NOVELTY - A lithium secondary battery has positive electrode (1) containing positive mix layer, negative electrode (2) containing negative mix layer, nonaqueous electrolyte and separator (3). The positive mix layer contains lithium-nickel complex oxide (I) as positive electrode active material. The negative mix layer contains material (M1) including silicon and oxygen as constitutent elements as negative electrode active material. In the material (M1), atomic ratio of oxygen with respect to silicon is 0.5-1.5. Nonaqueous electrolyte contains compound (C1) having a nitrile group in a molecule.    USE - Lithium secondary battery is used for mobile telephone, notebook computer and electric vehicle.    ADVANTAGE - The lithium secondary battery can be used stably for a long time even if continuously charged at high voltage of 4.3 V or more.    DETAILED DESCRIPTION - A lithium secondary battery has positive electrode containing positive mix layer including positive electrode active material on surface(s) of collector, negative electrode containing negative mix layer including a negative electrode active material on surface(s) of collector, nonaqueous electrolyte and separator. The positive mix layer contains lithium-nickel complex oxide of formula: Li1+yNi1-a-b-cCoaMnbM1cO2 (I) as positive electrode active material. The negative mix layer contains material (M1) including silicon and oxygen as constitutent elements as negative electrode active material. In the material (M1), atomic ratio of oxygen with respect to silicon is 0.5-1.5. The nonaqueous electrolyte contains compound (C1) having a nitrile group in a molecule.    M1=magnesium, aluminum, titanium, iron, copper, zinc, gallium, germanium, zirconium, niobium, molybdenum, tin, tungsten, boron, phosphorus or bismuth;    y=(-0.15) to 0.15;    a,b=0.05-0.3;    c=0-0.03;and    a+b+c=0.5 or less.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of the lithium secondary battery.    Positive electrode (1)    Negative electrode (2)    Separator (3)    Battery case (4)    Insulator (5)