A positive-electrode active material contains a compound represented by the following composition formula (1): LixMeyOαXβ  (1) where Me denotes one or more elements selected from the group consisting of Mn, Ni, Co, Fe, Al, Sn, Cu, Nb, Mo, Bi, Ti, V, Cr, Y, Zr, Zn, Na, K, Ca, Mg, Pt, Au, Ag, Ru, Ta, W, La, Ce, Pr, Sm, Eu, Dy, and Er, X denotes two or more elements selected from the group consisting of F, Cl, Br, I, N, and S, and x, y, α, and β satisfy 0.75≤x≤2.25, 0.75≤y≤1.50, 1≤α