Active material for secondary batteries, secondary battery, and electronic device

Provided is a secondary battery which is capable of achieving excellent battery characteristics. This secondary battery is provided with a positive electrode, a negative electrode that contains an active material, and an electrolyte solution. The active material comprises: a core portion that is capable of absorbing and desorbing lithium ions; and a low crystalline or amorphous coating portion that is provided on at least a part of the surface of the core portion. The core portion contains Si and O as constituent elements, and if x is the atomic ratio of O to Si (O/Si), x satisfies 0 ≤ x < 0.5. The coating portion contains Si and O as constituent elements, and if y is the atomic ratio of O to Si (O/Si), y satisfies 0.5 ≤ y ≤ 1.8. The coating portion has voids, and at least some of the voids are provided with a carbon-containing material.