A non-aqueous lithium ion secondary battery is composed of a positive electrode layer, a negative electrode layer, and a non-aqueous electrolyte. The positive electrode layer contains positive electrode active material of the following formula: Li.sub.x Ni.sub.1-y Co.sub.y-z M.sub.z O.sub.2-a X.sub.b wherein M is Mg, Ca, Ba, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Nb, Mo, Ag, Ta, W, B, Al, Ga, In, C, Si, Ge, Sn, or Pb; X is a halogen atom; 0.2