Cathode active material and lithium ion secondary battery comprising the same

Abstract

A cathode active material with high durability and a lithium ion secondary battery. The cathode active material is a cathode active material represented by a general formula Li(1+a)NixCoyMnzWtO2 (−0.05≦a≦0.2, x=1−y−z−t, 0≦y<1, 0≦t<1, 0<t≦0.03), wherein the cathode active material satisfies the following formula (1): σ1/t1≦0.92  (1) where t1 is an element concentration average of insides and grain boundaries of primary particles of a W element, and σ1 is an element concentration standard deviation of the insides and grain boundaries of the primary particles of the W element.

Dependencies are inferred from the claim text.