Criteria for Reliable Electrochemical Impedance Measurements on Li-Ion Battery Anodes

Specially designed five-electrode cells contained two types of mixed ionic-electronic conductor ~MIEC! lithium-insertion anodes. These were graphite or Sn1.3Al0.3Ti1.7O1.95(PO4)3 tin composite oxide ~TCO! bonded powders sandwiched between nickel mesh current collectors as working lithium-ion anodes, with Li foils on both sides as reference electrodes, outside of which were two further Li foils, or a Li foil and an electrode identical to the graphite anode, as counter electrodes. The cells were used to investigate the influence of the counter and reference electrodes on the impedance of the working electrode. The impedance of the graphite anode measured using a Li foil counter electrode was higher than that using the graphite counter electrode. This was because the low electrochemical reaction kinetic rate on the Li counter electrode influenced the electric field and potential distribution in the intervening electrolyte, resulting in an unstable reference electrode potential. Using the only one Li foil as the counter electrode with the reference electrode on the opposite side can reduce the influence of the counter electrode~s! on its impedance. The transmissive impedance and ionic impedances of both types of MIEC anodes were also studied. © 2002 The Electrochemical Society. @DOI: 10.1149/1.1530150# All rights reserved.