| abstract |
A solid solution lithium-containing transition metal oxide includes a compound represented by chemical formula (1): Li 1.5 [Ni a Co b Mn c [Li] d ]O 3 , where a, b, c and d satisfy relationships: 0<a≦0.75, 0≦b≦0.5, 0<c≦1.0, 0.05≦d≦0.25, and a+b+c+d=1.5. A dQ/dV curve obtained in such a manner as to differentiate an open circuit voltage curve on a discharge side obtained by charging and discharging a lithium ion secondary battery using the compound as a positive electrode active material, fulfills math formula (1): A/B≦1.0 (where A represents a dQ/dV value at peak A located in a range from 3.0 V to 3.5 V in the dQ/dV curve, and B represents a dQ/dV value at peak B located in a range from 3.5 V to 4.0 V in the dQ/dV curve). |