LITHIUM-ION SECONDARY BATTERY

A lithium ion secondary battery that can increase battery capacity retention rate after repeated high-rate charge and discharge is provided. A lithium ion secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has a positive electrode active material-containing layer containing a positive electrode active material represented by formula (I) below formed on a positive current collector, and in the lithium ion secondary battery, the average primary particle size of the positive electrode active material is 0.50 µm or more and 2 µm or less, and the average surface roughness Ra of the surface of the positive current collector in contact with the positive electrode active material-containing layer is 0.2 µm or more and 0.6 µm or less. In formula (I) below, M is at least one metal atom selected from the group consisting of Co, Ni, Fe, Mn, Cu, Mg, Zn, Ti, Al, Si, B, and Mo, and 0