Negative electrode active material, raw material for a negative electrode active material, negative electrode, lithium ion secondary battery, method for producing a negative electrode active material, and method for producing a lithium ion secondary battery

1. A negative electrode active material in a state before being incorporated into a slurry for producing a negative electrode, the negative electrode active material comprising:

a particle of negative electrode active material containing (i) silicon-based material consisting of SiO x (0.5≤x≤1.6) and (ii) any one or more of Li 2 SiO 3 , Li 4 SiO 4 , Li 2 O and Li 2 CO 3 ;

wherein the intensity A of a peak in a Si-region given in the chemical shift region of from −50 to −95 ppm and the intensity B of a peak in a SiO 2 -region given in the chemical shift region of from −96 to −150 ppm in a 29 Si-MAS-NMR spectrum of the silicon-based material satisfy a relationship that A/B≥0.8.

2. The negative electrode active material according to claim 1 ,

wherein the particle of negative electrode active material has at least one peak corresponding to any one or more of Li 2 SiO 3 and Li 4 SiO 4 in a region given in the chemical shift region of from −50 to −95 ppm in a 29 Si-MAS-NMR spectrum; and

the particle of negative electrode active material has a peak corresponding to metal Si in a region given in the chemical shift region of from −50 to −95 ppm in a 29 Si-MAS-NMR spectrum.

3. The negative electrode active material according to claim 2 , wherein the particle of negative electrode active material has a peak given in the chemical shift region of from −70 to −85 ppm in a 29 Si-MAS-NMR spectrum.

4. The negative electrode active material according to claim 2 , wherein the particle of negative electrode active material has at least two peaks given in the chemical shift region of from −50 to −95 ppm in a 29 Si-MAS-NMR spectrum.

5. The negative electrode active material according to claim 1 , wherein the particle of negative electrode active material contains any two or more of Li 2 SiO 3 , Li 4 SiO 4 , Li 2 O, and Li 2 CO 3 .

6. The negative electrode active material according to claim 1 , wherein the Li 2 SiO 3 has a diffraction peak near 38.2680° in which the full width at half maximum (2θ) is 0.75° or more in an X-ray diffraction.

7. The negative electrode active material according to claim 1 , wherein the Li 4 SiO 4 has a diffraction peak near 23.9661° in which the full width at half maximum (2θ) is 0.2° or more in an X-ray diffraction.

8. The negative electrode active material according to claim 1 , wherein the Li 2 SiO 3 and the Li 4 SiO 4 are amorphous.

9. The negative electrode active material according to claim 1 , wherein the negative electrode active material has a diffraction peak attributable to Si (111) crystal face in which the full width at half maximum (2θ) is 1.2° or more in an X-ray diffraction, and the size of the crystallite corresponding to the crystal face is 7.5 nm or less.

10. The negative electrode active material according to claim 1 , wherein the particle of negative electrode active material has a median diameter of 0.5 μm or more and 20 μm or less.

11. The negative electrode active material according to claim 1 , wherein the particle of negative electrode active material has carbon material on its surface.

12. The negative electrode active material according to claim 11 , wherein the average thickness of the coating carbon material is 1 nm or more and 5000 nm or less.

13. A raw material for a negative electrode active material comprising the negative electrode active material according to claim 1 ; and a carbon material.

14. A negative electrode comprising:

a negative electrode active material layer formed by the raw material for a negative electrode active material according to claim 13 ; and

a negative electrode current collector,

wherein

the negative electrode active material layer is formed on the negative electrode current collector; and

the negative electrode current collector contains carbon and sulfur, and each content is 100 ppm or less.

15. A lithium ion secondary battery, wherein the lithium ion secondary battery uses a negative electrode containing the negative electrode active material according to claim 1 .

16. A method for producing a negative electrode active material, prior to producing a slurry for producing a negative electrode comprising the negative electrode active material, the method comprising:

doping a particle of negative electrode active material, which contains a silicon-based material consisting of SiO x (0.5≤x≤1.6), with any one or more of Li 2 SiO 3 , Li 4 SiO 4 , Li 2 O and Li 2 CO 3 ,

wherein the intensity A of a peak in a Si-region given in the chemical shift region of from −50 to −95 ppm and the intensity B of a peak in a SiO 2 -region given in the chemical shift region of from −96 to −150 ppm in a 29 Si-MAS-NMR spectrum satisfy a relationship that A/B≥0.8.

17. A method for producing a lithium ion secondary battery, comprising:

preparing a negative electrode by using a negative electrode active material made by the method for producing a negative electrode active material according to claim 16 ; and

producing a lithium ion secondary battery by using the prepared negative electrode.

18. The method for producing a negative electrode active material according to claim 16 , wherein the particle of negative electrode active material has at least one peak corresponding to any one or more of Li 2 SiO 3 and Li 4 SiO 4 in a region given in the chemical shift region of from −50 to −95 ppm in a 29 Si-MAS-NMR spectrum.

19. The method for producing a negative electrode active material according to claim 16 , wherein the particle of negative electrode active material has a peak corresponding to metal Si in a region given in the chemical shift region of from −50 to −95 ppm in a 29 Si-MAS-NMR spectrum.

20. The method for producing a negative electrode active material according to claim 16 , wherein the doping is performed using an inner-bulk reforming apparatus.