JP6447013B2 - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  In recent years, in response to the growing awareness of the global environment and energy conservation, hybrid vehicles (Hybrid Electric Vehicle, HEV), plug-in hybrid vehicles (Plug-in Hybrid Electric Vehicle, PHEV), electric vehicles (Electric Vehicle), EV) demand is increasing. As a battery to be mounted on these environmentally-friendly vehicles, a lithium ion secondary battery having a long life and a high capacity as compared with conventional batteries such as a lead storage battery and a nickel metal hydride battery has attracted attention.

  In order to improve the travel distance of environmentally-friendly vehicles, lithium ion secondary batteries are required to be further reduced in size and weight. In addition, a high input / output characteristic is required for a mechanism that generates and recovers a large amount of electric power necessary for repeating start and stop in a short time (seconds).

  A lithium ion secondary battery is composed of constituent members such as a positive electrode, a negative electrode, a separator, and an electrolyte, and among them, the negative electrode is one of the most important constituent members that determines the battery characteristics of the lithium ion secondary battery. A carbon material is generally used as a material for the negative electrode, and the carbon material is roughly classified into a graphite-based carbon material and an amorphous-based carbon material.

  The graphite-based carbon material has a structure in which hexagonal network surfaces of carbon atoms are regularly stacked, and has an advantage that high capacity and high density can be achieved. On the other hand, since the insertion / extraction of lithium ions proceeds from only the end portions of the laminated network surfaces and charging / discharging is performed, the input / output characteristics are low. In addition, since the crystallinity is high, there is a problem that the reactivity with the electrolytic solution is high and the life characteristics of the lithium ion secondary battery are deteriorated.

  On the other hand, since the amorphous carbon material has low crystallinity, the irreversible capacity of the battery is large and the specific gravity is small. Therefore, the energy density of the battery is inferior to that of graphite. However, since the crystallinity is low, the input / output characteristics are high, and the reaction with the electrolytic solution is suppressed, so that the life characteristics are superior to those of graphite.

  In HEV and the like, which have a high penetration rate among environmentally friendly vehicles, higher input / output is more important than higher energy density. In such applications where high input / output is required, an amorphous carbon material is more advantageous as a negative electrode material for a lithium ion secondary battery than a graphite carbon material.

  Amorphous carbon materials include non-graphitizable carbon (hard carbon) in which crystals do not easily develop even when heat-treated at a high temperature of 2500 ° C. or higher, and graphitizable carbon (soft carbon) in which crystals easily develop. There are two types. Since hard carbon has a problem that it is costly to apply to automobile applications due to the high raw material price and the necessity of a crystallization prevention process, soft carbon is attracting attention.

  However, since the soft carbon immediately after pulverization for particle size adjustment has a large specific surface area and high reactivity with the electrolytic solution, there is room for improvement in charge / discharge efficiency and cycle characteristics. Therefore, a method for solving the above problem by covering the surface of soft carbon with a carbon layer using isotropic pitch or the like as a coating precursor has been proposed (for example, Patent Documents 1 to 5).

Patent No. 5333963 Patent No. 5320645 JP 2006-324237 A International Publication No. 2011/105444 JP2011-175919A

  Evaluation of the negative electrode material formed with a coated carbon layer having a thickness of 50 nm or more with an isotropic pitch or the like as a precursor by the methods described in Patent Documents 1 and 2 showed an increase in resistance at a low temperature, an electrode It has been found that there are problems such as a decrease in energy density of the battery due to a decrease in density. It has also been clarified that there is a problem that particle aggregation occurs during the production of the electrode. On the other hand, as described in Patent Documents 3 to 5, the irreversible capacity decreases when the carbon coating ratio is reduced, but the particle size is reduced (average particle diameter of 20 μm or less) in order to improve the input / output characteristics. It was found that there is a trade-off relationship between the tap density and the energy density (electrode density).

  Thus, development of a negative electrode material for a lithium ion secondary battery that is excellent in both input / output characteristics and energy density while using an amorphous carbon material is demanded. Then, an object of this invention is to provide the negative electrode material for lithium ion secondary batteries which can form the negative electrode which is excellent in input-output characteristics and energy density, the negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery.

Specific means for solving the above-described problems are as follows.
<1> In the volume cumulative distribution (%) of particle size measured by laser diffraction method, the particle diameter D ₁₀ (μm) when the particle diameter is 10% from the smaller particle diameter and 50% from the smaller particle diameter. The particle diameter D ₅₀ (μm) at the time and the particle diameter D ₉₀ (μm) at 90% from the smaller particle diameter satisfy the following expressions (1) and (2), and the tap density T A negative electrode material for a lithium ion secondary battery, wherein (g / cm ³ ) is amorphous carbon particles satisfying the following formula (3).
(1) D ₉₀ / D ₁₀ ≦ 10.0
(2) 3.0 ≦ D ₅₀ ≦ 20.0
(3) D ₅₀ × 0.018 + 0.42 ≦ T

<2> The negative electrode material for a lithium ion secondary battery according to <1>, wherein the amorphous carbon particles further satisfy the following formula (4).
(4) 5.0 ≦ D ₅₀ ≦ 12.0

<3> The negative electrode material for a lithium ion secondary battery according to <1> or <2>, wherein an R value obtained in Raman spectrum measurement of the amorphous carbon particles is 0.70 or more and less than 1.40.

<4> Any one of <1> to <3>, wherein the amorphous carbon particles have a specific surface area determined from a nitrogen adsorption measurement at 77K of 1.0 m ² / g or more and less than 7.0 m ² / g. The negative electrode material for lithium ion secondary batteries as described in the item.

<5> the non true density of the amorphous carbon particles is less than 2.00 g / cm ³ or more ^{2.24g / cm 3, <1>} ~ <4> any lithium ion secondary battery according to one of Negative electrode material.

<6> The negative electrode material for a lithium ion secondary battery according to any one of <1> to <5>, having a carbon layer on at least a part of the surface of the amorphous carbon particles.

<7> The negative electrode material for a lithium ion secondary battery according to <6>, wherein the carbon layer has a thickness of 1 nm or more and less than 50 nm.

<8> A negative electrode for a lithium ion secondary battery, comprising the negative electrode material for a lithium ion secondary battery according to any one of <1> to <7>.

<9> A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to <8>, a positive electrode, and an electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries which can form the negative electrode which is excellent in input-output characteristics and energy density, the negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery are provided.

It is a diagram showing the relationship between the negative electrode material of the particle diameter _{D 50} and ([mu] m) and a tap density T (g / cm ^3). It is a diagram showing the relationship between the particle diameter of the negative electrode material D _{50 (μm)} and a tap density T (g / cm ³⁾ of Examples and Comparative Examples.

  In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. . In the present specification, a numerical range indicated by using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. In the present specification, the amount of each component in the composition means the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. To do. In this specification, the term “layer” includes a configuration formed in a part in addition to a configuration formed in the entire surface when observed as a plan view.

<Anode material for lithium ion secondary battery>
The negative electrode material for lithium ion secondary batteries of the present invention (hereinafter also simply referred to as “negative electrode material”) is 10% from the smaller particle size in the volume cumulative distribution (%) of the particle size measured by the laser diffraction method. Particle diameter D ₁₀ (μm) at the time, particle diameter D ₅₀ (μm) when the particle diameter is 50% from the smaller particle diameter (hereinafter, D ₅₀ is also referred to as an average particle diameter), and from the smaller particle diameter The particle diameter D ₉₀ (μm) at 90% satisfies the following formulas (1) and (2), and the tap density T (g / cm ³ ) satisfies the following formula (3). Carbon particles.
(1) D ₉₀ / D ₁₀ ≦ 10.0
(2) 3.0 ≦ D ₅₀ ≦ 20.0
(3) D ₅₀ × 0.018 + 0.42 ≦ T

  In the present invention, the term “amorphous carbon” means carbon having an interplanar spacing d002 of 3.40 mm or more measured by an X-ray diffractometer (XRD). The surface spacing d002 of the carbon 002 plane is the carbon 002 plane that appears at a diffraction angle 2θ = 24 ° to 26 ° from the diffraction profile obtained by irradiating the sample with X-rays (CuKα rays) and measuring the diffraction lines with a goniometer Can be calculated using the Bragg equation. Further, the surface distance d002 of the carbon 002 plane can be automatically calculated by analysis software attached to the X-ray diffractometer. The interplanar spacing d002 of the carbon 002 plane can be adjusted, for example, by adjusting the heat treatment temperature for the negative electrode material.

  Although the negative electrode material of the present invention is an amorphous carbon material, it can form a negative electrode excellent in both input / output characteristics and energy density. Although the reason is not clear, the present inventors presume as follows. That is, the negative electrode material of the present invention can suppress the decrease in tap density and increase the electrode density even if the particle size of the negative electrode material is reduced due to, for example, the properties of the amorphous carbon particles (surface state, etc.). Therefore, it is considered that a negative electrode material for a lithium ion secondary battery capable of forming a negative electrode excellent in both input / output characteristics and energy density, which could not be achieved by a negative electrode material using an amorphous carbon material so far, is obtained. .

The amorphous carbon particles that are the negative electrode material of the present invention have a particle diameter D ₁₀ (μm) of 10% from the smaller particle diameter in the volume cumulative distribution (%) of the particle size measured by the laser diffraction method. The particle diameter D ₉₀ (μm) at 90% from the smaller particle diameter satisfies the following formula (1).
(1) D ₉₀ / D ₁₀ ≦ 10.0

If the value of D ₉₀ / D ₁₀ of the amorphous carbon particles exceeds 10.0, the particle size distribution is too wide, the specific surface area is too large, and the charge / discharge efficiency tends to decrease. In addition, a sufficiently high tap density cannot be obtained, and the electrode density becomes insufficient, and the energy density tends to decrease.
The value of D ₉₀ / D ₁₀ can be controlled by adjusting the abundance ratio of fine powder and coarse powder, for example, by processing such as crushing, pulverization, classification, and sieving. These treatments may be performed on the amorphous carbon particles prepared as the negative electrode material, or may be performed on the raw material in the process of manufacturing the amorphous carbon particles.

The value of D ₉₀ / D ₁₀ of the amorphous carbon particles is preferably 2.0 or more. When the value of D ₉₀ / D ₁₀ is 2.0 or more, an increase in cost due to excessive classification can be effectively suppressed. The value of D ₉₀ / D ₁₀ of the amorphous carbon particles is more preferably 2.5 to 8.0, and further preferably 3.0 to 7.0. If the D ₉₀ / D ₁₀ of the amorphous carbon particles is 2.5 or more, an increase in resistance due to a decrease in the contact point between the particles can be effectively suppressed, and if it is 8.0 or less, the specific surface area It is possible to effectively suppress a decrease in charge / discharge efficiency associated with an increase in.

The amorphous carbon particles that are the negative electrode material of the present invention have a particle diameter D ₅₀ (μm) of 50% from the smallest particle diameter in the volume cumulative distribution (%) of the particle size measured by the laser diffraction method. The following formula (2) is satisfied.
(2) 3.0 ≦ D ₅₀ ≦ 20.0

If D ₅₀ of the amorphous carbon particles is less than 3.0 [mu] m, no effect of preventing the reduction of sufficient tap density can not be obtained. In addition, the particles may be too fine and adhesion to the current collector may be insufficient. If D ₅₀ exceeds 20.0 μm, sufficient input / output characteristics cannot be improved. Further, the resistance at a low temperature (for example, 0 ° C. or lower) may increase. From the viewpoint of obtaining a negative electrode material that is superior in balance between input / output characteristics and energy density, D ₅₀ is preferably 4.0 μm to 15.0 μm, and more preferably 5.0 μm to 12.0 μm.
D ₅₀ of, for example, can be controlled crushing, pulverization, classification by sieving or the like.
The volume particle size distribution (D ₁₀ , D ₅₀ and D ₉₀ ) of the negative electrode material can be measured using, for example, a laser diffraction particle size distribution measuring device (SALD-3000J, Shimadzu Corporation).

Amorphous carbon particles is negative electrode material of the present invention, the tap density T (g / cm ³⁾ satisfies the following formula (3).
(3) D ₅₀ × 0.018 + 0.42 ≦ T

As a result of verifying the correlation between the tap density T and D ₅₀ of the amorphous carbon particles, the inventors have found that the amorphous carbon particles have a high input / output ratio where the tap density T and D ₅₀ satisfy the condition of the expression (3). It has been found that both realization and high energy density can be realized. That is, the input / output characteristics tend to improve as the D ₅₀ value of the amorphous carbon particles is decreased, while the tap density T tends to decrease. For this reason, the improvement in input / output characteristics as a negative electrode material and the improvement in energy density are in a trade-off relationship. By adjusting the correlation between the tap density T and D ₅₀ of the amorphous carbon particles to a specific region (so that the tap density T and D _{50 of the} amorphous carbon particles satisfy the formula (3)), Even in such a trade-off relationship, the present inventors have found that the balance between the input / output characteristics as the negative electrode material and the energy density is excellent.

The fact that the tap density T and D ₅₀ of the amorphous carbon particles do not satisfy the condition of the formula (3) (in the region indicated by “1” in FIG. 1) is a balance between input / output characteristics and energy density as the negative electrode material. Means that the tap density T and D _{50 of} the amorphous carbon particles satisfy the condition of the expression (3) (in the region indicated by “2” in FIG. 1). It means that the input / output characteristics and energy density are balanced. From the viewpoint of obtaining a negative electrode material that is superior in balance between input / output characteristics and energy density, it is preferable that the tap density T and D ₅₀ of the amorphous carbon particles satisfy the condition of the following formula (4).
(4) D ₅₀ × 0.018 + 0.45 ≦ T

From the viewpoint of high energy density is obtained, it is preferable that the tap density T of the amorphous carbon particles is 0.45 g / cm ³ or more, and more preferably 0.50 g / cm ³ or more. Moreover, the tap density T of the amorphous carbon particles is preferably 1.20 g / cm ³ or less, more preferably 1.00 g / cm ³ or less.

The tap density T of the amorphous carbon particles in the present invention is the volume measured after slowly filling the negative electrode material with 100 ml ± 1 ml in a 150 ml cylinder, measuring the mass, and dropping the cylinder 250 times from a height of 5 cm. (G / cm ³ ) calculated from The tap density T is controlled by changing conditions such as carbon layer formation, compounding, granulation, crushing, classification, and sieving on the core material, which are performed as necessary in the production of amorphous carbon particles. be able to.

  The R value obtained in the Raman spectrum measurement of the amorphous carbon particles is preferably 0.70 or more and less than 1.40. When the R value is 0.70 or more, the crystallinity is not too high and the deterioration of the input / output characteristics tends to be effectively suppressed. If the R value is less than 1.40, the crystallinity is not too low and the particles do not become too hard, and the decrease in energy density due to the decrease in electrode density tends to be effectively suppressed. The R value is more preferably 0.75 or more and less than 1.20. When the R value is 0.75 or more, an increase in electrode expansion due to insertion of lithium ions during charging tends to be effectively suppressed. When the R value is less than 1.20, a decrease in energy density due to an increase in irreversible capacity tends to be effectively suppressed.

The R value of the amorphous carbon particles can be measured, for example, with a microscopic laser Raman spectrometer (DXR Raman microscope, Thermo Fisher Scientific). As measurement conditions, the laser wavelength can be 532 nm, the laser output can be 2 mW, the exposure time can be 2 seconds, and the number of exposures can be 4 times. R values from the spectrum obtained by Raman ^measurement, a peak Ig detected in a range of 1570cm ^-1 ~1620cm ^-1, it is calculated from the intensity ratio of peaks Id detected in a range of 1330cm ^-1 ~1360cm -1 (R value = Id / Ig). The R value described in this specification is an average value of each R value obtained by measuring 25 points by multipoint measurement. The R value of the amorphous carbon particles can be controlled by selecting the raw material of the amorphous carbon particles, the conditions for forming the carbon layer described later, selecting the precursor of the carbon layer, adjusting the thickness of the carbon layer, and the like.

Specific surface area determined from nitrogen adsorption measurements at 77K of the amorphous carbon particles is preferably less than 1.0 m ² / g or more 7.0 m ² / g. When the specific surface area is 1.0 m ² / g or more, an increase in resistance at low temperatures can be effectively suppressed, and when the specific surface area is less than 7.0 m ² / g, an increase in irreversible capacity due to the reaction between the particles and the electrolyte is further suppressed. Tend to be. The specific surface area of the amorphous carbon particles is more preferably 1.2 m ² / g or more and less than 5.5 m ² / g. When the specific surface area is 1.2 m ² / g or more, an increase in resistance at a low temperature tends to be further suppressed, and when it is less than 5.5 m ² / g, a decrease in capacity at high temperature storage is further suppressed. There is a tendency. The specific surface area of the amorphous carbon particles in the present invention is a value obtained by using the BET method from the adsorption isotherm obtained from the nitrogen adsorption measurement at 77K.

True density of the amorphous carbon particles is preferably less than 2.00 g / cm ³ or more 2.24 g / cm ^3. When the true density is 2.00 g / cm ³ or more, the irreversible capacity tends to increase and the energy density tends to be effectively reduced. When the true density is less than 2.24 g / cm ³ , The decrease tends to be effectively suppressed. The true density of the amorphous carbon particles in the present invention is a value determined by a pycnometer method using butanol.

  Amorphous carbon particles exist on at least part of the surface of the core amorphous carbon particles and the core amorphous carbon particles, and are different in crystallinity from the core amorphous carbon particles. It is preferable to have a structure having (hereinafter also referred to as a carbon layer). When the amorphous carbon particles have the carbon layer on at least a part of the surface, the reaction with the electrolytic solution is suppressed, and the charge / discharge efficiency and the cycle characteristics tend to be improved.

  When the amorphous carbon particles have a carbon layer, the crystallinity of the carbon layer is preferably lower than the crystallinity of the amorphous carbon particles. When the crystallinity of the carbon layer is lower than the crystallinity of the amorphous carbon particles, lithium ions can be easily inserted and removed, and the input / output characteristics tend to be improved.

  When the amorphous carbon particles have a carbon layer, the thickness of the carbon layer is preferably 1 nm or more and less than 50 nm. When the thickness of the carbon layer is 1 nm or more, the surface of the amorphous carbon particles as the core can be sufficiently covered, and the reaction between the portion of the amorphous carbon particles where the carbon layer does not exist and the electrolytic solution There is a tendency that the increase in irreversible capacity due to is sufficiently suppressed. If the thickness of the carbon layer is less than 50 nm, the increase in resistance at low temperatures due to the presence of too many carbon layers having low crystallinity on the surface tends to be sufficiently suppressed. The thickness of the carbon layer is more preferably 2 nm or more and less than 35 nm. When the thickness of the carbon layer is 2 nm or more, it is difficult to be influenced by the crystallinity of the amorphous carbon particles serving as the nucleus, the reaction with the electrolyte is sufficiently suppressed, and the charge / discharge efficiency and the cycle characteristics tend to be improved. . Also, if the carbon layer thickness is less than 35 nm, the electrode density is somewhat reduced due to the excessive hardness of the carbon layer with low crystallinity, and the energy density tends to be sufficiently suppressed. is there.

  The thickness of the carbon layer when the amorphous carbon particles have a carbon layer can be measured, for example, by observing the particles with a transmission electron microscope. Specific examples of the transmission electron microscope include a scanning transmission electron microscope (HD-2700, Hitachi High-Technologies Corporation), a field emission transmission electron microscope (JEM-2100F, JEOL Ltd.), and the like. In addition, when observing with a transmission electron microscope, you may observe the cross section of the amorphous carbon particle obtained by FIB (focused ion beam, Focused Ion Beam) processing. In the present specification, the amorphous carbon is excluded except for the carbon portion that has penetrated into the amorphous carbon particles and the carbon portion that exists in the joint portion of the particles that are produced when the amorphous carbon particles are granulated or combined. The average value obtained by measuring the thickness of the carbon portion located on the surface of the particle at any five points is defined as the thickness of the carbon layer.

(Method for producing negative electrode material)
The method for producing the negative electrode material of the present invention is not particularly limited as long as amorphous carbon particles satisfying the above formulas (1) to (3) can be obtained with D ₁₀ , D ₅₀ and D ₉₀ and the tap density T. . Examples of the method for producing amorphous carbon particles satisfying the formulas (1) to (3) include a method including a step of applying a force such as a shearing force to the amorphous carbon particles. Specific examples of the step of applying a force such as a shearing force to the amorphous carbon particles include a step of rubbing the amorphous carbon particles. Specifically, as a method of rubbing the amorphous carbon particles, a mixture of amorphous carbon particles and other materials contained as necessary is put into a cylinder in which a rotor blade is arranged, and the inner wall of the cylinder is Examples thereof include a method of rubbing the mixture with the rotary blade, a method of stirring and kneading the mixture using a heating kneader, and a method of rubbing the mixture in the fluidized bed.

  Examples of apparatuses equipped with a method for rubbing amorphous carbon particles include a high-speed shear type composite machine (Hosokawa Micron Corporation), a dry particle composite apparatus (Hosokawa Micron Corporation), and a high-speed paddle mixer (MIX sr. l), fluidized bed granulator (Paurec Co., Ltd.) and the like.

  When the carbon layer is formed on at least a part of the surface of the amorphous carbon particles, the step of applying a force such as a shearing force to the amorphous carbon particles is performed by using an organic compound as a carbon precursor on the surface of the amorphous carbon particles. It may be performed together with the step of adhering. Specifically, for example, a mixture containing amorphous carbon particles and an organic compound is introduced into an apparatus such as a cylinder having a rotating blade, a heating kneader, and the like, and the composite treatment is performed. An organic compound can be attached to the surface of the amorphous carbon particles while applying a force such as a shearing force to the surface.

  The method for producing the amorphous carbon particles is not particularly limited. For example, raw materials such as thermoplastic resin, naphthalene, anthracene, phenanthrene, coal tar, tar pitch, etc. are calcined in an inert atmosphere at 800 ° C. or higher, and this is then used with a hammer mill, pin mill, vibration mill, jet mill, etc. It can produce by grind | pulverizing and adjusting so that it may have a desired average particle diameter. Moreover, you may heat-process with respect to the raw material before baking. When heat treatment is performed, for example, the raw material is previously heat treated with an apparatus such as an autoclave, coarsely pulverized by a known method, and then calcined in an inert atmosphere of 800 ° C. or higher as described above, and thereafter Amorphous carbon particles can be obtained by adjusting the particle size by pulverization. The amorphous carbon particles may be soft carbon or hard carbon. From the viewpoint of cost, soft carbon is preferable.

  When the amorphous carbon particles have a carbon layer on at least a part of the surface, the method for forming the carbon layer is not particularly limited. For example, after an organic compound (carbon precursor) that remains carbonaceous by heat treatment is attached to the surface of amorphous carbon particles, the organic compound is carbonized by heat treatment in an inert atmosphere. A carbon layer can be formed on at least part of the surface of the particle.

  The organic compound (carbon precursor) that remains carbonaceous by heat treatment is not particularly limited. For example, the pitch generated by thermally decomposing ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt cracking pitch, polyvinyl chloride, etc .; synthetic pitch produced by polymerizing naphthalene etc. in the presence of super strong acid, etc. it can. Further, thermoplastic materials such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral; thermosetting materials such as phenol resin and furan resin can also be used.

  The heat treatment conditions for the amorphous carbon particles brought into contact with the organic compound may be appropriately determined in consideration of the carbonization rate of the organic compound, and are not particularly limited. For example, the heat treatment is preferably performed in the range of 800 ° C. to 1300 ° C. in an inert atmosphere. When the temperature of the heat treatment is 800 ° C. or higher, the firing of the organic matter proceeds sufficiently and the increase in the first irreversible capacity due to the increase in the specific surface area tends to be suppressed. When the temperature of the heat treatment is 1300 ° C. or lower, an increase in resistance due to an excessive decrease in specific surface area tends to be suppressed. Examples of the inert atmosphere include nitrogen, argon, helium and the like.

  Specifically, as a method of forming the carbon layer on at least a part of the surface of the amorphous carbon particles, the mixture obtained after adding the amorphous carbon particles while dissolving or dispersing the organic compound in the solvent is mixed. A method of removing the solvent by heating the liquid (wet method), a method of mixing amorphous carbon particles and an organic compound in a solid state, respectively, and kneading the resulting mixture while applying a shearing force (dry method) And a method of forming a carbon layer in a gas phase such as a CVD method (gas phase method). From the viewpoint of improving the tap density and adjusting the particle size distribution, a wet method or a dry method is preferable.

  Among the above methods, the dry method is preferable from the viewpoint of cost and manufacturing process reduction. Furthermore, according to the dry method, the step of attaching the organic compound to at least a part of the surface of the amorphous carbon particles and the step of applying a force such as a shearing force to the amorphous carbon particles can be performed collectively. It is also advantageous in that it can be done.

  Amorphous carbon particles obtained through the above steps are subjected to pulverization treatment, classification treatment, sieving treatment, etc., as necessary, and adjusted to an optimum particle size distribution. Thereby, the negative electrode material of this invention can be obtained.

<Anode for lithium ion secondary battery>
The negative electrode for lithium ion secondary batteries of this invention contains the negative electrode material of this invention, and another component as needed. Examples of other components include a binder and an additive. Examples of the additive include a thickener and a conductive auxiliary agent.

  As binder, ethylenically unsaturated carboxylic acid such as styrene-butadiene copolymer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate, etc. Esters; acrylic polymers obtained using ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid as monomers; polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene And polymer compounds having high ionic conductivity such as polyacrylonitrile. A binder may be used individually by 1 type, or may be used in combination of 2 or more type. The amount of the binder is not particularly limited, but is preferably 1 part by mass to 20 parts by mass with respect to 100 parts by mass in total of the negative electrode material and the binder. The above (meth) acrylate means acrylate or methacrylate, and (meth) acrylonitrile means acrylonitrile or methacrylonitrile.

  As a thickener, carboxymethylcellulose, sodium salt of carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid, sodium salt of polyacrylic acid, alginic acid, sodium salt of alginic acid, oxidized starch, phosphorylated starch, Casein etc. are mentioned. A thickener may be used individually by 1 type, or may be used in combination of 2 or more type.

  Examples of the conductive aid include natural graphite, artificial graphite, carbon black (acetylene black, thermal black, furnace black, etc.), conductive oxide, conductive nitride, and the like. By including a conductive auxiliary agent, the conductivity as an electrode can be further improved. A conductive support agent may be used individually by 1 type, or may be used in combination of 2 or more type.

  The amount of additives such as thickeners and conductive additives is not particularly limited as long as it does not deteriorate the characteristics of the lithium ion secondary battery, but is 0.1% by mass with respect to the total amount of the negative electrode material and the additives. It is preferable that it is more than 10.0 mass% above.

  The method for producing the lithium ion secondary battery negative electrode is not particularly limited. For example, a paste-like negative electrode material slurry containing a negative electrode material, a binder, various additives added as necessary, and a solvent is prepared, and the obtained negative electrode material slurry is placed on a current collector. It can be produced by applying, drying, and compression molding by a molding method such as a roll press if necessary. In addition, the paste-like negative electrode material slurry can be formed into a sheet shape, a pellet shape, or the like, and can be produced by integrating it with a current collector by a forming method such as a roll press.

  The negative electrode material slurry is prepared by, for example, stirring and kneading the components constituting the negative electrode material slurry using a stirrer, a ball mill, a super sand mill, a pressure kneader, etc., and adjusting the viscosity as necessary. Can do.

  The solvent used for the preparation of the negative electrode material slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the binder. Examples thereof include organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, and γ-butyrolactone. The usage-amount of a solvent will not be restrict | limited especially if a negative electrode material slurry can be made into desired states, such as a paste. For example, the amount can be 60 parts by mass or more and less than 150 parts by mass with respect to 100 parts by mass of the negative electrode material.

  The type and shape of the current collector are not particularly limited, and can be selected according to the purpose. For example, aluminum foil, nickel foil, copper foil, aluminum mesh, nickel mesh, copper mesh, etc. can be mentioned.

  The method in particular of apply | coating a negative electrode material slurry to a collector is not restrict | limited, A well-known method can be selected suitably. Specific examples include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method. The coating amount of the negative electrode material paste is not particularly limited and can be selected according to the purpose.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention contains the negative electrode for lithium ion secondary batteries of this invention, a positive electrode, and electrolyte (preferably electrolyte solution). A lithium ion secondary battery can be obtained by disposing a negative electrode and a positive electrode so as to face each other with a separator interposed therebetween and injecting an electrolytic solution.

  The positive electrode is produced by forming a positive electrode material layer containing an additive such as a positive electrode active material and, if necessary, a thickener and a conductive aid, on the surface of the current collector in the same manner as the negative electrode. .

  The positive electrode active material is not particularly limited, and can be appropriately selected as necessary. For example, a lithium-containing metal composite oxide containing at least lithium and at least one metal selected from the group consisting of iron, cobalt, nickel, and manganese is preferable. Specific examples of the lithium-containing metal composite oxide include lithium manganese composite oxide, lithium cobalt composite oxide, and lithium nickel composite oxide.

  The lithium-containing metal composite oxide further includes at least one metal selected from the group consisting of Al, V, Cr, Fe, Co, Sr, Mo, W, Mn, B, and Mg, a lithium site, or A lithium-containing metal composite in which sites such as manganese, cobalt, and nickel are substituted can also be used. A positive electrode active material may be used individually by 1 type, or may be used in combination of 2 or more type.

  The positive electrode has a positive electrode material slurry containing a positive electrode active material, a binder, a solvent capable of dissolving or dispersing the binder, and an additive added as necessary, on at least one surface of the current collector. It can be made by applying and then drying to remove the solvent and rolling if necessary.

  As the binder, the solvent, the additive, and the current collector, those exemplified in the section of the negative electrode for lithium ion secondary batteries can be similarly used.

  The electrolyte used in the lithium ion secondary battery of the present invention is not particularly limited, and a known one can be used. For example, a non-aqueous lithium ion secondary battery can be manufactured by using an electrolytic solution in which an electrolyte is dissolved in an organic solvent.

As _{the electrolyte, LiPF 6, LiClO 4, LiBF} 4, LiClF 4, LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiC ( CF ₃ SO ₂ ) ₃ , LiCl, LiI and the like can be mentioned.

  Examples of the organic solvent include carbonate solvents such as propylene carbonate, ethylene carbonate, and diethyl carbonate; lactone solvents such as γ-butyrolactone; chain ether solvents such as 1,2-dimethoxyethane, dimethyl ether, and diethyl ether; tetrahydrofuran, 2 -Cyclic ether solvents such as methyltetrahydrofuran, dioxolane, 4-methyldioxolane; sulfolane solvents such as sulfolane; sulfoxide solvents such as dimethyl sulfoxide; nitrile solvents such as acetonitrile, propionitrile, benzonitrile; N, N- Examples include amide solvents such as dimethylformamide and N, N-dimethylacetamide; and polyoxyalkylene glycol solvents such as diethylene glycol. An organic solvent may be used individually by 1 type, or may be used in combination of 2 or more type.

  Various known separators can be used as the separator. Examples of the separator include paper, polypropylene, polyethylene, glass fiber, and ceramic.

  The method for producing the lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode for lithium ion secondary batteries of the present invention is used, and materials such as known positive electrodes, electrolytes for lithium ion secondary batteries, separators, etc. Can be prepared by a known method.

  The structure of the lithium ion secondary battery is not particularly limited, and can be selected according to the application. For example, a structure in which a positive electrode, a negative electrode, and a separator are stacked and wound in a flat spiral shape, a structure in which a flat laminate of the positive electrode, the negative electrode, and the separator is enclosed in an exterior body are generally used.

  Although the lithium ion secondary battery of this invention is not specifically limited, It is used as a paper-type battery, a button-type battery, a coin-type battery, a laminated battery, a cylindrical battery, a square battery, etc.

Since the lithium ion secondary battery of the present invention is excellent in input / output characteristics and energy density, it can be suitably used for electric vehicles, hybrid vehicles, power tools, industrial storage batteries and the like that require high input / output characteristics.

  The negative electrode material for lithium ion secondary batteries of the present invention can also be applied to uses other than lithium ion secondary batteries. That is, the present invention can also be applied to an electrochemical device (for example, a hybrid capacitor) having a charge / discharge mechanism that inserts and desorbs lithium ions.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The materials used in the examples and reference examples were prepared by the method described below or obtained from the suppliers described below. “%” Is based on mass.

<Example 1>
(1) Production of negative electrode material and measurement of various characteristics (1-1) Production of negative electrode material Coal coal tar was heat-treated at 400 ° C using an autoclave to obtain raw coke. The raw coke was pulverized and then calcined in an inert atmosphere at 1200 ° C. to obtain a coke lump. The coke mass was pulverized and classified using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 7 μm. Then removed fines so that the value of D _{90 /} D ₁₀ is within the range of 2 to 10, to adjust the volume particle size distribution of lump coke after grinding and classification. Thereafter, the coarse powder was removed with a 300 mesh sieve to produce amorphous carbon particles (core material).

  100 parts by mass of the amorphous carbon particles obtained in the above step and 9 parts by mass of coal tar pitch (softening point 98 ° C., residual carbon ratio 50%) were mixed to obtain a mixture. This mixture was put into a device (dry particle compounding device) in which rotating blades were arranged in the cylinder and the mixture was rubbed between the inner wall of the cylinder and the rotating blades (dry particle compounding device) and sealed. Subsequently, the carbon composite which the coal tar pitch adhered to the surface was produced by performing the process which rubs a mixture for 20 minutes with a load of 24 kW.

Next, amorphous carbon particles having a carbon layer formed on the surface by carbonizing the coal tar pitch by heating to 900 ° C. at a heating rate of 20 ° C./hour in a nitrogen atmosphere and holding at 900 ° C. for 1 hour. Got. The amorphous carbon particles were crushed with a cutter mill, and a negative electrode material was produced through a 300-mesh standard sieve. The cumulative volume distribution (D ₁₀ , D ₅₀ and D ₉₀ ), tap density, interplanar spacing d002 of the carbon 002 surface, crystallinity (R value), carbon layer thickness, specific surface area and true density of the obtained negative electrode material Each was measured by the method described below. The results are shown in Table 1. In addition, the relationship between D ₅₀ and tap density T is shown in FIG. The straight line in FIG. 2 is T = D ₅₀ × 0.018 + 0.42.

(1-2) Volume cumulative distribution (D ₁₀ , D ₅₀ and D ₉₀ )
The volume cumulative distribution was measured by the following method.
A measurement sample (5 mg) was placed in a 0.01% by mass aqueous solution of a surfactant (Esomine T / 15, Lion Corporation), and dispersed with a vibration stirrer. The obtained dispersion was put into a sample water tank of a laser diffraction particle size distribution analyzer (SALD3000J, Shimadzu Corporation), circulated with a pump while applying ultrasonic waves, and measured by a laser diffraction method. The measurement conditions were as follows. When the particle size of the obtained volume cumulative distribution is 10% from the smaller particle size (volume cumulative 10% particle size) is D ₁₀ (μm), and when the particle size of the volume cumulative distribution is 50% from the smaller particle size ( The volume cumulative 50% particle diameter) was defined as D ₅₀ (μm), and the volume cumulative distribution when the particle diameter reached 90% from the smaller one (volume cumulative 90% particle diameter) was defined as D ₉₀ (μm). Hereinafter, in the examples and comparative examples, the volume cumulative distribution was measured in the same manner.
・ Light source: Red semiconductor laser (690nm)
Absorbance: 0.10 to 0.15
-Refractive index: 2.00-0.20i

Note that the value of D _{90 /} D ₁₀ of the amorphous carbon particles is individually D ₉₀ and D ₁₀ in the above measurement, respectively, (values rounded to the second decimal place) value up to two decimal places The values up to the first decimal place (values obtained by rounding off the second decimal place) obtained by calculating D ₉₀ / D ₁₀ from these values were obtained.

(1-3) Tap density The sample was slowly filled in a 150 ml cylinder so as to be 100 ml ± 1 ml, and the mass was measured. Thereafter, the tap density T (g / cm ³ ) was calculated from the volume measured after dropping the cylinder 250 times from a height of 5 cm.

(1-4) Interplanar spacing d002 of the carbon 002 plane
The interplanar spacing d002 of the carbon 002 plane was measured by the following method.
The sample was filled in the concave portion of the quartz sample holder and set on the measurement stage. Measurement was performed with an X-ray diffractometer (MultiFlex (2 kW), Rigaku Corporation) under the following measurement conditions. Note that the surface spacing d002 of the carbon 002 plane was calculated using analysis software attached to the X-ray diffractometer.
-Radiation source: CuKα ray (wavelength = 0.15418 nm)
・ Output: 40kV, 20mA
・ Sampling width: 0.010 °
-Scanning range: 10 ° to 35 °
・ Scanning speed: 0.5 ° / min

(1-5) Crystallinity (R value)
The crystallinity (R value) was calculated from the Raman spectrum measured by the following method.
A microscopic laser Raman spectroscope (DXR Raman microscope, Thermo Fisher Scientific) was used as a measuring apparatus. The measurement conditions were as follows.
・ Laser wavelength: 532 nm
・ Laser output: 2mW
・ Exposure time: 2 seconds ・ Number of exposures: 4 times

The wave number of the obtained spectrum is the wave number of each peak obtained by measuring the reference substance inden (Wako Class 1, Wako Pure Chemical Industries, Ltd.) under the same conditions as described above, and the theoretical wave number of each peak of indene. Correction was performed using a calibration curve obtained from the difference between the two.
Raman spectra obtained after ^correction, and calculates the peak Ig detected in a range of 1570cm ^-1 ~1620cm ^-1, the R value from the intensity ratio of the peaks Id detected in a range of 1330cm ^-1 ~1360cm -1 (R value = Id / Ig).

(1-5) Carbon layer thickness The carbon layer thickness was measured by the following method.
The measurement sample was observed with a scanning transmission electron microscope (HD-2700, Hitachi High-Technologies Corporation), and the thickness of the carbon layer was measured from the obtained sample image. In the measurement, amorphous carbon is excluded except for the carbon portion that has penetrated into the inside of the amorphous carbon particles and the carbon portion that exists in the joint portion of the particles generated when the amorphous carbon particles are granulated or combined. The average value obtained by measuring the thickness of the carbon portion located on the surface of the particle at arbitrary five points was taken as the thickness of the carbon layer.

(1-6) Specific surface area The specific surface area was measured by the following method.
A nitrogen adsorption measuring device (AUTOSORB-1, QUANTACHROME) was used as the measuring device. When performing the measurement, after pre-treatment of the sample described later, the measurement temperature was set to 77K, and the measurement pressure range was set to less than 1 in relative pressure (equilibrium pressure with respect to the saturated vapor pressure).
As a pretreatment, the measurement cell charged with 0.05 g of sample was automatically deaerated and heated with a vacuum pump. The detailed conditions of this treatment were set such that the pressure was reduced to 10 Pa or less, heated at 110 ° C., held for 3 hours or more, and then naturally cooled to room temperature (25 ° C.) while maintaining the reduced pressure.

(1-7) True Density The true density was measured using a true density meter device (Micromeritics Accupic 1330, Shimadzu Corporation).

(2) Production of negative electrode 5% by mass of polyvinylidene fluoride (PVDF) N-methyl-2-pyrrolidone (92% by mass) with respect to 92 parts by mass of the negative electrode material produced in (1) above. NMP) solution was added. Next, the slurry was further diluted with NMP so that the total solid content mass was 46 parts by mass, and kneaded to prepare a slurry.

This slurry was applied onto the rolled copper foil with a comma coater with the clearance adjusted so that the coating amount per unit area was 6.7 mg / cm ² using a coating machine, and the conditions were 90 ° C. and 10 minutes. Primary drying was performed. Subsequently, it vacuum-dried on conditions of 105 degreeC and 1 hour, NMP and a water | moisture content were fully removed, and the electrode was produced. Then, it compressed so that the negative electrode density might be 1.05 g / cm < ³ > with a roll press machine, and produced the test negative electrode.

(3) Production of Battery A 2010 type coin cell was produced as the battery as follows.
The test negative electrode described in the above (2) was punched into a circle having a diameter of 14 mm to produce a negative electrode.
Metal lithium was used as the counter electrode. As an electrolytic solution, LiPF ₆ was dissolved to a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 3 to 7, and vinyl chloride was dissolved therein. What added carbonate so that a density | concentration might be 0.5 mass% was used. As the separator, a polyethylene microporous film having a thickness of 20 μm was used.

(4) Evaluation (4-1) Evaluation of Aggregated Particles The negative electrode slurry described in (2) above is dropped into a deep groove of a grind gauge (BYK, Gardner), and the scraper is moved at a constant speed in a direction of 0 μm depth. Then, the scale at the position where the linear mark was first generated was read. Out of 5 tests, when the value of the scale is 50 μm or more occurs 2 times or more, it is judged as defective (defect, indicated as Y in Table 1), and less than 2 times is good (no defect, table 1 was displayed as N).

(4-2) Measurement of electrode density Of the negative electrode described in (2) above, the negative electrode before being compressed by a roll press machine is punched into a size of 16 mm in diameter, and 5 MPa by a mini press (RIKEN SEIKI Co., Ltd.). Compressed at a pressure of The mass and thickness of the compressed electrode were measured, and the electrode density was calculated from the value obtained by subtracting the mass and thickness of the copper foil. The average value of three tests was taken as the electrode density of the negative electrode. In this measurement, the higher the numerical value of the electrode density, the more negative electrode material can be introduced per unit volume, and the higher the energy density.

(4-3) Evaluation of Initial Efficiency Using the battery described in (3) above, charging was performed at a constant current density corresponding to 0.1 C until the battery voltage was 0 V (V vs. Li / Li ⁺ ). Thereafter, the battery was charged at a constant voltage of 0 V until the current density attenuated to a value corresponding to 0.01 C, and the capacity at the time of charging was calculated. After a 30-minute rest after charging was completed, the battery was discharged to 1.5 V at a constant current density corresponding to 0.1 C, and the capacity at the time of discharge was calculated. Further, the initial efficiency (discharge capacity / charge capacity × 100,%) was calculated from the ratio of the capacity during charging and discharging. The results are shown in Table 1. Note that xC means a current value at which charging or discharging is completed in 1 / x time (x is an arbitrary numerical value). That is, for example, the above “constant current density corresponding to 0.1 C” means a current value at which discharge is completed in (1 / 0.1) hours.

(4-4) Charging load characteristic evaluation (I / O characteristic evaluation)
Using the battery described in (3) above, the battery was charged at a constant current density corresponding to 0.1 C until the battery voltage reached 0 V (V vs. Li / Li ⁺ ), and then the current density at a constant voltage of 0 V. Until the battery decays to a value corresponding to 0.01C. After a 30-minute rest after charging was completed, the battery was discharged to 1.5 V at a constant current density corresponding to 0.1 C. Thereafter, charging at a current corresponding to 0.1C, 0.5C, 1C, 3C and 5C and discharging at a current corresponding to 0.1C are repeated, and the charging capacity at each rate is 0.1C. The ratio to the charge capacity was calculated and used as the input / output characteristics. Table 1 shows the ratio (%) of the charge capacity charged at 5C to the charge capacity at 0.1C as input / output characteristics.

<Example 2>
A negative electrode material, a slurry, an electrode and a battery were prepared in the same manner as in Example 1 except that the coal tar pitch described in (1) of Example 1 was changed to 32 parts by mass of polyvinyl alcohol (carbonization rate: 14%). Similar measurements and evaluations were made. The results are shown in Table 1 and FIG.

<Example 3>
Except that the coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 10 μm. Produced a negative electrode material, slurry, electrode and battery in the same manner as in Example 1, and performed the same measurement and evaluation. The results are shown in Table 1 and FIG.

<Example 4>
The same procedure as in Example 1 except that the coal tar pitch described in (1) of Example 1 was changed to 6.9 parts by mass of a coal tar pitch having a high softening point (softening point 150 ° C., residual carbon ratio 65%). A negative electrode material, a slurry, an electrode and a battery were prepared, and the same measurement and evaluation were performed. The results are shown in Table 1 and FIG.

<Example 5>
The coal tar pitch described in (1) of Example 1 was changed to 7.4 parts by mass of a powdered phenol resin (residual carbon ratio 61%) and stirred and kneaded at 200 ° C. for 1 hour using a heating kneader. A negative electrode material, a slurry, an electrode, and a battery were produced in the same manner as in Example 1 except that the carbon composite was produced, and the same measurement and evaluation were performed. The results are shown in Table 1 and FIG.

<Example 6>
Except that the coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle size (D ₅₀ ) of the coke mass after pulverization and classification was around 15 μm. Produced a negative electrode material, slurry, electrode and battery in the same manner as in Example 1, and performed the same measurement and evaluation. The results are shown in Table 1 and FIG.

<Example 7>
The coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 15 μm. A negative electrode material, a slurry, an electrode and a battery were produced in the same manner as in Example 1 except that the coal tar pitch was changed to 32 parts by mass of polyvinyl alcohol (carbonization rate: 14%), and the same measurement and evaluation were performed. The results are shown in Table 1 and FIG.

<Example 8>
The coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 15 μm. The negative electrode material, slurry, electrode and battery were the same as in Example 1 except that the coal tar pitch was changed to 6.9 parts by mass of the coal tar pitch having a high softening point (softening point 150 ° C., residual carbon ratio 65%). The same measurement and evaluation were performed. The results are shown in Table 1 and FIG.

<Example 9>
The coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 15 μm. , Except that coal tar pitch was changed to 7.4 parts by mass of powdered phenol resin (residual carbon ratio 61%) and that a carbon composite was prepared by stirring and kneading at 200 ° C. for 1 hour using a heating kneader. Produced a negative electrode material, slurry, electrode and battery in the same manner as in Example 1, and performed the same measurement and evaluation. The results are shown in Table 1 and FIG.

<Example 10>
The coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 15 μm. A negative electrode material, slurry, electrode, and battery were prepared in the same manner as in Example 1 except that the mass of the coal tar pitch was changed to 4 parts by mass, and the same measurement and evaluation were performed. The results are shown in Table 1 and FIG.

<Reference Example 1>
A negative electrode material, a slurry, an electrode and a battery were prepared in the same manner as in Example 1 except that the composite condition described in (1) of Example 1 was set to 2 minutes at a load of 24 kW, and the same measurement and evaluation were performed. went. The results are shown in Table 1 and FIG.

<Reference Example 2>
The classification process after crushing the coke mass described in Example 1 (1) was performed except that the operation for removing fine powder was not performed until the value of D ₉₀ / D ₁₀ was in the range of 2 to 10. In the same manner as in Example 1, a negative electrode material, a slurry, an electrode, and a battery were prepared and evaluated in the same manner. The results are shown in Table 1.

<Reference Example 3>
The coke mass described in (1) of Example 1 was pulverized using an impact pulverizer equipped with a classifier so that the average particle diameter (D ₅₀ ) of the coke mass after pulverization and classification was around 15 μm, Except that the mass of the coal tar pitch was changed to 18 parts by mass, a negative electrode material, a slurry, an electrode, and a battery were produced in the same manner as in Example 1, and the same measurement and evaluation were performed. The results are shown in Table 1 and FIG.

<Reference Example 4>
Other than the use of natural graphite particles (TIMREX KS10, TIMCAL Ltd.) having an average particle diameter (D ₅₀ ) of 6.2 μm instead of the amorphous carbon particles (core material) described in (1) of Example 1. Produced a negative electrode material, slurry, electrode and battery in the same manner as in Example 1, and performed the same measurement and evaluation. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 2, according to the present invention, the lithium ion secondary battery having excellent charge / discharge efficiency and charge / discharge input / output characteristics and improved energy density (electrode density), which is a problem of amorphous carbon materials. It turned out that the negative electrode material for secondary batteries and the negative electrode for lithium ion secondary batteries can be provided. Further, it was found that by using the negative electrode material of the present invention, it is possible to produce a negative electrode with good appearance without aggregated particles.

Furthermore, the negative electrode material described in Examples 1-5 is an average particle diameter D ₅₀ less among Examples 1 to 10, while maintaining a high charge-discharge efficiency and high energy density, the lithium ion secondary batteries for HEV It was found that charge / discharge input / output characteristics which are strongly demanded can be improved.

  The negative electrode material described in Reference Example 1 in which the composite time has been shortened is considered to be that the tap density does not satisfy Formula (3) because the composite treatment is not sufficiently performed, and the electrode density of the electrode is reduced. It is done.

The negative electrode material of Reference Example 2 in which the value of D ₉₀ / D ₁₀ is greater than 10.0 is considered to have deteriorated charge / discharge efficiency due to a wide particle size distribution and a large specific surface area. Further, it is considered that the tap density does not satisfy the formula (3), and the electrode density is reduced.

  The negative electrode material described in Reference Example 3 having a thick carbon layer and a low tap density is considered to have a reduced tap density because the tap density does not satisfy the formula (3). Moreover, it became clear that the problem of the appearance defect that aggregated particles occur frequently at the time of electrode coating occurs.

  In Reference Example 4 in which natural graphite particles are used as the core material instead of amorphous carbon particles, the R value is less than 0.70 and the crystallinity is high.

Claims (7)

In the cumulative volume distribution (%) of the particle size measured by the laser diffraction method, the particle diameter D ₁₀ (μm) when the particle diameter is 10% from the smaller particle diameter and the particle when the particle diameter is 50% from the smaller particle diameter The diameter D ₅₀ (μm) and the particle diameter D ₉₀ (μm) at 90% from the smaller particle diameter satisfy the following expressions (1) and (2), and the tap density T (g / cm ³ ) is an amorphous carbon particle satisfying the following formula (3), has a carbon layer on at least a part of the surface of the amorphous carbon particle, and the thickness of the carbon layer is 1 nm or more and less than 35 nm. A negative electrode material for a lithium ion secondary battery.
(1) D ₉₀ / D ₁₀ ≦ 10.0
(2) 3.0 ≦ D ₅₀ ≦ 20.0
(3) D ₅₀ × 0.018 + 0.42 ≦ T The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the amorphous carbon particles further satisfy the following formula (4).
(4) 5.0 ≦ D ₅₀ ≦ 12.0   3. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein an R value obtained in a Raman spectrum measurement of the amorphous carbon particles is 0.70 or more and less than 1.40. The specific surface area determined from nitrogen adsorption measurements at 77K amorphous carbon particles is less than 1.0 m ² / g or more 7.0 m ² / g, according to any one of claims 1 to 3 Negative electrode material for lithium ion secondary batteries. The true density of the amorphous carbon particles is less than 2.00 g / cm ³ or more 2.24 g / cm ^3, a negative for a lithium ion secondary battery according to any one of claims 1 to 4 electrode material .   The negative electrode for lithium ion secondary batteries containing the negative electrode material for lithium ion secondary batteries of any one of Claims 1-5.   The lithium ion secondary battery containing the negative electrode for lithium ion secondary batteries of Claim 6, a positive electrode, and electrolyte.