JP2007076929A - Manufacturing method for graphitized powder of mesocarbon microspheres - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a graphitized material which has high crystalinity and spherical shape, and is suitable to be used as a material for lithium-ion secondary batteries. <P>SOLUTION: The manufacturing method is for the graphitized powder consisting of mesocarbon microspheres and comprises the steps of: peeling off a surface part of the sintered powder of mesocarbon microspheres and obtaining the mixture of peeled surface portions and remaining portions; removing the peeled portions from the above mixture to obtain the remaining portions; and graphitizing the remaining portions to obtain the graphitized powder of mesocarbon microspheres. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing mesocarbon microsphere graphitized powder suitable for a negative electrode material for a lithium ion secondary battery.

In recent years, with the miniaturization or high performance of electronic devices, there is an increasing demand for higher energy density of batteries. In this situation, a lithium ion secondary battery using lithium as a negative electrode has attracted attention because it has the advantages of high energy density and high voltage.
In this lithium ion secondary battery, it is known that when lithium metal is used as it is as a negative electrode, lithium is deposited in a dendrite state during charging, so that the negative electrode deteriorates and the charge / discharge cycle is short. There is also a possibility that lithium deposited in a dendritic state penetrates the separator, reaches the positive electrode, and is short-circuited.

For this reason, each material for positive and negative electrodes is composed of two kinds of intercalation compounds with different oxidation-reduction potentials, each functioning as a lithium ion support, and the non-aqueous solvent enters and exits during the charge / discharge process. Lithium ion secondary batteries are being studied.
As this negative electrode material, it has been proposed to use a carbon material that has the ability to occlude and release lithium ions and can prevent the precipitation of lithium metal. A wide variety of structures, structures, and forms such as a graphite crystalline structure or a disordered layer structure are known as carbon materials, and the electrode performance including the operating voltage during charging / discharging varies greatly. Among them, graphite materials that are particularly excellent in charge / discharge characteristics and exhibit high discharge capacity and potential flatness are promising.

As the crystalline graphite structure develops, this graphite material can easily form an intercalation compound with lithium, and a large amount of lithium is inserted between layers of the carbon network surface, so that a high discharge capacity can be obtained. Has been reported (for example, see Non-Patent Document 1).
In addition, the graphite material forms various layer structures depending on the amount of lithium inserted, and is flat in a region where they coexist and exhibits a high potential close to lithium metal (for example, see Non-Patent Document 2).
As described above, it is considered that a high output can be obtained when an assembled battery is formed using a graphite material. Generally, the theoretical capacity (limit value) of a carbon anode material is finally determined by combining graphite and lithium. When the ideal graphite intercalation compound LiC ₆ is formed, the discharge capacity is 372 mAh / g.

Examples of the negative electrode material for a lithium ion secondary battery using such a graphite material include those described in Patent Document 1 shown below.
In Patent Document 1, a graphite precursor such as bulk mesophase, mesophase spherule, and raw coke containing a specific amount of volatile matter is subjected to mechanochemical treatment that can simultaneously apply shearing force and compressive force, and then graphitized. By suppressing the fusion of materials during graphitization (high temperature heating) performed in a non-oxidizing atmosphere, the surface of the nucleus made of highly crystalline graphite is relatively low compared to the nucleus. In other words, a graphite material in which a uniform low crystalline thin film does not peel from the core is described.
A lithium ion secondary battery using such a graphite material as a negative electrode material can reduce the irreversible capacity while maintaining a high discharge capacity, and further greatly improve the initial charge / discharge efficiency. It is stated that you can.

By the way, it is preferable that the graphite material functioning as a lithium ion carrier as described above has a spherical shape.
For example, when the graphite material is flake-like natural graphite, or has a non-spherical shape such as a needle shape or a fiber shape, the graphite material has a larger specific surface area than that of a spherical shape. This is because the decomposition reaction of the electrolyte solution of the lithium ion secondary battery occurs at the time of charge and discharge, which may cause a decrease in coulomb efficiency and gas generation due to decomposition of the electrolyte solution.

On the other hand, if it is a spherical graphite material such as mesocarbon microsphere graphitized powder, problems such as a decrease in Coulomb efficiency as described above hardly occur.
However, the conventional mesocarbon microsphere graphitized powder has relatively low crystallinity and a low discharge capacity compared with, for example, natural graphite. When the mesocarbon spherules are removed from the aromatic pitch matrix or the aliphatic pitch matrix, pitch and metacarbon, which are non-graphitizable carbon, remain on the surface of the mesocarbon spherules. The crystallinity of carbon spherules is low.
JP 2003-171110 A T.A. IIJIMA et al., “Application of Carbon Fibers and Pitch Cokes for Negative Electrodes of Lithium Rechargeable Batteries”, Electrochemistry and Industrial Physical Chemistry, The Electrochemical Society of Japan, July 1993, vol 61, No. 2, p. 1383 T.A. Ohzuku, “Formation of Lithium -Graphite Intercalation Compounds in Nonaqueous Electrolytes and Their Application as a Negative Electrade for a Lithium Ion Cell”, J. Electrochem. Soc., USA, The Electrochemical Society. Inc, September 1993, vol 140, No9, p. 2490

Thus, the graphite material used as the negative electrode material for the lithium ion secondary battery preferably has high crystallinity and is spherical.
However, conventionally, such a graphite material does not exist, and development thereof has been desired.

  The inventor of the present invention uses a specific type of graphite material, and further graphitized powder produced by removing the low crystal portion and using the remaining high crystal portion to achieve high crystallinity that solves the above problem. It was found to be a graphite material having a spherical shape.

That is, the present invention includes the following (1) to (5).
(1) A method for producing mesocarbon microsphere graphitized powder, in which the surface portion of the mesocarbon microsphere fired powder is peeled off by a peeling means to obtain a mixture of the peeled portion and the remaining portion which are the peeled surface portions. A mesocarbon comprising: a peeling step; a removing step of removing the peeled portion from the mixture to obtain the remaining portion; and a graphitizing step of obtaining a mesocarbon microsphere graphitized powder by graphitizing the remaining portion. Method for producing small spherical graphitized powder.
(2) The mesocarbon microsphere fired powder is a mesocarbon microsphere fired powder obtained by treating mesocarbon microspheres in a non-oxidizing atmosphere at 400 to 1300 ° C. Method for producing small spherical graphitized powder.
(3) The method for producing mesocarbon microsphere graphitized powder according to (1) or (2), wherein the peeling means is a mechanochemical treatment.
(4) The method for producing mesocarbon microsphere graphitized powder according to any one of (1) to (3), wherein the abundance ratio of the peeled portion in the mixture is 1 to 5% by mass.
(5) The method for producing mesocarbon microsphere graphitized powder according to any one of (1) to (4), wherein the mesocarbon microsphere graphitized powder is a negative electrode material for a lithium ion secondary battery.

  Since the lithium ion secondary battery negative electrode material manufactured by such a method has a high crystallinity comparable to that of natural graphite, the discharge capacity is high. Furthermore, since it is spherical, compared to flake-shaped natural graphite, etc., the decomposition reaction of the electrolyte solution of the lithium ion secondary battery is less likely to occur during charging and discharging, the Coulomb efficiency is lowered, and the gas generation due to the decomposition of the electrolyte solution Is unlikely to occur.

The present invention is a method for producing mesocarbon microsphere graphitized powder, wherein the surface portion of the mesocarbon microsphere fired powder is peeled off by a peeling means, and the mixture of the peeled portion and the remaining portion, which is the peeled surface portion, is obtained. A mesocarbon comprising: an exfoliating step to be obtained; a removing step for removing the exfoliated portion from the mixture to obtain the remaining portion; and a graphitizing step for obtaining a mesocarbon microsphere graphitized powder by graphitizing the remaining portion. This is a method for producing small spherical graphitized powder.
Such a method for producing mesocarbon microsphere graphitized powder is hereinafter also referred to as “the production method of the present invention”.

  The production method of the present invention uses mesocarbon spheroids as a raw material. And a peeling process, a removal process, and a graphitization process are comprised.

First, the mesocarbon microsphere sintered powder will be described.
The mesocarbon small sphere sintered powder used in the production method of the present invention is obtained by sintering mesocarbon small spheres.

This mesocarbon microsphere is a spherical product obtained by condensation or stacking of aromatic components in tar or pitch.
For example, filtration residue obtained by filtering small spheres showing optical anisotropy generated in a pitch matrix when coal-based and / or petroleum-based pitch is heat-treated, or separated from the pitch matrix using an organic solvent It is a small sphere.

The heat treatment of the coal-based and / or petroleum-based pitch may be performed under reduced pressure, normal pressure, or increased pressure. The temperature range of this heat treatment is usually 300 to 1200 ° C., preferably 350 to 600 ° C., and the heat treatment time is not particularly limited, but is about 0.5 to 100 hours.
This heat treatment is preferably performed in a reducing atmosphere (oxygen concentration of about 3% by volume or less), but can also be performed in a slight (weak) oxidizing atmosphere. Note that this heat treatment may be performed a plurality of times.
Furthermore, the treatment after the heat treatment is not particularly limited, and the mesocarbon spherules may be separated and pulverized by any method. For example, the separation can be performed by heating and pressure filtration, heating and vacuum filtration, or the like.

Such mesocarbon spherules are almost spherical (spherical shape, elliptical in cross section, indeterminate shape with rounded corners, and a shape close to a spherical shape as a whole) The average aspect ratio (ratio between the maximum long axis length and the length of the axis perpendicular thereto) is 3 or less, preferably 2 or less, and is more preferably spherical, that is, the aspect ratio is closer to 1. . Moreover, although an average particle diameter is not specifically limited, It is preferable that it is 5-100 micrometers, and it is more preferable that it is 5-30 micrometers.
The aspect ratio and the average particle diameter here are obtained by performing cross-sectional observation with a scanning electron microscope on 100 particles and measuring the maximum long axis length of the particle and the length of the axis perpendicular thereto. is there. The aspect ratio is a ratio between the maximum long axis length and the length of the axis perpendicular to the maximum long axis length, and an average of 100 particles is obtained. For the average particle diameter, the average value of the maximum long axis length and the length of the axis perpendicular to the maximum axis length is obtained, and that value is taken as the diameter of one observed particle. The same operation is repeated for 100 particles, and the average value is obtained. Is what we asked for.
Hereinafter, the aspect ratio and average particle diameter of the mesocarbon microsphere sintered powder and the graphitized product thereof indicate values measured by the same method.

  In addition, the mesocarbon microspheres obtained by such a method have different crystallinity between the surface portion and the inside, and the inside has a higher crystallinity than the surface portion and is similar to natural graphite.

  Such mesocarbon spherules are fired to obtain a fired body, and mesocarbon spherule fired powder used as a raw material in the production method of the present invention.

  Although the method of this baking process is not specifically limited, As a preferable processing method, for example, the mesocarbon microspheres obtained by the above method are 400 to 1300 ° C., preferably 450 to 600 ° C. in a non-oxidizing atmosphere. The processing method which performs the process of 0.5-3h, Preferably 1-2h can be mentioned.

  Here, the non-oxidizing atmosphere means an atmosphere having an oxygen concentration of 1% by volume or less. Components other than oxygen are not particularly limited, and examples thereof include nitrogen, argon, carbon dioxide, and carbon monoxide. The mesocarbon spherules may be calcined in a reaction vessel that has been intentionally adjusted to such an oxygen concentration. However, if the mesocarbon spherules are calcined in a sealed vessel that is substantially shielded from the atmosphere, the mesocarbon spherules may be calcined. Since reducing gas (carbon monoxide or carbon dioxide) is generated from the carbon microspheres, the inside of the sealed container can be made a non-oxidizing atmosphere. The amount of volatile components in the obtained mesocarbon microsphere fired powder is preferably less than 2.0% by mass.

  If the baking treatment is performed in such a temperature range in a non-oxidizing atmosphere in such a temperature range, the low crystalline portion on the surface of the mesocarbon microspheres and the inside can be peeled off by a peeling means described later. . If this treatment temperature is too low, a low crystal portion tends to remain on the surface of the mesocarbon microsphere sintered powder even after applying the peeling means described later. On the other hand, if this treatment temperature is too high, the low crystalline portion of the surface becomes hard and the peeling means described later tends to be difficult to peel.

  In addition, the method of this baking process may be another method, and as a result of the baking process, the low crystal portion on the surface of the mesocarbon microspheres can be easily peeled off from the inside thereof by the peeling means described later. Any method can be used.

Next, the peeling process which the manufacturing method of this invention comprises is demonstrated.
The peeling process which the manufacturing method of this invention comprises is a process of peeling the surface part of the said mesocarbon microsphere baking powder by a peeling means, and obtaining the mixture of the peeling part which is the said surface part which peeled, and the remainder.

Here, the peeling means is a mechanical means for applying a shearing force and / or a compressive force to the mesocarbon small sphere fired powder, and is preferably a mechanical means for simultaneously applying the shearing force and the compressive force. It is further preferable to apply a frictional force.
The mechanical means is preferably a mechanochemical treatment.
Further, this mechanochemical treatment is preferably an apparatus capable of simultaneously applying a compressive force and a shear force to the mesocarbon microsphere sintered powder. For example, a kneader such as a pressure kneader, two rolls, rotating ball mill, hybridization system (manufactured by Nara Machinery Co., Ltd.), mechanomicros (manufactured by Nara Machinery Co., Ltd.), mechanofusion system (Hosokawa Micron Co., Ltd.) Etc.) can be used.

Among these, a device that simultaneously applies a shearing force and a compressive force by utilizing a difference in rotational speed, for example, a mechanofusion system manufactured by Hosokawa Micron Corporation having a schematic mechanism shown in FIGS. 3 (a) to 3 (b) is preferable.
This apparatus uses a rotary drum 11, an internal member (inner piece) 12 having a rotational speed different from that of the rotary drum 11, a circulation mechanism 14 for a mesocarbon microsphere sintered powder 13, and a discharge mechanism 15. While applying centrifugal force to the mesocarbon microsphere sintered powder 13 supplied between the inner member 12 and the inner member 12, the inner member 12 simultaneously applies compressive force and shear force due to the speed difference from the rotating drum 11. By repeated addition, mechanochemical treatment can be performed.
When using an apparatus (FIG. 3) having such a rotating drum and an internal member, the peripheral speed difference between the rotating drum and the internal member is preferably 5 to 50 m / s, more preferably 20 to 50 m / s, The distance between the two is preferably 1 to 50 mm, more preferably 1 to 30 mm, and the treatment time is preferably 5 to 60 min, more preferably 20 to 60 min.
If treated under such operating conditions, it is possible to exfoliate almost all portions having relatively lower crystallinity than the inside formed on the surface of the mesocarbon microsphere sintered powder, and the crystallinity is high. It is preferable because there is almost no peeling to the inner part.

Further, for example, a hybridization system manufactured by Nara Machinery Co., Ltd., whose schematic mechanism is shown in FIG. 2, can be used.
This device uses a device having a fixed drum 21, a rotor 22 that rotates at high speed, a circulation mechanism 24 and a discharge mechanism 25 for a mesocarbon spheroid sintered powder 23, a blade 26, a stator 27, and a jacket 28. An apparatus for supplying the compacted powder 23 between the fixed drum 21 and the rotor 22 and adding a compressive force and a shearing force due to the speed difference between the fixed drum 21 and the rotor 22 to the mesocarbon microsphere sintered powder 23. It may be used for mechanochemical treatment.
In the case of using an apparatus (FIG. 2) including such a fixed drum-high-speed rotating rotor, the peripheral speed difference between the fixed drum and the rotor is preferably 10 to 100 m / s, more preferably 50 to 100 m / s. The time is preferably 30 s to 5 min, more preferably 2 to 5 min.
If treated under such operating conditions, it is possible to exfoliate almost all portions having relatively lower crystallinity than the inside formed on the surface of the mesocarbon microsphere sintered powder, and the crystallinity is high. It is preferable because there is almost no peeling to the inner part.

  In addition, a known conductive material, ion conductive material, surfactant, metal compound, binder, etc., as long as the effect of the present invention is not impaired before, during or after the mechanochemical treatment. These various additives may be added to the mesocarbon microsphere fired powder.

The operating condition of the apparatus in such a peeling means is such that the abundance ratio of the peeling part in the mixture of the peeling part and the remaining part obtained is 1 to 5% by mass, preferably 2 to 3% by mass. It is preferable to select.
This is because the existence ratio (% by mass) of the portion having relatively lower crystallinity than the inside formed on the surface portion of the mesocarbon microsphere sintered powder is the total mass of the mesocarbon microsphere sintered powder. It is because it is 1-5 mass% with respect to it. This is a finding found by the present inventors.
Therefore, if the operating conditions are selected so that the ratio of the exfoliation part in the mixture is in such a range, the crystalline property is relatively higher than the inside formed on the surface of the mesocarbon microsphere sintered powder. This is preferable because the portion having a lower height and the peeled portion more coincide with each other. When it is lower than such a range, the low crystal part is mixed into the remainder, which is not preferable. On the other hand, if it is high, the high crystal portion is mixed in the peeling portion and is removed in the removal step described below, which is not preferable. Further, if the peeling portion is operated under such an operating condition that the existence ratio of the peeling portion becomes too high, the shape of the remaining portion tends to be unable to maintain a spherical shape.

  In the peeling step included in the production method of the present invention, the surface portion of the mesocarbon microsphere fired powder is peeled by such a peeling means. And the mixture of this peeling part and the remainder can be obtained.

Here, the shape of the peeled portion is often in the form of a flake or plate. Moreover, the magnitude | size is about 5 micrometers or less by an average particle diameter.
Moreover, since this peeling part substantially corresponds | corresponds with the part with relatively low crystallinity with respect to the inside formed in the surface part of the said mesocarbon microsphere sintered powder, crystallinity is low.
Here, “low crystallinity” means that the average lattice spacing d ₀₀₂ of the (002) plane in the X-ray wide angle diffraction of the peeled portion is more than 0.34 nm.
The average lattice spacing d ₀₀₂ of (002) plane in the X-ray wide angle diffraction, using a CuKα ray as an X-ray, using a high-purity silicon as a standard substance the diffraction peak of (002) plane of the peeling portion Measure and calculate from the peak position. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 17th Committee of the Japan Society for the Promotion of Science). Specifically, “Carbon Fiber” [Sugirou Otani, pages 733-742 (March 1986) ), Measured by the method described in Modern Editorial Company].

  On the other hand, this remaining part is a part other than the peeled part of the mesocarbon microsphere sintered powder. The shape of the remaining portion is substantially spherical like the mesocarbon small sphere sintered powder, and the average aspect ratio is substantially the same. Moreover, an average particle diameter becomes a little smaller than the said mesocarbon microsphere baking powder, is 28-30 micrometers, and it is preferable that it is 29-30 micrometers.

Further, the remaining portion has a relatively high crystallinity with respect to the peeling portion.
Here, “high crystallinity” means that the average lattice spacing d ₀₀₂ of the (002) plane in the X-ray wide angle diffraction measured by the same method as in the case of the peeled portion is 0.34 nm or less. To do. The balance is preferably crystalline so that the average lattice spacing is not more than 0.337 nm, more preferably not more than 0.3365 nm.

Next, the removal process which the manufacturing method of this invention comprises is demonstrated.
The removing step included in the production method of the present invention is a step of removing the peeling portion from the mixture to obtain the remaining portion.

In the removing step included in the manufacturing method of the present invention, a method for removing the peeling portion from the mixture of the peeling portion and the remaining portion is not particularly limited. It is possible to apply a method capable of removing most of the peeling part (90% by mass or more, preferably 95% by mass or more, more preferably 99% by mass or more of the peeling part) from the mixture.
For example, the separation part and the remaining part can be separated by specific gravity sorting or wind sorting using the difference in shape and specific gravity.

  By such a method, most of the peeling portion can be removed from the mixture. And the said remainder can be obtained. The remaining portion obtained here may contain some of the peeled portions that could not be removed, but even such a case is within the scope of the present invention.

Next, the graphitization process included in the production method of the present invention will be described.
The graphitization step included in the production method of the present invention is a step of graphitizing the remaining part obtained in the removal step to obtain mesocarbon microsphere graphitized powder.

In this graphitization treatment, the remainder obtained in the removing step is graphitized by heating in a non-oxidizing atmosphere using a container such as a crucible.
Here, the non-oxidizing atmosphere means an atmosphere having an oxygen concentration of 3% by volume or less. The remainder may be graphitized in a reaction vessel that is intentionally adjusted to such an oxygen concentration. However, if the remainder is graphitized in a sealed container that is substantially cut off from the atmosphere, a reducing gas (monoxide) is obtained from the remainder. Carbon or carbon dioxide) is generated, so that the inside of the sealed container can be made a non-oxidizing atmosphere.

  The heating temperature is not particularly limited, but it is preferably as high as possible from the viewpoint of increasing crystallinity. Specifically, 2500 ° C. or higher is preferable, and 2800 ° C. or higher is more preferable. The upper limit of the heating temperature is 3150 ° C., preferably 3000 ° C., from the viewpoint of preventing an increase in specific surface area due to excessive high crystallization, heat resistance of the apparatus and sublimation of graphite.

  Under such a non-oxidizing atmosphere, it can be suitably used as a negative electrode material for a lithium ion secondary battery by heating for 0.5 to 50 hours, preferably 2 to 20 hours in the above temperature range. Mesocarbon microsphere graphitized powder having a high degree of graphitization can be obtained.

The mesocarbon microsphere graphitized powder obtained by the production method of the present invention (hereinafter also referred to as “graphitized powder of the present invention”) has a shape close to a sphere, for example, a lump shape, an irregular shape with a rounded corner, It has a spherical shape or an elliptical cross section, an average particle diameter of 5 to 100 μm, an average aspect ratio of 3 or less, and can be preferably used as a material for a negative electrode of a lithium ion secondary battery. The average particle size is preferably 5 to 30 μm, more preferably 15 to 30. The average aspect ratio is preferably 2 or less, and more preferably 1.3 or less.
This nearly spherical shape contributes to improvement of rapid charge / discharge efficiency (high rate characteristics) and cycle characteristics as a negative electrode material for a lithium ion secondary battery.

  In addition, the graphitized powder of the present invention has high crystallinity, and the average lattice spacing measured by the same method as that for the peeled portion and the remaining portion is 0.34 nm or less. The graphitized powder property of the present invention is preferably such that the average lattice spacing is not more than 0.337 nm, more preferably not more than 0.3365 nm.

Moreover, since the graphitized powder of the present invention is almost spherical, it can exhibit a high bulk density. A high bulk density is advantageous because it can reduce the destruction of the material when the negative electrode is produced at a high density.
The bulk density is preferably 0.5 g / cm ³ or more, and particularly preferably 0.7 g / cm ³ or more.

Furthermore, the specific surface area of the graphite powder of the present invention can be arbitrarily designed according to the characteristics of the lithium ion secondary battery, the properties of the negative electrode mixture paste, and the like. However, if the nitrogen gas adsorption BET specific surface area exceeds 20 m ² / g, the safety and initial charge / discharge efficiency of the lithium ion secondary battery may be reduced. In general, the nitrogen gas adsorption BET specific surface area is preferably 0.3 to ⁵ m ² / g, and particularly preferably 3 m ² / g or less.
The true density is preferably 2.24 g / cm ³ or more.

The graphitized powder of the present invention obtained by the production method of the present invention can be used for applications other than the negative electrode of a lithium ion secondary battery, for example, a conductive material for a fuel cell separator, graphite for a refractory, etc., taking advantage of its characteristics. Although it can be diverted, it is preferably used as a negative electrode material for a lithium ion secondary battery.
Next, a lithium ion secondary battery negative electrode using the graphitized powder of the present invention and a lithium ion secondary battery using the same will be described.

<Lithium ion secondary battery>
A lithium ion secondary battery usually has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main battery components, and the positive and negative electrodes are each composed of a lithium ion carrier, and the non-aqueous solvent enters and exits between layers in the charge / discharge process. .
In essence, this is a battery mechanism in which lithium ions are doped into the negative electrode during charging and are dedoped from the negative electrode during discharging.
The lithium ion secondary battery using the graphitized powder of the present invention is not particularly limited except that the graphitized powder of the present invention is used as a negative electrode material, and other battery components are general lithium ion secondary batteries. According to the elements of

<Negative electrode>
The production of the negative electrode from the graphitized powder of the present invention can be carried out in accordance with a normal molding method. However, the performance of the graphitized powder of the present invention is sufficiently derived, and the moldability to the powder is high, There is no limitation as long as it is a method capable of obtaining an electrochemically stable negative electrode.
At the time of producing the negative electrode, a negative electrode mixture obtained by adding a binder to the graphitized powder of the present invention can be used.
As the binder, it is desirable to use one having chemical stability and electrochemical stability with respect to the electrolyte, and it is usually preferable to use it in an amount of about 1 to 20% by mass in the total amount of the negative electrode mixture.

Specifically, for example, a negative electrode mixture is prepared by adjusting the graphitized powder of the present invention to an appropriate particle size by classification or the like and mixing with a binder, and this negative electrode mixture is usually used as a current collector. The negative electrode mixture layer can be formed by coating on one side or both sides.
In this case, a normal solvent can be used.

  The shape of the current collector used for the negative electrode is not particularly limited, but a foil or a net-like material such as a mesh or expanded metal is used. Examples of the current collector include copper, stainless steel, and nickel.

<Positive electrode>
As a material for the positive electrode (positive electrode active material), it is preferable to select a material that can be doped / dedoped with a sufficient amount of lithium ions. Examples of such a positive electrode active material include transition metal oxides, transition metal chalcogenides, vanadium oxides and lithium-containing compounds thereof, and general formula M _X Mo ₆ S _8-y (where X is 0 ≦ X ≦ 4, Y is a numerical value in the range of 0 ≦ Y ≦ 1, and M represents a metal such as a transition metal), activated carbon, activated carbon fiber, or the like.

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. Specifically, the lithium-containing transition metal oxide is LiM (1) _1-p M (2) _p O ₂ (wherein P is a numerical value in the range of 0 ≦ P ≦ 1, M (1), M (2) consists of at least one transition metal element.) Or LiM (1) _2-q M (2) _q O ₄ (wherein Q is a numerical value in the range of 0 ≦ Q ≦ 1, M (1) , M (2) is composed of at least one transition metal element).
In the above, examples of the transition metal element represented by M include Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, and Sn, and preferably Co, Fe, Mn, Ti, and Cr. , V, and Al.

The lithium-containing transition metal oxide as described above includes, for example, Li, transition metal oxides or salts as starting materials, these starting materials are mixed according to the composition, and in a temperature range of 600 to 1000 ° C. in an oxygen atmosphere. It can be obtained by firing. The starting material is not limited to oxides or salts, and can be synthesized from hydroxides.
The positive electrode active material may be used alone or in combination of two or more. For example, a carbon salt such as lithium carbonate can be added to the positive electrode.

  In order to form a positive electrode with such a positive electrode material, for example, a positive electrode mixture comprising a positive electrode material, a binder, and a conductive agent for imparting conductivity to the electrode is applied to both surfaces of the current collector. Form a layer. As the binder, any of those exemplified for the negative electrode can be used. As the conductive agent, for example, a carbon material, graphite, or carbon black is used.

  The shape of the current collector is not particularly limited, and a box shape or a mesh shape such as a mesh or expanded metal is used.

  In forming the negative electrode and the positive electrode as described above, conventionally known various additives such as a conductive agent and a binder can be appropriately used.

<Electrolyte>
As the electrolyte used in the lithium ion secondary battery using the graphitized powder of the present invention, an electrolyte salt used in a normal non-aqueous electrolyte can be used, and for example, a lithium salt can be used. In particular, LiPF ₆ and LiBF ₄ are preferably used from the viewpoint of oxidation stability.
The electrolyte salt concentration in the electrolytic solution is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 3.0 mol / l.

  The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte battery or a polymer gel electrolyte battery.

  In the case of a liquid non-aqueous electrolyte solution, an aprotic organic solvent such as ethylene carbonate, propylene carbonate, or dimethyl carbonate can be used as the solvent.

When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, it includes a matrix polymer gelled with a plasticizer (non-aqueous electrolyte). , Fluorinated polymers such as polyethylene oxide and its crosslinked polymers, polymethacrylate, polyacrylate, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, etc. Can be used.
Among these, it is desirable to use a fluorine-based polymer such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer from the viewpoint of redox stability.

As the electrolyte salt and non-aqueous solvent constituting the plasticizer contained in these polymer solid electrolyte and polymer gel electrolyte, any of those described above can be used. In the case of a gel electrolyte, the concentration of the electrolyte salt in the nonaqueous electrolytic solution that is a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.
The method for producing such a solid electrolyte is not particularly limited. For example, a polymer compound that forms a matrix, a method of mixing a lithium salt and a solvent, and melting by heating, a polymer compound in a suitable organic solvent, After dissolving the lithium salt and the solvent, the method of evaporating the organic solvent, and the polymerizable monomer, the lithium salt and the solvent as the raw material of the polymer electrolyte are mixed, and then irradiated with ultraviolet rays, electron beams, molecular beams, etc. Examples thereof include a method for producing a polymer electrolyte by polymerization.
Moreover, 10 to 90 mass% is preferable, and, as for the addition ratio of the solvent in the said solid electrolyte, More preferably, it is 30 to 80 mass%. When the addition ratio of the solvent is 10 to 90% by mass, the electrical conductivity is high, the mechanical strength is high, and film formation is easy.

  In the lithium ion secondary battery using the graphitized powder of the present invention, a separator can also be used.

In the lithium ion secondary battery using the graphitized powder of the present invention, the gel electrolyte can be used because the initial charge / discharge efficiency is improved.
The gel electrolyte secondary battery is configured by laminating a negative electrode containing the graphitized powder of the present invention, a positive electrode, and a gel electrolyte in the order of, for example, a negative electrode, a gel electrolyte, and a positive electrode, and accommodating them in a battery exterior material. . In addition to this, a gel electrolyte may be further disposed outside the negative electrode and the positive electrode. In such a gel electrolyte secondary battery using the graphitized powder of the present invention as a negative electrode, the gel electrolyte contains propylene carbonate, and has a particle size small enough to make the impedance sufficiently low as the graphitized powder of the present invention. Even when is used, the irreversible capacity can be kept small. Therefore, a large discharge capacity is obtained and a high initial charge / discharge efficiency is obtained.

  Furthermore, the structure of the lithium ion secondary battery using the graphitized powder of the present invention is arbitrary, and the shape and form thereof are not particularly limited, and include a cylindrical shape, a square shape, a coin shape, a button shape, and the like. Can be selected arbitrarily. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is desirable to have means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging. In the case of a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure enclosed in a laminate film can also be used.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. Further, in the following examples and comparative examples, a button-type secondary battery for evaluation having the configuration shown in FIG. 1 was prepared using the graphitized powder produced in each, and its discharge capacity, initial charge / discharge efficiency The rapid discharge efficiency and cycle characteristics were measured.

<Example 1>
<Preparation of graphitized powder of the present invention>
Coal tar pitch (manufactured by Kawasaki Steel Co., Ltd., PK-QL) was heated in a non-oxidizing atmosphere (oxygen concentration of 3% by volume or less) at a temperature of 500 ° C. for 3 hours. Carbon spherules were generated.

  Next, the same amount of tar oil (boiling point 160 to 280 ° C.) was added to the coal tar pitch to form a slurry. Further, the mesocarbon microspheres were separated from the slurry by filtering the slurry.

  Next, the mesocarbon spherules were fired at a temperature of 600 ° C. for 2 hours in a non-oxidizing atmosphere (oxygen concentration of 1% by volume or less). Then, the fired product obtained was subjected to air classification, and those having a size of 5 μm or less were removed to obtain mesocarbon microsphere fired powder.

Next, the mesocarbon microsphere fired powder obtained was subjected to mechanochemical treatment using a mechanofusion system (manufactured by Hosokawa Micron Corporation) shown in FIG.
Here, the processing conditions were a peripheral speed difference between the rotating drum and the internal member: 20 m / s, a distance of 30 mm between them, and a processing time of 30 min.

Next, the mesocarbon microsphere calcined powder subjected to mechanochemical treatment was subjected to air classification, and those having a size of 5 μm or less were removed. The removed part of 5 μm or less is referred to as “peeling part A”. Further, a portion other than the peeling portion A is referred to as “remaining portion A”.
The air classifier used here was a Classie N-20 type manufactured by Seishin Enterprise Co., Ltd., and the operating conditions were a rotor rotational speed of 2000 rpm and an air volume of 15 m ³ / min.
Here, the ratio (mass%) of the peeling portion A to the total amount of mesocarbon microsphere fired powder subjected to mechanochemical treatment was 3 mass%.

Next, the remainder A was filled in a graphite crucible, and the surroundings of the crucible were filled with coke breeze and heated at 3000 ° C. for 24 hours for graphitization.
And mesocarbon microsphere graphitized powder was obtained. The graphitized powder was not fused or deformed, and the particle shape was maintained.
This graphitized powder is designated as graphitized powder A.

Next, the true specific gravity and specific surface area of the obtained graphitized powder A were measured. The measurement results are shown in Table 1.
In addition, the measuring method of true specific gravity is the pycnometer method which used 1-butanol as an osmotic solution.
The specific surface area was measured by the flow method BET 1-point method.

Next, using this graphitized powder A, a working electrode (negative electrode) was produced. This will be described with reference to FIG.
<Preparation of negative electrode mixture paste>
90% by mass of the graphitized powder obtained above and 10% by mass of polyvinylidene fluoride as a binder are mixed using N-methylpyrrolidone as a solvent, and stirred at 2000 rpm for 30 minutes using a homomixer, organic A solvent-based negative electrode mixture paste was prepared.

<Manufacture of working electrode (negative electrode)>
The negative electrode mixture paste was applied to a copper foil (current collector 7b) with a uniform thickness, and the solvent was evaporated at 90 ° C. in vacuum to dry the paste. Next, the negative electrode mixture applied on the copper foil is pressed by a roller press and punched into a circular shape having a diameter of 15.5 mm, whereby a working electrode (negative electrode) made of a negative electrode mixture layer in close contact with the current collector is obtained. 2) was produced.

<Manufacture of counter electrode>
The lithium metal foil was pressed against a nickel net and punched into a cylindrical shape with a diameter of 15.5 mm to produce a current collector (7a) made of nickel net and a counter electrode 4 made of lithium metal foil in close contact with the current collector. .

<Electrolyte>
LiClO ₄ was dissolved at a concentration of 1 mol / l in a mixed solvent of 10 mol% propylene carbonate, 50 mol% ethylene carbonate and 40 mol% diethyl carbonate to prepare a non-aqueous electrolyte.
The obtained nonaqueous electrolytic solution was impregnated into a polypropylene porous body to produce a separator 5 impregnated with the electrolytic solution.

<Production of evaluation battery>
A button-type secondary battery shown in FIG. 1 was manufactured as an evaluation battery.
The exterior cup 1 and the exterior can 3 have a sealed structure that is caulked through an insulating gasket 6 at the peripheral edge thereof, and the current collector 7a made of nickel net in the order from the inner surface of the exterior can 3; A battery system in which a disk-shaped counter electrode 4 made of lithium foil, a separator 5 impregnated with an electrolyte solution, a disk-shaped working electrode (negative electrode) 2 made of a negative electrode mixture, and a current collector 7b made of copper foil are laminated. .

In the evaluation battery, the separator 5 impregnated with the electrolyte solution was laminated between the working electrode 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a, and then the working electrode 2 was mounted on the exterior. In the cup 1, the counter electrode 4 is accommodated in the outer can 3, the outer cup 1 and the outer can 3 are combined, and the outer peripheral portion of the outer cup 1 and the outer can 3 is caulked and sealed with an insulating gasket 6. Manufactured.
This evaluation battery is a battery composed of a working electrode (negative electrode) 2 containing graphitized powder A that can be used as a negative electrode active material in a real battery, and a counter electrode 4 made of lithium metal foil.
The evaluation battery manufactured as described above was subjected to the following charge / discharge test at a temperature of 25 ° C.

<Charge / discharge test>
Constant current charging is performed until the circuit voltage reaches 0 mV at a current value of 0.9 mA, switching to constant voltage charging is performed when the circuit voltage reaches 0 mV, and charging is continued until the current value reaches 20 μA, and then 120 min. Paused.
Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 2.5V. At this time, the charge capacity and the discharge capacity were obtained from the energization amount in the first cycle, and the initial charge / discharge efficiency was calculated from the following equation.
Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity) × 100
In this test, the process of doping lithium ions into the graphitized powder A was charged, and the process of dedoping from the graphitized powder A was discharge.

<Rapid discharge efficiency test>
In the second cycle, after charging in the same manner as in the first cycle, constant current discharge was performed at a current value of 18 mA until the circuit voltage reached 2.5V. At this time, rapid discharge efficiency (high rate characteristics) was evaluated from the discharge capacity in the first cycle according to the following equation.
Rapid discharge efficiency (%) = (second cycle discharge capacity / first cycle discharge capacity) × 100

<Cycle characteristic test>
In addition to the above evaluation, charging / discharging was repeated 100 times under the same conditions as in the first cycle, and the cycle characteristics were evaluated according to the following formula.
Cycle characteristics (%) = (100th cycle discharge capacity / first cycle discharge capacity) × 100

The above test was performed with the electrode density of the negative electrode being 1.65 g / cm ³ , and the measured discharge capacity per 1 g of graphitized powder A (mAh / g), initial charge / discharge efficiency (%), rapid discharge efficiency ( %) And cycle characteristic (%) values (battery characteristics) are shown in Table 1.
As shown in Table 1, the lithium ion secondary battery using the graphite material of the present invention for the working electrode (corresponding to the negative electrode of the actual battery) shows a high discharge capacity regardless of the electrode density of the negative electrode. And high initial charge / discharge efficiency (ie, small irreversible capacity).
Further, the rapid discharge efficiency (%) and the cycle characteristics showed excellent values and maintained good values even when the electrode density was increased.

<Example 2>
In Example 1, the mechanochemical treatment performed for 30 minutes was set to 15 minutes, and the other treatment methods, treatment conditions, measurement items, and the like were all the same.
The measurement results are shown in Table 1.

<Example 3>
In Example 1, the mechanochemical treatment performed for 30 minutes was set to 60 minutes, and the other treatment methods, treatment conditions, measurement items, and the like were all the same.
The measurement results are shown in Table 1.

<Comparative Example 1>
In Example 1, the mechanochemical treatment performed for 30 minutes was not performed, and a test was performed in which all other treatment methods, treatment conditions, measurement items, and the like were the same.
The measurement results are shown in Table 1.

<Comparative example 2>
In Example 1, mechanochemically treated mesocarbon microsphere fired powder was subjected to air classification to remove particles of 5 μm or less, but in Comparative Example 2, this operation was not performed.
And the test which made all the other processing methods, processing conditions, a measurement item, etc. the same was done.
The measurement results are shown in Table 1.

  The graphitized powder of the present invention obtained by the production method of the present invention can be diverted to uses other than the negative electrode of a lithium ion secondary battery, for example, a conductive material for a fuel cell separator, graphite for refractory, and the like. .

FIG. 1 is a cross-sectional view of an evaluation battery used in the present invention. FIG. 2 is a schematic view of a mechanochemical processing apparatus used in the present invention. FIG. 3A is a view for explaining the mechanism of operation of the mechanochemical processing apparatus used in the present invention, and FIG. 3B is a schematic view showing the configuration of the apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Separator 6 Insulating gasket 7a, 7b Current collector 11 Rotating drum 12 Internal member (inner piece)
13 Mesocarbon spheroid sintered powder 14 Circulation mechanism 15 Discharge mechanism 21 Fixed drum 22 Rotor 23 Mesocarbon spheroid sintered powder 24 Circulation mechanism 25 Discharge mechanism 26 Blade 27 Stator 28 Jacket

Claims (5)

A method for producing mesocarbon microsphere graphitized powder,
A peeling step of peeling the surface portion of the mesocarbon microsphere fired powder by a peeling means to obtain a mixture of the peeled portion and the remaining portion that are the peeled surface portion;
A removal step of removing the peeling portion and obtaining the remaining portion from the mixture;
Graphitizing the remaining part to obtain mesocarbon microsphere graphitized powder; and
A process for producing mesocarbon microsphere graphitized powder comprising:   The mesocarbon microsphere graphitized powder according to claim 1, wherein the mesocarbon microsphere fired powder is a mesocarbon microsphere fired powder obtained by treating a mesocarbon microsphere in a non-oxidizing atmosphere at 400 to 1300 ° C. Powder manufacturing method.   The method for producing mesocarbon microsphere graphitized powder according to claim 1 or 2, wherein the peeling means is a mechanochemical treatment.   The method for producing mesocarbon microsphere graphitized powder according to any one of claims 1 to 3, wherein an abundance ratio of the peeled portion in the mixture is 1 to 5 mass%.   The method for producing mesocarbon microsphere graphitized powder according to any one of claims 1 to 4, wherein the mesocarbon microsphere graphitized powder is a negative electrode material for a lithium ion secondary battery.

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