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

1. A negative electrode active material comprising

a negative electrode active material particle,

wherein

the negative electrode active material particle comprises a silicon compound particle comprising a silicon compound (SiO x : 0.5≤x≤1.6),

the silicon compound particle comprises crystalline Li 2 SiO 3 and Li 2 Si 2 O 5 in at least part of the silicon compound particle,

among a peak intensity A derived from Li 2 SiO 3 , a peak intensity B derived from Si, a peak intensity C derived from Li 2 Si 2 O 5 , and a peak intensity D derived from SiO 2 which are obtained from a 29 Si-MAS-NMR spectrum of the silicon compound particle, the peak intensity A or the peak intensity C is the highest intensity, and

the peak intensity A and the peak intensity C satisfy a relationship of the following formula 1,

C/ 3≤ A≤ 3 C.   formula 1:

2. The negative electrode active material according to claim 1 , wherein a sum of the peak intensity A and the peak intensity C takes a value four times or more as large as a sum of the peak intensity B and the peak intensity D in the 29 Si-MAS-NMR spectrum.

3. The negative electrode active material according to claim 1 , wherein the peak intensity B is higher than the peak intensity D in the 29 Si-MAS-NMR spectrum.

4. The negative electrode active material according to claim 1 , wherein a peak that is derived from amorphous silicon appears in a region near a chemical shift value of −130 ppm in the 29 Si-MAS-NMR spectrum.

5. The negative electrode active material according to claim 1 , wherein

in the negative electrode active material,

a half-value width (2θ) of a diffraction peak attributable to a Si (111) crystal plane obtained by an X-ray diffraction using Cu-Kαray is 1.2° or more, and

a crystallite's size corresponding to the crystal plane is 7.5 nm or less.

6. The negative electrode active material according to claim 1 , wherein

a test cell is prepared, the test cell comprising a counter lithium and a negative electrode, which comprises a mixture of the negative electrode active material and a carbon-based active material;

in the test cell, charge in which a current is flowed so as to insert lithium into the negative electrode active material and discharge in which a current is flowed so as to release lithium from the negative electrode active material are executed for 30 times; and

when a graph is drawn showing a relationship between an electric potential V of the negative electrode and a differential value dQ/dV, which is obtained by differentiating a discharge capacity Q in each charge and discharge with the electric potential V with a standard of the counter lithium, the differential value dQ/dV upon discharging on and after Xth time (1≤X≤30) has a peak in a range of 0.40 V to 0.55 V of the electric potential V of the negative electrode.

7. The negative electrode active material according to claim 1 , wherein the negative electrode active material particles have a median diameter of 1.0 μm or more and 15 μm or less.

8. The negative electrode active material according to claim 1 , wherein the negative electrode active material particle contains a carbon material at a surface layer portion.

9. The negative electrode active material according to claim 8 , wherein the carbon material to be coated has an average thickness of 5 nm or more and 5000 nm or less.

10. A mixed negative electrode active material comprising:

the negative electrode active material according to claim 1 ; and

a carbon-based active material.

11. The mixed negative electrode active material according to claim 10 , wherein a ratio of the negative electrode active material relative to a total amount of the mixed negative electrode active material is 10% by mass or more.

12. A method for producing a negative electrode active material which comprises a negative electrode active material particle comprising a silicon compound particle, the method comprising the steps of:

making silicon compound particles comprising a silicon compound (SiO x : 0.5≤x≤1.6);

inserting lithium into the silicon compound particles so as to include crystalline Li 2 SiO 3 and Li 2 Si 2 O 5 in at least part of the silicon compound particles to prepare negative electrode active material particles;

selecting, from the negative electrode active material particles, such a negative electrode active material particle that, among a peak intensity A derived from Li 2 SiO 3 , a peak intensity B derived from Si, a peak intensity C derived from Li 2 Si 2 O 5 , and a peak intensity D derived from SiO 2 which are obtained from a 29 Si-MAS-NMR spectrum of the negative electrode active material particle, the peak intensity A or the peak intensity C is the highest intensity, and the peak intensity A and the peak intensity C satisfy a relationship of the following formula 1,

C/ 3≤ A≤ 3 C   formula 1:

and

producing a negative electrode active material by using the selected negative electrode active material particle.

13. The method according to claim 12 , wherein the inserting lithium includes mixing the silicon compound particles with a solution containing dissolved lithium metal.

14. The method according to claim 12 , further comprising, before the selecting, heating the negative electrode active material particles at a heat treatment temperature in a range of 500° C. or more and 680° C. or less.