Quality assessment of unactivated cells by A.C. impedance techniques

A.C. impedance measurements are demonstrated to be very effective in assessing the quality of reserve activated battery cells during fabrication. The impedance of four-cell bipolar batteries was measured over the frequency range 0.1 - 20 kHz. A parallel RC circuit was determined to be a good model for the unactivated cells. Capacitance is a sensitive measure of cell spacing consistency. Uniform and defect-free cells have a variation of ±3% in capacitance, and a sensitivity analysis of capacitance to cell spacing shows that this is equivalent to a ±1.5% variation in cell spacing. Bode plots identify defective cells with high resistance shorts not detectable through capacitance measurements.