A lithium ion secondary battery with increased durability and capacity includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a current collector foil and an electrode mixture layer disposed on a surface of the current collector foil. The positive electrode mixture layer includes a superficial layer portion and a deep layer portion. The superficial layer portion opposes the negative electrode via the separator. The deep layer portion is disposed between the superficial layer portion and the current collector foil. The superficial layer portion contains positive electrode active material particles having an average particle diameter larger than an average particle diameter of positive electrode active material particles contained in the deep layer portion. A space ratio between the positive electrode active material particles in the superficial layer portion is lower than a space ratio between the positive electrode active material particles in the deep layer portion.