Real-time Imaging of the Electric Conductivity Distribution inside a Rechargeable Battery Cell

Abstract

The aim of this study is to observe the spatial inhomogeneity of a rechargeable battery's electric conductivity distribution. Therefore, we have developed a system that uses the measurement results of a minute magnetic field that leaks from the cell to visualize, in real time, the cell's electric conductivity distribution. This system has a magnetic detection capability of 30 pT/Hz 0.5 (at 1 Hz); it measures the magnetic field distribution in the 240 × 240-mm range. This system has the ability to detect the 500-μA electric current that flows in a rechargeable battery 5 mm away from the sensor module. Because the magnetic signals are detected at the frequency synchronized with the alternating current flowing in the cell, this system is not affected by environmental magnetic field noise. Using this system, we have successfully visualized the short-circuit spot in a cell with significant self-discharge. Furthermore, we observe that the magnetic field distribution changes continually when the short circuit is being generated. The coordinate where the magnetic field distribution changed and the coordinate where metal precipitates were confirmed significant agreement.

Magnetic field microscope using high-sensitivity giant magneto-resistance sensor with AC field modulation

“…The magnetic field microscope system used for this study was developed by Integral Geometry Science Inc. [13][14][15][16] A schematic diagram of the magnetic field microscope system is shown in Fig. 2.…”

“…One promising application of such a sensor is magnetic field microscopes, in which small magnetic fields from defects in a semiconductor chip or lithium-ion battery are detected as magnetic field images. [13][14][15][16][17][18] In a semiconductor chip, a defect may result in a point short circuit and cause a small abnormal current. 13,17,18) In lithium-ion batteries, dendritic metal precipitated on an electrode [19][20][21] may cause a short circuit between electrodes and lead to thermal runaway.…”

“…For detecting small magnetic fields with a sufficiently high signal-to-noise ratio (SNR), the AC method is generally used. [13][14][15][16] In this method, an AC current or voltage is applied to the sample and a small AC magnetic field under the noise level is selectively detected by the phase detection method (lock-in amplifier). 25,26) The frequency used for this method is typically in the range of 1 Hz to 1 kHz for a magnetic field microscope.…”

“…31) MI sensors are currently used for magnetic microscopes to detect defects in semiconductor chips 13) and lithium-ion batteries. [14][15][16] For MR sensors, tunneling MR sensors with a detectivity in the order of pT/√Hz have been actively studied. [32][33][34][35] GMR sensors have less detectivity, 31) but they have an advantage of low-cost fabrication.…”

Power Batteries Health Monitoring: A Magnetic Imaging Method Based on Magnetoelectric Sensors

“…The TMR sensor also plays an important role in battery magnetic imaging. Researchers inversed the conductivity distribution in batteries according to the test results of magnetic field distribution, which furthered the identification of defect locations and short-circuit current intensity [ 15 , 16 , 17 ]. Nowadays, the resolution of the TMR sensor can reach several pT at the excitation frequency [ 18 ].…”