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 investigat ed by comparison, with the conventional direct current (dc) charging. The i mpedance spectra and cycling voltammograms of Li-ion batteries cycled by bo th protocols have been measured. The individual electrodes in the batteries have also been examined using XRD and SEM.. The results show that pulse ch arging is helpful in eliminating concentration polarization, increasing, th e power transfer rate, and lowering charge time by removing the need for co nstant voltage charging in the conventional protocol. Pulse charging interr upts dc charging with short relaxation periods and short discharge pulses d uring charging, and also improves the active material utilization giving th e battery higher discharge capacity and longer cycle life. Impedance measur ements show that the magnitude of the interfacial resistance of the batteri es cycled both by pulse charging and de charging is small. However, at the same number of cycles, the interfacial resistance of the pulse charged batt ery is larger than that of dc charged. The batteries after 300 cycles charg ed by pulse charging show higher peak currents during both forward and reve rse scans indicating higher reversibility of the electrodes. XRD and SEM st udies of the individual electrodes indicate that pulse charging maintains t he 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.