Negative electrode active material for lithium ion battery
The present invention provides a negative electrode active material for lithium ion batteries which has high adhesiveness and followability to a negative electrode active material in volume expansion and contraction during charging and discharging, excellent contact and adhesiveness to a conductive aid, a binder, and a current collector, and a high suppressing effect on decomposition of an electrolyte solution. Due to these features, the negative electrode active material for lithium ion batteries is capable of achieving excellent cycle characteristics and rate characteristics and high coulombic efficiency. The present invention also provides a negative electrode for lithium ion secondary batteries and a lithium ion secondary battery each including the negative electrode active material for lithium ion batteries, and a method for producing a negative electrode active material for lithium ion batteries. Provided is a negative electrode active material for lithium ion batteries, including: a negative electrode active material; and a coating layer containing an amorphous carbon on a surface of the negative electrode active material, the amorphous carbon constituting the coating layer having a ratio of a peak derived from a sp2 component to a peak derived from a sp3 component of 1 or higher as determined by 13 C solid-state NMR, and a ratio of a peak derived from aromatic carbon having a bond with a hydroxy group to the peak derived from the sp2 component of 0.2 or lower.
1. A negative electrode active material for lithium ion batteries, comprising:
a negative electrode active material; and
a coating layer containing an amorphous carbon on a surface of the negative electrode active material,
the amorphous carbon constituting the coating layer having
a ratio of a peak derived from a sp2 component to a peak derived from a sp3 component of 1 or higher as determined by 13 C solid-state NMR, and
a ratio of a peak derived from aromatic carbon having a bond with a hydroxy group to the peak derived from the sp2 component of 0.2 or lower,
wherein in analysis of the coating layer by time-of-flight secondary ion mass spectrometry (TOF-SIMS), at least one selected from the group consisting of a mass spectrum derived from a benzene ring and a mass spectrum derived from a naphthalene ring is detected, and
the negative electrode active material is a silicon-containing compound.
2. The negative electrode active material for lithium ion batteries according to claim 1 , which has a zeta potential of 0 to −60 mV.
3. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein the amorphous carbon constituting the coating layer is derived from carbon contained in an oxazine resin.
4. The negative electrode active material for lithium ion batteries according to claim 3 ,
wherein the oxazine resin is naphthoxazine resin.
5. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein the amorphous carbon constituting the coating layer has a peak intensity ratio of G band to D band of 1.0 or higher as determined by Raman spectroscopy.
6. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein the coating layer has a nitrogen content of 0 to 5% by weight.
7. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein the coating layer has an average thickness of 0.5 nm to 1.0 μm.
8. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein in analysis of the coating layer by an X-ray diffraction method, no peak is detected at a position where 2θ is 26.4°.
9. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein in analysis of the coating layer by an X-ray diffraction method, no peak is detected at a position where 2θ is 36°.
10. The negative electrode active material for lithium ion batteries according to claim 1 ,
wherein the negative electrode active material is in a particle form having an average particle size of 10 to 200 nm.
11. A negative electrode for lithium ion secondary batteries, comprising:
the negative electrode active material for lithium ion batteries according to claim 1 ;
a carbon material;
a conductive aid; and
a binder.
12. The negative electrode for lithium ion secondary batteries according to claim 11 ,
wherein the binder is at least one selected from the group consisting of styrene-butadiene rubber, carboxymethylcellulose, polyvinylidene fluoride, polyimide, acrylic resin, and butyral resin.
13. A lithium ion secondary battery comprising the negative electrode for lithium ion secondary batteries according to claim 11 .
14. A method for producing the negative electrode active material for lithium ion batteries according to claim 1 , the method comprising:
preparing a mixed solution containing formaldehyde, an aliphatic amine, and dihydroxy naphthalene;
adding a negative electrode active material to the mixed solution and reacting the mixed solution; and
performing heat treatment.
15. A method for producing the negative electrode active material for lithium ion batteries according to claim 1 , the method comprising:
preparing a mixed solution containing triazine and dihydroxy naphthalene;
adding a negative electrode active material to the mixed solution and reacting the mixed solution; and
performing heat treatment.