NEGATIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY COMPRISING COMPOSITE COMPRISING SILICON PHASE FINE PARTICLE AND OXIDE SURROUNDING THE SILICON PHASE PARTICLE AND CARBON MATERIAL, AND ITS PREPARATION METHOD

摘要

PURPOSE: A negative electrode active material for a lithium secondary battery and its preparation method are provided, to improve cycle lifetime and to obtain a high capacity by preventing the mechanical breakage of an active material. CONSTITUTION: The negative electrode active material comprises a composite comprising a Si phase fine particle and an oxide surrounding the Si phase particle; and a carbon material. Preferably the oxide comprises a material selected from the group consisting of Al, Ti, Zr, Nb, Cr, Fe, Li, Mn, Ni, Co, Sn, V, In, Cr, Y, Ge, Ta, Mg, Ca, Mo, Sb, Ti, Zr, P, B, N and their mixture. Preferably the surface of the negative electrode active material is modified by coating a low crystalline or amorphous carbon material. The method comprises the steps of mixing a silicon oxide and a material having an abstract value of oxide formation enthalpy (H_for) greater than that of the silicon oxide and a negative oxide formation enthalpy value by the mechanochemical process or thermochemical reaction to reduce the silicon oxide to prepare the composite; and mixing the composite and the carbon material.