JP4973247B2 - Carbon material for electrodes - Google Patents

Description

 The present invention relates to a carbon material for an electrode. Specifically, the present invention relates to a carbon material for an electrode and a multi-layer structure carbon material for an electrode that can constitute a non-aqueous secondary battery having a high capacity and good rapid charge / discharge characteristics.

In recent years, secondary batteries having a high capacity have become necessary with the miniaturization of electronic devices. In particular, lithium secondary batteries having a higher energy density than nickel / cadmium batteries and nickel / hydrogen batteries have attracted attention. At first, it was attempted to use lithium metal as the negative electrode material. However, as charging and discharging were repeated, lithium precipitated in a resinous state (dendritic state), reached the positive electrode through the separator, and shorted both electrodes. It turns out that there is a risk of end. For this reason, carbon-based materials that can avoid the generation of dendrites have attracted attention in place of metal electrodes.

 As a non-aqueous electrolyte secondary battery using a carbon-based material, a battery using a non-graphitizable carbon material having a low crystallinity as a negative electrode material was first put on the market. Subsequently, batteries using graphites with a high degree of crystallinity have been put on the market and have reached the present day. The electric capacity of graphite is 372 mAh / g, which is theoretically the maximum, and a battery with a high charge / discharge capacity can be obtained if the electrolyte is appropriately selected. Further, the use of a carbonaceous material having a multilayer structure as disclosed in JP-A-4-171777 has been studied. This is because of the advantages of graphite with high crystallinity (high capacity and small irreversible capacity) and disadvantages (decomposes propylene carbonate electrolyte) and the advantage of carbonaceous material with low crystallinity (excellent stability with electrolyte) ) And shortcomings (large irreversible capacity), and based on the idea of making up for each other while taking advantage of each other's strengths.

 Graphite (graphite and multilayer carbonaceous material containing graphite) has higher crystallinity and higher true density than non-graphitizable carbon materials. Therefore, if a negative electrode is constituted using these graphites, high electrode filling properties can be obtained, and the energy density per volume of the battery can be increased. When a negative electrode is formed using graphite powder, a slurry is prepared by mixing the powder and binder and adding a dispersion medium, and this is applied to a metal foil as a current collector, and then the dispersion medium is dried. The method is commonly used. At this time, the compression molding is generally performed for the purpose of pressure-bonding the powder to the current collector, uniforming the electrode plate thickness, and improving the electrode plate capacity. By this compression process, the electrode plate density of the negative electrode is improved, and the energy density per volume of the battery is further improved.

 However, industrially available ordinary highly crystalline graphite materials have a scaly, scaly, or plate-like particle shape. When these graphite particles are made into an electrode plate through the above electrode plate manufacturing process, the electrode plate density increases according to the degree of compression, but on the other hand, the movement of lithium ions is hindered because the particle gap is not sufficiently secured. There is a problem that the rapid charge / discharge performance as a battery is lowered. Furthermore, when plate-like graphite particles are formed as electrodes, the powder plate surfaces are arranged in parallel with the electrode plate surfaces with a high probability due to the influence of the slurry application step and electrode plate compression step. Therefore, the edge surfaces of the graphite crystallites constituting the individual powder particles are formed in a positional relationship perpendicular to the electrode surface with a relatively high probability. When charging / discharging in such an electrode plate state, the lithium ions that move between the positive and negative electrodes and that are inserted / extracted into the graphite must once wrap around the powder surface. This is a significant disadvantage. Furthermore, there is a problem that the voids left in the formed electrode are closed with respect to the outside of the electrode because the particles have a plate shape. That is, since the free circulation of the electrolyte solution outside the electrode is hindered, there is a problem that the movement of lithium ions is hindered.

 On the other hand, a spherical mesocarbon microbead graphitized product has been proposed and commercialized as a negative electrode material for securing a gap necessary for the movement of lithium ions in the electrode plate. If the shape is spherical, even after the electrode plate compression process described above, the individual powder particles are not selectively arranged, the isotropic orientation of the edge surface is maintained, and ions move in the electrode plate. The speed is maintained well. Furthermore, since the voids remaining inside the electrode are in a state of being connected to the outside of the electrode due to the spherical shape of the particles, the movement of lithium ions is relatively free, and the electrode structure can be adapted to rapid charge / discharge. Become. However, since mesocarbon microbeads have a low crystal structure level as graphite, the limit of electric capacity is as low as 300 mAh / g, and it is already widely known that the mesocarbon microbeads are inferior to scaly, scaly, or plate-like graphite.

 Paying attention to these problems, inventions that define the shape of graphite used in non-aqueous electrolyte secondary batteries have been made. For example, Japanese Patent Application Laid-Open No. 8-180873 discloses an invention that defines the ratio of scale-like particles to particles that are relatively non-scale-like. On the other hand, Japanese Patent Application Laid-Open No. 8-83610 describes that, on the contrary, scaly particles are preferable.

Practical batteries are required to have electrodes having both high electric capacity and excellent rapid charge / discharge characteristics. However, an electrode that sufficiently satisfies such a demand has not yet been provided. For this reason, in particular, it is strongly desired to improve the rapid charge / discharge properties of scaly, scaly, and plate-like graphite materials. Therefore, the present invention has been made to solve the problems of the prior art. That is, an object to be solved is to provide a carbon material for an electrode that has a high electrode filling property, a high energy density, and an excellent rapid charge / discharge property.

 As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, in order to improve the performance of the electrode, the shape and fillability of the graphite material for the electrode are important. The use of graphite or carbonaceous materials with high filling capacity and high electrochemical capacity has led to the finding that excellent electrodes with high capacity, rapid charge / discharge characteristics, and cycle characteristics can be obtained. .

（上式において、ＴＤは炭素材料のタップ密度（単位ｇ／ｃｍ³）、ＡＰは炭素材料の平均粒径（単位μｍ）を表す） The carbon material for an electrode of the present invention has been completed based on such knowledge, and has an average particle diameter of 2 to 35 μm and a plane distance (d002) between (002) planes by wide-angle X-ray diffraction method is 0. Less than 337 nm, a BET specific surface area of less than 18 m ² / g, and a tap density within a range represented by the following formula.

(In the above formula, TD represents the tap density (unit: g / cm ³ ) of the carbon material, and AP represents the average particle size (unit: μm) of the carbon material)

Electrode carbon material of the present invention, the ratio of the peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum (hereinafter referred to as "R value") of 0.9 or less, the peak of 1580 cm ^-1 It is preferable that the half value width of is 26 cm ⁻¹ or less. A carbon material for an electrode having a true density of 2.21 g / cm ³ or more, a crystallite size of 80 nm or more, an average particle diameter of 30 μm or less, and a tap density of 0.7 g / cm ³ or more. In particular, it can be selected and used. The present invention also provides a multi-layered carbon material for electrodes produced by mixing these carbon materials for electrodes with an organic compound and then carbonizing the organic compound.

The battery using the carbon material for an electrode or the multi-layer structure carbon material for an electrode of the present invention is characterized by a large capacity, a small irreversible capacity observed in an initial cycle, and excellent quick charge / discharge characteristics. Further, the battery has high storage stability and reliability when left at high temperatures, and discharge characteristics at low temperatures are also extremely excellent. Therefore, the carbon material for an electrode and the multi-layer structure carbon material for an electrode of the present invention can be effectively used for production of a battery such as a lithium battery.

BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the carbon material for an electrode, the multilayer carbon material for an electrode, and the electrode of the present invention will be described in detail.

Carbon Material for Electrode The carbon material for an electrode of the present invention has an average particle size, a (002) plane spacing (d002) by a wide angle X-ray diffraction method, a BET specific surface area, and a tap density within a predetermined range. It is a feature. The average particle size of the electrode carbon material of the present invention is in the range of 2 to 35 μm. The average particle size is preferably in the range of 4 to 30 μm, more preferably in the range of 5 to 27 μm, and still more preferably in the range of 7 to 19 μm. In addition, the range described by "-" in this specification shows the range containing the numerical value described before and behind "-". The carbon material for an electrode of the present invention has a (002) plane spacing (d002) of less than 0.337 nm according to the wide-angle X-ray diffraction method. Moreover, the BET method specific surface area of the carbon material for electrodes of the present invention is less than 18 m ² / g. The BET specific surface area is preferably 15 m ² / g or less, and more preferably 13 m ² / g or less.

粉体粒子の充填構造は、粒子の大きさ、形状、粒子間相互作用力の程度等によって左右されるが、本明細書では充填構造を定量的に議論する指標としてタップ密度を使用している。 Furthermore, the tap density of the carbon material for an electrode of the present invention is within the range represented by the above (Formula 1). In this specification, “tap density” means the bulk density after tapping 1000 times, and is represented by the following formula.

The packing structure of the powder particles depends on the size, shape, degree of interaction force between particles, etc., but in this specification, tap density is used as an index for quantitatively discussing the packing structure. .

ここで、ρは充填の終局におけるかさ密度、ρｎはｎ回充填時のかさ密度、ｋおよびＡは定数である。本明細書でいう「タップ密度」は、２０ｃｍ³セルへの１０００回タップ充填時のかさ密度（ρ₁₀₀₀）を終局のかさ密度ρとみなしたものである。 Various formulas have been proposed to express the tap filling behavior, and the following (Formula 2) can be given as an example.

Here, ρ is the bulk density at the end of filling, ρn is the bulk density at the time of filling n times, and k and A are constants. The “tap density” referred to in this specification is a bulk density (ρ ₁₀₀₀ ) when a 20 cm ³ cell is filled with 1000 taps, and is regarded as the ultimate bulk density ρ.

As long as the carbon material for electrodes of the present invention satisfies these conditions, other physical properties are not particularly limited. However, preferred ranges of other physical properties are as follows. The R value in the argon ion laser Raman spectrum is preferably 0.9 or less, more preferably 0.7 or less, and most preferably 0.5 or less. Further, the half width of the peak of 1580 cm ^-1 in the argon ion laser Raman spectrum is preferably 26cm ^-1 or less, 25 cm ^-1 or less is more preferable. Furthermore, the true density of the electrode carbon material of the present invention is preferably at 2.21 g / cm ³ or more, and more preferably at 2.23 g / cm ³ or more, 2.25 g / cm ³ or more Is more preferable.

 The carbon material for an electrode of the present invention may be a naturally occurring carbon material or an artificially produced carbon material. Moreover, the manufacturing method of the carbon material for electrodes of the present invention is not particularly limited. Therefore, the electrode carbon material having the above characteristics can be selected and obtained by using a sorting means such as sieving or air classification. The most preferable production method is a method of producing a carbon material for an electrode by modifying a naturally occurring carbon material or an artificially produced carbon material by applying mechanical energy treatment. Therefore, this mechanical energy processing will be described below.

The carbon material to which mechanical energy treatment is applied is a natural or artificial graphite powder or a carbonaceous powder that is a graphite precursor. These graphite powders and carbonaceous powders preferably have an interplanar spacing (d002) of less than 0.340 nm, a crystallite size (Lc) of 30 nm or more, and a true density of 2.25 g / cm ³ or more. Among them, the surface spacing (d002) is more preferably less than 0.338 nm, and even more preferably less than 0.337 nm. The crystallite size (Lc) is more preferably 80 nm or more, and even more preferably 100 nm or more. The average particle size is preferably 10 μm or more, more preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more. The upper limit of the average particle diameter is preferably 1 mm or less, more preferably 500 μm or less, still more preferably 250 μm or less, and even more preferably 200 μm or less.

 The graphite powder and the carbonaceous powder can be used as raw materials regardless of whether they have high crystallinity or low crystallinity. A raw material with low crystallinity has a relatively low plane orientation and a disordered structure. Therefore, by performing mechanical energy treatment, it is easy to obtain a processed product having a relatively isotropic and rounded grinding surface. Further, the crystallinity can be improved by further heat treatment after the mechanical energy treatment.

 Among the carbon materials to which mechanical energy treatment is applied, as highly crystalline carbon materials with a developed carbon hexagonal network structure, highly oriented graphite with a hexagonal network surface grown greatly in a plane orientation, An isotropic high-density graphite in which graphite particles are gathered in the same direction can be given. Suitable examples of highly oriented graphite include natural graphite from Sri Lanka or Madagascar, so-called quiche graphite deposited as supersaturated carbon from molten iron, and some artificial graphite having a high degree of graphitization. .

 Natural graphite is classified into flake graphite (Flake Glaphite), scaly graphite (Crystalline (Vein) Glaphite), and soil graphite (Amorphousu Glaphite), depending on its properties ("Pulverized Process Technology Assembly" (Inc.) (Refer to "HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES" (published by Noyes Publications)). The degree of graphitization is highest at 100% for scaly graphite, followed by 99.9% for scaly graphite, but as low as 28% for soil graphite. The quality of natural graphite is determined mainly by the production area and the vein. Scaly graphite is produced in Madagascar, China, Brazil, Ukraine, Canada, etc., and scaly graphite is produced mainly in Sri Lanka. Soil graphite is mainly produced in the Korean peninsula, China, Mexico, etc. Among these natural graphites, soil graphite generally has a small particle size and low purity. On the other hand, scaly graphite and scaly graphite have advantages such as a low degree of graphitization and a low amount of impurities, and therefore can be preferably used in the present invention.

 Artificial graphite can be produced by heating petroleum coke or coal pitch coke at 1500 to 3000 ° C. in a non-oxidizing atmosphere. In the present invention, any artificial graphite can be used as a raw material as long as it exhibits high orientation and high electrochemical capacity after mechanical energy treatment and heat treatment.

 The mechanical energy treatment for these carbon materials is performed so that the average particle size ratio before and after the treatment is 1 or less. The “average particle size ratio before and after treatment” is a value obtained by dividing the average particle size after treatment by the average particle size before treatment. The average particle size here is a volume-based particle size distribution measured with a laser type particle size distribution measuring machine. When measured with a laser particle size distribution measuring device, particles having an anisotropic shape are averaged isotropically to obtain a particle size distribution substantially converted as a sphere.

 In the mechanical energy treatment performed to produce the electrode carbon material of the present invention, the average particle size ratio before and after the treatment is set to 1 or less. On the other hand, when granulated, the average particle size ratio becomes 1 or more and the tap density also increases. The granulated powder is not preferable because it is expected to return to the state before the treatment in the final molding process.

 In the mechanical energy treatment, the particle size is reduced and at the same time the particle shape is controlled so that the average particle size ratio before and after the treatment of the powder particles is 1 or less. Among engineering unit operations that can be used for particle design such as grinding, classification, mixing, granulation, surface modification, and reaction, mechanical energy treatment belongs to grinding treatment.

 Grinding refers to applying a force to a substance to reduce its size and adjusting the particle size, particle size distribution, and fillability of the substance. The pulverization process is classified according to the type of force applied to the substance and the processing form. The force applied to a substance is roughly classified into four types: a crushing force (impact force), a crushing force (compression force), a crushing force (grinding force), and a scraping force (shearing force). On the other hand, the treatment mode is roughly divided into two types: volume pulverization in which cracks are generated and propagated inside the particles, and surface pulverization in which the particle surfaces are scraped off. Volume pulverization proceeds by impact force, compression force, and shear force, and surface pulverization proceeds by grinding force and shear force. The pulverization is a process in which various kinds of force applied to these substances and various processing forms are combined. The combination can be appropriately determined according to the processing purpose.

 The pulverization may be performed using a chemical reaction such as blasting or volume expansion, but is generally performed using a mechanical device such as a pulverizer. The pulverization treatment used in the production of the carbon material for an electrode of the present invention is preferably a treatment that finally increases the proportion of the surface treatment regardless of whether or not volume pulverization is performed. This is because the surface grinding of the particles is important to take the corners of the graphite or carbonaceous particles and introduce roundness into the particle shape. Specifically, the surface treatment may be performed after the volume pulverization has progressed to some extent, the surface treatment may be performed without proceeding with the volume pulverization, or the volume pulverization and the surface treatment may be performed simultaneously. Also good. It is preferable to carry out a pulverization treatment so that the surface pulverization finally proceeds and the angle is removed from the surface of the particles.

 The apparatus for performing the mechanical energy treatment is selected from those capable of performing the above preferred treatment. As a result of investigations by the present inventors, it has been found that an apparatus that repeatedly gives mechanical effects such as compression, friction, shearing force, etc. including the interaction of particles mainly with impact force to the particles is effective. Specifically, it has a rotor with a large number of blades installed inside the casing, and when the rotor rotates at high speed, a machine such as impact compression, friction, shear force, etc. is applied to the carbon material introduced inside. It is preferable to use an apparatus that performs a surface treatment while applying volumetric pulverization. Further, it is more preferable to have a mechanism that repeatedly gives mechanical action by circulating or convection of the carbon material.

 An example of such a preferred apparatus is a hybridization system manufactured by Nara Machinery Co., Ltd. When processing using this apparatus, the peripheral speed of the rotating rotor is preferably 30 to 100 m / sec, more preferably 40 to 100 m / sec, and further preferably 50 to 100 m / sec. preferable. Further, the treatment can be performed by simply passing the carbon material, but it is preferable to circulate or stay in the apparatus for 30 seconds or longer, and it is preferable to circulate or stay in the apparatus for 1 minute or longer. More preferred.

 When the true density of the carbonaceous powder used as a raw material is less than 2.25 and the crystallinity is not so high, it is preferable to perform a heat treatment for further improving the crystallinity after performing the mechanical energy treatment. The heat treatment is preferably performed at 2000 ° C. or more, more preferably at 2500 ° C. or more, and further preferably at 2800 ° C. or more.

 By performing such mechanical energy treatment, it is possible to introduce roundness into the graphite particles or the carbonaceous particles and to improve the filling properties of these particles. It is important to introduce roundness to the particles as described below. In order to improve the filling property of the powder particles, it has been conventionally known that smaller particles should be filled so as to be able to enter voids formed between the particles. For this reason, it is considered that the filling is improved if the particle size is reduced by performing treatment such as pulverization on the carbonaceous powder or the graphite particles. On the other hand, it will decline. This is considered to be because the particle shape becomes more irregular by grinding.

 On the other hand, the greater the number of particles (coordination number n) in contact with one particle (particle of interest) in the powder particle group, the lower the proportion of voids in the packed bed. Therefore, the ratio of the particle size and the composition ratio (that is, the particle size distribution) are important as factors affecting the filling rate. However, this study was conducted with a model spherical particle group, and the particles of graphite powder and carbonaceous powder handled in the present invention are scaly, scaly, and plate-like, and are simply general pulverization and classification. Even if an attempt is made to increase the filling rate by controlling the particle size distribution only by, etc., the intended high filling state cannot be produced.

 In general, scaly, scaly, and plate-like graphite or carbonaceous particles tend to deteriorate in packing properties as the particle diameter decreases. This is because the particles are more irregularly shaped by crushing; projections such as “crushing”, “peeling” and “bending” are generated and increased on the surface of the particles; This is probably because the resistance between adjacent particles increases due to the adhesion of the particles with a certain degree of strength and the filling property is deteriorated. When these irregularities are reduced and the particle shape is close to a sphere, the decrease in filling property is reduced even if the particle size is reduced. Theoretically, both large and small particle size carbon powders have the same degree. It will indicate the tap density.

 In the study by the present inventors, it has been confirmed that, in the case of carbonaceous or graphitic particles having a true density and an average particle diameter substantially equal, the tap density increases as the shape becomes spherical. That is, in order to increase the tap density, it is important to make the shape of the particles round and close to a spherical shape. When the particle shape is close to a spherical shape, the powder filling property is greatly improved.

 In the present invention, the tap density of the powder is adopted as an index of the degree of spheroidization for the above reasons. When the filling property of the granular material after the processing is higher than that before the processing, it can be considered that the particles are spheroidized by the processing method used. In addition, when the tap density of the carbon material obtained when the treatment is performed while greatly reducing the particle size is higher than the tap density of the carbon material having the same particle size obtained by general grinding, This can be thought of as a result.

Multi-layer structure carbon material for electrode The multi-layer structure carbon material for electrode of the present invention is prepared by mixing an organic compound that is carbonized by a firing step and a carbon material for electrode of the present invention having the above characteristics, It can be prepared by calcination. The organic compound mixed with the electrode carbon material is not particularly limited as long as it is carbonized by firing. Accordingly, it may be an organic compound that promotes carbonization in the liquid phase or an organic compound that promotes carbonization in the solid phase.

 Examples of organic substances that promote carbonization in the liquid phase include coal tar pitch from soft pitch to hard pitch, coal heavy oil such as coal liquefied oil, DC heavy oil such as asphalten, heat such as crude oil and naphtha. Examples include heat-treated pitches such as ethylene tar pitch, FCC decant oil, and Ashland pitch obtained by heat-treating petroleum heavy oils such as naphthatal, which are by-produced during cracking, and cracked heavy oils; be able to. Furthermore, vinyl polymers such as polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, and polyvinyl alcohol, substituted phenol resins such as 3-methylphenol formaldehyde resin and 3,5-dimethylphenol formaldehyde resin, and aromatics such as acenaphthylene, decacyclene, and anthracene Examples thereof include hydrocarbons, nitrogen ring compounds such as phenazine and acridine, and sulfur ring compounds such as thiophene.

 Examples of organic compounds that promote carbonization in the solid phase include natural polymers such as cellulose, chain vinyl resins such as polyvinylidene chloride and polyacrylonitrile, aromatic polymers such as polyphenylene, furfuryl alcohol resins, and phenols. -Thermosetting resins, such as formaldehyde resin and imide resin, thermosetting resin raw materials, such as a furfuryl alcohol, etc. can be mentioned.

As a method for producing the multilayer carbon material for an electrode of the present invention from these organic compounds and the electrode carbon material, a typical production method comprising the following steps can be exemplified.
(1st process) The process of mixing the carbon material for electrodes, an organic compound, and a solvent as needed using various commercially available mixers, kneaders, etc., and obtaining a mixture.
(2nd process) The process of obtaining the intermediate substance which removed the solvent by heating the said mixture as it is or stirring as needed.
(Third Step) A step of heating the mixture or the intermediate substance to 500 to 3000 ° C. in an inert gas atmosphere such as nitrogen gas, carbon dioxide gas, argon gas or the like in a non-oxidizing atmosphere to obtain a carbonized substance.
(4th process) The process which grind | pulverizes, crushes, classifies, etc. with respect to the said carbonization substance, and carries out powder processing.

 In mixing in the first step, a solvent may or may not be used. When a solvent is used, its type and amount are not particularly limited. In the first step, the organic compound can be attached to the surface of the powder particles of the electrode carbon material by mixing the organic compound and the electrode carbon material. The heating temperature in the second step is usually 300 ° C. or higher, preferably 400 ° C. or higher, more preferably 500 ° C. or higher. The upper limit is not particularly limited, but is usually 3000 ° C. or lower, preferably 2800 ° C. or lower, more preferably 2500 ° C. Below, it is 1500 degrees C or less more preferably. Although the second step can be omitted, the third step is usually performed after the second step is performed to obtain an intermediate substance.

 In the third heat treatment, the heat history temperature condition is important. The lower limit temperature varies slightly depending on the type of organic compound and the thermal history, but is usually 500 ° C. or higher, preferably 700 ° C. or higher, and more preferably 900 ° C. or higher. On the other hand, the upper limit temperature can be raised to a temperature that does not have a structural order that basically exceeds the crystal structure of the carbonaceous or graphite particles of the electrode carbon material. Accordingly, the temperature of the heat treatment is usually 3000 ° C. or lower, preferably 2800 ° C. or lower, more preferably 2500 ° C. or lower, and particularly preferably 1500 ° C. or lower. The heating rate, cooling rate, heat treatment time, etc. can be arbitrarily set according to the purpose. Further, after heat treatment in a relatively low temperature region, the temperature can be raised to a predetermined temperature.

 The fourth step is a step of performing powder processing by performing pulverization, crushing, classification treatment, or the like as necessary, but may be omitted. In addition, the fourth step can be performed before the third step, or can be performed both before and after the third step. The reactor used in these steps may be a batch type or a continuous type. One or a plurality of groups may be used.

The ratio of the carbonaceous material derived from the organic compound in the multilayer structure carbon material for electrodes of the present invention (hereinafter referred to as “coverage”) is usually 0.1 to 50% by weight, preferably 0.5 to 25% by weight, more preferably. Is adjusted to 1 to 15% by weight, more preferably 2 to 10% by weight. Moreover, the multilayer structure carbon material for electrodes of the present invention has a volume-based average particle diameter of 2 to 70 μm, preferably 4 to 40 μm, more preferably 5 to 35 μm, and still more preferably 7 to 25 μm. The specific surface area measured using the BET method is preferably in the range of ¹ to 10 m ² / g, more preferably 1 to 7 m ² / g, still more preferably 1 to 4 m ² / g. Furthermore, the multi-layer structure carbon material for an electrode of the present invention comprises graphite as a nucleus in a Raman spectrum analysis using an argon ion laser beam having a wavelength of 5145 cm ⁻¹ and a diffraction diagram of an X-ray wide angle diffraction using a CuKα ray as a radiation source. It is preferable not to exceed the crystallinity of the carbonaceous particles or carbonaceous particles.

R value becomes like this. Preferably it is 0.01-1.0, More preferably, it is 0.05-0.8, More preferably, it is 0.1-0.7. Further, the tap density may be further improved than the nuclear graphite material used by the carbon coating, but it is desirable to control it within the range of 0.7 to 1.4 g / cm ³ . By the multilayer structure, the tap density of the carbon material for an electrode serving as a nucleus may be further improved, and the shape may be further rounded.

Electrode An electrode can be produced using the carbon material for an electrode or the multilayer structure carbon material for an electrode of the present invention. In particular, the multi-layer structure carbon material for an electrode of the present invention can be used very preferably for the production of an electrode. The production method is not particularly limited, and can be produced according to a commonly used method. As a typical method, a binder or a solvent is added to a carbon material for an electrode or a multilayer carbon material for an electrode to form a slurry, and the resulting slurry is applied to a metal current collector substrate such as a copper foil. The method of apply | coating and drying can be mentioned. Also, the electrode carbon material or the multi-layered carbon material for electrodes can be roll-pressed as it is or consolidated by a compression molding machine to improve the packing density of the electrode plate and increase the electrode amount per unit volume. You can also. Further, it can be formed into an electrode shape by compression molding or the like.

 As binders that can be used for electrode production, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, and cellulose that are stable to solvents, styrene-butadiene rubber, isoprene rubber, butadiene rubber, Rubber polymers such as ethylene / propylene rubber, styrene / butadiene / styrene block copolymer, hydrogenated product thereof, styrene / ethylene / butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer, hydrogenated product thereof Thermoplastic elastomeric polymers such as products, soft resinous polymers such as syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / a-olefin (2 to 12 carbon atoms) copolymer, Polyvinylidene fluoride, polytetrafluoroe Ren, fluoropolymer polytetrafluoroethylene-ethylene copolymer, an alkali metal ion, can be exemplified a polymer composition having a particularly ionic conductivity of lithium ions.

Examples of the polymer having ion conductivity include polyether polymer compounds such as polyethylene oxide and polypropylene oxide, crosslinked polymers of polyether compounds, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinyl pyrrolidone, polyvinylidene carbonate, poly A system in which a polymer compound such as acrylonitrile is combined with a lithium salt or an alkali metal salt mainly composed of lithium, or an organic compound having a high dielectric constant such as propylene carbonate, ethylene carbonate, or g-butyrolactone is linear A system in which a low-viscosity organic compound such as a carbonate is blended can be used. The ionic conductivity at room temperature of such an ion conductive polymer composition is preferably 10 ⁻⁵ s / cm or more, more preferably 10 ⁻³ s / cm or more.

 Various forms can be taken as a mixed form of the carbon material for electrodes or the multilayered carbon material for electrodes and the binder. For example, it is possible to take a form in which both particles are mixed, a form in which a fibrous binder is entangled with carbonaceous particles, or a form in which a binder layer adheres to the surface of carbonaceous particles. . The mixing ratio of the two is preferably 0.1 to 30% by weight, more preferably 0.5 to 10% by weight of the binder with respect to the carbon material for electrodes or the multilayer carbon material for electrodes. preferable. When the binder of 30% by weight or more is added, the internal resistance of the electrode is increased. Conversely, when the binder is 0.1% by weight or less, the binding property between the current collector and the carbon material for an electrode or the multilayer carbon material for an electrode is increased. It tends to be inferior.

The electrode made of the carbon material for an electrode or the multi-layer structure carbon material for an electrode according to the present invention has a density of the active material layer on the electrode consolidated by roll press or compression molding of 0.5 to 1.6 g / By setting it to cm ³ , preferably 0.7 to 1.55 g / cm ³ , the capacity per unit volume of the battery can be maximized without impairing high-efficiency discharge and low-temperature characteristics. At this time, the tap density of the carbon material of the present invention is high, that is, the carbon material is nearly spherical, so that the voids in the electrode are rarely closed, and thus the lithium ion diffusion is performed more smoothly. It is done.

 A battery composed of a metal chalcogenide-based positive electrode for a commonly used lithium ion battery and an organic electrolyte mainly composed of a carbonate-based solvent is used as a negative electrode, and has a large capacity. The recognized irreversible capacity is small, the battery has high storage stability and reliability when left at high temperatures, and is extremely excellent in high-efficiency discharge characteristics and low-temperature discharge characteristics. It should be noted that there is no restriction on the selection of members necessary for the battery configuration such as the positive electrode and the electrolytic solution.

 Hereinafter, the present invention will be described more specifically with specific examples. The materials, amounts used, ratios, operations and the like shown in the following specific examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Example 1) Hybrid system NHS-1 manufactured by Nara Machinery Co., Ltd. (referred to as “apparatus a” in Table 1) or T-400 turbomill (4J model) manufactured by Turbo Industry Co., Ltd. (in Table 1) 100 g of graphite was processed using “apparatus b”. Eight types of carbon materials for electrodes were prepared by setting the type of graphite raw material, the type of processing apparatus, the peripheral speed of the rotor, and the processing time as shown in Table 1.

The following physical properties were measured for each of the prepared carbon materials for electrodes.
(1) Average particle size Surfactant polyoxyethylene (20) 2% by volume aqueous solution (about 1 ml) of sorbitan monolaurate is mixed with carbon material for electrodes, and laser diffraction particle size with ion-exchanged water as dispersion medium The volume-based average particle diameter (median diameter) was measured with a distribution meter (LA-700 manufactured by Horiba, Ltd.).
(2) About 15% X-ray standard high-purity silicon powder is added to and mixed with the carbon material for X-ray diffraction electrodes, and the resulting mixture is packed in a sample cell and monochromated with a graphite monochromator. As a result, a wide-angle X-ray diffraction curve was measured by a reflective diffractometer method, and an interplanar spacing (d002) and a crystallite size (Lc) were determined using the Gakushin method.

(3) BET specific surface area Using AMS-8000 manufactured by Okura Riken Co., Ltd., heated to 350 ° C. for preliminary drying, and after flowing nitrogen gas for 15 minutes, measurement was performed by the BET one-point method by nitrogen gas adsorption.
(4) using the tap density powder density measuring instrument (Inc. Seishin Enterprise Co., Ltd. Tap Denser KYT-3000), using a mesh opening 300μm sieve as sieve electrode carbon material is transmitted, the tap cells of 20 cm ³ After dropping the powder and filling the cell to the full, tap with a stroke length of 10 mm was performed 1000 times, and the tap density at that time was measured.
(5) A true density 0.1% surfactant aqueous solution was used, and measurement was performed by a liquid phase replacement method using a pycnometer.

(6) using a Raman measurement manufactured by JASCO Corporation NR-1800, in the Raman spectrum analysis using an argon ion laser beam having a wavelength of 514.5 nm, the intensity of the peak PA around the 1580 cm ^-1 IA, a range of 1360 cm ^-1 The intensity IB of the peak PB was measured, and the intensity ratio R = IB / IA and the half width of the peak near 1580 cm ⁻¹ were measured. At this time, the carbon material for electrodes in a powder state was filled into the cell by natural dropping, and measurement was performed by rotating the cell in a plane perpendicular to the laser beam while irradiating the sample surface in the cell with the laser beam.

The measurement results of these physical properties are summarized in Table 1.

Table 2 shows the physical properties of graphite used as a raw material.

（上式において、Ｋは炭素材料の量（ｋｇ）、Ｔは石油系タールの量（ｋｇ）、Ｄは混練物の脱タール処理前の量（ｋｇ）、Ｎは熱処理後の熱処理物回収量（ｋｇ）である） (Example 2) 3 kg of a predetermined carbon material listed in Table 3 and 1 kg of petroleum-based tar are put into an M20 type Ladige mixer (internal volume 20 liters) manufactured by Matsubo Co., Ltd. and kneaded. It was. Subsequently, the temperature was raised to 700 ° C. in a nitrogen atmosphere and detarring was performed, and then the temperature was raised to 1300 ° C. and heat treatment was performed. The obtained heat-treated product was crushed with a pin mill and classified for the purpose of removing coarse particles. Finally, four types of multi-layer structure carbon materials were prepared. About each multilayer structure carbon material, the R value of the coverage, average particle diameter, BET specific surface area, tap density, and Raman measurement was measured. The coverage was determined according to the following equation, and the other values were determined by the same method as in Example 1.

(In the above equation, K is the amount of carbon material (kg), T is the amount of petroleum-based tar (kg), D is the amount before detarring of the kneaded product (kg), and N is the amount of heat-treated product recovered after heat treatment (Kg))

The results are summarized in Table 3.

(Test Example) A half cell was prepared using the prepared carbon material, and the charge / discharge characteristics were tested.
1) Preparation of half-cell A carbon material of 5 g and a dimethylacetamide solution of polyvinylidene fluoride (PVdF) added at 10% by weight in terms of solid content was stirred to obtain a slurry. This slurry was applied onto a copper foil by the doctor blade method and pre-dried at 80 ° C. Further, after being consolidated by a roll press so that the electrode plate density becomes 1.4 g / cm ³ or 1.5 g / cm ³ , it is punched into a disk shape having a diameter of 12.5 mm and dried at 110 ° C. under reduced pressure. An electrode was obtained. Thereafter, a coin cell in which the electrode and the lithium metal electrode were opposed to each other centering on the separator impregnated with the electrolytic solution was prepared, and a charge / discharge test was performed. As the electrolytic solution, a solution in which lithium perchlorate was dissolved at a ratio of 1.5 mol / liter in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a weight ratio of 2: 8 was used.

2) In the measurement current density 0.16 mA / cm ² of the irreversible capacity to 0V was charged and then discharged from the first charge capacity when discharged at a current density of 0.33 mA / cm ² until 1.5V first The value obtained by subtracting the capacity was taken as the irreversible capacity.
3) repeated three times discharge to 1.5V at the charging and a current density of 0.33 mA / cm ² up to 0V at a measuring current density 0.16 mA / cm ² of the discharge capacity and rapid discharge characteristics, the third time that The discharge capacity was recorded as “discharge capacity”. Then performed to 0V charging at a current density of 0.16 mA / cm ^2, discharge, respectively it current density 2.8 mA / cm ² conducted at 5.0 mA / cm ² to 1.5V, resulting capacitance was a rapid discharge capacity at each current density 2.8 mA / cm ² and 5.0 mA / cm ^2, was used as an index of the rapid discharge characteristics.

These test results are summarized in Table 4.

Claims (9)

A carbon material for a negative electrode of a lithium ion battery comprising spheroidized graphite as a raw material or graphitic particles obtained by spheroidizing graphite so that an average particle size ratio before and after pulverization is 1 or less, and the average particle of the carbon material A diameter of 2 to 35 μm, a (002) plane spacing (d002) by a wide angle X-ray diffraction method of less than 0.337 nm, a crystallite size (Lc) of 80 nm or more, a BET specific surface area of less than 18 m ² / g, and A carbon material for a negative electrode of a lithium ion battery, wherein the true density is 2.21 g / cm ³ or more. Lithium-ion battery negative electrode carbon material of claim 1, wherein the ratio of the peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum is 0.9 or less. Claim 1 or 2 lithium ion battery negative electrode carbon material, wherein the ratio of the peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum is 0.7 or less. Lithium-ion battery negative electrode carbon according to claim 1, the ratio of the peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum, characterized in that more than 0.5 material. The carbon material for a lithium ion battery negative electrode according to any one of claims 1 to 4, wherein the tap density is 0.77 g / cm ³ or more. The carbon material for a lithium ion battery negative electrode according to any one of claims 1 to 5, wherein the tap density is 1.2 g / cm ³ or less.  A multilayered carbon material for a lithium ion battery negative electrode produced by mixing the carbon material according to any one of claims 1 to 6 and an organic compound and then carbonizing the organic compound. It consists of an active material layer containing the carbon material for lithium ion battery negative electrodes in any one of Claims 1-6, or the multilayer structure carbon material for lithium ion battery negative electrodes of Claim 7, and a collector. An electrode for a lithium ion battery.   A lithium ion battery comprising the lithium ion battery electrode according to claim 8 as a negative electrode and a metal chalcogenide electrode as a positive electrode.