Effect of calcium or yttrium doping on cation ordering and electrochemical performance of Li(Ni0.80-xCo0.15Al0.05Mx)O-2 (M = Ca, Y) as a Li-ion battery cathode

The electrochemical performance of Li(Ni-0.80-xCo(0.15)Al(0.05)M(x))O-2 (NCA) cathode was demonstrated to be improved by calcium and yttrium doping. Samples were synthesized by ultrasonic sound-assisted co-precipitation method which satisfied precipitation of nano-sized particles around 20 nm. Doping elements were introduced to the structure by solid-state reaction route and single phase, layered Li-0.993(Ni0.804Co0.154Al0.035Y0.014)O-2 +/-sigma and Li-0.991(Ni0.801Co0.152Al0.037Y0.019)O-2 +/-sigma samples were successfully synthesized. Lattice parameters and site occupancy of the atoms were calculated by Rietveld refinement. Occupancy refinement of the atomic sites confirmed that doping elements occupied the transition metal layer as it was aimed. The presence of doping elements in the transition metal layer stabilized nickel and decreased the amount of cation mixing. Y-doped NCA sample exhibited the highest initial specific discharge capacity (157 mAh g(-1)) and Ca-doped sample showed the highest rate capability. Pristine NCA showed the lowest capacity, in any case, indicating the necessity of further treatment to achieve improvement in NCA cathode