WO2004056703A1

WO2004056703A1 - Composite graphite particles and production method therefor, and cathode material of lithium ion secondary battery and lithium ion secondary battery using this

Info

Publication number: WO2004056703A1
Application number: PCT/JP2003/016241
Authority: WO
Inventors: Kunihiko Eguchi; Makiko Ijiri; Kazuteru Tabayashi; Hidetoshi Morotomi; Kazuyuki Murakami
Original assignee: Jfe Chemical Corporation
Priority date: 2002-12-19
Filing date: 2003-12-18
Publication date: 2004-07-08
Also published as: CN101350407B; TW200414579A; CN1726168A; CN100422077C; TWI243498B; KR100704096B1; CN101350407A; KR20050084413A

Abstract

A lithium ion secondary battery capable of very successfully achieving both performances that have been conventionally incompatible and difficult to accomplish concurrently - a high initial charging/discharging efficiency and a large discharge capacity, and also being provided with both of excellent quick discharge characteristics and cyclic characteristics; and constituting materials thereof. Specifically, composite graphite particles comprising a carbon material, lower in crystallinity than graphite having an X-ray diffraction interplanar spacing d002 of less than 0.337 nm, on the at least surface portion of the graphite, wherein the aspect ratio of the composite graphite particles is up to 3, 0.5-20 mass% of the composite graphite particles consists of the carbon material, and a ratio (I1580/I1360) between a peak intensity (I1580 ) at 1580 cm-1 at the Raman spectrum of the composite graphite particles and a peak intensity (I1360)at 1360 cm-1 is at least 0.1 and less than 0.3, and a production method therefore; and a cathode material and a lithium secondary battery using the composite graphite particles.

Description

Composite graphite particles, method for producing the same, negative electrode material of lithium ion secondary battery using the same, and lithium ion secondary battery

The present invention relates to a lithium ion secondary battery having a large discharge capacity, a high initial charge / discharge efficiency, and excellent fast discharge characteristics and cycle characteristics, and a constituent material thereof. Specifically, composite graphite particles composed of at least two kinds of materials having different physical properties and a method for producing the same, and a negative electrode material lithium ion secondary battery using the composite graphite fine particles. About. Background art

In recent years, as electronic devices have become smaller and more sophisticated, there has been an increasing demand for higher energy density batteries. Lithium-ion rechargeable batteries are attracting attention because they can operate at higher voltage than other rechargeable batteries and can increase the energy density. A lithium ion secondary battery has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main components. Lithium ions generated from the non-aqueous electrolyte move between the negative electrode and the positive electrode during the discharging and charging processes, forming a secondary battery.

Usually, a carbon material is used as the negative electrode material of the above-mentioned lithium ion secondary battery. As such a carbon material, black | &, which has particularly excellent charge / discharge characteristics and exhibits large discharge capacity and potential flatness, is considered to be promising (Japanese Patent Publication No. Sho 62-234433). As the three-dimensional crystal regularity (also referred to as crystallinity in this application) consisting of condensed polycyclic hexagonal network planes (also referred to as carbon network planes in this application) develops, graphite will stabilize the intercalation compound with lithium. Easy to form. Therefore, it is reported that the higher the crystallinity of graphite, the greater the amount of lithium inserted between the layers of the carbon mesh surface, and the greater the discharge capacity. (Electrochemistry and Industrial Physical Chemistry, 61 (2), 1383 (1993), etc.). It has also been reported that various layer structures are formed depending on the amount of lithium introduced into the carbon netting layer, and in the region where they coexist, they exhibit a flat and high potential close to that of lithium metal (J. Electrochem. Soc., Vol. 140, 9, 2490 (1993)). Therefore, when a lithium ion secondary battery is assembled using graphite as a negative electrode material, high output can be obtained. In general, the theoretical capacity when graphite is used as the negative electrode material is defined as the discharge capacity when graphite and lithium ultimately form LiC ₆ , an ideal graphite intercalation compound. The capacity is 372 mAh / g.

However, in a lithium-ion secondary battery using graphite as the negative electrode material, the higher the crystallinity of graphite, the more easily side reactions such as decomposition of the electrolytic solution occur on the graphite surface during the first charge. This side reaction continues until the decomposition products accumulate and grow on the graphite surface, and the thickness of the graphite is such that the electrons of the graphite cannot directly move to a solvent or the like. Since the side reaction at the time of the first charge does not participate in the battery reaction, the so-called irreversible capacity which cannot be taken out as electricity in the first discharge process is significantly increased. In other words, there is a problem that the ratio of the initial discharge capacity to the initial charge capacity (also referred to as initial charge / discharge efficiency in the present application) decreases (J. Electrochem. Soc., Vol. 117 222 (1970), etc.). The irreversible capacity is represented by the following equation.

Irreversible capacity = Initial charge capacity-Initial discharge capacity

In addition, the solvent molecules and lithium ions co-intercalate, causing the graphite surface layer to flake off and the newly exposed graphite surface to react with the electrolyte, resulting in lower initial charge / discharge efficiency. (J. Electrochem. Soc., Vo 1.137, 2009 (1990)) o

As a means for compensating for such a decrease in the initial charge / discharge efficiency, a method of adding a cathode material for a secondary battery is known. However, the addition of extra cathode material creates a new problem of reducing energy density. As described above, lithium ion secondary batteries using graphite as the negative electrode material Achieving both a high discharge capacity and high initial charge / discharge efficiency is a conflicting requirement that depends on the crystallinity of graphite.

As a method to solve this, a two-layer structure is used, in which the core is high crystalline graphite, which is advantageous for increasing the discharge capacity, and its surface is covered with low crystalline graphite or carbon, which is advantageous for improving the initial charge and discharge efficiency. Has been proposed. This is because low-crystalline carbon has a low discharge capacity, but low decomposition reactivity with electrolyte.

The prior art using such a two-layer carbon material having different crystallinity can be roughly classified as follows.

(1) Coating the surface of highly crystalline graphite as a nucleus with low-crystalline carbon derived from hot gas of organic compounds such as propane and benzene (for example, Japanese Patent Application Laid-Open No. Hei 4-368778, JP-A-5-275076).

(2) After coating or impregnating pitch or curable resin with high crystalline graphite as a nucleus in a liquid phase, calcination is performed at a temperature of about 1 000 ° C to produce low crystalline carbon on the surface layer. What is formed (for example, JP-A-4-1368778, JP-A-5-94838, JP-A-5-217604, JP-A-6-84516, JP-A-07-302595, 11-54123, JP-A-2000-229924, JP-A-2000-3708).

However, none of these methods is still sufficient for the recently required level of large discharge capacity.

The method (1) has a problem in productivity because the production steps are complicated and costly from the viewpoint of industrial production. In addition, since the low-crystalline carbon on the surface is coated in an extremely thin film, the specific surface area is high and the initial charge / discharge efficiency is low.

In the above method (2), the low-crystalline carbon of the surface layer is fused together when fired at about 1000 ^, and when the low-crystalline carbon of the surface layer is crushed, the low-crystalline carbon of the surface layer is reduced to graphite or nucleus. There is a problem that powder characteristics such as specific surface area and bulk density, and battery characteristics such as initial charge / discharge efficiency are reduced. In the above methods (1) and (2), the charge / discharge during rapid charge / discharge is repeated because the nucleus graphite and the low-crystalline carbon of the surface layer have different expansion and contraction behavior upon charge / discharge. As a result, the low-crystalline carbon on the surface layer may peel off, causing the same problem as described above.

The discharge capacity of a battery largely depends on the discharge capacity per volume of graphite constituting the negative electrode. Therefore, in order to increase the discharge capacity of the battery, it is more advantageous to fill graphite with a large discharge capacity per unit weight (mAhZg) at a high density. However, when a negative electrode is formed by filling graphite at a high density, the adhesion between graphite and the low-crystalline carbon of the surface layer tends to be insufficient in the above methods (1) and (2). Then, the low-crystalline carbon film is peeled off from the graphite, the surface of the graphite having high reactivity with the electrolyte is exposed, and the initial charge / discharge efficiency may decrease.

In addition, in JP-A-2000-3708, it is shown in Examples that a graphite is coated with a pitch and then heat-treated at 2800 ° C., but the formed film has low crystallinity (Raman spectroscopy). The R value is 0.32, and the method of measuring the R value will be described later.) However, the same problem as described above occurs. In addition, although flaked graphite flakes are used as the core material, the graphite has a large aspect ratio and the graphite is oriented when a negative electrode is manufactured. Invited.

In the case of Japanese Patent Publication No. 2001-89118, in which the particle shape of the composite graphite is made closer to a sphere, apart from the above-described prior art, a certain effect is recognized in the rapid charge / discharge characteristics and cycle characteristics. However, the publication does not mention the difference in crystallinity between the outermost layer and the inner layer. According to this manufacturing method, a plurality of flat coats and pitches are mixed, fired, pulverized to an aspect ratio of 5 or less, and then graphitized. Only the initial charge / discharge efficiency remains low. The present invention is a trade-off when graphite is used for the negative electrode material of a lithium ion secondary battery. It is an object of the present invention to obtain a lithium-ion secondary battery having both high discharge capacity and high initial charge / discharge efficiency, as well as excellent rapid discharge characteristics and cycle characteristics. Specifically, an object of the present invention is to provide a novel composite graphite particle capable of satisfying the performance, a method for producing the same, and a negative electrode material and a lithium ion secondary battery using the composite graphite particle. Disclosure of the invention

That is, the present invention relates to composite graphite particles having a carbon material having lower crystallinity than graphite at least on a surface portion of graphite having an X-ray diffraction plane spacing of less than 0.337 M *. in an aspect ratio of particles of 3 or less, the composite 0.5 to 20 mass% of the graphite particles are carbon materials, 1360 cm for 1580Cm- ¹ peak intensity (1 ₁₅₈₀₎ in Ramansu Bae spectrum of the composite graphite particles The invention is directed to a composite graphite particle having a ratio (1 ₁₅₈ ./1 _136. ) _Of the peak intensity ( _{-136 β} ) of ₋₁ from 0.1 or more to less than 0.3. In addition, the composite graphite particles have an X-ray diffraction plane spacing of the carbon material of less than 0.343ηπ * and a ratio of the graphite to the plane spacing d ₀₀₂ of from 1.001 or more to less than 1.02. Is preferred.

Further, it is preferable that any of the composite graphite particles is obtained by granulating flaky graphite.

Also, in the present application, spheroidal graphite is granulated and spheroidized by mechanical external force, and the spherical graphite particles become 0.5 to 20% by mass in terms of carbon amount. The resin alone or the mixture of the resin and the pitch is heated and carbonized. The invention also provides a composite graphite particle coated with a carbide layer comprising: Furthermore, the present application relates to a group comprising a mixture of a thermosetting resin, a precursor of a thermosetting resin, and a raw material of a thermosetting resin to granulated graphite obtained by shaping flaky graphite into a spherical shape by mechanical external force. Also provided is an invention of composite graphite particles coated with 0.5 to 20% by mass of a carbonizing material obtained by mixing and carbonizing a carbonizable material containing at least one resin material selected from the group consisting of: In the composite graphite particles, the carbonizable material is a mixture of the resin material and tars, and the resin material is strongly used at a mass ratio of Z tars of 5/95 to 100/0. Are preferred. W Also, in any of the above composite graphite particles, the resin material is at least one selected from the group consisting of a phenolic resin, a precursor of a phenolic resin, and a mixture of monomers of a phenolic resin. Are preferred.

Further, the present invention also provides an invention of a negative electrode material of a lithium ion secondary battery including any of the composite graphite particles disclosed above. The invention also provides a lithium ion secondary battery using any of these negative electrode materials.

Further, the present application is directed to a granulation step in which flaky graphite is made spherical by mechanical external force, and 80 to 99.5% of composite graphite particles obtained in a subsequent carbonization step are added to the obtained granulated graphite. A carbonizable material containing at least one resin material selected from the group consisting of a thermosetting resin, a precursor of a thermosetting resin, and a raw material of a thermosetting resin is mixed so as to become granulated graphite. The present invention also provides a method for producing composite graphite particles, comprising the steps of: carbonizing the obtained mixture at 2000 ° 0 to 3200. In this manufacturing method, the carbonizable material is a mixture of the resin material and tars, and the resin material is Z tars = 5Z95 to 100% (mass ratio). Preferably, there is.

In any of the production methods, the resin material is preferably at least one selected from the group consisting of a phenolic resin, a precursor of a phenolic resin, and a mixture of monomers of a phenolic resin.

Further, in any of the above production methods, it is more preferable to further perform a step of thermally curing the resin material at 200 to 300 ° C. before the carbonizing step.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing the structure of a button-type evaluation battery used for a charge / discharge test.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. .

In the present invention, the d-spacing of X-ray diffraction is used. 02 is less than 0.337 nm at least on the surface of graphite In another aspect, the composite graphite particles include a carbon material having a lower crystallinity than the graphite, wherein the composite graphite particles have an aspect ratio of 3 or less and 0.5 to 20% by mass of the composite graphite particles. a carbon-material, or the composite graphite ratio of 1360Cm- 1 peak intensity 1580Cm- ¹ of relative peak intensity (1 ₁₅₈₀₎ in Ramansu Bae vector particles _{_{(1 1360) (Ι 158β Ζΐ}} 1360) is 0.1 or more Are less than 0.3.

Graphite

The graphite constituting the core material of the composite graphite particles of the present invention is a measured value of X-ray diffraction d. _It is a highly crystalline graphite having a _Q2 of less than 0.337 nm. As such graphite, for example, commercially available flaky natural graphite is typical. The higher the crystallinity of graphite, the more the crystallinity grows in a regular manner, and it generally has a scaly shape. In addition, it is important to note that the shape of the composite particles finally obtained reflects the shape of the graphite, and that the shape of the graphite is preferably close to spherical, and the aspect ratio (the length of the long axis to the short axis of the particles) It is preferable to use graphite having a ratio of 3 or less. Such graphite can be produced, for example, using flaky graphite as a raw material by the following method. As the flaky graphite, commercially available products or various shapes of graphite such as coarse-grained natural graphite and artificial graphite can be used. In the case of non-scale graphite, such as coarse-grained natural graphite or artificial graphite, it is preferable to first form a scale using a known pulverizer to form a scale. At this time, it is more preferable to adjust the average particle size of the ground product to 5 to 60 / zm. As a grinding device, a counter jet mill (manufactured by Hosokawa Micron Co., Ltd.), a current jet (Nisshin Engineering Co., Ltd.) or the like can be used. The scaly black | & obtained by pulverization etc. has an acute portion on its surface, but in the present invention, it is shaped into a sphere by applying a mechanical external force to it, and the surface becomes smooth and granulated. Preference is given to graphite. In this granulation step, usually, a plurality of ground flake graphite is used to prepare granulated black having an aspect ratio of 3 or less. However, the present invention does not exclude the use of ground flake graphite alone. The method of applying a mechanical external force to form a spherical shape is not particularly limited.For example, a method of mixing a plurality of flaky graphite in the presence of a granulating aid such as an adhesive or a resin, a method of mixing a plurality of flaky graphite A method of applying mechanical external force to graphite without using an adhesive, a combination of both, etc. No. However, it is more preferable to apply mechanical external force without using such a granulating aid to granulate into a spherical shape. GRANUREX (Freund Industrial

Granulators, such as New Grass Machines (manufactured by Seishin Enterprise), Agromaster (manufactured by Hosoka Micron Corp.), and a high predication system.

Devices with shear compression and zero force, such as (Nara Machinery Co., Ltd.), Mechano Micros Co., Ltd. (Nara Machinery Co., Ltd.), Mechano Fusion System (Hosokawa Micron Co., Ltd.) can be used. Granulation can also be performed by operating the operating conditions using the above-described milling device.

The granulated graphite shaped into a sphere may be any one obtained by rolling one flake graphite, or one obtained by aggregating and granulating a plurality of flake graphite. In particular, it is preferable that a plurality of flaky graphites exhibit a concentrically granulated shape.

More specific specifications of graphite as the core material of the composite graphite particles of the present invention are specifically described below.The average particle diameter is 5 to 60 m, the aspect ratio is 3 or less, and the specific surface area is 0.5 to 10 m. ² / _g , the size (Lc) of the crystallite in the C axis direction in X-ray diffraction is 40 nm or more, d. _Q2 was measured by Raman spectroscopy using the Oyopi argon laser than 0. 33 7nm 1360cm- ¹ Pando intensity (1 _136.) And 1580Cm- ¹ Pando ratio 1 _1360/1 ₁₅₈₀ of the intensity (1 ₁₅₈₀₎ (R Value) is 0.06 to 0.25, and the half width of 1580cm- ¹ band is 10 to 60.

Carbon material

In the composite graphite particles of the present invention, at least the surface portion of the graphite is coated with a carbon material. The carbon material may be any material as long as it gives the properties of the composite graphite particles described below. Usually, the carbon material is preferably obtained by applying a carbonizable material to the above-mentioned granulated graphite, impregnating and Z or mixing, and then performing a carbonization treatment by heating. The carbonizable material referred to in the present application refers to a material that can be carbonized and / or graphitized by heating. Such heating is generally above 700 ° C., preferably between 800 and 320 °. Therefore, the carbonization treatment referred to in the present application includes the graphitization treatment. The temperature is particularly preferably from 2000 to 3200 ° C. In addition, at least the surface portion of graphite referred to in the present application is black Refers to the entire surface or a part of the outer surface of lead. Although it is a typical example of the present application, when granulated graphite is a secondary particle composed of a plurality of (scale-like) graphite by a granulation treatment, it refers to the outer surface of the secondary particle or a part thereof. In the case of such secondary particles, the carbonizable material may penetrate into the interior of the secondary particles and be carbonized. Of course, the carbon material may be formed inside graphite alone. However, the composite graphite particles of the present invention are optimally such that the entire outer surface of the graphite is coated with the carbon material. A preferred coverage is 50 to 100%.

In the present application, the carbonizable material described above is a mixture of a resin material and tars, and the mass ratio of the resin material to the tars is such that the resin material Z the tars = 5/95 to 10 It is preferably 0-0. More preferably, it is 30 to 70/30. When the proportion of the resin material is 5% or more, the graphitization (crystallization) of the formed carbide layer sufficiently proceeds, and at the same time, the effect of improving the initial charge / discharge efficiency increases. The use of a mixture of the resin material and the tars is preferable because the degree of graphitization (crystallinity) of the carbon material can be adjusted so that the effect of the present invention is maximized.

The term "tars" as used in the present application refers to carbon material precursors such as tar produced during wood carbonization, coal tar obtained from coal, and heavy oil produced from petroleum, and includes those obtained by polycondensing these as raw materials. . Specifically, pitches such as coal pitch, partamesophase pitch, and petroleum pitch are also included in the tars of the present invention. Each of these forms a graphite structure when heat treated alone at about 3000. Optically, it may be isotropic or anisotropic

The resin material referred to in the present application is at least one kind selected from the group consisting of a resin itself, a resin precursor, and a mixture of a resin synthesis raw material. The resin precursor also includes a reaction intermediate, an oligomer, a polymerization intermediate, and the like. An example of a mixture of resin raw materials is a mixture containing a monomer, a polymerization initiator, and the like, and a resin obtained by heating, stirring, and leaving the mixture.

In the present invention, as the resin material, at least one selected from the group consisting of a thermosetting resin, a mixture of raw materials of the thermosetting resin, and a precursor of the thermosetting resin is used. Is preferred.

When a thermosetting resin is carbonized at a high temperature, the resulting carbide has on average a high degree of crystallinity equivalent to graphite and may contain a graphite portion. In this effort, it is referred to as carbon material and is distinguished from core material graphite because it includes parts that have carbon.

As the thermosetting resin, a resin having a large amount of carbon remaining after the heat treatment is desirable, and examples thereof include a urea resin, a maleic acid resin, a coumarone resin, a xylene resin, and a phenol resin.

In the present invention, it is more preferable to use, as the resin material, at least one selected from the group consisting of a phenol resin, a mixture of phenol resin raw materials, and a precursor of the phenol resin. More specifically, the phenolic resin itself

(Highly condensed products of optionally substituted phenols and aldehydes represented by formaldehyde), initial condensates of phenols and aldehydes (precursors of phenolic resin), and phenols Any mixture of aldehydes and aldehydes (monomer mixture) can be used.

The crystallinity of the carbon material constituting the composite graphite particles of the present invention is lower than the crystallinity of the core graphite, but the plane spacing d in X-ray diffraction. . Preferably, ₂ satisfies 0.343ηπ *. Is less than d ₀₀₂ is 0. 343 nm carbon material, the discharge capacity is improved, and the upper direction adhesiveness of carbon material and graphite. The difference in crystallinity between graphite and carbon material is d for carbon material versus c for graphite. . More preferably, the ratio of ₂ is in the range from 1.001 or more to less than 1.02. If the ratio is 1.001 or more, the initial charge / discharge efficiency is further improved, and the adhesion of the carbon material, which is less than 1.02, is further improved.

Composite graphite particles

The composite graphite particles of the present invention are composite graphite particles having a carbon material having lower crystallinity than the graphite on at least a surface portion of graphite having an X-ray diffraction plane spacing d oo ₂ of less than 0.337 nm *. there, the aspect ratio of the composite graphite particles is 3 or less, the 0.5 to 20 mass ^_0/0 of the composite graphite particles are carbon materials, 1580Cm- ¹ in Ramansu Bae spectrum of the composite graphite particles Of peak intensity to 1360 cm (1 _158.) - (. 1 ₁₃₆₎ 1 peak intensity ratio of (1 ₁₅₈ ./ ₁₃₆₀₎ again indicates that the 0.1 less than 3 from 0.1 1 or more, more detailed description I do.

The composite graphite particles are also characterized by an almost spherical shape with an aspect ratio of 3 or less. The above-described graphite is used as a core material, and a carbon material having lower crystallinity than the graphite is present at least on a surface portion thereof. The crystallinity of the surface of the composite graphite particles can be specified by the R value of Raman spectroscopy, and the 1360 _cm- i band intensity (I) and the 1580 cm- ¹ band intensity (I) measured by Raman spectroscopy using an argon laser. 1 ₁₅₈₀ ) ratio I / 1 ₁₅₈ . Value) must be greater than or equal to 0.10 and less than 0.30. When the R value is less than 0.1 or 0.3 or more, the initial charge / discharge efficiency may decrease in any case. Particularly preferred R values are from 0.1 to 0.2.

Further, the ratio of the carbon material in the present application is expressed in terms of the amount of carbon, and the ratio of the carbon material in the composite graphite particles is defined in the range of 0.5 to 20% by mass. This ratio corresponds to 80-99.5% of the composite graphite particles being occupied by the granulated graphite. After the carbonization step, to mix the carbonizable material so that 80-99.5% of the composite black mouth and particles are occupied by the granulated graphite, the residual carbon ratio depends on the type of carbonizable material selected. Since they are different, they cannot be specified unconditionally. Usually, about 1 to 70 mass% of carbonizable material is mixed with graphite graphite. As a more specific example, when the carbonizable material is a phenol resin or the like, about 2 to 50% by mass, preferably about 20 to 35% by mass is mixed. Using this as a reference, an appropriate mixing ratio can be found if necessary. If the proportion of the carbon material in the composite graphite particles is less than 0.5% by mass, it is difficult to completely cover the active graphite surface, and the initial charge / discharge efficiency may be reduced. On the other hand, when the content exceeds 20% by mass, the proportion of the carbon material having a relatively low discharge capacity is too large, and the discharge capacity of the composite graphite particles decreases. Also, the ratio of raw materials (thermosetting resins and tar pitches) for forming carbon materials is large, and particles are fused and shrunk in the coating process and the subsequent heat treatment process. The carbon particles of the graphite particles may be partially separated and peeled off, leading to a decrease in the initial charge / discharge efficiency. The ratio of the carbon material is particularly 3 to 15 mass. / ₀ , more preferably 8 to 12% by mass. Roughly speaking, preferable physical properties of the composite graphite particles of the present invention include an average particle diameter of 5 to 60 μm, a specific surface area of 0.5 to 10 ra ² / g, and a crystallite in the C-axis direction in X-ray diffraction. The size (Lc) is 40ηιη or more, d. _e2 is preferably 0.337 nm or less. If the average particle diameter dust ratio is within the specified range, the discharge capacity and the initial charge / discharge efficiency are high, and other battery characteristics such as rapid charge / discharge characteristics and cycle characteristics are further improved. . When the specific surface area is less than 10 mVg, it is easy to adjust the viscosity of the negative electrode mixture paste (a mixture of the negative electrode material and the binder dispersion) when forming the negative electrode, and the adhesive force by the binder is also improved. X-ray diffraction Lc and d. . _{If 2} is within the specified value, a sufficient discharge capacity can be obtained.

In the present application, it is desirable that the carbon material covers the outer surface of the graphite, and the carbon material portion of the composite graphite particles is also referred to as a carbide layer.

Method for producing composite black bell particles

In the present application, the granulated step of making flake graphite spherical by mechanical external force, the obtained granulated graphite, 80 to 99.5% of the composite graphite particles obtained in the subsequent carbonization step, the granulated graphite Mixing a carbonizable material containing at least one resin material selected from the group consisting of a thermosetting resin, a precursor of the thermosetting resin, and a mixture of raw materials of the thermosetting resin, And a method for producing composite graphite particles, comprising a step of carbonizing the obtained mixture at 2000 to 3200 °.

An example of the method for producing the composite graphite particles of the present invention will be described. As described above, it is desirable to use scaly graphite that has been preformed into a spherical shape by a granulation operation or the like. When the granulated graphite is coated with a thermosetting resin alone or a mixture of a thermosetting resin and a tar, for example, the coating material and the granulated graphite are put into a mixer, and the coating material is coated. Kneading is performed by applying a strong shearing force in the temperature range above the softening point. Alternatively, a method of mixing a solution or dispersion of the coating material with granulated black bell and then drying and removing the solvent or the dispersion medium is used. In particular, it is desirable that the thermosetting resin be a low molecular weight substance (precursor of the resin) or a monomer mixture, and the high molecular weight be obtained by heating simultaneously with coating the granulated graphite. Similarly, when tars are included in the coating material, It is effective to advance the polycondensation of tars.

In the present invention, as a thermosetting resin essential as a coating material, phenol resin J! Is preferred, and when the granulated graphite is coated with a phenol resin, a phenol resin precursor or a monomer of the phenol resin is used. It is preferable to use an inclusion. The phenolic resin precursor or monomer-containing phenolic resin can be easily melted or turned into solution by heating, and can be uniformly coated on granulated graphite. Further, the phenolic resin layer formed by heating at the same time as the coating is characterized in that it adheres strongly to the granulated graphite.

The coating material can be coated with a plurality of compositions in a homogeneous or dispersed state. The coating material can be coated multiple times by changing its composition. For example, the granulated graphite is coated as a first layer with a phenolic resin composed of phenol and formaldehyde, and then as a second layer is coated with a xylenolene resin composed of dimethylphenol (xylenol) and formaldehyde. After the granulated graphite is coated with a pitch as a first layer, a phenol resin can be coated as a second layer.

The coating amount of the coating material should be set so that the ratio of the carbide layer to the composite graphite particles is finally 0.5 to 20% by mass.

It is preferable that the thermosetting resin is cured in the range of 200 to 300 after coating the granulated graphite with the coating material or simultaneously with the coating treatment. In this curing step, light volatile components contained in the thermosetting resins and tars are volatilized. Therefore, it is preferable that the temperature is raised over a sufficient time, usually 4 hours or more. Maintaining such a temperature rise time results in a more complete coating and smooth curing, which increases the adhesion between the coating material and the granulated graphite.

After the curing step, if necessary, the particle size is preferably adjusted by crushing, sieving, or the like, followed by firing. The firing is preferably performed at 2000 or more. The temperature is more preferably 2500-3200, and further preferably 2800-3200 ° C. For the firing treatment, a general graphitization furnace represented by an Acheson furnace can be used. Performing in a non-oxidizing atmosphere 200 is preferred. In the present application, a negative electrode material containing any of the composite graphite particles described above is also provided.

The composite graphite particles of the present invention can be diverted to applications other than the negative electrode, such as conductive materials for fuel cell separators and graphite for refractories, taking advantage of their characteristics. It is suitable as a negative electrode material.

That is, the negative electrode material of the present invention is required to contain at least the composite graphite particles described above. Therefore, the composite graphite particles of the present invention themselves are also the negative electrode material of the present invention. For lithium ion secondary batteries, a negative electrode mixture obtained by mixing the composite graphite particles of the present invention with a binder, a negative electrode mixture paste obtained by adding a solvent, and a negative electrode mixture paste applied to a current collector, etc. Are also within the range of the negative electrode material of the present invention. Hereinafter, a negative electrode material of a lithium ion secondary battery using the composite graphite particles of the present invention, and further, a lithium ion secondary battery will be described.

Anode material for lithium ion secondary battery

The present application also provides an invention of a negative electrode material for a lithium ion secondary battery having any of the above-described composite graphite particles of the present invention.

The negative electrode of the present invention is obtained by solidifying or shaping the above-described negative electrode material of the present invention. The formation of the negative electrode can be carried out according to a usual molding method, but the performance of the composite graphite particles is sufficiently brought out, the shapeability with respect to the powder is high, and it is chemically and electrochemically stable. There is no particular limitation as long as the method can obtain a negative electrode.

When manufacturing the negative electrode, a negative electrode mixture obtained by adding a binder to composite graphite particles can be used. As the binder, it is desirable to use a binder having chemical stability and electrochemical stability to the electrolyte and the electrolyte solution solvent. For example, fluoroplastics such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, styrene butadiene wrapper, carboxymethyl ce? Reloise etc. are used You. These can be used in combination.

Usually, it is preferable to use the binder in an amount of about 1 to 20% by mass based on the whole amount of the negative electrode mixture.

Specifically, the negative electrode mixture layer is prepared by mixing a composite graphite particle adjusted to an appropriate particle size by classification or the like with a binder to prepare a negative electrode mixture. It can be formed by applying to one or both surfaces of a current collector. At this time, a normal solvent can be used. The negative electrode mixture is dispersed in the solvent to form a paste, and then applied to the current collector and dried, so that the negative electrode mixture layer is uniformly and firmly formed. Thus, a negative electrode bonded to the substrate can be obtained. The paste can be prepared by stirring with various mixers.

For example, the composite graphite particles of the present invention and a fluorine-based resin powder such as polytetrafluoroethylene are mixed and kneaded in a solvent such as isopropyl alcohol, and then coated to form a negative electrode mixture layer. . Further, the composite graphite particles of the present invention, a fluorine-based resin powder such as polyvinylidene fluoride or a water-soluble binder such as carboxymethyl cellulose are mixed with a solvent such as N-methylpyrrolidone, dimethylformamide or water or alcohol. After forming a slurry, the mixture may be applied to form a negative electrode mixture layer.

The thickness of the negative electrode mixture comprising the mixture of the composite graphite particles and the binder according to the present invention when applied to the current collector is preferably from 10 to 300 μπι.

After the formation of the negative electrode mixture layer, pressure bonding such as press pressure can further increase the adhesive strength between the negative electrode mixture layer and the current collector.

In the lithium ion secondary battery of the present invention, the shape of the current collector used for the negative electrode is not particularly limited, but a foil shape, a mesh shape, a mesh shape such as expanded methanol, or the like is used. Examples of the current collector include copper, stainless steel, and Eckel. The thickness of the current collector is preferably about 5 to 20 μm in the case of a foil. The present invention further provides a lithium ion secondary battery using the above-described negative electrode material.

Lithium ion secondary battery

A lithium-ion secondary battery usually includes a negative electrode material, a positive electrode material, and a nonaqueous electrolyte as main battery components. Each of the positive electrode material and the negative electrode material becomes a lithium ion carrier. This is a battery mechanism in which lithium ions are doped into the negative electrode during charging, and are removed from the negative electrode during discharging. The lithium ion secondary battery of the present invention is not particularly limited except that a negative electrode material containing the composite graphite particles of the present invention is used. Other components are the same as those of general lithium ion secondary batteries.

ίPositive electrode material ί

As the positive electrode material (positive electrode active material) used in the lithium ion secondary battery of the present invention, a lithium compound is used, and it is preferable to select a material capable of doping and dedoping a sufficient amount of lithium. For example, lithium-containing compounds such as lithium-containing transition metal oxides, transition metal lucogenides, vanadium oxides and their Li compounds, and the general formula M _s Mo ₆ S ₈ — _y (where X is 0≤X 4, Y is a numerical value in the range of 0≤Y≤1, and Μ represents a metal such as a transition metal), activated carbon, activated carbon m, and the like. Vanadium oxide is such as represented by _{_{_{V 2 0 5, V 6 0}}} 13, V 2 0 4, V 3 0 8.

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. The composite oxide may be used alone or in combination of two or more. The lithium-containing transition metal oxide is, specifically, L iM (1) _X _ _X M (2) _x O ₂ (where X is a numerical value in the range of 0 ≤ X ≤ 4, M (1) , M (2) consists of at least one transition metal element.) Or L iM (1)! _ _Y M (2) _y 0 ₄ (where X is a number in the range of, M (1), M (2) consists of at least one transition metal element. You. ).

In the formula, transition metal elements represented by M (1) and M (2) are represented by Co, Ni, Mn, Cr, Ti, V, Fe, Zn, A1, In, S n, etc., and preferred are Co, Fe, Mn, Ti, Cr, V, A1 and the like.

The lithium-containing transition metal oxide is, for example, an oxide or a salt of Li or a transition metal as a starting material, and the starting materials are mixed according to a desired composition of the metal oxide. 00 ° C ~: It can be obtained by firing in the temperature range of L0000. The starting materials are not limited to oxides and salts, and may be hydroxides and the like.

In the lithium ion secondary battery of the present invention, the above-mentioned lithium compound may be used alone or in combination of two or more as the positive electrode active material. Further, an alkali carbonate such as lithium carbonate can be added to the positive electrode material.

For the positive electrode material, a positive electrode mixture composed of, for example, the above-described lithium compound and a binder and a conductive agent for imparting conductivity to the electrode is applied to one or both surfaces of the current collector to form a positive electrode mixture layer. It is obtained by doing. As the binder, any of those exemplified for the negative electrode can be used. As the conductive agent, a carbon material such as graphite or carbon black is used.

Similarly to the negative electrode material, the positive electrode material is formed into a paste by dispersing the positive electrode mixture in a solvent, and the paste-like positive electrode mixture is applied to a current collector and dried to form a positive electrode mixture layer. After forming the positive electrode mixture layer, pressure bonding such as pressurization may be further performed. Thereby, the positive electrode mixture layer is uniformly and firmly adhered to the current collector. The shape of the current collector is not particularly limited, and a box shape, a mesh shape, a mesh shape such as expanded metal, or the like is used. For example, the current collector may be an aluminum foil, a stainless steel foil, a nickel foil, or the like. The thickness is preferably from 10 to 40 μm. (Non-aqueous electrolyte)

The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention is an electrolyte salt used in ordinary non-aqueous electrolytes, and includes Li PF ₆ , Li BF ₄ , Li As F ₆ , and Li C _{10 4, L i B (C} 6 H 5), L i C l, L i Br, L i CF 3 SO. , L i CH ₃ S0 ₃ , L i N (CF ₃ SO ₂ ) ₂ , L i C (CF ₃ SO ₂ ) ₃ , L i N (CF 3CH ₂ OSO ₂ ) ₂ , L i N (CF ₃ CF ₃ OS0 ₂ ) ₂ , L i N (HCF ₂ CF ₂ CH ₂ OS 0 ₂ ) ₂ , L i N ((CF ₃ ) ₂ CHO SO ₂ ) ₂ , L i B [(C ₆ H ₃ ((CF ₃ ) _{_{2) 4, L i Al C}} 1 4, L i S i lithium salt of F ₆ and the like. in _{particular, L i PF 6, L i} BF 4 are preferable from the viewpoint of oxidation stability.

The concentration of the electrolyte salt in the electrolytic solution is preferably from 0.1 to 5 mol Z liter, and more preferably from 0.5 to 3.0 mol Z liter.

The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a solid electrolyte or a polymer electrolyte such as a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer solid electrolyte, a polymer gel electrolyte battery, etc. .

In the case of a liquid non-aqueous electrolyte solution, solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl carbonate, and the like, 1, 1, 1 or 1, 2-dimethoxyethane, 1, 2 —Diethoxyxan, tetrahydrofuran, 2-methyl / letetrahydrofuran, γ-petit mouth lactone, 1,3-dioxofuran, 4-methylinole 1,3-dioxolan, anisol, ether such as getyl ether, sulfolane, methylsulfolane Nitriles such as acetone, acetonitrile, chloronitrile, propionitrile, etc., trimethyl borate, tetramethyi ^^, nitromethane, dimethylformamide, dimethylformamide, Ν-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene. Downy chloride Nzoiru, bromide base Nzoinore, tetrahydrocannabinol Chio Fen, Jimechirusu An aprotic organic solvent such as rufoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, dimethyl sulfite and the like can be used. When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, a polymer gelled with a plasticizer (non-aqueous electrolyte) is used as a matrix. Examples of the polymer constituting the matrix include ether polymers such as polyethylene oxide and cross-linked products thereof, polymetharylate polymer compounds, atalylate polymer compounds such as polyatalylate, and polyvinylidene fluoride (polyvinylidene fluoride). PVDF) Fluorinated polymer compounds such as vinylidenefluoridehexafluoropropylene copolymer are particularly preferred.

A plasticizer is compounded in the polymer solid electrolyte or the polymer gel electrolyte. As the plastic material, the above-mentioned electrolyte salt or non-aqueous solvent can be used. In the case of the polymer gel electrolyte, the concentration of the electrolyte salt in the non-aqueous electrolyte as a plasticizer is preferably 0.1 to 5 mol // liter, more preferably 0.5 to 2.0 mol / liter.

The method for producing the solid electrolyte is not particularly limited. For example, a method of mixing a polymer compound that forms a matrix, a lithium salt and a non-aqueous solvent (plasticizer), and heating to melt the polymer compound, an organic solvent A method in which a polymer compound, a lithium salt and a non-aqueous solvent (plasticizer) are dissolved in an organic solvent, and then the organic solvent is evaporated. And then irradiating the mixture with an ultraviolet ray, an electron beam or a molecular beam to form a polymer.

Further, the addition rate of the nonaqueous solvent (plasticizer) in the solid electrolyte is preferably from 10 to 90% by mass, and more preferably from 30 to 80% by mass. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and the film will not be easily formed.

(Separator 1)

In the lithium ion secondary battery of the present invention, it is possible to use one separator. it can. The material of the separator is not particularly limited, and examples thereof include a woven fabric, a nonwoven fabric, and a synthetic resin microporous membrane. In particular, a synthetic resin microporous membrane is preferable, and among them, a polyolefin-based microporous membrane is preferable in terms of thickness, film strength, film resistance, and the like. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane obtained by combining these.

Also, a gel electrolyte can be used without using a separator.

In a secondary battery using a gel electrolyte, a negative electrode material containing the composite graphite particles, a positive electrode material, and a gel electrolyte are laminated in the order of, for example, a negative electrode material, a gel electrolyte, and a positive electrode material. It is configured to be accommodated in. Further, a gel electrolyte may be provided outside the negative electrode material and the positive electrode material.

Furthermore, the structure of the lithium-ion secondary battery of the present invention is not particularly limited, and its shape and form are not particularly limited. Depending on the application, on-board equipment, required charge / discharge capacity, and the like, a cylindrical type can be used. It may be of any shape or form of square, square, coin, or button. In order to obtain a safer non-aqueous electrolyte battery with higher safety, it is desirable to have a means for detecting a rise in battery internal pressure and interrupting the current when an abnormality such as overcharging occurs. In the case of a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure enclosed in a laminate film may be used. Example

Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

In the following Examples and Comparative Examples, composite graphite particles were evaluated by producing a button-type secondary battery for evaluation having a configuration as shown in FIG. However, an actual battery can be manufactured according to a known method based on the concept of the present invention. In the battery for evaluation, the working electrode was expressed as a negative electrode, and the counter electrode was expressed as a positive electrode. <Preparation of negative electrode mixture paste>

The composite graphite particles 9 8 mass ^_0/0, 1% by weight of a styrene-butadiene La Par as a binder to prepare a negative electrode mixture paste was slurried in addition to water carboxymethylcellulose port over scan at a rate of 1 wt% .

Production of negative electrode material>

The above-mentioned negative electrode mixture paste was applied on a copper foil (current collector) in a uniform thickness, and further heated at 90 ° C in a vacuum to evaporate the solvent and dried. Next, the negative electrode mixture applied on the copper foil is pressed by a roller press, and is punched together with the copper foil into a circular shape having a diameter of 15.5 thighs. A negative electrode 2 composed of a negative electrode mixture layer adhered to b was manufactured.

Manufacturing of positive electrode materials>

A lithium metal foil is pressed against a nickel net and punched out into a cylindrical shape having a diameter of 15.5 mm to form a current collector 7a made of a nickel net and a positive electrode 4 made of a lithium metal foil adhered to the current collector. Manufactured.

LiPF ₆ was dissolved in a mixed solvent of 33 vol% of ethylene carbonate and 67 vol% of ethyl methyl carbonate at a concentration of 1 mol / dm ³ to prepare a non-aqueous electrolyte. The obtained non-aqueous electrolyte was impregnated into a porous polypropylene body to produce a separator 5 impregnated with the electrolyte.

Manufacturing of evaluation batteries>

A button-type secondary battery having the structure shown in FIG. 1 was produced as an evaluation battery. First, a separator 5 impregnated with an electrolyte solution is interposed between a negative electrode (working electrode) 2 in close contact with the current collector 7b and a positive electrode (counter electrode) 4 in close contact with the current collector 7a. Thereafter, the outer cup 1 and the outer can 3 are combined so that the negative electrode current collector 7b is accommodated in the outer can 1 and the positive electrode current collector 7a is accommodated in the outer can 3. At that time, an insulating gasket 6 was interposed between the outer edges of the outer cup 1 and the outer can 3, and both the outer edges were caulked to close tightly. The following charging / discharging β test was performed on the evaluation battery fabricated as described above at a temperature of 25. The following batteries were subjected to the following charge / discharge test at a temperature of 25 for the evaluation batteries manufactured as described above.

GU Charge and Release Test>

Constant current charging is performed with a current value of 0.9 mA until the circuit voltage reaches OraV. Next, when the circuit voltage reaches OmV, switch to constant voltage charging, and continue charging until the current value reaches 20 μλ. After that, it was paused for 120 minutes.

Next, a constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 2.5 V. The charge capacity and discharge capacity were obtained from the amount of current in the first cycle, and the initial charge / discharge efficiency was calculated from the following equation.

(Discharge capacity of the first cycle)

Initial charge / discharge efficiency (%) = X100

(Charge capacity in the first cycle) In this test, the process of doping lithium ions into the composite graphite particles was defined as charging, and the process of undoping lithium ions from the composite graphite particles was defined as discharging.

Table 2 shows the measured battery characteristics such as the measured discharge capacity (raAh / g) and initial charge / discharge efficiency (%) per 1 g of the composite graphite particles.

As shown in Table 2, the lithium ion secondary battery using the composite graphite particles of the present invention for the negative electrode shows a large discharge capacity and high initial charge / discharge efficiency.

Next, as a second cycle, after charging in the same manner as the first cycle, constant current discharging was performed at a current value of 0.20 mA until the circuit voltage reached 25 V. At this time, the rapid discharge efficiency was evaluated from the discharge capacity in the first cycle and the discharge capacity in the second cycle according to the following equation. (2nd cycle discharge capacity)

Rapid discharge efficiency (%) = ^: X 100

(Discharge capacity in the first cycle) In addition to these evaluation tests, constant-current charging is performed at a current value of 6 raA until the circuit voltage reaches 0 mV. Next, when the circuit voltage reaches O mV, the mode switches to constant voltage charging, and charging is continued until the current value reaches 20 μλ. Then, it was paused for 120 minutes.

Next, constant current discharge was performed at a current value of 6raA until the circuit voltage reached 2.5V. This charge / discharge cycle was repeated 20 cycles, the discharge capacity at the 1st cycle and the 20th cycle was determined, and the cycle characteristics were calculated from the following equation.

(Discharge capacity of the 20th cycle)

Cycle characteristics (%) = X 1 0 0

(1st cycle discharge capacity)

Granulated graphite having the physical properties shown in Table 1 was used in the following Examples and Comparative Examples as the graphite constituting the core material of the composite graphite particles of the present invention.

The granulated graphite was granulated by circulating flaky natural graphite having an average particle diameter of 30 m in a machine using an air jet mill 200AFG manufactured by Hosokawa Micron Corporation at an air pressure of 300 kPa for 1 hour. Things. Of the obtained granulated graphite, fine powder having a particle diameter of 5 βm or less and insufficient granulation was removed. Coarse powder was removed so that it was under a 75 μm sieve. Granulated graphite

Specific surface area Average particle size Aspect ratio Lc La d () 02 Half width

(m ² / g) (nm) (nm) (nm)

3.8 20 2.0 55 56 0.3356 0.08 25

Example 1

A solution of 25 g of phenol resin (40% residual carbon) added to a mixture of 500 g of ethylene glycol and 2.5 g of hexamethylenetetramine was dissolved in a solution prepared by granulation. 2) 90 g was added and the mixture was stirred in a dispersed state. Next, the solvent was distilled off at 150 ° C. under reduced pressure to obtain resin-coated granulated graphite. The resin-coated graphite particles were heated to 270 ° C. in air over 5 hours, and further kept at 27 O for 2 hours to cure the resin-coated material. This hard dangling product was crushed so as to be below a .75 / zm sieve. Next, a pre-carbonization treatment was performed at 1000 ° C. in a nitrogen atmosphere, and further a carbonization was performed at 3000 ° C. to obtain a composite graphite particle of the present invention having a coating amount of 10%.

Note that, in order to estimate the crystallinity of the carbide 餍 of Example 1, the coating material of Example 1 was not added with granulated graphite, and the same heat history as in Example 1 was applied to prepare the carbide of the coating material. . Measured by X-ray diffraction d. . ₂ 0.3366Nm, a Lc38nm, it is somewhat less crystallinity than the granulation graphite used as the core material d _M2, Lc (Table 1) was confirmed. Example 2

To a solution consisting of 39 g of phenol, 66 g of 37% formalin and 4 g of hexamethylenetetramine was added 110 g of granulated graphite (average particle size 20 μπκ aspect ratio 2) and stirred in a dispersed state. . Heat to 90 ° C to polymerize monomer and granulate black The lead was coated with a phenol resin and filtered to obtain resin-coated graphite particles. These coated graphite particles had a coating layer of 20% (10% in terms of residual carbon) as a resin component. The temperature of the coated graphite particles was raised to 270 ^ in air over 5 hours, and the temperature was further maintained at 270 ° C for 2 hours to cure the coating layer. This cured product was pulverized so as to be below a 75 m sieve. The pre-carbonization treatment was performed at 1000 ° C. in a nitrogen atmosphere, and the carbonization was further performed at 3000 ° C. to obtain the composite graphite particles of the present invention having a coating amount of 10%. Example 3

6.7 g of coal pitch (softening point 105, carbon residue 60%) and 15 g of phenol resin (carbon residue 40%) were added to a mixture of 500 g of Tanole gas oil and 1.5 g of hexamethylenetetramine. To the solution thus obtained, 9 Og of granulated graphite (average particle size: 20 jum, agitation ratio: 2) was added and stirred in a dispersed state. Next, the tar gas oil as a solvent was distilled off under reduced pressure at 150 to obtain a graphite coated with pitchino resin. The temperature of the coated graphite particles was raised to 270 ° C in air over 5 hours, and the temperature was further maintained at 270 ° C for 2 hours to cure the coating material. This cured product was pulverized so as to be below a 75-m sieve. Next, a pre-carbonization treatment was performed at 1000 ° C. in a nitrogen atmosphere, and further a carbonization was performed at 3000 ° C. to obtain composite graphite particles of the present invention having a coating amount of 10%. Example 4

ノー 20 g of phenol, 33 g of 37% honoremarin, 2 g of hexamethylenetetramine, and fine powder of coal-based mesophase pitch (average particle size 4 jm, softening point 350 ° C, residual carbon 80%) 7.5 g 110 g of granulated graphite (average particle diameter 20 / xm, aspect ratio 2) was added to the mixed solution and stirred in a dispersed state. At 90, the above components were polymerized and coated with granulated graphite. Next, the coated graphite particles were taken out by filtration. This granulated graphite was covered with a pitch composite resin (18% as a pitch composite resin, and 10% in terms of residual carbon). The resin-coated graphite particles are exposed to up to 270 in air. The temperature was raised over time, and the temperature was further maintained at 270 ° C. for 2 hours to cure the coating material. This cured product was crushed so as to be below a 75 μm sieve. Next, a pre-carbonization treatment was performed at 1000 ° C. in a nitrogen atmosphere, and further a carbonization was performed at 3000 ° C. to obtain composite graphite particles of the present invention having a coating amount of 10%. Comparative Example 1

1 g of phenol resin (residual carbon 40%) is added to a mixture of 500 g of ethylene glycolone and 0.1 g of hexamethylene methylenetetramine, and granulated graphite (average particle size 20 / ini, asbestos) is added to the solution. Ratio 2) 100 g was added and stirred in a dispersed state. The solvent was distilled off at 150 ° C. under reduced pressure to obtain resin-coated graphite particles. The temperature of the coated graphite particles was increased to 270 in air over a period of 0.5 hours, and the temperature was further maintained at 270 ° C. for 2 hours to cure the resin coating layer. The cured product was unframed under a 75 / zm sieve. Precarbonization was performed at 1000 at a nitrogen atmosphere and carbonization was further performed at 3000 to obtain a composite graphite particle of a comparative example having a coating amount of 0.4%. Comparative Example 2

Phenol tree 3 g (40% residual carbon) 60 g of a mixture of 500 g tar gas oil and 6 g hexamethylenetetramine was mixed with granulated graphite (average particle size 20 μm, aspect ratio 2) 76 g was added and stirred in a dispersed state. The solvent was distilled off at 150 ° C under reduced pressure to obtain resin-coated graphite particles. The coated graphite particles were heated in air to 270 over 5 hours, and were further kept at 270 for 2 hours to cure the coating. This cured product was pulverized so as to be under a 75 / zm sieve. By pre-carbonizing at 1000 at a nitrogen atmosphere and carbonizing at 3000 further, composite graphite particles of a comparative example having a coverage of 24% were obtained. Comparative Example 3

0.6 g of phenolic resin (residual carbon 40%) and coal-based pitch (softening point 105 ^, Granulated graphite (average particle size 20 / m, aspect ratio 2) was added to a solution obtained by mixing 0.4 g, 500 g of tar gas oil, and 0.1 g of hexamethylenetetramine. ) 100 g was added and stirred in a dispersed state. Next, the tar gas oil as a solvent was distilled off at 150 ° C. under reduced pressure to obtain coated graphite particles. The temperature of the resin-coated graphite particles was raised to 270 ° C. in air over 5 hours, and the temperature was further maintained at 270 for 2 hours to harden the coating material. This cured product was pulverized so as to be below a 75 μm sieve. Next, a pre-carbonization treatment was performed at 1000 ° C in a nitrogen atmosphere, and carbonization was further performed at 3000 ° C to obtain composite graphite particles of a comparative example having a coating amount of 0.48%. Comparative Example 4

Granulated graphite (30 g of phenolic resin (residual carbon 40%), coal-based pitch (softening point 105 ° C, residual carbon 60%), 20 g of Tanole gas oil, and 6 g of hexamethylenetetramine The average particle size was 20 m, and the aspect ratio was 2) 76 g, and the mixture was stirred in a dispersed state. Next, the tar gas oil as a solvent was distilled off under reduced pressure at 150 to obtain resin-coated graphite particles. The resin-coated graphite particles were heated in air to 270 ° C over 5 hours, and kept at 270 for 2 hours to cure the coating material. This hardened product was crushed so as to be below a 75 / Xm sieve. Next, pre-carbonization treatment was performed at 1000 ° C in a nitrogen atmosphere, and carbonization was further performed at 3000 ° C to obtain composite graphite particles of a comparative example having a coating amount of 24%. Comparative Example 5

In Example 1, granulated graphite of a comparative example was obtained in the same manner as in Example 1 except that no coating treatment was performed. Comparative Example 6

Coal pitch (softening point 105, residual carbon 60%) 16.7 ₂ is dissolved in tar gas oil 50 (^), and 90 g of granulated graphite (average particle size 20 / zm, aspect ratio 2) is added and dispersed. It was stirred in the state. Next, the tar gas oil as a solvent was distilled off at 150 ° C. under reduced pressure to obtain pitch-coated graphite. The coated graphite particles were pre-carbonized at 1000 ° C. in a nitrogen atmosphere and pulverized so as to be under a 75 / m sieve. By further carbonizing at 3000 ° C, composite graphite particles corresponding to the prior art having a coating amount of 10% were obtained. Comparative Example 7

In Example 1, carbonization at 3000 ° C. was not performed. Except for this, composite graphite particles corresponding to the prior art were obtained in the same manner as in Example 1. Comparative Example 8

In Example 1, the graphite particles were obtained by applying a mechanical external force to scaly natural graphite, but did not result in spheroidization, and were subjected to a squaring treatment with the scaly shape (average particle diameter 15 ii m, Except for using the aspect ratio 3.5), a composite graphite particle corresponding to the prior art was obtained in the same manner as in Example 1. Table 2-1 and Table 2-2 show the powder characteristics and battery characteristics of the composite graphite particles of Examples and Comparative Examples.

In Examples 1 to 4 of the present invention, the granulated graphite is coated with a carbon material having an appropriate R value. Although the discharge capacity is slightly reduced as compared with Comparative Example 5 having no carbonized material, it can be seen that the high discharge capacity is maintained and the initial charge / discharge efficiency, rapid discharge efficiency, and cycle characteristics are excellent. In particular, in Examples 2 and 4 in which a monomer-containing phenolic resin was used as a raw material as thermosetting resins, rapid discharge efficiency and cycle characteristics were excellent.

On the other hand, in Comparative Example 5 having no carbonized material, and in Comparative Examples 1 and 3 in which the coating of the granulated graphite with the carbonized material was insufficient, the initial charge / discharge efficiency, rapid discharge efficiency, and cycle characteristics were remarkably low. Conversely, in Comparative Examples 2 and 4, where the amount of carbonized material was larger than the preferred range, the carbonized material was peeled off due to the crushing of the composite graphite particles fused during coating, and the effect of improving the initial charge / discharge efficiency, etc. Poor. In addition, the discharge capacity is significantly reduced. Peeling of the carbonized material can also be confirmed from the increase in specific surface area.

In the case of Comparative Example 6, which corresponds to the prior art in which no thermosetting resin is used as the carbonized material, the crystallinity of the carbonized material becomes too high, the R value decreases, and the initial charge / discharge efficiency decreases. . Furthermore, in the case of Comparative Example 7 in which the carbonization temperature was lowered from 3000 ° C to 1000, the discharge capacity was significantly reduced, and the rapid discharge efficiency and cycle characteristics were low. In the case of Comparative Example 8 in which the aspect ratio of the granular graphite was out of the range of the present invention, which corresponds to the prior art, the rapid discharge efficiency and the cycle characteristics were low due to the scale shape of the composite graphite particles. It will be.

Table 2—Sample Carbon material raw material Carbon material ratio Final carbonization temperature Specific surface area Raman spectroscopy κ / ο) V ⁰ r * J v, m / g) K 储 ill. u.ia Real]! S15! 12 Hue / Luma 1 10 UUU 0.9 Ul o Example 3 Example: ι /-ル樹 Β (Α> +5 ash thread = 6: 4) 3000 1.1 0.11

Noe / Ile ΐ / Ma (A)

Real junohue—t. Τ (Β) 1 UCA: oUUU KO U.lo

■ K half father! 11F 1 / -le iSB U.4U UUU A

1 1 /-U fl dUUU U! ノールノール TSίlfl BS frt A, “*« 5 ”TT ^ ^ f R, Q000 20 iO Comparative Example 4 ：: π / -Resin (A) + Coal 'Nochi (B) 24 (A: B = 6: 4) 3000 3.1 0.28 Comparative Example 5 0 3000 3.8 0.08 Comparative Example 6 Coal-based! : 'Kuchi 10 3000 1.4 0,07 Comparative Example 7 Coal-based Bipti 10 1300 1.9 0.48 Comparative Example 8 F-Inole resin 10 3000 2.8 0.25

Table 2-2 Sample discharge capacity Initial charge / discharge efficiency Rapid discharge efficiency

(, MAh / rf (%) (%) (%) Example 1 363 95 91 92 Example 2 365 95 93

Example 3 360 94. 94 95 Example 4 362 95 95 Comparative Example "! 371 on 74 84 Comparative Example 2 344 gi 81 88 Comparative Example 3 371 90 75 85 Comparative Example 4 342 91 85 89 Comparative Example 5 370 87 71 82 Comparative Example 6 366 88 90 91 Comparative Example 7 347 92 87 88 Comparative Example 8 363 91 69 78

Industrial applicability

Advantageous Effects of Invention According to the present invention, composite graphite particles suitable as a negative electrode material of a lithium ion secondary battery are provided with good productivity and low cost. Lithium-ion secondary batteries using these composite graphite particles as the anode material can not only achieve both high initial charge / discharge efficiency and large discharge capacity, which have been difficult to achieve in the past, but also have excellent performance. It also has both rapid discharge characteristics and cycle characteristics. Accordingly, the composite graphite particles of the present invention can satisfy the recent demand for higher density of battery energy. Further, the device equipped with the negative electrode material and the lithium secondary battery of the present invention can be reduced in size and improved in performance, and can contribute to a wide range of industries.

Claims

Scope of claim Claim 1

A composite graphite particle having a carbon material having lower crystallinity than graphite at least on a surface portion of graphite having an X-ray diffraction plane distance d _M2 of less than 0.337 nm, wherein the composite graphite particle Of the composite graphite particles is 0.5 to 20% by mass of the carbon material, and the composite graphite particles have a peak intensity of 1580 cm- ¹ ( _1158β ) of 1580 cm- ¹ in the Raman spectrum. Ratio of 1 peak intensity (1 ₁₃₆₀ ) /! ) Is a composite graphite particle having a value of 0.1 or more and less than 0.3. Claim 2

X-ray diffraction plane spacing d of the carbon material. . _2. The composite graphite particles according to claim 1, wherein ₂ is less than 0.343 nm and the ratio of the graphite to the interplanar spacing d _M2 is from 1.001 to less than 1.02. Claim 3

2. The composite graphite and particles according to claim 1, wherein said graphite is obtained by granulating flaky graphite. Claim 4

Spheroidal graphite particles obtained by granulating flaky graphite by mechanical external force become 0.5 to 20% by mass in terms of carbon content. A carbonized layer formed by heating and carbonizing resin alone or a mixture of resin and pitch. Coated composite graphite particles. Claim 5

Granulated graphite obtained by making flaky graphite into a sphere by mechanical external force, at least one selected from the group consisting of a thermosetting resin, a precursor of a thermosetting resin, and a mixture of raw materials of a thermosetting resin. Composite graphite particles coated with 0.5 to 20% by mass of a carbonized material, obtained by mixing and carbonizing a carbonizable material containing the above resin material. m required -term 6

The composite graphite particle according to claim 5, wherein the carbonizable material is a mixture of the resin material and tars, and the ratio of the resin material / tars is 5 to 95 to 100 (mass ratio). . Claim 7

The composite graphite particles according to claim 5, wherein the resin material is at least one selected from the group consisting of a phenolic resin, a precursor of a phenolic resin, and a mixture of monomers of a phenolic resin. Claim 8

A negative electrode material for a lithium ion secondary battery comprising the composite graphite particles according to claim 1. Claim 9

A lithium ion secondary battery using the negative electrode material according to claim 8. Claim 10

A granulation process of making flake graphite spherical by mechanical external force;

• The precursor of thermosetting crosslinking resin and thermosetting resin is added to the obtained granulated graphite so that 80 to 99.5% of the composite graphite particles obtained in the subsequent carbonization step become the granulated graphite. Mixing a carbonizable material containing at least one resin material selected from the group consisting of a body and a mixture of raw materials of a thermosetting resin, and

• Carbonization of the resulting mixture at 2000 ° (~ 3200)

A method for producing composite graphite particles comprising: Claim 11

The composite graphite particles according to claim 10, wherein the carbonizable material is a mixture of the resin material and tars, and the resin material z tars = 5 to 95 to 100 (mass ratio). Child manufacturing method. Claim 12

The method for producing composite black bell particles according to claim 10, wherein the resin material is at least one selected from the group consisting of a phenolic resin, a precursor of a phenolic resin, and a monomer mixture of a phenolic resin. Claim 13

The method for producing composite graphite particles according to any one of claims 10 to 12, further comprising, before the carbonizing step, a step of thermally curing the resin material at 200 to 300.