JP4542352B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention is a lithium ion secondary battery that can obtain a lithium ion secondary battery that has high initial charge / discharge efficiency and is capable of high-speed charge / discharge even when a negative electrode is produced using an aqueous binder. The present invention relates to a negative electrode material for use, a negative electrode containing the negative electrode material, and a lithium ion secondary battery using the negative electrode and excellent in initial charge / discharge efficiency and rapid charge / discharge efficiency.

  In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for higher energy density of batteries. Under such circumstances, lithium ion secondary batteries have attracted attention as batteries that have high energy density and can be increased in voltage.

  The negative electrode of a lithium ion secondary battery is usually composed of a negative electrode material, a current collector, and a binder (binder resin) for binding the negative electrode materials to each other and the negative electrode material and the current collector. Specifically, a negative electrode mixture paste is prepared from a negative electrode material and a binder, and then the paste is applied onto a current collector such as a copper foil and pressed to produce a negative electrode.

As a negative electrode material of a lithium ion secondary battery, graphite having excellent charge / discharge characteristics and high discharge capacity and potential flatness is mainly used (Patent Document 1).
Graphite (graphitic material) used as a negative electrode material is mesophase graphite obtained by heat treatment of graphite particles such as natural graphite and artificial graphite, as well as mesophase pitch using tar and pitch as raw materials, such as mesophase microspheres. For example, fine particles.

  Natural graphite tends to be oriented during the production of the negative electrode due to its scaly shape. When this is used as the negative electrode material of a lithium ion secondary battery, the discharge capacity is large, but the initial charge / discharge efficiency and cycle characteristics (charge / charge characteristics) are large. The ratio of the discharge capacity to the initial discharge capacity when the discharge was repeated) and the rapid charge / discharge efficiency were low.

  Therefore, it is proposed to improve the initial charge / discharge efficiency, cycle characteristics and rapid charge / discharge efficiency as a negative electrode material for lithium ion secondary batteries by coating the surface of natural graphite or artificial graphite with an organic compound and firing or graphitizing. (Patent Documents 2 to 4).

  On the other hand, the graphite particles obtained by heat-treating mesophase pitch, especially mesophase spheroids, are spherical or nearly spherical in shape, and are randomly laminated during the production of the negative electrode, so good cycle characteristics and rapid charge / discharge Although it has efficiency, depending on the kind of the binder used for producing the negative electrode, the charge / discharge characteristics may not be sufficiently exhibited. For example, when the binder dispersion medium is an organic solvent, the charge / discharge characteristics as the negative electrode material can be sufficiently exerted, but in the case of an aqueous solvent, the charge / discharge characteristics such as the charge rate can be reduced. There is. In recent years, from the viewpoints of environment and safety, in view of the situation in which the use of an aqueous solvent, and therefore an aqueous binder, is desired, even when an aqueous binder is used, it is The advent of graphite particles capable of fully exhibiting discharge characteristics is awaited.

For this purpose, there is a proposal to improve the charge / discharge characteristics of the negative electrode material by improving the conductivity of the graphite particles, and a method of mixing pseudographitic carbon black with graphite (Patent Document 5). ), A method of adding porous carbon powder to natural graphite (Patent Document 6), and a method of attaching amorphous carbon such as ketjen black and acetylene black to a negative electrode material (Patent Document 7).
There is also a proposal to improve the charge / discharge characteristics of the negative electrode material by improving the hydrophilicity of the graphite particles. The graphite particles are mechanochemically treated in the presence of hard fine particles, and the hard fine particles are converted into graphite particles. A method of embedding and integrating (Patent Document 8) has been proposed.

However, the various negative electrode materials described above also have the following problems.
For example, in order to completely coat the surface of natural graphite or artificial graphite, it is necessary to use a large amount of the coating material, and the fusion of the coating material during the heat treatment tends to increase. Further, depending on the subsequent heat treatment temperature, there is a concern that the charge / discharge capacity of the negative electrode material may decrease. In addition, increasing the charge / discharge capacity per volume of the negative electrode is particularly effective for increasing the capacity of the lithium ion secondary battery. For this purpose, the density of the negative electrode using a coated graphite material is increased. (1.6g / cm ³ or more) to increase the pressure at the time of pressing the electrode plate or to repeat rolling several times, the interface between the coated carbon or graphite and the core graphite is brittle For some reason, the particles as the negative electrode material may break. At that time, because the newly generated interface is active, the reactivity with the electrolyte is high, and the initial charge / discharge efficiency may be reduced, and the high energy density of the lithium ion secondary battery cannot be accommodated. There is a drawback. Further, when the core material graphite is highly crystalline, the negative electrode material particles are oriented due to the densification of the negative electrode, and there is a problem that the charge characteristics and discharge characteristics of the lithium ion secondary battery deteriorate.

  In addition, in the method of adding carbon black or porous carbon powder as the conductive material, the conductive material particles are small, so that it is difficult to disperse the conductive material in the negative electrode material. Not enough. In general, since the charge / discharge efficiency and discharge capacity of carbon black itself are lower than those of graphite-based negative electrode materials, the initial charge / discharge efficiency of the negative electrode is reduced, even if conductivity can be ensured by adding a large amount. Therefore, the charge capacity of the lithium ion secondary battery cannot be increased.

  Similarly, in the method of adhering carbon black such as ketjen black and acetylene black to the negative electrode material particles, in order to increase the conductivity, secondary particles in which a large amount of fine carbon black is aggregated are adhered. Although it is necessary, there is a problem in that the charge / discharge efficiency and the discharge capacity are reduced as described above.

  In addition, when composite particles in which graphite particles are mechanochemically treated in the presence of hard fine particles and hard fine particles are embedded and integrated in graphite are used for the negative electrode material, the mechanochemical treatment makes the graphite particles hydrophilic. Because it improves, the discharge capacity can be increased without lowering the charge / discharge efficiency of the lithium ion secondary battery, but this is about the same as the untreated product when the density is increased to cope with the high energy density. There is a problem that the charge / discharge characteristics deteriorate.

Japanese Examined Patent Publication No. 62-23433 JP-A-5-307959 Japanese Patent Laid-Open No. 10-334916 JP 11-343108 A Japanese Patent No. 3367060 JP-A-10-275615 JP-A-11-265716 JP 2003-132889 A

Furthermore, although the above-described improved technology certainly has improved conductivity, charge / discharge characteristics often deteriorate due to higher density. In natural graphite, the main cause is considered to be the orientation due to the shape of the particles, but the graphite particles hydrophilized by mechanochemical treatment have reduced surface roughness and are highly adhered. One of the causes is considered to inhibit the diffusion of lithium ions in the electrolyte solution of the lithium ion secondary battery between the particles.
If these problems can be solved, a negative electrode material that can be used at a high density can actually be used, the capacity of the lithium ion secondary battery can be increased, and the industrial utility value is great.

In other words, a negative electrode material that can be produced using a water-based binder, a negative electrode that has been densified in order to meet the further increase in capacity of lithium ion secondary batteries, and has a discharge capacity, initial charge and discharge efficiency, There is a demand for a negative electrode material excellent in rapid charge / discharge efficiency.
Therefore, the present invention provides a lithium ion secondary excellent in excellent discharge capacity, initial charge / discharge efficiency, rapid charge efficiency, and rapid discharge efficiency even when a negative electrode having a high density of 1.6 g / cm ³ or more is produced. Provided are a negative electrode material for a battery, a negative electrode produced using the negative electrode material, and a lithium ion secondary battery having good discharge capacity, initial charge / discharge efficiency, rapid charge efficiency, and rapid discharge efficiency using the negative electrode. Is the purpose.

In the present invention, carbonized and / or graphite particles having an average particle diameter of more than 100 nm and 1 μm or less are attached to the hydrophilicized graphite particles by mechanochemical treatment. carbonaceous and / or a negative electrode material for a lithium ion secondary battery is an average value of the maximum height of the graphite particles 70nm or more, the negative electrode for a lithium ion secondary battery comprising an aqueous binder is exposed to the outside And the electrode density of the said negative electrode for lithium ion secondary batteries is 1.6 g / cm < ³ > or more, It is a negative electrode for lithium ion secondary batteries characterized by the above-mentioned.

In the negative electrode for a lithium ion secondary battery of the present invention, it is preferable that the hydrophilized graphite particles are made hydrophilic by mechanochemical treatment after graphitizing mesophase spherules or a pulverized product thereof.

In the negative electrode for a lithium ion secondary battery of the present invention, the carbonaceous and / or graphitic particles are preferably thermal carbon black and / or a graphitized product thereof.

  The present invention also provides a lithium ion secondary battery using the negative electrode for a lithium ion secondary battery.

The negative electrode material made of the graphite particles of the present invention has a high discharge capacity and initial charge / discharge efficiency, and is particularly prepared as a negative electrode with a high density of 1.6 g / cm ³ or more, and used as a negative electrode for a lithium ion secondary battery. Sometimes it shows good rapid charge / discharge efficiency. Therefore, the lithium ion secondary battery of the present invention satisfies the recent demand for higher energy density of the battery, and is effective in reducing the size and performance of the mounted device.

Hereinafter, the present invention will be described more specifically.
The present invention relates to a negative electrode material for a lithium ion secondary battery, characterized in that carbonaceous and / or graphitic particles having an average particle diameter of more than 100 nm and 1 μm or less are adhered to hydrophilic graphite particles. A negative electrode material for a lithium ion secondary battery, wherein the adhesion is achieved by mechanochemical treatment of the hydrophilic graphite particles and the carbonaceous and / or graphite particles. .

(Hydrophilic graphite particles)
In the present invention, the hydrophilized graphite particles refer to graphite particles that have been subjected to a treatment for imparting hydrophilicity to the graphite particles. By using the hydrophilic graphite particles, the binder (particularly the aqueous binder) is uniformly dispersed around the hydrophilic graphite particles in the negative electrode mixture described later, and the entire negative electrode mixture Is greatly improved, and charging characteristics and discharging characteristics are improved. The hydrophilicity of the graphite particles can be known by measuring the contact angle between the graphite particles and water, or measuring the penetration rate and penetration amount of water into the graphite particles. In the present invention, 15 g of graphite particles are filled at 250 ° C. into a cylindrical container made of a wire mesh and filter paper having an inner diameter of 36 mm, tapping is repeated 180 times, and then the bottom of the container is brought into contact with the water surface to penetrate water. The amount was measured as the degree of hydrophilicity. For example, when the permeation time is 30 sec, the permeation amount is 0.5 g or more, preferably 0.8 g or more, and more preferably 1.0 g or more is regarded as hydrophilic.

  In the present invention, the hydrophilization treatment refers to a treatment for imparting hydrophilicity, and the hydrophilization treatment method includes a method of attaching a water-soluble resin to graphite particles, and the graphite particles in a gas phase or a liquid phase. Although it depends on a usual method such as a method of oxidizing, a method of hydrophilizing graphite particles by mechanochemical treatment is particularly preferable. In the present invention, a mixture of graphite particles hydrophilized by various methods can also be used. Moreover, as long as adhesion of carbonaceous and / or graphite particles is not impaired, graphite particles that have not been hydrophilized may be mixed.

  The graphite particles (precursor) subjected to hydrophilization treatment such as mechanochemical treatment may be any as long as they have a layer structure into which lithium ions can be inserted. A carbon material having a high degree of conversion is preferable. For example, coal-based tar, mesophase calcined carbon (bulk mesophase) obtained by heating pitch, mesophase microspheres, coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.) Examples include those heat-treated at temperature (graphitized), petroleum-based tar, pitch-heated (graphitized), mesophase carbon fiber graphitized, resin carbide graphitized mesophase, artificial graphite, natural graphite, etc. Is done. The heat treatment includes all heating steps such as a step of carbonizing a mesophase pitch (bulk mesophase, mesophase microsphere), a step of graphitizing, and the like. Of course, it may be a combination of the exemplified graphite particles. Graphite particles to be mechanochemically treated are preferably mesophase spheroid graphite particles, bulk mesophase graphitized materials, artificial graphite, and natural graphite. In particular, mesophase spherulite graphite particles are preferred in terms of charge / discharge characteristics. preferable.

The graphite particles subjected to mechanochemical treatment suitable as hydrophilicized graphite particles preferably have the following physical properties. That is, in order to obtain a high discharge capacity, the graphite particles subjected to the mechanochemical treatment are crystals having a lattice spacing d ₀₀₂ of the carbon network layer in X-ray diffraction of 0.34 nm or less, particularly 0.337 nm or less. It is preferable that the graphite particles have high properties. For the lattice spacing d ₀₀₂ , CuKα rays are used as X-rays, high purity silicon is used as a standard material, the (002) diffraction peak of the graphite particles is measured, and d ₀₀₂ is calculated from the peak position. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 117th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” (Suguro Otani, pages 733-742 (March 1986) ), A modern editing company), and the like.

The average particle diameter of the graphite particles subjected to the mechanochemical treatment is not particularly limited, but is usually 1 to 100 μm, preferably 5 to 40 μm. The average particle diameter is adjusted by the thickness of the negative electrode. The average particle diameter is a particle diameter at which the cumulative frequency of the particle size distribution measured by a laser diffraction particle size distribution meter is 50% by volume. Further, if the specific surface area of the graphite particles is too large, the irreversible capacity is increased and the safety of the battery is lowered. Therefore, the specific surface area is preferably 20 m ² / g or less, more preferably 0.1 to ⁵ m ² / g. It is. The specific surface area is measured by a nitrogen gas adsorption BET method. The true specific gravity of the graphite particles is preferably 2.2 or more. The true specific gravity is measured by a liquid phase substitution method using butanol or the like.
The form of the graphite particles subjected to the mechanochemical treatment is not particularly limited, but is preferably spherical, granular, scaly, fibrous or the like.

  As long as the graphite particles subjected to mechanochemical treatment do not impair the object of the present invention, other carbon materials (including amorphous hard carbon), organic substances, mixtures with metal compounds, granulated substances It may be a coating or a laminate. Further, it may be subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, oxidation treatment and the like.

(Mechanochemical treatment)
The mechanochemical treatment refers to a treatment in which a compressive force and a shear force are simultaneously applied to the graphite particles. Although the shearing force and compressive force are usually larger than general stirring force, these mechanical stresses are preferably applied to the surface of the graphite particles, and preferably do not destroy the particle skeleton of the graphite particles. When the particle skeleton of the graphite particles is destroyed, when used as a negative electrode material, the irreversible capacity tends to increase. In general, the shearing force and compressive force are preferably such that the reduction rate of the average particle diameter of the graphite particles by mechanochemical treatment is suppressed to 20% or less.

  As long as the mechanochemical treatment apparatus is an apparatus capable of simultaneously applying a compressive force and a shearing force to an object to be treated (graphite particles or even hard fine particles), the type and structure of the apparatus are not particularly limited. For example, a kneader such as a pressure kneader, two rolls, a rotating ball mill, a high-speed impact dry powder compounding device such as a hybridization system (manufactured by Nara Machinery Co., Ltd.), Mechano Micros (Nara Machinery Co., Ltd.) And a mechano-fusion system (manufactured by Hosokawa Micron Co., Ltd.) and the like can be used.

Among them, an apparatus that applies a shearing force and a compressing force simultaneously using a difference in rotational speed is preferable. Specifically, an apparatus (for example, FIG. 1 (FIG. 1)) that includes a rotating drum (rotating rotor), an internal member (inner piece) having a rotational speed different from that of the drum, and a circulation mechanism (for example, a circulating blade) of the workpiece. (A) to (B) using a meso-fusion system manufactured by Hosokawa Micron Co., Ltd.) and applying a centrifugal force to the workpiece supplied between the rotating drum and the internal member, The mechanochemical treatment is preferably performed by simultaneously applying a compressive force and a shearing force due to a speed difference from the rotating drum.
In addition, a device that applies a compressive force and a shearing force due to a speed difference between the fixed drum and the rotating rotor to the object to be processed by passing the object to be processed between the fixed drum (stator) and a rotating rotor that rotates at high speed (for example, A hybrid system manufactured by Nara Machinery Co., Ltd., whose schematic mechanism is shown in FIG. 2, is also preferable.

The conditions of the mechanochemical treatment vary depending on the apparatus used, and cannot be generally stated. For example, an apparatus including a rotating drum 11 and an internal member (inner piece) 12 as shown in FIGS. Is used, the workpiece 13 is supplied to the rotary drum 11, the peripheral speed difference between the rotary drum 11 and the internal member 12 is 5 to 50 m / sec, the distance between the two is 1 to 100 mm, and the processing time is 3 It is preferable to operate under a condition of ~ 90 min. The workpiece 13 is circulated by a circulation mechanism 14 in the apparatus, subjected to mechanochemical treatment, and discharged from a discharge mechanism 15.
In addition, when using an apparatus including the fixed drum 21 and the high-speed rotating rotor 22 having the blades 26 as shown in FIG. 2, the workpiece 23 is supplied to the circulation mechanism 24, and the fixed drum 21 and the rotating rotor 22 are connected to each other. It is preferable to operate under conditions where the peripheral speed difference is 10 to 100 m / sec and the processing time is 30 sec to 10 min. The workpiece 23 is circulated by a circulation mechanism 24 in the apparatus, subjected to mechanochemical treatment, and discharged from a discharge mechanism 25. The apparatus is provided with a stator 27 and a jacket 28.

When the mechanochemical treatment is performed on the graphite particles, it is preferable to perform the treatment in the presence of hard fine particles.
The hard fine particles only have to have an average particle size smaller than the average particle size of the graphite particles and are harder than the graphite particles, and other conditions are not particularly limited. When the hard fine particles are aggregates, the average particle size of the primary particles may be smaller than the average particle size of the graphite particles. If the average particle diameter of the hard fine particles is larger than 1 nm, hydrophilicity can be imparted to the graphite particles. When the average particle diameter is 100 nm or less, the contact between the graphite particles is not hindered, and the charge / discharge characteristics are not adversely affected.

  The hard fine particles may or may not contribute to conductivity and charge / discharge characteristics, and may be metals, metal oxides, metal nitrides, metal borides, metal carbides, and the like. Hard fine particles having hydrophilicity are preferred, and fine particles of metal oxides such as anhydrous silica (gas phase silica), titanium oxide, and aluminum oxide produced by a vapor phase method are particularly suitable. By using the hard fine particles having hydrophilicity, in addition to imparting hydrophilicity to the graphite particles by mechanochemical treatment, higher hydrophilicity can be imparted.

For the mechanochemical treatment of the graphite particles, it is preferable to use the hard fine particles as described above usually at a ratio of 0.01 to 10% by mass with respect to the graphite particles. The hard fine particles used in the mechanochemical treatment do not need to remain in the negative electrode material produced thereafter, but 0.01 to 5% by mass, preferably 0.01 to 0.5% by mass with respect to the graphite particles. It is preferable to be embedded and integrated at a ratio of The hard fine particles may be dry blended with the graphite particles in advance and subjected to mechanochemical treatment, or may be added during the mechanochemical treatment of the graphite particles.
As long as the charge and discharge characteristics expected by the present invention are not impaired either before, during or after mechanochemical treatment of graphite particles, known conductive materials, ion conductive materials, surfactants, polymers Various additives such as compounds can be added.

By mechanochemical treatment, hydrophilicity is imparted to the graphite particles, and in the case of coexisting hard fine particles, the hydrophilicity becomes larger, and the convex portions on the surface are polished and smoothed to obtain fine particles. The surface changes to a rough surface, and the slipperiness of the surface is improved. In addition, as a result of improvement in surface characteristics such as reduction in crystallinity or orientation of the surface, graphite particles having an increased R value in Raman spectroscopy can be obtained.
The mechanism by which the surface modification effect is obtained is not necessarily clear, but it is presumed that the surface of the graphite particles is polished by the shearing force under compression by mechanochemical treatment. In particular, in the mechanochemical treatment in the presence of hard fine particles, the effect of polishing the surface of the graphite particles is enhanced, and the hard fine particles are embedded in the vicinity of the surface of the graphite particles and integrated, thereby promoting the effect of the present invention. It is thought to be the cause. Therefore, in the present invention, it is preferable to use graphite particles that have been hydrophilized by mechanochemical treatment, particularly mechanochemical treatment in which hard fine particles coexist.

(Carbonaceous and / or graphite particles)
The particles attached to the hydrophilic graphite particles are carbonaceous and / or graphitic particles. Specifically, natural graphite, artificial graphite, carbon black, acetylene black, thermal carbon black, ketjen black, fullerene, vapor grown carbon fiber or graphitized product thereof, graphite nanofiber, anthracite, phenol resin carbide or graphitized product thereof Such as resin carbide or graphitized product thereof. What mixed these 2 or more types, and what mixed these with another carbonaceous material can also be used.

The average particle size of the carbonaceous and / or graphite particles is preferably as small as possible. However, even if it is too small, the initial charge / discharge efficiency is small, and it is disadvantageous from the viewpoint of manufacturing equipment and handling. Must be: In particular, when the particles are not aggregated, the average particle diameter of the primary particles is preferably 200 to 500 nm. Further, when the particles are aggregated to form secondary particles, the average particle size of the secondary particles may be more than 100 nm and 1 μm or less. In this case, the average particle size of the primary particles is not particularly limited, The average particle diameter of the primary particles is preferably 20 to 50 nm. Thermal carbon black is particularly preferable because the average particle diameter of primary particles is about 200 to 400 nm, the cohesive force is weak, and even if agglomerated, it deaggregates to primary particles with a weak force.
When the particle size of the carbonaceous and / or graphite particles is 100 nm or more, it is measured with a laser diffraction particle size distribution meter. When the particle size is less than 100 nm, a plurality of ( The maximum diameter and the diameter perpendicular to each of the maximum diameter are measured, and the average is defined as the particle diameter, and a plurality of average values of the particle diameters are defined as the average particle diameter.
The specific surface area of the particles, also differ by the primary particle size may be a 1 to 1,000 m ² / g, more preferably 2~60m ² / g, in particular to be 3 to 10 m ² / g preferable. If the specific surface area is too small, the resistance may increase when used as a negative electrode. If the specific surface area is too large, the reactivity with the electrolytic solution may increase and the initial charge / discharge efficiency may be reduced.

(Adhesion of carbonaceous and / or graphite particles)
When adhering the carbonaceous and / or graphitic particles to the hydrophilized graphite particles, if the both are only stirred dry, the particles are partially agglomerated due to aggregation, resulting in poor adhesion efficiency. It is necessary to take measures such as increasing the ratio. In addition, there is a dry method of mixing by a ball mill or the like, but there is a possibility that pulverization of the hydrophilic graphite particles may occur at the same time. In the dry method, a method of attaching the particles while applying a shearing force and a compressive force to the hydrophilic graphite particles by mechanochemical treatment is preferable. In particular, it is efficient to attach the particles to mesophase graphite particles that have been hydrophilized by mechanochemical treatment by mechanochemical treatment using the same device as the mechanochemical treatment device used for hydrophilization treatment.

  When adhering the carbonaceous and / or graphitic particles to the hydrophilized graphite particles, the mixing ratio of the particles to the graphite particles varies depending on the type of the particles. It is 0.2-5 mass% with respect to a total, Preferably it is 0.8-2 mass%. If the mixing amount of the particles is small, the rapid charge / discharge efficiency, which is the effect of the present invention, may be insufficiently improved. When the mixing amount is large, the discharge capacity of the negative electrode material becomes small.

  Specifically, after a mechanochemical treatment is applied to a mixture of graphite particles and hard (inorganic) fine particles, carbonaceous particles and / or graphite particles are mixed with the mixture, and further mechanochemical treatment is performed. . A mixture obtained by mixing carbonaceous particles and / or graphite particles with hydrophilic graphite particles may be mechanochemically treated. In consideration of factors affecting the shearing force during the mechanochemical treatment, that is, the clearance between the rotor and the inner wall of the container, the rotational speed of the rotor, the treatment time, etc., the carbonaceous and / or graphite particles are hydrophilic. Although it adheres to the graphitized graphite particles, it is preferably carried out under conditions that are not buried. When the mechanochemical treatment is performed until the carbonaceous and / or graphite particles are buried, the charge / discharge characteristics expected by the present invention cannot be obtained. Here, burying means that the carbonaceous particles and / or graphitic particles are embedded in the hydrophilized graphite particles, and the particle diameter is 2 / A state in which three or more are embedded in the graphite particles. Further, the adhesion means that when the carbonaceous and / or graphite particles are clearly recognized by observation with an electron microscope, and the cross section of the carbonaceous and / or graphite particles is observed with a scanning electron microscope, The average value of the maximum height of the carbonaceous and / or graphite particles exposed to the outside of the hydrophilized graphite particles at 10 or more points on the adhesion portion is 70 nm or more. Further, the average value of the maximum height is preferably 100 nm or more and 1 μm or less.

  By the mechanochemical treatment, graphite particles in which fine carbonaceous and / or graphite particles are adhered to the hydrophilic graphite particles are obtained. The carbonaceous and / or graphitic particles adhering to the graphite particles substantially maintain the form before adhesion, and the carbonaceous and / or graphitic particles do not substantially overlap on the graphite particles. It is adhering and it is preferable to exist without peeling off from the surface even when preparing the negative electrode paste.

When the graphite particles are used as a negative electrode material for a lithium ion secondary battery, the carbonaceous matter adhered to the hydrophilic graphite particles even when the negative electrode is densified to 1.6 g / cm ³ or more and The graphite particles create minute gaps between the hydrophilized graphite particles, and the electrolyte can move back and forth through the gaps, thereby improving lithium ion diffusibility. As a result, good charge / discharge characteristics are exhibited while maintaining high discharge capacity and high initial charge / discharge efficiency. In particular, the negative electrode is prepared from a negative electrode mixture paste prepared from graphite particles, other graphitic materials and a binder, as described later, and the binder at the time of preparing the paste is water-soluble and Even in the case of a water-dispersible binder (aqueous binder), charge / discharge characteristics equivalent to those in the case where the binder dispersion medium is an organic solvent system can be obtained.

(Negative electrode material)
The negative electrode material of the present invention is a hydrophilic graphite particle to which carbonaceous and / or graphite particles are attached. When the negative electrode is prepared using the negative electrode material of the present invention, the negative electrode material is prepared. In addition, conductive materials, modifiers, additives and the like that are usually used may be mixed. For example, natural graphite, artificial graphite, carbon black, vapor grown carbon fiber, low crystalline carbon particles, or a graphitized product thereof may be mixed. These mixing amounts cannot be generally described, but are 0.1 to 50% by mass as a total amount.
The method for producing the negative electrode material is carried out based on a conventionally known method for producing a negative electrode material.

The negative electrode mixture paste is prepared using a known stirrer, mixer, kneader, kneader or the like. Specifically, the hydrophilic carbonaceous particles to which the carbonaceous and / or graphite particles of the present invention are adhered, and, if necessary, other graphitic materials, a binder and a solvent, It can prepare by stirring with a rotational speed of 300-3000 rpm with a type homomixer.
As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferable. In addition to the organic binder that dissolves and / or disperses in the organic solvent, the binder can be dissolved and dissolved in the aqueous solvent. A wide range of water-based binders are / are dispersed. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol (water-soluble), resin such as carboxymethyl cellulose (water-soluble), rubber such as styrene butadiene rubber (water-dispersible), etc. are used. However, it is particularly preferable to use an aqueous binder such as carboxymethyl cellulose, polyvinyl alcohol, and styrene butadiene rubber. These can also be used together. In general, the binder is preferably used at a ratio of 0.5 to 20% by mass in the total amount of the negative electrode mixture.
As the solvent, a normal solvent used for the preparation of the negative electrode mixture is used, and specific examples include N-methylpyrrolidone, dimethylformamide, water, alcohol and the like. Use of an aqueous solvent is preferable from the viewpoint of environmental pollution and safety.

(Negative electrode)
The negative electrode of the present invention is manufactured by a normal negative electrode manufacturing method using the negative electrode mixture paste. That is, it is manufactured by a method in which a negative electrode mixture paste is applied to one side or both sides of a current collector and dried to form a negative electrode mixture layer.
After forming the negative electrode mixture layer, pressure bonding such as pressing is performed in order to obtain a negative electrode mixture layer having a high density of 1.6 g / cm ³ or more. Thereby, the negative electrode mixture layer is densified, and at the same time, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.
The layer thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 20 to 200 μm.
Any method uses hydrophilic graphite particles to which the carbonaceous and / or graphitic particles are attached, so that a negative electrode mixture layer uniformly and firmly adhered to the current collector is formed. .
The shape of the current collector used for the negative electrode is not particularly limited, but a foil or a net-like material such as a mesh or expanded metal is used. Examples of the material for the current collector include copper, stainless steel, and nickel. In the case of a foil, the thickness of the current collector is preferably 5 to 20 μm.

  The negative electrode can be manufactured according to a normal molding method by dry-mixing the hydrophilic graphite particles to which the carbonaceous and / or graphite particles are adhered and resin powders such as polyethylene and polyvinyl alcohol. . For example, the negative electrode can be produced by hot press molding the mixture in a mold.

  The reason why the lithium ion secondary battery including the negative electrode prepared from the aqueous binder and the current collector using the negative electrode material of the present invention exhibits excellent charge / discharge characteristics even when the negative electrode is densified is clear. However, in the present invention, when the density of the negative electrode is increased, the electrolyte solution that has been hindered because the hydrophilic graphite particles are in close contact with each other in the conventional negative electrode material. This is presumably because the lithium ion diffusibility was improved by being helped by the minute gaps created by the carbonaceous and / or graphitic particles adhering to the graphite particles interposed between the graphite particles.

(Positive electrode)
As the positive electrode material (positive electrode active material), a material capable of inserting / extracting a sufficient amount of lithium is preferably selected. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal chalcogenides, vanadium oxides (V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , V ₃ O _8, etc.) and lithium compounds such as lithium compounds thereof. Containing compound, represented by the general formula M _X Mo ₆ S _8-y (where X is a number in the range of 0 ≦ X ≦ 4, Y is 0 ≦ Y ≦ 1, M represents a metal such as a transition metal) Chevrel phase compounds, activated carbon, activated carbon fibers and the like can be used.
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.

Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-p M ² _p O ₂ (wherein P is a numerical value in the range of 0 ≦ P ≦ 1, and M ¹ and M ² are at least one kind of transition) A metal element) or LiM ¹ _2-q M ² _q O ₄ (where Q is a numerical value in the range of 0 ≦ Q ≦ 2, and M ¹ and M ² are at least one transition metal element) It is. Transition metal elements represented by M are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, and the like, and Co, Ni, Mn, Cr, Ti, V, Fe are preferable. , Al and the like.

More specific examples of the lithium-containing transition metal _{oxide, LiCoO 2, Li p Ni q} M 1-q O 2 ( wherein the transition metal element M in the formulas except the Ni, P is 0.05 ≦ p ≦ 1.10 Q is a numerical value in the range of 0.5 ≦ q ≦ 1.0. A preferred transition metal is at least one selected from Co, Mn, Cr, Ti, V, Fe, and Al. More _{specifically, LiNiO 2, LiMnO 2, LiMnO} 4, LiNi 0.9 Co 0.1 O 2, LiNi 0.5 Co 0.5 O 2 and the like.

The lithium-containing transition metal oxide as described above includes, for example, lithium, transition metal oxides or salts as starting materials, these starting materials are mixed according to a desired composition, and are heated at 600 to 1000 ° C. in an oxygen atmosphere. It can be obtained by firing at a temperature. The starting material is not limited to oxides or salts but may be hydroxides.
In the present invention, the positive electrode active material may be used alone or in combination of two or more. For example, an alkali carbonate such as lithium carbonate can be added to the positive electrode material.

  In order to form a positive electrode with such a positive electrode material, for example, a positive electrode mixture comprising a positive electrode material, a binder, and a conductive agent for imparting conductivity to the electrode is applied to both surfaces of the current collector. Form a layer. As the binder, any of those exemplified for the negative electrode can be used. As the conductive agent, for example, a carbon material, graphite or carbon black is used.

The shape of the current collector is not particularly limited, and a box shape or a net shape such as a mesh or expanded metal is used. Examples of the current collector substrate include aluminum, stainless steel, and nickel. The thickness is preferably 10 to 40 μm.
Also in the case of the positive electrode, as in the case of the negative electrode, the positive electrode material mixture layer may be formed into a paste by dispersing the positive electrode material mixture in a solvent, and this positive electrode material mixture paste may be applied to a current collector and dried. After the positive electrode mixture layer is formed, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.

  In forming the negative electrode and the positive electrode as described above, conventionally known various additives such as a conductive agent and a binder can be appropriately used.

(Electrolytes)
As the electrolyte salt in the present invention, an electrolyte salt used in a normal nonaqueous electrolytic solution can be used. Specifically, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , 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 Lithium salts such as CHOSO ₂ ] ₂ , LiB [C ₆ H ₃ (CF ₃ ) ₂ ] ₄ , LiAlCl ₄ , LiSiF ₄ can be used. In particular, LiPF ₆ and LiBF ₄ are preferably used from the viewpoint of oxidation stability.
The electrolyte salt concentration in the organic electrolyte is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 3.0 mol / l.

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

  In order to obtain a liquid nonaqueous electrolyte solution, the solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl 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, methylsulfolane, acetonitrile, chloronitrile, propionitrile, trimethyl borate , Tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, nitrobenzene, benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl Aprotic organic solvents such as til sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, and dimethyl sulfite can be used.

When the non-aqueous electrolyte is a polymer electrolyte, it includes a matrix polymer compound that is gelled with a plasticizer (non-aqueous electrolyte). Examples of the matrix polymer compound include polyethylene oxide and its crosslinked product. Ether-based polymer compounds, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, fluorine-based polymer compounds such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer, etc. are used alone or in combination. be able to.
Among these, it is preferable to use a fluorine-based polymer compound such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer from the viewpoint of redox stability.

  As the electrolyte salt and the solvent constituting the plasticizer contained in the polymer electrolyte, those described above can be used. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt in the electrolytic solution that is a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.

The method for producing the polymer electrolyte is not particularly limited, and examples thereof include a method in which a polymer compound constituting a matrix, a lithium salt and a solvent are mixed, heated and melted / dissolved. In addition, after dissolving a polymer compound, a lithium salt, and a solvent in an organic solvent for mixing, the organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a solvent are mixed, and ultraviolet rays, electron beams, or molecules are mixed. Examples thereof include a method of polymerizing a polymerizable monomer by irradiating a line or the like to obtain a polymer electrolyte.
The ratio of the solvent in the polymer electrolyte is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. Within this range, electrical conductivity is high, mechanical strength is high, and film formation is easy.

(Lithium ion secondary battery)
A lithium ion secondary battery usually includes a negative electrode, a positive electrode, and a non-aqueous electrolyte as main battery components, and each of the positive electrode and the negative electrode includes a lithium ion carrier. Lithium ions enter and exit in the charge / discharge process. A battery mechanism is formed in which lithium ions are occluded in the negative electrode during charging and are desorbed from the negative electrode during discharging.
The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode material containing the graphite particles of the present invention is used as the negative electrode material, and other battery components are those of a general lithium ion secondary battery. According to the element.

  Although the separator used for the lithium ion secondary battery of this invention is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous film made of polyethylene and polypropylene, or a microporous film in which these are combined.

  In the lithium ion secondary battery of the present invention, a gel electrolyte can also be used. The gel electrolyte secondary battery is generally composed of a negative electrode, a positive electrode, and a gel electrolyte. For example, the gel electrolyte secondary battery is configured by laminating a negative electrode, a gel electrolyte, and a positive electrode in this order and housing the battery in a battery exterior material. In addition, in addition to this, a gel electrolyte may be arranged outside the negative electrode and the positive electrode.

  The structure of the lithium ion secondary battery of the present invention is arbitrary, and the shape and form thereof are not particularly limited, and can be arbitrarily selected from a cylindrical shape, a square shape, a coin shape, a button shape, and the like. . In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include a means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging. A structure encapsulated in an aluminum laminate film or the like can also be used.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples. Further, in the following examples and comparative examples, a negative secondary material containing graphite particles was used to produce a button-type secondary battery for evaluation having a configuration as shown in FIG. 3 and the charge / discharge characteristics of the graphite particles were evaluated. did. A real battery can be manufactured according to a well-known method based on the objective of this invention.

In the following examples and comparative examples, the physical properties of graphite particles and the like were measured by the following methods.
The average particle size of the graphite particles and the average particle size of the carbonaceous and / or graphite particles are measured using a laser diffraction particle size distribution meter, and the cumulative frequency of the particle size distribution is 50% by volume percentage. The diameter. However, the average particle diameter of the carbonaceous furnace carbon black used as the carbonaceous and / or graphitic particles of Comparative Example 5 is an average value of 100 particles measured using a scanning electron microscope (magnification 10,000 times). It is.
The true specific gravity was measured by a liquid phase substitution method using butanol.
The lattice spacing d ₀₀₂ was determined by the aforementioned X-ray wide angle diffraction method.
The specific surface area was measured by the BET method using nitrogen gas adsorption.
The amount of water penetration (hydrophilicity) was determined by filling 15 g of graphite particles into a cylindrical container made of wire mesh and filter paper having a bottom of 36 mm at 25 ° C., and using a powder tester (PTR; manufactured by Hosokawa Micron Corporation) for 60 minutes per minute. This is the amount of penetration (mass) after 30 seconds of contact after 3 minutes of tapping for 3 minutes and tapping 180 times, and then contacting the bottom of the container with the water surface. The amount of penetration was measured using a penet analyzer (manufactured by Hosokawa Micron Corporation).
The height of the exposed portion of the carbonaceous and / or graphite particles is determined by scanning electron microscope observation (5000 times) of the cross section of the hydrophilicized graphite particles to which the carbonaceous and / or graphite particles are attached. Ten places of adhesion were selected, and the maximum height at which the carbonaceous and / or graphite particles at each adhesion area were exposed to the outside of the hydrophilized graphite particles was measured and taken as the average value.

Example 1
(Preparation of hydrophilized graphite particles)
Mesophase microspheres (manufactured by JFE Chemical Co., Ltd., average particle size: 24 μm) obtained by heat treatment of coal tar pitch were graphitized at 3000 ° C. to obtain mesophase microsphere graphite particles. The particles were spherical, the lattice spacing d ₀₀₂ was 0.3362 nm, and the true specific gravity was 2.228. The specific surface area was 0.45 m ² / g, and the penetration amount was 0.15 g (30 sec).

Next, the graphite particles were subjected to mechanochemical treatment under the following conditions using a mechanochemical treatment apparatus having a schematic structure as shown in FIG. 2 (“Hybridization System” manufactured by Nara Machinery Co., Ltd.). That is, by processing at a rotating rotor peripheral speed of 40 m / sec under a processing time of 6 min, the compressive force mainly including impact force and intermolecular interaction is dispersed while dispersing the graphite particles put into the apparatus. Mechanical actions such as frictional force and shearing force were repeatedly applied. The obtained graphite particles had a spherical shape, the average particle size was 24 μm, the specific surface area was 1.2 m ² / g, and the penetration amount was 1.3 g (30 sec).

(Adhesion of carbonaceous particles)
The hydrophilized graphite particles and 1 part by mass of thermal carbon black (manufactured by Engineered Carbons, MT N990; average particle diameter (average primary particle diameter) of 310 nm, specific surface area of 8 parts per 99 parts by mass of the graphite particles 5 m ² / g) was put in the mechanochemical treatment apparatus shown in FIG. 2, and the mechanochemical treatment was performed under the conditions of a peripheral speed of the rotating rotor of 12 m / sec and a treatment time of 3 minutes. It was confirmed from the observation with an electron microscope that the carbon black adhered to the surface of the graphite particles without being overlaid by the treatment.

(Preparation of negative electrode mixture paste)
The graphite particles with the carbon black adhered thereto are put into a planetary mixer, and 1.5 parts by mass of carboxymethylcellulose sodium, carboxy-modified styrene butadiene rubber latex emulsion (JSR Co., Ltd.) with respect to 97 parts by mass of the graphite particles in solid content. ) Produced) 1.5 parts by mass and water were added and mixed, followed by stirring to prepare an aqueous solvent-based negative electrode mixture paste.

(Production of working electrode (electrode using negative electrode material according to the present invention))
The negative electrode mixture paste was applied on a copper foil (current collector) (thickness: 16 μm), further heated to 90 ° C. in a vacuum to volatilize the solvent and dried. Next, the formed negative electrode mixture layer is pressed by a roller press, and further punched into a circular shape having a diameter of 15.5 mm, whereby a working electrode having a negative electrode mixture layer (thickness 60 μm) adhered to the copper foil is obtained. Produced.

(Production of counter electrode)
A lithium metal foil is pressed onto a nickel net and punched into a circular shape with a diameter of 15.5 mm, and consists of a current collector made of nickel net (thickness 250 μm) and a lithium metal foil (thickness 500 μm) in close contact with the current collector A counter electrode was produced.

(Electrolyte)
LiPF ₆ was dissolved at a concentration of 1 mol / dm ^{3 in} a mixed solvent of ethylene carbonate 33 mol% -methyl ethyl carbonate 67 mol% to prepare a non-aqueous electrolyte. The obtained nonaqueous electrolytic solution was impregnated into a polypropylene microporous membrane to produce a separator impregnated with the electrolytic solution.

(Production of evaluation battery)
A button-type evaluation battery shown in FIG. 3 was produced as an evaluation battery.
The exterior cup 31 and the exterior can 33 have a sealed structure that is caulked with an insulating gasket 36 at the peripheral edge thereof, and the current collector 37 a made of nickel net and the lithium foil in the inside from the inner surface of the exterior can 33. A disk-shaped counter electrode 34, a separator 35 impregnated with an electrolyte solution, a disk-shaped working electrode 32 having a negative electrode mixture layer, and a current collector 37 b made of copper foil.

In the evaluation battery, the separator 35 impregnated with the electrolytic solution was stacked between the working electrode 32 in close contact with the current collector 37b and the counter electrode 34 in close contact with the current collector 37a, and then the working electrode 32 was placed in the outer cup 31. In addition, the counter electrode 34 was accommodated in the outer can 33, the outer cup 31 and the outer can 33 were combined, and the peripheral portion of the outer cup 31 and the outer can 33 was caulked with an insulating gasket 36 and sealed. .
The evaluation battery is a battery composed of a working electrode 32 containing graphite particles that can be used as a negative electrode active material and a counter electrode 34 made of a lithium metal foil in an actual battery.

The evaluation battery produced as described above was subjected to the following charge / discharge test at a temperature of 25 ° C., and the discharge capacity, initial charge / discharge efficiency, and rapid charge / discharge efficiency were measured. The measurement results of these charge / discharge characteristics are shown in Table 2.
Each measurement method is described below.
(Electrode density)
The thickness of the current collector is t ₁ [cm], the mass per unit area is W ₁ [g / cm ² ], and the hydrophilized graphite particles to which the carbonaceous and / or graphitic particles of the present invention are attached A negative electrode paste having a thickness of t ₂ [cm] produced by applying a negative electrode mixture paste with a binder having a mass ratio of P [%] and pressurizing is punched out with a predetermined area S [cm ² ]. When the mass of the negative electrode after punching is W ₂ [g], it can be obtained by the following formula. In addition, the said mass is the value measured with the top plate type automatic balance and thickness with the micrometer.
Electrode density [g / cm ³ ] = {(W ₂ / S−W ₁ ) / (t ₂ −t ₁ )} × (P / 100)

(Discharge capacity, initial charge / discharge efficiency)
After performing constant current charging until the circuit voltage reaches 0 mV at a current value of 0.9 mA, when the circuit voltage reaches 0 mV, switching to constant voltage charging is continued until the current value reaches 20 μA. It was. The charging capacity was determined from the amount of electricity applied during that time. Then, it rested for 120 minutes.
Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity was obtained from the energization amount during this period. This was the first cycle. The initial charge / discharge efficiency was calculated from the following equation.
Initial charge / discharge efficiency (%) = (discharge capacity in the first cycle / charge capacity in the first cycle) × 100
In this test, the process of occluding lithium ions in the negative electrode material was charged, and the process of desorbing from the negative electrode material was discharge.

(Rapid charging efficiency)
Subsequently, as the second cycle, the current value was set to 4.5 mA which is five times that of the first cycle, constant current charging was performed until the circuit voltage reached 0 mV, the charge capacity was obtained, and the quick charge efficiency was calculated from the following equation.
Rapid charge efficiency (%) = (Constant current charge capacity in the second cycle / Discharge capacity in the first cycle) x 100

(Rapid discharge efficiency)
Subsequently, high-speed discharge was performed in the third cycle. The current value was 13.5 mA, 15 times the first cycle, and constant current discharge was performed until the circuit voltage reached 2.5V. From the obtained discharge capacity, the rapid discharge efficiency was calculated by the following formula.
Rapid discharge efficiency (%) = (discharge capacity in the third cycle / discharge capacity in the first cycle) × 100

(Example 2)
In Example 1, when the graphite particles of mesophase spherules were hydrophilized by mechanochemical treatment, anhydrous silica (“Aeosil 300”: Nippon Aerosil Co., Ltd.), which is a hard fine particle, was added to 100 parts by mass of the graphite particles. The mesophase spherules were mechanochemically made hydrophilic in the same manner as in Example 1 except that 0.2 parts by mass (manufactured, average particle diameter: 7 nm) was mixed and the treatment time was 8 min. The obtained hydrophilic graphite particles had a spherical shape, the average particle size was 24 μm, the specific surface area was 1.8 m ² / g, and the permeation amount was 2.1 g (30 sec).
Further, the hydrophilized graphite particles were subjected to mechanochemical treatment in the same manner as in Example 1 to deposit thermal carbon black. A negative electrode mixture paste was prepared, a negative electrode was produced, and an evaluation battery was produced in the same manner as in Example 1 except that the obtained graphite particles were used to change the thickness of the negative electrode material layer and the electrode density.
It was confirmed from observation by an electron microscope that the thermal carbon black was adhered to the surface of the graphite particles without being overlaid by the mechanochemical treatment. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

(Example 3)
Thermal carbon black (manufactured by Engineered Carbons, MT N990; average particle size 310 nm) was placed in a graphitization furnace and graphitized at 3000 ° C. to produce graphitic carbon black (average particle size (average primary particle size) 310 nm, specific surface area 8.2 m ² / g) was obtained and used as the adherent graphite particles.
In Example 2, graphitic particles of mesophase spherules were graphitized and mechanochemically treated in the same manner as in Example 2 except that the graphitic carbon black was used instead of carbonaceous thermal carbon black as the adhesion particles. The carbon black was adhered to the hydrophilic graphite particles by hydrophilization and mechanochemical treatment. The obtained hydrophilic graphite particles had a spherical shape, the average particle size was 24 μm, the specific surface area was 1.8 m ² / g, and the permeation amount was 2.1 g (30 sec).
Further, except for changing the thickness of the negative electrode mixture layer and the electrode density by using the graphite particles having the deposit, the preparation of the negative electrode mixture paste, the production of the negative electrode, and the production of the evaluation battery are performed in the same manner as in Example 1. Went.
It was confirmed from the observation with an electron microscope that the carbon black adhered to the surface of the graphite particles without being overlaid by the treatment. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

Example 4
Mesophase microspheres (manufactured by JFE Chemical Co., Ltd., average particle diameter: 28 μm) obtained by heat treatment of coal tar pitch were graphitized at 3000 ° C. to obtain mesophase microsphere graphite particles. The particles were spherical, the lattice spacing d ₀₀₂ was 0.3362 nm, and the true specific gravity was 2.228. The specific surface area was 0.45 m ² / g, and the amount of water permeation was 0.15 g (30 sec). This was subjected to mechanochemical treatment for hydrophilization.
In Example 3, mechanochemical treatment for hydrophilization using mesophase small sphere graphite particles having different average particle diameters instead of mesophase small sphere graphite particles (average particle diameter: 24 μm) of Example 3 Except that, graphite thermal carbon black was adhered to the hydrophilic graphite particles in the same manner as in Example 2. The obtained graphite particles having deposits were spherical, the average particle size was 28 μm, the specific surface area was 1.9 m ² / g, and the permeation amount was 2.0 g (30 sec).
Further, using the graphite particles having the obtained deposit, except for changing the thickness of the negative electrode mixture layer and the electrode density, the preparation of the negative electrode mixture paste, the preparation of the negative electrode mixture, A negative electrode and an evaluation battery were produced. It was confirmed from the observation with an electron microscope that the carbon black adhered to the surface of the graphite particles without being overlaid by the treatment. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

(Comparative Example 1)
In Example 1, except that the adhesion of carbonaceous thermal carbon black to the hydrophilized graphite particles is omitted, graphitized mesophase spherules and hydrophilized graphite by mechanochemical treatment are the same as in Example 1. Particles were produced. Further, except for changing the thickness of the negative electrode mixture layer, the production of the negative electrode mixture, the production of the negative electrode, and the production of the evaluation battery were performed in the same manner as in Example 1. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

(Comparative Example 2)
In a planetary mixer, 99 parts by mass of the hydrophilized graphite particles of Example 1 and 1 part by mass of the graphitized carbon black of Example 3 were placed and stirred for 5 minutes at 60 rpm in a dry process. A mixture not attached to the hydrophilic graphite particles was obtained. The absence of adhesion was confirmed by observation with a scanning electron microscope.
In Example 1, in place of the graphite particles to which the graphite thermal carbon black was adhered, the mixture was used, and the negative electrode mixture layer was different in thickness and electrode density from that of the negative electrode mixture. Production, production of a negative electrode, and production of an evaluation battery were performed. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

(Comparative Example 3)
In a planetary mixer, 99 parts by mass of the hydrophilized graphite particles of Example 4 and 1 part by mass of the graphitized carbon black of Example 3 were placed and stirred for 5 minutes at 60 rpm in a dry process. A mixture not attached to the hydrophilic graphite particles was obtained. The absence of adhesion was confirmed by observation with a scanning electron microscope.
In Example 1, in place of the graphite particles to which the graphite thermal carbon black was adhered, the mixture was used, and the thickness of the negative electrode mixture layer and the electrode density were changed. Production, production of a negative electrode, and production of an evaluation battery were performed. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

(Comparative Example 4)
In Example 3, except that the hydrophilization treatment by mechanochemical treatment of graphite particles of mesophase spherules is omitted, graphite by mechanochemical treatment on mesophase spherules not subjected to hydrophilization treatment is the same as in Example 3. Quality carbon black was deposited. Further, except for changing the thickness of the negative electrode mixture layer and the electrode density, the negative electrode mixture, the negative electrode, and the evaluation battery were prepared in the same manner as in Example 1. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

(Comparative Example 5)
In Example 1, it hydrophilized like Example 1 except using 1 mass part of furnace black [Tokai Carbon Co., Ltd. product, # 5500 (average particle diameter of 25 nm)] instead of carbonaceous thermal carbon black. Mechanochemical treatment of the graphite particles and the furnace black was performed. Further, except for changing the thickness of the negative electrode mixture layer and the electrode density, the negative electrode mixture, the negative electrode, and the evaluation battery were prepared in the same manner as in Example 1. It was confirmed by observation with a scanning electron microscope that the furnace black did not maintain a structure structure and was in a primary particle state. The charge / discharge characteristics were measured in the same manner as in Example 1. The measurement results are shown in Table 2.

From the comparison between Example 2 and Comparative Example 1, when the carbonaceous particles and / or the graphite particles having an average particle diameter in a specific range are attached to the graphite particles, the rapid charging is performed as compared with the case where the adhesion is not caused. It is clear that efficiency and rapid discharge efficiency are excellent.
From the comparison between Example 3 and Comparative Example 2 and Example 4 and Comparative Example 3, when the graphite particles are attached to the hydrophilized graphite particles, the graphite particles are hydrophilized. It is clear that the charge / discharge characteristics (initial charge / discharge efficiency, rapid charge efficiency, rapid discharge efficiency) are superior to the case where the mixture is merely mixed.
From the comparison between Example 3 and Comparative Example 4, it is clear that the use of hydrophilized graphite particles is superior in rapid charge efficiency and rapid discharge efficiency compared to the case where no graphite particles are used.
From the comparison between Example 2 and Comparative Example 5, when the average particle diameter of the carbonaceous particles to be deposited is more than 100 nm and 1 μm or less, the discharge capacity is higher and the charge capacity is higher than when the average particle diameter is 25 nm. It is clear that the discharge characteristics (initial charge / discharge efficiency, rapid charge efficiency, rapid discharge efficiency) are excellent, and the balance between the characteristics is good.
Furthermore, it is clear from the comparison between Example 1 and Example 2 that the rapid charge efficiency and the rapid discharge efficiency are particularly excellent when hard fine particles are present during the hydrophilization treatment by the mechanochemical treatment.

  The negative electrode material of the present invention can be used for a conductive material for a fuel cell separator, graphite for a refractory, etc., in addition to being used for a negative electrode of a lithium ion secondary battery, taking advantage of the characteristics.

Schematic explanatory drawing which shows the structure of the mechanochemical processing apparatus used in the Example. Schematic explanatory drawing which shows the structure of the mechanochemical processing apparatus used in the other Example. The schematic sectional drawing of the evaluation battery for evaluating the battery characteristic of the negative electrode material of this invention.

Explanation of symbols

11 Rotating drum 12 Internal member (inner piece)
DESCRIPTION OF SYMBOLS 13 To-be-processed object 14 To-be-processed object circulation mechanism 15 To-be-processed object discharge mechanism 21 Fixed drum 22 Rotor 23 To-be-processed object 24 To-be-processed object circulation mechanism 25 To-be-processed object discharge mechanism 26 Blade 27 Stator 28 Jacket 31 Outer cup 32 Working electrode 33 Exterior can 34 Counter electrode 35 Electrolyte solution impregnated separator 36 Insulating gasket 37a, 37b Current collector

Claims (4)

Carbonaceous and / or graphite particles having an average particle diameter of more than 100 nm and 1 μm or less are attached to the hydrophilicized graphite particles by mechanochemical treatment and exposed to the outside of the hydrophilicized graphite particles. and carbonaceous and / or lithium-ion secondary battery negative electrode material the average value of the maximum height of the graphite particles is 70nm or more, a negative electrode for a lithium ion secondary battery comprising an aqueous binder,
The negative electrode for a lithium ion secondary battery, wherein an electrode density of the negative electrode for a lithium ion secondary battery is 1.6 g / cm ³ or more. 2. The lithium ion secondary battery according to claim 1 , wherein the hydrophilized graphite particles are obtained by graphitizing mesophase spherules or a pulverized product thereof and then hydrophilizing by mechanochemical treatment. the negative electrode. 3. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the carbonaceous and / or graphitic particles are thermal carbon black and / or a graphitized product thereof . The lithium ion secondary battery using the negative electrode for lithium ion secondary batteries of any one of Claims 1-3 .

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