JP7263284B2 - Manufacturing method of negative electrode material for lithium ion secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a negative electrode material for a lithium ion secondary battery, a method for producing a negative electrode material for a lithium ion secondary battery, and a material for producing 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 being 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 for automotive applications has increased rapidly, and the characteristics required for automotive applications are high capacity, long life, high input/output, and an excellent balance of these characteristics. It is required that Therefore, a negative electrode material with high energy density and low expansion and contraction is required, and graphite particles are widely used as a negative electrode material that satisfies these characteristics.

In negative electrode materials for lithium ion secondary batteries using graphite materials, it is known that the discharge capacity can be improved by increasing the crystallinity of the graphite material. In addition to high discharge capacity, excellent high-speed charge/discharge characteristics are required.

For the purpose of improving the performance of negative electrode materials for lithium ion secondary batteries using such graphite particles, composite particles obtained by combining graphite particles have been proposed (see, for example, Patent Document 1).

In Patent Document 1, 2 to 50 parts by weight of carbon black and pitch are mixed with 100 parts by weight of a base material in which natural graphite is formed into a spherical shape, impregnated and coated with natural graphite particles, and fired at 900 ° C. to 1500 ° C. , discloses graphite particles (A) for lithium ion secondary batteries having a BET specific surface area of 2 m ² /g or more and having fine projections formed on the surface. According to Patent Document 1, it is possible to provide a negative electrode material for a lithium ion secondary battery that has a high discharge capacity per unit volume, a small capacity loss during initial charge and discharge, and excellent high-speed charge and discharge characteristics. It is

JP 2011-233541 A

However, as a result of investigation by the present inventors, it was found that the graphite particles for lithium ion secondary batteries described in Patent Document 1 tend to cause a decrease in initial efficiency when used as a negative electrode material for lithium ion secondary batteries. .
This is because the pitch is used as a binder when the graphite particles are coated with carbon black, so the composite graphite particles are strongly bonded to each other via the pitch adhered to the carbon black surface, and are pulverized after firing. It is thought that this is because a strong impact is generated when trying to obtain composite graphite particles, and the resulting composite graphite particles tend to be pulverized, easily leading to an increase in the specific surface area.

Further, there has been a strong demand for a negative electrode material for lithium ion secondary batteries that can improve high-speed charge/discharge characteristics. There has been a demand for a negative electrode material for lithium ion secondary batteries that has excellent discharge characteristics.

Accordingly, the present invention provides a negative electrode material for a lithium ion secondary battery having excellent initial efficiency and high-speed charge/discharge characteristics, a method for producing the negative electrode material for the lithium ion secondary battery, and a material for producing the negative electrode material for the lithium ion secondary battery. It is intended to

Under the above technical background, the inventors of the present invention conducted intensive studies and found that an amorphous carbonized binding material layer derived from a resin solution was provided on the surface of graphite particles, and through the amorphous carbonized binding material layer, Composite graphite particles in which a predetermined amount of amorphous carbon particles are fixed by means of the composite graphite particles suppress an increase in the specific surface area and increase the path of lithium ions to obtain a negative electrode material for a lithium ion secondary battery that is excellent in high-speed discharge characteristics. and completed the present invention based on this finding.

That is , the present invention
(1 ) A method for producing a negative electrode material for a lithium ion secondary battery, comprising:
a coating step of obtaining resin-coated graphite particles in which the graphite particles are coated with a resin by mixing graphite particles and a resin solution in the absence of pitch ;
10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of the graphite particles are mixed with the resin-coated graphite particles, and the amorphous carbon particles are coated on the surfaces of the resin-coated graphite particles. a step of obtaining amorphous carbon particle-attached graphite particles to which
A method for producing a negative electrode material for a lithium ion secondary battery, characterized by comprising a calcining and carbonizing step of calcining and carbonizing the amorphous carbon particle-attached graphite particles,
( 2 ) The lithium ion secondary battery according to ( 1 ) above, wherein the graphite particles have an average particle size D50 of 5.0 to 30.0 μm, and the amorphous carbon particles have an average particle size of 50 to 300 nm. A method for producing a negative electrode material for
(3) The obtained negative electrode material for lithium ion secondary batteries is
Composed of composite graphite particles having graphite particles and a coating layer containing amorphous carbon particles and an amorphous carbonized binder material and covering the graphite particles,
The composite graphite particles have a coverage of 50% or more in which the amorphous carbon particles cover the graphite particles when the surface is observed.
A method for producing the negative electrode material for a lithium ion secondary battery according to (1) or (2) above,
( 4 ) Amorphous carbon particle-attached graphite particles , in which amorphous carbon particles are attached to the surface of graphite particles together with a resin in the absence of pitch , are composed of a plurality of bonded aggregates,
The bonded aggregate contains 10.0 to 40.0 parts by mass of the amorphous carbon particles per 100.0 parts by mass of the graphite particles, and is characterized in that the material for producing a negative electrode material for a lithium ion secondary battery ( Hereinafter, appropriately referred to as material 1 for producing a negative electrode material for a lithium ion secondary battery according to the present invention),
( 5 ) The surface of the graphite particles is composed of a plurality of adhered aggregates of an amorphous carbonized binder material that does not contain carbonized pitch and amorphous carbon particle-coated graphite particles that are coated with amorphous carbon particles. ,
The fixed aggregate contains 10.0 to 40.0 parts by mass of the amorphous carbon particles per 100.0 parts by mass of the graphite particles,
The tap density change rate, which indicates the change rate of the tap density before and after pulverization, is 10% or more.
A manufacturing material for a negative electrode material for a lithium ion secondary battery, characterized in that the specific surface area change rate, which indicates the change rate of the nitrogen adsorption specific surface area, is 20% or less when the nitrogen adsorption specific surface area is 60% (hereinafter referred to as appropriate according to the present invention Manufacturing material 2 for negative electrode material for lithium ion secondary battery)
It provides

INDUSTRIAL APPLICABILITY According to the present invention, a negative electrode material for lithium ion secondary batteries having excellent initial efficiency and high-speed charge/discharge characteristics, a method for producing the negative electrode material for lithium ion secondary batteries, and a material for producing the negative electrode material for lithium ion secondary batteries are provided. can do.

1 is a schematic cross-sectional view of an example of the form of composite graphite particles constituting a negative electrode material for a lithium ion secondary battery according to the present invention; FIG. FIG. 2 is a schematic diagram for explaining a method of calculating a coverage ratio of amorphous carbon particles covering graphite particles in composite graphite particles constituting a negative electrode material for a lithium ion secondary battery according to the present invention. FIG. 2 is a schematic diagram for explaining a method of calculating the embedding ratio of amorphous carbon particles embedded in an amorphous carbonized binder material in composite graphite particles constituting a negative electrode material for a lithium ion secondary battery according to the present invention; be. FIG. 3 is a schematic cross-sectional view showing a bound aggregate in which a plurality of amorphous carbon particle-attached graphite particles, in which amorphous carbon particles are attached to the surfaces of graphite particles together with a resin, are bound.

First, the negative electrode material for lithium ion secondary batteries according to the present invention will be described.
The negative electrode material for lithium ion secondary batteries according to the present invention is
a coating step of obtaining resin-coated graphite particles in which the graphite particles are coated with a resin by mixing the graphite particles and a resin solution;
10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of the graphite particles are mixed with the resin-coated graphite particles, and the amorphous carbon particles are coated on the surfaces of the resin-coated graphite particles. a step of obtaining amorphous carbon particle-attached graphite particles to which
obtained by performing a calcining and carbonizing step of calcining and carbonizing the amorphous carbon particle-attached graphite particles,
Composed of composite graphite particles having graphite particles and a coating layer containing amorphous carbon particles and an amorphous carbonized binder material and covering the graphite particles,
The composite graphite particles are characterized in that the amorphous carbon particles cover the graphite particles with a coverage of 50% or more when the surface is observed.

The negative electrode material for a lithium ion secondary battery according to the present invention is composed of composite graphite particles obtained by performing the coating step, the step of obtaining amorphous carbon particle-attached graphite particles, and the calcining and carbonizing step, The details of these steps are as described later in the description of the method for producing a negative electrode material for a lithium ion secondary battery according to the present invention.
The negative electrode material for a lithium ion secondary battery according to the present invention is obtained by performing at least the coating step, the step of obtaining amorphous carbon particle-attached graphite particles, and the calcining and carbonizing step. It is permissible to perform other steps as long as the effect of the above is not impaired.

A negative electrode material for a lithium ion secondary battery according to the present invention will be described as appropriate with reference to FIGS. 1 to 3. FIG. FIG. 1 is a schematic cross-sectional view of one embodiment of composite graphite particles constituting a negative electrode material for a lithium ion secondary battery according to the present invention.

In FIG. 1, a composite graphite particle 10 constituting a negative electrode material 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 comprises amorphous carbon particles 3 and an amorphous carbonized binder material 2, with the amorphous carbon particles 3 typically embedded in the layer of amorphous carbonized binder material 2, It is fixed to the composite graphite particles 10 constituting the negative electrode material for lithium ion secondary batteries. In the composite graphite particles 10 constituting the negative electrode material for lithium ion secondary batteries, almost all the amorphous carbon particles 3 constituting the composite graphite particles are in contact with the surfaces of the graphite particles 1 .

In the negative electrode material for a lithium ion secondary battery according to the present invention, the graphite particles serving as the core material of the composite graphite particles include spherical graphite particles in which flat graphite is aggregated into a spherical shape. The graphite particles may consist of natural graphite, or may consist of artificial graphite.

The average lattice spacing d(002) of the graphite particles is 0.3360 nm or less, and the average lattice spacing d(002) of the graphite particles is 0.3360 nm or less, so that the reversible capacity can be sufficiently increased. can. The average lattice spacing d(002) of graphite particles is preferably 0.3358 nm or less in order to further improve the reversible capacity.

In the present application documents, the average lattice spacing d (002) is measured using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.), using X-rays obtained by monochromaticizing Cu-Kα rays with a Ni filter. Using high-purity silicon as a standard material, X-ray powder diffractometry is performed. From the intensity and half-value width of the diffraction peak of the carbon (002) plane obtained, the Gakushin method established by the 117th committee of the Japan Society for the Promotion of Science It is a value obtained according to

In the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries of the present invention, the coating layer includes amorphous carbon particles and an amorphous carbonized binder material (amorphous carbonized resin).
The amorphous carbonized binding material is obtained by baking the resin covering the graphite particle surface to be amorphous carbonized, and has an average lattice spacing d(002) of 0.3370 nm or more.

As exemplified in FIG. 1, in the composite graphite particles 10, the amorphous carbon particles 3 are usually fixed to the graphite particles 1 such that a portion thereof is embedded in the amorphous carbonized binding material 2. there is

Examples of amorphous carbon particles include, but are not limited to, 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, and the average lattice spacing d(002) of the amorphous carbon particles is 0.3370 nm or more. The reaction resistance tends to decrease, and when used as a negative electrode material for a lithium ion secondary battery, excellent high-speed charge/discharge characteristics can be easily exhibited.
The average lattice spacing d(002) of the amorphous carbon particles is preferably 0.3400 nm or more in order to further improve high-speed charge/discharge performance. It is more preferably 3500 nm or more.

The average particle size of the amorphous carbon particles when observing the surface of the composite graphite particles is preferably 50 to 300 nm. It is possible to easily obtain composite graphite particles excellent in high-speed charge/discharge characteristics as a negative electrode material for lithium ion secondary batteries while suppressing an increase in .
The average particle size of the amorphous carbon particles when the surface of the composite graphite particles is observed is more preferably 100 nm or more in order to further suppress the increase in irreversible capacity. 200 nm or less is more preferable.

In addition, in the present application documents, the average particle size of the amorphous carbon particles when observing the surface of the composite graphite particles means the value obtained as follows.
That is, the surface of the composite graphite particles is observed with a scanning electron microscope (SEM, JSM7900F manufactured by JEOL Ltd.), and the amorphous carbon particles on the composite graphite particles are arbitrarily selected from the obtained SEM image. Using analysis software (WINROOF manufactured by Mitani Shoji Co., Ltd.), the diameter of the circumscribed circle of the amorphous carbon particles is calculated as the particle diameter. In the same way, 1000 or more amorphous carbon particles are arbitrarily extracted from the SEM image to determine the particle size of each particle, and the arithmetic average value thereof is taken as the average particle size of the amorphous carbon particles in surface observation.

The thickness of the amorphous carbonized bonding material in cross-sectional observation (the thickness of the amorphous carbonized bonding material 2 indicated by reference numeral 8 in FIG. 3 to be described later) is appropriately selected, and is 15 nm when considering the embedding of the coating particles. It is preferably ˜1 μm. When the thickness of the amorphous carbonized bonding material in cross-sectional observation is within the above range, the amorphous carbon particles are sufficiently fixed and embedded, and when used as a negative electrode material for lithium ion secondary batteries, high speed Composite graphite particles having excellent charge-discharge characteristics can be easily obtained.

In the lithium ion secondary battery negative electrode material of the present invention, the thickness of the amorphous carbonized bonding material in cross-sectional observation was determined by scanning one particle arbitrarily extracted from the composite graphite particles with a scanning electron microscope (SEM, Japan). Observe the cross section with JSM7900F manufactured by Denshi Co., Ltd.), measure the thickness of the cross section of the amorphous carbonized bonding material in the obtained SEM image at arbitrarily 10 points, calculate their average, and calculate the value. It is the thickness of the cross section of the amorphous carbonized bonding material.
Then, at least 10 composite graphite particles are arbitrarily extracted, the thickness of the cross section of the amorphous carbonized bonding material is obtained for each particle, the thicknesses are averaged, and the thickness of the amorphous carbonized bonding material in cross section observation is obtained. Let it be the thickness of the cross section.

A negative electrode material for a lithium ion secondary battery according to the present invention comprises composite graphite particles having graphite particles and a coating layer containing amorphous carbon particles and an amorphous carbonized binder material and covering the graphite particles.
In the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention, the coverage of the graphite particles with the amorphous carbon particles is 50% or more when the surface is observed. Since the coverage of the amorphous carbon particles is 50% or more when the surface is observed, when the composite graphite particles are used as a negative electrode material for a lithium ion secondary battery, excellent high-speed charge/discharge characteristics can be easily achieved. be able to.
In the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention, the coverage rate at which the amorphous carbon particles cover the graphite particles when the surface is observed further improves the high-speed charge and discharge properties. is more preferably 70% or more, and more preferably 80% or more for particularly improving high-speed charge/discharge properties.
Although the upper limit of the coverage is not particularly limited, it is usually 90% or less.

In the present application documents, the method of calculating the coverage ratio of the amorphous carbon particles covering the graphite particles when observing the surface of the composite graphite particles will be described with reference to FIG. 2 as follows.
FIG. 2(A) shows the vicinity of the surface of the composite graphite particles 10 constituting the negative electrode material for the lithium ion secondary battery shown in FIG. It is a schematic diagram, and as exemplified in FIG. 2(A), in the SEM observation image, the observation range is surrounded by a frame (dashed line) 9 so that 50 or more arbitrary amorphous carbon particles 3 are included. do.
FIG. 2(B) shows the total area α of the amorphous carbon particles 3 within the observation range shown in FIG. ).
After calculating each of the above areas using image analysis software (WINROOF manufactured by Mitani Shoji Co., Ltd.), the coverage of the amorphous carbon particles at each observation point is determined by the following formula (1).
Coverage (%) of amorphous carbon particles at each observation point = (total area α of amorphous carbon particles within observation range/area β of entire observation range) × 100 (1)
Then, the surface of the composite graphite particles was observed at 10 locations with a scanning electron microscope (SEM) to determine the coverage of the amorphous carbon particles at each observation location. It is defined as a coverage ratio at which the amorphous carbon particles cover the graphite particles when the surface is observed.

FIG. 3 is an enlarged view of the vicinity of the surface of the negative electrode material for lithium ion secondary batteries shown in FIG. In the particles, the coating layer is usually in a state in which a portion of the amorphous carbon particles 3 is embedded in the amorphous carbonized binder material 2 provided in a layer on the surface of the graphite particles 1 .

In the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention, the ratio of the amorphous carbon particles embedded in the amorphous carbonized binding material when observing the cross section of the composite graphite particles A certain embedding ratio is preferably 50 to 80%, and when the composite graphite particles are cross-sectionally observed, the embedding ratio of the amorphous carbon particles is within the above range, so that excellent high-speed charge-discharge characteristics can be easily exhibited. can be done.
In the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention, the ratio of the amorphous carbon particles embedded in the amorphous carbonized binding material when observing the cross section of the composite graphite particles A certain embedding ratio is more preferably 60 to 80% in order to improve high-speed charge/discharge characteristics.

In this application document, the method for calculating the embedding ratio, which is the ratio of the amorphous carbon particles buried in the amorphous carbonized binder material, when observing the cross section of the composite graphite particles, will be described with reference to FIG. It is as follows.
That is, as shown in FIG. 3, when the cross section of the composite graphite particles 10 constituting the negative electrode material for a lithium ion secondary battery is observed with a scanning electron microscope (SEM, JSM7900F manufactured by JEOL Ltd.), amorphous The intersections of the outline of the carbon particles 3 and the outer outline of the amorphous carbonized bonding material 2 are defined as intersections 6a and 6b. A portion (hatched portion in FIG. 3A) on the graphite particle 1 side of the line connecting the intersection points 6a and 6b is the buried portion 5 of the amorphous carbon particles 3. As shown in FIG. Then, the area γ of the buried portion 5 of the amorphous carbon particles 3 (hatched area in FIG. 3A) and the area δ of the entire amorphous carbon particles 3 7 (hatched area in FIG. 3B) are After calculating using image analysis software (WINROOF manufactured by Mitani Shoji Co., Ltd.), the embedding ratio (%) of each amorphous carbon particle is determined by the following formula (2).
Buried ratio (%) of each amorphous carbon particle by cross-sectional observation = (Area γ of the buried portion of the amorphous carbon particle/Overall area δ of the amorphous carbon particle) × 100 (2)
Then, the embedding ratio of each amorphous carbon particle is calculated for 10 points by observing the cross section with a scanning electron microscope (SEM), and the arithmetic average value is taken as the embedding ratio of the amorphous carbon particle.

In the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention, the ratio of the amorphous carbon particles to 100.0 parts by mass of the graphite particles is preferably 10.0 to 40.0 parts by mass. . Since the proportion of amorphous carbon particles is 10.0 to 40.0 parts by mass with respect to 100 parts by mass of graphite particles, it is possible to easily improve high-speed charge/discharge characteristics while suppressing an increase in irreversible capacity during the initial charge. can do. The ratio of the amorphous carbon particles to 100.0 parts by mass of the graphite particles is more preferably 20.0 parts by mass or more in order to further improve the high-speed charge/discharge property. 30.0 parts by mass or less is preferable in order to suppress the increase in the irreversible capacity during the initial charge.

The composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention preferably have a tap density of 0.60 g/cm ^{3 or} more. , there are few fine particles and most of the particles are within a relatively narrow particle size range, so that an increase in the specific surface area is suppressed and excellent initial efficiency can be easily exhibited.
The tap density of the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention is more preferably 0.70 g / cm ³ or more in order to further improve the initial efficiency. Then, 0.80 g/cm ³ or more is more preferable.
The upper limit of the tap density of the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention is not particularly limited, but the above tap density makes it possible to secure inter-particle conductive paths and liquid immersion. 1.20 g/cm ³ or less is preferable.

In addition, in this application document, the tap density is measured by putting 5 g of graphite particle powder into a 25 ml graduated cylinder and tapping 1000 times with a gap of 10 mm using a tapping type powder reduction degree 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 after repetition and the mass of the composite graphite particle powder put into the graduated cylinder.
Tap density (g/cm ³ ) = mass (g) of powder put into graduated cylinder/value of apparent volume after repeating tapping 1000 times (cm ³ ) (3)

The average particle diameter _D50 of the composite graphite particles in the laser diffraction particle size distribution is preferably 5.0 to 30.0 μm, and the average particle diameter _D50 of the composite graphite particles in the laser diffraction particle size distribution is 5.0 to 30.0 μm. As a result, the reaction specific surface area increases, the reaction resistance decreases, and excellent high-speed charge/discharge characteristics are exhibited, and the moving speed of lithium ions in the graphite particles can be easily improved.
The average particle diameter _D50 of the composite graphite particles in the laser diffraction particle size distribution is more preferably 7.0 μm or more in order to suppress the increase in irreversible capacity during the initial charge, and is 25 in order to further improve the high-speed charge/discharge performance. 0 μm or less is more preferable, and 20.0 μm or less is even more preferable for particularly improving high-speed charging/discharging performance.

The particle size distribution index SPAN ((D ₉₀ −D ₁₀ )/D ₅₀ ) of the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention is preferably less than 2.0, and the particle size distribution index SPAN ((D ₉₀ −D ₁₀ )/D ₅₀ ) is less than 2.0, the number of fine particles is small, and the majority of the particles are within a relatively narrow particle size range. Excellent initial efficiency can be easily exhibited in the ion secondary battery.
The particle size distribution index SPAN ((D ₉₀ −D ₁₀ )/D ₅₀ ) of the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention suppresses an increase in the specific surface area and is a lithium ion secondary battery. It is more preferably less than 1.0 because it can easily exhibit even better initial efficiency at .

In addition, in this application document, D ₁₀ , D ₅₀ (average particle diameter) and D ₉₀ of powder or particles are measured using a laser diffraction particle size distribution analyzer (LA-960S manufactured by Horiba, Ltd.). The cumulative particle size when measuring the distribution means the particle size of 10%, 50% and 90% respectively.

The nitrogen adsorption specific surface area (N ₂ SA) of the composite graphite particles constituting the negative electrode material for a lithium ion secondary battery of the present invention is preferably 3.0 to 7.0 m ² /g, and the nitrogen adsorption specific surface area of the composite graphite particles is within the above range, it is possible to easily suppress a decrease in initial efficiency when used as a negative electrode material for a lithium ion secondary battery.
The nitrogen adsorption specific surface area (N ₂ SA) of the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries of the present invention is 3.0 to 5.0 m ² /g in order to further suppress the decrease in initial efficiency. more preferred.

In addition, in the present application documents, the nitrogen adsorption specific surface area (N ₂ SA) of the powder or particles is measured using a fully automatic surface area measuring device (Gemini V manufactured by Shimadzu Corporation), and the relative pressure in the nitrogen adsorption isotherm is 0.05. It means a value calculated by the BET multipoint method in the range of ~0.2.

The Raraman R (Raman spectrum intensity ratio R) of the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention is preferably 0.3 or more, and the composite graphite constituting the negative electrode material for lithium ion secondary batteries When the Raman R of the particles is within the above range, the particle surfaces are sufficiently amorphous, so the reaction resistance is low and the high-speed charge/discharge characteristics of the negative electrode material for lithium ion secondary batteries are easily improved. be able to.
The Raraman R (Raman spectrum intensity ratio R) of the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention is more preferably 0.4 or more in order to further improve the high-speed charge/discharge performance.

In the present application documents, Raman R is measured with a Raman spectrometer (HR800, manufactured by Horiba, Ltd.) equipped with a Nd/YAG laser with a wavelength of 532 nm, and is due to crystal defects in the surface layer and mismatching of the lamination structure. The spectrum I 1360 near 1360 cm ⁻¹ attributed to the disorder of the crystal structure is divided by the spectrum I 1580 near 1580 cm ⁻¹ attributed to the E2g-type vibration corresponding to the lattice vibration in the carbon hexagonal plane, Raman R=( I 1360/I 1580) means the average value measured at 10 or more points in an irradiation area of 100 μm ² .

The composite graphite particles constituting the negative electrode material for a lithium ion secondary battery according to the present invention preferably have an average lattice spacing d (002) of 0.3360 nm or less, and the average lattice spacing d (002 ) is 0.3360 nm or less, the reversible capacity can be sufficiently improved when used as a negative electrode material for a lithium ion secondary battery.
In the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention, the average lattice spacing d(002) is more preferably 0.3358 nm or less in order to further improve the reversible capacity.

In the present application documents, the average lattice spacing d (002) is measured using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.), using X-rays obtained by monochromaticizing Cu-Kα rays with a Ni filter. Using high-purity silicon as a standard material, X-ray powder diffractometry is performed. From the intensity and half-value width of the diffraction peak of the carbon (002) plane obtained, the Gakushin method established by the 117th committee of the Japan Society for the Promotion of Science means the value determined according to

The negative electrode material for lithium ion secondary batteries according to the present invention can be suitably produced by the production method according to the present invention, which will be described in detail below.

ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries which were excellent in the initial efficiency and the high-speed charging/discharging characteristic can be provided.

Next, a method for producing a negative electrode material for lithium ion secondary batteries according to the present invention will be described.
A method for producing a negative electrode material for a lithium ion secondary battery according to the present invention includes a coating step of mixing graphite particles and a resin solution to obtain resin-coated graphite particles in which the graphite particles are coated with a resin;
10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of the graphite particles are mixed with the resin-coated graphite particles, and the amorphous carbon particles are coated on the surfaces of the resin-coated graphite particles. a step of obtaining amorphous carbon particle-attached graphite particles to which
and a calcining and carbonizing step of calcining and carbonizing the amorphous carbon particle-attached graphite particles.

In the production method according to the present invention, resin-coated graphite particles in which the graphite particles are coated with the resin are obtained by mixing the graphite particles and the resin solution in the coating step.

The graphite particles used in the coating step are not particularly limited, but are preferably spherical aggregates of flat graphite. The graphite particles may consist of natural graphite, or may consist of artificial graphite.

In the production method according to the present invention, the average particle diameter _D50 of the graphite particles is preferably 5.0 to 30.0 μm, and when the average particle diameter _D50 of the graphite particles is within the above range, the reaction specific surface area is increased. As a result, the reaction resistance tends to decrease, and the movement speed of lithium ions in the graphite particles tends to increase.
In the production method according to the present invention, the average particle diameter _D50 of the graphite particles is more preferably 7.0 μm or more in order to suppress the increase in irreversible capacity during the initial charge, and further improves the high-speed charge-discharge performance. Above, 25.0 μm or less is more preferable, and 20.0 μm or less is even more preferable in order to particularly improve high-speed charging/discharging performance.

In the production method according to the present invention, the average lattice spacing d(002) of the graphite particles is 0.3360 nm or less, and the average lattice spacing d(002) of the graphite particles is within the above range. can be made large enough.
In the production method according to the present invention, the average lattice spacing d(002) of the graphite particles is preferably 0.3358 nm or less in order to further improve the reversible capacity.

The resin constituting the resin solution used in the coating step is used as a binder, and is not particularly limited as long as it is carbonized in the calcining and carbonizing step to form an amorphous carbon material.
Examples of the resin include one or more selected from thermoplastic resins such as polyvinyl chloride resins and acrylic resins, and synthetic resins such as thermosetting resins such as phenol resins and urea resins.

The solvent constituting the resin solution used in the coating step is not particularly limited, and may be one or more selected from water, alcohols such as diethylene glycol, and mixtures thereof.

The resin concentration constituting the resin solution is a concentration that produces 4.0 to 16.0 parts by mass of an amorphous carbonized binding material per 100.0 parts by mass of graphite particles after the calcination and carbonization treatment described later. When the concentration of the resin constituting the resin solution is within the above range, the amorphous carbon particles can be adhered to the graphite particles with a desired adhesion force.
The concentration of the resin constituting the resin solution is 6.0 to 14.0 parts per 100.0 parts by mass of the graphite particles in order to control the deposition rate of the amorphous carbon particles within the desired range after the calcination and carbonization treatment described later. It is more preferable that the concentration is such that 0 parts by mass of the amorphous carbonized binding material is produced. In order to further control the deposition rate of the amorphous carbon particles within the desired range, 8 parts by mass of the graphite particles per 100.0 parts by mass of the graphite particles More preferably, the concentration produces 0.0 to 12.0 parts by weight of the amorphous carbonized bonding material.

The viscosity of the resin solution is preferably 0.005 to 40 Pa s, and the viscosity of the resin constituting the resin solution is within the above range, so that the amorphous carbon particles are uniformly attached to the graphite particles in a desired manner. It can be attached by force. The viscosity of the resin solution is more preferably 0.3 to 10 Pa·s in order to control the deposition rate of the amorphous carbon particles within the desired range.
In addition, in this application document, the viscosity of the resin solution means a value measured by a rotary b-type viscometer.

In the coating step, the amount of the resin mixed and brought into contact with the graphite particles is preferably 10.0 to 60.0 parts by mass per 100.0 parts by mass of the graphite particles, and mixed and brought into contact with the graphite particles in the coating step. When the amount of the resin is within the above range, the binding area with the coated particles is increased, the binding force is increased, and uniform coating becomes possible.
In the coating step, the amount of the resin mixed and brought into contact with the graphite particles is more preferably 10.0 to 50.0 parts by mass per 100.0 parts by mass of the graphite particles in order to enable more uniform coating. In particular, it is more preferably 10.0 to 40.0 parts by mass to enable uniform coating.

In the coating step, the method of mixing the graphite particles and the resin solution is not particularly limited, and examples thereof include a method of mixing using a mixer such as a kneader, trimix, high speed mixer, Henschel mixer and the like.

In the coating step, the mixing temperature for mixing the graphite particles and the resin solution is not particularly limited, but it is preferable to adjust the viscosity of the resin to 0.005 to 40 Pa·s.

In the manufacturing method according to the present invention, in the coating step, the graphite particles are mixed with a resin solution and brought into contact with each other to adhere the resin, thereby forming a binder for fixing the amorphous carbon particles to be described later.
At this time, by appropriately adjusting the concentration, viscosity, or amount used of the resin solution, the amount of adhesion to the graphite particles and the amorphous carbon particles described later, and the thickness of the resin layer on the graphite particle surface can be easily controlled. For this reason, when the agglomerates obtained by calcination and carbonization are pulverized to obtain composite graphite particles, the impact is reduced, the generation of fine powder is suppressed, and the particle size distribution is narrow and uniform. Composite graphite particles can be easily obtained.
Therefore, according to the production method of the present invention, it is possible to easily produce composite graphite particles that exhibit excellent initial efficiency when used as a negative electrode material for lithium ion secondary batteries.

In the production method according to the present invention, the resin-coated graphite particles obtained in the coating step are mixed with 10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of the graphite particles, Amorphous carbon particle-attached graphite particles are obtained in which amorphous carbon particles are attached to the surfaces of the resin-coated graphite particles.

The amorphous carbon particles are not particularly limited, but may include, for example, one or more selected from carbon black such as furnace black and thermal black.

In the production method according to the present invention, the average particle size of the amorphous carbon particles is preferably 50 to 300 nm, and the average particle size of the amorphous carbon particles is within the above range, thereby increasing the irreversible capacity. can be easily obtained as a negative electrode material for a lithium ion secondary battery while suppressing the high-speed charge/discharge characteristics.
In the production method according to the present invention, the average particle size of the amorphous carbon particles is more preferably 100 nm or more in order to further suppress the increase in irreversible capacity, and is 200 nm in order to further improve the high-speed charge/discharge performance. The following are more preferred.

In the present application documents, the average particle size of the amorphous carbon particles used in the production method according to the present invention is determined by a transmission electron microscope (TEM, H-7650 type transmission electron microscope manufactured by Hitachi, Ltd.). When each amorphous carbon particle was observed using the image analysis software (WINROOF manufactured by Mitani Shoji Co., Ltd.), the diameter of the circumscribed circle of each amorphous carbon particle was defined as the particle diameter of each 10,000 particles. means the arithmetic mean value when the particle diameter of the amorphous carbon particles is determined.

In the production method according to the present invention, the average lattice spacing d(002) of the amorphous carbon particles is 0.3370 nm or more, and the average lattice spacing d(002) of the amorphous carbon particles is within the above range. With this, the reaction resistance of the particle surface is likely to be lowered, and excellent high-speed charge/discharge characteristics are likely to be exhibited.
In the production method according to the present invention, the average lattice spacing d(002) of the amorphous carbon particles is preferably 0.3400 nm or more in order to improve high-speed charge/discharge characteristics. It is more preferably 0.3500 nm or more because it can be improved.

In the production method according to the present invention, when the amorphous carbon particles are carbon black, the DBP oil absorption of the carbon black is preferably 300 ml/100 g or less, and the DBP oil absorption of the carbon black is 300 ml/100 g or less. Therefore, it is possible to suppress an increase in the specific surface area of the obtained composite graphite particles and easily suppress an increase in the irreversible capacity during the initial charge when used as a negative electrode material for a lithium ion secondary battery.
In the production method according to the present invention, when the amorphous carbon particles are carbon black, the DBP oil absorption of the carbon black is more preferably 250 ml/100 g or less in order to further suppress the increase in the irreversible capacity, and the increase in the irreversible capacity. is more preferably 200 ml/100 g or less in order to particularly suppress the

In the production method according to the present invention, 10.0 to 40.0 parts by mass of the amorphous carbon particles per 100.0 parts by mass of the graphite particles (constituting the resin-coated graphite particles) are added to the resin-coated graphite particles. Mix.
When the mixed amount of the amorphous carbon particles is within the above range, when the obtained composite graphite particles are used as a negative electrode material for a lithium ion secondary battery, an increase in the irreversible capacity during the initial charge is suppressed, High-speed charge/discharge performance can be easily improved.
In the production method according to the present invention, the amorphous carbon particles are mixed with the resin-coated graphite particles. 20.0 parts by mass or more is more preferable for further improving high-speed charge/discharge properties, and 30.0 parts by mass or less is more preferable for suppressing an increase in irreversible capacity during the initial charge.

In the production method according to the present invention, by mixing amorphous carbon particles with resin-coated graphite particles, amorphous carbon particle-attached graphite particles in which the amorphous carbon particles are attached to the surface of the resin-coated graphite particles are obtained. get

The treatment temperature when the specific amorphous carbon particles are mixed with the resin-coated graphite particles is not particularly limited, but it is preferable to adjust the viscosity of the resin to 0.005 to 40 Pa·s.

In the step of mixing resin-coated graphite particles with amorphous carbon particles, the mixing means may include one or more mixing devices selected from kneaders, trimixes, high-speed mixers, Henschel mixers, and the like.
In the production method according to the present invention, when the resin-coated graphite particles and the amorphous carbon particles are mixed using a Henschel mixer (FM20C manufactured by Mitsui Mining Co., Ltd.), for example, a Henschel mixer containing the resin-coated graphite particles is used. Amorphous carbon particles such as carbon black are put into the tank of the mixer, and after reaching a predetermined temperature, they are treated at a peripheral speed of 30 m/s for 15 minutes. When the amount of the amorphous carbon particles exceeds 30 parts by mass with respect to 100 parts by mass of the graphite particles constituting the resin-coated graphite particles, the amorphous carbon particles are divided into three parts and added in order to obtain composite graphite particles. The uniformity of coating of amorphous carbon particles can be easily improved.

In the production method according to the present invention, the amorphous carbon particle-attached graphite particles, which are resin-coated graphite particles with amorphous carbon particles attached to their surfaces, are subjected to a sintering and carbonizing step of sintering and carbonizing.

The temperature at which the amorphous carbon particle-attached graphite particles are calcined and carbonized is preferably 800° C. or higher. When the calcined carbonization temperature is within the above range, it is possible to sufficiently remove unburned components contained in carbon black and the like. can. The temperature for calcining and carbonizing the amorphous carbon particle-attached graphite particles is more preferably 1000° C. or higher in order to remove the unburned portion.
Although the upper limit of the temperature for calcination and carbonization is not particularly limited, the temperature for calcination and carbonization of the amorphous carbon particle-attached graphite particles is preferably 3000° C. or less, and more preferably 2000° C. or less from the viewpoint of improving high-speed charge/discharge characteristics.

The time for calcination and carbonization of the amorphous carbon particle-attached graphite particles is preferably 1 hour or more, and the calcination and carbonization time of 1 hour or more sufficiently removes particularly unburned components contained in carbon black and the like. can do.
The time for calcining and carbonizing the amorphous carbon particle-attached graphite particles is more preferably 2 hours or more in order to remove the unburned portion.

The atmosphere in which the amorphous carbon particle-attached 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 present invention, the calcined carbide obtained by performing the carbonization calcination step may be subjected to a pulverization treatment and, if necessary, a classification treatment or the like.

Examples of the negative electrode material for lithium ion secondary batteries obtained by the manufacturing method according to the present invention include the negative electrode material for lithium ion secondary batteries according to the present invention.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the negative electrode material for lithium ion secondary batteries which were excellent in the initial efficiency and the high-speed charging/discharging characteristic can be provided.

Next, materials for manufacturing the negative electrode material for lithium ion secondary batteries according to the present invention will be described.
The manufacturing material 1 of the negative electrode material for lithium ion secondary batteries according to the present invention is
The amorphous carbon particle-attached graphite particles, in which the amorphous carbon particles are attached to the surface of the graphite particles together with the resin, are composed of a bound aggregate in which a plurality of the particles are bound,
The bound aggregate contains 10.0 to 40.0 parts by mass of the amorphous carbon particles per 100.0 parts by mass of the graphite particles.

The manufacturing material 1 of the negative electrode material for lithium ion secondary batteries according to the present invention should be called an intermediate for manufacturing the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention. In the production method according to the present invention, resin-coated graphite particles are mixed with amorphous carbon particles to obtain amorphous carbon particle-attached graphite particles in which the amorphous carbon particles are attached to the surfaces of resin-coated graphite particles. It corresponds to the one obtained by performing the process.
For this reason, the details of the graphite particles, the amorphous carbon particles and the resin that constitute the bound aggregates in the production material 1 of the negative electrode material for lithium ion secondary batteries according to the present invention are described in the production method according to the present invention. The contents are the same as those described in the description.
In addition, as described in the production method of the present invention, the material 1 for producing a negative electrode material for a lithium ion secondary battery according to the present invention is obtained by mixing resin-coated graphite particles with amorphous carbon particles and obtaining a resin-coated material. It can be produced by performing a step of obtaining amorphous carbon particle-attached graphite particles in which the amorphous carbon particles are attached to the surface of graphite particles, and the details are as described in the explanation of the production method according to the present invention. is.

In the manufacturing material 1 of the negative electrode material for a lithium ion secondary battery according to the present invention, the bound aggregate contains 10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of graphite particles. and the ratio 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, and in the negative electrode material for the lithium ion secondary battery obtained, at the time of the first charge High-speed charge/discharge characteristics can be easily improved while suppressing an increase in irreversible capacity. The ratio of the amorphous carbon particles to 100.0 parts by mass of the graphite particles is more preferably 20.0 parts by mass or more in order to further improve the high-speed charge/discharge property. is more preferably 30.0 parts by mass or less in order to suppress the increase in the irreversible capacity during the initial charge.

FIG. 4 is a schematic cross-sectional view showing a bound aggregate 30 in which a plurality of amorphous carbon particle-attached graphite particles 20, in which amorphous carbon particles 3 are attached to the surfaces of graphite particles 1 together with a resin, are bound.
As illustrated in FIG. 4, a manufacturing material 1 for a negative electrode material for a lithium ion secondary battery according to the present invention is composed of a bound aggregate 30 in which a plurality of amorphous carbon particle-attached graphite particles 20 are bound. The crystalline carbon particle-attached graphite particles 20 are bound to each other with an appropriate binding force through the film-like resin.
For this reason, when the above-mentioned bound aggregates are calcined and carbonized and then pulverized, the pulverization process can be performed without applying excessive impact force between particles, so that composite graphite particles having a narrow particle size distribution and uniform particle size can be obtained. It can be suitably prepared, and an increase in the specific surface area of the resulting composite graphite particles can be suppressed. For this reason, it is possible to provide composite graphite particles that can exhibit excellent initial efficiency when used as a negative electrode material for lithium ion secondary batteries.

Further, the material 2 for producing a negative electrode material for a lithium ion secondary battery according to the present invention is amorphous carbon particle-coated graphite particles in which the surfaces of graphite particles are coated with an amorphous carbonized binding material and amorphous carbon particles. consists of a plurality of fixed aggregates,
The fixed aggregate contains 10.0 to 40.0 parts by mass of the amorphous carbon particles per 100.0 parts by mass of the graphite particles,
The specific surface area change rate, which indicates the change rate of the nitrogen adsorption specific surface area, is 20% or less when the tap density change rate, which indicates the change rate of the tap density before and after pulverization, is 10% to 60%. be.

The production material 2 of the negative electrode material for lithium ion secondary batteries according to the present invention should also be called an intermediate for producing the composite graphite particles constituting the negative electrode material for lithium ion secondary batteries according to the present invention. In the production method according to the present invention, the adhered aggregate corresponds to that obtained by performing a calcining and carbonizing step of calcining and carbonizing the amorphous carbon particle-attached graphite particles.
For this reason, in the manufacturing material 2 of the negative electrode material for a lithium ion secondary battery according to the present invention, the details of the graphite particles, the amorphous carbon particles and the resin, which are the raw materials of the adhered aggregates, are described in the manufacturing method according to the present invention. The contents are the same as those described in the description.
In addition, the production material 2 of the negative electrode material for a lithium ion secondary battery according to the present invention is subjected to a calcination and carbonization step of calcining and carbonizing the amorphous carbon particle-attached graphite particles as described in the production method according to the present invention. The details are as described in the description of the manufacturing method according to the present invention.

In the manufacturing material 2 of the negative electrode material for lithium ion secondary batteries according to the present invention, the adhered aggregates contain 10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of graphite particles. In the negative electrode material for a lithium ion secondary battery obtained by the fixed aggregate containing 10.0 to 40.0 parts by mass of amorphous carbon particles with respect to 100.0 parts by mass of graphite particles, the first time It is possible to easily improve high-speed charge/discharge characteristics while suppressing an increase in irreversible capacity during charging. The ratio of the amorphous carbon particles to 100.0 parts by mass of the graphite particles constituting the adhered aggregates is more preferably 20.0 parts by mass or more in order to further improve the high-speed charge/discharge property. It is 30.0 parts by mass or less in order to suppress the generation of isolated particles and to suppress the increase in irreversible capacity during the initial charge.

The manufacturing material 2 of the negative electrode material for lithium ion secondary batteries according to the present invention has a nitrogen adsorption specific surface area when the tap density change rate, which represents the change rate of the tap density before and after pulverization of the adhered aggregate, is 10% to 60%. It is characterized in that the specific surface area change rate, which indicates the change rate of , is 20% or less.

The manufacturing material 2 of the negative electrode material for lithium ion secondary batteries according to the present invention has a nitrogen adsorption specific surface area when the tap density change rate, which represents the change rate of the tap density before and after pulverization of the adhered aggregate, is 10% to 60%. is 20% or less, and the specific surface area change rate before and after pulverization of the adhered aggregates is within the above range, thereby reducing damage to the composite graphite particles during impact pulverization, By suppressing the increase in the specific surface area, it is possible to easily reduce the increase in the irreversible capacity during the initial charge.
The manufacturing material 2 of the negative electrode material for lithium ion secondary batteries according to the present invention has a nitrogen adsorption specific surface area when the tap density change rate, which represents the change rate of the tap density before and after pulverization of the adhered aggregate, is 10% to 60%. is preferably 15% or less for further suppressing an increase in irreversible capacity, and more preferably 10% or less for particularly suppressing an increase in irreversible capacity.

In addition, in the present application documents, the pulverization of the adhered aggregates when calculating the tap density change rate and the specific surface area change rate is performed at a rotation speed of 4000 rpm using a super rotor (SR25) manufactured by Nisshin Engineering Co., Ltd. This is done by processing with
In addition, the tap density and nitrogen adsorption specific surface area before and after pulverization mean the values measured by the above-described method, and the tap density change rate and specific surface area change rate are calculated by the following formulas (4) and (5), respectively. means value.
Tap density change rate = (tap density after pulverization - tap density before pulverization) / (tap density before pulverization) x 100 (4)
Specific surface area change rate = (nitrogen adsorption specific surface area after pulverization - nitrogen adsorption specific surface area before pulverization) / (nitrogen adsorption specific surface area before pulverization) x 100 (5)

The manufacturing material 2 of the negative electrode material for a lithium ion secondary battery according to the present invention is composed of a fixed aggregate in which a plurality of amorphous carbon particle-coated graphite particles are fixed, and each amorphous carbon particle-coated graphite particle is formed into a film. It is fixed with a moderate fixing force through the amorphous carbonized bonding material.
Therefore, when pulverizing the adhered aggregates, the pulverization process can be performed without applying excessive impact force between the particles, so that composite graphite particles with a narrow particle size distribution and uniform particle size can be suitably prepared. Even when the tap density change rate is 10% to 60%, the specific surface area change rate can be suppressed to 20% or less.
Therefore, when the manufacturing material 2 of the negative electrode material for lithium ion secondary batteries according to the present invention is used as the negative electrode material for lithium ion secondary batteries, excellent initial efficiency can be exhibited.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing material of the negative electrode material for lithium ion secondary batteries excellent in initial efficiency and high-speed charging/discharging characteristics can be provided.

(Example 1)
100.0 parts by mass of natural graphite (average particle diameter (D ₅₀ ) 10.4 μm, BET adsorption specific surface area 7.4 m ² /g, tap density 0.76 g/cm ³ ), and an aqueous resin solution (manufactured by Sumitomo Bakelite Co., Ltd. PR-56265: water = 4:1 (mass ratio)) and 20.0 parts by mass were put into a mixer (Henschel mixer manufactured by Mitsui Mining Co., Ltd.) and mixed at 40°C for 15 minutes. Next, at 40 ° C., 20.0 parts by mass of furnace black (S-TA manufactured by Tokai Carbon Co., Ltd.) with an average particle size of 122 nm is added to 100.0 parts by mass of the natural graphite, and mixed for 10 minutes. bottom.
The obtained powder was calcined and carbonized at 1000° C. for 2 hours in a nitrogen gas atmosphere. Next, after pulverizing the obtained fired powder at 4000 rpm using a pulverizer (super rotor: SR25 manufactured by Nisshin Engineering Co., Ltd.), classifying with a classifier (device name: sieve classification, mesh size 45 μm), Composite graphite particles (90% coverage, tap density 0.96 g/cm ³ , average particle diameter D ₅₀ 12.5 µm, particle size distribution index SPAN 0.9, nitrogen adsorption specific surface area 4.9 m ² /g) as under-sieves A negative electrode material for a lithium ion secondary battery was obtained.
The tap density change rate before and after the pulverization treatment was 20%, and the specific surface area change rate was 13%.
Table 1 shows the analysis results and evaluation results of the obtained negative electrode material for lithium ion secondary batteries.

(Example 2)
In Example 1, an aqueous resin solution (PR-56265 manufactured by Sumitomo Bakelite Co., Ltd.: water = 4: 1 (mass ratio)) was changed to an aqueous resin solution (PR-56265 manufactured by Sumitomo Bakelite Co., Ltd.: water = 1: 1 (mass ratio )) in the same manner as in Example ₁ ^except that the A negative electrode material for a lithium ion secondary battery having a nitrogen adsorption specific surface area of 4.3 m ² /g) was obtained.
The tap density change rate before and after pulverization was 21%, and the specific surface area change rate was 7%.

(Comparative example 1)
In Example 1, except that 40.0 parts by mass of pitch was used instead of 20.0 parts by mass of the resin aqueous solution (PR-56265: water = 4:1 (mass ratio) manufactured by Sumitomo Bakelite Co., Ltd.) 1, composite graphite particles (75% coverage, tap density 0.91 g/cm ³ , average particle diameter D ₅₀ 17.1 μm, particle size distribution index SPAN 1.0, nitrogen adsorption specific surface area 6.1 m ² /g ) was obtained as a negative electrode material for a lithium ion secondary battery.

(Comparative example 2)
In the same manner as in Example 1, except that the amount of furnace black (S-TA manufactured by Tokai Carbon Co., Ltd.) with respect to 100.0 parts by mass of natural graphite was changed from 20.0 parts by mass to 5.0 parts by mass. Lithium ion dice made of composite graphite particles (12% coverage, tap density 0.94 g/cm ³ , average particle diameter D ₅₀ 12.1 μm, particle size distribution index SPAN 0.9, nitrogen adsorption specific surface area 4.7 m ² /g). A negative electrode material for a secondary battery was obtained.

(Comparative Example 3)
In the same manner as in Example 1, except that the amount of furnace black (S-TA manufactured by Tokai Carbon Co., Ltd.) with respect to 100.0 parts by mass of natural graphite was changed from 20.0 parts by mass to 50.0 parts by mass. Lithium ion dice made of composite graphite particles (coverage 95%, tap density 0.92 g/cm ³ , average particle diameter D ₅₀ 14.3 μm, particle size distribution index SPAN 1.1, nitrogen adsorption specific surface area 6.4 m ² /g). A negative electrode material for a secondary battery was obtained.

<Scanning electron microscope (SEM) measurement conditions at the time of coverage measurement>
Analyzer: JSM7900F manufactured by JEOL Ltd.
An electron beam accelerated at an acceleration voltage of 2 to 5 kV is applied to the sample and a secondary electron image is observed.

<Transmission electron microscope (TEM) measurement conditions when measuring the average particle size of carbon black>
Analysis device: Transmission electron microscope (TEM, Hitachi Ltd. H-7650 type transmission electron microscope Acceleration voltage: 100 kV

<Measurement conditions for average particle size _D50 and SPAN>
Analyzer: LA-960S manufactured by Horiba Ltd.
Light source: semiconductor laser (650 nm)
The powder was added to an aqueous solution containing 10% by mass of an amphoteric surfactant with respect to 100 parts by mass of distilled water, and dispersed by ultrasonic waves. The dispersed powder is flowed into a measuring cell in the device and irradiated with a laser. The average particle diameter _D50 and SPAN were determined from the particle size distribution obtained by detecting and analyzing the scattered light with a ring-shaped detector.

<Tap density measurement conditions>
Put 5 g of graphite particle powder into a 25 ml graduated cylinder and repeat tapping 1000 times at a gap of 10 mm using a tapping type powder reduction measuring instrument manufactured by Tsutsui Rikagaku Kikai Co., Ltd. It was calculated by the following formula (3) from the mass of the graphite particle powder put into the cylinder.
Tap density (g/cm ³ ) = mass (g) of powder put into graduated cylinder/value of apparent volume after repeating tapping 1000 times (cm ³ ) (3)

(Battery characteristic evaluation method)
Using the composite graphite particles obtained in each example and comparative example, the electrode plate density was measured by the following method, and various battery characteristics were obtained by producing laminated batteries.

<Plate density>
(1) Preparation of electrode sheet To 90.2% by weight of composite graphite particles, 9.8% by weight of organic binder polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone is added and stirred. Mix to prepare a negative electrode mixture paste.
After applying the obtained negative electrode mixture paste on a copper foil (current collector) having a thickness of 20 μm by a doctor blade method, it was heated at 90° C. for 90 minutes in a dryer and further at 130° C. for 11 hours in a vacuum. The solvent is completely evaporated 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 composite graphite particles per unit area of the electrode sheet.

(2) Measurement of Electrode Density The electrode sheet is cut into strips with a width of 6 cm and rolled by a roller press so that the electrode density becomes 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 arithmetic average value of the electrode plate densities obtained by the following formula (6) from each weight A (g) and the thickness B (cm) of the central portion was taken as the electrode plate density.

Electrode plate density (g/cm ³ ) = {(A (g) - copper foil weight (g)) × weight ratio of composite graphite particles in negative electrode mixture layer (0.902)}/{(B (cm) -Copper foil thickness (cm) × electrode area (cm ² )} (6)
<Production of laminated battery>
The same electrode sheet as that used for the measurement of the electrode plate density was prepared and used as a negative electrode.
On top of that, as a battery for evaluation, the positive electrode (Li metal, separator (polypropylene), and negative electrode are laminated in order, and after attaching a Ni tab, the laminate is aluminum-laminated, and the laminated battery is placed in an inert atmosphere. The electrolyte used was a 1:1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in which 1 mol/dm ³ of lithium salt LiPF ₆ was dissolved.Charging was performed at a current density of 0.2 mA/cm ² . After constant current charging was completed at a final voltage of 5 mV, the constant potential was maintained until the lower limit current reached 0.02 mA/cm ^2. Discharge was performed at a current density of 0.2 mA/cm ² to a final voltage of 1.5 V. The discharge capacity after 3 cycles was taken as the reversible capacity.The initial efficiency is the value (%) obtained by dividing the discharge capacity at the 1st cycle by the charge capacity at the 1st cycle.The charge capacity at 5C is 3 cycles. This is the charge capacity when the battery is fully charged in 12 minutes after the fully discharged state.

Table 1 shows the raw material blends (parts by mass) used in the above Examples and Comparative Examples and the characteristics of the obtained composite graphite particles. Table 1 shows the battery characteristics when laminated batteries were produced using the electrodes (negative electrodes) made of the negative electrode materials obtained in the above Examples and Comparative Examples.

From Table 1, the negative electrode materials for lithium ion secondary batteries obtained in Examples 1 to 3 were subjected to a coating step, a step of obtaining amorphous carbon particle-attached graphite particles, and a calcination carbonization step as specific steps. Since it consists of the obtained specific composite graphite particles, it can be seen that excellent initial efficiency and high-speed charge/discharge characteristics can be exhibited when used in a lithium ion secondary battery.

On the other hand, from Table 1, the negative electrode materials for lithium ion secondary batteries obtained in Comparative Examples 1 to 3 did not use resin in the coating process (Comparative Example 1), and the composite graphite particles had a coverage of 50 % (Comparative Example 2), or the amount of amorphous carbon particles per 100.0 parts by mass of graphite particles used in the step of obtaining amorphous carbon particle-attached graphite particles is outside the predetermined range (Comparative Example 3 ), the initial efficiency or high-speed charge/discharge characteristics are inferior when used in a lithium ion secondary battery.

INDUSTRIAL APPLICABILITY According to the present invention, a negative electrode material for lithium ion secondary batteries having excellent initial efficiency and high-speed charge/discharge characteristics, a method for producing the negative electrode material for lithium ion secondary batteries, and a material for producing the negative electrode material for lithium ion secondary batteries are provided. can do.

REFERENCE SIGNS LIST 1 graphite particles 2 amorphous carbonized binding material 3 amorphous carbon particles 4 coating layer 5 amorphous carbon particle embedded portion 6a, 6b intersection point
7 Whole amorphous carbon particles 8 Thickness of amorphous carbonized binding material 9 Frame line 10 Composite graphite particles 20 Amorphous carbon particle-attached graphite particles 30 Bonded aggregates

Claims (3)

A method for producing a negative electrode material for a lithium ion secondary battery, comprising:
a coating step of obtaining resin-coated graphite particles in which the graphite particles are coated with a resin by mixing graphite particles and a resin solution in the absence of pitch;
10.0 to 40.0 parts by mass of amorphous carbon particles per 100.0 parts by mass of the graphite particles are mixed with the resin-coated graphite particles, and the amorphous carbon particles are coated on the surfaces of the resin-coated graphite particles. a step of obtaining amorphous carbon particle-attached graphite particles to which
A method for producing a negative electrode material for a lithium ion secondary battery, comprising: a calcining and carbonizing step of calcining and carbonizing the amorphous carbon particle-attached graphite particles. 2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the graphite particles have an average particle diameter D50 of 5.0 to 30.0 μm, and the amorphous carbon particles have an average particle diameter of 50 to 300 nm. Production method. The obtained negative electrode material for lithium ion secondary batteries is
Composed of composite graphite particles having graphite particles and a coating layer containing amorphous carbon particles and an amorphous carbonized binder material and covering the graphite particles,
3. The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the composite graphite particles have a coverage of 50% or more that the amorphous carbon particles cover the graphite particles when the surface is observed. manufacturing method .

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