Multi-Reference Electrode Lithium-Ion Pouch Cell Design for Spatially Resolved Half-Cell Potential and Impedance Measurements

Reliable experimental methods for measuring local potentials in lithium-ion battery cells are challenging but vital for a deep understanding of internal processes at the individual electrode level, and to parameterize and validate electrochemical models. Different three-electrode setups and reference electrodes (REs) have been developed in recent years. Some are based on custom laboratory setups or are small, e.g. coin cell sized. This work addresses internal potentials and half-cell impedances in the widely used single-layer pouch (SLP) cell format and proposes a novel multi-reference electrode cell design, enabling spatially resolved measurements. For the first time, it is shown how multiple 25 mu m and 50 mu m thin gold wire REs, together with a larger LTO-RE, can be used to study occurring inhomogeneities, considering the geometrical anode overhang. Special attention is given to the subtleties of the measurements and their interpretation. Multiple REs allow plausibility checks and confirm stability for both types during a continuous measurement period of more than 7,500 h (>10 months), demonstrating suitability, e.g. for long-term cycling measurements. Results from electrochemical impedance spectroscopy (EIS) and half-cell potential measurements at low currents of C/100 and during fast charging at up to 3C highlight the versatility of the easily reproducible cell design.