▎ 摘　　要

NOVELTY - A porous silicon-based carbon composite comprises silicon particles capable of intercalating and de-intercalating lithium, a magnesium compound, and carbon. The molar ratio of magnesium atoms with respect to silicon atoms in the composite is 0.02-0.3. The molar ratio of oxygen atoms with respect to silicon atoms in the composite is 0.4-0.9. USE - Porous silicon-based carbon composite is used for forming negative electrode active material of lithium secondary battery (all claimed) used as power source for electronic device e.g. power storage system and automobiles. ADVANTAGE - The porous silicon-based carbon composite provides lithium secondary battery with high initial efficiency, capacity retention rate, and discharge capacity. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) manufacture of the porous silicon-based carbon composite, which involves obtaining a silicon composite oxide powder using a silicon-based raw material and a magnesium-based raw material, etching the silicon composite oxide powder using an etching solution comprising a fluorine-containing compound, filtering and drying the obtained composite for obtaining a porous silicon composite, and forming a carbon layer on the surface of the porous silicon composite by a chemical-thermal decomposition deposition method; and (2) negative electrode active material, which comprises the porous silicon-based carbon composite.