Scanning mmWave Radar for Inspection of Thin Li-Ion Battery Electrode Films

The electrical properties of thin conductive films are important for the overall performance of many engineered systems but are especially important for Li-ion battery electrodes. Electrical measurements of electrodes are challenging because the thin conductive films are attached to conductive metal substrates. Estimating film electrical heterogeneity typically has been performed either by destructive or contact methods. In this work, 60-GHz mmWave imaging radar is used to spatially map the radar-reflection properties of films in a noncontact measurement. Theoretical radar returns for battery electrode films are reviewed, and a sensitivity analysis to conductivity and thickness changes is performed. A scanning system was constructed to move a radar module and radar-absorbing conduit across a battery film. Radar returns were recorded and mapped, demonstrating how this method could be used to study the evolution of film properties during manufacturing processes and for Li-ion battery film quality control. A paint analog and poly(vinylidene fluoride) (PVDF)-based carbon black (CB) film were used to demonstrate significant radar return changes during drying processes. Scanning of a commercial-quality Li-ion battery electrode film is reported. Film irregularities and blemishes impact the quality of scanned reflection data from the electrode film. Scanning mmWave radar could be an inexpensive method to interrogate the properties of thin films in manufacturing processes.