WO2020213628A1 - Composite carbon particles, method for manufacturing same and use thereof - Google Patents

Abstract

The present invention provides composite carbon particles for a lithium ion secondary battery which shows well-balanced and excellent low-temperature charge and discharge rate characteristics, high-temperature storage characteristics and high-temperature cycle characteristics and has low internal resistance and high coulombic efficiency. The composite carbon particles according to the present invention each comprise a carbon particle (A) and a carbonaceous coating layer (B) that coats the surface thereof, wherein the carbonaceous coating layer (B) comprises a carbonaceous coating film layer (B1) and fine carbon particles (B2) and, in differential thermal analysis (DTA) in the atmosphere, has one peak in a temperature range of from 200°C inclusive to 620°C exclusive and two or more peaks in a temperature range of from 620°C inclusive to 1000°C inclusive.

Description

Composite carbon particles, their manufacturing methods and their uses

The present invention relates to composite carbon particles, a method for producing the same, a negative electrode active material containing the composite carbon particles, a negative electrode containing the negative electrode active material, and a lithium ion secondary battery using the negative electrode.

A lithium ion secondary battery is used as a power source for portable electronic devices. Initially, lithium-ion batteries had many problems such as insufficient battery capacity and short charge / discharge cycle life. Nowadays, such problems have been overcome, and lithium-ion secondary batteries are used from light electric devices such as mobile phones, notebook computers and digital cameras to high electric devices such as electric tools and electric bicycles that require power. The application is expanding. Furthermore, lithium-ion secondary batteries are particularly expected to be used as power sources for automobiles, and research and development of electrode materials, cell structures, etc. are being actively promoted.

Lithium-ion secondary batteries used as power sources for automobiles are required to have excellent low-temperature charge / discharge rate characteristics, high-temperature storage characteristics, high-temperature cycle characteristics, low internal resistance, and high coulombic efficiency. Various methods have been taken for this.

A carbon material is used as the negative electrode active material of the lithium ion secondary battery. Further, it has been proposed to form a coating layer on the surface in order to repair surface defects of the carbon material or to impart properties different from those of the carbon material used as the core material.

Patent Document 1 describes composite carbon particles having an amorphous carbon layer formed on the surface using a petroleum-based pitch as a coating material.
Patent Document 2 describes composite carbon particles in which a pyrolytic carbon layer is formed on the surface by a CVD treatment.

Patent Document 3 describes composite carbon particles in which graphene is used as a coating material and graphene is adhered to the surface.
Patent Document 4 describes carbon composite silicon in which a graphene sheet is attached to a silicon surface.

Patent Document 5 describes a method for producing a graphene shell having a graphene film as a shell structure.
Non-Patent Document 1 describes multilayer graphene, and Non-Patent Document 2 describes bilayer graphene.

Patent Document 6 discloses composite particles of graphite particles, amorphous carbon, and carbon fine particles.
Patent Document 7 discloses composite particles of graphite particles, pitch carbides, and carbon black.

Patent Documents 8 to 10 disclose differential thermal analysis of composite particles containing graphite particles and a coated carbon layer.

Japanese Patent No. 4531174 Japanese Patent No. 5898628 International Release 2017/168882 Japanese Unexamined Patent Publication No. 2013-60355 Japanese Patent No. 5794418 Japanese Unexamined Patent Publication No. 2014-60148 International Publication No. 2007/086603 JP-A-2014-107029 JP-A-2018-170247 Japanese Unexamined Patent Publication No. 2016-100208

With the conventional technique of forming a coating layer using pitch, it is possible to produce composite carbon particles in which an amorphous carbon (amorphous carbon) layer is formed on the surface of carbon particles. However, the amorphous carbon layer has insufficient high-temperature characteristics, and it is difficult to control the thickness of the amorphous carbon layer uniformly. Therefore, the electron conductivity is also non-uniform, so that the internal resistance is high and the rate characteristics are also insufficient. Met.

When forming a carbonaceous coating layer by CVD treatment, it is difficult to form a thin and uniform layer on a core material having large irregularities such as carbon particles, and in order to form a uniform layer, the coating layer should be thickened. , It was necessary to form a buffer layer inside, resulting in inadequate high temperature cycle characteristics and high temperature storage characteristics.

In the graphene coating technique described in Patent Document 3, amorphous carbon is used for binding the core material and graphene, and the high temperature characteristics are insufficient.
The technique for coating graphene described in Patent Document 4 is to attach a coating layer using an electrophoresis method, and it is not possible to form a graphene layer on the surface of carbon particles.

The graphene shell using the graphene film as the shell described in Patent Document 5 is a technique of using a catalyst metal inside, and the graphene layer cannot be coated on the surface of carbon particles.
The composite particles described in Patent Document 6 are covered with an amorphous carbon layer, and the composite particles described in Patent Document 7 are covered with pitch carbides, both of which have insufficient high temperature characteristics.

An object of the present invention is to provide composite carbon particles for a lithium ion secondary battery having excellent low temperature charge / discharge rate characteristics, high temperature storage characteristics, and high temperature cycle characteristics in a well-balanced manner, low internal resistance, and high Coulomb efficiency. is there.

The present invention has, for example, the following configuration.
[1] Composite carbon particles including carbon particles (A) and a carbon coating layer (B) that coats the surface thereof, wherein the carbon coating layer (B) is a carbon coating layer (B1) and carbon fine particles (B1). A composite carbon particle containing B2) and having one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower in differential thermal analysis (DTA) in air.

[2] The variation coefficient of the R value measured by Raman spectroscopy (ratio of 1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG) (ID / IG) ) is zero. The composite carbon particle according to the above [1], which is 50 or less.

[3] (the ratio of the 1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG) (ID / IG) ) R value measured by Raman spectroscopy is 0.10 or more 1. The composite carbon particle according to the above [1] or the above [2], which is 50 or less.

[4] The composite carbon particles according to any one of [1] to [3] above, wherein the average surface spacing d002 of the (002) plane measured by the X-ray diffraction method is 0.3354 nm or more and 0.3370 nm or less.

[5] The 50% particle size (D50) in the volume-based cumulative particle size distribution by the laser diffraction method is 1.0 μm or more and 50.0 μm or less, and the tapping density of 400 times is 0.30 g / cm ³ or more and 1.50 g / cm ³ The composite carbon particle according to any one of the following [1] to [4].

[6] The composite carbon particles according to any one of [1] to [5] above, wherein the BET specific surface area is 0.1 m ² / g or more and 40.0 m ² / g or less.
[7] The composite according to any one of [1] to [6] above, wherein (the BET specific surface area of the composite carbon particles) / (the BET specific surface area of the carbon particles (A)) is 0.30 or more and 10.00 or less. Carbon particles.

[8] The ratio of the composite carbon particles and the carbon particles R value measured by Raman spectroscopy of (A) (1350cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG) (ID / IG)) ratio ((R value of composite carbon particles) / (R value of carbon particles (A))) is 1.50 or more and 20.0 or less. Any of the above [1] to [7]. The composite carbon particles described in Crab.

[9] The composite carbon particle according to any one of the above [1] to [8], wherein the carbon particle (A) is a graphite particle.
[10] The composite carbon particle according to any one of [1] to [9], wherein the carbon particle (A) contains silicon.

[11] The composite carbon according to any one of [1] to [10], wherein the average particle size of the primary particles of the carbon fine particles (B2) is 10 nm or more and 500 nm or less, and the maximum value of the secondary particle diameter is 1000 nm or less. particle.

[12] The composite carbon particles according to any one of [1] to [11], wherein the carbonaceous coating layer (B1) has a thickness of 0.1 nm or more and 30.0 nm or less.
[13] The composite carbon particles according to any one of [1] to [12], wherein the carbonaceous coating layer (B1) contains a single-layer graphene layer or a multi-layer graphene layer.

[14] The method for producing the composite carbon particles according to any one of [1] to [13] above.
70.0 parts by mass or more and 99.89 parts by mass or less of carbon particles (A), 0.1 parts by mass or more and 20.0 parts by mass or less of a hydroxycarboxylic acid compound having at least one carboxy group and one or more hydroxy groups, and carbon The ratio of the fine particles (B2) to 0.01 parts by mass or more and 10.0 parts by mass or less (however, the total of the carbon particles (A), the hydroxycarboxylic acid compound, and the carbon fine particles (B2) is 100 parts by mass. A method for producing composite carbon particles, which comprises a step of heat-treating the mixture contained in.).

[15] The method for producing the composite carbon particles according to any one of [1] to [13] above.
70.0 parts by mass or more and 99.89 parts by mass or less of carbon particles (A), 0.1 parts by mass or more and 20.0 parts by mass or less of a polycarboxylic acid compound having two or more carboxy groups without having a hydroxy group, And the ratio of carbon fine particles (B2) to 0.01 parts by mass or more and 10.0 parts by mass or less (however, the total of the carbon particles (A), the polycarboxylic acid compound, and the carbon fine particles (B2) is 100 parts by mass. A method for producing composite carbon particles, which comprises a step of heat-treating the mixture contained in (1).

[16] The method for producing the composite carbon particles according to any one of [1] to [13] above.
A hydroxycarboxylic acid compound having 70.0 parts by mass or more and 99.89 parts by mass or less of carbon particles (A), each having one or more carboxy groups and one or more hydroxy groups, and a polycarboxylic acid having no hydroxy groups and having two or more carboxy groups. The total ratio of the acid compound to 0.1 parts by mass or more and 20.0 parts by mass or less, and the carbon fine particles (B2) to 0.01 parts by mass or more and 10.0 parts by mass or less (however, with the carbon particles (A)) A method for producing composite carbon particles, which comprises a step of heat-treating a mixture containing the hydroxycarboxylic acid compound, the polycarboxylic acid compound, and the carbon fine particles (B2) in an amount of 100 parts by mass.).

[17] The negative electrode active material containing the composite carbon particles according to any one of the above [1] to [13].
[18] A negative electrode containing the negative electrode active material according to 17 above and a current collector.
[19] A lithium ion secondary battery using the negative electrode according to 18.

According to the present invention, a carbon coating layer containing carbon fine particles is formed on the surface of carbon particles, which is excellent in low temperature charge / discharge rate characteristics, high temperature storage characteristics, and high temperature cycle characteristics, has low internal resistance, and has high Coulomb efficiency. Composite carbon particles can be provided.

6 is a scanning electron micrograph of the composite carbon particles produced in Example 5. 6 is a scanning electron micrograph of the composite carbon particles produced in Example 7. 6 is a scanning electron micrograph of the composite carbon particles produced in Comparative Example 5. 6 is a scanning electron micrograph of the composite carbon particles produced in Comparative Example 9. It is the R value imaging result of the composite carbon particle produced in Example 5. It is the R value imaging result of the composite carbon particle produced in Comparative Example 5.

Hereinafter, embodiments of the present invention will be described in detail.
[1] Composite carbon particles The composite carbon particles in one embodiment of the present invention include carbon particles (A) and a carbonic coating layer (B) that coats the surface thereof, and the carbonic coating layer (B) is carbonic. It contains a coating layer (B1) and carbon fine particles (B2). The composite carbon particles have one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower in differential thermal analysis (DTA) in air.

The carbon particles (A) are not particularly limited, and known carbon particles such as soft carbon and hard carbon, amorphous carbon particles and graphite particles can be used, but graphite particles are preferably used. Since graphite particles have high crystallinity, they are excellent in discharge capacity, high temperature cycle characteristics, and high temperature storage characteristics. The carbon particles (A) also include those whose surface is partially or wholly coated with amorphous carbon.

Among the graphite particles, artificial graphite particles are preferable, and artificial graphite particles having a solid structure are more preferable. When the inside has a solid structure, in-particle peeling hardly occurs even if expansion and contraction are repeated due to charging and discharging, and high-temperature cycle characteristics and high-temperature storage characteristics are excellent.

The carbon particles (A) can contain metals, metal oxides or alloys. Metals, metal oxides or alloys are not limited as long as they occlude and release lithium, but for example, silicon (Si) (hereinafter, also simply referred to as "silicon"), tin, zinc and their oxides and alloys, etc. Can be mentioned.

Further, the carbon particles (A) preferably contain silicon. There is no limitation on the form containing silicon, but the inside of the pores in the composite or porous carbon particles obtained by the method of carbonizing the petroleum pitch by heat-treating the mixture of silicon and petroleum pitch in an inert atmosphere. A composite in which silicon is filled is preferable. Porous carbon particles can be produced by a known production method, and can be achieved, for example, by the same production method as activated carbon or by appropriately heat-treating the polymer. The method of including silicon is not limited, but the porous carbon particles are exposed to the silane gas at a high temperature in the presence of a silicon-containing gas, preferably silane, for example by chemical vapor deposition (CVD). It is obtained by producing silicon in the pores of. Graphite may be contained in these composites.

The carbon coating layer (B) may have a structure in which carbon fine particles (B2) are adhered to the surface of the carbon coating layer (B1), or a part or all of the carbon fine particles (B2) may be a carbon coating layer. The structure may be embedded in (B1). Further, in each case, a part or all of the surface of the carbon fine particles (B2) may be covered with the carbonaceous coating layer (B1).

The carbon fine particles (B2) are preferably amorphous carbon fine particles such as coal fine powder, vapor phase carbon powder, carbon black, Ketjen black, and acetylene black. Of these, carbon black is more preferable. By using carbon black, the input / output characteristics at low temperatures tend to be higher.

The differential thermal analysis (DTA) peak of carbon material shows the exothermic peak due to combustion at different temperatures due to the crystal structure of the carbon component. Therefore, the composite carbon particles of the present invention composed of the three components of the carbon particles (A) serving as the core material, the carbon coating layer (B1), and the carbon fine particles (B2) have three or more peaks. However, when the carbonaceous coating layer (B1) and the carbon fine particles (B2) have similar components, they may show the same peak. In this case, the effect of the composite particles composed of different components is small, and the effect of improving the battery characteristics is not sufficient.

When the composite carbon particles in one embodiment of the present invention are subjected to differential thermal analysis in air, they have one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower. A peak of 200 ° C. or higher and lower than 620 ° C. indicates that a thin carbonaceous coating layer (B1) having thermal stability is provided. Having two or more peaks at 620 ° C. or higher and 1000 ° C. or lower indicates that the carbon particles (A) and the carbon fine particles (B2) are composed of different components. In this case, the carbon particles (A), the carbon coating layer (B1), and the carbon fine particles (B2) have different crystal structures, and the effects of the composite particles are sufficiently exhibited to improve the battery characteristics in a well-balanced manner.

One peak of the composite carbon particles of 200 ° C. or higher and lower than 620 ° C. is more preferably 500 ° C. or higher, further preferably 585 ° C. or higher, and most preferably 600 ° C. or higher.
One peak of the composite carbon particles of 200 ° C. or higher and lower than 620 ° C. is more preferably 618 ° C. or lower, further preferably 615 ° C. or lower.

The two or more peaks of the composite carbon particles shown at 620 ° C. or higher and 1000 ° C. or lower are more preferably 650 ° C. or higher, further preferably 680 ° C. or higher, and most preferably 700 ° C. or higher.
The two or more peaks of the composite carbon particles shown at 620 ° C. or higher and 1000 ° C. or lower are more preferably 950 ° C. or lower, further preferably 900 ° C. or lower, and most preferably 880 ° C. or lower.

The average particle size of the primary particles of the carbon fine particles (B2) is preferably 10 nm or more, more preferably 15 nm or more, further preferably 20 nm or more, and particularly preferably 30 nm or more. When the average particle size of the primary particles is 10 nm or more, agglutination is suppressed and uniform dispersibility is excellent. The average particle size of the primary particles is preferably 500 nm or less, more preferably 200 nm or less, further preferably 100 nm or less, particularly preferably 70 nm or less, and most preferably 60 nm or less. When the average particle size of the primary particles is 500 nm or less, the size is sufficiently small and the uniform dispersibility is excellent.

The average particle size of the primary particles of the carbon fine particles (B2) is measured by the method using the scanning electron microscope (SEM) described in the examples.
The maximum value of the secondary particle diameter of the carbon fine particles (B2) in the composite carbon particles is preferably 1000 nm or less, more preferably 500 nm or less, further preferably 300 nm or less, and particularly preferably 100 nm or less. When the maximum value of the secondary particle size is 1000 nm or less, the carbon fine particles (B2) are uniformly dispersed, and the low temperature rate characteristic in the lithium ion secondary battery is excellent.

The maximum value of the secondary particle diameter of the carbon fine particles (B2) is measured by the method using the scanning electron microscope (SEM) described in the examples.
The carbonaceous coating layer (B1) preferably contains a graphene layer. Graphene is a two-dimensional sheet-like substance in which carbon atoms are continuous in a honeycomb shape, and has superior conductivity, chemical stability, and high mechanical strength than amorphous carbon. By coating the surface of the carbon particles (A) with graphene, it is possible to suppress the volume change of the carbon particles and improve the conductivity, and the negative electrode material for the lithium ion secondary battery having excellent durability and charge / discharge characteristics. Is obtained. The graphene is more preferably formed as a graphene layer on the surface of the carbon particles (A), and further preferably to cover almost the entire surface of the carbon particles (A). Further, it is more preferable that the surface of the carbon particles (A) is directly covered with a single-layer graphene layer or a multi-layer graphene layer. It is more preferable that the carbonaceous coating layer (B) is composed of only a graphene layer and carbon fine particles (B2). The graphene layer consisting of one layer is called a single-layer graphene layer, and the graphene layer consisting of two or more layers is called a multilayer graphene layer. Further, the graphene layer also includes a functional group-modified graphene layer in which graphene has a functional group containing a component other than carbon, and may contain, for example, graphene oxide having an oxygen functional group added.

The carbon coating layer (B) may have a structure in which carbon fine particles (B2) are adhered to the surface of the carbon coating layer (B1), or a part of the carbon fine particles (B2) may be attached to the surface of the carbon coating layer (B1). ) May be embedded in the structure. Further, in each case, a part or all of the surface of the carbon fine particles (B2) may be covered with the carbonaceous coating layer (B1).

The thickness of the carbonaceous coating layer (B1) is preferably 0.1 nm or more. 0.1 nm corresponds to the thickness of a single layer of graphene. From the viewpoint of providing a certain level of conductivity, chemical stability, and mechanical strength, the thickness of the carbon coating layer (B1) is more preferably 1.0 nm or more, and even more preferably 2.0 nm or more. The thickness of the carbonaceous coating layer (B1) is preferably 30.0 nm or less. When the thickness of the carbon coating layer (B1) is 30.0 nm or less, the formation of the excess carbon coating layer (B1) is suppressed, and the high temperature storage characteristics and the high temperature cycle characteristics can be maintained well. From the same viewpoint, 20.0 nm or less is more preferable, 10.0 nm or less is further preferable, and 5.0 nm or less is most preferable.

The thickness of the carbon coating layer (B1) is measured by observation with a transmission electron microscope (TEM). From the viewpoint of measurement accuracy, the number of measurement points is 30 or more. The arithmetic mean is taken as the thickness of the carbonaceous coating layer (B1). Specifically, it can be measured by the method described in Examples.

The R value measured by the Raman spectroscopic analysis of the composite carbon particles in one embodiment of the present invention is preferably 0.10 or more. When the R value is 0.10 or more, the electrical resistance on the surface of the composite carbon particles is lowered, and a lithium ion secondary battery having good low-temperature charge / discharge characteristics can be obtained. From the same viewpoint, the R value is more preferably 0.15 or more, and most preferably 0.18 or more. The R value measured by Raman spectroscopy of the composite carbon particles is preferably 1.50 or less. This is because when the R value is 1.50 or less, the crystallinity of the surface is not too low, so that good high-temperature storage and high-temperature cycle characteristics can be maintained. From the same viewpoint, the R value is more preferably 0.60 or less, and further preferably 0.50 or less.

The R value means the intensity ratio (ID / IG) of the peak intensity (ID) near 1350 cm ^{-1 and} the peak intensity (IG) near 1580 cm ^-1 observed by Raman spectroscopy. The state of the surface of the composite carbon particles can be evaluated from the R value. The smaller the R value, the higher the crystallinity of the surface of the composite carbon particles. The peak intensity represents the height of the peak. The R value may be measured by using the microscopic Raman spectroscopic analysis described in the examples, or by using ordinary Raman spectroscopic analysis.

The ratio (ID / IG of a composite R value measured by Raman spectroscopy of carbon particles (1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity in an embodiment of the present invention (IG) )) The coefficient of variation is preferably 0.50 or less. When the coefficient of variation of the R value is 0.50 or less, the variation in the coating state is small, so that the effect of reducing the resistance is large, and the high temperature cycle characteristics and the low temperature rate characteristics are improved. From the same viewpoint, the coefficient of variation is more preferably 0.45 or less, and further preferably 0.40 or less.

The coefficient of variation of the R value is obtained by measuring the R value at multiple points by microscopic Raman spectroscopy and dividing the standard deviation value by the average value of the R values. The variation of the coating can be evaluated by obtaining the coefficient of variation. The larger the coefficient of variation, the larger the variation in the R value, indicating poor coating uniformity, and the smaller the coefficient of variation, the smaller the variation in the R value, indicating that the coating uniformity is high.

In the microscopic Raman spectroscopy, a microlaser Raman spectroscope with high spatial resolution is used to measure multiple R values for the same sample. From the viewpoint of measurement accuracy, the score is 50 points or more, preferably 100 points or more. Typically, the laser irradiation position is shifted after each measurement so that the location is different each time. If the spatial resolution is too low (that is, if the overlap of irradiation positions is too large), the variation between particles is difficult to be reflected in the R value, and the accuracy of the evaluation result may decrease.

In the composite carbon particles according to one embodiment of the present invention, the composite carbon particles and the 1580cm around ^-1 R value measured by Raman spectroscopy and (1350 cm ^-1 vicinity of the peak intensity (ID) of the carbon particles (A) The ratio ((R value of composite carbon particles) / (R value of carbon particles (A))) to the peak intensity (IG) of (ID / IG) is 1.50 or more and 20.00 or less. Is preferable. When the ratio is 1.50 or more, the carbon coating layer (B) is formed on the surface of the carbon particles (A), the effect of lowering the resistance is large, and the low temperature rate characteristic is improved. From the same viewpoint, the ratio is more preferably 1.70 or more, and most preferably 1.80 or more. On the other hand, (R value of composite carbon particles) / (R value of carbon particles (A)) is preferably 20.00 or less. When the ratio is 20.00 or less, the formation of an excess carbonic coating layer (B) is suppressed, whereby high temperature storage stability and high temperature cycle characteristics can be maintained well. From the same viewpoint, the ratio is more preferably 7.00 or less, and most preferably 5.00 or less. Examples of the method of satisfying the above ratio include a method of using graphite particles as the carbon particles (A).

The average plane spacing d002 of the (002) planes measured by the X-ray diffraction method of the composite carbon particles in one embodiment of the present invention is preferably 0.3354 nm or more. This is the theoretical lower limit of graphite. The d002 is preferably 0.3370 nm or less. When d002 is 0.3370 nm or less, the discharge capacity becomes large, and a battery satisfying the energy density required for a large battery can be obtained. From the same viewpoint, d002 is more preferably 0.3367 nm or less, and further preferably 0.3364 nm or less. When graphite particles are used as the carbon particles (A), d002 is preferably in the above range.

The 50% particle diameter (D50) of the composite carbon particles in one embodiment of the present invention is preferably 1.0 μm or more. When D50 is 1.0 μm or more, agglutination of particles is suppressed and it becomes easy to prepare a slurry for electrode coating. From the same viewpoint, D50 is more preferably 3.0 μm or more, and most preferably 5.0 μm or more. D50 is preferably 50.0 μm or less. This is because when D50 is 50.0 μm or less, the electrical resistance of the electrode is reduced and the rate characteristics are improved. From the same viewpoint, 30.0 μm or less is more preferable, and 10.0 μm or less is most preferable.

In the present specification, the “50% particle size (D50)” means a particle size that is cumulatively 50% in the volume-based particle size distribution obtained by a laser particle size distribution measuring instrument.
The 400-fold tapping density of the composite carbon particles in one embodiment of the present invention is preferably 0.30 g / cm ³ or more. When the tapping density is 0.30 g / cm ³ or more, the electrode density reached at the time of pressing can be sufficiently increased, and a battery having a high energy density can be obtained. From the same viewpoint, the tapping density is more preferably 0.40 g / cm ³ or more, and most preferably 0.50 g / cm ³ or more. The 400-fold tapping density is preferably 1.50 g / cm ³ or less. When the tapping density is 1.50 g / cm ³ or less, the electrolytic solution permeability of the obtained electrode can be sufficiently increased, and a battery having high input / output characteristics can be obtained. From the same viewpoint, the tapping density is more preferably 1.20 g / cm ³ or less, 0.80 g / cm ³ or less is most preferred.

The BET specific surface area of the composite carbon particles in one embodiment of the present invention is preferably 0.1 m ² / g or more. When the BET specific surface area is 0.1 m ² / g or more, high-speed charging / discharging is possible. From the same viewpoint, BET specific surface area is more preferably equal to or greater than ^{1.0m 2 / g, 3.0m 2 /} g or more is most preferred. The BET specific surface area is preferably 40.0 m ² / g or less. When it is 40.0 m ² / g or less, agglutination is suppressed, so that it is easy to prepare a slurry, side reactions when used as a battery are suppressed, and coulomb efficiency, high-temperature storage stability and high-temperature cycle characteristics are excellent. From the same viewpoint, it is preferably 12.0 m ² / g or less, and more preferably 9.0 m ² / g or less.

In the composite carbon particles according to one embodiment of the present invention, (BET specific surface area of the composite carbon particles) / (BET specific surface area of the carbon particles (A)) is preferably 10.00 or less. When the ratio is 10.0 or less, the carbon fine particles (B2) are uniformly dispersed, and the high temperature storage characteristics and the high temperature cycle characteristics are excellent. From the same viewpoint, the ratio is more preferably 2.00 or less, and even more preferably 1.50 or less. The ratio is preferably 0.30 or more. When the ratio is 0.30 or more, the coating amount does not become excessive, and the high temperature cycle characteristics and the high temperature storage characteristics are kept good. From the same viewpoint, the ratio is more preferably 0.50 or more, and most preferably 0.60 or more. For the BET specific surface area of the carbon particles (A), the value of the carbon particles used as the raw material is used.

The d002, D50, 400 times tapping density and BET specific surface area described herein are measured by the methods described in the Examples.
[2] Method for producing composite carbon particles In the method for producing composite carbon particles in one embodiment of the present invention, the carbon particles (A) are 70.0 parts by mass or more and 99.89 parts by mass or less, and the carboxylic acid compound is 0.1. The ratio of parts by mass to 20.0 parts by mass and carbon fine particles (B2) from 0.01 parts by mass to 10.0 parts by mass (however, the carbon particles (A), the carboxylic acid compound, and the carbon fine particles (however,) The step of heat-treating the mixture containing B2) and 100 parts by mass.) Is included.

The mixture can be obtained by a mixing step of mixing the carbon particles (A), the carboxylic acid compound and the carbon fine particles (B2) to obtain a mixture.
Further, the heat treatment step (heat treatment step) can be performed, for example, as a step of heat-treating the obtained mixture at 500 ° C. or higher and 2000 ° C. or lower.
[2-1] Mixing Step In the mixing step, carbon particles (A), a carboxylic acid compound, and carbon fine particles (B2) are mixed to obtain a mixture.

In the mixing step, the carbon particles (A) and the carboxylic acid compound may be mixed first, and then the mixture and the carbon fine particles (B2) may be mixed, or the carbon particles (A) and the carbon fine particles (B2) may be mixed first. The mixture may be mixed with the carboxylic acid compound, or the carboxylic acid compound and the carbon fine particles (B2) may be mixed first, and then the mixture and the carbon particles (A) may be mixed. Alternatively, the carbon particles (A), the carboxylic acid compound and the carbon fine particles (B2) may be mixed at the same time.

Examples of the carboxylic acid compound used in one embodiment of the present invention include a polycarboxylic acid compound having no hydroxy group and having two or more carboxy groups in one molecule (also simply referred to as “polycarboxylic acid compound”), and one. Examples thereof include hydroxycarboxylic acid compounds having one or more carboxylic acid groups and one or more hydroxy groups in the molecule (also simply referred to as “hydroxycarboxylic acid compounds”).

Examples of such polycarboxylic acid compounds include succinic acid (melting point 185 ° C.), glutaric acid (95 ° C.), maleic acid (131 ° C.), phthalic acid (210 ° C.), and terephthalic acid (300 ° C.). ), Oxaloacetic acid (161 ° C.), and malonic acid (135 ° C.). Examples of the hydroxycarboxylic acid include malic acid (melting point 130 ° C.), citric acid (153 ° C.), tartaric acid (168 ° C. (L form), 151 ° C. (meso form), 206 ° C. (racemic form)). , Gallic acid (250 ° C) and salicylic acid (159 ° C). By using such a carboxylic acid compound, in the heat treatment step described later, the molecules can be dehydrated to form a denser network structure, and the carbon particles can be covered more widely, thinner and more firmly.

Among them, a compound containing two or more carboxy groups and one or more hydroxyl groups in one molecule is more preferable, and malic acid, citric acid, and tartaric acid (L-form) are particularly preferable.
The carboxylic acid compound may be one kind or may contain two or more kinds. That is, two or more kinds of polycarboxylic acid compounds may be used, two or more kinds of hydroxycarboxylic acid compounds may be used, or a polycarboxylic acid compound and a hydroxycarboxylic acid compound may be used in combination. The above carboxylic acid compound can also be combined with a compound containing one carboxy group in one molecule.

That is, as the carboxylic acid compound, for example, it can be used in the following three aspects. The first embodiment uses only a hydroxycarboxylic acid compound as a carboxylic acid compound, the second aspect uses only a polycarboxylic acid compound as a carboxylic acid compound, and the third aspect is hydroxy as a carboxylic acid compound. This is an embodiment in which a carboxylic acid compound and a polycarboxylic acid compound are used.

The melting point of the carboxylic acid compound is preferably 500 ° C. or lower. When the melting point is within this range, the carboxylic acid compound is less thermally decomposed and the coating effect is enhanced. From the same viewpoint, the melting point is more preferably 400 ° C. or lower, and even more preferably 300 ° C. or lower. The melting point of the carboxylic acid compound is preferably 100 ° C. or higher. When the melting point is in this range, the carboxylic acid compound is easy to handle and the yield after the mixing treatment is high. From the same viewpoint, the melting point is more preferably 120 ° C. or higher, and even more preferably 140 ° C. or higher.

The mixture obtained in the mixing step may contain materials other than the carbon particles (A), the carboxylic acid compound and the carbon fine particles (B2), but the mixture is only the carbon particles (A), the carboxylic acid compound and the carbon fine particles (B2). It is preferably composed of. It is preferable to use a carboxylic acid compound in a powder state. The mixing method is preferably dry mixing, and a commercially available mixer or stirrer can be used. Specific examples include mixers such as ribbon mixers, V-type mixers, W-type mixers, one-blade mixers, and nower mixers.

The carboxylic acid compound used in the present invention has a lower viscosity than the pitch and polymer used for conventional coating, and the functional group of the carboxylic acid compound interacts with the functional group on the carbon fine particles. It becomes possible to disperse well. As a result, it is considered that the maximum value of the secondary particle diameter of the carbon fine particles becomes smaller than that in the conventional case.

The blending amount of the carbon particles (A), the carboxylic acid compound and the carbon fine particles (B2) in the mixture is 100 parts by mass when the total of the carbon particles (A), the carboxylic acid compound and the carbon fine particles (B2) is 100 parts by mass. , Carbon particles (A) are 70.0 parts by mass or more and 99.89 parts by mass or less, carboxylic acid compounds are 0.1 parts by mass or more and 20.0 parts by mass or less, and carbon fine particles (B2) are 0.01 parts by mass or more and 10 parts. .0 parts by mass or less is preferable. In other words, as the mixture, for example, carbon particles (A) are 70.0 parts by mass or more and 99.89 parts by mass or less, hydroxycarboxylic acid compound is 0.1 parts by mass or more and 20.0 parts by mass or less, and carbon fine particles ( B2) is 0.01 parts by mass or more and 10.0 parts by mass or less (however, the total of the carbon particles (A), the hydroxycarboxylic acid compound, and the carbon fine particles (B2) is 100 parts by mass). (1st aspect), carbon particles (A) are 70.0 parts by mass or more and 99.89 parts by mass or less, polycarboxylic acid compound is 0.1 parts by mass or more and 20.0 parts by mass or less, and carbon. The ratio of the fine particles (B2) to 0.01 parts by mass or more and 10.0 parts by mass or less (however, the total of the carbon particles (A), the polycarboxylic acid compound, and the carbon fine particles (B2) is 100 parts by mass. ), The carbon particles (A) are 70.0 parts by mass or more and 99.89 parts by mass or less, and the hydroxycarboxylic acid compound and the polycarboxylic acid compound are 0.1 parts by mass in total. 20.0 parts by mass or less, and 0.01 parts by mass or more and 10.0 parts by mass or less of carbon fine particles (B2) (however, the carbon particles (A), the hydroxycarboxylic acid compound, and the polycarboxylic acid compound The total of the carbon fine particles (B2) and the carbon fine particles (B2) is 100 parts by mass), and a mixture (third aspect) is mentioned.

The reason why the blending amount of the carboxylic acid compound is 0.1 parts by mass or more is that the carbon particles (A) are sufficiently covered with the carboxylic acid compound. From this viewpoint, the amount of the carboxylic acid compound is more preferably 1.0 part by mass or more, further preferably 2.0 parts by mass or more. The reason why the blending amount of the carboxylic acid compound is 20.0 parts by mass or less is to suppress the formation of an excessive carbonaceous coating layer (B1), thereby maintaining good high-temperature storage stability and high-temperature cycle characteristics. From this viewpoint, the amount of the carboxylic acid compound is more preferably 10.0 parts by mass or less, and further preferably 8.0 parts by mass or less.

The reason why the blending amount of the carbon fine particles (B2) is 0.01 part by mass or more is that the carbon fine particles (B2) are sufficiently contained on the surface, the effect of lowering the resistance is large, and the low temperature rate characteristics are improved. From this viewpoint, the amount of carbon fine particles (B2) is more preferably 0.1 part by mass or more, and further preferably 1.0 part by mass or more. The reason why the blending amount of the carbon fine particles (B2) is 10.0 parts by mass or less is that the size of the secondary particles is suppressed because the carbon fine particles (B2) do not become excessive, and the uniform carbon coating layer (B) has. This is because it is formed. From this viewpoint, the amount of carbon fine particles (B2) is more preferably 8.0 parts by mass or less, and further preferably 6.0 parts by mass or less.

The ratio of the amount (mass) of the carbon fine particles (B2) to the amount of the carboxylic acid compound (amount of carbon fine particles / amount of the carboxylic acid compound) is preferably 0.05 or more. When the ratio is 0.05 or more, carbon fine particles (B2) are sufficiently contained on the surface of the carbon particles, and the low temperature rate characteristic is improved. From the same viewpoint, 0.10 or more is more preferable, and 0.20 or more is further preferable. The ratio of the amount of carbon fine particles to the amount of the carboxylic acid compound is preferably 1.50 or less. When the ratio is 1.50 or less, the secondary particle diameter of the carbon fine particles (B2) becomes sufficiently small, and a uniform carbonic coating layer (B) is formed. From the same viewpoint, 1.30 or less is more preferable, and 1.10 or less is further preferable.
[2-2] Heat Treatment Step The step of heat-treating the mixture is not particularly limited as long as composite carbon particles can be obtained. The heat treatment step (heat treatment step) can be performed by using a heat treatment apparatus such as a rotary kiln, a roller herscren, or an electric tubular furnace. By the heat treatment step, composite carbon particles in which the surface of the carbon particles (A) is coated with the carbonic coating layer (B) are obtained.

The heat treatment temperature in the heat treatment step is preferably 500 ° C. or higher, more preferably 700 ° C. or higher, and further preferably 900 ° C. or higher in order to sufficiently promote carbonization of the carboxylic acid compound, suppress residual hydrogen and oxygen, and improve battery characteristics. Most preferably. Further, in order to suppress graphitization and maintain good charge / discharge rate characteristics, the heat treatment temperature is preferably 2000 ° C. or lower, more preferably 1500 ° C. or lower, and most preferably 1200 ° C. or lower. The treatment time is not particularly limited as long as carbonization has progressed sufficiently, but is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 50 minutes or more.

The heat treatment step is preferably carried out in an inert gas atmosphere. Examples of the inert gas for the Mactive gas atmosphere include argon gas and nitrogen gas.
The composite carbon particles after the heat treatment may be appropriately crushed and sieved.
[3] Negative Electrode Active Material of Lithium Ion Secondary Battery The negative electrode active material of the lithium ion secondary battery according to the embodiment of the present invention contains the above composite carbon particles.

The negative electrode active material consists of the composite carbon particles only, or contains the composite carbon particles and other components. Examples of other components include other carbon materials and conductivity-imparting agents (conductive aids). When other carbon materials or conductivity-imparting agents are included For example, 0.01 to 200 parts by mass, preferably 0.01 to 100 parts by mass, of spherical natural graphite or artificial graphite is blended with respect to 100 parts by mass of the composite carbon particles. You can use things. By using a mixture of other graphite materials, it is possible to obtain a negative electrode active material having the excellent properties of the other graphite materials while maintaining the excellent properties of the composite carbon particles.

Such a negative electrode active material can be obtained by mixing composite carbon particles with other carbon materials or the like. At the time of mixing, the mixing material can be appropriately selected according to the required battery characteristics, and the mixing amount can be determined.

Further, carbon fiber can be blended in the negative electrode active material. The blending amount is preferably 0.01 to 20 parts by mass, and more preferably 0.5 to 5 parts by mass in 100 parts by mass of the negative electrode active material.
Examples of the carbon fibers include organic carbon fibers such as PAN-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers, and vapor-phase carbon fibers. Of these, vapor phase carbon fibers having high crystallinity and high thermal conductivity are particularly preferable. When the carbon fibers are adhered to the surface of the composite carbon particles, the vapor phase carbon fibers are particularly preferable.

As an apparatus for mixing the composite carbon particles with other materials, a commercially available mixer or stirrer can be used. Specific examples include mixers such as ribbon mixers, V-type mixers, W-type mixers, one-blade mixers, and nower mixers. Mixing by a device in which shearing force and mechanical energy such as impact and compression are simultaneously applied is preferable. For example, a high-speed stirrer in which shearing force and impact are applied to the powder by a high-speed swirling flow, and a dry mixer having a structure in which the distance between the mixing blade and the inner wall of the container is narrow and the powder is pressed against the inner wall of the container are preferable. Examples of such a mixer include Mechanofusion (registered trademark, manufactured by Hosokawa Micron Co., Ltd.), Nobilta (registered trademark, manufactured by Hosokawa Micron Co., Ltd.), Composit (registered trademark, manufactured by Nippon Coke Industries Co., Ltd.), and Multipurpose Mixer. (Manufactured by Nippon Coke Industries Co., Ltd.), hybridization system (registered trademark, manufactured by Nara Machinery Co., Ltd.) and the like.
[4] Electrode Paste The electrode paste in one embodiment of the present invention contains the negative electrode active material, a binder, and a solvent. The electrode paste is obtained by kneading the negative electrode active material and the binder. For kneading, equipment such as a ribbon mixer, a screw type kneader, a Spartan luzer, a ladyge mixer, a planetary mixer, and a universal mixer can be used. The electrode paste can be formed into a sheet shape, a pellet shape, or the like.

Examples of the binder used for the electrode paste include fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, and rubber-based materials such as SBR (styrene-butadiene rubber).

The amount of the binder used is preferably 1 to 30 parts by mass and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.
Examples of the solvent used for kneading include those suitable for each binder, for example, toluene, N-methylpyrrolidone and the like in the case of a fluorine-based polymer; water and the like in the case of SBR; and dimethylformamide, isopropanol and the like. In the case of a binder that uses water as a solvent, it is preferable to use a thickener such as carboxymethyl cellulose (CMC) in combination. The amount of the solvent and the thickener is adjusted so that the electrode paste has a viscosity that can be easily applied to the current collector.
[5] Negative electrode The negative electrode in one embodiment of the present invention is a negative electrode containing the negative electrode active material and a current collector. The negative electrode usually includes a current collector and a negative electrode active material on the current collector. The negative electrode can be obtained by applying the electrode paste on a current collector, drying it, and pressure-molding it. The negative electrode can be suitably used as a negative electrode for a lithium ion secondary battery. The layer containing the active material formed from the electrode paste is also generally referred to as an active material layer.

Examples of the current collector include foils such as aluminum, nickel, copper, and stainless steel, and meshes. The coating thickness of the electrode paste is preferably 50 to 200 μm. The method of applying the electrode paste is not particularly limited, and examples thereof include a method of applying with a doctor blade, a bar coater, or the like, and then molding with a roll press or the like.

Examples of the pressure molding method include molding methods such as roll pressurization and press pressurization. The pressure for pressure molding is preferably 1 × 10 ³ to 3 × 10 ³ kg / cm ² .
[6] Lithium Ion Secondary Battery The lithium ion secondary battery according to the embodiment of the present invention is a lithium ion secondary battery using the negative electrode. A lithium ion secondary battery generally has a structure in which a positive electrode and a negative electrode are immersed in an electrolyte or an electrolyte. The lithium ion secondary battery according to the embodiment of the present invention may use the negative electrode as the negative electrode, and other members are not particularly limited.

A lithium-containing transition metal oxide is usually used as the positive electrode active material for the positive electrode of the lithium ion secondary battery, and at least selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W is preferable. An oxide mainly containing one kind of transition metal element and lithium, in which a compound having a molar ratio of lithium to the transition metal element of 0.3 to 2.2 is used, more preferably V, Cr, Mn,. An oxide mainly containing at least one transition metal element selected from Fe, Co and Ni and lithium, and a compound having a molar ratio of lithium to the transition metal of 0.3 to 2.2 is used. In addition, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B and the like may be contained in a range of less than 30 mol% with respect to the mainly existing transition metal. Among the above positive electrode active materials, the general formula Li _x MO ₂ (M is at least one of Co, Ni, Fe, Mn, x = 0.02 to 1.2) or Li _y Z ₂ O ₄ (Z). Contains at least Mn and may further contain Co, Ni, Fe, Mn. It is preferable to use at least one material having a spinel structure represented by y = 0.02 to 2).

In lithium ion secondary batteries, a separator may be provided between the positive electrode and the negative electrode. Examples of the separator include non-woven fabrics mainly composed of polyolefins such as polyethylene and polypropylene, cloths, micropore films, and those obtained by combining them.

Known organic electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used as the electrolytes and electrolytes constituting the lithium ion secondary battery in the preferred embodiment of the present invention, but organic electrolytes are used from the viewpoint of electrical conductivity. preferable.

Note that there are no restrictions on the selection of materials required for the battery configuration other than the above.

Hereinafter, examples will be specifically described in the present invention. It should be noted that these are merely examples for explanation and do not limit the present invention.
The methods for evaluating composite carbon particles of Examples and Comparative Examples, the method for producing a battery, the method for measuring the characteristics of a battery, and the raw materials used in each example are as follows.
[1] Evaluation of composite carbon particles [1-1] 50% particle size (D50)
Using a Malvern Mastersizer 2000 (registered trademark) as a laser diffraction type particle size distribution measuring device, put a 5 mg sample in a container, add 10 g of water containing 0.04 mass% of a surfactant, and add 10 g for more than 5 minutes. Sonication was performed to obtain a 50% particle size (D50) in the volume-based cumulative particle size distribution.
[1-2] Tapping density (tap density)
Using Autotap manufactured by Quantachrome as a tap density measuring device, 50 g of a sample was placed in a 250 mL glass cylinder, and the density after tapping 400 times was measured. This is a measurement method based on ASTM B527 and JIS K5101-12-2, but the drop height of the auto tap is 5 mm.
[1-3] BET Specific Surface Area Using NOVA2200e manufactured by Quantachrome as a BET specific surface area measuring device, 3 g of a sample is placed in a sample cell (9 mm × 135 mm), and dried under vacuum conditions at 300 ° C. for 1 hour. , The measurement was performed. N ₂ was used as the gas for measuring the BET specific surface area.
[1-4] Average surface spacing d002
A mixture of composite carbon particles and standard silicon (manufactured by NIST) mixed so as to have a mass ratio of 9: 1 was filled in a glass sample plate (sample plate window 18 × 20 mm, depth 0.2 mm) as follows. The measurement was performed under various conditions.

XRD device: Rigaku SmartLab (registered trademark)
X-ray type: Cu-Kα ray Kβ ray removal method: Ni filter X-ray output: 45 kV, 200 mA
Measurement range: 24.0 to 30.0 deg.
Scan speed: 2.0 deg. / Min.
The Gakushin method was applied to the obtained waveform to obtain the value of the average surface spacing d002. (See Iwashita et al., Carbon vol. 42 (2004), p. 701-714).
[1-5] R value and coefficient of variation of R value JASCO Corporation NRS-5100 was used as a microlaser Raman spectroscope, and measurement was performed at an excitation wavelength of 532.36 nm.

The ratio of the peak intensity (ID) near 1350 cm ^{-1 and} the peak intensity (IG) near 1580 cm ^-1 in the Raman spectrum is defined as the R value (ID / IG).
Microlaser Raman spectroscopic imaging was performed on the composite carbon particles in the following regions.

Measurement point: 22 x 28 points Measurement step: 0.32 μm
Measurement area: 7.0 x 9.0 μm
From the above measurements, 100 points were randomly extracted from the region corresponding to the composite carbon particles, and the value obtained by dividing the standard deviation of the obtained R value by the average value of the R value was used as the coefficient of variation.

Further, the average value of the R values was taken as the R value of the composite carbon particles.
[1-6] State and thickness of carbonaceous coating layer (B1) observed by transmission electron microscope (TEM) Composite carbon particles are dispersed in ethanol, collected on a microgrid mesh, and measured under the following conditions. went.

Transmission electron microscope device: Hitachi H-9500
Acceleration voltage: 300kV
Observation magnification: The state of the carbonaceous coating layer (B1) was observed from the measurement of 30,000 times. One composite carbon particle was randomly selected, and the coating layer on the surface of the composite carbon particle was observed in five visual fields at the above magnification, and the thickness of the coating layer at two locations per visual field was measured. The thickness of the coating layer at each location was taken as an average value of the coating layer length of 10 nm. This measurement was performed on three randomly selected composite carbon particles, and a total of 30 points of data were obtained, and the average was taken as the thickness of the coating layer. Moreover, the layer structure of the graphene layer, the amorphous carbon layer and the like was determined by evaluating the FFT (Fast Fourier Transform) pattern.
[1-7] Observation with scanning electron microscope (SEM) JSM-7600 manufactured by JEOL Ltd. was used as a scanning electron microscope device, and measurement was performed at a magnification of 5,000 to 30,000 (WD is about 10 mm, Acceleration voltage 1.0 keV, secondary electron image, GB-High).

The surface condition of the composite carbon particles was observed from the measurement under the above conditions. One composite carbon particle is randomly selected, and the length of the major axis of the primary particles and secondary particles of carbon fine particles (B2) existing on the surface of the composite carbon particle is observed at the above magnification for 5 fields or more, and per field. The length of the major axis of the primary particle and the secondary particle at 5 points was measured. This measurement was performed on four randomly selected composite carbon particles, and a total of 100 points of data were obtained. The average particle size of the primary particles of the carbon fine particles (B2) was obtained from the average value of the major axis of 100 primary particles. The maximum value of the secondary particle diameter of the carbon fine particles (B2) was obtained from the maximum value of the major axis of 100 secondary particles. When there were no secondary particles, the maximum value of the secondary particle size was the maximum value of the primary particle size.
[1-8] Differential Thermal Analysis (DTA)
For differential thermal analysis (DTA), EXSTAR6000 TG / DTA manufactured by SII Nanotechnology Co., Ltd. was used. A 10 mg sample was placed on a platinum pan, and the temperature was raised to 1000 ° C. at 5 ° C./min under a flow of 100 ml / min of air for measurement. As a standard substance, 10 mg of Al ₂ O ₃ was used.
[2] Fabrication of battery [2-1] Preparation of paste for electrodes 96.5 g of composite carbon particles obtained in each of Examples and Comparative Examples described later, and 0 carbon black (manufactured by TIMCAL, C65) as a conductive auxiliary agent. .5 g, 1.5 g of carboxymethyl cellulose (CMC) as a thickener and 80 to 120 g of water were appropriately added to adjust the viscosity, and fine particles of an aqueous binder (Polysol (registered trademark) LB150, manufactured by Showa Denko Co., Ltd.) were dispersed. 1.5 g of the dispersion was added, and the mixture was stirred and mixed to prepare a slurry-like dispersion having sufficient fluidity, which was used as an electrode paste.
[2-2] Preparation of Negative Electrode 1 The electrode paste was applied on a high-purity copper foil to a thickness of 150 μm using a doctor blade, and vacuum dried at 70 ° C. for 12 hours. After punching with a punching machine so that the coated portion has a size of 4.2 cm × 4.2 cm, it is sandwiched between ultra-steel press plates and pressed so that the electrode density is 1.3 g / cm ^3, and the negative electrode 1 is pressed. Made. The thickness of the active material layer after pressing is 65 μm.
[2-3] Preparation of Negative Electrode 2 After punching the copper foil coated with the above electrode paste into a circle of 16 mmφ, the electrode density is 1.3 g / cm ^{3 in} the same manner as for the negative electrode 1. Pressing was performed to prepare a negative electrode 2. The thickness of the active material layer after pressing is 65 μm.
[2-4] Preparation of positive electrode 95 g of LiFe ₂ PO ₄ (D50: 7 μm), 1.2 g of carbon black (manufactured by TIMCAL, C65) as a conductive auxiliary agent, vapor phase carbon fiber (manufactured by Showa Denko Co., Ltd.) , VGCF (registered trademark) -H) (0.3 g), polyvinylidene fluoride (PVdF) as a binder (3.5 g), and N-methyl-pyrrolidone were appropriately added and mixed to prepare a slurry for a positive electrode.

This positive electrode slurry is applied onto an aluminum foil having a thickness of 20 μm with a roll coater so that the thickness is uniform, and after drying, a roll press is performed to punch out the coated portion so that the coated portion is 4.2 cm × 4.2 cm. A positive electrode was obtained. The thickness of the active material layer after pressing is 65 μm.
[2-5] Preparation of Electrolyte Solution 1.2 mol of LiPF ₆ as an electrolyte in a mixed solution of 3 parts by mass of EC (ethylene carbonate), 2 parts by mass of DMC (dimethyl carbonate) and 5 parts by mass of EMC (ethyl methyl carbonate). / L was dissolved, and 1 part by mass of VC (vinylene carbonate) was added as an additive to prepare an electrolytic solution.
[2-6] Battery assembly (bipolar cell)
A nickel tab was welded to the copper foil portion of the negative electrode 1 and an aluminum tab was welded to the aluminum foil portion of the positive electrode by an ultrasonic welding machine. The active material layer side of the negative electrode 1 and the active material layer side of the positive electrode are opposed to each other and laminated through a polypropylene film microporous film, packed with an aluminum laminate film, the electrolytic solution is injected, and then the opening is heat-melted. It was sealed by wearing to prepare a bipolar cell.
(Counterpolar lithium cell (half cell))
In a cell with a screw-in lid made of polypropylene (inner diameter of about 18 mm), a separator (polypropylene microporous film (cell guard 2400)) is sandwiched between the active material layer side of the negative electrode 2 and the metallic lithium foil punched to 16 mmφ. A counter electrode lithium cell was produced by laminating, adding an electrolytic solution, and crimping with a crimping machine.
[3] Evaluation of battery [3-1] Measurement of initial Coulomb efficiency A test was conducted in a constant temperature bath set at 25 ° C. using a counter electrode lithium cell. Constant current charging was performed at 0.02 mA from the rest potential to 0.005 V. Next, the constant voltage charging was switched to 0.005 V, and the constant current charging and the constant voltage charging were charged for 40 hours in total, and the initial charge capacity (a) was measured.

A constant current discharge was performed at 0.2 mA with an upper limit voltage of 1.5 V, and the initial discharge capacity (b) was measured.
The value obtained by expressing the initial discharge capacity (b) / initial charge capacity (a) as a percentage, that is, 100 × (b) / (a) was defined as the initial coulomb efficiency.
[3-2] Measurement of reference capacity A test was conducted in a constant temperature bath set at 25 ° C. using a bipolar cell. After charging the cell with a constant current of 0.2C (the current value for discharging a fully charged battery in 1 hour is 1C, the same applies hereinafter) with the upper limit voltage of 4V, the cutoff current value is 0.85mA and the constant voltage is 4V. I charged it. Then, constant current discharge was performed at a lower limit voltage of 2 V and 0.2 C. The above operation was repeated a total of four times, and the fourth discharge capacity was set as the reference capacity (c) of the bipolar cell.
[3-3] Measurement of high temperature cycle characteristics The test was conducted in a constant temperature bath set at 55 ° C. using a bipolar cell. For charging, constant current charging was performed at a constant current value of 85 mA (equivalent to 5C) with an upper limit voltage of 4 V from the rest potential, and then constant voltage charging was performed at a cutoff current value of 0.34 mA and 4 V.

Then, a constant current discharge was performed at 85 mA with a lower limit voltage of 2 V.
Under the above conditions, 500 cycles of charging and discharging were repeated, and the high temperature cycle discharging capacity (d) was measured. The high temperature cycle discharge capacity (d) measured under the above conditions / the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (d) / (c) was defined as the high temperature cycle capacity retention rate.
[3-4] Measurement of internal resistance (DC-IR) The test was conducted in a constant temperature bath set at 25 ° C. A constant current discharge was performed at 0.1 C from a fully charged state to 50% of the fully charged capacity. After a 30-minute rest, the internal resistance (DC-IR) (e) of the bipolar cell was determined by Ohm's law (R = ΔV / 0.017) from the amount of voltage drop when 17 mA was discharged for 5 seconds.
[3-5] Measurement test of high temperature storage / recovery characteristics Using a bipolar cell, a test was conducted in a constant temperature bath set at 25 ° C. for both charging and discharging. The cell was charged at a constant current of 0.2 C with an upper limit voltage of 4 V, and then charged at a constant voltage of 4 V with a cutoff current value of 0.34 mA. The charged cell was allowed to stand in a constant temperature bath set at 60 ° C. for 4 weeks, and then discharged at a constant current of 0.2 C at a lower limit voltage of 2 V to measure the discharge capacity. This discharge capacity was defined as the high temperature storage capacity (f). The high temperature storage capacity (f) with respect to the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (f) / (c) was defined as the value of the high temperature holding characteristic.

After measuring the storage capacity, the cell was charged at a constant current of 0.2 C with an upper limit voltage of 4 V, and then charged at a constant voltage of 4 V with a cutoff current value of 0.34 mA. Then, a constant current discharge was performed at a lower limit voltage of 2 V and 0.2 C, and the discharge capacity was measured. This discharge capacity was defined as the high temperature recovery capacity (g). The high temperature recovery capacity (g) with respect to the reference capacity (c) of the bipolar cell was expressed as a percentage, that is, 100 × (g) / (c) was taken as the value of the high temperature recovery characteristic.
[3-6] Low temperature charge / discharge rate measurement A test was conducted using a bipolar cell. The cell was constantly charged at 0.2 C with an upper limit voltage of 4 V in a constant temperature bath set at 25 ° C., and then charged at a constant voltage of 4 V with a cutoff current value of 0.34 mA. The charged cell was discharged with a constant current at a lower limit voltage of 2V and 1C in a constant temperature bath set at −20 ° C., and the discharge capacity was measured. This discharge capacity was defined as the low temperature discharge capacity (h). The value of the low temperature discharge capacity (h) with respect to the reference capacity (c) of the bipolar cell expressed as a percentage, that is, 100 × (h) / (c) was taken as the value of the low temperature discharge rate characteristic.

After measuring the low temperature discharge capacity, the temperature inside the constant temperature bath was returned to 25 ° C., and constant current discharge was performed at a lower limit voltage of 2 V and 0.2 C. The cell was charged at a constant current of 1C with an upper limit voltage of 4V in a constant temperature bath set at −20 ° C., and then charged with a constant voltage of 4V with a cutoff current value of 0.34mA, and the charging capacity was measured. This charging capacity was defined as the low temperature charging capacity (i). The low temperature charge capacity (i) with respect to the reference capacity (c) of the bipolar cell was defined as a percentage value, that is, 100 × (i) / (c) was defined as the value of the low temperature charge rate characteristic.
[4] Raw material Carbon particles (A)
[Graphite particles (SCMG®)]
Showa Denko KK, 50% particle size (D50): 6.0 μm, BET specific surface area: 5.9 m ² / g, Raman R value 0.10, solid structure.

[Silicon-containing graphite particles (SiG)]
65 parts by mass of SCMG (registered trademark), 13 parts by mass of silicon fine particles (D50 = 100 nm), and 32 parts by mass of petroleum-based pitch (10 μm, residual coal ratio 70%) are mixed, fired at 1000 ° C. in a nitrogen atmosphere, and then pulverized. I got it. This SiG had a D50 of 10.0 μm, a BET specific surface area of 3.0 m ² / g, a Raman R value of 0.36, and a silicon content of 13 wt%.

Raw material of carbonaceous coating layer (B1): Carbonaceous coating material shown in Tables 1 and 2.
Carbon fine particles (B2): carbon black (manufactured by TIMCAL, SUPER C65), BET specific surface area: 62 m ² / g, average particle size of primary particles: 50 nm (measured by the above SEM observation).
Examples 1-26, Comparative Examples 1-22, 26, 27:
In each Example and each Comparative Example, the raw materials and ratios shown in Tables 1 and 2 were put into a multipurpose mixer (manufactured by Nippon Coke Industries Co., Ltd.), and dry mixing was performed at room temperature for 10 minutes. The mixture was heat-treated in an electric tubular furnace for 1 hour at the temperatures shown in Tables 1 and 2 under a nitrogen gas atmosphere to obtain composite carbon particles or carbon particles. In addition, in Tables 1 and 2, "none" in the column of the heat treatment step means that the corresponding heat treatment step is not performed.

Various physical properties of the obtained composite carbon particles were measured. In addition, a battery was prepared and evaluated using the obtained composite carbon particles. The results are shown in Tables 3-6.
SEM photographs of the composite carbon particles obtained in Examples 5 and 7 and Comparative Examples 5 and 9 are shown in FIGS. 1 to 4, respectively. The R value imaging results of the composite carbon particles obtained in Example 5 and Comparative Example 5 are shown in FIGS. 5 and 6, respectively. In R-value imaging, the absence of shading indicates that the variation in R-value is small (the coefficient of variation is small).
Comparative Examples 23-25, 28:
Nitrogen gas containing 0.05 g / L of benzene was introduced into the fluid reaction reactor at 1 L / min, and the mixture of carbon particles (A) and carbon fine particles (B2) was in a fluid state at 900 ° C. for the time shown in Table 2. Chemical Vapor Deposition (CVD) treatment was performed. The amount of benzene used in the CVD treatment was 1 to 5% by mass.

For the obtained composite carbon particles, various physical properties were measured in the same manner as in the examples, and a battery was manufactured. The results are shown in Tables 4 and 6.

The composite carbon particles of the examples are composite carbon particles including the carbon particles (A) and the carbonic coating layer (B) that coats the surface thereof, and the carbonic coating layer (B) is the carbonic coating layer (B1). ) And carbon fine particles (B2), and has one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower in differential thermal analysis in air. It can be seen that the results of the battery evaluation of each example are superior to those of the comparative example.

As is clear from the comparison between Examples and Comparative Examples 1 and 2, one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower in the differential thermal analysis in air. The composite carbon particles having a peak have well-balanced improvement in high temperature characteristics and low temperature characteristics as compared with carbon particles having only one peak at 620 ° C. or higher and 1000 ° C. or lower.

As is clear from the comparison between Examples 2, 5 and 8 and Comparative Example 3, one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower in the differential thermal analysis in air. The composite carbon particles having the peak of 620 ° C. or higher and 1000 ° C. or lower are superior in all of the initial Coulomb efficiency, high temperature characteristics and low temperature characteristics as compared with the composite carbon particles having only two peaks.

As is clear from the comparison between Examples 1, 4 and 7 and Comparative Example 7, one peak at 200 ° C. or higher and lower than 620 ° C. and two peaks at 620 ° C. or higher and 1000 ° C. or lower in the differential thermal analysis in air. The composite carbon particles having the above peaks are superior in low temperature characteristics to the composite carbon particles having one peak at 200 ° C. or higher and lower than 620 ° C. and one peak at 620 ° C. or higher and 1000 ° C. or lower.

As is clear by comparing Examples 1 to 3 and Comparative Examples 4 to 6, one peak at 200 ° C. or higher and lower than 620 ° C. and 620 ° C. or higher and 1000 ° C. or lower in the differential thermal analysis in air. Composite carbon particles having two or more peaks are superior to composite carbon particles having three peaks at 620 ° C. or higher and 1000 ° C. or lower in terms of initial Coulomb efficiency and high temperature characteristics.

Even if the carboxylic acid compound is used, if the amount is too small, it does not have one peak at 200 ° C. or higher and lower than 620 ° C., and the effect of using the carboxylic acid compound is not sufficiently exhibited (Comparative Examples 8, 9 and 10).

Composite carbon particles using a compound that does not contain a predetermined carboxy group or hydroxy group as a carbonaceous coating material do not have a peak at 200 ° C or higher and lower than 620 ° C in differential thermal analysis in air, and have battery characteristics at high temperatures. Is inferior (Comparative Examples 11 to 14). Composite carbon particles using both a carboxylic acid compound and pitch as the carbonaceous coating also do not have a peak at 200 ° C. or higher and lower than 620 ° C. in differential thermal analysis in air, and the battery characteristics at high temperatures are inferior. (Comparative Examples 15 to 22). Further, in this case, since the coefficient of variation of the R value is large, the coating is non-uniform and the coating effect is not sufficiently obtained. When the coating is performed by the CVD treatment, the differential thermal analysis in air is performed. It does not have one peak at 200 ° C. or higher and lower than 620 ° C., and it is difficult to control the carbonaceous coating layer thinly and uniformly with respect to particles having large irregularities such as carbon particles, and the battery characteristics at high temperature. Is not sufficient (Comparative Examples 23 to 25, 28).

When pitch, which is soft carbon, and PVA (polyvinyl alcohol) resin, which is hard carbon, are used simultaneously as the coating layer forming material as the carbonaceous coating material, the differential thermal analysis in air differs between 625 ° C, 650 ° C, and 886 ° C. A differential thermal peak is observed, and both high temperature characteristics and low temperature characteristics are not sufficient (Comparative Example 26).

As is clear from comparing Examples 25 and 26 with Comparative Example 27, even when silicon-containing graphite carbon particles (SiG) are used as the carbon particles (A), a graphene layer and carbon fine particles (B2) are formed on the surface. The composite carbon particles in which the carbonic coating layer (B) containing the above is formed are the composite carbon particles in which the carbonic coating layer (B) containing the amorphous layer and the carbon fine particles (B2) is formed on the surface of the carbon particles (A). Compared to, it is excellent in initial cooling efficiency and high temperature characteristics.

Claims (19)

1. It is a composite carbon particle containing a carbon particle (A) and a carbon coating layer (B) covering the surface thereof, and the carbon coating layer (B) is composed of a carbon coating layer (B1) and carbon fine particles (B2). A composite carbon particle containing, and having one peak at 200 ° C. or higher and lower than 620 ° C. and two or more peaks at 620 ° C. or higher and 1000 ° C. or lower in differential thermal analysis (DTA) in air.
2. Coefficient of variation of R values measured by Raman spectroscopy (ratio (ID / IG) of 1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG)) is 0.50 or less The composite carbon particle according to claim 1.
3. R value measured by Raman spectroscopy (ratio of 1350 cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG) (ID / IG) ) is 0.10 to 1.50 The composite carbon particle according to claim 1 or 2.
4. The composite carbon particles according to any one of claims 1 to 3, wherein the average surface spacing d002 of the (002) planes measured by the X-ray diffraction method is 0.3354 nm or more and 0.3370 nm or less.
5. Is 50% particle size (D50) of the 1.0μm or 50.0μm or less in volume-based cumulative particle size distribution by laser diffraction method, it is 400 times the tapping density of 0.30 g / cm ³ or more 1.50 g / cm ³ or less The composite carbon particle according to any one of claims 1 to 4.
6. The composite carbon particles according to any one of claims 1 to 5, wherein the BET specific surface area is 0.1 m ² / g or more and 40.0 m ² / g or less.
7. The composite carbon particle according to any one of claims 1 to 6, wherein (BET specific surface area of the composite carbon particle) / (BET specific surface area of the carbon particle (A)) is 0.30 or more and 10.00 or less.
8. Wherein the ratio of the composite carbon particles and the carbon particles R value measured by Raman spectroscopy of (A) (1350cm ^-1 vicinity of the peak intensity (ID) and 1580 cm ^-1 vicinity of the peak intensity (IG) (ID / IG))) ((R value of composite carbon particles) / (R value of carbon particles (A))) is 1.50 or more and 20.00 or less according to any one of claims 1 to 7. Composite carbon particles.
9. The composite carbon particle according to any one of claims 1 to 8, wherein the carbon particle (A) is a graphite particle.
10. The composite carbon particle according to any one of claims 1 to 9, wherein the carbon particle (A) contains silicon.
11. The composite carbon particle according to any one of claims 1 to 10, wherein the average particle size of the primary particles of the carbon fine particles (B2) is 10 nm or more and 500 nm or less, and the maximum value of the secondary particle diameter is 1000 nm or less.
12. The composite carbon particles according to any one of claims 1 to 11, wherein the carbonaceous coating layer (B1) has a thickness of 0.1 nm or more and 30.0 nm or less.
13. The composite carbon particles according to any one of claims 1 to 12, wherein the carbonaceous coating layer (B1) includes a single-layer graphene layer or a multi-layer graphene layer.
14. The method for producing composite carbon particles according to any one of claims 1 to 13.
    70.0 parts by mass or more and 99.89 parts by mass or less of carbon particles (A), 0.1 parts by mass or more and 20.0 parts by mass or less of a hydroxycarboxylic acid compound having at least one carboxy group and one or more hydroxy groups, and carbon The ratio of the fine particles (B2) to 0.01 parts by mass or more and 10.0 parts by mass or less (however, the total of the carbon particles (A), the hydroxycarboxylic acid compound, and the carbon fine particles (B2) is 100 parts by mass. A method for producing composite carbon particles, which comprises a step of heat-treating the mixture contained in.).
15. The method for producing composite carbon particles according to any one of claims 1 to 13.
    70.0 parts by mass or more and 99.89 parts by mass or less of carbon particles (A), 0.1 parts by mass or more and 20.0 parts by mass or less of a polycarboxylic acid compound having two or more carboxy groups without having a hydroxy group, And the ratio of carbon fine particles (B2) to 0.01 parts by mass or more and 10.0 parts by mass or less (however, the total of the carbon particles (A), the polycarboxylic acid compound, and the carbon fine particles (B2) is 100 parts by mass. A method for producing composite carbon particles, which comprises a step of heat-treating the mixture contained in (1).
16. The method for producing composite carbon particles according to any one of claims 1 to 13.
    A hydroxycarboxylic acid compound having 70.0 parts by mass or more and 99.89 parts by mass or less of carbon particles (A), each having one or more carboxy groups and one or more hydroxy groups, and a polycarboxylic acid having no hydroxy groups and having two or more carboxy groups. The total proportion of the acid compound is 0.1 parts by mass or more and 20.0 parts by mass or less, and the carbon fine particles (B2) are 0.01 parts by mass or more and 10.0 parts by mass or less (however, with the carbon particles (A)). A method for producing composite carbon particles, which comprises a step of heat-treating a mixture containing the hydroxycarboxylic acid compound, the polycarboxylic acid compound, and the carbon fine particles (B2) in an amount of 100 parts by mass.).
17. A negative electrode active material containing the composite carbon particles according to any one of claims 1 to 13.
18. A negative electrode containing the negative electrode active material and a current collector according to claim 17.
19. A lithium ion secondary battery using the negative electrode according to claim 18.

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