Negative-electrode active substance, method for manufacturing same, and lithium-ion secondary cell

A negative-electrode active substance containing silicon oxide, wherein the negative-electrode active substance has excellent performance as a negative-electrode active substance for a lithium secondary cell, and, in regard to the silicon oxide after at least one charging cycle, when the solid NMR ( 29 Si-DDMAS) of the Si has been measured, the sums S1, S2, and S3 satisfy the expressions 0.42≤S1/S1+S2+S3)≤0.55 (formula (1)) and 0.21≤S1+S2+S3)≤0.26 (formula (2)), where S1 is the sum of the areas under peaks of the group of signals attributed to silicon having Si-Si bonds), S2 is the sum of the areas under the peaks of the group of signals attributed to silicon having the structure Si(OH) 4-n (OSi) n (n=3, 4)), and S3 is the sum of the areas under the peaks of the group of signals attributed to silicon having the structure Si(OLi) 4-n (OSi) n (n=0, 1, 2, 3)).