JP2014152040A - Method for producing spheroidized graphite, spheroidized graphite produced thereby, spheroidized graphite-containing anode for lithium ion secondary battery, and lithium ion secondary battery including the anode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for efficiently producing spheroidized graphite in which a metal-containing substance is encapsulated.SOLUTION: The method for producing spheroidized graphite comprises the steps of: executing spheroidization by using a spheroidization device having a spiral flow passage; and folding flaky graphite of a metal-containing substance-encapsulated state to obtain the spheroidized graphite.

Description

  The present invention relates to a method for producing spheroidized graphite used as a negative electrode material for a lithium ion secondary battery, and more particularly to a method for producing spheroidized graphite including a metal-containing substance capable of improving the negative electrode capacity. The present invention also relates to a negative electrode containing the spheroidized graphite and a lithium ion secondary battery including the negative electrode.

  With the downsizing of electronic devices, demand for high-capacity secondary batteries is increasing. In particular, lithium ion secondary batteries, which have higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries and are excellent in high-current charge / discharge characteristics, are attracting attention. Although increasing the capacity of lithium ion secondary batteries has been extensively studied in the past, it is required to achieve further increase in capacity.

Graphite is known as a negative electrode material for lithium ion secondary batteries. Graphite is relatively inexpensive, and lithium ion secondary batteries using graphite are frequently used as negative electrode materials because of their excellent cycle characteristics and small electrode expansion.
On the other hand, when graphite is used as the negative electrode material, the theoretical capacity has a limit value of 372 mAh / g, and further increase in capacity only by graphite cannot be expected. Therefore, in recent years, an attempt has been made to apply a metal-containing material having a large theoretical capacity instead of graphite.

In particular, Si has a large theoretical capacity value and is expected to be applied as a negative electrode. However, since the volume expansion during reaction with lithium is large, there is a problem that peeling from the current collector occurs and the electrode is cracked. .
Therefore, attempts have been made to achieve high capacity by using together with carbon materials such as graphite.

  For example, in Patent Documents 1 and 2, carbon nanowires, carbon nanotubes, and the like are dipped in molten Si to obtain a nanofilament composite material in which a Si layer is formed on the nanowire and nanotube surfaces. It is disclosed that a negative electrode material having a capacity and excellent cycle characteristics can be obtained.

US Patent Application Publication No. 2009/0269511 US Patent Application Publication No. 2009/0169996

Aiming to increase the capacity of lithium ion secondary batteries, although attempts have been made to produce composites of carbon materials and metal-containing substances such as Si, the surface is coated with a metal-containing substance such as Si, Alternatively, only a material containing a metal-containing substance such as Si is produced.
Conventionally, when graphite is spheroidized, it is spheroidized by applying a strong physical impact. When spheroidized by such a strong physical impact, the density of graphite is simultaneously reduced. Will also be high. Therefore, even if graphite after spheroidizing treatment and a metal-containing substance are mixed, it is difficult for the metal-containing substance to be included in the graphite.
On the other hand, even when graphite before spheroidizing treatment and a metal-containing substance are mixed and spheroidized, the conventional spheronizing treatment is performed while removing the fine powder, There is almost no inclusion of metal-containing materials.

  The present invention has been made under such circumstances, and an object thereof is to provide a new production method for efficiently producing spheroidized graphite containing a metal-containing substance.

  As a result of intensive studies to solve the above problems, the present inventors folded the flaky graphite by applying a gentle impact to the mixture in a state where the flaky graphite and the metal-containing substance were mixed in advance. The inventors have found that spheroidizing graphite containing a metal-containing substance can be obtained by spheronizing, and the present invention has been completed.

That is, the outline of the present invention is as follows.
(1) A method for producing spheroidized graphite comprising a preparation step of preparing a mixture of scaly graphite and a metal-containing substance, and a spheronization step of spheronizing the mixture,
The spheronization step is performed using a spheronization processing apparatus having a spiral channel, and the spheroidized graphite is folded and spheroidized in a state of containing a metal-containing material.
(2) The method for producing spheroidized graphite according to (1), wherein in the preparation step, a weight ratio between the scaly graphite and the metal-containing substance is 99: 1 to 90:10.
(3) The method for producing spheroidized graphite according to (1) or (2), wherein the metal-containing substance contains at least one selected from the group consisting of Si, Sn, Al, and SiO.
(4) The peak intensity ratio Rc (= I (110) / I (004)) corresponding to the lattice planes (110) and (004) obtained by wide-angle X-ray diffraction measurement of the produced graphite is 0.00. The method for producing spheroidized graphite according to any one of (1) to (3), which is 05 or more and 0.22 or less.
(5) The method for producing spheroidized graphite according to any one of (1) to (4), wherein the produced graphite has a volume-based average particle size (d50) of 3 μm or more and 50 μm or less.
(6) The method for producing spheroidized graphite according to any one of (1) to (5), further including a compression molding step.
(7) Spheroidized graphite produced by the method according to any one of (1) to (6).
(8) A negative electrode for a lithium ion secondary battery comprising a current collector and an active material layer formed on the current collector, wherein the active material contains the spheroidized graphite according to (7) A negative electrode for a lithium ion secondary battery.
(9) A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, wherein the negative electrode is a negative electrode for a lithium ion secondary battery according to (8) Ion secondary battery.

  The present invention can provide a new production method for efficiently producing spheroidized graphite containing a metal-containing substance. By using a substance having a higher capacity than graphite as the metal-containing substance, the capacity of the negative electrode can be increased.

It is a schematic diagram showing the spheroidization processing apparatus used in the Example. It is a schematic diagram showing the spheroidization processing apparatus which can be used conveniently in this invention. It is a SEM image showing the cross section of the spheroidized graphite manufactured in Example 1 (drawing substitute photograph). It is a SEM image showing the cross section of the spheroidized graphite manufactured in Example 1 (drawing substitute photograph).

Hereinafter, the present invention will be described in more detail, but the present invention is not limited to specific embodiments.
The method for producing spheroidized graphite according to an embodiment of the present invention includes a preparation step of preparing a mixture of scaly graphite and a metal-containing substance, and a spheronization step of spheroidizing the mixture.

In the preparation step, flake graphite and a metal-containing substance are mixed. In the present embodiment, it is preferable that the metal-containing substance is included in the spheroidized graphite to increase the negative electrode capacity. That is, it is preferably a metal-containing material having a theoretical capacity larger than that of graphite. Note that the metal-containing substance is a concept including a simple metal, a compound of a metal and another element, an alloy containing a metal and another substance, and the like.
Examples of the metal-containing substance having a theoretical capacity larger than that of graphite include Si, Sn, Al, and SiOx. Among these, Si or SiOx (0 <x <2) is preferable. x is preferably 0.2 or more, more preferably 0.4 or more, and still more preferably 0.6 or more. Moreover, 1.8 or less is preferable, 1.6 or less is more preferable, 1.4 or less is further more preferable, and it is especially preferable that it is 1, ie, SiO. Most preferably, it is Si.
As a method for producing SiOx, for example, SiO ₂ powder and metal Si powder are mixed at a specific ratio, and after the mixture is charged into a reactor, the temperature is increased to 1000 ° C. or higher in a state where the pressure is reduced to normal pressure or a specific pressure. Warm and hold to generate SiOx gas. The gas can be collected, cooled and precipitated to obtain SiOx particles.
The average particle diameter (d50) of the metal-containing substance is not particularly limited, and is usually 0.1 μm or more, preferably 1.0 μm or more, and usually 10 μm or less, preferably 7 μm or less. The average particle diameter (d50) is determined by a laser diffraction / scattering particle size distribution measuring method or the like.
The specific surface area of the metal-containing substance by the BET method is usually 0.5 m ² / g or more, preferably 1 m ² / g or more, and usually 60 m ² / g or less, preferably 40 m ² / g or less.

The mixing ratio of the scaly graphite and the metal-containing substance is not particularly limited, but the production method of this embodiment can efficiently encapsulate the metal-containing substance in the graphite, and the amount of the metal-containing substance in the mixture is small. May be. The weight ratio of flaky graphite to the metal-containing substance is preferably 99: 1 to 90:10, and more preferably 99: 1 to 95: 5.
The mixing method is not particularly limited and can be performed by a known dry method, but when mixed with a too strong force, the edge of the flaky graphite tends to be scraped off and fine powder is generated. It is sufficient to shake the metal-containing substance several times in the bag.

The scaly graphite used as a raw material is not particularly limited as long as it is usually used as a raw material for a negative electrode of a lithium ion secondary battery. However, preferred physical property values are shown below.
(1) 002 plane spacing (d002) and Lc
The surface interval (d002) of the 002 plane by the X-ray wide-angle diffraction method of flaky graphite is usually 3.37 mm or less and Lc is 900 mm or more, and the surface distance (d002) of the 002 surface is 3.36 mm or less and Lc is 950 mm. The above is preferable. The face spacing (d002) and the crystallite size (Lc) are values indicating the crystallinity of the negative electrode material bulk. The smaller the (002) face spacing (d002) value, the larger the crystallite size. Larger (Lc) indicates a negative electrode material with higher crystallinity, and the capacity increases because the amount of lithium entering the graphite layer approaches the theoretical value. When the crystallinity is low, excellent battery characteristics (high capacity and low irreversible capacity) when high crystalline graphite is used for the electrode are not exhibited. It is particularly preferable that the above-mentioned ranges are combined for the interplanar spacing (d002) and the crystallite size (Lc). X-ray diffraction is measured by the following method. Carbon powder is mixed with X-ray standard high-purity silicon powder of about 15% by mass of the total amount, and the material is CuKα rays monochromatized with a graphite monochromator, and the wide angle X is measured by the reflective diffractometer method. A line diffraction curve is measured. Thereafter, the interplanar spacing (d002) and the crystallite size (Lc) are obtained using the Gakushin method.

(2) Tap density The packing structure of powder particles depends on the size, shape, degree of interaction force between particles, etc., but this specification is one of the indicators for quantitatively discussing the packing structure. It is also possible to apply a tap density as In the study by the present inventors, it has been confirmed that the lead density of the lead-like particles whose true density is almost equal to the average particle diameter shows a higher tap density as the shape is spherical. That is, in order to increase the tap density, it is important to make the shape of the particles round and close to a spherical shape. When the particle shape is close to a spherical shape, the powder filling property is greatly improved. The tap density of the flaky graphite is usually 0.1 g / cm ³ or more, preferably 0.2 g / cm ³ or more, and more preferably 0.3 g / cm ³ or more.
The tap density is a cylindrical shape having a diameter of 1.6 cm and a volume capacity of 20 cm ³ using “Tap Denser KYT-4000” manufactured by Seishin Enterprise Co., Ltd., which is a powder density measuring device. After dropping scaly graphite through a sieve with an opening of 300 μm into the tap cell and filling the cell fully, tap with a stroke length of 10 mm was performed 1000 times, and the density obtained from the volume and the weight of the sample was tapped. Defined as density.

(3) Raman R value The argon ion laser Raman spectrum is used as an index showing the surface properties of particles. Raman R value is the peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity near 1580 cm ^-1 in the argon ion laser Raman spectrum of the flake graphite is usually 0.05 to 0.9, 0.05 or 0. It is preferably 7 or less, more preferably 0.05 or more and 0.5 or less. The R value is an index representing the crystallinity in the vicinity of the surface of the carbon particle (from the particle surface to about 100 °), and the smaller the R value, the higher the crystallinity or the disordered crystal state. The Raman spectrum is measured by the method shown below. Specifically, the sample particle is naturally dropped into the Raman spectrometer measurement cell, and the sample cell is filled with the sample. While irradiating the measurement cell with an argon ion laser beam, the measurement cell is placed in a plane perpendicular to the laser beam. Measure while rotating. Note that the wavelength of the argon ion laser light is 514.5 nm.

(4) 3R / 2H
The X-ray wide angle diffraction method of scaly graphite is used as an index representing the crystallinity of the entire particle. In the scale-like graphite, the ratio 3R / 2H of the intensity 3R (101) of the 101 plane based on the rhombohedral crystal structure by the X-ray wide angle diffraction method and the intensity 2H (101) of the 101 plane based on the hexagonal crystal structure is usually 0. It is preferably 1 or more and 0.15 or more, and more preferably 0.2 or more. The rhombohedral crystal structure is a crystal form in which a stack of graphite network structures is repeated every three layers. The hexagonal crystal structure is a crystal form in which a stack of graphite network structures is repeated every two layers. In the case of scaly graphite showing a crystal form with a large proportion of rhombohedral crystal structure 3R, the acceptability of Li ions is higher than graphite particles with a small proportion of rhombohedral crystal structure 3R.

(5) BET specific surface area The specific surface area of the scaly graphite by the BET method is usually 1 m ² / g or more and 30 m ² / g or less, preferably ² m ² / g or more and 15 m ² / g or less, and preferably 5 m ² / g or more and 10 m or less. More preferably, it is ² / g or less. If the specific surface area of the flaky graphite is too small, the acceptability of Li ions is deteriorated, and if it is too large, a decrease in battery capacity due to an increase in irreversible capacity tends to be prevented. The BET specific surface area (SA) was measured by the BET method by a nitrogen gas adsorption flow method using a specific surface area measuring device “Belsorb mini” manufactured by Bell Japan. Specifically, about 1.0 g of a sample (flaky graphite) is filled in a cell, heated to 350 ° C. and pretreated, then cooled to liquid nitrogen temperature, and 30% nitrogen and 70% He gas. Was saturated and adsorbed, then heated to room temperature, and the amount of desorbed gas was measured. From the obtained results, the specific surface area was calculated by the usual BET method.

(6) Pore volume The pore volume in the range of 10 nm to 100000 nm by the mercury intrusion method of flaky graphite is usually preferably 0.3 ml / g or more, preferably 0.4 ml / g or more, and 0.5 ml / g or more. It is more preferable. If the pore capacity is too small, the area where Li ions enter and exit tends to be small, and the battery performance tends to deteriorate. The pore volume is measured by the following method. A mercury porosimeter is used as an apparatus for mercury porosimetry. A sample (negative electrode material) is degassed at room temperature under vacuum and pretreated. Subsequently, mercury is introduced under reduced pressure, the pressure is increased stepwise, and the amount of mercury intrusion is measured. From the mercury intrusion curve thus obtained, the pore distribution and the pore volume are calculated using the Washburn equation.

(7) Average particle size The average particle size (d50) of the flake graphite is usually 5 μm or more, preferably 30 μm or more, more preferably 50 μm or more, and usually 500 μm or less, preferably 300 μm or less, more preferably 100 μm or less. . If the average particle size is too small, an increase in irreversible capacity due to an increase in specific surface area tends to be prevented. On the other hand, if the average particle size is too large, the rapid charge / discharge performance tends to be prevented from being lowered due to the decrease in the contact area between the electrolyte and the scaly graphite particles.
The volume-based average particle size (d50) is obtained by suspending about 0.3 g of scaly graphite in an aqueous solution to which a surfactant is added, and a commercially available laser diffraction / scattering type particle size distribution analyzer “SALD-2000J manufactured by Shimadzu Corporation”. The volume-based average particle diameter (d50) of the scaly graphite is defined as the volume-based median diameter in the measuring apparatus while being irradiated with the ultrasonic waves built in the apparatus.

(8) Aspect ratio The aspect ratio is an index representing the physical properties of the flake graphite. The aspect ratio of the flaky graphite is usually 3 or more, preferably 5 or more, more preferably 10 or more, and still more preferably 15 or more. Moreover, it is 1000 or less normally, Preferably it is 500 or less, More preferably, it is 100 or less, More preferably, it is 50 or less. When the aspect ratio is too large, there is a tendency that large particles having a particle size of about 100 μm tend to be formed. Too small particles do not form a strong granule because the contact area is small when pressed from one direction. Even if the particles are granulated, the small specific surface area of the flake graphite is reflected, and the specific surface area tends to be a granulated body exceeding 30 m ² / g.
The aspect ratio was measured as follows. The scaly graphite is photographed with an electron microscope, and for 20 particles in an arbitrarily selected region, a / b is obtained by setting the longest diameter of each particle to a (μm) and the shortest diameter to b (μm). An average value of 20 particles of / b is defined as an aspect ratio.

  The scaly graphite is not particularly limited with respect to the production method. Scaly graphite produced naturally as ore may be used as a raw material as it is. Scaly graphite is produced all over the world, including China, Brazil, Madagascar, Zimbabwe, India, Sri Lanka, Mexico and the Korean Peninsula. Although the properties differ little by little depending on the production area, the production area, properties, and types of the scaly graphite used in the present embodiment are not particularly limited.

The manufacturing method of this embodiment has the characteristic in the spheronization process. The spheronization process is carried out using a spheronization processing apparatus having a spiral flow path, so that the flaky graphite is folded and spheroidized in a state of containing the metal-containing substance.
Conventionally, when graphite is spheroidized, a strong physical impact has been applied. When spheroidized by such a strong physical impact, the density of graphite also increases. Therefore, even if graphite after spheroidizing treatment and a metal-containing substance are mixed, it is difficult for the metal-containing substance to be included in the graphite.
On the other hand, even when graphite before spheroidizing treatment and a metal-containing substance are mixed and spheroidized, the conventional spheronizing treatment is performed while removing the fine powder, There is almost no inclusion of metal-containing materials.

  Unlike the conventional graphite spheronization method, the spheronization process of this embodiment is performed at the end of the scale graphite by performing the spheronization process using a spheronization process apparatus having a spiral flow path. Gives a gentle impact, repeats folding, and gradually progresses to spheroidization. In such a slowly progressing spheronization process, the metal-containing material is encapsulated in the folded graphite.

A specific example of a spheronization processing apparatus having a spiral channel will be described with reference to the drawings.
FIG. 1 shows a spiral tube spheronization apparatus 10 which is an example of a spheronization processing apparatus having a spiral flow path. The spiral tube spheroidizing apparatus 10 has a spiral cylindrical tube 3, and a mixture of flaky graphite and a metal-containing substance is introduced from the inlet 1 of the cylindrical tube, and then slowly passed through the cylindrical tube 3. Folded graphite is formed into a sphere while containing a metal-containing substance.
FIG. 2 shows a screw tube spheronization device 20 which is an example of a spheronization processing device having a spiral flow path. The screw tube spheroidizing device 20 includes a cylindrical core member 11 and a shell member 12 having a cylindrical space in the center, and has a spiral groove 13 on the inner wall of the shell member 12. By closely contacting the inner wall of the shell member 12, a spiral flow path is formed between the spiral groove 13 and the core member 11 existing on the inner wall of the shell member 12. A mixture of flaky graphite and a metal-containing substance is introduced from the inlet 1 and the flaky graphite is gently folded by passing through a spiral groove 13 to be spherical while enclosing the metal-containing substance.
In addition, although not shown in the figure, the scale can be gently adjusted by passing a mixture of scaly graphite and a metal-containing substance through a fluid agitator (static mixer) in which a flow path is provided in a cylindrical casing by a plurality of undulating blade elements. The glassy graphite can be folded and spheroidized while enclosing the metal-containing substance.

Manufacturing conditions in the case of performing spheronization using the spiral tube spheronizing device 10 or the screw tube spheronizing device 20 are not particularly limited, and the spheroidized graphite according to the present embodiment is manufactured as appropriate by those skilled in the art. be able to. Hereinafter, preferable conditions will be described in the case where the spiral tube spheroidizing apparatus 10 is used.
The material of the cylindrical tube 3 is not particularly limited as long as it is a metal material that can withstand impacts due to collision with scaly graphite, pressurization conditions and decompression conditions, for example, metals such as copper, tin, iron, stainless steel, etc. These alloys are mentioned. Among these, copper and stainless steel, which are easy to process and inexpensive, are preferable.
Further, the centerline average roughness Ra indicating the surface roughness of the inner wall of the cylindrical tube 3 is usually 0.5 μm or more, preferably 2 μm or more, more preferably 5 μm or more. Moreover, it is 20 micrometers or less normally, Preferably it is 15 micrometers or less, More preferably, it is 10 micrometers or less. Even when the scaly graphite moves the same distance inside the cylindrical tube, it is preferable that Ra is larger because the scaly graphite is easily bent when the scaly graphite collides with the inner wall, and can be spheroidized more efficiently. In order to increase Ra, it is preferable that the inner wall of the cylindrical tube 3 is roughened with another metal or pickled. Ra is measured based on JIS B0601.

The flake graphite supplied into the cylindrical tube 3 is preferably oriented so that the surface area with respect to the air flux direction is minimized so that the air resistance is reduced. At this time, in order to efficiently spheroidize the flaky graphite, the cylindrical tube 3 has an angle far from the vertical (when the flaky graphite collides with the inner wall (
It is spirally wound so as to collide at a shallow angle. That is, it does not collide perpendicularly to the airflow direction as in the case of a square shape or a linear shape having a portion that is bent at a right angle, and does not collide at an angle close to vertical (deep angle). With such a shape, the inertial force (centrifugal force) increases the probability that the scaly graphite collides with the inner wall at a shallow angle, and therefore the probability that the collision energy is used for spheroidization increases. As a result, the yield of the spheroidized carbon material is improved and the generation of fine powder is suppressed.

  The inner diameter of the cylindrical tube 3 is usually 0.5 mm or more, preferably 1 mm or more, more preferably 2 mm or more. Moreover, it is 1000 mm or less normally, Preferably it is 15 mm or less, More preferably, it is 10 mm or less, More preferably, it is 8 mm or less. The larger the inner diameter, the larger the processing amount of the powder, so that the efficiency of the spheroidizing process is good. In consideration of the amount of gas for supplying the powder and the amount of electricity of the apparatus, it is preferable from the viewpoint of production efficiency and cost that the inner diameter is within the above range.

The length of the spiral is usually 0.25 m or more, preferably 0.5 m or more, more preferably 1 m or more. Moreover, it is 30 m or less normally, Preferably it is 20 m or less, More preferably, it is 10 m or less. From the viewpoint of pressure loss, the length of the spiral is preferably within the above range. Further, in order to obtain a sufficient number of collisions between the scaly graphite and the inner wall of the cylindrical tube and to efficiently perform the spheronization treatment, the length of the spiral is preferably within the above range.
The number of turns of the spiral is usually 2 or more, preferably 5 or more, more preferably 10 or more. The number of spiral turns is preferably large so that a sufficient number of collisions between the scaly graphite and the inner wall of the cylindrical tube can be obtained.

  The spiral curvature diameter is usually 30 mm or more, preferably 50 mm or more, more preferably 70 mm or more. Moreover, it is 1000 mm or less normally, Preferably it is 300 mm or less, More preferably, it is 200 mm or less. In order to increase the probability that the collision energy is used for spheroidization, the spiral curvature diameter is preferably within the above range. In order to increase the probability of collision at an angle that is neither too deep nor too shallow, and to suppress the generation of fine powder as much as possible, it is preferable that the spiral curvature diameter be within the above range.

The supply of the flaky graphite into the cylindrical tube may be performed under pressure or reduced pressure. In the case of pressurizing conditions, examples of the gas to be supplied include air and nitrogen gas. In the case of the reduced pressure condition, the pressure is reduced by reducing the pressure in the cylindrical tube with a vacuum pump. The pressure reduction by a vacuum pump, which is a simple method, may be used, but the pressurization condition may be used in that a large change in atmospheric pressure can be generated.
Moreover, the gas flow rate of the discharge part in pressurization conditions is 50 m / s or more normally, Preferably it is 100 m / s or more, More preferably, it is 150 m / s or more. Moreover, it is 300 m / s or less normally, Preferably it is 250 m / s or less, More preferably, it is 200 m / s or less. On the other hand, the gas flow rate of the supply section under reduced pressure is usually 20 m / s or more, preferably 40 m / s or more, more preferably 60 m / s or more. Moreover, it is 200 m / s or less normally, Preferably it is 150 m / s or less, More preferably, it is 100 m / s or less.
The gas flow rate is preferably within the above range in order to increase the probability that the collision energy is used for spheroidization. Moreover, in order to suppress the collision energy of scaly graphite and suppress generation | occurrence | production of a fine powder as much as possible, it is preferable to make a gas flow rate into the said range.

The supply amount of scaly graphite is usually 0.5 g / min or more, preferably 2 g / min or more, more preferably 3 g / min or more. Further, it is usually 10,000 g / min or less, preferably 50 g / min or less, more preferably 30 g / min or less, and still more preferably 10 g / min or less. In order to use the area where the powder collides in the cylindrical tube to the maximum, it is preferable to be within the above range.

The spheroidizing graphite according to the present embodiment can be obtained by repeating the spheronizing process a plurality of times using the spheroidizing apparatus as exemplified above.
The number of spheroidizing treatments is usually 3 times or more, preferably 5 times or more, more preferably 10 times or more, usually 50 times or less, preferably 40 times or less, depending on the length of the flow path of the processing apparatus. Preferably it is 30 times or less.
In addition, mixing with a metal containing substance may be performed for every several times of processes, and may be performed only for the first time. What is necessary is just to adjust suitably according to the amount of metal-containing substance inclusion required.

  Graphite spheroidized by the production method of this embodiment has a peak intensity ratio Rc (= I (110) / I (004) corresponding to lattice planes (110) and (004) obtained by wide-angle X-ray diffraction measurement. ) Is usually 0.05 or more, preferably 0.10 or more, more preferably 0.15 or more, and still more preferably 0.20 or more. Although an upper limit is not specifically limited, Usually, it is 0.30 or less.

The Rc (= I (110) / I (004)) of graphite was calculated as follows. 0.5 g of graphite was put in a pressure cell, pressed at 600 kgf / cm ² for 5 seconds, and a sample molded into a pellet shape was measured by X-ray diffraction on the sample and (110) plane of graphite on the sample by X-ray diffraction. The chart with the (004) plane is measured, the peak is separated by fitting the measured chart using the asymmetric Pearson VII as a profile function, and the integrated intensity of the peaks of the (110) plane and the (004) plane is calculated. Calculated. The intensity ratio represented by I (110) / I (004) was calculated from the obtained integrated intensity, and was defined as Rc.

Further, it spheronized graphite by the manufacturing method of this embodiment, a tap density of typically 0.75 g / cm ³ or more, preferably 0.80 g / cm ³ or more, be a conventional 1.10 g / cm ³ or less , Preferably 1.05 g / cm ³ or less.
The graphite spheroidized by the manufacturing method of this embodiment does not have a high tap density because the spheroidization gradually proceeds. Therefore, when manufacturing a negative electrode, you may perform compression molding. The compression molding can be performed at a pressure of 20 kg / cm ² or more and 200 kg / cm ² or less, for example. For the tap density, a method similar to the measurement of the tap density of the flake graphite can be used.

Further, the graphite spheroidized by the production method of the present embodiment preferably has a volume-based average particle size (d50) of usually 5 μm or more, 10 μm or more, and more preferably 15 μm or more. Moreover, it is 50 micrometers or less normally, it is preferable that it is 40 micrometers or less, and it is more preferable that it is 35 micrometers or less.
Graphite that has been spheroidized by the production method of the present embodiment has a tendency that the average particle diameter tends to be relatively large because spheroidization proceeds slowly. The volume-based average particle diameter (d50) can be measured by the same measurement method as the volume-based average particle diameter of the flaky graphite.

Further, the graphite spheroidized by the production method of the present embodiment has a BET specific surface area (SA) of usually 1 m ² / g or more, preferably 3 m ² / g or more, more preferably 5 m ² / g or more. 50 m ² / g or less, preferably 20 m ² / g or less, more preferably 10 m ² / g or less. The BET specific surface area (SA) can be measured by the same measurement method as the BET specific surface area (SA) of the scaly graphite.

Further, the graphite spheroidized by the production method of this embodiment has an aspect ratio of usually 10 or less, preferably 5 or less, more preferably 3 or less. If the aspect ratio is too large, the particle shape is not spherical or elliptical, but discoid or plate-like, and becomes close to scale-like graphite. On the other hand, when the aspect ratio is small, the particle shape becomes elliptical or spherical, and the continuity of the voids between the particles when used as an electrode is secured, the mobility of lithium ions is increased, and the rapid charge / discharge characteristics are excellent. Show the trend. The aspect ratio is the ratio of the length of the major axis to the minor axis of the particle, and the minimum value is 1. Therefore, the lower limit of the aspect ratio is usually 1. The aspect ratio can be measured by the same measurement method as that for the scale-like graphite.

Further, the graphite spheroidized by the production method of the present embodiment has a surface spacing (d002) of 002 planes by an X-ray wide angle diffraction method of usually 0.337 nm or less. If the d002 value is too large, it indicates that the crystallinity is low, and the initial irreversible capacity may increase. On the other hand, the theoretical value of the interplanar spacing of the 002 plane of graphite is 0.335 nm and is usually 0.335 nm or more.
Moreover, Lc by the X-ray wide angle diffraction method of spheroidized graphite is usually 90 nm or more, preferably 95 nm or more. When Lc is too small, it indicates that the crystallinity is lowered, and there is a tendency to decrease the capacity due to the increase of the irreversible capacity. In addition, d002 and Lc can be measured by the same measuring method as d002 and Lc of the scale-like graphite.

The graphite spheroidized by the production method of this embodiment is used as a carbon material for producing a negative electrode for a lithium ion secondary battery, and in that case, it may be used as a multilayer structure carbon material, or , And may be used together with other multilayer carbon materials.
The multi-layer structure carbon material is a carbon material in which carbon is coated on the surface of spheroidized graphite. Multi-layered carbon materials are made by mixing petroleum-based or coal-based tars and pitches, resins such as polyvinyl alcohol, polyacrylonitrile, phenolic resin, and cellulose with a solvent if necessary in a non-oxidizing atmosphere. It is obtained by firing at 500 ° C to 2500 ° C, preferably 700 ° C to 2000 ° C, more preferably 800-1500 ° C. If necessary, pulverization and classification may be performed after firing. The coverage, which is the amount of amorphous carbon coating the spheroidized graphite particles, is usually in the range of 0.1 to 20%, preferably in the range of 0.2 to 15%, more preferably 0.4 to 10%. % Range. If the amount of the coated amorphous carbon is too small, the high acceptability of Li ions possessed by the amorphous carbon cannot be fully utilized, and the rapid chargeability is lowered. When the amount of the coated amorphous carbon is large, the influence of the irreversible capacity of the amorphous carbon amount is increased, and the resulting capacity tends to be reduced.

Another embodiment of the present invention is a negative electrode for a lithium ion secondary battery comprising a current collector and an active material layer formed on the current collector, wherein the active material contains the spheroidized graphite. .
In order to produce a negative electrode using spheroidized graphite by the production method according to the present embodiment, a negative electrode material containing spheroidized graphite and a binder resin are mixed into a slurry with an aqueous or organic solvent, and if necessary, A thickener may be added to and applied to the current collector and dried. As the binder resin, it is preferable to use a resin that is stable with respect to the non-aqueous electrolyte and water-insoluble. For example, rubbery polymers such as styrene, butadiene rubber, isoprene rubber, ethylene / propylene rubber; synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate, and aromatic polyamide; styrene / butadiene / styrene block copolymers and hydrogenated products thereof, Thermoplastic elastomers such as styrene / ethylene / butadiene, styrene copolymer, styrene / isoprene, styrene block copolymer and hydride thereof; syndiotactic-1,2-polybutadiene, ethylene / vinyl acetate copolymer, ethylene Soft resinous polymers such as copolymers with α-olefins having 3 to 12 carbon atoms; fluorine such as polytetrafluoroethylene / ethylene copolymers, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene It can be used as the polymer. Examples of the organic medium include N-methylpyrrolidone and dimethylformamide.

The binder resin is usually used in an amount of 0.1 parts by mass or more, preferably 0.2 parts by mass or more with respect to 100 parts by mass of the negative electrode material. When the ratio of the binder resin is too small, the binding force between the negative electrode materials or between the negative electrode material and the current collector is weak, and the negative electrode material is peeled off from the negative electrode to deteriorate the recycle characteristics in which the battery capacity is reduced. On the other hand, when the ratio of the binder resin is too large, the capacity of the negative electrode is reduced, and problems such as the entry and exit of lithium ions into the negative electrode material are hindered. Accordingly, the binder resin is preferably used so that it is at most 10 parts by mass, usually 7 parts by mass or less, with respect to 100 parts by mass of the negative electrode material.
As the thickener added to the slurry, water-soluble celluloses such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, polyvinyl alcohol, polyethylene glycol, and the like may be used. Of these, carboxymethylcellulose is preferred. The thickener is usually used in an amount of 0.1 parts by mass or more, preferably 0.2 parts by mass or more, usually 10 parts by mass or less, preferably 7 parts by mass or less with respect to 100 parts by mass of the negative electrode material.

As the negative electrode current collector, copper, copper alloy, stainless steel, nickel, titanium, carbon, or the like that is conventionally known to be used for this purpose may be used. The shape of the current collector is usually a sheet shape, and those having an uneven surface, or using a net, punching metal or the like are also preferable.
After applying a slurry of negative electrode material and binder resin to the current collector and drying, pressurize to increase the density of the electrode formed on the current collector, thereby increasing the battery capacity per unit volume of the negative electrode layer Is preferred. The density of the electrode is usually 1.2 g / cm ³ or more, preferably 1.3 g / cm ³ or more, and usually 1.9 g / cm ³ or less, preferably 1.8 g / cm ³ or less. If the electrode density is too small, the thickness of the electrode increases, and the amount that can be accommodated in a battery of a certain size decreases, resulting in a decrease in battery capacity. When the electrode density is too large, the interparticle voids in the electrode are reduced, the amount of the electrolyte solution retained in the voids is reduced, and the mobility of Li ions is deteriorated, thereby reducing the rapid charge / discharge characteristics.

Another embodiment of the present invention is a lithium ion secondary battery that includes a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, and the negative electrode is the negative electrode.
The lithium ion secondary battery according to this embodiment can be prepared according to a conventional method except that the above negative electrode is used. As a positive electrode material, lithium such as lithium cobalt composite oxide whose basic composition is represented by LiCoO ₂ , lithium nickel composite oxide represented by LiNiO ₂ , lithium manganese composite oxide represented by LiMnO ₂ or LiMn ₂ O ₄ Transition metal complex oxides, transition metal oxides such as manganese dioxide, and mixtures of these complex oxides, as well as TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , CrO ₃ , V ₃ O ₃ , FeO ₂ , GeO ₂ , LiNi _0.33 Mn _0.33 Co _0.33 O _2, or the like may be used. A positive electrode can be produced by slurrying a mixture of these positive electrode materials with a binder resin with an appropriate solvent, and applying and drying to a current collector. The slurry preferably contains a conductive material such as acetylene black or ketjen black. Moreover, you may contain a thickener as desired. As the thickener and the binder resin, those well-known for this application, for example, those exemplified as those used for the production of the negative electrode may be used. The compounding ratio with respect to 100 parts by mass of the positive electrode material is usually 0.5 parts by mass or more, preferably 1 part by mass or more, and usually 20 parts by mass or less, preferably 15 parts by mass or less. The thickener is usually 0.2 parts by mass or more, preferably 0.5 parts by mass or more, and usually 10 parts by mass or less, preferably 7 parts by mass or less. When the binder resin is slurried with water, it is usually 0.2 parts by mass or more, preferably 0.5 parts by mass or more, and usually 10 parts by mass or less, preferably 7 parts by mass or less, such as N-methylpyrrolidone. When it is slurried with an organic solvent that dissolves the binder resin, it is usually 0.5 parts by mass or more, preferably 1 part by mass or more, and usually 20 parts by mass or less, preferably 15 parts by mass or less. As the positive electrode current collector, aluminum, titanium, zirconium, hafnium, niobium, tantalum, or an alloy thereof may be used. Of these, aluminum, titanium, tantalum or an alloy thereof is preferably used, and aluminum or an alloy thereof is most preferably used.

As the electrolytic solution, a solution in which various lithium salts are dissolved in a conventionally known non-aqueous solvent can be used. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, cyclic esters such as γ-butyrolactone, crown ethers, 2- Cyclic ethers such as methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuran, 1,3-dioxolane, chain ethers such as 1,2-dimethoxyethane, etc. may be used. Usually some of these are used together. Of these, it is preferable to use a cyclic carbonate and a chain carbonate, or another solvent in combination.

Further, compounds such as vinylene carbonate, vinyl ethylene carbonate, succinic anhydride, maleic anhydride, propane sultone, diethyl sulfone, difluorophosphate such as lithium difluorophosphate, and the like may be added. Furthermore, an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene may be added.
Examples of the electrolyte dissolved in the non-aqueous solvent include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) _3, or the like may be used. The concentration of the electrolyte in the electrolytic solution is usually 0.5 mol / liter or more, preferably 0.6 mol / liter or more, and usually 2 mol / liter or less, preferably 1.5 mol / liter or less.

The separator interposed between the positive electrode and the negative electrode is preferably a porous sheet or non-woven fabric of polyolefin such as polyethylene or polypropylene.
In the lithium ion secondary battery according to this embodiment, the negative electrode / positive electrode capacity ratio is preferably designed to be 1.01 or more and 1.5 or less, more preferably 1.2 or more and 1.4 or less. .

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, it cannot be overemphasized that the scope of the present invention is not limited only to an Example.
<Example 1>
Scale graphite (particle size (d50) 46 μm, SA: 5 m ² / g, tap density: 0.55 g / cm ³ ), and silicon (particle size (d50) 1.8 μm) in a weight ratio of 98: 2 in a bag The mixture was shaken several times to prepare a mixed powder of flaky graphite and silicon.
Next, using the spiral tube spheronizing device (tube inner diameter 1.74 mm, device total length 1.6 m, spiral curvature diameter 80 mm) shown in FIG. 1, the inlet pressure is set to 0.42 MPa with a pressurizing pump, and the gas velocity at the outlet is set. 245 m / s, gas flow rate 35 L / min. As above, the mixed powder was charged from the charging port and spheroidized.
In the spheronization treatment, the same operation as described above was repeated 28 times. The obtained spheroidized graphite was molded at a pressure of 120 kg / cm ² using an IR molding machine to obtain a negative electrode material. 3 and 4 show SEM images of the negative electrode material, and Table 1 shows the physical properties.
In addition, the white part which exists in the solid line circle in FIG.3 and FIG.4 is Si, and the white part shown by the arrow is an impurity derived from a raw material.

<Example 2>
A negative electrode material was obtained in the same manner as in Example 1 except that the silicon particle size (d50) was 5 μm and the spheronization treatment was performed 25 times. The physical properties are shown in Table 1.

<Battery performance evaluation>
The negative electrode material manufactured in Examples 1 and 2, acetylene black (HS-100) as a conductive material, and polyamic acid NMP solution were added and mixed so that the weight ratio of Si: acetylene black: polyimide was 70:10:20. did. After the obtained mixture was applied, it was preliminarily dried at 90 ° C. for 1 hour. The pre-dried electrode was pressed by a roll press and then heat treated at 350 ° C. for 1 hour under a nitrogen stream to be cured.

The obtained negative electrode was transferred to a glove box under an argon atmosphere, and 1 mol / L-LiPF ₆ electrolysis was performed using a mixed solution of fluoroethylene carbonate (FEC) / dimethyl carbonate (DMC) = 2/8 (weight ratio) as an electrolyte. A coin battery (lithium ion secondary battery) was manufactured using the liquid, Celgard 2325 as a separator, and a lithium metal counter electrode as a counter electrode.

  About the manufactured lithium ion secondary battery, the charge capacity and the discharge capacity were measured at the rates of 0.05C and 0.2C, and the initial efficiency was calculated. These results are shown in Table 2.

DESCRIPTION OF SYMBOLS 10 Spiral tube spheronizer 1 Input port 2 Collection port 3 Cylindrical tube 4 Pressure pump 5 Feeder 6 Hopper 20 Screw tube spheronizer 11 Core member 12 Shell member 13 Groove 14 Lid

Claims (9)

A method for producing spheroidized graphite comprising a preparation step of preparing a mixture of flaky graphite and a metal-containing substance, and a spheronization step of spheronizing the mixture,
The spheronization step is performed using a spheronization processing apparatus having a spiral channel, and the spheroidized graphite is folded and spheroidized in a state of containing a metal-containing material.   2. The method for producing spheroidized graphite according to claim 1, wherein in the preparation step, a weight ratio of the flaky graphite to the metal-containing substance is 99: 1 to 90:10.   The method for producing spheroidized graphite according to claim 1 or 2, wherein the metal-containing substance contains at least one selected from the group consisting of Si, Sn, Al, and SiO.   The produced spherical graphite has a peak intensity ratio Rc (= I (110) / I (004)) corresponding to lattice planes (110) and (004) obtained by wide-angle X-ray diffraction measurement of 0.05. The method for producing spheroidized graphite according to any one of claims 1 to 3, which is 0.22 or less.   The method for producing spheroidized graphite according to any one of claims 1 to 4, wherein the produced spheroidized graphite has a volume-based average particle diameter (d50) of 3 µm or more and 50 µm or less.   Furthermore, the manufacturing method of the spheroidized graphite of any one of Claim 1 to 5 including a compression molding process.   Spheroidized graphite produced by the method according to any one of claims 1 to 6.   A lithium ion secondary battery negative electrode comprising a current collector and an active material layer formed on the current collector, wherein the active material contains the spheroidized graphite according to claim 7. Negative electrode for ion secondary battery.   A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte solution, wherein the negative electrode is a negative electrode for a lithium ion secondary battery according to claim 8. battery.