We have developed detection system for liquid components of lithium-ion batteries with High-Tc RF Superconducting QUantum Interference Device (RF-SQUID). In the previous experimental system, liquid was not flown but metallic sample stack on a fishing line in the pseudo nylon tube was moved by an electric motor ^[1]. The results using the system suggested that it is possible to detect stainless steel spheres with a minimum diameter of approximately 25 μm ^[1]. Thus we tried to develop a new system to detect metallic contaminant in the liquid. The rf SQUID was patterned with an YBa₂Cu₃O_7-δ on a 10 mm × 10 mm SrTiO₃ bi-crystal substrate (36.8 degree). The outer diameter and inner diameter of the RF-SQUID pattern are 9 mm × 9 mm and 100 µm × 100 µm. The width of the Josephson junction was 4 mm. The flux white noise level was 60 µΦ₀/Hz^1/2. The schematic of the detection system is shown in Fig.1. The RF-SQUID was installed in a microscope-type cryostat. The rectangular cross-sectional pipe was placed below the RF-SQUID so that the space between the RF-SQUID and a liquid flow becomes as small as possible. These components were installed in a two-layered µ-metal magnetically shielded cylinder. A stainless steel (Fe - 18%Cr - 8%Ni) wire was cut by Ga Focused Ion Beam for the preparation of metallic contaminant samples. The sample piece was cylindrical with a diameter of 50 µm and a length of 50 µm. Tap water was used as the liquid in which the sample piece was moved. The typical signal when the sample piece was detected by the RF-SQUID is shown in Fig.2. The magnetic signal of 8.7 mV_P-P could be obtained with a signal-to-noise ratio (SNR) of more than five (Threshold: SNR > 3). The detection of smaller metallic contaminants is in progress.

[1] S. Tanaka, M. Sagawa, K. Hayashi, and T. Ohtani, “Development of Metallic Contaminant Inspection System Using High-Tc rf-SQUID for Li-ion Battery Liquid Components”, IEEE Trans. on Appl. Supercond., 2986315_1-4, (2020).

Keywords: High-Tc SQUID, Contaminant detection, Lithium ion battery, Battery slurry