JP2021152996A - Negative electrode material for lithium ion secondary battery and production method thereof - Google Patents

Abstract

To provide a negative electrode material for a lithium ion secondary battery arranged to use a graphite material, which is superior in high-speed charge/discharge characteristic.SOLUTION: A negative electrode material for a lithium ion secondary battery comprises: graphite particles; and a coating layer which contains an amorphous carbon particles and an amorphous carbonization-binding material, and which coats each graphite particle. According to surface observation, the coverage of the amorphous carbon particle is 50% or larger. In cross sectional observation, the percentage of the amorphous carbon particles buried is 10-90%.SELECTED DRAWING: Figure 1

Description

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

Lithium-ion secondary batteries are installed in many devices such as mobile phones and personal computers, and are used in various fields because of their high capacity, high voltage, small size and light weight.

In recent years, the demand for lithium-ion secondary batteries has been rapidly increasing for in-vehicle use, and the characteristics required for in-vehicle use are high capacity, long life, high input / output, and an excellent balance of these characteristics. Is required to be. Therefore, a negative electrode material having a high energy density and a small expansion / contraction is required, and a negative electrode material made of graphite particles has been widely used as a negative electrode material satisfying these characteristics.

Then, for the purpose of improving the performance of the negative electrode material for a lithium ion secondary battery using such graphite particles, various composite particles in which graphite particles are composited have been developed.

For example, in Patent Document 1, a positive electrode that releases and stores lithium ions, a negative electrode that stores and releases lithium ions released from the positive electrode, and the lithium ions move between the positive electrode and the negative electrode. A negative electrode material used for a lithium ion secondary battery composed of an electrolytic solution to be generated, from a granular mother particle capable of storing and releasing the lithium ion and the mother particle integrated on the surface of the mother particle. Also disclosed is a negative electrode material for a lithium ion secondary battery, which is composed of composite particles composed of granular child particles made of carbon having a small particle size. According to Patent Document 1, a negative electrode material for a lithium ion secondary battery, which can provide a high energy density and a high output density and can maintain a high energy density and an output density of a battery even under a high load, is provided. It is stated that it can be done.

Further, Patent Document 2 describes a composite graphite having a core material made of artificial graphite and a coating layer containing a non-powder-like amorphous carbon material and a powder-like conductive carbon material and covering the core material. The ratio of the mass of the non-powdered amorphous carbon material to the mass of the core material of the particles is 0.2 to 3.8 mass%, and the mass of the powdery state is relative to the mass of the core material. Composite graphite particles in which the proportion of the mass of the conductive carbon material is 0.3 to 5.0 mass% are disclosed. According to Patent Document 2, it is described that the input / output characteristics of the lithium ion secondary battery can be improved.

Further, Patent Document 3 describes a graphite granule (A) formed by aggregating a plurality of scaly graphites, and the graphite in the internal voids and / or the outer surface of the graphite granules (A). The carbonaceous layer (B) having a lower crystallinity than the granulated product (A) is a composite graphite particle formed by filling and / or coating, and the carbonaceous layer (B) contains carbonaceous fine particles. The composite graphite particles characterized by the above are disclosed. Patent Document 3 describes that it is possible to provide a negative electrode material for a lithium ion secondary battery, which can obtain high discharge capacity, high initial charge / discharge efficiency, and further excellent high rate characteristics and cycle characteristics.

Here, in a negative electrode material for a lithium ion secondary battery using a graphite material, it is known that the capacity is increased by increasing the crystallinity of the graphite material. In particular, in in-vehicle applications, the negative electrode material for a lithium ion secondary battery is required to have high capacity and excellent high-speed charge / discharge characteristics.

Patent Document 4 describes that 100 parts by weight of a base material formed by spherically shaping natural graphite is mixed with 2 to 50 parts by weight of carbon black and a pitch, impregnated and coated with natural graphite particles, and fired at 900 ° C to 1500 ° C. However, graphite particles (A) for a lithium ion secondary battery having a BET specific surface area of 2 m ^{2 / g or more having microprojections formed on the surface are disclosed.} According to Patent Document 4, it is possible to provide a negative electrode material for a lithium ion secondary battery, which has a high discharge capacity per unit volume, a small capacity loss during initial charge / discharge, and excellent high-speed charge / discharge characteristics. Have been described.

Japanese Unexamined Patent Publication No. 11-265716 International Publication No. 2018/110263 Japanese Unexamined Patent Publication No. 2004-63321 Japanese Unexamined Patent Publication No. 2011-233541

However, there is an increasing demand for improving the high-speed charge / discharge characteristics of the negative electrode material for lithium ion secondary batteries, and lithium ions having even better high-speed charge / discharge characteristics than the negative electrode material for lithium ion secondary batteries of Patent Document 4. Negative electrode materials for secondary batteries are required.

Therefore, an object of the present invention is to provide a negative electrode material for a lithium ion secondary battery using a graphite material, which is excellent in high-speed charge / discharge characteristics.

Against the background of the above technical background, the present inventor has made extensive studies, and as a result, the surface of the graphite particles is covered with an amorphous carbonized bonding material, and the amorphous carbon particles are embedded in the layer at a predetermined burial ratio. Since it is possible to increase the pass of lithium ions, it has been found that a negative electrode material for a lithium ion secondary battery having excellent high-speed charge / discharge characteristics can be obtained, and the present invention has been completed.

That is, the present invention (1) comprises graphite particles and a coating layer containing amorphous carbon particles and an amorphous carbonized bonding material and covering the graphite particles.
The coverage of the amorphous carbon particles in surface observation is 50% or more,
The burial ratio of the amorphous carbon particles in the cross-sectional observation is 30 to 90%.
The present invention provides a negative electrode material for a lithium ion secondary battery, which is characterized by the above.

The lithium ion secondary battery of the present invention (2) is _{characterized in that the average particle size (D 50} ) of the negative electrode material for the lithium ion secondary battery is 5.0 to 30.0 μm. It provides a negative electrode material for use.

Further, in the present invention (3), binder-coated graphite particles in which the graphite particles are coated with a binder by mixing the binder with graphite particles having _{an average particle diameter (D 50) of 5.0 to 30.0 μm.} And the coating process to obtain
The binder is obtained by mixing 10.0 to 40.0 parts by mass of amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm with 100.0 parts by mass of the graphite particles, and then compressing and rubbing the particles. A process of embedding the amorphous carbon particles in the binder layer of the coated graphite particles to obtain the amorphous carbon particle-embedded binder-coated graphite particles, and an embedding step.
A calcining carbonization step of calcining carbonizing the binder-coated graphite particles in which the amorphous carbon particles are embedded,
The present invention provides a negative electrode material for a lithium ion secondary battery obtained by performing the above.

Further, in the present invention (4), binder-coated graphite particles in which the graphite particles are coated with a binder by mixing the binder with graphite particles having _{an average particle diameter (D 50) of 5.0 to 30.0 μm.} And the coating process to obtain
Amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm are mixed with 100.0 parts by mass of the graphite particles by 10.0 to 40.0 parts by mass, and then the amount of residual carbon after carbonization is 2. By coating with a resin solution in an amount of 0 parts by mass or more, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin, and the amorphous carbon particle-attached binder-coated graphite particles are re-coated. The recoating process to obtain the coating and
A calcining carbonization step of calcining and carbonizing the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles.
The present invention provides a negative electrode material for a lithium ion secondary battery obtained by performing the above.

Further, in the present invention (5), binder-coated graphite particles in which the graphite particles are coated with a binder by mixing the binder with graphite particles having _{an average particle diameter (D 50) of 5.0 to 30.0 μm.} And the coating process to obtain
The binder is obtained by mixing 10.0 to 40.0 parts by mass of amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm with 100.0 parts by mass of the graphite particles, and then compressing and rubbing the particles. A process of embedding the amorphous carbon particles in the binder layer of the coated graphite particles to obtain the amorphous carbon particle-embedded binder-coated graphite particles, and an embedding step.
A calcining carbonization step of calcining carbonizing the binder-coated graphite particles in which the amorphous carbon particles are embedded,
The present invention provides a method for producing a negative electrode material for a lithium ion secondary battery, which is characterized by having.

Further, in the present invention (6), binder-coated graphite particles in which the graphite particles are coated with a binder by mixing the binder with graphite particles having _{an average particle diameter (D 50) of 5.0 to 30.0 μm.} And the coating process to obtain
Amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm are mixed with 100.0 parts by mass of the graphite particles by 10.0 to 40.0 parts by mass, and then the amount of residual carbon after carbonization is 2. By coating with a resin solution in an amount of 0 parts by mass or more, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin, and the amorphous carbon particle-attached binder-coated graphite particles are re-coated. The recoating process to obtain the coating and
A calcining carbonization step of calcining and carbonizing the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles.
The present invention provides a method for producing a negative electrode material for a lithium ion secondary battery, which is characterized by having.

According to the present invention, it is possible to provide a negative electrode material for a lithium ion secondary battery using a graphite material, which is excellent in high-speed charge / discharge characteristics.

It is sectional drawing of the form example of the negative electrode material for a lithium ion secondary battery of this invention. It is an enlarged view near the surface of the negative electrode material for a lithium ion secondary battery shown in FIG. 1. It is a figure which shows the form example of the negative electrode material for a lithium ion secondary battery of this invention. It is a schematic cross-sectional view for manufacturing the negative electrode material for a lithium ion secondary battery of the 1st aspect of this invention. It is a schematic cross-sectional view for manufacturing the negative electrode material for a lithium ion secondary battery of the 2nd aspect of this invention.

The negative electrode material for a lithium ion secondary battery of the present invention comprises graphite particles, amorphous carbon particles, and a coating layer containing amorphous carbon particles and an amorphous carbonized bonding material and covering the graphite particles.
The coverage of the amorphous carbon particles in surface observation is 50% or more,
The burial ratio of the amorphous carbon particles in the cross-sectional observation is 30 to 90%.
It is characterized by.

The negative electrode material for a lithium ion secondary battery of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view of a morphological example of the negative electrode material for a lithium ion secondary battery of the present invention. FIG. 2 is an enlarged view of the vicinity of the surface of the negative electrode material for a lithium ion secondary battery shown in FIG. 1, and is a diagram for explaining the burial ratio of amorphous carbon particles. FIG. 3 is a diagram showing a morphological example of the negative electrode material for a lithium ion secondary battery of the present invention, and is a diagram for explaining the coverage of amorphous carbon particles.

In FIG. 1, the negative electrode material 10 for a lithium ion secondary battery is composed of graphite particles 1 and a coating layer 4 covering the graphite particles 1. The coating layer 4 contains the amorphous carbon particles 3 and the amorphous carbonized bonding material 2, and the amorphous carbon particles 3 are embedded in the layer of the amorphous carbonized bonding material 2 to form lithium ions. It is fixed to the negative electrode material 10 for a secondary battery. Further, in the negative electrode material 10 for a lithium ion secondary battery, the amorphous carbon particles 3 may or may not be in contact with the surface of the graphite particles 1.

As shown in FIG. 2, in the cross section of the negative electrode material 10 for a lithium ion secondary battery, the intersection of the contour of the amorphous carbon particles 3 and the outer contour of the amorphous carbonized bonding material 2 is the intersection 6a, the intersection. It is set to 6b. The portion on the graphite particle side of the line connecting the intersection 6a and the intersection 6b (the portion shown by the diagonal line in FIG. 2A) is the buried portion 5 of the amorphous carbon particles 3. The total area 7 of the amorphous carbon particles 3 is a portion shown by a diagonal line in FIG. 2 (B). Then, the burial ratio (%) of the amorphous carbon particles in the cross-sectional observation is calculated by the following equation (1):
Amorphous carbon particle burial ratio (%) in cross-sectional observation = (area of burial portion 5 of amorphous carbon particle 3 / total area of amorphous carbon particle 3 7) × 100 (1)
Demanded by. For convenience of explanation, in FIG. 2, only the outlines of the graphite particles, the amorphous carbonized bonding material, and the amorphous carbon particles are shown by solid lines.

Further, in FIG. 2, reference numeral 8 is the thickness of the amorphous carbonized bonding material 2.

As shown in FIG. 3, in the surface observation of the negative electrode material 10 for a lithium ion secondary battery, it surrounds an arbitrary calculation range 9 (the range shown by the dotted line in FIG. 3) of the negative electrode material 10 for a lithium ion secondary battery. .. Further, the total area of the amorphous carbon particles 3 in the calculation range 9 is the area of the portion indicated by the diagonal line in FIG. 3 (B). The coverage (%) of the amorphous carbon particles in the surface observation is calculated by the following equation (2):
Coverage of amorphous carbon particles (%) in surface observation = (total area of amorphous carbon particles 3 within calculation range 9 / total area of calculation range 9) × 100 (2)
Demanded by.

The negative electrode material for a lithium ion secondary battery of the present invention comprises graphite particles and a coating layer covering the graphite particles.

The graphite particles are spheroidized graphite, which is a spherical aggregate of flat graphite. The graphite particles may be natural graphite or artificial graphite.

The average lattice spacing d (002) of the graphite particles is 0.3360 nm or less. When the average lattice spacing d (002) of the graphite particles is 0.3360 nm or less, the reversible capacitance becomes sufficiently large. The average lattice spacing d (002) of the graphite particles is preferably 0.3358 nm or less in that the reversible capacitance is further increased.

The coating layer covers the graphite particles and contains amorphous carbon particles and an amorphous carbonized bonding material. The amorphous carbonized bonding material is a portion of the amorphous carbon material forming the coating layer other than the amorphous carbon particles.

The amorphous carbon particles are fixed to the negative electrode material for a lithium ion secondary battery of the present invention so as to be embedded in a layer of an amorphous carbonized bonding material.

The amorphous carbon particles are not particularly limited, and examples thereof include carbon black such as furnace black and thermal black.

The average lattice spacing d (002) of the amorphous carbon particles is 0.3370 nm or more. When the average lattice spacing d (002) of the amorphous carbon particles is 0.3370 nm or more, the reaction resistance of the particle surface is lowered and high-speed charging / discharging is excellent. The average lattice spacing d (002) of the amorphous carbon particles is more preferably 0.3400 nm or more in that the high-speed charge / discharge performance is further improved, and particularly preferably in that the high-speed charge / discharge performance is further improved. Is 0.3500 nm or more.

The average particle size of the amorphous carbon particles in the surface observation is preferably 50 to 300 nm. Since the average particle size of the amorphous carbon particles in the surface observation is 50 to 300 nm, the material has excellent high-speed charge / discharge characteristics while suppressing an increase in irreversible capacity. The average particle size of the amorphous carbon particles in the surface observation is more preferably 100 nm or more in that the increase in irreversible capacity can be further suppressed, and more preferably in that the high-speed charge / discharge performance is further improved. Is 200 nm or less.

In the negative electrode material for the lithium ion secondary battery of the present invention, the average particle size of the amorphous carbon particles in the surface observation is one particle of the negative electrode material for the lithium ion secondary battery extracted arbitrarily, using a scanning electron microscope. The surface is observed by (SEM), and amorphous carbon particles are arbitrarily selected from the obtained SEM images, and the diameter of the circumscribing circle of the particles is defined as the particle diameter. Then, at least 10 amorphous carbon particles are arbitrarily extracted from the SEM image, the diameters of the amorphous carbon particles are obtained for each particle, the diameters are averaged, and the amorphous carbon particles in the surface observation are observed. The average particle size of.

The average lattice spacing d (002) of the amorphous carbonized bonding material is 0.3370 nm or more. When the average lattice spacing d (002) of the amorphous carbonized bonding material is 0.3370 nm or more, the reaction resistance of the particle surface is lowered and high-speed charging / discharging is excellent. The average lattice spacing d (002) of the amorphous carbonized bonding material is more preferably 0.3400 nm or more in that the high-speed charge / discharge performance is further improved, and is further improved in the high-speed charge / discharge performance. Particularly preferably, it is 0.3500 nm or more.

The thickness of the amorphous carbonized bonding material in the cross-sectional observation is not particularly limited, but a thickness of 15 nm or more is preferable in order to bury it in the coating particles.

In the negative electrode material for the lithium ion secondary battery of the present invention, the thickness of the amorphous carbonized bonding material in the cross-sectional observation is determined by scanning one particle of the negative electrode material for the lithium ion secondary battery extracted arbitrarily with a scanning electron microscope. The cross section is observed by (SEM), the thickness of the cross section of the amorphous carbonized bonding material in the obtained SEM image is arbitrarily measured at 10 points, the average thereof is calculated, and the value is calculated as amorphous carbon. It is the thickness of the cross section of the chemical bonding material. Then, at least 10 particles are arbitrarily extracted from the negative electrode material for the lithium ion secondary battery, the thickness of the cross section of the amorphous carbonized bonding material is obtained for each particle, the thicknesses are averaged, and the amorphous in the cross-sectional observation. It is the thickness of the cross section of the carbonized bonding material.

The following equation (1) in cross-sectional observation of the negative electrode material for a lithium ion secondary battery of the present invention:
Amorphous carbon particle burial ratio (%) in cross-sectional observation = (area of the buried portion of amorphous carbon particles in cross-sectional observation / total area of amorphous carbon particles in cross-sectional observation) × 100 (1)
The burial rate of the amorphous carbon particles in the cross-sectional observation obtained in 1) is 30 to 90%. When the burial ratio of the amorphous carbon particles in the cross-sectional observation is 30 to 90%, the high-speed charge / discharge characteristics are enhanced. The burial ratio of the amorphous carbon particles in the cross-sectional observation is more preferably 50% or more in that the burial effect is fully exhibited and the high-speed charge / discharge performance is improved, and high-speed filling due to a decrease in the specific surface area. It is more preferably 80% or less in terms of suppressing deterioration of the discharge performance.

In the present invention, the burial ratio of the amorphous carbon particles in the cross-sectional observation can be obtained by observing the cross-section of one particle of the negative electrode material for a lithium ion secondary battery arbitrarily extracted by a scanning electron microscope (SEM). The burial ratio of amorphous carbon particles in the SEM image is determined. Then, at least 10 particles are arbitrarily extracted from the SEM image, the burial ratio of the amorphous carbon particles is obtained for each particle, and they are averaged to obtain the burial ratio of the amorphous carbon particles in the cross-sectional observation.

The following equation (2) in the surface observation of the negative electrode material for a lithium ion secondary battery of the present invention:
Coverage of amorphous carbon particles in surface observation (%) = (total area of amorphous carbon particles within the calculation range in surface observation / area of the entire calculation range in surface observation) × 100 (2)
The coverage of the amorphous carbon particles in the surface observation obtained in 1) is 50% or more. When the coverage of the amorphous carbon particles in the surface observation is 50% or more, the high-speed charge / discharge characteristics are enhanced. The coverage of the amorphous carbon particles in the surface observation is more preferably 70% or more in that the high-speed charge / discharge performance is further improved, and particularly preferably 80 in that the high-speed charge / discharge performance is further improved. % Or more.

In the present invention, the coverage of amorphous carbon particles in surface observation is obtained by observing the surface of one particle of an arbitrarily extracted negative electrode material for a lithium ion secondary battery with a scanning electron microscope (SEM). A calculation range is determined from the SEM image obtained, and the coverage of amorphous carbon particles in that range is obtained. Then, at least 10 particles of the negative electrode material for the lithium ion secondary battery are arbitrarily extracted, the coverage of the amorphous carbon particles is obtained for each particle, and they are averaged to obtain the coverage of the amorphous carbon particles in the surface observation. And.

_{The average particle size (D 50} ) of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 5.0 to 30.0 μm. _{When the average particle size (D 50} ) of the negative electrode material for a lithium ion secondary battery is 5.0 to 30.0 μm, the reaction specific surface area is increased, the reaction resistance is lowered, and the high-speed charge / discharge characteristics are excellent. _{The average particle size (D 50} ) of the negative electrode material for a lithium ion secondary battery of the present invention is more preferably 7.0 μm or more, and further preferably 7.0 μm or more, in that it is possible to suppress an increase in irreversible capacity at the time of initial charging. It is more preferably 25.0 μm or less in terms of improving the high-speed charge / discharge performance, and particularly preferably 20.0 μm or less in terms of further improving the high-speed charge / discharge performance.

In the present invention, D ₅₀ (average particle size) of the powder or particles is the particle size when the integrated particle size is 50% when the volume-based integrated particle size distribution is measured using a laser diffraction particle size distribution measuring device. ..

The specific surface area of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 10.0 m ² / g or less. When the specific surface area of the negative electrode material for the lithium ion secondary battery is 10.0 m ² / g or less, it is possible to suppress an increase in the irreversible capacity at the time of initial charging. The specific surface area of the negative electrode material for a lithium ion secondary battery of the present invention is more preferably 7.5 m ² / g or less in that it is possible to suppress an increase in irreversible capacity at the time of initial charging, and further, at the time of initial charging. ^{It is particularly preferably 5.0 m 2} / g or less in that the increase in irreversible capacity can be suppressed. The specific surface area of the negative electrode material for a lithium ion secondary battery of the present invention ^{is preferably 1.0 m 2} / g or more in that deterioration of high-speed charge / discharge performance can be suppressed.

The tap density of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 0.80 g / cm ³ or more. When the tap density of the negative electrode material for the lithium ion secondary battery is 0.80 g / cm ³ or more, the load can be reduced in the electrode pressing process, and the damage to the particles can be reduced. .. The tap density of the negative electrode material for a lithium ion secondary battery of the present invention is more preferably 0.90 g / cm ³ or more, and more preferably 0.90 g / cm 3 or more, in that the load is further reduced in the electrode pressing step and the damage to the particles is reduced. It is particularly preferably 1.00 g / cm ³ or more in terms of reducing damage to the battery. The tap density of the negative electrode material for a lithium ion secondary battery of the present invention is more preferably 1.20 g / cm ³ or less in that it is possible to secure an interparticle conductive path and secure liquid immersion property.

The Raman R value of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 0.30 or more. When the Raman R value of the negative electrode material for a lithium ion secondary battery is 0.30 or more, the particle surface is sufficiently amorphized, so that the reaction resistance is low and the high-speed charge / discharge performance is improved. The Raman R value of the negative electrode material for a lithium ion secondary battery of the present invention is particularly preferably 0.40 or more in that the high-speed charge / discharge performance is further improved. The Raman R value of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 1.20 or less in that an increase in irreversible capacity at the time of initial charging can be suppressed.

The initial capacity of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 340 mAh / g or more. When the initial capacity of the negative electrode material for a lithium ion secondary battery is 340 mAh / g or more, it is possible to secure a sufficient energy density when the battery is assembled. The initial capacity of the negative electrode material for a lithium ion secondary battery of the present invention is particularly preferably 345 mAh / g or more in that a sufficient energy density can be secured.

The method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention _{is to mix graphite particles having an average particle diameter (D 50} ) of 5.0 to 30.0 μm with a binder. A coating step of obtaining binder-coated graphite particles in which graphite particles are coated with a binder,
The binder-coated graphite is obtained by mixing 10.0 to 40.0 parts by mass of amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm with 100.0 parts by mass of the graphite particles, compressing and rubbing them. An embedding step of embedding the amorphous carbon particles in the binder layer of the particles to obtain the amorphous carbon particle embedding binder-coated graphite particles, and
A calcined carbonization step of calcining carbonized graphite particles coated with an amorphous carbon particle-embedded binder,
It is characterized by having.

The method for producing the negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention will be described with reference to FIG. FIG. 4 is a schematic cross-sectional view for explaining a method for manufacturing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention. For convenience of explanation, in FIG. 4, only the outlines of the graphite particles and the binder are shown by solid lines.

In FIG. 4, first, the graphite particles 1 and the binder 11 are mixed to obtain a binder-coated graphite particles 12 in which the graphite particles 1 are coated with the binder 11 as shown in (A). Next, the amorphous carbon particles 3 are mixed with the binder-coated graphite particles 12 to obtain the amorphous carbon particle-attached binder-coated graphite particles 13 as shown in (B). Next, the amorphous carbon particle-adhered binder-coated graphite particles 13 are compressed and rubbed to embed the amorphous carbon particles 3 in the binder layer 11 to obtain the amorphous carbon particle-embedded binder-coated graphite particles 14. Next, by firing the amorphous carbon particle-embedded binder-coated graphite particles 14, the binder is carbonized and converted into an amorphous carbonized bonding material to obtain a negative electrode material for a lithium ion secondary battery.

The method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention includes a coating step, an embedding step, and a calcining carbonization step.

In the coating step (hereinafter, also referred to as coating step (1)) according to the method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention, graphite particles are mixed with a binder to obtain graphite. This is a step of obtaining binder-coated graphite particles in which the particles are coated with a binder.

The graphite particles according to the coating step (1) are spheroidized graphite, and flat graphite is agglomerated into spheres. The graphite particles may be natural graphite or artificial graphite.

_{The average particle size (D 50} ) of the graphite particles according to the coating step (1) is preferably 5.0 to 30.0 μm. When the average particle size (D ₅₀ ) of the graphite particles is 5.0 to 30.0 μm, the reaction resistance decreases due to the increase in the reaction specific surface area, and in addition, the movement speed of lithium ions in the graphite particles is also high. Become. The average particle size (D ₅₀ ) of the graphite particles is more preferably 7.0 μm or more in that it is possible to suppress an increase in irreversible capacity at the time of initial charging, and further improve high-speed charge / discharge performance. , More preferably 25.0 μm or less, and particularly preferably 20.0 μm or less in terms of improving high-speed charge / discharge performance.

The d (002) of the graphite particles according to the coating step (1) is 0.3360 nm or less. When the average lattice spacing d (002) of the graphite particles is 0.3360 nm or less, the reversible capacitance becomes sufficiently large. The d (002) of the graphite particles is preferably 0.3358 nm or less in that the reversible capacity is further increased.

The binder according to the coating step (1) is not particularly limited as long as it is carbonized in the firing carbonization step and becomes an amorphous carbon material, and examples thereof include coal tar pitch and phenol resin.

In the coating step (1), the mixing amount of the binder with respect to 100.0 parts by mass of the graphite particles is preferably 10.0 to 40.0 parts by mass. Since the mixing amount of the binder is 10.0 to 40.0 parts by mass with respect to 100.0 parts by mass of the graphite particles, it is possible to embed and immobilize the coated particles while suppressing the irreversible capacity at the time of initial charging. It becomes. The mixing amount of the binder with respect to 100.0 parts by mass of the graphite particles is more preferably 20.0 parts by mass or more in that the particle surface is covered and the increase in irreversible capacity at the time of initial charging can be suppressed. It is more preferably 30.0 parts by mass or less in that the generation of carbonized components of excess binder can be suppressed and the increase in irreversible capacity at the time of initial charging can be suppressed.

In the coating step (1), the method of mixing the graphite particles and the binder is not particularly limited, and examples thereof include a method of mixing using a heating mixer such as a Henschel mixer, a high speed mixer, or a kneader.

In the coating step (1), the mixing temperature when the graphite particles and the binder are mixed is equal to or higher than the softening point temperature in the case of a binder solid at room temperature, and is not particularly limited in the case of a binder liquid at room temperature. When a resin is used, it is usually below the curing temperature. The mixing time is preferably 10 to 30 minutes.

In the embedding step according to the method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention, amorphous carbon particles are mixed with the binder-coated graphite particles obtained by performing the coating step (1) and compressed. And by rubbing, the amorphous carbon particles are embedded in the binder layer of the binder-coated graphite particles, and the amorphous carbon particles-embedded binder-coated graphite particles are obtained.

The amorphous carbon particles involved in the embedding step are not particularly limited, and examples thereof include furnace black and thermal black.

The average lattice spacing d (002) of the amorphous carbon particles involved in the embedding step is 0.3370 nm or more. When the average lattice spacing d (002) of the amorphous carbon particles is 0.3370 nm or more, the reaction resistance of the particle surface is lowered and high-speed charging / discharging is excellent. The average lattice spacing d (002) of the amorphous carbon particles is more preferably 0.3400 nm or more in that the high-speed charge / discharge property is further improved, and particularly preferably in that the high-speed charge / discharge performance is further improved. Is 0.3500 nm or more.

The arithmetic mean particle size of the amorphous carbon particles involved in the embedding step is preferably 50 to 300 nm. Since the average particle size of the amorphous carbon particles in surface observation is 50 to 300 nm, the material has excellent high-speed charge / discharge characteristics while suppressing a decrease in irreversible capacity. The arithmetic mean particle size of the amorphous carbon particles is more preferably 100 nm or more in that the high-speed charge / discharge property is further improved, and more in that the increase in irreversible capacity at the time of initial charging can be suppressed. It is preferably 200 nm or less.

The arithmetic average particle size of the amorphous carbon particles involved in the embedding step is determined by observing the amorphous carbon particles with a transmission electron microscope (TEM) and using the diameter of the circumscribing circle of the particles in the obtained image as the particle size. It is an average value of the particle diameters of 10,000 particles measured using image software (WINROOF manufactured by Mitani Shoji Co., Ltd.).

When the amorphous carbon particles involved in the embedding step are carbon black, the DBP oil absorption amount of the carbon black is preferably 300 ml / 100 g or less. When the DBP oil absorption amount of carbon black is 300 ml / 100 g or less, it is possible to suppress an increase in the specific surface area and suppress an irreversible capacity at the time of initial charging. The DBP oil absorption amount of carbon black is more preferably 250 ml / 100 g or less in that it is possible to suppress an increase in irreversible capacity at the time of initial charging, and further, it is possible to suppress an increase in irreversible capacity at the time of initial charging. In particular, it is 200 ml / 100 g or less.

In the embedding step, the mixing amount of the amorphous carbon particles with respect to 100.0 parts by mass of the graphite particles is preferably 10.0 to 40.0 parts by mass. Since the mixed amount of the amorphous carbon particles is 10.0 to 40.0 parts by mass with respect to 100.0 parts by mass of the graphite particles, the irreversible capacity at the time of initial charging is suppressed and the high-speed charge / discharge performance is improved. It becomes possible. The mixing amount of the amorphous carbon particles with respect to 100.0 parts by mass of the graphite particles is more preferably 20.0 parts by mass or more in terms of further improving the high-speed charge / discharge property, and isolated without being coated. It is more preferably 30.0 parts by mass or less in that the particles to be charged can be suppressed and the increase in irreversible capacity at the time of initial charging can be suppressed.

In the embedding step, the method of embedding the amorphous carbon particles in the binder layer of the binder-coated graphite particles by mixing the amorphous carbon particles with the binder-coated graphite particles, compressing and rubbing the particles is not particularly limited. It is a method of applying mechanical energy by utilizing compression and friction, and examples thereof include a method of compressing and rubbing using a device such as a hybridizer and a mechanofusion system.

In the embedding step, the treatment temperature when the amorphous carbon particles are mixed with the binder-coated graphite particles and compressed and rubbed is not particularly limited as long as it is equal to or higher than the softening point temperature of the binder, but is ± 20 ° C. with respect to the softening point. Temperature is preferred. If the treatment temperature is too high with respect to the softening point, the fluidity of the binder increases and it is easy to form granules containing only coated particles, and if the treatment temperature is too low, the pitch layer becomes hard and it is difficult to embed the coated particles. Become.

An example of the conditions when the embedding process is performed using a hybridizer device (NHS-I type manufactured by Nara Machinery Co., Ltd.) is shown below. Amorphous carbon particle-adhered binder (pitch) -coated graphite particles are put into the apparatus and treated at 1,200 rpm (rotational peripheral speed 20 m / s). When the temperature inside the device is stabilized at a temperature above the softening point of the binder (pitch), the softened binder layer (pitch layer) is formed by processing at a rotation speed of 6,400 rpm (rotational peripheral speed 80 m / s). Embed amorphous carbon particles.

The calcined carbonization step (hereinafter, also referred to as calcined carbonization step (1)) according to the method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention is a binder-coated graphite particle in which amorphous carbon particles are embedded. Is a step of calcining and carbonizing.

The temperature at which the amorphous carbon particle-embedded binder-coated graphite particles are calcined and carbonized is preferably 800 ° C. or higher, more preferably 1000 ° C. or higher. When the calcination carbonization temperature is in the above range, it is possible to sufficiently remove unburned components contained in amorphous carbon particles such as carbon black. On the other hand, if the firing carbonization temperature is less than the above range, the unburned components contained in the amorphous carbon particles such as carbon black cannot be sufficiently removed, and the battery characteristics deteriorate. The firing carbonization time is appropriately selected. The upper limit of the temperature for calcining and carbonizing is not particularly limited, but the temperature for calcining and carbonizing the graphite particles adhering to amorphous carbon particles is preferably 3000 ° C. or lower, and more preferably 2000 ° C. or lower in terms of improving high-speed charge / discharge characteristics. ..

The atmosphere when the amorphous carbon particle-embedded binder-coated graphite particles are calcined and carbonized is an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.

In the method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention, the calcined carbide obtained by performing the carbonization firing step (1) may be subjected to a pulverization treatment and a classification treatment, if necessary. ..

As described above, the negative electrode material for a lithium ion secondary battery of the present invention can be obtained by performing the method for producing a negative electrode material for a lithium ion secondary battery according to the first aspect of the present invention.

The method for producing the negative electrode material for a lithium ion secondary battery according to the second aspect of the present invention _{is to mix graphite particles having an average particle diameter (D 50} ) of 5.0 to 30.0 μm with a binder. A coating step of obtaining binder-coated graphite particles in which graphite particles are coated with a binder,
Amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm are mixed with 100.0 parts by mass of the graphite particles by 10.0 to 40.0 parts by mass, and then the amount of residual carbon after carbonization is 2. By coating with a resin solution in an amount of 0 parts by mass or more, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin, and the amorphous carbon particle-attached binder-coated graphite particles are re-coated. The recoating process to obtain the coating and
A calcining carbonization step of calcining and carbonizing the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles.
It is characterized by having.

A method for producing a negative electrode material for a lithium ion secondary battery according to a second aspect of the present invention will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view for explaining a method for manufacturing a negative electrode material for a lithium ion secondary battery according to a second aspect of the present invention. For convenience of explanation, in FIG. 5, only the outlines of the graphite particles, the binder and the resin are shown by solid lines.

In FIG. 5, first, by mixing the graphite particles 1 and the binder 11, as shown in (A), the binder-coated graphite particles 12 in which the graphite particles 1 are coated with the binder 11 are obtained. Next, the amorphous carbon particles 3 are mixed with the binder-coated graphite particles 12 to obtain the amorphous carbon particle-attached binder-coated graphite particles 13 as shown in (B). Next, a resin solution is mixed with the amorphous carbon particle-adhered binder-coated graphite particles 13, the surface of the binder layer 11 is covered with the resin solution, and then dried to cover the surface of the binder layer 11 with the resin 15. Then, a recoated material 16 of the binder-coated graphite particles adhering to the amorphous carbon particles is obtained. Next, by firing the recoated material 16 of the binder-coated graphite particles adhering to the amorphous carbon particles, the binder and the resin are carbonized and converted into an amorphous carbonized bonding material, which is a negative electrode material for a lithium ion secondary battery. Is obtained.

The method for producing a negative electrode material for a lithium ion secondary battery according to the second aspect of the present invention includes a coating step, a recoating step, and a calcining carbonization step.

In the coating step (hereinafter, also referred to as coating step (2)) according to the method for producing a negative electrode material for a lithium ion secondary battery according to the second aspect of the present invention, graphite particles are mixed with a binder to obtain graphite. This is a step of obtaining binder-coated graphite particles in which the particles are coated with a binder.

The graphite particles according to the coating step (2) are spheroidized graphite, and flat graphite is agglomerated into spheres. The graphite particles may be natural graphite or artificial graphite.

_{The average particle size (D 50} ) of the graphite particles according to the coating step (2) is preferably 5.0 to 30.0 μm. When the average particle size (D ₅₀ ) of the graphite particles is 5.0 to 30.0 μm, the reaction resistance decreases due to the increase in the reaction specific surface area, and in addition, the movement speed of lithium ions in the graphite particles is also high. Become. The average particle size (D ₅₀ ) of the graphite particles is more preferably 7.0 μm or more in that it is possible to suppress an increase in irreversible capacity at the time of initial charging, and further improve high-speed charge / discharge performance. , More preferably 25.0 μm or less, and particularly preferably 20.0 μm or less in terms of improving high-speed charge / discharge performance.

The d (002) of the graphite particles according to the coating step (2) is 0.3360 nm or less. When the average lattice spacing d (002) of the graphite particles is 0.3360 nm or less, the reversible capacitance becomes sufficiently large. The d (002) of the graphite particles is preferably 0.3358 nm or less in that the reversible capacity is further increased.

The binder according to the coating step (2) is not particularly limited as long as it is carbonized in the firing carbonization step and becomes an amorphous carbon material, and examples thereof include coal tar pitch and phenol resin.

In the coating step (2), the mixing amount of the binder with respect to 100.0 parts by mass of the graphite particles is preferably 10.0 to 30.0 parts by mass. Since the mixing amount of the binder is 10.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the graphite particles, it is possible to embed and immobilize the coated particles while suppressing the irreversible capacity at the time of initial charging. It becomes. The mixing amount of the binder with respect to 100.0 parts by mass of the graphite particles is more preferably 15.0 parts by mass or more in that the particle surface is covered and the increase in irreversible capacity at the time of initial charging can be suppressed. It is more preferably 20.0 parts by mass or less in that the generation of carbonized components of excess binder can be suppressed and the increase in irreversible capacity at the time of initial charging can be suppressed.

In the coating step (2), the method of mixing the graphite particles and the binder is not particularly limited, and examples thereof include a method of mixing using a heating mixer such as a Henschel mixer, a high speed mixer, or a kneader.

In the coating step (2), the mixing temperature when the graphite particles and the binder are mixed is equal to or higher than the softening point temperature in the case of a binder solid at room temperature, and is not particularly limited in the case of a binder liquid at room temperature. When a resin is used, it is usually below the curing temperature. The mixing time is preferably 10 to 30 minutes.

In the recoating step according to the method for producing the negative electrode material for a lithium ion secondary battery of the second aspect of the present invention, amorphous carbon particles are mixed with the binder-coated graphite particles obtained by performing the coating step (2). Next, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin by coating with a resin solution to obtain a recoated product of the binder-coated graphite particles to which the amorphous carbon particles are attached. ..

In the recoating step, first, the amorphous carbon particles are mixed with the binder-coated graphite particles obtained in the coating step (2), so that the amorphous carbon particles are formed on the surface of the binder layer of the binder-coated graphite particles. Amorphous carbon particles are attached to obtain binder-coated graphite particles.

The amorphous carbon particles involved in the recoating step are not particularly limited, and examples thereof include furnace black and thermal black.

The average lattice spacing d (002) of the amorphous carbon particles involved in the recoating step is 0.3370 nm or more. When the average lattice spacing d (002) of the amorphous carbon particles is 0.3370 nm or more, the reaction resistance of the particle surface is lowered and high-speed charging / discharging is excellent. The average lattice spacing d (002) of the amorphous carbon particles is more preferably 0.3400 nm or more in that the high-speed charge / discharge property is further improved, and particularly preferably in that the high-speed charge / discharge performance is further improved. Is 0.3500 nm or more.

The arithmetic mean particle size of the amorphous carbon particles involved in the recoating step is preferably 50 to 300 nm. Since the average particle size of the amorphous carbon particles in surface observation is 50 to 300 nm, the material has excellent high-speed charge / discharge characteristics while suppressing a decrease in irreversible capacity. The arithmetic mean particle size of the amorphous carbon particles is more preferably 100 nm or more in that the increase in irreversible capacity at the time of initial charging can be suppressed, and further, the increase in irreversible capacity at the time of initial charging can be suppressed. In that respect, it is 200 nm or less.

The arithmetic average particle size of the amorphous carbon particles involved in the recoating step is determined by observing the amorphous carbon particles with a transmission electron microscope (TEM) and using the diameter of the circumscribing circle of the particles in the obtained image as the particle size. , An average value of the particle diameters of 10,000 particles measured using image software (WINROOF manufactured by Mitani Shoji Co., Ltd.).

When the amorphous carbon particles involved in the recoating step are carbon black, the DBP oil absorption amount of the carbon black is preferably 300 ml / 100 g or less. When the DBP oil absorption amount of carbon black is 300 ml / 100 g or less, it is possible to suppress an increase in the specific surface area and suppress an irreversible capacity at the time of initial charging. The DBP oil absorption amount of carbon black is more preferably 250 ml / 100 g or less in that it is possible to suppress an increase in irreversible capacity at the time of initial charging, and further, it is possible to suppress an increase in irreversible capacity at the time of initial charging. In particular, it is 200 ml / 100 g or less.

In the recoating step, the mixing amount of the amorphous carbon particles with respect to 100.0 parts by mass of the graphite particles is preferably 10.0 to 40.0 parts by mass. Since the mixed amount of the amorphous carbon particles is 10.0 to 40.0 parts by mass with respect to 100.0 parts by mass of the graphite particles, the irreversible capacity at the time of initial charging is suppressed and the high-speed charge / discharge performance is improved. It becomes possible. The mixing amount of the amorphous carbon particles with respect to 100.0 parts by mass of the graphite particles is more preferably 20.0 parts by mass or more in that the high-speed charge / discharge property is further improved, and the irreversible capacity at the time of initial charging. It is more preferably 30.0 parts by mass or less in that the increase can be suppressed.

In the recoating step, the method of mixing the binder-coated graphite particles and the amorphous carbon particles is not particularly limited, and examples thereof include a method of mixing using a heating mixer such as a Henschel mixer, a high-speed mixer, or a kneader. ..

In the recoating step, the mixing temperature when the binder-coated graphite particles and the amorphous carbon particles are mixed is equal to or higher than the softening point temperature in the case of a solid binder at room temperature, and particularly in the case of a liquid binder at room temperature. Although not limited, when a resin is used, it is usually below the curing temperature. The mixing time is preferably 10 to 30 minutes.

In the recoating step, the graphite particles to which the amorphous carbon particles are attached are then coated with a resin solution to recoat the graphite particles to which the amorphous carbon particles are attached with a resin, and the amorphous carbon particles are coated with a resin. A recoated product of binder-coated graphite particles adhering to quality carbon particles is obtained.

The resin involved in the recoating step is particularly limited as long as it is carbonized in the firing carbonization step and the amount of residual carbon after carbonization can be adjusted to 2.0 parts by mass or more with respect to 100.0 parts by mass of graphite particles. Not done. Examples of the resin involved in the recoating step include thermoplastic resins such as polyvinyl chloride resin and acrylic resin, and synthetic resins such as thermosetting resins such as phenol resin and urea resin. Among these, water-soluble phenol resin Is preferable.

The resin solution is a solution in which the resin is dissolved in a solvent. The solvent is not particularly limited as long as the resin is dissolved, and examples thereof include water, ethanol, and diethylene glycol.

The mixed amount of the resin (mixed amount of the resin component and excluding the solvent) is such that the amount of residual coal after carbonization is 2.0 parts by mass or more with respect to 100.0 parts by mass of the graphite particles. When the amount of the resin mixed is such that the amount of residual carbon after carbonization is 2.0 parts by mass or more with respect to 100.0 parts by mass of the graphite particles, the gap generated between the amorphous carbon particles and the graphite particles is formed. It is possible to fill and improve the high-speed charge / discharge characteristics. The mixed amount of resin (mixed amount of resin content, excluding solvent) suppresses carbonization of excess resin, and it is possible to suppress an increase in irreversible capacity at the time of initial charging. However, the amount is preferably 14.0 parts by mass or less with respect to 100.0 parts by mass of the graphite particles.

The viscosity of the resin solution is not particularly limited, but is 1500 mPa · s or less, preferably 2 to 1000 mPa · s. When the viscosity of the resin solution is in the above range, the resin solution easily permeates into the gap between the amorphous carbon particles and the graphite particles or the gap between the amorphous carbon particles. If it is less than the above range, the fluidity becomes high, and it becomes difficult to uniformly coat the amorphous carbon particles in the mixing container.

In the recoating step, the method of mixing the resin solution with the binder-coated graphite particles adhering to the amorphous carbon particles is not particularly limited, and examples thereof include a method of mixing using a mixer such as a Henschel mixer or a high-speed mixer. ..

In the recoating step, the mixing temperature when the resin solution is mixed with the binder-coated graphite particles adhering to the amorphous carbon particles is appropriately selected at a temperature equal to or lower than the boiling point of the solvent of the resin solution.

Further, an example of conditions in the case where the amorphous carbon particle-adhered binder-coated graphite particles and the resin solution are mixed by using a Henschel mixer device (FM20C manufactured by Mitsui Mining Co., Ltd.) in the recoating step is shown below. After mixing the binder-coated graphite particles and the amorphous carbon particles, after confirming that the temperature of the amorphous carbon particle-attached binder-coated graphite particles has dropped to around room temperature, a phenol resin solution (Sumitomo Bakelite Co., Ltd.) PR56265: Water = 1: 1) was added to 100.0 parts by mass of graphite particles by 10.0 parts by mass and treated at a peripheral speed of 30 m / s, whereby between the amorphous carbon particles and the graphite particles. The gap or the gap between the amorphous carbon particles is filled with the resin solution.

Then, in the recoating step, the amorphous carbon particles adhered to the binder-coated graphite particles are mixed with a resin solution diluted with a solvent such as water to reduce the viscosity, so that the amorphous carbon particles and the graphite particles are separated from each other. The resin solution permeates the gaps or the gaps between the amorphous carbon particles, and the surface of the binder layer of the amorphous carbon particle-attached binder-coated graphite particles is covered with the resin solution, and then dried to be removed from the resin solution. By removing the solvent, the surface of the binder layer of the amorphous carbon particle-attached binder-coated graphite particles is recoated with the resin, and a recoated product of the amorphous carbon particle-attached binder-coated graphite particles is obtained.

The calcined carbonization step (hereinafter, also referred to as calcined carbonization step (2)) according to the method for producing a negative electrode material for a lithium ion secondary battery according to the second aspect of the present invention is a binder-coated graphite particle having amorphous carbon particles attached. This is a step of calcining and carbonizing the recoated product of.

The temperature at which the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles is calcined and carbonized is preferably 800 ° C. or higher, more preferably 1000 ° C. or higher. When the calcination carbonization temperature is in the above range, it is possible to sufficiently remove unburned components contained in amorphous carbon particles such as carbon black. On the other hand, if the firing carbonization temperature is less than the above range, the unburned components contained in the amorphous carbon particles such as carbon black cannot be sufficiently removed, and the battery characteristics deteriorate. The firing carbonization time is appropriately selected. The upper limit of the temperature for calcining and carbonizing is not particularly limited, but the temperature for calcining and carbonizing the graphite particles adhering to amorphous carbon particles is preferably 3000 ° C. or lower, and more preferably 2000 ° C. or lower in terms of improving high-speed charge / discharge characteristics. ..

The atmosphere when the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles is calcined and carbonized is an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.

In the method for producing a negative electrode material for a lithium ion secondary battery according to the second aspect of the present invention, the calcined carbide obtained by performing the carbonization firing step (2) may be subjected to a pulverization treatment and a classification treatment, if necessary. ..

As described above, the negative electrode material for a lithium ion secondary battery of the present invention can be obtained by performing the method for producing a negative electrode material for a lithium ion secondary battery according to the second aspect of the present invention.

The physical properties, characteristics, and performance of the negative electrode material for a lithium ion secondary battery obtained by performing the method for producing a negative electrode material for a lithium ion secondary battery of the present invention are the same as those of the negative electrode material for a lithium ion secondary battery of the present invention described above. Similar to physical properties, characteristics and performance.

The negative electrode material for a lithium ion secondary battery of another embodiment of the present invention can be obtained by carrying out the method for producing a negative electrode material for a lithium ion secondary battery of the first or second embodiment of the present invention. It is a negative electrode material for the next battery. That is, in the negative electrode material for a lithium ion secondary battery of the present invention, _{graphite particles having an average particle diameter (D 50} ) of 5.0 to 30.0 μm are mixed with a binder, so that the graphite particles are coated with the binder. The coating step (1) for obtaining the binder-coated graphite particles, and
The binder is obtained by mixing 10.0 to 40.0 parts by mass of amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm with 100.0 parts by mass of the graphite particles, and then compressing and rubbing the particles. A process of embedding the amorphous carbon particles in the binder layer of the coated graphite particles to obtain the amorphous carbon particle-embedded binder-coated graphite particles, and an embedding step.
In the calcining carbonization step (1) of calcining carbonizing the binder-coated graphite particles embedded with amorphous carbon particles,
It is a negative electrode material for a lithium ion secondary battery that can be obtained. The negative electrode material for a lithium ion secondary battery of the present invention can at least perform a coating step (1), an embedding step, and a calcining carbonization step (1), and impairs the effect of the present invention. It is permissible to carry out other steps to the extent that it does not exist.

Further, in the negative electrode material for a lithium ion secondary battery of the present invention, _{graphite particles having an average particle diameter (D 50} ) of 5.0 to 30.0 μm are mixed with a binder so that the graphite particles are coated with the binder. The coating step (2) for obtaining the binder-coated graphite particles, and
Amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm are mixed with 100.0 parts by mass of the graphite particles by 10.0 to 40.0 parts by mass, and then the amount of residual carbon after carbonization is 2. By coating with a resin solution in an amount of 0 parts by mass or more, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin, and the amorphous carbon particle-attached binder-coated graphite particles are re-coated. The recoating process to obtain the coating and
The calcined carbonization step (2) in which the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles is calcined and carbonized,
It is a negative electrode material for a lithium ion secondary battery that can be obtained. The negative electrode material for a lithium ion secondary battery of the present invention can be obtained by performing at least a coating step (2), a recoating step, and a calcining carbonization step (2), and the effect of the present invention can be achieved. It is permissible to carry out other steps as long as they are not impaired.

The coating step (1), the embedding step and the calcined carbonization step (1) and the coating step (2), the recoating step and the calcined carbonization step (2) relating to the negative electrode material for the lithium ion secondary battery of another embodiment of this invention are carried out. , The same as the coating step, the embedding step and the calcined carbonization step according to the method for manufacturing the negative electrode material for a lithium ion secondary battery of the present invention.

In the present invention, the specific surface area (SA) uses a fully automatic surface area measuring device ((BELSORP-miniX manufactured by Microtrac Bell)) and has multiple BET points in the range of relative pressure of 0.05 to 0.2 on the nitrogen adsorption isotherm. It means the value calculated by the method.

In the present invention, the tap density is obtained after 5 g of graphite particle powder is put into a 25 ml graduated cylinder and tapping is repeated 1000 times with a gap of 10 mm using a tapping type powder reduction measuring instrument (manufactured by Tsutsui Rikagaku Kikai Co., Ltd.). It means a value calculated by the following formula (3) from the value of the apparent volume and the mass of the graphite particle powder charged into the measuring cylinder.

Tap density (g / cm ³ ) = mass of powder charged into the graduated cylinder (g) / value of apparent volume after repeated tapping 1000 times (cm ³ ) (3)

In the present invention, the plate density means a value measured by the following method.

(1) Preparation of Electrode Sheet To 90.2% by weight of spherical aggregates of graphite particles, 9.8% by weight of polyvinylidene fluoride (PVDF), an organic binder dissolved in N-methyl-2pyrrolidone, was added as a solid content. Stir and mix to prepare a negative electrode mixture paste.
The obtained negative electrode mixture paste is applied onto a copper foil (current collector) having a thickness of 20 μm by the doctor blade method, and then heated at 90 ° C. under normal pressure for 90 minutes and further at 130 ° C. under vacuum for 11 hours to prepare a solvent. It is completely volatilized to obtain an electrode sheet having a basis weight of 3.5 ± 0.2 mg / cm ^2.
Here, the basis weight means the weight of the graphite particle spherical aggregates per unit area of the electrode sheet.

(2) Measurement of electrode plate density The electrode sheet is cut into strips having a width of 6 cm and rolled by a roll press so ^{that the electrode plate density is 1.2 g / cm 3.} The pressed electrode sheet is cut into a length of 2.8 cm and a width of 5.5 cm. The electrode plate density was calculated and confirmed by the following formula (4) from each weight A (g) and the thickness B (cm) of the central portion.

Electrode plate density (g / cm ³ ) = {(A (g) -copper foil weight (g)) x weight ratio of graphite particle spherical aggregates in the negative electrode mixture layer (0.902)} / {(B (B (B) cm) -Copper foil thickness (cm)) x electrode area (cm ² )} (4)

In the present invention, the average lattice spacing d (002) is high-purity silicon using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.) and X-rays obtained by monochromaticizing Cu-Kα rays with a Ni filter. Was measured by powder X-ray diffraction method using The value.

In the present invention, Raman R is measured by a Raman spectroscopic analyzer (manufactured by Horiba Seisakusho Co., Ltd., HR800) equipped with an Nd / YAG laser having a wavelength of 532 nm, and has a crystal structure due to crystal defects on the surface layer and inconsistency of the laminated structure. the 1360 cm ^-1 spectral neighboring I1360 attributable to disturbances, divided by the spectrum I1580 near 1580 cm ^-1 attributable to E2g vibration corresponding to the lattice vibration of the carbon hexagonal net plane, the Raman spectrum intensity ratio R = I1360 / I1580 Asked as. The average value measured at 10 points or more in an irradiation area of 100 μm ^{2 was used as a representative value.}

(Example 1)
Coal tar pitch with respect to 100.0 parts by mass of spherical natural graphite (average lattice spacing d (002): 0.3356 nm, specific surface area: 7.4 m ^{2 /} g) with an average particle size (D _{50) of 10.4 μm.} (PKQL manufactured by JFE Chemical Co., Ltd., softening point 70 ° C.) 20.0 parts by mass was put into a mixer (Henshell mixer manufactured by Mitsui Mining Co., Ltd.) and mixed at 90 ° C. for 15 minutes. Then, at 90 ° C., 20.0 parts by mass of furnace black (manufactured by Tokai Carbon Co., Ltd., S-TA) having an arithmetic mean particle size of 122 nm was added, and the mixture was further mixed for 10 minutes. The obtained mixed powder was put into a hybridizer device (manufactured by Nara Machinery Co., Ltd.) and treated at a rotation speed of 6400 rpm for 3 minutes while maintaining the maximum temperature in the device at 75 ° C. ± 5 ° C.
The obtained powder was calcined by calcining at 1000 ° C. in a nitrogen gas atmosphere. Next, the obtained calcined powder is crushed (device name: Super Rotor, manufactured by Nisshin Engineering Co., Ltd.) and classified (device name: sieve classification, opening 45 μm), and the subsieving component is used as a negative electrode material for a lithium ion secondary battery. Manufactured as.

(Example 2)
Coal tar pitch with respect to 100.0 parts by mass of spherical natural graphite (average lattice spacing d (002): 0.3356 nm, specific surface area: 7.4 m ^{2 /} g) with an average particle size (D _{50) of 10.4 μm.} (PKQL manufactured by JFE Chemical Co., Ltd., softening point 70 ° C.) 20.0 parts by mass was put into a mixer (Henshell mixer manufactured by Mitsui Mining Co., Ltd.) and mixed at 90 ° C. for 15 minutes. Then, at 90 ° C., 20.0 parts by mass of furnace black (manufactured by Tokai Carbon Co., Ltd., S-TA) having an arithmetic mean particle size of 122 nm was added, and the mixture was further mixed for 10 minutes. When the temperature inside the tank reached 40 ° C., 10.0 parts by mass of an aqueous resin solution (PR56165 manufactured by Sumitomo Bakelite Co., Ltd .: water = 1: 1) was added, and the mixture was further mixed for 10 minutes. Then, the obtained mixed powder was dried.
The obtained powder was calcined by calcining at 1000 ° C. in a nitrogen gas atmosphere. Next, the obtained calcined powder is crushed (device name: Super Rotor, manufactured by Nisshin Engineering Co., Ltd.) and classified (device name: sieve classification, opening 45 μm), and the subsieving component is used as a negative electrode material for a lithium ion secondary battery. Manufactured as. The amount of carbon remaining after carbonization of the resin in the aqueous resin solution after calcining is 2.5 parts by mass with respect to 100.0 parts by mass of spherical natural graphite.
Table 1 shows the analysis results and evaluation results of the obtained negative electrode material for a lithium ion secondary battery.

(Comparative Example 1)
Coal tar pitch with respect to 100.0 parts by mass of spherical natural graphite (average lattice spacing d (002): 0.3356 nm, specific surface area: 7.4 m ^{2 /} g) with an average particle size (D _{50) of 10.4 μm.} (PKQL manufactured by JFE Chemical Co., Ltd., softening point 70 ° C.) 20.0 parts by mass was put into a mixer (Henshell mixer manufactured by Mitsui Mining Co., Ltd.) and mixed at 90 ° C. for 15 minutes. The obtained powder was calcined by calcining at 1000 ° C. in a nitrogen gas atmosphere. Next, the obtained calcined powder is crushed (device name: Super Rotor, manufactured by Nisshin Engineering Co., Ltd.) and classified (device name: sieve classification, opening 45 μm), and the subsieving component is used as a negative electrode material for a lithium ion secondary battery. Manufactured as.

(Comparative Example 2)
The same procedure as in Example 1 was carried out except that the amount of furnace black added was 5.0 parts by mass.

(Comparative Example 3)
The procedure was the same as in Example 1 except that the embedding step with the hybridizer was omitted.

(Comparative Example 4)
The same procedure as in Example 1 was carried out except that the rotation speed of the hybridizer was set to 8000 rpm.

(Analysis method)
・ SEM analyzer and conditions Analyzer: JSM7900F manufactured by JEOL Ltd.
An electron beam accelerated at an acceleration voltage of 2-5 kv is applied to the sample, and the secondary electron image is observed.
Cross-section data preparation device: IB-19530CP manufactured by JEOL Ltd.
The electrode sheet is cut out to a predetermined size, and a shielding plate is installed at the processing position. By irradiating with an argon ion beam, it is cut along the edge of the shielding plate.
-TEM analyzer and conditions Analyzer: Hitachi H-7650 transmission electron microscope (100 kV)
After carbon black was dispersed in an organic solvent such as acetone, it was dropped onto a grid with an amorphous carbon film, dried, and observed at an acceleration voltage of 100 kV.
-Laser diffraction particle size distribution measuring device and analytical conditions Analytical device: manufactured by HORIBA, Ltd .: LA-960
Light source: Semiconductor laser (650 nm)
The powder was ultrasonically dispersed in an aqueous solution containing 10% by mass of an amphoteric surfactant with respect to 100 parts by mass of distilled water. The dispersed powder is flowed to a measurement cell in the apparatus and irradiated with a laser. The particle size distribution is obtained by detecting and analyzing the scattered light with a ring-shaped detector.

(Evaluation method)
(Making laminated batteries)
Using the above-mentioned working electrode and counter electrode, a positive electrode (Li metal), a separator (polypropylene), and a negative electrode (test negative electrode material) are laminated in this order as an evaluation battery, and a Ni tab is attached, and then the laminate is made of aluminum. Laminated and the laminated battery was assembled in an inert atmosphere. As the electrolytic solution, a 1: 1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) ^{in which 1 mol / dm 3} lithium salt LiPF _{6 was dissolved was used.} Charging has a current density of 0. After the constant current charging is completed at ² mA / cm 2 and the final voltage 5 mV, the constant potential is maintained until the ^{lower limit current becomes 0.02 mA / cm 2.} For discharge, constant current discharge was performed at a current density of 0.2 mA / cm ^{2 up to a} final voltage of 1.5 V, and the discharge capacity after the end of 3 cycles was defined as a reversible capacity. The initial efficiency is a value (%) obtained by dividing the discharge capacity of the first cycle by the charge capacity of the first cycle. The charge capacity of 5C is the charge capacity when fully charged in 12 minutes from the fully discharged state after 3 cycles.

As can be seen from the results in Table 1, Examples 1 and 2 have a high capacity and a 5C charge capacity is higher than that of Comparative Examples 1 to 4, so that Examples 1 and 2 have a high capacity. At the same time, it can be seen that the high-speed charge / discharge characteristics are superior to those of Comparative Examples 1 to 4. Further, in Examples 1 and 2, the initial efficiency is high and the irreversible capacity can be suppressed.

According to the present invention, it is possible to provide a method for manufacturing a negative electrode material for a lithium ion secondary battery and a negative electrode material for a lithium ion secondary battery, which are excellent in high-speed charge / discharge characteristics.

1 Graphite particles 2 Amorphous carbonized bonding material 3 Amorphous carbon particles 4 Coating layer 5 Buried parts 6a, 6b intersections
7 Whole amorphous carbon particles 8 Thickness of amorphous carbonized bonding material 9 Calculation range 10 Negative material for lithium ion secondary battery 11 Binder 12 Binder coated graphite particles 13 Amorphous carbon particles Adhering binder coated graphite particles 14 Aspherical Quality Carbon particles embedded binder-coated graphite particles 15 Resin 16 Amorphous carbon particles-attached binder-coated graphite particles recoated

Claims (6)

It comprises graphite particles and a coating layer containing amorphous carbon particles and an amorphous carbonized bonding material and covering the graphite particles.
The coverage of the amorphous carbon particles in surface observation is 50% or more,
The burial ratio of the amorphous carbon particles in the cross-sectional observation is 30 to 90%.
Negative electrode material for lithium-ion secondary batteries. The negative electrode material for a lithium ion secondary battery according to claim 1, _{wherein the average particle size (D 50) of the negative electrode material for a lithium ion secondary battery is 5.0 to 30.0 μm.} A coating step of mixing graphite particles having an average particle diameter (D ₅₀ ) of 5.0 to 30.0 μm with a binder to obtain binder-coated graphite particles in which the graphite particles are coated with a binder.
The binder is obtained by mixing 10.0 to 40.0 parts by mass of amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm with 100.0 parts by mass of the graphite particles, and then compressing and rubbing the particles. A process of embedding the amorphous carbon particles in the binder layer of the coated graphite particles to obtain the amorphous carbon particle-embedded binder-coated graphite particles, and an embedding step.
A calcining carbonization step of calcining carbonizing the binder-coated graphite particles in which the amorphous carbon particles are embedded,
A negative electrode material for lithium-ion secondary batteries that can be obtained. A coating step of mixing graphite particles having an average particle diameter (D ₅₀ ) of 5.0 to 30.0 μm with a binder to obtain binder-coated graphite particles in which the graphite particles are coated with a binder.
Amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm are mixed with 100.0 parts by mass of the graphite particles by 10.0 to 40.0 parts by mass, and then the amount of residual carbon after carbonization is 2. By coating with a resin solution in an amount of 0 parts by mass or more, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin, and the amorphous carbon particle-attached binder-coated graphite particles are re-coated. The recoating process to obtain the coating and
A calcining carbonization step of calcining and carbonizing the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles.
A negative electrode material for lithium-ion secondary batteries that can be obtained. A coating step of mixing graphite particles having an average particle diameter (D ₅₀ ) of 5.0 to 30.0 μm with a binder to obtain binder-coated graphite particles in which the graphite particles are coated with a binder.
The binder is obtained by mixing 10.0 to 40.0 parts by mass of amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm with 100.0 parts by mass of the graphite particles, and then compressing and rubbing the particles. A process of embedding the amorphous carbon particles in the binder layer of the coated graphite particles to obtain the amorphous carbon particle-embedded binder-coated graphite particles, and an embedding step.
A calcining carbonization step of calcining carbonizing the binder-coated graphite particles in which the amorphous carbon particles are embedded,
A method for producing a negative electrode material for a lithium ion secondary battery. A coating step of mixing graphite particles having an average particle diameter (D ₅₀ ) of 5.0 to 30.0 μm with a binder to obtain binder-coated graphite particles in which the graphite particles are coated with a binder.
Amorphous carbon particles having an arithmetic average particle diameter of 50 to 300 nm are mixed with 100.0 parts by mass of the graphite particles by 10.0 to 40.0 parts by mass, and then the amount of residual carbon after carbonization is 2. By coating with a resin solution in an amount of 0 parts by mass or more, the graphite particles to which the amorphous carbon particles are attached are recoated with the resin, and the amorphous carbon particle-attached binder-coated graphite particles are re-coated. The recoating process to obtain the coating and
A calcining carbonization step of calcining and carbonizing the recoated material of the binder-coated graphite particles adhering to the amorphous carbon particles.
A method for producing a negative electrode material for a lithium ion secondary battery.

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