Cathodic properties of (Al, Mg) co-doped LiNi_0.7Co_0.3O₂

Li(Ni_0.7Co_0.3)_1-a-bAl_aMg_b O₂ (a=0.00, 0.05 and a=0.05; b=0.02,0.05) compounds were synthesized and characterized by X-ray diffraction (XRD). Their cathodic behavior in coin cells with Li-metal anode and liquid electrolyte was studied by charge-discharge cycling at 0.11C (1C=180 mA/g) and 0.5C rate between 2.7 and 4.3 V and by cyclic voltammetry. The initial discharge capacity values of a=0.05, b=0.02; a=0.05, b=0.05 are 158 and 160 mA h/g, respectively, at 0.11C rate. At 0.5C rate, phases with a=0.05, b=0.02; a=0.05, b=0.05 show better capacity retention (82% and 90%, respectively) as compared to a=0.00, b=0.00; a=0.05, b=0.00 (62% and 67%, respectively) in the range 5-50 cycle. Cyclic voltammograms clearly indicate qualitative and quantitative changes as a result of Al- and (Al, Mg)-doping to give better reversibility of the cathode. Differential scanning calorimetry (DSC) data on the charged cathodes shows an increase in the decomposition temperature (T_d) by 25-34 °C accompanied by decreased heat evolution indicating better thermal stability of these (Al, Mg) co-doped (a=0.05; b=0.02,0.05) cathodic compositions as compared to pristine LiNi_0.7Co_0.3O₂ (a=b=0.0).