Negative electrode active material for lithium secondary battery and method of preparing the same

A method of preparing a negative electrode active material, comprising:

• forming a carbon coating layer on a silicon-based precursor represented by SiOx (0<x≤2);
• and
• thermally treating the silicon-based precursor on which the carbon coating layer is formed to prepare a silicon-based composite represented by SiOa (0<a<1) having a surface on which the carbon coating layer is distributed by removing impurities,
• wherein the silicon-based composite has a bimodal pore structure including mesopores and macropores,
• wherein the thermal treatment includes thermally reducing the silicon-based precursor with a metal reducing agent in an inert atmosphere,
• wherein in the silicon-based composite, a ratio of crystalline silicon and crystalline silica contained therein is expressed as 1−(3/2):(a/2), and
• wherein the silicon-based composite represented by SiOa (0<a<1) consists of crystalline silicon and crystalline silica, and no amorphous silicon is present.