The effects of pulse charging on cycling characteristics of commercial lithium-ion batteries

The effects of a pulse charging technique on charge-discharge behavior and cycling characteristics of commercial lithium-ion batteries were investigated by comparison, with the conventional direct current (dc) charging. The impedance spectra and cycling voltammograms of Li-ion batteries cycled by both protocols have been measured. The individual electrodes in the batteries have also been examined using XRD and SEM.. The results show that pulse charging is helpful in eliminating concentration polarization, increasing, the power transfer rate, and lowering charge time by removing the need for constant voltage charging in the conventional protocol. Pulse charging interrupts dc charging with short relaxation periods and short discharge pulses during charging, and also improves the active material utilization giving the battery higher discharge capacity and longer cycle life. Impedance measurements show that the magnitude of the interfacial resistance of the batteries cycled both by pulse charging and de charging is small. However, at the same number of cycles, the interfacial resistance of the pulse charged battery is larger than that of dc charged. The batteries after 300 cycles charged by pulse charging show higher peak currents during both forward and reverse scans indicating higher reversibility of the electrodes. XRD and SEM studies of the individual electrodes indicate that pulse charging maintains the stability of the LiCoO2 cathode better than dc charging and inhibits the increase in the thickness of the passive film on the anode during cycling. (C) 2001 Elsevier Science B.V. All rights reserved.