Negative electrode active material containing silicon clathrate II
Provided is a negative electrode active material that contains silicon clathrate II and that is suitable for a negative electrode of a lithium ion secondary battery. The negative electrode active material includes a silicon material in which silicon clathrate II represented by composition formula Na x Si 136 (0≤x≤10) is contained and a volume of a pore having a diameter of not greater than 100 nm is not less than 0.025 cm 3 /g.
1. A negative electrode active material comprising a silicon material in which silicon clathrate II represented by composition formula Na x Si 136 (0≤x≤10) is contained and a volume of a pore having a diameter of not greater than 100 nm is not less than 0.025 cm 3 /g.
2. A negative electrode comprising the negative electrode active material according to claim 1 .
3. A lithium ion secondary battery comprising the negative electrode according to claim 2 .