Development of low-impedance standard for safety evaluation of storage cells

In order to establish reliable diagnostic method for safety evaluation of storage cells, we are developing a low-impedance measurement system traceable to DC and LF electrical standards. Preliminary impedance measurements for lithium-ion battery cells in the range of 10 mHz - 10 kHz demonstrated that the impedance value for unused cells is clearly distinguished from that for used-up cells. Impedance spectra for the unused cells which are obtained under 100 mΩ indicate that the evaluations of the uncertainties should be required for detecting a faint sign or a symptom of degradations of storage devices.