Studies on the cycle life of commercial lithium ion batteries during rapid charge–discharge cycling

The impedance spectra of Li-ion batteries as a function of the number of charge–discharge cycles have been measured to study the cycle life of the commercial Li-ion battery (prismatic Sanyo UF653467) during cycling at 1 C charge–discharge rate. The individual electrodes in the batteries have been examined using XRD, transmission electron microscopy (TEM) and SEM. The results show that the Nyquist plots of commercial lithium-ion batteries are comprised of an inductive tail at high frequency followed by two semicircles at medium and low frequencies. The size of the semicircles at low frequency increase during cycling due to the increase in interfacial resistances of both cathode and anode. Thus, it may be used to predict the cycle life of the battery. XRD, TEM and SEM studies of the individual electrodes show that the cation disorder, microcracks of the LiCoO2 particles in the cathode and the increase in thickness of the passive film on the anode due to the reduction of the electrolyte are linked to the capacity fade of the battery during cycling.