A lithium-ion secondary battery (100A) includes a positive electrode current collector (221A) and a positive electrode active material layer (223A) retained on the positive electrode current collector (221A). The positive electrode active material layer (223A) contains positive electrode active material particles, a conductive agent, and a binder. The positive electrode active material particles (610A) each include a shell portion (612) made of primary particles (800) of a layered lithium-transition metal oxide, a hollow portion (614) formed inside the shell portion (612), and a through-hole (616) penetrating through the shell portion (612). The primary particles (800) of the lithium-transition metal oxide have a major axis length of less than or equal to 0.8 μm in average of the positive electrode active material layer (223A).