Yttrium-doped Li(Ni, Co)O2: an improved cathode for Li-ion batteries

Yttrium-doped mixed oxides, Li(Ni0.7−yYyCo0.3)O2, y=0.00–0.05 have been synthesized and characterized. Their cathodic behavior has been examined in cells with lithium metal as anode. The limit for Y solubility is ≤0.05. The beneficial effect of Y is evident by way of increased capacity — retention during charge–discharge cycling, up to 100 cycles at 0.2C rate and up to 50 cycles at 1C rate. Cyclic voltammograms indicate that the phase transitions which usually occur in LiNiO2 during cycling, are suppressed by Co- and Y-doping but not completely eliminated. A reduced hysteresis in the anodic and cathodic peak voltages observed for y=0.05 is an indication of excellent reversibility of the electrode. Thermal stability of the charged cathode is not, however, improved by Y-doping.