| abstract |
(57) [Problem] To provide a lithium ion secondary battery having significantly improved low-temperature characteristics and rate characteristics as compared with conventional ones. SOLUTION: The positive electrode is composed of an active material composed of Li—Co-based composite oxide particles satisfying 7 ≦ 20 / (specific surface area × average particle diameter) ≦ 9, a granular conductive material having a particle diameter of 3 μm or more, and particles. Diameter 2 μm or less, or a conductive material having an aspect ratio of 3 or more and a fiber diameter of 2 μm or less, between the positive electrode and the negative electrode, a salt, a compatible solvent, and vinylidene fluoride. A solid electrolyte layer mainly composed of a fluorine polymer having a main unit of a ride and a fluorine polymer is interposed. |