WO2007148553A1

WO2007148553A1 - Negative-electrode active material for lithium ion secondary battery

Info

Publication number: WO2007148553A1
Application number: PCT/JP2007/061712
Authority: WO
Inventors: Masamitsu Katsuura; Toshiaki Sogabe; Koichi Morita
Original assignee: Osaka Gas Chemicals Co., Ltd.
Priority date: 2006-06-20
Filing date: 2007-06-11
Publication date: 2007-12-27
Also published as: JP2008027897A

Abstract

A negative-electrode active material for lithium ion secondary battery, comprising a granulated substance obtained by subjecting a mixture of a metal powder capable of lithium ion occlusion and release and at least one graphite charge material selected from the group consisting of a flake graphite and an artificial graphite of 0.336 nm or less (002)-face interplanar spacing to pulverization in high-velocity air current and granulation, wherein part of the graphite as the charge material is pulverized so as to have a structure of laminate of the graphite charge material and pulverizate thereof in which at the surface or interior thereof, a metal powder is dispersed. This negative-electrode active material for lithium ion secondary battery is a novel active material of high performance, simultaneously realizing high charge/discharge capacity and excellent cycle characteristics.

Description

Specification

Negative electrode active material for lithium ion secondary battery

Technical field

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

Background art

[0002] Lithium ion secondary batteries are widely used as power sources for electronic devices such as mobile phones and laptop computers. A lithium ion secondary battery has a configuration in which a positive electrode and a negative electrode capable of inserting and extracting lithium ions face each other, and a separator is interposed between the positive electrode and the negative electrode. These positive electrode, negative electrode and separator are housed in a metal container, and a non-aqueous electrolyte is injected into the metal container.

[0003] Currently, development of a negative electrode material having a high charge / discharge capacity (electric capacity) is being promoted in order to increase the capacity of a lithium ion secondary battery. Conventionally, carbon materials such as graphite powder have been mainly used as negative electrode active materials. The theoretical electric capacity of graphite is 372 mAh / g, and various developments have been carried out to obtain higher charge / discharge capacity. ing.

[0004] For example, it has been attempted to use a carbon material such as graphite in combination with another material having a higher theoretical electric capacity than graphite. In addition, silicon, tin, aluminum and the like that are alloyed with lithium are being studied. Among these materials, silicon has a high theoretical electric capacity (4198 mAhZg), and lithium ion secondary batteries using this as part of the negative electrode material have been reported. For example, Patent Document 1 below discloses a carbon material having a structure in which composite particles containing at least silicon and carbon are dispersed around graphite particles.

[0005] However, silicon has a property of expanding when lithium is absorbed, and has a significantly higher expansion rate than other materials such as graphite. Therefore, when silicon is used as a part of the negative electrode active material of a lithium-ion secondary battery, if the lithium is repeatedly occluded and released by charging and discharging, the silicon itself will repeatedly expand and contract. As a result, a phenomenon in which silicon does not endure expansion and contraction and silicon becomes finer and desorbs from the carbon material. Occurs. In this case, since silicon itself has no electronic conductivity, the current collection characteristics are deteriorated, or the pulverized silicon and the non-aqueous electrolyte react to decompose the non-aqueous electrolyte. This causes a malfunction. For this reason, the negative electrode material containing silicon has a drawback in that the charge / discharge capacity decreases remarkably when charge / discharge is repeated, and sufficient cycle characteristics cannot be obtained. No. 255529

Disclosure of the invention

Problems to be solved by the invention

[0006] The present invention has been made in view of the current state of the prior art described above, and its main purpose is to provide a high charge / discharge capacity and excellent cycle characteristics in a negative electrode active material for a lithium ion secondary battery. It is to provide a novel negative electrode active material having excellent performance, and a lithium ion secondary battery using the negative electrode active material.

Means for solving the problem

[0007] The present inventor has intensively studied to achieve the above-described object. As a result, according to the method of using a mixture of a graphite raw material and a metal powder capable of occluding and releasing lithium ions as a raw material, and colliding this in a high-speed air stream to pulverize and granulate the raw material powder, Part of the powder is pulverized to form a granulated body with a structure in which the graphite raw material and its powder are agglomerated and laminated, and the metal powder is found to have a structure dispersed on the surface and inside of the granulated body. did. Further, by having such a structure, even when the metal powder repeatedly expands and contracts by occlusion and release of lithium and is refined, a large amount of the metal powder is present inside the granulated body. By doing so, it was found that expansion and contraction were performed in the voids inside the granulated body, and detachment from the granulated body was prevented. As a result, it was possible to maintain a high charge / discharge capacity, and it was found to have excellent cycle characteristics, and the present invention was completed here.

That is, the present invention provides the following negative electrode active material for lithium ion secondary batteries and a lithium ion secondary battery using the active material.

1. at least one graphite raw material selected from the group consisting of scaly graphite and artificial graphite having a (002) plane spacing of 0.336 nm or less, and a metal capable of inserting and extracting lithium ions A granulated product obtained by pulverizing and granulating a mixture with a powder in a high-speed air stream, and a part of graphite as a raw material is pulverized to form a structure in which the graphite raw material and the pulverized product are laminated. And a negative electrode active material for a lithium ion secondary battery having a granulated force with a metal powder dispersed on the surface and inside thereof.

2. The above-mentioned item 1, comprising a granulated material obtained from a mixture of a graphite raw material having an average particle size of 5 to 150 μm and a metal powder having an average particle size of 0.01 to 2 μm. Negative electrode active material for lithium ion secondary battery.

3. The negative electrode active material for a lithium ion secondary battery according to item 1 or 2, wherein the tap density of the granulated body is 10% or more higher than the tap density of the raw material mixture.

4. The negative electrode active material for a lithium ion secondary battery according to any one of the above items 1 to 3, comprising a granulated body obtained using silicon powder as the metal powder.

5. The negative electrode active material for a lithium ion secondary battery according to any one of the above items 1 to 4, comprising a granulated body obtained using natural graphite as a graphite raw material.

6. The lithium ion according to any one of the above items 1 to 5, comprising a granulated material obtained by using a raw material containing 0.3 to 40% by mass of a metal powder, wherein the total amount of the graphite raw material and the metal powder is 100% by mass. Negative electrode active material for um ion secondary battery.

7. The negative electrode for a lithium ion secondary battery according to any one of the above items 1 to 6, comprising a granulated material obtained by pulverizing and granulating a raw material mixture subjected to wet or dry premixing in a high-speed air stream Active material.

8. Surface force of the granule according to any one of the above items 1 to 7 A negative electrode active material for a lithium ion secondary battery comprising a granule coated with a carbon precursor or a carbonized product thereof.

9. A lithium ion secondary battery comprising the negative electrode active material for a lithium ion secondary battery according to any one of the above items:! To 8 as a constituent element.

Hereinafter, the negative electrode active material for a lithium ion secondary battery of the present invention will be specifically described.

[0010] completion

In the negative electrode active material for a lithium ion secondary battery of the present invention, the raw material is a graphite raw material and a lithium raw material. It is used in combination with a metal powder that can occlude and release thium ions.

[0011] As the graphite raw material, at least one selected from the group consisting of scaly graphite and artificial black lead having a (002) plane spacing of 0.336 nm or less can be used. The above-mentioned surface spacing is a value obtained by X diffraction method.

Among these graphite raw materials, scaly graphite is divided into scaly or leafy thin scaly graphite (flaky graphite) and scaly graphite having a massive shape. In the present invention, scaly graphite is used. And lump scaly graphite can be used. In particular, natural graphite consisting of scaly graphite with high crystallinity is easy to form a granulated body because of its soft material, and has good ability to absorb and release calcium, and has high electric capacity, flatness at low potential. This is preferable in that it has discharge characteristics.

[0013] As the artificial graphite, artificial graphite having a crystal plane (002) plane spacing of 0.336 nm or less can be used. As such artificial graphite, for example, graphite or quiche graphite obtained by heat-treating graphitizable carbon such as needle coatus at a temperature of about 3000 ° C. can be used. These artificial graphites have a structure and structure close to that of scaly graphite.

[0014] The average particle size of the graphite raw material may be about 5 to about 150 μΐη, but the preferred particle size varies depending on the target granulated particle size. For example, if the average particle size of the target granule is about 7 to 10 μΐη, about 5 to 40 / im is appropriate, and about 7 to 30 μΐη is preferable 10 to 10 More preferably, it is about 20 μΐη. If the target granule has an average particle size of 20 μm, 20 to 120 μm is appropriate.

In the present specification, the average particle diameter means a particle diameter (D50) corresponding to a cumulative frequency of 50%, measured using a laser diffraction scattering method.

[0016] The specific surface area of the graphite material is preferably to be 0. 5 to 20 m ² / g approximately instrument:! ~ And more preferably about 10 m ² / g. The specific surface area in this case is a value measured by the BET method.

[0017] The metal powder is not particularly limited as long as it is a metal powder capable of occluding and releasing lithium ions. Specific examples of such metal powders include silicon, germanium, tin, lead, aluminum, indium, titanium, and alloys containing these. The The alloy may be an alloy containing a metal that does not occlude and release lithium ions in addition to the above-described alloy composed of a combination of metal components. In this case, the content of the metal component in the alloy is not particularly limited, but is preferably about 50% by mass or more in order to obtain a sufficient capacity.

In particular, silicon is preferable in that it has a high theoretical electric capacity of 4198 mAhZg.

Silicon may be either a polycrystal or a single crystal.

The average particle diameter of the metal powder is suitably about 2 μm or less, preferably about 1 μm or less, more preferably about 0.5 × m or less. When the particle size of the metal powder is too large, the particle size becomes larger than the void part of the granulated body formed by graphite, so the amount of metal powder present in the void part is reduced and the cycle characteristics are reduced. I can't improve it enough. Regarding the lower limit of the particle size of the metal powder, it is preferable that the particle size is not particularly limited. With a normal pulverization method, it is possible to produce fine powders with an average particle size of about 0.01 x m, and metal powders with this size can be used effectively.

[0020] Usually, the above-described metal powder having a small particle diameter can be obtained by pulverization using a jet mill, a stirring tank type stirring mill (bead mill or the like), and the like. For example, a stirring tank type stirring mill (bead mill or the like) can be used to pulverize in a wet manner using an organic solvent such as isopropyl alcohol, methyl alcohol, or ethyl alcohol as a medium.

[0021] The mixing ratio of the graphite raw material and the metal powder is not particularly limited because the appropriate mixing ratio varies depending on the density and electric capacity of the metal powder to be used. However, the electric capacity of the obtained granule is not limited. It is preferable to set the ratio to a value that exceeds the theoretical capacity of graphite, 372 mAh / g. In general, it is preferable that the total amount of the graphite raw material and the metal powder is 100% by mass, and the ratio of the metal powder is about 0.3 to 40% by mass. preferable. If the ratio of the metal powder is lower than this, it is difficult to obtain a discharge capacity of 372 mAhZg or more in most cases, and if it exceeds the above range, expansion and contraction of the negative electrode active material when inserting and extracting lithium increase. This is preferable because the cycle characteristics deteriorate. For example, when using silicon powder as the metal powder, The proportion of the powder is preferably about 0.5 to 25% by mass.

[0022] Method for producing negative electrode active material basket

In the present invention, the graphite raw material and metal powder are collided in a high-speed air current to pulverize a part of the graphite raw material to form a structure in which the graphite raw material and the pulverized material are laminated. A granulated body in which metal powder is dispersed on the surface and inside can be obtained.

[0023] As a specific manufacturing method, for example, a high-speed air current collision method described in JP-A-6-210152 can be employed. Hereinafter, this method will be specifically described with reference to FIG. 1 and FIG.

FIG. 1 and FIG. 2 are conceptual explanatory views showing an example of a granulating apparatus that can be used for producing the granulated body of the present invention. 1 and 2, 1 is the casing of the apparatus, 2 is a cover after that, 3 is a front cover thereof, 4 is a rotor that is in the casing 1 and rotates at high speed, and 5 is a predetermined interval around the outer periphery of the rotor 4. A plurality of impact pins arranged in a radial pattern with a general arrangement of hammer type or blade type. 6 is a rotating shaft that rotatably supports the rotor 4 in the casing 1, 7 is a collision ring that is provided along the outermost raceway surface of the impact pin 5 and with a certain space around it. The collision ring 7 can be an uneven type or a circumferential plane type having various shapes. The force varies depending on the size of the device. The gap between the outermost raceway surface of the impact pin 5 and the collision ring 7 is preferably 0.5 to 0 mm. 8 is an on-off valve that fits closely to the granule discharge port provided by cutting out a part of the collision ring 7, 9 is the valve shaft of the on-off valve 8, 10 is the on-off valve 8 operated via the valve shaft 9 19 is a controller, 11 is open at one end of the inner wall of the collision ring 7, and the other end is opened at the front cover 3 located at the center of the rotor 4 to form a closed circuit. A circulation circuit, 12 is a raw material hopper, 13 is a chute for raw material supply that connects the raw material hopper 12 and the circulation circuit 11, and 14 is an open / close valve provided in the middle of the chute. 15 is an impact chamber provided between the outer periphery of the rotor ₄ and the collision ring 7, 16 is a circulation port to the circulation circuit 11 opened in a part of the inner wall of the collision ring 7, and 17 is a discharge pipe for the granulated material. Are shown respectively. In addition, since this apparatus is a complete batch type apparatus, the atmospheric temperature in the apparatus may increase with time. The collision ring 7 has a jacket structure 18. In this case, it is possible to control the atmospheric temperature in the shock chamber 15 and the circulation circuit 11 at a constant level by flowing cooling water there.

[0025] In order to produce a granulated body using the above-described apparatus, first, the on-off valve 14 provided in the middle of the chute for supplying the raw material is closed, and the on-off valve 8 at the granule discharge port is opened. In the closed state, the rotating shaft 6 is driven by the driving means (not shown) to rotate the rotor 4. At this time, an abrupt air flow is generated with the rotation of the impact pin 5, and the circulation circuit 11 opens from the circulation port 16 opened to a part of the inner wall of the collision ring 7 by the fan effect based on the centrifugal force of the air flow. A circulating flow of airflow returning from the opening at the center of the front cover 3 to the impact chamber 15 around the front cover 3, that is, a complete self-circulating flow is formed. The amount of circulating air generated per unit time at this time is significantly larger than the total volume of the impact chamber and the circulation system, so a huge number of air circulation cycles are formed in a short time. Since the circulating air volume is proportional to the outer peripheral speed of the rotor, the air circulation cycle per unit time increases as the outer peripheral speed of the rotor increases.

[0026] The rotation of the rotor is preferably performed at an outer peripheral speed of 30 to about 150 m / s, more preferably about 50 to 100 m / s. At this time, an abrupt air flow is generated with the rotation of the blade, and a fan effect based on the centrifugal force of the air flow forms a circulating air flow that returns from the circulation port to the rotor through the circulation path. . For example, an air circulation cycle of about 700 to 800 times / minute is performed.

Next, the on-off valve 14 is opened, and when the mixed powder of the graphite raw material and the metal powder is injected into the raw material hopper 12, the mixed powder enters the impact chamber 15 through the chute 13 from the raw material hopper 12. . After confirming that the mixed powder does not remain in the raw material hopper 12, the on-off valve 14 is closed.

[0028] The mixed powder is momentarily impacted by a large number of impact pins 5 of the rotor 4 that rotates at a high speed in the impact chamber 15, and further collides with the surrounding impact ring 7. Furthermore, impacts, compression, and shearing force are applied due to the collision of graphite raw materials. Then, accompanying the circulating flow of the airflow, it returns to the impact chamber 15 again through the circulation circuit 11 and receives the same action again. In this way, by repeatedly receiving the same action, the graphite particles, whose corners have been sequentially dropped in a process of several minutes, increase in thickness while capturing the pulverized small particles and become agglomerated. Thus, a granulated body in which the metal powder is dispersed on the surface and inside thereof is formed.

[0029] After the above operation is completed, the on-off valve 14 is opened, and the on-off valve 8 of the granule discharge port is moved to the position indicated by the chain line to open, and the obtained granule is discharged.

[0030] Negative electrode active material of the present invention

In the granulated body obtained by the above-described method, the graphite raw material as a raw material collides in a collision area where jet air currents collide with each other, and a part thereof, in particular, a corner portion of the graphite raw material is pulverized. And the graphite raw material from which the corner | angular part was dropped capture | acquires the grind | pulverized small particle, Furthermore, when graphite particle | grains are laminated | stacked, it increases in thickness and becomes a lump, and the granule of graphite is formed. The formed granule has a shape close to a sphere compared to the graphite used as a raw material, and a void portion is formed between the laminated graphites inside the granule. In the manufacturing process of such a granulated body, the metal powder is uniformly mixed with graphite and is dispersed on the surface and inside of the obtained granulated body.

[0031] The obtained granulated body is nearly spherical compared to the graphite used as a raw material, and has a higher tap density than the raw material mixture. Usually, the tap density of the granulate obtained by the above method is preferably about 10% or more higher than the tap density of the raw material mixture, and more preferably about 25% or more. preferable. In this specification, the tap density is measured using a commercially available tap density meter (TAPDENSER KYT-4000 manufactured by Seishin Enterprise Co., Ltd.). The density at the point when the bulk density of the powder disappeared and became constant.

[0032] The obtained granulated body preferably has an average particle size of about 5 to 30 μΐη, more preferably about 7 to 20 μΐη. In particular, for a negative electrode active material used in a high-power lithium ion secondary battery that requires high-speed charge / discharge, the average particle size is preferably about 7 to 12 μm.

[0033] As shown in FIG. 3, the granulated body obtained by the above-described method is laminated in a state in which it is oriented in various directions so that the graphite particles 22 overlap each other. As described above, the graphite 22 is laminated in various directions, thereby forming a structure in which voids 24 and unevenness are generated from the inside of the granulated body to the surface 23. In addition, since the scaly graphite in a state where corner portions are cut off is piled up, the granulated body has a shape close to a sphere. For this reason, the negative electrode active material When used as, lithium Li can penetrate into the inside of the negative electrode active material from all directions, so that a large area in which lithium Li can penetrate / separate can be taken, and a high lithium storage capacity can be obtained.

Further, as shown in FIG. 3, the metal powder 21 is present in a large amount in the void portion 24 formed only by the surface 23 of the granulated body. For this reason, the metal powder repeatedly expands and contracts by occluding / releasing lithium, and even when the metal powder is refined by repetition of the expansion and contraction, expansion and contraction occurs inside the void portion 24. As a result, the pulverized metal powder is prevented from being detached from the granulated body having graphite power. As a result, even if the metal powder is repeatedly expanded and contracted to be miniaturized, the high charge / discharge capacity obtained by adding the metal powder with little deterioration in battery performance can be maintained for a long time.

[0035] Further, even if the metal powder present on the surface 23 falls off, the ratio of the metal powder to the whole metal powder is small, so that the conductivity of the negative electrode active material is hardly reduced.

[0036] Therefore, when the above-mentioned granulated body is used as a negative electrode active material of a lithium ion secondary battery, graphite is used by combining graphite and a metal powder capable of occluding and releasing lithium ions. Compared to the case where it is used alone, it has a high charge / discharge capacity, and further, due to the granule having the specific structure described above, even when charge / discharge is repeated, the decrease in charge / discharge capacity is small. It has excellent cycle characteristics.

[0037] Preliminary mixing

In the present invention, the graphite raw material and the metal powder may be preliminarily mixed by a dry method or a wet method as a premixing step before the granulated body of the graphite raw material and the metal powder is produced by the above-described method.

[0038] When dry premixing is performed, for example, a shearing crusher or a ball mill can be used. A shear crusher mixes materials while applying a shearing force by rotating a blade at a high speed. In this case, the mixing time is preferably several minutes to 30 minutes.

[0039] Also, in the ball mill, when it is preferable to mix the materials using rubber balls, the metal powder is more uniformly dispersed. In this case, the mixing time is preferably about 30 minutes to 60 minutes. [0040] The metal powder can also be premixed in a wet manner. That is, the preliminary mixing can be performed by dispersing the metal powder and the graphite raw material in alcohol or the like, stirring and mixing, and then evaporating the organic solvent using an evaporator or a dryer.

[0041] It should be noted that after evaporating a solvent such as alcohol, the metal powder and the graphite are in a state of being slightly hardened. In this case, it is preferable to sufficiently loosen the solidified state using a ball mill or the like. In this case, in addition to the ball mill, a compression crusher, a shear crusher, a roller mill, an impact shear mill, an agitation mill, a jet mill, a laika machine, a mortar, a mortar, and the like can be used.

[0042] By using the powder premixed by such a method to produce a granulated body of the graphite raw material and the metal powder by the above-described method, a granulated body in which the metal powder is more uniformly dispersed can be obtained. You can get power S.

[0043]

The surface of the granule obtained by the above-described high-speed air-flow impact method may be further coated with a carbon precursor or a carbonized product thereof. By covering the surface, it is possible to cover the active sites of graphite, reduce the specific surface area, reduce the reactivity with the electrolytic solution, and suppress the decomposition of the electrolytic solution. Furthermore, by covering the surface, expansion and contraction of the metal powder can be suppressed, and detachment of the metal powder from the granulated body can also be suppressed.

[0044] Examples of the carbon precursor include various cellulose, polyacrylamide, polyethyleneimine, phenol resin, furan resin, epoxy resin, polyvinyl chloride, and polyvinyl alcohol in addition to coal-based or petroleum-based pitch and tar. These synthetic resins can be used. The pitch may be an isotropic pitch or an anisotropic pitch. These carbon precursors can also be used in combination of two or more.

[0045] The method of coating the surface of the granulated body with the carbon precursor described above is not particularly limited. For example, a mixture of the carbon precursor and the granulated body at room temperature may be used to soften the carbon precursor. A method of bringing the temperature to a temperature above the point, a method of mixing the carbon precursor and the granulated material at a temperature above the softening point of the carbon precursor, and immersing the granulated material in a liquid carbon precursor or a solution of the carbon precursor The method to do is applicable. [0046] The method of mixing the carbon precursor and the granulated material is not particularly limited. That's fine.

[0047] In the case of the method of mixing the carbon precursor and the granulated body at a temperature equal to or higher than the softening point of the carbon precursor, the mixing operation of the carbon precursor and the granulated body is performed at or above the softening point of the carbon precursor used. At a temperature of. The upper limit of the temperature is not particularly limited, but when the purpose is coating with a carbon precursor, the temperature may be set to a temperature not higher than the carbonization temperature of the carbon precursor. The pressure during stirring may be any of atmospheric pressure, pressurization, and reduced pressure.

[0048] The ratio of the carbon precursor to the granulated body may be a ratio that provides an effect such as suppressing the decomposition of the electrolytic solution. If an excessive amount of carbon precursor is added, the granules are excessively agglomerated and are liable to adhere, which is not preferable. Usually, it is preferable to set the amount of carbon precursor to about 0.:! To about 50 parts by mass with respect to 100 parts by mass of the granulated product. ~: More preferably about 15 parts by mass.

[0049] In the method of immersing the granule in a liquid carbon precursor or a solution of the carbon precursor, for example, when pitch or tar is used, the viscosity is reduced by heating, or The viscosity may be adjusted by mixing with an organic solvent. The organic solvent is not particularly limited, and for example, toluene, quinoline, acetone, hexane, benzene, xylene, methanolenophthalene, alcohols, coal oil, petroleum oil, and the like can be used.

[0050] The synthetic resin is usually used after being dissolved in an organic solvent. The organic solvent is not particularly limited, and is appropriately selected from, for example, toluene, quinoline, acetone, hexane, benzene, xylene, methylnaphthalene, alcohols and the like.

[0051] The stirring method is not particularly limited. For example, a ribbon mixer, a screw kneader, a universal mixer, or the like can be used. The stirring conditions are appropriately selected according to the viscosity of the mixture, the organic solvent to be used, and the like. Usually, the viscosity of the liquid carbon precursor or carbon precursor solution is 500 Pa's or less. preferable. Usually, the treatment temperature should be in the range of about 10 to 200 ° C. The pressure during stirring can be under atmospheric pressure, under pressure, under reduced pressure, or even with a deviation.

[0052] After immersing the granulated body in a liquid carbon precursor or a solution of the carbon precursor, The coated granulate is separated from the liquid carbon precursor or carbon precursor solution. As a separation method, methods such as centrifugation, squeeze filtration, and gravity sedimentation separation may be applied as appropriate. The temperature at the time of separation is not particularly limited, but it may usually be in the range of about 10 to 200 ° C.

[0053] By drying the separated granulated body, a granulated body surface-coated with a carbon precursor is obtained. The drying temperature is not particularly limited, but is usually about 100 to 300 ° C. When a thermosetting synthetic resin is used as the carbon precursor, it can be cured with the resin component remaining by drying in a temperature range higher than the curing temperature of the synthetic resin. Further, after drying, it is also possible to carry out a separate heat treatment within the temperature range of the synthetic resin to 300 ° C. to cure the synthetic resin as the coating component while leaving the resin component.

[0054] In the method of immersing the granulated body in a liquid carbon precursor or a solution of the carbon precursor, the coating amount by the carbon precursor is the same as in the case of mixing the granulated body and the carbon precursor. It is preferable to set the amount of carbon precursor to about 0.:! To about 50 parts by mass with respect to 100 parts by mass of the granules. It is even better to make it about a part. The coating amount with the carbon precursor can be appropriately adjusted, for example, by changing the concentration of the solution containing the carbon precursor.

[0055] After the surface of the granule is coated with the carbon precursor by the method described above, the carbon precursor may be carbonized. The carbonization treatment may be performed by heat-treating the granule whose surface is coated with a carbon precursor in an inert gas stream such as nitrogen or a non-oxidizing atmosphere such as a reducing atmosphere. The heat treatment temperature is preferably about 800 to 1200 ° C. When carbonizing in a nitrogen gas atmosphere, the carbonization temperature is preferably 1000 ° C. or lower so that the metal powder and nitrogen do not react. The holding time at the highest temperature is not particularly limited and can be, for example, about several minutes to 2 hours. If the rate of temperature rise is too high, agglomeration between the granulated bodies tends to occur. Therefore, an economic temperature rise rate may be selected in consideration of suppressing the occurrence of agglomeration. For example, it can be about 10 to 200 ° C./hour. Even if agglomeration occurs, in most cases, it can be easily crushed by applying a light shear force. [0056] By the above carbonization, about 1 to 60% by mass of the carbon precursor coated with the granule remains as a carbide. For example, when the carbon precursor is pitch, the residual rate due to carbonization is about 50% by mass. In addition, when the carbon precursor is phenol resin, the residual ratio due to carbonization is about 50% by mass, and in the case of polybutyl alcohol, it is about 5% by mass or less.

[0057] The coating method with the carbon precursor or the carbonized product thereof is not limited to the above-described method. For example, a hydrocarbon such as benzene, toluene, xylene, etc. is thermally decomposed to form a thermally decomposed carbon layer. The coating treatment can also be performed by chemical vapor deposition.

[0058] Lithium ion secondary thunder pond

The above-mentioned granulated body made of a graphite raw material and a metal powder is useful as a negative electrode active material for a lithium ion secondary battery. A lithium ion secondary battery using the negative electrode active material can be produced by a known method. That is, the above-mentioned granulated material is used as the negative electrode active material, and the positive electrode active material is MnO, LiCoO, LiNiO, LiNi Co O, LiMnO, LiMn O,

2 2 2 1-y y 2 2 2 4

A known positive electrode active material such as LiFeO can be used. Examples of the electrolyte include ethylene power

2

LiPF, a mixed solvent of an organic solvent such as carbonate and a low boiling point solvent such as dimethyl carbonate, jetyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxymethane, and ethoxymethoxyethane. Electrolyte solutes such as LiBF, LiClO, LiCF SO

6 4 4 3 3

The solution etc. which melt | dissolved can be used. Furthermore, a lithium ion secondary battery can be assembled according to a conventional method using other known battery components.

The invention's effect

[0059] The negative electrode active material of the present invention contains, as an active ingredient, a metal powder capable of occluding and releasing graphite and lithium ions, and has a higher charge / discharge capacity than when graphite is used alone. It is.

[0060] Further, even when the metal raw material is formed into a structure in which the graphite raw material and the pulverized product thereof are laminated, and the metal powder is dispersed on the surface and inside thereof, The high charge / discharge capacity obtained by adding the metal powder with little deterioration in performance can be maintained for a long time.

[0061] Furthermore, even if the metal powder existing on the surface falls off, the ratio to the whole metal powder is small. Therefore, the conductivity of the negative electrode active material is rarely impaired.

Accordingly, the lithium ion secondary battery using the negative electrode active material of the present invention has a high charge / discharge capacity and excellent cycle characteristics.

Brief Description of Drawings

FIG. 1 is a conceptual explanatory diagram of a negative electrode active material production apparatus of the present invention.

2 is an explanatory side sectional view of the apparatus of FIG.

FIG. 3 is a conceptual diagram showing a schematic configuration of a negative electrode active material of the present invention.

[Fig. 4] Scanning electron microscope (SEM) photograph of the cross section of the granulate obtained in Example 8 (a) Silicon surface analysis by energy dispersive X-ray fluorescence analysis (EDS) in the same field (b) It is drawing which shows a result.

Explanation of symbols

[0064] 1 casing of the granulator,

2 Rear cover,

3 Front cover,

4 Π '

5 Impact pin

6 rotation axis,

7 Collision ring

8 On-off valve,

9 Valve shaft of on-off valve,

10 Actuator

11 Circulation circuit,

12 raw material hopper,

13 Chute for raw material supply,

14 On-off valve,

15 shock chamber,

16 Circulation port to the circulation circuit,

17 Granule discharge pipe 18 jacket

19 Controller

21 Metal powder

22 Graphite particles

23 Granule surface

24 Gap

BEST MODE FOR CARRYING OUT THE INVENTION

[0065] Hereinafter, the present invention will be described in more detail with reference to examples.

[0066] Example 1

Polycrystalline silicon powder with an average particle size of 1 μm was pulverized using a commercially available bead mill, 5 g of silicon powder (average particle size 0 · 2 / m) and natural graphite (flaky graphite) (average particle size of 10 / m 95 g of true specific gravity 2.25 and specific surface area 8.8 m ² / g) were used as raw materials. As an apparatus for producing the granulated material, an apparatus having the structure shown in Fig. 1 (Hybridization System NHS-1 manufactured by Nara Machinery Co., Ltd.) is used. , And mixed for 3 minutes at 8000 rpm (peripheral speed 96 m / s). This operation was repeated 5 times to obtain 500 g of a granulated body.

[0067] The average particle diameter of the obtained granulated body was 7. The tap density was 0.77 g / cc.

. Incidentally, the tap density measured after the mixture of natural graphite and silicon powder before granulation was mixed uniformly according to the method described above was 0.57 gZcc.

[0068] Next, 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the granulated material obtained by the above-described method, and mixed for 1 hour using a rocking mixer. Thereafter, the temperature is raised to 900 ° C. over 15 hours in a nitrogen gas atmosphere, and the temperature is maintained at 900 ° C. for 2 hours. The surface of the granulated body is covered with pitch carbide to obtain a negative electrode active material. It was.

[0069] The silicon content of the negative electrode active material obtained in the above method, 4. a 7 mass%, average particle diameter of 7. 5 xm, a specific surface area of 6. 7m ² / g.

[0070] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above method, the battery characteristics of the lithium ion secondary battery were evaluated by the following method.

First, a water-dispersed styrene-butadiene rubber (SB) is used as a binder for the negative electrode active material. A slurry containing a negative electrode active material was prepared by adding appropriate amounts of R), carboxymethylcellulose (CMC) and water and stirring.

[0072] Next, this slurry was applied to a thickness of about 100 to 1 10 μΐη on a 50 × 200 (mm) foil, dried, and then the density of the active material was 1. 5 to: 1. A negative electrode plate was manufactured by pressing to 6 gZcc. This negative electrode plate was cut and divided into a size of 1 cm ² and dried to produce a negative electrode.

[0073] Next, using this negative electrode, an electrode cell was assembled in a glove box in an argon gas atmosphere. At this time, 1M LiPF was replaced with ethylene carbonate (EC).

Using a nonaqueous electrolytic solution dissolved in a mixed solvent of 6Z ethyl methyl carbonate (EMC) = 1/2 (volume ratio), the electrolytic solution was injected until the negative electrode was completely immersed.

[0074] Next, the electrode cell was transferred from the glove box into a constant temperature bath at 25 ° C, and the lithium counter electrode, the negative electrode, and the reference electrode terminal were connected to the charging / discharging device connection cord, and evaluation measurement was performed. In this measurement, the battery was charged at a constant current at a current density of 1. OmA / cm ² and then switched to a constant voltage at a voltage of 10 mV for 12 hours. The discharge conditions were: 1. OmA / cm ² constant current discharge, cut-off voltage was 1.2V.

As a result of the above battery characteristic evaluation, the discharge capacity was 464 mAh / g, and the initial efficiency was 86%.

[0076] Example 2

Example using 10 g of silicon powder (average particle size 0.2 μτη) and 90 g of natural graphite (flaky graphite) (average particle size 10 / m, true specific gravity 2.25) as in Example 1 Using the same granule production apparatus as in Example 1, 500 g of granule was obtained in the same manner as in Example 1.

[0077] The obtained granulated product had an average particle size of 6.6 µm and a tap density of 0.80 g / cc. In addition, the tap density measured after uniformly mixing the mixture of natural graphite and silicon powder before granulation according to the method described above was 0.59 gZcc.

[0078] Next, 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the granulated material obtained by the above-described method, and the mixture was mixed under the same conditions as in Example 1. By heating, the surface of the granule was coated with pitch carbonized material to obtain a negative electrode active material.

[0079] The average particle diameter of the negative electrode active material obtained by the above method is 7.0 μm, and the specific surface area is 8.9 m. ² g.

[0080] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 465 mAh / g, and the initial efficiency was 87%.

[0081] Next, the electrolyte was 1M LiPF and ethylene carbonate (EC).

A cycle characteristic evaluation test was performed in the same manner by changing to a non-aqueous electrolyte dissolved in a mixed solvent of 6 Z jetyl carbonate (DEC) = 1/1 (volume ratio). As a result, the discharge capacity in the first cycle was 604 mAhZg, and the value obtained by dividing the discharge capacity in the second cycle by the discharge capacity in the first cycle (percent capacity ratio) was 96%.

[0082] Example 3

Example 1 using 15 g of silicon powder (average particle size 0.2 xm) crushed in the same manner as in Example 1 and 85 g of natural graphite (flaky graphite) (average particle size 10 / m, true specific gravity 2.25) Using the same granule production apparatus, 500 g of a granule was obtained in the same manner as in Example 1.

[0083] The average particle diameter of the obtained granulated body was 7.2 / im, and the tap density was 0.88 g / cc.

. Incidentally, the tap density measured after uniformly mixing the mixture of natural graphite and silicon powder before granulation according to the above-described method was 0.61 g / cc.

[0084] Next, 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the granulated material obtained by the above-described method, mixed under the same conditions as in Example 1, and then under the same conditions as in Example 1. By heating, the surface of the granule was coated with pitch carbonized material to obtain a negative electrode active material. In the obtained negative electrode active material, the amount of silicon was 14.0% by mass.

[0085] The negative electrode active material obtained by the above method has an average particle diameter of 7.5 μm and a specific surface area of 8.4 m.

² / g.

[0086] Evaluation of thunder pond characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 578 mAh / g, and the initial efficiency was 85%.

[0087] Next, the electrolyte was 1M LiPF and ethylene carbonate (EC) Z jetyl carbon. The cycle characteristics were evaluated in the same manner by changing to a non-aqueous electrolyte dissolved in a mixed solvent with a volume ratio (DEC) of 1/1 (volume ratio). As a result, the discharge capacity in the first cycle was 648 mAh / g, and the value obtained by dividing the discharge capacity in the second cycle by the discharge capacity in the first cycle (percent capacity ratio) was 96%.

[0088] Example 4

Using a shearing crusher, 95 parts by mass of graphite similar to Example 1 and 5 parts by mass of silicon powder similar to Example 1 were mixed in advance. The tap density of this mixture was 0.57 gZcc.

[0089] 100 g of the obtained mixture was sampled, and 500 g of a granulated product was obtained in the same manner as in Example 1 using the same granulated product production apparatus as in Example 1. The average particle size of the granulated product was 7.5 zm, and the tap density was 0.78 g / cc.

[0090] Next, 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the granulated material obtained by the above-described method, and the mixture was mixed under the same conditions as in Example 1. Then, under the same conditions as in Example 1. By heating, the surface of the granule was coated with pitch carbonized material to obtain a negative electrode active material. In the obtained negative electrode active material, the silicon content was 4.7% by mass.

The average particle diameter of the negative electrode active material obtained by the above method was 7.7 / m, and the specific surface area was 6.8 m ² / g.

[0092] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 577 mAh / g and the initial efficiency was 85%.

[0093] Example 5

A granulated body (500 g) was obtained in the same manner as in Example 4 except that 90 parts by mass of graphite and 10 parts by mass of silicon powder were used as raw materials. The tap density of the mixture before granulation was 0.59 gZcc. The average particle size of the granulation was 6.8 x m and the tap density was 0.80 g / cc.

[0094] Next, 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the granulated body obtained by the above-described method, and the mixture was mixed under the same conditions as in Example 1, and then under the same conditions as in Example 1. By heating, the surface of the granule was coated with pitch carbonized material to obtain a negative electrode active material. In the obtained negative electrode active material, the silicon content was 9.3 mass%. [0095] The negative electrode active material obtained by the above method has an average particle diameter of 7.0 μm and a specific surface area of 8.5 m.

/ g.

[0096] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 620 mAh / g, and the initial efficiency was 85%.

[0097] Example 6

A granulated body (500 g) was obtained in the same manner as in Example 4 except that 85 parts by mass of graphite and 15 parts by mass of silicon powder were used as raw materials. The tap density of the mixture before granulation was 0.61 gZcc. The average particle size of the granulation was 6. The tap density was 0.85 g / cc.

[0098] Next, 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the granulated material obtained by the above-described method, and the mixture was mixed under the same conditions as in Example 1. Then, under the same conditions as in Example 1. By heating, the surface of the granule was coated with pitch carbonized material to obtain a negative electrode active material. In the obtained negative electrode active material, the amount of silicon was 14.0% by mass.

[0099] The average particle diameter of the negative electrode active material obtained by the above method is 6.8 / im, and the specific surface area is 8.9m.

/ g.

[0100] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 670 mAh / g, and the initial efficiency was 84%.

[0101] Example 7

Silicon powder having an average particle size of 1 μm was pulverized using a bead mill using isopropyl alcohol as a medium to obtain silicon powder having an average particle size of 0.2 × m. The obtained pulverized product was in a state where silicon powder having an average particle size of 0.2 zm was dispersed in alcohol. To this dispersion, 90 parts by mass of natural graphite (flaky graphite) (average particle size 20 μm, true specific gravity 2.25, specific surface area 4.5 m ² Zg) is added to 10 parts by mass of silicon and mixed by stirring. did. Thereafter, the alcohol was evaporated using an evaporator.

[0102] In the next stage, the mixture of the silicon powder and natural graphite obtained by the above-described method is used as a rubber bowl. It was put into a ball mill with Nore and further mixed.

[0103] 90 g of the mixture obtained by the above method was collected and mixed at 8000 rpm for 3 minutes using the same granule production apparatus as in Example 1 to obtain a granule. This operation was repeated 95 times to obtain 8.5 kg of granulated material. The tap density of the mixture before granulation was 0.60 gZcc. The average particle size of the granulation was 16.1 x m and the tap density was 0.93 g / cc.

[0104] Next, 30 parts by mass of an isotropic pitch was added to 100 parts by mass of the obtained granulated body, and mixed for 1 hour using a Nauta mixer. Thereafter, the temperature is raised to 900 ° C. over 15 hours in a nitrogen gas atmosphere, and the temperature is maintained at 900 ° C. for 2 hours, and the surface of the granule is covered with pitch carbonized material to obtain a negative electrode active material. It was. In the obtained negative electrode active material, the amount of silicon was 8.7% by mass.

[0105] The average particle diameter of the negative electrode active material obtained by the above method was 16.5 μm, and the specific surface area was 4.3 mZg.

[0106] Evaluation of battery characteristics

Using the negative electrode active material obtained by the method described above, 1M LiPF was used as the electrolyte.

Evaluation test of battery characteristics in the same manner as in Example 1 using a non-aqueous electrolyte dissolved in a mixed solvent of 6 carbonate (EC) / jetyl carbonate (DEC) = 1/1 (volume ratio) Went.

As a result, the discharge capacity in the first cycle was 565 mAh / g, and the initial efficiency was 90%. The value obtained by dividing the discharge capacity at the second cycle by the discharge capacity at the first cycle (percent capacity ratio) is 98%, and the value obtained by dividing the discharge capacity at the 10th cycle by the discharge capacity at the first cycle. Was 90%, indicating good cycle characteristics.

[0108] Example 8

Silicon powder having an average particle size of 1 μm was pulverized using a bead mill using isopropyl alcohol as a medium to obtain silicon powder having an average particle size of 0.2 × m. The obtained pulverized product was in a state where silicon powder having an average particle size of 0.2 zm was dispersed in alcohol. To this dispersion, 85 parts by mass of natural graphite (flaky graphite) (average particle size of 20 μm, true specific gravity of 2.25) with respect to 15 parts by mass of silicon was added and mixed by stirring. Thereafter, the alcohol was evaporated using an evaporator. [0109] Next, the mixture of silicon powder and natural graphite obtained by the above-described method was placed in a ball mill together with a rubber bonole and further mixed.

[0110] 80 g of the mixture obtained by the above-described method was sampled and mixed at 8000 rpm for 3 minutes using the same granule production apparatus as in Example 1 to obtain a granule. This operation was repeated 96 times to obtain 7.6 kg of granules. The tap density of the mixture before granulation was 0.62 gZcc. The average particle diameter of the granulated body was 9. O x m, and the tap density was 0.88 g / cc.

[0111] 15 parts by mass of an isotropic pitch was added to 100 parts by mass of the obtained granulated material, and mixed for 1 hour using Nauter mixer. Thereafter, the temperature was raised to 900 ° C. over 15 hours in a nitrogen gas atmosphere, and the temperature was maintained at 900 ° C. for 2 hours to coat the surface of the granulated body with pitch carbonized material. Next, 15 parts by mass of isotropic pitch is added to 100 parts by mass of the granulated material coated with pitch carbonized material, and mixed for 1 hour using a Nauta mixer, and 900 ° C in a nitrogen gas atmosphere. The temperature was raised to 15 hours and held at 900 ° C. for 2 hours, and the surface of the granulated body was coated with pitch carbonized material to obtain a negative electrode active material. In the obtained negative electrode active material, the amount of silicon was 12.9 mass ⁰ /. Met.

[0112] The average particle diameter of the negative electrode active material obtained by the above method was 9.3 _β m, and the specific surface area was 7.2 m ² g.

[0113] Fig. 4 shows the silicon of the negative electrode active material obtained in Example 8 by means of energy dispersive X-ray fluorescence analysis (EDS) in the same field of view as the scanning electron microscope (SEM) photograph (a) of the cross section. The surface analysis (b) is shown. The sample for observation was obtained by placing the negative electrode active material in an epoxy resin and polishing it, and observed the cut surface at a magnification of 4000 times.

[0114] Surface analysis (b) of silicon revealed that silicon was dispersed inside. The brightest white area has a silicon concentration of about 35% by mass, and the silicon concentration decreases as it darkens.

[0115] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 633 mAh / g, and the initial efficiency was 82%. [0116] Example 9

Silicon powder having an average particle size of 1 im was pulverized using isopropyl alcohol as a medium using a bead mill to obtain silicon powder having an average particle size of 0.2 μΐη. The obtained pulverized product was in a state where silicon powder having an average particle size of 0.2 zm was dispersed in alcohol. To this dispersion, 99 parts by mass of natural graphite (flaky graphite) (average particle size 20 zm, true specific gravity 2.25) with respect to 1 part by mass of silicon was added and stirred. Thereafter, the alcohol was evaporated using an evaporator.

[0117] Next, the mixture of silicon powder and natural graphite obtained by the above-described method was placed in a ball mill together with a rubber bonole and further mixed.

[0118] 90 g of the mixture obtained by the above-described method was collected and mixed at 8000 rpm for 3 minutes using the same granule production apparatus as in Example 1 to obtain a granule. This operation was repeated 20 times to obtain 1.8 kg of granulated material. The tap density of the mixture before granulation was 0.56 gZcc. The average particle size of the granulation was 9.8 μΐη, and the tap density was 0 · 90 g / cc.

[0119] Next, 20 parts by mass of an isotropic pitch was added to 100 parts by mass of the obtained granulated product, and mixed for 1 hour using a Nauta mixer. Thereafter, the temperature is raised to 900 ° C. over 15 hours in a nitrogen gas atmosphere, and the temperature is maintained at 900 ° C. for 2 hours, and the surface of the granule is covered with pitch carbonized material to obtain a negative electrode active material. It was.

[0120] In the obtained negative electrode active material, the silicon content was 0.9 mass%. The average particle diameter of the negative electrode active material was 10.0 μΐη, and the specific surface area was 4.8 m ² / g.

[0121] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 392 mAh / g, and the initial efficiency was 88%.

[0122] Example 10

A granulated body was obtained in the same manner as in Example 9 except that 98 parts by mass of natural graphite (flaky graphite) was used with respect to 2 parts by mass of silicon.

[0123] The surface of the obtained granule was coated with pitch carbonized material in the same manner as in Example 9 to obtain a negative electrode active material. The tap density of the mixture before granulation was 0.57 g / cc. . The average particle diameter of the granulated body was 9.2 / im, and the tap density was 0.87 g / cc.

[0124] In the obtained negative electrode active material, the silicon content was 1.8% by mass. The average particle diameter of the negative electrode active material was 9.5 μΐη, and the specific surface area was 4.2 m ² / g.

[0125] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 404 mAh / g, and the initial efficiency was 88%.

[0126] Example 11

A granulated product was obtained in the same manner as in Example 9 except that 97 parts by mass of natural black bell (scale-like black bell) was used with respect to ₃ parts by mass of silicon.

[0127] The surface of the obtained granulated body was coated with pitch carbonized material in the same manner as in Example 9 to obtain a negative electrode active material. The tap density of the mixture before granulation was 0.58 g / cc.

. The average particle diameter of the granulated body was 9.0 / im, and the tap density was 0.83 g / cc.

[0128] In the obtained negative electrode active material, the silicon content was 2.7% by mass. The average particle diameter of the negative electrode active material was 9.2 μΐη, and the specific surface area was 4.6 m ² / g.

[0129] Evaluation of battery characteristics

Using the negative electrode active material obtained by the above-described method, a battery characteristic evaluation test was performed in the same manner as in Example 1. As a result, the discharge capacity was 421 mAh / g and the initial efficiency was 88%.

[0130] Comparative Example 1

Commercially available spheroidized graphite (natural flaky graphite spheroidized; average particle size 15 / m) 13.5 kg and polycrystalline silicon powder with average particle size lxm were ground using a commercially available bead mill Silicon powder (average particle size 0.2 zm) l. 5 kg was put into a Nauta mixer and mixed for 1 hour.

[0131] 10 parts by mass of an isotropic pitch was added to 100 parts by mass of the obtained mixture, and the mixture was mixed for 1 hour using a Nauter mixer. Thereafter, the temperature was raised to 900 ° C. over 15 hours in a nitrogen gas atmosphere, and the temperature was maintained at 900 ° C. for 2 hours to coat the surface of the mixture with pitch carbonized product. Next, with respect to 100 parts by mass of the mixture coated with pitch carbonized material, isotropic pipe Add 15 parts by mass of the mixture, mix for 1 hour using a Nauta mixer, raise the temperature to 900 ° C in a nitrogen gas atmosphere over 15 hours, hold at 900 ° C for 2 hours, and remove the surface of the mixture. A negative electrode active material was obtained by coating with pitch carbonized material.

[0132] In the obtained negative electrode active material, the silicon content was 8.9 mass%. The average particle diameter of the negative electrode active material was 16. The specific surface area was 4.4 m ² Zg.

[0133] As a result of evaluating the battery characteristics in the same manner as in Example 1, the discharge capacity was 467 mAh / g, and the initial efficiency was 86%. The value obtained by dividing the discharge capacity at the 6th cycle by the discharge capacity at the 1st cycle (percent capacity ratio) was 75%.

Claims

The scope of the claims

[1] A mixture of scaly graphite and at least one graphite raw material selected from the group consisting of artificial graphite having a (002) plane spacing of 0.336 nm or less and a metal powder capable of occluding and releasing lithium ions. A granulated body obtained by pulverization and granulation in a high-speed air stream,

A negative electrode for a lithium ion secondary battery comprising a granulated body in which a part of graphite as a raw material is pulverized to form a structure in which graphite raw materials and pulverized products thereof are laminated, and metal powder is dispersed on the surface and inside thereof. Active material.

[2] A granulated product obtained by using a mixture of a graphite raw material having an average particle size of 5 to 150 μm and a metal powder having an average particle size of 0.01 to 2 μm as a raw material. The negative electrode active material for lithium ion secondary batteries as described in 2.

[3] The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the tap density of the granulated body is 10% or more higher than the tap density of the raw material mixture.

[4] The negative electrode active material for a lithium ion secondary battery according to [1], comprising a granulated body obtained by using silicon powder as the metal powder.

[5] The negative electrode active material for a lithium ion secondary battery according to claim 1, comprising a granule obtained using natural graphite as a graphite raw material.

[6] The lithium ion secondary according to claim 1, comprising a granulated body obtained by using a raw material containing 0.3 to 40% by mass of the metal powder, with the total amount of the graphite raw material and the metal powder being 100% by mass. Negative electrode active material for batteries.

7. The negative electrode active material for a lithium ion secondary battery according to claim 1, comprising a granulated material obtained by pulverizing and granulating a raw material mixture that has been wet or dry premixed in a high-speed air stream.

[8] A negative electrode active material for a lithium ion secondary battery, comprising a granule in which the surface of the granule according to claim 1 is covered with a carbon precursor or a carbonized product thereof.

[9] A lithium ion secondary battery comprising the negative electrode active material for a lithium ion secondary battery according to claim 1 as a constituent element.

[10] A lithium ion secondary battery comprising the negative electrode active material for a lithium ion secondary battery according to claim 8 as a constituent element.