LiCo1-yByO2 As Cathode Materials for Rechargeable Lithium Batteries

Several substituted layered lithium cobaltates of formula Li0.999Co1-yByO2 (0.05 <= y <= 0.35) were synthesized and characterized by X-ray powder diffraction, Raman and FTIR spectroscopy, magnetic measurements, and ESR experiments. The compounds have been investigated as cathode materials in rechargeable lithium batteries and galvanostatic cycling are reported. Structural data showed that particles crystallized in the R (3) over barm structural symmetry and single-phased can be grown free of any impurity up to the boron concentration y <= 0.25, except for the presence of nickel impurity, as Ni is always present in the cobalt precursors. The voltage profiles of electrochemical cells including these compounds as the cathode were monitored against Li anode. The overall capacity of the oxides has been reduced by the sp metal substitution. However, more stable cycling performances have been observed compared to the performances of the native oxides. At 4.4 V cutoff voltage, the Li//LiCo0.75B0.25O2 cell exhibits an almost constant gravimetric capacity of ca. 127 mA h/g up to the 16th cycle. The origin of the benefit of boron doping is discussed.