Development of Metallic Contaminant Detection System Using High-Tc RF SQUIDs for Li-ion Battery Slurry

We developed a metallic contaminant detector using a high-Tc (HTS) rf-SQUID for a lithium-ion battery slurry. For manufacturers producing industrial products, problems arising from metallic contaminants are critical issues requiring effective solutions. A detection system using a SQUID is a powerful tool for sensitive inspections on production lines. In this study, the slurry of a lithium-ion battery is the target of the inspection. Since slurry flows in a tube at the production lines, the SQUID sensor should be installed as close to the slurry as possible to obtain higher sensitivity. Therefore, we designed a micro scope type SQUID cryostat, in which the SQUID can approach the target as close as 1mm. We supposed the inner dimension of the slurry tube as 50 mm in diameter. The sample, a steel ball with diameter of 300 micrometers, was stuck on a thin fishing line and drawn by a motor in the tube. The signals scaled inversely well with the cube of the stand-off distance; it was found that the signal with a distance of 44 mm could be detected by extrapolating the slope line if the signal- to- noise ratio SNR > 3 was supposed as a threshold. The dependence on the sample diameter was also evaluated. After the systematic evaluation, the results suggested that a steel ball with a diameter of $33\ \mu \mathrm{m}$ can be detected.