[Object]There is provided an active material for a
lithium secondary battery, which has a high initial efficiency and a high
discharge capacity, and particularly has a high
discharge capacity at a low temperature (excellent low-temperature characteristic), and a
lithium secondary battery using the active material.[Solution]An active material for a
lithium secondary battery, which contains a
solid solution of a lithium
transition metal composite oxide having an α-NaFeO2
crystal structure, wherein the composition ratio of
metal elements contained in the
solid solution satisfies, Li1+x−yNayCoaNibMncO2+d (0<y≦0.1, 0.4≦c≦0.7, x+a+b+c=1, 0.1≦x≦0.25, −0.2≦d≦0.2), the active material has an X-
ray diffraction pattern attributable to a
space group R3-m (P3112), and in the
Miller index hkl, the half width of the
diffraction peak of the (003) is 0.30° or less and the half width of the
diffraction peak of the (114) plane is 0.50° or less. Further, the average of three
oxygen position parameters determined from
crystal structure analysis by the Rietveld method on the basis of the X-
ray diffraction pattern is preferably 0.264 or less.