A cathode composition for a lithium-ion battery having the formula Li[M¹_(1-x)Mn_x]O₂ where 0x1 and M¹ represents one or more metal elements, with the proviso that M¹ is a metal element other than chromium. The composition is in the form of a single phase having an O3 crystal structure that does not undergo a phase transformation to a spinel crystal structure when incorporated in a lithium-ion battery and cycled for 100 full charge-discharge cycles at 30 C. and a final capacity of 130 mAh/g using a discharge current of 30 mA/g.