Lithium-containing silicon oxide powder and making method

A lithium ion secondary cell having a high capacity, improved first charge/discharge efficiency and improved cycle performance is obtainable using as the negative electrode material a lithium-containing silicon oxide powder having the formula: SiLixOy wherein x and y are 0 < x < 1.0 and 0 < y < 1.5, with the lithium being fused and partially crystallized.