Contaminant Detection System using High Tc SQUID for Inspection of Lithium Ion Battery Cathode Sheet

We report the fabrication of magnetic metallic contaminant detectors using multiple high-Tc SQUIDs (superconducting quantum interference devices) for a lithium-ion battery cathode sheet. Finding ultra-small metallic foreign matter is an important issue for a manufacturer because metallic contaminants carry the risk of an internal short. When contamination occurs, the manufacturer of the product suffers a great loss from recalling the tainted product. Hence, a detection method of small contaminants is required. Preventing such accidents is also an important issue for manufacturers of industrial products. Given the lower detection limit for practical X-ray usage is in the order of 1 mm, a detection system using a SQUID is a more powerful tool for sensitive inspections. We design and set up an eight-channel roll-to-roll high-Tc dc-SQUID inspection system for a lithium ion battery cathode sheet. We report the evaluation results that the detection of a small φ18 -μm steel particle on a lithium-ion battery cathode sheet was successfully done.