The effects of overlithiation on the structural modifications and cell performances of Li[Li-x(NizCo1-2zMnz)(1-x)]O-2 materials with different ratios of Co/(Ni+Mn) were investigated. We prepared the Li[Li-x(NizCo1-2zMnz)(1-x)]O-2 with a series of compositions of z = 0.1-0.4 and x = 0.00-0.10 by a spray-drying method. We found that the effects of overlithiation on cell performances may depend on the Co/(Ni +Mn) ratio; the discharge capacity of the overlithiated Li[Li-0.05(Ni0.05Co0.83Mn0.11)(0.95)]O-2 was more severely degraded than the stoichiometric Li(Ni0.04Co0.84Mn0.12)O-2 with cyclings, whereas Li[Li-0.05(Ni0.37Co0.23Mn0.40)(0.95)]O-2 showed better capacity-retention ability and C-rate capability than those of Li(Ni0.34Co0.22Mn0.44)O-2 because of decreasing structural disorder (cation mixing) by overlithiation. We also found that structural modifications of the synthesized materials during first charging were changed by overlithiation but mainly depended on the Co/(Ni + Mn) ratio. (c) 2007 The Electrochemical Society.