JP2009181767A - Composite carbon material for negative electrode material of lithium secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite carbon material for negative electrodes of lithium ion secondary battery, having higher capacity than the theoretical capacity of graphite, high energy density, excellent charging/discharging cycle characteristics, and excellent initial irreversible capacity. <P>SOLUTION: A composite carbon material for negative electrodes of lithium ion secondary battery includes graphite core particles and a carbide layer formed on the surface of each graphite core particle. The carbide layer contains metal particles or metal compound particles which store and discharge lithium or a set of metal particles or metal compound particles which store and discharge lithium and graphite particles. The particle size aspect ratio is 1.0-2.0. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composite carbon material for a negative electrode material of a lithium ion secondary battery used as a negative electrode material of a lithium ion secondary battery used in a site requiring high capacity, such as a notebook computer, and a method for producing the same.

  Lithium secondary batteries used in notebook computers and mobile phones are required to have higher capacities. However, since the capacity of the current graphite negative electrode material almost reaches the theoretical capacity of 372 mAh / g, a negative electrode material having a large theoretical capacity is desired.

  Metal-based negative electrode materials that can be alloyed with lithium typified by Si and Sn have a large theoretical capacity. However, the metal-based negative electrode material has a large theoretical capacity, but has a drawback of low electrical conductivity, large expansion during a charge / discharge cycle, and severe capacity deterioration. For this reason, the metal-based negative electrode material needs to be imparted with conductivity and relaxed.

  Until now, as a method of imparting conductivity to the metal-based negative electrode material, (i) coating of a carbon precursor on the metal-based material, (ii) doping of a transition metal, (iii) composite of the metal-based material and carbon Has been carried out.

  However, although the metal-based negative electrode material obtained by the method (i) and the method (ii) can impart conductivity, the conductivity is gradually reduced by the refinement of the metal accompanying expansion and contraction of the charge / discharge cycle. Has a disadvantage that it is far from the practical level.

  In addition, as a metal material obtained by the method (iii), for example, in Japanese Patent Application Laid-Open No. 2004-185975 (Patent Document 1), mechanochemical using Si with mechanical impact force on graphite particles is disclosed. A composite material having a three-layer structure, which is fixed by treatment and further covered with a carbon layer, is disclosed. Japanese Patent Laid-Open No. 2002-8652 (Patent Document 2) states that Si is attached to the surface of graphite particles, and at least a part of the graphite particles and at least a part of the surface of the composite are covered with carbon. A featured composite carbon material is disclosed. Japanese Patent Laid-Open No. 2002-255529 (Patent Document 3) or Japanese Patent Application Laid-Open No. 2006-49266 (Cited Document 4) discloses graphite particles having an average particle diameter of 15 μm and carbon using a phenol resin on Si particles. Disclosed is a composite carbon material having a structure in which Si / carbon black composite particles are adhered onto graphite particles obtained by wet-mixing composite particles with black attached using isopropyl alcohol / phenol resin solution and then calcined by firing. Yes.

  However, Patent Document 1 and Patent Document 2 have a problem that the Si particles themselves break down after a cycle, and most of the Si hardly functions after several cycles.

  Moreover, in patent document 3 and patent document 4, in addition to the said problem, since it was an uneven | corrugated shape, there existed a problem that the packing density was small and the energy density per volume became small as a result. In addition, the uneven shape is peeled off during the pressing process, resulting in an increase in irreversible capacity. Furthermore, since carbon black itself has a large initial irreversible capacity, there is also a problem that the cycle life is short.

  In order to extend the life of the metal-based material, it is necessary to increase the life of the Si particles themselves. As a technique for this, Si particles are miniaturized. However, in the technique of miniaturizing Si particles, the cycle life is remarkably improved as compared with the case of using large particles, but due to the expansion and contraction after the cycle, separation from the current collector occurs gradually, resulting in There is a problem that the cycle deteriorates. In addition, in order to extend the life of the metal-based material, a method of thinning is also performed. However, in addition to the same problem as miniaturization, the battery occupies the active capacity when the battery is assembled. There is also a problem that the material thickness is reduced and the battery capacity is reduced.

In JP 2003-17051 A (Patent Document 5), a graphite / SiO mixed powder is finely pulverized with a ball mill, dispersed in furfuryl alcohol, added with hydrochloric acid, polymerized, and calcined at 1000 ° C. Thus, ₂ to 10 nm of Si is dispersed in a 0.1 to 1 μm SiO ₂ matrix, and this SiO ₂ / Si composite and graphite composite is dispersed in a 5 to ₂₀ μm carbon matrix. A composite carbon material is disclosed.

  However, although the composite carbon material of Patent Document 5 has a long life, it is unsuitable for industrial use, and the carbon matrix formed from furfuryl alcohol is amorphous and has a low specific gravity at the stage of processing at 1000 ° C. As a result, since the electrode plate density is low, the capacity per unit weight is large, but the capacity per unit volume is small, and there is a problem that the merit of using high capacity Si cannot be utilized.

JP 2004-185975 A (Claims) JP 2002-8652 A (Claims) JP 2002-255529 A (paragraph numbers 0050 to 0051) JP 2006-49266 A (paragraph numbers 0073 to 0075) JP 2003-17051 A (paragraph number 0098)

  That is, a negative electrode material for a lithium ion secondary battery having excellent charge / discharge cycle characteristics and high energy density has not yet been achieved.

  Therefore, an object of the present invention is for a negative electrode material for a lithium ion secondary battery having a capacity higher than the theoretical capacity of graphite, high energy density, excellent charge / discharge cycle characteristics, and excellent initial irreversible capacity. It is to provide a composite carbon material. Moreover, the subject of this invention is providing the manufacturing method which can manufacture industrially the composite carbon material for negative electrode materials of such a lithium ion secondary battery.

  As a result of intensive studies to achieve the above object, the inventors of the present invention formed a coating layer made of a carbonaceous material in advance on graphite particles serving as a nucleus, and then formed graphite core particles having a coating layer and lithium. Metal particles or metal compound particles that occlude and release, or metal inclusion particles that occlude and release lithium or metal inclusion particles that encapsulate metal compound particles, are rubbed and compressed into the coating layer. Alternatively, the metal compound particles can be embedded and the surface of the coating layer can be smoothed, and then carbonized and calcined, whereby graphite core particles and metal particles that have a smooth surface and occlude and release lithium. Alternatively, a composite carbon material for a negative electrode material of a lithium ion secondary battery comprising a carbide layer embedded with metal compound particles and a composite obtained in this manner is obtained. Material cost, the capacity is higher than the theoretical capacity of graphite, high energy density and has excellent charge-discharge cycle characteristics, and, found to exhibit excellent initial irreversible capacity, thereby completing the present invention.

That is, the present invention comprises graphite core particles and a carbide layer formed on the surface of the graphite core particles,
In the carbide layer, metal particles or metal compound particles that occlude and release lithium, or metal particles or metal compound particles that occlude and release lithium and graphite fine particles are embedded,
The particle diameter aspect ratio is 1.0 to 2.0,
A composite carbon material for a negative electrode material of a lithium ion secondary battery is provided.

Further, the present invention provides a method in which graphite core particle powder, a carbonaceous material, and a meltable organic material are heated and kneaded to coat the surface of the graphite core particle with the coating layer composed of the carbonaceous material and the meltable organic material. And a first step of obtaining an elementary powder of graphite core particles having the coating layer,
A powder of graphite core particles having the coating layer and a metal particle or metal compound particle powder that occludes and releases lithium, or a metal inclusion that encloses metal particles or metal compound particles that occlude and release lithium. A powder of carbonaceous particles, and by friction and compression of the obtained mixed powder, the metal particles or metal compound particles are applied to the coating layer of the graphite core particle elementary powder having the coating layer, Alternatively, the metal-encapsulated particles are embedded and sized to obtain a sized powder of graphite core particles having a coating layer embedded with metal particles or metal compound particles having a particle diameter aspect ratio of 1.0 to 2.0. Two steps,
A sized powder of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is calcined and carbonized at 850 to 1,400 ° C. in a non-oxidizing atmosphere to obtain a negative electrode material for a lithium ion secondary battery A third step of obtaining a composite carbon material for use,
A composite carbon material for a negative electrode material of a lithium ion secondary battery is provided.

Further, the present invention provides a method in which graphite core particle powder, a carbonaceous material, and a meltable organic material are heated and kneaded to coat the surface of the graphite core particle with the coating layer composed of the carbonaceous material and the meltable organic material. And a first step of obtaining an elementary powder of graphite core particles having the coating layer,
A powder of graphite core particles having the coating layer and a metal particle or metal compound particle powder that occludes and releases lithium, or a metal inclusion that encloses metal particles or metal compound particles that occlude and release lithium. A powder of carbonaceous particles, and by friction and compression of the obtained mixed powder, the metal particles or metal compound particles are applied to the coating layer of the graphite core particle elementary powder having the coating layer, Alternatively, a sized powder of graphite core particles embedded with the metal-encapsulating carbonaceous particles and sized, and having a coating layer embedded with metal particles or metal compound particles having a particle diameter aspect ratio of 1.0 to 2.0. A second step to obtain;
A sized powder of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is calcined and carbonized at 850 to 1,400 ° C. in a non-oxidizing atmosphere to obtain a negative electrode material for a lithium ion secondary battery A third step of obtaining a composite carbon material for use,
The manufacturing method of the composite carbon material for negative electrode materials of a lithium ion secondary battery characterized by having.

  According to the present invention, the composite carbon for a negative electrode material of a lithium ion secondary battery having a capacity higher than the theoretical capacity of graphite, high energy density, excellent charge / discharge cycle characteristics, and excellent initial irreversible capacity. Material can be provided. Moreover, the subject of this invention can provide the manufacturing method which can manufacture the composite carbon material for negative electrode materials of such a lithium ion secondary battery industrially.

The method for producing a composite carbon material for a negative electrode material of a lithium ion secondary battery according to the present invention comprises heating and kneading graphite core particle powder, a carbonaceous material, and a fusible organic substance, to the surface of the graphite core particle. A first step of coating a coating layer made of a carbonaceous material and the fusible organic substance, and obtaining a granular powder of graphite core particles having the coating layer;
A powder of graphite core particles having the coating layer and a metal particle or metal compound particle powder that occludes and releases lithium, or a metal inclusion that encloses metal particles or metal compound particles that occlude and release lithium. The powder of carbonaceous particles is mixed, and the resulting mixed powder is rubbed and compressed to form the metal particles or the metal compound particles on the coating layer of the graphite core particle powder having the coating layer. Alternatively, the sized powder of graphite core particles having a coating layer in which the metal-containing carbonaceous particles are embedded and sized, and a metal particle or metal compound particle having a particle diameter aspect ratio of 1.0 to 2.0 is embedded. A second step of obtaining
A sized powder of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is calcined and carbonized at 850 to 1,400 ° C. in a non-oxidizing atmosphere to obtain a negative electrode material for a lithium ion secondary battery A third step of obtaining a composite carbon material for use,
It is a manufacturing method of the composite carbon material for negative electrode materials of the lithium ion secondary battery which has this.

  In the first step according to the method for producing a composite carbon material for a negative electrode material of a lithium ion secondary battery of the present invention, the graphite core particle powder, the carbonaceous material, and the meltable organic substance are heated and kneaded. In this step, the surface of the graphite core particles is coated with the coating layer made of a mixture of the carbonaceous material and the fusible organic material to obtain a granular powder of graphite core particles having the coating layer.

  The graphite core particle powder according to the first step is not particularly limited, and examples thereof include natural graphite or artificial graphite, artificial graphite electrode crushed products, coke, and mixtures thereof. Examples of the shape of the powder include a spherical shape or a scale-like shape, and those that have been previously pulverized, classified, or previously spheroidized may be used. Examples of the artificial graphite related to the graphite core particle powder include artificial graphite having a thermal history of 2500 ° C. or higher. The graphite core particle powder is preferably spherical or scale-like natural graphite or artificial graphite having a thermal history of 2500 ° C. or higher in that the charge / discharge capacity is increased.

  The graphite core particle powder is obtained, for example, by pulverizing and classifying natural graphite, artificial graphite, a pulverized product of artificial graphite electrode, coke or the like using a pulverizer such as a roller mill or an impact pulverizer.

  The aspect ratio of the graphite core particle powder is spheroidized in the second step, which will be described later, and the aspect ratio becomes 1.0 to 2.0, and this shape is maintained in the third step, which will be described later. Therefore, the aspect ratio of the graphite core particle powder used in the first step may be 2.0 or more. Therefore, the aspect ratio of the graphite core particle powder is not particularly limited, but when the aspect ratio of the graphite core particle powder is 2.0 or less, the filling property in the negative electrode of the lithium ion secondary battery becomes high. Therefore, it is preferable in terms of excellent charge / discharge capacity.

  The graphite core particle powder may be spheroidized in advance, but as a method of spheroidizing, for example, non-spherical graphite particles such as flaky graphite may be used at high speed using a hybridization system. A method of spheroidizing treatment by collision between particles, wear and compression by the impact method in airflow is mentioned. Examples of the graphite core particle powder that has been spheroidized in advance include spheroidized graphite manufactured by Chuetsu Graphite Industries Co., Ltd.

  The volume-based median diameter of the graphite core particle powder is preferably 1 to 30 μm. When the volume-based median diameter of the graphite core particle powder is larger than the above range, when a large current is discharged as a lithium ion secondary battery, the intragranular diffusion distance of lithium ions becomes long, and the output characteristics tend to be low. When preparing a negative electrode of a lithium ion secondary battery, it is difficult to make the film thickness thin and uniform during coating of the active material, and the output characteristics per volume are likely to be low. If the volume-based median diameter of the graphite core particle powder is smaller than the above range, the specific surface area becomes too large and the initial irreversible capacity tends to increase. In the present invention, the volume-based median diameter is a value measured by a laser diffraction type particle size distribution measuring apparatus (SALD 2000 manufactured by Shimadzu Corporation), and is a median diameter based on volume.

  The (002) plane spacing d (002) of the graphite core particle powder measured by the X-ray wide angle diffraction method is preferably 0.3500 nm or less, particularly preferably 0.3400 nm or less, more preferably 0.3358 nm or less. is there. When the interplanar spacing d (002) of the (002) plane measured by the X-ray wide angle diffraction method of the graphite core particle powder exceeds the above range, the discharge reversible capacity becomes less than 330 mAh / g. In the present invention, a CuKα ray monochromatized with a graphite monochromator is used to measure a wide-angle X-ray diffraction curve by a reflective diffractometer method, and the interplanar spacing d (002) is determined using a Gakushin method. Was measured.

  Examples of the carbonaceous material include pitch, tar, organic polymers such as phenolic resins that are liquid at room temperature, epoxy resins, and the like, and since the pitch is highly viscous, lithium is occluded and released in the next second step. Metal particles or metal compound particles powder that absorbs or releases metal particles or metal compound carbon particles that encapsulate and release lithium, and the carbonization by firing in the third step. It is preferable in that the carbonization rate at the time increases. The pitch related to the carbonaceous material is not particularly limited, and coal tar pitch, petroleum pitch, organic synthetic pitch obtained by polycondensation of a condensed polycyclic aromatic hydrocarbon compound, and heteroatom-containing condensed polycyclic aroma. An organic synthetic pitch obtained by polycondensation of a group hydrocarbon compound is exemplified, and among these, coal tar pitch is preferable.

  The softening point of the pitch relating to the carbonaceous material is preferably 70 to 250 ° C, particularly preferably 70 to 150 ° C, and more preferably 70 to 90 ° C, as measured by the ring and ball method. If the pitch softening point is less than the above range, in the second step, the pitch melt will adhere to the inner wall of the apparatus, and it is likely to cause a problem that continuous operation cannot be performed. Since the softened state of the pitch deteriorates, the dispersibility tends to deteriorate, and in the second step, spheroidization tends to be difficult. Moreover, you may use the pitch which adjusted the softening point to the said range by mixing 2 or more types of pitches from which a softening point differs, or adding tar.

  The pitch related to the carbonaceous material is a pitch in which free carbon is removed by a method such as filtration or a quinoline insoluble content is less than 1% in that the initial charge / discharge loss as a negative electrode material is reduced. Is preferred.

  The fusible organic substance according to the first step refers to an organic substance having a viscosity at a heating temperature of 20 Pa · s or less at the time of heating and kneading in the first step. Examples of the fusible organic substance include synthetic oil, natural oil, Examples include stearic acid, synthetic wax, and natural wax. The meltable organic matter preferably has a volatile content of 50% or more when heated to 400 ° C. in air, and a residual carbon ratio of 3% or less when heated to 800 ° C. in an inert atmosphere. is there. In the first step, when the graphite core particle powder and the carbonaceous material such as the pitch are heated and mixed, the carbonaceous material needs to be in a molten state with a low viscosity. The fusible organic material is used to reduce the viscosity. For this reason, the meltable organic material preferably has a small molecular weight, and is preferably one that prevents excessive pulverization of graphite core particles during heating and kneading. In addition, the fusible organic substance also acts as a lubricant in the second step, and has an effect of preventing the granulated powder from being pulverized. In addition, when considering the production aspect, the fusible organic substance also has an effect of suppressing metal wear of the apparatus and an effect of suppressing adhesion of pitch to the inside of the apparatus. Further, in the third step, when the sized powder of graphite core particles having a coating layer in which the metal or metal compound is embedded is calcined, the fusible organic matter contained in the sized powder is volatilized. There is also an effect of expelling oxygen around the sized powder by the gas pressure at the time, or an effect of reducing the oxygen concentration by reacting the fusible organic substance with oxygen. Therefore, the fusible organic substance is an organic substance that volatilizes 50% or more when heated to 400 ° C. in the air, and if the volatile content is less than 50%, the oxygen concentration around the granulated powder is not easily lowered. The crystallinity of carbon derived from the carbonaceous material is likely to be reduced, and the reversible capacity is also likely to be reduced. In addition, since the remaining carbon content in the meltable organic matter lowers the reversible capacity, it is desirable that the remaining coal rate is as low as possible. Therefore, the meltable organic matter was heated to 800 ° C. in an inert atmosphere. It is preferable that the remaining charcoal rate at the time is 3% or less. In addition, this inert atmosphere refers to the atmosphere of inert gas, such as nitrogen gas, helium gas, and argon gas.

The blending amount of the carbonaceous material at the time of heat kneading in the first step is preferably 5 to 40 parts by weight with respect to 100 parts by weight of the graphite core particle powder, and 5 to 30 parts by weight. Particularly preferred is 5 to 25 parts by weight. When the blending amount of the carbonaceous material is less than the above range, it is difficult to uniformly coat the surface of the graphite core particles with the carbonaceous material, and the fine part of the particle size distribution is likely to be broad and easily spread. .
Further, if the amount of the carbonaceous material exceeds the above range, the particles are excessively aggregated, so that it is difficult to disintegrate individual granulated particles one by one, and the particle size of the composite carbon material Tends to be large, the thickness of the coating layer tends to be uneven, and the powder of the carbonaceous material alone tends to exist. In addition, since a coarse lump is formed, the composite carbon material needs to be pulverized, and the initial charge / discharge loss tends to increase as battery characteristics. Further, in the second step, excess carbonaceous material adheres to the inside of the apparatus, so that a problem that makes continuous operation difficult is likely to occur.

  The blending amount of the meltable organic substance in the first step is preferably 1 to 30 parts by weight, and preferably 3 to 20 parts by weight with respect to 100 parts by weight of the graphite core particle powder. Particularly preferred. When the blending amount of the fusible organic material is less than the above range, in the second step, external energy is excessively applied, and as a result, a lot of fine powder is likely to remain, and it is difficult to remove the fine powder. If it exceeds the above range, it is difficult to size the graphite core particles having the coating layer in the second step, and a coarse lump is likely to be formed.

In the first step, the graphite core particle powder, the carbonaceous material, and the meltable organic substance are kneaded while being heated. As a method of kneading the graphite core particle powder, the carbonaceous material, and the meltable organic substance in the first step,
(I) A method in which the graphite core particle powder and the meltable organic substance are first heat-kneaded and then the carbonaceous material is added and heat-kneaded. (Ii) The graphite core particle powder and the carbonaceous material are previously added. (Iii) A method of heat-kneading the graphite core particle powder, the carbonaceous material and the meltable organic material,
Etc. Among these, the methods (i) and (iii) are preferable in that excessive pulverization of the graphite core particle powder can be prevented.

  The heating temperature at the time of heat kneading in the first step is a temperature exceeding the softening point of the carbonaceous material, preferably 20 ° C. or more higher than the softening point of the carbonaceous material.

  An example of the operation of the heat kneading operation in the first step is as follows. The graphite core particle powder, the carbonaceous material and the meltable organic substance are put into a kneading apparatus, and the temperature in the apparatus container is set to the carbon temperature while kneading. The temperature is raised to a predetermined temperature exceeding the softening point of the material and kneaded sufficiently while heating. The time for heating and kneading is appropriately selected depending on the capacity of the kneading apparatus, the shape of the kneading blade, the graphite core particle powder, the carbonaceous material and the meltable organic material, etc., but exceeds the melting point of the carbonaceous material. The temperature is usually 10 minutes to 2 hours. After heating and kneading, the mixture is cooled to room temperature to obtain a graphite core particle powder having the coating layer.

  The kneading apparatus for performing heat kneading in the first step is not particularly limited as long as it can normally stir or knead while heating the powder, and is provided with a mixer, a kneader, and a pressure lid. A pressure kneader may be used.

  In this way, in the first step, the graphite core particle powder, the carbonaceous material, and the fusible organic substance are heated and kneaded to thereby form the carbonaceous material on the particle surface of the graphite core particles. And the coating layer which consists of this meltable organic substance is coat | covered, and the granular powder of the graphite core particle which has this coating layer is obtained.

  The thickness of the covering layer of the elementary powder of graphite core particles having the covering layer obtained by the first step is preferably 0.3 μm or less, particularly preferably 0.01 to 0.2 μm. When the thickness of the covering layer of the graphite core particle powder having the covering layer is within the above range, the capacity of the lithium ion secondary battery is hardly deteriorated.

  The volume-based median diameter measured by the laser diffraction method of the graphite core particle elementary powder having the coating layer obtained in the first step is not particularly limited, but is approximately 5 to 40 μm.

  Next, the second step according to the method for producing the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention is performed.

  In the first embodiment of the second step, the graphite core particle elementary powder having the coating layer is mixed with the metal particle or metal compound particle powder that occludes and releases lithium, and the resultant mixture is obtained. By rubbing and compressing the powder, the metal particles or metal compound particles are embedded in the coating layer of the graphite core particles having the coating layer, and the metal particles or metal compound particles that absorb and release lithium are embedded. This is a step of obtaining a sized powder of graphite core particles having a coating layer (hereinafter also referred to as second step (A)). In the second step (A), the graphite core particles may be rubbed and compressed to produce fine graphite particles. In such a case, the fine graphite particles are also separated from the coating layer. Embedded in. Hereinafter, the metal particles that occlude and release the lithium according to the second step (A) are also referred to as the metal particles according to the second step (A), and also according to the second step (A). The metal compound particles that occlude and release lithium are also referred to as metal compound particles according to the second step (A). That is, the second step (A) is a step of directly embedding the metal particles or metal compound particles that occlude and release lithium in the coating layer.

  Alternatively, the second embodiment of the second step is the following: a metal-encapsulated carbonaceous particle including a graphite core particle elementary powder having the coating layer, and metal particles or metal compound particles that occlude and release lithium. Are mixed, and the resulting mixed powder is rubbed and compressed to embed the metal-containing carbonaceous particles in the coating layer of the graphite core particles having the coating layer, and the metal particles or metal compound This is a step of obtaining a sized powder of graphite core particles having a coating layer in which the particles are embedded (hereinafter also referred to as second step (B)). In the second step (B), the graphite core particles may be rubbed and compressed to produce graphite fine particles. In such a case, the graphite fine particles may also be used as the coating layer. Embedded in. Hereinafter, the metal-encapsulated carbonaceous particles encapsulating the metal particles or metal compound particles that occlude and release lithium are also referred to as metal-encapsulated carbonaceous particles according to the second step (B). That is, in the second step (B), the metal particles or metal compound particles that occlude and release lithium are embedded in the coating layer through the metal-containing carbonaceous particles according to the second step (B). It is.

  In addition, in the second steps (A) and (B), the mixed powder is rubbed and compressed, whereby the graphite core particle elementary powder having the coating layer has a particle diameter aspect ratio of 1.0 to 2. Sized to 0.0.

  As the metal particles according to the second step (A), those having low crystallinity such as Si and amorphous Si have a small expansion amount when occluded lithium ions and a small amount of contraction when lithium ions are released, and cycle characteristics. Is preferable in that it is good.

Examples of the metal compound particles according to the second step (A) include SiO _x , and metal alloys such as Si—Mg, Si—Al, and Si—Fe containing silicon. Among these, SiO _x (wherein 0.8 ≦ x ≦ 1.5), the calcining carbonization in the third step can cause disproportionation reaction of SiO to form fine Si, and SiO ₂ is an expansion relaxation material. Is preferable, and SiO (wherein x = 1) is particularly preferable.

  In the second step (A), the metal particles according to the second step (A) and the metal compound particles according to the second step (A) may be combined.

The maximum particle diameter of the metal particles according to the second step (A) and the metal compound particles according to the second step (A) is preferably 2 μm or less, and particularly preferably 0.1 to 2 μm. When the metal compound powder according to the second step (A) is SiO _x , it is separated into a fine Si phase and a SiO ₂ phase by calcination carbonization in the third step. In order to ensure conductivity, the particle size of the metal compound powder according to the second step (A) is preferably as small as possible. As the particle size of the metal compound powder according to the second step (A) is larger, the Si phase at the center of the particle is covered with the SiO ₂ phase of the insulator, and the function of insertion / extraction of lithium as the active material is increased. It becomes easy to be disturbed.
Further, when the thickness of the carbide layer of the composite carbon material exceeds 3 μm, capacity deterioration is likely to occur, and it is difficult to form a coating layer having a thickness of 3 μm. Therefore, the thickness of the carbide layer of the composite carbon material is preferably 3 μm or less, but the maximum particle diameter of the metal particles according to the second step (A) and the metal compound particles according to the second step (A) is 2 μm. When the thickness exceeds 50 μm, it is difficult to embed the metal particles according to the second step (A) and the metal compound particles according to the second step (A) in the coating layer having a thickness of 3 μm or less.

  In the second step (A), the mixing amount of the metal particles according to the second step (A) or the metal compound particles according to the second step (A) Preferably it is 0.5-50 weight part with respect to 100 weight part, Most preferably, it is 1-30 weight part. If the mixing amount of the metal particles according to the second step (A) or the metal compound particles according to the second step (A) is less than the above range, it is difficult to obtain an effect of increasing the capacity, while the above range. If it exceeds 1, it will be difficult to uniformly impart conductivity to a metal such as Si, and cycle characteristics will tend to be low.

  The metal-encapsulated carbonaceous particles according to the second step (B) are substances in which metal particles or metal compound particles that occlude and release lithium become carbides by firing carbonization of pitches, polymers, etc., or carbides such as pitches, polymers, etc. The particles are encapsulated in the particles.

  In the metal-encapsulated carbonaceous particles according to the second step (B), the metal particles or the substance in which the metal compound particles are encapsulated is a baked polymer such as pitch, phenol resin, epoxy resin, furan resin, or the like. Substances that become carbides by carbonization, or carbides such as pitch and polymer, these are graphite fine particles in the carbide layer of the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by performing the third step. Will exist.

In the metal-encapsulated carbonaceous particles according to the second step (B), the encapsulated metal particles include Si. In addition, in the metal-encapsulated particles according to the second step (B), examples of the encapsulated metal compound powder include SiO _x , metal alloys such as Si—Mg, Si—Al, and Si—Fe containing silicon. Of these, SiO _x (wherein 0.8 ≦ x ≦ 1.5) means that disproportionation reaction of SiO occurs and fine Si is formed by calcination carbonization in the third step. SiO ₂ is preferable in that it functions as an expansion relaxation material, and SiO _x (wherein x = 1) is particularly preferable.

  The metal-encapsulated carbonaceous particles according to the second step (B) may be those in which both metal particles and metal compound particles are encapsulated.

  The maximum particle size of the metal-containing carbonaceous particles according to the second step (B) is preferably 2 μm or less, and particularly preferably 0.1 to 2 μm. If the thickness of the carbide layer of the composite carbon material exceeds 3 μm, capacity deterioration is likely to occur, and it is difficult to form a coating layer having a thickness of 3 μm. Therefore, the thickness of the carbide layer of the composite carbon material is Although it is preferably 3 μm or less, when the maximum particle diameter of the metal-containing carbonaceous particles according to the second step (B) exceeds 2 μm, the coating layer having a thickness of 3 μm or less is formed on the second layer (B). It tends to be difficult to embed the metal-containing carbonaceous particles according to the above.

As a method for producing the metal-containing carbonaceous particles according to the second step (B),
(I) The powder of the metal particles or metal compound particles and pitch are mixed, heated and kneaded, the metal particles or metal compound particles are mixed in the molten pitch, then cooled and solidified, pulverized, Next, a method of oxidizing the surface to make it infusible,
(II) a method of polymerizing and solidifying the metal particles or the metal compound particles in a state of being dispersed in the monomer,
(III) A method in which the metal-encapsulated particles obtained by the method (I) or (II) are calcined and carbonized,
Etc. In the method (II), the powder of the carbon particles such as graphite, acetylene black, carbon black, and non-oxidized powder, pitch, resin, polymer, etc. It is also possible to use a powder of a substance that carbonizes by firing and carbonizing in a neutral atmosphere.

  In the second step, the use of the metal-containing carbonaceous particles according to the second step (B) increases the shape stability of the particles during firing carbonization in the third step, and a composite carbon material Since a carbide such as fine graphite can be embedded in the carbide layer, it is preferable in terms of providing conductivity and enhancing expansion relaxation.

  In the second step (B), the mixing amount of the metal-containing carbonaceous particles according to the second step (B) is preferably 0 with respect to 100 parts by weight of the elementary powder of graphite core particles having the coating layer. 0.5 to 50 parts by weight, particularly preferably 1 to 30 parts by weight. If the mixing amount of the metal-encapsulating carbonaceous particles according to the second step (B) is less than the above range, it is difficult to obtain the effect of increasing the capacity. It tends to be difficult to impart conductivity to the metal, and the cycle characteristics tend to be low.

  In the second step, the graphite core particles having the coating layer and the metal particles according to the second step (A) or the metal compound particles according to the second step (A), or The metal-containing carbonaceous particles according to the second step (B) are mixed, and the resulting mixed powder is rubbed and compressed.

  In the second step, the mixed powder is repeatedly rubbed and compressed using a mechano-fusion system (manufactured by Hosokawa Micron Corporation), a hybridizer (manufactured by Nara Machinery Co., Ltd.), etc., and externally applied to the mixed powder. Continue adding mechanical energy. Accordingly, the powder of the graphite core particles having the coating layer is coated with the metal particles according to the second step (A) or the metal compound particles according to the second step (A), or The metal-encapsulated carbonaceous particles according to the second step (B) and graphite fine particles generated by the friction and compression of the graphite core particles are embedded. It is closed by adding mechanical energy, and the particle diameter aspect ratio is sized to 1.0 to 2.0.

  Thus, by the second step, the particle diameter aspect ratio is 1.0 to 2.0, and the graphite fine particles generated by friction and compression of the graphite core particles, the metal particles or A sized powder of graphite core particles having a coating layer embedded with metal compound particles is obtained.

  A device for friction and compression of the mixed powder, that is, a specific device for applying mechanical energy from the outside is not limited to the above device, and can mix and compress the mixed powder. If it is.

  Examples of a method for imparting mechanical energy to the mixed powder include a method using a hybridizer (manufactured by Nara Machinery Co., Ltd.) shown in FIG. In the hybridizer shown in FIG. 1, graphite core particles having the coating layer, metal particles according to the second step (A) or metal compound particles according to the second step (A), Or the metal inclusion | inner_cover carbonaceous particle which concerns on this 2nd process (B) is thrown in from the raw material inlet 1, and the rotation part 8 is rotated for 1 minute-3 minutes at the rotational peripheral speed 20-100 m / s. At this time, an elementary powder of graphite core particles having the coating layer put into the gap between the drum 6 and the rotating portion 8 through the raw material circulation path 2, the metal particles according to the second step (A), or the second Due to the difference in rotational speed between the drum 6 and the rotating portion 8 with respect to the powder of the metal compound particles according to the step (A) or the mixed powder with the metal-containing carbonaceous particles according to the second step (B). Mechanical energy is applied to the mixed powder by the generated frictional force, compressive force, and impact force. In addition, 3 is a stator, 4 is a jacket, 5 is a raw material discharge | emission part, 7 is a braid | blade.

  The temperature inside the hybridizer when mechanical energy is applied to the mixed powder by the hybridizer shown in FIG. 1 increases due to the application of mechanical energy, but the carbonaceous material of the first step It is preferable to adjust the temperature to a softening point + 20 ° C. or lower. When the temperature in the hybridizer exceeds the softening point of the carbonaceous material + 20 ° C., the carbonaceous material melts and elutes from the gaps between the granulated particles, and the eluted carbonaceous material enters the hybridizer. Since it becomes easy to adhere, regular continuous operation tends to be difficult. Note that the adjustment to a temperature below the softening point of the carbonaceous material + 20 ° C. means, for example, that when the softening point of the carbonaceous material is 90 ° C., the temperature inside the hybridizer is set to 110 ° C. or below. is there.

  The rotational peripheral speed of the rotating part 8 when mechanical energy is applied to the mixed powder by the hybridizer shown in FIG. 1 is preferably 20 to 100 m / s. When the rotating peripheral speed of the rotating unit 8 is less than 20 m / s, the mechanical energy received by the mixed powder is small, the graphite fine particles, the metal particles according to the second step (A), or the second step. It becomes difficult to embed the metal compound particles according to (A) or the metal-encapsulated carbonaceous particles according to the second step (B), and even if it exceeds 100 m / s, the case of 100 m / s and lithium ion There is no great difference in the performance of the composite carbon material for the negative electrode material of the secondary battery, and the upper limit is preferably set to 100 m / s in consideration of cost, device safety, and the like. The treatment time when mechanical energy is applied to the mixed powder with the hybridizer is preferably 30 seconds to 5 minutes, particularly preferably 1 minute to 3 minutes. When the treatment time is less than 30 seconds, embedding is difficult to occur, and even when it exceeds 5 minutes, the physical properties of the carbon particle powder for a lithium ion secondary battery negative electrode material hardly change. The time is particularly preferably 2 minutes or less.

  Further, in the second step, when the frictional force and compressive force on the mixed powder are too strong and the graphite core particles having the coating layer are destroyed, the first step is performed in order to reduce wear. The meltable organic substance relating to the process can be added. At that time, the amount of the meltable organic substance to be charged is appropriately determined in consideration of cost and processing time.

In the second step, the processing conditions for friction and compression of the mixed powder, for example, when using the hybridizer, the rotational peripheral speed, processing time, processing temperature, etc. of the rotating unit 8 are set as described above. By appropriately selecting as described above, the particle diameter aspect ratio can be adjusted to 1.0 to 2.0.
Since the particle size aspect ratio obtained by performing the second step is adjusted to a particle size aspect ratio of 1.0 to 2.0, the shape is maintained even in the next third step, so that the third step can be performed. The composite carbon material for negative electrode material has a small particle diameter aspect ratio of 1.0 to 2.0, and can exhibit high capacity characteristics as a composite carbon material for negative electrode material of a lithium ion secondary battery.

  In the graphite core particles having a coating layer in which the metal particles or metal compound particles obtained by performing the second step are embedded, the thickness of the coating layer is 3 μm or less in that capacity deterioration is unlikely to occur. It is particularly preferably 0.5 to 1.5 μm.

  Next, the third step according to the method for producing the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention is performed. In the third step, the sized powder of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is calcined and carbonized at 850 to 1,400 ° C. in a non-oxidizing atmosphere to obtain lithium ions. This is a step of obtaining a composite carbon material for a negative electrode material of a secondary battery.

  In the third step, the calcining carbonization temperature when calcining the carbonized particles of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is 850 to 1,400 ° C., preferably 850 1,350 ° C., particularly preferably 900 to 1,100 ° C. In the third step, if the calcination carbonization temperature is less than the above range, volatilization of the fusible organic matter is not sufficient, and low-molecular organic unburned components in the carbonaceous material remain, and lithium ion The secondary battery is deteriorated in charge / discharge efficiency and cycle characteristics. In the third step, if the firing carbonization temperature exceeds the above range, a metal such as Si reacts with carbon to form a metal carbide such as SiC, which is not preferable.

In particular, when the metal compound particles embedded in the coating layer are SiO _x , the SiO _x is heated by the calcination carbonization in the third step, so that the SiO _x becomes Si and SiO ₂ by a disproportionation reaction. Separate into two phases. For example, when x = 1, the following formula:
2SiO → Si + SiO ₂
It is as follows.
This disproportionation reaction proceeds at a temperature higher than 800 ° C., and the higher the temperature, the larger the Si phase crystals and the smaller the half width of the Si (220) peak.
Further, at a temperature higher than 1400 ° C., Si reacts with carbon and changes to SiC. Since SiC is completely inactive with respect to insertion of lithium, when SiC is generated, the capacity of the active material is lowered.
Therefore, when the metal compound particles embedded in the coating layer are SiO _x , the firing temperature is 850 to 1,400 ° C., preferably 850 to 1,350 ° C., particularly preferably 900 to 1,100 ° C. It is.

  In the third step, calcination carbonization is performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere is an inert gas atmosphere such as nitrogen gas, helium gas, or argon gas, or a carbonaceous material such as the pitch. Is an atmosphere that carbonizes without oxidative consumption.

  Thus, in the third step, the metal particles or metal compound particles are embedded by firing and carbonizing the granulated graphite core particles having the coating layer in which the metal particles or metal compound particles are embedded. For the negative electrode material of the lithium ion secondary battery of the present invention, the fusible organic material is volatilized from the graphite core particles having the coating layer, and the carbonaceous material constituting the coating layer is carbonized to become a carbide layer. A composite carbon material is obtained.

  In addition, when there is an uncarburized substance in the metal-containing carbonaceous particles according to the second step (B) that has the second step (B), in the third step, the metal particles or the metal compound In addition to volatilization of the fusible organic matter from the graphite core particles having the coating layer in which the particles are embedded, the carbonaceous material constituting the coating layer is carbonized to form a carbide layer. The uncarburized substance in the metal-encapsulated carbonaceous particles in the second step (B) is carbonized to become graphite fine particles, and the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention is obtained.

  After performing the third step, the composite carbon material powder for the negative electrode material of the lithium ion secondary battery obtained by performing the third step can be crushed or classified as necessary. The crushing device for performing the crushing is not particularly limited, and devices such as a turbo mill (manufactured by Matsubo Co., Ltd.), a quick mill (manufactured by Seishin Enterprise Co., Ltd.), a super rotor (manufactured by Nisshin Engineering Co., Ltd.), etc. Illustrated. In the classification, the composite carbon material for the negative electrode material of the lithium ion secondary battery can be adjusted to a minimum particle diameter of 1 μm or more, a maximum particle diameter of 55 μm or less, and a median diameter of 5 to 25 μm.

Thus, the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by performing the method for producing the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention, that is, the lithium ion secondary battery of the present invention. The composite carbon material for negative electrode material comprises graphite core particles and a carbide layer formed on the surface of the graphite core particles,
In the carbide layer, metal particles or metal compound particles that occlude and release lithium, or metal particles or metal compound particles that occlude and release lithium and graphite fine particles are embedded,
The particle diameter aspect ratio is 1.0 to 2.0.
It is a composite carbon material for a negative electrode material of a lithium ion secondary battery.

In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, the particle diameter aspect ratio is 1.0 to 2.0, preferably 1.0 to 1.6, particularly preferably 1.0 to 1.3. is there. When the particle aspect ratio is in the above range, the chargeability at the negative electrode is balanced with the electrolyte content, and the charge / discharge capacity is increased. When the particle diameter aspect ratio is larger than 2.0, the graphite layer direction is likely to be oriented parallel to the substrate when the active material layer is applied, the active material layer is easily peeled off from the substrate, and the cycle characteristics deteriorate. Arise.
The particle diameter aspect ratio is adjusted by selecting the friction or compression conditions in the second step, for example, the rotational speed of the hybridizer, the graphite core particle powder in the first step, and the carbonaceous material. Is possible. In the present invention, in SEM (scanning electron microscope) observation, 100 particles are arbitrarily selected from the composite carbon material for a negative electrode material, and an average value of values obtained by dividing the longest diameter of the particles by the minimum diameter, The particle diameter is the aspect ratio.

Si is mentioned as a metal particle which occludes and discharge | releases this lithium which concerns on the composite carbon material for negative electrode materials of the lithium ion secondary battery of this invention. In addition, as the metal compound particles that occlude and release lithium according to the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention, SiO _y or Si—Mg containing silicon, Si—Al, Si—Fe Among them, SiO _y (wherein 0.8 ≦ y ≦ 1.5) is particularly preferable. Since the silicon and silicon oxide particles generated by the disproportionation reaction of silicon oxide are fine in Si and SiO ₂ functions as an expansion relaxation material, the lithium ion secondary battery has a high capacity and a long capacity. This is particularly preferable in terms of life.

  In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, the thickness of the carbide layer is preferably 3 μm or less from the viewpoint that capacity deterioration hardly occurs, particularly 0.5 to 1.5 μm. preferable.

  In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, the graphite core particles are preferably natural graphite or artificial graphite having a thermal history of 2500 ° C. or higher from the viewpoint of high battery capacity.

  In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, it is the first time that the carbide layer is made of a carbide having a pitch from which free carbon is removed or a pitch having a quinoline insoluble content of less than 1%. This is preferable in that charge / discharge loss is reduced.

  In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, the maximum particle diameter of the metal particles or metal compound particles that occlude and release lithium is 2 μm or less in that the conductivity is increased. Preferably, it is 0.1-1 micrometer. The amount of the metal particles or metal compound particles contained in the composite carbon material is preferably 2 to 20% by weight with respect to the composite carbon material. When the amount of metal particles or metal compound particles contained in the composite carbon material is less than 2% by weight, there is no increase in charge / discharge capacity, and when it exceeds 20% by weight, capacity deterioration tends to occur.

  In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, the ratio of the thickness of the carbide layer to the maximum particle diameter of the metal particles or metal compound particles that occlude and release lithium (thickness of the carbide layer / metal particles) Alternatively, the maximum particle diameter of the metal compound particles) is preferably 1.5 to 4 from the viewpoint that capacity deterioration hardly occurs, and particularly preferably 1.5 to 2. The ratio of the thickness of the carbide layer to the maximum particle size of the metal particles or metal compound particles that occlude and release lithium is obtained in the first step, the amount of the carbonaceous material in the first step. The thickness of the coating layer of graphite core particles having the coating layer, the particle size of the metal particles according to the second step (A) or the metal compound particles according to the second step (A), the second step (B) By adjusting the particle size of the metal particles or metal compound particles encapsulated in the metal-encapsulated carbonaceous particles according to the above, or by adjusting the conditions for friction and compression of the powder in the second step, etc. It becomes possible.

In the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, the tapping density is preferably 1.0 to 1.3 g / cm ³ .

It is preferable that the BET specific surface area of the composite carbon material for negative electrode materials of the lithium ion secondary battery of the present invention is 1.5 to ⁵ m ² / g. If the BET specific surface area of the composite carbon material is less than the above range, the reaction area required for desorption / insertion of lithium ions is small, so that it is difficult to maintain the output characteristics. It becomes too large and a large loss is likely to occur during the first charge. The specific surface area is adjusted by adjusting the thickness of the coating layer to be coated in the first step, the friction or compression conditions in the second step, for example, the rotation speed in the hybridizer, and the pulverizer after performing the third step. It is possible to adjust the pulverizing conditions by adjusting the pulverizing conditions, and after the third step, classification is performed and the classification conditions are adjusted. The BET specific surface area is a value calculated by the BET 10-point method using N ₂ gas. In the present invention, the nitrogen adsorption specific surface area is large after performing preliminary drying at 350 ° C. for 30 minutes under a nitrogen flow with respect to the measurement object using a surface area meter (manufactured by Shimadzu Corporation, fully automatic surface area measuring device). This is a value measured by a nitrogen adsorption BET 10-point method using a gas flow method using a nitrogen-helium mixed gas accurately adjusted so that the value of the relative pressure of nitrogen with respect to atmospheric pressure is 0.3.

  The volume-based median diameter D50 of the composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention is preferably 5 to 30 μm, particularly preferably 10 to 25 μm, and more preferably 10 to 20 μm. When the volume-based median diameter of the composite carbon material is less than 5 μm, dispersion in the liquid during slurry preparation tends to be poor, and the specific surface area becomes small. On the other hand, when the volume-based median diameter of the composite carbon material exceeds 30 μm, when a large current is discharged as a lithium ion secondary battery, the intragranular diffusion distance of lithium ions becomes long and the output characteristics tend to be low. In addition, the thickness of the active material applied is limited, and when designing an electrode structure with excellent output characteristics, it is difficult to apply a thin and uniform active material layer. In the present invention, the volume-based median diameter is a median diameter measured by a laser diffraction method, and is a median diameter measured by SALD manufactured by Shimadzu Corporation. The volume-based median diameter is adjusted by adjusting the particle diameter of the graphite core particle powder and the blending amount of the carbonaceous material in the first step, and pulverizing using a pulverizer after performing the third step. Then, it is possible to adjust the pulverization conditions, perform classification after performing the third step, and adjust the classification conditions.

  The particle diameter aspect ratio of the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention is preferably 1.0 to 2.0, particularly preferably 1.0 to 1.6, and more preferably 1.0 to 1.3. If the particle diameter aspect ratio of the composite carbon material exceeds 2.0, the graphite layer direction is likely to be aligned parallel to the base during active material coating, and the active material layer is easily peeled off from the base, resulting in cycle characteristics. It tends to be lower.

  In the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention, the crystallinity inside the particles will be discussed in terms of the plane spacing d (002) of the (002) plane of the graphite crystallite obtained by the X-ray diffraction method. Is reasonable. The interlayer distance of the d (002) plane of the graphite crystallite of the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention is preferably 0.3400 nm or less, particularly preferably 0.3370 nm or less, and more preferably 0.8. 3354-0.3365 nm. When the interlayer distance of the d (002) plane of the graphite crystallite of the composite carbon material for the negative electrode material of the lithium ion secondary battery of the present invention exceeds the above range, the discharge reversible capacity tends to be small. Natural graphite exhibits a value close to 0.3354 nm of ideal graphite, and graphitizable coke can be reduced to 0.3365 nm or less by performing a heat treatment at 2,800 ° C. or higher. In the present invention, the interlayer distance of the d (002) plane of the graphite crystallite is such that CuKα rays are used as an X-ray source, high-purity silicon is used as a standard material, and the peak position of the diffraction pattern on the (002) plane is half It is a value calculated from the price range based on the Gakushin method.

  The example of the composite carbon material for negative electrode materials of the lithium ion secondary battery of this invention is demonstrated with reference to FIGS. 3 to 5, 21 is a composite carbon material for a negative electrode material of the lithium ion secondary battery of the present invention, 22 is a graphite core particle, 24 is a carbide layer, and 23 is embedded in the carbide layer 24. Si particles (metal particles that occlude and release lithium metal) are shown. The Si particles 23 may partially protrude from the carbide layer 24 as shown in FIG. 3, or may be entirely embedded in the carbide layer 24 as shown in FIG. 4 or FIG. Good. Further, the Si particles may be in contact with the graphite core particles 22 as shown in FIG. 3 or FIG. 4, or may not be in contact with the graphite core particles as shown in FIG. Further, even if the thickness of the carbide layer 24 is smaller than the particle size of the Si particles 23 as shown in FIG. 3, or the same as the particle size of the Si particles 23 as shown in FIG. Alternatively, it may be larger than the particle size of the Si particles as shown in FIG. 3 to 5 are schematic cross-sectional views of the composite carbon material 21 for a negative electrode material of the inventive lithium ion secondary battery.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects. In addition, these Examples show one embodiment of this invention, and this invention is not limited to these.

Example 1
<Manufacture of composite carbon material for negative electrode material of lithium ion secondary battery>
(First step)
When 100 parts by weight of spherical natural graphite having an average particle diameter of 13.8 μm and a graphite crystallite d (002) plane distance of 0.3358 nm is heated to 400 ° C. in the air as a fusible organic substance, 70 % Volatilized and 5 parts by weight of molten machine oil with a residual carbon ratio of 0.6% when heated to 800 ° C. in an inert atmosphere is mixed and heated and kneaded in a kneader at 150 ° C. for 30 minutes. Thereafter, 10 parts by weight of coal tar pitch (softening point: 90 ° C.) is added to 100 parts by weight of spherical natural graphite, and further heated and kneaded at 150 ° C. for 30 minutes, and then cooled to 25 ° C. to obtain powder A. It was.

(Second step)
Next, 100 parts by weight of the obtained powder A and SiO (atomic ratio Si / O = 1.0) adjusted to an average particle diameter of 0.3 μm and a maximum particle diameter of 0.5 μm were mixed with 25 parts by weight. A mixed powder was obtained.

  Next, the mixed powder is put into the hybridizer apparatus, and the mixture is treated at a rotational speed of 8000 rpm (rotational peripheral speed: 100 m / s) for 3 minutes while maintaining the maximum temperature in the apparatus at 75 ° C. ± 5 ° C. The powder was taken out from the apparatus and cooled to 25 ° C. to obtain Powder B.

(Third process)
The obtained powder B was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Next, it is crushed by a crushing device (Nisshin Engineering Co., Ltd., Super Rotor), classified by a classification device (Nisshin Engineering Co., Ltd., turbo classifier), and composite carbon for negative electrode material of a lithium ion secondary battery. Material C was obtained. The physical properties are shown in Tables 1 and 2.

Measuring method of each characteristic (1) Volume-based median diameter measured with an average particle diameter laser diffraction type particle size distribution measuring apparatus (SALD2000, manufactured by Shimadzu Corporation) (2) d (002) (nm) by X-ray diffraction method
The measurement by the X-ray diffraction method is performed using a Cu (Kα ray) graphite monochromator as a target, a slit as a diverging slit = 1 degree, a light receiving slit = 0.1 mm, and a scattering slit = 1 degree. A surface interval d (002) is obtained.
(3) Tap density (g / cm ³ )
This is a value after 5 g of composite carbon material particles are placed in a 25 ml graduated cylinder, and tapping is repeated 1000 times with a gap of 10 mm from the diaphragm.
(4) Specific surface area (m ² / g)
Using a surface area meter (Shimadzu fully automatic surface area measuring device), after performing preliminary drying at 350 ° C. for 30 minutes under nitrogen flow, the relative pressure value of nitrogen relative to atmospheric pressure becomes 0.3. It is a value measured by a nitrogen adsorption BET 10-point method by a gas flow method using a nitrogen-helium mixed gas adjusted accurately as described above.
(5) Aspect ratio By scanning electron microscope observation, 100 particles are arbitrarily selected, the maximum diameter of the particles is divided by the minimum diameter, and the average value is defined as the particle diameter aspect ratio.
(6) Thickness of coating layer Thickness of coating layer = (average particle size of composite particles−average particle size of raw material graphite core particles) / 2
(7) Measurement of Si amount and SiC amount (a) The produced composite carbon material particles (about 1 g) are weighed to form powder a, and this powder a and 100 g of solid sodium hydroxide are placed in a glass beaker. The mixture is heated and stirred with a magnetic stirrer at 60 ° C. for 1 hour, cooled, washed with purified water, and the filtration residue (carbon, SiC, Si) from which sodium hydroxide has been removed is dried to obtain powder b. Weigh the dried powder b.
(B) The dried powder was stirred in a hydrofluoric acid solution at 25 ° C. for 1 hour, washed with purified water to remove the hydrofluoric acid, and the filtered residue (carbon, SiC) was dried to obtain a powder. c is obtained. Weigh the dried powder c.
((Weight of powder b−weight of powder c) / weight of powder a) × 100
Was the amount of Si (% by weight).
((Weight of powder a−weight of powder b) / weight of powder a) × 100
Was the SiOx amount (% by weight).
(C) Measurement of SiC amount Powder c is incinerated.
(Weight of ashing residue / weight of powder a) × 100 was defined as the SiC amount (% by weight).
(8) Measurement of Volatile Content According to JIS-M8812 industrial analysis method of coals and cokes, a weight loss rate after heat treatment at 900 ° C. for 30 minutes using a magnetic crucible was defined as a volatile content.

<Creation of lithium ion secondary battery>
(Preparation of slurry)
An appropriate amount of 1 wt% carboxymethylcellulose (CMC) aqueous solution as a thickener is added to 100 parts by weight of the composite carbon material C for negative electrode material of the lithium ion secondary battery obtained as described above, and stirred for 30 minutes. After mixing, an appropriate amount of 40 wt% styrene-butadiene rubber (SBR) aqueous solution was added as a binder and stirred for 5 minutes to prepare a negative electrode mixture paste.

(Production of working electrode)
The obtained negative electrode mixture paste was applied onto a copper foil (current collector) having a thickness of 18 μm and heated to 130 ° C. in a vacuum to completely evaporate the solvent. The obtained sheet was rolled with a roller press so that the electrode plate density was 1.5 g / cc, and punched with a punch to obtain a working electrode.

(Preparation of counter electrode)
Under an inert atmosphere, a lithium metal foil was punched into a nickel mesh (current collector) punched out with a punch to obtain a counter electrode.

(Preparation of reversible discharge capacity button type battery)
Using the above working electrode and counter electrode, a button type battery shown in FIG. 2 as an evaluation battery was assembled in an inert atmosphere. As the electrolytic solution, a 1: 1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in which 1 mol / dm ³ of the lithium salt LiPF ₆ was dissolved was used. Charging current density 0.2 mA / cm ^2, after finishing the constant current charging at a final voltage 5 mV, holding a constant potential to the lower limit current 0.02 mA / cm ^2. The discharge was a constant current discharge to a final voltage of 1.5 V at a current density of 0.2 mA / cm ² , and the discharge capacity after the end of 5 cycles was defined as a reversible discharge capacity. In FIG. 2, 9 is a negative electrode side stainless steel cap, 10 is a negative electrode, 11 is a copper foil, 12 is an insulating gasket, 13 is an electrolyte-impregnated separator, 14 is a nickel mesh, 15 is a positive electrode side stainless steel cap, and 16 is a positive electrode.

(Production of button-type battery for cycle durability evaluation)
Change the counter electrode to lithium cobalt oxide and assemble a button-type battery in the same manner as above, and repeatedly charge and discharge between 4.1 V and 3.0 V at 20 ° C. and a current density of 0.2 C 100 times. After that, the capacity maintenance rate was examined. Table 3 shows the measurement results.

(Example 2)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of the d (002) plane of the graphite crystallite of 0.3358 nm, the average particle size of 14.1 μm and the d (002) plane of the graphite crystallite of Spherical natural graphite having an interlayer distance of 0.3362 nm is used, and SiO (atomic ratio Si) adjusted to an average particle size of 1 μm and a maximum particle size of 2 μm is used instead of SiO adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm. /O=1.0), except that the same method as in Example 1 was used. The results are shown in Tables 1 to 3.

(Example 3)
Instead of spherical natural graphite having an average particle diameter of 13.8 μm and an interlayer distance of the d (002) plane of the graphite crystallite of 0.3358 nm, the average particle diameter of 10.9 μm and the d (002) plane of the graphite crystallite of The same procedure as in Example 1 was performed except that scaly natural graphite having an interlayer distance of 0.3357 nm was used. The results are shown in Tables 1 to 3.

Example 4
Instead of firing and carbonizing at 1000 ° C. in a nitrogen gas atmosphere, the same method as in Example 1 was performed except that firing and carbonizing at 900 ° C. in a nitrogen gas atmosphere. The results are shown in Tables 1 to 3.

(Example 5)
Instead of firing and carbonizing at 1000 ° C. in a nitrogen gas atmosphere, the same method as in Example 1 was performed except that firing and carbonizing was performed at 1,350 ° C. in a nitrogen gas atmosphere. The results are shown in Tables 1 to 3.

(Example 6)
Instead of adding 10 parts by weight of coal tar pitch (softening point: 90 ° C.) to 100 parts by weight of spherical natural graphite, coal tar pitch (softening point: 90 ° C.) is added to 100 parts by weight of spherical natural graphite. The procedure was the same as in Example 1 except that 5 parts by weight was added. The results are shown in Tables 1 to 3.

(Example 7)
Instead of adding 10 parts by weight of coal tar pitch (softening point: 90 ° C.) to 100 parts by weight of spherical natural graphite, coal tar pitch (softening point: 90 ° C.) is added to 100 parts by weight of spherical natural graphite. The same procedure as in Example 1 was performed except that 25 parts by weight was added. The results are shown in Tables 1 to 3.

(Example 8)
Instead of adding 25 parts by weight of SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm, a metal inclusion obtained as follows The same procedure as in Example 1 was performed except that 40 parts by weight of carbonaceous particles A were added. The results are shown in Tables 1 to 3.
<Method for Producing Metal-Included Carbonaceous Particle A>
50 parts by weight of SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm, an average particle size of 10 μm, and the d (002) plane of the graphite crystallite 50 parts by weight of scaly natural graphite having an interlayer distance of 0.3354 nm is mixed, and then 30 parts by weight of pitch (softening point: 70 ° C.) is added and kneaded. It adjusted so that it might become 1 micrometer or less, and the metal inclusion carbonaceous particle A was obtained.

Example 9
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 13.1 μm and the d (002) plane of the graphite crystallites Instead of spherical natural graphite with an interlayer distance of 0.3356 nm, SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm is changed to 25 parts by weight. Then, the same method as in Example 1 was performed except that SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm was 18 parts by weight. The results are shown in Tables 1-3.

(Example 10)
Instead of setting SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm to 25 parts by weight, the average particle size is 0.3 μm and the maximum particle size is The process was performed in the same manner as in Example 1 except that 40 parts by weight of SiO (atomic ratio Si / O = 1.0) adjusted to 0.5 μm was used. The results are shown in Tables 1-3.

Example 11
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 12.9 μm and the d (002) plane of the graphite crystallites Instead of spherical natural graphite with an interlayer distance of 0.3355 nm, SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm is changed to 25 parts by weight. Then, the same method as in Example 1 was performed except that SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm was 18 parts by weight. The results are shown in Tables 1-3.

(Comparative Example 1)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 12.9 μm and the d (002) plane of the graphite crystallites The same procedure as in Example 1 was performed except that spherical natural graphite having an interlayer distance of 0.3364 nm was used and no fusible organic material was mixed. The results are shown in Tables 1 to 3.

(Comparative Example 2)
Instead of spherical natural graphite having an average particle diameter of 13.8 μm and an interlayer distance of the d (002) plane of the graphite crystallite of 0.3358 nm, the average particle diameter of 14.2 μm and the d (002) plane of the graphite crystallite of Spherical natural graphite having an interlayer distance of 0.3361 nm was used, and SiO (atomic ratio Si) adjusted to an average particle size of 2 μm and a maximum particle size of 3 μm was used instead of SiO adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm. /O=1.0), except that the same method as in Example 1 was used. The results are shown in Tables 1 to 3.

(Comparative Example 3)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 13.7 μm and the d (002) plane of the graphite crystallites Instead of adding 10 parts by weight of the coal tar pitch (softening point: 90 ° C.) to 100 parts by weight of the spherical natural graphite, the spherical tar graphite (softening point: 90) is used. ℃) was added in the same manner as in Example 1 except that 3 parts by weight of 100 parts by weight of spherical natural graphite was added. The results are shown in Tables 1 to 3.

(Comparative Example 4)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 13.8 μm and the d (002) plane of the graphite crystallites Instead of adding 10 parts by weight of the coal tar pitch (softening point: 90 ° C.) to 100 parts by weight of the spherical natural graphite, the spherical tar graphite (softening point: 90) is used. ℃) was added in the same manner as in Example 1 except that 50 parts by weight of 100 parts by weight of spherical natural graphite was added. The results are shown in Tables 1 to 3.

(Comparative Example 5)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 13.8 μm and the d (002) plane of the graphite crystallites The same method as in Example 1 except that spherical natural graphite having an interlayer distance of 0.3367 nm is used and calcined at 800 ° C. in a nitrogen gas atmosphere instead of calcining at 1000 ° C. in a nitrogen gas atmosphere. I went there. The results are shown in Tables 1 to 3.

(Comparative Example 6)
Instead of firing and carbonizing at 1000 ° C. in a nitrogen gas atmosphere, the same method as in Example 1 was performed except that firing and carbonizing was performed at 1,500 ° C. in a nitrogen gas atmosphere. The results are shown in Tables 1 to 3.

(Comparative Example 7)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 11.5 μm and the d (002) plane of the graphite crystallites The same method as in Example 1 was performed except that calcined coke having an interlayer distance of 0.3412 nm was used. The results are shown in Tables 1 to 3.

(Comparative Example 8)
Instead of spherical natural graphite having an average particle size of 13.8 μm and an interlayer distance of 0.3358 nm between the d (002) planes of the graphite crystallites, the average particle size of 13.4 μm and the d (002) plane of the graphite crystallites The same procedure as in Example 1 was performed, except that spherical natural graphite having an interlayer distance of 0.3355 nm was used, and SiO adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm was not mixed. The results are shown in Tables 1 to 3.

(Comparative Example 9)
Instead of spherical natural graphite having an average particle diameter of 13.8 μm and an interlayer distance of the d (002) plane of the graphite crystallite of 0.3358 nm, the average particle diameter of 11.8 μm and the d (002) plane of the graphite crystallite of Instead of spherical natural graphite having an interlayer distance of 0.3401 nm, SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm is changed to 25 parts by weight. Then, the same method as in Example 1 was performed except that 50 parts by weight of SiO (atomic ratio Si / O = 1.0) adjusted to an average particle size of 0.3 μm and a maximum particle size of 0.5 μm was used. . The results are shown in Tables 1-3.

From Table 1 and Table 2, in Comparative Example 1 in which no fusible organic material is added, the aspect ratio is increased to 2.7, and the average particle diameter is decreased due to the breakage of the graphite core particles, and the tap density is decreased. For this reason, the first irreversible capacity increases and the capacity maintenance rate decreases.
Further, when the particle diameter of SiO, which is a raw material of Si, which is a bearer of high capacity as in Comparative Example 2, is increased, the aspect ratio is increased to 2.3, the capacity is decreased, and the capacity maintenance ratio is also decreased.
In Comparative Example 3, the amount of coal tar pitch added is too small, so the thickness of the carbide layer becomes too thin, the initial irreversible capacity increases, and the capacity retention rate decreases. On the other hand, in Comparative Example 4, since the amount of coal tar pitch added is too large, the thickness of the carbide layer becomes too thick, leading to an increase in the initial irreversible capacity.
Moreover, in the comparative example 5 with a low calcination carbonization temperature, an initial irreversible capacity | capacitance increases or a capacity | capacitance maintenance factor falls. In Comparative Example 6 where the calcination carbonization temperature is low, since the formation reaction of Si in the disproportionation reaction of SiO does not occur, the initial irreversible capacity increases or the reversible capacity decreases.
As shown in Example 8, by using Si-containing carbonaceous particles, the initial irreversible capacity is lowered, and the capacity retention rate can be improved.
Further, in Comparative Example 8 in which no SiO was added, the reversible capacity was low as in Comparative Example 6. In Comparative Example 9 in which SiO is excessively added, the capacity retention rate is low.

It is a schematic diagram of a hybridizer. It is sectional drawing of the battery for evaluation of an Example and a comparative example. It is typical sectional drawing of the composite carbon material 21 for negative electrode materials of the lithium ion secondary battery of this invention. It is typical sectional drawing of the composite carbon material 21 for negative electrode materials of the lithium ion secondary battery of this invention. It is typical sectional drawing of the composite carbon material 21 for negative electrode materials of the lithium ion secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material inlet 2 Raw material circulation path 3 Stator 4 Jacket 5 Raw material outlet 6 Drum 7 Blade 8 Rotating part 9 Negative side stainless cap 10 Negative electrode 11 Copper foil 12 Insulating gasket 13 Electrolyte impregnation separator 14 Nickel mesh 15 Positive side stainless cap 16 Positive electrode 21 Composite carbon material 22 for negative electrode material of the lithium ion secondary battery of the present invention 22 Graphite core particle 23 Si particle 24 Carbide layer

Claims (13)

A graphite core particle, and a carbide layer formed on the surface of the graphite core particle,
In the carbide layer, metal particles or metal compound particles that occlude and release lithium, or metal particles or metal compound particles that occlude and release lithium and graphite fine particles are embedded,
The particle diameter aspect ratio is 1.0 to 2.0,
A composite carbon material for a negative electrode material of a lithium ion secondary battery.   2. The composite carbon material for a negative electrode material of a lithium ion secondary battery according to claim 1, wherein the metal particles or metal compound particles that occlude and release lithium are silicon or a silicon compound containing an alloy.   3. The composite carbon material for a negative electrode material of a lithium ion secondary battery according to claim 1, wherein the carbide layer has a thickness of 3 μm or less.   4. The composite carbon material for a negative electrode material for a lithium ion secondary battery according to claim 3, wherein the maximum particle diameter of the metal particles or metal compound particles that occlude and release lithium is 2 μm or less.   The ratio of the thickness of the carbide layer to the maximum particle size of the metal particles or metal compound particles that occlude and release lithium (the thickness of the carbide layer / the maximum particle size of the metal particles or metal compound particles) is 1.5 to 4. 5. The composite carbon material for a negative electrode material for a lithium ion secondary battery according to claim 3, wherein the composite carbon material is a lithium ion secondary battery.   The composite carbon material for a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the graphite core particles are natural graphite or artificial graphite having a thermal history of 2500 ° C or higher. .   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the carbide layer is made of a carbide of a pitch whose content of tar or quinoline insoluble content from which free carbon is removed is less than 1%. Composite carbon material for negative electrode material. A graphite core particle powder, a carbonaceous material, and a meltable organic material are heated and kneaded to coat the surface of the graphite core particle with a coating layer made of the carbonaceous material and the meltable organic material. A first step of obtaining an elementary powder of graphite core particles having,
A powder of graphite core particles having the coating layer and a metal particle or metal compound particle powder that occludes and releases lithium, or a metal inclusion that encloses metal particles or metal compound particles that occlude and release lithium. A powder of carbonaceous particles, and by friction and compression of the obtained mixed powder, the metal particles or metal compound particles are applied to the coating layer of the graphite core particle elementary powder having the coating layer, Alternatively, the metal-encapsulated particles are embedded and sized to obtain a sized powder of graphite core particles having a coating layer embedded with metal particles or metal compound particles having a particle diameter aspect ratio of 1.0 to 2.0. Two steps,
A sized powder of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is calcined and carbonized at 850 to 1,400 ° C. in a non-oxidizing atmosphere to obtain a negative electrode material for a lithium ion secondary battery A third step of obtaining a composite carbon material for use,
A composite carbon material for a negative electrode material of a lithium ion secondary battery. A graphite core particle powder, a carbonaceous material, and a meltable organic material are heated and kneaded to coat the surface of the graphite core particle with a coating layer made of the carbonaceous material and the meltable organic material. A first step of obtaining an elementary powder of graphite core particles having,
A powder of graphite core particles having the coating layer and a metal particle or metal compound particle powder that occludes and releases lithium, or a metal inclusion that encloses metal particles or metal compound particles that occlude and release lithium. A powder of carbonaceous particles, and by friction and compression of the obtained mixed powder, the metal particles or metal compound particles are applied to the coating layer of the graphite core particle elementary powder having the coating layer, Alternatively, a sized powder of graphite core particles embedded with the metal-encapsulating carbonaceous particles and sized, and having a coating layer embedded with metal particles or metal compound particles having a particle diameter aspect ratio of 1.0 to 2.0. A second step to obtain;
A sized powder of graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded is calcined and carbonized at 850 to 1,400 ° C. in a non-oxidizing atmosphere to obtain a negative electrode material for a lithium ion secondary battery A third step of obtaining a composite carbon material for use,
The manufacturing method of the composite carbon material for negative electrode materials of a lithium ion secondary battery characterized by having.   10. The composite carbon material for a negative electrode material for a lithium ion secondary battery according to claim 9, wherein the carbonaceous substance is a pitch having a content of tar or quinoline insolubles from which free carbon has been removed of less than 1%. Manufacturing method.   11. The lithium ion according to claim 9, wherein the graphite core particles having a coating layer in which the metal particles or metal compound particles are embedded have a thickness of 0.5 to 4 μm. The manufacturing method of the composite carbon material for negative electrode materials of a secondary battery.   The method for producing a composite carbon material for a negative electrode material for a lithium ion secondary battery according to any one of claims 9 to 11, wherein the maximum particle size of the metal powder or metal compound powder is 2 µm or less.   12. The negative electrode of a lithium ion secondary battery according to claim 9, wherein the maximum particle diameter of the metal-encapsulated carbonaceous particle powder containing the metal particles or the metal compound particles is 2 μm or less. A method for producing a composite carbon material.

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