LITHIUM ION SECONDARY BATTERY

Provided is a lithium ion secondary battery having excellent energy density and output density as well as excellent charge-and-discharge cycle characteristics. In a lithium ion secondary battery 1, a positive electrode 2 and a negative electrode 3 are alternately adj acent to each other via separators 4 and 5. The positive electrode 2 includes a positive electrode current collector composed of a metal porous body, a first positive electrode active material 21 held on one side of the positive electrode current collector, and a second positive electrode active material 22 held on the other side. The negative electrode 3 includes a negative electrode current collector composed of a metal porous body, a first negative electrode active material 31 held on one side of the negative electrode current collector, and a second negative electrode active material 32 held on the other side. The first positive electrode active material 21 faces the first negative electrode active material 31, and the positive electrode active material 22 faces the second negative electrode active material 32.