during an incoming goods inspection procedure before these cells were integrated into an application. A detailed statistical analysis of the measured data is performed to assess the parameter spread between individual cells and the usability of the method for cell quality grading.
Furthermore, the results of aging tests performed on a subset of the measured cells are discussed. These show a high correlation between the EIS assessment at begin-of-life and the resulting cycle life of the cells.