JP2013062236A - Conductive assistant for lithium secondary battery electrode, conductive assistant fluid dispersion for lithium secondary battery electrode including the same, and positive electrode for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive assistant for a lithium ion battery electrode, capable of exhibiting excellent performance.SOLUTION: The present invention relates to a conductive assistant for a lithium secondary battery electrode. The conductive assistant for a lithium secondary battery electrode is a polymer composite comprising polar polythiophene and a multilayer carbon nanotube having a primary diameter of 10-200 nm, and a weight ratio of the multilayer carbon nanotube relative to the polar polythiophene is 100-500 wt.%.

Description

  The present invention relates to a conductive auxiliary agent for a lithium secondary battery electrode comprising polar polythiophene and multi-walled carbon nanotubes, a conductive auxiliary agent dispersion for a lithium secondary battery electrode containing the same, and a positive electrode for a lithium secondary battery. More specifically, an excellent lithium secondary battery that imparts high dispersibility by combining a specific amount of polar polythiophene with a multi-walled carbon nanotube having a specific structure capable of providing high conductivity to the positive electrode for a lithium secondary battery. The present invention provides a conductive additive for an electrode and a positive electrode for a lithium secondary battery having high capacity and high output.

  Compared to conventional nickel cadmium batteries and nickel metal hydride batteries, lithium secondary batteries can be made smaller and lighter as batteries with higher voltage and higher energy density. Widely used in communication electronic equipment. In the future, as one of the means to solve environmental problems, it is expected that the use will be expanded to in-vehicle applications mounted on electric vehicles and hybrid electric vehicles, and industrial applications such as electric tools. High capacity and high output are eagerly desired.

  A lithium secondary battery is composed of a positive electrode and a negative electrode having an active material capable of reversibly removing and inserting lithium ions, and a separator separating the positive electrode and the negative electrode in a container and filled with a non-aqueous electrolyte. Yes.

The positive electrode is formed by applying an electrode material containing an active material, a conductive additive and a binder to a metal foil current collector such as aluminum and press-molding it. Generally, the positive electrode active material is typified by lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), spinel type lithium manganate (LiMn ₂ O ₄ ), etc. A powder of a composite oxide of lithium and a transition metal (hereinafter sometimes referred to as a lithium metal oxide) is used, a metal oxide such as V ₂ O ₅ , TiS ₂ , MoS ₂ , and NbSe _2. Although metallic compounds such as lithium metal oxides are used, especially lithium metal oxides have excellent performance as small batteries, but they contain so-called rare earths with a low Clarke number, and are avoided from the viewpoint of cost and stable supply. In particular, in recent years, lithium iron phosphate (LiFePO ₄ ) containing iron, which is a resource-rich and inexpensive material, has been developed and used. I'm starting.

  Also, the negative electrode is formed by applying an electrode material containing an active material, a conductive additive and a binder to a metal foil current collector such as copper as in the case of the positive electrode, and in general, as the active material of the negative electrode, Lithium alloys such as metallic lithium and Li-Al alloys, silicon compounds whose basic constituent elements are SiO, SiC, SiOC, etc., conductive polymers doped with lithium such as polyacetylene and polypyrrole, and layers in which lithium ions are incorporated into the crystal Compounds, carbon materials such as natural graphite, artificial graphite, and hard carbon are used.

  The role of the conductive assistant in the structure of these positive and negative electrodes is to obtain an efficient conductive path from the active material to the current collector, and an electrode for a lithium secondary battery (hereinafter sometimes referred to as a lithium ion battery). It is an indispensable constituent material.

  However, since the battery capacity per electrode weight decreases when the content of the conductive auxiliary agent is large, it is better that the amount of the conductive auxiliary agent is as small as possible, and a highly conductive conductive auxiliary agent that can ensure conductivity with a smaller amount. There is a need for agents.

  In recent years, many active materials such as olivine-based positive electrode active materials that have not been put into practical use because of their low conductivity despite their high capacity have been studied. Is required.

  Examples of materials conventionally used as conductive assistants include acetylene black and ketjen black. These are inexpensive and have appropriate dispersibility. However, since their crystallinity is low, their conductivity is lower than that of graphite or the like, and it is necessary to add a large amount.

  Therefore, attempts have been made to introduce carbon nanotubes as conductive assistants (Patent Document 1, etc.).

  A carbon nanotube is a carbon fiber having a diameter on the nanometer scale, and is known to have excellent mechanical properties and conductivity. If the potential of carbon nanotubes can be extracted and used as a conductive additive, a high-capacity and high-power lithium ion battery electrode may be produced.

  In addition, when carbon nanotubes are used as conductive materials, examples of composites of polythiophene and carbon nanotubes include those used as conductive materials for transparent electrodes (Patent Document 2), and conductive materials for organic FETs. Examples of use are disclosed (Patent Documents 3 and 4), an example in which a water-soluble conductive polymer and a multi-walled carbon nanotube are combined and water-solubilized (Patent Document 5).

  Further, as an example in which polythiophene and multi-walled carbon nanotubes are combined for use in a lithium ion battery, an example (Patent Document 6) used as a positive electrode active material is disclosed.

Japanese Patent No. 2513418 JP 2008-103329 A JP 2010-18696 A JP 2011-126727 A JP 2009-245903 A Japanese Patent No. 3913208

  As described above, attempts have been made to introduce carbon nanotubes as conductive assistants for lithium secondary batteries (Patent Document 1, etc.). However, since carbon nanotubes have a large surface area and are very likely to aggregate due to intermolecular forces, and it is difficult to form a conductive path in the battery electrode, the effect of using carbon nanotubes as a conductive aid is ineffective. The inventors have found that this is sufficient.

  Therefore, in order to apply carbon nanotubes as a conductive aid for lithium ion battery electrodes, it was considered that an additive for improving dispersibility was necessary.

  Here, in Patent Documents 2 to 6, there are examples in which polythiophene is dispersed. This method can improve the dispersibility while ensuring the conductivity of the carbon nanotubes, and is considered to be a very effective method for extracting the potential as a conductive additive.

  However, all of Patent Documents 2 to 6 deal with carbon nanotubes having a diameter of less than 10 nm, and such small-diameter carbon nanotubes have a large specific surface area, so that a large amount of polythiophene is actually required. If it does so, the ratio of a carbon nanotube will become small, and it was not suitable for practical use as a conductive support agent for lithium ion battery electrodes.

  The present invention provides a conductive additive for a lithium ion battery electrode that can be combined with a specific structure of multi-walled carbon nanotubes and a specific amount of polar polythiophene to exhibit excellent performance.

  In the present invention, polar polythiophene is used for solubilization in a highly polar solvent. Furthermore, by selecting a carbon nanotube having a suitable diameter, a carbon nanotube / polythiophene composite composite that functions as an excellent conductive aid is provided.

That is, the present invention is (1) a polymer composite composed of multi-walled carbon nanotubes having a primary diameter of 10 nm to 200 nm and polar polythiophene, and the weight ratio of the multi-walled carbon nanotubes is 100 wt% to 500 wt% with respect to polar polythiophene. A conductive additive for a lithium secondary battery electrode, characterized in that:
(2) The conductive auxiliary agent for a lithium secondary battery electrode according to (1), wherein the multi-walled carbon nanotube has a primary diameter of 50 nm to 150 nm.
(3) The conductive additive for a lithium secondary battery electrode according to (1) or (2), wherein the weight ratio of the multi-walled carbon nanotube is 200 wt% to 400 wt% with respect to polar polythiophene.
(4) For the lithium secondary battery electrode according to any one of (1) to (3), wherein the polar polythiophene is soluble in N-methylpyrrolidone, γ-tyrolactone, dimethylacetamide, or water at a weight concentration of 1% or more. Conductive aid.
(5) Conductivity for lithium secondary battery electrode in which the conductive assistant for lithium secondary battery electrode according to any one of (1) to (4) is dispersed in N-methylpyrrolidone, γ-butyrolactone, dimethylacetamide, or water Auxiliary dispersion.
(6) A positive electrode for a lithium secondary battery containing a positive electrode active material, a binder polymer, and a conductive additive, wherein the lithium according to any one of (1) to (4) is contained in at least a part of the conductive additive. A positive electrode for a lithium secondary battery, comprising a conductive additive for a secondary battery electrode.
It is.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the conductive support agent for lithium ion battery electrodes which can exhibit the outstanding performance by combining the multi-layer carbon nanotube of a specific structure, and a specific amount of polar polythiophene.

The multi-walled carbon nanotube used in the present invention is fibrous carbon having a diameter of 10 nm to 200 nm, and has a structure in which a plurality of graphene sheets are wound concentrically. CNT can be obtained by an arc discharge method, a chemical vapor deposition method (CVD method), a laser ablation method, or the like.
The conductivity (volume resistivity) of the multi-walled carbon nanotube is preferably 1.0 [Ω · cm] or less, more preferably 1.0 × 10 ⁻¹ [Ω · cm], and 1.0 × 10 ⁻⁶ [Ω · cm]. It is especially preferable that it is -1.0 * 10 ^<-2 > [ohm * cm]. The lower the volume resistivity, the higher the performance as a conductive additive.

  The primary diameter of the multi-walled carbon nanotube used in the present invention is 10 nm to 200 nm, but a multi-walled carbon nanotube of 50 nm to 150 nm is preferably used. Multi-walled carbon nanotubes have a larger number per weight than conventional ketjen black and acetylene black as a conductive aid for lithium ion battery electrodes, and it is easy to obtain a conductive path. From the viewpoint of the number per unit weight, the lower the primary diameter of the multi-walled carbon nanotube, the easier it is to obtain a conductive path.

  However, if the primary diameter is too small, it is very easy to agglomerate, and problems in electrode production tend to occur. Further, also in the production of a polymer composite described later, it is possible to improve the dispersion force with a smaller amount of polar polythiophene as the primary diameter is larger. When the primary diameter is 10 nm or less, aggregation is remarkable, and the amount of polar polythiophene required is large, so application as a conductive additive is difficult. On the other hand, if the primary diameter is 200 nm or more, the number per unit weight is small and it is not suitable as a conductive additive. The primary diameter mentioned here is the diameter of a single yarn of a multi-walled carbon nanotube.

  The single yarn diameter of the multi-walled carbon nanotube can be measured by an electron microscope. By observing the multi-walled carbon nanotubes at a magnification of 100,000 to 200,000 times with an electron microscope, randomly selecting 100 locations, measuring the diameter, and taking the number average, the diameter of the single-walled carbon nanotube can be determined. .

  The length of the multi-walled carbon nanotube is not particularly limited, but is preferably long for forming the path, and shorter in terms of increasing the number. Generally, carbon nanotubes with a length of about 0.1 μm to 3 μm are commercially available, and any length can be used without any problem.

  Multi-walled carbon nanotubes are less expensive than thin-walled carbon nanotubes of 10 nm or less, and are highly practical as conductive assistants for battery electrodes. By imparting high dispersibility according to the present invention, high-conductivity conductive assistants are inexpensively provided. An agent can be provided.

  The polar polythiophene in the present invention refers to a polythiophene side chain containing a polar group, and is represented by the following general formula (1).

R is a side chain containing a polar group. Either the 3-position or the 4-position may be sufficient, and both may be substituted. The polar group may be an acidic group or may include an ether structure, an acetyl structure, or a ketone structure.

  For example, examples of the acidic group include a sulfonic acid group, a hydroxyl group, and a carboxylic acid group. Examples of those containing an ether structure include alkoxy groups such as methoxy group, ethoxy group and n-propoxy group, alkoxyalkyl groups such as methoxyethyl group, ethoxyethyl group and n-propoxyethyl group, and methoxyethoxy having a plurality of ether structures. Group, ethoxyethoxy group, methoxyethoxyethoxy group and the like. Examples of those containing an acetyl structure or a ketone structure include an alkylcarbonyl group and an alkoxycarbonyl group.

  In particular, it is preferable that the solubility in a polar solvent for battery paste such as N-methylpyrrolidone, γ-butyrolactone, dimethylacetamide is high, and it is preferable that the solubility is 1% or more.

  The molecular weight of the polar polythiophene is not particularly limited, but the preferred molecular weight is 800 to 100,000 in terms of weight average molecular weight.

  A known method can be used for the synthesis of the conjugated polymer used in the present invention. For example, a method in which monomers having two polymerizable functional groups are reacted with each other, and a method in which monomers having two different polymerizable functional groups are reacted in an iron or nickel catalyst are exemplified.

  The method for removing impurities of the conjugated polymer used in the present invention is not particularly limited, but is basically a production step for removing raw materials and by-products used in the synthesis process, and includes a reprecipitation method, a soxhlet method. An extraction method, a filtration method, an ion exchange method, a chelate method, or the like can be used. In particular, when removing low molecular weight components, a reprecipitation method and a Soxhlet extraction method are preferably used. Two or more of these methods may be combined.

  The polymer composite in the present invention refers to a composite of the above-mentioned multi-walled carbon nanotube and polar polythiophene, and refers to a state in which a part or all of the surface of the multi-walled carbon nanotube is covered with the polar polythiophene.

  Multi-walled carbon nanotubes and polar polythiophene can be coated mainly by π-π interaction derived from the conjugated structure of the aromatic ring and thiophene ring of the graphite structure on the surface of the carbon nanotube, and interaction by intermolecular force. It is estimated that

  The method of making the composite is not particularly limited, but (I) a method in which multi-walled carbon nanotubes are added to and mixed with molten polar polythiophene, and (II) polar polythiophene is dissolved in a solvent, and multi-walled carbon nanotubes are dissolved therein. (III) A method in which multi-walled carbon nanotubes are predispersed in advance with ultrasonic waves, etc., and a conjugated polymer is added and mixed therewith. (IV) A polar polythiophene and a multi-layer in a solvent. For example, a method of adding carbon nanotubes and irradiating the mixed system with ultrasonic waves may be used. In the present invention, any method may be used, and any method may be combined, but the method (IV) is preferable from the viewpoint of efficient complexation.

  As the solvent used when the polar polythiophene and the multi-walled carbon nanotube are combined, a solvent having a high solubility of the polar polythiophene is preferable, and a solvent having a solubility of the polar polythiophene exceeding 1 wt% is more preferable. In order to form a composite, a dispersion containing polar polythiophene and multi-walled carbon nanotubes can be preferably dispersed by treating with an ultrasonic disperser. As the ultrasonic disperser, an ultrasonic homogenizer capable of directly applying energy to the dispersion is preferable.

  The weight ratio of the multi-walled carbon nanotubes in the present invention is 100 wt% to 500 wt%, more preferably 200 wt% to 400 wt% with respect to the polar polythiophene. Since it is used as an electrode conduction aid, if the weight ratio of the multi-walled carbon nanotubes is too small, a large amount of polar polythiophene is introduced into the electrode, causing a problem of electrode adhesion deterioration. Moreover, when there are too many weight ratios of a multi-layer carbon nanotube, the dispersibility with respect to a polar solvent will fall, and dispersion | distribution of the carbon nanotube in an electrode will worsen.

  Compared with thin-walled carbon nanotubes having a fiber diameter of 10 nm or less, multi-walled carbon nanotubes having a fiber diameter of 10 nm to 200 nm have a relatively small surface area, so that the weight ratio of carbon nanotubes to polar polythiophene can be increased. Specifically, by selecting a ratio of 500 wt% or less in weight ratio to produce a polymer composite, it becomes possible to disperse in a polar solvent. When the weight ratio of the carbon nanotubes is 500 wt% or more with respect to polythiophene, the dispersion force cannot be improved, and the carbon nanotubes aggregate when used as an electrode paste, and the performance as a conductive additive cannot be exhibited.

  Further, when the weight ratio of the carbon nanotubes is 100 wt% or less with respect to the polythiophene, the ratio of the polythiophenes is large and the conductive properties of the carbon nanotubes are hindered. By making the weight ratio of the carbon nanotubes 100 wt% or more with respect to polythiophene, it becomes possible to use the carbon nanotubes as a conductive aid without impairing the excellent conductive properties of the carbon nanotubes.

  As described above, by selecting the weight ratio of the carbon nanotubes to 100 wt% or more and 500 wt% or less with respect to polythiophene, the carbon nanotubes having a large diameter can be dispersed in the polar solvent for battery electrodes while maintaining the excellent conductive properties.

  The polymer composite is mixed with an electrode active material, a binder polymer, and a conductive additive and used as a positive electrode or a negative electrode.

As the positive electrode active material is not particularly limited, lithium cobaltate (LiCoO _2), lithium nickelate (LiNiO _2), spinel type lithium manganese oxide (LiMn ₂ O ₄₎ lithium metal oxide such _{as, V} 2 O ₅ or the like of the metal oxide or _{TiS 2,} MoS 2, NbSe _2, etc. of the metal compound-based, lithium iron phosphate, etc. olivine such as lithium manganese phosphate and the like.

  The negative electrode active material is not particularly limited, but carbonaceous materials such as natural graphite, artificial graphite, and hard carbon, silicon compounds having SiO, SiC, SiOC, etc. as basic constituent elements, manganese oxide that can undergo a conversion reaction with lithium ions ( Examples thereof include metal oxides such as MnO) and cobalt oxide (CoO).

  The binder polymer may be selected from fluorine polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), and rubbers such as natural rubber.

  The conductive auxiliary agent may be only the polymer composite of the present invention or may be added to others. The conductive auxiliary agent to be added is not particularly limited, but examples thereof include furnace black, ketjen black, and acetylene black. Examples thereof include carbon blacks, natural graphite (such as flake graphite), graphite such as artificial graphite, conductive fibers such as carbon fibers and metal fibers, and metal powders such as copper, nickel, aluminum and silver.

  In many cases, polar solvents such as N-methylpyrrolidone, γ-butyrolactone, dimethylacetamide, and water are used as paste solvents for lithium ion battery electrodes. In the present invention, polar polythiophene is used as a polymer that is soluble in these solvents and can be combined with carbon nanotubes. Polar polythiophene is a conductive polymer and can improve dispersibility in a polar solvent without inhibiting the excellent conductivity of the carbon nanotube.

  The method for producing the electrode is not particularly limited, but it is produced by kneading the binder polymer, electrode active material, conductive additive, and solvent with various dispersing and kneading machines to form a paste, and applying and drying the current collector. .

  Examples of the dispersion / kneading technique include a technique using an automatic mortar, three rolls, a bead mill, a planetary ball mill, a self-revolving mixer, a wet jet mill, a homogenizer, and a planetary mixer.

  Examples of the method of applying the paste obtained by dispersing and kneading to the current collector include application by a bar coater / doctor blade, slit coater, die coater, blade coater and the like.

  The polymer composite is highly useful as a dispersion, and good dispersion can be obtained even if it is introduced as a dispersion during the lithium ion battery electrode paste kneading step.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely and in detail, this invention is not restrict | limited only to these Examples. The physical property values in the examples were measured by the following methods.

A. Method for Measuring Viscosity Yield Value The yield value of the paste was measured using a viscometer (Rheotech, model number RC20). A cone plate (C25-2) was used as a probe, and each viscosity was measured by increasing the shear rate step by step for 30 steps at a shear rate of 0 to 500 per second at a temperature of 25 ° C. The yield value was calculated from the intercept by plotting Kasson for shear rate and shear stress.

B. Capacitance measurement method A lithium foil cut to a diameter of 16.1 mm and a thickness of 0.2 mm was used as a negative electrode, and a cell guard # 2400 (manufactured by Celgard) separator cut to a diameter of 17 mm was used. A 2042 type coin battery was prepared using a solvent of ethylene carbonate: diethyl carbonate = 7: 3 containing 1M of LiPF ₆ as an electrolytic solution and an electrolytic solution. Charge / discharge measurement was performed three times at a rate of 1 C, an upper limit voltage of 4.0 V, and a lower limit voltage of 2.5 V, and the capacity at the third discharge was defined as the discharge capacity.

[Example 1]
3 parts by weight of poly (thiophene-3- [2- (2-methoxyethoxy) ethoxy-2,5-diyl] sulfonate (Sigma Aldrich, part number 699799, see formula below), which is a polar polythiophene, and multi-walled carbon nanotubes (Primary diameter: 65 nm, MWNT manufactured by Hodogaya Chemical Co., Ltd.) 10 parts by weight in 487 parts by weight of N-methyl-2-pyrrolidone (NMP), and dispersed for 30 minutes with an ultrasonic disperser. A composite dispersion was obtained.

  Of these, 100 parts by weight of the polymer composite dispersion (including 2 parts by weight of multi-walled carbon nanotubes), 80 parts by weight of lithium iron phosphate as the electrode active material, and 8 parts by weight of acetylene black (AB) as the conductive auxiliary agent Then, 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder was mixed with a planetary mixer to obtain an electrode paste. The yield value of this electrode paste was measured and found to be 4.5 Pa.

  The electrode paste was applied to aluminum foil (thickness: 18 μm) using a doctor blade (300 μm) and dried at 200 ° C. for 15 minutes to obtain an electrode plate. Using the electrode plate, the discharge capacity of the electrode was measured and found to be 150 mAh / g.

[Example 2]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that the amount of polar polythiophene was changed to 5 parts by weight. The yield value of this electrode paste was measured and found to be 2.6 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. When the discharge capacity of the electrode was measured using the electrode plate, it was 138 mAh / g.

[Example 3]
An electrode paste was obtained by kneading the same method and composition as in Example 1 except that the diameter of the multi-walled carbon nanotube was 150 nm (made by Showa Denko KK, VGCF-H). The yield value of this electrode paste was measured and found to be 3.2 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. Using the electrode plate, the discharge capacity of the electrode was measured and found to be 153 mAh / g.

[Example 4]
An electrode paste was obtained by kneading by the same method and composition as in Example 3 except that the amount of polar polythiophene was changed to 5 parts by weight. The yield value of this electrode paste was measured and found to be 2.0 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. Using the electrode plate, the discharge capacity of the electrode was measured and found to be 143 mAh / g.

[Example 5]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that the diameter of the multi-walled carbon nanotube was 15 nm (made by Showa Denko KK, VGCF-X). The yield value of this electrode paste was measured and found to be 9.5 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. When the discharge capacity of the electrode was measured using the electrode plate, it was 131 mAh / g.

[Example 6]
An electrode paste was obtained by kneading by the same method and composition as in Example 3 except that the amount of polar polythiophene was changed to 5 parts by weight. The yield value of this electrode paste was measured and found to be 3.7 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. When the discharge capacity of the electrode was measured using the electrode plate, it was 145 mAh / g.

[Comparative Example 1]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that the amount of polar polythiophene was 1 part by weight. The yield value of this electrode paste was measured and found to be 253 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. Using the electrode plate, the discharge capacity of the electrode was measured and found to be 110 mAh / g.

[Comparative Example 2]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that the amount of polar polythiophene was 30 parts by weight. The yield value of this electrode paste was measured and found to be 2.6 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. When the discharge capacity of the electrode was measured using the electrode plate, it was 98 mAh / g.

[Comparative Example 3]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that only 10 parts of multi-walled carbon nanotubes were dispersed in 487 parts by weight of N-methyl-2-pyrrolidone without using polar polythiophene. The yield value of this electrode paste was measured and found to be 546 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. Using the electrode plate, the discharge capacity of the electrode was measured and found to be 95 mAh / g.

[Comparative Example 4]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that the diameter of the multi-walled carbon nanotube was 5 nm. The yield value of this electrode paste was measured and found to be 1501 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. When the discharge capacity of the electrode was measured using the electrode plate, it was 111 mAh / g.

[Comparative Example 5]
An electrode paste was obtained by kneading by the same method and composition as in Example 1 except that the diameter of the multi-walled carbon nanotube was 300 nm. The yield value of this electrode paste was measured and found to be 5.2 Pa.

  The electrode paste was applied and dried in the same manner as in Example 1 to obtain an electrode plate. When the discharge capacity of the electrode was measured using the electrode plate, it was 104 mAh / g.

  Table 1 summarizes the conditions and results of Examples 1 to 4 and Comparative Examples 1 to 5.

  Since the conductive auxiliary agent of the present invention can increase the capacity of an electrode for a lithium secondary battery, it can be suitably used for producing a high-performance lithium secondary battery.

Claims (6)

A polymer composite comprising a multi-walled carbon nanotube having a primary diameter of 10 nm to 200 nm and a polar polythiophene, wherein the weight ratio of the multi-walled carbon nanotube is 100 wt% to 500 wt% with respect to the polar polythiophene. Conductive aid for secondary battery electrode. 2. The conductive additive for a lithium secondary battery electrode according to claim 1, wherein the primary diameter of the multi-walled carbon nanotube is 50 nm to 150 nm. 3. The conductive auxiliary agent for a lithium secondary battery electrode according to claim 1, wherein the weight ratio of the multi-walled carbon nanotube is 200 wt% to 400 wt% with respect to the polar polythiophene. The conductive additive for a lithium secondary battery electrode according to any one of claims 1 to 3, wherein the polar polythiophene is soluble in N-methylpyrrolidone, γ-tyrolactone, dimethylacetamide, or water at a weight concentration of 1% or more. 5. A conductive auxiliary agent dispersion for a lithium secondary battery electrode, wherein the conductive auxiliary agent for a lithium secondary battery electrode according to any one of claims 1 to 4 is dispersed in N-methylpyrrolidone, γ-butyrolactone, dimethylacetamide, or water. A lithium secondary battery electrode containing a positive electrode active material, a binder polymer, and a conductive auxiliary agent, wherein at least a part of the conductive auxiliary agent is for a lithium secondary battery electrode according to any one of claims 1 to 4. The electrode for lithium secondary batteries characterized by including a conductive support agent.