No abstract

We have developed a system using high-temperature radio frequency superconducting quantum interference device (RF-SQUID) for detecting metallic contaminants in the liquid component of a lithium-ion battery. Although we have executed detection experiments using a simulated system without liquid in the past[1], we have developed a new system to inspect real liquid components. Small cylindrical metallic contaminant samples were fabricated using a gallium-focused ion beam to evaluate the detection performance. Tap water containing the metallic contaminant sample was poured into the tube using a pump, and the magnetic signal of the contaminant matter was detected using the RF-SQUID. Among the tested small metallic contaminant samples, the volume of a minimum detectable metallic contaminant was evaluated to be 2 × 104 μm3, which corresponded to that of a spherical sample with a diameter of 33 μm and a sensitivity of a signal-to-noise ratio of more than three. Moreover, the dependence of the detected signal strength on the volume of the metallic contaminant samples is discussed here.

The market for high-performance lithium-ion (Li-ion) batteries is growing rapidly as automobiles become electrified. The presence of small metallic particles of the order of 10 µm in a battery is likely to cause failure; therefore, it is important to eliminate them. We have developed a prototype system for detecting metallic foreign matter in liquid components for Li-ion batteries using a high-temperature superconducting radio-frequency superconducting quantum interference device, which is a highly sensitive magnetic sensor. Signal waveforms of a magnetized metallic piece passing through a trench located below the SQUID were measured. We found that the waveform depended on the direction of the magnetic dipole at the time of detection and could be roughly divided into six categories to explain all the experimental results. The maximum magnitude obtained for each sample was plotted against the equivalent spherical diameter of the sample. Our results indicate that the signal intensity was proportional to the cube of the sample diameter and that particles larger than φ20 µm × 30 µm (equivalent spherical diameter 23 µm) were detected with signal-to-noise ratio ≥3.

The operation of the RF SQUID is restricted by the condition that the inductance parameter β L must be in the range of 1−3. However, since both ends of the Josephson junction (JJ) of RF-SQUID are shorted, it is difficult to non-destructively estimate the critical current (IC ). Thus, we proposed a technique for the non-destructive measurement of the IC of a high-temperature superconducting (HTS) RF-SQUID ring by evaluating the behaviour of the flux in superconducting thin films using a SQUID magnetometer. A superconducting ring sample with JJ was placed below the HTS SQUID magnetometer and cooled down to 77 K. The change in the SQUID output was monitored on application of the magnetic field. When increasing the field, the waveforms indicated that the screening current of the ring sample exceeded the I C of the JJ, and the JJ became a normal-conducting state. As a result, we estimated the IC of the JJ of this sample as 134 μA using the values of mutual inductance and the coupling coefficient α between the coil and the sample.