JP2014152042A - Carbon material, negative electrode for lithium ion secondary battery including the same, and lithium ion secondary battery having the negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon material having a novel structure in which the carbon material is highly conglobated but its tapped density is not too high, thus voids being present in the material, and such voids may contain metal particles having a higher capacity than graphite.SOLUTION: In the carbon material, a ratio Rc(=I(110)/I(004)) of the peak intensity corresponding to the lattice plane (110) to the peak intensity corresponding to the lattice plane (004) by wide angle x-ray diffraction measurements is 0.05 or more and 0.22 or less, and a tapped density is 0.75 g/cmor more and 0.92 g/cmor less.

Description

  The present invention relates to a carbon material used for a lithium ion secondary battery, and also relates to a negative electrode containing the carbon material 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.

  As a negative electrode material of a lithium ion secondary battery, a carbon material that is preferable in terms of cost and durability is often used. As a method for increasing the capacity of a lithium ion secondary battery, a design is made in which as many charge / discharge active materials as possible are packed in a limited battery volume by increasing the electrode density.

  Natural graphite, which is a raw material for the carbon material, is a scaly powder, and when used as a carbon material, it is spheroidized to increase the electrode density. As a spheronization processing method, for example, the use of an apparatus disclosed in Patent Document 1 has been proposed.

  In addition, it has been proposed to use a device having a path in which a straight line is bent to the left and right several times and a Z-shape is continuous when processing scaly graphite. By using such an apparatus, it is spheroidized natural graphite that is made into a substantially spherical shape by bending the ends of the scaly graphite particles, and has an average circularity of 0.899 or more, and spheroidized natural graphite. Spherical natural graphite having the edge surfaces oriented in the same direction can be obtained.

Japanese Patent Laying-Open No. 2005-066378 Japanese Patent No. 4274090

For the negative electrode used in the lithium ion secondary battery, it is desired to increase the electrode density in order to increase the capacity.
The present inventors consider that it is generally necessary to increase the sphericity of the carbon material in order to increase the electrode density with the aim of increasing the capacity of the lithium ion secondary battery. In order to obtain a carbon material having a high spheroidization degree, a spheronizing device is used, as disclosed in Patent Document 1, which imparts an impact force to the flaky graphite by collision to spheroidize. When such an apparatus is used, the spheroidization degree of the carbon material increases, but at the same time the tap density becomes very high. In addition, the scaly graphite may be broken by a strong impact, a large amount of fine powder is generated, and the particle size is reduced.
On the other hand, the graphite obtained by the method disclosed in Patent Document 2 has a conical shape, a cylindrical shape, or an irregular spherical shape. Therefore, even if manufactured by the method disclosed in Patent Document 2, it is difficult for the average circularity to be 0.942 or more, and the lattice planes (110) and (004) as defined in the present invention are used. It was only possible to obtain a graphite having a high peak intensity ratio corresponding to the above, that is, graphite that does not increase to the sphericity of the carbon material of the present invention.

  The present invention provides a carbon material having a new structure, and in spite of a high degree of spheroidization, the tap density is not too high, in other words, a carbon material having voids in the carbon material is provided. The task is to do. A carbon material with such a structure has a high degree of spheroidization, and an appropriate tap density, that is, an appropriate gap exists in the carbon material, so that it becomes a flat particle shape when compression molding at the time of electrode creation. It is considered that the void portion is difficult to be compressed, so that the orientation ratio of the carbon material in the electrode is increased and the diffusion rate of lithium is increased. Furthermore, since voids exist inside, it is possible to enclose a metal-containing substance having a higher capacity than graphite in the voids.

  As a result of intensive studies to solve the above problems, the present inventors adopted a method different from the conventional method in which spheroidization was performed simply by applying an impact force, It was conceived that a carbon material having a high degree of spheroidization and an appropriate tap density can be obtained by folding and spheroidizing scaly graphite by applying a moderate impact.

That is, the outline of the present invention is as follows.
(1) The ratio Rc (= I (110) / I (004)) of peak intensities corresponding to the lattice planes (110) and (004) obtained by wide-angle X-ray diffraction measurement is 0.05 or more and 0.22 A carbon material having a tap density of 0.75 g / cm ³ or more and 0.92 g / cm ³ or less. (2) The carbon material according to (1), wherein the volume-based average particle size (d50) is 3 μm or more and 50 μm or less.
(3) The carbon material according to (1) or (2), wherein the flaky graphite is folded by a spheronization treatment apparatus having a spiral flow path.
(4) 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 is any one of (1) to (3) The negative electrode for lithium ion secondary batteries containing the carbon material of description.
(5) 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 (4) Ion secondary battery.

  According to the present invention, a carbon material having a new structure can be provided. The carbon material provided by the present invention is a carbon material that has a high spheroidization degree but does not have a too high tap density, in other words, has a void inside. Since the carbon material provided by the present invention has voids inside, it is possible to enclose a metal-containing substance having a higher capacity than graphite in the voids. In addition, since moderate voids exist in the carbon material, it is considered that when the negative electrode is formed by compression molding, the orientation ratio of the carbon material in the electrode is increased and the lithium diffusion rate is 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 spheroidized graphite which concerns on the embodiment of this invention (drawing substitute photograph). It is a SEM image showing the cross section of the spheroidized graphite which concerns on the embodiment of this invention (drawing substitute photograph).

Hereinafter, the present invention will be described in more detail, but the present invention is not limited to specific embodiments.
The carbon material according to the embodiment of the present invention has a feature that the tap density is not high despite the high degree of spheroidization, unlike the conventional carbon material. Specifically, 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 is 0.05 or more, 0 The carbon material has a tap density of 0.75 g / cm ³ or more and 0.92 g / cm ³ or less.
The carbon material which concerns on this embodiment turns into a carbon material which a space | gap exists inside by satisfy | filling the said requirements. A carbon material with such a structure has a high degree of spheroidization, and an appropriate tap density, that is, an appropriate gap exists in the carbon material, so that it becomes a flat particle shape when compression molding at the time of electrode creation. It is considered that the void portion is difficult to be compressed, so that the orientation ratio of the carbon material in the electrode is increased and the diffusion rate of lithium is increased. Furthermore, since voids exist inside, it is possible to enclose a metal-containing substance having a higher capacity than graphite in the voids.

Specifically, 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 carbon material is preferably 0. 0.08 or more, more preferably 0.10 or more, still more preferably 0.12 or more, particularly preferably 0.15 or more, preferably 0.21 or less, more preferably 0.20 or less.
The Rc (= I (110) / I (004)) of the carbon material was calculated as follows. A sample of 0.5 g of carbon material placed in a pressure cell, pressurized at 600 Kgf / cm ² for 5 seconds, and molded into a pellet shape was subjected to black X-ray diffraction on the sample by X-ray diffraction (110 ) And (004) planes are measured, and the measured chart is subjected to peak separation by fitting using asymmetric Pearson VII as a profile function, and the peaks of the (110) plane and (004) plane are measured. The integrated intensity was calculated. The intensity ratio represented by I (110) / I (004) was calculated from the obtained integrated intensity, and was defined as Rc.

The tap density is preferably 0.78 g / cm ³ or more, more preferably 0.80 g / cm ³ or higher, preferably 0.91 g / cm ³ or less, more preferably 0.90 g / cm ³ or less, more preferably is 0.895 g / cm ³ or less, particularly preferably 0.891 g / cm ³ or less.
The tap density is a powder density measuring device, a powder density measuring device, a “Tap Denser KYT-4000” manufactured by Seishin Enterprise Co., Ltd., having a diameter of 1.6 cm and a volume capacity of 20 cm ³ . The carbon material is dropped into a cylindrical tap cell through a sieve having an opening of 300 μm, and the cell is fully filled, and then a tap with a stroke length of 10 mm is performed 1000 times, and the density obtained from the volume at that time and the weight of the sample is obtained. Defined as tap density.

In order to produce a carbon material having such a high spheroidization degree and a feature that the tap density is not high, a gradual impact is applied to the end portion of the scaly graphite, and the end portion is repeatedly folded, What is necessary is just to advance spheroidization gently. In the conventional method, the spheroidization is promoted by colliding with the wall surface from the front. However, in this embodiment, the flaky graphite is inclined with respect to the wall surface in order to bend the flaky graphite by a gentle impact. It is preferable to make it collide. Further, it is more preferable that the scaly graphite collides with the curved surface structure.
As the spheronization processing apparatus for slowly advancing spheronization, an apparatus having a spiral flow path is preferably exemplified. Specifically, using a spiral tube spheronizing apparatus 10 having a helical cylindrical tube 3 as shown in FIG. 1, scale-like graphite is introduced from the inlet 1 of the cylindrical tube and allowed to pass through the cylindrical tube 3. Then, there is a method of gently folding the flaky graphite.
In addition, the core member 11 includes a cylindrical core member 11 and a shell member 12 having a cylindrical space at the center. The inner wall of the shell member 12 includes a spiral groove 13, and the outer wall of the core member 11 and the inner wall of the shell member 12 are provided. , The screw tube spheroidizing device 20 that forms a spiral channel between the spiral groove 13 existing on the inner wall of the shell member 12 and the core member 11, There is a method in which flaky graphite is gently folded by introducing flaky graphite from 1 and passing through a spiral groove 13.
In addition, although not shown, there is a method in which the flaky graphite is gently folded by passing the flaky graphite through a fluid stirring device (static mixer) in which a flow path is provided in a cylindrical casing by a swell blade element. .

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 carbon material according to the present embodiment can be manufactured by appropriately setting by those skilled in the art. Can do. Hereinafter, preferable conditions for achieving the carbon material according to the present embodiment 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 is spirally wound so that the flaky graphite collides with the inner wall at an angle (shallow angle) far from the vertical. Is formed. 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 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.

In addition to these processing apparatuses and manufacturing conditions, it is important to repeat the spheronization process a plurality of times in order to manufacture the carbon material according to this embodiment. By this operation, it is considered that the flaky graphite is gently folded, that is, the orientation ratio is not high but the orientation ratio is high. Specifically, the number of spheroidization treatments is usually 3 times or more, preferably 5 times or more, more preferably 10 times or more, and usually 50 times or less, preferably depending on the length of the flow path of the processing apparatus. It may be 40 times or less, more preferably 30 times or less.
In addition, as another control method, with the progress of spheronization, a method of controlling the charging speed of the flake graphite to be charged into the apparatus and the amount of air to be supplied is effective, and by adopting such a method, The production amount is increased while suppressing the generation of fine powder, and the carbon material of this embodiment can be produced efficiently.

Moreover, the raw material used when manufacturing the carbon material of this embodiment will not be specifically limited if it is scaly graphite, However, A preferable physical-property value is 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 can use the same method as the measurement of the tap density of the carbon material according to the present embodiment.

(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, 1.0 g of a sample (about scaly 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 volume-based average particle diameter (d50) of the carbon material of this embodiment is usually preferably 3 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.
In the spheronization apparatus that imparts impact force to the flaky graphite by collision to spheroidize as disclosed in Patent Document 1, since the graphite is reduced in size by impact, the graphite having a high degree of spheroidization is At the same time, the average particle size is reduced. On the other hand, in this embodiment, since the end of the scale graphite is gently impacted and folded repeatedly, and the spheroidization proceeds slowly, the graphite particle size does not decrease. Therefore, the carbon material of this embodiment tends to have a relatively large average particle diameter. 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.

The carbon material of this 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, and usually 50 m ² / g or less, preferably It is 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.

  The carbon material of this embodiment has an aspect ratio of usually 3 or less, preferably 2 or less, more preferably 1.3 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.

In the carbon material of this embodiment, the interplanar spacing (d002) of the 002 plane by the X-ray wide angle diffraction method is 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 a carbon material is 90 nm or more normally, Preferably it is 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 carbon material according to this embodiment is used as a carbon material for producing a negative electrode for a lithium ion secondary battery. In this case, the carbon material may be used as a multi-layer structure carbon material or other multi-layers. It may be used with a structural carbon material.
The multi-layer structure carbon material is a carbon material in which carbon is coated on the surface of the carbon material according to the present embodiment. 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 is the carbon material.
In order to produce a negative electrode using the carbon material according to the embodiment of the present invention, a mixture of a negative electrode material and a binder resin is made into a slurry with an aqueous or organic solvent, and a thickener is added to the slurry if necessary. What is necessary is just to apply | coat to a collector and to dry. 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, and ethylene / propylene rubber; synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate, and aromatic polyamide; styrene, butadiene,
Thermoplastic elastomers such as styrene block copolymers and their hydrogenated products, styrene / ethylene / butadiene, styrene copolymers, styrene / isoprene, styrene block copolymers and their hydrides; syndiotactic-1,2-polybutadiene , Ethylene / vinyl acetate copolymer, soft resin-like polymer such as copolymer of ethylene and α-olefin having 3 to 12 carbon atoms; polytetrafluoroethylene / ethylene copolymer, polyvinylidene fluoride, poly Fluorinated polymers such as pentafluoropropylene and polyhexafluoropropylene can be used. 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.
<Examples 1-3>
Using the spiral tube spheronizing device shown in FIG. 1 (tube inner diameter 1.74 mm, device total length 1.6 m, spiral curvature diameter 80 mm), the inlet pressure is 0.42 MPa with a pressure pump, and the gas velocity at the outlet is 245 m / s. The gas flow rate is 35 L / min. As above, flaky graphite (particle diameter (d50) 46 μm, SA: 5 m ² / g, tap density: 0.55 g / cm ³ ) was introduced from the inlet, and the first spheronization treatment was performed. From the second time on, powder was supplied at a speed exceeding the previous powder charge speed.
The spheronization treatment was performed 15 times in Example 1, 20 times in Example 2, and 30 times in Example 3. Table 1 shows the physical properties of the obtained graphite.

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 (5)

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 is 0.05 or more and 0.22 or less. ,
A carbon material having a tap density of 0.75 g / cm ³ or more and 0.92 g / cm ³ or less.   The carbon material according to claim 1 whose volume standard average particle diameter (d50) is 3 micrometers or more and 50 micrometers or less.   The carbon material according to claim 1 or 2, wherein the flaky graphite is folded by a spheroidizing apparatus having a spiral flow path.   It is a negative electrode for lithium ion secondary batteries provided with a collector and the active material layer formed on this collector, Comprising: This active material is carbon in any one of Claims 1-3. A negative electrode for a lithium ion secondary battery containing a material. A lithium ion secondary battery comprising a positive and negative electrodes 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 4. battery.