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

Nawfal Al-Zubaidi R-Smith,Albert Groebmeyer,Sascha Wagner,Mykolas Ragulskis,Bob Zollo,Johannes Pumsleitner,Manuel Kasper,Ferry Kienberger

doi:10.1109/tim.2021.3100331

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.

Highlights

To prove that the alternating current internal resistance (ACIR) values are independent of the channel and the cell position within the tray, the tray was rotated by 180° with respect to the fixture, and the ACIR was measured again
The ability of detecting such minor differences is of relevance for battery pack producers because cells need to have the same performance within a battery pack, otherwise the pack may show lower performance or premature retirement [30]
The plot of state of health (SoH) versus ACIR shows that cells with high ACIR values have correspondingly lower SoH values

Summary

Introduction

In this study we demonstrate grading and testing of 256 cylindrical cells that are placed in a 16x16 tray by performing multiplexed measurements using alternating current internal resistance (ACIR) and open circuit voltage (OCV). The ACIR measurement method consists of generating a sinusoidal alternating current (AC) excitation signal with a current amplitude IAC at a single frequency, typically 1 kHz which is applied to the battery under test. For battery characterization and classification, the ACIR excitation current is typically kept low to maintain the cell under stable and linear conditions. The ACIR method can be considered as a subset of broad-band frequency electrochemical impedance spectroscopy (EIS), with ACIR measuring only at a single frequency point of 1 kHz. Typically, only the real part of ACIR is used, which is called internal resistance (Rint).

Methods

Results

Conclusion