Active material and lithium ion secondary battery

An active material comprising a layered structure and a composition represented by the formula (1) below, the active material having:

• a ratio of a half width FWHM003 of a diffraction peak at a (003)-plane to a half width FWHM104 of a diffraction peak at a (104)-plane represented by the formula (2) below, where both the peaks are obtained by X-ray powder diffraction;
• and
• an average primary particle diameter of 0.2 μm to 0.5 μm.
• LiyNiaCobMncMdOx (1)
• [wherein the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and a, b, c, d, x and y satisfy the following formulae:
• 1.9≦(a+b+c+d+y)≦2.1, 1.0<y≦1.3, 0<a≦0.3, 0<b≦0.25, 0.3≦c≦0.7, 0<d≦0.1, and 1.9≦x≦2.1], and
• FWHM003/FWHM104≦0.57 (2).