Negative electrode material for nonaqueous secondary battery
To provide a carbon material capable of suppressing excessive reactivity with an electrolytic solution and excellent in a rapid charge/discharge characteristics. A carbon material for lithium ion secondary batteries, which satisfies: (i) a tap density≧0.75 g/cm 3 ; (ii) a Raman R value≧0.23 and a half width of D band Δν D <45 cm −1 , in which the D band appears in the vicinity of 1,358 cm −1 of the Raman spectrum; and (iii) 4 m 2 /g≦BET specific surface area (SA)≦11 m 2 /g.
1. A carbon material, having:
(i) a tap density≧0.75 g/cm 3 ;
(ii) a Raman R value≧0.23 and a half width of D band Δν D <45 cm −1 , wherein the D band appears in the vicinity of 1,358 cm −1 of the Raman spectrum; and
(iii) 4 m 2 /g≦BET specific surface area SA, ≦11 m 2 /g,
wherein the carbon material is suitable for a lithium ion secondary battery.
2. The carbon material of claim 1 , wherein an element ratio of oxygen (O) to carbon (C) determined by X-ray photoelectron spectroscopy (XPS) is 0.03<O/C≦2.4.
3. The carbon material of claim 1 , wherein a thickness of an amorphous carbon layer present on a basal surface exposed to a particle surface observed by a transmission electron microscope, TEM, does not exceed 50 nm.
4. The carbon material of claim 1 , wherein a particle of the material, observed by TEM,
has, in an edge portion, a structure comprising a single layer or maximally two layers, in which edge surfaces exposed to a particle surface are connected with each other to form a U-shaped curved surface, and
has a fine folded structure irregular in an a-axis direction.
5. The carbon material of claim 1 , wherein pH of the water slurry is 7.5 or more and less than 11.
6. The carbon material of claim 1 , wherein a particle of the material, observed by a scanning electron microscope (SEM), is natural graphite giving a spherical shape as a whole, and
the particle observed by TEM has, in the edge portion, a structure comprising a single layer or maximally two layers in which edge surfaces exposed to a particle surface are connected with each other to form a U-shaped curved surface, and has a fine folded structure irregular in the a-axis direction.
7. The carbon material of claim 1 , wherein
the Raman R value is not less than the Raman R value of a raw material graphite particle, and
Rr, which is the Raman R value of the carbon material/Raman R value of the raw material graphite particle, is 1.0<Rr≦1.5.
8. The carbon material of claim 1 , wherein
the half width Δν D of D band appearing in the vicinity of 1,358 cm −1 of the Raman spectrum is not more than the half width Δν D of D band of a raw material graphite particle, and
a ratio Δν D r therebetween, Δν D of the carbon material/Δν D of the raw material graphite particle, is Δν D r≦≦0.99.
9. The carbon material of claim 1 , wherein
the BET specific surface area, SA, is larger than SA of a raw material graphite particle,
the ratio SA_r therebetween, SA of the carbon material/SA of the raw material graphite particle, is 1.03≦SA_r≦1.5,
the tap density is larger than the tap density of the raw material graphite particle, and
a ratio Tap_r therebetween, tap density of said carbon material/tap density of the raw material graphite particle, is 1.01≦Tap_r≦1.3.
10. The carbon material of claim 1 , obtained by heat-treating a spherical or spheroidal natural graphite particle having a tap density≧0.6 g/cm 3 in N 2 ,
wherein after the heat treating, a weight increase occurs due to an N 2 addition reaction.
11. The carbon material of claim 10 , wherein a heat treatment temperature T in the heat treating is 500° C.≦T<1,250° C. and
a time for the heat treating is 36 hours or more.
12. The carbon material of claim 1 , wherein a ratio of an irreversible capacity to the SA is 4.5 mAh/m 2 or less, in which the irreversible capacity is measured with the carbon material as an electrode active material of a lithium ion secondary battery and performing a sweep for three cycles with an Li counter electrode in an interelectrode potential difference range from 0 to 1.5 V while setting a density of the electrode active material to 1.7 g/cm 3 .
13. The carbon material of claim 1 , which has no amorphous carbon structure attributable to a heat-treated product of pitch, tar, or resin.
14. The carbon material of claim 1 , wherein a raw material graphite particle thereof is a spherical natural graphite particle, and a total CO generation amount on a surface of the raw material graphite particle as determined by temperature-programmed desorption method, TPD-MS, measurement and SA measurement, is from 0.4 to 3.5 μmol/m 2 .
15. A carbon material, comprising:
the carbon material of claim 1 ; and
a negative electrode carbon material other than that,
in a ratio of 2:8 to 9:1 by mass.
16. A negative electrode sheet, comprising the carbon material of claim 1 as a negative electrode active material.
17. A lithium ion secondary battery, comprising the negative electrode sheet of claim 16 .
18. A lithium ion secondary battery, comprising:
a negative electrode comprising the carbon material of claim 1 in a negative electrode sheet;
a positive electrode; and
an electrolytic solution,
wherein an active material density of the negative electrode sheet is 1.6 g/cm 3 or more and the electrolytic solution comprises a chain carbonate.
19. The carbon material of claim 2 , wherein a thickness of an amorphous carbon layer present on a basal surface exposed to a particle surface observed by a transmission electron microscope, TEM, does not exceed 50 nm.
20. The carbon material of claim 2 , wherein a particle of the material, observed by TEM,
has, in an edge portion, a structure comprising a single layer or maximally two layers, in which edge surfaces exposed to a particle surface are connected with each other to form a U-shaped curved surface, and
has a fine folded structure irregular in an a-axis direction.