JPH07296814A - Secondary battery electrode graphite material and its manufacture - Google Patents

Abstract

PURPOSE:To provide an electrode graphite material that makes possible a nonaqueous solvent type secondary battery having a large charge and discharge capacity, a high active material utilization factor, a discharge curve of excellent flatness, and a good quick charge and discharge characteristic and to provide a method for manufacturing the material. CONSTITUTION:A graphite material, which is obtained when petroleum, or coal type, tar or pitch is crosslinked and graphitized under reduced pressure or in an inert gas atmosphere at or above 1800 deg.C, has a (002) face whose average layer-to-layer spacing d(002) as determined by X-ray diffraction method is 0.336 to 0.350nm. The size Lc(002) of crystallites in (c)-axis direction is in excess of 15nm and not greater than 50nm and the size La(110) of crystallites in (a)-axis direction is 5-50nm, and an optical anisotropic composition as observed by a polarizing microscope shows a fine mosaic structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite material for a secondary battery electrode, and more specifically, a graphite material suitable as an electrode material for a high energy density non-aqueous solvent secondary battery and a method for producing the same. It is about.

[0002]

2. Description of the Related Art With the reduction in size and weight of VTRs and small communication devices, the demand for high energy density secondary batteries as their power source has increased, and nonaqueous solvent type lithium secondary batteries have been proposed (for example, JP-A-57-208079,
JP-A-62-90863, JP-A-62-1220
66, Japanese Patent Laid-Open No. 2-66856). These are the ones in which the risk of internal short circuit due to the generation of dendrites is eliminated by using lithium doped with carbon instead of using lithium metal for the negative electrode, and charge / discharge cycle characteristics, storage stability, etc. are improved. Is.

By the way, in order to produce a battery having a high energy density, it is important that the carbon material forming the negative electrode can dope and dedope a large amount of lithium. In order to increase the energy density per battery volume, it is important to use a carbon material with a large doping / dedoping capacity of the active material per unit weight and to fill the negative electrode of the battery with as much carbon material as possible. .

In the above-mentioned known technique, graphite or a carbonaceous material obtained by carbonizing an organic material is used as a carbon material for a negative electrode of a non-aqueous solvent type lithium secondary battery.

Graphite has a large true density of 2.27 g / cm ³ and is advantageous in filling a large amount of carbon material in the negative electrode. However, the graphite intercalation compound is formed by doping the graphite with lithium. However, the larger the size of the crystallite in the c-axis direction, the more strain is repeatedly generated in the crystallite due to doping / dedoping and the crystal breakage easily occurs. . Therefore, the secondary battery constituted by using a graphite material having a developed graphite structure having a large crystallite in the c-axis direction is inferior in repeated charge / discharge performance. Further, the doping and dedoping reaction of lithium into graphite proceeds from the edge surface of graphite, but in a graphite material having a large crystallite size in the a-axis direction, the dope and dedoping reaction is slow because the edge surface is small. Therefore, in a battery using such a graphite material, when trying to perform rapid charge and discharge, the doping capacity and the dedoping capacity are sharply reduced, or the overvoltage becomes high and the decomposition of the electrolytic solution is likely to occur. There is also.

Further, in the so-called non-graphitizable carbon material obtained by carbonizing phenol resin or furan resin,
A high doping / dedoping capacity can be obtained per unit weight, but the true density is small at about 1.6 g / cm ^3, and the weight per volume is small. Therefore, the energy density per volume is not necessarily high in the secondary battery in which the negative electrode is formed by using these non-graphitizable carbon materials. Further, there is a problem in that the thynium doped in the negative electrode carbon material is not completely undoped, a large amount of lithium remains in the negative electrode carbon material, and the active material lithium is wastefully consumed.
Further, there is a problem that the electric potential at the time of discharging decreases with the amount of discharging.

[0007]

The present invention has been made in order to solve the above problems, and has a large true density, a large lithium doping / dedoping capacity per unit weight, and a large doping capacity. Graphite material for electrodes that enables a high energy density secondary battery that has a small irreversible capacity of the active material required as a difference in dedoping capacity, a small capacity decrease due to rapid charge and discharge, and an excellent flatness of discharge curve And its manufacturing method.

[0008]

Means for Solving the Problems The present inventors have a large charge / discharge capacity by controlling the microstructure of a graphite material appropriately, the capacity decrease due to rapid charge / discharge is small, and charge / discharge cycle characteristics are improved. It has been found that a graphite material which is excellent in non-aqueous solvent secondary battery with excellent irreversible capacity (high utilization rate of active material) can be obtained.

That is, the graphite material for a non-aqueous solvent type secondary battery electrode of the present invention was obtained by a powder X-ray diffraction method (00
2) The average inter-layer spacing of the planes (hereinafter sometimes abbreviated as “d ₀₀₂ ”) is 0.336 to 0.350 nm, and the crystallite size in the c-axis direction (hereinafter sometimes abbreviated as Lc _(002)). Is more than 15 nm and 50 nm or less, and the size of the crystallite in the a-axis direction (hereinafter sometimes abbreviated as “La ₍₁₁₀₎ .” Is 5 to 50 nm, which is an optical difference observed by a polarization microscope. Mosaic (fi
It is characterized by having a ne mosaic structure.

The graphite material having such characteristics is obtained by subjecting petroleum-based or coal-based tar or pitch to a crosslinking treatment and then subjecting it to a graphitization treatment at 1800 ° C. or higher under reduced pressure or in an inert gas atmosphere. Can be manufactured by.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The first characteristic to be satisfied by the graphite material of the present invention is that the average layer spacing d _{002 of} (002) planes determined by an X-ray diffraction method is 0.336 to 0.350 nm, c
Axial crystallite size Lc ₍₀₀₂₎ exceeds 15 nm 5
0 nm or less, the crystallite size La ₍₁₁₀₎ in the a-axis direction is 5
˜50 nm. In a secondary battery using as a negative electrode a graphite material having a graphite structure with an Lc ₍₀₀₂₎ of more than 50 nm, the graphite material may be decomposed or the electrolyte may be decomposed due to doping or dedoping of the active material. Easy and not preferable. Further, a graphite material having La ₍₁₁₀₎ of more than 50 nm is not preferable because the edge portion of the crystallite is reduced and the doping and dedoping speed of the active material becomes slow. Further, a carbonaceous material having a d ₀₀₂ of more than 0.350 nm is not preferable because the flatness of the discharge curve deteriorates. Preferably d ₀₀₂ is 0.336 to 0.345
nm, Lc ₍₀₀₂₎ exceeds 15 nm and 40 nm or less, La
₍₁₁₀₎ is 10 to 50 nm, and more preferably d ₀₀₂ is 0.
337-0.342nm, Lc ₍₀₀₂₎ is 20-40n
m and La ₍₁₁₀₎ are 15 to 50 nm.

The second characteristic that the graphite material of the present invention should have is that when the graphite material is observed with a polarizing microscope,
That is, an optically anisotropic structure having a fine mosaic structure is observed.

In the graphite material having such a structure, fine crystallites are randomly arranged, and crystal strain due to doping / dedoping of the active material between the crystal layers becomes isotropic as a whole, so that the active material becomes active. Crystal collapse due to material doping / dedoping is suppressed. The secondary battery including the negative electrode composed of such a graphite material has good charge / discharge cycle characteristics. The dimension of the anisotropic unit constituting the optically anisotropic structure is preferably 10 μm or less, more preferably 5 μm or less.

When a secondary battery electrode is formed by using a graphite material, the graphite material is made into fine particles of about 100 μm or less, and a binder is added thereto, followed by pressure molding to obtain a current collector and an electric material. And a method in which a paste-like composition composed of fine particles of a graphite material and a binder is applied to the surface of a current collector such as a metal foil and then dried.

Therefore, in order to increase the energy density per battery volume, it is advantageous that the true density of the graphite material is large. The graphite material of the present invention has the above d ₀₀₂ , Lc
₍₀₀₂₎ , within the range where the crystal structure is controlled to be determined by La ₍₁₁₀₎ , the true density is 1.90 g / cm ³ or more, preferably 2.00 g / cm ³ or more, and more preferably 2.10 g.
/ Cm ³ or more is preferable.

The graphite material of the present invention can be manufactured, for example, by the following method.

That is, after petroleum-based or coal-based tar or pitch is subjected to a crosslinking treatment, it is subjected to a graphitization treatment at 1800 ° C. or higher under reduced pressure or in an inert gas atmosphere.

The cross-linking treatment for tar or pitch is carried out for the purpose of controlling the fine structure of the graphite material obtained by carbonizing and graphitizing the cross-linked tar or pitch. The method of the present invention appropriately controls the fine structure of the obtained graphite material by the combination of the degree of crosslinking by this crosslinking treatment (degree of crosslinking) and the conditions for the subsequent graphitization.

The degree of cross-linking of the tar or pitch which has been subjected to the cross-linking treatment is determined by further polishing the carbonaceous sample obtained by heat-treating the tar or pitch at, for example, 1000 ° C. for 1 hour in a nitrogen stream, and subjecting it to crossed Nicols. Then, for example, it can be known by a cross-linking degree determination method of observing with a polarization microscope at 1000 times. The observed optically anisotropic structure shows a so-called flow structure when the degree of crosslinking is small (see, for example, FIG. 2 which is a polarization microscope photograph of the graphite material obtained in Comparative Example 1 described later), but the degree of crosslinking is As the size increases, a fine mosaic structure (for example, see FIG. 1, which is a polarization microscope photograph of the graphite material obtained in Example 4 described later) is exhibited. As the degree of cross-linking increases, the size of the anisotropic unit of the optically anisotropic structure observed becomes smaller, and finally the optically anisotropic structure is not observed, and isotropic (for example, Comparative Example 2 described later) 3) which is a polarization micrograph of the carbonaceous material obtained in 1.). The optically anisotropic structure observed by the above method after the crosslinking treatment does not change so much depending on the temperature of the subsequent heat treatment. Therefore,
Finally, by observing the optically anisotropic structure of the carbon or graphitic material obtained by carbonization or graphitization, it is possible to determine the degree of crosslinking of tar or pitch before the carbonization treatment, that is, after the crosslinking treatment. It is possible. When the heat treatment temperature is the same, the d ₀₀₂ of the carbonaceous material generally obtained after the heat treatment increases with an increase in the degree of crosslinking, and Lc ₍₀₀₂₎ and La are increased.
₍₁₁₀₎ decreases. When the degree of cross-linking is the same, d ₀₀₂ and Lc ₍₀₀₂₎ and La ₍₁₁₀₎ of the carbonaceous material generally obtained decrease with increasing heat treatment temperature.

In the method of the present invention, the cross-linking treatment is carried out to such an extent that the optically anisotropic structure of the carbonaceous material observed by the above-mentioned method for judging the degree of cross-linking becomes a structure having a fine mosaic structure and isotropic. It will be stopped before. The cross-linking treatment is
Preferably, the dimension (major axis standard) of an anisotropic (mosaic) unit that constitutes the finely mosaic optical anisotropic structure is 10 μm.
m or less, more preferably 5 μm or less.
The lower limit of the anisotropy unit is that the mosaic unit can be sufficiently confirmed in a 1000-fold polarization micrograph and can be distinguished from the isotropic phase.

In the production method of the present invention, as raw materials for the graphite material, petroleum tar and pitch produced as by-products during ethylene production, coal tar produced during coal carbonization, and low boiling point components of coal tar are removed by distillation. Petroleum-based or coal-based tars or pitches such as quality components, pitch, tar and pitch obtained by liquefaction of coal can be used. Further, two or more of these tars and pitches may be mixed and used.

The cross-linking treatment of tar or pitch can be carried out by a method of heat treatment by adding nitric acid, acetyl nitrate, sulfur or the like to tar or pitch, a method of oxidizing tar or pitch with an oxidizing agent, and the like. As the oxidizer, O ₂ , O ₃ , NO ₂ , a mixed gas obtained by diluting these with air, nitrogen, or the like, an oxidizing gas such as air, or an oxidizing liquid such as sulfuric acid, nitric acid, or hydrogen peroxide solution is used. be able to.

The method in which nitric acid, acetyl nitrate, sulfur, etc. are added to tar or pitch having a low softening point and subjected to a heat treatment at 150 to 400 ° C. to carry out a crosslinking treatment also has an effect of improving the carbonization rate of the raw material, This is a preferable method because the yield of obtaining the carbonaceous material is improved.

Among them, the method using nitric acid is a preferable method because a uniform crosslinking reaction can be carried out and the reaction can be easily controlled. Furthermore, nitric acid is economically advantageous because it is inexpensive.

When the cross-linking treatment is carried out using nitric acid, nitric acid is added to tar or pitch as a raw material and reacted with stirring, and the temperature is gradually raised to 150 to 450 ° C., preferably 300 to 400 ° C. for 10 minutes. Hold for about 4 hours to react. When nitric acid is added to tar or pitch, heat is generated, so in order to suppress runaway reaction, add nitric acid gradually,
It is preferable that the reaction system is cooled, the temperature is kept at 40 ° C. or lower, the reaction is performed for about 1 to 3 hours, and then the temperature is raised. It is also possible to remove low-boiling components present in the reaction system by distillation during or after the reaction. By removing low-boiling components, it is possible to reduce the amount of volatile components generated in the subsequent carbonization / graphitization process, reduce the burden on the carbonization / graphitization equipment, and improve workability. You can

The concentration of nitric acid used is not particularly limited, but is preferably about 50 to 68%. The amount of nitric acid added varies depending on the hydrogen / carbon atomic ratio (H / C) of the tar or pitch used. The range can be determined almost appropriately by increasing or decreasing the amount of the graphite material so that the graphite material having an appropriate degree of crosslinking can be obtained by the above-described method for determining the degree of crosslinking.

As another method of cross-linking treatment, there is a method in which tar or pitch having a low softening point is distilled, air-blown or other method is used to oxidize pitch treated with an oxidizing agent. In this case, a method in which the pitch is formed into a fine powder shape, a fiber shape, or a film shape and then oxidized may be adopted, but the following method is preferable in order to uniformly and easily perform the oxidation.

That is, to a pitch such as petroleum pitch or coal pitch, an aromatic compound having 2 to 3 rings having a boiling point of 200 ° C. or more or a mixture thereof is added as an additive and heated and mixed to obtain a pitch molded body. Next, with a solvent that has a low solubility in pitch and a high solubility in additives, the additive is extracted and removed from the pitch molded body to form a porous pitch, which is then oxidized using an oxidizing agent. is there.

The purpose of the above-mentioned aromatic additive is to make the molded product porous by extracting and removing the additive from the molded pitch product to facilitate the crosslinking treatment by oxidation. Such additives are selected from, for example, one or a mixture of two or more of naphthalene, methylnaphthalene, phenylnaphthalene, benzylnaphthalene, methylanthracene, phenanthrene, biphenyl and the like. The amount added to the pitch is 10 to 5 with respect to 100 parts by weight of the pitch.
A range of 0 parts by weight is preferred.

The pitch and the additives are mixed in a molten state by heating in order to achieve uniform mixing. The mixture of pitch and additive is preferably molded into particles having a particle size of 1 mm or less so that the additive can be easily extracted from the mixture. The molding may be performed in a molten state, or may be performed by a method such as pulverizing after cooling the mixture.

Solvents for extracting and removing the additive from the mixture of pitch and the additive include aliphatic hydrocarbons such as butane, pentane, hexane and heptane, a mixture mainly containing aliphatic hydrocarbons such as naphtha and kerosene, and methanol. And aliphatic alcohols such as ethanol, propanol and butanol are preferable.

By extracting the additive from the mixture of pitch and the additive molded body with such a solvent, the additive can be removed from the molded body while maintaining the shape of the molded body. At this time, a through hole for the additive is formed in the molded body,
It is presumed that a pitch compact having uniform porosity can be obtained.

The porous pitch thus obtained is
Oxidation is performed using the above-mentioned oxidizing agent, and crosslinking treatment is performed. As the oxidant, a gas containing oxygen such as air or a mixed gas of air and another gas such as combustion gas is used, and the temperature is 120 ° C.
It is simple and economically advantageous to carry out the cross-linking treatment at ˜300 ° C. In this case, if the softening point of the pitch is low,
The pitch to be used preferably has a softening point of 150 ° C. or higher because the pitch is melted during oxidation and oxidation becomes difficult.

The degree of the cross-linking treatment is surely based on the above-mentioned cross-linking degree judging method, but when oxidizing with a gas containing oxygen, as a guide, the oxygen content by the elemental analysis of the porous pitch after the oxidation treatment is used. Is preferably 1 to 5%.

In the method of the present invention, the graphitization treatment is carried out under reduced pressure or in an inert gas atmosphere at 1800 ° C. or higher, preferably 2200 ° C. or higher, more preferably 2600 ° C. or higher. Examples of the inert gas include argon gas and helium gas.

The temperature of the graphitization treatment is determined depending on the degree of cross-linking, but if it is less than 1800 ° C., graphitization is insufficient, which is not preferable.

The graphitization treatment can be carried out by continuously raising the temperature of the crosslinked pitch obtained by subjecting tar or pitch to the crosslinking treatment to the graphitization treatment temperature.
It is preferable to perform graphitization after firing and carbonizing at a temperature of 800 ° C. or lower, preferably 800 to 1200 ° C.

When a fine powdery graphite material is required, the graphite material obtained after the completion of graphitization can be crushed, but the tar or pitch is subjected to the crosslinking treatment as described above. A carbon precursor whose volatile content is 15% or less, which is obtained by further heat-treating the obtained (crosslinked pitch) in an inert gas atmosphere at 350 to 700 ° C. prior to graphitization to promote polycondensation and at the same time remove low-boiling components. And the average particle size 1
A fine powdery graphite material can be produced by pulverizing to a particle size of 00 μm or less, preferably 50 μm or less and then carbonizing and graphitizing.

The volatile content of the carbon precursor is set to 15% or less in order to prevent melting of the crushed particles and fusion of the crushed particles during the carbonization treatment. The volatile content of the carbon precursor is preferably 10% or less, more preferably 5% or less.

Since the carbon precursor before carbonization is much easier to pulverize and less abrasion of the pulverizer than the carbonized one, the method of pulverizing before carbonization is very advantageous.
Further, reducing the volatile content of the carbon precursor is preferable because it reduces the generation of tar and decomposition gas in the carbonization step and reduces the load of the carbonization step.

When the electrode of the non-aqueous solvent type secondary battery is formed by using the graphite material of the present invention, the graphite material is made into fine particles having an average particle size of about 5 to 100 μm, if necessary,
Polyvinylidene fluoride, polytetrafluoroethylene,
A method of forming a layer having a thickness of, for example, 10 to 200 μm by bonding to a conductive current collector made of, for example, a circular or rectangular metal plate with a binder that is stable to a non-aqueous solvent such as polyethylene. The electrode is manufactured by. The preferable addition amount of the binder is 1 to 20% by weight based on the graphite material.
Is. If the amount of the binder added is too large, the electrical resistance of the obtained electrode increases, the internal resistance of the battery increases, and the battery characteristics deteriorate, which is not preferable. On the other hand, if the amount of the binder added is too small, the binding between the graphite material particles and the current collector is insufficient, which is not preferable. Note that the above is the value for a relatively small capacity secondary battery, but in order to form a larger capacity secondary battery, a mixture of the graphite fine particles and the binder is formed by a method such as press molding. It is also possible to manufacture a molded body having a larger thickness and electrically connect the molded body to a current collector.

The graphite material of the present invention can be used as a positive electrode material of a non-aqueous solvent type secondary battery by utilizing its good doping property. However, as described above, the non-aqueous solvent type secondary battery can be used. It is preferably used for the constitution of a negative electrode of a secondary battery, particularly a negative electrode for doping lithium as a negative electrode active material of a lithium secondary battery.

In this case, the positive electrode material is LiCoO 2.
Complex metal chalcogenides such as ₂ , LiNiO ₂ and LiMnO ₄ are preferable, and they are formed with a suitable binder and a carbon material for imparting conductivity to the electrode to form a layer on the conductive current collector.

The non-aqueous solvent type electrolytic solution used in combination with the positive electrode and the negative electrode is generally formed by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent, for example, one of organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane. Alternatively, two or more kinds can be used in combination. Further, as the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , L
iCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr,
_{LiB (C 6 H 5) 4} , LiN (SO 2 CF 3) 2 or the like is used.

When a secondary battery is constructed using the graphite material of the present invention, a mixed solvent of ethylene carbonate and diethyl carbonate, dimethyl carbonate, diethoxyethane or the like is preferable as the non-aqueous solvent, and LiPF ₆ is used as the electrolyte. , LiBF ₄ are preferred. LiPF _{6 in} a mixed solvent of ethylene carbonate and diethyl carbonate,
A non-aqueous solvent type electrolytic solution in which LiBF ₄ or both of them are dissolved is particularly preferable because decomposition of the non-aqueous solvent is less likely to occur during charge / discharge of the secondary battery.

In a secondary battery, generally, the positive electrode layer and the negative electrode layer formed as described above are opposed to each other through a liquid-permeable separator made of a non-woven fabric or other porous material, if necessary. It is formed by immersing in.

[0047]

In the present invention, the tar or pitch is subjected to a cross-linking treatment and then graphitized to appropriately control the fine structure of the resulting graphitic material to obtain a high density and high active material. While having the doping and dedoping capacity of
The irreversible capacity required as the difference between the doping capacity and the dedoping capacity is small, and it is possible to obtain a graphite material suitable as a secondary battery electrode material.

Further, by controlling the size of the crystallite of the graphite material, it is possible to facilitate the doping and dedoping reaction of the active material into the graphite material on which the electrode is formed, and to perform the rapid doping and the capacity associated with the dedoping. The drop is prevented.

Further, by rapidly arranging the fine anisotropic structure of the graphite material in a disordered manner, the electrode is rapidly doped,
The dedoping reaction is enabled, the strain of the crystallite at the time of doping / dedoping the active material is reduced, and the strain direction is dispersed, so that the collapse of the graphite material due to the doping / dedoping of the active material is prevented.

Therefore, the graphite material of the present invention has excellent characteristics as a graphite material for an electrode of a high energy density non-aqueous solvent secondary battery, which is excellent in rapid charge / discharge properties.

The measurement of d ₀₀₂ , Lc ₍₀₀₂₎ , La ₍₁₁₀₎ , true density, volatile content of pitch, softening point and observation under a polarizing microscope of the carbon or graphite material described in the present specification are as follows. I went like this.

"D of graphitic material₀₀₂, Lc₍₀₀₂₎and
La₍₁₁₀₎": The graphite material powder is mixed with an aluminum sample sample.
Filled in a single color with a graphite monochromator
The converted CuKα line (wavelength λ = 0.15418 nm)
X-ray diffraction diagram by the reflection type diffractometer method as the source
Get the shape. To correct the diffraction pattern, Lorentz polarization factor,
Kα without correction for absorption factor, atomic scattering factor, etc.
₁, Kα₂Only the correction of the double line of Rachinger
The method was performed. (002) Peak position of diffraction line
Is the center of gravity method (the center of gravity of the diffraction line is determined and the corresponding
2θ value to find the peak position)
Compensation using (111) diffraction line of high-purity silicon powder for quality
Correctly, from the Bragg formula below, d₀₀₂Was calculated.

Lc ₍₀₀₂₎ is the full width at half maximum of the (002) diffraction line of the carbonaceous sample and (11 of the high-purity silicon powder for standard substance).
1) β _1/2 was obtained from the half width of the diffraction line using the Alexander curve, and was calculated by the Scherrer's formula below. Here, the shape factor K is 0.9.

La ₍₁₁₀₎ is the full width at half maximum of the (110) diffraction line of the carbonaceous sample and (33) of the high-purity silicon powder for standard substances.
1) β _1/2 was obtained from the half width of the diffraction line using the Alexander curve, and was calculated by the Scherrer's formula below. Here, the shape factor K is 0.9.

D ₀₀₂ = λ / (2 · sin θ) (Bragg's formula) L = K · λ / (β _1/2 cos θ) (Scherrer's formula) “True Density”: The true density is defined in JIS R7212. According to the method, it was measured by the butanol method.

"Volatile": Volatile is JIS R7212
The measurement was performed according to the method specified in. However, the sample was heated at 800 ° C. for 30 minutes.

"Softening point": Shimadzu's high-performance floater
Using a star, 1g of sample crushed to 250μm or less
Cross-sectional area of 1 cm with a 1 mm diameter nozzle at the bottom² Shi
Filling the linder, 9.8N / cm²(10 kg / cm
²) Is added and the temperature is raised at a rate of 6 ° C./min. Warm
With increasing temperature, the powder particles soften and the filling rate improves.
The volume of powder decreases, but the volume decreases above a certain temperature.
Will stop. If the temperature is further raised, the cylinder bottom
The sample melts and flows out from the cheat. Sample powder at this time
Is defined as the softening point of the sample.
It For samples with a high softening point, test from the nozzle.
In some cases, there is no outflow of fees.

"Polarization microscope observation": When the sample is in powder form, about 10% by weight of the powder sample is added to the liquid epoxy resin and mixed well, and then the mold made of silicone rubber (diameter 25
mm) and the sample is granular or agglomerated, the sample is made to have a particle size of several mm, embedded in several liquid epoxy resins filled in the above mold, and held at 120 ° C. for 24 hours to remove the epoxy resin. After the curing, the cured epoxy resin was cut at an appropriate position so that the sample was exposed on the surface, the cut surface was polished, and observation with a polarizing microscope was performed under a crossed Nicol at 1000 times.

The expression that the dimension of the anisotropic unit constituting the optically anisotropic structure is "A μm or less" means that any 10 non-overlapping regions of the graphite material sample are observed by the above-mentioned polarization microscope observation. An optically anisotropic structure in which the total area of anisotropic units in which the maximum dimension of anisotropic units is A μm or more in the visual field is 10% or less of the total area of the graphite material. It means the anisotropic unit size inside.

[0060]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 A reactor having an internal volume of 20 liters equipped with a stirrer had a residual carbon content of 14.1% and a density of 1.09 g.
15 kg of ethylene bottom oil of / cm ³ was charged, cooled with stirring to keep the temperature at 40 ° C. or lower, and 2 kg of 61% nitric acid was added and reacted for 2 hours. Next, after holding at 80 ° C. for 1 hour, the temperature was raised to 380 ° C. at 100 ° C./hour, reacted at 380 ° C. for 2 hours and then cooled to obtain a crosslinked pitch.

The yield of this crosslinked pitch was 36.1% with respect to the raw material ethylene bottom oil.

This crosslinked pitch has a softening point of 284 ° C., a volatile content of 28.3%, an oxygen content of 0.5%, and a nitrogen content of 1.3.
%, And the H / C atomic ratio was 0.63.

This crosslinked pitch was heated to 600 ° C. in a nitrogen stream.
After heat treatment for 1 hour, cool and pulverize, average particle size 25μ
m carbon precursor particles were obtained. The carbon precursor fine particles are carbonized in a nitrogen stream at 1000 ° C. for 1 hour, and further, A
Graphitization treatment was carried out at 2800 ° C. for 1 hour in an air stream to obtain a graphite material.

The characteristics of the obtained graphite material are shown in Table 1 below.

Example 2 68 kg of petroleum-based pitch having a softening point of 210 ° C., a quinoline insoluble content of 1% by weight, and an H / C atomic ratio of 0.63% and naphthalene of 32 kg were mixed in an internal volume of 300 liters equipped with a stirring blade. It was charged in a pressure resistant container, heated to 190 ° C., dissolved and mixed, cooled to 80 to 90 ° C. and extruded to obtain a cord-shaped molded body having a diameter of about 500 μm. Then,
This string-shaped molded product was crushed so that the ratio of diameter to length was about 1.5, and the crushed product obtained was heated to 90 ° C. for 0.53.
% Polyvinyl alcohol (saponification degree 88%) aqueous solution, stirred and dispersed, and cooled to obtain a spherical pitch molded body. After removing most of the water by filtration, the naphthalene in the pitch molded body was extracted and removed with n-hexane in an amount of about 6 times the weight of the spherical pitch molded body.

The spherical pitch porous body thus obtained was subjected to an oxidation treatment by holding it at 165 ° C. for 1 hour while passing heated air to obtain oxidized pitch.

The oxygen content of this oxidized pitch was 2%.

This oxide pitch was subjected to 480 in a nitrogen atmosphere.
It heat-processed at 1 degreeC for 1 hour, and the carbon precursor whose volatile matter was 4.7% was obtained. This carbon precursor was crushed to obtain an average particle size of about 25μ.
m of carbon precursor fine particles.

Next, the carbon precursor fine particles were carbonized in a nitrogen stream at 1000 ° C. for 1 hour and further graphitized in an Ar stream at 2000 ° C. for 1 hour to obtain a graphite material.

The characteristics of the obtained graphite material are shown in Table 1 below.

(Examples 3 to 5) The same procedure as in Example 2 was carried out except that the graphitization treatment temperatures were 2400 ° C. (Example 3), 2800 ° C. (Example 4) and 3000 ° C. (Example 5), respectively. Graphite materials were obtained respectively.

The characteristics of the obtained graphite materials are shown in Table 1 below.

The graphite materials obtained in the above Examples 1 to 5 all showed a fine mosaic optical anisotropic structure as a result of observation with a polarizing microscope. Representatively, a polarized light micrograph (× 1000) of the graphite material according to Example 4 is shown in FIG. 1.

(Comparative Example 1) The petroleum pitch used in Example 2 was heat-treated at 600 ° C for 1 hour in a nitrogen stream, cooled and pulverized to obtain carbon precursor fine particles having an average particle diameter of 25 µm. The carbon precursor particles were carbonized in a nitrogen stream at 1000 ° C. for 1 hour, and further graphitized in an Ar stream at 2800 ° C. for 1 hour to obtain a carbon material.

The characteristics of the obtained carbon material are shown in Table 1 below.

When this carbon material was observed with a polarizing microscope, a polarizing microscope photograph (1000 times) showed that the optically anisotropic structure did not show a mosaic structure but a flow structure as shown in FIG.

(Comparative Example 2) The spherical pitch porous body obtained in Example 2 was subjected to an oxidation treatment while being held at 260 ° C for 1 hour while passing heated air to obtain an oxidized pitch.

The oxygen content of this oxidized pitch was 16%.

This oxide pitch was adjusted to 600 in a nitrogen atmosphere.
After heat treatment at ℃ for 1 hour, crushed and average particle size is about 2
5 μm carbon precursor fine particles were used. Next, the carbon precursor fine particles were carbonized in a nitrogen stream at 1200 ° C. for 1 hour and further graphitized in an Ar stream at 2800 ° C. for 1 hour to obtain a carbon material.

When this carbon material was observed with a polarization microscope, a polarization microscope photograph (× 1000) showed that the optically anisotropic structure did not show a mosaic structure, as shown in FIG. 3, but showed optical isotropy. .

The characteristics of this carbon material are shown in Table 1 below.

Comparative Example 3 Polyvinyl chloride (PVC) having an average degree of polymerization of 700 was treated in the same manner as in Comparative Example 1 to obtain a carbon material.

When this carbon material was observed with a polarizing microscope, the optically anisotropic structure did not show a mosaic structure but showed a flow structure.

The characteristics of this carbon material are shown in Table 1 below.

(Comparative Example 4) Polyvinylidene chloride (PVD)
C) was treated in the same manner as in Comparative Example 1 to obtain a carbon material. When this carbon material was observed with a polarization microscope, a polarization microscope photograph (1000 times) showed that the optically anisotropic structure was isotropic without showing a mosaic structure as shown in FIG.

The characteristics of this carbon material are shown in Table 1 below.

(Comparative Example 5) 37% to 47.1 g of phenol.
% Formalin (121.6 g) was added, the mixture was heated to 60 ° C. and stirred, then, 29% aqueous ammonia (3.8 g) was added dropwise, and then the mixture was reacted at 80 ° C. for 6 hours. Next, after cooling this to room temperature, 6.4 g of lactic acid was added to neutralize the reaction liquid to obtain a candy-shaped initial condensate. The initial condensate was condensed at 150 ° C. for 12 hours to give a resol-type resin. This resin was precalcined in a nitrogen stream at 500 ° C. for 1 hour to obtain a carbon precursor, which was then pulverized to obtain carbon precursor fine particles having an average particle size of 25 μm. Next, the carbon precursor fine particles are carbonized in a nitrogen stream at 1000 ° C. for 1 hour, and further carbonized in an Ar stream.
Graphitization treatment was performed at 800 ° C. for 1 hour to obtain a carbon material.

When this carbon material was observed with a polarizing microscope, no optically anisotropic structure was observed and it was isotropic.

The characteristics of this carbon material are shown in Table 1 below.

(Comparative Example 6) Flake-like natural graphite (Nippon Graphite Trading Co., Ltd. CP) produced in Madagascar was used.

This natural graphite has a fixed carbon content of 97%, an ash content of 2%, a volatile content of 1%, and an average particle size of 7 μm. The properties of this natural graphite are shown in Table 1 below.

(Doping / Undoping Test of Active Material) Using the carbon materials obtained in the above Examples and Comparative Examples, a non-aqueous solvent secondary battery was prepared in the following manner, and its characteristics were evaluated. did.

The graphite material of the present invention is suitable for use as the negative electrode of a non-aqueous solvent secondary battery, but the effect of the present invention is to obtain the dope capacity, dedoping capacity and graphite without dedoping of the battery active material. The amount remaining in the quality material (irreversible capacity)
In order to evaluate accurately without being affected by variations in the performance of the counter electrode, a lithium secondary battery using a large excess of lithium metal with stable characteristics as the counter electrode (negative electrode) and the graphite material obtained above as the positive electrode. Was constructed and its characteristics were evaluated.

That is, the positive electrode (carbon or graphite material electrode) was manufactured as follows. 90 parts by weight of the particulate carbon or graphite material produced as described above, 10 parts by weight of polyvinylidene fluoride, N-methyl-2-pyrrolidone is added to form a paste, and uniformly coated on a copper foil, After drying, it is peeled from the copper foil and punched into a disk shape with a diameter of 21 mm. This was pressed against a stainless steel mesh disk having a diameter of 21 mm by a press to be a pressure-bonded positive electrode. The amount of carbon material in the positive electrode was adjusted to about 40 mg.

As the negative electrode, a metal lithium thin plate having a thickness of 1 mm punched into a disk shape having a diameter of 21 mm was used.

Using the positive electrode and the negative electrode produced as described above, the electrolyte solution was prepared by adding LiPF ₆ at a ratio of 1 mol / liter to a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. Was used to form a non-aqueous solvent type lithium secondary battery using a polypropylene microporous membrane as a separator.

In the lithium secondary battery having such a structure, the carbon material was doped with lithium and dedoped to obtain the capacity at that time.

Doping is carried out at a constant current density of 1.0 mA / cm ² until the terminal voltage reaches 10 mV.
After the terminal voltage reaches 10 mV, the terminal voltage is 10 mV
It was carried out at a constant voltage. Conducting time for doping is 10
It was time. The value obtained by dividing the quantity of electricity at this time by the weight of the carbon material used was defined as the dope capacity and expressed in units of mAh / g.

Next, in the same manner, an electric current was passed in the opposite direction to dedope the lithium doped in the carbon material. The dedoping was performed at a constant current density of 1.0 mA / cm ² until the terminal voltage reached 3.0V. The value obtained by dividing the quantity of electricity at this time by the weight of the carbon material used is defined as the dedoping capacity,
It is expressed in the unit of mAh / g.

Then, the irreversible capacity was determined as the difference between the doping capacity and the dedoping capacity. The value obtained by dividing the dedoping capacity by the doping capacity was multiplied by 100 to obtain the discharge efficiency (%).
This is a value indicating how effectively the active material was used.

Table 2 below shows the battery characteristics of the lithium secondary battery in which each carbon material obtained as described above was used as a positive electrode.
Also, the volumetric capacity (mAh / mAh) obtained by multiplying each doping capacity and dedoping capacity by the true density of each carbon material.
Expressed in units of cm ³ . ) Are also shown in Table 2.

From Table 2, the secondary batteries using the graphite materials obtained in the examples of the present invention were compared with the batteries using the carbon materials obtained in Comparative Examples 2, 3, 4, 5 and 6, and were doped. It can be seen that both the dedoping capacity is large and the irreversible capacity is small.

The carbon materials obtained in Comparative Examples 2, 4 and 5 are non-graphitizable carbons as is clear from Table 1. In the secondary batteries using these, the true density of the electrode material is small and the It is also found to be disadvantageous in terms of capacity (see Table 2).

The secondary battery using the natural graphite of Comparative Example 6 has a large irreversible capacity. However, this is because the crystallite of the natural graphite is so large that lithium is difficult to be inserted between the graphite layers, and the electrolyte solution due to overvoltage is generated. It is considered that the amount of electricity consumed for decomposition was observed as irreversible capacity.

(Rapid Charge / Discharge Test) Next, a rapid charge / discharge test of a secondary battery having the carbon material obtained in the present invention and the comparative example as a positive electrode was conducted by the following method.

As the carbon material, the graphite material obtained in Example 4 and the carbon materials obtained in Comparative Examples 1, 3 and 6 having a large graphite structure of Lc ₍₀₀₂₎ and La ₍₁₁₀₎ were used. Then, a lithium secondary battery similar to the above-mentioned doping / dedoping test was constructed and a comparative test was conducted.

For each battery, the current density was 0.5 mA /
cm ² , 1 mA / cm ² , ² mA / cm ² , 3 mA / c
Doping / de-doping was performed while changing to m ² .

Doping is carried out by the above-mentioned predetermined constant current density (initial current density) until the terminal voltage reaches 10 mV.
After the terminal voltage reached 10 mV, the doping was performed at a constant voltage of 10 mV.
When the initial current density is XmA / cm ² and the doping time is Y hours, the product of X and Y is 1
It was set to 0. The dedoping was performed at the same current density as the initial current density at the time of doping, and the end point was when the terminal voltage reached 1.5V.

FIG. 5 shows the relationship between the de-doping capacity and the initial current density when the first doping / de-doping is performed.

Referring to Table 1 and FIG. 5, the practice of the present invention.
Optical anisotropy observed by a polarizing microscope obtained in the example
Graphite material showing a fine mosaic structure
The secondary batteries used are L obtained in Comparative Examples 1, 3 and 6.
c ₍₀₀₂₎, La₍₁₁₀₎Batteries using large carbon materials
Capacity when charged and discharged at a higher current density compared to
Is large, and it can be seen that rapid charge / discharge is possible.

[0112]

[Table 1]

[0113]

[Table 2]

[Brief description of drawings]

FIG. 1 is a polarizing microscope photograph (1000 ×) of a graphite material obtained in Example 4 of the present invention.

FIG. 2 is a polarization micrograph (× 1000) of the carbon material obtained in Comparative Example 1.

FIG. 3 is a polarization micrograph (× 1000) of the carbon material obtained in Comparative Example 2.

FIG. 4 is a polarization micrograph (× 1000) of the carbon material obtained in Comparative Example 4.

FIG. 5 is a diagram showing a relationship between a current density and a dedoping capacity of a secondary battery having a carbon material obtained by the present invention and a comparative example as a positive electrode.

Claims (6)

[Claims] 1. The average layer spacing d _{002 of} (002) planes determined by X-ray diffraction is 0.336 to 0.350 nm, and c
Axial crystallite size Lc ₍₀₀₂₎ exceeds 15 nm 5
0 nm or less, the crystallite size La ₍₁₁₀₎ in the a-axis direction is 5
Graphite material for non-aqueous solvent secondary battery electrodes, characterized in that the structure of the optically anisotropic structure observed by a polarization microscope shows a fine mosaic structure. 2. The graphite material for a non-aqueous solvent secondary battery electrode according to claim 1, which has a true density of 1.90 g / cm ³ or more. 3. An X-ray diffraction method, characterized in that after petroleum-based or coal-based tar or pitch is subjected to a crosslinking treatment, it is graphitized at 1800 ° C. or higher under reduced pressure or in an inert gas atmosphere. The obtained average layer surface spacing d ₀₀₂ of the (002) plane is 0.336 to 0.350 nm, and the crystallite size Lc _{(002) in} the c-axis direction is more than 15 nm and 50 nm or less,
For a non-aqueous solvent secondary battery electrode in which the crystallite size La ₍₁₁₀₎ in the a-axis direction is 5 to 50 nm and the structure of the optically anisotropic structure observed by a polarization microscope shows a fine mosaic structure. Graphite material manufacturing method. 4. The production of a graphite material for a non-aqueous solvent secondary battery electrode according to claim 3, wherein nitric acid is added to petroleum-based or coal-based tar or pitch to carry out a crosslinking treatment. Law. 5. A pitch forming process comprising adding one or more two or three-ring aromatic compounds having a boiling point of 200 ° C. or higher as an additive to a petroleum-based or coal-based pitch, followed by heating and mixing, and then forming the pitch. Body, and then a solvent having a low solubility in the pitch and a high solubility in the additive is used to extract and remove the additive from the pitch molded body, and oxidize the obtained porous pitch to perform a crosslinking treatment. The method for producing a graphite material for a non-aqueous solvent-based secondary battery electrode according to claim 3, which is performed. 6. The method for producing a graphite material for a non-aqueous solvent secondary battery electrode according to claim 5, wherein the porous pitch is oxidized with a gas containing oxygen to carry out a crosslinking treatment.