Synthesis and characterization of LiNi1-x-yCoxMnyO2 as the cathode materials of secondary lithium batteries

LiNi1-x-yCoxMnyO2 (0 less than or equal to x 0.5, 0 less than or equal to y less than or equal to 0.3) were prepared by heating Ni1-x-yCoxMny(OH)(2) a nd LiNO3 in flowing oxygen for 10 h at 550 degrees C, followed by another h eating at 750 degrees C. The XRD patterns of LiNi1-x-yCoxMnyO2 (0 less than or equal to x less than or equal to 0.5, 0 less than or equal to y less th an or equal to 0.3) samples with different x and y values show a pure phase of layered hexagonal structure. The lattice parameters a, c and the unit c ell volume are found to decrease with increasing x in LiNi1-xCoxO2 The part ial substitution of Ni by Co and Mn as in LiNi1-xCoxO2 and LiNi1-yCo0.2MnyO 2 has a positive effect on lithium stoichiometry. However, lithium deficien cy is still found after a prolonged thermal treatments (24 h). Among the do ped materials synthesized, LiNi0.8Co0.2O2 and LiNi0.7Co0.2Mn0.1O2 have show n the best characteristics in terms of initial capacity and cycle life. (C) 1999 Elsevier Science S.A. All rights reserved.