Abstract
While three-electrode coin cells are common and can distinguish electrochemical performance from anode and cathode, the electrochemical performance in such a small format cell would be different when cells scaled up in large format. A simple and practical three-electrode pouch cell has been designed which has not been reported in open literature. Due to its simple structure with no specific fittings or parts, the three-electrode pouch cell can be used in the development of large batteries with electrode geometries for automotive or large storage applications which is incapable from the three-electrode coin cells. This three-electrode pouch cell allows us to distinguish the voltage and resistance in individual electrode and monitor the electrode balance in large format cells. An example is provided in this work where the cell is cycled between 3.0V and 4.6V and is composed of an A12 graphite anode, a LiNi0.5Mn0.3Co0.2O2 (NMC 532 or NCM 523) cathode, a lithium foil reference, a microporous tri-layer membrane, and an electrolyte. By applying a hybrid pulse power characterization (HPPC) technique to this three-electrode pouch cell, resistances from both the anode and cathode are calculated. Resistances measured using HPPC are about 1.2 Ohm-cm2 at the anode and about 40 Ohm-cm2 at the cathode where the voltages for the resistances are near 4.3 V between the cathode and anode, 4.4 V between the cathode and lithium reference, and 0.1 V between the anode and lithium reference. Resistances using electrochemical impedance spectroscopy (EIS) are also compared with those obtained from HPPC. Differential voltage and differential capacity are analyzed to understand charge and discharge processes at both the anode and cathode and at different C-rates.
