KR100575971B1 - Mesophase spherular graphitized substance, anode material, anode, and lithium ion secondary battery using same - Google Patents

Abstract

In the present invention, a compressive force and a shear force are simultaneously applied to the graphitized material of the mesophase globules, and the average lattice spacing (d ₀₀₂ ) in X-ray diffraction is less than 0.337 nm and an argon laser light having a wavelength of 514.5 nm. in the Raman spectrum, the ratio (I _D / I _G) of the intensity I _D of the peak present in the region of 1350 to 1370cm ^-1 to the intensity I _G of the peak in the range of 1570 to 1630cm ^-1 0.4 using It is an invention of the method of manufacturing the graphitized material of the mesophase globules of 2 or 2. Moreover, it is also invention regarding the graphitized material of the mesophase globule which combines the requirements of the said X-ray diffraction and Raman spectrum. The obtained graphitized mesophase globules are suitable for the negative electrode and negative electrode materials of lithium secondary batteries, and have a high rapid charge rate which has not been achieved conventionally while maintaining a large discharge capacity and a high initial charge and discharge rate even when an aqueous negative electrode mixture paste is used. A lithium secondary battery having can be obtained.

Description

Graphite of mesophase globules, negative electrode material, negative electrode and lithium ion secondary battery using the same {MESOPHASE SPHERULAR GRAPHITIZED SUBSTANCE, ANODE MATERIAL, ANODE, AND LITHIUM ION SECONDARY BATTERY USING SAME}             

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery excellent in three performances, that is, discharge capacity, initial charge and discharge efficiency, and rapid charge efficiency. In particular, the present invention relates to a lithium ion secondary battery capable of maintaining discharge capacity and initial charge / discharge efficiency without degrading rapid charging efficiency even when a negative electrode made of an aqueous negative electrode mixture paste is used. The present invention also relates to graphitized materials of such negative electrode and negative electrode materials for lithium ion secondary batteries, and mesophase globules constituting them, and methods for producing the same.

In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for higher energy density of batteries. Lithium ion secondary batteries are attracting attention to increase the energy density because they can be higher voltage than other secondary batteries. The lithium ion secondary battery has a negative electrode, a positive electrode, and a nonaqueous electrolyte as main components. Lithium ions generated from the nonaqueous electrolyte move between the negative electrode and the positive electrode in the discharge / charge process to become a secondary battery.

Usually, a carbon material is used as a negative electrode material of the said lithium ion secondary battery. As such carbon materials, graphite having a laminated structure so as to easily occlude / discharge lithium ions at the time of charging / discharging is used, and mainstream uses graphite which has high discharge capacity and potential flatness.

Graphite materials, such as artificial graphite, pitch-type carbon fiber, or mesophase carbon fiber, are known as a graphite material, such as natural graphite and the high temperature baking body of coke. Japanese Patent Laid-Open No. 1993-290833 also discloses meso-phase graphitized materials obtained by heat-treating meso-phase pitches made of tar or pitch.

Among the graphite materials, natural graphite has an advantage of high discharge capacity. However, since it has a fish scale shape, it is easily oriented when forming a negative electrode, and the contact between the nonaqueous electrolyte and graphite is incomplete, resulting in rapid charge and discharge characteristics (also referred to as a rate characteristic). Degrades. Moreover, the expansion and contraction of graphite accompanying charging and discharging becomes one direction, and a problem arises that a cycle characteristic falls because the contact between graphite cannot be maintained. On the other hand, the graphitized product obtained by heat-treating a mesophase pitch, especially the graphitized material of the mesophase globule produced | generated in pitch, has a spherical shape or the shape close to a spherical shape. Therefore, it is easy to laminate | stack at random at the time of negative electrode formation, and can contain a nonaqueous electrolyte uniformly in a negative electrode. In addition, the stretching direction of graphite accompanying charge and discharge becomes random. As a result, it exhibits good rapid charge and discharge characteristics and cycle characteristics.

According to Japanese Patent Laid-Open No. 1993-290833, a carbonaceous mesophase globule produced by maintaining pitches at a heat melting temperature of 350 to 500 ° C is obtained. Graphitizations obtained by carbonizing this and then graphitizing at 2500 to 2900 ° C are disclosed. In the publication, the graphitized material of the mesophase globules has an average particle diameter of 25 µm, an average lattice spacing (d ₀₀₂ ) in X-ray diffraction of 0.3365 to 0.3390 nm, and 1580 cm ^-1 in argon laser Raman spectroscopy. It is proposed as a negative electrode material of a lithium ion secondary battery that the ratio of the peak intensity of 1360 cm ^{-1 to} the peak intensity of is in the range of 0.2 to 0.4.

However, if a negative electrode is manufactured using the graphitized material of mesophase globules, and a lithium ion secondary battery is formed using the negative electrode, the performance of the battery can be sufficiently obtained depending on the type of solvent used during the production of the negative electrode. You may not be able to.

Usually, in order to manufacture a negative electrode, a carbon material and a binder (binder resin) are first mixed in a solvent (Hereafter, it contains a solvent and / or a dispersion medium), and it pastes. Next, the obtained paste (this is called a negative electrode mixture paste) is applied to a current collector such as copper flakes and then pressurized to obtain a negative electrode. When non-aqueous solvents, such as an organic solvent, are used as a solvent in this pasting process, the outstanding lithium ion secondary battery with large discharge capacity and high initial charge / discharge efficiency and quick charge efficiency is obtained.

On the other hand, in recent years, use of an aqueous solvent, that is, an aqueous negative electrode mixture paste, has been desired from the viewpoint of environment and safety. By the way, when using an aqueous solvent (medium containing water) as said solvent, battery characteristics, such as rapid charging efficiency, may fall. That is, when the graphitized material of the mesophase globules is used as the negative electrode material, the performance of the obtained lithium ion secondary battery depends on the solvent type of the negative electrode mixture paste. This is also referred to herein as the solvent dependency of a lithium ion secondary battery.

The inventors of the present invention use a known meso-phase globular graphite disclosed in Japanese Patent Application Laid-Open No. 1993-290833 or the like as a negative electrode material, prepare a negative electrode using an aqueous or non-aqueous medium, and use lithium ion. The solvent dependence of the secondary battery was examined. As a result, it was confirmed that the use of an aqueous medium degrades the fast charge characteristic.

In view of such a situation, an object of the present invention is to obtain an excellent lithium ion secondary battery having a large discharge capacity and high initial charge / discharge efficiency and rapid charge efficiency even when an aqueous negative electrode mixture paste is used. In addition, an object of the present invention is to provide a negative electrode and negative electrode material for lithium ion secondary batteries excellent in these three performances, and a graphitized material of mesophase globules constituting the same, and a method of manufacturing the same.

Summary of the Invention

That is, in the present invention, the average lattice spacing d ₀₀₂ in X-ray diffraction is less than 0.337 nm, and a peak present in a region of 1570 to 1630 cm ⁻¹ in a Raman spectrum using an argon laser light having a wavelength of 514.5 nm. The ratio (I _D / I _G ) of the intensity I _D of the peak present in the region of 1350 to 1370 cm ⁻¹ with respect to the intensity I _{G of} is more than 0.4 and 2 or less, which is a graphitized product of mesophase globules.

Moreover, it is preferable that the graphitized material of this meso-phase globule has a volume conversion average particle diameter of 3-50 micrometers, and the specific surface area is 1-20 m <^2> / g.

In addition, in the graphitized material of any of the mesoform globules, fine particles having a hardness higher than that of the mesoform globules and having an average particle diameter smaller than the average particle diameter of the graphitized particles of the mesoform globules are embedded in the surface. It is preferable that the said microparticles | fine-particles are 1 or more types chosen from the group which consists of a silica, an alumina, and titanium oxide.

Moreover, this invention also provides invention of the negative electrode material for lithium ion secondary batteries containing any one of the graphitized material of the said mesophase globules.

Moreover, it is preferable that this negative electrode material further contains graphite other than the graphitized material of the said mesophase globules. In particular, it is more preferable that the crystallinity further contain graphite coated with a carbon material which is lower than the crystallinity of the graphitized material of the mesophase globules.

Moreover, this invention also provides invention of the negative electrode for lithium ion secondary batteries which consists of any one of the said negative electrode materials.

In addition, the present invention also provides an invention of a lithium ion secondary battery having any one of the negative electrodes.

In addition, in this application, the compressive force and the shear force are simultaneously applied to the graphitized material of the mesophase globules, and the average lattice spacing (d ₀₀₂ ) in X-ray diffraction is less than 0.337 nm, and argon laser light having a wavelength of 514.5 nm. in the Raman spectrum, the ratio (I _D / I _G) of the intensity I _D of the peak present in the region of 1350 to 1370cm ^-1 to the intensity I _G of the peak in the range of 1570 to 1630cm ^-1 0.4 using Also provided is an invention of a method of producing a graphitized product of mesophase globules greater than 2 or less.

Moreover, in this manufacturing method, the method of performing the said process in the presence of microparticles | fine-particles whose hardness is higher than the hardness of the graphitized material of the said mesophase globules and whose average particle diameter is smaller than the average particle diameter of the said mesosphere globules is preferable. In particular, the production method is more preferably at least one member selected from the group consisting of silica, alumina and titanium oxide.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the evaluation battery for evaluating the characteristic of graphite.

2 is a schematic explanatory diagram of an apparatus for performing a process of simultaneously applying a compressive force and a shearing force.

3 is a schematic explanatory diagram of another apparatus for performing a process of simultaneously applying a compressive force and a shearing force.

Fig. 4 is a diagram showing the water penetration rate (hydrophilicity) of the graphitized material of mesophase globules obtained in Examples and Comparative Examples.

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

First, the graphitized material of the mesophase globules according to the present invention will be described.

<Graphite of mesophase globules>

The mesophase globules according to the present invention are generally made of a carbon material which is prone to graphitization by high temperature heat treatment. Examples of such carbon materials include petroleum or coal tars and pitches. For example, when coal tar is heated to 350 to 500 ° C., polycyclic aromatic molecules are polycondensed to form large, resulting in mesophase globules which are globules having optical anisotropy. The mesophase globules can be separated and purified by an organic solvent such as benzene, toluene, quinoline, tar heavy oil, tar heavy oil or washing oil from a pitch matrix having optical isotropy. The meso-like globules obtained are not necessarily limited to spherical shapes, but are often spherical or have a shape close to a spherical shape. Therefore, it is generally called "mesosphere globules" among those skilled in the art, and is routinely distinguished from other carbon materials.

When the isolated mesophase globules are first calcined at 300 ° C. or higher in a non-oxidizing atmosphere, and finally subjected to high temperature treatment above 2000 ° C., the graphitized material of the mesophase globules which is the raw material of the present invention can be obtained. Since the graphitized material of the mesophase globules is substantially maintained in the shape before graphitization, it is often a spherical shape or a shape close to the spherical shape. The graphitized material of the mesophase globules of the present application may be one obtained by subjecting the final high temperature treatment to more than 2000 ° C. after grinding the mesophase globules. Since the mesophase globules have optical anisotropy, even when they are ground and graphitized, excellent battery performance is exhibited as a negative electrode material without any problem of orientation such as natural graphite. However, excessive pulverization may increase the irreversible capacity, which is not preferable. The grinding | pulverization can employ | adopt a well-known grinding | pulverization method and a processing method suitably. Grinding is preferably carried out after primary firing at 300 ° C or higher and before final high temperature treatment. The graphitized products of mesophase globules are also referred to as graphitized materials of mesosphere globules.

In addition, the final high temperature treatment in a non-oxidizing atmosphere is preferably performed at 2500 ° C or higher, more preferably at 2800 ° C or higher. However, the upper limit temperature of the final high temperature treatment is usually about 3300 ° C. even if high, in order to avoid sublimation, decomposition, or the like of graphitized materials.

When the mesophase globules are subjected to final high temperature treatment at a temperature exceeding 2000 ° C. and graphitized, graphitized products of mesosphere globules having an average lattice spacing (d ₀₀₂ ) of less than 0.337 nm in X-ray diffraction are conventionally obtained. It is becoming. However, this graphitized material has an intensity of a peak present in an area of 1350 to 1370 cm ⁻¹ with respect to an intensity I _G of a peak present in an area of 1570 to 1630 cm ^{−1 in} an Raman spectrum using an argon laser light having a wavelength of 514.5 nm. ratio (I _D / I _G) in the I _D is 0.35 or less.

In the present invention, the above-mentioned conventional mesophase globular graphite (hereinafter, simply referred to as "raw material graphite") was subjected to a surface modification treatment to increase the I _D / I _G ratio.

That is, in the present invention, a compressive force and a shear force are simultaneously applied to the graphitized material of the mesophase globules, and the average lattice spacing (d ₀₀₂ ) in the X-ray diffraction is less than 0.337 nm and an argon laser having a wavelength of 514.5 nm. in the Raman spectrum with a light, non-1570 to (I _D / I _G) of the intensity I _D of a peak in an area of about 1630cm intensity I _G of the peak in the range of 1350 to 1370cm ^-1 is ^-1 It is an invention of the method of manufacturing the graphitized material of the mesophase globules more than 0.4 and 2 or less. It is also an invention of the graphitized substance itself of mesophase globules that combines the requirements of such X-ray diffraction and Raman spectra.

The graphitized product (hereinafter also referred to as &quot; modified graphitized product &quot;) of the mesophase globules obtained according to the present invention has an average lattice spacing (d ₀₀₂ ) in the C-axis direction in X-ray diffraction, preferably less than 0.337 nm. Is less than 0.3365 nm. In this way, the graphite having a short average lattice spacing d ₀₀₂ has high crystallinity, that is, graphitization degree is also high. Therefore, when used as a negative electrode material of a lithium ion secondary battery, a lithium ion secondary battery with high discharge capacity can be obtained.

In addition, the average lattice spacing d ₀₀₂ is a X-ray diffraction method using CuKα rays as X-rays and using high-purity silicon as a standard material [Carbon fiber, p.733-742 (1986) G) means the value measured by.

Modified graphitates of the present invention have a specific Raman spectrum. Specifically, in the Raman spectrum using an argon laser light having a wavelength of 514.5 nm, the intensity of the peak present in the region of 1570 to 1630 cm ⁻¹ is I _D , and the intensity of the peak present in the region of 1350 to 1370 cm ⁻¹ is determined. the peak intensity ratio I _D / I _G at the time of a I _D in the range of greater than 0.4 second or less.

In addition, the peak intensity demonstrated herein means the intensity | strength by peak height.

When a negative electrode is produced using the modified graphitized material that satisfies the above-mentioned requirements of both X-ray diffraction and Raman spectrum, and used in a lithium ion secondary battery, solvent dependency of the lithium ion secondary battery is eliminated. That is, even if an aqueous negative electrode mixture paste is used, the discharge capacity and initial charge / discharge efficiency of the lithium ion secondary battery are maintained, and the rapid charging characteristics are also not reduced. In addition, in this case, when the said I _D / I _G ratio is 0.4 or less, rapid charge characteristic may fall. On the other hand, when the I _D / I _G ratio exceeds 2, the discharge capacity tends to decrease. It is particularly preferable that the modified graphite product of the present invention is in the range of 0.45 to 1 in terms of the I _D / I _G ratio.

The present inventors understand that the influence of the I _D / I _G ratio on the solvent dependency is due to the surface modification of the graphitized material of the meso-phase globules as a raw material. The mechanism by which the surface modification effect is obtained is not clear, but it is considered that the graphite surface is polished by applying compressive and shearing forces simultaneously. Therefore, it is thought that a large amount of hydrophilic groups appear on the surface of the raw graphite, and the hydrophilicity of the graphite is improved. Therefore, the treatment which simultaneously applies the compressive force and the shearing force (hereinafter, simply referred to as "surface modification treatment") performed in the present invention can also be referred to as a kind of mechanochemical treatment in which chemical properties are changed or imparted by mechanical or physical treatment. As a means of confirming hydrophilicity provision to the surface of a raw graphite material, it can evaluate by measuring the contact angle of the graphitized material and the water after the said surface modification process, or the penetration rate of water, the penetration amount measurement, etc.

The apparatus used for the surface modification treatment of the present invention is preferable as long as the compressive force and the shear force can be simultaneously applied to the object to be treated, and the apparatus structure is not particularly limited.

As such a device, for example, a pressure kneader, a kneader such as two rolls, a rotary ball mill, a hybridization system (manufactured by Nara Machinery Co., Ltd.), a mechano micros (manufactured by Nara Machine Works, Ltd.), a mechano A fusion system (made by Hosokawa Micron Co., Ltd.) etc. can be used.

Among these, the apparatus which simultaneously gives a shear and a compression force using a rotation speed difference is used preferably. For example, Hosokawa Micron Co., Ltd. Mekano fusion system which shows a typical mechanism is shown to FIG. 3A-B. The apparatus has a rotating drum (rotor 31), an inner member (inner piece 32) having a different rotational speed than the drum, and a circulation mechanism (e.g., a circulation blade 33) of the workpiece. Symbol 35 is the discharge damper and 36 is the product. The raw graphite material 34 supplied between the rotor and the inner piece receives the centrifugal force caused by the rotation of the rotor and simultaneously receives the compressive force and the shear force due to the speed difference between the inner piece and the rotor. In addition, the raw graphite is repeatedly subjected to such compressive force and shear force by a circulation mechanism.

As another example, the hybridization system which is the product of Nara Machinery Co., Ltd. which was shown typically in FIG. 2 is mentioned. Symbol 23 is a blade, 25 is a circulation path, 26 is a cooling or heating jacket, 27 is a discharge valve and 28 is an outlet. The raw graphite material supplied from the inlet 24 receives the compressive force and the shear force simultaneously and repeatedly caused by the speed difference between the rotor 22 and the fixed drum (stator 21) rotating at high speed.

In the method of the present invention, the shearing force and the compressive force simultaneously applied to the raw graphite material are usually larger than normal stirring. However, these mechanical stresses are preferably applied to the surface of the raw material graphitized material, and it is preferable that the mechanical stress is not broken up to the particle skeleton of the graphitized material. When the particle skeleton of the graphite is broken, it tends to cause an increase in the irreversible capacity of the lithium secondary battery. Specifically, the surface modification treatment is preferably performed such that the reduction rate of the average particle diameter of the raw graphite is suppressed to 20% or less.

For example, in the case of using a device having a rotating drum and an inner member, the main speed difference between the rotating drum and the inner member is 5 to 50 m / sec, a distance of 1 to 100 mm and a treatment time of 3 to 90 minutes. It is preferable.

In addition, in the case of a device equipped with a fixed drum / high speed rotor, it is preferable to carry out under conditions of a peripheral speed difference of 10 to 100 m / sec and a treatment time of 30 seconds to 10 minutes between the fixed drum and the rotary rotor.

By the production method of the present invention exemplified above, graphitized mesosphere globules that satisfy both the requirements of the X-ray diffraction and the Raman spectrum, which are modified graphitized products of the present invention, are obtained.

The shape of the modified graphite product of the present invention is also preferably a spherical shape or a shape close to the spherical shape. However, since the compressive force and the shearing force are also subjected to the treatment at the same time, the particles may be in the form of amorphous or granular particles.

It is preferable that the modified graphitized material of this invention is 3-50 micrometers in average particle diameter by volume conversion. When the average particle diameter is 3 μm or more, when used as a negative electrode material of a lithium ion secondary battery, the irreversible increase in capacity and the safety of the battery are not caused. Moreover, if it is 50 micrometers or less, the lithium ion secondary battery with favorable adhesiveness of a negative electrode can be obtained.

As for the said average particle diameter, 5-30 micrometers is especially preferable. In addition, the true volume of the modified graphite is preferably 2.2 or more.

Moreover, it is preferable that the specific surface area of the modified graphite product of this invention is 1-20m <^2> / g in the specific surface area of nitrogen gas adsorption BET method. If it is 20 m <^2> / g or less, the irreversible capacity of a battery will not increase and it is suitable also from a safety point of view. 5 m <^2> / g or less is more preferable. Moreover, when it is 1 m <^2> / g or more, the outstanding battery characteristic will be easy to be obtained when an aqueous negative electrode mixture paste is used.

In the modified graphitized product of the present invention, it is preferable that fine particles having a hardness higher than that of the modified graphite product itself and having an average particle diameter smaller than the average particle diameter of the modified graphite product are embedded in the surface.

Such a modified graphitized product of the present invention is obtained by subjecting the surface modification treatment of the raw graphite material to coexistence of the fine particles. As the fine particles, any one can be used without particular limitation as long as the particles have an average particle diameter smaller than the average particle diameter of the modified graphite product and are hard. In the case where the fine particles are aggregates, the particle diameter of the primary particles is preferably smaller than that of the modified graphite product. Although the form and average particle diameter of the said microparticles | fine-particles are not prescribed | regulated, if it is about 1 nm or more, the surface modification effect of a raw graphite material can be obtained. Moreover, it is preferable to make an upper limit about 100 nm so as not to disturb the contact of the modified graphite products of this invention obtained, and to not adversely affect charge / discharge characteristics.

The fine particles may or may not contribute to conductivity or charge / discharge. Specifically, metal, metal oxide, metal nitride, metal boride, metal carbide, etc. are illustrated.

Among these, hard microparticles | fine-particles which have hydrophilicity are preferable. Among them, fine particles of silica, alumina and various metal oxides are preferable. In particular, at least one fine particle selected from the group consisting of silica, alumina and titanium oxide is preferably used. Silica, alumina and titanium oxide are preferably produced by a gas phase method. Silica is preferably anhydrous silica.

If surface modification of the raw graphite is carried out in the presence of hard fine particles having these hydrophilic properties, the resulting modified graphite is further improved in hydrophilicity.

At the time of such a surface modification process, about 0.01-10 mass% of the said microparticles | fine-particles can be used normally with respect to raw material graphite. In addition, the fine particles may be previously blended with the raw graphite material to provide the surface modification treatment, or may be added during the treatment of the raw graphite material.

The fine particles used are preferably embedded in an amount of about 0.01 to 5% by mass, more preferably about 0.01 to 0.5% by mass relative to the product graphite, and are preferably integrated.

In the surface modification treatment in which the fine particles coexist, in addition to hydrophilicity, a modified graphitized surface having a finely roughened surface is obtained. It is considered that the effect of the present invention is also enhanced to increase the polishing effect of the graphitized surface and to embed the fine particles in the vicinity of the surface of the raw graphite.

In this invention, various additives, such as a well-known conductive material, an ion conductive material, surfactant, a high molecular compound, can be added in the range which does not impair the effect of this invention. The addition time may be any one of the surface modification treatment before, during and after the treatment.

<Negative electrode material for lithium ion secondary battery>

The present application also provides a negative electrode material for a lithium ion secondary battery containing the modified graphite product of the present invention described above.

Usually, in order to manufacture the negative electrode for lithium ion secondary batteries, a carbon material and a binder are first mixed and mixed in a solvent (including a solvent and / or a dispersion medium), and it pastes. Next, the obtained paste (called negative electrode mixture paste) is applied to the current collector, and then the solvent is removed and solidified and / or molded by a press or the like to obtain a negative electrode. The negative electrode material of the present invention means both the material up to this solidification and / or the shaping process. That is, it is a requirement that the above-mentioned modified graphitized material is contained in this negative electrode material at least. Therefore, the modified graphitized material of the present invention is also the negative electrode material for a lithium ion secondary battery of the present invention. Moreover, the negative electrode mixture which mixed the modified graphite product of this invention, and the binder, the negative electrode mixture paste obtained by adding a solvent, and apply | coating this to the electrical power collector are also the scope of the negative electrode material of this invention.

In the present invention, when any one of the modified graphitized materials of the present invention is used as the negative electrode material, the rapid charging efficiency of the lithium secondary battery does not decrease even when the aqueous negative electrode mixture paste method is used.

It is considered that the excellent graphite material exhibits excellent rapid charging characteristics because the raw material graphite is surface-modified by hydrophilization and roughening of the surface thereof.

Therefore, it is considered that the modified graphitized material is in close contact with the binder even in the aqueous system, and even if the charging and discharging is repeated, the modified graphitized material, the aqueous binder, and the current collector can be in firm contact with each other. In addition, it is thought that the binder can be uniformly thinned and interposed between the modified graphite products, and the factors that inhibit conductivity, ion conductivity, electrolyte permeability, and the like are suppressed.

EMBODIMENT OF THE INVENTION Below, the negative electrode material for lithium ion secondary batteries of this invention is demonstrated in detail.

The negative electrode material of the present invention can also be used by adding graphite (hereinafter referred to as &quot; other graphite &quot;) other than the modified graphitized material (graphitized mesophase globule treated with surface modification) of the present invention.

In the case where other graphite is used in combination, the combination of other graphite whose shape and / or average particle diameter is different from the modified graphite product of the present invention is preferable since the rapid charging efficiency is improved.

Specific examples include a combination of a spherical modified graphitized product of the present invention with other flaky and / or fibrous graphite, a combination of a spherical shaped and / or fibrous other graphite with a scaled present invention. In the case of spherical shapes with each other, for example, the modified graphite product of the present invention having an average particle diameter of about 30 μm is combined with another graphite having an average particle diameter of about 10 μm.

Although the said other graphite is not specifically limited, Specifically, the conventional mesosphere globular graphite (raw material graphite) etc. which are not processed to apply compressive force and a shear force simultaneously are mentioned. In addition, coal tar, mesophase calcined carbon (bulk mesophase) obtained by heating the pitch, and cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.) are finally heat treated at 2500 ° C. or higher to obtain graphite. It can also be illustrated. Or graphitized by heat treatment of petroleum tar and pitch. Moreover, artificial graphite, natural graphite, etc. can also be illustrated as said other graphite. The other graphite may be a combination of the graphite materials exemplified above.

It is preferable to use the graphite which is coated with the carbon material whose crystallinity is lower than the crystallinity of the modified graphitized material (graphite of the said surface-modified mesosphere spherical body) of this invention among other graphite mentioned above.

The graphite having a low crystalline coating referred to herein means a graphite whose core material is relatively higher than that of the coating material. The carbon material (hereinafter also referred to as coating material) as the coating material is lower crystalline than graphite of the core material (hereinafter also referred to as core material) and is lower crystalline carbon than modified graphitized material (graphite of the surface-modified mesosphere globules). Carbonaceous or graphite carbon material. The coating material is preferably present inside and / or on the surface of the core particles, but it is preferable that at least half of the coating material is present on the surface of the core material.

In X-ray diffraction of the graphite after coating, the crystallinity of the core material and the crystallinity of the coating material cannot be judged individually. Therefore, the crystallinity of the coating material is defined as the average lattice plane spacing (d ₀₀₂ ) in X-ray diffraction when the coating material is obtained by heat treatment alone. That is, the preferable average lattice spacing d ₀₀₂ of the coating material is 0.337 nm or more, more preferably 0.340 nm or more. The intensity ratio (I _D / I _G ) in the Raman analysis generally represents 0.15 or more.

As a manufacturing method of the said coated graphite, an organic compound is affixed and / or impregnated to a core material, and this can be obtained by carrying out final high temperature treatment at the temperature of 900 degreeC or more and less than 2800 degreeC. Particularly preferred are those obtained by final high temperature treatment at temperatures above 1150 ° C. and below 2300 ° C. If the final high temperature treatment is below 900 ° C or above 2800 ° C, good rapid charging efficiency is not obtained.

Although the core material can be selected from various natural graphites and artificial graphites, scale graphite, block graphite, spherical graphite and the like are preferable. The core is preferably to have a suitable gap. It is preferable that the particle diameter of a core material is 1-30 micrometers. Although the specific surface area of a core material does not matter in particular, It is preferable that it is 0.5 m <^2> / g or more. The crystallinity of the core material is such that the average lattice spacing d ₀₀₂ in X-ray diffraction is less than 0.337 nm.

As a raw material of a coating material, the organic compound which carbon content remains by heat processing is selected. It is preferable to contain almost no heavy metals or light metal elements such as inhibiting charge and discharge reactions or promoting decomposition of the electrolyte solution. In particular, thermosetting resins, thermoplastic resins, coal-based or petroleum-based heavy oils, tars, pitches, and the like are preferable. In particular, it is preferable to include carbonaceous fine particles (fine powder of coal, primary QI (QI is quinoline insoluble), carbon black, fine particles of carbon or graphite). The raw material of these coating | covering materials can be melt | dissolved or disperse | distributed as it is, or a solvent, and after mixing with graphite of a core material, it can heat-process.

As for the mixing ratio with respect to the core material of a coating material, 0.5-30 mass% of coating materials are preferable with respect to the total amount after final high temperature processing, especially 3-20 mass%. If the coating material is excessive, the discharge capacity is lowered. When the coating material is excessively low, initial charge and discharge efficiency is lowered.

Although the addition amount of the said other graphite changes also with the shape, average particle diameter, etc. of other graphite and the modified graphite product of this invention, It is preferable that it is about 0.5-90 mass% with respect to the sum total measurement of other graphite and the modified graphite product of this invention. When the upper limit of the addition is preferably about 70% by mass, the rapid charging efficiency can be made more excellent.

For example, when the modified graphite product of the present invention has an average particle diameter of 20 to 30 µm, as the other graphite, 5 to 40 mass% of scale (planar dimension: 3 to 15 µm) natural graphite and / or artificial graphite are used.

Alternatively, when the modified graphite product of the present invention has an average particle diameter of 5 to 15 µm, 20 to 70 mass% of coated graphite (graphite having a low crystalline coating material having an average particle diameter of 15 to 30 µm) is used as the other graphite.

Although the mixing method of the said modified graphite and the said other graphite is not specifically limited, It is common to use various mixers in a dry state as powder.

Moreover, as long as it does not impair the objective of this invention, other carbon materials (including amorphous hard carbon etc.), an organic substance, a mixture with a metal compound, granulated materials, a coating material, and a laminated body may be sufficient. Furthermore, various chemical treatments, heat treatments, oxidation treatments, etc. in the liquid phase, the gas phase, and the solid phase may be performed.

In addition, it is preferable to use the organic binder which has chemical stability and electrochemical stability with respect to electrolyte as a binder used for a negative electrode mixture paste in this invention. For example, fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, carboxymethyl cellulose, styrene butadiene rubber and the like are used. These can also be used together.

Among the above, in order to achieve the object of the present invention and to maximize the effect, it is particularly preferable to use a binder such as carboxymethyl cellulose (water-soluble), polyvinyl alcohol (water-soluble), styrene-butadiene rubber (water dispersibility).

It is preferable to use a binder normally in the quantity of about 0.5-20 mass% in the total amount of negative electrode mixture.

Next, the anode material will be described in more detail with reference to the manufacturing method of the cathode. For example, the negative electrode mixture is prepared by adjusting the modified graphitized material of the present invention to an appropriate particle size by classification and the like and mixing with a binder. This negative electrode mixture is dispersed in a solvent to form a paste, and then usually applied to one or both surfaces of the current collector. Subsequently, when this is dried, the negative electrode mixture layer is uniformly and firmly adhered to the current collector, so that the negative electrode mixture layer can be formed.

More specifically, any one of the modified graphitized materials of the present invention, for example, carboxymethyl cellulose, styrene butadiene rubber, and the like may be used as a binder, mixed with a solvent such as water, alcohol, etc., and then applied as a slurry. Alternatively, fluorine-based resin powders such as polytetrafluoroethylene and polyvinylidene fluoride may be mixed with a solvent such as isopropyl alcohol, N-methylpyrrolidone, and dimethylformamide to form a slurry and then applied.

Above all, in consideration of the influence on safety and environmental aspects in drying and removing the solvent, an aqueous negative electrode formed by dissolving and / or dispersing a binder such as carboxymethyl cellulose and styrene butadiene rubber using water or a hydrous alcohol as a solvent. Preference is given to using a mixture paste.

The paste can be prepared by stirring using a known stirrer, mixer, kneader, kneader or the like.

In this invention, it is suitable that the application thickness at the time of apply | coating a negative electrode mixture paste to an electrical power collector is 10-200 micrometers.

In addition, the modified graphite product of the present invention may be dry mixed with resin powders such as polyethylene and polyvinyl alcohol, and hot pressed in a mold to form a negative electrode. In this case, it is natural that the solvent dependency of the lithium ion secondary battery disappears. The discharge capacity and rapid charge / discharge efficiency of the lithium ion secondary battery may decrease when the binder is excessive. In dry mixing, a large amount of binder is required to obtain sufficient negative electrode strength, and therefore, the above-described wet (method of dispersing the binder in a solvent) mixing is preferable.

After the negative electrode mixture layer is formed, pressing and pressing are performed to further increase the adhesive strength between the negative electrode mixture layer and the current collector.

It does not specifically limit as a shape of the electrical power collector used for a negative electrode. Thin or mesh-like ones such as mesh and expanded metal may be used. Examples of the current collector include copper, stainless steel, nickel, and the like. As for the thickness of an electrical power collector, when thin, about 5-20 micrometers is preferable.

<Negative electrode for lithium ion secondary battery>

This invention also provides invention of the negative electrode for lithium ion secondary batteries which consists of the negative electrode material of this invention.

The negative electrode of the present invention is obtained by solidifying and / or shaping the negative electrode material of the present invention described above. The formation of the negative electrode can be carried out in accordance with a conventional molding method, but is not limited at all if it is a method capable of sufficiently drawing the performance of the graphitized material, and having a high formability to the powder, and a chemically and electrochemically stable negative electrode. Do not.

Although the modified graphitized material of the present invention is particularly suitable as the negative electrode material and negative electrode of the lithium ion secondary battery described above, the modified graphitized material can also be used for applications other than the negative electrode material by utilizing its characteristics. In the present invention, a lithium ion secondary battery using a negative electrode is also provided.

<Lithium ion secondary battery>

A lithium ion secondary battery usually has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main battery components. The positive electrode and the negative electrode become carriers of lithium ions, respectively. Lithium ions are doped in the negative electrode during charging and de-doped from the negative electrode during discharge.

The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode obtained from the negative electrode material containing the modified graphitized material of the present invention is used. About other components, it corresponds to the element of the general lithium ion secondary battery.

It is preferable to select a material capable of doping / dedoping a sufficient amount of lithium as the material of the positive electrode (anode active material). As such a positive electrode active material, the complex chalcogenide of lithium and a transition metal, especially the composite oxide of lithium and a transition metal is illustrated.

The composite oxide of lithium and transition metal (also called lithium-containing transition metal oxide) may be a solution of lithium and two or more transition metals. Specifically, LiM (1) _1-X M (2) _X O ₂ (wherein X is a value in the range of 0 ≦ X ≦ 1, and M (1) and M (2) consist of at least one transition metal element). ) Or LiM (1) _2-Y M (2) _Y O ₄ (wherein Y is a value in the range 0 ≦ Y ≦ 1, and M (1) and M (2) consist of at least one transition metal element) Represented by

In the above, examples of the transition metal element represented by M include Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn and the like.

More specifically, LiCoO ₂ or Li _X Ni _Y M _1-Y O ₂ (M is at least one selected from the transition metal elements, preferably Co, Fe, Mn, Ti, Cr, V, Al, except Ni, 0.05 ≤ x ≤ 1.10, 0.5 ≤ Y ≤ 1.0.

Such lithium-containing transition metal oxides can be obtained by, for example, using Li, an oxide or a salt of a transition metal as starting materials, mixing these starting materials according to their composition and firing at a temperature range of 600 ° C. to 1000 ° C. in an oxygen-containing atmosphere. Can be. Starting materials are not limited to oxides or salts, and can be synthesized from hydroxides and the like.

In the present invention, the positive electrode active material may be used alone or in combination of two or more of the above compounds. For example, carbonates such as lithium carbonate may be added to the positive electrode.

An anode is formed by this anode material. For example, a positive electrode mixture layer is formed by applying a positive electrode mixture composed of a positive electrode material, a binder, and a conductive agent to impart conductivity to the electrodes on both surfaces of the current collector. As the binder, any of those exemplified in the negative electrode can be used. As the conductive agent, for example, graphite is used.

The shape of the current collector is not particularly limited, and a thin shape or a mesh shape such as a mesh or expanded metal is used. For example, aluminum, stainless steel, nickel, etc. are mentioned as a material of an electrical power collector. It is preferable that it is 10-40 micrometers as the thickness.

Also in the case of the positive electrode, the positive electrode mixture layer may be formed by dispersing the positive electrode mixture in a solvent like a negative electrode to form a paste, and applying the paste-like positive electrode mixture to a current collector and drying it. After forming a positive electrode mixture layer, you may further crimp | press, such as press press. As a result, the positive electrode mixture layer is uniformly and firmly adhered to the current collector.

When forming an anode as mentioned above, various additives, such as a conventionally well-known electrically conductive agent and a binder, can be used suitably.

As the electrolyte used in the present invention, an organic electrolyte composed of a solvent and an electrolyte salt, a polymer electrolyte composed of a polymer and an electrolyte salt, and the like can be used. Examples of electrolyte salts include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ), LiCl, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ CH ₂ OSO ₂ ) ₂ , LiN (CF ₃ CF ₂ OSO ₂ ) ₂ , LiN (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ , LiN ((CF ₃ ) ₂ CHOSO _{2 ) 2, LiB [C 6 H} 3 (CF 3) 2] 4, LiAlC1 4, LiSiF _6, etc. can be used. In particular, LiPF ₆ and LiBF ₄ are preferably used in view of oxidation stability.

The electrolyte salt concentration in the organic electrolyte is preferably 0.1 to 5 mol / liter, and more preferably 0.5 to 3.0 mol / liter.

Examples of the solvent of the organic electrolyte include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, 1,1-or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, sulfolane, methylsulfolan, acetonitrile, chloronitrile, propionitrile, trimethyl borate , Tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, nitrobenzene, benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2 Aprotic organic solvents, such as oxazolidone, ethylene glycol, and dimethyl sulfite, can be used.

In the case of using the nonaqueous electrolyte as a polymer electrolyte, a matrix polymer gelled with a plasticizer (nonaqueous electrolyte) is included, but the matrix polymer may be an ether polymer such as polyethylene oxide or a crosslinked product thereof, polymethacrylate, polyacrylate, Fluorine type polymers, such as a polyvinylidene fluoride and a vinylidene fluoride-hexafluoropropylene copolymer, etc. can be used individually or in mixture.

Among them, it is preferable to use fluorine-based polymers such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer from the viewpoint of redox stability and the like.

As the electrolyte salt or the solvent constituting the plasticizer contained in the polymer electrolyte, any of the above-mentioned ones can be used. 0.1-5 mol / liter is preferable and, as for the electrolyte salt concentration in the electrolyte solution which is a plasticizer, 0.5-2.0 mol / liter is more preferable.

There is no restriction | limiting in particular as a manufacturing method of such a polymer electrolyte, For example, the method of mixing, heating, and melting a high molecular compound, a lithium salt, and a solvent which form a matrix is mentioned. In addition, after dissolving the polymer compound, the lithium salt and the solvent in a suitable organic solvent for mixing, the method of evaporating the organic solvent for mixing and the monomer, lithium salt and solvent are mixed, and irradiated with ultraviolet rays, electron beams or molecular beams to the polymer to The method of forming is mentioned.

Moreover, 10-90 mass% is preferable, and, as for the addition ratio of the solvent in a polymer electrolyte, More preferably, it is 30-80 mass%. If it is said 10-90 mass%, electrical conductivity is high, mechanical strength is high and it is easy to form a film.

In the lithium ion secondary battery of this invention, a separator can also be used.

It does not specifically limit as a separator. Examples thereof include woven fabrics, nonwoven fabrics, and synthetic resin microporous membranes. In particular, a microporous membrane made of synthetic resin is preferably used. Among them, polyolefin-based microporous membranes are preferred in terms of thickness, film strength, and film resistance. Specifically, it is a microporous membrane made of polyethylene and a polypropylene, or a microporous membrane having a combination thereof.

In the lithium ion secondary battery of the present invention, a polymer electrolyte can also be used in that the initial charge and discharge efficiency is high.

Lithium ion secondary batteries using a polymer electrolyte are generally called polymer cells. A negative electrode, a positive electrode, and a polymer electrolyte containing the modified graphite product of the present invention can be constituted. For example, it is laminated | stacked in order of a negative electrode, a polymer electrolyte, and a positive electrode, and is accommodated in a battery exterior material. In addition, a polymer electrolyte may be disposed outside the cathode and the anode. In a polymer battery using the modified graphitized material of the present invention as a negative electrode material, propylene carbonate can be contained in the polymer electrolyte. Generally, propylene carbonate has a severe electrolytic reaction with graphite, but has a low decomposition reactivity with respect to the modified graphite product of the present invention.

In addition, the structure of the lithium ion secondary battery which concerns on this invention is arbitrary, and is not specifically limited about the shape and form. Cylindrical, square, coin type, button type and the like can be arbitrarily selected. In order to obtain a more stable hermetically sealed nonaqueous electrolyte battery, it is preferable to have a means for detecting a rise in the internal voltage of the battery in the event of an abnormality such as overcharging and blocking current. In the case of a polymer battery using a polymer electrolyte, the polymer battery can also have a structure enclosed in a laminated film.

Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In addition, in the following example and the comparative example, the graphitized material produced and evaluated the button type secondary battery for evaluation of the structure shown in FIG. However, the 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 represented by the negative electrode and the opposite electrode by the positive electrode.                 

In the following Examples and Comparative Examples, the physical properties of the particles were measured as follows.

The average particle diameter was measured by the laser diffraction particle size distribution meter. The average lattice spacing was determined by X-ray diffraction.

The specific surface area is the BET specific surface area by nitrogen gas adsorption.

Hardness was measured by the following method. The graphitized material was filled with 5 g of a cylindrical container (inner diameter of 20 mm) and tapped 200 times. Thereafter, a steel round bar having the inner diameter of the cylindrical container is pushed from the upper portion of the sample filling surface, and subjected to a compression test at a constant speed, at the inflection point of the detection load (the point where the detection load is reduced based on the breakage of particles). The load is expressed in relative values. That is, the inflection point load of the graphite used in Example 1 mentioned later was set to 1, and the relative value of the inflection point load of each graphite and hard fine particle was shown.

Raman analysis of the graphitized material was carried out by NR-1800 manufactured by Nippon Spectroscopy Co., Ltd. using an argon laser light having a wavelength of 514.5 nm.

Example 1

(1) Preparation of Cathode Materials

The mesophase globules (Kawasaki Steel Co., Ltd. product, average particle diameter: 25 micrometers) formed by heat-treating coal tar pitch were graphitized at 3000 degreeC, and the graphitized material (raw material graphitized material) of mesophase globules was obtained. This graphite was spherical in shape, had an average lattice spacing (d ₀₀₂ ) of 0.3362 nm, and a specific gravity of 2.228 (density 2.228 g / cm ³ ). In addition, the specific surface area was 0.45 m ² / g. The relative value of longitude is one.

Next, the graphitized material was subjected to a treatment of simultaneously applying a compressive force and a shearing force under the following conditions using a treatment apparatus (manufactured by Nara Machinery Co., Ltd.) (hybridization system) of the schematic structure shown in FIG. 2.

That is, by processing under the conditions of a processing time of 6 minutes at the circumferential speed of the rotating rotor at 40 m / sec, the compressive force and the shearing force were simultaneously and repeatedly applied while dispersing the graphitized material introduced into the apparatus.

The graphitized substance after the treatment which simultaneously applies the compressive force and the shearing force had a spherical shape, and the average particle diameter was 24 µm. The intensity ratio (I _D / I _G ratio) by Raman analysis was 0.47. The average lattice spacing d ₀₀₂ was maintained at 0.3362 nm.

(2) Preparation of negative electrode mixture paste

The negative electrode mixture paste of the aqueous solvent and the organic solvent was prepared using the graphitized substance (modified graphitized substance) after the treatment which simultaneously applies the compressive force and the shearing force obtained above.

<Preparation of Aqueous Cathode Mixture Paste>

97 mass% of modified graphitized materials and 1 mass% of carboxymethyl cellulose and 2 mass% of styrene butadiene rubber were mixed as water as a solvent, and stirred at 500 rpm for 5 minutes using a homo mixer to prepare an aqueous negative electrode mixture paste.

<Preparation of Cathode Mixture Paste of Organic Machine>                 

90 mass% of modified graphitized materials and 10 mass% of polyvinylidene fluoride as a binder were mixed with N-methylpyrrolidone as a solvent, and stirred at 500 rpm using a homo mixer for 5 minutes to prepare an organic negative electrode mixture paste.

(3) Production of cathode

The said negative electrode mixture paste was apply | coated to the provision foil (current collector) in uniform thickness, and the solvent was volatilized at 90 degreeC in vacuum, and it dried. Next, the negative electrode mixture applied on this copper foil was pressurized by the roller press. Thereafter, a negative electrode 2 made of a negative electrode mixture layer was punched into a circular shape having a diameter of 15.5 mm and adhered to the current collector 7b.

(4) Production of anode

The lithium metal foil was crimped to a nickel net, integrated into a circular shape having a diameter of 15.5 mm, and punched to produce a positive electrode 4 made of lithium metal foil adhered to the current collector 7a of the nickel net.

(5) electrolyte

LiPF ₆ was dissolved in a solvent mixed at a ratio of 33 mol% of ethylene carbonate and 67 mol% of methyl ethyl carbonate so as to have a concentration of 1 mol / dm ³ , thereby preparing a nonaqueous electrolyte solution. The separator 5 in which the obtained nonaqueous electrolyte solution was impregnated into the polypropylene porous body was produced.

(6) Production of evaluation battery

As an evaluation battery, a button type secondary battery having the structure of FIG. 1 was produced.

First, the separator 5 in which the electrolyte solution is impregnated is laminated between the negative electrode 2 in close contact with the current collector 7b and the positive electrode 4 in close contact with the current collector 7a. Thereafter, the exterior cup 1 and the exterior can 3 are joined so that the negative electrode current collector 7b side is accommodated in the exterior cup 1 and the positive electrode current collector 7a side is accommodated in the exterior can 3. At this time, the insulating gasket 6 was interposed between the outer cup 1 and the outer can 3 so as to fix and seal both peripheral parts.

About the evaluation battery produced as mentioned above, the following charging / discharging test was done under the temperature of 25 degreeC.

(7) charge and discharge test

Initial discharge efficiency

Charge 0.9mA of constant current until the circuit voltage reaches 0mV. Next, switch to constant voltage charging and continue charging until the current value is 20 μA. After that, it stopped for 120 minutes.

Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5V. At this time, charge capacity and discharge capacity were calculated | required from the electricity supply amount in a 1st cycle, and initial stage charging and discharging efficiency was computed from following Formula.

Initial charge and discharge efficiency (%) = (discharge capacity / charge capacity) × 100

In this test, the process of doping lithium ions in the graphitized material was called charging and the process of dedoping from the graphitized material was discharged.

Rapid charging efficiency

Subsequently, fast charging was performed as a second cycle.

The current value is 5 times 4.5mA, and constant current charging is performed until the circuit voltage reaches 0mV. From the obtained charging capacity, the rapid charging efficiency was calculated using the following formula.

Rapid charge efficiency (%) = (constant current charge capacity in 2nd cycle) / (discharge capacity in 1st cycle) * 100

(8) Hydrophilicity evaluation of negative electrode material

The hydrophilicity of the obtained negative electrode material was evaluated as follows. 15 g of the modified graphitized product of the present invention was filled into a cylindrical container made of a wire mesh and filter paper, and was tapped 160 times. Then, the bottom part of the said container was made to contact water surface, and the change with time of water penetration amount was measured.

Table 1 shows the values of the discharge capacity (mAh / g), initial charge and discharge efficiency (%), and rapid charge efficiency (%) per 1 g of the modified graphitized material measured above. In addition, the evaluation result of hydrophilicity is shown in FIG.

Example 2

The process (1) of Example 1 was performed in the presence of the following anhydrous silica, and the negative electrode material was prepared. Conditions other than that were implemented similarly to Example 1.

That is, in the step (1) of Example 1, 100 parts by mass of the raw graphite material and 0.2 parts by mass of anhydrous silica (AEROSIL 300 manufactured by Japan Aerosol Co., Ltd., average particle diameter 7 nm, relative hardness 4.2) The process was carried out in the same manner as in Example 1 except that the treatment device was placed in the treatment apparatus and the treatment time was 2 minutes.

The graphitized substance after the said surface modification process was spherical, and the average particle diameter was 23 micrometers. The intensity ratio (I _D / I _G ratio) in the Raman analysis was 0.57. The average lattice spacing d ₀₀₂ in X-ray diffraction was 0.3362 nm.

This negative electrode material was evaluated in the same manner as in Example 1. Battery characteristics are shown in Table 1, and the hydrophilicity of the negative electrode material is shown in FIG.

Example 3

In Example 1, (1) The apparatus which performs the process which simultaneously applies a compressive force and a shearing force at the time of preparation of a negative electrode material, the processing apparatus of the schematic structure shown in FIGS. 3A-B (Hokawa Micron Mekano Fusion system) It carried out similarly to Example 1 except having carried out the surface modification process on the following conditions instead of the following.

In other words, the graphite was repeatedly treated at the same time by repeatedly compressing and shearing the graphitized material at a distance of 5 mm between the rotating drum and the inner member, at a circumferential speed of 20 m / sec and a processing time of 60 minutes. The graphitized substance after the said surface modification process was spherical, and the average particle diameter was 25 micrometers.

The said intensity ratio (I _D / I _G ratio) in Raman analysis was 0.45. The average lattice spacing d ₀₀₂ in X-ray diffraction was 0.3362 nm.

Next, a negative electrode mixture paste, a negative electrode, and a lithium ion secondary battery were produced.

This negative electrode material was evaluated in the same manner as in Example 1. Battery characteristics are shown in Table 1, and the hydrophilicity of the negative electrode material is shown in FIG.

Example 4

0.5 mass parts of titanium oxide (P25, the average particle diameter of 21 nm, hardness relative value 4.6) coexist in 100 mass parts of raw material graphite materials similar to Example 3, and it is performed by processing time 10 minutes. The same surface modification treatment was performed as in Example 3. The graphitized substance after the said surface modification process was spherical, and the average particle diameter was 24 micrometers.

The said intensity ratio (I _D / I _G ratio) in Raman analysis was 0.63. The average lattice spacing d ₀₀₂ in X-ray diffraction was 0.3362 nm.

Next, a negative electrode mixture paste, a negative electrode, and a lithium ion secondary battery were produced.

This negative electrode material was evaluated in the same manner as in Example 1. Battery characteristics are shown in Table 1, and the hydrophilicity of the negative electrode material is shown in FIG.

As shown in Examples 1 to 4 of Table 1, the lithium ion secondary battery using the negative electrode material of the present invention as a negative electrode has a large discharge not only when using an organic negative electrode mixture paste, but also using an aqueous negative electrode mixture paste. It has been confirmed that the capacity and high initial charge and discharge efficiency are maintained and at the same time have a high rapid charging efficiency.

In addition, as shown in Fig. 4 (Examples 1 to 4), the negative electrode material of the present invention greatly increased the amount of water penetrating by the treatment of simultaneously applying the compressive force and the shearing force. In addition, the amount of water permeation further increased by carrying out the treatment in the presence of hard fine particles. In addition, for comparison, the raw graphite was pulverized to produce the same as the specific surface area of the modified graphite of the present invention. Although the same water supply test was performed to this, the increase of the water penetration amount was not observed. In this respect, the negative electrode material of the present invention was considered to be highly hydrophilized.

Comparative Example l

The raw graphite material of Example 1 (Raman analysis value I _D / I _G ratio = 0.20) was used in place of the modified graphite material of Example 1 without performing the surface modification treatment. A negative electrode mixture was prepared in the same manner as in Example 1, to prepare a negative electrode and a lithium ion secondary battery. The hydrophilicity of this raw material graphite is shown in FIG. Table 1 shows the results of the battery characteristics.

As shown in FIG. 4, the negative electrode material shows little hydrophilicity.

In addition, as shown in Table 1, an organic negative electrode mixture paste was used as a lithium ion secondary battery using a graphitized material (raw graphitized material) of meso-phase globules that was not subjected to simultaneous compressive and shearing forces as a negative electrode material. In the case of Example 1, the discharge capacity, high initial charge and discharge efficiency, and high rapid charge efficiency are the same as in Example 1, but it can be seen that the rapid charge efficiency is lowered when the aqueous negative electrode mixture paste is used.

Comparative Example 2

The raw material graphite in Example 2 and anhydrous silica were mixed for 30 minutes at a stirring speed of 700 rpm using Henschel Mixer (manufactured by Mitsui Chemical Co., Ltd.). Using the obtained mixture, a negative electrode material was prepared in the same manner as in Example 2. On the other hand, in this mixing process, compressive force and shear force could not be applied simultaneously.                 

After stirring and mixing, the strength ratio (I _D / I _G ratio) in Raman analysis of the mixture was 0.21. The average lattice spacing d ₀₀₂ in X-ray diffraction was 0.3362 nm. In addition, the silica and the graphite are separated by a wind classifier, and the intensity ratio (I _D / I _G ratio) in the Raman analysis of the graphite body alone and the average lattice spacing (d ₀₀₂ ) in the X-ray diffraction are determined. As a result, it was the same analysis value as the mixture containing anhydrous silica.

A negative electrode mixture paste was prepared in the same manner as in Example 1 except that the mixture of the above-obtained graphite and silica anhydride was used, and a negative electrode and a lithium ion secondary battery were produced. Battery characteristics are shown in Table 1.

As shown in Table 1, a lithium ion secondary battery using graphite as an anode material that was not subjected to the treatment of simultaneously applying compressive and shearing forces even when mixed under anhydrous silica coexistence had a rapid charging efficiency when an aqueous negative electrode mixture paste was used. It can be seen that it is low.

Example 5

Instead of the raw material graphitized material of Example 4, the graphitized product (average particle diameter 17 mu m) of the mesophase globule pulverized product obtained by pulverizing mesophase globules in advance and then graphitizing at 3000 占 폚 was used. The conditions other than that were the same as Example 4, and also performed the process which simultaneously apply a compressive force and a shearing force.

The graphitized product of the mesophase globule pulverized product before the surface modification treatment was a mixture of spherical and irregular shapes. The average lattice spacing (d ₀₀₂ ) was 0.3362 nm, true specific gravity was 2.228, and the specific surface area was 0.95 m ² / g. The relative value of hardness was 0.9.

The graphitized material after the surface modification treatment was also a mixture of spherical and amorphous forms, and the average particle diameter did not change to 17 µm. However, the specific surface area was 3.45 m ² / g and the intensity ratio (I _D / I _G ) in Raman analysis was 0.75. The average lattice spacing d ₀₀₂ in X-ray diffraction was 0.3362 nm.

In the same manner as in Example 4, a negative electrode mixture paste was prepared, and a negative electrode and a lithium ion secondary battery were produced. Table 1 shows battery characteristics evaluated in the same manner as in Example 4.

Comparative Example 3

In Example 5, a negative electrode material was prepared in the same manner as in Example 5 except that the compressive force and the shear force were not simultaneously applied, and a negative electrode and a lithium ion secondary battery were produced. Table 1 shows battery characteristics evaluated in the same manner as in Example 5.

As shown in Table 1, in the lithium ion secondary battery using the graphitized material of Comparative Example 3 having a low intensity ratio (I _D / I _G ) in the Raman analysis as a negative electrode, the aqueous negative electrode mixture paste was rapidly used. Low charging efficiency On the other hand, in Example 5, in which the strength ratio (I _D / I _G ) in Raman analysis was increased by the treatment of applying compressive force and shearing force simultaneously, rapid charging efficiency was remarkably improved even when an aqueous negative electrode mixture paste was used. In addition, the initial charge and discharge efficiency was also improved. In addition, even when the organic negative electrode mixture paste was used, further improved effects of rapid charging efficiency and initial charge / discharge efficiency were recognized.

Examples 6-11

A mixture of the modified graphitized material produced by any one of Examples 1 to 4 and the other graphitized material shown in Table 2 was used for the negative electrode of the lithium ion secondary battery. In the same manner as in Example 1, a negative electrode mixture paste was prepared, and a negative electrode and a lithium ion secondary battery were produced. Evaluation similar to Example 1 was performed. The results are shown in Table 2.

Comparative Example 4

The mixture of the raw material graphitized material of Example 1 and natural graphite (SNO-10 by SEC Corporation) was used for the negative electrode material of a lithium ion secondary battery. In the same manner as in Example 1, a negative electrode mixture paste was prepared, and a negative electrode and a lithium ion secondary battery were produced. Evaluation similar to Example 1 was performed. The results are shown in Table 2.

Below, the negative electrode material which contained the graphite whose crystallinity was coat | covered with the carbon material lower than the crystallinity of the modified graphitized material of this invention with the said modified graphitized material is illustrated concretely.

Example 12

(1) Preparation of graphite coated with a carbon material whose crystallinity is lower than that of the modified graphite product of the present invention

Natural graphite (BF10A manufactured by Nakagoshi Graphite Co., Ltd., average particle diameter 10 μm, average lattice spacing (d ₀₀₂ ) is 0.3356 nm as the core material in the autoclave, and the intensity ratio (I _D / I _G ratio) in Raman analysis is 0.09) ) Was added, and a solution in which 20 parts by mass of coal tar pitch was dissolved in 100 parts by mass of tar heavy oil was put as a raw material of the carbon material covering the core material, and heated to 140 ° C under stirring. After heating was continued, tar heavy oil was removed by distillation under reduced pressure to obtain graphite having a pitch attached and / or impregnated to the surface and / or the inside. Next, this was placed in a stainless crucible and calcined at 500 ° C. under inert gas flow in a calcining furnace. Then, it grind | pulverized with the atomizer. Furthermore, it baked at 1300 degreeC and obtained the graphite (henceforth a "coated graphite") whose crystallinity is coat | covered with the carbon material lower than the crystallinity of the modified graphitized material of this invention.

The carbon material coated with graphite is finally heat treated at 1300 ° C., and the crystallinity is lower than that of the modified graphite product of the present invention. In order to confirm this, only coal tar pitch was put into a stainless crucible independently, and it baked at 500 degreeC under inert gas circulation in a baking furnace. Thereafter, it was pulverized with an atomizer. This was also calcined at 1300 ° C. to obtain a carbon material. As a result of analyzing the crystallinity of this carbon material, the average lattice spacing d ₀₀₂ in X-ray diffraction was 0.343 nm. As described above, it can be seen that the crystallinity of the carbon material alone coated with graphite is lower than that of the modified graphite product of the present invention. In addition, the coverage of this carbon material was 8 mass% of the whole. The said intensity ratio (I _D / I _G ratio) in the Raman analysis of the said coated graphite was 0.28, and the average particle diameter was 13 micrometers.

(2) Preparation of negative electrode material and negative electrode mixture paste

The coated graphite obtained above and the modified graphite product prepared by the method of Example 1 were mixed in a mass ratio of said modified graphite product: said coated graphite = 60:40, and it was carried out similarly to Example 1, and it was an aqueous solvent and an organic type system. The negative electrode mixture paste of the solvent was prepared, respectively.

Using this negative electrode material, a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1. Evaluation similar to Example 1 was performed also about the characteristic of the obtained lithium ion secondary battery. In addition, the following rapid discharge efficiency was also measured. The results are summarized in Table 3.

Rapid discharge efficiency

After the initial charge and discharge, high-speed discharge was performed in a second cycle. After charging in the same manner as in the first time, the current value was set to 18 times 20 mA and constant current discharge was performed until the circuit voltage reached 1.5V. From the obtained discharge capacity, the rapid discharge efficiency was calculated using the following formula.

Rapid discharge efficiency (%) = (discharge capacity in 2nd cycle) / (discharge capacity in 1st cycle) * 100

Example 13

The mesophase globules (manufactured by Kawasaki Steel Co., Ltd.) having an average particle diameter of 25 µm used in Example 1 were ground to an average particle diameter of 14 µm using an atomizer, and then graphitized at 3000 ° C to obtain a raw material graphitized material. This was subjected to a treatment in which compressive force and shear force were simultaneously applied under the same conditions as in Example 1 to obtain a modified graphitized product. The obtained modified graphitized product had an average particle diameter of 13 µm and the intensity ratio (I _D / I _G ratio) in Raman analysis of 0.83. The modified graphite was used in place of the modified graphite used for the negative electrode material of Example 12. Other conditions were the same as in Example 12, to prepare a negative electrode material, a negative electrode mixture paste, a negative electrode, and a lithium ion secondary battery. Evaluation similar to Example 12 was performed about the characteristic of the obtained lithium ion secondary battery. The results are shown in Table 3.

Comparative Example 5

The raw graphite material used in Example 1 was used instead of the modified graphite material used for the negative electrode material of Example 12. Other conditions were the same as in Example 12, to prepare a negative electrode material, a negative electrode mixture paste, a negative electrode, and a lithium ion secondary battery. Evaluation similar to Example 12 was performed about the characteristic of the obtained lithium ion secondary battery. The results are shown in Table 3.

As shown in Comparative Example 5 of Table 3, instead of the negative electrode material (modified graphitized material) of the present invention, a lithium ion secondary battery using unmodified raw graphite and coated graphite has an organic negative electrode mixture paste. In contrast to the excellent characteristics, the use of an aqueous negative electrode mixture paste lowers the discharge capacity, rapid charge efficiency and rapid discharge efficiency.

Comparative Example 6

In Example 12, the coated graphite was used alone without using the modified graphite. Other conditions were the same as in Example 12, to prepare a negative electrode material, a negative electrode mixture paste, a negative electrode, and a lithium ion secondary battery. Evaluation similar to Example 12 was performed about the characteristic of the obtained lithium ion secondary battery. The results are shown in Table 3.

As shown in Comparative Example 6 of Table 3, the lithium ion secondary battery using the coated graphite alone without using the negative electrode material (modified graphitized material) of the present invention had a high discharge capacity when the aqueous negative electrode mixture paste was used. And high initial charge and discharge efficiency, but low rapid charge efficiency and rapid discharge efficiency. The reason for this is that the coated graphite uses scale-shaped natural graphite as the core material, and therefore, the coated graphite in the negative electrode is oriented and the contact between the nonaqueous electrolyte and the coated graphite is incomplete.

As shown in Examples 12 to 13 of Table 3, the lithium ion secondary battery using the negative electrode material (a mixture of modified graphite and coated graphite) of the present invention was used not only in the case of using an organic negative electrode mixture paste, Even when the negative electrode mixture paste was used, it was confirmed that a large discharge capacity and a high initial charge and discharge efficiency were maintained and also a high rapid charging efficiency. In particular, it has been confirmed that by mixing coated graphite coated with a low crystalline carbon material, it is possible to maintain a higher discharge capacity and maintain high rapid charge efficiency, rapid discharge efficiency, and initial charge and discharge efficiency. By using the mixture of the modified graphite and coated graphite of the present invention as a negative electrode material, the problems of low rapid charging efficiency and low rapid discharge efficiency when the coated graphite is used alone (Comparative Example 6) have been solved.

The novel modified graphite product obtained by the surface modification treatment of the present invention is highly crystalline, but the outermost surface is disturbed, and surface properties such as wettability are improved. Such modified graphite is preferable as a negative electrode and negative electrode material of a lithium ion secondary battery. In particular, even when the negative electrode is manufactured using the aqueous negative electrode mixture paste instead of the organic mixture paste, a lithium ion secondary battery having high rapid charging efficiency which has not been achieved conventionally while maintaining a large discharge capacity and high initial charge and discharge efficiency is obtained. can do. Therefore, not only demands in terms of environment and safety, but also recent demands for high energy density of batteries can be satisfied. In addition, it can contribute to miniaturization and high performance of the equipment to be mounted.

Claims (13)

In the Raman spectrum using an argon laser beam having an average lattice spacing d _{002 of} less than 0.337 nm in X-ray diffraction, and having an wavelength of 514.5 nm, the intensity I _G of the peak present in the region of 1570 to 1630 cm ⁻¹ is obtained. Mesophase, in which the ratio (I _D / I _G ) of the intensity I _D of the peak present in the region of 1350 to 1370 cm ⁻¹ is greater than 0.4 and 2 or less, and the amount of water permeation after 1 minute to 15 g of graphite is 1 g or more. ) Graphitization of globules. The method of claim 1, Graphitized products of mesosphere globules having an average particle diameter of 3 to 50 µm and a specific surface area of 1 to 20 m ² / g. The method of claim 1, A graphite product of mesosphere globules in which fine particles having a hardness higher than that of the graphitized particles of the mesophase globules and whose average particle diameters are smaller than the average particle diameter of the graphite particles of the mesophase globules are embedded in the surface. The method of claim 3, wherein A graphitized product of mesophase globules wherein the fine particles are at least one member selected from the group consisting of silica, alumina and titanium oxide. A negative electrode material for a lithium ion secondary battery containing the graphitized material of the mesophase globules according to claim 1. The method of claim 5, wherein A negative electrode material further containing graphite other than the graphitized material of the mesophase globules according to claim 1. The method of claim 5, wherein A negative electrode material further containing graphite whose crystallinity is coated with a carbon material which is lower than the crystallinity of the graphitized material of the mesophase globules. The negative electrode for lithium ion secondary batteries which consists of a negative electrode material of any one of Claims 5-7. A lithium ion secondary battery having a negative electrode according to claim 8. A method for producing the graphitized product of mesophase globules according to claim 1, wherein the mechanochemical treatment of applying compressive and shearing forces simultaneously to the graphitized product of mesophase globules. The method of claim 10, The manufacturing method which performs the said process in the presence of microparticles | fine-particles whose hardness is higher than the hardness of the graphitized material of the said mesophase globules, and whose average particle diameter is smaller than the average particle diameter of the said mesophase globules. The method of claim 10, The fine particles are at least one member selected from the group consisting of silica, alumina and titanium oxide. The method of claim 10, And the mechano chemical treatment is a treatment in which a compressive force and a shearing force are simultaneously applied such that a reduction rate of the average particle diameter of the mesophase globules is 20%.

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