Negative electrode active substance, mixed negative electrode active substance material and method for producing negative electrode active substance

The present invention is a negative electrode active substance containing negative electrode active substance particles, which is characterized in that: the negative electrode active substance particles contain silicon compound particles containing a silicon compound (SiO x , wherein 0.5 ≤ x ≤ 1.6); the silicon compound particles contain an Li compound; elemental Al and elemental Na are contained as constituent elements of the negative electrode active substance particles; and the mass ratio of the elemental Na to the elemental Al, namely M Na /M Al satisfies formula 1. Consequently, the present invention provides a negative electrode active substance which is capable of stabilizing a slurry that is formed during the production of a negative electrode for secondary batteries, and which is capable of improving the initial charge/discharge characteristics and cycle characteristics if used as a negative electrode active substance for a secondary battery. 0.022 ≤ M Na /M Al ≤ 61 Formula 1