JPH10255803A - Carbon material for negative electrode of secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide carbon material for a negative electrode which, while having a large discharging capacity, has high charging and discharging efficiency even if the discharging capacity is large and is excellent in its cycle characteristics, and its manufacturing method. SOLUTION: This carbon material used for a negative electrode of a nonaqueous electrolyte secondary battery has its A/B ratio of 1.0-1.3, which is an asymmetric parameter of an ESR spectrum signal at 25 deg.C observed by an electron spin resonance analisis method (ESR), and has its R value, I1360 /I1580 ratio of 0.01-0.3, which is a ratio of peak strength I1350 at a Raman shift of 1360cm<-1> in a Raman spectrum observed by a laser Raman spectrometry to peak strength I1580 at a Raman shift of 1580cm<-1> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon material for a negative electrode of a non-aqueous electrolyte secondary battery and a method for producing the same.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries have been spotlighted in recent years because of their high energy density and excellent charge / discharge cycle characteristics, load characteristics, and safety. This battery is already expected to be in large demand for video cameras, notebook computers, mobile phones, and the like, and is expected to be applied as a battery for electric vehicles in the future.

In general, a non-aqueous electrolyte secondary battery has a configuration in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween, and these are immersed in a non-aqueous electrolyte. As this non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent is used. Further, a lithium-containing composite oxide is used for the positive electrode, and a carbon material is used for the negative electrode.

At present, graphite materials are widely used as the carbon material. Generally, carbon materials include natural graphite, artificial graphite, graphitizable carbon (such as vapor-grown carbon fiber),
There are non-graphitizable carbon (such as PAN-based carbon fiber) and amorphous carbon (such as coke). Of these, those other than natural graphite and artificial graphite are used after being graphitized.

[0005] Graphitization is performed to maintain graphite at a high temperature to grow graphite crystals in the material. By this graphitization treatment, a plurality of graphite crystallites (one crystal having the same orientation) are generally formed in the material. Also,
In the negative electrode of the non-aqueous electrolyte secondary battery, it is considered that the lithium ions in the non-aqueous electrolyte are mainly charged or discharged between carbon lattice planes of graphite crystallites or discharged therefrom. I have.

By the way, the graphite-based material has excellent cycle characteristics and a flat potential, so that it is possible to provide a non-aqueous electrolyte secondary battery having a higher energy density. Among graphite materials, natural graphite is 372 mAh / g.
It is known to exhibit a large discharge capacity. However, natural graphite cannot provide such a high discharge capacity at a high current density used in a practical battery, and is therefore said to be substantially about 300 to 320 mAh / g.

On the other hand, the vapor-grown carbon fiber produced by the vapor-phase growth method can be provided as a graphite-based material because it can be easily graphitized. Moreover, the graphitized vapor-grown carbon fiber does not lower the discharge capacity even when the current density is increased, as compared with natural graphite. Therefore, the vapor grown carbon fiber is suitable as a negative electrode material.

This vapor grown carbon fiber is also described in Japanese Patent Application Laid-Open No. Hei 6-73615 filed by the present applicant. And, in this publication, a diameter of 2.2 μ
m, length 14.6 μm, spin concentration 3.7 × 10 ¹⁸ sp
ins / g of graphitized vapor grown carbon fiber
An electrode cell is assembled, and the charge / discharge amount (mAh /
g) and the result of measurement of Coulomb efficiency (%).

[0009]

However, the conventional carbon materials generally do not always have a sufficiently satisfactory discharge capacity. Moreover, among such carbon materials, those having the largest discharge capacity have a problem that the charge / discharge efficiency is lower than those having a smaller discharge capacity. Further, such a carbon material has a problem that the cycle characteristics are deteriorated due to low charge / discharge efficiency. The problems with regard to the discharge capacity, charge / discharge efficiency, and cycle characteristics were not limited to graphitized vapor-grown carbon fibers, but were also applicable to general graphite-based materials. Here, the cycle characteristics refer to the manner in which the discharge capacity changes when charge and discharge are repeated.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a negative electrode having a large discharge capacity, high charge / discharge efficiency even with a large discharge capacity, and excellent cycle characteristics. An object of the present invention is to provide a carbon material for use and a method for producing the same.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has paid attention to the abundance ratio of a crystalline structure portion and an amorphous structure portion in a graphite-based material. Here, the inside of the graphite crystallite is a crystal structure part, and the space between graphite crystallites is an amorphous structure part. Since the inside (crystal structure portion) of the graphite crystallite is a place where lithium ions are occluded, the charge / discharge capacity decreases as the amount of lithium ion decreases. On the contrary,
Since the amorphous structure portion has structural distortion, it serves as a passage for lithium ions to enter and exit graphite crystallites. Therefore, if the abundance is small, lithium ions cannot enter and exit the graphite crystallites, and also in this case, the charge / discharge capacity is reduced. As a result, regardless of the amount of the crystalline structure portion and the non-crystalline structure portion, the discharge capacity is reduced regardless of the amount of the crystalline structure portion and the amorphous structure portion, and it is considered that the abundance ratio has an optimal range. The inventor paid attention to the above for the reasons described above.

On the other hand, the abundance ratio between the crystal structure portion and the non-crystal structure portion is determined by the A / B ratio, which is an asymmetry parameter of the signal of the ESR spectrum observed by electron spin resonance analysis (ESR), and the laser Raman Raman shift of Raman spectrum observed by spectroscopy is 1360
cm ^-1 peak intensity I ₁₃₆₀ and Raman shift of 1580c
R which is a ratio of I ₁₃₆₀ / I ₁₅₈₀ to the peak intensity I _{1580 of} m ⁻¹
You can know from the value. Thus, the present inventors have reached the present invention by using this method to investigate in detail the relationship between the abundance ratio of the crystalline structure portion and the amorphous structure portion and the charge / discharge capacity.

[0013]

SUMMARY OF THE INVENTION Therefore, the present invention according to claim 1 of the present invention relates to a method for preparing a carbon material used for a negative electrode of a non-aqueous electrolyte secondary battery using an electron spin resonance (ES) method.
The A / B ratio, which is the asymmetry parameter of the signal of the ESR spectrum at 25 ° C. observed by R) is 1.
0 to 1.3, and the Raman shift of the Raman spectrum observed by laser Raman spectroscopy is 1360c.
m ^-1 peak intensity I ₁₃₆₀ and Raman shift of 1580 cm
^The R value, which is the ratio I ₁₃₆₀ / I ₁₅₈₀ to the peak intensity I _{1580 of} ⁻¹ , is 0.01 to 0.3.

The carbon material having the A / B ratio and the R value within the above ranges has a specific surface area of 0.2 to 0.2.
5 m ² / g, carbon lattice spacing d ₀₀₂ is 0.3354 or more
0.3374 nm, the crystal size Lc in the c-axis direction is 50
It is preferably from 2,000 nm to achieve the effects of the present invention. Further, as described in claim 3, the diameter is from 1 to 2,000 nm.
More preferably, it is a vapor grown carbon fiber having a length of 4 μm and a length of 3 to 30 μm.

The vapor-grown carbon fiber is produced by subjecting the vapor-grown carbon fiber produced from the vapor phase to a graphitization treatment and then to a cutting treatment. . In this case, in the cutting process, the carbon fibers are cut with a high impact force by colliding the carbon fibers with each other by a blade rotating at a linear speed of 50 to 100 m / sec. Alternatively, as described in claim 6, it is preferable that the carbon fibers are compressed and cut by applying hydrostatic pressure at a pressure of 500 to 1500 kgf / cm ² .

[0016]

Embodiments of the present invention will be described below in detail. First, the carbon material for a negative electrode of the present invention has an asymmetry parameter of a signal of an ESR spectrum at 25 ° C. observed by electron spin resonance analysis (ESR), that is, an A / B ratio in the range of 1.0 to 1.3. And the Raman shift of the Raman spectrum observed by laser Raman spectroscopy is 1360 cm ^-1.
Peak intensity I at ₁₃₆₀ and Raman shift of 1580 cm ^-1
₁₅₈₀ ratio I ₁₃₆₀ / I _1580: R value is 0.01 with
0.3.

Here, the asymmetry parameter A / B ratio will be described. According to the ESR, an ESR spectrum in which the horizontal axis represents the magnetic field strength and the vertical axis represents the signal intensity is observed for a graphite-based material sample, for example, as shown in FIG. This spectrum has a magnetic field strength of 3230-3.
Two peaks appear in the signal intensity around 250 G (Gauss). Thus, the peak that appears on the side with the weaker magnetic field strength is called peak A, and the peak that appears on the side with the stronger magnetic field is called peak B, and the ratio of this peak A to peak B (A / A
B) is called the asymmetry parameter.

When the asymmetry parameter A / B ratio is close to 0, it means that the abundance ratio of the amorphous structure portion in the sample is high (therefore, the abundance ratio of the crystal structure portion is low). This means that the higher the A / B ratio, that is, the higher the asymmetry of the signal, the higher the proportion of the crystalline structure in the sample (the lower the proportion of the non-crystalline structure in the sample).

For example, natural graphite has a very high crystallinity,
Extremely few amorphous structure parts. Therefore, natural graphite 2
The A / B ratio at 5 ° C. is about 3.0, indicating high signal asymmetry. On the other hand, the carbon material of the present invention has high crystallinity like natural graphite, but has a considerable amount of amorphous structure.
Therefore, the A / B ratio is 1.0 to 1.3, and the asymmetry of the signal is lower than that of natural graphite.

Next, the R value will be described. According to the laser Raman spectroscopy, a Raman spectrum in which the horizontal axis is Raman shift and the vertical axis is signal intensity is observed for a graphite material sample, for example, as shown in FIG. The spectrum peak appears which Raman shift is due to the crystal structure of the graphite in the vicinity of 1580 cm ^-1, also Raman shift peak appears due to the non-crystalline structure in the vicinity of 1360 cm ^-1. When the former peak intensity is I ₁₅₈₀ and the latter peak intensity is I ₁₃₆₀ , the peak intensity ratio I ₁₃₆₀
/ I ₁₅₈₀ is called the R value. When the R value is large, it means that the proportion of the amorphous structure portion in the sample is large.

In order to increase the charge / discharge capacity, the crystal structure of graphite may be developed to increase the crystallite. This is because, as the crystallite becomes larger, the number of carbon lattice planes increases, and the number of lithium ions that can be stored between the planes also increases. However, if the crystallites become too large, the abundance of the non-crystalline structure in the entire fibrous carbon (or particulate carbon) decreases. Lithium ions can pass into and out of the crystal structure through the amorphous structure due to structural distortion, but if the amount is small, lithium ions in the non-aqueous electrolyte can easily migrate inside the crystal structure. , And as a result, the charge / discharge capacity does not increase.

Conversely, when the number of non-crystalline structures increases, the number of carbon lattice planes decreases, and the number of lithium ions that can be stored between the planes decreases. As a result, the charge / discharge capacity does not increase. Due to these conflicting circumstances, it is considered that there is an optimum range for the abundance ratio of the crystalline structure portion and the amorphous structure portion in the carbon material. This optimum range is the range of the A / B ratio and the range of the R value of the present invention.

In the present invention, A /
Among carbon materials having a B ratio and an R value, the specific surface area is 0.2 to ⁵ m ² / g, and the carbon lattice spacing d ₀₀₂ is 0.33.
Crystals having a crystal size Lc of 50 to 2000 nm in the c-axis direction (direction perpendicular to the carbon lattice plane) of 54 to 0.3374 nm are preferred.

If the specific surface area is less than 0.2 m ² / g, the individual fibers or particles constituting the carbon material become too large. Depending on the size itself, the surface of the negative electrode may be uneven, or may not be dense even when compressed by a roll press. Conversely,
When the specific surface area exceeds 5 m ² / g, the contact area between the carbon material and the non-aqueous electrolyte increases, and the reactivity between them increases, and the irreversible capacity (the charge capacity and the discharge capacity of the discharge capacity) increases due to the side reaction. Difference) increases and the charge / discharge efficiency decreases.

The above d ₀₀₂ and Lc are values measured by the X-ray diffraction method. The case where d ₀₀₂ is 0.3354 nm is the case of a graphite single crystal, and is the minimum value of d ₀₀₂ . d
_{When 002} exceeds 0.3374 nm, graphitization is insufficient, and the charge / discharge capacity is reduced.

When Lc is less than 50 nm, the graphitization is also insufficient, and the charge / discharge capacity is reduced. Conversely, if Lc exceeds 2000 nm, individual fibers or particles constituting the carbon material become too large, and as in the case where the specific surface area is less than 0.2 m ² / g, there is a problem in producing a negative electrode. May occur.

The carbon material further has a diameter of 1 to
It is preferable to use a vapor grown carbon fiber having a length of 4 μm and a length of 3 to 30 μm. The vapor-grown carbon fiber is preferable because it is easily graphitized and has a very stable structure in which carbon lattice planes are stacked concentrically, so that a high cycle life can be expected.

When the diameter of the vapor grown carbon fiber is less than 1 μm or more than 4 μm, neither can be sufficiently graphitized. For this reason, the charge / discharge capacity is reduced. On the other hand, when the length is less than 3 μm, the specific surface area becomes too large, so that the charging / discharging efficiency is reduced as described above.
On the other hand, if it exceeds 30 μm, the individual fibers constituting the carbon material become too long, and the specific surface area becomes 0.2%.
As in the case of less than m ² / g, there is a possibility that a problem may occur when manufacturing the negative electrode.

In the case of producing this vapor grown carbon fiber, the vapor grown carbon fiber having a length of 50 to 100 μm produced from the vapor phase is first subjected to a graphitization treatment, and then to the graphitized carbon fiber. Cut carbon fiber, 3 ~ 30μm
Preferably, the length is By such a production method, a carbon material having the A / B ratio and the R value of the present invention is produced.

What is important here is the order of the graphitizing process and the cutting process. The reason why the cutting treatment is preferably performed after the graphitization treatment is considered to be as follows. That is, the crystal structure develops by the graphitization treatment, and the crystallite size Lc in the c-axis direction (the direction perpendicular to the carbon lattice plane) increases accordingly. However, if the cutting process is performed before the graphitization, the cutting process is performed in a state where the crystal structure is not developed. Moreover, during the cutting process, the structural distortion and the shift between the crystallites originally existing between the crystallites are so severe that they cannot be repaired even in the graphitization process in the subsequent step. Therefore, the growth of crystallites in the a-axis direction (direction parallel to the carbon lattice plane) is hindered, or excessive structural distortion or misalignment between crystallites hinders the passage of lithium ions, and is electrochemically inactive. The location is provided in the carbon fiber.

In the cutting process, the degree of the cutting process, that is, the degree of impact or hydrostatic pressure applied to the carbon fibers during cutting is important. If this degree is appropriate, the strain in the crystallite is alleviated, and the size Lc of the crystallite in the c-axis direction (direction perpendicular to the carbon lattice plane) is reduced.
Increase. Therefore, the crystal structure of graphite develops and the discharge capacity increases. Also, the strain between crystallites increases conversely, resulting in an amorphous structure that allows lithium ions to pass between crystallites more easily. This also increases the discharge capacity.

Therefore, the cutting process is performed for 50 to 100 m.
/ Sec is a high impact treatment in which the carbon fibers are cut with a high impact force by colliding the carbon fibers with each other with a blade rotating at a linear speed of 500 kg / sec.
^It is preferable to perform hydrostatic pressure treatment in which carbon fibers are compressed and cut by applying hydrostatic pressure at a pressure of ² . In order to perform the former high impact treatment, for example, a hybridizer can be used.

In high impact treatment, the linear velocity is 100 m / s
ec or the pressure is 1500k in hydrostatic pressure treatment
If it exceeds gf / cm ² , the degree of the cutting treatment is too strong. In this case, the strain in the crystallites rather increases,
Lc cannot be improved. In addition, in the case of the high impact treatment, fine particles are generated during the cutting treatment and adhere to the surface of the carbon fiber, so that the specific surface area of the carbon fiber increases. The increase in specific surface area of carbon fiber
As described above, the charge / discharge efficiency is reduced, which is a major cause of deterioration in cycle characteristics. In addition, in this case, the distortion between crystallites is so great that it is impossible for lithium ions to enter and exit. Therefore, in this case, the effect of the present invention is not exhibited.

On the contrary, when the linear velocity is 50
m / sec or less than 5 in hydrostatic pressure treatment.
If it is less than 00 kgf / cm ² , the degree of cutting treatment is too weak. In this case, the strain in the crystallite is not relaxed, and as a result, Lc does not increase. Therefore, the graphite crystal structure does not develop and the discharge capacity does not increase. Further, the distortion between crystallites does not increase, and as a result, an amorphous structure that allows lithium ions to easily pass between crystallites is not formed. That is, also in this case, the effect of the present invention is not exhibited.

The carbon material of the present invention described above can be used as a negative electrode of the following nonaqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery has, for example, a configuration in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween, and these are immersed in a non-aqueous electrolyte. Here, the non-aqueous electrolyte is obtained by dissolving a lithium salt in an organic solvent. Examples of lithium salts include LiClO ₄ , LiP
F ₆ , LiBF ₄ , LiAsF _{6 and the} like are used, and two or more of these can be used in combination. As the organic solvent, for example, propylene carbonate (P
C), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC),
Ethyl methyl carbonate (EMC) is used,
A mixed solvent composed of two or more of these can also be used.

The positive electrode is obtained by adhering a positive electrode material (a positive electrode active material) to a current collector made of a metal foil. As the current collector, a belt-like aluminum foil is usually used. A mixture of a lithium-containing composite oxide and a conductive material as a positive electrode material is attached to both surfaces of the current collector. As the lithium-containing composite oxide, for example, lithium cobalt oxide (LiCo
O ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ) and the like are used. The conductive material is added to enhance the conductivity of the positive electrode active material, and carbon black, graphite powder, carbon fiber typified by acetylene black, carbon fiber, and the like can be used for this.

The lithium-containing composite oxide and the conductive material are usually in the form of powder. These powders are mixed and dispersed in a binder solution, and the mixture is applied to the surface of the current collector. This is then dried and then compressed by a roll press or the like to form a positive electrode. The binder solution is obtained by dissolving a binder (binder) in an organic solvent. With this binder,
The powdery lithium-containing composite oxide and the conductive material are bound to each other and between the powder and the current collector. As the binder, for example, polyvinylidene fluoride (PVDF) is used, and as the organic solvent, for example, N-methyl-2-pyrrolidone (NMP) is used.

The negative electrode is obtained by attaching a negative electrode material (negative electrode active material) to a current collector made of a metal foil. Usually, a strip-shaped copper foil is used as the current collector. The carbon material of the present invention is adhered to both surfaces of the current collector as a negative electrode material. As the carbon material, a powdery material is usually used.
The individual shapes of the powder include a fibrous shape and a particulate shape.

The powdery carbon material is mixed and dispersed in a binder solution as in the case of the positive electrode, and the mixture is applied to the surface of the current collector. Then, it is dried and then compressed by a roll press or the like to become a negative electrode. Also in this case, for example, polyvinylidene fluoride (PVDF) is used as the binder, and N-
Methyl-2-pyrrolidone (NMP) is used.

As the separator, a porous strip film is used. This film is made of, for example, polypropylene. A positive electrode lead is welded to the positive electrode, and a negative electrode lead is welded to the negative electrode. The positive electrode and the negative electrode are spirally wound via a separator, and the spiral positive and negative electrodes are housed in, for example, a cylindrical battery can. And
The negative electrode lead is welded to the battery can, and the positive electrode lead is welded to the positive electrode cap. Next, the non-aqueous electrolyte is injected into the battery can, and then the positive electrode cap is swaged to the battery can to seal the battery can. Thereby, the non-aqueous electrolyte secondary battery is completed.

[0041]

EXAMPLES Hereinafter, the carbon material of the present invention will be described more specifically with reference to examples. The examples are illustrative of the invention and do not limit the invention.

Example 1 (1) Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 2 μm and a length of 70 μm produced from a gas phase was cut in an argon gas atmosphere.
Graphitization was performed at 800 ° C. for 30 minutes to obtain graphitized carbon fibers. 50 g of the graphitized carbon fiber is filled in a hybridizer (NHS-1 manufactured by Nara Machinery Co., Ltd.), and the blade is rotated at a linear velocity of 88 m / sec for 1 minute to convert the carbon fiber with high impact force. Cut. The cut carbon fiber had an average diameter of 2 μm, an average length of 12 μm, a specific surface area of 2.4 m ² / g, a d ₀₀₂ of 0.3359 nm, and L
c was 100 nm. This is shown in Table 1.

(2) ESR measurement 4 mg of carbon fiber prepared in (1) and 100 m of potassium chloride
g was mixed in a mortar, and the mixture was filled into a quartz sample tube having a diameter of 5 mm and a length of 270 mm. After the sample tube was evacuated under vacuum, an argon gas was sealed therein and ESR measurement was performed. The ESR device used was ES-10 manufactured by Nikkiso Co., Ltd. Magnetic field sweep range 335.5 ± 15mT, magnetic field modulation 1
The measurement was performed at 00 kHz (0.2 mT), a microwave output of 8 mW, and a sweep time of 2 min, and the measurement temperature was 25 ° C. Ratio A / B of peak A and peak B in the obtained ESR spectrum
I asked. Table 2 shows the results.

(3) Raman measurement Using U-1000 manufactured by Joban Yvon,
A very small amount of the carbon fiber prepared in (1) is adhered to a cloudy glass, and focused to 1 μm with an argon laser (wavelength 514.
5 nm, output 250 mW), and condenses Raman scattering by backscattering, condensing time 1 sec, sending step 1
to obtain a Raman spectrum by integrating three times the range of the 1200～1800Cm ^-1 in cm ^-1. Then, R values of the Raman spectra, i.e., Raman shift peak intensity I ₁₃₆₀ and Raman shifts around 1360 cm ^-1 was calculated the ratio I ₁₃₆₀ / I ₁₅₈₀ of the peak intensity I ₁₅₈₀ of around 1580 cm ^-1.
Table 2 shows the results.

(4) Evaluation by charge / discharge test 0.1 g of PVDF as a binder was mixed with N as an organic solvent.
Dissolved in 0.8 ml of MP. 0.9 g of the carbon fiber prepared in (1) was added thereto, and the mixture was sufficiently mixed in a mortar. This mixture is applied to a 1 × 5 cm nickel mesh with an application area of 1 × 1
cm, and dried at 110 ° C. for 24 hours to obtain a working electrode. Using this working electrode, a counter electrode made of metallic lithium, and a reference electrode made of metallic lithium,
A three-electrode beaker cell was prepared.

The non-aqueous electrolyte was mixed with a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 1: 1, volume ratio), and LiClO 2
₄ was dissolved to a concentration of 1 mol / l. The charge / discharge test was performed at a current density of 25 mA / g and a potential of 0 to 2.5 V between the working electrode and the reference electrode. Then, the charge capacity, the discharge capacity, and the charge / discharge efficiency of the first cycle and the 100th cycle were measured. The results are shown in Table 3 and FIG.
(The 100th cycle is omitted).

Although the plotted points are connected by a straight line in the graph of FIG. 5, this means that the plotted points are simply connected so as to be easily understood, and that the plotted points are not necessarily linear. It does not do. This is the same in FIGS.

Example 2 (1) Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 1 μm and a length of 50 μm produced from a gas phase was mixed in an argon gas atmosphere.
Graphitization was performed at 800 ° C. for 30 minutes to obtain graphitized carbon fibers. 50 g of the graphitized carbon fiber is filled in a hybridizer (NHS-1 manufactured by Nara Machinery Co., Ltd.), and the blade is rotated at a linear velocity of 60 m / sec for 2 minutes to thereby reduce the carbon fiber with a high impact force. Cut. The cut carbon fiber has an average diameter of 1 μm, an average length of 7 μm, a specific surface area of 4.8 m ² / g, a d ₀₀₂ of 0.3362 nm, and Lc
Was 100 nm. This is shown in Table 1.

Using this carbon fiber, ESR measurement, Raman measurement, and charge / discharge test were performed in the same manner as in Example 1.
The results are shown in Tables 2 and 3, and FIG. 5 (the 100th cycle is omitted).
Shown in

Example 3 (1) Preparation of Carbon Fiber A vapor-grown carbon fiber having a diameter of 4 μm and a length of 60 μm produced from a vapor phase was mixed with an argon gas atmosphere under an argon gas atmosphere.
Graphitization was performed at 800 ° C. for 30 minutes to obtain graphitized carbon fibers. 50 g of the graphitized carbon fiber was compression-cut by applying hydrostatic pressure at 1000 kgf / cm ² using a hydrostatic isostatic press. The cut carbon fiber had an average diameter of 4 μm, an average length of 28 μm, a specific surface area of 1.7 m ² / g, d ₀₀₂ of 0.3363 nm, and Lc of 100 nm. This is shown in Table 1.

Using this carbon fiber, an ESR measurement, a Raman measurement, and a charge / discharge test were performed in the same manner as in Example 1.
The results are shown in Tables 2 and 3, and FIG. 5 (the 100th cycle is omitted).
Shown in

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

The relationship between the A / B ratio, the discharge capacity and the charge / discharge efficiency of the carbon materials of Examples 1 to 3,
The relationship among the values, the discharge capacity and the charge / discharge efficiency is shown in FIGS. 1 to 4 (the 100th cycle is omitted in each figure).

Next, for comparison with the above-mentioned examples, those not included in the scope of the present invention were produced and tested. Comparative Example 1 (1) Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 3 μm and a length of 70 μm produced from a vapor phase was mixed under an argon gas atmosphere.
Graphitization was performed at 800 ° C. for 30 minutes to obtain graphitized carbon fibers. 50 g of the graphitized carbon fiber is filled in a hybridizer (NHS-1 manufactured by Nara Machinery Co., Ltd.), and the blade is rotated at a linear velocity of 120 m / sec for 2 minutes to thereby reduce the carbon fiber with a high impact force. Cut. The cut carbon fiber had an average diameter of 3 μm, an average length of 5 μm, a specific surface area of 8.1 m ² / g, a d ₀₀₂ of 0.3363 nm, and L
c was 100 nm. This is shown in Table 4.

This carbon fiber is different from that of Example 1 in that
Linear speed and processing time in the cutting process are 88 m / sec,
The difference is that it changed from 1 minute to 120 m / sec for 2 minutes. Using this carbon fiber, ESR was performed in the same manner as in Example 1.
Measurement, Raman measurement, and charge / discharge test were performed. The results are shown in Tables 5 and 6, and in FIG. 5 (the 100th cycle is omitted).

Comparative Example 2 (1) Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 1 μm and a length of 50 μm produced from a vapor was mixed with an argon gas in an atmosphere of 2 μm.
Graphitization was performed at 800 ° C. for 30 minutes to obtain graphitized carbon fibers. 50 g of the graphitized carbon fiber is filled in a hybridizer (NHS-1 manufactured by Nara Machinery Co., Ltd.), and the blade is rotated at a linear velocity of 40 m / sec for 2 minutes to thereby reduce the carbon fiber with a high impact force. Cut. The cut carbon fiber has an average diameter of 1 μm, an average length of 35 μm, a specific surface area of 2.6 m ² / g, d ₀₀₂ of 0.3367 nm, and L
c was 50 nm. This is shown in Table 4.

This carbon fiber is different from that of Example 1 in that
Linear speed and processing time in the cutting process are 88 m / sec,
The difference is that it changed from 1 minute to 40 m / sec for 2 minutes. ESR measurement, Raman measurement, and charge / discharge test were performed using this carbon fiber in the same manner as in Example 1. The results are shown in Tables 5 and 6, and in FIG. 5 (the 100th cycle is omitted).

Comparative Example 3 (1) Production of Carbon Fiber A 50 g vapor-grown carbon fiber having a diameter of 2 μm and a length of 70 μm produced from a gas phase was hybridized with a hybridizer (NHS-1 manufactured by Nara Machinery Co., Ltd.). And a linear velocity of 88 m /
The carbon fibers were cut with high impact force by rotating the blades for one minute in sec. This carbon fiber was graphitized in an argon gas atmosphere at 2800 ° C. for 30 minutes to obtain a graphitized carbon fiber. The carbon fiber after the treatment has an average diameter of 2 μm, an average length of 10 μm, and a specific surface area of 1.
2 m ² / g, d ₀₀₂ is 0.3366 nm, Lc is 70 n
m. This is shown in Table 4.

This carbon material is different from that of Example 1 in that
The difference is that a graphitization process is performed after the cutting process.
Using this carbon material, ESR measurement was performed in the same manner as in Example 1.
Raman measurement and charge / discharge test were performed. The results are shown in Tables 5 and 6, and in FIG. 5 (the 100th cycle is omitted).

[0062]

[Table 4]

[0063]

[Table 5]

[0064]

[Table 6]

Further, the relationship between the A / B ratio and the discharge capacity and charge / discharge efficiency of the carbon materials of Comparative Examples 1 to 3 described above.
The relationship among the values, the discharge capacity and the charge / discharge efficiency is shown in FIGS. 1 to 4 (the 100th cycle is omitted in each figure).

As is clear from FIGS. 1 and 2, A / B
The carbon material of the comparative example whose ratio was smaller than the range of the present invention had a discharge capacity (first cycle) of 340 mAh / g.
Although the charge / discharge efficiency (first cycle) is 75
%, And the carbon material of the comparative example whose A / B ratio is out of the range of the present invention is larger than that of the present invention.
Although the cycle (cycle) is as high as 92 to 93%, the discharge capacity (first cycle) is extremely small at 290 to 310 mAh / g.

On the other hand, the carbon material of this example has a discharge capacity (first cycle) of 340 to 360 mAh / g, which is larger than that of the comparative example, and a charge / discharge efficiency (first cycle) of 92 to 93%. High enough.

As is clear from FIGS. 3 and 4,
The carbon material of Comparative Example 1 in which the R value was out of the range of the present invention had a discharge capacity (first cycle) of 340 mAh.
/ G, but the charge / discharge efficiency (first cycle) is extremely low at 75%. In addition, about Comparative Examples 2 and 3,
Since the peak of I ₁₃₆₀ was not observed and the R value was not obtained, it is not shown in FIGS.

On the other hand, the carbon material of this example has a discharge capacity (first cycle) of 340 to 360 mAh / g, which is larger than that of the comparative example, and a charge / discharge efficiency (first cycle) of 92 to 93%. High enough.

As is clear from Table 6, Comparative Example 1
Has a very large charge capacity in the first cycle (453 mAh / g) but very low charge / discharge efficiency (75%). However, at the 100th cycle, the charge / discharge efficiency becomes sufficiently high (98%). Further, the carbon materials of Comparative Examples 2 and 3 have slightly higher charge capacity in the first cycle (308 to 337 mAh / g), but have sufficiently high charge and discharge efficiency (92 to 93%). The charging and discharging efficiency is 100%. As a result, the carbon materials of Comparative Examples 1 to 3 all have a small discharge capacity at the 100th cycle (28).
0-310 mAh / g). That is, the comparative example is 320 mA
Even if an attempt is made to obtain a discharge capacity of about h / g or more, the charge / discharge efficiency of a large-capacity battery is low, so that it is 280-31.
This shows that only a discharge capacity of about 0 mAh / g can be obtained.

On the other hand, as is apparent from Table 3, all of the carbon materials of this example have a large discharge capacity and a high charge / discharge efficiency in the first cycle. Furthermore, at the 100th cycle, the charge / discharge efficiency is all 100%.
As a result, the discharge capacity at the 100th cycle of the carbon material of this example was all large, and it can be seen that the cycle characteristics were superior to those of the comparative example.

As is clear from FIG. 5, the carbon material of the comparative example has a discharge capacity of 290 to 340 mAh / g, whereas the carbon material of the present example has a discharge capacity of 340 to 3
60 mAh / g, which is the same as or larger than the comparative example. Moreover, the carbon material of the comparative example has a discharge capacity of 290 to 290.
When it is as small as 310 mAh / g, the charge / discharge efficiency is 92 to
Although it is as high as 93%, when the discharge capacity is as large as 340 mAh / g, the charge / discharge efficiency is extremely low as 75%. In contrast, the discharge capacity of the carbon material of this example was 340 to 360.
mAh / g, and the charge / discharge efficiency is as high as 92 to 93%. (Refer to the description of Tables 3 and 6 above)

[0073]

As described in detail above, according to the first aspect of the present invention, the carbon material used for the negative electrode of the nonaqueous electrolyte secondary battery is observed by electron spin resonance analysis (ESR). The A / B ratio, which is an asymmetric parameter of the signal of the ESR spectrum at 25 ° C., is 1.0 to 1.
Is 3, and the Raman spectra Raman shifts observed by laser Raman spectroscopy are peak intensities I ₁₃₆₀ Raman shift of 1360 cm ^-1 is the ratio I ₁₃₆₀ / I ₁₅₈₀ of the peak intensity I ₁₅₈₀ of 1580 cm ^-1 R Value is 0.0
Since it is 1 to 0.3, a carbon material for a negative electrode having a large discharge capacity, high charge / discharge efficiency even with a large discharge capacity, and excellent cycle characteristics is provided.

According to the second aspect of the present invention, the specific surface area is 0.2 to ⁵ m ² / g, the carbon lattice spacing d ₀₀₂ is 0.3354 to 0.3374 nm, and the crystal size in the c-axis direction Since Lc is 50 to 2,000 nm, it is suitable as a carbon material for a negative electrode having the effects of the first aspect.

According to the third aspect of the present invention, since the carbon fiber is a vapor-grown carbon fiber having a diameter of 1 to 4 μm and a length of 3 to 30 μm, the carbon for a negative electrode having the effect of the first aspect of the invention is provided. It is suitable as a material.

According to a fourth aspect of the present invention, in the method for producing a carbon material used for a negative electrode of a non-aqueous electrolyte secondary battery, the vapor-grown carbon fiber produced from the gas phase is used. Since the cutting treatment is performed after the graphitization treatment, a carbon material for a negative electrode having a large discharge capacity, high charge / discharge efficiency even with a large discharge capacity, and excellent cycle characteristics can be manufactured. .

According to the fifth aspect of the present invention, in the cutting process, the carbon fibers are cut with a high impact force by hitting the carbon fibers with each other by a blade rotating at a linear speed of 50 to 100 m / sec. Therefore, it is suitable as the manufacturing method according to the fourth aspect.

According to the sixth aspect of the present invention, the carbon fiber is compressed and cut by applying a hydrostatic pressure at a pressure of 500 to 1500 kgf / cm ^2. It is suitable as a method for producing.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an A / B ratio and a discharge capacity (first cycle) in a carbon material.

FIG. 2 is a graph showing a relationship between an A / B ratio and a charge / discharge efficiency (first cycle) in a carbon material.

FIG. 3 is a graph showing a relationship between an R value and a discharge capacity (first cycle) in a carbon material.

FIG. 4 is a graph showing the relationship between the R value and the charge / discharge efficiency (first cycle) of a carbon material.

FIG. 5 is a graph showing the relationship between the first cycle discharge capacity and charge / discharge efficiency of a carbon material.

FIG. 6 is a graph showing an example of an ESR spectrum.

FIG. 7 is a graph showing an example of a Raman spectrum.

Claims (6)

[Claims] An A / B ratio which is an asymmetry parameter of a signal of an ESR spectrum at 25 ° C. observed by electron spin resonance analysis (ESR) in a carbon material used for a negative electrode of a nonaqueous electrolyte secondary battery. Is 1.0-1.
Is 3, and the Raman spectra Raman shifts observed by laser Raman spectroscopy are peak intensities I ₁₃₆₀ Raman shift of 1360 cm ^-1 is the ratio I ₁₃₆₀ / I ₁₅₈₀ of the peak intensity I ₁₅₈₀ of 1580 cm ^-1 R Value is 0.0
A carbon material characterized by being 1 to 0.3. 2. The specific surface area is 0.2 to ⁵ m ² / g, the carbon lattice spacing d ₀₀₂ is 0.3354 to 0.3374 nm, and the crystal size Lc in the c-axis direction is 50 to 2000 nm. The carbon material according to claim 1, wherein 3. The carbon material according to claim 1, wherein the carbon material is a vapor grown carbon fiber having a diameter of 1 to 4 μm and a length of 3 to 30 μm. 4. A manufacturing method for manufacturing a carbon material used for a negative electrode of a non-aqueous electrolyte secondary battery, wherein a graphitizing process is performed on a vapor-grown carbon fiber in a state generated from a gas phase, and then a cutting process is performed. A method for producing a carbon material, comprising: 5. The method according to claim 1, wherein the cutting process is performed at 50 to 100 m / sec.
The method for producing a carbon material according to claim 4, wherein the carbon fibers are cut with a high impact force by colliding the carbon fibers with each other by a blade rotating at a linear velocity. 6. The cutting process according to claim 1, wherein the cutting process is performed at 500 to 1500 kgf.
The carbon fiber is compressed and cut by applying hydrostatic pressure at a pressure of / cm ^2.
The method for producing a carbon material as described above.