Active Material and Process for Producing the Same

An active material includes a core portion, and a coating portion arranged on a surface of the core portion. The core portion contains elemental lithium (Li), elemental manganese (Mn), and elemental oxygen (O). The coating portion contains an element A (A is at least one selected from the group consisting of Ti, Zr, Ta, Nb, and Al) and elemental oxygen (O). W/(T×S) is more than 0 and 15% by mass/(cm/g) or less, wherein T (nm) represents an average thickness of the coating portion, S (m/g) represents a specific surface area of the active material, and W (% by mass) represents an amount of element A contained in the coating portion.