JP2017183113A - Composite active material for lithium ion secondary battery, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a composite active material which allows a high initial charging capacity and a high initial coulomb efficiency to be ensured and which can offer a lithium ion secondary battery having a superior cycle life; and a method for manufacturing the composite active material.SOLUTION: A composite active material for a lithium ion secondary battery comprises: Si or a Si alloy; and a carbonaceous material or a combination of the carbonaceous material and graphite. The composite active material consists of generally spherical complex particles of which the average particle diameter (D50) is 1-40 μm, the ratio C(002)/C(111) of X-ray diffraction intensities of C(002) and Si(111) planes measured by a powder X-ray method is 0.6-3.0, and the average circularity is 0.7-1.0.SELECTED DRAWING: None

Description

  The present invention relates to a composite active material for a lithium ion secondary battery and a method for producing the same.

  Conventionally, graphite is mainly used as the negative electrode material of lithium ion secondary batteries, but for higher capacity, metals such as silicon and tin, which have high theoretical capacity and are capable of occluding and releasing lithium ions. A method of using as a negative electrode material has been studied.

  On the other hand, it is known that an active material made of a metal material capable of inserting and extracting lithium ions significantly expands when alloyed with lithium by charging. Therefore, the active material is cracked and refined, and the structure of the negative electrode using these is also broken and the conductivity is cut. Therefore, the negative electrode using these metal materials has a problem that the capacity is remarkably lowered with the passage of cycles.

  In response to this problem, a technique has been proposed in which these metal materials are made into fine particles and combined with carbonaceous material or graphite. Such composite particles have significantly higher cycle characteristics than the use of these materials alone as a negative electrode material, because these metal materials are alloyed with lithium and conductivity is ensured by carbonaceous materials and graphite even when they are miniaturized. It is known to improve. For example, in Patent Document 1, the active material of the negative electrode includes fine particles having a carbonaceous material layer formed on the surface, and the fine particles are composed of at least one element selected from Mg, Al, Si, Ca, Sn, and Pb. In addition, it is disclosed that the average particle diameter is 1 to 500 nm, and the atomic ratio of the fine particles in the active material is 15% by weight or more.

  Patent Document 2 discloses metal-carbon composite particles in which metal particles are embedded in a plurality of phases of carbon, and the carbon contains graphite and amorphous carbon. The metal particles include Mg, Al, It is described that any one of Si, Zn, Ge, Bi, In, Pd, and Pt is used, and the average particle diameter is preferably 0.1 to 20 μm. Patent Document 3 discloses a so-called core shell in which the composite active material includes graphite core particles, a carbon coating (shell) that covers the graphite core particles, and metal particles that are dispersed and located inside the carbon coating. The graphite core particles have an average particle size of 1 to 20 μm, the coating thickness of the carbon coating is 1 to 4 μm, and the metals alloyed with lithium include Cr, Sn, Si, Al, Mn, Ni , Zn, Co, In, Cd, Bi, Pb, and V, and at least one substance selected from the group consisting of V and an average particle size of 0.01 to 1.0 μm is preferable.

Furthermore, Patent Document 4 discloses a mixing step of obtaining a mixture by mixing expanded graphite or flaky graphite having a BET specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions, and adding a spherical shape to the mixture. A composite active material for a lithium secondary battery having a spheroidizing step of manufacturing a substantially spherical composite active material for a lithium secondary battery containing a battery active material that can be combined with graphite and lithium ions A method is disclosed, and the battery active material that can be combined with lithium ions contains at least one element selected from Si, Sn, Al, Sb, and In, and the average particle diameter is preferably 1 μm or less. Yes.

Japanese Patent Laid-Open No. 10-3920 JP 2000-272911 A JP 2010-129545 A Japanese Patent No. 5227483

  However, the previously proposed composite active materials have not had sufficient initial discharge capacity and initial coulomb efficiency. The present invention relates to a composite active material for a lithium ion secondary battery that is composed of Si or Si alloy (hereinafter collectively referred to as “Si compound”) and a carbonaceous material or a carbonaceous material and graphite. An object of the present invention is to provide a composite active material that can provide a lithium ion secondary battery that has an initial charge capacity and a high initial coulombic efficiency and has an excellent cycle life, and a method for producing the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that in a composite active material for a lithium ion secondary battery comprising a Si compound and a carbonaceous material or a carbonaceous material and graphite, the composite material Composite that provides a lithium ion secondary battery having high initial charge capacity, initial Coulomb efficiency, and excellent cycle life by controlling the X-ray diffraction intensity ratio and shape of graphite (002) surface and silicon (111) surface of The present inventors have found that an active material can be obtained and have completed the present invention.

  That is, the present invention provides a composite active material for a lithium ion secondary battery comprising Si or a Si alloy and a carbonaceous material or a carbonaceous material and graphite, wherein the composite active material has an average particle size (D50) of 1 to 40 μm. The X-ray diffraction line intensity ratio C (002) / Si (111) between the C (002) plane and the Si (111) plane measured by powder method X-ray is 0.6 to 3.0, and the average circularity The present invention relates to a composite active material for a lithium ion secondary battery, wherein the composite particles are substantially spherical composite particles having a particle size of 0.7 to 1.0.

  Hereinafter, the active material of the present invention will be described in detail.

  Si as an active material is a general grade metal silicon having a purity of about 98% by weight, a chemical grade metal silicon having a purity of 2 to 4N, polysilicon having a purity higher than 4N purified by chlorination and distillation, and single crystal growth Polishing or cutting of ultra-high purity single crystal silicon that has undergone a deposition process by the method, or those doped with elements of Group 13 or 15 of the periodic table to be p-type or n-type, or wafers generated in the semiconductor manufacturing process There is no particular limitation as long as it has a purity equal to or higher than that of general-purpose grade metal silicon, such as scraps of waste and waste wafers that have become defective in the process.

  The Si alloy referred to as a composite active material for a lithium ion secondary battery is an alloy containing Si as a main component. In the Si alloy, the element contained other than Si is preferably one or more elements of Groups 2 to 15 of the periodic table, and the selection and / or addition amount of the element having a melting point of the phase contained in the alloy of 900 ° C. or more Is preferred.

  In the composite active material for a lithium secondary battery of the present invention, the average particle diameter (D50) of the Si compound is preferably 0.01 to 5 μm, more preferably 0.01 to 1 μm, and particularly preferably 0.05 to 0. .6 μm. If it is smaller than 0.01 μm, the capacity and initial efficiency due to surface oxidation are drastically reduced, and if it is larger than 5 μm, cracking is severely caused by expansion due to lithium insertion, and cycle deterioration tends to be severe. The average particle size (D50) is a volume average particle size measured with a laser particle size distribution meter.

  The content of the Si compound is preferably 10 to 80 parts by mass, particularly preferably 15 to 50 parts by mass. When the content of the Si compound is less than 10 parts by mass, a sufficiently large capacity cannot be obtained as compared with the conventional graphite, and when it is greater than 80 parts by mass, cycle deterioration tends to become severe.

  The carbonaceous material referred to as a composite active material for lithium ion secondary batteries is an amorphous or microcrystalline carbon material, easily graphitized carbon (soft carbon) that is graphitized by heat treatment exceeding 2000 ° C., and hardly graphitized. Non-graphitizable carbon (hard carbon) is mentioned.

  The hard carbon is preferably obtained by carbonizing a precursor such as a resin or a resin composition. By carbonizing, the resin or resin composition is carbonized and can be used as a carbon material for a lithium ion secondary battery. Examples of the resin or resin composition that is the raw material (precursor) of the hard carbon include polymer compounds (for example, thermosetting resins and thermoplastic resins). The thermosetting resin is not particularly limited. For example, a phenol resin such as a novolac type phenol resin or a resol type phenol resin; an epoxy resin such as a bisphenol type epoxy resin or a novolac type epoxy resin; a melamine resin; a urea resin; Examples include cyanate resins; furan resins; ketone resins; unsaturated polyester resins; urethane resins. In addition, modified products obtained by modifying these with various components can also be used.

  The thermoplastic resin is not particularly limited. For example, polyethylene, polystyrene, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, polyethylene terephthalate, polycarbonate, polyacetal, polyphenylene ether, poly Examples include butylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, and polyetheretherketone.

  Among these, one kind or a combination of two or more kinds can be used.

  Among these, particularly preferred hard carbon raw materials (precursors) include phenolic resins such as novolac type phenolic resins and resol type phenolic resins.

  The shape of the hard carbon precursor is not particularly limited, and any shape such as powder, plate, granule, fiber, lump, and sphere can be used. These precursors are preferably dissolved in a solvent used when various components are mixed.

  The weight average molecular weight of the hard carbon precursor used is preferably 1000 or more, more preferably 1,000,000 or less, from the viewpoint that the effect of the present invention is more excellent.

  The soft carbon is preferably obtained by carbonizing a precursor such as a resin or a resin composition. By carbonizing, the resin or resin composition is carbonized and can be used as a carbon material for a lithium ion secondary battery. The resin or resin composition that is the raw material (precursor) of the soft carbon is not particularly limited, and coal-based pitch (for example, coal tar pitch), petroleum-based pitch, mesophase pitch, coke, low molecular weight heavy oil, Alternatively, derivatives thereof are exemplified, and coal-based pitch (for example, coal tar pitch), petroleum-based pitch, mesophase pitch, coke, low molecular weight heavy oil, or derivatives thereof are preferable. Especially, the soft carbon obtained from precursors, such as coal pitch, is preferable at the point which the effect of this invention is more excellent.

  The shape of the soft carbon precursor is not particularly limited, and any shape such as powder, plate, granule, fiber, lump, and sphere can be used. These precursors are preferably dissolved in a solvent used when various components are mixed.

  The weight average molecular weight of the soft carbon precursor used is preferably 1000 or more, more preferably 1,000,000 or less, from the viewpoint that the effect of the present invention is more excellent.

  In the composite active material for a lithium secondary battery of the present invention, when a carbonaceous material is contained, the content of the carbonaceous material is preferably 90 to 10 parts by mass, and particularly preferably 60 to 10 parts by mass. When the content of the carbonaceous material is less than 10 parts by mass, the carbonaceous material cannot cover the Si compound, the conductive path becomes insufficient, and the capacity deterioration easily occurs. When the content is larger than 90 parts by mass, the capacity is sufficient. I can't get it.

  Examples of the graphite component include natural graphite materials and artificial graphite. Among them, exfoliated graphite obtained by exfoliating natural graphite usually called graphite is preferable.

  In the present specification, exfoliated graphite means graphite having 400 or less graphene sheets stacked. The graphene sheets are bonded to each other mainly by van der Waals force.

  The number of graphene sheets laminated in exfoliated graphite is such that the battery active material that can combine with lithium ions and exfoliated graphite are more evenly dispersed, and the expansion of the battery material using the composite active material for lithium secondary batteries is further suppressed. And / or in terms of more excellent cycle characteristics of the lithium secondary battery (hereinafter simply referred to as “the effect of the present invention is more excellent”), preferably 300 layers or less, more preferably 200 layers or less, 150 More preferred is a layer or less. From the viewpoint of handleability, 5 or more layers are preferable.

  The number of graphene sheets stacked in exfoliated graphite can be measured using a transmission electron microscope (TEM).

  The average thickness of exfoliated graphite is preferably 40 nm or less, and more preferably 22 nm or less, in that the effect of the present invention is more excellent. The lower limit is not particularly limited, but is usually 4 nm or more because the production procedure becomes complicated.

  The average thickness is measured by observing exfoliated graphite by electron microscope observation (TEM), measuring the thickness of 10 or more layers of laminated graphene sheets in exfoliated graphite, and calculating the value as arithmetic. By averaging, an average thickness is obtained.

  The exfoliated graphite is obtained by exfoliating a graphite compound between its layer surfaces.

  Examples of exfoliated graphite include so-called expanded graphite.

  The expanded graphite contains graphite, for example, scaly graphite is treated with concentrated sulfuric acid, nitric acid, hydrogen peroxide, etc., and these chemicals are intercalated into the gaps in the graphene sheet, and further heated. It is obtained by widening the gap between the graphene sheets when the intercalated chemical solution is vaporized. As will be described later, a predetermined composite active material for a lithium secondary battery can be produced using expanded graphite as a starting material. That is, expanded graphite can also be used as the graphite component in the composite active material for a lithium secondary battery.

  Examples of the graphite component include expanded graphite that has been spheroidized. The procedure of the spheronization process will be described in detail later. As will be described later, when the expanded graphite is subjected to spheronization treatment, it is spheroidized together with other components (for example, hard carbon and soft carbon precursors, battery active materials that can be combined with lithium ions). Processing may be performed.

The specific surface area of the graphite component is not particularly limited, but is preferably 10 m ² / g or more and more preferably 20 m ² / g or more in terms of more excellent effects of the present invention. The upper limit is not particularly limited, but the specific surface area is preferably 200 m ² / g or less in that the production procedure is complicated and the synthesis is difficult.

  In addition, the specific surface area of a graphite component is measured using the BET method (JIS Z 8830, one point method) by nitrogen adsorption.

The graphite component preferably has a purity of 99.9% by weight or more, or an impurity amount of 1000 ppm or less, an S amount of 0.3% by weight or less, and / or a BET specific surface area of 40 m ² / g or less. If the purity is less than 99.9% by weight or the amount of impurities is more than 1000 ppm, the irreversible capacity due to the formation of SEI derived from impurities increases, so the initial charge / discharge efficiency, which is the discharge capacity with respect to the initial charge capacity, decreases. Tend. Moreover, since the irreversible capacity | capacitance similarly becomes high when S amount becomes higher than 0.3 weight%, initial charge / discharge efficiency becomes low. More preferably, the amount of S is preferably 0.1% by weight or less. If the BET specific surface area of graphite is higher than 40 m ² / g, the area where it reacts with the electrolytic solution increases, so the initial charge / discharge efficiency decreases.

  Impurity is measured by ICP emission spectroscopic analysis using the following 26 elements (Al, Ca, Cr, Fe, K, Mg, Mn, Na, Ni, V, Zn, Zr, Ag, As, Ba, Be, Cd. , Co, Cu, Mo, Pb, Sb, Se, Th, Tl, U). Further, the amount of S is measured by ion chromatography (IC) measurement after filtering and filtering by an oxygen flask combustion method.

  In the composite active material for a lithium secondary battery of the present invention, when a carbonaceous material and a graphite component are included, the content of each is preferably 5 to 60 parts by mass and 20 to 80 parts by mass, and 10 to 55 parts by mass. A ratio of 30 to 70 parts by mass is particularly preferable. When the content of the carbonaceous material is less than 5 parts by mass, the carbonaceous material cannot cover the Si compound and graphite, adhesion between the Si compound and graphite becomes insufficient, and formation of active material particles tends to be difficult. Moreover, when larger than 60 mass parts, the effect of the graphite whose electroconductivity is higher than a carbonaceous material is not fully drawn out. On the other hand, when the content of the graphite component is less than 20 parts by mass, the effect of graphite having higher conductivity than that of the carbonaceous material is not sufficient, and when it is more than 80 parts by mass, a sufficiently large capacity is obtained as compared with conventional graphite. I can't.

The shape of the composite active material for a lithium secondary battery of the present invention is not particularly limited, but preferably has a substantially spherical shape from the viewpoint of more excellent effects of the present invention. In addition, the substantially spherical shape means that particles produced by pulverization or the like have rounded corners, spherical or spheroid shapes, discs or oblong shapes with thick rounded corners, or those deformed And the roundness is 0.7 to 1.0. The circularity was measured by image analysis of a particle image taken with a scanning electron microscope. That is, when the projected area (A) and the perimeter (PM) of a particle are measured from a photograph and the area of a perfect circle having the same perimeter (PM) is (B), the circularity is defined as A / B. The When the radius of the true circle is r, PM = 2πr and B = πr ² are established, and from this, the circularity A / B = A × 4π / (PM) ² is calculated. Thus, the sphericity of any 100 or more composite particles was obtained, and the average value was defined as the average circularity of the composite particles. At this time, the average value of the substantially spherical particles excluding the flat fine particles having a minor axis length of less than 1 μm can be used as the average circularity of the composite particles. When the shape is rounded, the bulk density of the composite particles is increased, and the packing density when the negative electrode is formed is increased.

  X-ray diffraction line intensity ratio C (002) / Si (111) of C (002) plane and Si (111) plane of the composite particles measured by powder method X-ray in the composite active material for lithium secondary battery of the present invention is It is 0.6-3.0, Preferably it is 0.6-2.0, Most preferably, it is 0.7-1.5.

  The particle size (D50: 50% volume particle size) of the composite active material for a lithium secondary battery is not particularly limited, but is preferably 2 to 40 μm, more preferably 5 to 35 μm, in terms of more excellent effects of the present invention. More preferably, it is 30 μm.

  The particle size (D90: 90% volume particle size) is not particularly limited, but is preferably 10 to 75 μm, more preferably 10 to 60 μm, and even more preferably 20 to 45 μm, in that the effect of the present invention is more excellent.

  Further, the particle size (D10: 10% volume particle size) is not particularly limited, but 1 to 20 μm is preferable and 2 to 10 μm is more preferable in that the effect of the present invention is more excellent.

  D10, D50 and D90 correspond to the particle sizes of 10%, 50% and 90% from the fine particle side of the cumulative particle size distribution measured by the laser diffraction scattering method, respectively.

  In the measurement, the composite active material for the lithium secondary battery is added to the liquid and mixed vigorously using ultrasonic waves, and the prepared dispersion is introduced into the apparatus as a sample to perform the measurement. As the liquid, it is preferable to use water, alcohol, or a low-volatile organic solvent for work. At this time, the obtained particle size distribution diagram preferably shows a normal distribution.

The specific surface area of the composite active material for lithium secondary battery of the present invention is preferably 0.5~45m ² / g, more preferably 0.5 to 30 m ² / g, particularly preferably 0.5 to 10 m ² / g It is. By setting it as this range, the solid electrolyte layer (SEI) formed on the active material surface by contact with the electrolytic solution and charge / discharge can be suppressed, and the initial Coulomb efficiency and the capacity retention rate can be improved.

  The specific surface area (BET specific surface area) of the composite active material for a lithium secondary battery is measured by a nitrogen adsorption multipoint method after vacuum drying the sample at 300 ° C. for 30 minutes.

  The composite active material for a lithium secondary battery of the present invention has a structure in which the battery active material is sandwiched between thin graphite layers having a thickness of 0.2 μm or less, and the structure extends in a laminated and / or network form. The graphite thin layer is preferably curved in the vicinity of the surface of the active material particles to cover the active material particles.

  When the thickness exceeds 0.2 μm, the electron transfer effect of the graphite thin layer is reduced. When the graphite thin layer is linear when viewed in cross section, its length is preferably at least half the size of the composite active material particles for lithium secondary batteries for electron transfer, and the size of the composite material particles for lithium secondary batteries More preferably, they are comparable. When the graphite thin layer is network-like, it is preferable for electron transfer that the network of the graphite thin layer is connected to more than half of the size of the active material particles, and more preferably about the same size as the size of the active material particles. .

  In the composite active material for a lithium secondary battery of the present invention, it is preferable that the graphite thin layer bends in the vicinity of the surface of the active material particles to cover the active material particles. By adopting such a shape, the electrolyte enters from the end face of the graphite thin layer, the battery active material or the end face of the graphite thin layer is in direct contact with the electrolyte, and a reaction product is formed during charge and discharge, which reduces efficiency. Risk is reduced.

  Next, the manufacturing method of the composite active material for lithium secondary batteries of this invention is demonstrated.

  The method for producing a composite active material for a lithium secondary battery according to the present invention includes a step of mixing Si or a Si alloy, a carbon precursor, and optionally a graphite component, a step of granulating / consolidating, and a mixture of 90 to 720 seconds of pulverization and spheronization to form substantially spherical composite particles, a step of firing the composite particles in an inert atmosphere, a step of mixing a carbon precursor and the composite particles or the fired powder, The method includes a step of heating the mixture in an inert atmosphere to obtain composite particles in which the carbon film is fired powder or carbon-coated.

  As the Si compound as a raw material, it is preferable to use a powder having an average particle diameter (D50) of 0.01 to 5 μm. In order to obtain a Si compound having a predetermined particle diameter, the above-described Si compound raw material (ingot, wafer, powder, etc.) is pulverized by a pulverizer, and in some cases, a classifier is used. In the case of a lump such as an ingot or a wafer, it can be first pulverized using a coarse pulverizer such as a jaw crusher. After that, for example, a ball or bead is used to move the grinding medium, and the impact force, frictional force, or compression force of the kinetic energy is used to grind the material to be crushed, the media agitation mill, or the compression force of the roller. Rotation of a roller mill that pulverizes, a jet mill that collides crushed objects with the lining material or collides with each other at high speed, and pulverizes by the impact force of the impact, and a rotor with a fixed hammer, blade, pin, etc. It can be finely pulverized by using a hammer mill, pin mill, disk mill that pulverizes the material to be crushed using the impact force of the colloid, a colloid mill that uses shear force, or a high-pressure wet-on-front collision disperser "Ultimizer" .

  The pulverization can be used for both wet and dry processes. For further fine pulverization, very fine particles can be obtained, for example, by using a wet bead mill and gradually reducing the diameter of the beads. In order to adjust the particle size distribution after pulverization, dry classification, wet classification, or sieving classification can be used. In the dry classification, the process of dispersion, separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge are performed sequentially or simultaneously, mainly using air flow. Pre-classification (adjustment of moisture, dispersibility, humidity, etc.) before classification, or the moisture in the airflow used so that the classification efficiency is not lowered due to the influence of shape, air flow disturbance, velocity distribution, static electricity, etc. Adjust the oxygen concentration. In a dry type in which a classifier is integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

  As another method for obtaining a Si compound having a predetermined particle size, a method in which the Si compound is heated and evaporated by plasma, laser, or the like, and solidified in an inert atmosphere, or CVD or plasma CVD using a gas raw material is used. These methods are suitable for obtaining ultrafine particles of 0.1 μm or less.

  The carbon precursor as a raw material is not particularly limited as long as it is a carbon-based compound mainly composed of carbon and becomes a carbonaceous material by heat treatment in an inert atmosphere. The graphitizable carbon (soft carbon), graphite Examples include non-graphitizable carbon (hard carbon) that is difficult to form.

  As the raw material graphite component, natural graphite, artificial graphite obtained by graphitizing the pitch of petroleum or coal, and the like can be used, and scale-like, oval or spherical, cylindrical, fiber-like, and the like are used. In addition, these graphite components are subjected to acid treatment, oxidation treatment, and then expanded by heat treatment, and part of the graphite layer is peeled off to form an accordion, or by pulverized expanded graphite or ultrasonic waves, etc. Graphene or the like exfoliated can also be used. Expanded graphite or a pulverized product of expanded graphite is superior in flexibility to other graphites, and in the process of forming composite particles, which will be described later, the pulverized particles can be rebound to easily form substantially spherical composite particles. Can be formed. In view of the above, it is preferable to use expanded graphite or a pulverized product of expanded graphite. The raw material graphite component is preliminarily adjusted to a size that can be used in the mixing step, and the particle size before mixing is 1 to 100 μm for natural graphite or artificial graphite, or 5 μm to crushed expanded graphite or expanded graphite, or graphene. It is about 5 mm.

  Mixing with these Si compounds, carbon precursors, and, if necessary, graphite components, when the carbon precursors are softened or liquefied by heating, Si compounds, carbon precursors, and further necessary under heating Depending on the process, the graphite component can be kneaded. When the carbon precursor is dissolved in a solvent, an Si compound, a carbon precursor, and, if necessary, a graphite component are added to the solvent, and the Si compound and carbon are dissolved in the solution in which the carbon precursor is dissolved. It can be carried out by dispersing and mixing the precursor and, if necessary, the graphite component, and then removing the solvent. The solvent to be used can be used without particular limitation as long as it can dissolve the carbon precursor. For example, when pitch or tar is used as the carbon precursor, quinoline, pyridine, toluene, benzene, tetrahydrofuran, creosote oil or the like can be used. When polyvinyl chloride is used, tetrahydrofuran, cyclohexanone, nitrobenzene or the like can be used. When phenol resin or furan resin is used, ethanol, methanol or the like can be used.

  As a mixing method, when the carbon precursor is heat-softened, a kneader (kneader) can be used. In the case of using a solvent, in addition to the above-described kneader, a Nauter mixer, a Roedige mixer, a Henschel mixer, a high speed mixer, a homomixer, or the like can be used. Further, the jacket is heated with these apparatuses, and then the solvent is removed with a vibration dryer, a paddle dryer or the like.

  With these devices, the carbon precursor is solidified, or stirring in the process of solvent removal is continued for a certain amount of time, so that the mixture of Si compound, carbon precursor, and, if necessary, the graphite component is granulated and consolidated. Is done. Further, the carbon precursor is solidified or the mixture after removing the solvent is compressed by a compressor such as a roller compactor and coarsely pulverized by a crusher, whereby granulation and consolidation can be achieved. The size of the granulated / consolidated product is preferably 0.1 to 5 mm in view of ease of handling in the subsequent pulverization step.

  The granulation / consolidation methods include ball mills that pulverize the material to be crushed using compressive force, media agitation mills, roller mills that pulverize using the compressive force of rollers, and crushed material to lining material at high speed. A jet mill that collides or collides with particles and pulverizes by the impact force of the impact, and a hammer mill and pin mill that crushes the material to be crushed using the impact force of the rotation of a rotor with a fixed hammer, blade, pin, etc. A dry pulverization method such as a disk mill is preferred. In order to adjust the particle size distribution after pulverization, dry classification such as air classification and sieving is used. In the type in which the pulverizer and the classifier are integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

  The granulated and consolidated mixture is pulverized and spheroidized by the above-mentioned pulverization method to adjust the particle size, and then passed through a special spheronizing device, and the above-mentioned jet mill and rotor There is a method of spheroidizing by repeating a method of pulverizing an object to be crushed using an impact force caused by rotation or extending a processing time. Specialized spheroidizing devices include Hosokawa Micron's Faculty (registered trademark), Nobilta (registered trademark), Mechano-Fusion (registered trademark), Nippon Coke Industries' COMPOSI, Nara Machinery Co., Ltd. hybridization system, Earth Technica's Examples include kryptron orb and kryptron eddy.

  The time for pulverization and spheronization treatment in the pulverization step is 90 seconds to 720 seconds, preferably 90 seconds to 540 seconds. When a batch type pulverizer with a long residence time in the apparatus for the pulverized product is used in this pulverization process, the pulverization is dominant at the initial stage of pulverization and the pulverization proceeds, and the particle size of the pulverized product becomes small. Since the physical energy required for pulverization cannot be given to the pulverized product when the particle size is smaller than the particle size, the progress of pulverization stops, and in the middle to late stages of pulverization, the grain growth due to the bonding of the pulverized particles becomes dominant and the particles enlarge . If the pulverization time is too long, the length of the graphite thin layer on the continuous line when the active material is viewed in cross section is shortened. If the particle enlargement and the electron conductivity decrease, the cycle retention rate, initial charge capacity, and initial coulomb efficiency tend to decrease, so it is necessary to optimize the grinding time.

  By performing the pulverization and spheronization treatment, substantially spherical composite particles can be obtained.

  The obtained composite particles are fired in an argon gas or nitrogen gas stream or in a vacuum. The firing temperature is preferably 300 to 1200 ° C, particularly preferably 600 to 1200 ° C. When the firing temperature is less than 300 ° C., the electric resistance between the graphite layer and Si inside the composite particles and the composite particles increases due to the remaining unheated components of the carbon precursor, and the discharge capacity tends to decrease. It is in. On the other hand, when the firing temperature exceeds 1200 ° C., there is a strong possibility that a reaction between the Si compound and the amorphous carbon derived from the carbon precursor or the graphite component occurs, and the discharge capacity tends to decrease.

  Further, the composite active material for a lithium secondary battery of the present invention is a carbon film obtained by firing the carbon-coated composite particles, the spheroidized composite particles or the fired powder and the carbon precursor obtained in the previous step in an inert atmosphere. It is preferable to manufacture by carrying out the step of coating the inside and outside of the composite particles or fired powder.

  Examples of the carbon precursor to be used include coal-based pitch (for example, coal tar pitch), petroleum-based pitch, mesophase pitch, coke, and low molecular weight heavy oil.

  When carbon composite particles, spheroidized composite particles or calcined powder and carbon precursor are fired in an inert atmosphere to coat the carbon film inside or outside of the composite particles or calcined powder, the carbon precursor is crucible or the like , Heated in an inert atmosphere so as not to come into direct contact with the composite particles, or by adding a hydrocarbon gas such as methane, ethane, ethylene, acetyl, propylene to the inert atmosphere and heating, It is preferable to coat the carbon film in the gas phase inside or outside of the fired powder, carbon-coated composite particles, or carbon-coated fired powder.

  Furthermore, the composite active material for a lithium secondary battery of the present invention is manufactured by performing a step of air classification of spherically processed powder, calcined powder or carbon-coated powder after the step of coating the carbon film in the gas phase. It is preferable to do.

  As a method of air classification, the particle size of the powder to be classified is adjusted by adjusting the operating conditions such as the rotational speed of the rotor and the differential pressure by introducing the powder into an air classifier such as ATP-50 manufactured by Hosokawa Micron. Can be controlled.

  The composite active material for lithium secondary batteries of the present invention is useful as an active material used for battery materials (electrode materials) used in lithium secondary batteries.

  A method for producing a negative electrode for a lithium secondary battery using the composite active material is not particularly limited, and a known method can be used.

  For example, a composite active material for a lithium secondary battery and a binder can be mixed, pasted using a solvent, and applied onto a copper foil to form a negative electrode for a lithium secondary battery.

  In addition to the copper foil, the current collector is preferably a current collector having a three-dimensional structure in that the battery cycle is more excellent. Examples of the current collector material having a three-dimensional structure include carbon fiber, sponge-like carbon (a sponge-like resin coated with carbon), metal, and the like.

  As a current collector (porous current collector) having a three-dimensional structure, a metal or carbon conductor porous body, a plain weave wire mesh, expanded metal, lath net, metal foam, metal woven fabric, metal nonwoven fabric, A carbon fiber woven fabric or a carbon fiber non-woven fabric may be used.

  As the binder to be used, known materials can be used, for example, fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene, SBR, polyethylene, polyvinyl alcohol, carboxymethyl cellulose, polyacrylic acid, glue and the like are used. It is done.

  Examples of the solvent include water, isopropyl alcohol, N-methylpyrrolidone, dimethylformamide and the like.

  In addition, when making into a paste, you may stir and mix using a well-known stirrer, a mixer, a kneader, a kneader, etc. as needed as mentioned above.

  When preparing a coating slurry using a composite active material for a lithium secondary battery, it is preferable to add conductive carbon black, carbon nanotube, or a mixture thereof as a conductive material. The shape of the composite active material for a lithium secondary battery obtained by the above process is often relatively granulated (particularly substantially spherical), and the contact between particles tends to be point contact. In order to avoid this adverse effect, a method of blending carbon black, carbon nanotubes or a mixture thereof into the slurry can be mentioned. Since carbon black, carbon nanotubes, or a mixture thereof can be intensively aggregated in the capillary part formed by contact with the composite active material when the slurry solvent is dried, contact loss (increased resistance) associated with the cycle is prevented. I can do it.

The blending amount of carbon black, carbon nanotube, or a mixture thereof is not particularly limited, but is preferably 0.2 to 4 parts by mass with respect to 100 parts by mass of the composite active material for a lithium secondary battery, 0.5 to 2 More preferably, it is part by mass. Examples of the carbon nanotube include a single wall carbon nanotube and a multi-wall carbon nanotube.
(Positive electrode)
As a positive electrode used for a lithium secondary battery having a negative electrode obtained using the composite active material, a positive electrode using a known positive electrode material can be used.

As a manufacturing method of a positive electrode, a well-known method is mentioned, The method etc. which apply | coat the positive electrode mixture which consists of positive electrode material, a binder, and a electrically conductive agent to the surface of a collector are mentioned. Examples of the positive electrode material (positive electrode active material) include metal oxides such as chromium oxide, titanium oxide, cobalt oxide, and vanadium pentoxide, LiCoO ₂ , LiNiO ₂ , LiNi _1-y Co _y O ₂ , and LiNi _{1-xy. Co x Al y O 2, LiMnO} 2, LiMn 2 O 4, LiFeO 2 lithium metal oxides such as titanium sulfide, chalcogen compounds of transition metals such as molybdenum sulfide, or polyacetylene, polyparaphenylene, conductive polypyrrole Conjugated polymer substances having
(Electrolyte)
As an electrolytic solution used in a lithium secondary battery having a negative electrode obtained by using the composite active material, a known electrolytic solution can be used.

For example, as an electrolyte salt contained in the _{electrolyte, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5), LiCl, LiBr, LiCF 3 SO 3, LiCH 3 SO 3, LiN (CF 3 _{SO 2) 2, LiC (CF} 3 SO 2) 3, LiN (CF 3 CH 2 OSO 2) 2, LiN (CF 3 CF 3 OSO 2) 2, LiN (HCF 2 CF 2 CH 2 OSO 2) 2, LiN {(CF ₃ ) ₂ CHOSO ₂ } ₂ , LiB {C ₆ H ₃ (CF ₃ ) ₂ } ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ Lithium salts can be used. In particular, LiPF ₆ and LiBF ₄ are preferable from the viewpoint of oxidation stability.

  The electrolyte salt concentration in the electrolyte solution is preferably 0.1 to 5 mol / liter, and more preferably 0.5 to 3 mol / liter.

  Examples of the solvent used in the electrolytic solution include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2 -Ethers such as methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxofuran, 4-methyl-1,3-dioxolane, anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, acetonitrile, chloronitrile, propionitrile, etc. Nitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzoyl chloride, Benzoyl, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazoline, ethylene glycol, may be used an aprotic organic solvent such as dimethyl sulfite.

In place of the electrolytic solution, a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte may be used. Examples of the polymer compound constituting the matrix of the polymer solid electrolyte or polymer gel electrolyte include ether polymer compounds such as polyethylene oxide and cross-linked products thereof, methacrylate polymer compounds such as polymethacrylate, and acrylate compounds such as polyacrylate. Fluorine polymer compounds such as polymer compounds, polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene copolymers are preferred. These can also be mixed and used. From the viewpoint of oxidation-reduction stability, a fluorine-based polymer compound such as PVDF or vinylidene fluoride-hexafluoropropylene copolymer is particularly preferable.
(Separator)
A well-known material can be used as a separator used for the lithium secondary battery which has a negative electrode obtained using the said composite active material. For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are illustrated. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred from the viewpoint of film thickness, membrane strength, membrane resistance, and the like. Specifically, it is a microporous film made of polyethylene and polypropylene, or a microporous film in which these are combined.

  The lithium secondary battery uses the negative electrode, the positive electrode, the separator, the electrolyte, and other battery components (for example, a current collector, a gasket, a sealing plate, a case, etc.), and is cylindrical, square, or It can have a form such as a button type.

  The lithium secondary battery of the present invention is used in various portable electronic devices, particularly notebook computers, notebook word processors, palmtop (pocket) computers, mobile phones, mobile faxes, mobile printers, headphone stereos, video cameras, and mobile TVs. , Portable CDs, portable MDs, electric shaving machines, electronic notebooks, transceivers, power tools, radios, tape recorders, digital cameras, portable copying machines, portable game machines, and the like. In addition, electric vehicles, hybrid vehicles, vending machines, electric carts, load leveling power storage systems, household power storage devices, distributed power storage systems (built into stationary appliances), emergency power supply systems, etc. It can also be used as a secondary battery.

  According to the present invention, by optimizing the pulverization time of the composite particles, the composite particles are flattened, the crystallinity of graphite is improved, and a composite suitable for forming a negative electrode having high capacity, excellent Coulomb efficiency, and cycle characteristics. An active material is obtained.

Cross-sectional SEM image of consolidated particles obtained in Example 1 SEM image of the composite active material obtained in Example 1 Cross-sectional SEM image of the composite active material obtained in Example 2 Cross-sectional SEM image of the composite active material obtained in Comparative Example 1

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

Example 1
A chemical grade metal Si (purity 3N) having an average particle size (D50) of 7 μm was mixed with ethanol at 25% by weight, and a finely pulverized wet bead mill using zirconia beads having a diameter of 0.3 mm was performed for 6 hours. An ultrafine Si slurry having a D50) of 0.3 μm and a dry BET surface area of 60 m ² / g was obtained.

  Immerse natural graphite with a particle diameter of about 0.5 mm (width in the (200) plane direction) and a thickness of about 0.02 mm in a solution of concentrated sulfuric acid with 1 wt% sodium nitrate and 7 wt% potassium permanganate added for 24 hours. Then, it was washed with water and dried to obtain acid-treated graphite. This acid-treated graphite was placed in a vibrating powder feeder, placed on nitrogen gas at a flow rate of 10 L / min, passed through a mullite tube having a length of 1 m and an inner diameter of 11 mm heated to 850 ° C. with an electric heater, and released from the end face to the atmosphere. A gas such as sulfurous acid was exhausted at the top, and expanded graphite was collected at the bottom in a stainless steel container. The expanded graphite had a width in the (200) plane direction of about 0.5 mm and maintained the original graphite value. However, the thickness expanded to about 4 mm and about 200 times, and the appearance was coiled. It was confirmed that the layer peeled and was in the form of an accordion.

  119 g of the ultrafine Si slurry, 200 g of the expanded graphite, 125 g of a resol-type phenol resin (weight average molecular weight (Mw) = 460), and 5.0 L of ethanol were mixed and stirred for 22 minutes by an in-line mixer. Thereafter, the mixed solution was transferred to a rotary evaporator, heated to 40 ° C. with a warm bath while rotating, and evacuated with an aspirator to remove the solvent. Thereafter, it was spread on a bat in a fume hood and dried for 2 hours while being evacuated, passed through a mesh with a mesh opening of 2 mm, and further dried for 2 days to obtain about 567 g of a dry mixture (light bulk density 295 g / L).

  This mixed dried product was passed through a three-roll mill twice, and granulated and consolidated to a particle size of about 2 mm and a light bulk density of 478 g / L. In FIG. 1, the secondary electron image by the FE-SEM of the cross section which cut | disconnected the obtained compacted particle with the ion beam is shown. It can be seen that the graphite layer that is compressed and connected in a layered manner has a structure in which Si particles are embedded.

  Next, this granulated / consolidated product was placed in a new power mill and pulverized at 21000 rpm for 180 seconds while cooling with water, and at the same time, spheroidized to obtain a spheroidized powder having a light bulk density of 471 g / L.

  The obtained powder was put into an alumina boat and fired at a maximum temperature of 900 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Thereafter, a composite active material having an average particle diameter (D50) of 20 μm and a light bulk density of 591 g / L was obtained through a mesh having an opening of 45 μm.

  An SEM image of the obtained composite active material particles is shown (FIG. 2). It can be seen that the composite active material particle graphite thin layer (12) is curved and has a substantially spherical shape covering the active material particles.

The specific surface area by the BET method using nitrogen gas was 82 m ² / g. In powder X-ray diffraction, a diffraction line corresponding to the (002) plane of graphite and a diffraction line corresponding to the (100) plane of Si are seen, and the peak intensity ratio C (002) / Si (111) is 1.39. there were.

"Preparation of negative electrode for lithium ion secondary battery"
The obtained composite active material is 92.5% by weight (content in the total solid content; the same shall apply hereinafter), acetylene black 0.5% by weight as a conductive auxiliary, and gelled polyacrylic acid 7 as a binder. A negative electrode mixture-containing slurry was prepared by mixing wt% and water.

The obtained slurry was applied to a copper foil having a thickness of 18 μm using an applicator so that the solid content was 3.1 mg / cm ² and dried at 110 ° C. in a vacuum dryer for 0.5 hours. . After drying, it was punched into a circle of 14 mmφ, uniaxially pressed under conditions of a pressure of 0.6 t / cm ² , and further heat-treated at 110 ° C. for 3 hours under vacuum to form a lithium ion secondary layer having a thickness of 30 μm. A negative electrode for a secondary battery was obtained.

"Production of evaluation cells"
In the glove box, the evaluation cell was prepared by dipping the negative electrode, a 24 mmφ polypropylene separator, a 21 mmφ glass filter, a 18 mmφ 0.2 mm thick metal lithium and a stainless steel foil of the base material into the electrolyte solution in the glove box. After that, the layers were laminated in this order, and finally the lid was screwed in. The electrolytic solution used was a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1. The cell for evaluation was further put in a sealed glass container containing silica gel, and an electrode through a silicon rubber lid was connected to a charge / discharge device (SM-8 manufactured by Hokuto Denko).

"Evaluation conditions"
The evaluation cell was cycle tested in a constant temperature room at 25 ° C. Charging was performed after charging to 0.01 V at a constant current of 2.2 mA until the current value reached 0.2 mA at a constant voltage of 0.01 V. The discharge was performed at a constant current of 2.2 mA up to a voltage value of 1.5V. The initial discharge capacity and initial charge / discharge efficiency were the results of the initial charge / discharge test.

  In addition, the cycle characteristics were evaluated as the capacity retention rate by comparing the discharge capacity after 50 charge / discharge tests under the charge / discharge conditions with the initial discharge capacity.

Example 2
The granulated / consolidated product produced in Example 1 was put into a new power mill and pulverized at 21000 rpm for 360 seconds while cooling with water, and spheroidized at the same time to obtain a spheroidized powder having a light bulk density of 555 g / L.

  The obtained powder was put into an alumina boat and fired at a maximum temperature of 900 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Thereafter, a composite active material having an average particle diameter (D50) of 16 μm and a light bulk density of 664 g / L was obtained through a mesh having an opening of 45 μm.

  In FIG. 3, the secondary electron image by the FE-SEM of the cross section which cut | disconnected the obtained composite active material with the ion beam is shown. It can be seen that the graphite layer connected in a layered manner has a structure in which Si particles are embedded as in the consolidated particles shown in FIG.

The specific surface area by the BET method using nitrogen gas was 71 m ² / g. In powder X-ray diffraction, a diffraction line corresponding to the (002) plane of graphite and a diffraction line corresponding to the (100) plane of Si are seen, and the peak intensity ratio C (002) / Si (111) is 0.79. there were.

"Preparation of negative electrode for lithium ion secondary battery"
The obtained composite active material is 92.5% by weight (content in the total solid content; the same shall apply hereinafter), acetylene black 0.5% by weight as a conductive auxiliary, and gelled polyacrylic acid 7 as a binder. A negative electrode mixture-containing slurry was prepared by mixing wt% and water.

The obtained slurry was applied to a copper foil having a thickness of 18 μm using an applicator so that the solid content was 3.1 mg / cm ² and dried at 110 ° C. in a vacuum dryer for 0.5 hours. . After drying, it was punched into a circle of 14 mmφ, uniaxially pressed under conditions of a pressure of 0.6 t / cm ² , and further heat-treated at 110 ° C. for 3 hours under vacuum to form a lithium ion layer having a negative electrode mixture layer having a thickness of 29 μm. A negative electrode for a secondary battery was obtained.

"Production of evaluation cells"
In the glove box, the evaluation cell was prepared by dipping the negative electrode, a 24 mmφ polypropylene separator, a 21 mmφ glass filter, a 18 mmφ 0.2 mm thick metal lithium and a stainless steel foil of the base material into the electrolyte solution in the glove box. After that, the layers were laminated in this order, and finally the lid was screwed in. The electrolytic solution used was a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1. The cell for evaluation was further put in a sealed glass container containing silica gel, and an electrode through a silicon rubber lid was connected to a charge / discharge device (SM-8 manufactured by Hokuto Denko).

"Evaluation conditions"
The evaluation cell was cycle tested in a constant temperature room at 25 ° C. Charging was performed after charging to 0.01 V at a constant current of 2.2 mA until the current value reached 0.2 mA at a constant voltage of 0.01 V. The discharge was performed at a constant current of 2.2 mA up to a voltage value of 1.5V. The initial discharge capacity and initial charge / discharge efficiency were the results of the initial charge / discharge test.

  In addition, the cycle characteristics were evaluated as the capacity retention rate by comparing the discharge capacity after 50 charge / discharge tests under the charge / discharge conditions with the initial discharge capacity.

Comparative Example The granulated / consolidated product produced in Example 1 was placed in a new power mill and pulverized at 21000 rpm for 1260 seconds while cooling with water, and spheroidized at the same time to obtain a spheroidized powder having a light bulk density of 666 g / L.

  The obtained powder was put into an alumina boat and fired at a maximum temperature of 900 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Thereafter, a composite active material having an average particle diameter (D50) of 24 μm and a light bulk density of 782 g / L was obtained through a mesh having an opening of 45 μm.

  In FIG. 4, the secondary electron image by the FE-SEM of the cross section which cut | disconnected the obtained composite active material with the ion beam is shown. Unlike Example 1 and Example 2, almost no graphite layer connected in a layered form was observed, the cut graphite and Si particles were mixed, and large cracks were observed in the composite active material. It is done.

The specific surface area by the BET method using nitrogen gas was 78 m ² / g. In the powder X-ray diffraction, a diffraction line corresponding to the (002) plane of graphite and a diffraction line corresponding to the (100) plane of Si are seen, and the peak intensity ratio C (002) / Si (111) is 0.35. there were.

"Preparation of negative electrode for lithium ion secondary battery"
The obtained composite active material is 92.5% by weight (content in the total solid content; the same shall apply hereinafter), acetylene black 0.5% by weight as a conductive auxiliary, and gelled polyacrylic acid 7 as a binder. A negative electrode mixture-containing slurry was prepared by mixing wt% and water.

The obtained slurry was applied to a copper foil having a thickness of 18 μm using an applicator so that the solid content was 3.1 mg / cm ² and dried at 110 ° C. in a vacuum dryer for 0.5 hours. . After drying, it was punched into a 14 mmφ circle, uniaxially pressed under conditions of a pressure of 0.6 t / cm ² , and further heat-treated at 110 ° C. for 3 hours under vacuum to form a negative electrode mixture layer having a thickness of 22 μm. A negative electrode for a secondary battery was obtained.

"Production of evaluation cells"
In the glove box, the evaluation cell was prepared by dipping the negative electrode, a 24 mmφ polypropylene separator, a 21 mmφ glass filter, a 18 mmφ 0.2 mm thick metal lithium and a stainless steel foil of the base material into the electrolyte solution in the glove box. After that, the layers were laminated in this order, and finally the lid was screwed in. The electrolytic solution used was a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1. The cell for evaluation was further put in a sealed glass container containing silica gel, and an electrode through a silicon rubber lid was connected to a charge / discharge device (SM-8 manufactured by Hokuto Denko).

"Evaluation conditions"
The evaluation cell was cycle tested in a constant temperature room at 25 ° C. Charging was performed after charging to 0.01 V at a constant current of 2.2 mA until the current value reached 0.2 mA at a constant voltage of 0.01 V. The discharge was performed at a constant current of 2.2 mA up to a voltage value of 1.5V. The initial discharge capacity and initial charge / discharge efficiency were the results of the initial charge / discharge test.

  In addition, the cycle characteristics were evaluated as the capacity retention rate by comparing the discharge capacity after 50 charge / discharge tests under the charge / discharge conditions with the initial discharge capacity.

Claims (11)

In a composite active material for a lithium ion secondary battery comprising Si or Si alloy, carbonaceous material or carbonaceous material, and graphite, the composite active material has an average particle diameter (D50) of 1 to 40 μm, powder method X-ray The X-ray diffraction line intensity ratio C (002) / C (111) between the C (002) plane and the Si (111) plane measured in Step 1 is 0.6 to 3.0, and the average circularity is 0.7 to A composite active material for a lithium ion secondary battery, wherein the composite active material is a substantially spherical composite particle of 1.0. 3. The lithium ion secondary battery according to claim 1, wherein an average particle diameter (D50) of the Si or Si alloy is 0.01 to 5 μm, and a carbonaceous material covers at least an active material surface. Composite active material. The Si or Si alloy has a structure sandwiched between carbonaceous materials and a thin graphite layer having a thickness of 0.2 μm or less, and the structure spreads in a laminated and / or network shape, and the thin graphite layer is an active material. 3. The composite active material for a lithium ion secondary battery according to claim 1, wherein the active material particles are curved in the vicinity of the surface of the particles, and the surface of the outermost layer is covered with a carbonaceous material. The graphite is composed of 26 elements (Al, Ca, Cr, Fe, K, Mg, Mn, Na, Ni, V, Zn, Zr, Ag, As, Ba, Be, Cd, Co, Cu, by ICP emission spectroscopy. , Mo, Pb, Sb, Se, Th, Tl, U) Ion chromatography (IC) measurement by oxygen flask combustion method when the purity determined from the semi-quantitative value of impurities is 99.9% by weight or more, or the impurity amount is 1000 ppm or less amount S 0.3 wt% or less by law, and / or a composite active material for lithium ion secondary battery according to any one of claims 1 to 3, equal to or less than the BET specific surface area of 40 m 2 / ^g . 5. The lithium ion secondary battery according to claim 1, wherein the content of the Si or Si alloy is 10 to 80 parts by mass, and the content of the carbonaceous material is 90 to 10 parts by mass. Composite active material. The content of the Si or Si alloy is 10 to 60 parts by mass, the content of the carbonaceous material is 5 to 60 parts by mass, and the content of the graphite component is 20 to 80 parts by mass. The composite active material for lithium ion secondary batteries in any one of -4. Si or Si alloy, carbon precursor, if necessary, a step of mixing graphite components, a step of granulation / consolidation, and a mixture is pulverized and spheronized for 90 seconds to 720 seconds to form substantially spherical composite particles. A step of forming, a step of firing the composite particles in an inert atmosphere, a step of mixing the carbon precursor and the composite particles or the fired powder, and heating the mixture in an inert atmosphere to form a carbon film. The method for producing a composite active material for a lithium secondary battery according to any one of claims 1 to 6, further comprising a step of obtaining fired powder or carbon-coated composite particles. The carbon-coated composite particles, spheroidized composite particles or calcined powder obtained in claim 7 and the carbon precursor are calcined in an inert atmosphere to coat the carbon film on the inside and outside of the composite particles or calcined powder. The manufacturing method of the composite active material for lithium secondary batteries of Claim 7 characterized by the above-mentioned. The lithium secondary battery according to claim 7 or 8, wherein after the step of coating in the gas phase, a step of air classification of the pulverized and spherically processed powder, the fired powder, or the carbon-coated powder is performed. A method for producing a composite active material. The step of firing the composite particles and the calcined powder together with the carbon precursor in an inert atmosphere, and the heating of the carbon precursor in the inert atmosphere to produce the calcined powder or carbon-coated composite particles or the carbon-coated calcined powder. The method for producing a composite active material for a lithium secondary battery according to any one of claims 7 to 9, wherein the temperature in the step of coating the inside and outside with a gas phase is 300 to 1200 ° C, respectively. The lithium secondary battery containing the composite active material for lithium secondary batteries in any one of Claims 1-6.

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