WO2021241749A1

WO2021241749A1 - Carbon–silicon composite

Info

Publication number: WO2021241749A1
Application number: PCT/JP2021/020498
Authority: WO
Inventors: 雅人藤田; 鎭碩白; 祐司伊藤; 浩文井上
Original assignee: 昭和電工株式会社
Priority date: 2020-05-28
Filing date: 2021-05-28
Publication date: 2021-12-02
Also published as: JP2021187733A

Abstract

This carbon–silicon composite includes a carbonaceous material and silicon, wherein: a carbon–silicon composite with a cylindrical shape is included; the average diameter is at least 5 μm and no greater than 30 μm; the average length is at least 1 μm and less than 50 μm; in a DTA curve produced by DTA measurement in air, an exothermic peak is present at 800°C or below; in a Raman spectrum, a peak produced by silicon is present at 450–495 cm⁻¹; the ratio ISi/IG of the intensity ISi of the peak produced by silicon and the intensity IG of a G band is 0.35 or less; and the half-width of a peak produced by the 111 plane of silicon in an XRD pattern utilizing the Cu–Kα line is at least 3.0 degrees. This carbon–silicon composite enables manufacturing of products in a short period of time, which leads to conservation of silicon sources. Moreover, when this carbon–silicon composite is used as a negative electrode material in a lithium ion secondary battery, the battery will have excellent cycle characteristics.

Description

Carbon-silicon complex

The present invention relates to a carbon-silicon composite having a columnar shape (hereinafter, also referred to as a composite), a negative electrode active material containing the carbon-silicon composite, a negative electrode mixture layer containing the negative electrode active material, and the negative electrode. The present invention relates to a lithium ion secondary battery including a mixture layer.

Secondary batteries used in IT equipment such as smart phones and tablet PCs, vacuum cleaners, electric tools, electric bicycles, drones, and automobiles require negative electrode active materials that have both high capacity and high output. As a negative electrode active material, silicon (theoretical specific capacity: 4200 mAh / g) having a higher theoretical specific capacity than graphite (theoretical specific capacity: 372 mAh / g) currently used is attracting attention.

However, the volume of silicon (Si) expands and contracts up to about 3 to 4 times with the electrochemical insertion and desorption of lithium. It is known that a lithium ion secondary battery using silicon has extremely low cycle characteristics because the silicon particles self-destruct or peel off from the electrode due to this. For this reason, it is currently being actively studied to use silicon as a whole with a structure in which the degree of expansion and contraction is reduced, instead of simply replacing it with graphite. Among them, many attempts have been made to combine with carbonaceous materials.

As a negative electrode active material having a high capacity and a long life, a method of producing silicon in the pores of the porous carbon by exposing the porous carbon particles to silane gas at a high temperature (Special Table 2018-534720; Patent Document 1). The silicon-carbon composite material obtained by is disclosed.

Special Table 2018-534720 Gazette Publication of Patent Application No. 2012-11079 Publication of patent application 2010-525549

In Patent Document 1, porous carbon is often in the form of particles. The preferred particle shape has not been discussed. Regarding the pore distribution, since the proportion of micropores is small, it is expected that it will take a long time to impregnate the desired silicon. Since the carbon fibers in the negative electrode active materials of Patent Documents 2 and 3 do not have pores, it is expected that the durability against expansion and contraction of silicon will be inferior.

In the present invention, the problems to be solved are the saving of the silicon raw material at the time of manufacturing the carbon-silicon composite and the improvement of the cycle characteristics in the lithium ion secondary battery.

In the present invention, a carbon-silicon composite is prepared by performing CVD with a silicon-containing gas using a columnar carbonaceous material and precipitating silicon on the surface and pores of the carbonaceous material. Was solved.

That is, the present invention includes the following configurations [1] to [13].
[1] A carbon-silicon complex containing a carbonaceous material and silicon.
Contains a carbon-silicon complex with a columnar shape,
The average diameter is 5 μm or more and 30 μm or less.
The average length is 1 μm or more and less than 50 μm.
In the DTA curve measured by DTA in air, the exothermic peak exists below 800 ° C.
In the Raman spectrum, the peak due to Si ^{exists at 450 to 495 cm -1} , and the ratio of the intensity ISi of the peak due to Si to the intensity IG of the G band, ISi / IG is 0.35 or less.
In the XRD pattern using Cu-Kα rays, the half width of the peak due to the 111 planes of Si is 3.0 deg. That's it,
Carbon-silicon complex.
[2] The adsorption performance of the carbonaceous material reaches 100% within an elapsed time of 200 min when the equilibrium adsorption performance of the weight increment per weight of the carbonaceous material is set to 100% in the adsorption performance test. 1] The carbon-silicon composite.
[3] The carbon-silicon complex according to [1] or [2], wherein the 90% particle size DV90 in the volume-based cumulative particle size distribution is 50 μm or less.
[4] A carbon-silicon complex containing a carbonaceous material and silicon.
In the Raman spectrum, the peak due to Si ^{exists at 450 to 495 cm -1} , and the ratio of the intensity ISi of the peak due to Si to the intensity IG of the G band, ISi / IG is 0.35 or less.
In the XRD pattern using Cu-Kα rays, the half width of the peak due to the 111 planes of Si is 3.0 deg. That's all
The 90% particle size DV90 in the volume-based cumulative particle size distribution is 50 μm or less.
The adsorption performance of the carbonaceous material reaches 100% within an elapsed time of 200 min when the equilibrium adsorption performance of the weight increment per weight of the carbonaceous material is set to 100% in the adsorption performance test.
Carbon-silicon complex.
[5] The carbon-silicon complex according to any one of [1] to [4], wherein the 10% particle size DV10 in the volume-based cumulative particle size distribution is 2.0 μm or more.
[6] The carbon-silicon complex according to any one of [1] to [5], which has a BET specific surface area of 50 m ^{2 / g or less.}
[7] The carbon-silicon complex according to any one of [1] to [6], which has an oxygen content of 10% by mass or less.
[8] The carbon-silicon complex according to any one of [1] to [7], wherein the silicon content is 10% by mass or more and less than 70% by mass.
[9] The carbonaceous material has a pore volume of 0.30 cm ³ / g or more, a ratio of the volume of micropores to the volume of all pores is 90% or more, and occupies the volume of all pores. The carbon-silicon composite according to any one of [1] to [8], which has a pore distribution in which the ratio of the sum of the volumes of the meso pores and the macro pores is less than 10%.
[10] The carbonaceous composite according to any one of [1] to [9], wherein the carbonaceous material has an R value of 0.30 or more and 1.30 or less in the Raman spectrum.
[11] The negative electrode active material containing the carbon-silicon complex according to any one of [1] to [10].
[12] A negative electrode mixture layer containing the negative electrode active material according to [11].
[13] A lithium ion secondary battery including the negative electrode mixture layer according to [12] The present invention also includes the following configurations [1a] to [14a].
[1a]
A carbon-silicon complex containing carbonaceous materials and silicon,
It has a columnar shape and has a columnar shape.
The average diameter is 5 μm or more and 30 μm or less.
The average length is 1 μm or more and less than 50 μm.
In the DTA curve measured by DTA in air, the exothermic peak exists below 800 ° C.
In the Raman spectrum
The peak due to Si exists at 450 to 495 cm-1,
The ratio ISi / IG of the intensity ISi of the peak due to Si and the intensity IG of the G band is 0.35 or less.
In the XRD pattern using Cu-Kα rays, the half width of the peak due to the 111 planes of Si is 3.0 deg. That's it,
Carbon-silicon complex.
[2a]
The carbon-silicon complex according to the preceding item [1a], which has a BET specific surface area of 50 m ^{2 / g or less.}
[3a]
The carbon-silicon complex according to the preceding item [1a] or [2a], wherein the 10% particle size (DV10) is 3.0 μm or more and the 90% particle size (DV90) is 50 μm or less in the volume-based cumulative particle size distribution.
[4a]
The carbon-silicon complex according to any one of the above items [1a] to [3a], which has an oxygen content of 10% by mass or less.
[5a]
The carbon-silicon complex according to any one of the above items [1a] to [4a], wherein the silicon content is 10% by mass or more and less than 70% by mass.
[6a]
The carbonaceous material reaches 100% within an elapsed time of 200 min when the equilibrium adsorption performance of the weight increment per weight of the carbonaceous material is set to 100% in the adsorption performance test. The carbon-silicon composite according to any one of [5a].
[7a]
The carbonaceous material has a pore volume of 0.30 cm ³ / g or more, an average pore diameter of 0.40 to 5.0 nm, and a ratio of micropores to all pores of 92% or more. The carbon-silicon complex according to any one of the preceding items [1a] to [6a], which has a pore distribution in which the ratio of the sum of the meso pores and the macro pores is less than 8%.
[8a]
The carbonaceous material according to any one of the above items [1a] to [7a], wherein the carbonaceous material has an R value of 0.3 or more and 1.3 or less in the Raman spectrum.
[9a]
A method for producing a carbon-silicon complex, which comprises the following steps (A) and (B).
Step (A): A columnar shape having an average diameter of 5 μm or more and 30 μm or less, an average length of 1 μm or more and less than 50 μm, and an exothermic peak of 800 ° C. or less in the DTA curve measured by DTA in air. Step of preparing the existing carbonaceous material Step (B): A step of allowing a silicon-containing gas to act on the heated carbonaceous material to precipitate silicon in the pores and on the surface of the carbonaceous material [10a].
According to the above item [9a], the carbonaceous material reaches 100% within an elapsed time of 200 min when the equilibrium adsorption performance of the weight increment per weight of the carbonaceous material is set to 100% in the adsorption performance test. The method for producing a carbon-silicon composite according to the above.
[11a]
The carbonaceous material has a pore volume of 0.3 cm ³ / g or more, an average pore diameter of 0.4 to 5.0 nm, and a ratio of micropores to all pores of 92% or more. The method for producing a carbon-silicon composite according to the above item [9a] or [10a], which has a pore distribution in which the ratio of the sum of the mesopores and the macropores is less than 8%.
[12a]
The method for producing a carbon-silicon composite according to any one of claims [9a] to [11a], wherein the carbonaceous material has an R value of 0.3 or more and 1.3 or less in the Raman spectrum.
[13a]
An electrode mixture layer containing the carbon-silicon complex and graphite particles according to any one of the above items [1a] to [8a].
[14a]
A lithium ion secondary battery including the electrode mixture layer according to the preceding item [13a].

The carbon-silicon complex of the present invention can produce a product in a short time, which leads to saving of a silicon source. Further, when used as a negative electrode active material of a lithium ion secondary battery, it has excellent cycle characteristics.

FIG. 1 is a scanning electron microscope (SEM) photograph of the carbon-silicon composite produced in Example 1.

Hereinafter, embodiments of the present invention will be described.
[1] Carbon-Silicon Composite The carbon-silicon composite according to the present invention is composed of a carbonaceous material and silicon deposited on its surface and in pores.

The complex preferably contains a complex having a columnar shape. As used herein, the term "cylindrical" includes the shape of a cylinder or elliptical column having a fractured surface at the bottom surface. FIG. 1 shows an example of the carbon-silicon composite of the present invention having a columnar shape. Such a shape can be confirmed by SEM. The average diameter of the complex is preferably 5 μm or more, more preferably 7 μm or more, still more preferably 10 μm or more. This is because if the average diameter of the complex is 5 μm or more, side reactions with the electrolytic solution can be reduced.

The average diameter of the complex is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. This is because if the average diameter of the complex is 30 μm or less, an electrode slurry having good coatability can be prepared.

In the present specification, the average diameter of the complex is defined as follows. In the image taken by a scanning electron microscope (SEM), the particles of the complex are regarded as a broken right-sided cylinder consisting of a bottom surface and a side surface formed by a fracture surface. The average diameter is measured for particles that are found to be substantially parallel to the SEM image plane in the height direction of the right cylinder. In the SEM image, two points where the straight line drawn in the direction of 90 ° with respect to the height direction of the right cylinder of the particle and the two contour lines formed by the side surfaces of the particle intersect are defined as P and Q. The length of the line segment PQ is measured at 10 different points per particle, and the average value is taken as the diameter of the composite particle. This is measured for 10 particles, and the value obtained by averaging these diameters is taken as the average diameter of the complex particles.

The average length of the complex is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. This is because if the average length of the complex is 1 μm or more, side reactions with the electrolytic solution can be reduced.

The average length of the complex is preferably less than 50 μm, more preferably 40 μm or less, still more preferably 30 μm or less. This is because if the average length of the complex is less than 50 μm, an electrode slurry having good coatability can be prepared, and the density of the electrodes can be easily increased.

In the present specification, the average length of the complex is defined as follows. In the image obtained by a scanning electron microscope (SEM), the average length is measured for the particles whose height direction of the right cylinder is recognized to be substantially parallel to the SEM image plane. In the SEM image, the lengths of the two contour lines formed by the side surfaces of the particles are measured, and the average value of the two lengths is taken as the length of the complex particle. This is measured for 10 particles, and the value obtained by averaging these lengths is taken as the average length of the complex particles.

The average diameter and average length of the complex can be measured by analyzing the image observed by SEM with image analysis software such as ImageJ (manufactured by the National Institutes of Health).

In the carbon-silicon composite according to the present invention, it is preferable that the exothermic peak appears at 800 ° C. or lower in the DTA curve measured by DTA in air. This is because when the temperature at which the exothermic peak appears is 800 ° C. or lower, the carbonaceous material has no crystal and has a surface on which silicon is easily supported. From this viewpoint, it is more preferable that the exothermic peak in the DTA measurement appears at 750 ° C. or lower, and further preferably at 700 ° C. or lower.

The DTA measurement can be performed by, for example, a TG-DTA device known in the art.
The carbon-silicon complex according to the present invention has a peak due to silicon (Si) in the Raman spectrum at 450 to 495 cm ^-1 . The intensity of the peak appearing at ^{450 to 495 cm -1} due to silicon is referred to as ISi. Normally, crystalline silicon when there is a peak in the 450 ~ 495cm ^-1 since the peak appears in the vicinity of 520 cm ^-1, the carbon - silicon complex indicates that it has an amorphous silicon. When silicon is amorphous, expansion and contraction during charging and discharging are performed relatively isotropically, so that the cycle characteristics can be improved.

The carbon-silicon composite according to the present invention has a ratio ISi / IG of the intensity ISi of the peak due to the silicon and the intensity IG of the G band according to the Raman spectrum of 0.35 or less. The appearance of the silicon peak in the Raman spectrum indicates that silicon is precipitated in the pores on or near the surface of the carbon-silicon complex. When this value is 0.35 or less, it indicates that the amount of silicon deposited on the surface is small and the amount of silicon in the carbon pores near the surface of the complex is small. This leads to an improvement in cycle characteristics in that the proportion of silicon that comes into direct contact with the electrolytic solution is reduced. The ISi / IG is preferably 0.30 or less, more preferably 0.25 or less.

The intensity of the peak is the height from the baseline to the peak top.
The G band in the Raman spectrum is the ^{peak appearing near 1600 cm -1} obtained when the carbonaceous material is measured, and the D band is the peak near ^{1350 cm -1} obtained when the carbonaceous material is also measured. That is.

The carbon-silicon composite according to the present invention has a half-value width of the peak on the 111th surface of Si of 3.0 deg in the XRD pattern measured by powder XRD using Cu-Kα rays. That is all. The half width of the peak on the 111th surface of Si is 3.0 deg. As a result, the size of the crystallite becomes small, which leads to the suppression of the destruction of the silicon region due to charging / discharging. From the same viewpoint, the half width is 4.0 deg. The above is preferable, and 5.0 deg. The above is more preferable.

The carbon-silicon complex according to the present invention preferably has a BET specific surface area of 50 m ² / g or less. This is because having such a BET specific surface area can reduce side reactions with the electrolytic solution. From this viewpoint, the BET specific surface area is ^{more preferably 30 m 2} / g or less, and further preferably 20 m ² / g or less.

The BET specific surface area is usually measured by a dedicated measuring device known in the art. Nitrogen is usually used as the adsorbed gas, but carbon dioxide, argon, or the like may also be used.

The carbon-silicon composite according to the present invention preferably has a 10% particle size and a DV10 of 2.0 μm or more in a volume-based cumulative particle size distribution. This is because when the DV10 is 2.0 μm or more, the side reaction with the electrolytic solution can be reduced. Further, the powder has excellent handleability, it is easy to prepare a slurry having a viscosity and a density suitable for coating, and it is easy to increase the density when it is used as an electrode. From this viewpoint, the DV10 is more preferably 3.5 μm or more, and further preferably 4.0 μm or more.

The carbon-silicon composite according to the present invention preferably has a 90% particle size and a DV90 of 50 μm or less in a volume-based cumulative particle size distribution. When the DV90 is 50 μm or less, the diffusion length of lithium in each particle is shortened, so that the rate characteristics of the lithium ion battery are excellent, and when the slurry is applied to the current collector, streaks and abnormal unevenness are obtained. Does not occur. From this point of view, the DV90 is more preferably 40 μm or less, and further preferably 30 μm or less. These volume-based cumulative particle size distributions are measured, for example, by a laser diffraction type particle size distribution meter.

The silicon-carbon complex preferably has an oxygen content of 10% by mass or less. When the oxygen content in the complex is 10% by mass or less, the irreversible capacity of the negative electrode active material for the lithium ion secondary battery can be reduced. From the same viewpoint, the oxygen content is preferably 9% by mass or less, more preferably 8% by mass or less. The lower limit of the oxygen content is not particularly limited, but is preferably 0% by mass, more preferably 0.5% by mass.

The oxygen content in the silicon-carbon complex can be measured by, for example, an oxygen-nitrogen simultaneous measuring device.
The carbon-silicon composite according to the present invention preferably has a silicon content of 10% by mass or more and less than 70% by mass. When the silicon content is 10% by mass or more, it is possible to obtain a specific volume of about 600 mAh / g or more in calculation, which greatly exceeds the theoretical specific volume of graphite. From this viewpoint, the content is more preferably 20% by mass or more, further preferably 30% by mass or more.

Since the carbonaceous composite according to the present invention has a silicon content of less than 70% by mass, the carbonaceous material as a carrier can absorb the volume change due to expansion and contraction. From this viewpoint, the content is more preferably 65% by mass or less, and further preferably 60% by mass or less.

The silicon content in the carbon-silicon complex can be determined by the fundamental parameter method (FP method) or the like in the fluorescent X-ray analyzer.
[2] Carbonaceous Material The carbonaceous material used as a raw material for the carbon-silicon composite according to the present invention is preferably a porous carbonaceous material. The porous carbonaceous material is a carbonaceous material having a total pore volume of 0.2 cm ³ / g or a BET specific surface area of 200 m ² / g or more per 1 g. The adsorption performance is such that the toluene saturated vapor pressure at 25 ° C. is at a flow rate of 0.12 L / min, the pressure is atmospheric pressure +2.5 (± 0.1) kpa, and the weight is 1.000 g (± 0.001 g). When the equilibrium adsorption performance of weight increment per sample weight is set to 100%, it is preferable that the adsorption performance reaches 100% within an elapsed time of 200 min. A porous carbonaceous material having such adsorption performance is preferable because the adsorption rate of silane is high and a large amount of silicon can be supported inside the pores, for example, in CVD using a monosilane-containing gas. From the same viewpoint, it is more preferable that the adsorption performance reaches 100% within 185 min, and it is further preferable that the adsorption performance reaches 100% within 170 min.

The carbonaceous material used as the raw material of the carbon-silicon composite according to the present invention preferably has a total pore volume of 0.30 cm ³ / g or more per gram. When the total pore volume is 0.30 cm ³ / g or more, the expansion / contraction of the entire complex due to the insertion / desorption of lithium is reduced in the material in which silicon is precipitated. From this point of view, the total pore volume having a the carbonaceous material is more preferably 0.33 cm ³ / g or more, more preferably 0.35 cm ³ / g or more.

The carbonaceous material used as the raw material of the carbon-silicon composite according to the present invention preferably has a ratio of micropores in all pores of 90% or more and a total ratio of mesopores and macropores of less than 10%. With such a pore distribution, the adsorption of silicon-containing gas such as silane gas proceeds rapidly. Further, since fine silicon having better cycle characteristics is deposited, a negative electrode active material having excellent cycle characteristics can be produced. From this viewpoint, the ratio of the micropores is more preferably 93% or more, and even more preferably 94% or more. The total ratio of the meso pores and the macro pores is more preferably 8% or less, further preferably 5% or less.

Macropores are pores with a pore diameter of 50 nm or more and 100 nm or less. Mesopores are pores with a pore diameter larger than 2 nm and smaller than 50 nm. Micropores are pores having a pore diameter of 2 nm or less. The micropore ratio is a value obtained by dividing the pore volume of micropores calculated by the NLDFT method by the pore volume of 0 to 100 nm or less calculated by the NLDFT method, and multiplying by 100. Indicated by the formula.

Micropore ratio =
100 × (micropore pore volume calculated from NLDFT method) / (pore volume calculated from 0 to 100 nm or less calculated from NLDFT method)
The total ratio of mesopores and macropores is calculated from the NLDFT method by subtracting the value obtained by subtracting the micropore pore volume calculated from the NLDFT method from the pore volume of 0 to 100 nm or less calculated by the NLDFT method. It is a value obtained by multiplying the value divided by the pore volume from 0 to 100 nm or less by 100. That is, it is as follows.

Ratio of total of meso and macro holes =
100 × (pore volume of 0 to 100 nm or less calculated by NLDFT method-micropore pore volume calculated by NLDFT method) / (pore volume of 0 to 100 nm or less calculated by NLDFT method)
To investigate the pore distribution of the carbonaceous material, for example, the adsorption isotherm by the gas adsorption method is analyzed by a known method. Nitrogen is used as the adsorbed gas in the measurement in the present invention.

The carbonaceous material used as the raw material of the carbon-silicon composite according to the present invention has an R value (ID / IG) of 0.30 or more, which is the ratio of the intensity ID of the D band to the intensity IG of the G band according to the Raman spectrum. It is preferably 1.30 or less. When the R value is 0.30 or more, the negative electrode using this complex has a sufficiently low reaction resistance, which leads to an improvement in the rate characteristics of the battery. On the other hand, when the R value is 1.30 or less, it means that there are few defects in the carbonaceous layer. When the R value is 1.30 or less, side reactions are reduced and the Coulomb efficiency is improved. From the same viewpoint, the R value is more preferably 0.50 or more, and further preferably 0.70 or more. Further, the R value is more preferably 1.20 or less, and further preferably 1.10 or less.

Even after obtaining the carbon-silicon composite, by selecting appropriate conditions, silicon can be eluted and no effect can be left on the carbonaceous material as the carrier. This makes it possible to investigate the physical characteristics of the carbonaceous material as a raw material even from the state of the carbon-silicon complex. For example, the adsorption performance of toluene, the pore distribution, and the R value in the Raman spectrum can be investigated.

[3] Method for Producing Carbon-Silicon Composite The method for producing a carbon-silicon composite of the present invention is not particularly limited, and specifically, as described above, a fibrous porous carbonaceous material was obtained. Later, silane gas was added to the cylindrical porous carbon material in which a large number of micropores were formed from the side surface of the cylinder toward the central axis, which was obtained by crushing this fibrous porous carbon material and classifying it as necessary. A method of producing a carbon-silicon composite by precipitating silicon in the pores using the above method can be mentioned. In addition, after obtaining a fibrous porous carbonaceous material, silicon is precipitated in the pores of the porous carbonaceous material using silane gas without crushing or classification to obtain a carbon-silicon composite. Therefore, the carbon-silicon composite may be crushed and further classified according to need.

Here, the complex has been described by regarding it as a cylinder. The "central axis" of a cylinder is a line connecting the centers of circles between the bottom surfaces of the cylinder.
An example of a suitable method for producing a carbon-silicon composite according to the present invention includes the following steps (A) and (B).

Step (A): A columnar shape having an average diameter of 5 μm or more and 30 μm or less and an average length of 1 μm or more and less than 50 μm, and an exothermic peak in the DTA curve measured by DTA in air exists at 800 ° C. or less. The process of obtaining a carbonaceous material.

Step (B): A step of allowing a silicon-containing gas to act on a heated carbonaceous material to deposit silicon on the surface and pores of the carbonaceous material.
(Step (A))
In the step (A), the shape is a columnar shape having an average diameter of 5 μm or more and 30 μm or less, an average length of 1 μm or more and less than 50 μm, and an exothermic peak in DTA measurement exists at 800 ° C. or less. Under the conditions of pressure of 0.12 L / min, pressure of atmospheric pressure +2.5 (± 0.1) kpa, and weight of 1.000 g (± 0.001 g), the equilibrium adsorption performance of weight increment per sample weight is 100. The percentage is not particularly limited as long as a carbonaceous material having an adsorption performance of 100% can be obtained within an elapsed time of 200 min. Here, the definitions of the average diameter and the average length are the same as the definitions in the complex described above. As a method for producing such a carbonaceous material, for example, fibrous carbon is produced by pyrolyzing an organic compound or polymer into a fibrous form, and the obtained fibrous carbon is crushed. Be done. The physical characteristics of the fibrous carbon are appropriately adjusted depending on the type of the organic compound or polymer as a raw material, the conditions of thermal decomposition, and the conditions of oxidation treatment and activation treatment. Examples of fibrous carbon include carbon fiber and activated carbon fiber, and activated carbon fiber is particularly preferable.

Further, after activating the fibrous carbon to obtain a fibrous porous carbonaceous material having pores, the fibrous porous carbonaceous material is crushed and classified as necessary to obtain carbonaceous material. It is also preferable to obtain the material. When manufactured by such a method, it is possible to obtain a cylindrical porous carbonaceous material in which a large number of micropores are formed from the side surface of the cylinder toward the central axis. When such a carbonaceous material is used, when the silicon deposited in the pores expands and contracts due to the insertion and desorption of lithium, the expansion and contraction in the height direction of the cylinder depends on the skeleton of the activated carbon fiber. It is suppressed by stress. Further, since the pores extend in the direction from the central axis of the cylinder to the side surface, the volume of the expanded silicon can be released. As a result, it is considered that the size of the complex does not change so much and a negative electrode active material having excellent cycle characteristics can be obtained.

The equipment used for crushing is not limited, but it can be performed using commercially available crushers and crushers such as jet mills, hammer mills, roller mills, pin mills, and vibration mills. Further, it is also possible to use two or more types of these crushers and crush them in two stages.

The carbonaceous material has the characteristics described in the above [2] carbonaceous material, that is, the adsorption performance of toluene, the pore volume, the ratio of micropores, the total ratio of mesopores and macropores, and the R value of Raman spectrum. It is preferable to have.

(Step (B))
In the step (B), for example, when a carbonaceous material is placed in a chamber of a CVD apparatus and a silicon-containing gas is allowed to act on the carbonaceous material in a heated state, silane gas enters the inside of the pores of the carbonaceous material, which further becomes. A CVD step is preferred in which silicon can be deposited on the surface of the carbonaceous material or in the pores by thermal decomposition. As a method for this, for example, the apparatus and method shown in Patent Document 1 can be used.

Examples of the silicon-containing gas used include silane (SiH ₄ ) -containing gas, disilane-containing gas, and trisilane-containing gas, and silane-containing gas is preferable. Further, the silicon-containing gas may contain other gases, and for example, a gas such as nitrogen, argon, helium, or hydrogen may be mixed as the carrier gas. Various CVD conditions such as gas composition ratio, gas flow rate, temperature program, and selection of fixed bed / fluidized bed are appropriately adjusted while observing the nature of the product. If the silicon-containing gas is allowed to act on the heated carbonaceous material for too long, the silicon deposited on the surface increases and leads to deterioration of the electrode due to expansion and contraction. Therefore, the action time is 10 hours or less, and 7 hours or less. preferable.

For the carbon-silicon complex according to the present invention, the surface of the complex particles may be coated with carbon or a metal oxide. As such a method, for example, CVD with a carbonaceous gas, a method of adhering a carbon precursor such as an organic compound or a polymer compound to the surface of the composite, and then firing to form carbon, a metal oxide precursor. A method of forming a metal oxide particle or a metal oxide layer on the surface of the composite particle by utilizing thermal decomposition or a sol-gel reaction after adhering the compound to the surface of the particle can be mentioned.

[4] Negative electrode mixture layer The negative electrode mixture layer according to the present invention contains the carbon-silicon composite described in the above [1] as a negative electrode active material.

In the negative electrode mixture layer, the carbon-silicon complex functions as a negative electrode active material. The negative electrode mixture layer of the present invention can be used as a negative electrode mixture layer for a lithium ion secondary battery. The negative electrode mixture layer is generally composed of a negative electrode active material binder and a conductive auxiliary agent as an optional component.

As a method for producing the negative electrode mixture layer, for example, a known method as shown below can be used. A slurry for forming a negative electrode mixture is prepared using a negative electrode active material, a binder, a conductive auxiliary agent as an optional component, and a solvent. The slurry is applied to a current collector such as copper foil and dried. This is further vacuum dried and then roll pressed. The pressure during the roll press is usually 100 to 500 MPa. The obtained product may be referred to as a negative electrode sheet. The negative electrode sheet is obtained by pressing and consists of a negative electrode mixture layer and a current collector. Then cut or punch to the required shape and size.

In the present invention, a negative electrode sheet that has been adjusted to a size and shape to be incorporated in a lithium ion secondary battery and has a current collector tab attached to a current collector is referred to as a negative electrode in the present invention.
As the negative electrode active material, the carbon-silicon composite of the present invention may be used alone, but other negative electrode active materials may be used together. When other negative electrode active materials are used together, the complex is usually used by mixing the other negative electrode active materials. Examples of other negative electrode active materials include those generally used as negative electrode active materials for lithium ion secondary batteries. Examples thereof include graphite, hard carbon, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), alloy-based active materials such as silicon and tin, and composite materials thereof. These negative electrode active materials are usually in the form of particles. As the negative electrode active material other than the carbon-silicon composite, one kind may be used or two or more kinds may be used. Among them, graphite particles and hard carbon are particularly preferably used. One of the preferred embodiments of the negative electrode mixture layer of the present invention is that it contains a carbon-silicon complex and graphite particles.

As the binder, any binder generally used in the negative electrode mixture layer of the lithium ion secondary battery can be freely selected and used. For example, polyethylene, polypropylene, ethylene propylene tarpolymer, butadiene rubber, styrene butadiene rubber (SBR), butyl rubber, acrylic rubber, polyvinylidene fluoride (PVdF), polyvinylidene fluoride (PTFE), polyethylene oxide, polyepicrolhydrin, polyphospha. Examples thereof include zen, polyacrylonitrile, carboxymethyl cellulose (CMC) and salts thereof, polyacrylic acid, polyacrylamide and the like. One kind of binder may be used, or two or more kinds of binders may be mixed and used. The amount of the binder is preferably 0.5 to 30 parts by mass with respect to 100 parts by mass of the negative electrode active material.

The conductive auxiliary agent is not particularly limited as long as it serves to impart electron conductivity and dimensional stability (buffering action against volume change due to insertion / removal of lithium) to the electrode. For example, carbon nanotubes, carbon nanofibers, vapor phase carbon fibers (for example, "VGCF (registered trademark) -H" manufactured by Showa Denko Co., Ltd.), conductive carbon black (for example, "Denka Black (registered trademark)" electrochemical Industrial Co., Ltd., "SUPER C65" Imeris Graphite & Carbon, "SUPER C45" Imeris Graphite & Carbon, Conductive Graphite (for example, "KS6L" Imeris Graphite & Carbon, "SFG6L" Imeris (Manufactured by Graphite & Carbon Co., Ltd.), etc. The amount of the conductive auxiliary agent is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the negative electrode active material.

The conductive auxiliary agent preferably contains carbon nanotubes, carbon nanofibers, and vapor-phase carbon fibers, and the fiber length of these conductive auxiliary agents is preferably ½ or more of the length of Dv50 of the carbon-silicon composite. preferable. With this length, these conductive auxiliaries can be bridged between the negative electrode active materials including the carbon-silicon complex, and the cycle characteristics can be improved. The single wall type and multi-wall type with a fiber diameter of 15 nm or less have the same amount of addition, and the number of bridges increases. Further, since it is more flexible, it is more preferable from the viewpoint of improving the electrode density.

The solvent for preparing the slurry for electrode coating is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), isopropanol, tetrahydrofuran (THF), and water. In the case of a binder that uses water as a solvent, it is also preferable to use a thickener in combination. The amount of solvent can be adjusted so that the slurry has a viscosity that makes it easy to apply to the current collector.

[5] Lithium Ion Secondary Battery The lithium ion secondary battery according to the present invention includes the negative electrode mixture layer. The lithium ion secondary battery is usually composed of a negative electrode composed of the negative electrode mixture layer and a current collector, a positive electrode composed of a positive electrode mixture layer and a current collector, and a non-aqueous electrolyte solution and a non-aqueous polymer electrolyte existing between the negative electrodes. Includes at least one, as well as a separator, and a battery case for accommodating them. The lithium ion secondary battery may include the negative electrode mixture layer, and other configurations including conventionally known configurations can be adopted without particular limitation.

The positive electrode mixture layer usually consists of a positive electrode material, a conductive auxiliary agent, and a binder. As the positive electrode in the lithium ion secondary battery, a general configuration in a normal lithium ion secondary battery can be used.

The positive electrode material is not particularly limited as long as it can reversibly insert and remove electrochemical lithium and these reactions are sufficiently higher than the standard redox potential of the negative electrode reaction. For example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , LiCo _0.6 Mn _0.2 Ni _0.2 O ₂ , LiCo _0.8 Mn _0.1 Ni _0.1 O ₂ , carbon coated LiFePO 4 , Or a mixture thereof can be preferably used.

As the conductive auxiliary agent, the binder, and the solvent for preparing the slurry, those mentioned in the section of the negative electrode are used. Aluminum foil is preferably used as the current collector.
The non-aqueous electrolyte solution and the non-aqueous polymer electrolyte used in the lithium ion battery are not particularly limited. For example, _{lithium salts such as LiClO 4} , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li can be used as ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, butylene carbonate, acetonitrile. , Propionitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone and other organic electrolytes; gel-like polymer electrolytes containing polyethylene oxide, polyacrylic nitrile, polyfluoroviriniden, polymethylmethacrylate and the like. A solid polymer electrolyte containing a polymer having an ethylene oxide bond or the like can be mentioned.

Further, a small amount of an additive generally used for an electrolytic solution of a lithium ion battery may be added to the non-aqueous electrolytic solution. Examples of the substance include vinylene carbonate (VC), biphenyl, propane sultone (PS), fluoroethylene carbonate (FEC), ethylene salton (ES) and the like. VC and FEC are preferred. The amount to be added is preferably 0.01 to 20% by mass with respect to 100% by mass of the non-aqueous electrolytic solution.

The separator can be freely selected from those that can be used in a general lithium ion secondary battery, including the combination thereof, and examples thereof include a microporous film made of polyethylene or polypropylene. Further, such a separator mixed with particles such as SiO2 and Al2O3 as a filler, and a separator adhered to the surface can also be used.

The battery case is not particularly limited as long as it can accommodate the positive electrode and the negative electrode, and the separator and the electrolytic solution. In addition to those standardized in the industry such as battery packs, 18650 type cylindrical cells, coin type cells, etc. that are usually on the market, those packed with aluminum packaging material, etc. can be freely designed and used. can.

Each electrode can be stacked and then packed for use. In addition, single cells can be connected in series and used as a battery or module.
The lithium ion secondary battery according to the present invention is a power source for electronic devices such as smartphones, tablet PCs, and mobile information terminals; a power source for electric motors such as electric tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; fuel cells, and the sun. It can be used for storage of electric power obtained by optical power generation, wind power generation, and the like.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The physical characteristics were measured and the battery was evaluated as follows.
[SEM observation]
SEM observation was performed under the following conditions.
(Method)
The sample was supported on a carbon tape, and in the case of observing the particles, the observation was carried out as it was.
SEM: Scanning electron microscope device: Regulus8220 (manufactured by Hitachi High-Tech Co., Ltd.)
Acceleration voltage: 1 to 20 kV
Observation magnification: 500 to 6,000 times (select appropriately according to the size of the particles)
The definition and measurement method of the average diameter and the average length of the carbon-silicon composite according to the present invention are as described above. Image recognition software ImageJ (manufactured by the National Institutes of Health, USA) was used to identify and measure each figure in the SEM image.

[Measurement of total pore volume] [Measurement of pore distribution]
The pore distribution was measured under the following conditions.
・ High-precision gas adsorption amount measuring device: Microtrac Bell Co., Ltd. BELSORP MAX II
Adsorbed gas: Nitrogen pretreatment; Under vacuum, measured at 300 ° C for 5 hours Relative pressure (P / P0) Lower limit: 10 ^-8 Order measurement Relative pressure (P / P0) Upper limit: 0.990 or more is relative pressure P / P ₀ The pore volume at the maximum value was defined as the total pore volume (P ₀ is the saturated vapor pressure).
Analysis: NLDFT method-Calculation of micropore ratio, total ratio of mesopores and macropores Macropores are pores with a pore diameter of 50 nm or more and 100 nm or less. Mesopores are pores with a pore diameter larger than 2 nm and smaller than 50 nm. Micropores are pores having a pore diameter of 2 nm or less. The micropore ratio is a value obtained by dividing the pore volume of micropores calculated by the NLDFT method by the pore volume of 0 to 100 nm or less calculated by the NLDFT method, and multiplying by 100. Indicated by the formula.

Ratio of total of meso and macro holes =
100 × (pore volume of 0 to 100 nm or less calculated by NLDFT method-micropore pore volume calculated by NLDFT method) / (pore volume of 0 to 100 nm or less calculated by NLDFT method)
[Fever peak]
-Measuring device: TG-DTA2000SE (manufactured by NETZSCH Japan Co., Ltd.)
・ Measurement temperature: Room temperature to 1000 ° C
・ Sample amount: 9-11 mg
・ Temperature rise rate: 10 ° C / min
・ Measurement atmosphere: Air
・ Flow rate: 100 ml / min
[Raman spectroscopy]
Using a small spatula, place the sample on the glass preparation and spread it evenly so that the underlying glass preparation is not exposed. The range for expanding the sample is wider than the measurement range described later. This is so that only the complex particles are spread within the measurement range. This sample was measured by the following method.

・ Microscopic Raman spectroscopic measuring device: LabRAM HR Evolution manufactured by HORIBA, Ltd.
-Excitation wavelength: 532 nm
・ Exposure time: 10 seconds ・ Number of integrations: 2 times ・ Diffraction grating: 300 lines / mm (600 nm)
-Measurement range: length 60 μm x width 60 μm
-Number of points: 30 points evaluation with vertical feed of 12 μm and horizontal feed of 15 μm The height from the baseline to the peak top was taken as the intensity. It was calculated measured peak intensity ID of around 1350 cm ^-1 from the spectral ratio of the intensity IG of a peak in the vicinity of (amorphous component derived) and 1600 cm ^-1 (derived from graphite component) (ID / IG). This ratio (ID / IG) was measured at two points, and the average value was used as the R value (ID / IG) as an index for evaluating the carbon quality of the carbonaceous layer.

In addition, the ratio (ISi / IG) of the intensity ISi of the peak derived from amorphous silicon appearing in 450 to 495 cm ^{-1 and the IG was calculated.} The ratio of (ISi / IG) measured at two points, and this the average value as I _Si / I _G and the degree of indication of deposition of silicon into the carbonaceous material surface.

[XRD measurement]
The sample was filled in a glass sample plate (sample plate window 18 × 20 mm, depth 0.2 mm), and measurement was performed under the following conditions.

-XRD device: SmartLab (registered trademark) manufactured by Rigaku Co., Ltd.
・ X-ray type: Cu-Kα ray ・ Kβ ray removal method: Ni filter ・ X-ray output: 45kV, 200mA
-Measurement range: 10.0 to 80.0 deg.
-Scan speed: 10.0 deg. / Min
For the obtained XRD pattern, background removal and smoothing were performed using analysis software (PDXL2, manufactured by Rigaku Co., Ltd.), and then peak fitting was performed to determine the peak position and intensity.

[Measurement of adsorption performance]
JIS K1474: Of 2014 7.13, n with a dilution ratio of 1 / n is optionally 10 and usually 10 is used, but it was carried out at a toluene saturated vapor pressure of 25 ° C. with n = 1. In JIS, the air flow rate was changed from 2L / min to 0.12L / min. The sample amount was changed from 5 to 10 g in JIS to 1.000 g (± 0.001 g). The pressure was increased to atmospheric pressure +2.5 (± 0.1) kpa. Under this condition, when the equilibrium adsorption performance of weight increment per sample weight was set to 100%, the time for the adsorption performance to reach 100% within an elapsed time of 200 min was measured.

[BET specific surface area measurement]
(Method)
Place the sample in a sample cell (9 mm x 135 mm) so that the total surface area of the sample is 2 to 60 m ² , dry it at 300 ° C. for 1 hour under vacuum conditions, measure the sample weight, and measure by the following method. rice field.
-Device: NOVA4200e manufactured by Quantachrome.
・ Measurement gas: Nitrogen ・ Relative pressure setting value in the measurement range: 0.005 to 0.995
(Method of calculation)
(Calculation method of BET specific surface area)
The BET specific surface area of the porous carbonaceous material was calculated by the BET multipoint method from the adsorption isotherm data with a relative pressure of around 0.005 to less than 0.08.

The BET specific surface area of the carbon-silicon composite was calculated by the BET multipoint method from the adsorption isotherm data of three points with relative pressures of around 0.1, 0.2 and 0.3.
[Measurement of particle size distribution]
Add 2 drops of 100-fold diluted 100-fold diluted powder to 1 cup of ultra-small spartel and 32% by mass of nonionic surfactant (SIRAYA palm fruit detergent high power) to 15 mL of water and ultrasonically disperse for 3 minutes. I let you. This dispersion is put into a laser diffraction type particle size distribution measuring instrument (LMS-2000e) manufactured by Seishin Enterprise Co., Ltd., and the volume-based cumulative particle size distribution is measured, and the diameter is 10% (DV10), 50% diameter (DV50), 90% diameter. (DV90) was determined.

[Oxygen content measurement]
The measurement was performed under the following conditions.
・ Oxygen / nitrogen / hydrogen analyzer: EMGA-920 manufactured by HORIBA, Ltd.
-Carrier gas: About 20 mg of argon powder was weighed in a nickel capsule and measured by an oxygen-nitrogen simultaneous analyzer. That is, the sample was decomposed under the atmosphere of an inert gas, and the generated gas was quantified by the infrared absorption method.

[Measurement of silicon content]
(Method)
The sample was filled in a sample cup, the measurement was carried out by the following method, and the Si concentration (Si element content) was calculated by mass% using the fundamental parameter method (FP method).
・ Fluorescent X-ray device: NEX CG manufactured by Rigaku
・ Tube voltage: 50kV
・ Tube current: 1.00mA
・ Sample cup: Φ32 12mL CH1530
・ Sample weight: 2-4g
・ Sample height: 5-18 mm
The FP method was carried out using the analysis software attached to the device.

[Manufacturing of negative electrode sheet for coin half cell]
Styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as binders. Specifically, an aqueous solution in which SBR having a solid content ratio of 40% was dispersed and an aqueous solution in which solid content CMC powder was dissolved were obtained.

As a mixed conductive auxiliary agent, carbon black (SUPER C 45 (registered trademark), manufactured by Imeris Graphite & Carbon Co., Ltd.) and vapor-grown carbon fiber (VGCF (registered trademark) -H, manufactured by Showa Denko KK) are 3: 2. A mixture was prepared in the mass ratio of.

90 parts by mass of the negative electrode active material, 5 parts by mass of the mixed conductive auxiliary agent, and 2.5 parts by mass of the CMC solid content produced in Examples and Comparative Examples described later, so that the CMC aqueous solution and the SBR solid content are 2.5 parts by mass. As described above, the SBR aqueous solution was mixed, an appropriate amount of water for adjusting the viscosity was added thereto, and the mixture was kneaded using a rotation / revolution mixer (manufactured by Shinky Co., Ltd.) to obtain a slurry for forming a negative electrode mixture layer.

The slurry for forming the negative electrode mixture layer is uniformly coated on a copper foil having a thickness of 20 μm using a doctor blade so as to have a thickness of 150 μm, dried on a hot plate, and then vacuum dried to coat the negative electrode. I got a work sheet. The dried negative electrode coated sheet was pressed with a uniaxial press at a pressure of 3 MPa to obtain a negative electrode sheet for battery evaluation. The thickness of the obtained negative electrode sheet was 62 μm including the thickness of the copper foil.

[Measurement of electrode density]
The negative electrode sheet (current collector + negative electrode mixture layer) after pressing was punched into a circular shape having a diameter of 16 mm, and its mass and thickness were measured. From these values, the mass and thickness of the separately measured current collector (circular shape with a diameter of 16 mm) were subtracted to obtain the mass and thickness of the negative electrode mixture layer. The electrode density of the negative electrode was calculated from these values. In the case of the positive electrode, the electrode density was determined by the same method.
[Preparation of lithium counter electrode cell]
The negative electrode sheet was punched to 16 mmφ, pressure-molded by a uniaxial press, and the density of the negative electrode mixture layer was adjusted to 1.4 g / cc to obtain a negative electrode.

The electrode density of the negative electrode (negative electrode density) was calculated as follows. The mass and thickness of the negative electrode obtained by the above method are measured. The mass and thickness of the negative electrode mixture layer were obtained by subtracting the mass and thickness of the collector foil punched to 16 mmφ, which was separately measured, and the electrode density (negative electrode density) was calculated from the values.

In a polypropylene insulating gasket (inner diameter of about 18 mm), a separator (polypropylene microporous film) impregnated with an electrolytic solution is formed by using the above-mentioned negative electrode and a 1.7 mm-thick metal lithium foil punched out to 17.5 mmφ. It was sandwiched and laminated. At this time, the surface of the negative electrode mixture layer of the negative electrode was laminated so as to face the metallic lithium foil with the separator interposed therebetween. This was placed in a 2320 coin type cell and sealed with a caulking machine to obtain a test cell (lithium counter electrode cell).

[Manufacturing of negative electrode sheet for laminated cell]
A # 1380 carboxymethyl cellulose (CMC) aqueous solution manufactured by Daicel Chemical Co., Ltd. was used as a binder.

As mixed conductive auxiliary agents, carbon black (SUPER C 45 (registered trademark), Imeris Graphite & Carbon) and carbon nanotubes (Cnano) and vapor-grown carbon fiber (VGCF (registered trademark) -H, Showa Denko Co., Ltd. A mixture of (manufactured by the company) with a mass ratio of 1.2: 0.4: 0.4 was prepared.

90 parts by mass of the negative electrode material, 2 parts by mass of the mixed conductive auxiliary agent, and 8 parts by mass of the CMC solid content manufactured in Examples and Comparative Examples described later are mixed, and an appropriate amount of water for adjusting the viscosity is added thereto to rotate. -Kneading was performed using a revolution mixer (manufactured by Shinky Co., Ltd.) to obtain a slurry for forming a negative electrode mixture layer.

The slurry was coated on a copper foil having a thickness of 20 μm using a roll coater so as to have a basis weight of 6 mg / cm ^2, and dried to obtain a negative electrode sheet. The obtained negative electrode sheet was rolled to a density of 1.6 g / cm ³ to obtain a negative electrode sheet. The thickness of the obtained negative electrode sheet was 60 to 70 um including the thickness of the copper foil.

[Preparation of positive electrode sheet]
95 g of NiMnCo622, 0.72 g of carbon black (SUPER C 65 (registered trademark), manufactured by Imeris Graphite & Carbon) as a conductive auxiliary agent, 1.68 g of CNT, 0.60 g of VGCF and polyvinylidene fluoride as a binder. 2 g of vinylidene (PVdF) was weighed and stirred and mixed while appropriately adding N-methyl-2-pyrrolidone (NMP) to obtain a slurry for positive electrode coating.

The slurry was applied onto an aluminum foil having a thickness of 20 μm using a roll coater to ^{a thickness of 13.2 mg / cm 2 with} a basis weight, and dried to obtain a positive electrode sheet. The obtained positive electrode sheet was rolled to a density of 3.2 g / cm ³ to obtain a positive electrode sheet. The thickness of the obtained positive electrode sheet was 60 to 70 μm including the thickness of the aluminum foil.

[Fine adjustment of positive / negative electrode capacity ratio]
When manufacturing a lithium-ion secondary battery with the positive and negative electrodes facing each other, it is necessary to consider the balance between the capacities of both. That is, if the capacity of the negative electrode is too small, metallic lithium precipitates on the negative electrode after lithium has been inserted to the limit during battery charging, which causes deterioration of cycle characteristics. On the contrary, if the capacity of the negative electrode is too large, the cycle characteristics are improved, but the battery is charged and discharged with a small load, so that the energy density is low.

In order to prevent this, a positive electrode sheet having a constant capacity is used, and for the negative electrode sheet, a cell having a lithium counter electrode is used to measure the specific capacity of the negative electrode material in advance, and the negative electrode with respect to the capacity QC of the positive electrode sheet is used. The thickness of the negative electrode coating slurry at the time of coating was finely adjusted so that the ratio of the capacity QA of the sheet was 1.2.

[Manufacturing of two-electrode cell]
It punched the negative electrode sheet and positive electrode sheet, to obtain a negative electrode strip and the positive electrode piece 20 cm ² area 21.84cm ^2. An aluminum tab was attached to the aluminum foil of the positive electrode piece, and a nickel tab was attached to the copper foil of the negative electrode piece. A polypropylene microporous film was sandwiched between the negative electrode pieces and the positive electrode pieces, which was placed in a bag-shaped aluminum laminated packaging material (SPALF), and an electrolytic solution was injected into the bag-shaped aluminum laminated packaging material (SPALF). Then, the opening was sealed by heat fusion to obtain a two-electrode cell for evaluation.

The electrolytic solution in the lithium counter electrode cell and the two-electrode cell is a solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3: 5: 2, and vinylene carbonate (VC) is added to the solvent. It is a liquid obtained by mixing 1% by volume and 2% by volume of fluoroethylene carbonate (FEC), and further dissolving the electrolyte LiPF6 at a concentration of 1 mol / L.
[Measurement of initial Coulomb efficiency]
The test was conducted using a lithium counter electrode cell. First, discharge was performed from the rest voltage to 0.005 V in the CC (constant current: constant current) mode in which the magnitude of the current was 0.1 C. Here, 1C is the capacity of the sample electrode of this lithium counter electrode cell calculated from the theoretical specific capacity (silicon: 4200 mAh / g, graphite particles: 372 mAh / g, carbonaceous material: 0 mAh / g). It is the magnitude of a constant current that can be discharged or charged in one hour. After reaching 0.005V, the discharge was switched to the CV (constant voltage: constant voltage) mode, and the charge was performed with the cutoff current set to 0.005C. The specific volume at this time is defined as the initial insertion specific volume.

Next, charging was performed in the CC mode with the upper limit voltage set to 1.5 V and the magnitude of the current set to 0.1 C. The specific volume at this time is defined as the initial desorption specific volume.
Here, the specific capacity is a value obtained by dividing the capacity of the battery measured at the time of discharging or charging by the mass of the negative electrode material according to the present invention used in the sample electrode of the lithium counter electrode cell. The test was conducted in a constant temperature bath set at 25 ° C. The initial Coulomb efficiency was defined by the following equation.

Initial Coulomb efficiency (%) = 100 x (Initial desorption specific volume) / (Initial insertion ratio capacity)
[Measurement of charge / discharge cycle characteristics]
The measurement was performed using a two-electrode cell. The aging condition was that four cycles of charging and discharging were repeated. 1 cycle: Charge to 3.4V at 45 ° C. 0.03C, degas once, then restart charging (CC mode) at 0.1C, raise to 4.25V, and then CV mode (0.01C CV). -Cut) was used for charging. After that, the battery was discharged to 2.8 V at 0.1 C. 2 cycles: Charging / discharging (CC-CV (1/20 cut) / CC) was performed at 0.2 C, and then degassing was performed. 3.4 cycle: Charging / discharging (CC-CV (1/20 cut) was repeated twice at 25 ° C. 0.2C. After that, the charging / discharging cycle characteristics were measured at 1C. 1C here is 1C. This is the magnitude of the constant current required to change the two-electrode cell from a fully charged state to a fully discharged state in one hour. Charging is a CC mode and cutoff current with a current of 1C with an upper limit voltage of 4.2V. The discharge was performed in the CV mode at 0.05 C. The discharge was performed in the CC mode with a current of 1 C with the lower limit voltage set to 2.8 V. The charge / discharge operation after aging was repeated for 100 cycles as the first cycle, and then The discharge capacity retention rate after 100 cycles defined by the equation was calculated.

Discharge capacity retention rate (%) after 100 cycles =
100 x (discharge capacity in the 100th cycle) / (discharge capacity in the 1st cycle)
The following shows the preparation method, the source, and the physical property values of the carbon-silicon complex raw material (carbonaceous material, graphite particles).
[Carbonaceous material]
<Carbonaceous materials 1-11, 13, 16-18>
Activated carbon fibers having an average diameter of 15 μm were crushed using a jet mill or a wonder blender to obtain carbonaceous materials 1 to 11, 13, 16 to 18 having different cylindrical shapes. Table 1 shows the physical characteristics of carbonaceous materials.
<Carbonaceous materials 12, 14, 15>
Activated carbon particles having a Dv50 of 7 μm were used as carbonaceous materials 12, 14, and 15. Table 1 shows the physical characteristics of carbonaceous materials.
<Carbonaceous material 19>
Carbon nanotubes (CNTs) having an average diameter of 0.02 μm and an average length of 3 μm were used as the carbonaceous material 19. Table 1 shows the physical characteristics of carbonaceous materials.
[Graphite particles 1]
Artificial graphite with BET 2.7 m ² / g, DV 107 μm, DV 50 14 μm, DV 90 27 μm, initial insertion specific volume 360 mAh / g, and initial Coulomb efficiency 92% was used as graphite particles 1.

[Examples 1 to 11, Comparative Examples 1, 3 to 7]
Table 1 shows the carbonaceous materials shown in Table 2 at a set temperature of 400 ° C., a pressure of 760 torr, and a flow rate of 100 sccm in a tube furnace having a gas flow containing 1.3% by volume of monosilane mixed with argon nitrogen gas. Time treatment was performed to precipitate silicon on the surface of the carbonaceous material and in the pores to obtain a carbon-silicon composite. Table 2 shows the material property values of the obtained carbon-silicon complex. After mixing, graphite particles 1 were mixed with the carbon-silicon composite so that the silicon concentration was 5.6% by mass when the negative electrode active material was 100% by mass to obtain a negative electrode active material. The battery characteristics are shown in Table 2. FIG. 1 is a scanning electron microscope (SEM) photograph of the carbon-silicon composite produced in Example 1.
[Comparative Examples 2 and 8]
Table 2 shows the carbonaceous materials shown in Table 2 at a set temperature of 400 ° C., a pressure of 760 torr, and a flow rate of 100 sccm in a tube furnace having a gas flow containing 1.3% by volume of monosilane mixed with argon nitrogen gas. The carbon-silicon composite was obtained by precipitating silicon on the surface of the carbonaceous material and in the pores. Table 2 shows the material property values of the obtained carbon-silicon complex. Since the silicon content was extremely low and could not be mixed according to the same criteria as in Examples 1 to 11 and Comparative Examples 1, 3, 4, 6 and 7, the graphite particles were 180% by mass with respect to 20% by mass of the carbon silicon composite. % Was mixed to obtain a negative electrode active material. The battery characteristics are shown in Table 2.
[Comparative Example 9]
36 parts by mass of nanosilicon (50% diameter in number-based cumulative distribution: 90 nm, 90% diameter in number-based cumulative distribution: 150 nm) and petroleum pitch (softening point: 214 ° C., carbonization rate: 72.35% by mass, QI Content: 0.12% by mass, TI content: 47.75% by mass) 64 parts by mass was placed in a 10 L plastic container and dry blended. A dry-blended mixed powder of nanosilicon and petroleum pitch was put into a raw material hopper of a twin-screw extruder TEM-18SS (manufactured by Toshiba Machine Co., Ltd.). The kneading conditions in the twin-screw extruder were a temperature of 250 ° C., a screw rotation speed of 700 rpm, and a mixed powder charging speed of 2 kg / h. At the time of kneading, the work was carried out while circulating nitrogen gas at 1.5 L / min.

After kneading with a twin-screw extruder, it was coarsely crushed with a hammer and then finely pulverized with a jet mill STJ-200 (manufactured by Seishin Enterprise Co., Ltd.) to obtain nanosilicon-containing particles. The nanosilicon content in the nanosilicon-containing particles was 36% by mass, and the 50% diameter (D50) in the volume-based cumulative distribution was 10 μm.

Petroleum-based coke was coarsely crushed with a hammer and crushed with a bantam mill (Made by Hosokawa Micron, mesh 1.5 mm). This was pulverized with a jet mill STJ-200 (manufactured by Seishin Enterprise Co., Ltd.) under the conditions of a pulverization pressure of 0.6 MPa and a pusher pressure of 0.7 MPa. The crushed material was heat-treated in an Achison furnace at 3000 ° C. to obtain graphite particles 2.

4.8 kg of nanosilicon-containing particles and 5.2 kg of graphite particles 2 were weighed, charged into Cyclomix CLX-50 (manufactured by Hosokawa Micron), and mixed for 10 min at a peripheral speed of 24 m / sec.

An alumina saggar (90 mm x 90 mm x 50 mm) is filled with 80 g of mixed powder, set in the center of a tube furnace (inner diameter 130 mm, room temperature 500 mm), and heated to 1050 ° C at 150 ° C / h under nitrogen flow. After holding for 1 h, the temperature was lowered to room temperature at 150 ° C./h. After recovering the heat-treated product from the alumina saggar, the heat-treated product was crushed with a bantam mill (Hosokawa Micron Co., Ltd., mesh 0.5 mm), and coarse powder was cut using a stainless steel sieve having an opening of 45 μm to obtain a carbon-silicon composite. Table 2 shows the material property values. After mixing, graphite particles 1 were mixed with the carbon-silicon composite so that the silicon concentration was 5.6% by mass when the negative electrode active material was 100% by mass to obtain a negative electrode active material. The battery characteristics are shown in Table 2.

The characteristics of the batteries using the complexes of Examples 1 to 11 are excellent in cycle characteristics, but the characteristics of the batteries using the complexes of Comparative Examples 1 to 9 are inferior in cycle characteristics. In Comparative Examples 1, 3 and 4, a particulate carbonaceous material was used as the carbonaceous material, and since the micropore ratio was low, it is considered that the adsorption performance was inferior and the cycle characteristics were inferior. In Comparative Example 2, since the pore volume and the micropore ratio were small, silicon was generated in the vicinity of the surface, and it is considered that the cycle characteristics were inferior due to the increase in ISi / IG. In Comparative Example 5, since the silicon CVD processing time was lengthened, the amount of surface-precipitated Si increased, and it is considered that the cycle characteristics were inferior. In Comparative Example 6, since columnar porous carbon having a long average length was used as the carbonaceous material, the average length of the complex and Dv90 were large, the electrode coatability was poor, and the expansion and contraction was large. Therefore, it is considered that the cycle characteristics were low. In Comparative Example 7, it is considered that the adsorption performance was inferior, the micropore ratio was small, and the total ratio of the mesopores and the macropores was large, so that coarse silicon was produced and the cycle characteristics were inferior. In Comparative Example 8, since CNT was used as the carbonaceous material, the average diameter was small and the pore volume was small, so that sufficient silicon could not be contained in the pores, and a large amount of silicon was deposited on the surface. It is probable that the result was inferior in characteristics. Comparative Example 9 is a complex containing graphite as a carbonaceous material, and it is considered that the cycle characteristics are inferior because the 111-plane peak half width of Si is small, that is, the crystallinity of silicon is high.

Claims

A carbon-silicon complex containing carbonaceous materials and silicon.
Contains a carbon-silicon complex with a columnar shape,
The average diameter is 5 μm or more and 30 μm or less.
The average length is 1 μm or more and less than 50 μm.
In the DTA curve measured by DTA in air, the exothermic peak exists below 800 ° C.
In the Raman spectrum, the peak due to Si exists at 450 to 495 cm -1 , and the ratio of the intensity ISi of the peak due to Si to the intensity IG of the G band, ISi / IG is 0.35 or less.
In the XRD pattern using Cu-Kα rays, the half width of the peak due to the 111 planes of Si is 3.0 deg. That's it,
Carbon-silicon complex.
According to claim 1, the carbonaceous material reaches 100% within an elapsed time of 200 min when the equilibrium adsorption performance of the weight increment per weight of the carbonaceous material is set to 100% in the adsorption performance test. The carbon-silicon composite described.
The carbon-silicon complex according to claim 1 or 2, wherein the 90% particle size DV90 in the volume-based cumulative particle size distribution is 50 μm or less.
A carbon-silicon complex containing carbonaceous materials and silicon,
In the Raman spectrum, the peak due to Si exists at 450 to 495 cm -1 , and the ratio of the intensity ISi of the peak due to Si to the intensity IG of the G band, ISi / IG is 0.35 or less.
In the XRD pattern using Cu-Kα rays, the half width of the peak due to the 111 planes of Si is 3.0 deg. That's all
The 90% particle size DV90 in the volume-based cumulative particle size distribution is 50 μm or less.
The adsorption performance of the carbonaceous material reaches 100% within an elapsed time of 200 min when the equilibrium adsorption performance of the weight increment per weight of the carbonaceous material is set to 100% in the adsorption performance test.
Carbon-silicon complex.
The carbon-silicon complex according to any one of claims 1 to 4, wherein the 10% particle size DV10 in the volume-based cumulative particle size distribution is 2.0 μm or more.
The carbon-silicon complex according to any one of claims 1 to 5, wherein the BET specific surface area is 50 m 2 / g or less.
The carbon-silicon complex according to any one of claims 1 to 6, wherein the oxygen content is 10% by mass or less.
The carbon-silicon composite according to any one of claims 1 to 7, wherein the silicon content is 10% by mass or more and less than 70% by mass.
The carbonaceous material has a pore volume of 0.30 cm 3 / g or more, a ratio of the volume of micropores to the volume of all pores is 90% or more, and a mesopores to the volume of all pores. The carbon-silicon composite according to any one of claims 1 to 8, which has a pore distribution in which the ratio of the sum of the volumes to the macropores is less than 10%.
The carbonaceous material according to any one of claims 1 to 9, wherein the carbonaceous material has an R value of 0.30 or more and 1.30 or less in the Raman spectrum.
Negative electrode active material containing the carbon-silicon complex according to any one of claims 1 to 10.
Negative electrode mixture layer containing the negative electrode active material according to claim 11.
A lithium ion secondary battery including the negative electrode mixture layer according to claim 12.