JP5906578B2 - Positive electrode mixture for lithium ion secondary battery, positive electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Description

The present invention relates to a positive electrode mixture for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery.

  A lithium ion secondary battery (hereinafter also simply referred to as “battery”) is a battery in which insertion and extraction of lithium ions are performed reversibly in a positive electrode and a negative electrode. A battery is a system in which a lithium ion contained in a positive electrode is occluded in a negative electrode and a capacity is developed during charging. An oxide containing lithium is used for the positive electrode material, and a carbon material or a lithium-containing oxide is used for the negative electrode material.

  Various studies have been made to improve the capacity of the battery, but the capacity of the positive electrode material is about the theoretical capacity of 280 mAh / g. However, it is actually used at about 110 to 160 mAh / g from the viewpoint of efficiency and life. The positive electrode active material has low conductivity, and carbon black (hereinafter abbreviated as “CB”) or acetylene black (hereinafter abbreviated as “AB”) as a conductive agent is 1 to the positive electrode active material. % Or more are required to be mixed. And thereby, the capacity | capacitance of a battery can be enlarged.

  However, since the ratio of the positive electrode active material is decreased by mixing the conductive agent, the capacity per unit weight and volume of the battery itself is reduced. Further, when the conductive agent is reduced, there is a problem that the capacity is significantly deteriorated when the battery is used at a high output.

On the other hand, when a carbon material is used for the negative electrode, the theoretical capacity calculated on the assumption that the carbon material has changed to LiC ₆ is 372 mAh / g. From the viewpoint of efficiency and life, it is actually used at about 200 to 320 mAh / g.

  When comparing the positive electrode with the negative electrode, the negative electrode has a larger capacity per weight. Therefore, in order to improve the battery capacity, the positive electrode is used relative to the negative electrode coating amount, using a material that expresses more capacity in the positive electrode. It is necessary to devise such as applying more.

As an example of a technique for solving the above problem, Patent Document 1 discloses that a compound represented by a chemical formula LiMO ₂ (M is any kind of metal selected from Co, Ni and Mn) is treated with an acid. A non-aqueous electrolyte battery including a proton-containing positive electrode active material obtained by a manufacturing method including a process is disclosed.

  In addition, as a technique for producing a composite material for a lithium battery positive electrode that has high conductivity as a conductive agent and sufficiently secures a diffusion path of Li, Patent Document 2 discloses positive electrode active material particles and fibrous carbon in a solvent. A method for producing a composite material for a lithium battery positive electrode including a step of spray granulating a slurry in which carbon nanotubes are dispersed is disclosed.

JP 2007-53116 A JP 2009-176720 A

  Even when the proton-containing positive electrode active material described in Patent Document 1 is used, capacity deterioration at high output may occur.

  In the method for producing a composite material for a lithium battery positive electrode described in Patent Document 2, the fiber length of the fibrous carbon used in the production is 50 nm to 50 μm, and the fiber length is relatively short. Per volume and weight, such as high ratio of conductive agent to positive electrode active material, mixing carbon black as a carbon material other than fibrous carbon, and not considering capacity degradation at high output However, it does not provide sufficient means for solving the problem of reduction of the per capita capacity and capacity degradation at high power.

  An object of the present invention is to increase the capacity of a lithium ion secondary battery by reducing the amount of a conductive agent mixed with the positive electrode and to suppress deterioration of the lithium ion secondary battery capacity at high output.

  In the present invention, as a conductive agent of the positive electrode mixture of the lithium ion secondary battery, one containing carbon nanotubes having a diameter of 0.5 to 10 nm and a length of 10 μm or more is used.

  ADVANTAGE OF THE INVENTION According to this invention, the quantity of the electrically conductive agent mixed with a positive electrode in a lithium ion secondary battery can be reduced, a capacity | capacitance can be enlarged, and the deterioration of the capacity | capacitance in high output can be suppressed.

It is a partial expanded sectional view which shows the structure of the conventional positive electrode. It is a schematic block diagram which shows the positive electrode material of an Example. It is a partial expanded sectional view which shows the structure of the positive electrode of an Example. It is a partial expanded sectional view which shows the structure of the positive electrode of another Example. It is a fragmentary sectional view which shows the structure of a lithium ion secondary battery.

  The present invention relates to a conductive agent for a positive electrode of a lithium ion secondary battery that suppresses capacity deterioration when discharging at a high output, and a lithium ion secondary battery using the same.

  Hereinafter, a conductive agent for a positive electrode of a lithium ion secondary battery according to an embodiment of the present invention, a positive electrode material, a positive electrode mixture, a positive electrode, and a lithium ion secondary battery using the same will be described.

  The conductive agent for a lithium ion secondary battery positive electrode is a conductive agent used for a positive electrode (or a positive electrode mixture) of a lithium ion secondary battery, and has a diameter of 0.5 to 10 nm and a length of 10 μm or more. It contains carbon nanotubes (Carbon Nanotube: CNT).

  Here, the positive electrode mixture includes a positive electrode active material, a conductive agent, and a binder. The positive electrode has a configuration in which a positive electrode mixture is applied to a current collector.

  In addition, this invention discovered the new use of the carbon nanotube with a small diameter and long length. That is, the carbon nanotubes having the above dimensions are applied to a conductive agent for a lithium ion secondary battery positive electrode.

  In the conductive agent for a lithium ion secondary battery positive electrode, the carbon nanotube is preferably a single-walled carbon nanotube.

  In the conductive agent for a lithium ion secondary battery positive electrode, the carbon purity of the carbon nanotube is preferably 99.9% or more on a weight basis. If the carbon purity of the carbon nanotube is 99.9% or more, the addition weight as a conductive agent is very small, and short circuit and capacity deterioration during charging / discharging of the battery are unlikely to occur.

  In the conductive agent for a lithium ion secondary battery positive electrode, the carbon nanotubes are preferably stable (storable) in a water-dispersed state (a state dispersed in water).

  The positive electrode material (positive electrode material for a lithium ion secondary battery) includes the conductive agent for a positive electrode of the lithium ion secondary battery and a positive electrode active material.

  In the positive electrode material, the positive electrode active material is preferably a lithium oxide having an olivine structure.

  In the positive electrode material, the positive electrode active material is preferably olivine manganese.

  In the positive electrode material, the content of carbon nanotubes is preferably 0.1 to 0.6% on a weight basis.

  The positive electrode mixture (a positive electrode mixture for a lithium ion secondary battery) includes the positive electrode material and a binder.

  The positive electrode (positive electrode for a lithium ion secondary battery) has a configuration in which the positive electrode mixture is applied to a current collector.

  The lithium ion secondary battery includes the positive electrode, the negative electrode, a separator, and an electrolytic solution.

  With the above configuration, the capacity of the battery can be increased, and deterioration of the capacity can be suppressed. And even if it enlarges, a high safety | security battery with a long lifetime can be provided.

  Hereinafter, characteristics of the CNT of the example will be described.

  The CNT has a cylindrical shape formed by winding a single sheet of graphite, and is a kind of fibrous carbon. CNT is known to have high conductivity because the bonds between carbon atoms on the surface of graphite are continuous over a very long distance. From the viewpoint of constructing more conductive paths, fibrous carbon having a small fiber diameter is preferable. Fibrous carbon is obtained by an arc discharge method, a laser evaporation method, a chemical vapor deposition method or the like using a hydrocarbon gas or the like.

The CNT manufacturing method includes an arc discharge method in which a graphite electrode containing a metal catalyst such as Ni, Co, Y, Fe or the like is evaporated by an arc discharge under an atmospheric gas such as He, Ar, CH ₄ , H ₂ , A YAG laser is applied to a graphite mixed with a metal catalyst such as Ni—Co or Pd—Rd to evaporate it, and then sent to an electric furnace heated to about 1200 ° C. with an Ar air stream. Pentacarbonyl iron (Fe There is a HiPCo method in which carbon monoxide is thermally decomposed at a high pressure using (CO) ₅ ).

  The positive electrode material containing CNT used as the conductive agent obtained as described above can be formed into a positive electrode used as an electrode by the following method.

  That is, after a positive electrode mixture paste obtained by adding a solvent to a mixture containing a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and the like and kneading sufficiently is applied to one or both sides of the positive electrode current collector and dried. By forming a positive electrode mixture layer having a predetermined thickness and pole density by pressing or the like, a positive electrode is obtained.

  As for the aspect ratio of CNT, for example, the smaller the concentration ratio of hydrocarbon (benzene or the like) and the atmospheric gas such as hydrogen gas, the smaller the diameter of the produced CNT and the larger the aspect ratio. Moreover, the shorter the reaction time, the smaller the diameter of the produced CNT and the larger the aspect ratio.

  CNT includes single-walled carbon nanotubes (single-wall carbon nanotubes (SWCNTs)) in which one surface of graphite is cylindrical, and multi-walled carbon nanotubes (multi-walled carbon nanotubes) in which graphite surfaces are overlapped. (Malti-Wall Carbon Nanotube: MWCNT).

  Since SWCNT is a single graphene sheet, SWCNT has a feature that its diameter can be made smaller than that of MWCNT. On the other hand, in the case of MWCNT, since the diameter becomes large, a defect may occur in a part of the graphene sheet that overlaps inside when growing in the length direction. If it does so, electronic conductivity may fall.

  In addition, MWCNT may be inferior in electronic conductivity to SWCNT because the overlap of graphene layers interacts with electronic conductivity. SWCNT has excellent electron conductivity when the graphene sheet is free of defects, but is inferior to that when defects are observed.

  When the graphene sheet forming SWCNT or MWCNT is ideal and the fiber diameter is smaller than that of MWCNT, SWCNT is preferable as a conductive agent because it has better electronic conductivity than MWCNT. However, this is not the case when the diameter and length of the MWCNT are equivalent to those of the SWCNT.

  The CNTs of the examples are those dispersed in water (dispersed in an aqueous solution). CNTs generally have a property of easily aggregating, but by dispersing in water, there is an advantage that they are easily mixed and dispersed rather than being mixed with a positive electrode active material in a powder state. In addition, when dispersed in water, CNTs having long fibers are less likely to be broken, so that handling of the CNTs is facilitated.

  A water-dispersed CNT is mixed with a positive electrode active material to form a slurry, and then dried to obtain a positive electrode material (CNT-containing positive electrode material) containing CNT. Desirably, SWCNT is used as the CNT. By drying the slurry once as described above, the CNTs are fixed on the surface of the positive electrode active material. For this reason, when a slurry of a positive electrode mixture is prepared by mixing a binder and a solvent, only the CNTs do not aggregate and the internal resistance of the positive electrode becomes uniform.

  On the other hand, when the positive electrode mixture slurry is prepared, if the positive electrode active material and the CNT are added and mixed separately, only the CNT may be aggregated.

  SWCNTs may be dispersed in a solvent containing an organic solvent. The solvent may be an organic solvent such as NMP or ethanol, or a mixture of these with a binder such as polyvinylidene fluoride (PVDF).

The positive electrode active material is not particularly limited, but a positive electrode active material having an olivine type crystal structure is desirable. Lithium manganese composite oxide (LiMnPO ₄ ) having an olivine type crystal structure is more preferable.

  When the lithium manganese composite oxide having an olivine type crystal structure contains at least one of Mg and Al, higher cycle characteristics and high temperature storage characteristics can be obtained.

Further, a polyanionic compound such as LiMn ₂ O ₄ having a spinel structure or LiMnSO ₄ can also be used. Further, Group I metal compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS, CuSO ₄ , Group IV metal compounds such as TiS ₂ , SiO ₂ , SnO, V ₂ O ₅ , V ₆ O ₁₂ , VO _x , Group V metal compounds such as Nb ₂ O ₅ , Bi ₂ O ₃ and Sb ₂ O ₃ , Group VI metal compounds such as CrO ₃ , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ and SeO ₂ , MnO ₂ , Group VIII metal compounds such as Mn ₂ O ₃ , Group VIII metal compounds such as Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , FePO ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , and CoO are used as the positive electrode active material. It may be added.

  In addition, conductive polymer compounds such as disulphide, polypyrrole, polyaniline, polyparaphenylene, polyacetylene, and polyacene materials, pseudographite-structured carbonaceous materials, and the like are added to the positive electrode active material or the surface of the positive electrode active material is coated. You may use what was made as positive electrode materials.

  The configuration of the positive electrode active material particles is not particularly limited, and may be formed of a single crystal without agglomeration, and a plurality of particles (primary particles) formed of a single crystal. Particles (secondary particles) formed by individual assembly (aggregation) may be used. When using particles formed of a single crystal, the particle size is preferably 1 nm to 10 μm. If the particle size is too large, there is a possibility that the output performance is deteriorated because there is little contact between particles.

  In addition, when there is too little CNT addition amount with respect to a positive electrode active material, the effect of a electrically conductive agent will not fully be acquired. On the other hand, when the amount of CNT added is too large, when a positive electrode mixture slurry containing a positive electrode active material, CNT, binder, and solvent is produced, CNT aggregates are generated in the slurry, and the viscosity rapidly increases. Happens. When this slurry is applied to the surface of the current collector, agglomerates of CNTs are caught on the application blade, streaks are generated on the application surface, and problems such as the inability to apply with a constant film thickness occur.

  The proportion of CNT in the positive electrode material composed of CNT and the positive electrode active material is preferably 0.1 to 0.6% on a weight basis. In consideration of producing a stable slurry, 0.1 to 0.25% is more preferable.

  It is desirable to use a carbon material as the negative electrode active material. The following are mentioned as an example of a carbon material.

That is, natural graphite, artificial graphite, amorphous carbon, fibrous carbon, powdered carbon, petroleum pitch-based carbon, and coal coke-based carbon. These carbon materials preferably have a diameter of 0.01 to 10 μm, and in the case of fibrous carbon, the fiber length is preferably 2 μm to 10 mm. Further, it is also possible to use oxides such as _Li 4 _Ti 5 _{O 12} as the negative electrode active material. Li ₄ Ti ₅ O ₁₂ has a working potential with respect to metallic lithium of about 1.5 V, no lithium dendride deposition, and high safety. Therefore, a battery having a large capacity and high safety is manufactured. Can do.

  Hereinafter, the positive electrode conductive agent will be described.

  Conventionally, what is generally used as a positive electrode conductive agent is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber, copper, nickel, aluminum, silver, gold, etc. One type of conductive material (electron conductive material) such as metal fiber or conductive ceramic material is used, or a mixture of two or more types is used. Among these, acetylene black is preferably used from the viewpoints of conductivity and coatability. The added amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight. When mixing two or more types, physical mixing is performed. The ideal place is uniform mixing. Therefore, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, or a planetary ball mill is used in a dry or wet manner.

  However, it is necessary to add at least about 1 to 50% of the conductive agent, which is a problem in manufacturing a compact and large-capacity battery.

  The CNTs of the examples are for reducing the amount of conductive agent contained in the positive electrode, promoting the increase in capacity of the battery, and extending the life of the battery.

  Examples of CNTs will be described in detail below. In the following description, when simply referred to as “CNT”, it means the CNT of the example.

  In the CNT production method of the example, a carbon source is supplied to the surface of a catalyst supported by a support to synthesize CNT. The catalyst is heated to a high temperature by heating the support, and a raw material gas containing a carbon source is supplied to synthesize CNT. The synthesized CNTs are recovered, and then the catalyst is regenerated, and the support and the catalyst are repeatedly used for synthesis.

(catalyst)
In the present specification, the “catalyst” refers to a catalyst supported on a support and means a general catalyst. This catalyst is in contact with a supplied carbon source to mediate, promote, improve efficiency, etc. of CNT synthesis. “Catalyst” means a material having a role of taking in a carbon source and discharging CNTs. Furthermore, the “catalyst” is a metal nanoparticle having a size on the order of nanometers, and is held on a support formed of a solid material, a semi-solid material, or the like.

(Type of support)
The support is a structure for holding a catalyst, a catalyst carrier (definition will be described later), a catalyst cap material (definition will be described later) and the like in the reactor. In general, the support is preferably a solid material. The support is preferably one that can increase the surface area per unit volume of the support as much as possible, and specifically, one having a specific surface area of 0.1 to 10.0 mm ² / mm ³ or more is preferable. Further, it is desirable that the support has a honeycomb structure known as a structure in which hexagonal pipes having a hexagonal cross section are arranged, for example. Other than the honeycomb structure, a structure in which a large number of plate materials are arranged, a structure in which corrugated plate materials are arranged, a structure in which square pipes having rectangular cross sections are arranged, or the like may be used.

  From the viewpoint of heat resistance, corrosion resistance, chemical resistance, mechanical strength characteristics, etc., it is preferable to use ceramics for the material of the support. For the support, it is desirable to use a known ceramic such as alumina or silicon carbide containing one or more elements selected from the group consisting of Si, Al, Zr and Mg. However, the support is not limited to ceramics, and an alloy material containing one or more elements selected from Fe, Co, and Ni may be used.

(Catalyst / catalyst carrier production)
The catalyst of the example is manufactured as follows.

  The catalyst of the examples is supported by bringing a liquid raw material obtained by dissolving the catalyst raw material in a solvent into contact with the surface of the support and drying it. In this case, the support may be dipped after being dipped in the liquid material and dried, or may be carried by passing the mist of the liquid material on the support. As the liquid raw material, an aqueous solution of a metal inorganic salt such as nitrate, phosphate or chloride, an alkoxide, or an organic solution of a metal organic salt such as acetate can be used.

  The catalyst may be supported by gasifying the catalyst raw material and bringing the gas raw material into contact with the surface of the support. In this case, the gaseous material of the catalyst is supplied to a high temperature support and the catalyst is supported on the support.

  Alternatively, the liquid material may be supplied to a high temperature support, the liquid material may be evaporated on the surface of the high temperature support, and the catalyst may be supported on the surface of the support. As a raw material for the catalyst, an aqueous solution of a metal inorganic salt such as nitrate, phosphate or chloride, an alkoxide, or an organic solution of a metal organic salt such as acetate can be used. In particular, in the case of an Fe catalyst, ferrocene is preferable.

  The catalyst preferably contains one or more elements selected from the group consisting of Fe, Co, Ni, Mo and Cr as its components. The catalyst is preferably formed on the surface of a catalyst carrier containing one or more elements selected from the group consisting of Si, Al, Mg, Zr and Mo.

Here, the “catalyst support” is a material to which metal nanoparticles are attached, and an oxide such as SiO ₂ , Al ₂ O ₃ , aluminosilicate, MgO, a nitride such as Si ₃ N ₄ or AlN, or It is made of a carbide such as SiC. However, the support may also serve as a carrier.

As the Al source of the catalyst carrier, inorganic salts containing Al such as Al (NO ₃ ) ₃ , AlCl ₃ and organic aluminum are preferable. As the Si source of the catalyst carrier, an inorganic or organic substance containing Si can be used, but TEOS is preferable from the viewpoint of easy handling. The catalyst may be partially covered with a catalyst cap material containing one or more elements selected from the group consisting of Si, Al, Mg, Zr and Mo. The “catalyst cap material” described here is a material having a function of sandwiching the catalyst between the catalyst carrier or the support by partially covering the surface of the catalyst. The “catalyst cap material” is an oxide film naturally formed on the surface of the catalyst.

In the present specification, the “catalyst cap material” is an oxide such as SiO ₂ , Al ₂ O ₃ , MgO or the like formed on the metal nanoparticles, a nitride such as Si ₃ N ₄ , AlN, or SiC. It is defined as a layer made of carbides. This “catalyst cap material” may improve the characteristics of the catalyst by an action such as suppressing aggregation of metal nanoparticles.
An organic raw material or an inorganic raw material containing these elements can be used as a raw material for the catalyst and the carrier raw material Al, Fe, or Co.

Specifically, as an Al source of the catalyst and the carrier raw material, aluminum chloride (AlCl ₃ ), aluminum isopropoxide (Al (iso-OC ₃ H ₇ ) ₃ ), aluminum acetylacetonate (Al (iso-C ₅ H) One or more substances selected from the group consisting of ₇ O ₂ ) ₃ ) and trimethylaluminum (Al (CH ₃ ) ₃ ) are preferred.

Tris (2,4-pentanedionato) iron (III) (Fe (C ₅ H ₇ FeO ₂ ) ₃ ), ferrocene ((C ₅ H ₅ ) ₂ Fe), iron nitrate (III) nonahydrate _{(Fe (NO 3) 3 ·} 9H 2 O) and one or more materials selected from the group consisting of iron carbonyl (Fe _{(CO) 5)} are preferred.

Tris (2,4-pentanedionato) cobalt (III) (Co (C ₅ H ₇ O ₂ ) ₃ ) and cobalt nitrate (II) hexahydrate (Co (NO ₃₎ 1) One or more substances selected from the group consisting of ₂ · 6H ₂ O) are preferred.

(Heating support)
The following method may be employed for heating the support described above.

  In the embodiment, CNT is synthesized by a thermal CVD method. This thermal CVD method is a method in which a gas or liquid raw material is heated and vaporized, and a thin film is formed in the vapor phase of the vapor or by a chemical reaction on the substrate surface. An apparatus that gives this chemical reaction energy in the form of thermal energy from a base material or reaction vessel wall is known as a thermal CVD method.

  In this heating method, the entire reactor may be heated by a heating furnace. Further, the support may be heated by energization. That is, current heating is a method in which only the support is heated instead of heating the entire reactor with a heating furnace. In addition, as a heating means, an electric furnace, a combustion furnace, heat exchange, or infrared heating can be used. Further, when the support is formed of a conductive material, electric heating or induction heating can also be used as the heating means.

  Here, the temperature in the heated reactor is preferably equal to or higher than the melting temperature of the catalyst particles and lower than the decomposition temperature of the carbon source. The temperature range for growing SWCNTs by CVD using a supported catalyst is preferably about 400 to 1200 ° C. In addition, when SWCNT is synthesized using a support having a honeycomb structure, a temperature range of 600 to 1000 ° C. is particularly preferable.

(Carbon raw material)
The raw material of the carbon source may include one or more selected from the group consisting of alkanes (paraffin hydrocarbons), alkenes (olefin hydrocarbons), alcohols, ethers, aldehydes, ketones, aromatics, acetylenes, and carbon monoxide. desirable. Thermal CVD may be performed by supplying a gas containing a carbon source material to the catalyst described above at 0.001 MPa (0.01 atm) to 1.013 MPa (10 atm).

(Mixed gas including carbon raw material and carrier gas)
A volatile compound as a carbon raw material is vaporized and mixed with a carrier gas such as hydrogen, argon, nitrogen, etc., and sent to the catalyst. The mixed gas preferably contains oxygen as an element.

(Separation / collection)
Since the synthesized CNTs are stacked or stay on or near the surface of the catalyst, catalyst cap material, catalyst carrier, support, etc., it is necessary to separate them and collect only the CNTs. Separation of the synthesized CNT is preferably performed by an unsteady gas pulse or a steady gas flow. The unsteady gas pulse means that the flow rate of an inert gas such as argon or nitrogen is changed in a pulse shape at a constant period. A steady gas flow refers to an inert gas flow with a constant flow rate.

  The synthesized CNTs are separated from or near the surface of the catalyst, catalyst cap material, catalyst carrier, support and the like by the dynamic pressure of these gas flows. The kinetic energy of a fluid has a pressure dimension, which is dynamic pressure. A gas containing CNTs separated by the dynamic pressure is filtered through a filter to collect CNTs.

  Alternatively, the gas containing the separated CNTs can be brought into contact with the liquid to collect the CNTs in the liquid. Alternatively, the separated CNT-containing gas can be collected by thermophoresis by bringing the gas containing the CNT into contact with a solid wall or liquid wall having a temperature lower than the temperature of the gas flow.

(Catalyst regeneration)
The catalyst regeneration treatment in the examples refers to periodically or irregularly regenerating a catalyst that has deteriorated, deactivated or consumed due to the production of CNTs. The regeneration process of the catalyst may be accompanied by an oxidation process of the catalyst. This oxidation treatment may be a method of heat treatment with oxygen in the air. An oxidizing agent may be used for the oxidation treatment. As the oxidizing agent, oxygen or water vapor can be used. Water vapor and oxygen contained in the coexisting gas can also be used as the oxidizing agent.

After the oxidation treatment, the catalyst is reduced by sending a reducing gas to the surface of the catalyst and bringing it into contact therewith. Further, after the oxidation treatment, the catalyst may be reduced by sending a carbon source to the catalyst surface and bringing it into contact. Thereby, the regeneration process of a catalyst can be performed.
In the reduction treatment of the catalyst, a method of flowing a reducing gas such as hydrogen, or a method of mixing hydrogen as a carrier gas when the catalyst raw material is formed by sputtering and using this hydrogen as a reducing agent may be used. Further, the regeneration process of the catalyst may be accompanied by replenishment of elements contained in the catalyst.

  The above oxidation treatment and reduction treatment use a known oxidizing agent and reducing agent according to the type of catalyst selected. The above replenishment may be performed by sending a gas containing an element constituting the catalyst into contact with the surface of the catalyst. Further, the above replenishment may be performed by previously containing a catalyst element in the catalyst and / or the support and gradually diffusing this element on the surface of the catalyst carrier.

As the reducing gas, hydrogen (H ₂ ), ammonia (NH ₃ ), or the like can be used. The carbon source itself can also be used as a reducing agent. Examples of the carbon source include alkanes such as CH ₄ and C ₂ H ₆ , alkenes such as C ₂ H ₄ and C ₃ H ₆ , alkynes such as C ₂ H ₂ , alcohols such as CH ₃ OH and C ₂ H ₅ OH, and the like. CO can be used. Furthermore, molecules containing C, H and O as constituent elements such as aldehydes and ketones can also be used as the carbon source.

(SWCNT)
The CNT manufacturing method of the embodiment is capable of manufacturing CNTs having various structures, and is particularly suitable for manufacturing SWCNTs.

(CNT production method)
The outline of the manufacturing method of CNT of an Example is as follows.

  The manufacturing method of CNT of an Example has the characteristics in the manufacturing method of CNT for synthesize | combining continuously in large quantities.

  First, a nanoparticle catalyst is supported on a support formed of a solid having a large specific surface area (first step).

  CNTs are grown on the surface of the nanoparticle catalyst (support) by heating the nanoparticle catalyst supported on the support and supplying a carbon source that is a volatile compound mixed in a carrier gas (second step) .

  After the synthesis of CNTs, CNTs stacked or staying on or near the surface of the support, catalyst, catalyst cap material, catalyst carrier, etc. are separated by blowing a gas such as an inert gas (third step). The gas is blown in a pulsed manner that repeats speed fluctuations at a constant cycle, or at a constant speed.

  Thereafter, the separated CNTs are collected (fourth step).

  Thereafter, the support carrying the nanoparticle catalyst is regenerated (fifth step). That is, in order to repeatedly use the support, the catalyst on the support is regenerated. However, this support may be regenerated at regular or irregular intervals.

  After regeneration of the catalyst, the process returns to the second step, the nanoparticle catalyst is heated together with the support, and a carbon source is supplied to grow CNTs. Thereafter, the third to fifth steps are repeated.

  As described above, the support carrying the nanoparticle catalyst is regenerated and CNTs are continuously synthesized.

  A method for dispersing and preparing the obtained CNT in water will be described below.

  As a dispersion preparation method, these are added and dispersed in water in a lump, and a dispersion aid is previously mixed in water to prepare an aqueous solution of the dispersion aid, and CNT is mixed in this aqueous solution. The latter method is preferred.

  The carbon nanotubes can be uniformly dispersed in the positive electrode material by a process of previously mixing the carbon nanotubes dispersed in water (dispersed in an aqueous solution) with the positive electrode active material.

  Dispersing aids that can be used for dispersing CNTs include fatty acids having 6 to 22 carbon atoms (for example, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, Linoleic acid, linolenic acid, stearic acid, etc.), metal soaps composed of the above fatty acids and alkali metals (Li, Na, K etc.) or alkaline earth metals (Mg, Ca, Ba etc.), aliphatic amines, Silane coupling agents, coupling agents such as titanium coupling agents, higher alcohols, polyalkylene oxide phosphates, alkyl phosphates, alkyl borate esters, sarcosinates, polyalkylene oxide esters, compounds such as lecithin, alkyle Nonionic surfactants such as noxide and glycerin, higher grades Lumins, quaternary ammonium salts, cationic surfactants such as phosphonium, sulfonium, anionic surfactants such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester, phosphate ester group, amino acids, aminosulfonic acid, Amphoteric surfactants such as sulfates or phosphates of amino alcohols; carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyacrylic acid, polyvinyl alcohol or modified products thereof, polyacrylamide, polyhydroxy (meth) acrylate, styrene-maleic There are water-soluble polymers such as acid copolymers. Of these, water-soluble polymers having carboxymethyl cellulose or lower are preferable because the conductive agent which is a carbon compound is particularly well dispersed, and carboxymethyl cellulose, polyvinyl alcohol or a modified product thereof, and a styrene-maleic acid copolymer are particularly preferable. These dispersing aids can be used alone or in combination of two or more.

  In order to disperse CNTs in water, a known disperser or dispersion method such as a mixer or a homoblender can be used.

  The CNTs of the examples can function as a conductive agent by themselves, but other conductive agents can be added as necessary.

  Other conductive agents are not particularly limited, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber; One type of conductive material such as metal powder such as copper, nickel, aluminum, silver, or gold, metal fiber, or conductive ceramic material may be used, or two or more types may be used. Among these, acetylene black is desirable from the viewpoints of conductivity and coatability. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.

  These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, a planetary ball mill, or the like can be used in a dry or wet manner.

  Hereinafter, the negative electrode will be described.

  If necessary, a conductive agent, a binder, a filler, and the like can be added to the electrode mixture for the negative electrode.

  The conductive agent is not particularly limited, and natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber; copper, One type of conductive material such as metal powder such as nickel, aluminum, silver, or gold, metal fiber, or conductive ceramic material may be used, or two or more types may be used. Among these, acetylene black is desirable from the viewpoints of conductivity and coatability. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.

  These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, a planetary ball mill, or the like can be used in a dry or wet manner.

  The binder used for the positive electrode mixture and the negative electrode mixture is tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber. Further, thermoplastic resins such as carboxymethyl cellulose, polymers having rubber elasticity, polysaccharides, and the like can be used. A mixture of two or more of these can also be used.

  It is desirable that a binder having a functional group that reacts with lithium, such as a polysaccharide, be deactivated by, for example, methylation. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.

  Moreover, it is also possible to mix CNT in said binder. By mixing CNT in the binder, the binder containing CNT enters the gap between the positive electrode active material and the filler, and the conduction between the particles can be improved. In this case, the binder plays a role as a conductive binder.

  The filler used for the positive electrode mixture and the negative electrode mixture is not particularly limited, and olefin polymers such as polypropylene and polyethylene, aerogel, zeolite, glass, carbon, and the like can be used. The amount of filler added is preferably 0 to 30% by weight.

  Furthermore, for the purpose of increasing the capacity, a substance containing a chalcogen element (sulfur, selenium and tellurium) can be added. The added chalcogen element adds a disulfide group (S—S bond) to the electrode material and gives further charge / discharge capacity. The amount of chalcogen element added is preferably 0 to 30% by weight.

  The current collector of the electrochemically active substance is not particularly limited as long as it is an electronic conductor that does not adversely affect the constructed battery. For example, as a current collector for positive electrode, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., as well as aluminum for the purpose of improving adhesiveness, conductivity and oxidation resistance. A material whose surface is treated with carbon, nickel, titanium, silver or the like can be used.

  Current collector for negative electrode includes copper, nickel, iron, stainless steel, titanium, aluminum, baked carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., adhesiveness, conductivity and oxidation resistance For the purpose of improving the quality, a material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. The surface of these materials may be oxidized.

  As the current collector, in addition to a foil shape, a film shape, a sheet shape, a net shape, a punched shape, an expanded shape, a lath body, a porous body, a foamed body, a formed body of a fiber group, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

  Among these current collectors, an aluminum foil excellent in oxidation resistance is preferable for the positive electrode, and a copper foil, nickel foil, iron that is stable in a reduction field, excellent in conductivity, and inexpensive at the negative electrode. Foil and alloy foils containing parts thereof are preferred. Furthermore, it is desirable that the foil has a rough surface surface roughness Ra of 0.2 μm or more with excellent adhesion between the electrochemically active material layer and the current collector. An electrolytic foil is excellent as a current collector having such a rough surface.

  Hereinafter, a method of adding CNT to the electrode will be described.

  For the CNTs of the examples, after preparing a dispersion thereof, a positive electrode active material is added and mixed, dried, and then mixed with a binder and a conductive agent other than CNTs to form a positive electrode mixture. Here, the positive electrode active material is added, mixed, and dried once.

  The CNTs of the examples are characterized by being long (long fibers) and high purity. Specifically, the CNTs of the examples have a diameter of 2 to 8 nm, a length of about 1 mm, and a carbon purity of 99.9% by weight or more. Therefore, the positive electrode active material particles can be efficiently connected, and the electron conductivity between the particles can be increased.

  Hereinafter, it demonstrates using drawing.

  FIG. 1 is a partially enlarged sectional view showing a microscopic structure of a conventional positive electrode.

  The positive electrode includes a current collector 151 and a positive electrode mixture layer coated on the surface (both surfaces). In the drawing, the vicinity of one surface of the current collector 151 is shown.

  In this figure, the positive electrode mixture layer includes a positive electrode active material 101, conductive agents 103 and 113, and a binder 104. The positive electrode active material 101 is primary particles, and a plurality of primary particles are aggregated to form secondary particles 102. The range of one secondary particle 102 is represented by a broken-line circle. The positive electrode mixture layer is a layer in which a plurality (a large number) of secondary particles 102 are overlapped. The binder 104 enhances the adhesion between the secondary particles 102 and between the secondary particles 102 and the current collector 151. As the conductive agents 103 and 113, those in the form of very fine particles are generally used as compared with the positive electrode active material 101. The conductive agents 103 and 113 are attached to the surface (or the vicinity of the surface) of the positive electrode active material 101 and collect electric charges generated in the positive electrode active material 101 when the positive electrode active material 101 occludes / releases lithium ions. It has a function of transmitting to the body 151. Among these, the conductive agent 113 has a function of conducting the secondary particles 102 to each other.

  In the conventional configuration shown in this figure, since all of the conductive agents 103 and 113 do not directly contribute to conduction, it is necessary to increase the addition amount of the conductive agents 103 and 113. Further, since the conductive agents 103 and 113 are particles, there is also a contact resistance between these particles, and this contact resistance is considered to be a factor of the internal resistance of the battery.

  FIG. 2 is a schematic configuration diagram illustrating a positive electrode material of an example.

  In this figure, the positive electrode material has a configuration including a positive electrode active material 101 and carbon nanotubes 105 and 115 which are conductive agents. The positive electrode active material 101 is primary particles, and a plurality of primary particles are aggregated to form secondary particles 102. The range of one secondary particle 102 is represented by a broken-line circle.

  Among the carbon nanotubes 105 and 115, the carbon nanotube 105 enters between the positive electrode active materials 101 that are primary particles, contacts the surfaces of the plurality of positive electrode active materials 101, and enhances conductivity. On the other hand, the carbon nanotubes 115 enter between the secondary particles 102 and contribute to conduction between the secondary particles 102. In addition, since the carbon nanotubes 105 and 115 are fibrous and long, some of the carbon nanotubes 105 and 115 have a portion protruding like a whisker outside the secondary particle 102.

  FIG. 3 is a partially enlarged cross-sectional view showing the configuration of the positive electrode of the example.

  That is, the positive electrode shown in this figure is obtained by mixing the positive electrode material shown in FIG. 2 with the binder 104 and coating it on the surface (both sides) of the current collector 151. In the drawing, the vicinity of one surface of the current collector 151 is shown.

  In this figure, the carbon nanotubes 105 and 115 have a function as a conductive agent. The carbon nanotubes 105 and 115 have a portion protruding to the outside of the secondary particle 102, and a part thereof is in contact with the current collector 151.

  Since the carbon nanotubes 105 and 115 have long fibers, the probability that each one of the carbon nanotubes 105 and 115 contacts the positive electrode active material 101 or another carbon nanotube 105 or 115 in some form and contributes to conduction is higher than that of the particulate conductive agent. It is considered high. For this reason, even if it is a case where the addition amount of the carbon nanotubes 105 and 115 is small, the electroconductivity of a positive mix layer can be improved. Further, since the carbon nanotubes 105 and 115 electrically connect the positive electrode active material 101 to the current collector 151 with a smaller number than the particulate conductive agent, the contact resistance is reduced.

  If the carbon nanotubes 105 and 115 are too short, the intended purpose of electrically connecting the positive electrode active material 101 to the current collector 151 in a small number is not achieved. On the other hand, when the carbon nanotubes 105 and 115 are long, the probability of contact with a large number of positive electrode active materials 101 increases, and the probability of contact with the current collector 151 also increases.

  The thickness of the positive electrode mixture layer may be about 10 to 20 μm, as shown in Examples described later. Moreover, the primary particle diameter of the positive electrode active material 101 is about 1 nm to 10 μm, and the secondary particle diameter of the positive electrode active material 101 is about 1 to 20 μm. Therefore, the length (fiber length) of the carbon nanotubes 105 and 115 is preferably 10 μm or more, more preferably 20 μm or more, further preferably 50 μm or more, further preferably 100 μm or more, and particularly preferably 500 μm or more.

  Here, the fiber length refers to the total length of the carbon nanotubes 105 and 115 (fibers). That is, when the fiber is bent, it means the length of the curve along the fiber.

  In addition, since the carbon nanotubes 105 and 115 are made of a single sheet of graphite in the shape of a cylinder, if the diameter is too large, the filling efficiency per volume will decrease, hindering the increase in capacity and conductivity. May be a factor. Therefore, the diameter of the carbon nanotubes 105 and 115 is preferably 0.5 to 10 nm, more preferably 0.5 to 5 nm, and particularly preferably 1 to 5 nm.

  In the embodiment shown in this figure, a positive electrode material including the positive electrode active material 101 and the carbon nanotubes 105 and 115 is prepared by kneading, then once dried, and then mixed with the binder 104. For this reason, the primary particles of the positive electrode active material 101 contained in the dried positive electrode material are aggregated to form secondary particles. For this reason, the binder 104 often adheres to the surface of the secondary particles of the positive electrode active material 101, and few binders enter the secondary particles of the positive electrode active material 101. This configuration is considered effective from the viewpoint of improving conductivity.

  FIG. 4 is a partially enlarged cross-sectional view showing the configuration of a positive electrode in which a particulate conductive agent is added in addition to carbon nanotubes.

  In this figure, the conductivity of the positive electrode mixture layer can be increased by the synergistic effect of the carbon nanotubes 105 and 115 and the conductive agents 103 and 113. Since there are the carbon nanotubes 105 and 115, a small amount of the conductive agent 103 and 113 is sufficient.

  Next, the structure of the lithium ion secondary battery of an Example is demonstrated.

  FIG. 5 shows an example of a wound nonaqueous electrolyte secondary battery. In this figure, the same parts are denoted by the same reference numerals, and redundant description may be omitted.

  In this figure, a separator is provided between the positive electrode 1 and the negative electrode 3 so that the positive electrode 1 coated with a positive electrode material on both sides of the current collector and the negative electrode 3 coated with a negative electrode material on both sides of the current collector are not in direct contact. The electrode group is formed by arranging 2 and winding. This electrode group is inserted in a battery can 4 made of SUS. The separator 2 is formed of a microporous polypropylene film.

In the battery can 4, 1.0 mol / liter of LiPF ₆ was dissolved in a non-aqueous electrolyte (for example, ethylene carbonate (EC) and dimethyl carbonate (DMC) in a mixed solvent with a volume ratio of 1: 2. Stuff). The battery can 4 is sealed using a battery lid 11 to which a gasket 9 is attached. A positive electrode tab 5 which is a lead piece of the positive electrode 1 is electrically connected to the battery lid 11. A negative electrode tab 6 that is a lead piece of the negative electrode 3 is electrically connected to the bottom of the battery can 4. A PTC element 10 (positive temperature coefficient element) is provided between the inner lid 7 and the battery lid 11 so as to electrically cut off the current when the temperature rises. Also, an internal pressure release valve 8 is provided inside the battery lid 11 so that it is opened when the internal pressure of the battery becomes a predetermined value or more.

  For the positive electrode 1, a current collector exposed portion not coated with the positive electrode mixture paste is provided at one end of the positive electrode current collector, and a tab is welded to a part or both ends to form a positive electrode tab 5. Alternatively, the positive electrode tab 5 may be formed by folding the current collector exposed portion to provide a positive electrode lead at one or both ends of the current collector and welding a tab to a part or both electrode portions of the current collector.

  For the negative electrode 3, a negative electrode current collector exposed portion not coated with the negative electrode mixture paste is provided on a part of the negative electrode current collector, and a tab is welded to a part or both ends to form a negative electrode tab 6. Alternatively, the negative electrode tab 6 may be formed by folding the current collector exposed portion to provide a negative electrode lead at one or both ends of the current collector and welding a tab to a part or both electrode portions of the current collector.

  As the battery can 4, a metal can such as iron, stainless steel, and aluminum can be used. From the viewpoint of energy density per weight, a metal resin composite material in which a metal foil and a resin film are laminated is preferable.

Examples of the metal foil used for the metal resin composite material include aluminum, iron, nickel, copper, SUS steel, titanium, gold, silver, and the like, as long as the foil does not have a pinhole, but is preferably a lightweight and inexpensive aluminum. Use foil. Moreover, as a resin film used for a metal resin composite material, a resin film excellent in piercing strength such as a polyethylene terephthalate film and a nylon film is used for a part to be an outer surface of a battery, and a part to be an inner surface of a battery is It is preferable to use a thermoplastic and fusible film such as a polyethylene film or a nylon film. From the viewpoint of solvent resistance, it is desirable to seal the opening of such a resin film with a thermoplastic resin.
The separator 2 can be a polyolefin-based, polyester-based, polyacrylonitrile-based, polyphenylene sulfide-based, polyimide-based or fluororesin-based microporous membrane or nonwoven fabric. Of these, the microporous membrane having low wettability (hydrophobic) needs to be treated with a surfactant or the like.

  The porosity of the separator 2 is preferably 98% by volume or less from the viewpoint of strength. Further, from the viewpoint of charge / discharge characteristics, the porosity is preferably 20% by volume or more.

  However, when the surface treatment is performed on the negative electrode side of the separator 2, the porosity may not be in the above range.

The nonaqueous electrolyte used for the nonaqueous electrolyte battery is not limited. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate Esters; chain esters such as methyl acetate and methyl butyrate; ethers such as tetrahydrofuran or derivatives thereof, 1,3-dioxane, 1,2-dimethoxyethane, and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxalane or derivatives thereof; sulfolane, LiClO ₄ alone or their mixture of two or more solvents such as sultone or a derivative _{thereof, LiBF 4, LiAsF 6, LiPF} 6 _{LiCF 3 SO 3, LiCF 3 CO} 2, LiSCN, including _{LiBr, LiI, Li 2 SO 4} , Li 2 B 10 Cl 10, NaClO 4, NaI, NaSCN, NaBr, KClO 4, KSCN , etc. Li, a Na or K Inorganic ion salt, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , ( C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate _{, (C 2 H 5) 4} N-benzoate, (C 2 H 5) quaternary ammonium salts, such as 4 N-phtalate, lithium stearyl sulfonate, octyl sulfo One or a mixture of two or more organic ion salts such as lithium nitrate and lithium dodecylbenzenesulfonate can be used.

  The electrolytic solution can be injected after the separator 2 is sandwiched between the positive electrode 1 and the negative electrode 3 and stacked or wound. As the injection method, it is possible to inject at normal pressure, but it is also possible to use a vacuum impregnation method or a pressure impregnation method.

  As the non-aqueous electrolyte, an ionic liquid or a lithium conductive solid electrolyte (at -20 to 60 ° C., which is solid or solid) can also be used. This solid electrolyte is composed of a polymer containing the salt. Examples of the polymer electrolyte containing the salt include a polyethylene oxide derivative in which the lithium salt is dissolved or a polymer containing at least the derivative, a polypropylene oxide derivative or a polymer containing at least the derivative, polyphosphazene, the derivative, and an ion dissociation group. Polymer matrix material (gel electrolyte) impregnated with non-aqueous electrolyte in polymer containing, phosphate ester polymer derivative, polyvinylpyridine derivative, bisphenol A derivative, polyacrylonitrile, polyvinylidene fluoride, fluoro rubber, etc., inorganic solid electrolyte, etc. These ion conductive compounds are mentioned.

  Next, the structure of a positive electrode and a negative electrode is demonstrated using an Example. However, the present invention is not limited to the following examples.

(Preparation of positive electrode)
First, a method for producing a positive electrode active material will be described.

Lithium acetate dihydrate [Li (CH ₃ COO) · 2H ₂ O], manganese acetate tetrahydrate [Mn (CH ₃ COO) ₂ · 4H ₂ O], and ammonium dihydrogen phosphate [NH ₄ H ₂ PO ₄ ] was weighed so as to have a molar ratio of 1: 1: 1, and these were dissolved in pure water as a solvent to prepare a raw material mixture. Next, glycolic acid [C ₂ H ₄ O ₃ ] as a gelling agent is added to the obtained raw material mixture so that the molar ratio of lithium acetate dihydrate: glycolic acid = 1: 5 is obtained, The obtained composition was baked at 600 ° C. in the atmosphere to synthesize LiMnPO ₄ to obtain a positive electrode active material.

  The CNT dispersion was added to the positive electrode active material so that the positive electrode active material and the conductive agent CNT were in a weight ratio of 94.8: 0.20, and stirred and mixed with a magnetic stirrer. The mixed solution of the positive electrode active material and the CNT dispersion liquid is powdered by removing moisture by heat drying under reduced pressure or heat drying in air, and then vacuum dried at 100 ° C. for 2 hours to obtain a CNT-containing positive electrode material (Positive electrode material).

  A paste was prepared by mixing an NMP solution having a PVDF concentration of 12 wt% so that the weight ratio of CNT-containing positive electrode material and PVDF as a binder was 95: 5. The average value of the length (full length) of the CNTs used in this example is about 1 mm.

  This paste was applied to an aluminum foil having a thickness of 20 μm and then dried at 80 ° C.

  Then, after vacuum-drying at 120 degreeC, it pressed so that the porosity of a mixture layer might be 35%, and it was set as the positive electrode.

(Preparation of negative electrode)
Using graphite as the negative electrode active material, the paste was prepared by mixing 95% by weight of this negative electrode active material, 5% by weight of acetylene black, and 5% by weight of NMP solution having a PVDF (binder) concentration of 13% by weight. Produced. This paste was applied to a copper foil having a thickness of 10 μm and then dried at 80 ° C. Then, after vacuum-drying at 100 degreeC, it pressed so that the porosity of a mixture layer might be 35%, and was set as the negative electrode.

(Electrolyte)
A non-aqueous treatment solution in which 1M LiPF ₆ was dissolved in a mixed solvent having a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) of 3: 7 was prepared and used as an electrolytic solution.

(Production of battery)
The battery was produced as a wound battery shown in FIG. Using the above positive electrode and negative electrode and a polyethylene separator having a thickness of 30 μm, these were stacked and wound to form an electrode group, inserted into a battery can, and an electrolyte was injected to obtain a battery.

(Battery charge / discharge evaluation)
The battery produced as described above was charged and discharged 3 cycles at a constant current of 0.5 mA / cm ² and a charge voltage of 4.3 V and a discharge voltage of 2 V (initial charge / discharge). Thereafter, the battery was charged to a charging voltage of 4.3 V at a constant current of 0.5 mA / cm ² and discharged at a current density of 8 mA / cm ² to 2 V (the fourth cycle). . Next, the battery was charged to a charging voltage of 4.3 V at a constant current of 0.5 mA / cm ² and discharged to ² V at a current density of 13 mA / cm ² (5th cycle). ).

Using the discharge capacity at the third cycle in the initial charge / discharge as a reference (denominator), the ratio of the discharge capacity at a discharge current density of 8 mA / cm ² (fourth cycle) and 13 mA / cm ² (fifth cycle) was calculated. , respectively, and the capacity retention rate of 8 mA / cm ² and 13mA / cm ² (%).

  Example 1 except that the CNT dispersion was added to the positive electrode active material and mixed so that the positive electrode active material and the conductive agent CNT were 94.9: 0.10 in weight ratio when the positive electrode was produced. In the same manner as described above, an electrode was prepared and measured.

(Reference example)
When preparing the positive electrode, the CNT dispersion is added to the positive electrode active material and mixed so that the positive electrode active material and the conductive agent CNT have a weight ratio of 93.95: 0.050. After the PVDF is mixed, acetylene black (AB) is mixed so that the positive electrode active material, CNT, and AB are in a weight ratio of 93.95: 0.050: 1.0 when PVDF is mixed. Except for the above, an electrode was produced and measured in the same manner as in Example 1.

  This example shows that a positive electrode mixture having a high capacity retention rate can be produced by adding a small amount of a conductive auxiliary agent in addition to CNT.

  Example 1 except that the CNT dispersion was added to the positive electrode active material and mixed so that the positive electrode active material and the conductive agent CNT were in a weight ratio of 94.5: 0.50 when the positive electrode was produced. In the same manner as described above, an electrode was prepared and measured.

(Comparative Example 1)
When producing the positive electrode, a dispersion containing AB was added to the positive electrode active material so that the weight ratio of the positive electrode active material and the conductive agent AB was 94.8: 0.20 without using the CNTs of the examples. Except that they were mixed in the same manner as in Example 1, an electrode was prepared and measured.

(Comparative Example 2)
When producing the positive electrode, without using the CNT of the example, a dispersion containing AB was added to the positive electrode active material so that the positive electrode active material and the conductive agent AB had a weight ratio of 93.95: 0.10. Except that they were mixed in the same manner as in Example 1, an electrode was prepared and measured.

(Comparative Example 3)
When producing the positive electrode, the CNT of the example was not used, but the positive electrode active material and the CNT as the conductive agent of the comparative example (Sigma-Aldrich, product name: SWeNT CG100, diameter 0.7 to 1.3 nm, length 450 nm The electrode was prepared in the same manner as in Example 1 except that the CNT dispersion was added to the positive electrode active material and mixed so that the weight ratio was 93.95: 0.20. And measured.

(Comparative Example 4)
When producing a positive electrode, neither CNT nor AB was used. The positive electrode mixture was prepared by mixing an NMP solution having a PVDF concentration of 12% by weight so that the positive electrode active material and the PVDF as the binder were in a weight ratio of 95: 5. Otherwise, electrodes were prepared and measured in the same manner as in Example 1.

(Comparative Example 5)
Example 1 except that the CNT dispersion was added to the positive electrode active material and mixed so that the positive electrode active material and the conductive agent CNT were in a weight ratio of 94.95: 0.05 when producing the positive electrode. In the same manner as described above, an electrode was prepared and measured.

  Table 1 summarizes the CNT addition amount, capacity retention rate, and the like for the examples and comparative examples.

本表より、実施例のＣＮＴを水に分散した液（水分散液）を用いることにより、高出力で高い容量維持率を保つ電池が作製できることがわかる。

From this table, it can be seen that by using a liquid (aqueous dispersion) in which the CNTs of the examples are dispersed in water, a battery that maintains a high capacity retention rate with a high output can be produced.

Among these, the case where the electrode which mixed CNT0.05% of reference example and AB1% was used was the most effective. The reference example was excellent also in the applicability | paintability of the electrode.

  According to the present invention, the capacity of the battery can be increased, and the capacity can be maintained even when the output is increased.

  1: positive electrode, 2: separator, 3: negative electrode, 4: battery can, 5: positive electrode tab, 6: negative electrode tab, 7: inner lid, 8: internal pressure release valve, 9: gasket, 10: PTC element, 11: battery Lid, 101: positive electrode active material, 102: secondary particles, 103, 113: conductive agent, 104: binder, 105, 115: carbon nanotube, 151: current collector.

Claims (5)

Including a conductive agent, a positive electrode active material, and a binder,
The conductive agent is obtained by dispersing an electron conductive material having only a carbon nanotube having a diameter of 0.5 to 10 nm and a length of 10 μm or more. The carbon purity of the carbon nanotube is 99 on a weight basis. 0.9% or more, and the ratio of the carbon nanotubes in the total amount of the carbon nanotubes and the positive electrode active material is 0.1 to 0.6% on a weight basis,
The positive electrode active material is a lithium oxide having an olivine structure,
The positive electrode mixture for a lithium ion secondary battery, wherein the carbon nanotubes are mixed and dispersed with the positive electrode active material in a state of being dispersed in water using a dispersion aid.   2. The positive electrode mixture for a lithium ion secondary battery according to claim 1, wherein the carbon nanotube is a single-walled carbon nanotube.   The positive electrode mixture for a lithium ion secondary battery according to claim 1, wherein the positive electrode active material is olivine manganese.   A positive electrode for a lithium ion secondary battery comprising a current collector coated with the positive electrode mixture for a lithium ion secondary battery according to any one of claims 1 to 3.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein the positive electrode is a positive electrode for a lithium ion secondary battery according to claim 4. battery.

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