A Comparison of NMC/Graphite Pouch Cells and Commercially Available LiCoO2/Graphite Pouch Cells Tested to High Potential

Li[Ni0.4Mn0.4Co0.2]O2 (NMC442)/graphite pouch cells containing the additives prop-1-ene-1,3-sultone, 1,3,2-dioxathiolane-2,2-dioxide and tris-(trimethyl-silyl) phosphite were compared to a variety of commercially available LiCoO2 (LCO)/graphite cells using charge-hold-discharge cycling experiments up to potentials between 4.2 and 4.4 V. Simultaneous electrochemical impedance spectroscopy measurements were made during cycling at 40°C. The effects of a 24 hour hold at the top of charge on the impedance and capacity retention were investigated for NMC and LCO cells, and to the subsequent changes to the positive and negative electrodes of some of the LCO cells. Only the LCO cells cycled to 4.2 V remained competitive against the NMC cells cycled to 4.4 V. LCO cells tested with this protocol to upper cutoff potentials of 4.35 V and 4.4 V exhibited severe capacity fade and positive electrode damage.