Lithium secondary battery

A lithium secondary battery, comprising:

• a negative electrode containing silicon as a negative electrode active material;
• a positive electrode containing a positive electrode active materials;
• and
• a non-aqueous electrolyte, wherein
• the positive electrode active material is a layered lithium-transition metal composite oxide represented by the chemical formula LiaNixMnyCozO2, where a, x, y, and z satisfy the expressions 0≦a≦1.3, x+y+z=1, 0<x≦0.5, 0≦y≦0.5, and 0<z, and contains 0.2 weight % or greater of lithium carbonate, and
• a theoretical electrical capacity ratio of the positive electrode to the negative electrode (positive electrode/negative electrode) is 0.89 or less.

A lithium secondary battery, comprising:

• a negative electrode containing silicon as a negative electrode active material;
• a positive electrode containing a positive electrode active material;
• and
• a non-aqueous electrolyte, wherein
• the positive electrode active material is a layered lithium-transition metal composite oxide represented by the chemical formula LiaNixMnyCozO2, where a, x, y, and z satisfy the expressions 0≦a≦1.3, x+y+z=1, 0<x≦0.5, 0≦y≦0.5, and 0<z, and contains 0.2 weight % or greater of lithium carbonate,
• a theoretical electrical capacity ratio of the positive electrode to the negative electrode (positive electrode/negative electrode) is 0.89 or less, and
• the non-aqueous electrolyte contains carbon dioxide dissolved therein.