The electrochemical and thermal stabilities of Li[Ni0.58Co0.28-xMn0.14+x]O-2 (x = 0-0.14) materials as cathodes for lithium secondary batteries were investigated. Increasing Mn content compared to Co in Li[Ni0.58Co0.28-xMn0.14+x]O-2 resulted in elongations of the a and c axes due to an increase in the Ni2+/Ni3+ ratio. The X-ray absorption near edge spectra of Li[Ni0.58Co0.28-xMn0.14+x]O-2 (x = 0-0.14) confirmed that the oxidation state of Ni changed from 3+ to 2+ with increasing Mn content. Variation in Mn content (0.14-0.28) did not affect the discharge capacity but increased the cycling and thermal stabilities. The electrochemical and thermal properties of the Li[Ni0.58Co0.14Mn0.28]O-2 cathode material were superior to those of Li[Ni0.58Co0.21Mn0.21]O-2 and Li[Ni0.58Co0.28Mn0.14]O-2. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3497304] All rights reserved.