Abstract: An anode active material for a secondary battery according to an embodiment of the present application includes lithium-silicon composite oxide particle. The lithium-silicon composite oxide particles include at least one selected from the group consisting of Li2SiO3 and Li2Si2O5 and have a phase fraction ratio defined by Equation 1 of 1.0 or less. A content of particles having a diameter of less than 3 ?m is 5 vol % or less based on a total volume of the lithium-silicon composite oxide particles.

Abstract: An anode active material for a secondary battery includes a plurality of composite particles. The composite particles include carbon-based particles containing pores therein. A silicon-containing coating layer is formed inside the pores or on a surface of the carbon-based particles. A surface oxide layer is formed on the silicon-containing coating layer. The surface oxide layer contains silicon oxide. A silicon oxidation number ratio of the composite particle is predefined.