JP2008305661A - Negative electrode material for lithium ion secondary battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbonaceous negative electrode material for a lithium ion secondary battery superior in high density filling, output characteristics, cycle characteristics, and charge and discharge efficiency, and its manufacturing method. <P>SOLUTION: The manufacturing method of the carbonaceous negative electrode material of the lithium ion secondary battery has a process of obtaining the carbonaceous particles covered by a pitch and a fusible organic material by heating and mixing the carbonaceous particles of a volume reference median diameter of 1 μm to 30 μm, pitch having softening point of 70°C to 250 °C, and the fusible organic material of which the volatile portion when heated to 400°C in the air is 50% or more, and of which the carbon residue when heated to 800°C in an inert atmosphere is 3% or less, and a process of obtaining spheroidized carbonaceous particles covered with the pitch and the fusible organic material of the particle diameter aspect ratio of 1.0 to 2.0 by compressing and making friction of the carbonaceous particles covered with the obtained pitch and the fusible organic material. The obtained spheroidized carbonaceous particles are subsequently calcined and carbonized, cracked, and classified at temperatures of 1,000 to 3,000°C in a non-oxidizing atmosphere. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery capable of high density filling, high capacity, and large current discharge, and a method for producing the same.

  Lithium secondary batteries using organic electrolytes of lithium salts as non-aqueous electrolyte secondary batteries are lightweight and have high energy density, and are expected as power sources for small electronic devices or power storage batteries. The demand for rapid charging has become more advanced as the performance of mobile phones and laptop computers, where batteries are mainly used, has become more sophisticated, while lithium-ion secondary batteries for hybrid cars and electric vehicles have achieved higher capacities. Improvement of characteristics and output characteristics is an important issue.

  Initially, metallic lithium was used as the negative electrode material for lithium secondary batteries, but metallic lithium eluted into the electrolyte as lithium ions during discharge, and when lithium ions were deposited on the negative electrode surface as metallic lithium during charging. It is difficult to deposit in a smooth and original state, and it tends to deposit in a dendritic form. Since this dendrite has extremely strong activity, the electrolyte solution is decomposed, so that the battery performance is lowered and the charge / discharge cycle life is shortened. Furthermore, there is a risk that dendrites grow and reach the positive electrode, causing both electrodes to short-circuit.

  In order to remedy this drawback, it has been proposed to use a carbon material instead of metallic lithium. A carbon material is suitable as a negative electrode material because there is no problem of precipitation in the form of dendrites upon occlusion and release of lithium ions. That is, the graphite material has high lithium ion occlusion / release properties, and since the occlusion / release reaction is performed quickly, the charge / discharge efficiency is high, the theoretical capacity is 372 mAh / g, and the potential during charge / discharge is also high. There is an advantage that a high voltage battery is obtained which is almost equal to metallic lithium.

  However, in the case of a graphite material having a high degree of graphitization and a highly developed hexagonal network structure, the reaction with the electrolytic solution is likely to occur, and the battery performance is impaired. For example, the battery capacity decreases when charging and discharging are repeated. In order to solve this problem, the property of the carbon material centering on the graphite material is improved. For example, the surface of the graphite material having a high graphitization degree is made of a carbonaceous material having a low graphitization degree. Many proposals have been made, such as a multilayer structure with a coating.

  In addition, since graphite is in the form of particles such as scales, scales, plates, etc., for example, since the particles are arranged at the time of electrode plate production and the movement of lithium ions is hindered, the rapid charge / discharge characteristics of the battery in particular are reduced. In addition, the charge / discharge capacity is low, and there is a need for improvement. Attempts have been made to facilitate the movement of lithium ions by spheroidizing the graphite material to randomly orient the graphite layer during electrode plate production. ing.

  In order to solve the problems due to the above particle shape, mechanical energy treatment such as pulverization is performed, the corners of scaly and scaly graphite particles are taken, and a multilayer structure coated with a carbonaceous material having a low graphitization degree It has also been proposed to use carbon materials. For example, non-aqueous two-dimensional carbon material containing carbonaceous or graphite particles subjected to mechanical energy treatment so that the apparent density ratio before and after treatment is 1.1 or more and the median diameter ratio before and after treatment is 1 or less. An electrode for a secondary battery, a non-aqueous secondary battery electrode including a multilayered carbon material obtained by mixing the treated carbonaceous or graphite particles with an organic compound and then carbonizing the organic compound has been proposed (patent) Reference 1).

In addition, as a negative electrode material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, (1) a (002) plane spacing (d002) by a wide angle X-ray diffraction method is less than 3.37 angstroms and a C-axis direction the size of the crystallite (Lc) of at least 1000 angstroms or more, (2) R value is the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum is 0.3 or less, and The full width at half maximum of 1580 cm ⁻¹ peak is 24 cm ⁻¹ or less, (3) the average particle size is 10 to 30 μm, and the average thickness of the thinnest part is at least 3 μm or more and the average particle size or less, (4) by BET method a specific surface area of 3.5 m ² / g or more 10.0 m ² / g or less, (5) the tapping density is 0.5 g / cc or more 1.0 g / cc or less (6) A massive graphite powder exhibiting a characteristic of (110) / (004) X-ray diffraction peak intensity ratio of 0.015 or more by a wide angle X-ray diffraction method is used as a nucleus, and the surface of the nucleus is coated with a carbon precursor. Thereafter, a non-aqueous electrolyte secondary battery using a carbonaceous powder having a multilayer structure in which a surface layer of a carbonaceous material is formed by firing in a temperature range of 700 to 2800 ° C. in an inert gas atmosphere is disclosed (patent) Reference 2). However, these have the problem that the tapping density is low and the battery capacity cannot be increased.

In order to solve such problems, the present applicant has obtained (1) an average particle diameter of 10 to 40 μm, a specific surface area of 10 m ² / g or less, (2) X-ray diffraction obtained by mechanical pulverization and classification. The distance (002) between the (002) planes of the graphite crystallite by the method is less than 0.337 nm, the crystallite size Lc in the C-axis direction is 100 nm or more, (3) the true specific gravity is 2.18 to 2.25, (4 ) tapping specific gravity 1.0 to 1.3, (5) the value of peak intensity ratio R of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum is greater than 0.5, and, 1580 cm ^-1 peak The carbonaceous material formed by heat treatment at a temperature of 800 to 2800 ° C. in an inert atmosphere after depositing a carbon precursor on the surface of a graphite particle having a half-width of more than 26 cm ⁻¹ as a nucleus Covered A negative electrode material for a non-aqueous electrolyte secondary battery made of a carbon material having a two-layer structure has been proposed (see Patent Document 3). In the above method, graphite particles are mechanically pulverized in advance by applying pressure and shearing force to form a spherical shape. There is a problem in that the shape of graphite as a raw material is limited because of the use of the particles.

  On the other hand, in order to provide a negative electrode material that uses natural graphite and has a high capacity, a small capacity loss during initial charge / discharge, and excellent high-speed chargeability and cycle characteristics, it is also high capacity and capacity loss. In order to provide a lithium-ion secondary battery Western negative electrode material that has low density, high-density filling properties, and excellent load characteristics (rapid charge / discharge characteristics), each is granulated and formed into a substantially spherical shape using a binder in advance. In addition, a method for producing a negative electrode material that is impregnated and coated with a binder pitch and then baked has been proposed (see Patent Documents 4 and 5). In these methods, a substantially spherical binder is granulated. It is necessary to select a material that does not melt or dissolve when the molded body is coated with pitch, and then a complicated process of impregnating the pitch is required. In addition, since the tap density of the substantially spherical body cannot be increased due to pitch impregnation (max 0.95), there is a problem that adjustment is difficult.

  Further, the present applicant suppresses exposure of a new active surface of graphite generated by pulverization, has a small irreversible capacity, a method for producing a negative electrode material for a lithium ion secondary battery having a large reversible capacity, and graphite particles, Pitch with a quinoline insoluble content of 0.3% or less, fixed carbon content of 50% or more, volatile content of 50% or more when heated to 400 ° C in air, and residual carbon ratio when heated to 800 ° C in an inert atmosphere Has proposed a method for producing a negative electrode material for a lithium ion secondary battery, characterized by melting and kneading 3% or less of a fusible organic material, firing and carbonizing and kneading the kneaded material, and then pulverizing (Patent Document 6). In order to obtain a negative electrode material having a high electric capacity by this method, it is necessary to use graphite particles that have been spheroidized in advance.

  As a method for simultaneously chamfering graphite particles and coating with a binder that becomes a carbonaceous material with low graphitization degree, it has high capacity, excellent cycle characteristics and rapid charge / discharge characteristics, and in addition, the voltage during discharge is continuous. As a method for producing composite carbon particles to obtain a high-performance lithium secondary battery in which the voltage change at the end of discharge becomes gradual, after fusing a binder to the surface of graphite, It is proposed that the binder be carbonized by firing (see Patent Document 7). However, as a specific method, the binder is fused to the surface of the graphite using a mechanofusion heater. While composite carbon particles with an average particle diameter of 20 μm formed by spheroidization by the applied pressure and shearing force of the heater are formed, mechanofusion heating is performed because the binder has no lubricity. Graphite particles graphite particles is crushed while being chamfered by strong agitation force is generated without bonding to the graphite particles, there is a drawback that it can not exhibit sufficient cycle characteristics.

  In addition, a method of spheroidizing after kneading natural graphite and pitch has been proposed (see Patent Document 8), but in this case as well, since the pitch is not lubricous, powerful stirring of the mechanochemical treatment apparatus is performed. There is a drawback that graphite particles that are crushed while the graphite particles are chamfered by force are generated without being bonded to the graphite particles, and sufficient cycle characteristics cannot be exhibited.

Further, the carbon material is spheroidized or similar spheroidized by a mechanical mechanical pulverization process and simultaneously assembled into a primary stable structure, and a pulverizer that imparts friction and shear forces between the surfaces is used. And a step of assembling fine carbon powder particles refined in a spheronization or similar spheronization process into a secondary stable structure on the surface of a single substance, and a step of heat-treating the assembly. Although a method for producing a negative electrode active material for a lithium secondary battery has also been proposed (see Patent Document 9), even if graphite and solid pitch are mixed and stirred and mixed in a temperature range in which the pitch does not melt, the pitch remains inside the graphite material. Even if the obtained composite particles are spherical, there are many voids remaining inside, and it is difficult to increase the density of the electrode plate when filling as a negative electrode active material. Is
Japanese Patent Laid-Open No. 10-334915 Japanese Patent Laid-Open No. 11-054123 Japanese Patent Laid-Open No. 2004-079344 JP 2004-031038 A JP 2004-179075 A Japanese Patent Application No. 2005-377139 JP 11-011919 A JP 2003-173778 A Japanese Patent Laid-Open No. 2005-302725

  The present invention has been made to solve the above-mentioned conventional problems in the negative electrode material for lithium ion secondary batteries and the manufacturing method thereof, and its purpose is to control the shape and surface crystal structure of the carbonaceous particles. To provide a negative electrode material for a lithium ion secondary battery having high density filling, excellent output characteristics, cycle characteristics, and charge / discharge efficiency by randomly orienting the graphite layer direction during electrode plate production, and a method for producing the same is there.

In order to achieve the above object, a negative electrode material for a lithium ion secondary battery according to claim 1 is a carbonaceous negative electrode for a lithium secondary battery obtained by firing and carbonizing carbonaceous particles coated with pitch and a meltable organic substance. A material having a volume-based median diameter of 5 to 30 μm, a particle diameter aspect ratio of 1.0 to 2.0, a BET specific surface area of 1.5 to 5.0 m ² / g, and measured by an X-ray wide angle diffraction method. The (002) plane spacing d (002) is less than 0.3500 nm, and the Raman spectrum intensity ratio R = I ₁₃₆₀ / I ₁₅₆₀ has characteristics of 0.60 or less. The tapping specific gravity is desirably 1.0 to 1.3.

  The method for producing a negative electrode material for a lithium ion secondary battery according to claim 2 is heated to 400 ° C. in air, carbonaceous particles having a volume-based median diameter of 1 μm to 30 μm, a pitch having a softening point of 70 ° C. to 250 ° C. Carbon coated with pitch and meltable organic matter by heating and mixing with meltable organic matter having a volatile content of 50% or more and a residual carbon ratio of 3% or less when heated to 800 ° C. in an inert atmosphere The carbonaceous particles coated with the obtained pitch and meltable organic matter were compressed and rubbed to coat the pitch and meltable organic matter having a particle diameter aspect ratio of 1.0 to 2.0. A step of obtaining spheroidized carbonaceous particles, characterized in that the obtained spheroidized carbonaceous particles are subsequently calcined and carbonized at a temperature of 1,000 to 3,000 ° C. in a non-oxidizing atmosphere, and crushed and classified. .

  According to a third aspect of the present invention, there is provided a method for producing a negative electrode material for a lithium ion secondary battery according to the second aspect, wherein the (002) plane spacing d (002) of the carbonaceous particles measured by X-ray wide angle diffraction is 0.3500 nm. It is less than or less.

  The method for producing a negative electrode material for a lithium ion secondary battery according to claim 4 is the method according to claim 2 or 3, wherein the carbonaceous particles coated with the pitch and the meltable organic substance obtained by heating and mixing were measured by a laser diffraction method. The volume-based median diameter is 10 to 40 μm.

  In the present invention, the pitch is filled in every corner of the graphite material, and the graphite material is spheroidized in a temperature range where the pitch is softened, so that the pitch penetrates into the voids inside the graphite material in a molten state. Then, after spheronizing in the softening point temperature range of the pitch, the above-mentioned conventional problem can be solved by calcination of the pitch component.

  In addition, the composite carbon particles with high yield by sieving and classification, spherical particle size, and sharp-grained particle size distribution coated with carbon on the edge surface of carbon are excellent in charge capacity and cycle characteristics. In addition, a negative electrode material for a lithium ion secondary battery can be provided.

  According to the present invention, by controlling the shape and surface crystal structure of the carbonaceous particles and randomly orienting the graphite layer direction during electrode plate production, high density packing and excellent output characteristics, cycle characteristics, and charge / discharge efficiency are achieved. Provided are a negative electrode material for a lithium ion secondary battery and a method for producing the same.

  In the present invention, the surface of carbonaceous particles is thinly and uniformly coated, and the surface area of carbonaceous particles is reduced while reducing the crystallinity of the carbonaceous particles, and the surface smoothness and sphericity of the carbonaceous particles are high. Can be manufactured. In other words, it is possible to manufacture with high charge / discharge efficiency, high density filling, and high capacity but excellent output characteristics.

The method for producing a negative electrode material for a lithium ion secondary battery according to the present invention aims to improve the output characteristics at the time of spheroidization of carbonaceous particles and charge / discharge efficiency, packing density, and large current discharge in a lithium ion secondary battery Thus, it becomes possible to obtain a negative electrode material for a lithium ion secondary battery excellent in high density filling, high capacity, and output characteristics.
I. Coating pitch uniformly on the surface of carbonaceous particles;
B. Spheroidizing the surface of the carbonaceous particles mechanically using a pulverizer that imparts friction and shear force between the surfaces;
C. Forming an amorphous surface on the surface of carbonaceous particles

Hereinafter, the manufacturing process will be described.
"material"
a. Carbonaceous particles Carbonaceous particles satisfying the following characteristics are suitable, specifically, flaky natural graphite particles and artificial graphite particles, pulverized powder of artificial graphite electrodes, coke powder, and other carbon precursor calcined carbides, etc. A mixture of can be applied. Since the carbonaceous particles used as these raw materials satisfy the following characteristics, the final powder is suitable as a negative electrode material for a lithium ion secondary battery.
(1) The aspect ratio is not limited. In the present invention, even if the aspect ratio is 3.0 or more, the aspect ratio becomes 1.0 to 2.0 without spheroidizing after carbonization.
(2) Volume-based median diameter measured by laser diffraction method is 1 μm to 30 μm
It is a value measured by a laser diffraction particle size distribution analyzer (SALD2000 manufactured by Shimadzu Corporation), and is represented by a median diameter (μm) based on volume.

  The carbonaceous particles used as a raw material are obtained by pulverizing and classifying scaly natural graphite, artificial graphite, a pulverized product of artificial graphite electrode, coke and the like using a pulverizer such as a roller mill or an impact pulverizer. When the volume-based median diameter 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 are deteriorated. In addition, when producing a negative electrode for a lithium ion secondary battery, it is difficult to make the film thickness thin and uniform during the application of the active material layer, so that the output characteristics per volume are further reduced. A more preferable volume-based median diameter is 25 μm or less, and further preferably 20 μm or less. When the volume-based median diameter is less than 1 μm, the specific surface area increases.

(3) The distance (d) of the (002) plane measured by X-ray wide angle diffraction method is less than 0.3500 m. Using CuKα ray monochromatized with a graphite monochromator, wide angle X ray is obtained by a reflective diffractometer method. A diffraction curve is measured and measured using the Gakushin method. When exceeding 0.3500 nm, the discharge reversible capacity of the final powder becomes 330 mAh / g or less, which is inconvenient. Usually, it is 0.3500 nm or less, More preferably, it is 0.3400 nm or less, More preferably, it is 0.3358 nm or less.

b. A pitch having a softening point of 70 to 250 ° C. measured by the ring and ball method is preferable. When the softening point measured by the ring and ball method is lower than 70 ° C., the carbon precursor is easily melted, and in the second step described below, the pitch elution is attached to the inner wall of the apparatus, and the continuous continuous operation cannot be performed. A malfunction occurs. Moreover, when it exceeds 250 degreeC, since the softened state of a carbon precursor is not good and spheroidization does not advance well in the following 2nd process, it is unpreferable. Usually, it is 70-250 degreeC, More preferably, it is 70-150 degreeC, More preferably, it is 70-90 degreeC. Moreover, you may use the pitch adjusted to 70-250 degreeC by the method of mixing 2 or more types of pitches from which a softening point differs, or the method of adding tar. In order to reduce the initial charge / discharge loss as the negative electrode material, it is more preferable to use a pitch obtained by removing free carbon by a method such as filtration or a pitch having a quinoline insoluble content of less than 1%.

c. Melting organic matter A melting organic matter having 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 can be suitably used. When melt-kneading carbonaceous particles and pitch, the organic material must be in a low-viscosity molten state, a meltable organic material is used, a smaller molecular weight is preferable, and no excessive pulverization occurs during kneading. Those having the are preferred. During the spheronization in the next step, it also acts as a lubricant and has the effect of preventing the carbon particles from being pulverized. In consideration of production, it is preferable to maintain lubricity in order to suppress metal wear of the apparatus and adhesion of the carbon precursor to the inside of the apparatus.

  Furthermore, during firing carbonization performed in a subsequent process, it is performed in a non-oxidizing atmosphere in which oxygen (air) is shut off. At this time, oxygen around the firing object is caused by gas pressure when the organic matter contained in the firing object is volatilized. There is also an effect that the oxygen concentration is lowered by reacting organic matter and oxygen. Therefore, an organic substance that volatilizes 50% or more when heated to 400 ° C. in air is used. If the volatile content is less than 50%, the oxygen concentration around the object to be fired is not sufficiently lowered, the crystallinity of pitch-derived carbon is lowered, and the reversible capacity is also lowered. In addition, since the residual carbon content in the meltable organic matter decreases the reversible capacity, it is desirable that the residual carbon ratio is as low as possible. The residual carbon ratio when heated in an inert atmosphere and heated to 800 ° C. is 3% or less is used. Examples of such fusible organic substances include synthetic oil, natural oil, stearic acid, synthetic wax, natural wax and the like.

The process according to the present invention will be described.
<First step> (pitch coating and granulation of carbonaceous particles)
In the present invention, it is possible to apply a technique of spheroidizing using a spheroidizing device after the pitch permeation / coating is completed by another device instead of the spheroidizing device. In order to infiltrate and coat the pitch into the graphite material, a kneader (kneader) or other mixer excellent in mass productivity is preferably used industrially. In this case, the pitch can be penetrated and covered to the inside of the graphite material without being limited to the inner volume of the spheroidizing device. Further, a pressure kneader provided with a pressure lid may be used.

  The carbonaceous particles are put into a kneader, the temperature in the container is raised to a predetermined temperature exceeding the softening point of the pitch while kneading, and the pitch is added and kneaded sufficiently. By kneading, the destruction of the particles and the fine powder portions of the particle size distribution are combined, and part of the granulation proceeds simultaneously. However, the addition of the fusible organic material of the present invention suppresses particle breakage. Therefore, it becomes a mixture of particles coated on the surface and particles in a state where fine particles are granulated with a pitch. The powder obtained by heating and mixing has a volume-based median diameter measured by a laser diffraction method of 10 to 40 μm. The time for kneading depends on the capacity of the kneader, the shape of the kneading blade, the amount of raw material charged, etc., but is 10 minutes to 2 hours at a temperature exceeding the melting point of the pitch. Then, it cools to room temperature and the carbonaceous particle which coat | covered the pitch is obtained.

(B) Ratio of pitch to carbonaceous particles It is preferably 5 to 40 parts by weight with respect to 100 parts by weight of graphitic carbon particles. When the amount is less than 5 parts by weight, it is difficult to uniformly coat the surface of the carbonaceous particles with a pitch, and since there is a large portion of fine particles with a particle size distribution that cannot be granulated, there is a problem that the electrode is broad. This is because sometimes the density of the negative electrode material decreases and the battery capacity decreases. When the amount exceeds 40 parts by weight, it becomes difficult to crush each individual particle because the graphite powder aggregates, and the particle size of the finally obtained composite particle becomes too large and is obtained by crushing. The thickness of the pitch coating film on the surface of the graphitic carbon particles becomes non-uniform, and powder with a single pitch tends to exist. In addition, since a coarse lump is formed, a pulverization process is required, and the initial charge / discharge loss is increased as battery characteristics. Further, in the second step (spheronization), an extra pitch adheres to the inside of the apparatus, which causes a problem that continuous continuous operation cannot be performed. The ratio is appropriately adjusted depending on the type of raw material used, but is usually 5 to 40 parts by weight, more preferably 10 to 30 parts, and still more preferably 15 to 25 parts.

(B) Ratio of fusible organic substance to carbonaceous particles and timing of addition 1-30 parts by weight per 100 parts by weight of graphitic carbon particles. A more preferable range is 3 to 20 parts by weight. When the amount is less than 3 parts by weight, finely divided carbonaceous particles remain when the carbonaceous particles coated with the pitch in the next step are spheroidized, so that removal is difficult and the yield is reduced. When the amount exceeds 30 parts by weight, it becomes difficult to spheroidize the carbonaceous particles coated with the pitch of the next step, and also when the carbonaceous particles coated with the pitch of the next step are spheroidized, a coarse lump is formed. There are problems that are formed.

The meltable organic material is kneaded by the following method.
(1) A method in which carbonaceous powder and a meltable organic substance are sufficiently heated and kneaded, and then pitch is added and kneaded.
(2) A method in which carbonaceous powder and pitch are heat-kneaded, and then a meltable organic substance is added and kneaded.
(3) A method of heat-kneading carbonaceous powder, pitch and meltable organic matter.
As a method for preventing excessive pulverization of the carbonaceous powder, the carbon powder of (1) and the meltable organic material are sufficiently heated and kneaded, and then a pitch is added and kneaded, and the carbon powder of (3) A method in which pitch and meltable organic matter are kneaded with heat is a preferred embodiment.

<< Second Step >> (spheroidization of carbonaceous particles coated with pitch and meltable organic matter)
By repeatedly applying mechanical energy from the outside by repeatedly compressing, rubbing, and colliding the resulting carbonaceous particles coated with pitch and meltable organic matter, the surface of the particles is gradually scraped off. And spheroidized. Since the carbon fine powder generated by the spheroidization is embedded in the particle surface through the softened pitch and fusible organic substance mixed layer, the particle diameter aspect ratio is adjusted to 1.0 to 2.0. Moreover, the fine powder from which the particle | grain surface was scraped off gradually after the spheroidization process does not remain. In addition, the graphite crystal layer of carbon particles is also bent, and finally settles into a stable sphere with a small frictional resistance between the grains. At this time, the mixed layer of pitch and meltable organic material is softened, and the surface is smoothed by friction between the grains. Specific devices for applying mechanical energy from the outside include mechano-fusion systems (manufactured by Hosokawa Micron Corporation), hybridizers (manufactured by Nara Machinery Co., Ltd.), and the like, but are limited to these apparatuses. It is not a thing.

  For example, as a method of imparting mechanical energy to the powder, the powder obtained in the first step in the hybridizer (manufactured by Nara Machinery Co., Ltd.) shown in FIG. And processed at a rotational peripheral speed of 20 to 100 m / s for 1 to 3 minutes. The hybridizer uses the compressive force, frictional force, and collision force generated by the difference in rotational speed between the drum 6 and the rotating part 8 for the raw material introduced into the gap between the drum 6 and the rotating part 8 through the raw material circulation path 2. A device that provides mechanical energy. 3 is a stator, 4 is a jacket, 5 is a raw material discharge part, and 7 is a blade.

  The temperature inside the apparatus during the hybridizer treatment rises due to the application of mechanical energy, but is preferably adjusted to the following temperature of (pitch softening point + 20 ° C.). In the case of the temperature atmosphere exceeding (pitch softening point + 20 ° C.), the molten pitch is eluted from the particle gap, and the eluted pitch adheres to the inside of the apparatus. Conversely, if the pitch softening point is 250 ° C. or higher, the softened state is poor and spheroidization becomes difficult, which is not preferable.

  The rotational peripheral speed is preferably 20 to 100 m / s. A rotational peripheral speed of 20 m / s or less is not preferable because the mechanical energy received by the particles is small and spheroidization does not proceed. The powder obtained at a rotational peripheral speed of 100 m / s or more and 100 m / s does not differ greatly in performance, and the upper limit is preferably set to 100 m / s in consideration of cost, safety of the apparatus, and the like. When the treatment time is 30 seconds or less, the particle diameter aspect ratio is still large, and when the treatment time is 5 minutes or more, the particle diameter aspect ratio does not change. Therefore, the treatment time is preferably 30 seconds to 5 minutes. Considering production, 1 to 3 minutes is more preferable. In addition, when the frictional force and compressive force between the grains are too strong, and the rotational peripheral speed increases and the destruction of the grains occurs, the above-described fusible organic matter is added to reduce the wear between the grains. It is preferable to do this. The input amount is appropriately adjusted in consideration of the input amount, cost, and processing time.

«Third step» (carbonization, disintegration, classification of spheroidized carbonaceous particles coated with pitch and meltable organic matter)
Spherical carbonaceous particles coated with pitch and fusible organic matter obtained by the treatment that imparts mechanical energy are volatilized of fugitive organic matter at 1,000 to 3,000 ° C. in a non-oxidizing atmosphere. Firing and carbonizing the pitch. Then, the powder obtained by crushing and classifying is used as a negative electrode material for a lithium ion secondary battery. If it is less than 1,000 ° C., the volatilization of the fusible organic substance is not sufficient, and the low molecular organic unburned portion of the pitch remains, which is not preferable because the charge / discharge efficiency of the lithium ion secondary battery is deteriorated and the cycle characteristics are deteriorated. If it exceeds 3,000 ° C., graphite crystallites of the carbonized component of the pitch develop and the high-speed discharge efficiency decreases, which is not preferable. Moreover, when it exceeds 3,000 degreeC, since the heat processing cost is high and causes the increase in manufacturing cost, it is unpreferable.

  Examples of the crushing device include Matsubo's turbo mill, Seisin Corporation's quick mill, and Nisshin Engineering's super rotor. In the classification step, the minimum particle size is adjusted to 1 μm or more, the maximum particle size is 55 μm or less, and the median particle size is adjusted to 5 to 30 μm. By the above method, it becomes possible to produce spheroidized carbonaceous particles in which the surface of carbonaceous particles suitable as a negative electrode material for a lithium ion secondary battery is coated with a carbon binder.

By the above steps, the volume-based median diameter was 10 to 30 μm, the particle diameter aspect ratio was 1.0 to 2.0, the BET specific surface area was 1.5 to 5.0 m ² / g, and measured by the X-ray wide angle diffraction method. The (002) plane spacing d (002) is less than 0.3500 nm, the Raman spectrum intensity ratio R = I ₁₃₆₀ / I ₁₅₆₀ is 0.60 or less, and the tapping specific gravity is preferably 1.0 to 1.3. Thus, a carbonaceous negative electrode material for a lithium secondary battery comprising spheroidized carbonaceous particles is obtained.

The properties of the spheroidized carbonaceous particles obtained by the present invention will be described.
"Specific surface area"
The BET specific surface area is a value calculated by BET using N ₂ gas and a 10-point method. Note that the nitrogen adsorption specific surface area was preliminarily dried at 350 ° C. for 30 minutes under a nitrogen flow with respect to the measurement target (here, a graphite material) using a surface area meter (manufactured by Shimadzu Corporation). Then, the value measured by a nitrogen adsorption BET 10-point method by a gas flow method using a nitrogen helium mixed gas that is accurately adjusted so that the value of the relative pressure of nitrogen with respect to atmospheric pressure is 0.3. The BET specific surface area of the final powder obtained is preferably 1.5 to ⁵ m ² / g. If it is less than 1.5 m ² / g, the output area cannot be maintained because the reaction area required for lithium ion desorption / insertion is small, and if it exceeds 5 m ² / g, the reaction area is large and a large loss occurs during the first charge. Absent. The specific surface area can be adjusted by adjusting the thickness of the pitch covering the graphitic carbon particles, the speed of the hybridizer, the pulverizer, and the classification conditions.

《Volume-based particle size》
The median diameter measured by the laser diffraction method is preferably 5 to 30 μm. The median diameter is a value measured by SALD2000 manufactured by Shimadzu Corporation. Particles of less than 5 μm are not preferred because of poor dispersion in the liquid during slurry preparation and a large specific surface area. When the volume-based median diameter 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 are deteriorated. In addition, the film thickness at the time of active material layer coating is limited, and it becomes difficult to apply a thin and uniform active material layer when designing an electrode structure with more excellent output characteristics. Usually, it is 5-30 micrometers, More preferably, it is 10-25 micrometers, More preferably, it is 10-20 micrometers. The particle size can be adjusted by adjusting the particle size of the graphitic carbon particles, the carbon precursor blending ratio, the rotational speed of the pulverizer, and the classification conditions.

<Particle diameter aspect ratio>
The particle diameter aspect ratio is preferably 1.0 to 2.0. In SEM observation, 100 spheroidized graphitic carbon particles are arbitrarily selected, and the value obtained by dividing the longest diameter of the particles by the minimum diameter and the average value thereof are defined as the particle diameter aspect ratio. 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, and the active material layer is easily peeled off from the substrate, resulting in deterioration of cycle characteristics. . The particle diameter aspect ratio is usually 1.0 to 2.0, more preferably 1.0 to 1.6, and still more preferably 1.0 to 1.3.

<< Raman Spectrum >>
It is appropriate to discuss the disorder of the crystal structure of the particle surface layer using the Raman spectrum. Measured with a Raman spectroscopic analyzer (NR1100, manufactured by JASCO Corporation) using an Ar laser with a wavelength of 514.5 nm, 1360 cm ⁻ attributable to disorder of the crystal structure due to crystal defects on the surface layer and misalignment of the laminated structure, etc. the spectrum _{I 1360} of near ¹ is obtained by dividing the spectrum _{I 1580} near 1580 cm ^-1 attributable to the _{E 2 g} vibration corresponding to the lattice vibration of the carbon hexagonal net plane. The disorder ratio of the crystal structure of the particle surface layer can be expressed by the intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀ of the Raman spectrum.

In order to have excellent output characteristics while suppressing capacity loss at the time of initial charge, 0.60 or less is preferable. The adjustment of the Raman spectrum intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀ can be adjusted by selecting the hybridizer, the rotational speed of the pulverizer, the graphitic carbon particles to be used, and the carbon precursor.

<< Distance between d (002) planes of graphite crystallites obtained by X-ray diffraction method >>
It is appropriate to discuss the crystallinity inside the particle in terms of the plane spacing d (002) plane of the (002) plane of the graphite crystallite obtained by the X-ray diffraction method. Using CuKα ray as an X-ray source and high-purity silicon as a standard material, d (002) is calculated based on the Gakushin method from the peak position and half-value width of the diffraction pattern on the (002) plane. d (002) is preferably less than 0.3500 nm, and if it is 0.3500 nm or more, the discharge reversible capacity becomes small, which is not preferable. Natural graphite has a value close to 0.3354 nm of ideal graphite, and graphitizable coke can be made less than 0.3400 nm by performing a heat treatment at 2,800 ° C. or higher. Usually, it is 0.3500 nm or less, More preferably, it is 0.3400 nm or less, More preferably, it is 0.3358 nm or less.

  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
(Powder preparation)
Coal tar pitch (PK manufactured by JFE Chemical Co., Ltd.) with respect to 100 parts by weight of scaly natural graphite having a median diameter of 10.9 μm and d (002) = 0.3355 nm (manufactured by Chuetsu Graphite Industries Co., Ltd., BF-10A) -QL, softening point 70 ° C) (carbon precursor) 30 parts by weight, 70% volatilized when heated to 400 ° C in the air as a meltable organic substance, and when heated to 800 ° C in an inert atmosphere 5 parts by weight of a molten machine oil (linear organic polymer) having a residual carbon ratio of 0.6% was kneaded in a Werner type kneader at 150 ° C. for 30 minutes, and then cooled to room temperature.

  Next, the obtained powder was put into a hybridizer apparatus (NHS-I type, manufactured by Nara Machinery Co., Ltd.), while maintaining the maximum temperature in the apparatus at 75 ° C. ± 5 ° C. It processed for 3 minutes at 800 rpm (rotational peripheral speed 60m / s). The obtained powder was a spheroidized powder in which individual particles were independent and the aspect ratio was 1.5. The production conditions are shown in Table 1.

  Subsequently, the obtained spheroidized powder was put into a graphite crucible and calcined at 1,000 ° C. in a nitrogen gas atmosphere. Subsequently, it was crushed (device name: Nisshin Engineering Co., Ltd. Super Rotor) and classified (device name: Nisshin Engineering Co., Ltd. turbo classifier) to adjust the median diameter to 13.6 μm. The obtained carbon particles were used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties.

(Production of lithium ion secondary battery)
(Preparation of slurry)
An appropriate amount of a 1 wt% carboxymethylcellulose (CMC) aqueous solution as a thickener is added to 100 parts by weight of the carbon particles and stirred and mixed for 30 minutes, and then an appropriate amount of 40 wt% styrene-butadiene rubber (SBR) aqueous solution is used as a binder. The mixture was stirred and mixed 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.

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

(Production of button type battery for reversible discharge capacity evaluation)
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 a 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.

In the output characteristic evaluation, the output characteristic of the negative electrode material was examined by the capacity retention rate when discharged at 10 mA / cm ² from the fully charged state of SOC = 100%. The measurement results are shown in Table 2.

(Production of button-type battery for cycle durability evaluation)
After changing the counter electrode to lithium cobalt oxide and assembling the button-type battery, charging and discharging was repeated 100 times between 4.1 V and 3.0 V at a current density of 60 ° C. and 0.2 C. The capacity maintenance rate of was examined. The measurement results are shown in Table 2.

Example 2
20 weights of coal tar pitch (PK-E manufactured by JFE Chemical Co., Ltd., softening point 89 ° C) to 100 parts by weight of petroleum-based needle coke graphitized product with a median diameter of 19.2 µm and d (002) = 0.3359 nm Part, stearin having a volatile content of 63% when heated to 400 ° C. in air instead of the molten machine oil of Example 1, and a residual carbon ratio of 0.4% when heated to 800 ° C. in an inert atmosphere 5 parts by weight of the acid was kneaded in a kneader at 150 ° C. for 60 minutes, and then cooled to room temperature.

  Next, the obtained powder was put into a hybridizer apparatus (NHS-I type, manufactured by Nara Machinery Co., Ltd.), and the rotation speed was 8,000 rpm while maintaining the maximum temperature in the apparatus at 85 ± 5 ° C. It processed for 30 seconds at (rotational peripheral speed 100m / s). The obtained powder was a spheroidized powder in which individual particles were independent and the aspect ratio was 1.7. The production conditions are shown in Table 1.

  Subsequently, the obtained powder was put into a graphite crucible and calcined at 2100 ° C. in a nitrogen gas atmosphere. Subsequently, crushing and classification were performed in the same manner as in Example 1 to adjust the median diameter to 20.2 μm. The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. The powder physical properties are shown in Table 2. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Example 3
Mesophase pitch (MCP manufactured by JFE Chemical Co., Ltd.) with respect to 100 parts by weight of artificial graphite electrode pulverized powder (Oriental Sangyo Co., Ltd., AT-No. 10S) having a median diameter of 25.5 μm and d (002) = 0.359 nm -250D, softening point 250 ° C.), 5 parts by weight, 63% volatile content when heated to 400 ° C. in air instead of the melting machine oil of Example 1, when heated to 800 ° C. in an inert atmosphere 5% by weight of stearic acid having a residual carbon ratio of 0.4% was kneaded in a kneader at 250 ° C. for 90 minutes, and then cooled to room temperature.

  Next, the obtained powder was put into a hybridizer apparatus (NHS-I type, manufactured by Nara Machinery Co., Ltd.), and the rotation speed was 8,000 rpm while keeping the maximum temperature in the apparatus at 250 ± 5 ° C. It was processed for 5 minutes at a rotational peripheral speed of 100 m / s. The obtained powder was a spheroidized powder in which individual particles were independent and the aspect ratio was 1.7. The production conditions are shown in Table 1.

  Subsequently, the obtained powder was put into a graphite crucible and calcined at 3,000 ° C. in a nitrogen gas atmosphere. Subsequently, crushing and classification were performed in the same manner as in Example 1 to adjust the median diameter to 27.3 μm. The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. The powder physical properties are shown in Table 2. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Example 4
A spheroidized graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGC-15) having a median diameter of 17.0 μm and d (002) = 0.355 nm was used in place of the scale-like natural graphite used in Example 1. The same processing as in Example 1 was performed to adjust the median diameter to 16.4 μm. (See Table 1) The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Comparative Example 1
In Example 1, except that the melted mechanical oil as a meltable organic material is not used, it is melt kneaded in the same manner as in Example 1, and the kneaded product is calcined, graphitized and pulverized, and sieved in the same manner as in Example 1. The median diameter was adjusted to 12.9 μm. (See Table 1) The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Comparative Example 2
In Example 1, a volatile matter when heated to 400 ° C. in air instead of molten machine oil was 60%, and a residual carbon ratio when heated to 800 ° C. in an inert atmosphere was 4.4% ( Except for the use of (polyvinyl chloride), it was melt-kneaded in the same manner as in Example 1, and the kneaded product was calcined, graphitized and pulverized and sieved in the same manner as in Example 1 to give a median diameter of 13.1 μm. It was adjusted. (See Table 1) The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Comparative Example 3
In Example 1, the median diameter was adjusted to 15.4 μm by firing carbonization, graphitization, pulverization, and sieving by the same method as in Example 1 except that the treatment by the hybridizer apparatus was not performed. (See Table 1) The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Comparative Example 4
Instead of the scale-like natural graphite used in Example 1, spheroidized graphite (CGC-15, manufactured by Nippon Graphite Industry Co., Ltd.) having a median diameter of 17.0 μm and d (002) = 0.3355 nm was used. 40 parts by weight of tar pitch (JK Chemical Co., Ltd. PK-QL, softening point 70 ° C.) was kneaded with a Werner type kneader at 150 ° C. for 30 minutes, and then cooled to room temperature.

  Next, the obtained powder was put into a hybridizer apparatus (NHS-I type, manufactured by Nara Machinery Co., Ltd.), while maintaining the maximum temperature in the apparatus at 75 ° C. ± 5 ° C. It processed for 3 minutes at 800 rpm (rotational peripheral speed 60m / s). The obtained powder was a mixture of powders with individual particles and a chamfered powder with an aspect ratio of 1.6. The production conditions are shown in Table 1.

  Subsequently, the obtained spheroidized powder was put into a graphite crucible and calcined at 1,000 ° C. in a nitrogen gas atmosphere. Subsequently, crushing and classification were performed in the same manner as in Example 1 to adjust the median diameter to 15.6 μm. The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties.

Comparative Example 5
To 100 parts by weight of spheroidized graphite (Nippon Graphite Industries Co., Ltd., CGC-15) having a median diameter of 17.0 μm and d (002) = 0.355 nm, coal tar pitch (PFE-QL manufactured by JFE Chemical Co., Ltd.) , The softening point is 70 ° C.), 70% is volatilized when heated to 400 ° C. in the air as a meltable organic substance, and the residual carbon ratio when heated to 800 ° C. in an inert atmosphere is 0. 5 parts by weight of 6% molten mechanical oil was kneaded in a Werner type kneader at 150 ° C. for 30 minutes, and then cooled to room temperature.

  Next, the same processing as in Example 4 was performed without performing processing by the hybridizer apparatus, and the median diameter was adjusted to 17.4 μm. (See Table 1) The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties. As in Example 1, a button type battery was prepared and a charge / discharge test was performed. The measurement results are shown in Table 2.

Comparative Example 6
Coal tar pitch (PK manufactured by JFE Chemical Co., Ltd.) with respect to 100 parts by weight of scaly natural graphite having a median diameter of 10.9 μm and d (002) = 0.3355 nm (manufactured by Chuetsu Graphite Industries Co., Ltd., BF-10A) -QL, softening point 70 ° C) was kneaded in a Werner type kneader for 30 minutes at 150 ° C, and then cooled to room temperature.

  Subsequently, the obtained powder was put into a graphite crucible and calcined at 1,000 ° C. in a nitrogen gas atmosphere. Subsequently, crushing and classification were performed in the same manner as in Example 1 to adjust the median diameter to 13.6 μm. The production conditions are shown in Table 1. The obtained carbon particles are used as a negative electrode material powder for a lithium ion secondary battery. Table 2 shows the powder physical properties.

  As shown in Table 2, in Examples 1 to 4 according to the present invention, it is possible to suppress an increase in specific surface area by suppressing the destruction of graphite crystallites, and has a high initial efficiency. Since the diameter aspect ratio is 2 or less, the adhesion between the battery substrate and the active material layer is strong, the cycle retention ratio is also high, and it is recognized that excellent battery characteristics are achieved.

It is a figure which shows the hybridizer which provides mechanical energy with respect to powder. It is a figure which shows a button type battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material inlet 2 Raw material circulation path 3 Stator 4 Jacket 5 Raw material discharge part 6 Drum 7 Blade 8 Rotating part 9 Negative electrode side stainless cap 10 Negative electrode 11 Copper foil 12 Insulation gasket 13 Electrolyte impregnation separator 14 Nickel mesh 15 Positive electrode side stainless steel cap 16 Positive electrode

Claims (4)

A carbonaceous negative electrode material for a lithium secondary battery obtained by firing and carbonizing carbonaceous particles coated with pitch and meltable organic matter, having a volume-based median diameter of 5 to 30 μm and a particle diameter aspect ratio of 1.0 to 2.0, BET specific surface area of 1.5 to 5.0 m ² / g, (002) plane spacing d (002) measured by X-ray wide angle diffraction method is less than 0.3500 nm, Raman spectral intensity ratio R = A negative electrode material for a lithium ion secondary battery, wherein I ₁₃₆₀ / I ₁₅₆₀ has a characteristic of 0.60 or less.   Carbonaceous particles with a volume-based median diameter of 1 μm to 30 μm, pitches with a softening point of 70 ° C. to 250 ° C., volatile content when heated to 400 ° C. in air is 50% or more, and 800 ° C. in an inert atmosphere. A step of obtaining carbonaceous particles coated with pitch and meltable organic matter by heating and mixing with a meltable organic matter having a residual carbon ratio of 3% or less when heated, and the resulting pitch and meltable organic matter are coated. A step of obtaining spherical carbonaceous particles coated with a pitch and a meltable organic substance having a particle diameter aspect ratio of 1.0 to 2.0 by compressing and rubbing the obtained carbonaceous particles, and the obtained spherical carbonaceous particles Is subsequently calcined at a temperature of 1,000 to 3,000 ° C. in a non-oxidizing atmosphere, and pulverized and classified. A method for producing a negative electrode material for a lithium ion secondary battery.   The negative electrode material for a lithium ion secondary battery according to claim 2, wherein the (002) plane spacing d (002) of the carbonaceous particles measured by an X-ray wide angle diffraction method is less than 0.3500 nm. Manufacturing method.   4. The lithium ion according to claim 2, wherein the carbonaceous particles coated with the pitch and the meltable organic substance obtained by heating and mixing have a volume-based median diameter of 10 to 40 μm as measured by a laser diffraction method. A method for producing a negative electrode material for a secondary battery.

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