JP6974934B2 - 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 relates to an electrode mixture layer for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery formed by using a carbon material having excellent oxidation resistance.

Carbon nanomaterials, especially 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, and thus have high performance. It is used as a nanofiller for composite materials. Its applications are not limited to reinforcing nanofillers aimed at improving mechanical strength, but by taking advantage of the high conductivity of carbon materials, it is an additive material for electrodes of various batteries and capacitors, electromagnetic shielding materials, and antistatic materials. It is being studied for use as a conductive nanofiller for a resin or as a nanofiller to be blended in an electrostatic coating material for resins. In addition, it is expected to be used as a field electron emission material such as a flat display by taking advantage of its chemical stability, thermal stability, and fine structure as a carbon material. Among them, it is highly expected that the conductivity will be improved by adding it to a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries are required to have a higher energy density, and one approach is to increase the voltage of the battery. However, under high voltage, a side reaction different from the charge / discharge reaction of the battery occurs due to the problem of oxidation resistance of the electrolytic solution and the conductive auxiliary agent which are the constituent materials of the battery. Therefore, there is a concern that energy efficiency may be reduced and safety problems may occur due to gas generation.

Patent Document 1 proposes the addition of an additive in order to suppress the decomposition reaction of the electrolytic solution, but sufficient measures have not been taken regarding the oxidation resistance of the conductive auxiliary agent.

Japanese Unexamined Patent Publication No. 2008-10330

For non-aqueous electrolyte secondary batteries, studies are underway to increase the voltage in order to further improve the performance. However, if a non-aqueous electrolyte secondary battery in which a conventional carbon material is used as a conductive auxiliary agent is used as it is at a high voltage, side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution occur. As a result, there is a problem that the energy efficiency is lowered.

An object of the present invention is a carbon material and a carbon-based conductive auxiliary agent having excellent oxidation resistance, which are less likely to cause side reactions such as decomposition of an electrolytic solution and a reaction between a conductive auxiliary agent and an electrolytic solution under high voltage, and a carbon-based conductive auxiliary agent. It is an object of the present invention to provide the electrode mixture layer for a non-aqueous electrolyte secondary battery, the electrode for a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery used.

As a result of diligent studies in view of the above-mentioned prior art, the present inventors have found that by using a carbon material exhibiting predetermined electrochemical properties as a conductive auxiliary agent, side reactions under high voltage can be suppressed. The present invention has been completed.

That is, the present invention that solves the above problems is described below.

[1] An electrode mixture layer for a non-aqueous electrolyte secondary battery containing at least a carbon material.
An ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C.) ratio =) containing _{LiPF 6} having a concentration of 1 mol / L, with the electrode composed of the electrode mixture layer for the non-aqueous electrolyte secondary battery as the working electrode and the lithium metal as the counter electrode. In the cyclic voltammogram (CV) measured in the range of 2.5 to 5 V (vs. Li / Li +) using 3/7), the integrated value of the reduction current / the integrated value of the oxidation current is 0.6 or less. An electrode mixture layer for a non-aqueous electrolyte secondary battery, characterized in that it does not exhibit a certain electrochemical reaction.

[2] The carbon material comprises an electrode containing a 100 part mass portion of an electrode mixture layer for a non-aqueous electrolyte secondary battery composed of 50 parts by mass of the carbon material and 50 parts by mass of polyvinylidene fluoride, and a lithium metal as a working electrode. Using an ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C.) ratio = 3/7) containing _{LiPF 6} having a concentration of 1 mol / L as a counter electrode, 2.5 to 4.4 V (vs. Li / Li +). ) In the cyclic voltammogram (CV) measured in the potential range of), the following equation (1)
IA / IB <0.02 ・ ・ ・ Equation (1)
(Here, IA is the largest of the current values when the oxidation current reaches the maximum value when the cyclic voltammogram measurement is performed in the potential range of 2.5 to 4.4 V (vs. Li / Li +). IB refers to the current value at 5 V when cyclic voltamogram measurement is performed within the potential range of 2.5 to 5 V (vs. Li / Li +).)
The electrode mixture layer for a non-aqueous electrolyte secondary battery according to [1], which is a carbon material satisfying the above conditions.

[3] The non-water-free material according to [1] or [2], wherein the crystal plane spacing (d002) of the carbon material contained in the electrode mixture layer is 0.335 to 0.340 nm measured by an X-ray diffraction method. Electrode mixture layer for electrolyte secondary batteries.

[4] The non-aqueous according to any one of [1] to [3], wherein the crystallite length (La) of the carbon material contained in the electrode mixture layer is 30 to 500 nm measured by an X-ray diffraction method. Electrode mixture layer for electrolyte secondary batteries.

[5] The electrode mixture layer for a non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the metal content of the carbon material contained in the electrode mixture layer is 50 ppm or less.

[6] The electrode mixture for a non-aqueous electrolyte secondary battery according to any one of [1] to [5], wherein the carbon material contained in the electrode mixture layer has an average length of the smallest dimension of 50 to 1000 nm. layer.

[7] The carbon material contained in the electrode mixture layer is fibrous carbon, and the ratio (L / D) of the average effective length (L) to the average fiber diameter (D) is 30 or more [1]. The electrode mixture layer for a non-aqueous electrolyte secondary battery according to any one of [6] to [6].

[8] The non-aqueous electrolyte secondary battery according to [7], wherein the content ratio of the fibrous carbon having an effective length longer than the average effective length (L) is 48% or less based on the number of the fibrous carbons. Electrode mixture layer.

[9] The electrode for a non-aqueous electrolyte secondary battery having the electrode mixture layer for the non-aqueous electrolyte secondary battery according to any one of [1] to [8].

[10] A non-aqueous electrolyte secondary battery having the electrode mixture layer for the non-aqueous electrolyte secondary battery according to any one of [1] to [8].

According to the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery capable of suppressing the reaction between the carbon-based conductive auxiliary agent and the electrolytic solution under high voltage and achieving excellent energy efficiency.

FIG. 1 is a histogram showing the effective length distribution of fibrous carbon constituting the electrode mixture layer of Example 1. FIG. 2 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Example 1. FIG. 3 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrodes of Example 1. FIG. 4 shows the charge / discharge measurement results of the battery in Example 1. FIG. 5 is a histogram showing the effective length distribution of the fibrous carbon constituting the electrode mixture layer of Example 2. FIG. 6 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Example 2. FIG. 7 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrodes of Example 2. FIG. 8 shows the charge / discharge measurement results of the battery in Example 2. FIG. 9 is a histogram showing the effective length distribution of the fibrous carbon constituting the electrode mixture layer of Reference Example 1. FIG. 10 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Reference Example 1. FIG. 11 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrode of Reference Example 1. FIG. 12 shows the charge / discharge measurement results of the battery in Reference Example 1. FIG. 13 is a histogram showing the effective length distribution of the fibrous carbon constituting the electrode mixture layer of Reference Example 2. FIG. 14 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Reference Example 2. FIG. 15 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrode of Reference Example 2. FIG. 16 is a battery charge / discharge measurement result in Reference Example 2. FIG. 17 is a histogram showing the effective length distribution of the fibrous carbon constituting the electrode mixture layer of Reference Example 3. FIG. 18 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Reference Example 3. FIG. 19 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrode of Reference Example 3. FIG. 20 shows the charge / discharge measurement results of the battery in Reference Example 3. FIG. 21 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Comparative Example 2. FIG. 22 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrode of Comparative Example 2. FIG. 23 is a battery charge / discharge measurement result in Comparative Example 2. FIG. 24 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 5 V (vs. Li / Li +) using the electrode of Comparative Example 1. FIG. 25 is a cyclic voltammetry (CV curve) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using the electrode of Comparative Example 1. FIG. 26 is a battery charge / discharge measurement result in Comparative Example 1.

Hereinafter, the present invention will be described.

1. 1. Electrode mixture layer for non-aqueous secondary batteries 1-1. Properties of Electrode Mixture Layer for Non-Aqueous Electrolyte Secondary Battery The present invention is an electrode mixture layer for non-aqueous electrolyte secondary battery containing a carbon material (hereinafter, also simply referred to as “electrode mixture layer”). The electrode mixture layer of the present invention may further contain an active material other than the carbon material, a binder, and other carbon-based conductive auxiliary agents.

The electrode mixture layer of the present invention is an ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C.)) containing _{LiPF 6} having a concentration of 1 mol / L, with the electrode composed of the electrode mixture layer as the working electrode and the lithium metal as the counter electrode. ) Ratio = 3/7), in the cyclic voltamogram (CV) measured in the range of 2.5 to 5 V (vs. Li / Li +), the integrated value of the reduction current / the integrated value of the oxidation current is 0. It is characterized in that it does not show an electrochemical reaction of 6 or less.

That is, the electrode mixture layer of the present invention is characterized in that it does not show an irreversible electrochemical reaction in the potential range of 2.5 to 5 V (vs. Li / Li +). Here, the "irreversible electrochemical reaction" is an ethylene carbonate / ethylmethyl carbonate mixture containing _{LiPF 6} having a concentration of 1 mol / L as a solvent, a lithium metal as a counter electrode, and an electrode made of the electrode mixture layer as a working electrode. In the cyclic voltamogram (CV) measured in the range of 2.5 to 5 V (vs. Li / Li +) using a solution (3/7 volume ratio), the integrated value of the reduction current / the integrated value of the oxidation current is 0. It means that it is 6.6 or less.

The electrode mixture layer of the present invention preferably does not show an electrochemical reaction in which the integrated value of the reduction current / the integrated value of the oxidation current is 0.7 or less, and does not show an electrochemical reaction of 0.8 or less. Is more preferable, and it is further preferable not to show an electrochemical reaction of 0.85 or less. The integrated value of the reduction current / the integrated value of the oxidation current is larger than 0.6. By using an electrode mixture layer that does not show an irreversible electrochemical reaction, the electrolyte can be decomposed and the conductive auxiliary agent and the electrolyte can be decomposed under high voltage. It is possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as a reaction with and are unlikely to occur.

The thickness (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, further preferably 90 μm or more, and further preferably 100 μm or more. Is particularly preferred. The upper limit of the film thickness is not particularly limited, but is generally less than 1000 μm, and particularly preferably less than 800 μm. If the film thickness is less than 50 μm, a large amount of separators and current collectors will be used when trying to manufacture an arbitrary capacity cell, and the volume occupancy of the electrode mixture layer in the cell will decrease. This is unfavorable in terms of energy density and severely limits its use. When the film thickness is 1000 μm or more, cracks are likely to occur in the electrode mixture layer, which is relatively difficult to manufacture. Further, when the film thickness is 1000 μm or more, the transport of Li ions is likely to be hindered and the resistance is likely to increase. The method for measuring the film thickness of the electrode mixture layer is not particularly limited, but the film thickness can be measured using, for example, a micrometer. The thickness of the electrode mixture layer in the present invention means the thickness of only the electrode mixture layer, which does not include the thickness of the current collector described later.

1-2. Carbon material contained in the electrode mixture layer for a non-aqueous electrolyte secondary battery The carbon material contained in the electrode mixture layer of the present invention is 100 parts by mass consisting of 50 parts by mass of the carbon material and 50 parts by mass of polyvinylidene fluoride. Ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C) ratio) containing _{LiPF 6} having a concentration of 1 mol / L, with the electrode containing the electrode mixture layer for a non-aqueous electrolyte secondary battery as the working electrode and the lithium metal as the counter electrode. In a cyclic voltammogram (CV) measured in a potential range of 2.5 to 4.4 V (vs. Li / Li +) using = 3/7), the following equation (1)
IA / IB <0.02 ・ ・ ・ Equation (1)
(Here, IA is the largest of the current values when the oxidation current reaches the maximum value when the cyclic voltammogram measurement is performed in the potential range of 2.5 to 4.4 V (vs. Li / Li +). IB refers to the current value at 5 V when cyclic voltamogram measurement is performed within the potential range of 2.5 to 5 V (vs. Li / Li +).)
It is preferable that the carbon material satisfies the above conditions.

That is, it is preferable that the carbon material contained in the electrode mixture layer of the present invention does not exhibit an electrochemical reaction within the potential range of 2.5 to 4.4 V (vs. Li / Li +). Here, "does not show an electrochemical reaction" includes 100 parts by mass of an electrode mixture layer composed of 50 parts by mass of the carbon material and 50 parts by mass of polyvinylidene fluoride (W # 7200, manufactured by Kureha Co., Ltd.). An ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C.) ratio = 3/7, manufactured by Kishida Chemical Co., Ltd.) containing _{LiPF 6} having a concentration of 1 mol / L as a solvent is prepared by using an electrode as a working electrode and a lithium metal as a counter electrode. It means that there is no substantial peak in the cyclic voltammogram (CV) measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). Here, "having no substantial peak" means satisfying the above equation (1).

By forming an electrode mixture layer that does not show an electrochemical reaction within the potential range of 2.5 to 4.4 V (vs. Li / Li +), the electrolytic solution can be decomposed and the conductive auxiliary agent and the electrolytic solution can be decomposed under high voltage. It is possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as a reaction with and are unlikely to occur.

The carbon material contained in the electrode mixture layer of the present invention preferably has high crystallinity. That is, the crystal plane spacing (d002) measured by the X-ray diffraction method is preferably 0.335 to 0.340 nm, and more preferably 0.335 to 0.339 nm. When the range is in the range of 0.335 to 0.340 nm, the graphite crystallinity is high and the oxidation resistance is excellent.

Further, the carbon material contained in the electrode mixture layer of the present invention preferably has a crystallite length (La) of 10 to 500 nm, more preferably 30 to 500 nm, and more preferably 50 to 500 nm. It is even more preferably 100 to 500 nm, even more preferably 120 to 500 nm. If it is less than 10 nm, the oxidation resistance of the carbon material is not sufficient. On the other hand, the crystallite size is measured by the X-ray diffraction method, but since the measurement error becomes large when the crystal is greatly developed, the measurement limit is practically 500 nm.

The carbon material contained in the electrode mixture layer of the present invention preferably has a graphene (net plane group) thickness (Lc) of 1.0 to 130 nm. If it is less than 1.0 nm, the conductivity of the carbon material is significantly lowered, which is not preferable.

The carbon material contained in the electrode mixture layer of the present invention preferably has high conductivity in a state where the packing density is low. This is because a carbon material having high conductivity in a state where the packing density is low can impart conductivity at a lower addition 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. If it exceeds 1 Ω · cm, the amount of carbon material added to improve the conductivity is large, which is not preferable. The lower limit is not particularly limited, but is generally about 0.0001 Ω · cm.

The carbon material contained in the electrode mixture layer of the present invention preferably has a total content of metal elements of 50 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less. When the metal content exceeds 50 ppm, the battery is likely to be deteriorated due to the catalytic action of the metal. In the present invention, the content of the metal element means the total content of Li, Na, Ti, Mn, Fe, Ni and Co. In particular, the Fe content is preferably 5 ppm or less, more preferably 3 ppm or less, and even more preferably 1 ppm or less. When the Fe content exceeds 5 ppm, the battery is particularly liable to deteriorate, which is not preferable.

The carbon material contained in the electrode mixture layer of the present invention preferably contains 0.5% by mass or less of hydrogen, nitrogen, and ash in the carbon material, and more preferably 0.3% by mass or less. preferable. When the hydrogen, nitrogen, and ash contents in the carbon material are all 0.5% by mass or less, structural defects of the graphite layer are further suppressed, and side reactions in the battery can be suppressed, which is preferable.

The carbon material contained in the electrode mixture layer of the present invention preferably has a length of the smallest dimension of 50 to 1000 nm, more preferably 100 to 800 nm, and even more preferably 150 to 600 nm. , 200-500 nm is particularly preferred. Here, the "minimum dimension length" means the fiber diameter when the carbon material is elongated and fibrous, the diameter when it is spherical, and the minor diameter when it is flat.

The carbon material contained in the electrode mixture layer of the present invention is substantially composed of carbon, and examples thereof include graphite, graphene, carbon nanohorn, fullerene, carbon black, activated carbon, and carbon fiber. The carbon material of the present invention is characterized by its high crystallinity.

The carbon material contained in the electrode mixture layer of the present invention has a high effect of forming a conductive network in the electrode mixture layer, and is preferably fibrous carbon from the viewpoint of improving battery output and battery durability. .. The fibrous carbon includes, for example, a gas phase growth carbon material such as carbon nanotubes and carbon nanoribbons, but since it is necessary to use a highly crystalline carbon material, carbon fibers made from pitch are preferable to PAN-based carbon fibers.

The average fiber diameter of the fibrous carbon is preferably 50 to 900 nm. The upper limit is preferably 600 nm or less, more preferably 500 nm or less, further preferably 400 nm or less, further preferably 300 nm or less, and particularly preferably 250 nm or less. Most preferably, it is 200 nm or less. The lower limit is preferably 50 nm or more, more preferably 100 nm or more, and further preferably 150 nm or more.
If it is less than 50 nm, the bulk density is very small and the handleability is poor. Further, when the electrode mixture layer is formed, the electrode strength tends to decrease. If it exceeds 900 nm, gaps are likely to 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 photographic drawing taken at a magnification of 2,000 times by a field emission scanning electron microscope.

The effective length of the fibrous carbon and its average effective length are preferably 1 to 100 μm, more preferably 1 to 50 μm, and even more preferably 5 to 20 μm. If it is less than 1 μm, the conductivity in the electrode mixture layer, the strength of the electrode, and the electrolyte liquid retention property are lowered, which is not preferable. If it exceeds 100 μm, the dispersibility of the fibrous carbon is impaired, which is not preferable. That is, if the fibrous carbon is too long, the fibrous carbon tends to be 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 length of fibrous carbon is defined by the effective length, not the actual fiber length. This is because the fibrous carbon does not always contribute to the conductivity at the actual fiber length in the electrode mixture layer. For example, the fibers may be bent or curled in the electrode mixture layer, and the actual fiber length may not contribute to the conductivity. In the present invention, the effective length of fibrous carbon is defined as the length of the longest line segment in contact with a single fibrous carbon at both ends. In other words, it is the maximum linear distance at which elemental fibrous carbon can conduct. That is, when the fibrous carbon has a perfect linear structure, the effective length is substantially equal to the actual fiber length. When the fibrous carbon has a branched structure or is rounded, it means the length of the maximum line segment connecting two points on the single fibrous carbon.

The ratio (L / D) of the average effective length (L) of the fibrous carbon contained in the electrode mixture layer of the present invention to the average fiber diameter (D) is preferably 30 or more, and preferably 40 or more. More preferred. By setting the ratio (L / D) to 30 or more, the conductive path is efficiently formed in the electrode mixture layer, and the cycle characteristics of the obtained battery can be enhanced. If it is less than 30, the formation of the conductive path in the electrode mixture layer tends to be insufficient, and the resistance value of the electrode mixture layer in the film thickness direction may not be sufficiently lowered. The upper limit of the ratio (L / D) is not particularly limited, but is generally 3000 or less, preferably 500 or less, and more preferably 300 or less. If it exceeds 3000, the dispersibility of the fibrous carbon is impaired, which is not preferable.

When the fibrous carbon is, for example, carbon fiber, the electrode mixture layer of the present invention contains a plurality of carbon fibers having an average fiber diameter of 50 to 900 nm and an aspect ratio of 30 or more (hereinafter, simply ". Also referred to as "carbon fiber aggregate") is preferable. In this carbon fiber aggregate, the content ratio of carbon fibers having an effective length longer than the average effective length is preferably 48% or less based on the number of carbon fiber aggregates. When it is 48% or less, it contains long carbon fibers having an effective length far exceeding the average effective length, which is advantageous for forming a long-distance electron conduction path. The content ratio of carbon fibers having an effective length longer than the average effective length is more preferably 45% or less, further preferably 42% or less, further preferably 40% or less, and 35% or less. Is particularly preferable, and 30% or less is particularly preferable. The content ratio of the carbon fibers having an effective length longer than the average effective length is preferably 5% or more, and more preferably 10% or more.

In the carbon fiber aggregate in the present invention, it is preferable that the mode of the effective length of the carbon fiber when the section is divided into 5 μm is smaller than the average effective length of the carbon fiber aggregate. That is, in the effective length distribution (based on the number of carbon fibers) of the aggregates of carbon fibers, it is preferable that the effective length of the highest peak top is smaller than the average effective length. Further, in the effective length distribution (based on the number of lines), it is preferable that there is only one peak top. By using carbon fibers having such a distribution, long-distance conductive paths are formed by carbon fibers having a long effective length, and carbon fibers having a long effective length are oriented in the in-plane direction by carbon fibers having a short effective length. It is possible to increase the action of inhibiting this. As a result, it becomes easy to form a conductive path in the film thickness direction of the electrode mixture layer.

1-3. Method for Producing Carbon Material A method for producing carbon fiber, which is a preferable form as a carbon material contained in the electrode mixture layer of the present invention, will be described below. The method for producing the carbon fiber contained in the electrode mixture layer of the present invention is not particularly limited, but the carbon fiber can be produced, for example, by going through the steps (1) to (4) described below.
(1) A step of forming a resin composition composed of a thermoplastic resin and a carbon precursor in a molten state to fiberize the carbon precursor to obtain a resin composite fiber.
(2) Stabilization step of stabilizing the resin composite fiber to obtain the resin composite stabilized fiber,
(3) A thermoplastic resin removing step of removing the thermoplastic resin from the resin composite stabilized fiber and separating only the stabilized fiber.
(4) A carbonization firing step of heating stabilized fibers in an inert atmosphere to carbonize or graphitize them to obtain carbon fibers.

<Thermoplastic resin>
The thermoplastic resin used in the method for producing carbon fibers contained in the electrode mixture layer of the present invention can produce resin composite fibers and needs to be easily removed in the thermoplastic resin removing step. Examples of such thermoplastic resins include polyacrylate polymers such as polyolefins, polymethacrylates and polymethylmethacrylates, polystyrenes, polycarbonates, polyarylates, polyesters, polyamides, polyester carbonates, polysulfones, polyimides, polyetherimides, polyketones and polylactic acid. Is exemplified. Among these, polyolefin is preferably used.

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

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), preferably 0.1 to 5 g / min. It is more preferably 10 min, and particularly preferably 0.1 to 3 g / 10 min. When the MFR is in the above range, the mesophase pitch can be satisfactorily microdispersed in the thermoplastic resin. Further, when the resin composite fiber is formed, the fiber is stretched to control the molecular orientation of the carbon precursor to improve the crystallinity of the obtained carbon fiber and to reduce the fiber diameter of the obtained carbon fiber. It can be made smaller. The thermoplastic resin used in the present invention has a glass transition temperature of 250 ° C. or lower in the case of amorphous and a melting point of 300 ° C. or lower in the case of crystalline from the viewpoint that it can be easily melt-kneaded with the carbon precursor. Is preferable.

<Carbon precursor>
It is preferable to use a mesophase pitch as the carbon precursor. Hereinafter, a case where a mesophase pitch is used as the carbon precursor will be described. The mesophase pitch is a pitch that can form an optically anisotropic phase (liquid crystal phase) in a molten state. Examples of the mesophase pitch used in the present invention include those using a distillation residue of coal or petroleum as a raw material and those using an aromatic hydrocarbon such as naphthalene as a raw material. For example, the coal-derived mesophase pitch can be obtained by a treatment mainly for hydrogenation / heat treatment of coal tar pitch, a treatment mainly for hydrogenation / heat treatment / solvent extraction, or the like.

The optically anisotropic content (mesophase ratio) of the mesophase pitch is preferably 80% or more, and more preferably 90% or more.

The mesophase pitch preferably has a softening point of 100 to 400 ° C, more preferably 150 to 350 ° C.

<Resin composition>
The resin composition composed of a thermoplastic resin and a mesophase pitch (hereinafter, also referred to as a mesophase pitch composition) used in the method for producing carbon fibers contained in the electrode mixture layer of the present invention is a thermoplastic resin and the heat thereof. It is preferable that the plastic resin contains 1 to 150 parts by mass of a mesophase pitch with respect to 100 parts by mass of the plastic resin. The content of the mesophase pitch is more preferably 5 to 100 parts by mass. If the content of the mesophase pitch exceeds 150 parts by mass, a resin composite fiber having a desired dispersion diameter cannot be obtained, and if it is less than 1 part by mass, the target carbon fiber cannot be produced at low cost. It is not preferable because it occurs.

In order to produce carbon fibers having a fiber diameter of 900 nm or less, the dispersion diameter of the mesophase pitch in the thermoplastic resin is preferably 0.01 to 50 μm, more preferably 0.01 to 30 μm. If the dispersion diameter of the mesophase pitch in the thermoplastic resin deviates from the range of 0.01 to 50 μm, it may be difficult to produce the 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 phase is spherical, and when the island phase is elliptical, it means the diameter. It means the major axis diameter.

The dispersion diameter of 0.01 to 50 μm is preferably maintained within the above range even after the mesophase pitch composition is held at 300 ° C. for 3 minutes, and is maintained even after being held at 300 ° C. for 5 minutes. It is more preferable that the product is maintained at 300 ° C. for 10 minutes, and it is particularly preferable that the product is maintained at 300 ° C. for 10 minutes. In general, when the mesophase pitch composition is kept in a molten state, the mesophase pitch is aggregated over time in the mesophase pitch composition. If the mesophase pitch is aggregated and the dispersion diameter exceeds 50 μm, it may be difficult to produce the desired carbon fiber. The aggregation rate of the mesophase pitch in the mesophase pitch composition varies depending on the thermoplastic resin used and the type of mesophase pitch.

The mesophase pitch composition can be produced by kneading the thermoplastic resin and the mesophase pitch in a molten state. The melt-kneading of the thermoplastic resin and the mesophase pitch can be performed using a known device. For example, one or more types selected from the group consisting of a uniaxial kneader, a biaxial kneader, a mixing roll, and a Banbury mixer can be used. Among these, it is preferable to use a biaxial kneader for the purpose of satisfactorily microdispersing the mesophase pitch in the thermoplastic resin, and in particular, it is preferable to use a biaxial 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 is preferably 100 to 400 ° C, preferably 150 to 350 ° C. If the kneading temperature is less than 100 ° C., the mesophase pitch does not become a molten state and it is difficult to microdisperse it in the thermoplastic resin, which is not preferable. On the other hand, if the temperature exceeds 400 ° C., the decomposition of the thermoplastic resin and the mesophase pitch proceeds, which is not preferable. The melt-kneading time is preferably 0.5 to 20 minutes, more preferably 1 to 15 minutes. If the melt-kneading time is less than 0.5 minutes, microdispersion of the mesophase pitch is difficult, which is not preferable. On the other hand, if it exceeds 20 minutes, the productivity of carbon fibers is significantly reduced, which is not preferable.

The melt-kneading is preferably carried out in an inert atmosphere having an oxygen gas content of less than 10% by volume, more preferably in an inert atmosphere having an oxygen gas content of less than 5% by volume, and having an oxygen gas content of less than 5% by volume. It is particularly preferred to carry out under an inert atmosphere of less than 1% volume. The mesophase pitch used in the present invention is denatured by reacting with oxygen during melt-kneading, and may hinder microdispersion in the thermoplastic resin. Therefore, it is preferable to perform melt kneading in an inert atmosphere in order to suppress the reaction between oxygen and the mesophase pitch.

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

In order to obtain the carbon fiber used for the electrode mixture layer of the present invention, an orientation control operation for increasing the molecular orientation of the mesophase pitch contained in the resin composite fiber is performed at the stage of obtaining the resin composite fiber. The orientation control operation is performed by deforming the mesophase pitch in the molten state using a base. As such an orientation control operation, a method of applying strain due to shearing to the mesophase pitch in a molten state and a method of applying strain due to elongation can be exemplified. In particular, the method of applying strain due to elongation has a large effect of flow deformation.

Examples of the method of applying strain due to shearing include a method of increasing the linear velocity of the mesophase pitch composition in the melted state in the base flow path in the state where the mesophase pitch is melted. As a result, there is a method of applying strain due to shearing by increasing the passing speed when the mesophase pitch composition in a molten state passes through the mouthpiece flow path.

As a method of applying strain due to elongation, a method of gradually increasing the linear velocity of the melted mesophase pitch composition toward the discharge side by using a mouthpiece in a state where the mesophase pitch is melted can be mentioned. Specifically, a method of forming a throttle portion in the mouthpiece flow path and gradually reducing the cross-sectional area of the flow path toward the discharge side (deformation inside the mouthpiece) or discharging the mesophase pitch composition from the mouthpiece to the cast surface. Then, a method of picking up at a line speed higher than the discharge line speed (deformation outside the base) can be mentioned. In the case of deformation inside the mouthpiece, the mesophase pitch whose molecular orientation is enhanced by the deformation is subsequently reduced in orientation by thermal relaxation under the molten state. On the other hand, in the case of deformation outside the base, the mesophase pitch whose molecular orientation is enhanced by the deformation is reduced in fluidity by subsequent cooling, and the orientation of the mesophase pitch is maintained. Therefore, as an orientation control operation, a method of applying strain due to elongation outside the base is preferable.

It is important for these methods to control the shear strain rate and the extension strain rate.
The shear rate and the extension strain rate inside the base are preferably ^{10 to 10000s -1} , respectively, and preferably 100 to 10000s ^-1. If it is less than 10s- ¹ , the molecular orientation of the mesophase pitch cannot be sufficiently enhanced. If it exceeds 10000s- ¹ , the deformation of the mesophase pitch cannot follow and it cannot be formed into a fibrous form. The shear strain rate and extension strain rate may be set in the above range, and the set values should not deviate from the range of plus or minus 5%, more preferably plus or minus 3%, and particularly plus or minus 1%. .. The elongation strain rate outside the base is ¹ to 10000s ^-1 , preferably 10 to 5000s -1.

The introduction angle θ formed in the throttle portion of the mouthpiece is 30 to 90 degrees, preferably 40 to 80 degrees, and more preferably 45 to 75 degrees. When a mouthpiece within the above range is used, strain due to shearing is appropriately applied when the melted mesophase pitch composition passes through the mouthpiece flow path, and the molecular orientation of the mesophase pitch can be enhanced.

The distance from the deformation start point to the deformation end point outside the mouthpiece of the mouthpiece is preferably 5 to 100 mm. As the lower limit value, 6 mm is preferable, 7 mm is more preferable, and 8 mm is particularly preferable. As the upper limit value, 90 mm is preferable, 80 mm is more preferable, 70 mm is further preferable, 60 mm is particularly preferable, and 50 mm is most preferable. Here, the distance from the deformation start point to the deformation end point outside the mouthpiece means the shortest distance from the tip of the slit gap of the mouthpiece to the cast surface, and when a cooling drum is used, the shortest distance to the moving surface of the cooling drum. To say.

The temperature during the operation for increasing the molecular orientation of the mesophase pitch needs to be higher than the melting temperature of the mesophase pitch, preferably 150 to 400 ° C, more preferably 180 to 350 ° C. When the temperature exceeds 400 ° C., the deformation relaxation rate of the mesophase pitch increases, and it becomes difficult to maintain the morphology of the fibers.

The draft ratio, which is the ratio of the discharge line speed to the take-up speed when the deformation is performed outside the base, needs to be 2 to 100, and is preferably 3 to 100. If it is smaller than 2, it is not preferable because the fiber diameter distribution of carbon fibers becomes wide. Further, if it is larger than 100, the deformation of the pitch cannot follow and it cannot be formed into a fibrous form, which is not preferable.

Moreover, the manufacturing process of the resin composite fiber may have a cooling process. Examples of the cooling step include, in the case of melt spinning, a method of cooling the atmosphere downstream of the spinneret. In the case of melt film formation, a method of providing a cooling drum downstream of the rectangular base can be mentioned. By providing the cooling step, the region where the mesophase pitch is deformed by the elongation can be adjusted, and the strain rate can be adjusted. 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 stabilizing fiber>
In the resin composite fiber obtained as described above, the mesophase pitch fiber contained in the resin composite fiber is stabilized (also referred to as infusibilization) to produce a resin composite stabilized fiber. Stabilization can be performed by known methods such as gas airflow treatment using air, oxygen, ozone, nitrogen dioxide, halogen, etc., solution treatment using an acidic aqueous solution, etc., but insolubilization by gas airflow treatment from the viewpoint of productivity. Is preferable.

As the gas component to be used, air, oxygen, or a mixed gas containing the same is preferable from the viewpoint of ease of handling, and it is particularly preferable to use air from the viewpoint of cost. The oxygen gas concentration 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 long time to stabilize the mesophase pitch contained in the resin composite fiber, which is not preferable.

The stabilization reaction temperature is preferably 50 to 350 ° C, more preferably 60 to 300 ° C, even more preferably 100 to 300 ° C, and particularly preferably 200 to 300 ° C. The stabilization treatment time is preferably 10 to 1200 minutes, more preferably 10 to 600 minutes, even more preferably 30 to 300 minutes, and particularly preferably 60 to 210 minutes.

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

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

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

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

When the thermoplastic resin is thermally decomposed under reduced pressure, a trace amount of oxygen or an inert gas may be present as long as the above atmospheric pressure is maintained. In particular, the presence of a trace amount of inert gas has the advantage of suppressing fusion between fibers due to thermal deterioration of the thermoplastic resin, which is preferable. The trace amount of oxygen referred to here means that the oxygen concentration is 30% by volume or less, and the trace amount of inert gas means that the inert gas concentration is 20% by volume or less. The type of inert gas used is as described above.

The thermal decomposition temperature is preferably 350 to 600 ° C, more preferably 380 to 550 ° C. When the thermal decomposition temperature is less than 350 ° C., the thermal decomposition of the stabilized fiber can be suppressed, but the thermal decomposition of the thermoplastic resin may not be sufficiently performed. On the other hand, if the temperature exceeds 600 ° C., the thermoplastic resin can be sufficiently thermally decomposed, but even the stabilized fibers 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, more preferably 0.5 to 10 hours.

In the production method of the present invention, it is preferable that the stabilizing step and the thermoplastic resin removing step are carried out by holding ^{the resin composite fiber or the resin composite stabilized fiber on the supporting base material at a density of 2 kg / m 2 or less.} By holding it on the supporting base material, it is possible to suppress the 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, and it becomes possible to maintain the air permeability. ..

As the material of the supporting base material, it is necessary that it does not deform or corrode due to solvent or heating. Further, the heat resistant temperature of the supporting base material is preferably 600 ° C. or higher because it is necessary that the supporting base material is not deformed by the thermal decomposition temperature of the above-mentioned thermoplastic resin removing step. Examples of such a material include a metal material such as stainless steel and a ceramic material such as alumina and silica.

Further, the form of the supporting base material is preferably a shape having air permeability in the direction perpendicular to the plane. A mesh structure is preferable as such a shape. The mesh opening is preferably 0.1 to 5 mm. When the mesh size is larger than 5 mm, the fibers tend to aggregate on the mesh line due to the heat treatment, and the stabilization of the mesophase pitch and the removal of the thermoplastic resin may be insufficient, which is not preferable. On the other hand, when the mesh opening is less than 0.1 mm, the air permeability of the support base material in the direction perpendicular to the plane may decrease due to the decrease in the opening rate of the support base material, which is not preferable.

<Carbonization firing process>
The carbon fiber of the present invention can be obtained by carbonizing and / or graphitizing the stabilized fiber in an inert atmosphere. As the container used at that time, a crucible-shaped container made of graphite is preferable. Here, carbonization means heating at a relatively low temperature (preferably about 1000 ° C.), and graphitization means growing graphite crystals by heating at a higher temperature (preferably about 3000 ° C.). say.

Examples of the inert gas used during carbonization and / or graphitization of the stabilized fiber include nitrogen, argon and the like. The oxygen concentration in the inert atmosphere is preferably 20% by volume or less, more preferably 10% by volume or less. The firing temperature during carbonization and / or graphitization is preferably 500 to 3500 ° C, more preferably 800 to 3000 ° C. In particular, the firing temperature at the time of graphitization is preferably 2000 to 3200 ° C, more preferably 2100 to 3000 ° C. If the temperature at the time of graphitization is less than 2000 ° C., crystal growth may be hindered, the crystallite length may be insufficient, and the conductivity may be significantly lowered. Further, when the graphitization temperature exceeds 3200 ° C., the oxygen content of the carbon fibers tends to decrease, although it is preferable in terms of crystal growth. The firing time is preferably 0.1 to 24 hours, more preferably 0.2 to 10 hours.

<Grinding process>
The method for producing carbon fibers contained in the electrode mixture layer of the present invention may include a pulverization treatment step. The pulverization treatment is preferably carried out in the thermoplastic resin removing step and / or the carbonization firing step. As a pulverization method, it is preferable to apply a fine pulverizer such as a jet mill, a ball mill, a bead mill, an impeller mill, a cutter mill or the like, and after pulverization, classification may be performed as necessary. In the case of wet pulverization, the dispersion medium is removed after pulverization, but if secondary agglutination occurs remarkably at this time, subsequent handling becomes very difficult. In such a case, it is preferable to perform a crushing operation using a ball mill, a jet mill or the like after drying.

1-4. Substances contained in the electrode mixture layer for non-aqueous electrolyte secondary batteries
As a non-aqueous electrolyte secondary battery manufactured by using the electrode mixture layer of the present invention, a lithium ion secondary battery can be mentioned as a typical battery. Hereinafter, the positive electrode active material and the negative electrode active material used in the lithium ion secondary battery will be described.

<Positive electrode active material>
As the positive electrode active material contained in the electrode mixture layer of the present invention, one or more of the conventionally known materials known as positive electrode active materials in the non-aqueous electrolyte secondary battery may be used. It can be appropriately selected and used. For example, in the case of a lithium ion secondary battery, a lithium-containing metal oxide capable of storing and releasing lithium ions is suitable. The lithium-containing metal oxide is a composite oxide containing lithium and at least one element selected from the group consisting of Co, Mg, Mn, Ni, Fe, Al, Mo, V, W, Ti and the like. 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 to 1.2, a = 0.1 to 0.9, b = 0.8 to 0.98, c = 1.2 to 1.96, z = At least one species selected from the group consisting of 2.01 to 2.3) and the like can be mentioned. 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 Oz} (where x, a, b and z are the same as above) can be mentioned. The value of x is a value before the start of charging / discharging, and increases / decreases depending on charging / discharging.

The positive electrode active material may be used alone or in combination of two or more. The average particle size of the positive electrode active material is preferably 10 μm or less, more preferably 0.05 to 7 μm, and even more preferably 1 to 7 μm. If the average particle size exceeds 10 μm, the efficiency of the charge / discharge reaction under a large current may decrease.

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 even more preferable. If it is less than 60% by mass, it may be difficult to apply it to power supply applications where energy density is required. If it exceeds 98.5% by mass, the amount of the binder may be too small to cause cracks in the electrode mixture layer, or the electrode mixture layer may be peeled off from the current collector. Further, the content of the carbon fiber or the carbon-based conductive auxiliary agent may be too small, and the conductivity of the electrode mixture layer may be insufficient.

<Negative electrode active material>
As the negative electrode active material contained in the electrode mixture layer of the present invention, one or more of the conventionally known materials known as the negative electrode active material in the non-aqueous electrolyte secondary battery may be used. It can be appropriately selected and used. For example, as a material capable of occluding / releasing lithium ions, a carbon material, an alloy containing Si and / or Sn, an oxide, or the like can be used. Among these, a carbon material is 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, the surface 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 from the viewpoint of increasing the battery capacity. preferable. Natural graphite refers to a graphite material that is naturally produced as an ore. Natural graphite is classified into two types, scaly graphite with high crystallinity and earth-like graphite with low crystallinity, depending on its appearance and properties. The scaly graphite is further divided into scaly graphite having a leaf-like appearance and scaly graphite having a lumpy appearance. Natural graphite, which is a graphitic material, is not particularly limited in terms of production area, properties, and type. Further, natural graphite or particles produced from natural graphite may be heat-treated before use.

Artificial graphite refers to graphite that is widely artificially made and a graphite material that is close to a perfect crystal of graphite. As a typical example, tar or coke obtained from dry distillation of coal, residue obtained by distillation of crude oil, etc. is used as a raw material and obtained through a firing step of about 500 to 1000 ° C. and a graphitization step of 2000 ° C. or higher. Can be mentioned. Quiche graphite obtained by reprecipitating carbon from molten iron is also a type of artificial graphite.

When an alloy containing Si and / or Sn is used as the negative electrode active material in addition to the carbon material, the expansion of the electrode during charging and discharging is performed as compared with the case where Si and / or Sn is used alone or each oxide is used. The rate becomes smaller and the cycle characteristics become better. 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, W, Ni, Mn, Zn, Cu and the like, Si and 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-mentioned materials may be used alone or in combination of two or more. The average particle size of the negative electrode active material is 10 μm or less. If the average particle size exceeds 10 μm, the efficiency of the charge / discharge reaction under a large current will decrease. The average particle size is preferably 0.1 to 10 μm, more preferably 1 to 7 μm.

<Binder>
As the binder used for the electrode mixture layer of the present invention, any binder that can be molded into an electrode and has sufficient electrochemical stability can be used. Examples of the binder include polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), fluoroolefin copolymer crosslinked polymer, polyimide, polyamideimide, and the like. It is preferable to use one or more selected from the group consisting of aramid, phenol resin and the like, and polyvinylidene fluoride (PVDF) is particularly preferable. The form when used as a binder is not particularly limited, and may be in a solid state or a liquid state (for example, an emulsion), a method for producing an electrode (particularly dry kneading or wet kneading), and dissolution in an electrolytic solution. It can be appropriately selected in consideration of sex 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 20% by mass, and even more preferably 5 to 20% by mass. If it is less than 1% by mass, cracks may occur in the electrode mixture layer or the electrode mixture layer may be peeled off from the current collector. If it exceeds 25% by mass, the amount of active material in the electrode is small, and the energy density of the obtained battery tends to decrease.

2. 2. Electrode for non-aqueous electrolyte secondary battery The second invention is an electrode for non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “electrode”) on which the 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 for 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 fibrous carbon, the binder, and other components as necessary, form a film by extrusion molding, roll and stretch the film, and then combine it with a current collector. It is a method of pasting together.
Another method is to prepare a slurry by mixing the electrode active material, the fibrous carbon, the binder, a solvent for dissolving the binder, and other components as necessary, and apply the slurry to the surface of the current collector. This is a method of pressing after removing the solvent.
In the case of the present invention, either method can be adopted, but since the latter method is preferable, the latter method will be described in detail below.

The solid content concentration in the slurry (meaning the ratio of the total mass of the components other than the solvent of the slurry to the total mass of the slurry) is preferably 10 to 30% by mass, preferably 15 to 25% by mass. Is more preferable. If the solid content concentration exceeds 30% by mass, it may be difficult to prepare a uniform slurry. Further, if 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 become non-uniform.

The solvent used for the slurry is not particularly limited as long as it is a solvent that 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 DMAc is preferred.

When the electrode is manufactured, if the tinx property in the slurry is too strong, it may be difficult to secure the fluidity suitable for coating. In such cases, a slurrying aid may be used. Examples of the slurrying aid include one or more selected from the group consisting of polyvinylpyrrolidone, carboxymethyl cellulose, polyvinyl acetate, polyvinyl alcohol and the like. In particular, it is preferable to use polyvinylpyrrolidone. By adding the above-mentioned slurrying aid, sufficient fluidity can be ensured even with a small amount of solvent, and the dispersibility of the carbon-based conductive auxiliary agent is significantly improved. In addition, the generation of cracks after removing the solvent can be suppressed. The amount of the slurrying aid added is preferably 10% by mass or less, more preferably 0.5 to 10% by mass, and 0. It is more preferably 5 to 8% by mass. If the amount of the slurrying aid added exceeds 10% by mass, on the contrary, the viscosity of the slurry may be sharply lowered, resulting in poor dispersion and difficulty in producing a suitable slurry. When the amount of the slurrying aid added is less than 0.5% by mass, the effect of the slurrying aid is unlikely to appear.

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

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

3. 3. Non-aqueous electrolyte secondary battery The third invention is a non-aqueous electrolyte secondary battery configured to include the electrode mixture layer of the present invention.
The non-aqueous electrolyte secondary battery of the present invention is configured by using the electrodes of the present invention for the positive electrode and / or the negative electrode, and using a known separator and electrolytic solution. Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery.

The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode having a positive electrode mixture layer formed on the surface of the current collector, an electrolyte layer containing an electrolyte, and a negative electrode mixture layer formed on the surface of the current collector. It is composed of a negative electrode, and is laminated so that the positive electrode mixture layer of the positive electrode and the negative electrode mixture layer of the negative electrode face each other, and the electrolyte layer is inserted between the positive electrode mixture layer and the negative electrode mixture layer. ..

The cell shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and any shape can be used. Specifically, for example, a cell shape such as a button type, a cylindrical type, or a square type can be mentioned. Further, it is also preferable to have an internal configuration in which a plurality of pairs of positive and negative electrodes and a separator are laminated. In this case, a known method such as a stack stacking type, a winding type, or a folded stacking type can be adopted. Examples of the exterior material of the non-aqueous electrolyte secondary battery of the present invention include metal cans and aluminum laminated resin films. In the non-aqueous electrolyte secondary battery of the present invention, since the predetermined carbon material added to the electrode mixture layer has a linear structure and has high conductivity, it is easy to form a conductive path. , Excellent charge / discharge characteristics can be obtained. Furthermore, the electrode strength is also improved.

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

In general, a non-aqueous electrolyte solution has a higher withstand voltage than an aqueous electrolyte solution and is characterized in that a high energy density can be obtained. As the non-aqueous solvent, known ones can be used without limitation, but propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, γ-valerolactone, acetonitrile, etc. Nitromethane, methoxy acetonitrile, nitroethane, N, N-dimethylformamide, 3-methoxypropionitrile, N-methylpyrrolidone, N, N'-dimethylimidazolidinone, dimethyl sulfoxide, sulfolane, 3-methylsulfolane, ethylmethylcarbonate, 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 has an appropriate boiling point, melting point, viscosity and relative permittivity, and among the above, 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 aliphatic groups. Examples thereof include lithium carboxylate, LiCl, LiBr, LiI, lithium chloroborane, borates, and imide salts. Examples of borates include bis (1,2-benzenediolate (2-) -O, O') lithium borate and bis (2,3-naphthalenedioleate (2-) -O, O') boric acid. Lithium, bis (2,2'-biphenyldiorate (2-) -O, O') lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O') lithium borate And so on. Examples of imide salts include imidelithium bistrifluoromethanesulfonate ((CF ₃ SO ₂ ) ₂ NLi) and imide lithium trifluoromethanesulfonate nonafluorobutane sulfonate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ )). ), Imidolithium bispentafluoroethanesulfonate ((C ₂ F ₅ SO ₂ ) ₂ NLi) and the like. The concentration of the electrolyte is preferably 0.5 to 2 mol / L. As the electrolyte, one of the above may be used alone, or two or more thereof may be used in combination. A known additive may be added to the electrolyte for the purpose of improving cycle stability, charge / discharge efficiency, and the like.
As the electrolytic solution used in the lithium ion secondary battery of the present invention, an ionic liquid typified by an ethylmethylimidazolium salt can also be preferably used, and in this case, it is not always dissolved in the above-mentioned non-aqueous solvent. There is no need to use it.

<Separator>
When the non-aqueous electrolytic solution as described above is used, it is common to use a separator in order to prevent the negative electrode active material layer and the electrode mixture layer of the present invention from coming into direct contact with each other. As the shape of the separator, a known shape such as a paper shape (film shape) or a porous film shape can be preferably adopted. As the material of the separator, for example, one or more kinds of materials selected from the group consisting of cellulose, aromatic polyamide, aliphatic polyimide, polyolefin, Teflon (registered trademark), polyphenylene sulfide and the like can be preferably 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 preventing a short circuit, but in the present invention, it is possible to apply a separator having a thickness of about 5 to 20 μm, which is sufficiently thinner than the conventional separator. When a thin separator is used, the internal resistance derived from the separator is reduced, so that the output is improved and the energy density of the cell is also improved.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. Various measurements and analyzes in the examples were carried out according to the following methods.

(1) Confirmation of the shape of fibrous carbon Observation and photography were performed using a desktop electron microscope (model NeoScope JCM-6000 manufactured by JEOL Ltd.). For the average fiber diameter of fibrous carbon, etc., 300 points were randomly selected from the obtained electron micrographs and the fiber diameter was measured, and the average value of all the measurement results (n = 300) was taken as the average fiber diameter. bottom. The average effective length was calculated in the same way.

(2) X-ray diffraction measurement of fibrous carbon The X-ray diffraction measurement is based on the JIS R7651 (2007) method using RINT-2100 manufactured by Rigaku Co., Ltd., and has a lattice spacing (d002) and crystallite size (Lc002) ( Hexagonal network area layer direction) and (La110) (carbon hexagonal network surface direction) were measured.

(3) Cyclic voltammetry measurement A bipolar cell having lithium as the counter electrode was prepared, and cyclic voltammetry measurement was performed using a potentiostat / galvanostat (SI1287 manufactured by Solartron) and an impedance analyzer (SI1260 manufactured by Solartron). The measurement was performed in a predetermined potential range with a sweep speed of 50 mV / s and a temperature of 25 ° C. It was decided to adopt the second cycle as the result of each measurement.

[Manufacturing Example 1]
First, a coal tar pitch having a softening point of 80 ° C. from which the quinoline insoluble component has 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. This hydrogenated coal tar pitch is heat-treated at 480 ° C. under normal pressure, and then reduced in pressure to remove low boiling points to obtain a crude mesophase pitch. A purified mesophase pitch was obtained by filtering this crude mesophase pitch at a temperature of 340 ° C. using a filter to remove foreign substances.

[Example 1]
<Manufacturing of fibrous carbon (CNF-1)>
84 parts by mass of linear low-density polyethylene (EVOLUE® SP1510, manufactured by Prime Polymer Co., Ltd., MFR = 1 g / 10 min) as a thermoplastic resin and the mesophase obtained in Production Example 1 as a thermoplastic carbon precursor. Melt 16 parts by mass of pitch (mesophase ratio 90.9%, softening point 303.5 ° C) with a twin-screw extruder in the same direction (“TEM-26SS” manufactured by Toshiba Machine Co., Ltd., barrel temperature 300 ° C, under nitrogen stream). Kneading was performed to prepare a mesophase pitch composition.
Next, this mesophase pitch composition was subjected to a melt spinning machine using a circular mouthpiece having a diameter of 0.2 mm and an introduction angle of 60 °, and a resin composite fiber having a fiber diameter of 100 μm (a sea-island type composite fiber containing the mesophase pitch fiber as an island component). Was produced. The base temperature was 340 ° C., the discharge rate was 3.8 g / base / hour, the shear rate was 1360s ^-1 , and the draft ratio, which is the ratio of the discharge line speed to the take-up speed, was 4. Under these conditions, the elongation strain rate inside the mouthpiece was 982s ^-1 , the deformation region outside the mouthpiece was 10 mm below the mouthpiece, and the extension strain rate was 9s ^-1 .
By holding the resin composite fiber in an oxidizing gas atmosphere, the mesophase pitch was stabilized and the resin composite stabilized fiber was obtained.
Next, the stabilized fiber was obtained by removing the thermoplastic resin from the resin composite stabilized fiber.
The obtained stabilized fibers were added to an ethanol / ion-exchanged water mixture solvent (volume ratio = 1/1) and dispersed by grinding with a mixer. The obtained dispersion was filtered.
The obtained stabilized fiber was heated from room temperature to 1000 ° C. under the condition of 5 ° C./min under nitrogen at a flow rate of 1 l / min, and after reaching 1000 ° C., it was held for 30 minutes for carbonization, and further, an argon gas atmosphere. Below, carbon fibers were produced by raising the temperature from room temperature to 3000 ° C. over 3 hours. The obtained carbon fiber was crushed using a dry jet mill.
The average fiber diameter (corresponding to the average length of the smallest dimension) of the obtained ultrafine carbon fibers was 250 nm, and no branched structure was observed. The average effective length was 15.1 μm. Further, the average plane spacing d002 of the (002) plane measured by the X-ray diffraction method is 0.3372 nm, the crystallinity length (La110) is 111 nm, and the thickness of the network plane group (Lc002) is 62 nm, which are crystalline. It was a high fibrous carbon. The metal content in the carbon fiber was 30 ppm (iron 10 ppm, sodium 20 ppm).

<Manufacturing of electrodes>
A slurry is prepared using 50 parts by mass of fibrous carbon (CNF-1) as a carbon-based conductive auxiliary agent, 50 parts by mass of polyvinylidene fluoride (W # 7200, manufactured by Kureha Corporation) as a binder, and N-methylpyrrolidone as a solvent. Made. The prepared slurry was applied to a current collector (aluminum foil having a thickness of 15 μm) and then dried at 120 ° C. for 3 hours to prepare an electrode. The thickness of the electrode mixture layer formed on the electrode was 17 μm.
The average effective length of fibrous carbon measured in a photograph taken with a digital microscope (VHX-200 manufactured by KEYENCE CORPORATION) after dissolving the electrode mixture layer of this electrode in a solvent and drying it is 15.1 μm (15.1 μm). The aspect ratio was 60). Further, FIG. 1 shows a histogram in which the effective length is measured. The content of fibrous carbon having an effective length longer than the average effective length was 42% based on the number of fibrous carbons as a whole.

<Cyclic voltammetry measurement>
Using the electrode as a working electrode, a bipolar cell (coin battery) having a lithium metal as a counter electrode was produced. As the electrolytic solution, an electrolytic solution composed of an ethylene carbonate / ethylmethyl carbonate mixed solution (3/7 volume ratio, manufactured by Kishida Chemical Co., Ltd.) containing _{LiPF 6 having a concentration of 1 mol / L was used.} A glass fiber non-woven fabric was used for the separator.
FIG. 2 shows a CV curve measured within a potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the ratio of the integrated value of the reduction current / the integrated value of the oxidation current was 0.9. That is, it was a reversible electrochemical reaction. Further, FIG. 3 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 2 and 3, the IA / IB ratio was 0. That is, no electrochemical reaction was shown in the potential range of 2.5 to 4.4 V (vs. Li / Li +). This makes it possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution are unlikely to occur under a high voltage.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed using a charge / discharge device (HJ-1005SD8 manufactured by Hokuto Denko Co., Ltd.). The charge and discharge conditions, 0.1 mA / cm ² constant current after charging to 5.0V, it was decided to discharge 0.1 mA / cm ² constant current to 2.5V. The measurement results are shown in FIG. As a result, the charge capacity was 22.7 mAh / g, the discharge capacity was 14.7 mAh / g, and the charge / discharge efficiency was 65%, which were good.

[Example 2]
<Manufacturing of fibrous carbon (CNF-2)>
75 parts by mass of linear low-density polyethylene (EVOLUE® SP1510, manufactured by Prime Polymer Co., Ltd., MFR = 1 g / 10 min) as a thermoplastic resin and the mesophase obtained in Production Example 1 as a thermoplastic carbon precursor. The same operation as in Example 1 was carried out except that 25 parts by mass of pitch (mesophase ratio 90.9%, softening point 303.5 ° C.) was melt-kneaded with a twin-screw extruder in the same direction to prepare a mesophase pitch composition. Fibrous carbon (CNF-2) was prepared. The average fiber diameter (corresponding to the average length of the smallest dimension) of the obtained fibrous carbon was 500 nm, and it was a fibrous carbon having excellent dispersibility. The average effective length was 17 μm. Further, from the results measured by the X-ray diffraction method, the lattice spacing (d002) of the fibrous carbon (CNF-2) is 0.3368 nm, the crystallinity length (La110) is 208 nm, and the thickness of the network plane group (Lc002). ) Was 51 nm, which was a highly crystalline fibrous carbon.

<Manufacturing of electrodes>
An electrode was produced by performing the same operation as in Example 1 except that fibrous carbon (CNF-2) was used as the carbon-based conductive auxiliary agent.
The average effective length of fibrous carbon measured in a photograph taken with a digital microscope (VHX-200 manufactured by KEYENCE CORPORATION) after dissolving the electrode mixture layer of this electrode in a solvent and drying it is 17.0 μm (17.0 μm). The aspect ratio was 34). Further, FIG. 5 shows a histogram in which the effective length is measured. The content of fibrous carbon having an effective length longer than the average effective length was 38% based on the number of fibrous carbons as a whole.

<Cyclic voltammetry measurement>
A bipolar cell having a lithium metal as a counter electrode was produced by performing the same operation as in Example 1 except that this electrode was used as a working electrode. FIG. 6 shows a CV curve measured in the potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the integrated value of the reduction current / the integrated value of the oxidation current was 0.87, which was good. Further, FIG. 7 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 6 and 7, the IA / IB ratio was 0. That is, no electrochemical reaction was shown in the potential range of 2.5 to 4.4 V (vs. Li / Li +). This makes it possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution are unlikely to occur under a high voltage.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed in the same manner as in Example 1. The measurement results are shown in FIG. The charge capacity was 26.5 mAh / g, the discharge capacity was 18.3 mAh / g, and the charge / discharge efficiency was 69%, which were good.

[ Reference example 1 ]
<Manufacturing of fibrous carbon (CNF-3)>
The same operation as in Example 1 was carried out except that the graphitization temperature was set to 2600 ° C. to prepare fibrous carbon (CNF-3). The average fiber diameter (corresponding to the average length of the smallest dimension) of the obtained fibrous carbon was 250 nm, and it was a fibrous carbon having excellent dispersibility. Further, from the results measured by the X-ray diffraction method, the lattice spacing (d002) of the fibrous carbon (CNF-3) was 0.3380 nm, the crystallinity length (La110) was 59 nm, and the thickness of the network plane group (Lc002). ) Was 48 nm, which was a highly crystalline fibrous carbon.

<Manufacturing of electrodes>
An electrode was produced by performing the same operation as in Example 1 except that fibrous carbon (CNF-3) was used as the carbon-based conductive auxiliary agent.
The average effective length of fibrous carbon measured in a photograph taken with a digital microscope (VHX-200 manufactured by KEYENCE CORPORATION) after dissolving the electrode mixture layer of this electrode in a solvent and drying it is 15.1 μm (15.1 μm). The aspect ratio was 60). Further, FIG. 9 shows a histogram in which the effective length is measured. The content of fibrous carbon having an effective length longer than the average effective length was 36% based on the number of fibrous carbons as a whole.

<Cyclic voltammetry measurement>
A bipolar cell having a lithium metal as a counter electrode was produced by performing the same operation as in Example 1 except that the electrode was used as a working electrode. FIG. 10 shows a CV curve measured in the potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the integrated value of the reduction current / the integrated value of the oxidation current was 0.84, which was good. Further, FIG. 11 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 10 and 11, the IA / IB ratio was 0. That is, no electrochemical reaction was shown in the potential range of 2.5 to 4.4 V (vs. Li / Li +). This makes it possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution are unlikely to occur under a high voltage.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed in the same manner as in Example 1. The measurement results are shown in FIG. The charge capacity was 26.8 mAh / g, the discharge capacity was 17.0 mAh / g, and the charge / discharge efficiency was 63%, which were good.

[ Reference example 2 ]
<Manufacturing of fibrous carbon (CNF-4)>
The same operation as in Example 1 was carried out except that the graphitization temperature was set to 2400 ° C. to prepare fibrous carbon (CNF-4). The average fiber diameter (corresponding to the average length of the smallest dimension) of the obtained fibrous carbon was 250 nm, and it was a fibrous carbon having excellent dispersibility. Further, from the results measured by the X-ray diffraction method, the lattice spacing (d002) of the fibrous carbon (CNF-4) is 0.3395 nm, the crystallinity length (La110) is 38 nm, and the thickness of the network plane group (Lc002). ) Was 34 nm, which was a highly crystalline fibrous carbon.

<Manufacturing of electrodes>
An electrode was produced by performing the same operation as in Example 1 except that fibrous carbon (CNF-4) was used as the carbon-based conductive auxiliary agent.
The average effective length of fibrous carbon measured in a photograph taken with a digital microscope (VHX-200 manufactured by KEYENCE CORPORATION) after dissolving the electrode mixture layer of this electrode in a solvent and drying it is 12.0 μm (12.0 μm). The aspect ratio was 48). Further, FIG. 13 shows a histogram in which the effective length is measured. The content of fibrous carbon having an effective length longer than the average effective length was 39% based on the number of fibrous carbons as a whole.

<Cyclic voltammetry measurement>
A bipolar cell having a lithium metal as a counter electrode was produced by performing the same operation as in Example 1 except that the electrode was used as a working electrode. FIG. 14 shows a CV curve measured in the potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the integrated value of the reduction current / the integrated value of the oxidation current was 0.82, which was good. Further, FIG. 15 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 14 and 15, the IA / IB ratio was 0. That is, no electrochemical reaction was shown in the potential range of 2.5 to 4.4 V (vs. Li / Li +). This makes it possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution are unlikely to occur under a high voltage.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed in the same manner as in Example 1. The measurement results are shown in FIG. The charge capacity was 26.0 mAh / g, the discharge capacity was 16.8 mAh / g, and the charge / discharge efficiency was 65%, which were good.

[ Reference example 3 ]
The same operation as in Example 1 was carried out except that the graphitization temperature was set to 2000 ° C. to prepare fibrous carbon (CNF-5). The average fiber diameter (corresponding to the average length of the smallest dimension) of the obtained fibrous carbon was 250 nm, and it was a fibrous carbon having excellent dispersibility. Further, from the results measured by the X-ray diffraction method, the lattice spacing (d002) of the fibrous carbon (CNF-5) is 0.3426 nm, and the thickness of the network plane group (Lc002) is 25 nm, which is highly crystalline. It was fibrous carbon.

<Manufacturing of electrodes>
An electrode was produced by performing the same operation as in Example 1 except that fibrous carbon (CNF-5) was used as the carbon-based conductive auxiliary agent.
The average effective length of fibrous carbon measured in a photograph taken with a digital microscope (VHX-200 manufactured by KEYENCE CORPORATION) after dissolving the electrode mixture layer of this electrode in a solvent and drying it is 16.6 μm (16.6 μm). The aspect ratio was 64). Further, FIG. 17 shows a histogram in which the effective length is measured. The content of fibrous carbon having an effective length longer than the average effective length was 31% based on the number of fibrous carbons as a whole.

<Cyclic voltammetry measurement>
A bipolar cell having a lithium metal as a counter electrode was produced by performing the same operation as in Example 1 except that the electrode was used as a working electrode. FIG. 18 shows a CV curve measured in the potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the integrated value of the reduction current / the integrated value of the oxidation current was 0.82, which was good. Further, FIG. 19 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 18 and 19, the IA / IB ratio was 0. That is, no electrochemical reaction was shown in the potential range of 2.5 to 4.4 V (vs. Li / Li +). This makes it possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution are unlikely to occur under a high voltage.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed in the same manner as in Example 1. The measurement results are shown in FIG. The charge capacity was 21.4 mAh / g, the discharge capacity was 13.5 mAh / g, and the charge / discharge efficiency was 63%, which were good.

[ Comparative Example 2 ]
<Manufacturing of fibrous carbon (MWCNT)>
A catalyst containing Fe and Co was placed in a tubular quartz reactor, the inside of the reactor was replaced with nitrogen gas, and the temperature of the reactor was raised from room temperature to 690 ° C. over 60 minutes while flowing nitrogen gas. While maintaining the temperature of 690 ° C., the nitrogen gas was switched to the mixed gas A of the nitrogen gas and the hydrogen gas for a reduction reaction. After the reduction reaction, the mixed gas A was switched to the mixed gas B of hydrogen gas and ethylene gas to cause a gas phase growth reaction while maintaining the temperature of 690 ° C. The mixed gas B was switched to nitrogen gas, the inside of the reactor was replaced with nitrogen gas, and the mixture was cooled to room temperature.
The average fiber diameter (corresponding to the average length of the smallest dimension) of the obtained carbon fibers was 150 nm, and had a branched structure. The average effective length was 8 μm. Further, the average plane spacing d002 of the (002) plane measured by the X-ray diffraction method is 0.3383 nm, the crystallinity length (La110) is 44 nm, and the thickness of the network plane group (Lc002) is 28 nm, which are crystalline. It was a high fibrous carbon. The metal content was 82 ppm (43 ppm for iron and 39 ppm for Si).

<Manufacturing of electrodes>
An electrode was produced by performing the same operation as in Example 1 except that MWCNT was used as the carbon-based conductive auxiliary agent.

<Cyclic voltammetry measurement>
A bipolar cell having a lithium metal as a counter electrode was produced by performing the same operation as in Example 1 except that the electrode was used as a working electrode. FIG. 21 shows a CV curve measured within a potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the integrated value of the reduction current / the integrated value of the oxidation current was 0.81, which was good. That is, it is possible to provide a non-aqueous electrolyte secondary battery in which side reactions such as decomposition of the electrolytic solution and reaction between the conductive auxiliary agent and the electrolytic solution are unlikely to occur under a high voltage. Further, FIG. 22 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 21 and 22, the IA / IB ratio was 0.044.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed in the same manner as in Example 1. The measurement result is shown in FIG. The charge capacity was 9.1 mAh / g, the discharge capacity was 4.6 mAh / g, and the charge / discharge efficiency was 51%, which were good.

[Comparative Example 1]
<Manufacturing of electrodes>
An electrode was produced by performing the same operation as in Example 1 except that spherical carbon (AB, average particle diameter of 35 nm, which corresponds to the average length of the smallest dimension) was used as the carbon-based conductive auxiliary agent. .. AB had low crystallinity.

<Cyclic voltammetry measurement>
A bipolar cell having a lithium metal as a counter electrode was produced by performing the same operation as in Example 1 except that the electrode was used as a working electrode. FIG. 24 shows a CV curve measured within a potential range of 2.5 to 5 V (vs. Li / Li +). From this curve, the integrated value of the reduction current / the integrated value of the oxidation current was 0.48. Further, FIG. 25 shows a CV curve measured in the potential range of 2.5 to 4.4 V (vs. Li / Li +). From FIGS. 24 and 25, the IA / IB ratio was 0.124.

<Charge / discharge measurement>
Using the bipolar cell, charge / discharge measurement was performed in the same manner as in Example 1. The measurement result is shown in FIG. The charge capacity was 5.1 mAh / g, the discharge capacity was 1.7 mAh / g, and the charge / discharge efficiency was 33%.

Claims (6)

An electrode mixture layer for a non-aqueous electrolyte secondary battery containing at least fibrous carbon.
An ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C.) ratio =) containing _{LiPF 6} having a concentration of 1 mol / L, with the electrode composed of the electrode mixture layer for the non-aqueous electrolyte secondary battery as the working electrode and the lithium metal as the counter electrode. In the cyclic voltammogram (CV) measured in the range of 2.5 to 5 V (vs. Li / Li +) using 3/7), the integrated value of the reduction current / the integrated value of the oxidation current is 0.6 or less. An electrode mixture layer for non-aqueous electrolyte secondary batteries that does not show a certain electrochemical reaction.
The fibrous carbon has an electrode containing 100 parts by mass of an electrode mixture layer for a non-aqueous electrolyte secondary battery composed of 50 parts by mass of the fibrous carbon and 50 parts by mass of polyvinylidene fluoride as a working electrode, and a lithium metal as a counter electrode. 2.5 to 4.4 V (vs. Li / Li +) using an ethylene carbonate / ethylmethyl carbonate mixed solution (volume (25 ° C.) ratio = 3/7) containing _{LiPF 6} having a concentration of 1 mol / L. In the cyclic voltammogram (CV) measured in the potential range of, IA / IB is 0.044 or less (where IA is the cyclic voltammogram in the potential range of 2.5 to 4.4 V (vs. Li / Li +). The maximum current value when the oxidation current reaches the maximum value when the measurement is performed, and IB is a cyclic voltammogram measurement within the potential range of 2.5 to 5 V (vs. Li / Li +). The content ratio of the fibrous carbon which is the fibrous carbon of 5V and has an effective length longer than the average effective length (L) is the number standard. 48% or less, one peak top in the effective length distribution, and the ratio (L / D) of the average effective length (L) to the average fiber diameter (D) is 30 or more.
Wherein Ri der is 50ppm or less metal content of the fibrous carbon,
Crystallite length (La) is a non-aqueous electrolyte secondary cell electrode mixture layer, wherein 100~500nm der Rukoto measured by X-ray diffractometry of the fibrous carbon. The IA / IB is the following formula (1)
IA / IB <0.02 ... Equation (1)
The electrode mixture layer for a non-aqueous electrolyte secondary battery according to claim 1, which is a fibrous carbon satisfying the above conditions. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the crystal plane spacing (d002) measured by the X-ray diffraction method of the fibrous carbon contained in the electrode mixture layer is 0.335 to 0.340 nm. Electrode mixture layer. The electrode mixture layer for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the average length of the fibrous carbon contained in the electrode mixture layer in the smallest dimension is 50 to 1000 nm. The electrode for a non-aqueous electrolyte secondary battery having the electrode mixture layer for the non-aqueous electrolyte secondary battery according to any one of claims 1 to 4. A non-aqueous electrolyte secondary battery having the electrode mixture layer for the non-aqueous electrolyte secondary battery according to any one of claims 1 to 4.

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