ZIRCONIA-COATED LITHIUM COBALT OXIDE AS A LONG-CYCLING CATHODE FOR LITHIUM BATTERIES

摘要

A commercial sample of LiCoCo_2 was coated with ZrO_2 by sol-gel and mechano-thermal processes. The effects of the coating method and the precursor used in the sol-gel coating process were studied. Electron microscopic images of the coated particles revealed the presence of a compact coating over the cathode particles. XRD and ESCA results suggested the formation of substitutional compounds of the composition Li_xZr_yCo_(1-y)O_(2+0.5y) on the surface of the cathode. Coating levels of 0.3 and 1.0 wt.% were found to be optimal in terms of cyclability for the materials coated by the sol-gel and mechano-thermal methods, respectively. At these coating levels, the R-factor values, determined from XRD data, were the lowest. The maximum improvements in cyclability registered at a 0.2 C rate were about eight-fold with the sol-gel and mechano-thermal coating methods. Cyclic voltammetric studies showed that the coating led to a suppression of the cycle-limiting phase transitions accompanying the charge-discharge processes.