NEGATIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME

Provided is a negative electrode active material for a lithium secondary battery which includes: a silicon-silicon oxide-magnesium silicate composite comprising a silicon oxide (SiOx, 0 < x ≤ 2) matrix; and silicon (Si) crystal grains, MgSiO3 crystal grains and Mg2SiO4 crystal grains present in the silicon oxide matrix, wherein the MgSiO3 crystal grains have a crystal size of 5-30 nm and the Mg2SiO4 crystal grains have a crystal size of 20-100 nm in the silicon-silicon oxide-magnesium silicate composite, and the content ratio of MgSiO3 crystal grains to Mg2SiO4 crystal grains is 2:1-1:1 on the weight basis. A method for preparing the negative electrode active material for a lithium secondary battery is also provided.