Two- and three-electrode impedance studies on 18650 Li-ion cells

Two- and three-electrode impedance measurements were made on 18650 Li-ion cells at different temperatures ranging from 35°C to −40°C. The ohmic resistance of the cell is nearly constant in the temperature range studied although the total cell impedance increases by an order of magnitude in the same temperature range. In contrast to what is commonly believed, we show from our three-electrode impedance results that, the increase in cell impedance comes mostly from the cathode and not from the anode. Further, the anode and cathode contribute to both the impedance loops (in the NyQuist plot).