NOVELTY - An electrode consists of an electrode-mixture layer comprising particles of a lithium-containing complex oxide having a BET specific surface area of 0.3 m2/g or less. The content of primary particles having a size of 1 mu m or less is 30 vol.% or less with respect to all primary particles. The complex oxide contains nickel, manganese, cobalt, and titanium, chromium, iron, copper, zinc, aluminum, germanium, tin, magnesium, silver, tantalum, niobium, boron, phosphorus, zirconium, tungsten and/or gallium.    USE - Electrode is used for electrochemical elements e.g. non-aqueous secondary battery (claimed) and capacitor. Uses include but are not limited to mobile telephones, notebook computers, electric vehicles, electric tools, motor vehicles, bicycles, and other electric power storage applications.    ADVANTAGE - The electrode has excellent heat stability, and provides non-aqueous secondary batteries having high capacity and safety in high-temperature environment. Since decomposition of non-aqueous electrolyte in the electrochemical element by composite particles, and elution of manganese are suppressed, charging/discharging cycle characteristics of the electrochemical element are improved. The capacity per mass of active material is enlarged. The complex oxide is a material excellent in invertibility.    DETAILED DESCRIPTION - An electrode consists of an electrode-mixture layer comprising particles of a lithium-containing complex oxide having a BET specific surface area of 0.3 m2/g or less. The content of primary particles having a size of 1 mu m or less is 30 vol.% or less with respect to all primary particles. The complex oxide is of formula: Li1+xNi(1-y-z+b)/2Mn(1-y-z-b)/2CoyMzO2, where M is titanium, chromium, iron, copper, zinc, aluminum, germanium, tin, magnesium, silver, tantalum, niobium, boron, phosphorus, zirconium, tungsten and/or gallium, preferably titanium and/or magnesium, x is -0.15 to 0.15, y is 0-0.4, z is 0-0.03, b is -0.1 to 0.96, 1-y-z-b is greater than 0, and average valence of nickel is 2.2-2.9. An INDEPENDENT CLAIM is included for non-aqueous secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a top view and a sectional view of the non-aqueous secondary battery.    Positive electrode (1)    Negative electrode (2)    Separator (3)    Battery case (4)    Insulator (5)    Flat electrode coil (6)