NOVELTY - A solid solution comprises lithium-containing transition metal oxide. The lithium-containing transition metal oxide has layer structure site and site which changes to spinel structure by performing charging or discharging in a predetermined electric potential range. The spinel structure change ratio of layer structured site changes to a spinel structured site having spinel structure is 1, and the spinel structure change ratio of the transition metal oxide containing solid solution lithium is 0.25 to less than 1.    USE - Solid solution is used for positive electrode of nonaqueous electrolyte secondary battery (all claimed) for driving power supply and auxiliary power supply e.g. motor of an electric vehicle, fuel cell electric vehicle and hybrid electric vehicle.    ADVANTAGE - The solid solution has high discharge capacity and capacitance maintenance factor.    DETAILED DESCRIPTION - A solid solution comprises lithium-containing transition metal oxide of formula: Li1.5NiaCobMnc(Li)dO3. The lithium-containing transition metal oxide has layer structure site and site which changes to spinel structure by performing charging or discharging in a predetermined electric potential range. The spinel structure change ratio of layer structured site (Li2MnO3) changes to a spinel structured site having spinel structure (LiMn2O4) is 1, and the spinel structure change ratio of the transition metal oxide containing solid solution lithium is 0.25 to less than 1.    a=more than 0 and less than 1.4;    b=0 to less than 1.4;    c=more than 0 and less than 1.4;    d=more than 0.1 and 0.4 or less;    a+b+c+d=1.5;and    a+b+c=1.1 to less than 1.4.    An INDEPENDENT CLAIM is included for nonaqueous electrolyte secondary battery, which consists of positive electrode (11) and negative electrode (12).    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of lithium ion secondary battery.    Lithium ion secondary battery (1)    Positive electrode (11)    Negative electrode (12)    Electrolyte layer (13)    Cell layer (14)    Positive electrode lead (21)