JP6506668B2 - Pitch-based ultrafine carbon fiber, electrode mixture layer for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention provides a pitch-based ultrafine carbon fiber, an electrode mixture layer for a non-aqueous electrolyte secondary battery using the carbon fiber, an electrode for a non-aqueous electrolyte secondary battery in which the electrode mixture layer is formed, and the electrode The present invention relates to a non-aqueous electrolyte secondary battery comprising.

  Carbon nanomaterials, in particular, ultrafine carbon fibers having an average fiber diameter of 1 μm or less, have excellent properties such as high crystallinity, high conductivity, high strength, high elastic modulus, and light weight, so they have high performance. It is used as a nanofiller of composite materials. Its application is not limited to reinforcing nanofillers for the purpose of improving mechanical strength, and by utilizing the high conductivity of carbon materials, additives to electrodes of various batteries and capacitors, electromagnetic shielding materials, antistatic materials The application as a conductive nanofiller for the purpose, or as a nanofiller to be mixed with an electrostatic paint for resin is being studied. Further, taking advantage of the characteristics of chemical stability, thermal stability, and microstructure as a carbon material, applications as field electron emission materials such as flat displays are also expected.

  For example, Patent Document 1 includes (1) 100 parts by mass of a thermoplastic resin and at least one thermoplastic carbon precursor 1 selected from the group consisting of pitch, polyacrylonitrile, polycarbodiimide, polyimide, polybenzoazole and aramid. A step of forming a precursor molded body from a mixture consisting of 150 parts by mass, (2) subjecting the precursor molded body to a stabilization treatment to stabilize the thermoplastic carbon precursor in the precursor molded body, and a stabilized resin composition (3) removing the thermoplastic resin from the stabilized resin composition under reduced pressure to form a fibrous carbon precursor, (4) carbonizing or graphitizing the fibrous carbon precursor A method of producing carbon fiber is disclosed. Although carbon fibers produced by this method have good properties, they are insufficient as battery properties when used as an electrode material, and further improvement of charge and discharge efficiency is required.

  In order to further improve the charge and discharge efficiency, it is required to improve the affinity between the carbon fiber constituting the electrode material and the electrolytic solution. As a method of improving the affinity between the carbon fiber and the electrolytic solution, a method of immobilizing metal particles on the surface of the carbon fiber, a method of heating in the presence of an oxidizing gas, and addition of an additive such as a surfactant There is known a method of reducing the interface resistance with the electrolyte solution.

  In Patent Document 2, the surface of the carbon fiber is modified in order to improve the dispersibility between the fiber and the matrix and to enhance the interfacial strength by subjecting the carbon fiber produced by the vapor phase method to a surface oxidation treatment. Methods are disclosed that can be qualified. However, the preferred carbon fiber surface state and oxygen content are not disclosed at all, and the conductivity and the affinity with the electrolytic solution are not simultaneously satisfied.

  In Patent Document 3, a pitch-based ultrafine carbon fiber having a surface oxygen concentration ratio (O / C) of 0.02 or more, a uniform fiber diameter, excellent conductivity, and good dispersibility in an aqueous solvent Is disclosed. However, ultrafine carbon fibers having extremely high crystallinity and a fiber diameter of micron order or less are not specifically described. In addition, it is described that carbon fibers are formed into a film on a substrate, and the conductivity in the in-plane direction of the film is good.

International Publication No. 2009/125857 JP, 2006-140142, A JP, 2015-48561, A

  An object of the present invention is to provide a pitch-based ultrafine carbon fiber having improved affinity to an electrolytic solution and high conductivity. Furthermore, an electrode mixture layer for a non-aqueous electrolyte battery formed using this pitch-based ultrafine carbon fiber, an electrode on which the electrode mixture layer is formed, and a non-aqueous electrolyte secondary using the electrode It is about providing a battery.

  The inventors of the present invention conducted extensive studies in view of the above-mentioned prior art, and as a result, there is a certain degree of variation in fiber diameter, and by controlling the surface state of carbon fiber having high crystallinity, affinity to the electrolyte is obtained. It has been found that pitch-based ultrafine carbon fibers having high properties and high conductivity can be obtained, and the present invention has been completed.

  That is, the present invention which solves the above-mentioned subject is described below.

[1] The surface oxygen concentration ratio (O / C) measured by X-ray photoelectron spectroscopy is 0.02 or more and 0.15 or less,
CV value of fiber diameter is 10 to 50%,
And, a pitch based ultrafine carbon fiber characterized in that the crystallite size (d002) measured by the X-ray diffraction method is 0.340 nm or less.

[2] The intensity ratio (O = C / O-C) of O-C bond derived from O1s orbital and O = C bond measured by X-ray photoelectron spectroscopy is 1.4 or more, described in [1] Pitch based ultrafine carbon fiber.

[3] The pitch based ultrafine carbon fiber according to [1] or [2], having an average fiber diameter of 100 nm or more and less than 700 nm.

[4] The pitch based ultrafine carbon fiber according to any one of [1] to [3], which has an average aspect ratio of 30 to 1000.

[5] The pitch-based ultrafine carbon fiber according to any one of [1] to [4],
An electrode active material,
With a binder,
And an electrode mixture layer for a non-aqueous electrolyte secondary battery.

[6] current collector,
The electrode mixture layer for a non-aqueous electrolyte secondary battery according to [5], which is laminated on the current collector;
An electrode for a non-aqueous electrolyte secondary battery comprising:

[7] A non-aqueous electrolyte secondary battery comprising the electrode for a non-aqueous electrolyte secondary battery according to [6].

  According to the present invention, it is possible to obtain a pitch-based ultrafine carbon fiber which is excellent in affinity with the electrolytic solution and higher in conductivity in the film thickness direction in the electrode mixture layer than carbon fibers obtained in the prior art. it can. This pitch based ultrafine carbon fiber can be suitably used as a battery material.

  In addition to the battery material, the pitch-based ultrafine carbon fiber of the present invention may be a nano-filler for reinforcement, an additive material to an electrode of a capacitor, an electromagnetic wave shielding material, a conductive nano-filler for antistatic material, electrostatic for resin It is promising for use as a nanofiller to be mixed in a paint, and as a field electron emission material such as a flat display.

FIG. 1 shows the results of XPS measurement of CNF produced in Example 1. FIG. 2 shows the results of XPS measurement of CNF produced in Example 2. FIG. 3 shows the results of XPS measurement of CNF produced in Comparative Example 1. FIG. 4 is an XPS measurement result of CNF manufactured in Comparative Example 2.

  Hereinafter, the present invention will be described in detail.

1. Pitch based ultrafine carbon fiber for non-aqueous electrolyte secondary battery 1-1. Properties of pitch-based ultrafine carbon fiber According to a first aspect of the present invention, the surface oxygen concentration ratio (O / C) measured by X-ray photoelectron spectroscopy is 0.02 or more and 0.15 or less,
CV value of fiber diameter is 10 to 50%,
And it is a pitch type | system | group ultrafine carbon fiber characterized by the crystallite size (d002) measured by the X-ray-diffraction method being 0.340 nm or less.

  The pitch-based ultrafine carbon fiber of the present invention (hereinafter sometimes referred to simply as carbon fiber) is a surface oxygen concentration indicating the proportion of oxygen atoms to carbon atoms on the surface of carbon fibers as measured by X-ray photoelectron spectroscopy The ratio (surface O / C) is 0.02 or more and 0.15 or less, more preferably 0.02 or more and 0.10 or less, and still more preferably 0.02 or more and 0.06 or less. When the surface O / C is in this range, the affinity to an electrolytic solution, in particular, propylene carbonate is high, and carbon fibers can be dispersed uniformly in the electrode mixture layer.

  The carbon fiber of the present invention has an intensity ratio (O = C / O-C) between the O-C bond derived from the O1s orbital and the O = C bond whose surface is measured by X-ray photoelectron spectroscopy. Is preferred. When the strength ratio is 1.4 times or more, the high hydrophobic O 疎 水 C group is present at the surface of the carbon fiber more than the highly hydrophilic C—OH group, and thus the affinity to the electrolytic solution, in particular propylene carbonate is obtained. And the dispersibility of carbon fibers in the electrode mixture layer is high. It is more preferable that the intensity ratio of O—C bond to OCC bond (O = C / O—C) is 1.5 or more.

The average fiber diameter of the carbon fiber of the present invention is preferably 100 nm or more and less than 700 nm. The upper limit is preferably 600 nm or less, more preferably 500 nm or less, still more preferably 400 nm or less, and still more preferably 300 nm or less. The lower limit is preferably 110 nm or more, more preferably 120 nm or more, and still more preferably 150 nm or more.
If it is less than 100 nm, the bulk density is very small and the handling is inferior. In addition, when the electrode mixture layer is formed, the electrode strength tends to decrease. When the thickness is 700 nm or more, gaps may easily occur in the electrode mixture layer, and it may be difficult to increase the electrode density.
Here, the fiber diameter in the present invention means a value measured from a photograph taken at a magnification of 2000 times by a field emission scanning electron microscope.

  In the carbon fiber of the present invention, the CV value of the fiber diameter is in the range of 10 to 50%. By being in this range, the fiber diameter is well dispersed. Therefore, the contact property with the electrode active material which has various particle diameters can be made high, and the performance as a conductive support agent improves. As a result, the electrical conductivity in the film thickness direction of the electrode mixture layer can be increased. The CV value of the fiber diameter is more preferably in the range of 20 to 50%, and still more preferably in the range of 30 to 45%. Here, the CV value is a value obtained by dividing a standard deviation value by an average value and expressing it as a percentage (%).

  In the carbon fiber of the present invention, the distance (d002) between adjacent graphite sheets measured by wide-angle X-ray measurement is 0.340 nm or less, preferably 0.335 to 0.340 nm, 0.335 to 0 More preferably, it is .339 nm. When d 002 is in the range of 0.335 to 0.340 nm, the electrode mixture layer exhibits high conductivity in the film thickness direction.

  The average fiber length of the carbon fiber of the present invention is preferably in the range of 1 to 100 μm, more preferably 1 to 50 μm, and still more preferably 5 to 20 μm. If the thickness is less than 1 μm, the conductivity in the electrode mixture layer, the strength of the electrode, and the electrolyte retention property are unfavorably lowered. If it exceeds 100 μm, it is not preferable because the dispersibility of the pitch based ultrafine carbon fiber is impaired. That is, when the pitch-based ultrafine carbon fiber is too long, the pitch-based ultrafine carbon fiber is easily oriented in the in-plane direction of the electrode mixture layer. As a result, it becomes difficult to form a conductive path in the film thickness direction.

  The ratio (L / D) of the average fiber length (L) to the average fiber diameter (D) of the carbon fiber of the present invention is preferably 30 or more, more preferably 50 or more, and 100 or more. Is more preferred. By setting the ratio (L / D) to 30 or more, conductive paths can be efficiently formed in the electrode mixture layer, and electric conductivity in the film thickness direction can be increased. If it is less than 30, formation of the conductive path in the electrode mixture layer tends to be insufficient, and the resistance value in the film thickness direction of the electrode mixture layer may not be sufficiently reduced. The upper limit value of the ratio (L / D) is not particularly limited, but is preferably 1000 or less, and more preferably 800 or less.

The carbon fibers of the present invention preferably have a linear structure. Here, the linear structure means that the degree of branching is 0.01 piece / μm or less. Branching refers to a granular part in which carbon fibers are bonded to other carbon fibers at locations other than the end part, the main axis of carbon fibers is branched midway, and the main axis of carbon fibers is a branched secondary axis It means having. Note that vapor-grown ultrafine carbon fibers (VGCF) are known as carbon fibers having branching.
In addition, this carbon fiber should just have a fibrous form as a whole, for example, a carbon material less than 1 μm contacts or bonds to have a fiber form integrally (for example, Also included are those in which spherical carbon is linked in a beaded manner by fusion or the like, those in which a plurality of extremely short fibers are joined by fusion or the like, and the like.

The carbon fiber of the present invention preferably has high conductivity at a low packing density. This is because carbon fibers having high conductivity in the state of low packing density can impart conductivity at a lower added concentration. Specifically, the powder volume resistance when packed at a packing density of 0.4 g / cm ³ is preferably 1 Ω · cm or less, and more preferably 0.5 Ω · cm or less. When it exceeds 1 Ω · cm, the amount of carbon fiber required to improve the conductivity is increased, which is not preferable. The lower limit value is not particularly limited, but is generally about 0.0001 Ω · cm. In addition, the powder volume resistance when packed at a packing density of 0.8 g / cm ³ is preferably 0.1 Ω · cm or less, more preferably 0.050 Ω · cm or less, and still more preferably 0.030 Ω · cm or less. Still more preferably, it is 0.028 Ω · cm or less. When it exceeds 0.1 Ω · cm, the amount of carbon fiber required to improve the conductivity is increased, which is not preferable. The lower limit value is not particularly limited, but is generally about 0.0001 Ω · cm.

1-2. Method for Producing Carbon Fiber The method for producing the carbon fiber of the present invention is not particularly limited, and can be produced, for example, through the steps of (1) to (4) described below.
(1) forming a resin composition comprising 100 parts by mass of a thermoplastic resin and 1 to 150 parts by mass of a carbon precursor in a molten state to fiberize the carbon precursor to obtain a resin composite fiber,
(2) a stabilization step of stabilizing the resin composite fiber to obtain a resin composite stabilized fiber,
(3) A thermoplastic resin removing step of removing only the stabilized fiber by removing the thermoplastic resin from the resin composite stabilized fiber,
(4) A carbonization / firing step of heating the stabilized fiber under an inert atmosphere to carbonize or graphitize to obtain a carbon fiber.

<Thermoplastic resin>
The thermoplastic resin used in the method for producing a carbon fiber of the present invention needs to be easily removed after producing a resin composite fiber. As such a thermoplastic resin, polyacrylate polymers such as polyolefin, polymethacrylate, polymethylmethacrylate, polystyrene, polycarbonate, polyarylate, polyester, polyamide, polyestercarbonate, polysulfone, polyimide, polyetherimide, polyketone, polylactic acid Is illustrated. Among these, polyolefins are preferably used.

  Specific examples of the polyolefin include polyethylene, polypropylene, poly-4-methylpentene-1 and copolymers containing them. From the viewpoint of easy removal in the thermoplastic resin removal step, it is preferable to use polyethylene. As the polyethylene, homopolymers such as high density low density polyethylene, low density polyethylene such as vapor phase method, solution method, high pressure linear low density polyethylene, medium density polyethylene, high density polyethylene or ethylene and α-olefin And copolymers of ethylene and other vinyl monomers such as ethylene / vinyl acetate copolymer.

  The thermoplastic resin used in the present invention preferably has a melt mass flow rate (MFR) of 0.1 to 10 g / 10 min measured in accordance with JIS K 7210 (1999), and 0.1 to 5 g / min. It is more preferable that it is 10 min, and it is especially preferable that it is 0.1 to 3 g / 10 min. When the MFR is in the above range, the carbon precursor can be finely dispersed in the thermoplastic resin. Further, when the resin composite fiber is formed, the fiber diameter of the obtained carbon fiber can be further reduced by drawing the fiber. The thermoplastic resin used in the present invention has a glass transition temperature of 250 ° C. or less when it is amorphous and a melting point of 300 ° C. or less when it is crystalline because it can be easily melt-kneaded with the carbon precursor Is preferred.

<Carbon precursor>
As a carbon precursor, it is preferable to use mesophase pitch as a raw material. Hereinafter, the case of using mesophase pitch as a carbon precursor will be described. The mesophase pitch is a pitch capable of forming an optically anisotropic phase (liquid crystal phase) in a molten state. Examples of mesophase pitch used in the present invention include those using distillation residue of coal or petroleum as a raw material, and those using aromatic hydrocarbons such as naphthalene as a raw material. For example, mesophase pitch derived from coal is obtained by a treatment mainly based on hydrogenation and heat treatment of coal tar pitch, or a treatment mainly based on hydrogenation / heat treatment / solvent extraction.

More specifically, it can be obtained by the following method.
First, coal tar pitch having a softening point of 80 ° C. from which quinoline insolubles have been removed is hydrogenated at a pressure of 13 MPa and a temperature of 340 ° C. in the presence of a Ni-Mo catalyst to obtain a hydrogenated coal tar pitch. The hydrogenated coal tar pitch is heat-treated at 480 ° C. under normal pressure, and then depressurized to remove low boiling components to obtain crude mesophase pitch. The crude mesophase pitch is filtered at a temperature of 340 ° C. using a filter to remove foreign matter, whereby a purified mesophase pitch can be obtained.

  The optical anisotropy content (mesophase ratio) of the mesophase pitch is preferably 80% or more, more preferably 90% or more.

  Moreover, it is preferable that a softening point is 100-400 degreeC, and, as for the said mesophase pitch, it is more preferable that it is 150-350 degreeC.

<Resin composition>
A resin composition comprising a thermoplastic resin and mesophase pitch (hereinafter also referred to as mesophase pitch composition) used in the method for producing carbon fiber of the present invention comprises 100 parts by mass of the thermoplastic resin and 1 to 150 parts by mass of the mesophase pitch. And. The content of mesophase pitch is preferably 5 to 100 parts by mass. When the content of the mesophase pitch exceeds 150 parts by mass, resin composite fibers having a desired dispersion diameter can not be obtained, and when it is less than 1 parts by mass, the target carbon fibers can not be produced inexpensively. It is not preferable because it occurs.

  In order to produce a carbon fiber having a fiber diameter of less than 700 nm, the dispersion diameter of mesophase pitch in the thermoplastic resin is preferably 0.01 to 50 μm, and more preferably 0.01 to 30 μm. If the dispersion diameter of mesophase pitch in the thermoplastic resin deviates from the range of 0.01 to 50 μm, it may be difficult to produce a desired carbon fiber. In the mesophase pitch composition, the mesophase pitch forms a spherical or elliptical island phase, but the dispersion diameter in the present invention means the diameter when the island component is spherical, and the diameter when the island component is elliptical. The major axis diameter is meant.

  The dispersion diameter of 0.01 to 50 μm is preferably maintained after the mesophase pitch composition is maintained at 300 ° C. for 3 minutes, and more preferably maintained at 300 ° C. for 5 minutes. It is particularly preferable to maintain after holding at 300 ° C. for 10 minutes. Generally, when the mesophase pitch composition is kept in a molten state, the mesophase pitch agglomerates with time in the thermoplastic resin. When the mesophase pitch is aggregated and the dispersion diameter thereof exceeds 50 μm, it may be difficult to produce a desired carbon fiber. The aggregation rate of mesophase pitch in the thermoplastic resin varies depending on the type of thermoplastic resin and mesophase pitch used.

  The mesophase pitch composition can be produced by kneading a thermoplastic resin and mesophase pitch in a molten state. Melt-kneading of the thermoplastic resin and the mesophase pitch can be performed using a known apparatus. For example, one or more types selected from the group consisting of a single-screw kneader, a twin-screw kneader, a mixing roll, and a Banbury mixer can be used. Among them, it is preferable to use a twin-screw kneader for the purpose of finely dispersing mesophase pitch in a thermoplastic resin, and in particular, to use a twin-screw kneader in which each axis rotates in the same direction. preferable.

  The kneading temperature is not particularly limited as long as the thermoplastic resin and the mesophase pitch are in a molten state, but it is preferably 100 to 400 ° C., and preferably 150 to 350 ° C. When the kneading temperature is less than 100 ° C., the mesophase pitch does not go into a molten state, and it is difficult to microdisperse in a thermoplastic resin, which is not preferable. On the other hand, when it exceeds 400 ° C., decomposition of the thermoplastic resin and mesophase pitch proceeds unfavorably. Moreover, as time of melt-kneading, it is preferable that it is 0.5 to 20 minutes, and it is more preferable that it is 1 to 15 minutes. When the time of melt-kneading is less than 0.5 minutes, it is not preferable because micro-dispersion of mesophase pitch is difficult. On the other hand, when it exceeds 20 minutes, since productivity of carbon fiber falls remarkably, it is unpreferable.

  Melt-kneading is preferably performed in an inert atmosphere with an oxygen gas content of less than 10% by volume, more preferably in an inert atmosphere with an oxygen gas content of less than 5% by volume, and 1% by volume of oxygen gas content It is particularly preferred to carry out under an inert atmosphere of less than. The mesophase pitch used in the present invention may be denatured by reaction with oxygen during melt-kneading, which may inhibit microdispersion in the thermoplastic resin. For this reason, it is preferable to perform melt-kneading in an inert atmosphere to suppress the reaction between oxygen and the mesophase pitch.

<Resin composite fiber>
The method for producing a resin composite fiber from the above mesophase pitch composition is not limited as long as a desired carbon fiber can be produced, but a method of melt spinning the mesophase pitch composition from a spinneret, and melting a mesophase pitch composition from a rectangular spinneret The method of forming a film can be illustrated.

  In order to obtain the carbon fiber of the present invention, it is necessary to go through the operation of enhancing the initial orientation of the mesophase pitch contained in the resin composite fiber at the stage of obtaining the resin composite fiber. As an operation to enhance the initial orientation of the mesophase pitch contained in the resin composite fiber, it is necessary to add a deformation for enhancing the orientation of the mesophase pitch in the molten state, and as such a method, the mesophase pitch in the molten state is A method of applying strain by shear and a method of applying strain by extension can be exemplified.

As a method of applying a strain by shear, the mesophase pitch composition in the molten state flows in the nozzle channel by increasing the linear velocity of the mesophase pitch composition in the molten state using a die in the molten state of the mesophase pitch. In passing, shear strain can be applied.
Further, as a method of applying a strain due to elongation, a method of increasing the linear velocity of the mesophase pitch composition in a molten state toward the discharge side using a die in a state where the mesophase pitch is in a molten state can be mentioned. Specifically, a method of gradually reducing the cross-sectional area in the flow channel toward the discharge side, a method of taking out the mesophase pitch composition discharged from the die at a linear velocity higher than the discharge linear velocity, and the like can be mentioned.

  The temperature when passing through the operation to increase the initial orientation of mesophase pitch needs to be higher than the melting temperature of mesophase pitch, and is preferably 150 to 400 ° C., and more preferably 180 to 350 ° C. . When the temperature is higher than 400 ° C., the deformation relaxation rate of the mesophase pitch becomes large, and it becomes difficult to maintain the form of the fiber.

  Moreover, the manufacturing process of a resin composite fiber may have a cooling process. As a cooling process, the method of cooling the atmosphere of the downstream of a spinneret is mentioned, for example in the case of melt spinning. In the case of melt film formation, there is a method of providing a cooling drum downstream of the rectangular die. By providing a cooling step, it is possible to adjust the region in which the mesophase pitch is deformed by elongation and to adjust the speed of strain. Further, by providing a cooling step, the resin composite fiber after spinning or film formation is immediately cooled and solidified to enable stable molding.

<Resin composite stabilized fiber>
The resin composite fiber obtained as described above stabilizes (also referred to as infusibilization) the mesophase pitch fiber contained in the resin composite fiber to produce a resin composite stabilized fiber. Stabilization can be performed by a known method such as gas stream treatment using air, oxygen, ozone, nitrogen dioxide, halogen, etc., solution treatment using an acidic aqueous solution, etc. However, in terms of productivity, insolubilization by gas stream treatment Is preferred.

  The gas component to be used is preferably air, oxygen, or a mixed gas containing it from the viewpoint of ease of handling, and from the viewpoint of cost, it is particularly preferable to use air. The oxygen gas concentration to be used is preferably in the range of 10 to 100% by volume of the total gas composition. If the oxygen gas concentration is less than 10% by volume of the total gas composition, it takes a lot of time to stabilize the mesophase pitch contained in the resin composite fiber, which is not preferable.

  The reaction temperature for stabilization is preferably 25 to 350 ° C., and the treatment time for stabilization is preferably 10 to 300 minutes.

  Although the softening point of mesophase pitch is significantly increased by the above stabilization treatment, the softening point of mesophase pitch is preferably 400 ° C. or higher, more preferably 500 ° C. or higher, for the purpose of obtaining a desired carbon fiber. .

<Thermoplastic resin removal process>
Next, in the resin composite stabilized fiber obtained as described above, the thermoplastic resin contained therein is removed to separate the stabilized fiber. In this step, the thermoplastic resin is decomposed and removed while suppressing the thermal decomposition of the stabilized fiber. Examples of the method of decomposing and removing the thermoplastic resin include a method of removing the thermoplastic resin using a solvent and a method of thermally decomposing the thermoplastic resin to remove it.

  The thermal decomposition of the thermoplastic resin is preferably performed under an inert gas atmosphere. The inert gas atmosphere as referred to herein means a gas atmosphere of carbon dioxide, nitrogen, argon or the like, and the oxygen concentration thereof is preferably 30 ppm by volume or less, and more preferably 20 ppm by volume or less. As the inert gas used in this step, it is preferable to use carbon dioxide and nitrogen from the viewpoint of cost, and it is particularly preferable to use nitrogen.

  When removing a thermoplastic resin by thermal decomposition, it can also be performed under reduced pressure. By thermally decomposing under reduced pressure, the thermoplastic resin can be sufficiently removed. As a result, fusion between carbon fibers or graphitized fibers obtained by carbonizing or graphitizing the stabilized fibers can be reduced. The lower the atmospheric pressure, the better, but the pressure is preferably 50 kPa or less, more preferably 30 kPa or less, still more preferably 10 kPa or less, and particularly preferably 5 kPa or less. On the other hand, since a complete vacuum is difficult to achieve, the lower limit of the pressure is generally 0.01 kPa or more.

  When the thermoplastic resin is removed by thermal decomposition, a trace amount of oxygen or an inert gas may be present as long as the above-mentioned atmospheric pressure is maintained. In particular, the presence of a trace amount of inert gas is preferable because it is advantageous in that fusion between fibers due to thermal degradation of the thermoplastic resin is suppressed. The term “under a slight amount of oxygen atmosphere” means that the oxygen concentration is 30 ppm by volume or less, and “under a slight amount of inert gas atmosphere” means that the inert gas concentration is 20 ppm by volume or less. . The type of inert gas used is as described above.

  The thermal decomposition temperature is preferably 350 to 600 ° C, and more preferably 380 to 550 ° C. If the thermal decomposition temperature is less than 350 ° C., thermal decomposition of the stabilized fiber may be suppressed but thermal decomposition of the thermoplastic resin may not be sufficiently performed. On the other hand, when the temperature exceeds 600 ° C., although the thermal decomposition of the thermoplastic resin can be sufficiently performed, even the stabilized fiber may be thermally decomposed, and as a result, the yield at the time of carbonization tends to decrease. The thermal decomposition time is preferably 0.1 to 10 hours, and more preferably 0.5 to 10 hours.

In the production method of the present invention, the stabilization step and the thermoplastic resin removal step are preferably carried out by holding the resin composite fiber or the resin composite stabilized fiber on the support base at a coating weight of 2000 g / m ² or less. By holding the supporting substrate, aggregation of the resin composite fiber or the resin composite stabilized fiber due to the heat treatment at the time of the stabilization treatment or the removal of the thermoplastic resin can be suppressed, and the air permeability can be maintained. .

  As a material of the supporting base material, it is necessary that no deformation or corrosion is caused by a solvent or heating. The heat resistance temperature of the support base material is preferably not deformed at the thermal decomposition temperature in the above-mentioned thermoplastic resin removal step, and therefore, preferably has heat resistance of 600 ° C. or more. Examples of such a material include metal materials such as stainless steel, and ceramic materials such as alumina and silica.

  The shape of the supporting substrate is preferably a shape having air permeability in the direction perpendicular to the surface. As such a shape, a mesh structure is preferable. The mesh size of the mesh is preferably 0.1 to 5 mm. If the opening is larger than 5 mm, the fibers tend to agglomerate on the mesh line by heat treatment, which may make the stabilization of the mesophase pitch and the removal of the thermoplastic resin insufficient, which is not preferable. On the other hand, when the mesh size of the mesh is less than 0.1 mm, the air permeability of the supporting substrate in the direction perpendicular to the surface may be reduced due to the reduction of the porosity of the supporting substrate, which is not preferable.

<Carbonizing and firing process>
The carbon fiber of the present invention is obtained by carbonizing and / or graphitizing the above-mentioned stabilized fiber under an inert gas atmosphere. As a container used at that time, a crucible-like one made of graphite is preferable. Here, carbonization refers to heating at a relatively low temperature (preferably about 1000 ° C.), and graphitization refers to growing a graphite crystal by heating (preferably about 3000 ° C.) at a higher temperature. Say.

  As an inert gas used at the time of carbonization and / or graphitization of the above-mentioned stabilization fiber, nitrogen, argon, etc. are mentioned. The oxygen concentration in the inert gas is preferably 20 ppm by volume or less, more preferably 10 ppm by volume or less. 500-3500 degreeC is preferable and, as for the calcination temperature at the time of carbonization and / or graphitization, 800-3200 degreeC is more preferable. Especially as a calcination temperature in the case of graphitization, 2000 ° C or more and less than 3000 ° C are preferred, and 2100-2900 ° C are more preferred. When the temperature at the time of graphitization is less than 2000 ° C., crystal growth is hindered, the crystallite length may be insufficient, and the conductivity may be significantly reduced. Further, when the graphitization temperature is 3000 ° C. or more, although it is preferable from the viewpoint of crystal growth, the oxygen content present on the surface of the carbon fiber decreases, and the O / C tends to be smaller than 0.02. The firing time is preferably 0.1 to 24 hours, and more preferably 0.2 to 10 hours.

<Crushing treatment>
The method for producing a carbon fiber of the present invention may have a grinding treatment step. The grinding treatment is preferably carried out in a thermoplastic resin removal step and / or a carbonization and firing step. As a pulverizing method, it is preferable to apply a pulverizer such as a jet mill, a ball mill, a bead mill, an impeller mill, a cutter mill or the like, and classification may be carried out after pulverization if necessary. In the case of wet grinding, the dispersion medium is removed after grinding, but if secondary aggregation occurs significantly at this time, the subsequent handling becomes very difficult. In such a case, it is preferable to carry out the crushing operation using a ball mill, jet mill or the like after drying.

  The carbon fiber of the present invention does not need to be subjected to surface oxidation treatment which is usually known in order to enhance the dispersibility with the matrix resin and the dispersibility with water. For example, it is known to use mixed acid or hydrogen peroxide as surface oxidation treatment in order to increase the dispersibility of carbon fibers in water (for example, WO 2014/115852, paragraphs 0391, 0398). The mixed acid-treated carbon fiber has a very large surface O / C value, and in the case of hydrogen peroxide, the value is small and does not fall within the scope of the present invention. (See Examples 1 and 2 below).

2. Electrode mixture layer for non-aqueous secondary batteries A second aspect of the present invention is an electrode mixture layer for non-aqueous electrolyte secondary batteries (hereinafter, also simply referred to as "electrode mixture layer") using the above-mentioned carbon fiber. The electrode mixture layer contains at least the electrode active material, the carbon fiber of the present invention, and the binder. The electrode mixture layer of the present invention may further contain another carbon-based conductive aid.

  The thickness (film thickness) of the electrode mixture layer of the present invention is not particularly limited, but is preferably 50 μm or more, more preferably 70 μm or more, still more preferably 90 μm or more, and 100 μm or more Is particularly preferred. Although the upper limit of the film thickness is not particularly limited, it is generally less than 1000 μm and particularly preferably less than 800 μm. When it is going to manufacture arbitrary capacity cells as a film thickness is less than 50 micrometers, a separator and a collector will be used abundantly and the in-cell active material layer volume occupancy will fall. This is undesirable in terms of energy density, and the application is quite limited. When the film thickness is 1000 μm or more, cracks easily occur in the electrode mixture layer, and the manufacture is relatively difficult. In addition, when the film thickness is 1000 μm or more, the transport of Li ions is easily inhibited, and the resistance is easily increased. Although it does not specifically limit as a measuring method of the film thickness of an electrode mixture layer, For example, it can measure using a micrometer.

  As a nonaqueous electrolyte secondary battery manufactured using the electrode mixture layer of this invention, a lithium ion secondary battery is mentioned as a typical battery. Hereinafter, the positive electrode active material and the negative electrode active material used for the lithium ion secondary battery will be described.

<Positive electrode active material>
As a positive electrode active material contained in the electrode mixture layer of the present invention, in a non-aqueous electrolyte secondary battery, one or two or more arbitrary materials can be selected from conventionally known materials known as a positive electrode active material. It can be selected appropriately and used. For example, in the case of a lithium ion secondary battery, a lithium-containing metal oxide capable of inserting and extracting lithium ions is preferable. As this lithium-containing metal oxide, a complex oxide containing lithium and at least one element selected from the group consisting of Co, Mg, Mn, Ni, Fe, Al, Mo, V, W, Ti, etc. It can be mentioned.

_{Specifically, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Co b V 1-b O z, Li x Co b Fe 1-b O ₂ , Li _x Mn ₂ O ₄ , Li _x Mn _c Co _2-c O ₄ , Li _x Mn _c Ni _2-c O ₄ , Li _x Mn _c V _2-c O ₄ , Li _x Mn _c Fe _{2- c} O _4, (where, x = 0.02~1.2, a = 0.1~0.9 , b = 0.8~0.98, c = 1.2~1.96, z = And at least one selected from the group consisting of Preferred lithium-containing metal _{oxides, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Mn 2 O 4, Li x Co b V 1-b At least one selected from the group consisting of O _z (wherein x, a, b and z are as defined above) can be mentioned. The value of x is a value before the start of charge and discharge, and increases and decreases due to charge and discharge.

  The positive electrode active materials may be used alone or in combination of two or more. The average particle diameter of the positive electrode active material is preferably 10 μm or less, more preferably 0.05 to 7 μm, and still more preferably 1 to 7 μm. When the average particle size exceeds 10 μm, the efficiency of charge and discharge reaction under large current may be reduced.

  The content of the positive electrode active material in the electrode mixture layer of the present invention is preferably 60% by mass or more, more preferably 70 to 98.5% by mass, and 75 to 98.5% by mass. Is more preferred. If it is less than 60% by mass, it may be difficult to apply to power source applications where energy density is required. If it exceeds 98.5% by mass, the amount of the binder may be too small to cause a crack in the electrode mixture layer, or the electrode mixture layer may be peeled from the current collector. Furthermore, the content of the carbon fiber and the carbon-based conductive additive may be too small, and the conductivity of the electrode mixture layer may be insufficient.

<Anode active material>
As a negative electrode active material contained in the electrode mixture layer of the present invention, in a non-aqueous electrolyte secondary battery, one or two or more arbitrary materials can be selected from conventionally known materials known as a negative electrode active material. It can be selected appropriately and used. For example, as a material capable of storing and releasing lithium ions, a carbon material, any of Si and Sn, or an alloy or an oxide containing at least one of them can be used. Among these, carbon materials are preferable from the viewpoint of cost and the like. Examples of the carbon material include natural graphite, artificial graphite produced by heat-treating petroleum-based or coal-based coke, hard carbon obtained by carbonizing a resin, and mesophase pitch-based carbon material.

  When natural graphite or artificial graphite is used, from the viewpoint of increasing battery capacity, the spacing d (002) of the (002) plane of the graphite structure by powder X-ray diffraction is in the range of 0.335 to 0.337 nm preferable. Natural graphite refers to a graphitic material naturally produced as ore. Natural graphite can be divided into two types of scaly graphite having a high degree of crystallinity and earthy graphite having a low degree of crystallinity depending on its appearance and properties. The scaly graphite is further divided into scaly graphite having a leaf-like appearance and scaly graphite which is massive. The origin, properties, and type of natural graphite to be a graphitic material are not particularly limited. In addition, particles produced using natural graphite or natural graphite as a raw material may be subjected to heat treatment before use.

  Artificial graphite refers to a graphitic material close to a graphite and a fully crystallized graphite produced by an artificial method widely. Typical examples are those obtained through a baking process at about 500 to 1000 ° C. and a graphitization process at 2000 ° C. or more using tar and coke obtained from dry distillation of coal, residues of crude oil distilled, etc. as raw materials It can be mentioned. In addition, quiche graphite obtained by reprecipitating carbon from molten iron is also a kind of artificial graphite.

Using an alloy containing at least one of Si and Sn in addition to the carbon material as the negative electrode active material is more effective than using each of Si and Sn alone or using each oxide. It is effective in that it can be made smaller. Among these, Si-based alloys are preferable. As the Si-based alloy, at least one element selected from the group consisting of B, Mg, Ca, Ti, Fe, Co, Mo, Cr, V, Ni, Mn, Zn, Cu and the like, Si, Alloys and the like. _{Specifically, SiB 4, SiB 6, Mg} 2 Si, Ni 2 Si, TiSi 2, MoSi 2, CoSi 2, NiSi 2, CaSi 2, CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, VSi 2, At least one selected from the group consisting of WSi ₂ , ZnSi _{2 and the} like can be mentioned.

  In the electrode mixture layer of the present invention, as the negative electrode active material, the above-described materials may be used alone or in combination of two or more. Moreover, the average particle diameter of the said negative electrode active material shall be 10 micrometers or less. When the average particle size exceeds 10 μm, the efficiency of charge and discharge reaction under large current decreases. The average particle size is preferably 0.1 to 10 μm, and more preferably 1 to 7 μm.

<Binder>
As a binder used for the electrode mixture layer of this invention, it is possible to use an electrode which can be formed as long as it is a binder having sufficient electrochemical stability. Such binders include polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), fluoroolefin copolymer cross-linked polymer, polyimide, polyamide imide, It is preferable to use one or more selected from the group consisting of aramid, phenolic resin and the like, and polyvinylidene fluoride (PVDF) is particularly preferable. There is no particular limitation on the form when using as a binder, and it may be solid or liquid (for example, an emulsion), and may be a method of producing an electrode (in particular, dry kneading or wet kneading), dissolution in an electrolytic solution It can be selected appropriately in consideration of the nature and the like.

  The content of the binder in the electrode mixture layer of the present invention is preferably 1 to 25% by mass, more preferably 3 to 15% by mass, and still more preferably 5 to 10% by mass. When the amount is less than 1% by mass, cracks may occur in the electrode mixture layer, or the electrode mixture layer may be peeled from the current collector. If it exceeds 25% by mass, the amount of active material in the electrode decreases, and the energy density of the obtained battery tends to decrease.

(Carbon-based conductive auxiliary agent other than carbon fiber of the present invention)
The electrode mixture layer of the present invention can also contain a carbon-based conductive aid in addition to the carbon fiber of the present invention. Examples of carbon-based conductive assistants other than carbon fibers include carbon black, acetylene black, carbon nanotubes, VGCF, scaly carbon, graphene, and graphite. These carbon-based conductive assistants may be used alone or in combination of two or more.

The shape of these carbon-based conductive assistants is not particularly limited, but is preferably in the form of fine particles. It is preferable that it is 10-200 nm, and, as for the average particle diameter (primary particle diameter) of a carbon-type conductive support agent, it is more preferable that it is 20-100 nm. The aspect ratio of these carbon-based conductive additives is 10 or less, preferably 1 to 5, and more preferably 1 to 3.
It is preferable that content of carbon-type conductive support agents other than the carbon fiber in the electrode mixture layer of this invention is 0.5-5 mass%, and it is more preferable that it is 0.5-4 mass%, 1 It is further more preferable that it is -3 mass%.

3. 3. Electrode for Nonaqueous Electrolyte Secondary Battery A third aspect of the present invention is an electrode for nonaqueous electrolyte secondary battery (hereinafter, also simply referred to as “electrode”) in which the above-mentioned electrode mixture layer is formed. This electrode is formed by forming the electrode mixture layer of the present invention on the surface of a current collector.

The following two methods are generally used as a method of producing an electrode provided with the electrode mixture layer of the present invention. One method is to mix and knead the electrode active material, the carbon fiber, the binder, and other components as required, form a film by extrusion molding, roll and stretch it, and then bond it to a current collector Method.
Another method is to prepare a slurry by mixing the above electrode active material, the above carbon fiber, a binder, a solvent for dissolving the binder, and other components as required, and applying this slurry to the surface of the current collector After removing the solvent and pressing.
In the case of the present invention, although either method can be adopted, the latter method is preferred, so the latter method will be described in detail below.

  The solid content concentration in the above slurry (the proportion of the total mass of components other than the solvent of the above slurry to the total mass of the slurry) is preferably 10 to 30 mass%, and is 15 to 25 mass%. Is more preferred. When solid content concentration exceeds 30 mass%, uniform slurry preparation may be difficult. When the solid content concentration is less than 10% by mass, the viscosity of the slurry is insufficient, and the thickness of the electrode mixture layer laminated on the current collector may be nonuniform.

  The solvent used for the slurry is not particularly limited as long as the solvent dissolves the binder. Specifically, one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO) and the like can be mentioned, and in particular NMP or NMP DMAc is preferred.

  When manufacturing the electrode, if the thixotropy in the slurry is too strong, it may be difficult to secure the flowability suitable for coating. In such a case, a slurrying aid may be used. Examples of the slurrying aid include one or more selected from the group consisting of polyvinyl pyrrolidone, carboxymethyl cellulose, polyvinyl acetate, polyvinyl alcohol and the like. In particular, it is preferable to use polyvinyl pyrrolidone. By adding the above-described slurrying aid, sufficient fluidity can be ensured even with a small amount of solvent, and the dispersibility of the carbon-based conductive aid is also significantly improved. In addition, the occurrence of cracks after solvent removal can be suppressed. The addition amount of the slurrying aid is preferably 10% by mass or less, more preferably 0.5 to 10% by mass, with respect to the total of components other than the solvent in the slurry. It is more preferable that it is -8 mass%. Conversely, if the amount of the slurrying aid exceeds 10% by mass, the viscosity of the slurry may rapidly decrease, causing poor dispersion, which may make it difficult to produce a suitable slurry. When the addition amount of the slurrying aid is less than 0.5% by mass, the effect of the slurrying aid hardly appears.

  The slurry is applied to the surface of a current collector to be described later. As an application method, an appropriate application method such as a doctor blade can be adopted. After application, the solvent is removed, for example, by heat treatment at 60 to 100 ° C., preferably 75 to 85 ° C., preferably for 60 to 180 minutes. Then, the electrode of this invention can be manufactured by pressing the application | coating thing after solvent removal. Preferred pressing conditions are 1 to 5 minutes under a pressure of 10 to 30 Pa.

Any conductive material can be used as a current collector that constitutes the electrode. For example, metal materials of aluminum, nickel, iron, stainless steel, titanium or copper can be used. In particular, aluminum, stainless steel or copper is preferable, and it is more preferable to use aluminum or carbon coated aluminum.
The thickness of the current collector is preferably 10 to 50 μm.

4. Nonaqueous Electrolyte Secondary Battery A fourth invention of the present invention is a nonaqueous electrolyte secondary battery comprising the electrode of the present invention.
The non-aqueous electrolyte secondary battery of the present invention is configured using the electrode of the present invention for the positive electrode and / or the negative electrode, and using known separators and electrolytes. A lithium ion secondary battery is illustrated as a non-aqueous electrolyte secondary battery.

  The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode having a positive electrode material layer formed on the surface of a current collector, an electrolyte layer containing an electrolyte, and an electrode (negative electrode) of the present invention. The layer and the negative electrode material layer of the negative electrode face each other, and an electrolyte layer is inserted between the positive electrode material layer and the negative electrode material layer. Alternatively, the electrode (positive electrode) of the present invention, an electrolyte layer containing an electrolyte, and a negative electrode having a negative electrode material layer formed on the surface of a current collector, the positive electrode material layer of the positive electrode and the negative electrode material layer of the negative electrode face each other And, it is laminated so that the electrolyte layer is inserted between the positive electrode material layer and the negative electrode material layer. Alternatively, the electrode (positive electrode) of the present invention, an electrolyte layer containing an electrolyte, and the electrode (negative electrode) of the present invention, the positive electrode material layer of the positive electrode and the negative electrode material layer of the negative electrode face each other, and the positive electrode material layer and the negative electrode It laminates so that an electrolyte layer may be inserted between material layers.

  The cell shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and may be implemented in any shape. Specifically, for example, cell shapes such as a button type, a cylindrical type, and a square type can be mentioned. In addition, it is also preferable to have an internal configuration in which a plurality of pairs of positive and negative electrodes and a separator are stacked, and in this case, it is possible to adopt a known stack stack type, wound type, folded stack type, or the like. As an exterior material of the nonaqueous electrolyte secondary battery of this invention, a metal can, an aluminum laminated resin film etc. can be mentioned, for example. In the non-aqueous electrolyte secondary battery of the present invention, a predetermined carbon fiber added to the electrode mixture layer has a linear structure and high conductivity, so it is easy to form a conductive path. , Excellent charge and discharge characteristics can be obtained. Furthermore, the electrode strength is also improved.

<Electrolyte layer>
As an electrolyte layer which comprises a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte which melt | dissolved electrolytes, such as lithium salt, in non-aqueous solvent is used.
The electric conductivity at 25 ° C. of the electrolytic solution used in the non-aqueous electrolyte secondary battery of the present invention is preferably 1 × 10 ⁻² S / cm or more.

  In general, non-aqueous electrolytes are characterized by having a high withstand voltage and a high energy density as compared to aqueous electrolytes. As the non-aqueous solvent, known ones can be used without limitation, and propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, γ-valerolactone, acetonitrile, Nitromethane, methoxyacetonitrile, nitroethane, N, N-dimethylformamide, 3-methoxypropionitrile, N-methylpyrrolidone, N, N'-dimethylimidazolidinone, dimethylsulfoxide, sulfolane, 3-methylsulfolane, ethyl methyl carbonate, etc. Can be mentioned. These non-aqueous solvents may be used alone or in combination of two or more. It is important that the solvent used for the electrolytic solution have an appropriate boiling point, melting point, viscosity, and relative dielectric constant, and among the above-mentioned solvents, those mainly composed of propylene carbonate or γ-butyrolactone are preferably used.

Examples of the electrolyte used in the non-aqueous electrolyte secondary battery of the present invention include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , and lower aliphatics. Lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, borates, imido salts and the like can be mentioned. As borates, lithium bis (1,2-benzenediolate (2-)-O, O ') borate and bis (2,3-naphthalenediolate (2-)-O, O') borate Lithium, bis (2,2'-biphenyldiolate (2-)-O, O ') lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O') lithium borate Etc. As imide salts, lithium trifluoromethanesulfonic acid imide lithium ((CF ₃ SO ₂ ) ₂ NLi), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium imide (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) And lithium bis (pentafluoroethane) sulfonic acid imide ((C ₂ F ₅ SO ₂ ) ₂ NLi). The concentration of the electrolyte is preferably 0.5 to 2 mol / L. The electrolyte may be used singly or in combination of two or more of the above. A known additive may be added to the electrolyte for the purpose of improving cycle stability, charge / discharge efficiency, and the like.
As an electrolytic solution used for a lithium ion secondary battery of the present invention, an ionic liquid typified by ethyl methyl imidazolium salt can also be suitably used, and in this case, it is not necessarily dissolved in the above-mentioned non-aqueous solvent. There is no need to use it.

<Separator>
When using the above non-aqueous electrolyte solution, it is general to use a separator in order to prevent the negative electrode active material layer and the electrode mixture layer of the present invention from being in direct contact with each other. As the shape of the separator, a known shape such as paper (film) or porous film can be suitably adopted. As a material of the separator, for example, one or more types of materials selected from the group consisting of cellulose, aromatic polyamide, aliphatic polyimide, polyolefin, Teflon (registered trademark), polyphenylene sulfide and the like can be suitably used. Among these, cellulose paper, aromatic polyamide or aliphatic polyimide porous membrane is preferable from the viewpoint of heat resistance and thinning. The film thickness of the separator is preferably about 20 to 100 μm from the viewpoint of short circuit prevention, but in the present invention, it is also possible to apply a separator of about 5 to 20 μm which is sufficiently thin compared to the conventional separator. When a thin separator is used, the internal resistance derived from the separator is reduced, the output is improved, and the energy density of the cell is also improved.

  Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited thereto. Various measurements and analyzes in the examples were performed according to the following methods.

(1) Shape confirmation of carbon fiber Observation and photography were performed using the table-top electron microscope (The Nippon Denshi Co., Ltd. make, model NeoScope JCM-6000). Regarding the average fiber diameter of carbon fibers etc., 300 points were randomly selected from the obtained electron micrographs to measure the fiber diameter, and the average value of all the measurement results (n = 300) was taken as the average fiber diameter . It calculated similarly about average fiber length.

(2) X-ray Diffraction Measurement of Carbon Fiber According to JIS R7651 method using RINT-2100 manufactured by Rigaku Corporation, lattice spacing (d002), crystallite size (Lc) (hexagonal network area layer Directions) and (La) (carbon hexagonal mesh plane direction) were measured.

(3) Measurement method of powder volume resistivity The powder volume resistivity is measured by using a powder resistance system (MCP-PD51) manufactured by Dia Instruments Co., Ltd. under a load of 0.25 to 2.50 kN. It measured using the electrode unit of the method. The volume resistivity was taken as the powder volume resistivity of the sample from the value of the volume resistivity at a packing density of 0.8 g / cm ³ from the relationship diagram of the volume resistivity with the change of the packing density.

(4) Measurement of strength ratio of O-C bond to O = C bond (O = C / O-C) and oxygen content Strength of O-C bond and O = C bond on the surface of carbon fiber The ratio (O = C / O-C) and the measurement of oxygen content can be measured by XPS (Thermo Scientific K-Alpha, X-ray source; Al-Kα monochrome (1486.7 eV), X-ray spot size: 400 μm, Flood Gun) on, vacuum degree <5 × 10 ^-8 mbar, detection angle 0 °, measurement; elemental measurement (Narrow Scan Ols).

(5) Evaluation of wettability In order to confirm the affinity to the electrolytic solution, the evaluation of wettability was performed. Propylene carbonate is used as the electrolytic solution, and the evaluation device is a dynamic wettability tester WET-6200 (RHESCA) using a dipping speed of 1 mm / s, a dipping depth of 0.5 mm, and a dipping time of 300 sec. The wettability was evaluated from the above.
A sample for evaluation (carbon fiber) was placed in a holder for powder sample, and tapping was performed until the powder height did not change to prepare a sample for powder evaluation. It was immersed under the above conditions, and the wettability was evaluated from the immersion rate method.
○: immersion speed 0.01 or more ×: immersion speed less than 0.01

(6) Conductivity measurement Using the potentiostat / galvanostat (HA-151 manufactured by Hokuto Denko Co., Ltd.), the electrode resistance in the film thickness direction of the manufactured electrode is measured, and the electrical conductivity calculated from the resistance value is calculated I asked.

[Examples 1 and 2]
90 parts by mass of high density polyethylene (manufactured by Prime Polymer Co., Ltd. Hysex 5000 SR; melt viscosity 14 Pa · s at 600 s ⁻¹ ) as a thermoplastic resin and mesophase pitch AR-MPH (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as mesophase pitch 10 parts by mass was melt-kneaded with a co-directional twin-screw extruder (TEM-26SS manufactured by Toshiba Machine Co., Ltd., barrel temperature 310 ° C., under nitrogen stream) to prepare a mesophase pitch composition. In the mesophase pitch composition obtained under these conditions, the mesophase pitch was dispersed in the thermoplastic resin with a dispersion diameter of 0.05 to 2 μm. Moreover, although this mesophase pitch composition was hold | maintained at 300 degreeC for 10 minutes, aggregation of mesophase pitch was not recognized but the dispersion diameter was 0.05-2 micrometers.
Next, a resin composite fiber (long fiber) was produced from the above mesophase pitch composition with a melt spinning machine, from a die having a diameter of 0.2 mm under the condition of a die temperature of 390 ° C.
Next, a short fiber having a length of about 5 cm was produced from this resin composite fiber (long fiber). The short fibers were arranged in a non-woven fabric on a wire mesh having an opening of 1.46 mm and a wire diameter of 0.35 mm so as to have a basis weight of 30 g / m ² .

By holding the non-woven fabric made of this resin conjugate fiber in a hot air dryer at 215 ° C. for 3 hours, a non-woven fabric made of resin composite stabilized fiber was produced. Next, in a vacuum gas displacement furnace, after performing nitrogen substitution, the pressure was reduced to 1 kPa, and the thermoplastic resin was removed by heating from this state. The heating conditions were such that the temperature was raised to 500 ° C. at a temperature rising rate of 5 ° C./min, and then held at the same temperature for 60 minutes. The non-woven fabric consisting of the stabilized fiber was added to an ethanol solvent, and the stabilized fiber was dispersed in the solvent by applying vibration for 30 minutes with an ultrasonic oscillator. A non-woven fabric consisting of stabilized fibers was made by filtering the stabilized fibers dispersed in a solvent.
The non-woven fabric composed of the stabilized fiber was heated to 1000 ° C. at 5 ° C./min under a nitrogen gas flow in a vacuum gas displacement furnace and heat treated at the same temperature for 0.5 hour, and then cooled to room temperature. Next, this non-woven fabric is placed in a graphite crucible, and from a room temperature in vacuum using an ultra-high temperature furnace (type SCC-U-80 / 150, heat equalizing section 80 mm (diameter) × 150 mm (height)) manufactured by Kurata Giken Co., Ltd. The temperature was raised to 2000 ° C. at 10 ° C./min. After reaching 2000 ° C., an atmosphere of 0.05 MPa (gauge pressure) of argon gas (99.999%) is used, and then a temperature increase rate of 10 ° C./min is 2400 ° C. (for Example 2) or 2800 ° C. (Example) The temperature was raised to 1), and heat treatment was carried out at each temperature for 0.5 hour to graphitize to obtain a carbon fiber. The average fiber diameter, CV value, average aspect ratio (L / D) and crystallite size d 002 of the obtained carbon fiber were measured, and the results are shown in Table 1.
Moreover, the result of the peak derived from the O1s orbital of XPS measurement is shown in FIG. 1 (Example 1) and FIG. 2 (Example 2). As a result of performing the peak separation, it is shown that the peak appearing around 533 eV is derived from a C-O bond, and the peak around 531 eV is C = O, but the intensity ratio is also as described in Table 1 .

  Moreover, it measured about the volume resistance value and the wettability to electrolyte solution, and the result was described in Table 2. The obtained carbon fiber was an excellent carbon fiber having high conductivity and high affinity to the electrolytic solution.

2 parts by mass of the obtained carbon fiber as a carbon-based conductive auxiliary agent, 91 parts by mass of a positive electrode active material (LiFePO ₄ ; manufactured by Hosen Co., Ltd., SLFP-ES01), polyvinylidene fluoride (manufactured by Kureha Co., W A slurry was prepared using 7 parts by mass of # 7200) and N-methylpyrrolidone as a solvent. The produced slurry was applied to a current collector (a 15 μm thick aluminum foil) to produce an electrode. The electrode thickness was 120 μm, and the electrode density was 2.5 g / cm ³ . The results of the conductivity of the obtained electrode are shown in Table 2. Also from this result, the obtained carbon fiber was excellent in the conductivity, and the CV value of the conductivity was small and the homogeneity was high.

Comparative Example 1
A carbon fiber was produced under the same conditions as in Example 1 except that the final temperature of graphitization was 3000 ° C. The average effective fiber length and crystallite size of the obtained carbon fibers were measured, and the results are shown in Table 1.
Moreover, the result of the peak derived from the O1s orbital of XPS measurement is shown in FIG. As a result of performing the peak separation, it is shown that the peak appearing around 533 eV is derived from a C-O bond, and the peak around 531 eV is C = O, but the intensity ratio is also as described in Table 1 .
The volume resistivity and the wettability to the electrolyte were measured, and the results are shown in Table 2. The obtained carbon fiber is a carbon fiber which is excellent in conductivity but low in affinity to the electrolytic solution.

  An electrode was produced under the same conditions as in Example 1 using the obtained carbon fiber to measure the conductivity, and the results are shown in Table 2. Also from this result, although the obtained carbon fiber has excellent conductivity, the CV value of the electrical conductivity is high, and the homogeneity is a little inferior.

Comparative Example 2
A carbon fiber was produced under the same conditions as in Example 1 except that the final temperature of graphitization was 2000 ° C. The average effective fiber length and crystallite size of the obtained carbon fibers were measured, and the results are shown in Table 1. The result of the peak derived from the O1s orbital of XPS measurement is shown in FIG. Moreover, it measured about the volume resistance value and the wettability to electrolyte solution, and the result was described in Table 2. The obtained carbon fiber was a carbon fiber which is excellent in electrolytic solution affinity but low in conductivity.

  An electrode was produced under the same conditions as in Example 1 using the obtained carbon fiber to measure the conductivity, and the results are shown in Table 2. Also from this result, the obtained carbon fiber had low conductivity.

[Reference Example 1]
The carbon fiber obtained in Comparative Example 1 was placed in a hydrogen peroxide solution (hydrogen peroxide concentration: 30%), mixed for 3 hours, washed with deionized water, and then filtered and dried. The surface O / C value of the obtained carbon fiber was 0.018.

[Reference Example 2]
The carbon fiber obtained in Comparative Example 1 is placed in mixed acid (150 ml of concentrated sulfuric acid (95%) and 50 ml of concentrated nitric acid (60 to 61% mixed solution), mixed for 1 hour, and washed with ion exchanged water. Subsequently, the resultant was filtered and dried, and the surface O / C value of the obtained carbon fiber was 0.167.

Claims (7)

The surface oxygen concentration ratio (O / C) measured by X-ray photoelectron spectroscopy is 0.02 or more and 0.15 or less,
CV value of fiber diameter is 10 to 50%,
And, a pitch based ultrafine carbon fiber characterized in that the crystallite size (d002) measured by the X-ray diffraction method is 0.340 nm or less.   The pitch system according to claim 1, wherein the intensity ratio (O = C / O-C) between the O-C bond derived from the O1s orbital and the O = C bond measured by X-ray photoelectron spectroscopy is 1.4 or more. Extra fine carbon fiber.   The pitch based ultrafine carbon fiber according to claim 1 or 2, wherein the average fiber diameter is 100 nm or more and less than 700 nm.   The pitch based ultrafine carbon fiber according to any one of claims 1 to 3, which has an average aspect ratio of 30 to 1000. The pitch based ultrafine carbon fiber according to any one of claims 1 to 4;
An electrode active material,
With a binder,
And an electrode mixture layer for a non-aqueous electrolyte secondary battery. Current collector,
The electrode mixture layer for a non-aqueous electrolyte secondary battery according to claim 5, which is laminated on the current collector;
An electrode for a non-aqueous electrolyte secondary battery comprising:   A non-aqueous electrolyte secondary battery comprising the electrode for a non-aqueous electrolyte secondary battery according to claim 6.

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