Polarization Study and AC-Impedance Measurement of a Lithium-ion Battery with an Extra Positive-side and an Extra Negative-one Using Three Reference Electrodes

Abstract

Three reference electrodes (Li/Li⁺) were embedded to the three sides (symmetrical (R1), Extra Positive-side (R2) and Extra Negative-side (R3)) of a square lithium-ion battery (LIB) cell, and electrical potential changes of the positive (P) and negative (N) electrodes against the reference electrodes during charge and discharge were studied. AC impedance measurement also was conducted with the cell. During charge of the cell, the negative electrode potential at the Extra Positive-side (N-R2(+)) was maintained below 0 V vs. Li/Li⁺ which means the high risk of Li metal deposition at that area. Contrary to this, at the Extra Negative-side (N-R3(−)), the potential was maintained above 0 V vs. Li/Li⁺ during and after charge and discharge of the cell. AC impedance spectra of the positive electrode or the negative one against the three reference electrodes were quite different with each other. AC impedance spectra can be influenced by the relaxation current between the positive electrode (P) and the Extra Positive-side (P-Extra) or by that between the negative electrode (N) and the Extra Negative-side (N-Extra).