Multiplexed 16 × 16 Li-Ion Cell Measurements including Internal Resistance for Quality Inspection and Classification

Abstract

Characterization and classification of lithium-ion batteries (LIB) are of high relevance for cell and battery producers, especially with the rising demands on LIBs for electric vehicle applications. We present a compact measurement station with 256 multiplexed channels to measure the open-circuit voltage (OCV) and the alternating current internal resistance (ACIR) of a tray of 256 cylindrical cells. Four different cell types were distinguished based on the ACIR values ranging between 11 and 22 '\text{m}\Omega '. The measurement station performance was assessed based on the cell-fixture recontacting error and the electronic noise of the channels. Several calibration workflows of different complexity were evaluated. Data correction for the measure station was done by a two-term calibration procedure, including a short and gain correction. This resulted in a 67% improvement on the real part of ACIR and 83% on the imaginary part both compared to a bench-top-based reference system. Electromagnetic finite element method (FEM) modeling was done to model the cables and the cell fixture, including different wire lengths. The state of health (SoH) of cycled cells was computed, and their correlation to ACIR was discussed, including the electrochemical interpretation based on an equivalent electric circuit model. Overall, we show how this multiplexed measurement station can be used for classification and LIB quality control in battery manufacturing.